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IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII L

310306 4311

This is to certify that the

thesis entitled

”Aspects of the Ecology and Population Dynamics

' LIBRARY

Michigan State
University

 

of the Zimmerman Pine Moth, Diorxctria Zimmermani

(Grote)”

presented by

Robert B. Carlson

has been accepted towards fulfillment
of the requirements for

w. degree in Enigmo l ng

Q

       

ajor professor

I

Date M

 

 

 

 

 

 

 

 

ABSTRACT

ASPECTS OF THE ECOLOGY AND POPULATION DYNAMICS OF THE ZIMMERMAN
PINE MOTH, DIORYCTRIA ZIMMERMANI (GROTE)

by Robert B. Carlson
Certain aspects of the ecology and population dynamics of the

Zimmerman pine moth, Dioryctria zimmermani(GrotQ, were studied in

plantations of Scotch pine, Pinus sylvestris L., that were being grown

 

for Christmas trees. Inner bark temperatures were recorded on trees
with dense, medium, and no foliage by use of a 24—point recording
potentiometer in order to ascertain what effect increased foliage
density, as a result of shearing, has on the temperatures of the larval
micro-habitat. The temperatures within individual trees and between
trees of different foliage densities varied considerably. An attempt
is made to relate these variations to the ambient solar radiation and
ambient temperatures recorded in the plantation. By comparing tempera-
ture regimes found in dense and medium foliage trees with distributions
of larvae and damage symptoms on sheared and unsheared trees, it is
concluded that temperature does not materially affect the distribution
of the larvae on the host trees. Examination of the possible effect

of temperature differences on development of an insect was carried out
by using a hypothetical description of the relationship between develop-
ment and temperature. Although this comparison is not directly applin

cable to Q. zimmermani, developmental totals varied only up to 18% from

 

 

 

 

Robert B. Carlson

totals calculated from the ambient temperatures for the eight dates
which were examined. These calculations only included the periods of

diverging temperatures and therefore inclusion of the 8-10 hours of
uniform temperatures would reduce the variations given.

Through measurement of bark thickness it is concluded that
selection of planting stock with respect to this factor would not be
useful in reducing tree susceptability. Increased bark thickness in
whorl areas, however, does appear to be a significant factor in in—
creased attack by Q. zimmermani.

The relative frequencies of occurrence of various damage symptoms
were observed and regression equations calculated for infested trees
and infested whorls as predicted from infested terminal shoots, and
infested whorls as predicted from infested trees. The first two equa-
tions can be used to assess the degree of infestation in a plantation.
The mean numbers of dead trees, trees with dead lateral branches and
dead lateral branches for 100 tree samples from five plantations are
given. These damage symptoms are then discussed with regard to the
economics of control of this insect.

The distributions of infested trees, in one plantation, and in—
fested whorls among infested trees, as an average for 5 plantations,
are given. The distribution of trees is shown to be random and the
infested whorls per infested trees seems to approximate a log—normal
distribution. The truncated nature of the data, in the latter case,
may be cause for questioning the fit to a log—normal distribution.

The geographic distribution of the insect as a serious pest in
Christmas tree plantations of southwestern Michigan is given and the

possible reasons behind the observed distribution are di5cussed. The

 

 

 

 

 

«I

 

Robert B. Carlson

hypothesis is advanced that a northern limit may occur beyond which
high populations will not develop.

A study of the number of terminal abdominal spines on pupae col—
lected from 5 plantations is given. From this data it is concluded
that Q. zimmermani is the only species of Dioryctria present in the
plantations. The intraspecific differences in the number of terminal

spines on the pupae is quantified from these data.

 

 

ASPECTS OF THE ECOLOGY AND POPULATION DYNAMICS OF THE ZIMMERMAN

PINE MOTH, DIORYCTRIA ZIMMERMANI (GROTE)

BY
a

I \

Robert BY Carlson

A THESIS

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

DOCTOR OF PHILOSOPHY

Department of Entomology

1965

 

 

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to 2311mm. as.

cam-ml; cw amass 1311' m

3' 21' '2‘. :‘1 .i.'?T:'

.i‘

:‘l"

 

3'35?!“

 

ACKNOWLEDGEMENTS

I wish to thank all those persons who have assisted and inspired
me through the duration of my educational endeavors, with specific
appreciation being accorded to my wife, Kay.

Special thanks go to Dr. James w. Butcher whose interest and
assistance during the studies reported herein has been stimulating and
whose guidance during the course of my graduate work has given me con-
tinual incentive towards its completion.

I convey sincere appreciation to the other members of my graduate
committee; Dr. Gordon Guyer, Chairman, Department of Entomology,

Dr. Roger Hoopingarner, Department of Entomology, and Ceel Van Den Brink,
U.S. Weather Bureau in cooperation with M.S.U. The late Dr. Philip J.
Clark, Department of Zoology, served on the graduate committee during

the major part of my Ph.D. program. His sincerity and willingness to
assist, both in the classroom and in private consultation, were a

source of stimulation to me and to others who knew him.

Financial assistance on this project was furnished by the Depart-
ment of Entomology through arrangements made by Dr. Butcher and

Dr. Guyer. This assistance is gratefully acknowledged.

ii

 

 

 

 

 

TABLE OF CONTENTS

Page
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . 1
LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . 4
METHODS AND EQUIPMENT . . . . . . . . . . . . . . . . . . . . . 11
Temperature and Solar Radiation . . . . . . . . . . . . . . 11
Distribution of Larvae and Damage Symptoms . . . . . . . . 18
Relationship Between Bark Thickness and Infestation . . . . 19
Frequency of Occurrence of Various Damage Symptoms . . . . 20
Distribution of D. zimmermani as a Serious Pest . . . . , . - 20
Assessment of the Possibility of Occurrence of a
Species Complex . . . . . . . . . . . . . . . . . . . . . 21
DISCUSSION OF EQUIPMENT USAGE . . . . . . . . . . . . . . . . . 22
Recording Potentiometer . . . . . . . . . . . . . . . . . . 22
Recording Pyrheliograph . . . . . . . . . . . . . . . . . . 24
RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Temperature, Foliage Density and Solar Radiation . . . . . 26
Relationship between Inner Bark Temperatures and
Insect Distribution . . . . . . . . . . . . . . . . . . . 33
Possible Effects of the Observed Temperature
Differences on the Development of an Insect . . . . . . . 4O
Bark Thickness as a Factor in Tree Infestation . . . . . . 43
Relationships Between Frequencies of Occurrence
of Various Damage Symptoms . . . . . . . . 46
Distribution of Infested Trees and Infested Whorls
among Infested Trees . . . . . . . . . . . . . . . . . . 52
Species Characteristics of D. zimmermani Pupae . . . . . . 55
Geographical Distribution of D. zimmermani as a
Serious Pest in Christmas Tree Plantations in
Southwestern Michigan . . . . . . . . . . . . . . . . . . 57
SUMMARY OF CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . 60
LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . 62

iii

 

 

 

 

Table

LIST OF TABLES

Accumulated Solar Radiation and Accumulated Deviations
of Inner Bark Temperatures from Ambient

Maximum Temperatures (OF.) Recorded at Each Level of
Dense and Medium Foliage Trees

Accumulated Numbers of Developmental Units During
Periods of Diverging Temperatures and Their
Relationship to Number of Developmental Units
Calculated from Ambient Temperature

Mean Bark Thickness for Infested and Non-infested
Trees and the Results of Paired Comparison
Analyses of the Data

Mean Numbers of Trees Infested, Trees with Dead
Laterals, Dead Trees and Dead Laterals for 100
Trees

Analysis of Interplantation Differences in the

Numbers of Pupae with 6 and 8 Terminal
Abdominal Spines

iv

Page

27

38

41

43

51

57

 

 

 

 

Figure
l.

2.

LIST OF FIGURES

Placement of Thermocouple Junctions on Trees

Mean Deviations per Day of Inner Bark Temperatures
from Ambient Temperatures at Three Levels on Three
Trees of Varying Foliage Density

Vertical Distribution of Larvae and Pupae on
Scotch Pine

Distribution of Damaged Whorls on Dense (Sheared)
and Normal (Unsheared) Foliage Trees

Directional Distribution of Larvae and Pupae on
Scotch Pine

Relationship Between Infested Terminals and
Infested Trees

Relationship Between Infested Terminals and
Infested Whorls

Relationship Between Infested Trees and Infested
Whorls

Distribution of Infested Whorls Among Infested
Trees

Page

13

31

34

35

37

47

48

49

54

 

 

 

Plate

II.

III.

IV.

LIST OF PLATES

Trees Used for Evaluation of Foliage Density Effects
in Modification of Inner Bark Temperatures

Recording Potentiometer Housed in Weather Proof Case
and Recording Pyrheliograph

Diagramatic Sketch of the Manner in Which Bark
Thickness is Increased in the Whorl Areas of
Sheared Trees

Geographical Distribution of D. zimmermani as a
Serious Pest in Christmas Tree Plantations

vi

 

Page

12

15

45

58

 

 

 

 

INTRODUCTION

The Zimmerman pine moth, Dioryctria zimmermani (Grote), is a
serious pest of pine, particularly those grown as Christmas trees, in
certain areas of Michigan. The larvae of this insect attack both the
terminal shoots and the main stems. Terminal damage consists of a
tunneling down the center of the shoot with a resulting drooping or
flagging. Attack on the main stem consists of tunneling in the cambial
region, generally in the whorl area, and destruction of the cambial and
phloem tissue. The symptoms of the latter type of damage are occurrence
of pitch masses at points where the larvae break through the outer bark.
Attacks on the main stem often result in the death of lateral branches,
which are usually girdled at the base, and occasionally in the death of
the tree through complete girdling of the main stem. The loss of
lateral branches is perhaps the most important consideration with re—
spect to Christmas tree production due to its frequency of occurrence
and the rapid devaluation of deformed trees.

Scotch pine, Pinus sylvestris Linn., is the predominant choice

 

of tree growers engaged in production of Christmas trees in Michigan.
This species is not native to the United States but appears to be an
extremely good host plant for the apparently endemic Zimmerman pine

moth. Native species of conifers such as red pine, Pinus resinosa

 

Ait. and jack pine, Pinus banksiana Lamb., are also suitable hosts

)

 

but do not appear able to support high populations of this insect in

their natural state and they are not as popular for use as Christmas

1

 

 

 

2

trees. There is little doubt, hOwever, that natural stands and orna-
mental trees of these species haVe served as reservoirs for populations
of the Zimmerman pine moth and are important sources for original in-
festations of Scotch pine plantations.

This study was designed to determine if physical characteristics
of the trees, microclimatic conditions and modifications thereof thrdugh
cultural practices, influence tree susceptibility to attack by

D. zimmermani. The study was carried out exclusively in Scotch pine

plantations, due to the extensive use of this species, with the hope
that through this approach, cultdral practices could be recommended to
tree growers which might minimize future damage by this insect.

The research was based primarily on work done by the author
(Carlson 1962) on the biology and life history of Q. zimmermani. This
work raised questions concerning the effect of shearing on larval dis-
tribution and development. As the current study progressed, the rela-
tionships between degree of infestation and degree of damage, compari-
sons between frequencies of the two types of attack, distributions of
larvae and damaged trees, geographical distribution of the insect as a
serious pest and the possible existence of a "species complex” were
investigated.

Investigation of micro—habitats as they affect insects or other
small arthropods is an extremely difficult task. The problems encoun-
tered take two forms: (1) the practical difficulty of obtaining mean-
ingful data and (2) interpretation of the data obtained with respect to
the animal under investigation. The first is a result of a need for
specialized equipment. The latter is due to a general lack of informa—

tion on what physiological effects the modification of micro-habitats

 

 

——

3
have on the animals. Neither of these problems were completely overcome
in this study but a firm foundation is laid for further work in this

area .

 

 

 

LITERATURE REVIEW

Previous work on the Zimmerman pine moth has been oriented mainly
toward the taxonomy and life history of the insect. The latter studies
have had the primary objective of obtaining satisfactory control in high
value plantations (Schuder 1960, Carlson 1962, and Butcher and Carlson
1962). Rennels (1959) and Talerico (1963) have worked on this insect
as it occurs in forest plantations, with the emphasis again primarily
on life history and some attention given to population dynamics.

Rennels made observations on various tree and stand character-
istics and attempted to relate these to severity of infestation. In
this regard he showed a negative relationship between stand density and
infestation percentage in older plantations where stem infestations
predominate. This was hypothesized to be a relationship between inten-
sity of infestation and exposure to light or temperature. No explana-
tion is given as to why this relationship might occur.

The effect of pruning live branches was also investigated by
Rennels. In this case he termed his data inconclusive but on the basis
of reports by Kellicot (1879) and Craighead (1950) it was felt that
this practice appeared to increase the incidence of infestation.

Factors which were found to have no apparent effect on infesta-
tion incidence, according to Rennels, were; mixed plantings, source of
planting Stock, character of ground vegetation, litter depth, aspect of
the slope, soil quality and tree diameter or height. Bark thickness,

after reaching a minimum of 0.15 inches necessary to permit attack, was

4

 

 

 

 

5
also said to have no discernible effect.

Talerico (1963) showed a drop of nearly 90 percent in the number
of active infestation sites between June and August. Of this decrease,
8 to 18 percent and 18 to 39 percent were positively attributed to
parasitism in 1960 and 1961 respectively. The remaining portion of the
decline is said to be due to unknown causes, ”the larvae and pupae
simply disappearing unaccountably”. It should be noted here that no
such high proportion of missing insects has been observed by the author
in five years of study on this insect in Christmas tree plantations.
Although no extensive studies were carried out to support this observa—
tion, it was found that most inactive infestation sites were primarily
due to the insects moving back into the cambial—phloem region rather
than remaining in the pitch masses. These pitch masses appear to repre-
sent points where the larvae have accidently broken through the outer
bark, causing the flow of resin. Therefore, any examination of the
pitch mass may or may not yield an insect depending upon when the mass
was formed and how long the larva has had to tunnel away from the site.
It follows then, that this method of examination would yield a lower
number of active infestations later in the season. It should also be
noted here that the resin flow early in the season, during the period
of active tree growth, could be expected to be greater and hence a
greater number of obvious infestation sites would appear during this
period.

Carlson (1962) showed indications of seasonal changes in the
relative numbers of larvae found in each whorl area of the trees. From
this data it appeared that there was some factor, or factors, which in-

fluenced either survival or movement of the larvae, resulting in the

 

 

 

6
occurrence of a higher percentage of larvae in the center whorls later
in the season. It was surmised that temperature could be the factor
responsible. This study attempts to follow up this line of investiga-
tion by examining the temperature relationships within the trees.

Attempts at measuring micro-climatic influences are numerous.
The status of these types of investigations, however, has not been im-
proved much due to the extreme difficulty encountered in the interpre-
tation of results obtained. In most cases the studies have been too
much concerned with the methods of obtaining data. This study is no
exception to this generalization.

Wellington's (1957) review of climatological investigations in
entomology contains many very pertinent suggestions that might well be
considered by anyone contemplating such studies. The foundation of his
suggestions is that variability in micro~environment can be classified
in terms of general weather types, and investigations should be aimed at
extremes of situations encountered by the insect under the range of
weather types. This he terms the synoptic approach.

Wellington states that the micro-environment of the insect is one
portion of the total environment that can be most easily manipulated
for the partial control of insect pests. He gives examples where cul—
tural practices have been modified with a resultant increase in popula—
tions of pest species. These "negative" examples readily serve to show
how micro-climatic modification can affect an insect population and
thereby pose the possibility of creating ”positive” situations by cul-
tural manipulation.

According to Wellington, the effects on the insects of micro-

climate can take two forms: (1) effect on development and (2) effect

 

 

 

7
on behavior. He feels that investigations on the latter warrant more
attention than they generally receive. Since the insect must do certain
things just to survive, let alone develop, the preponderance of inves-
tigations taking the former approach seems, to him, to be out of balance.

Temperatures within plant tissues have been investigated by a
number of individuals. Wellington (1950) gives a relatively complete
review of investigations on the effects of solar radiation on insect
micro-habitats. His paper discusses many of the studies carried out
previous to its publication.

Two of the more pertinent studies, with respect to the one
described herein, have been carried out by Miller (1932) and Henson and
Shepherd (1952). The former study was concerned with the survival of
the western pine beetle, Dendroctonus brevicomis Lec., at high and low
temperatures. Miller inserted thermometers under the bark of the trees
in order to determine what temperatures the developing larvae and pupae
were subjected to. This he then related to pre—determined maximum and
minimum lethal temperatures. The latter study was concerned with the
temperatures occurring in the mines of Recurvaria milleri Busk., the
lodgepole needle miner. The investigators inserted thermocouple
junctions into the mines for determination of temperatures. They then
related the deviations in temperatures from the ambient to the amount
of solar radiation to which the needles were subjected. This gave a
”linear and extremely regular” relationship. Heating of the needles
through solar radiation increased the temperature in the mine by as
much as 7 degrees C. or 12 degrees F. Henson (1958) has also carried
out similar investigations on poplar-inhabiting insects.

The relationships between temperature and insect development have

long been a subject of study by entomologists. Some of the more complete

 

 

 

8
studies on this subject have been carried out by Shelford (1927),
Davidson (1944) and Pradhan (1945).

Shelford diScusses the practice of summing temperatures above a
threshold value for prediction of development of insects in the field.
This practice is predicated upon a straight line relationship between
temperature and developmental rates and had been, even before Shelford's
work, criticized on this basis. Working with the codling moth,
Carpocapsa pomonella Linn., Shelford established what he termed tables
of "developmental units" by rearing the different stages of the insect
under constant temperature conditions in the laboratory. The tables
take into account the non-linearity of a temperature-development rela-
tionship at the low extreme of temperature as well as the retarding
effects of high temperatures. It is pointed out in this work that very
substantial errors can result in calculation of development if other
factors, mainly humidity, are not taken into account. Finally,
Shelford points out the necessity of an accurate estimate of expected
development rates if one is to attempt evaluation of factors which
might have occasional, but important, bearings on the insect's develop-
ment in the field.

Davidson has proposed a logistic equation for the description of
developmental rates. This type of equation will account for non-
linearity in the medial ranges of temperatures as well as at the ex-
tremes, but does not adequately describe the retardation effect on
development at high temperatures. Andrewartha and Birch (1954) feel
that Davidson's equation method is the best description of developmental
rates yet proposed. The extremely complicated and tedious calculations

necessary to establish Shelford's developmental unit scheme of prediction

 

 

 

Ii"

 

9

is probably the most important single factor which would mitigate its
rise in most investigations of this type.

The studies by Shelford and Davidson are based primarily on labo-
‘ratory rearings at constant temperatures. Pradhan has attempted to
laridge the gap between this constant temperature criterion and the
Klariable temperatures encountered in the field. It is his contention
that Shelford, in summing ”developmental units" for field predictions,
is reverting back to making some of the same errors that make summing
<>f temperatures unwarranted. The main error being the assumption that
ea given temperature encountered in the field results in the same amount
c>f development as it does in the constant temperature conditions in the
]_aboratory. It is pointed out in this paper that subjecting an insect
to varying temperatures can alter the developmental response at a given
temperature from the response that would occur in the lab. Pradhan then
{Droposes formulae which he feels adequately describe development under

iEield conditions. Using Empoasca fabae Harris, he illustrates their

 

éipplication.

Unfortunately all of the above methods of describing development
Irequire a relatively large number of easily accessible insects, or a
{Dractical method of rearing the insect under investigation. This is
riot the case with D. zimmermani. These studies are therefore brought
c>ut in order to give a basis for evaluating possible effects of the
t:emperature differences encountered in this study rather than to form
a, basis for developmental work on this insect.

The taxonomic status of the genus Dioryctria has been described
qllite thoroughly by Heinrich (1956). Munroe (1959) gives the Canadian

SPecies of Dioryctria and Ross (1959) has published a key to species

 

 

 

10
occurring in British Columbia based on abdominal characteristics of the
pupae. In all of these publications 2. zimmermani and D. cambiicola
are described as being quite closely related. 0n the basis of this
close relationship, Heinrich states that the latter is doubtfully dis-
tinct from the former except as a possible race. Ross, however, gives
characteristics dealing with the number of terminal abdominal spines
and their degree of booking, which can apparently be used for separating
the two species. In this regard, D. zimmermani is said to be charac-
terized by ”ends of terminal spines, usually 6, strongly hooked."
2. cambiicola, on the other hand, is characterized by ”ends of terminal
spines, usually 8, almost straight or slightly hooked.” The character—
istics given by Ross led Carlson (1962) to speculate on the possible

existence of a species complex being present in Michigan. This led to

a re-examination of the possibility in the study reported here.

METHODS AND EQUIPMENT

Temperature and Solar Radiation

A method of evaluating extreme conditions was used for the deter-
mination of the effects of foliage density in modifying inner bark
temperature of Scotch pine. Three trees of differing foliage densities
were "wired" for temperature measurements. The first tree had the
dense foliage which results from shearing practices used in the Christmas
tree industry. The second tree was of medium foliage density, much as
would be found under normal conditions of growth. The third tree was
completely stripped of foliage in order to obtain the conditions at the
opposite extreme from the first. These trees are shown in Plate 1.

The wiring of the trees was accomplished by inserting thermo—
couple junctions under the bark at two compass points (north and south)
at each of three levels (upper, middle and lower whorl areas) on each
tree. Two junctions were also placed on the bark surface, at the same
compass points as above, at about mid—crown of each tree. The tempera—
ture readings obtained from these latter two points on each tree were
held to be invalid, due to inadequate shielding of the points, and
therefore are not considered in the subsequent discussion of results.
The placement of the junctions is illustrated graphically in Figure 1.

The junctions were formed by twisting together the leads of 30
(B. and S.) gauge, type T, copper-constantan thermocouple wire and spot
soldering the contacts thus formed. A small nail, slightly larger than
the junction, was forced under the bark at an angle from below and the

11

 

 

 

12

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mHUmmmm NHHmZHQ mU<HAom mo ZOHH<DA<>M mom mama mMMMH

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13

1"! ---- Outer Bark

1,
/} ——————— _ I Thermocouple

) Junction
1

.1" l '1
________ l, ‘ i, Lead Wire

1 —'(To Potent-

/( ’1 H iometer)

.1 1
Bottom \ /}— —— — ———— J) I“

  

Locations on Trees Locations on Stem

[We—$5

Fig. l. Placement of thermocouple junctions on trees.

 

 

 

14
junction was inserted into the hole left after removal of the nail. The
bark was then pressed down over the protruding wire so that the point
was completely covered.

The copper—constantan leads were attached to a Brown "Electronik",
24 point, recording potentiometer. The complete cycle of 24 points was
recorded every 12 minutes, thereby giving 5 temperature readings at each
point each hour. The recorder was housed in a custom—made, weather-
proof case for field use (Plate 2) and a set of plug—in connectors,
specially made for use with copper-constantan leads, was used to increase
the portability of the machine by reducing the time required in setting
up for operation. The receptacle portions of these connectors were left
attached to the machine and the plug portions left attached to the
thermocouple leads at all times.

During part of the study the potentiometer was supplied with
electrical power generated by a small, portable, gasoline operated
alternator. This power source proved adequate for operation of the
instrument but the necessity of stopping the alternator for refueling
required interruption of temperature recordings. In view of this
situation it was decided to operate the instrument at periodic intervals.
This was, in most cases, once an hour for a period of three cycles.

During the rest of the study a source of line power was supplied
for operation of the potentiometer. This allowed continuous operation
of the recorder and temperatures were taken over 24 hour periods.

A Belfort recording pyr¢heliograph (Plate 2) was used to record
the ambient solar radiation in the plantation which the wired trees
were located. This instrument records Solar radiation in gram—calories

per square centimeter. In 1963 the pyrheliograph was geared to record

 

 

 

RECORDING P0

15
PLATE II

 

w 5., I ' ‘ V ‘. a I
TENTIOMETER HOUSED IN WEATHER PROOF CASE
AND RECORDING PYRHELIOGRAPH

 

—

16

over a period of one week per chart. This proved inadequate due to
overlapping of rising and falling segments of the line, in that the
trace line could not be followed during periods of intermittent clouds.
During the 1964 season this difficulty was alleviated by changing the
gears so that a recording of one day per chart was obtained. This gave
much more satisfactory results.

Ambient temperature was recorded in the plantation by means of a
Bendix—Friez hygrothermograph. The instrument was housed in a shelter
and positioned at a height of six feet.

Compilation of the temperature and solar radiation data proved
to be time consuming. How much of the data to use, what form to use in
presentation, and how to interpret the results were the major questions
which arose. It was decided that the primary consideration was effect
of foliage density on the temperatures to which the larvae may be sub—
jected. In order to assess this factor the cumulative deviations of
the temperatures at each recording point from the ambient temperatures
recorded on the hygrothermograph were calculated for each date when the
potentiometer was in operation. Using ambient temperature as the base
for calculation of deviations is a simple method for removing the ambient
temperature factor from consideration and allowing direct comparison be—
tween temperature measurement points on the same and different trees.
This then simplifies the interpretation of resulting temperatures with
regard to the foliage density of the trees and the ambient solar
radiation.

Evaluations of possible effects of temperature differences,
brought about by modifications of the micro-habitat, on the insect

under consideration was attempted. The first consideration in this

 

 

 

,

17
regard was the possibility that high temperatures might occur which
could prove lethal to the larvae. To evaluate this factor, the maximum
temperatures encountered at each point on the trees for each date were
recorded. The second effect considered was possible modification of
insect developmental rates. Considering the difficulty of obtaining
adequate numbers of D. zimmermani larvae and the lack of a good rearing
method it seemed impractical to develop an adequate description of the
specific temperature~developmental relationships. With this in mind,
and conscious of the hazards involved in the following approach, the
developmental relationships for another insect were used in an attempt
to assess this possibility. The developmental relationships used were
those presented by Shelford (1927) in his study of the codling moth,
Carpocapsa pomonella Linn. A complete description of how these rela-
tionships were worked out and a table of calculated developmental units
for larvae is given in Shelford's paper and will not be discussed here.
Suffice it to say that each temperature value at prescribed intervals
can be converted to a value described as the number of developmental
units for that temperature. In Shelford's study these developmental
units were then accumulated in an effort to predict the appearance of
certain stages in the insects life history. The use of the conversions
in this study does not imply any assumption that they can be applied to
2. zimmermani for predictive purposes. As mentioned above, it is an
attempt to evaluate possible temperature effects by incorporating some
of the information known about rates of insect development at dif—
ferent temperatures. These relationships have been discussed in the

literature review.

The data obtained from the recording pyrheliograph for the 1964

 

 

 

 

18
season were converted to cumulative gram calories for each day on which
temperatures were measured. These accumulations were made on readings
taken from the chart at hourly intervals. This method facilitates com-

parisons with the temperature deviations from ambient deseribed above.

Distribution of Larvae and Damage Symptoms

The vertical distribution of larvae on Scotch pine was taken
from previous studies (Carlson 1962).

The directional distribution of larvae was determined by extracting
larvae and pupae from trees in the plantation and recording the direction
on the tree at which they were found. The insects found midway between
two cardinal directions were split equally between the two directions
for the purpose of analysis. During the course of feeding the
D, zimmermani larvae may work around the tree but no effort was made to
determine whether there was any seasonal pattern to this movement. All
specimens were therefore pooled for the determination of the distribu—
tion regardless of the date on which they were collected.

The distribution of damage symptoms on trees was obtained by
recording the number and location of damaged whorls. This was done in
6 plantations using a 400 tree sample from each. Two of the plantations
were composed of unsheared trees and these were totaled separately to
give a comparative situation between sheared and unsheared trees. This
facilitated interpretation of distributions with respect to the tempera-
ture regimes encountered on these two types of trees.

The distribution of infested trees in a plantation was determined

by examination of every tree in one block. Each tree was plotted on a

map with an appropriate designation of infested, non—infested, or missing.

 

 

 

————————1

l9 '
This map was then taken into the lab for further analysis. The dis-
tribution of infested whorls among infested trees was determined from
the data accumulated for determination of vertical distribution of
damage symptoms. This data was retabulated with respect to the number

of trees showing each number of whorls infested.

Relationship Between Bark Thickness and Infestation l

 

Bark thickness measurements were taken with a Sandvik bark
measurement gauge. This instrument is calibrated in 1/16 inch intervals
and estimates were made to the nearest 1/10 of an interval when the
gauge was read.

The method of selecting trees for measurement was dictated by a
paired comparison plan of analysis. This method consisted of selecting
an infested tree and using an uninfested, adjacent tree as its comple-
ment for the paired comparison. During the 1963 season the bark measure—
ments were taken at points just below and a little to the side of the
point of infestation. On the uninfested trees the measurements were
taken at equivalent points. All of the paired trees were as similar as
possible in height and foliage density. During the 1964 season, due to
additional information obtained on problems encountered in bark thickness
measurement, the above procedure was changed somewhat. The trees were
selected by the same criteria but the bark thickness measurements were
taken at mid—crown rather than near the point of infestation. Three
measurements were taken at the same level but in different directions
on each tree. These were then averaged in order to balance possible

within-tree variability.

 

 

20

Frequency of Occurrence of Various Damage Symptoms

In this phase of the study 5 plantations were used. In each of
the plantations four sections were delimited and the number of infested
terminal shoots on one hundred trees was recorded for each section.
These counts were made about mid-July when most terminal damage is
plainly evident. Later in the summer these same sections (but not
necessarily the same trees) were used to determine the number and loca—
tion of infested whorls and the numbers and location of dead and dying
laterals, again on one hundred trees.

The relationships between damage symptom frequencies were deter—
mined by a series of regression analyses. Selection of plantations was
restricted to those which were judged to be representative of managed
Christmas tree stands. It was hoped that the regression analysis, then,
could be used to give growers a method of assessing the degree of in-
festation in their plantations by use of a simple survey of some con—

spicuous symptom, such as infested terminal shoots.
Distribution of D. zimmermani as a Serious Pest

A broad scale survey was carried out in an attempt to determine
the geographical limits of this insect as a serious pest in the western
part of the lower peninsula of Michigan. This survey was, for the most
part, accomplished by traversing the area with the object of delimiting
the northern and eastern extremes of the distribution. The extremely
irregular occurrence of pine plantations in areas with extensive pro-

duction of other agricultural crops complicates the interpretation of

this survey.

 

 

 

 

 

21

Assessment of the Possibility of Occurrence
of a Species Complex

In an effort to evaluate the use of pupal characteristics for
species determination of D. zimmermani and Dioryctria cambiicola Dyar,
pupal specimens were collected from 5 plantations within the area of
study. Previous studies (Carlson 1962) suggested the possible occur-
rence of the latter species on the basis of the number of terminal
spines on the pupal abdomen. These spines were counted for each speci—
men collected and the degree of hooking of the spines evaluated. This
gave a frequency of occurrence value for each plantation. These values

were then subjected to a Chi-square analysis.

 

 

 

___—____1

DISCUSSION OF EQUIPMENT USAGE

Recording Potentiometer

Any Scientific study which employs specialized equipment is
likely to experience equipment malfunctions and unforeseen complications.
It seems pertinent therefore to discuss some of the shortcomings, as
well as the advantages, in the use of the equipment and to suggest means
by which some of the problems may be overcome. No attempt will be made
to discuss the technical operation of the equipment or the technical
problems associated with the use of the instruments. This information
can be obtained from the manufacturers of the equipment. One publica-
tion which contains a discussion of some of the technical aspects of
temperature measurement by use of thermocouples is Fundamentals of
Thermometry by J. A. Hall (1953).

The Brown "Electronik" 24 point recordinglpotentiometer used in
this study can be a powerful tool for analysis of temperatures in the
insect microhabitat. Although not easily portable, due to its weight,
the instrument did prove usable in the field where the access roads
were near the site of installation.

Furnishing a power source for operation of the instrument does
not appear to be a problem. A portable gasoline operated alternator
used as a power source proved satisfactory but required suspension of
operation for refueling and hence a disruption of temperature measure—
ments. Increasing the fuel capacity on the alternator was precluded by

the type of fuel feed system, however this may be a means of reducing

22

 

 

 

23
the inconvenience with other portable power sources.

Perhaps the major difficulty in the use of this piece of equip—
ment is the problem of transferring the temperature values from the
chart to some usable form. This operation is time consuming and the
distinguishing of "point" numbers on the chart is difficult during
periods of uniform temperatures. This latter difficulty could easily
be corrected by increasing the chart speed from two inches per hour,
used during this study, to three inches or more. The increase would
effectively spread out the point numbers and make them more easily dis—
cernible. The time necessary for transferring data is more difficult
to offset. It appears that the only way the investigator can minimize
this problem is by transferring only as much data as he can effectively
use. In this study only one cycle of temperature readings per hour was
used. The remaining four cycles were quickly scanned to determine whether
any pertinent changes in temperatures occurred during the period and
also whether the temperatures used for that hour were comparable to
those not used. In studies where temperatures could be expected to
change more rapidly, transference of more than one cycle per hour may
be preferable.

One feature which is available with this particular potentiometer,
but was not on the instrument used, is a voiding mechanism. This
mechanism will cause the instrument to record at the low end of the
scale at anytime that the point to be recorded is not transmitting an
electrical current to the instrument. Without this feature the instru~
ment records approximately the same temperature as at the previous
point. In this study the recording points were attached to the machine

so that points where similar temperatures might be expected would not

 

 

 

 

—_—__———1

24
record one after the other. This gave a check system which effectively
revealed aberrant readings due to the above mentioned factor. It seems,
however, that inclusion of this feature would be useful in avoiding
aberrant readings, especially where portable usage necessitates frequent
handling of the lead connections.

The wire used to form the thermocouples, and as lead—ins to the
instrument, was 30 (B. and S.) gauge copper-constantan. Some difficulty
was encountered due to the tendency for the wire to break at the plugs
used to connect the leads to the instrument. The possibility of this
leading to errors in temperature measurement was reduced by checking
the connections before commencement of recording. At times when a
temperature reading appeared inordinately low at a certain point, a
check usually revealed a bad connection. It is felt that a heavier
gauge wire would be preferable when the instrument is in portable usage.

The biggest advantage to the use of this instrument is the oppor-
tunity to measure temperatures that an insect may experience over the
complete range of micro-habitats. The small size of the measuring
point, allowing for precise placement, and the continuous operation of
the machine, leaving the investigator free to perform other work, gives

definite advantages over other types of temperature measurement devices.

Recording Pyrheliograph

Very few problems were encountered in the use of the Belfort
recording pyrheliograph. The completely self contained operation of
this instrument makes it an ideal tool for field investigations. The
necessity of changing the chart speed to obtain clear trace lines during

periods of intermittent clouds was the only modification required. A

 

 

_——___1

25
minor problem was encountered in the deposition of dew on the globe
when temperatures were below the dew-point. This situation only occurred
in early morning and was easily corrected by wiping the globe with a
soft cloth.

This instrument should have numerous applications in studies of
insect ecology and possibly behavior. Some of the uses which come to
mind are studies of (1) solar radiation levels and flight behavior,
(2) solar radiation levels and general insect activity, and (3) solar
radiation as it effects temperatures. These are necessarily broad
topics but a review of Wellington's (1950) paper on solar radiation
and the insect microhabitat will form a good basis for developing

studies along these lines.

 

 

 

RESULTS

Temperature, Foliage Density and Solar Radiation

In order to ascertain the effect solar radiation has on inner
bark temperatures, and how foliage density modifies its influence,
temperature measurements were made on Scotch pine trees showing three
different degrees of foliage density as described in the section on
materials and methods. Solar radiation values were recorded continu-
ously during periods when temperature measurements were being recorded.

Table 1 shows the accumulated deviations of inner bark tempera-
tures from ambient temperatures for each measurement point on each tree
for each date that recordings were made. The deviations were accumulated
on an hourly basis from the time that the temperatures at different
points on the trees began to deviate from each other (in the A M.) until
the temperatures recorded at all points were within approximately 20F.
of each other (in the P M.). This period of time corresponds approxim
mately to the period of direct solar radiation as recorded on the
pyrheliograph. The dates in this table are arranged by ascending order
of accumulated solar radiation values.

Although none of the temperature measurement points showed a
consistent reaction in temperature deviations corresponding to increasing
solar radiation, several interesting results are evident which warrant
discussion. First of all, the relative effects of high, consistent
solar radiation as opposed to lower, varying solar radiation (due to

intermittent clouds) can be seen by comparison of the May 22 and

26

 

 

 

 

 

 

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29

July 22 data. On July 22, when the ambient temperature reached a high
of 93°F. and the solar radiation was irregular, even the most exposed
points on the dense and medium foliage trees showed negative deviations
from ambient temperature. This occurrence of negative deviations un-
doubtedly reflects a temperature lag at points in the inner bark. The
effect of solar radiation in offsetting this lag can be seen on May 22
when the ambient temperature reached 88°F. and the solar radiation was
consistent. In this case all of the exposed points showed positive
deviations. A general occurrence, which also reflects the effect of
solar radiation in offsetting the temperature lag, are the consistent

negative deviations from ambient at well shaded points and the positive

 

deviations from ambient at the exposed points. For example, at the
middle level on the north side of the dense foliage tree, on only one
of the eight dates--June 24—-did the temperatures exhibit a positive
deviation from ambient. However at the more exposed points, such as
the top of the dense tree, the deviations are predominantly positive.
The consistently positive deviations on June 24 reflect another
situation which warrants discussion. On this date the ambient tempera~
ture increased only lOOF. during the period of deviation accumulation
(from 60°F. to 70°F.). This increase was quite slow with the maximum
not being attained until 5 P.M. and a drop of several degrees occurring
between 7:00 and 9:00 A.M. This slow and small increase in ambient
temperature more than likely resulted in only minor temperature lags
in the inner bark and allowed a magnification of the solar radiation
effect in offsetting these lags. When this situation is compared to
that occurring on June 25, the above explanation seems to be supported.

On this latter date the ambient temperature showed a rapid rise from

 

 

30
54°F. at 6 A.M. to 80°F. at noon. In this case the shaded points showed
the negative deviations which can be expected even though the solar
radiation was somewhat higher than on the 24th.

In no case did a temperature measurement point on the tree
stripped of foliage exhibit an accumulated negative deviation from the
ambient temperature. On the other hand, 16 of the 43 values recorded
for the tree with medium foliage, and 29 of the 47 values recorded for
the tree with dense foliage were negative. When these situations are
combined with the means for all of the tabulated values for each tree-—
+115.7 for the bare, +18.2 for the medium and -23.9 for the dense—-the
extent to which foliage density modifies the effect of solar radiation
is apparent. Carrying this one step further, Figure 2 depicts the mean
temperature deviation values, including both the north and south ex~
posure, for each level on each type of tree. It is evident from this
that foliage intercepts increasing amounts of solar radiation as one
moves down the main stem of the tree. The increasing deviations on the
bare tree at the lower levels is probably indicative of the heating
effect of the ground surface near the base of the tree. Since there is
no way of knowing how closely the means for these eight dates approxi-
mates the mean conditions for the summer, care must be taken in any
attempt to use these data as representative conditions.

One factor which was not measured and whhzh could conceivably
have some effect on inner bark temperatures is the amount of wind
occurring during the periods of temperature measurement. If this factor
was significant it could be expected that both the positive and negative
deviations of sub-bark temperatures from the ambient would be reduced

during periods of high wind. At points of measurement which exhibit

 

 

 

 

 

 

 

 

           

 

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32
positive deviations due to solar radiation, some of the heating effect
of the radiation would be dissipated by movement of air over the bark.
At points exhibiting negative deviations due to shading, the wind would
bring air of ambient temperature to the bark surface more rapidly and
hence offset any temperature lag caused by cooler air being trapped
within the crown of the tree.

Any further studies of this type should include the measurement
of wind. This would preferably be measurements at mid-crown level of
the trees and recorded as miles of wind per period of temperature
measurement. Observations might also be made on the regularity of the
wind to evaluate any periods of high mileage accumulation that might
occur over brief periods.

Further use of the temperature data will be made in subsequent
sections on insect distribution and development but a brief summary of
the observations made to this point seems warranted here. From the
above information it can be seen that inner bark temperatures are
affected by several factors. In general, foliage density plays an
important role through the interception of solar radiation and perhaps
by trapping cooler air within the crown. The relationship between inner
bark and ambient temperature is affected by the rate and amount of
change in the ambient temperature during periods of measurement. This
latter effect is due to the relative lag in heat penetration through the
bark and the degree to which solar radiation can offset the lag. Final-
ly, wind may be a factor through dissipation of the heating effect of
solar radiation or by bringing air of ambient temperature into the

crown of the tree.

 

 

 

 

33

Relationship between Inner Bark Temperatures

and Insect Distribution

The vertical distributions of the eggs, larvae and pupae of
D. zimmermani on Scotch pine have been studied by Carlson (1962).
Figure 3 gives the results of these studies as the percentages of the
total numbers of insects found at each designated level of the trees
examined.

In the current study, the distribution of damage symptoms was
determined, rather than the distribution of insects. This modification
of procedure was carried out so that a larger number of trees, in
several plantations, could be examined. The increased number of planta—
tions examined allowed for inclusion of unsheared trees so that dis-
tribution comparisons could be made with the sheared trees. Determina-
tion of the distribution of actual insects on this scale was deemed
impractical due to the time needed for dissection of trees and the
number of trees required.

Figure 4 gives the distribution of damaged whorls on sheared and
unsheared trees expressed as percentages of the total numbers of damaged
whorls on each type of tree. Although an infested whorl may support
anywhere from one to six (or more) larvae, the distribution shown for
the sheared trees is similar to the distribution of actual insects as
shown in Figure 3. This has then been taken to indicate that the dis-
tribution of damaged whorls approximates the distribution of larvae.

On the sheared trees the highest percentages of both damaged
whorls and insects occur in the middle whorls. On the unsheared trees,

however, it appears that the upper whorls support a higher percentage

of attacks. The lower whorls on both types of trees remain relatively

 

 

 

 

 

34

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36
free from attack which corresponds to observations made by Rennels
(1959), in Illinois, on forest plantations.

The directional distribution of larvae and pupae was also deter~
mined in one plantation. Figure 5 shows the results of this study as
well as the results of a chi-square analysis of the data. From this it
can be stated that if no differences were present in the number of in—
sects present at each direction on the trees, a distribution showing
this much of a deviation could be expected a little more than 35 per-
cent of the time. It therefore appears that this insect shows no
general directional preference in feeding or pupation sites. This does
not, however, exclude the possibility of directional preferences in
single trees.

Temperature could influence the distribution of an insect in
two ways. First by the occurrence of lethal temperatures at certain
positions on the trees, thereby reducing the numbers in these areas.
Second, it could influence movement of larvae to areas on the trees
where optimum temperature conditions exist.

To evaluate the first possibility, the maximum temperatures re~
corded at each level of the trees, for each date, were determined.
These temperatures are given in Table 2 for three dates in 1963 and
eight dates in 1964. This table only includes temperatures from the
dense and medium foliage trees since they will be assumed to reflect
the conditions which would exist on sheared and unsheared trees re-
spectively.

Comparison of the maximum temperatures, with respect to their
location on the trees, and the distribution of damaged whorls reveals

one important consideration. This is the consistently higher temperatures

 

 

 

 

37

 

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38

TABLE 2.-—Maximum temperatures (0F.) recorded at each level of dense and
medium foliage trees. (TD = Top level of dense tree, MD = Middle level
of dense tree etc.)

Date TD MD BD TM MM BM Ambient
1964
August 12 64.9 63.1 64.5 70.2 65.4 65.6 65
June 24 75.4 73.7 71.8 76.0 79.8 72.6 70
June 25 85.4 80.2 81.7 88.8 89.3 79.7 80
August 26 82.3 72.4 74.4 86.6 84.2 75.8 73
May 22 92.2 89.0 75.0 91.3 92.2 83.9 88
July 22 92.4 86.0 84.8 110.0 95.8 88.4 93
May 27 72.5 66.6 64.4 72.7 72.7 69.1 64
May 28 68.2 64.5 60.4 71.8 70.2 64.5 62
1963
June 25 87.0 80.5 75.4 98.0 94.8 82.0 92
July 16 81.1 76.3 72.2 94.3 88.3 77.5 87

August 8 82.5 79.9 83.8 94.0 91.7 84.7 89

 

 

 

39

in the upper level of the medium foliage trees as compared to the upper
level of the dense foliage trees. If lethal temperatures were to occur
and influence distribution of the insects, it would be expected that the
upper levels of unsheared trees would show the results of these tempera-
tures through a reduction in numbers of attacks. In fact these whorls
should show the lowest numbers of attacks. This however is not the
case, as shown previously, and therefore it does not appear that lethal
temperatures are an important factor in determination of vertical dis-
tribution. The general observations above make it unnecessary to dis-
cuss specific temperatures for the dates shown and eliminate the need
for conjecture on maximum temperatures which might occur on dates other
than those shown. This discussion is not meant to imply a complete
absence of high temperature mortality but only to show that it probably
does not affect the distribution of D. zimmermani.

Evaluation of the possible movement of larvae to areas on the
trees where temperature conditions are closer to the optimum requires
a brief description of larval behavior. The larvae of D. zimmermani
overwinter in silken hibernacula which are spun by the larvae soon
after eclosion from the eggs. Approximately in mid-May the larvae
emerge from these hibernacula and begin to crawl around under bark
scales until suitable points of entry are found. At this point they
feed their way into the cambial region of the tree. It would seem that
a critical time for determination of vertical distribution would occur
when the larvae are seeking suitable points of entry in the spring.
However, Figure 3, showing the development of the distribution from
June to August does not indicate any such determination at this time.

If temperature were to be a factor, then, it would have to operate

 

 

 

 

 

 

40
after the larvae have entered the bark.

By examination of Figure 2 and Table 2 it does not appear that
enough of a difference in temperature gradients exist between the
sheared and unsheared trees to explain the differences in vertical dis-
tribution shown.

The directional distribution of larvae and pupae, as determined
by pooling data from many trees, is obviously not affected by tempera—
ture since no differences could be found between cardinal points. Again
it should be mentioned that differences may exist on separate trees.

No attempt was made to determine this.

In brief, it is difficult to visualize any way in which tempera-

ture influences the distribution of D. zimmermani on the trees on a

plantation wide basis.

Possible Effects of the Observed Temperature Differences
on the Development of an Insect

In an attempt to evaluate what effect the observed temperature
differences might have on the development of a hypothetical insect,
data on this relationship given by Shelford (1927) for the codling moth
ngpocapsa_pomonella were used. Shelford's basis for obtaining these
relationships is briefly described in the section on methods, and com—
pletely described in his publication. Table 3 shows the number of
developmental units which would result from the observed temperature
values at each point on the dense and medium foliage trees for each
date given. Also shown are the results which would be obtained if
ambient temperature values were used to find the number of develop-

mental units accumulated each date.

 

 

 

 

ID

 

41

 

 

 

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ENJ Em we; «SJ afiN Sim 03;. Nos; mom.~ swim Sim Sea ENJ fins H309

 

 

 

 

me In: osN mMN mwN NON mma 00H qma mmH NMN oNN me qu RN km:
HmH omH me wwa CNN --- «NH MNH qu Odd mma on mmfl woe wN mm:
mad :1: nmq and oqq mmq amN mNm oqq mmq MN¢ mmq med mod NN kmz
qqm In- mum Nwm mos moq owN Hmm Hmm Nmm me mmm mmm omq mN meow
qu II- MmN HmN com wNm mmH qMN qu H¢N oom mwN qu mmq oN .w:<
wMN NNN NoN omN mam moN NqN qu mNN oqN moN me qNN was qN mosh
Hod --u omq qu com Nom Nwm qu mmq mmq mmq Nod was mom NN zaom
00H omH mod 00H QON NNH mmH In- mmH «ma 00H HON mofl oNN NH .m5<
mm Zm m2 ZE mH 2H mm Zm m2 Z2 mH ZH .£E< Mm< mumn
oopH ESHUoZ oouH omcom
A.os3umpanmu uooHLEm Eouw woumfljoamo moan: Hmucwedofio>om n .LE<
was moaumfiwmu umHOm unoHnE< u Mm< mmonamoaxo susom n m .£ouoz u z mmoouu orb wo mao>oa Eouoom n m can
.meUHZ u E “QOH n Hv .oMSquwanu ucanEw Eouw pmomaooamo muflc: HoucoanHo>ow mo season On aflamcoflomflou

“Hwfiu cam mmHSDMHMQEou wcflmno>flp mo vaNMom wcflwsn wows: HmucoedoHo>w® mo masses: woumHSESoo<iu.m mum<H

 

 

 

 

 

42

From this it can be seen that the progression of developmental
unit totals approximates that of the temperature deviations from ambient
shown in Table 1. That is, the dense and medium foliage trees show a
decrease in developmental values from the upper to the lower levels on
the trees for any particular date. There are, however, a few deviations
from this general pattern. The most noticeable of these occurred on
July 22, 1964, when the ambient temperature reached a maximum of 93°F.
On this date the upper and middle levels of the dense trees showed very
little difference in the number of developmental units accumulated.
These values also only differed slightly from the ambient value, even
though the temperature deviations on this date were marked. The explana-
tion for this phenomenon lies in the fact that once temperatures reach
a certain level, further increases cause a retarding effect on develop-
ment. This was the foundation of Shelford's study, as discussed in the
literature review. Although the above data are not directly applicable
to D. zimmermani} they do illustrate a complicating factor which would
occur in any attempt to evaluate the effect shading or exposure might
have on temperatures and subsequently on the development of an insect.
At times an exposed section of the stem might be advantageous to
development and at other times a shaded section would be. When this is
considered along with the effects of wind, ambient temperature, and rate
of change of ambient temperatures, as discussed in the previous section,
evaluation of the effect of foliage density becomes rather complex.
In fact, if we consider the percent deviations of developmental units
calculated from temperatures recorded at each point in relation to those

calculated from the ambient temperature (last line in Table 3), the

wisdom of attempting such a study is in question. This of course is

 

 

 

 

 

 

 

43
based on a hypothetical developmental unit system and it does not seem
prudent to Suggest that no differences in the development rates of
D. zimmermani larvae on the different types of trees would occur. Hown
ever, when normal biological variability in developmental rates are con-
sidered (Shelford sets this at :181 of the total developmental units
required for completion of development for the codling moth), it seems

that little could be gained by establishing precise temperature-

development relationships for D. zimmermani.

Bark Thickness as a Factor in Tree Infestation

 

Paired comparison sampling was carried out during the 1963 and
1964 field seasons in two different plantations, in order to determine
what relationship exists between bark thickness and infestation.
Table 4 gives the results of the analyses of these studies.

TABLE 4.--Mean bark thickness for infested and non-infested trees and
the results of paired comparison analyses of the data

Sample N Inf Trees Non—inf. Trees Mean Deviation "t"
1963 18 0.143" 0.129" 0.014” 2.18%
1964 25 0.114” O 107” 0.007” 1.68

*Significant at 5% level.

For reasons given in the section on materials and methods, the
procedures used in taking bark thickness samples differed for the two
years. The 1963 study showed a significant difference between the mean
bark thickness on infested and nonuinfested trees. The 1964 study

showed no differences in mean bark thickness. It is felt that this

latter study, due to the method of measurement, is a better indication

 

 

 

 

 

44
of the situation which actually exists with respect to the inherent bark
thickness of the trees. This then would tend to discount the possibility
of selection of planting stock with thinner bark, as a means for reducing
susoeptability to Q. zimmermani.

Since in the first study bark measurements were taken near the
point of injury and since most of the injury occurs near the whorl areas,
the degree to which bark thickness is increased in these areas by the
proliferation of lateral branches, caused by shearing, may be a factor
in increasing infestation.

Rennels (1959) set a minimum bark thickness for successful com—
pletion of development of D. zimmermani larvae at 0.15 inches. It
appears from these studies that this value may be somewhat high since
pupae were found in areas on some trees where this minimum was not
reached. Assuming some minimum does exist however, the predominance of
attacks in the whorl areas may be a means by which a bark thickness be—
low the minimum on other parts of the tree is circumvented.

Bark thickness, then, gives another possible explanation for the
distributions of larvae and damage symptoms shown in Figures 3 and 4.

In this case, the increased bark thickness in the middle whorls of
sheared trees would afford the larva a better chance to attain and
maintain a feeding position. On the other hand, in unsheared trees

the bark thickness would not be expected to be increased as much due

to the smaller number of lateral branches arising from the whorls areas.
Plate 3 is an illustrative sketch of the way in which increased bark
thickness is affected by an increased number of laterals arising from

a whorl. It should be pointed out that on sheared trees the laterals

are distributed vertically, as well as horizontally, in the whorls so

 

 

 

45
that the bark is also thickened between the laterals in this direction.
By increasing both the extent of the whorl area and the thickness of the
bark, it follows that both the chance of maintaining a feeding position
and the amount of food material available to the larvae would be in-
creased. This would tend to allow an increased number of larvae to

occupy the whorls on the sheared trees.

PLATE III

flak/‘14!“ GROWTH SHEARED 7255

DIAGRAMATIC SKETCH OF THE MANNER IN WHICH BARK THICKNESS
IS INCREASED IN THE WHORL AREAS OF SHEARED TREES

 

 

 

 

46

Relationships Between Frequencies of Occurrence
of Various Damage Symptoms

Infestations of 2. zimmermani are characterized by three types
of damage symptoms: (a) flagging of infested terminals shoots, (b)
resin masses on the main stem and (c) dead lateral branches. The resin
masses on the stem generally occur in the whorl areas and therefore are
designated as infested whorls in this study. The relative frequencies
of these symptoms were determined with the ultimate aim of establishing
predictive techniques for rapid evaluation of the degree of infestation
present in Christmas tree plantations.

Figures 6 and 7 give the regression lines for infested terminal
shoots as a predictor of the numbers of trees and whorls infested per
one hundred trees, respectively. Since infested terminals are the most
readily discernible damage symptom, these relationships would be the
most easily used for predictive purposes. Figure 8 shows the regression
line and equation for infested trees as a predictor of infested whorls
per one hundred trees. Since it is quite a bit easier to examine a
tree and simply designate it as infested or not infested than it is to
examine every whorl, this relationship would serve as an efficient
method of estimating the number of whorls infested. The high correlaw
tion coefficient, .98, associated with this relationship is evidence of
the relative efficiency of this method.

Five plantations, representative of managed Christmas tree stands,
were used in this study. Four 100-tree samples were taken in each
plantation as described in the section on materials and methods. Due
to the variations present in plantations with respect to terminal damage

as related to infested trees and infested whorls, the regression lines

 

 

In. .

 

 

 

47

70

60

U1
0

.(_\
0

LA)
0

3.33 x —1.13
.967

N
O

Mean Number of Infested Trees/100 Trees

10

 

5 10 15 20 25
Mean Number of Infested Terminals/100 Trees

Fig. 6.--Relationship between infested terminals and infested
trees.

 

 

 

 

48

70

50

 

3O

    

5.630 x -2 756
- .99

20

Mean Number Infested Whorls/100 Trees

10

—”#'l
5 10 15 20 25
Mean Number of Infested Terminals/100 Trees

Fig. 7 --Relationship between infested terminals and infested
whorls.

 

 

 

 

 

 

49

80-

70

6O

50

40

    

30

1.6602 x +.6431
.980

Number of Infested Whorls/100 Trees

20

10

“mrfi’_f——l———_—_I—_l

10 20 3O 4O 50
Number of Infested Trees/100 Trees

Fig. 8.‘-Re1ationship between infested trees and infested whorls.

 

 

 

 

50
in Figures 6 and 7 were calculated from the means of the four samples.
Thus each plantation was treated as a separate entity. The line in
Figure 8 was calculated by using each sample as a separate entity,
irrespective of the plantation from which it came. This latter esti—
mate of the number of whorls infested would probably be the most accur-
ate and could be used when estimates are desired for a small number of
trees. The former estimate of infested whorls would be most efficient
for estimation on a plantation—wide basis.

To use these figures for predictive purposes, the appropriate
X-value (given on the axis) need be determined by counts in the planta»
tion. The Y—value (on the abscissa) can then be determined by substitu-
tion of X in the equation, or by drawing a vertical line to the regres-
sion line and a horizontal line from this intersection to the abscissa.
This will then give a Y-value for 100 trees. From Figure 6 a direct
reading of the percentage of trees infested in the plantation can also
be taken since it is on the basis of 100 trees. It is suggested that
at least two, 100 tree samples be taken, and the mean obtained, to get
a true indication of the X—value, used for prediction of the Y-values,
in Figure 6 and 7.

Data were also obtained on the relative number of dead lateral
branches and trees with dead lateral branches. Table 5 gives these
data as a mean value for 100 trees for each plantation. These data
were deemed sufficiently unreliable to preclude there use in predictive
equations due to the tendency of growers to cut out infested branches
or trees. The devaluation of trees due to this symptom, however, war—
rants the inclusion of the data to illustrate the situations which were

observed.

 

 

 

 

51

TABLE 5.--Mean numbers of trees infested, trees with dead laterals, dead
trees and dead laterals for 100 trees

Mean Number of Mean Number Mean Number of Mean Number
Location Trees Infested With Dead Lat.l Dead Laterals Dead Trees

Lacota 39.25 i 11.35 14.75 i 2.98 34.00 : 10.96 1.75
Borculo 37.00 i 5.23 6.25 i 1.71 9.50 i 2.38 O
Almena 33.50 i 7.14 6.75 i 4.19 10.00 i 6.98 .75
Bangor 21.75 i 4.60 3.75 i 1.89 6.75 i 5.12 2.00
M-50 19.00 t 6.05 5.50 i 3.11 10.00 i 6.38 0
Holiday 17.75 i 14.22 4.50 i 1.73 9.25 i 3.50 0

<N=4)

The levels of infestation constituting an intolerable situation
for the growers will have to await determination by an economic study
of the Christmas tree industry. This type of study would logically in-
clude all factors which go into production of trees. These would be
balanced against improvement of yields to obtain the most efficient
level of operation. A good illustration of this approach is given by
Marty and Mott (1964) in their evaluation of the economics involved in
control of the white pine weevil, Pissodes strobi Peck, under forestry
conditions. Some comments, however, can be made here with respect to
effectiveness of control measures and the costs involved in control of

D. zimmermani.

Studies on the control of the Zimmerman pine moth carried out by
Butcher and Carlson (1962), have shown that a reduction of more than
95% in trees infested can be obtained with one insecticide application.

This same paper also proposes the possibility of controlling other pest

species, when present, with the same application. The cost of such a

 

 

 

 

52
control program has been estimated at $5.00/acre or 1,000 trees (per~
sonal communications with J. W. Butcher). Currently the top price for

‘ a grade A, 6'—7' tree is $3.60 and this is reduced to $1.70 or less for

a deformed tree. At these rates, saving 5—6 top grade trees per acre
would constitute a profitable input. As pointed out above however, other
factors such as the number of top grade trees expected per acre, the age
of the trees when the population begins to build up, the ability of the
grower to demand top price for his trees and how much of the damage can
be repaired by removal of dead branches (to name a few) would have to
be taken into consideration. In the judgement of the author, a 15%
infestation in a plantation which is two or more years from harvest
would constitute an approximate level at which control should be con—
sidered and almost certainly undertaken. In areas of high risk
(where plantations have been known to sustain severe damage) this
figure could perhaps be reduced to 10%. Also, if 1% of the trees which
would be judged as top grade have dead branches, control should be
undertaken. One treatment should give effective control and keep the
population within reasonable limits for at least two years.

A complete study of the economics of pest control in Christmas
tree plantations would be a tremendous help in a more accurate assessm

ment of damage by D, zimmermani and for other pest species as well.

Distribution of Infested Trees and Infested Whorls
among Infested Trees
One block, containing 1,770 trees, was examined thoroughly in
a plantation showing 11% infested trees. A map was made in the field

upon which each tree was marked and the notation made as to whether or

not it was infested. This map was then brought into the lab and

 

 

 

 

 

53
divided into 28 quadrats, each 10 rows of trees square, and the number
of infested trees per quadrat was recorded.
The degree of non-randomness was calculated from these data by

use of the equation R = sz/Y, which is based on the assumption that for

a random distribution the variance, 52, should equal the mean, 2. This
resulted in an R value of 1.38, which indicates some tendency toward
grouping of infested trees. A chi-square test was run to determine
whether this departure from randomness was significant. A chi-square
value of 38.0 was obtained, which is associated with a greater than 10%
probability of obtaining this degree of departure by chance. From this
then, it appears that infested trees are randomly distributed within
the block of trees examined and likely within the plantation.

The distribution of infested whorls among infested trees was
determined from the data obtained for the analysis of the frequency of
occurrence of damage symptoms in the previous section. These data were
grouped with respect to the number of trees showing each number of in—
fested whorls, as depicted in Figure 9A. This gave a mean of 1.76
infested whorls per infested trees. The number of trees showing no
whorls infested was omitted in this distribution since it is a function
of the degree of infestation and not necessarily an indicator of a
biological phenomenon. The equation for the dotted line, which approxi-
mates the distribution, was calculated by making a square root trans-
formation of the original data and then developing an equation for the
transformed values by means of techniques described by Jensen (1964).

In an attempt to determine whether this distribution of infested

whorls approximated any standard distribution which had previously been

shown to represent biological data, the data were plotted on a

 

 

 

54

60

50

 
   
   
  

98

95

4o 90

80

Cumulative % of Trees

w
0

Number of Trees

2 3 4 5 6

20 h . of Whorls Infested

10

    
 

437: 9.285 - 1.805X + .0031 (x-i)‘r

 

13 X 36 \ \
_ w___ \ \fi
‘7 "_ 7*— . 1“"
l 2 3 4 5 6

Number of Whorls Infested

Fig. 9.--Distribution of infested whorls among infested trees.

 

 

 

 

 

55

logarithmic probability scale (Figure 9B). This plotting yielded a
fairly good fit to a straight line, thereby indicating a log—normal
distribution. Due to the extreme truncation of these data, over 50%
of the infested trees showing one infested whorl and the remaining
trees divided among only 5 categories, this fit cannot be considered as
proof-positive of the actual relationship which exists. However,
Williams (1964) refers to many studies which show the log—normal dis-
tribution to be applicable to discontinuous data of this type, such as
the frequency distributions of parasites on hosts and numbers of species
per genus. This appears to lend validity to its application in this
situation.

From these analyses then, it appears that infested trees show a

slight tendency toward clumping", but this is not statistically signif-
icant, and the distribution of infested whorls on infested trees
approaches the log—normal. This latter situation indicates a high pro-
portion of infested trees having only one infested whorl and that in-

festation of one whorl on a tree does not appear to increase the prob-

ability of other whorls, on the same tree, being infested.
Species Characteristics of D. zimmermani Pupae

In a previous study, carried out by Carlson (1962), it was sugw
gested that a Dipryctria complex existed in the Christmas tree planta-
tions of southern Michigan. This was based on the presence of pupae
which exhibited some characteristics of Dioryctria cambiicola Dyar, as
described by Ross (1959). Ross gives the number of terminal spines on
the pupae of D. gimmermani as ”usually six” and on D, cambiicola as

”usually eight”. This character was the prime factor in suggesting

 

 

 

 

 

 

56
the possibility of occurrence of 2. cambiicola. Since none of the adult
specimens submitted to Dr. E. G. Munroe of the Insect Systematics and
,Control Unit at Ottawa, Canada were found to be of this latter species,
subsequent examination of pupae from a series of plantations was carried
out to evaluate the frequency of occurrence of the character under con-
sideration.

Table 6 gives the numbers of pupae with six and eight terminal
abdominal spines for each of five plantations. A chi—square analysis
of these data failed to reveal any significant differences between
plantations in the proportions of pupae exhibiting these numbers of
terminal spines. Since it would not be expected that equal proportions
of two species would occur from one plantation to the next, it is not
readily conceivable that five plantations would fail to yield any dif-
ferences. On this evidence, along with the previously mentioned iden-
tification of adult specimens by Dr. Munroe, it seems unlikely that

D. cambiicola is present in this area. The variation in numbers of
terminal spines must therefore be attributed to intraspecific vari-
ability in Q. zimmermani.

The data given in Table 6 can also be interpreted so as to give

an expected frequency of occurrence for the number of terminal spines

present on Q. zimmermani pupae. This will serve to quantify the

 

 

"usually six” given by Ross. For this purpose, the proportions of
pupae with 8 terminal spines were subjected to an arc-sineIpEfZEEEEEE
transformation as described by Snedecor (1946). The mean was then ca1~
culated, from the transformed data, to be 22.5% with a standard devia-
tion of 5.9%. A similar analysis with respect to the frequency of
occurrence of 6 or 8 terminal spines on pupae of D. cambiicola would

be useful.

 

 

 

 

 

57

TABLE 6.—-Analysis of interplantation differences in the numbers of
pupae with 6 and 8 terminal abdominal spines

 

Plantation Number

 

 

I II III IV V Proportions
8 terminal spines l3 9 12 9 2 .23
6 terminal spines 21 41 36 45 10 .77
Totals 34 50 48 54 12
X2 = 6.953
d.f. = ¥
P z .25

The degree of hooking of the terminal spines, characterized by
Ross as ”strong” for D, zimmermani, appeared to be valid and consistent
for all of the pupal specimens examined in this study.

Geographical Distribution of Q. zimmermani as a Serious Pest
_-‘ffi_CHfiEfHEEITfEE_PIEHf5fi6HE—iE7S83EHWE§EE¥E"MIEEI§EE_—_

An attempt was made to obtain a rough estimation of the problem
level distribution of this species in pine plantations grown and mainw
tained for Christmas tree production. Plate 4 gives the locations of
areas where heavy infestations were observed, and the outline of the
major survey area. With the exception of the northern edge, it is dif-
ficult to assess the distribution shown. The major complicating factor
is the high increase in land usage for production of agricultural com-
modities, such as truck crops and dairy products, as one moves eastward
from Lake Michigan, and for fruit production as one moves south into

Van Buren, Cass and Berrien counties. This tends to interrupt the dis-

tribution of Christmas tree plantations and consequently the ability

 

 

 

 

 

58

PLATE IV

Mn SKESAN

 

4‘; - Boundary of Area

Surveyed
X - Heavy Infestation

o - Light Infestation

 

GEOGRAPHICAL DISTRIBUTION OF 2. zimmermani AS A SERIOUS PEST
IN CHRISTMAS TREE PLANTATIONS

 

 

 

59
of the insect to attain its full range of distribution. It is especially
critical in this type of situation since the trees are on a relatively
short rotation and population buildup would be enhanced in areas where
influx from other plantations is possible.

The northern edge of the distribution seems to be a "real" occur-
rence. In this area plantations are relatively numerous, yet the in-
cidence of high infestation abruptly drops off at about the Muskegon—
Ottawa county line. This has been supported by spot checks to north
and northeast of this area in plantations where Q. zimmermani has been
reported to be present. Invariably these plantations showed very light
infestations which could be termed economically insignificant. A
similar situation exists in forest plantings in the northern area of
the lower-peninsula where the insect is endemic but does not pose any
significant problems due to the low population levels present. The
reasons behind the apparent dropping off of population levels in the
northern areas are not clear. It does suggest, however, the possi-
bility of low temperatures becoming critical in the survival of over-
wintering larvae and presents a basis for further investigation of this

factor.

 

 

 

 

 

 

SUMMARY OF CONCLUSIONS

This study has been concerned primarily with certain aspects of
the ecology of Dioryctria zimmermani (Grote) as it occurs in plantations
of Scotch pine being grown for Christmas trees.

Investigation of comparative sub—bark temperatures of three trees
with differing foliage densities was carried out in an attempt to ascer-
tain the effect increased foliage density, as results from shearing
practices used in the Christmas tree industry, has on the microhabitat
temperatures to which the larvae are subjected. Temperatures between
the trees varied widely as did temperatures at the different crown
levels within single trees. By comparison of these temperature dis—
tributions with the distribution of insects on plantation trees, it
was concluded that temperature does not seem to play a role in deter-
mination of insect distribution on a plantation wide basis. An attempt
was also made to evaluate the temperature differences with respect to
how they might affect insect development. Using a hypothetical rela-
tionship between temperature and development, some of the problems
encountered in this type of study are pointed out. On the basis of the
hypothetical relationship it was shown that even with the considerable
temperature variability between and within trees it is possible that
the total effects of these differences on development could be
negligible.

Although bark thickness did not appear to have any significant

effect on tree susceptibility to attack, it is proposed that the increase

60

W4?“

 

 

 

 

 

61
in bark thickness and extent of whorl area, caused by shearing, appear
to play an important role in determining the degree of infestation.

The relationships between the frequency of occurrence of various
damage symptoms was determined and linear regression equations calculated.
These regression equations should prove useful in rapid evaluation of
the degree of infestation within a plantation.

The distribution of infested trees within a plantation was ana-
lyzed and it appears to be random. The distribution of infested whorls
on infested trees approximates a log-normal distribution but the ex-
tremely truncate nature of the data and the restricted size of the trees
from which the data were taken, make further confirmation of these con-
clusions desirable.

The geographical distribution of D. zimmermani as a serious pest
in southwestern Michigan appears, for the most part, to be dictated
only by the distribution of Christmas tree plantings. A notable ex-
ception to this occurs on the northern edge of the area surveyed where
the presence of the insect as a serious pest appears to drop off despite
a relatively continuous occurrence of Christmas tree plantations in
this area.

The possible occurrence of Dioryctria cambiicola in the plantas
tions of southwestern Michigan was examined and it was concluded that
it, in fact, did not occur. The data upon which this conclusion was
based were Subsequently used to quantify the intraspecies variability

of Q: Eimmermani with respect to the number of terminal abdominal

spines on the pupae.

 

 

 

 

 

LITERATURE CITED

Andrewartha, H. G. and L. C. Birch
1954. The Distribution and Abundance of Animals. Chicago,
University of Chicago Press.

Butcher, J. W. and R. B. Carlson

1962. Zimmerman Pine Moth Biology and Control. J. Econ. Ent.
55(5):668-671.

Carlson, R. B.
1962. The Life History and Biology of Dioryctria zimmermani
Grote (Lepidoptera: Phycitidae) in Southern Michigan.
Unpubl. M.S. Thesis, Michigan State University.

Davidson, J.
1944. On The Relationship Between Temperature and Rate of

Development of Insects at Constant Temperature. J Anim.
Ecol. 13:26-38.

Hall, J. A.
1959. Fundamentals of Thermometry. Institute of Physics
Monograph for Students. New York, Rheinhold.

Heinrich, C.
1956. American Moths of the Subwfamily Phycitinae. U.S. Natl.
Mus. Bul. 207:1-581, Illus.

Henson, W. R.
1958. The Effects of Radiation on the Habitat Temperatures of
Some Poplar—inhabiting Insects. Can. J. Zool. 36:463—478.

Henson, W. R. and R. F. Shepherd
1952. The Effects of Radiation on the Habitat Temperatures of
the Lodgepole Needle Miner, Recurvaria milleri Busk.

(Gelechiidae: Lepidoptera) Can. J. 2001. 30:144-153.

Jenson, C. E.
1964. Algebraic Description of Forms in Space. U.S. Dep. Agr.
Forest Service, Central For. Expt. Sta., Columbus, Ohio,
57 pp., Illus.

Kellicot, D. S.

1879. Observations on Nephoteryx zimmermani. Can. Ent. 2(6):
114-116.

Marty, R. and D. G. Mott
1964. Evaluating and Scheduling Whiteopine Weevil Control in the
Northeast. U.S. For. Serv. Res. Paper NE—l9.

62

 

 

 

63

Miller, J. M.

1931.

Munroe, E.
1959.

Pradhan, S.
1945.

Rennels, R.
1959.

Ross, D. A.
1959.

Schuder, D.
1960.

Shelford, V.
1927.

Snedecor, G.
1957.

Talerico, R.
1963.

Wellington,
1950.

‘ 1954.

1637.

Williams, c.
1964.

High and Low Lethal Temperatures for the Western Pine
Beetle. J. Agri. Res. 43:303-321.

Canadian Species of Dioryctria Zeller (Lepidoptera:
Pyralidae). Can. Ent. 91(2):65~72.

Insect Population Studies. II. Rate of Development Under
Variable Conditions in the Field. Proc. Natl. Inst. Sci.
India 11:74-80.

C.
The Natural History of the Zimmerman Pine Moth, Dioryctria
zimmermani Grote. Unpubl. Ph.D. Thesis, Univ. of Michigan.

Abdominal Characteristics of Dioryctria Pupae (Lepidoptera:
Pyralidae) from British Columbia. Can. Ent. 91(11):73l—734.

L.
The Zimmerman Pine Moth, Dioryctria zimmermani Grote.
Purdue Univ. Agr'l. Expt. Sta. Res. Bul. 698.

E.
An Experimental Investigation of the Relations of Codling
Moth to Weather and Climate. Illinois Natural History
Survey Bul. 26(5):311-437.

W.
Statistical Methods. Iowa State College Press, Ames, Iowa.
534 pp.

L.
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