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Evaluation of the Susceptibility of Four Scotch
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presented by

Eileen Amber Eliason

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”3-9.1

EVALUATION OF THE SUSCEPTIBILITY OF FOUR SCOTCH PINE CHRISTMAS
TREE VARIETIES TO INSECT PESTS

By

Eileen Amber Eliason

A THESIS

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Entomology

l 996

ABSTRACT

EVALUATION OF THE SUSCEPTIBILITY OF FOUR SCOTCH PINE CHRISTMAS
TREE VARIETIES TO INSECT PESTS

By

Eileen Amber Eliason

Four Scotch pine (Pinus sylvestris L.) Christmas tree varieties were tested for resistance
to Zimmerman pine moth (Lepidoptera: Pyralidae), European pine sawfly (Hymenoptera:
Diprionidae) and pine needle scale (Homoptera: Diaspididae). Insects were reared in
1994 and 1995 on trees at the Michigan State University Kellogg Experimental Forest,
Kalamazoo County. Differences among tree varieties in sawfly and scale survival and
fecundity were detected, but Zimmerman survival was too low to determine varietal
differences. Multiple regressions predicted Zimmerman pupal weight, sawﬂy
development and pupal weight, and scale survival and fecundity. In another study, trees
at Kellogg Forest and a ﬁeld in Montcalm County were monitored twice a month during
each summer. Natural feeding guild infestations under observation differed in abundance
and phenology, but sap-feeders were dominant. Inconsistent results of guild abundance
among varieties implicated factors other than resistance affecting community structure.

Alternatives to resistance acting on reared species and guilds are discussed.

ACKNOWLEDGMENTS

I would like to sincerely thank Dr. Deborah G. McCullough, my major professor, for
her support and direction. She taught me how to work hard and strive for good results,
and encouraged me when things got rough. She has been a good example to me
professionally, and I am constantly amazed at her ability to juggle her personal life,
extension work, research and teaching. Working with Deb has been truly rewarding.

I would also like to thank my committee for their contributions to my graduate
program. Dr. Mel Koelling generously provided infested Christmas trees to use in insect
rearing. Chatting with Mel in his office has always been enjoyable. Dr. Ed Graﬁus has
been very encouraging, and I’m grateful for his advice and calm approach to problem
solving. I also appreciate Dr. Bob Haack for his witty enthusiasm and sharp eye for
detail. The USDA Forest Service has been generous in supplying me with publications.

Special thanks are extended to the Michigan Agricultural Experiment Station by
supporting my research with the Status and Potential of Michigan Agriculture grant. The
continued financial support during my program was deeply appreciated. I also thank
those faculty members who served on the Hutson Awards committee for providing me

with comments on one aspect of my research, and for awarding me with a grant.

iii

I am especially indebted to Mr. Lyle Buss for his companionship, assistance, and
constructive criticism of my work. I thank the personnel at Kellogg Forest (Greg
Kowalewski, Karen Bushouse, Jim Curtis, John Vigneron, and Don Alkema) for
maintaining the Christmas tree plot, and the student employees that occasionally helped
me, including Kevin, Katie, Liz and Brian. I appreciate Mr. Wayne Korson for letting
me monitor trees on his ﬁeld, Mr. Lee Arend for providing me with Zimmerman pine
moth-infested trees, and Mr. Ron Flinn for letting me collect sawflies and scales from his
pine trees. I would also like to thank Mr. Peter Lorio of the USDA Forest Service for
providing the resin ﬂow technique used in this study. I am grateful to Jill Fisher for
analyzing the total foliar nitrogen, and for being so encouraging. Thanks also go to Dr.
J. Mark Scriber for being generous in allotting travel money for me to go to various
professional meetings.

Some of the most important contributions were by people who identiﬁed the natural
enemies found in this study. This includes Dr. Richard Snyder and Dr. Richard Leschen
from Michigan State University, Dr. John Luhman from the Minnesota Department of
Agriculture, Plant Protection Division, Mr. Robert C. Carlson and Mr. M. E. Schauff
from the USDA Agricultural Research Service, Systematic Entomology Laboratory, and
Mr. Richard Humber from the USDA-ARS, US Plant, Soil, and Nutrition Laboratory.

I am also grateful to my mom and grandmother for their encouragement and support,
and to my dad, who now more fully respects my love of biology. I’ll always be happy to

check out their plant problems.

iv

TABLE OF CONTENTS

LIST OF TABLES .................................................... vii
LIST OF FIGURES .................................................... x
INTRODUCTION ..................................................... 1
LITERATURE REVIEW ................................................ 3
Geographic Distribution .............................................. 3
Christmas Tree Management .......................................... 4
Integrated Pest Management (1PM) ..................................... 7
CHAPTER 1

Resistance of Four Scotch Pine Varieties to Three Insect Pests in Michigan ........ 9

Zimmerman Pine Moth Damage and Phenology .......................... 10
European Pine Sawﬂy Damage and Phenology ........................... 13
Pine Needle Scale Damage and Phenology .............................. 15
Materials and Methods .............................................. 18
Study Site .................................................... 18

Scotch Pine Varieties ........................................... 18

Tree Characteristics ............................................ 19
Weather Monitoring ............................................ 21

Insect Rearing ................................................. 21
Zimmerman Pine Moth ...................................... 21

European Pine Sawfly ....................................... 21

Pine Needle Scale ........................................... 22

Insect Survival ................................................. 23
Zimmerman Pine Moth ...................................... 23

European Pine Sawﬂy ....................................... 24

Pine Needle Scale ........................................... 25

Insect Fecundity ............................................... 25

Zimmerman Pine Moth ...................................... 25

European Pine Sawﬂy ....................................... 26

Pine Needle Scale ........................................... 26

Statistical Analysis ............................................. 27

Results .......................................................... 28

V

Tree Characteristics ............................................ 28

Weather Monitoring ............................................ 30

Insect Survival ................................................. 3O

Zimmerman Pine Moth ...................................... 30

European Pine Sawﬂy ....................................... 33

Pine Needle Scale ........................................... 36

Insect Fecundity ............................................... 39

Zimmerman Pine Moth ...................................... 39

European Pine Sawﬂy ........................................ 39

Pine Needle Scale ........................................... 40

Discussion ........................................................ 41

Differences Among Varieties ..................................... 41

Differences in Variety Resistance to Zimmerman Pine Moth ............ 43

Differences in Variety Resistance to European Pine Sawﬂy ............. 48

Differences in Variety Resistance to Pine Needle Scale ................. 50

CHAPTER 2

Phenology and Species Composition of Pest and Beneﬁcial Arthropods in Four

Varieties of Scotch Pine Christmas Trees in Southern Michigan ................. 78

Materials and Methods .............................................. 81

Study Sites ................................................... 81

Scotch Pine Varieties ........................................... 82

Species Composition and Phenology ............................... 82

Statistical Analysis ............................................. 83

Results .......................................................... 84

Scotch Pine Varieties ........................................... 84

Arthropod Communities in Scotch Pine Fields ....................... 84

Seasonal Changes in Feeding Guild Abundance ...................... 85

Feeding Guild Abundance Among Four Scotch Pine Varieties ........... 86

Species Composition of Feeding Guilds ............................ 87

Sap-Feeding Guild .......................................... 87

Defoliating Guild ........................................... 88

Shoot-Boring Guild ......................................... 89

Phloem-Boring Guild ....................................... 89

Beneﬁcial Arthropods Guild .................................. 90

Discussion ....................................................... 92

FINAL CONCLUSIONS .............................................. 110

APPENDIX 1 - Record Deposition of Voucher Specimens .................... 113

APPENDIX 1.1 - Voucher Specimen Data ................................. 114

LIST OF REFERENCES ............................................... 1 15

vi

LIST OF TABLES

Chapter 1

Table 1. Characteristics of four Scotch pine varieties according to Wright et a1.

(1966) and Ruby and Wright (1976) ........................... 57
Table 2. Mean tree growth measurements (:tSE) of four Scotch pine varieties

in 1994 and 1995 (n=12 trees per variety) ....................... 58
Table 3. Pearson’s product-moment (r) and Spearman rank (rs) correlations

among Scotch pine tree characteristics .......................... 59
Table 4. Mean monthly temperature and precipitation accumulation in 1994 and

1995 at Kellogg Forest near Kalamazoo, MI ..................... 60
Table 5. Cohort life table analysis for Zimmerman pine moth caged on Scotch

pine trees at Kellogg Forest in 1994 and 1995 (n=48 trees) .......... 61
Table 6. Analysis of Zimmerman pine moth survival during 1994 and 1995

using the Cochran’s Q test, X0053 (n=48 trees) ................... 62
Table 7. Mean grth and fecundity (iSE) of Zimmerman pine moth when

caged on four Scotch pine varieties in 1994 and 1995 (n=12 trees per

variety) ................................................. 63
Table 8. Pearson’s product-moment (r) and Spearman rank (rs) correlations

among Zimmerman pine moth and tree variables with varietal data

pooled .................................................. 64
Table 9. Cohort life table analysis for European pine sawﬂy in 1994 ........ 65
Table 10. Cohort life table analysis for European pine sawﬂy in 1995 ........ 66

Table 11. Mean values for European pine sawﬂy development (iSE) on four

varieties of Scotch pine in 1994 and 1995 (n=12 trees per variety) . . . . 67

vii

Table 12. Pearson’s product-moment (r) and Spearman rank (rs) correlations
among European pine sawﬂy and tree variables with varietal data
pooled together ........................................... 68

Table 13. Backward-stepping multiple regression predictions of European pine
sawﬂy development period (day), pupal weight and percentage nitrogen
in one-year old needles in 1994 (n = 39) and 1995 (n = 42) ......... 69

Table 14. Pearson’s product-moment (r) and Spearman rank (rs) correlations
among pine needle scale and tree variables ...................... 70

Table 15. Mean realized survival and fecundity (iSE) of pine needle scale on four
varieties of Scotch pine in 1994 and 1995 (n=12 trees per variety) . . . 71

Table 16. Backward-stepping multiple regression predictions of pine needle
scale survival and second generation fecundity in 1994 and 1995
(n=48 trees) .............................................. 72

Table 17. Backward-stepping multiple regression predictions of Zimmerman
pine moth pupal weight in 1994 (n=19) and 1995 (n=10) ........... 73

Table 18. Mean values for European pine sawﬂy fecundity (iSE) on four varieties
of Scotch pine in 1994 and 1995 (n=12 trees per variety) ........... 74

Chapter 2

Table 1. Arthropod pests and beneﬁcials monitored at Kellogg Forest and
Greenville in 1994 and 1995 ................................. 97

Table 2. Mean tree measurements (iSE) on four varieties of Scotch pine at
Kellogg Forest and Greenville in 1994 (n=18 trees per variety) ....... 98

Table 3. Mean number of arthropods per tree (iSE) in each feeding guild at
Kellogg Forest and Greenville in 1994 (varieties were pooled) ....... 99

Table 4. Results of two-factor analysis of variance with repeated measures for
feeding guilds at Kellogg Forest and Greenville in 1994 and 1995 . . . . 100

Table 5. Mean number of arthropods per tree (:tSE) in each feeding guild at
Kellogg Forest and Greenville in 1995 (varieties were pooled) ....... 101

Table 6. Mean number of arthropods per tree (iSE) in each feeding guild at
Kellogg Forest and Greenville in 1994 (n=1 8 trees per variety) ...... 102

viii

Table 7. Mean ratios of beneﬁcial to pest arthropod numbers per tree (iSE)
among varieties at Kellogg Forest and Greenville in 1994 and 1995 . . . 103

Table 8. Mean number of arthropods per tree (iSE) in feeding guilds at Kellogg
Forest and Greenville in 1995 (n=13 trees/variety at Kellogg Forest;
16 trees/variety at Greenville) ............................... 104

Table 9. Percentage of species within each guild and Chi-square values from
the Kruskal-Wallis analysis of variance to determine if species

abundance varied among varieties of Scotch pine at Kellogg Forest
in 1994 ................................................. 105

Table 10. Percentage of species within each guild and Chi-square values from
the Kruskal-Wallis analysis of variance to determine if species

abundance varied among varieties of Scotch pine at Greenville
in 1994 ................................................ 106

Table 11. Percentage of species within each guild and Chi-square values from
the Kruskal-Wallis analysis of variance to determine if species
abundance varied among varieties of Scotch pine at Kellogg Forest
in 1995 ................................................ 107

Table 12. Percentage of species within each guild and Chi-square values from
the Kruskal-Wallis analysis of variance to determine if species
abundance varied among varieties of Scotch pine at Greenville
in 1995 ................................................ 108

Chapter 1

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Chapter 2

Figure 1.

LIST OF FIGURES

Mean rate of resin ﬂow (iSE) (ml/24 h) for four varieties of Scotch
pine measured in May, June and July 1995 (n=12 trees per variety). . . . 73

Mean percentage survival of Zimmerman pine moth in 1994 and
1995 when reared on four varieties of Scotch pine ................ 74

Mean percentage survival of European pine sawﬂy in 1994 and
1995 in four varieties of Scotch pine ........................... 75

Linear regression and 95% conﬁdence interval of Zimmerman pine
moth female pupal weight and number of eggs laid per female in
1995 (n=10 females) (p<0.05) ................................ 76

Linear regression and 95% conﬁdence interval of European pine sawﬂy
female pupal weight with the number of eggs laid per female in 1995 . . 77

The proportion of arthropod feeding guilds at Kellogg Forest and
Greenville in 1994 and 1995 ................................. 109

INTRODUCTION

Scotch pine, Pinus sylvestris L., has been a valuable ornamental, forest and Christmas
tree species in Michigan since its importation from Europe and Asia in the early
nineteenth century (Bridgen and Hanover 1982, Giertych and Matyas 1991, Sowder
1966). It has long been a favorite Christmas tree species among growers and consumers.
In Michigan, Scotch pine is grown on about 39,000 ac (15,783 ha), and over three
million or 71% of Christmas trees harvested annually are Scotch pine (Mich. Agr. Stat.
Serv. 1994).

Geographic and climatic conditions in Europe and Asia affected isolated populations
of Scotch pine trees over time, exerting different selection pressures on each gene pool
(Giertych and Matyas 1991). Over 30 varieties of Scotch pine have been recognized
(Ruby and Wright 1976), differing in traits such as needle length, needle color and
moisture content, cone production, stem form, growth rate and monoterpene composition
(Carlisle 1958, Ruby and Wright 1976, Tobolski and Hanover 1971, Wright 1976).
Varieties also vary in degree of resistance to insects and diseases (Squillace et a1. 1975,
Steiner 1974, Wright and Wilson 1972, Wright et a1. 1975) and can be selectively bred to
further decrease their susceptibility to insect damage (Bridgen and Hanover 1982).

In the ﬁrst study, my objectives were to evaluate the resistance of four Scotch pine
varieties to three insect pests caged on trees. In the second study, I monitored ﬁve
arthropod feeding guilds on the same Scotch pine varieties and determined their

phenology and seasonal abundance at two locations in southern Michigan.

2

The thesis is structured to include a comprehensive literature review, two chapters
and ﬁnal conclusions. The literature review discusses the geographic distribution of
Scotch pine, traits of Christmas trees, Christmas tree management (e.g., planting, site
preparation and maintenance, shearing, pesticide applications and harvesting), and
integrated pest management (IPM) in Christmas tree production, including host plant
resistance. Chapter one presents the results from all tree measurements made at Kellogg
Forest, the life cycles, methods, results and discussions pertaining to the study of varietal
resistance to three insect pests, including Zimmerman pine moth (Dioryctria zimmermani
(Grote)), European pine sawﬂy (Neodiprion sertifer Geoff), and pine needle scale
(Chionaspis pinifoliae (F itch)). This chapter will be submitted for publication to the
Journal of Economic Entomology. Chapter two describes a study of the phenology of
ﬁve naturally occurring feeding guilds on the four Scotch pine varieties, the methods,
results and discussion. This chapter will be submitted to the journal Environmental

Entomology. The most important conclusions are summarized in the ﬁnal section.

LITERATURE REVIEW

Geographic Distribution. Scotch pine, Pinus sylvestris L., also known as Scots pine,
is one of the most widely distributed conifers in the world (Skilling 1990), and has been
grown for ornamental, windbreak, timber, and Christmas tree purposes (Bridgen and
Hanover 1982, Giertych and Matyas 1991). Scotch pine has two-needle fascicles, is
shade—intolerant, and is primarily monoecious (Giertych and Matyas 1991, Skilling
1990). Its natural distribution ranges from Scotland to the Paciﬁc Ocean and from
Scandinavia to the Mediterranean Sea (Giertych and Matyas 1991, Skilling 1990). This
species has been widely planted in North America during the twentieth century (Sowder
1966, Wright et a1. 1966). It can grow on a variety of soils, but well-drained sand and
gravel soil types are preferred (Skilling 1990). Over 30 geographic varieties of Scotch
pine have been recognized; varieties differ in needle length, color and moisture content,
cone production, stem form, growth rate and monoterpene concentration (Carlisle 1958,
Ruby and Wright 1976, Tobolski and Hanover 1971, Wright 1976). Varieties also vary
in degree of resistance to insects and diseases (Squillace et al. 1975, Steiner 1974, Wright
and Wilson 1972, Wright et al. 1967, 1975) and can be selectively bred to decrease
susceptibility to damage (Bridgen and Hanover 1982).

Traits important to tree breeders and Christmas tree growers include winter needle

color, needle length, stem form, and growth rate (Koelling and Heiligmann 1993, Sowder

4

1966). Variability among Scotch pine varieties from various geographic locations is
readily apparent (Wright and Bull 1963). For example, Scandinavian varieties typically
have yellow winter foliage, whereas varieties originating from central and southern
Europe possess green needles year-round (Heit 1964, Wright and Bull 1963). Needle
length is relatively short for northern varieties, intermediate for western European and
southern Eurasian varieties, and relatively long for central European varieties (Ruby and
Wright 1976). Although central and southern European varieties grow faster than
Scandinavian varieties, factors such as soil quality, nutrient availability, and the presence
of birds and phloem- and wood-boring insects can inﬂuence stem strength and
straightness (Skilling 1990).

Christmas Tree Management. Scotch pine Christmas trees are grown on a 7- to 10-
year rotation in Michigan and are usually managed intensively to minimize damage from
insects and diseases (Leefers et al. 1988). In most Christmas tree operations, seedlings
are placed in the soil using mechanical planters, a more efﬁcient method than hand-
planting (Koelling and Dombush 1992). Seedlings are grown from nursery stock instead
of natural reproduction (Skilling 1990), and using “certiﬁed seed” ensures the genetic
purity and quality of varieties (Haverbeke 1981, Koelling and Heiligmann 1993).
Stocking density averages 1,210 trees/ac (490 trees/ha), if trees are spaced 6 x 6 ft (1.8 x
1.8 m) apart (Koelling and Dornbush 1992). The Scotch pine varieties recommended for
planting as Christmas trees in the northern United States include iberica (Spanish),
aquitana (French Massif or Van’s), armena (Lake Superior Blue), and haguenensis

(Belgium) (Stadt and Hanover 1983). These varieties are valued as Christmas trees for

5?.

r.
U]:

and

5

having fast growth rates, green winter needle color, straight stems, dense foliage, and
durable branch strength (Koelling and Heiligmann 1993, Sowder 1966).

Site preparation and management in Christmas tree plantations include controlling
competing vegetation before and after seedlings have been planted. Herbaceous
vegetation growing around trees may provide habitat for small rodents, increase tree
susceptibility to diseases and certain insect pests, compete for sunlight and increase
competition for soil nutrients (Lantagne et al. 1990, Shick 1965). Methods of controlling
vegetation include mowing, herbicide application or, less commonly, planting a cover
crop (Koelling and Dombush I992). Fertilization may give other pine or non-pine
conifers a competitive edge over herbaceous vegetation, but it does not signiﬁcantly
increase grth rates in Scotch pine (Lantagne 1988).

The process of shearing Christmas trees, or cutting off newly expanded shoots,
reduces height growth and promotes the grth of adventitious buds near the cut end of
shoots (Hill 1989, Skilling 1990). The purpose of shearing is to produce trees with one
straight stem, a conical crown, and balanced, ﬁill foliage (Hill 1989, Johnson 1991). The
amount and quality of shearing is determined by tree age, time until harvest, the tool used
(e.g., machete, power clippers, hedge shears), and worker experience (Johnson 1991).
Trees are sheared annually in early summer beginning the second or third year following
planting until the year of harvest (Johnson et al. 1992, Koelling 1991). USDA grading
standards recommend that the tree base be sheared to two-thirds as wide as the height of
the tree (Koelling 1991).

Insecticides are widely used on Christmas trees against pests that damage stem form

and foliage. Both major and minor pests in the Lake States, their life cycles and

6

management are listed in several comprehensive Extension and USDA Forest Service
bulletins (Benyus 1983, Kachadoorian et al. 1995, McCullough and Ellis 1995). Despite
the short-term beneﬁts of using chemical controls, sole dependence on insecticides can
result in several negative effects. These effects can include loss of beneﬁcial arthropods,
secondary pest outbreaks, reinfestation of plants by surviving or newly invading
arthropods requiring the reapplication of sprays, and pesticide residues and drift (Stern et
al. 1959). Spraying on a regular, calendar basis is not the most effective means to
manage pests (Ascerno 1991).

Christmas tree harvesting occurs annually from mid-October through December, and
trees are either marketed wholesale or retail (Hill 1989). Prior to harvest, however, many
trees are painted with a blue-green colorant (Johnson 1989). This is intended to hide
some winter yellowing that occurs in certain varieties of Scotch pine and to make trees
look healthier (Hill 1989). Once cut, trees are placed on shakers to remove dead needles,
baled for transportation, inspected for quarantined pests, and shipped (Kidd 1993). Tree
quality (grade) and price depend on taper, freshness, cleanliness, stem form, foliage
density, and “handle” length (length from the bottom of the stem to the ﬁrst whorl of
branches) (Anonymous 1989). Trees are typically transported by truck to their intended
destination.

Growing and marketing Scotch pine Christmas trees depends on consumer demand
and the cost of managing trees throughout their rotation. The production of Scotch pine
in Michigan peaked in the 1980’s, when about 70% of all Christmas trees harvested in

Michigan were Scotch pine, costing consumers $8 to $15 per tree (Koelling et al. 1992,

7
Mich. Agr. Stat. Serv. 1994, Riessen 1995). With increasing competition among

growers, consumer demand for higher quality trees and increased management costs,
fewer acres of Scotch pine have been planted in recent years in Michigan (Koelling and
Heiligmann 1993, Koelling et al. 1992, Mich. Agr. Stat. Serv. 1994, Riessen 1995).
Since over 40 insects and diseases attack Scotch pine Christmas trees in the Great Lakes
region (Benyus 1983), growers have difﬁculty maintaining management standards to
keep trees healthy and undamaged (Riessen 1995).

Integrated Pest Management (IPM). From planting monocultures, introducing exotic
pests, and decreasing public tolerance for damage on plants, agricultural conditions have
become ideal for pest outbreaks (Stern et al. 1959, Pedigo 1996). This set of conditions
has resulted in growers spraying pesticides regularly in many agricultural systems to
minimize pest damage (Leslie and Cuperus 1993). An alternative to a complete reliance
on pesticides is “integrated pest management” or IPM, an approach that optimizes the
combined effects of biological, cultural and pesticide controls in a more environmentally
sound manner. An IPM program involves regular scouting or monitoring for pests, pest
identiﬁcation, evaluation of damage severity, determining and implementing a course of
action, and evaluating the effectiveness of the strategy (McCullough and Ellis 1995,
Turgeon and de Groot 1992). Instead of maintaining zero tolerance, the concept of
economic injury levels is used to identify the threshold at which management efforts are
implemented (Pedigo 1996, Stem et al. 1959).

Natural resistance to pests can be exploited in IPM to supplement other management
strategies (Nielsen 1989). Beck (1965) deﬁned resistance as “the collective heritable

characteristics by which a plant species, race, clone, or individual may reduce the

8

probability of successful utilization of that plant as a host by an insect species, race,
biotype, or individual.” This deﬁnition includes the concepts of “nonpreference” and
“antibiosis,” but not “tolerance” as deﬁned by Painter (1951). Painter (1951) described
resistance in ﬁve categories, ranging from immunity to high susceptibility. Host
resistance against insects can be reﬂected in insect host selection and survival,
developmental rate, fecundity and behavior (Beck 1965). Insects may respond to host
plant resistance by death, reduced fecundity, weight loss, increased development period,
or avoidance of the plant for feeding and/or ovipositing (Singh 1986).

Techniques used to evaluate plant varieties for insect resistance include controlled
caging studies and observations of ﬁeld populations of insects (Tingey 1986). Insect
density, immigration, emigration, and presence of non-target organisms in the test
environment can be controlled with caging procedures (Tingey 1986). However,
monitoring natural pest populations provides data on pest ecology under normal
conditions. In studies of host plant resistance, insect population levels, age structure,
phenology and the effect on crop yield should be analyzed, while minimizing
experimental error (Tingey 1986). In addition, traits in plants contributing to resistance
need to be determined, whether they are morphological, chemical stimuli, or nutrients
(Hanover 1975). After the preliminary step of evaluating varieties for degree of
resistance to pests, more thorough genetic and chemical tests to determine inheritance
and pathways are needed (Hanover 1975). Then selective breeding of varieties to

maximize resistance against pests can begin.

CHAPTER 1

Resistance of Four Scotch Pine Varieties to Three Insect Pests in Michigan

INTRODUCTION

Michigan is one of the largest producers of Scotch pine Christmas trees in the United
States (Riessen 1995). However, growers have been planting less Scotch pine during the
past few years due to its overabundance, low value and high management costs (Koelling
et al. 1992, Riessen 1995). If current management practices have contributed to the
decreasing supply and demand of this Christmas tree species, then alternative
management approaches should be considered. One such possibility is planting or
breeding varieties of Scotch pine that are resistant to major insect pests and diseases.
Some varieties have been observed to have higher or lower infestation levels of pests,
indicating greater or less resistance to attack (Ruby and Wright 1976, Steiner 1974,
Wright and Wilson 1972, Wright et al. 1967, 1975).

The objectives of this study were to: 1) determine if differences in tree growth traits
varied signiﬁcantly among four Scotch pine Christmas tree varieties in southern MI, 2)
determine if the survival and fecundity of Zimmerman pine moth (Dioryctria
zimmermani (Grote)), European pine sawﬂy (Neodiprion sertrfer (Geoff. )) and pine
needle scale (Chionaspis pinifoliae (F itch)) differed signiﬁcantly when reared on the four

varieties, and 3) determine which tree growth traits may affect insect performance.

ZIMMERMAN PINE MOTH DAMAGE AND PHENOLOGY

Zimmerman pine moth (Lepidoptera: Pyralidae) is a native phloem-borer of pine trees
in the North Central United States. It has become a signiﬁcant pest of Scotch pine in
southern Michigan and other states where Scotch pine was widely planted as a Christmas
tree species (Rennels 1960, Schuder 1960). Other hosts in the Lake States include
Austrian (Pinus m'gra Arnold), red (Pinus resinosa Ait.), Japanese-red (Pinus densiﬂora),
jack (Pinus banksiana Lamb), eastern white (Pinus strobus L.) and mugho pines (Pinus
mugo) (Carlson and Wilson 1967). Zimmerman pine moth is part of a phloem-boring
complex that includes two other native species that occasionally occur together in
Christmas trees, D. abietivorella Grote and D. cambiicola Dyar (Butcher and Carlson
1962, Carlson and Butcher 1967). Their taxonomy is described in Leidy and Neunzig
(1989), Neunzig et al. (1964b), and Neunzig and Merkel (1967).

Zimmerman pine moth is univoltine in Michigan. Adults emerge from July to
August, are active in late evening and night, and seem to be attracted to recently sheared
or pruned trees (Ruby and Wright 1976, Wright et al. 1975). Eggs are laid singly beneath
bark scales or in crevices on the main stem or branches of trees and hatch in about two
weeks. First instars do not feed or disperse after emergence, but spin small hibemaculae
in which to overwinter. In early April of the next year, larvae emerge, bore into the

phloem near the oviposition site, and feed until early August (Carlson and

10

Zln
orhe

$1,
5“

1 1
Butcher 1967, Carlson and Wilson 1967). Pupation occurs in the larval tunnel behind the

pitch mass in July and August, and adults emerge approximately two to three weeks later.

Typical attack sites are at the nodes of the upper three whorls of Christmas trees, on
larger branches, or at the base of terminal shoots (Carlson 1965). In spring and early
summer, soft, reddish pitch masses indicate larval feeding sites. The pitch mass is a
mixture of tree resin and reddish frass that congeal together on the bark surface. Larvae
clean their galleries by pushing pitch out one small hole they chew through the bark.
Pitch masses are soft and shiny in early summer, but harden and fade to a dull whitish-
yellow in late summer. The stem directly below the gallery may constrictor weaken
from partial or complete girdling, while tissue above the wound may swell due to
accumulation of photosynthates. Severe damage makes trees susceptible to windfall or
breakage during harvest and baling, and dead branches or gaps in the foliage reduce
Christmas tree grade and marketability (Butcher and Carlson 1962).

Managing this pest in Christmas tree plantations is difficult. Signs of infestation are
hard to detect and infestations may go unnoticed until fall, when pitch masses and dead
branches are more evident (Yonker and Schuder 1987). Persistent insecticides are
typically applied during April, when larvae emerge from hibemaculae to bore into the
phloem, but many growers also spray in the summer or fall (Appleby and Randell 1980,
Butcher and Carlson 1962). Despite this management effort, dense foliage prevents the
thorough pesticide coverage of stems and branches needed to kill larvae. In addition,
Zimmerman pine moth dispersal and feeding preference have had no predictable pattern,
other than certain trees seem to be attacked more often than others (Rennels 1960,

Schuder 1960, Yonker and Schuder 1987). These trees are referred to as “brood trees.”

12

The apparent attractiveness of certain trees to Zimmerman pine moth and the
subsequent population build-up on those trees suggest that some varieties of Scotch pine
may be more susceptible to attack than others (Harrell 1993, Wright et al. 1975). Given
the genetic variability of Scotch pine (Ruby and Wright 1976), its varieties may vary in
traits related to defense against phloem-borers like Zimmerman pine moth. Studies on
conifer resistance to phloem-boring insects, primarily bark beetles, have shown that trees
have several kinds of defense mechanisms. Defenses may include thick bark, a thin
phloem layer, increased number and size of resin ducts, or a high rate of resin ﬂow
(Lorio 1994, Schroeder 1990, Stroh and Gerhold 1965). Trees also use chemical
defenses, such as feeding deterrents or attractants (Dell and McComb 1979, Heikkenen
and Hrutﬁord 1965, Smith 1963). In addition, resistance may result from changes in tree

phenology and nutritional status (Blais 1957, Hanover 1975, Painter 1966).

EUROPEAN PINE SAWFLY DAMAGE AND PHENOLOGY

European pine sawﬂy (Hymenoptera: Diprionidae) is a univoltine, exotic pest of
pines in Michigan. It was introduced to the United States from Europe in 1925 and is
now a pest in Christmas tree plantations, nurseries and ornamental trees (Schaffner
1939). Preferred hosts include Scotch pine, red pine, Japanese-red pine, jack pine and
mugho pine (Wilson 1965).

Sawﬂy larvae hatch from eggs embedded in needles in late April or early May in
Michigan (Lyons 1964). Shortly after hatching, larvae form feeding groups (colonies)
and remain so until pupation. Early instars skeletonize one-year-old needles while older
larvae consume entire one-to-three-year-old needles. Sawﬂy males pass through ﬁve
larval stadia and females through six; the ﬁnal instar is an active, non-feeding larva.
Pupation typically occurs from mid- to late June when prespinning larvae drop to the
ground and spin cocoons in the duff near the tree base. Extended pupal diapause may
occur during unfavorable conditions or outbreaks, and may be inﬂuenced by hormonal
secretions, length of photoperiod, weather and host quality (Kolomiets et al. 1979).
Short-lived adults emerge from early September through October, mate and lay eggs in
the needles. The crowns of open-grown trees are favored oviposition sites (Kolomiets et

al. 1979).

13

Sc

P5

dia

3112

ten

14

European pine sawﬂy feeding can cause both physical and aesthetic damage to
Christmas trees. Gregarious feeding can create gaps in the foliage, reduce growth, and
during severe outbreaks, cause tree mortality (Wilson 1965). Gaps in the foliage are
considered defects and reduce a Christmas tree’s appearance and marketability (Lyons
1964). While shearing may correct minor damage, hiding gaps is difﬁcult. European
pine sawﬂy management in Christmas tree production typically includes a foliar
insecticide application in May. Although effective at killing sawﬂies, insecticide
applications may not be cost-effective for growers (Kolomiets et al. 1979), and
negatively affect beneﬁcial or non-target organisms.

Resistance of certain Scotch pine varieties to European pine sawﬂy attack has been
observed (Ghent 1959, Ruby and Wright 1976). Female sawﬂies one in on certain traits
when mating and ovipositing, which may contribute to a tree’s overall susceptibility
(Lyytikainen 1993b, Mopper et al. 1990). These traits may include needle length, width,
toughness, twistiness, color, and nutrient or resin content (Hardy and Allen 1975,
Olofsson 1989, Wilson 1965). High foliar resin acid concentrations, which vary among
Scotch pine varieties, are known to reduce early instar survival (Larsson et al. 1986).
Pschom-Walcher (1991) detected variety-dependent differences in length of pupal
diapause in cocoons and in adult emergence. Scotch pine varieties most resistant to
attack tend to originate from Scandinavia, while the most susceptible varieties are from

central Europe (Wright et al. 1967).

PINE NEEDLE SCALE DAMAGE AND PHENOLOGY

Pine needle scale (Homoptera: Diaspididae) is a serious pest of Scotch pine
Christmas trees (Pinus sylvestris L.) in Michigan. It is native to North America and
feeds on needles of Scotch pine, eastern white pine, mugho pine, spruce (Picea spp.) and
other ornamental and nursery trees (Dekle 1976, McKenzie 1956, Nakahara 1982). The
distribution of pine needle scale has been confused with the nearly identical scale
Chionaspis heterophyllae (Cooley) (Shour and Schuder 1987, Takagi and Kawai 1967),
and scale dispersal has been increased by transport of infested plants (Cumming 1953).
Heavy infestations of pine needle scale cause trees to look grayish instead of green, cause
premature needle drop, reduce tree vigor, reduce Christmas tree marketability (Cumming
1953, Turner 1930), and eventually cause tree mortality if needles are infested for more
than one consecutive year (Johnson and Lyon 1988).

Pine needle scale has two generations per year in Michigan (Cumming 1953, Shour
1986). Overwintering eggs hatch in late May, or phenologically, when lilacs are in
bloom (Beard and McLeod 1992). Hatching may occur over two to three weeks, and
crawlers disperse by wind or by walking (Brown 1958). First instars, or crawlers, are
mobile for up to four days, then settle and begin feeding. Males molt three times and
females molt twice before becoming adults. In both generations, adult females remain
sessile, and males develop wings as adults and ﬂy to ﬁnd a mate. Brown (1959) reported

that equal numbers of males and females are typically found in populations of pine
15

l6

needle scale. Second generation eggs hatch in late July and develop to adults during late
summer. Adults mate, females oviposit, and the eggs overwinter below the female
“armor” or “tests” until the following May.

Scale damage to trees is both aesthetic and physical. Green winter foliage is an
important trait in Christmas trees, but pine needle scale armor is white and easily visible
on needles (Luck and Dahlsten 1974). Scales insert their long stylets through needle
stomates and feed on mesophyll tissue, which causes needle discoloration (yellow bands),
kills cells at the feeding site, and reduces net photosynthesis (Cumming 1953, Walstad et
al. 1973). When many scales feed on the same needle, the needle dies and falls off the
branch.

Management of this pest is difﬁcult for Christmas tree growers because crawlers of
both generations emerge over several weeks and individual crawlers are only vulnerable
to insecticides for a few days (Beard and McLeod 1992, Burks 1994, Cumming 1953).
However, dormant oils can be sprayed on overwintering scales to suffocate eggs (Nielsen
1990). Natural enemies regulate low populations, but are susceptible to pesticides
sprayed on trees (Luck and Dahlsten 1975). The tinting that growers use to improve
foliage color in the fall may also be intended to hide small scale infestations, but the
white armor remains visible on foliage, and persists even after scales die (Beard and
McLeod 1992).

Few studies have addressed potential host plant resistance to scale insects. Nielsen
and Johnson (1973) suggested that tree varieties grown under identical conditions might
have different levels of resistance to pine needle scale. Studies with a similar insect, the

black pineleaf scale (Nuculaspis calrform'ca (Coleman)), indicated that populations could

l7

adapt to individual host trees, leading to the formation of genetically differentiated demes
(Alstad et al. 1980, Edmunds 1973, Edmunds and Alstad 1978, 1981). A study in Israel
showed that varieties of Pinus halepensis (Mill) differed in resistance to the Israeli pine
bast scale (Matsucoccusjosephi Bodenheimer et Harpaz) (Mendel 1984). Another study
testing the effect of location and age of Euonymus varieties on the euonymus scale
(Unaspis euonymi (Comstock)), found one variety that was consistently more infested

(Brewer and Oliver 1987).

MATERIALS AND METHODS

Study site

The ﬁeld site located at the Michigan State University W. K. Kellogg Experimental
Forest (Kalamazoo County, Michigan) was hand-planted with 27 Scotch pine varieties in
1987. The 0.8 ha ﬁeld was bordered by mature white spruce (Picea glauca (Moench)
Voss) and Scotch pine. Each variety was planted in two adjacent rows in a north-south
direction with 6 x 6 ft (1.8 x 1.8 m) between trees. Spacing increased in some areas of
the ﬁeld as trees were sold or culled due to insect and disease damage. Trees were
sheared each July and herbaceous vegetation was mowed monthly during the growing

season. Pesticides were not sprayed on or near the ﬁeld during this study.

Scotch Pine Varieties

Four Scotch pine varieties were chosen for this study: Pike Lake Improved (var.
aquitana), Land 0' Pine (var. hercynica), Belgium (var. haguenensis) and Riga (var.
rigensis). These varieties were selected based on physical differences, range of
geographic origin, and the results of previous research (Ruby and Wright 1976, Tobolski
and Hanover 1971, Wright et al. 1975). Traits that differed among these varieties
included needle length, winter needle color and growth rate (Table 1). Twelve trees of

each variety were randomly chosen for the study.

18

19

Tree Characteristics

Measurements taken in 1994 included tree height, basal diameter, stem diameters
between the top second and third whorls and the third and fourth whorls, percentage
needle moisture, amount of needle twist, and percentage of total foliar nitrogen. In 1995,
tree height, basal diameter, diameter at breast height (1.4 m), rate of stem resin ﬂow,
percentage needle moisture, amount of needle twist, and percentage of total foliar
nitrogen were measured.

To test the rate of resin flow in each Scotch pine variety, each experimental tree was
artiﬁcially wounded using methods of Lorio and Sommers (1986). Wounds were created
by pushing a 1.3 cm arch punch into the phloem, twisting the punch to ﬁnish the cut and
removing the bark. A small triangular notch was cut beneath the wound to direct resin
ﬂow. An aluminum tray was set into a horizontal cut below the notch and was secured to
the tree with two push pins. The resin was channeled into a 15 ml polystyrene graduated
conical tube held to the tree with electrical tape. All materials were removed from trees
after the sampling was complete. Resin was sampled for 24 h on 26 May, 14 June and 18
July 1995. In May and June, only one wound was made on the middle south and south-
east sides of each tree, respectively, to prevent interference with Zimmerman pine moth
development. In July, after Zimmerman pine moth larvae had completed feeding,
wounds were made on the east, northeast, north and northwest sides of each tree, and
results were averaged per tree. Sampling occurred on days with no precipitation and
began after 9 am for each sampling period.

Needle biomass and percentage moisture were calculated by collecting needles and

measuring fresh and dry needle weights (4O one-year-old needles/tree on 30 July and 60

20
one-year-old needles on 6 September 1994; 20 one-year-old needles/tree on 12 May, 26

May, 8 June and 15 September 1995). Needles were removed from the upper half of the
east side of the tree, placed in paper bags, transported in a cooler to the lab and weighed.
Needles were dried to a constant weight for 48 h at 43 °C in a drying oven and weighed
again. Percentage moisture was determined by dividing wet weight by dry weight and
multiplying by 100. Length of 20 randomly selected needles collected from each tree in
September was measured in both years, and 10 needles randomly selected from each tree
were ranked for amount of twist (1/4 turn = 1, 1/2 turn = 2, 3/4 turn = 3, and 1 turn = 4).
To test the amount of total foliar nitrogen potentially available to herbivores, shoots
were collected from trees in early November of both years (Leaf 1990). In 1994, current
and one-year-old shoots on the east side in the upper third of the crown of each
experimental tree were cut, placed in individual paper bags, transported to the laboratory
in a cooler, then frozen at 4 °C. The analysis was conducted separately for both needle
ages on each tree. In 1995, current-year needles were again cut from branches in the
upper third of the crown on the east side of trees. Needles were oven-dried for over 48 h
at 60 °C, then ground up and stored in vials until further testing. In 1995, three samples
from each tree were analyzed, and results were averaged. Ms. Jill Fisher from the
Forestry Department, Michigan State University analyzed total nitrogen by ﬂash
combustion using the Carlo Erba 1500 Series II Nitrogen Analyzer (F isons Instruments,

Massachusetts, USA).

2 1
Weather Monitoring

Personnel at Kellogg Forest maintained daily records of maximum and minimum
temperatures and precipitation. Temperature was recorded with a Belfort
hygrothermograph (company, city) and precipitation was measured with a Forest Service
type rain gauge. Degree days were calculated by determining the mean temperature of
the day and subtracting the base temperature (50 °F) (Agnello et al. 1993). The starting

date was 1 January 1994 and 1995.

Insect Rearing

Zimmerman Pine Moth. Scotch pine trees infested with Zimmerman pine moth
larvae were collected from ﬁve plantations in southern Michigan in April 1994 and May
1995 and transported to the laboratory. Stems and branches were examined for larval
activityby removing bark from infested areas with a knife and forceps. Larval galleries
were carefully excavated until the larvae were found. Single larvae were placed in
plastic containers with small chunks of phloem and bark, and were transported to
Kellogg Forest the following day. A piece of phloem with a larva on it was carefully
placed next to the bark of the experimental tree and was secured to the main stem with
thin nylon mesh. The mesh cage was wrapped around the tree between two whorls of
branches and fastened ﬁrmly on both ends with electrical tape. In 1994, two larvae were
caged on each tree between different whorls, and in 1995 one larva was caged per tree.
Larval handling was minimized to reduce stress.

European Pine Sawﬂy. First instars were collected from wild populations in three

areas in Ingham County, Michigan, and transported to Kellogg Forest on 1 May 1994 and

22

5 May 1995. Since European pine sawﬂy larvae are gregarious, 10 larvae were
randomly selected and placed in a nylon mesh cage on each tree. One cage was
positioned on the east side of each tree at mid-canopy, around a large branch containing
old and new shoots. Cages were closed at both ends with electrical tape and larvae were
allowed to develop. Adverse weather was not a problem in 1994, but in 1995 all caged
sawﬂy larvae, larvae from overwintering eggs, and local populations of wild larvae under
observation died on 10 May during a heavy rainstorm. A new cohort of second instars
was located and placed in cages on 15 May, as previously described.

Pine Needle Scale. Before introducing scales to experimental trees at Kellogg Forest,
I collected several Scotch pine branches infested with pine needle scale from three local
Christmas tree ﬁelds and returned them to the laboratory. Using a dissecting scope and
micrometer, I measured lengths and widths of the waxy armor and soft scale bodies,
counted the number of eggs laid by each female, and the number of scales on each
needle. The total number of scales measured was 205. I tried to determine if the number
of scales feeding on a needle was related to scale fecundity, permitting me to estimate the
number of crawlers hatching in the ﬁrst generation.

Branches with female scale bodies were collected from Scotch pine trees at private
Christmas tree plantations in Ingham County in early May 1994. In May, 20 fecund
females of similar size still attached to needles were placed on foliage in nylon mesh
cages located on the lower west side of each experimental tree. Crawlers hatched from
the infested introduced needles and moved onto living needles on experimental trees in
late May. This infestation process was repeated in 1995, but 40 female scales instead of

20 were fastened to foliage in mid-May to increase the sample size of scales on each tree.

23

Insect Survival

Zimmerman Pine Moth. After the initial infestation, larvae were checked on 8 June,
23 June, and 1 July 1994, and 12 June, 23 June, and 4 July 1995 for evidence of larval
establishment on host trees. Since larval instars could not be identiﬁed in the ﬁeld,
larvae were classiﬁed as "early" at the time of the ﬁrst check, "middle" at the second
check and "late" at the last check. Caged larvae were considered alive when pitch or
frass was present and dead when cadavers were found or in the absence of pitch masses.
When cadavers or parasitoids were found within pitch masses, they were removed using
forceps, placed in plastic containers and frozen. Specimens were later sent to specialists
at the USDA-ARS for identiﬁcation. Checks for pupae occurred twice a week until all
caged Zimmerman pine moth were accounted for. Pupae were kept in plastic containers
until adults emerged.

Scotch pine resistance to Zimmerman pine moth was evaluated by computing
percentage larval survival at three stages, length of development period (days and degree
days), growth rate (mg/degree day), percentage pupal survival (pupation to adult
emergence), pupal fresh weight (mg), and adult fresh weight (mg). Survival among
varieties was analyzed by hand using Cochran's Q test (Zar 1996), then pooled and
organized into a cohort life table (Krebs 1985). To measure larval growth rate, the unit
mg/degree day was used rather than mg/day to avoid possible confounding effects of
increasing temperatures during the growing season.

Neuter values (sex effect standardized) were determined for development period,
growth rate, pupal and adult weights by converting values for individual males to female-

equivalent values (I-Iaukioja and Neuvonen 1985). For example, the weight of an

24
individual male was changed to its neuter value by multiplying the male's weight by the

ratio of mean female weight to mean male weight on each Scotch pine variety. This
procedure was done to minimize sex-based variability in the data analysis, and it resulted
in larger sample sizes.

European Pine Sawﬂy. Larval survival was monitored weekly from May until
pupation began, then survival was monitored daily until the end of pupation.
Development period (day and degree day) from the time of caging until pupation was
determined for larvae on each tree. Growth rate was determined by dividing pupal
weight by the number of accumulated degree days. Neuter values (sex effect
standardized) were computed for pupal weight, adult weight, development period and
growth rate (Haukioja and Neuvonen 1985).

In 1994, pupae lying at the bottom of cages were vulnerable to parasitism and
predation. In 1995, pupae were placed in a small nylon mesh pouch and hung inside the
cage with a wire twist tie. Pupae were removed from pouches at the end of August,
when little parasitism was expected, and left in the foliage or at the bottom of cages.
After adult emergence, the remaining pupae were dissected to determine pupal fates.
Parasitoid specimens were collected from cages and sawﬂy pupae, and were later
identiﬁed to species by a specialist at the USDA-ARS.

Number of needles consumed and amount of frass produced in each cage were
determined after pupation to minimize larval disturbance. One-year-old needles missing
from the shoot with recent wounds at the fascicle were considered to be eaten by larvae.
Frequent visits to each cage disturbed accumulated frass and occasionally caused a small

amount to slip through the small mesh holes; I assumed that each cage lost a similar

25

amount. The collected frass was sifted and all needles, dead insects and exuviae were
removed. F rass was dried for 48 h at 43 °C, then weighed. Since the greatest amount of
feeding occured in later instars, measurements of needle biomass consumption and frass
production for each cage were divided by the number of larvae surviving through the
ﬁnal instar. This calculation allowed me to make comparisons among the amount of
needle biomass consumed, pupal weight, development time and growth rate.

Pine Needle Scale. Surviving pine needle scales were counted once in June and July,
twice in August, and once in October of both years. Live and dead scales were
determined based on the color and condition of the scale armor, presence of fungus on
scale bodies, and evidence of parasitism or predation (Luck and Dahlsten 1975). The
accuracy of counting scales varied due to extended crawler emergence and sampling
error, so only the data with a high degree of conﬁdence are presented. One coccinelid
found feeding on eggs was identiﬁed by a specialist at Michigan State University.

As second generation pine needle scale survival was determined in the lab, I also
tried to quantify needle damage by scales. I recorded the number of female scales
causing needle necrosis from their feeding, the location of the female on the needle
surface (ﬂat or round side), and whether needle necrosis was more prevalent depending

on where females were located.

Insect Fecundity
Zimmerman Pine Moth. Checks for pupae were done twice a week from early July
until late August. When live pupae were found, they were removed from pitch masses,

weighed in the laboratory within 12 h and placed in plastic containers until adult

26
emergence. Adults were kept alive in 1995 for 24 h to increase the likelihood of egg

production, then were frozen until dissections could be made. Adults were weighed and
sexed at the laboratory. Female adults were dissected and number of eggs was
determined.

European Pine Sawﬂy. Cages were checked daily from the ﬁrst day of pupation in
late May to early July. New pupae were removed from cages, transported to the
laboratory and weighed within 12 h. Pupae were returned to their cage after all larvae
from that cage had pupated. Adults emerged in the fall, mated, oviposited and died in
the cages. Several wild males were observed landing on cages, apparently attracted by
female pheromones, but no mating through the mesh was observed. I assumed that
virgin and mated females could produce similar numbers of eggs based on previous
reports (Benjamin et al. 1955, Grifﬁths 1959, Hardy and Allen 1975). Number of eggs
laid in each cage was counted and related to number of ovipositing females and number
of needles with eggs. In 1994, sawﬂy eggs were left to overwinter on the trees, but
branches were cut and brought to the laboratory in 1995.

Pine Needle Scale. After the initial infestation, scales were allowed to develop under
ﬁeld conditions. Branches were cut off the experimental trees in late October in both
years and brought to the laboratory. Infested needles were removed from branches and
stored in plastic bags in the freezer. During the winter, the number of eggs laid per
female was counted under a dissecting scope. The number of females examined for
fecundity varied, depending on survival on each tree. When possible, fecundity was
determined for 20 females from each infested branch in 1994, and 30 females in 1995.

T0 count eggs, an infested needle was held with forceps and the female armor was

27

carefully pried up on one side with a probe. Number of live eggs laid under the armor
was counted. Live eggs were oval and bright red, dead eggs were brown, and pieces of
white chorion gave evidence of hatched or predated eggs. Evidence of parasitism and

third generation egg hatch were noted for each adult female in 1995.

Statistical Analysis

Measurements of tree growth, insect survival and fecundity for each year were tested
for homogeneity of variance with the Levene test (IMP for Windows, Version 3.1, SAS
Institute 1995). The Shapiro-Wilk test was used to test for normality of data. A one-way
analysis of variance (AN OVA) was used to determine if results differed by variety when
data were normally distributed and variance was homogeneous (Zar 1996). Given non-
homogeneous variances, the Welch statistic was used to test the signiﬁcance of the
ANOVA. The [log (x+1)] transformation was applied to all insect survival and fecundity
data to adjust for non-normality, but tree measurements did not require transformation.
All ANOVAs signiﬁcant at the p<0.05 level were tested with Tukey’s Honestly
Signiﬁcant Difference multiple comparisons test to further evaluate differences among
varieties. When two variables were normally distributed, Pearson’s product-moment test
was used to analyze correlations. If one or both variables were not normally distributed,
Spearman’s nonparametric test was used to analyze the signiﬁcance of correlations. The
relationship between pupal weight and fecundity for Zimmerman pine moth and
European pine sawﬂy was tested using regression analysis. Backward-stepping multiple
regressions were used to predict insect survival and fecundity from tree growth variables

in both years.

RESULTS

Tree Characteristics

From 1994 to 1995, Belgium and Riga trees had signiﬁcantly greater basal diameter
growth than Land 0’ Pine and Pike Lake Improved trees (F =9.43, df=3, p<0.001) (Table
2). For all trees, mean basal diameters ranged from 6.4 to 9.7 cm in 1994, and grew an
additional 1.8 to 3.3 cm in 1995. Belgium and Pike Lake Improved trees had the largest
stem diameters in 1994 (F=21.11, df=3, p<0.001), but Belgium trees were tallest
(F =38.99, df=3, p<0.001). In 1995, stem diameters were signiﬁcantly smaller in Riga
trees than in the other three varieties (F=13.86, df=3, p<0.001), and tree height was
signiﬁcantly greater in Belgium trees (F =19.85, df=3, p<0.001). Mean tree height
ranged from 192 to 260 cm in 1994, and trees grew in height between 12 to 20 cm during
the following year. However, tree height was reduced by annual shearing, and height
growth from 1994 to 1995 was not signiﬁcantly different among varieties.

Rate of resin ﬂow was variable both within and among varieties (Figure 1). No
signiﬁcant differences among varieties occurred on any of the three sampling dates, or
when the results from all three sampling dates were averaged and analyzed. Basal stern
diameter was signiﬁcantly and negatively associated with the amount of resin ﬂowing on
14 June 1995, indicating that smaller stern diameters had higher rates of resin ﬂow

(Table 3).

28

29
In 1994, needle length was signiﬁcantly shorter for Riga and Pike Lake Improved

than for Belgium and Land 0’ Pine (F=5.42, df=3, p<0.01) (Table 2). Percentage
moisture in current-year needles on Riga was signiﬁcantly lower than in needles from the
other varieties (F=15.51, df=3, p<0.001), but moisture in one-year-old needles did not
differ signiﬁcantly among varieties. Percentage nitrogen in current-year needles and
needle twist did not differ among varieties. However, percentage nitrogen in one-year-
old needles was signiﬁcantly higher in Belgium trees than in Land 0’ Pine trees (F =2.96,
df=3, p<0.05) (Table 2). Signiﬁcant correlations were found among tree height, stem
diameter, basal diameter, percentage needle moisture, needle length, percentage nitrogen
in needles and needle twist (Table 3).

In 1995, Riga and Pike Lake Improved had the shortest needles and Belgium had the
longest needles (F=8. 16, df=3, p<0.001) (Table 2). In terms of foliage density, Pike
Lake Improved had signiﬁcantly more needles on 5 cm of shoot than the other varieties
(F=2.76, df=3, p=0.05). Percentage needle moisture was inconsistent among sampling
dates. No signiﬁcant differences were detected in early May, but in late May, percentage
foliage moisture was signiﬁcantly higher on Riga than on Land 0’ Pine trees (F=3 .95,
df=3, p<0.05). In early June, percentage foliage moisture was signiﬁcantly higher on
Land 0’ Pine than on Belgium trees (F =2.77, df=3, p<0.05). Percentage nitrogen in
current-year needles and needle twist did not signiﬁcantly differ among varieties (Table
2), and percentage nitrogen was not signiﬁcantly correlated with any other tree
measurement. Signiﬁcant correlations were found among tree height, stem diameter,

basal diameter, percentage needle moisture, length and density on shoots (Table 3).

30
Weather Monitoring

Winter and summer temperatures in 1994 were cooler than in 1995 at Kellogg Forest
(Table 4). Extremely cold temperatures occurred from 15 January to 20 January 1994,
when the maximum daily temperature was -12.2 °C and the minimum daily temperature
dropped to -29.4 °C. Temperatures in 1995 warmed up quickly in the spring and

remained hot all summer. Monthly precipitation totals were similar in both years.

Insect Survival

Zimmerman Pine Moth. I did not detect any signiﬁcant differences in larval or pupal
survival among Scotch pine varieties in 1994 (Figure 2). Percentage survival dropped
uniformly in all varieties during the middle larval instars, then survival remained
relatively constant from the last instar through adult emergence. Survival data from the
varieties were pooled and organized into a cohort life table (Table 5). Only 27% of the
larvae survived to the adult stage. Almost half of the mortality occurred before larvae
reached the middle instars. Overall survival of Zimmerman pine moth during each life
stage was not signiﬁcantly different when varieties were pooled and when larvae caged
between different whorls were tested (Table 6).

Again, in 1995, no signiﬁcant differences in larval or pupal survival were detected
among varieties (Figure 2). Although early larval survival was high, survival from the
middle to late instars rapidly dropped and then stabilized through to adult emergence.
After data from varieties were combined into a cohort life table, I determined that only

8% of the larvae originally caged on trees survived to the adult stage (Table 5). Over

31

two-thirds of the mortality had occurred before larvae reached the late instars. Overall
survival of Zimmerman pine moth during each life stage was again not signiﬁcant when
varieties were pooled (Table 6).

The factors causing mortality to Zimmerman pine moth larvae in 1994 included
parasitism, fungal infection, and unknown factors. Some of the 21 early larval deaths
categorized as “unknown” may have resulted from poor establishment after introduction
to the trees (Table 5). The parasitoid wasps that attacked Zimmerman pine moth larvae
were Exeristes comstockii (Cresson) (Hymenoptera: Ichneumonidae) and Hyssopus
rhyacioniae (Gahan) (Hymenoptera: Eulophidae), as identiﬁed by Dr. John Luhman of
the Minnesota Department of Agriculture, Plant Protection Division, and M. E. Schauff
of the USDA Systematic Entomology Laboratory. Parasitized larvae were found within
pitch masses as early as 22 June 1994. Of the 15 Zimmerman pine moth larvae known to
be parasitized, E. comstockii killed 10 of the larvae and Hyssopus rhycioniae killed 5
larvae. Exeristes comstockii laid one to four eggs on Zimmerman pine moth larvae,
which developed to the adult stage within the pitch masses. Those that attacked larvae
later in the summer overwintered as adults inside pitch masses and emerged in the spring.
I also found larvae infected with the fungus Hirsutella nodulosa (Petch), but had
confused symptoms of infection with evidence that larvae had drowned in pitch in
feeding tunnels. Dr. Richard Humber from the US Plant, Soil, and Nutrition Laboratory
provided the species identiﬁcation. The fungus accounted for eight larval deaths, in
addition to some larvae not developing diagnostic symptoms and were considered
“unknown.” It is possible that Zimmerman pine moth larvae escaped from cages and re-

entered the phloem in other areas on trees. Single exit holes were chewed through the

32

mesh used for cages, and I observed several larvae from wild populations exiting fresh
pitch masses and boring into new areas on stems of the experimental trees. Two pupae
died from being injured during removal from host trees.

In 1995, factors causing mortality to Zimmerman pine moth again included
parasitism, infection by Hirsutella nodulosa (Petch), and unknown factors. Parasitized
Zimmerman pine moth larvae were found within pitch masses beginning 22 July 1995.
Hyssopus rhyacioniae was the primary parasitoid throughout the summer, killing six of
the seven parasitized Zimmerman pine moth larvae (Table 5), but E. comstockii did kill
one Zimmerman pine moth larva. Hyssopus rhyacioniae had two or more generations
during the year, and its offspring completed development within a month after hatching
from eggs. I found 1 to 9 eggs laid on Zimmerman pine moth larvae by H. rhyacioniae
adults during the summer of 1995. These adults mated, laid eggs, the pupae
overwintered and ﬁnished development in early spring. Two larvae were obviously
infected with the fungus H. nodulosa in 1995, but some larvae that died from “unknown”
causes may have also been infected without the fungus being detected. Several unknown
mites were found on or near Zimmerman pine moth larvae infected with H. nodulosa, but
were not recognized at that time as being potential vectors of the fungus and were not
identiﬁed. One pupa died from being injured during removal from its host tree.

In 1994, after being caged, larvae fed on phloem until pupation, which occurred
between 15 June and 1 August. Adult emergence lasted from 26 June to 17 August 1994.
Mean development of healthy larvae lasted from 81 to 95 days (861 to 1,094 degree
days); means did not signiﬁcantly vary among Scotch pine varieties (Table 7). Mean

neuter pupal weights ranged from 85 mg to 95 mg, and mean adult weights ranged from

33
40 to 53 mg. Growth rate, pupal and adult weights also did not differ signiﬁcantly

among varieties. However, pupal weight was signiﬁcantly and positively correlated with
development period, indicating that larvae that fed longer had higher pupal weights
(Table 8). Pupal length was signiﬁcantly correlated with pupal weight. Stem diameter
between the upper second and third whorls on trees was positively correlated with pupal
weight and development period (days and degree days), which suggested that stem or
phloem thickness in areas where larvae fed could affect larval growth and development
(Table 8).

In 1995, larval development on experimental trees lasted 91 to 100 days, or 1682 to
1952 degree days until pupation (Table 7). Pupation lasted from 20 June to 1 August,
and adults emerged from 6 July to 17 August. The time required for the development of
each life stage appeared to be constant each year despite differences in degree day
accumulation. No signiﬁcant differences were found among varieties for development
period (days or degree days), grth rate, pupal or adult weight in 1995 (Table 7). Pupal
length was again signiﬁcantly correlated with pupal weight (Table 8).

European Pine Sawﬂy. Survival of European pine sawﬂy larvae, pupae and adults
varied among Scotch pine varieties, but differences were not always signiﬁcant at each
life stage. In 1994, sawﬂy larvae were present in the ﬁeld from approximately 26 April
to 12 June 1994, pupation began on 6 June, and adults were present from early
September to mid-October. Percentage survival to the adult stage was signiﬁcantly
higher for sawﬂies reared on Land 0’ Pine or Pike Lake Improved than for larvae reared

on Riga trees (F=2.89, df=3, p<0.05) (Figure 3). Overall survival did not signiﬁcantly

34

differ among Belgium, Land 0’ Pine and Pike Lake Improved; these three varieties were
therefore pooled and compared to Riga in cohort life tables (Table 9). Percentage
mortality was greatest during the period between the ﬁrst and third instars and during
pupation, but mortality was 21% higher for sawﬂies on Riga than on other varieties.
Early larval mortality may have resulted from an inability to establish colonies or feeding
sites. Only 39% of all pupae survived to become adults, while 2% emerged from pupae
poorly developed, 30% were parasitized, 17% were preyed upon, 3% had entered
extended diapause, and 9% died of unknown causes. The most common pupal parasitoid
was Pleolophus basizonus (Gravenhorst) (Hymenoptera: Ichneumonidae), and only
single parasitoids larvae were found developing within each sawﬂy cocoon.

In 1995, sawﬂy larvae began hatching from eggs on 1 May and were active in the
ﬁeld until 24 June 1995. Pupation began on 4 June, and adults were present from
September to mid-October. Degree day accumulation as determined by Kellogg Forest
personnel was more rapid in 1995 than in 1994 due to higher temperatures in early
summer (Table 4). It has been shown that with higher summer temperatures, European
pine sawﬂy eonymphal diapause in cocoons is intensiﬁed (Knerer 1983). This
apparently resulted in more rapid sawﬂy larval development and may have contributed to
later adult emergence.

In 1995, survival during the third instar was lowest for sawﬂies caged on Riga and
highest on Belgium and Pike Lake Improved (F=3.32, df=3, p<0.05) (Figure 3).

Survival to the last instar, pupal and adult stages did not signiﬁcantly differ among
varieties. Again, data on sawﬂy survival for varieties Belgium, Land 0’ Pine and Pike

Lake Improved were pooled and compared to Riga in cohort life tables (Table 10).

35
Percentage mortality during the ﬁrst through third instars and pupation was 9 to 13%

higher on Riga than on the other varieties. By 27 October 1995, 76% of all pupae
survived to become adults, while 2% emerged from pupae poorly developed, 5% had
reached the adult stage and died in the cocoon, 2% had entered extended diapause, and
11% died of unknown causes. Overall survival was higher in 1995 than in 1994 because
in 1995, ﬁrst instars killed in a heavy rainstorm were replaced with second instars, and I
protected pupae from parasitism by suspending them in mesh fabric within cages.

I expected to ﬁnd differences in needle consumption and sawﬂy growth rate given
the differences in survival. However, in 1994, there were no signiﬁcant differences
among varieties in needle biomass consumption or frass production (Table 11). Larval
growth rate was signiﬁcantly lower (F=5.56, df=3, p<0.01) and development period
(days) (F =4.06, df=3, p<0.01) and (degree days) (F=4.68, df=3, p<0.01) was
signiﬁcantly longer for sawﬂies on Riga, which suggests that compensatory feeding
occurred. Needle biomass consumed was positively correlated with development period
(degree days); larvae that fed longer before pupation consumed more needles (Table 12).
Percentage nitrogen and percentage moisture in needles were not signiﬁcantly correlated
with larval feeding or survival measurements. Backward-stepping multiple regressions
were able to signiﬁcantly predict larval development period using degree of twist of one-
year-old needles and tree height as predictors in 1994 (r2=0.23 ), but were unable to
predict biomass consumption or survival (Table 13).

In 1995, sawﬂies caged on Riga consumed signiﬁcantly more needle biomass than
sawﬂies on Land 0’ Pine or Pike Lake Improved (F =4.35, df=3, p<0.01) (Table 11).

This may indicate that larvae reared on Riga again did some compensatory feeding.

36

Frass production did not signiﬁcantly differ among sawﬂies on the four varieties. Larval
growth rate was signiﬁcantly lower on Land 0’ Pine and Pike Lake Improved than on
Belgium (F =5.73, df=3, p<0.001). Development period (degree days) was signiﬁcantly
longer for sawﬂies on Land 0’ Pine than on Belgium (F=2.82, df=3, p<0.05), indicating
that compensatory feeding may have occurred on Land 0’ Pine. Larval development
period lasted from 28 to 40 d. Larval development period (days and degree days) and
percentage foliar nitrogen were positively correlated with pupal weight (Table 12).
Percentage foliar nitrogen was not signiﬁcantly correlated with other larval feeding or
survival measurements. Backward-stepping multiple regressions were able to
signiﬁcantly predict larval development period using degree of twist of current-year
needles and tree height as predictors in 1995 (r2=0.19), but did not signiﬁcantly predict
needle biomass consumption or sawfly survival (Table 13).

Pine Needle Scale. Before beginning the main study, I measured armor of 205
female scales from wild populations to determine some basic information. On average,
the soft female body was 1.06 mm ($0.02) long and 0.48 mm (i001) wide. Mean armor
size was 2.27 mm (1003) long and 0.90 mm (£0.01) wide. Mean number of live eggs
laid per female was 18.3 ($0.8). I found a strong positive association between female
armor length and the number of eggs laid per female in 1994 (Table 14). Armor length
was correlated with body length, needle width and needle length. Body length was
negatively associated with scale density. F ecundity and scale density were not
signiﬁcantly correlated with needle length nor width.

Scale survival differed from the ﬁrst to second generations, but was difﬁcult to

37
accurately determine in the ﬁeld. Luck and Dahlsten (1975) also had difﬁculty in

accurately assessing ﬁeld scale densities, reducing the likelihood of detecting signiﬁcant
differences. In 1994, ﬁrst generation pine needle scale survival did not signiﬁcantly
differ among varieties of Scotch pine (Table 15). From the twenty females originally
used to infest experimental branches, only 15 to 28 crawlers per tree survived through
June. The population increased in the second generation to between 77 and 293 scales
per tree. Survival of second generation scales caged on Belgium trees was signiﬁcantly
lower than for scales caged on Pike Lake Improved trees (F =3.05, df=3, p<0.05) (Table
15). Using a backward-stepping multiple regression, I was unable to signiﬁcantly predict
scale survival using the tree traits measured in this study (Table 16). However, second
generation survival was signiﬁcantly correlated with percentage needle moisture in
August and basal diameter, but not tree growth rate (Table 14). First and second
generation survival were also correlated, indicating that if ﬁrst generation survival was
high, survival of the second generation should be high also. Rates of parasitism in the
ﬁeld and the species of parasitoids could not be determined.

In 1995, survival of ﬁrst generation scales reared on Riga trees was signiﬁcantly
higher than for scales on Land 0’ Pine trees (F =3.67, df=3, p<0.05) (Table 15). Survival
of second generation scales reared on Riga trees was signiﬁcantly higher than on
Belgium and Land 0’ Pine in early August (F=3.48, df=3, p<0.05) and mid-October
(F=4.87, df=3, p<0.05). Only 48 to 71 percent of female scales still attached to needles
in October had laid eggs. Using a backward-stepping multiple regression, basal diameter

and percentage needle moisture in May signiﬁcantly predicted second generation survival

38
(Table 16). Second generation survival was signiﬁcantly correlated with tree height,

stem diameter, basal diameter growth rate, and percentage needle moisture in May (Table
14). These associations suggested that tree vigor affected scale survival. However, ﬁrst
and second generation scale survival were not correlated, indicating that an external
factor (e.g., predation, parasitism) was more critical to survival than host factors, or
something I did not measure.

In 1995, causes of scale mortality included fungal infection, parasitism, or predation.
Some of the females who were still alive in October, but had not laid eggs may not have
been fertilized. Rates of parasitism in the ﬁeld and parasitoid species were not
determined. I found coccinelid larvae and adults, identiﬁed as Coccidophilus marginatus
(LeConte) by Dr. Richard Leschen at Michigan State University, feeding on natural and
study populations of pine needle scale. Adults chewed holes in female armor and fed on
eggs and female bodies in early spring and late summer. When infested branches were
removed from experimental trees and brought to the lab in October, C. marginatus larvae
of several instars were found beneath female scale armor, consuming eggs.

I did not ﬁnd any signiﬁcant differences in location of scale feeding and damage
among the four varieties in 1995. Between 71 and 88 percent of female pine needle
scales were found on the ﬂat side of needles (inner fascicle), while the rest were found on
the round outer side of the needle. Yellow bands of necrotic tissue resulted from the
feeding of 52 to 72 percent of the females examined. Of those females causing cell
necrosis, 76 to 92 percent of the damage was from females feeding on the ﬂat side, and 8

to 24 percent of the damage resulted from females feeding on the round side of needles.

39

Insect Fecundity

Zimmerman Pine Moth. Fecundity did not signiﬁcantly differ among varieties in
1995 (Table 7). Of the 10 females dissected, the number of eggs per female ranged from
10 to 44. Female survival was too low under ﬁeld conditions to determine differences
among varieties. However, fecundity was positively correlated with adult weight (Table
8) and could be predicted by pupal weight (Figure 4). In 1994, pupal weight was
positively correlated with development period. The signiﬁcant correlation between pupal
weight and tree stem diameter where larvae were caged in 1994 may also suggest that
tree growth or vigor affected Zimmerman pine moth fecundity (Table 8). In addition,
backward-stepping multiple regressions using tree variables as predictors signiﬁcantly
predicted pupal weight in both years (Table 17). In 1994, stem diameter, tree height and
percentage foliar nitrogen were signiﬁcant predictors (r2=0.62), while in 1995, basal
diameter, percentage foliar nitrogen, tree height and rate of resin ﬂow from May to June
predicted a signiﬁcant proportion of Zimmerman pine moth pupal weight (r2=0.95).

European Pine Sawﬂy. European pine sawﬂy pupal weight and fecundity on the four
varieties were measured (Table 18), although few females survived to the adult stage.
Sawﬂies caged on Riga had lower pupal weight than on Belgium and Pike Lake
Improved (F=3.53, df=3, p<0.05), but other variables did not signiﬁcantly differ among
varieties. The number of eggs laid per female ranged from 14 to 59, and the number of
eggs laid per needle ranged from 3 to 8. I found signiﬁcant correlations between pupal
weight and fecundity, needle biomass consumption and fecundity, and between tree
growth and fecundity (Table 12). Backward-stepping multiple regressions did not

signiﬁcantly predict pupal weight using any of the measured tree characteristics in 1994.

40
In 1995, females caged on Riga laid fewer eggs compared to the other varieties

(F=4.66, df=3, p<0.01) (Table 18). However, pupal weights were lower for females
caged on Land 0’ Pine and were highest on Belgium (F=4. 12, df=3, p<0.01). The
number of eggs laid per female ranged from 3 to 114 in 1995. Similarly, the number of
eggs laid per needle ranged from 1 to 8. I also detected signiﬁcant correlations among
pupal weight, development period (days and degree days), percentage foliar nitrogen, and
fecundity (Table 12). A regression between pupal weight and number of eggs laid per
female was statistically signiﬁcant (Figure 5), indicating that heavier pupae were more
fecund as adults. Backward-stepping multiple regressions did not signiﬁcantly predict
pupal weight using any of the measured tree characteristics.

Pine Needle Scale. I detected differences in scale fecundity among varieties in 1994
(Table 15). Number of eggs laid per female ranged from 15 to 48. Scales reared on Pike
Lake Improved laid more eggs per female than scales on the other varieties (F =6.79,
df=3, p<0.01). Using a backward-stepping multiple regression, I could not signiﬁcantly
predict second generation pine needle scale fecundity with the tree traits measured in this
study. Fecundity was not correlated with percentage foliar nitrogen or percentage
moisture content.

In 1995, females on Land 0’ Pine had signiﬁcantly lower fecundity than females on
the other varieties (F =4.97, df=3, p<0.05) (Table 18). The number of eggs laid per
female ranged from 17 to 55 on trees. Using a backward-stepping multiple regression, I
signiﬁcantly predicted second generation pine needle scale fecundity with percentage

needle moisture in May and September and percentage foliar nitrogen (Table 16).

DISCUSSION

Differences Among Varieties

The four Scotch pine varieties used in this study differed in traits potentially affecting
susceptibility to insect pests, including tree height, stem diameter, needle length, needle
density, percentage nitrogen and moisture in needles, and height and basal diameter
growth rates. The faster basal diameter growth rate in both Riga and Belgium trees was
unexpected. Riga trees typically had smaller stern diameters than the other three
varieties, which suggested that growth rates would be slower as well. Perhaps in the
reportedly faster growing varieties, like Belgium and Land 0’ Pine, growth rates had
declined over time, which comparatively increased the relative growth rate in Riga.
Greater needle density in Pike Lake Improved trees may have compensated for less leaf
area in short needles (Mooney et al. 1988, Sadof and Raupp 1991).

Some other tree variables, including growth and differences in monoterpene
concentration and resin acids, were previously studied in several Scotch pine Christmas
tree varieties in Michigan. Among the four varieties, Pike Lake Improved (var.
aquitana) and Riga (var. rigensis) were short and of similar heights, Land 0’ Pine (var.
hercynica) was moderately tall, and Belgium (var. haguenensis) was the tallest variety
with the fastest growth rate (Ruby and Wright 1976, Wright et al. 1966). From foliage
color ranks, southern European varieties (e.g., Pike Lake Improved) were greenest,

Scandinavian varieties (e. g., Riga) were yellowest and central European varieties had
41

42
intermediate hues of green (Ruby and Wright 1976, Wright et al. 1966). Needles were

longest in Belgium, moderately long in Land 0’ Pine, short in Riga, and shortest in Pike
Lake Improved (Ruby and Wright 1976, Wright et al. 1966). In general, Scandinavian
varieties (e. g. Riga) had lower concentrations of cortical monoterpenes (Tobolski and
Hanover 1971), higher concentrations of resin acids, lower oleoresin pressure and smaller
resin canal cross-sectional areas than the other varieties (Bridgen and Hanover 1982).
Nutrient differences in foliage among varieties were apparent, but statistical signiﬁcance
was not reported (Ruby and Wright 1976).

The correlations among tree variables indicated that most of the traits measured were
interrelated. For example, shearing may reduce tree height growth rate by removing
shoots and promoting lateral bud growth (Hill 1989, Langstrom et al. 1989), but it does
not eliminate the genetic effects contributing to varietal differences in growth rate,
considering the strong correlations among stem diameter, basal diameter and tree height.
Foliar moisture and nitrogen content are known to be correlated (Mattson 1980), but I
also found strong correlations between stem diameter and both foliar moisture and
nitrogen content. A negative correlation between basal diameter and rate of resin ﬂow in
June suggested that resin ﬂow decreased in trees with larger diameters, although this
association was not consistent. Even needle length was associated with tree height, stern
diameter and needle density. Understanding the interrelatedness of these tree variables
may contribute to understanding relationships between insect performance and variety

differences.

43

Differences in Variety Resistance to Zimmerman Pine Moth

Wright et al. (1975) suggested that fast-growing Scotch pine varieties from central
Europe (e.g., Belgium and Land 0’ Pine) were most susceptible to Zimmerman pine
moth infestation, northern European varieties (e.g., Riga) were moderate and southern
European varieties (e.g., Pike Lake Improved) were most resistant in mixed plantings.
These conclusions were based on observations of natural attack rates without considering
the survival or fecundity of Zimmerman pine moth reared on trees of each variety. Our
results did not indicate that Zimmerman pine moth survival and fecundity differed
signiﬁcantly among the four varieties. Therefore, we hypothesized that host selection
may be primarily determined by females during oviposition. Adults may be inﬂuenced
by cues such as volatiles emitted from resin at the site of larval feeding or shearing
wounds. Once adults deposit eggs and larvae develop in trees, parasitism and fungal
infection become important factors in larval survival, apparently outweighing potential
host plant differences.

Primary host selection by adult moths attracted to recently sheared or pruned trees
has been proposed by researchers studying other Dioryctria species (Asher 1970, Jactel et
al. 1994, Wright et al. 1975). Branch wounds on sheared Christmas trees need several
weeks to heal, and I suspect (but have no data for) that volatiles from sheared trees may
attract Zimmerman pine moth females searching for an oviposition site. I also suspect
that emerging adults may be affected by host stimuli (Jaenike 1988), such as volatiles in
pitch masses, which later attract adults to previously infested or wounded trees. If adults

still inside the pitch masses were forced to leave through the small exit hole made by

44

larvae, and were sensitive to the volatiles upon emergence, it seems possible that adults
would return to similar conditions when mating and ovipositing. Examples of early adult
host learning behavior in several insect orders are cited by Jaenike (1988). This could
pose problems for Christmas tree growers who continue to plant the same varieties of
Scotch pine and do not destroy infested trees.

In 1995, I tested whether larvae could have been “pitched out” by excessive stem
resin ﬂow when white crystallized resin-like specks were found on larval cadavers during
the previous summer. Due to low rates of resin ﬂow and low Zimmerman pine moth
survival from other factors, I could not determine a critical rate of resin flow at which
larvae could be killed, but I suspected that resin ﬂow may be more effective against small
Zimmerman pine moth larvae in May than later in the summer. Some level of resin ﬂow
must be acceptable to larvae because I observed several larvae pushing frass out of exit
holes in the bark to create pitch masses. In timber trees, southern pine beetle
(Dendroctonusﬁontalis Zimm.; Coleoptera: Scolytidae) success is negatively affected by
resin ﬂow in four southern pine species (Hodges et al. 1979). Lorio (1994) and Blanche
et al. (1992) found correlations between rates of resin ﬂow in loblolly pine (Pinus taeda
L.) and soil water storage, maximum temperature and cumulative water deﬁcit when
studied in relation to bark beetle attack, indicating important environmental effects on
tree susceptibility. It may be possible that the amount of resin annually lost by Christmas
trees due to shearing could reduce stem resin ﬂow and temporarily increase susceptibility
to phloem-borers, but this has not been studied. However, Jactel et al. (1994)

demonstrated that the level of attack by Dioryctria sylvestrella (Ratz) of pruned

45

maritime pine (Pinus pinaster) in France increased with the intensity of branch pruning.
Larval choice of feeding sites may be limited to areas on individual trees near the
oviposition site (Carlson and Butcher 1967). The multiple regression predictions of
pupal weight using stem diameter, tree height, percentage foliar nitrogen, and rate of
resin ﬂow suggest that an optimum stem size, bark or phloem thickness, whorl age, or
tree growth rate may exist for larval development (Carlson 1965, Jactel et al. 1994), but
adult oviposition preferences may not directly correspond to larval feeding preferences
(F atzinger and Merkel 1985). Percentage nitrogen may be one of the most limiting
factors of development since its concentration in phloem is low (Mattson 1980). Highest
concentrations of nitrogen occur in young, actively growing tissues (Mattson 1980). For
other phloem-feeders (e.g., bark beetles in slash pine, Pinus elliottii Engelm.), phloem
thickness affects the proportions of xylem, phloem and outer bark encountered while
insects tunnel (I-Iaack et al. 1984). Thicker phloem may contain relatively more
nutrients, provide larvae adequate space to excavate tunnels, and increase stem tissue
thickness to minimize chances of parasitism. In addition, if vigorous tree growth results
in thinner outer bark or greater bark cracking in younger whorls, larvae may more easily
enter the'phloem in those areas (Carlson 1962, Mauge 1987, Wright et al. 1975).
Zimmerman pine moth larval survival was reduced by parasitism and fungal infection
in both years. The parasitoids Exeristes comsrockii (Cresson) and H yssopus rhyacioniae
(Gahan) have been previously reported as natural enemies of Zimmerman pine moth
(Carlson and Butcher 1967, Carlson and Wilson 1967, Krombein et al. 1979, Neunzig et

al. 1964a) and other Dioryctria species (Hainze and Benjamin 1985, Neel and Sartor

46
1969, Wong 1972), but this is the ﬁrst record of Hirsutella nodulosa (Petch) infection on

Zimmerman pine moth larvae. Both parasitoids and fungus attacked multiple instars of
Zimmerman pine moth and killed larvae inside their tunnels.

The following life cycle for E. comstockii is from the life history study by Arthur
(1963). This ichneumonid parasitoid is native to North America and is distributed
throughout the United States. First generation adults become active in mid-May, the
second generation is present in late June and a partial third generation occurs during the
fall. Females can live up to 100 days if a food source is available, and males live up to a
month. Most females paralyze larval prey with their ovipositors before laying one or
more eggs on or near the larvae. Each female may be capable of laying up to 153 eggs,
and can lay 15 eggs per day. Eggs hatch in about two days, and development to adult
emergence may last up to one month. When temperatures drop in the fall, E. comstockii
larvae develop to the mature larval stage and remain protected in the host tunnel until
spring. Other hosts include Dioryctria disclusa Heinrich, Eucosma monitorana Heinrich,
Argyresthia laricella Kft., Laspeyresia caryana (Fitch), and other coleopterous and
lepidopterous hosts (Eidt and Sippel 1961, Lyons l957a,b, Townes and Townes 1960).

The life cycle and speciﬁc habits of Hyssopus rhyacioniae have not been determined.
Its taxonomy as reared from the pine tip moth, Rhyacioniaﬁustrana (Comstock), was
described by Gahan (1927). Hyssopus rhyacioniae is native to North America,
gregarious as larvae, and adults lay from 3 to 12 eggs on mature host larvae (Cushman
1927). Its mating behavior was described by Greenbaum (1976). Other known hosts for

this eulophid parasitoid include Dioryctria resinosella, Dioryctria taedae Schaber and

47
Wood, D. abietella (D. & S.), D. amatella (Hulst), and D. cambiicola (Dyar) (Hainze

and Benjamin 1985, Krombein et al. 1979, Schaber 1981).

H. nodulosa is an entomopathogenic fungus previously found on the coffee borer
(Zeuzera coﬂeae) in Sri Lanka and on the strawberry mite ( T arsonemus fragariae) in
England (Minter and Brady 1980). It has recently been found infecting spruce budworm
(Chorisloneuraﬁlmiferana (Clemens)) larvae in New Brunswick, Canada (Strongman et
al. 1990). Symptoms of infection include cessation of larval feeding, larval color
change, powdery white spores on larvae, hardened cadavers, elongated and slender
phialides, and slender synnemata (Poinar and Thomas 1984). The life cycle of this
species is uncertain, but like many entomopathogens, it may begin infecting a larva with
a germinating spore, which penetrates the larva’s cuticle (Poinar and Thomas 1984). The
invasive hypha enters the host’s tissues, then partially breaks apart and distributes
throughout the larva. When the dead larva is ﬁlled with mycelium, emergence hyphae
grow through the larva’s integument, produce conidia, which disperse externally.
Samples of conidia and synnemata are necessary for species identiﬁcation.

How compatible are current methods of Zimmerman pine moth control with the
biology of the previously described parasitoids and fungus? Early spring pesticide
applications to control Zimmerman pine moth larvae while they bore into the phloem
may not interfere with parasitoid or fungal life cycles. However, if insecticides are
sprayed in May or late June to control other Christmas tree pests, the parasitoids may be
active and could be killed. In addition, fungicides sprayed to manage needlecast and gall
rust diseases could kill any Hirsutella nodulosa present on trees, and insecticides or

miticides may kill mites if they vector the fungus. Hand removal of pitch masses in early

48

summer may expose larvae to greater parasitism, predation and pathogenic infection, but
this is labor-intensive and impractical in large ﬁelds. Another alternative would be to
keep flowering plants near or in ﬁelds to provide nectar sources for parasitoids. Syme
(1975) demonstrated that E. comstockii adults lived up to seven times longer when
provided with ﬂowers than when given no food. An optimal management system for
Zimmerman pine moth would combine the use of host plant resistance, management for

natural enemies, and selective use of pesticides.

Differences in Variety Resistance to European Pine Sawﬂy

Foliar resin acid concentration, nutrient and moisture content may be the most
limiting factors in European pine sawﬂy development (Larsson et al. 1986, Lyytikainen
1994). Unexpectedly, percentage foliar nitrogen and needle moisture in my study were
not signiﬁcantly related to sawﬂy performance. However, resin acid concentration can
inﬂuence by the amount of nitrogen available to trees, which changes resin duct size
(Bjorkman and Larsson 1991). Other studies have shown that large concentrations of
resin acids and chemical deterrents in needles increase sawﬂy larval development time
and early instar mortality (Bjorkman and Larsson 1991, Larsson et al. 1986, Niemela et
al. 1982), without affecting pupal survival (Bjorkman and Gref 1993). Bridgen and
Hanover (1982) determined that Scandinavian varieties of Scotch pine (eg., Riga) had the
highest resin acid concentrations, which may indicate why sawﬂies reared on Riga had
lower survival, needle consumption and pupal weight, and longer development period

than sawﬂies reared on the other varieties.

49

Alternatively, tree height and vigor may be important factors in oviposition site
preference by adult sawﬂies. Wright et al. (1967) showed that European pine sawﬂy
attack corresponded to tree height in different Scotch pine varieties, and I found that as
tree height and stem diameter increased, so did the number of eggs laid per female.
Females are known to search for taller trees or more exposed branches on which to lay
eggs (Hardy and Allen 1975), but Olofsson (1989) explained that this behavior could
result from females seeking optimal temperatures for oviposition or early egg and larval
development. Adult females do not travel far from larval host trees to mate and oviposit
(Henson 1964), except during outbreaks and heavy competition for oviposition sites
(Olofsson 1989); potential fecundity may be primarily determined by factors that
affected their larval development. In addition, resin duct size was found to be
signiﬁcantly larger on needles bearing eggs (Hardy and Allen 1975).

A small percentage of pupae in my study entered an extended diapause, but
differences were not signiﬁcant among varieties. In 1994, two pupae in extended
diapause were found on Riga, two on Belgium and three on Pike Lake Improved. In
1995, four were found on Riga, one on Land 0’ Pine and three on Pike Lake Improved.
This is not an uncommon occurrance for this species, but occurs more frequently during
outbreak or unfavorable conditions (Kolomiets et al. 1979). Pschom-Walcher (1965)
reported that in Europe, between 5% and 100% of European pine sawﬂy cocoons enter
extended diapause, depending on climate and altitude, and emerge as adults up to ﬁve
years from the beginning of diapause (Kolomiets et al. 1979). Extended or prolonged
diapause may be further inﬂuenced by hormonal secretions, length of photoperiod, high

cocoon temperatures, and host quality (Knerer 1983, Kolomiets et al. 1979).

50
The greatest mortality of European pine sawﬂy from factors other than varietal

resistance occurred during the pupal stage in 1994. The exotic ichneumonid Pleolophus
basizonus (Gravenhorst) parasitized about 30% of the 400 caged pupae. However, under
normal conditions, female parasitoids search for sawﬂy pupae on the ground, and rarely
search tree foliage (Kolomiets et al. 1979, Price 1970). Percentage parasitism did not
vary among the varieties on which sawﬂies were reared.

By protecting sawﬂies from pupal parasitism in 1995, 1 demonstrated the importance
of parasitism in reducing numbers of adult sawﬂies able to reproduce. Although pupal
parasitism occurs too late to prevent larval feeding damage in one year, a population
reduction in sawﬂy numbers the following year could result. By allowing natural
enemies and host plant resistance to manage sawﬂy populations in Christmas trees, most
damaged shoots could be sheared off without reducing tree value. Sawﬂy larvae can be
easily killed by an insecticide application in May or early June (McCullough and Ellis
1995, Wilson 1965), but this could be expensive on an annual basis. Pesticide
applications could also kill the ﬁrst generation Pleolophus basizonus adults emerging in
late May from overwintering alternate host pupae. Thus, by combining host plant
resistance, providing adequate habitat for natural enemies, and using pesticides
judiciously, European pine sawﬂy populations and the damage they cause can be

maintained below economic threshold levels.

Differences in Variety Resistance to Pine Needle Scale
Survival and fecundity of pine needle scale reared on Belgium and Land 0’ Pine

tended to be low, indicating that these varieties were more resistant than Riga and Pike

51
Lake Improved. The most important factors potentially contributing to resistance in

these varieties were percentage needle moisture and percentage nitrogen in needles.
Previous studies have shown that low water availability in trees limits the movement of
minerals through phloem sap, affecting sap-feeding insect feeding efﬁciency, survival
and fecundity (Hanks and Denno 1993). Foliage moisture content and nitrogen content
are known to be correlated (Mattson 1980), but I also found strong correlations between
stem diameter and both foliage moisture and nitrogen content. Stem diameter and
percentage moisture signiﬁcantly predicted second generation scale survival, while
percentage moisture and percentage nitrogen signiﬁcantly predicted second generation
scale fecundity in 1995. Stem diameters were smallest in Riga trees, but percentage
needle moisture was not consistently signiﬁcant among varieties. However, foliage
nitrogen concentration and scale survival were not correlated, despite other studies
demonstating this association (Kidd 1985, McClure 1977, 1980, Shaffer and Williams
1987). This could indicate that needle nitrogen content in the four varieties was adequate
for scale development, or that percentage nitrogen did not vary enough among varieties
to strongly affect scale survival and fecundity.

The increased scale survival on all varieties from the ﬁrst generation to the second in
1994 could be interpreted in several ways. One hypothesis could be that scales began to
adapt to each variety’s natural defenses. Edmunds and Alstad (1978) suggested that
scales form highly localized populations, and when scales from one population are
transferred to another tree, crawler survival is reduced, supposedly because scales are not

adapted to the new tree’s defenses. However, it is unlikely that selection favoring

52

genetic differentiation in scales would be strong enough to occur in less than hundreds of
generations (Unruh and Luck 1987). Evidence both supporting and refuting the
controversy of local adaptation or deme formation in sessile insects has been discussed
(Unruh and Luck 1987). A deme is a group of interbreeding individuals adapted to local
conditions (Krebs 1985, Unruh and Luck 1987), and one of the main requirements for
deme formation includes a long-lived host plant with sessile herbivores feeding on it
(Edmunds and Alstad 1978). Given that pine needle scale typically has two generations
each year in Michigan and Scotch pine Christmas tree have rotation times of 7- to 10-
years (Leefers et al. 1988), it seems unlikely that demes would have time to form.

In 1994, low ﬁrst generation scale survival and higher second generation survival on
all varieties may have been due to weather. Wind, rain and extreme temperatures can
facilitate crawler dispersal, dislodge scales or affect rate of development (McClure 1989),
and periods of cold temperatures in winter (-14° to -4° C) can cause mortality in
overwintering scales (Struble and Johnson 1964). I suspect that the mild 1994-1995
winter and hot summer in 1995 provided good conditions for scale survival and fecundity
(Sheffer and Williams 1987), but six days of -18° C (0° F) or below temperatures in
January 1994 may have increased egg mortality, resulting in lower ﬁrst generation
survival. Despite weather effects, pine needle scale fecundity was highest in Pike Lake
Improved trees in 1994, and scales on Land 0’ Pine trees had the lowest fecundity in
1995. Fecundity in 1994 averaged 28 to 39 eggs per female, and 30 to 45 eggs per
female in 1995, both somewhat lower than egg counts in New York (42 eggs per female)

(Nielsen and Johnson 1973) or in Saskachewan (47 eggs per female) (Cumming 1953).

53

Where pine needle scale crawlers establish feeding sites on a needle may be an
important factor in scale survival (Brown 1958, Luck and Dahlsten 1975). Several
studies have shown that scales prefer feeding on the inner side of needles, and that most
female crawlers move to new needles, while most males remain on older needles
(Cumming 1953, Luck and Dahlsten 1974, Walstad et al. 1973). I also found that female
scales primarily fed on the ﬂat, inner side of needles in all four varieties. Luck and
Dahlsten (1974) suggested that scale survival may be higher on the less exposed, ﬂat side
of needles, near the fascicle. Parasitoids and predators may have more difﬁculty ﬁnding
scales in this area.

Christmas tree shearing may not strongly affect pine needle scale survival or
fecundity. When trees are sheared in early summer (Hill 1989), ﬁrst generation scales
are still feeding on older needles, and second generation crawlers do not emerge until
July (Nielsen and Johnson 1973). Contact between densely stocked trees may facilitate
second generation wind-dispersal to uninfested trees, but crawler dispersal by walking is
limited to less than 11cm from the parent scale (Brown 1958). In addition, the greater
density of foliage caused by shearing may provide scales better access to other branches
within the same tree. Dispersing crawlers may fall onto lower branches and become
established there.

Greater parasitism and predation of scales in late summer 1995 may explain why
second generation survival decreased. 1 found immature parasitoids developing within
adult pine needle scale and coccinelid larvae were observed feeding on eggs, although

their precise impact on the population could not be determined. The increased scale

54

population size may have attracted more density-dependent parasitoids and predators
(Luck and Dahlsten 1975). Parasitoids known to attack pine needle scale include
A chrysocharis phenacapsia Yoshimoto, Aphytis chilensis Howard, Aphytis diaspidis
(Howard), Aphytis mytilaspidis (LeBaron), Aspidiotiphagus citrinus citrinus (Craw.),
C occobius varicomis (Howard), Coccophagusﬂavifrons Howard, Marietta mexicana
(Howard), Marietta pulchella (Howard), Physcus howardi Compere, and Prospaltella
bella Gahan. Known predators include Chilocorus stigma (Say), Chilocorus orbus Casey
var. monticolus Drea, Cryptoweisia atronitens (Casey), Mcroweisia misella LeConte
(Burden and Hart 1990, Krombein et al. 1979, Luck and Dahlsten 1974, Nielsen and
Johnson 1973). In this study, I found both larvae and adults of the coccinelid
Coccidophilus marginatus (LeConte) feeding on scale eggs. Several natural enemies
may be able to regulate scale populations at low levels, but are susceptible to pesticide
applications (Clarke et al. 1992, Luck and Dahlsten 1975, Negron and Clarke 1995).
Some variation in resistance to pine needle scale was demonstrated in this study, but
results were not always consistent. I would recommend that host plant resistance be used
in comination with biological and chemical control to reduce populations of pine needle
scale to low levels. Other cultural methods besides shearing could also be developed to
reduce crawler survival in both generations, which would enhance the management of

this pest.

55
Table 1. Characteristics of four Scotch pine varieties according to Wright et al. (1966)

 

 

and Ruby and Wright (1976).
Riga Belgium Land 0' Pine Pike Lake Imp.
Country of origin Sweden Belgium Germany France
Range of needle lengths 56 - 77 79 - 111 66 - 99 47 - 56
(mm)'
Winter needle colorb 2.5 6.2 5.1 7.9
Average height (% of mean 95 126 118 104

for all varieties)°

 

’ On six-year old trees
b Color ranks: 1 = yellow-green, 9 = blue-green

° On 13-year old trees

56

Table 2. Mean tree growth measurements (iSE) of four Scotch pine varieties in 1994

and 1995 (n = 12 trees per variety).l

 

 

Variable Riga Belgium Land O'Pine Pike Lake I.
1994
Needle length (mm) 55.3 (2.2)“ 68.9 (2.7)" 70.4 (3.2)" 5700.9)“
Percentage moisture

current-yearfoliage 48.70.06)‘ 52.70.93)" 55.90.84)" 55.6 (0.81)"

l-yearoldfoliage 47.50.42)“ 47.40.26)“ 49.20.14)“ 46.80.09)“
Needle twist

current-yearfoliage 3.5 (0.15)’ 3.7 (0.14)a 3.6 (0.22)a 3.8 (0.19)”

l-yearold foliage 3.9 (0.17)3 3.8 (0.15)3 3.7 (0.17)’ 3.5 (0.17)’
Percentage nitrogen

current-year foliage 1.7 (0.16)” 2.0 (0.07)a 1.9 (0.05)’l 1.8 (0.04)"

l-yearold foliage 1.6 (0.04)“" 1.7 (0.05)" 1.5 (0.05)“ 1.6 (0.04)“
Treeheight(cm) 192.2 (4.2)a 260.3 (4.0)d 230.6 (4.7)c 21050.6)"
Basal diameter(cm) 6350.23)“ 8.84 (0.34)" 9.58 (0.37)" 9.70 (0.39)"
Stem diameter (cm)

whorls2to3 2.82 (0.12)“ 3,510.16)" 3.40 (0.23)“" 3.77 (0.18)"

whorls3to4 4.34 (0.22)“ 4.57023)“ 4.39 (0.20)“ 514(022)"
1995
Needle length (mm) 5270.9)“ 6670.8)" 59.4 (2.9)“" 51609)“
No. fascicles/5cm shoot 36.00.8)“" 3440.9)“ 35.2 (2.0)“ 41.308)"
Percentage moisture

May 12 41.60.55)“ 41.00.55)“ 40.7(0.55)“ 41.1(0.55)“

May 26 45.1 (0.40)" 44.2 (0.40)“" 43.2 (0.40)“ 43.9 (0.40)“"

June8 43.4(1.17)“" 41.70.17)“ 46.20.17)" 42.8(1.17)“"
Needle Twist (current-year) 3.5 (0.1)11 3.8 (0.1)‘ 3.7 (0.2)‘ll 3.7 (0.2)’
Percentage nitrogen

current-year foliage 1.68 (0.03)ll 1.71 (0.03)'I 1.67 (0.03)" 1.64 (0.03)’I
Treeheight(cm) 212.2 (5.5)“ 272.8 (49)" 249.903)" 226.608)“
Basal diameter (cm) 9.27 (0.29)“ 12.09 (0.21)" 11.40 (0.32)" 11.51 (0.46)"
Diameteratbreastht(cm) 3160.25)“ 5.09 (0.27)" 4.85 (0.25)" 4.46 (0.34)"
Height growth: 1994-1995 20007)“ 13.0 (2.8)“ 19.8 (2.4)“ 1880.8)“
Basal diameter growth (cm) 2.91 (0.17)" 3.25 (0.26)" 1.84 (0.19)“ 1.82 (0.32)“

 

’ Means followed by the same letter did not signiﬁcantly differ at the p<0.05 level.

57

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58

Table 4. Mean monthly temperature and precipitation accumulation in 1994 and 1995 at

Kellogg Forest near Kalamazoo, MI.

 

 

Mean Maximum Mean Minimum Total
Year Month Temperature (°C) Temperature (°C) Precipitation (cm)
1994 January -6.8 -15.6 5.3
February -62 -l4.4 4.4
March 2.7 -5.7 4.5
April 11.8 1.6 10.0
May 17.1 4.0 3.2
June 23.5 11.4 14.9
July 23.9 14.3 11.]
August 25.6 14.9 15.7
September 22.4 12. 8 3 .0
October 17.8 9.0 4.6
November 12.2 4.9 11.5
December 6. 8 1 .7 3 .6
1995 January 3.1 -1.4 5.6
February 0.3 -6.1 2.5
March 10.3 1.4 3.4
April 14.4 5.3 9.5
May 22.1 8.5 10.4
June 29.1 14.6 8.4
July 30.7 17.2 7.2
August 30.7 19.3 12.8
September 20.8 8.3 5.4
October 16.9 5.6 9.5
November 3 .6 -3 .3 12.0

December -0.6 -7.8 2.8

 

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60

Table 6. Analysis of Zimmerman pine moth survival during 1994 and 1995 using the

Cochran’s Q test, X20053 (n = 48 trees).1

 

 

Year Life Stage Whorl Q Probability

1994 Early larvae 2 5.1 0.1 <p < 0.2
Middle larvae 3.3 0.4 <p < 0.3
Late larvae 2.6 p > 0.3
Pupae 1.3 p > 0.3
Early larvae 3 1.2 p > 0.3
Middle larvae 0.2 p > 0.3
Late larvae 0.2 p > 0.3
Pupae 1.0 p > 0.3

1995 Early larvae 3 3.3 0.3 <p < 0.4
Middle larvae 5.6 0.1 <p < 0.2
Late larvae 4.4 0.2 <p < 0.3
Pupae 4.4 0.2 <p < 0.3

 

’ Data from the four Scotch pine varieties were pooled.

61

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62

Table 8. Pearson’s product-moment (r) and Spearman rank (r,) correlations among

Zimmerman pine moth and tree variables with varietal data pooled.

 

 

Correlation

Year Variable Variable coefﬁcient p<

1994 Adult weight (mg) Pupal weight (mg) r = 0.811 0.001
Pupal length (mm) Pupal weight (mg) rs = 0.902 0.001
Pupal weight (mg) Development period (days) rs = 0.630 0.0]
Pupal weight (mg) Tree diameter, whorls 2-3 r = 0.511 0.0]
Development (days) Tree diameter, whorls 2-3 rs = 0.581 0.01
Development (days) Tree diameter, whorls 3-4 r, = 0.537 0.02

1995 Adult weight (mg) Pupal weight (mg) r = 0.948 0.01
Pupal length (mm) Pupal weight (mg) rs = 0.96 0.001
Adult weight (mg) Fecundity (number of eggs) r, = 0.396 0.05
Basal diameter (cm) Rate of resin flow in June rs = -0.58 0.05

 

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66

Table 12. Pearson’s product-moment (r) and Spearman rank (rs) correlations among

European pine sawﬂy and tree variables with varietal data pooled together.

 

 

Correlation

Year Variable Variable coefﬁcient p<

1994 Pupal weight (mg) Development period (days) rs = -0.367 0.05
Pupal weight (mg) Number of eggs laid/female rs = 0.447 0.01
Needle biomass eaten Development period (°DD) rs = 0.685 0.05
Tree height (cm) Development period (°DD) rs = -0.282 0.05

1995 Pupal weight (mg) Development period (days) rs = -0.494 0.001
Pupal weight (mg) Development period (°DD) rs = -0.492 0.001
Pupal weight (mg) % nitrogen in needles r = 0.272 0.05
Pupal weight (mg) Number of eggs laid/female rs = 0.292 0.05
No. eggs laid/female Tree height (cm) rs = 0.577 0.001
No. eggs laid/female Diameter at breast height (cm) rs = 0.460 0.001
No. eggs laid/female Basal diameter (cm) rs = 0.385 0.001

 

67

 

 

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8.0 was. Sod- 200; 8:
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no 30065000

 

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EwEB .0000 .903 00:00 60802050 30300 050 50008.5 00 00200600 023003. 3023: wE000006830—00m .2 0500.

68

Table 14. Pearson’s product-moment (r) and Spearman rank (rs) correlations among pine

needle scale and tree variables.l

 

 

Correlation
Variable Variable Coefficient p<
Preliminary study
Armor length (mm) Number of eggs laid per female r, = 0.581 0.001
Armor length (mm) Body length (mm) r = 0.303 0.05
Body length (mm) Scale density on each needle rs = -0.356 0.0]
Armor length (mm) Needle width (m) r = -0.377 0.01
Armor length (mm) Needle length (m) r = -0.229 0.01
1994
2nd generation survival % needle moisture (28 Aug.) rs = 0.307 0.05
2nd generation survival Basal diameter (cm) rs = 0.372 0.05
2nd generation fecundity Basal diameter (cm) rs = 0.350 0.05
1st generation survival 2nd generation survival rs = 0.573 0.001
2nd generation survival Number of eggs laid per female rs = 0.312 0.05
1995
2nd generation survival Tree height rs = -0.347 0.05
2nd generation survival Diameter at breast height rs = -0.41 3 0.05
2nd generation survival Basal diameter rs = -0.371 0.0]
2nd generation survival Basal diameter growth rate rs = 0.337 0.05
2nd generation survival % needle moisture (12 May) rs = 0.335 0.01
lst generation survival 2nd generation survival rs = 0.272 0.06]

 

' Varietal data were pooled in 1994 and 1995.

69

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72

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73

 

 

0.2 __—T
I Riga
0.175 - _F_ - - D Belgium
E Land 0' Pine
0.15 q I Pike Lake Imp.

 

 

 

 

 

0.125 -

0.1 -

 

 

0.075 -

 

 

0.05 -

Rate of resin flow (ml/24 h)

 

0.025 - y:

 

 

 

 

oJ

 

 

 

 

Figure 1. Mean rate of resin ﬂow (:tSE) (ml/24 h) for four varieties of Scotch pine
measured in May, June and July 1995 (n = 12 trees per variety).

74

 

 

Survival (%)
%

 

 

 

—l— Riga
“we—w Belgium
------A- Land 0' Pine

 

--O-- Pike Lake Imp.

 

 

 

 

 

 

 

 

 

Survival (%)

1°- 1995

 

 

 

 

+ Riga
--O---- Belgium
-------A- Land 0' Pine

 

---O—-- Pike Lake Imp.

 

 

A A
ﬁr l-‘l

 

 

r T
Early larvae Middle larvae

Late larvae

$ *—
Pupae Adults

Figure 2. Mean percentage survival of Zimmerman pine moth in 1994 and 1995 when

reared on four varieties of Scotch pine.

75

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

100- + Riga
-------0---—-- Belgium
30.
’3‘
E 60-
15
O:
t
= 40‘
U)
20..
0
100-
so-
0’3
v 604
T:
E 1995
i.-
=3 40-
m + Riga
we“ Belgium
20‘ -------0- Land 0' Pine
—-—A-- Pike Lake Imp.
0

 

 

l I l l
1st instar 3rd instar Ultimate instar Pupae

1
Adult

Figure 3. Mean percentage survival of Eurpean pine sawﬂy in 1994 and 1995 when

reared on four varieties of Scotch pine.

 

 

 

76

 

45

Y = 0.598x - 27.415

r2 = 0.527; p < 0.05

 

 

 

0 l l l I
60 70 so 90 100

 

Female pupal weight (mg)

Figure 4. Linear regression and 95% conﬁdence interval of Zimmerman pine moth female
pupal weight and number of eggs produced per female in 1995 (n=9 females).

77

 

 

 

 

 

120
Y = 2.020x - 86.554 0
100. r2: 0.250; p < 0.01 . o I ..... ,---*
.2 80-
a
.5.
G...
a». ..
m
on
an
0
e' 40-
z
20..
0-_.__,... , I 1

60 70 80 90
Female pupal weight (mg)

Figure 5. Linear regression and 95% conﬁdence interval of European pine sawﬂy

female pupal weight and number of eggs laid per female in 1995 (n=40).

tret

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win

Ha:

Chr

grox

and

CHAPTER 2

Phenology and Species Composition of Pest and Beneﬁcial Arthropods in Four
Varieties of Scotch Pine Christmas Trees in Southern Michigan

INTRODUCTION

Scotch pine, Pinus sylvestris L., has been a valuable ornamental, forest and Christmas
tree species in Michigan since it’s importation from Europe and Asia during the
twentieth century (Sowder 1966, Wright et al. 1966). It is grown for timber, as a
windbreak, and as a tree to decorate both outdoors and indoors at Christmas (Bridgen and
Hanover 1982, Giertych and Matyas 1991). Scotch pine has long been a favorite
Christmas tree species among growers and consumers. In Michigan, Scotch pine is
grown on approximately 39,000 acres, over three million trees are harvested annually,
and 71% of all Christmas trees out are Scotch pine (Mich. Agr. Stat. Serv. 1994).

Geographic and climatic conditions in Europe and Asia affected isolated populations
of Scotch pine trees over time, exerting different selection pressures on each gene pool
(Giertych and Matyas 1991). Over 30 separate varieties of Scotch pine have been
recognized (Ruby and Wright 1976). Varieties differ in traits such as needle length,
color and moisture content, cone production, stem form, grth rate and monoterpene
concentration (Bridgen et al. 1979, Carlisle 1958, Ruby and Wright 1976, Tobolski and

Hanover 1971, Wright 1976). Varieties also vary in degree of resistance to insects and
78

de

SU

816

{CC

dif:

scot

Spec

79
diseases (Squillace et al. 1975, Steiner 1974, Wright and Wilson 1972, Wright et al.

1975) and could be selectively bred to further decrease their susceptibility to damage
(Bridgen and Hanover 1982).

As with most agricultural commodities, growers and consumers tolerate only minimal
damage to Christmas trees. Scotch pine is grown on a 7- to 10-year rotation and many
ﬁelds are intensively managed to minimize damage from pests (Leefers et al. 1988).
Traits that can be affected by insect pests include growth rate, fullness and color of
foliage, stem and branch strength, and aesthetic qualities of Christmas trees (Koelling
and Heiligmann 1993, Sowder 1966). Insect pests can be grouped according to the type
of feeding damage they cause (Root 1967). Sap-feeding insects, such as scales, aphids
and adelgids create necrotic spots on needles and premature needle drop or provide entry
points for disease (W alstad et al. 1973). Defoliating insects, such as sawflies and some
chafer beetle adults, form gaps in the foliage, which can reduce tree growth rate and
detracts from a tree’s symmetrical shape (Dunn and Kennedy 1983). Phloem-borers,
such as weevils and Dioryctria spp. can weaken tree stems and branches, causing the
stem or limbs to break in the wind or during harvest (Jactel et al. 1994). Insects feeding
inside shoots, such as some bark beetles and some lepidopterans, cause shoots to bend,
redden and die (McKeague and Simmons 1978). Many of these types of insects are
difficult to control in Christmas tree fields.

Knowledge of insect phenology and seasonal abundance is important for planning
scouting, management activities, and estimating potential damage. Over 30 insect

species are known to infest Scotch pine in Michigan, but not all of them are considered

80
major pests (Benyus 1983). Given the different life cycles and feeding habits of each

species, growers may overuse pesticides as a control method (Ascerno 1991, Benyus
1983). Pesticide applications kill parasitoids and predators of pests, as well as non-target
arthropods, sometimes resulting in pest resurgence (Clarke et al. 1992, Luck and
Dahlsten 1975, Negron and Clarke 1995, Stem et al. 1959). An improved understanding
of whether pest management can be timed to avoid negatively impacting beneﬁcials and
non-targets and whether varietal differences affect beneﬁcial arthropod abundance is
needed. In addition, research is needed to determine if various pest species or feeding
guilds selectively attack certain Scotch pine varieties.

The objectives of this study included identifying the phenology and species
composition of beneﬁcial and pest arthropods and determining if differences existed

among four varieties of Scotch pine throughout the growing season in 1994 and 1995.

MATERIALS AND METHODS

Study Sites

Phenology and species composition of pest and beneﬁcial arthropods were monitored
at two ﬁeld locations. In the W. K. Kellogg Experimental Forest (Augusta, Kalamazoo
County, Michigan), a 0.8 ha ﬁeld with 27 Scotch pine varieties was hand-planted in
1987. Each variety was planted in two adjacent rows in a north-south direction, with 6 x
6 ft (1.8 x 1.8 m) between trees. Spacing increased as trees were sold or culled due to
insect and disease damage. Trees were sheared each July and herbaceous vegetation was
mowed monthly. Pesticides were used to control major pests before this project began,
but were not applied on or near trees during 1994 and 1995. The ﬁeld was bordered by
mature white spruce (Picea glauca (Moench) Voss) and Scotch pine.

The other ﬁeld site was in a private, 1.6 ha Christmas tree ﬁeld near Greenville,
Montcalm County, Michigan. In 1986, 19 varieties were planted in rows from north to
south with 6 x 6 ft (1.8 x 1.8 m) spacings between trees. The ﬁeld was adjacent to
agricultural land and a small woodlot. Trees were sheared annually and herbaceous
vegetation was mowed monthly. Pesticides were not applied to these trees in 1994 or
1995, and were only used once previously in the ﬁeld during a pine root collar weevil

(Hylobius radicis Buch., Coleoptera: Curculionidae) infestation in 1992.

81

82

Scotch Pine Varieties

The four varieties chosen for this study were Pike Lake Improved (var. aquitana),
Land 0' Pine (var. hercynica), Belgium (var. haguenensis) and Riga (var. rigensis).
They were selected based on their physical differences, range of geographic origin and
the results of previous research (Ruby and Wright 1976, Tobolski and Hanover 1971,
Wright et al. 1975). Primary differences among varieties were in origin, needle length,
winter needle color, and relative growth rate (Chapter 1, Table l) (Tobolski and Hanover
1971, Wright et al. 1966).

In 1994, 18 trees per variety were randomly selected from Riga, Land 0’ Pine and
Pike Lake Improved at Kellogg Forest. Only 13 trees were selected in Belgium because
other trees had been cut and sold as Christmas trees within the variety. At the Greenville
site, 36 trees per variety were randomly selected. Height, basal diameter, and stem
diameter between the top second and third whorls and the third and fourth whorls were
measured on all trees in 1994. In 1995, 13 trees per variety were selected at Kellogg
Forest, and 16 trees per variety were randomly selected at the Greenville site. Tree size

in 1995 was standardized at both locations by choosing trees of similar heights.

Species Composition and Phenology

Several insect pests and beneﬁcial arthropod groups were monitored on the
experimental trees (Table 1). Arthropod populations were counted twice a month on the
selected trees from early May to late August. Each tree was examined from top to

bottom from three directions (N, SE, SW) and total numbers of pests and beneﬁcials

83
according to species (when possible), feeding guild and date were determined. At the

time of each sampling occasion, arthropods were not removed from their feeding sites,
but tree damage was assessed and marked (ﬂagging tape or paint) or dead shoots were
removed to prevent subsequent recounting. Results for mobile arthropods (e. g.,
beneﬁcials, Lepidoptera, Coleoptera) varied in each sample, but sessile or non-dispersing
arthropods (e.g., scales) were recounted. Tree shearing each summer removed most early

summer shoot-boring damage.

Statistical Analysis

Before analysis, species and damage data were pooled into feeding guilds by month.
Results were transformed [log (x+1)] to adjust for non-normal distributions and
heterogeneous variances, then analyzed using a parametric two-factor ANOVA with
repeated measures to test for effects of ﬁeld location (Kellogg Forest vs. Greenville) and
variety (IMP for Windows, Version 3.1, SAS Institute 1995). Species differences among
varieties in each month at both locations were tested with the nonparametric Kruskal-
Wallis test since the assumptions of a parametric ANOVA were not met, and Chi-square
values are reported. Associations among arthropod abundance, tree height, basal
diameter and upper whorl diameters in 1994 were examined using the nonparametric
Spearman’s rank correlation test (Zar 1996). All analyses were conducted with an alpha

level of p<0.05.

RESULTS

Scotch Pine Varieties

Tree characteristics potentially relevant to arthropod feeding guilds differed among
varieties. Tree heights at Kellogg Forest ranged from 193 cm to 268 cm, while at
Greenville, tree heights ranged from 209 cm to 236 cm (Table 2). At Kellogg Forest,
Riga trees were the shortest (F=59.12, df=3, p<0.001), had the smallest basal diameter
(F=26.16, df=3, p<0.001), diameter at breast height (F =4.07, df=3, p<0.05), and the
shortest needles in 1994 (F =5.42, df=3, p<0.01), while Belgium trees were the tallest,
and the stern diameters were nearly identical in the other three varieties. At Greenville,
Riga trees were again the shortest (F =9.88, df=3, p<0.001), had the smallest basal
diameter (F=11.96, df=3, p<0.001) and diameter at breast height (F=8.21, df=3,
p<0.001), while Land 0’ Pine had the tallest trees, and stem diameters were nearly

identical in the other three varieties (Table 2).

Arthropod Communities in Scotch Pine Fields

Feeding guild abundance was dominated by sap-feeding insects at both Kellogg Forest
and Greenville in 1994 and 1995 (Figure l). The beneﬁcial arthropod guild represented
42% of the community at Kellogg Forest in 1994, but decreased slightly to 37% in 1995

as the percentage of sap-feeders increased. In addition, the percentage of shoot-borers,

84

85
defoliators and phloem-borers decreased from 9.5% in 1994 to 2.6% in 1995 at Kellogg

Forest. Sap-feeders at Greenville in 1994 comprised 91% of the community and

increased to 99.6% in 1995.

Seasonal Changes in Feeding Guild Abundance

Arthropod abundance in each feeding guild varied throughout the summer at Kellogg
Forest and Greenville in 1994 (Tables 3, 4). At Kellogg Forest, the number of sap-
feeders and phloem-borers declined over time, but not signiﬁcantly. In contrast, at
Greenville, the number of sap-feeders was signiﬁcantly higher during August and the
number of phloem-borers was higher in May than in other months. At Kellogg Forest,
defoliator abundance was higher during July than in the other months sampled (Tables 3,
4), but Greenville had a small, declining defoliator population. Shoot-borer abundance
was highest in June, and the abundance of beneﬁcial arthropods was highest in August at
both locations (Tables 3, 4).

In 1995, numbers of arthropods in each feeding guild varied from May through
August at both locations (Table 4, 5). At Kellogg Forest, numbers of sap-feeders and
shoot-borers were highest in June (Table 5). In contrast, at Greenville the number of
sap-feeders was highest in August and the number of shoot-borers did not vary
signiﬁcantly during the summer (Table 5). Defoliator abundance was highest in August
at Kellogg Forest, but numbers did not vary signiﬁcantly at Greenville (Table 5).
Phloem-borer abundance did not vary signiﬁcantly at either location in 1995, but the

abundance of beneﬁcial arthropods was highest in August at both locations (Table 5).

86
Feeding Guild Abundance Among Four Scotch Pine Varieties

Differences in total feeding guild abundance among the four Scotch pine varieties
were more apparent at Kellogg Forest than at Greenville in 1994 (Table 6). Shoot-borer
abundance was lowest on Riga at both Kellogg Forest (X2=33.4O, df=3, p<0.001) and
Greenville (X2=9.27, df=3, p<0.05) compared to other varieties. Total numbers of sap-
feeders and defoliators were not signiﬁcantly different among varieties at either location.
Although the number of phloem-borers was highest on Belgium at Kellogg Forest
(X2=24.74, df=3, p<0.001), differences among varieties were not signiﬁcantly different
at Greenville. Similarly, the abundance of beneﬁcial arthropods was higher on Riga at
Kellogg Forest (X2=34.08, df=3, p<0.001) (Table 6), but differences in beneﬁcial
arthropod numbers among varieties at Greenville did not signiﬁcantly differ.

The ratio of beneﬁcial to pest arthropods was signiﬁcant at both Kellogg Forest and
Greenville in 1994 (Table 7). From one to two beneﬁcials per pest arthropod were
present on trees at Kellogg Forest, and this ratio was signiﬁcantly higher on Riga trees
than on the other varieties (F=4.61, df=3, p<0.01). Pine needle scale abundance may
have lowered this ratio, so if pine needle scale numbers were excluded, the ratio
increased to up to ﬁve beneﬁcials for every one pest arthropod in Riga (F=11.09, df=3,
p<0.001) (Table 7). At Greenville, pest arthropods outnumbered beneﬁcials, except in
Belgium trees (F =3. 12, df=3, p<0.05) (Table 7). If pine needle scale numbers were
excluded, one to two beneﬁcials per pest arthropod were found on varieties, but the ratio
was signiﬁcantly higher in Belgium trees (F=4.58, df=3, p<0.01).

Fewer differences in total feeding guild abundance among the four varieties were

observed in 1995 than in 1994 at Kellogg Forest and Greenville (Table 8). Sap-feeder

87
abundance was highest on Belgium at Kellogg Forest (F=2.91, df=3, p<0.05), but did not

differ signiﬁcantly among varieties at Greenville. Shoot-borer abundance was highest on
Pike Lake Improved and lowest on Belgium at Greenville (F =3.44, df=3, p<0.05), but
differences were not signiﬁcant at Kellogg Forest. Number of beneﬁcial arthropods was
highest on Riga at Kellogg Forest (F =10.52, df=3, p<0.001), but did not differ among
varieties at Greenville.

The ratio of beneﬁcial to pest arthropods was signiﬁcant at Kellogg Forest, but not at
Greenville in 1995 (Table 7). Less than one beneﬁcial per pest arthropod was present on
most trees at Kellogg Forest, but the ratio was signiﬁcantly higher on Riga trees than on
the other varieties (F =3.07, df=3, p<0.05). If pine needle scale numbers were excluded,
the ratio increased only slightly, although it was still statistically higher in Riga trees
(F=3.53, df=3, p<0.05) (Table 7). At Greenville, pest arthropods greatly outnumbered
beneﬁcials, but differences did not signiﬁcantly differ among varieties (Table 7). Ratios
were increased if pine needle scale numbers were excluded, but again did not

signiﬁcantly differ among varieties.

Species Composition of Feeding Guilds

Sap-feeding Guild. The insects monitored in this guild were pine spittlebug, pine
needle scale, pine tortoise scale and aphids (Table 1). At Kellogg Forest and Greenville
in 1994, pine needle scale was the predominant sap-feeder (Tables 9, 10). Pine needle
scale numbers were higher on Riga than on Belgium at Greenville in August (Table 10).
Pine tortoise scale abundance was highest on Riga at Kellogg Forest in May and June

(Table 9). At Kellogg Forest, spittlebug abundance was highest on Belgium and lowest

88
on Land 0’ Pine and Pike Lake Improved in June and July (Table 9). However, at

Greenville in July and August, spittlebug numbers were highest on Land 0’ Pine and
lowest on Belgium and Pike Lake Improved in July and August (Table 10). Numbers of
aphids in May at Greenville were highest on Riga and lowest on Belgium, but in July
abundance was highest on Pike Lake Improved and lowest on Riga (Table 10).

In 1995, pine spittlebugs were the primary sap-feeders at Kellogg Forest (Table 1 1),
but at Greenville, pine needle scales were most abundant (Table 12). Pine needle scale
numbers were higher on Riga and Pike Lake Improved than on Land 0’ Pine at Kellogg
Forest in May, but did not signiﬁcantly differ the following months. Abundance of pine
tortoise scale was higher on Belgium than on Land 0’ Pine in June at Kellogg Forest
(Table 11). Numbers of pine spittlebug were higher on Riga than on Pike Lake
Improved in July and August at Kellogg Forest. Pine aphid abundance was higher on
Pike Lake Improved than on other varieties at Kellogg Forest in May and June (Table
11). Signiﬁcant differences in species abundance in the sap-feeding guild were not
detected at Greenville in 1995 (Table 12).

Defoliating Guild. The defoliators monitored were sawflies, chafer beetles,
grasshoppers and jack pine budworm (Table 1). In 1994, chafer beetles were
predominant at Kellogg Forest (Table 9), while jack pine budworm was the major
defoliator at Greenville (Table 10). More grasshoppers were found on Riga trees at
Kellogg Forest than on other varieties from June through August in 1994 (Table 9).
There were no signiﬁcant differences in species abundance in the defoliating guild
at Greenville in 1994 (Table 10). In general, fewer defoliators were found at Greenville

than at Kellogg Forest.

89

In 1995, chafer beetles were the most abundant defoliator at Kellogg Forest, while
there were more pine sawflies than other defoliators at Greenville (Tables 11, 12).
Signiﬁcant differences among varieties were not detected at the species level at either
location.

Shoot-boring Guild. The shoot-boring species monitored were eastern pine shoot
borer and the pine shoot beetle (Table 1). In June 1994, eastern pine shoot borer
abundance at Kellogg Forest was signiﬁcantly lower on Riga trees than on the other three
varieties, and lower on Land 0’ Pine trees in July (Table 10). At Greenville, eastern pine
shoot borer abundance was lower on Riga during June and July, but was higher on Riga
in May than on other varieties (Table 11). Pine shoot beetle abundance was higher on
Belgium than on Riga in June at Kellogg Forest, but numbers of pine shoot beetle were
not signiﬁcantly different among varieties at Greenville for any month (Table 11). Tree
shearing that occurred in late June removed most shoot-boring damage on trees, so the
numbers of shoot-borers on study trees dropped in July.

In 1995, the eastern pine shoot borer comprised more of the shoot-borer guild than
the pine shoot beetle at both locations (Tables 12, 13). Eastern pine shoot borer
abundance was not signiﬁcantly different among varieties at Kellogg Forest, but was
higher on Pike Lake Improved than on Riga and Belgium in July at Greenville. Pine
shoot beetle abundance was not signiﬁcantly different among varieties at either location
during the summer.

Phloem-boring Guild. The phloem-boring guild consisted of Zimmerman pine moth
and weevils, such as pales weevil (Hylobius pales Herbst.), pine root collar weevil

(Hylobius radicis Buch.) and white pine weevil (Pissodes strobi (Peck)) (Table 2).

9O

Zimmerman pine moth was found in greater proportions than the weevils at both Kellogg
Forest and Greenville in 1994 (Tables 10, 11). At Kellogg Forest in May and July 1994,
higher numbers of Zimmerman pine moth were found on Belgium than on other
varieties. At Greenville in May 1994, Land 0’ Pine had higher numbers of Zimmerman
pine moth than Riga, but Zimmerman pine moth was more abundant on Belgium than on
other varieties in June, according to the number of pitch masses found. Signiﬁcant
differences in weevil abundance among varieties were not detected at either location in
any month.

In 1995, there were proportionally more Zimmerman pine moth than weevils at both
locations (Tables 12, 13). No signiﬁcant differences in Zimmerman pine moth and
weevil abundance among varieties at either location for any month could be detected.

Beneﬁcial Arthropod Guild. The beneﬁcial arthropod guild consisted of sheet and
funnel web spiders, ladybird beetles, lacewings and parasitic wasps (Table 2). In 1994,
spiders represented most of the beneﬁcial arthropod guild at both Kellogg Forest and
Greenville (Tables 10, 11). At Kellogg Forest, numbers of spiders were higher on Riga
than on the other varieties from June through August. At Greenville in June, spider
abundance was higher on Belgium than on Pike Lake Improved. No signiﬁcant
differences for lacewings or parasitic wasps were detected at either location, but ladybird
beetle abundance was higher on Land 0’ Pine than on other varieties in May.

In 1995, spiders were again the most abundant species in the beneﬁcial arthropod
guild at Kellogg Forest and Greenville (Tables 12, 13). At Kellogg Forest, spider

abundance was higher on Riga than on the other varieties from May through August. At

91

Greenville in May, spider abundance was higher on Belgium than on Pike Lake
Improved. Spiders were an important source of scale mortality because I observed webs
covered with crawlers during peak emergence periods. In August at Kellogg Forest,
lacewing abundance was higher on Belgium than on Land 0’ Pine and Pike Lake
Improved. Parasitic wasp and ladybird beetle abundance did not signiﬁcantly differ at

either location.

DISCUSSION

The four Scotch pine varieties used in this study differed in traits potentially affecting
susceptibility to the different feeding guilds. Belgium and Land 0’ Pine had the tallest
trees, Pike Lake Improved was moderate, and Riga had the shortest trees and smallest
stem diameters at both locations. Although trees at Greenville were planted a year earlier
than at Kellogg Forest, varieties had similar stem diameters and tree height at both
locations. Variation in monoterpene concentration (Tobolski and Hanover 1971) and
resin acids (Bridgen and Hanover 1982) for these and other varieties have been studied in
Michigan. In addition to the environmental and genetic factors affecting tree growth
rates, the cultural practice of shearing reduces height growth and promotes lateral bud
growth (Hill 1989, Johnson 1991). If shearing is timed appropriately, in addition to
improving tree shape, it can also remove early shoot-feeding damage.

Some other tree variables, including differences in monoterpene concentration and
resin acids, were previously studied in these and other Scotch pine Christmas tree
varieties in Michigan. Among the four varieties, Pike Lake Improved (var. aquitana)
and Riga (var. rigensis) were short and of similar heights, Land 0’ Pine (var. hercynica)
was moderately tall, and Belgium (var. haguenensis) was the tallest variety with the
fastest grth rate (Ruby and Wright 1976, Wright et al. 1966). From foliage color

ranks, southern European varieties (e. g., Pike Lake Improved) were greenest,

92

93

Scandinavian varieties (e. g., Riga) were yellowest and central European varieties had
intermediate hues of green (Ruby and Wright 1976, Wright et al. 1966). Needles were
longest in Belgium, moderately long in Land 0’ Pine, short in Riga, and shortest in Pike
Lake Improved (Ruby and Wright 1976, Wright et al. 1966). In general, Scandinavian
varieties (e.g., Riga) had lower concentrations of cortical monoterpenes (Tobolski and
Hanover 197]), higher concentrations of resin acids, lower oleoresin pressure and smaller
resin canal cross-sectional areas than the other varieties (Bridgen and Hanover 1982).
Nutrient differences in foliage among varieties were apparent, but statistical signiﬁcance
was unknown (Ruby and Wright 1976).

Tree characteristics contributing to resistance to different arthropod feeding guilds
and species vary. Previous studies have shown that water availability in trees limits the
movement of minerals through phloem sap, affecting sap-feeding insect feeding
efficiency, survival and fecundity (see Hanks and Denno 1993). Resin acid
concentration, nutrient and moisture content of needles, and tree vigor may be important
factors in defoliator survival (Larsson et al. 1986, Lyytikainen 1994, Mopper et al.
1990). Shoot phenology, tree size and shoot diameter may be critical to shoot-boring
arthropods (Lawrence and Back 1995, McCullough and Smitley 1995, McKeague and
Simmons 1978). Phloem-borer success may be associated with rate of resin ﬂow,
phloem thickness, monoterpene concentration or intensity of branch pruning (Hodges et
al. 1979, Jactel et al. 1994, Wilson et al. 1975). Beneﬁcial arthropods need a stable food
supply and shelter from pesticide applications and other management methods (Arthur

1963, Clarke et al. 1992, Luck and Dahlsten 1975, Negron and Clarke 1995).

94
The communities of arthropods in the two Christmas tree ﬁelds differed in diversity.

Total numbers of sap-feeders and beneﬁcial arthropods were higher at Greenville than at
Kellogg Forest, but more shoot-borers, phloem-borers and defoliators were found at
Kellogg Forest. This variation between locations may have resulted from differences in
the density of Scotch pine Christmas trees in the area. The site at Kellogg Forest was
surrounded by mature deciduous and coniferous trees which may have harbored low
populations of several minor pests. Kellogg Forest was also isolated from other
Christmas tree ﬁelds; there were only 18 other Christmas tree operations in Kalamazoo
County (158 ha) (Mich. Agr. Stat. Serv. 1994). In contrast, the site near Greenville was
surrounded mostly by agricultural and Christmas tree ﬁelds; about 30 other Christmas
tree operations were located near Greenville (2,145 ha) (Mich. Agr. Stat. Serv. 1994).
The greater production of Christmas trees near Greenville may have contributed to higher
populations of arthropod pests in that experimental ﬁeld.

It was expected that the abundance of each feeding guild would vary throughout the
summer months, given the diverse life cycles of species within the guilds. Arthropods
most active in early summer were the phloem-borers and shoot-borers. By late summer,
numbers of defoliators, sap-feeders, and beneﬁcial arthropods had increased. Most of the
phloem-borer activity monitored was of the Zimmerman pine moth, which began feeding
in the spring and created visible pitch masses on the bark. Eastern pine shoot borer was
the primary species monitored in the shoot-boring guild. Larval activity of this insect in
shoots was completed by late June, and subsequent shearing removed damaged shoots.
Defoliator numbers had increased by the end of the summer because of the increasing

chafer beetle presence on trees. Sap-feeder abundance also rose through the summer

95

because of the multiple generations of the monitored species, such as aphids and pine
needle scale. In the beneﬁcial arthropod guild, numbers of ballooning spiders increased
gradually in agricultural systems and reached a peak in late summer (Nyffeler et al.
1994). The slower increase on Christmas trees in early summer may have been due to
the disruption of webs caused by shearing.

Total feeding guild abundance on the four Scotch pine varieties indicated resistance
in some varieties, but results were not always consistent. There were fewer shoot-borers
on Riga trees than on the other varieties, but previous studies on resistance to eastern
pine shoot borer noted that Pike Lake Improved was most heavily attacked, while
Belgium was more resistant (King 1971, Steiner 1974). Studies on resistance to sawflies
found that Scotch pine varieties from central Europe (e. g., Belgium and Land 0’ Pine)
were more susceptible to defoliation than Scandinavian varieties (e. g., Riga) (Ghent
1959, Wright et al. 1967), but differences were not detected in my study. My results also
suggest that phloem-borers and sap-feeders may have preferred Belgium trees as hosts.
However, sap-feeder abundance varied between years, months and locations, making
results less reliable. Others also suggested the presence of resistance in varieties against
phloem-borers (e.g., Zimmerman pine moth), where Belgium was considered one of the
most susceptible varieties (Harrell 1993, Wright et al. 1975).

The ratio of beneﬁcial arthropods to pest abundance was higher on Riga trees at
Kellogg Forest and higher on Belgium trees at Greenville than on other varieties. Pests
were more abundant than beneﬁcial arthropods due to the number of scales present. If
scales were excluded from the analysis, differences among varieties remained similar, but

the ratios increased. It was interesting to note that the ratios at Kellogg Forest and

 

96

Greenville were somewhat similar, although the Greenville ﬁeld had more pests than
beneﬁcials. The nearly 1:1 ratio of beneﬁcials to pest arthropods in unsprayed Christmas
tree ﬁelds suggests that for every pest killed by a pesticide spray, one beneﬁcial could be
killed. At Greenville, pesticide applications on neighboring agricultural ﬁelds may have
increased the emigration of beneﬁcials from those ﬁelds onto the unsprayed Christmas
tree ﬁeld. i
Varietal resistance to sap-feeding, defoliating, shoot-boring, phloem-boring and

beneﬁcial arthropod feeding guilds may not provide enough justiﬁcation for initiating

 

new tree breeding programs in the Christmas tree industry. I found very little evidence
of resistance to entire feeding guilds, although I did ﬁnd some resistance to individual
pest species. Of the feeding guilds studied, shoot-borers and defoliators were minor pests
in terms of their abundance and the amount of damage that they caused. Varieties may
have some resistance against phloem-borers, which have the potential to be major pests,
but numbers were too low in this study to detect strong differences. However, sap-
feeders were abundant and major pests, and it seems evident that the large numbers of
beneﬁcials present in ﬁelds were unable to regulate their population. If further studies
investigating varietal resistance are conducted, efforts should be concentrated on those

pests capable of causing the greatest economic injury.

 

97

 

 

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Table 6. Mean number of arthropods per tree (iSE) in each feeding guild at Kellogg

Forest and Greenville in 1994 (n=18 trees per variety).I

 

 

Arthropod guild Riga Belgium Land 0' Pine Pike Lake Imp.
Kellogg Forest
Sap-feeders 72.4 (26.3)“ 103.4 (41.2)“ 29.9 (10.5)“ 48.2 (12.6)“
Defoliators 4.8 (0.7)“ 4.2 (0.8)“ 6.4 (1.5)“ 6.3 (2.1)“
Shoot-borers 0.9 (0.3)“ 6.6 (1 .0)b 5.7 (0.8)b 4.3 (0.7)b
Phloem-borers 0.5 (0.3)“ 4.1 (0.9)b 1.3 (0.5)“ 0.4 (0.4)“
Beneﬁcials 80.3 (5.7)b 50.5 (3.6)“ 39.2 (2.3)“ 41.7 (3.3)“
Greenville
Sap-feeder52 3,302 (1090)“ 587.3 (185)“ 904.8 (235)“ 3058 (1075)“
Defoliators 0a 1.5 (1.1)8 0.1 (0.1)8 0.03 (0.03)8
Shoot-borers 0.8 (0.2)“ 2.0 (0.4)“ 2.2 (0.4)b 2.0 (0.4)“b
Phloem-borers 0.1 (0.1)“ 0.8 (0.4)“ 0.9 (0.3)“ 0.5 (0.2)“
Beneﬁcials 164.0 (13.9)“ 221.3 (18.4)“ 180.5 (15.5)“ 167.3 (13.6)“

 

' Guild means followed by the same letter did not signiﬁcantly differ at the p<0.05 level.

2 Field measurements were estimated due to high population sizes.

103

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104
Table 8. Mean number of arthropods per tree (iSE) in each feeding guild at Kellogg

Forest and Greenville in 1995 (n=13 trees per variety at Kellogg Forest; 16 trees per

 

 

variety at Greenville).l
Arthropod guild Riga Belgium Land 0' Pine Pike Lake Imp.
Kellogg Forest
Sap-feeders 158.2 (24.4)“ 266.5 (38.1)b 177.9 (23.2)“b 175.7 (26.0)”
Defoliators 4.1 (0.7)8 7.9 (2.8)a 6.6 (0.9)8 3.5 (0.8)‘1
Shoot-borers 0.9 (0.3)3 1.5 (0.5)"I 1.4 (0.5)a 3.0 (1.1)8
Phloem-borers 1.2 (0.9)3 2.2 (1.1)3 0.4 (0.4)8 0.7 (0.3)3
Beneﬁcials 163.8 (14.1)b 114.4 (12.0)a 89.1 (4.7)a 100.0 (6.2)a
Greenville
Sap-feeders2 49,747 (9590)a 32,151 (8430)8 30,189 (9230)“ 106,512 (44,400)8|
Defoliators 4.4 (2.5)3 15.6 (9.5)a 1.9 (0.6)8| 3.1 (1.8)a
Shoot-borers 0.1 (0.1)“b 0.0“ 0.1 (0.1)“b 0.8 (0.4)“
Phloem-borers 0.1 (0.1)“ 0.4 (0.4)“ 0.1 (0.1)3 0.3 (0.2)a
Beneﬁcials 216.3 (26.4)a 229.1 (29.4)3 229.4 (18.8)11 206.1 (25.8)a

 

' Guild means followed by the same letter did not signiﬁcantly differ at the p<0.05 level.

2 Field measurements were estimated due to high population sizes.

 

105
Table 9. Percentage of species within each guild and Chi-square values from the

Kruskal-Wallis analysis of variance to determine if species abundance varied among four

varieties of Scotch pine at Kellogg Forest in 1994.

 

 

 

Percentage Sampling period

Arthropod of guild May June July August
Sap-feeders:

Pine needle scale 75.6 ns ns ns ns

Pine tortoise scale 4.2 8.20“ 8.11* ns ns

Pine spittlebug 18.3 ns 9.69“ 2143*" ns

Pine aphids 1.9 843* ns ns ns
Defoliators:

Grasshoppers 13.1 - 10.17““ 10.36““ 12.41 **

Chafer beetles 86.9 - ns ns ns

Pine sawﬂies 0.0 - - - -

Jack pine budworm 0.0 - - - -
Shoot-borers:

Eastern pine shoot borer 67.3 - 24.11"" 8.36* ns

Pine shoot beetle 32.7 ns 2195*“ ns ns
Phloem-borers:

Weevils 7.5 ns ns ns -

Zimmerman pine moth 92.5 27.91 *** us 1123* -

Beneﬁcial arthropods:

Ladybird beetles 1.2 ns ns ns ns
Lacewings 0.2 - ns ns -
Parasitic wasps 0.1 - ns - -
Spiders 98.5 ns 1810*" 33.46“” 2898*"

 

" * = signiﬁcant at p<0.05; ** = signiﬁcant at p<0.01; *** = signiﬁcant at p<0.001.

- = Individuals of the species were not observed at the time of sampling.

106
Table 10. Percentage of species within each guild and Chi-square values from the

Kruskal-Wallis analysis of variance to determine if species abundance varied among four

varieties of Scotch pine at Greenville in 1994.

 

 

 

Percentage Sampling period

Arthropod of guild May June July August
Sap-feeders:

Pine needle scale 90.1 ns ns ns 8.93““

Pine tortoise scale 0.1 ns ns - -

Pine spittlebug 8.8 ns ns 16.40“" 17.94"“

Pine aphids 1 11.25““ ns 8.47““ ns
Defoliators:

Grasshoppers 7.8 - ns ns ns

Chafer beetles 2.2 - ns - -

Pine sawﬂies 30.4 ns ns - -

Jack pine budworm 59.6 - 8.83““ - -
Shoot-borers:

Bastem pine shoot borer 96.4 12.32" 8.54““ 10.08““ ns

Pine shoot beetle 3 .6 ns ns - -
Phloem-borers:

Weevils l 1.9 ns ns ns ns

Zimmerman pine moth 88.1 11.00““ 9.13““ ns -
Beneﬁcial arthropods:

Ladybird beetles 1.1 8.73““ ns ns ns

Lacewings 0. 1 ns ns ns 8.83 ““

Parasitic wasps 0.1 ns - - -

Spiders 98.7 ns 8.87““ ns ns

 

a ““ = signiﬁcant at p<0.05; *’“ = signiﬁcant at p<0.01; ““'“* = signiﬁcant at p<0.001.

- = Individuals of the species were not observed at the time of sampling.

 

 

107
Table 11. Percentage of species within each guild and Chi-square values from the

Kruskal-Wallis analysis of variance to determine if species abundance varied among four

varieties of Scotch pine at Kellogg Forest in 1995.

 

 

 

Percentage Sampling period

Arthropod of guild May June July August
Sap-feeders:

Pine needle scale 18.0 9.34““ ns ns ns

Pine tortoise scale 1.3 ns 14.23““ ns ns

Pine spittlebug 79.1 ns ns 13.24" 7.78““

Pine aphids 1.6 14.61““ 14.43“” 3.82 -
Defoliators:

Grasshoppers 25.3 - ns ns ns

Chafer beetles 61.8 - ns ns ns

Pine sawﬂies 12.9 ns - - -

Jack pine budworm 0.0 - - - -
Shoot-borers:

Eastern pine shoot borer 62.5 ns ns ns ns

Pine shoot beetle 37.5 ns ns ns -
Phloem-borers:

Weevils 10.3 ns ns ns ns

Zimmerman pine moth 89.7 ns ns ns ns
Beneﬁcial arthropods:

Ladybird beetles 1.2 ns ns - -

Lacewings 0.4 - ns ns 9.42““

Parasitic wasps 0.2 ns ns ns ns

Spiders 98.2 26.10“" 14.30“" 14.23"“ 10.93““

 

a ““ = signiﬁcant at p<0.05; ““““ = signiﬁcant at p<0.01; ““'“* = signiﬁcant at p<0.001.

- = Individuals of the species were not observed at the time of sampling.

108
Table 12. Percentage of species within each guild and Chi-square values from the

Kruskal-Wallis analysis of variance to determine if species abundance varied among four

varieties of Scotch pine at Greenville in 1995.

 

 

 

Percentage Sampling period

Arthropod of guild May June July August
Sap-feeders:

Pine needle scale 98.5 ns ns ns ns

Pine tortoise scale 0.2 ns ns ns ns

Pine spittlebug 1.2 ns ns ns ns

Pine aphids 0.1 ns ns ns ns
Defoliators:

Grasshoppers 3.4 - ns ns ns

Chafer beetles 0.1 - - - -

Pine sawﬂies 74.5 ns ns - ns

Jack pine budworm 22.0 - ns ns -
Shoot-borers:

Eastern pine shoot borer 86.7 - ns 9.41 ““ -

Pine shoot beetle 13.3 - ns - -
Phloem-borers:

Weevils 35.7 - ns - -

Zimmerman pine moth 64.3 - - ns ns
Beneﬁcial arthropods:

Ladybird beetles 6.5 ns ns ns ns

Lacewings 0.2 ns ns ns ns

Parasitic wasps 0.2 ns ns ns ns

Spiders 93.1 8.4““ ns ns ns

 

a * = signiﬁcant at p<0.05; ““““ = signiﬁcant at p<0.01; *** = signiﬁcant at p<0.001.

- = Individuals of the species were not observed at the time of sampling.

109

Kellogg Forest 1994 Kellogg Forest 1995

  

 

Sap-feeders
Shoot-borers
Defoliators

Phloem-borers

H0538!

Beneﬁcials

 

 

 

Greenville 1994 Greenville 1995

      

0.2%

Figure l. The proportion of arthropod feeding guilds on Scotch pine trees at Kellogg
Forest and Greenville in 1994 and 1995.

FINAL CONCLUSIONS

The four varieties of Scotch pine used in this study differed from each other in height,
stem diameter, basal diameter growth rate, needle length, percentage of moisture in
needles, needle density and in percentage of nitrogen in one-year-old needles when grown
under identical environmental conditions. These traits may contribute to greater genetic
resistance against one or more major insect pests. Percentage nitrogen and/or percentage
moisture in foliage were important traits in relation to Zimmerman pine moth, European
pine sawﬂy and pine needle scale success.

These varieties of Scotch pine did not exhibit any obvious resistance to Zimmerman
pine moth, a native pyralid in the Lake States. If it existed, the effects of host plant
resistance were not strong enough to detect, perhaps because many larvae were killed by
parasitism and disease. Conditions for larval development were inﬂuenced by tree stem
diameter, tree height, percentage nitrogen in foliage and rate of resin ﬂow. I could not
determine the impact of resin ﬂow on larvae, but suspected that it may be a source of
early larval mortality. Other important mortality factors included parasitism by Exeristes
comstockii (Hymenoptera: Ichneumonidae) and Hyssopus rhyacioniae (Hymenoptera:
Eulophidae) and fungal infection by Hirsutella nodulosa.

Differences in European pine sawﬂy survival, development and fecundity were found

among varieties. Sawﬂy performance was poor on Riga, slightly better on Land 0’ Pine,

“0

 

 

I 11
and fairly good on Belgium and Pike Lake Improved. I suspect that resin acid

concentration, although not measured in this study, combined with nutrient and moisture
content of foliage may have contributed to varietal resistance against larvae, while tree
height and vigor may have been important traits to ovipositing adult females. Pupal
parasitism by Pleolophus basizonus (Hymenoptera: Ichneumonidae) did not differ among
varieties, but reduced sawﬂy survival in 1994.

Differences in pine needle scale performance were found among varieties. Scale
survival and fecundity were higher on Pike Lake Improved and Riga than on Belgium
and Land 0’ Pine. Percentage needle moisture and tree stem diameter predicted scale
survival, and percentage nitrogen in needles and percentage needle moisture signiﬁcantly
predicted second generation scale fecundity. However, percentage nitrogen was not
correlated with survival, perhaps because nitrogen content did not vary enough among
varieties or was not limiting to scale performance. Deme formation was probably not
applicable for scales living on Christmas trees, but scale performance may be affected by
weather, dispersal mortality, and parasitism and predation. Evaluation of variety effects
on pine needle scale would be more accurate under more controlled environmental
conditions and over more than two scale generations.

Differences among varieties in resistance to natural infestations of arthropod guilds,
and the phenology and species composition of beneﬁcial and pest arthropods were also
evaluated. In general, numbers of arthropods increased throughout the summer,
primarily due to increasing numbers of scales and spiders on trees. Sap-feeders were

more abundant than other guilds at both locations, but higher percentages of defoliators,

 

112

shoot-borers, phloem-borers and beneﬁcials were present at Kellogg Forest than at
Greenville. Riga was more resistant than the other varieties to shoot-borers, while
Belgium was more susceptible to phloem-borers. No strong signiﬁcant differences
among varieties in numbers of defoliators or sap-feeders were detected. Number of
beneﬁcial arthropods was highest on Riga trees at Kellogg Forest, but ratios of
beneﬁcials to pests indicated close to a 1:1 correspondence on all varieties. Ratios of
beneﬁcials to pests were slightly higher in 1994 than in 1995.

From these results, I suggest that Land 0’ Pine was not a strongly preferred host for
any of the insects in this study, it had a moderate growth rate, moderate green needle
color, and it originated from a climate similar to the Lake States. This variety may
require less management for insect pests, and thus be an acceptable variety to grow as a
Christmas tree. Alternatively, Riga trees could be grown as windbreaks in areas where
foliage color and aesthetics are not as critical as in a Christmas tree ﬁeld. Further studies
to identify the speciﬁc mechanisms of resistance to these pests need to be conducted

before breeding programs for improved varieties can begin.

 

 

APPENDIX 1

APPENDIX 1

Record of Deposition of Voucher Specimens*

The specimens listed on the following sheet(s) have been deposited in
the named museun(s) as samples of those species or other taxa which were
used in this research. Voucher.recognition labels bearing the Voucher
No. have been attached or included in fluid-preserved specimens.

voucher No.: 1996.5

 

Title of thesis or dissertation (or other research projects):

Evaluation of the Susceptibility of Four Scotch Pine Christmas Tree Varieties to
Insect Pests

Museum(s) where deposited and abbreviations for table on following sheets:
Entomology Museum, Michigan State university (MSU)

Other Museums:

Investigator's Name (3) (typed)

 

Eileen A. Eliason

 

 

Date 15 July 1996

*Reference: Yoshimoto, C. M. 1978. Voucher Specimens for Entomology in
North America. Bull. Entomol. Soc. Amer. 24:141-42.

Deposit as follows:

Original: Include as Appendix 1 in ribbon copy of thesis or
dissertation.

Copies: Included as Appendix 1 in copies of thesis or dissertation.
Museum(s) files.
Research project files.

This form is available from and the Voucher No. is assigned by the Curator,
Michigan State University Entomology Museum.

113

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