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This is to certify that the

thesis entitled

Performance Response of the Spruce Budworm
l Choristoneura fumiferana, in Relation to Dietary
‘ and Foliar Levels of Sugar and Nitrogen

' presented by
Brian M. McLaughlin

has been accepted towards fulfillment
of the requirements for

MaSterS degree in finance—

 

. 41’
. AIAVMM

Major professor

 

.Date January 6, 1986

0-7639 MS U is an Waive Action/Equal Opportunity Institution

 

 

 

RETURNING MATERIALS:
IV153I_J Place in book drop to
LJBRARJES remove this checkout from

.ggggggggl-L your record. FINES will
be charged if book is

 

 

 

returned after the date
stamped below.

 

 

 

 

PERFORMANCE OF THE SPRUCE OUONORN,
gflQRISTQNEURA FUNIFERANA, IN RELATION TO DIETARY
‘INU FUETAR‘EEVEEE OF SUGAR AND NITROGEN

By

Brian M. McLaughlin

A THESIS

Submitted to
Michigan State University
in partia] fquiIIment of the requirements
for the degree of

MASTER OF SCIENCE

Department of EntomoIogy

1986

ABSTRACT
PERFORMANCE OF THE SPRUCE BUONORN,
EflQRISTQNEURA PUNIFERANA, IN RELATION TO DIETARY
AWE FUETTR‘EEVEES Ur SUGAR ANO NITROGEN
By

Brian Matthew McLaughlin

The effect of different sugar/nitrogen ratios on spruce

budworm (Choristoneura fumiferana) performance was measured

 

 

by manipulating these two nutrientsin artificial diets,
and by evaluating their performance on host trees (balsam
fir and white and black spruce) that differed in their
soluble sugar/nitrogen ratios. The optimal combination
of sugar (6 levels) and nitrogen (4 levels) in artificial
diets for all measured budworm performance variables was
12.8% sugar and 4.9% nitrogen. This combination had a
sugar/nitrogen ratio of 2.61/1. This optimal ratio
increased in low-level nitrogen diets.

Balsam fir and white spruce were equally suitable host
plants for most study areas. Foliar nitrogen and sugar
levels varied considerably within tree Species throughout
the life cycle of the budworm. There were no consistent
correlations between budworm performance and nitrogen or
sugar from year to year. There were, however, some
consistant correlations within single years for both tree

species.

To my grandfather and grandmother,

James and L. Mary McTigue

ii

ACKNOWLEDGEMENTS

My sincere thanks go in) my major professor, Bill
Mattson for his support and understanding. I would also like
to especially thank both Bob Haack and Marion Harris for
their countless hours of advice and enthusiasm. My committee
members, Jim Miller, Gary Simmons and Jim Hanover also gave
much useful advice.

Many thanks go to the proletariat of the lab. Bruce
Birr put in countless hours of time and advice on computer
analysis. My thanks also go to the rest of the members of
the lab; Rob Larwence, Brian Mitchell, Ernie white, Dan

Herms and Ariel Dybner, for helping on all fronts.

iii

TABLE OF CONTENTS

LIST OF TABLES ....................................... v1
LIST OF FIGURES ...................................... 1x
GENERAL INTRODUCTION ................................. 1
INTRODUCTION ......................................... 6
METHODS AND MATERIALS ................................ 9
RESULTS .............................................. 14
Diet matrix study ............................... 14
Combined female and male survival

to adult eclosion ..................... 14
Pupal weight ............................... 17
Adult weight ............................... 17
Pupal growth rate .......................... 26
Adult growth rate .......................... 31
Pupal development rate ..................... 31
Adult development rate ..................... 36

Optimal ratios of sugar to nitrogen
at different nitrogen levels ......... . 45
Pupal fresh weight .................... 45
Pupal growth rate (mg/da) ............. 47
Pupal development rate (%/da) ......... 47

Regressiom relationships between insect
performance and dietary sugar and

nitrogen concentrations ............... 50
Concentration of sugars remaining in
budworm frass ....................... 52
Addition of fatty acids to low level
nitrogen diets ....................... . 54
Field studies ................................... 56

Balsam fir and white spruce foliar sugar
and Bitrogen concentrations in relation

to ( D) accumulations ... .............. 56
Concentrations of nitrogen and sugars during

fifth and sixth larval stages . ........ 58

Northern Minnesota ............... 58

Lower Michigan/Wisconsin ......... 62

Insect Performance ......................... 63

Northern Minnesota ............... 63

Lower Michigan/Wisconsin ......... 63

iv

Regression relationships between insect-
performance and foliar sugar

and nitrogen .. ................... 67

Northern Minnesota ............... 67

Lower Michigan/Wisconsin ......... 67

DISCUSSION ........................................... 72
Diet Matrix Study ............................... 72
Field Studies ................................... 78
CONCLUSIONS .......................................... 80
REFERENCES CITED ..................................... 82

Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.

List of Tables

Percent larval survival to adult
eclosion. N=number experiments per

'treatment; 200 insects per experiment.

Diets at levels where blanks (----)
occur in tables 1-13 could not be

formulated with standard ingredients .....

Female pupal fresh weight (mg) 3 standard
error and number of insects surviving per
treatment .... ....... ......................

Male pupal fresh weight (mg) + standard
error and number of insects surviving per
treatment .................................

Female adult. weight (mg) + standard
error and number of insects surviving per
treatment .................................

Male adult weight (mg) + standard error and
number of insects surv1ving per treatment

Female pupal growth rate 1 standard error
and number of insects surviving per
treatment .................................

Male pupal growth rate + standard error and
number of insects surviving per treatment

Female adult. growth rate -+ standard
error and number of insects surviving per
treatment .......... .......................

Male adult growth rate + standard error and
number of insects surviving per treatment

Female pupal development rate + standard
error and number of insects surviving per
treatment ...................... ...........

Male pupal deveTOpment rate + standard
error and number of insects surviving per
treatment .................................

Female adult development rate + standard

error and number of insects surViving per
treatment .................................

vi

...... 15

..... 18

..... 20

..... 22

...... 24

..... 27

...... 29

......34

..... 37

..... 39

..... 41

Table 13.

Table 14.

Table 15.

Table 16.

Table 17.

Table 18.

Table 19.

Table 20.

Table 21.

Table 22.

Male adult develooment rate I standard
error and number of insects surviving per
treatment ............ ......... ..... . ........... 43

Regression relationships between insect
performance variables and dietary
nitrogen and sugar (p I .05) .u..u... ......... 51

Female pupal weight (mg) on diets
containing 2.45% nitrogen, 2.45% nitrogen
with linoleic and linolenic acids and 2.45%
nitrogen with wheat germ oil. Levels
where blanks (----) occur indicate zero
percent survival .u.u.u.n.u..n ..... .u..”55

Grand mean values I standard error for
nitrogen, sugar and sugar/nitrogen ratios
for field studies performed from 1981-
1982. n= number of trees per study .... ......... 60

Grand mean values I standard error for
nitrogen,scgar’and sugar/nitrogen ratios
for field studies performed from 1983-
1984. n= number of trees per study ".u. ...... 61

Grand mean values I standard error for
insect performance variables on a per
tree basis. n= number of trees per study ....... 64

Grand mean values I standard error for
insect performance variables on a per
tree basi&.n= number of trees per study .. ..... 65

Grand mean values I standard error for
insect performance variables on a per
tree basis. n= number of trees per study ....... 66

Regression relationships between insect
performance variables and selected host
plant nutrients. (+) or (-) indicates
significant (p I .05) positive or negative
correlation coefficients .u..u..n..u..n..“68

Regression relationships between insect
performance variables and selected host
plant nutrients. (+) or (-) indicates
significant (p < .05) positive or
negative correlation coefficients ............. 7O

vii

Table 23. Regression relationships between insect
performance variables and selected host
plant nutrients. (+) or (-) indicates
significant (p I .05) positive or negative
correlation coefficients ....................... 71

viii

List of Figures

Figure 1. Combined male and female larval survival
to the pupal stage (%)irlrelationship to
dietary levels of sugars and nitorgen (%
dw) ........................................... 16

Figure 2. Female pupal fresh weight (mg) in
relationship to dietary levels of sugars
and nitrogen (% dw) ........................... 19

Figure 3. Male pupal fresh weight (mg) in
relationship to dietary levels of sugars
and nitrogen (% dw) ........................... 21

Figure 4‘ Female adult dry weight (mg) in
relationship to dietary levels of sugars
and nitrogen (% dw) ........................... 23

Figure 5. Male adult dry weight (mg) in
relationship to dietary levels of sugars
and nitrogen (% dw) ........................... 25

Figure 6. Female pupal growth rate (mg/da) in
relationship to dietary levels of sugars
and nitrogen (% dw) ........................... 28

Fimwe 73 Male pupal growth rate (mg/da) in
relationship to dietary levels of sugars
and nitrogen (% dw) ........................... 3O

Ffigure 8. Female adult growth rate (mg/da) in
relationship to dietary levels of sugars
and nitrogen (% dw) ... ........................ 33

Fuwre 9. Male adult growth rate (mg/da) in
relationship to dietary levels of sugars
and nitrogen (% dw) ........................... 35

Figure 10. Female pupal development rate (%/da)
in relationship 'to dietary levels. of
sugars and nitrogen (% dw) ........ ...... ...... 38

Figure 11. Male pupal develooment rate (%/da) in

relationship to dietary levels of sugars
and nitrogen (% dw) ........................... 4O

ix

Figure 12. Female adult develooment rate (%/da)
in relationship to dietary levels of
sugars and nitrogen (% dw) .................... 42

Figure 13. Male adult development rate (%/da) in
relationship to dietary levels of sugars
and nitrogen (% dw) .................... ....... 44

Figure 14. Optimal ratios of sugar to nitrogen at
different nitrogen levels in relationship
to female pupal weight (mg) ................... 46

Figure 15. Optimal ratios of sugar to nitrogen at
different nitrogen levels in relationship
to female pupal growth rate (mg/da) ..... ...... 48

Figure 16. Optimal ratios of sugar to nitrogen at
different nitrogen levels in relationship
to female pupal development rate (%/da) . ...... 49

Figure 17. Percent dry weight sugar left in
frass in relationship to percent dry

weight sugar in artificial diet ............... 53
Figure 18. Balsam fir and white spruce foliar

sugar concentration in relation to

degree day accumulations ...................... 57

Figure 19. Balsam fir and white spruce foliar
nitrogen concentration 'hi relation to
degree day accumulations ....................... 59

GENERAL INTRODUCTION

The spruce budworm. Enerieiensere Isaiisrene
(Lepidoptera: Tortricidae), was first described in 1865 by
Clemens (Freeman 1958). Since 1865 the scientific name of
the spruce budworm has changed many times, receiving seven

different names under five different genera (Bakuzis and

 

was proposed by Freeman in 1947. The last taxonomic change
to affect the budworm occurred in 1953 when Freeman
distinguished between two forms of the spruce budworm:
2221121222232 Ieeiisreee. the spruce budworm and
gthigIggggIg 31333, the jack pine budworm (Bakuzis and
Hanson 1965L

The genus Egggigggggggg in North America is composed of
18 species, five of which are Spruce and fir feeders while
the remaining thirteen forage primarily on pines and a
variety of deciduous trees (Freeman 1958 and 1967, Powell
1964). The family Tortricidae is one of the largest families
of the Microlepidoptera with about 950 North American
species (Borror et al. 1981). In addition to the spruce
budworm there are many other economically important Species
in the family Tortricidae.Examples are the codling moth,
Cygjg pgmgggllg (LJ which is an important pest of apples
and other fruits, and the oriental fruit moth,§IgphglIIh3
9213333 (Busck) which is an oriental species that is widely

distributed in the United States and an important pest of

peaches and other fruits. The western spruce budworm,
Choristoneura occidentaljé (Freeman), is a close relative of
the eastern spruce budworm and is an important pest of

Douglas fir, Pseudotsuga menziesii (Mirb) Franco, white fir,

 

59133 59329123 (Cord. and Glend.) Hoopes, and Englemann
spruce, £1333 gggglmggflI(Parry), in the western United
States.

The range (H: the eastern spruce budworm in North
America follows the occurrence and distribution of its two

major host plants, balsam fir, AbieS balsamea (LJ Mill, and

 

white spruce, Picea glauca (Moench) V055, and extends from

 

Maine and New Brunswick in eastern North America to
Minnesota and Manitoba in midwestern North America
(Montgomery et al. 1982). The states most affected by the
spruce budworm are Maine, New Hampshire, New York, Michigan,
Wisconsin and Minnesota (Kucera and Orr 1981). The spruce
budworm has a one year life cycle with the larval period
beginning in late July or early August. Newly hatched larvae
seek protected locations on the host plant where they molt
to second instars and then enter diapause in preparation for
the onset of winter. In early spring (late April-early May)
these second instar larvae emerge and mine 1-year-old
needles or buds. Nhen current year buds begin to swell and
expand, larvae in needle mines migrate to this new food
source and there complete their larval development in about
four weeks (McGugan 1954). After about one week in the pupal

stage, moths emerge in early July and live from four to six

days, consuming water only and ovipositing on the foliage of
selected host trees. Stadler (1974) found that acCeptance of
oviposition Sites by female budworm was influenced by the
shape and chemical composition (alpha- and beta-pinene) of
the host plant substrate. Larvae hatch from eggs within one
week after oviposition and begin the entire cycle again.

Spruce budworm outbreaks occur periodically (every 40
to 70 years) and usually appear to originate in small areas
from which they spread rapidly and cover extensive regions
(Swaine et al. 1924, Graham and Orr 1940). Outbreaks that
are not controlled can last eight to ten years and terminate
when food supplies become scarce and tree mortality is high
(Hudak and Raske 1981). Balsam fir is the most vulnerable
host plant and usually dies after four to five consecutive
years of severe defoliation of current year foliage (Hudak
and Raske 1981). White spruce and red spruce, £1533 £22223
(SargJ, are less ‘vulnerable because they can usually
withstand defoliation for six or more consecutive years
before dying (Hudak and Raske 1981).

In areas where forests are valuable resources to local
economies, spruce budworm outbreaks can be devastating.
Uncontrolled outbreaks can cause economic losses ammounting
to millions of (Hfllars in forest-dependent economies
(Sterner and Davidson 1981). Control of spruce budworm
populations has traditionally been accomplished through the
aerial application of insecticides. Such programs for

budworm control are unique in entomology because they are

the largest and most Specialized pest control programs in
the world (Montgomery et al 1983). DDT was the first
pesticide used on the budworm, being applied in the late
1950's and early 1960's. Since the decline of chlorinated
hydrocarbon use in the 1960's and because of the high
financial and social costs of modern day chemical spray
programs, forest entomologists have tried to take a more
integrated approach to budworm control. Today, large scale
spray programs are still the most effective means of
controlling budworm outbreaks. However, the use of natural
enemies such as the parasitic wasps lgiggggIgmmg miggIgm
(Riley) and 25222192312 letsresgie (Nees): microbial
insecticides such as gggjllgg ghggiggjgggjg toxin; and
insect growth regulating compounds may be combined with
silvicultural practices and conventional spray programs to
control budworm populations (Montgomery et al. 1983).

The spruce budworm has been studied for over 70 years.
Until recently, the focus of this intensive research has
been centered on either its general biology and its
population dynamics or its impact upon the forest systems
that it inhabits. Forests systems supporting budworms have
traditionally been classified according to their physical
characteristics. such as Slope, soil type, species
composition, stand density and tree age. These
characteristics affect the growth and development of the
host trees and ultimately affect the growth and development

of spruce budworm populations. More recently, scientists

have focused on the finer details of insect/host plant
interactions to better understand the growth and behavior
of the spruce budworm. For example, the nutritional quality
of a host plant is directly determined by the quality and
quantity of chemicals in it's tissues that can be utilized
as food. Among the principal nutrients in Spruce budworm
host plants are soluble carbohydrates (sugar) and proteins
(nitrogen).

In the following pages, I have explored the response
(performance) of spruce budworm to varying levels and
ratios of soluble carbohydrates and nitrogen in artificial
diets. I have also determined the foliar sugar and nitrogen
content of selected host plants and correlated these
findings with spruce budworm performance on these same

trees.

INTRODUCTION

The Spruce budworm. 2222222222222 2222222222
(Clemens) (Lepidoptera: Tortricidae), is an outbreak insect
folivore that feeds primarily on the current growth of
balsam fir, 53133 Iglégmgg, white Spruce, 31553 913323 and
red spruce, £1533 £32322. in North America. Mechanisms
underlying the development and collapse of its outbreaks are
still largely unknown. However, variations in the
nutritional quality of host plants are suspect (Mattson et
al. 1983, Fleming 1983). Among the principal plant nutrients
required by insects are soluble carbohydrates and proteins.
Little (1970) reported that fructose, glucose, sucrose,
raffinose and starch were the predominant carbohydrates in
current and one-year old needle growth of balsam fir.
Similar findings were reported by Chalupa and Fraser (1968)
for white Spruce. Levels of total soluble sugars vary
greatly during the growing season (Little 1970) as well as
from year to year (Shaw and Little 1976). Little (1970) also
found seasonal variations in the total starch content of
developing shoots of balsam fir.

Harvey (1974) tested these carbohydrates as well as
others such as maltose and sorbitol for their nutritional
quality in Spruce budworm diet. He found that all were
basically acceptable except for starch. Harvey (1974) also
found that an absolute requirement for sugar could not be

demonstrated but nevertheless observed an increase in female

adult weight with increasing levels of sucrose. Both Harvey
(1975) and Shaw (1973) concluded that most starches were
nutritionally poor substitutes for sucrose in artificial
diets.

Soluble sugars are not only important as energy sources
but also as feeding stimulants. Heron (1965) and Albert and
Jerret (1980) found sugars to be among the most important
host plant chemicals to stimulate spruce budworm feeding.
Albert et al. (1982) further showed that budworm feeding
behavior is most strongly responsive to sucrose, followed by
fructose, inositol and glucose. Albert et al. (1982)
concluded that the behavioral feeding threshold for sucrose
is between 10-4 and 10-3 M, with the optimal feeding
response occurring between 0.01 to 0.05 M sucrose.

Less exacting studies have been done on the importance
of plant protein on spruce budworm growth and development.
Shaw and Little (1972, 1976) showed a rapid seasonal
decline in foliar nitrogen in current year needles of balsam
fir. Mattson et al. (1983) established a similar seasonal
decay in foliar nitrogen, for both balsam fir and white
spruce. Mattson et al. (1983) further demonstrated that
tree to tree variations in spruce budworm growth were
consistently positively correlated to foliar nitrogen. Shaw
et al. (1978) and Mattson et al. (1983) increased foliar
nitrogen levels in balsam fir through fertilization and
found that in response, budworm pupal weights increased.

Brewer et al. (1985) fertilized white fir seedlings at five

different nitrogen levels and found that pupal weight
gains for the western spruce budworm, 2523125222232
occidentaljg (Freeman) increased up to a nitrogen level of
2.41%, after which ‘they declined. McMorran (1965)
synthesized an artificial diet for the spruce budworm which
contained about 4.9% nitrogen on a dry weight basis and
found that female larvae reared on this diet attained an
average pupal fresh weight of 121.7 mg with a range of 93.5
to 154.0 mg. Harvey (1974) measured budworm performance on
diets containing about 6.34% nitrogen and little if any
soluble sugars and found low pupal weights, protracted
development and poor survival, although some surviving
females were able to lay viable eggs.

More recently, nutritional studies have focused on the
balance between soluble carbohydrates and protein (nitrogen)
and how varying the ratios of these two nutrients affects
insect growth. For example, Tsiropoulos (1981) found that

reproduction by the olive fruit fly, Dacus oleae (Gmelin),

 

was best under a carbohydrate/nitrogen ratio of 25/1, where
higher nitrogen contents reduced egg deposition. Naldbaur et
al. (1984) found that last instar larvae of the corn
earworm, 521123512 333 (Boddie), preferred and performed
best at a 1.56/1 carbohydrate/nitrogen ratio. Manipulation
of soluble carbohydrate/nitrogen ratios was done indirectly
by Shaw et al. (1978) for spruce budworm when they
fertilized young balsam fir trees. Fertilized trees had both

higher total nitrogen and total sugars and a higher

carbohydrate/nitrogen ratio than controls (5/1 vs 2/1).
Spruce budworm larvae reared on foliage of fertilized trees
had higher survival rates and higher pupal and adult
weights than those reared on unfertilized trees. Harvey
(1974) manipulated artificial diets in) obtain soluble
carbohydrate/nitrogen ratios ranging from 1.1/1 to 8.82/1
and found that higher ratios produced larger female pupae
than lower ratios.

The purpose of this study was to further define the
influence of soluble carbohydrate/nitrogen ratios on spruce
budworm performance by manipulating these two major
nutrients in artificial diets, and by evaluating budworm
performance on balsam fir and white spruce trees which

differed in their soluble carbohydrate/nitrogen ratios.

Methods and Materials

Insects were obtained as diapausing second instar
larvae from the rearing facility of the Forest Pest
Management Institute, Canadian Forest Service, at Sault Ste.
Marie, Canada. Larvae were reared on a meridic artificial
diet following the procedures of McMorran (1965). Four
larva were transferred to individual l-oz tranlucent plastic
creamer cups, capped with paper lids and then reared until
adult eclosion at 220CI10, ca. 50% RH, and a 16:8 L:D

photoperiod. Each treatment consisted of 50 creamer cups

totaling 200 insects per treatment. During early larval

10

instars creamer cups were examined every other day for
budworm progress. During later larval instars creamer cups
were checked daily and all pupae were removed and weighed
within 24 hours of pupation. Pupae were placed separately
into vials, returned to the incubator and allowed to
complete metamorphasis. Adults were frozen within 24 hours
after eclosion and dried at 750C for 24 hours before final
weighing.

To obtain nitrogen and carbohydrate levels other than
those'Hithe standard McMorran(1965) diet, the levels of
sucrose, casein, wheat germ and cellulose (all from ICN
Nutritional Biochemicals, Clevland, Ohio) were manipulated.
All other ingredients were kept constant. All diets
contained a constant dry weight by manipulation of these
variables. Hheat germ contains approximately 16.2% soluble
sugars (Fraser and Holmes 1957), which was accounted for in
calculations of % dry weight sugar in diets. Hheat germ and
casein were used as nitrogen sources with wheat germ
containing 6% nitrogen (Fraser and Holmes 1957) and casein
14% (ICN Nutritional Biochemicals; personal communication)
nitrogen by dry weight. Commercial brand alphacel
(cellulose) was found to contain 0.6% nitrogen (Kjeldahl
procedure; Mattson unpublished data), which was considered
unavailable because of the budworm's inability to hydrolyze
cellulose. The standard McMorran (1965) diet contains about
4.9% nitrogen of which casein makes up 74% and wheat germ

26%. This casein/wheat germ ratio was kept constant at all

11

nitrogen levels to avoid changing the balance of amino acids
in the diet.

A matrix design employing four nitrogen levels and six
sugar levels was used. Nitrogen levels were 1.5, 2.68, 5.36
and 7.0 grams or 1.38, 2.45, 4.90 and 6.41 on a % dry weight
basis. Sugar levels were 3.88, 7.0, 14.0, 21.0, 28.0, and
42.0 grams oriLSS, 6.41, 12.80, 19.23, 25.64, and 38.46 on
a % dry weight basis. Sugar/nitrogen ratios were calculated
on a gram/gram dry weight basis. Diets containing 4.9 grams
nitrogen and above were terminated at 40 days from
experiment initiation. Diets containing nitrogen levels
below 4.90 grams nitrogen were terminated at 50 days due to
protracted development. I used a two way analysis of
variance to measure the main effects of nitrogen and sugar
levels. on budworm performance. Insect performance was
measured using the following variables; fresh weight (fwt)
of pupae, dry weight (dwt) of adults, pupal and adult
growth rates (fwt of pupae or dwt of adult/days to develop)
developmental rate (100/days to develop) for pupal and adult
stages and survival of larvae to adult eclosion. Because
weight of female budworm pupae has been Shown to be
directly related to adult fecundity (Miller'1957), pupal
weight was used to estimate fecundity in this study.

Oils were added to diet media via an acetone solvent
when diets contained added fatty acids. This oil/acetone
solution was applied to the casein portion of the diet and

allowed to evaporate completely before mixing.

12

Insect frass from diets was collected and dried for 24
hours at 750C for soluble carbohydrate analysis. Frass
samples were extracted in quantities of 125 mg with 25 ml of
100% methanol on a shaker for 24 hours. Samples were then
centrifuged and 10 ml of the centrifuged extract was placed
in a sample concentrator and allowed to dry completely.
Samples were then reconstituted with 2 TNT of an 80/20
mixture of acetonitrile/water and filtered through C18 Sep
Pac cartridges (Haters Associates, Milford, Massachusetts)
and millipore prefilters (Haters Associates, Milford,
Massachusetts). A 75 ul sample of the concentrated extract
was then injected into an HPLC equipted with a Haters
carbohydrate analysis column (Haters Associates, Milford,
Massachusetts). Operating conditions ‘HH‘ HPLC soluble
carbohydrate analysis followed the general procedure
outlined in AOAC (1980 methods No. 31). Flow rate was 2
ml/min and eluting solvent used was acetonitrile/water
(80/20).An external standard,a refractive index detector
and a Hewlett Packard integrator were used to quantify the
three major sugars (fructose, glucose and sucrose) found in
budworm frass.

Field experiments were conducted at separate Sites near
International Falls (Minnesota), Antigo (Hisconsin) and
Hellston and Augusta (Michigan). Diapausing second instar
diapausing larvae were obtained as mentioned before from the
Canadian Forest Pest Management Institute, Canadian Forest

Service in Sault Ste Marie, Ontario. Four groups (25 larvae

13

per group) were placed on mid-crown branches in early spring
on each of 20 to 50 trees per site. Each group of insects
were securely enclosed within fine-mesh, translucent cloth
sleeve cages that were ca. 75-cm long. Insects were allowed
to develop until most had pupated in the field. Branches
were then removed from the trees and returned to the lab for
processing. Pupae were allowed to complete metamorphosis in
the lab at which point the newly emerged adults were frozen,
oven dried for 24 hours at 750C and weighed immediatly.
Foliage samples from other branches on experimental trees
were collected when larvae were in the fifth and sixth
developmental stages. Samples were put on ice in the field,
brought back to the laboratory and immediately frozen.
Samples were freeze-dried at a later date, cleaned and
ground to a fine powder with a micromill. Foliage samples
were processed and analyzed for the major soluble
carbohydrates in balsam fir and white spruce (fructose,
glucoseland sucrose)using the same procedures previously
outlined for frass carbohydrate analysis. Nitrogen analysis
were conducted by Mr. Bruce A. Birr (Technician, USFS,
Michigan State University) using the Kjeldahl procedure.
For more details concerning field experiment methods, please

see Mattson et al 1983.

RESULTS

Diet Matrix Study

 

The performance of male and female insects followed
Similar patterns among all diet treatments. Hence to avoid
unnecessary discussion, only female growth patterns will be
discussed for all parameters except survival. Data for both

sexes, however, are presented in the tables and figures.

Combined Female and Male Larval Survival to Adult Eclosion

Survival on diets containing 1.38% nitrogen was
extremely poor at all sugar levels ranging from a minimum of
0.5% (38.46% sugar) to a maximum of 5.8% (19.23% sugar),
(Tableel and Figurelj. Survival on diets containing twice
as much nitrogen (2.45%) increased about 10-fold, ranging
from a low of 24.5% (38.46% sugar) to a high of 52.2%
(12.80% sugar). Survival (HT diets containing 4.90% nitrogen
was even higher, ranging from 44.5% (19.23% sugar) to 72.0%
(12.80% sugar). The latter was, in fact, the highest mean

urvival for any sugar/nitrogen combination. At the highest
nitrogen level (6.41%), survival no longer increased and was
relatively uniform across all sugar levels ranging from

52.0% (3.55% sugar) to 59.0% (19.23% sugar).

14

Table 1.

15

Percent larval survival to adult eclosion. n=number
of experiments per treatment; 200 insects per
experiment. Diets at levels where blanks (----)
occur in tables 1-13 could not be formulated with
standard ingredients.

 

 

Nitrogen % Dry Height

 

Sugar Grand
% dw 1.38 2.45 4.90 6.41 Mean
3.55 2.5 28.0 54.0 52.0 34.1
n=2 n=2 n=4 n=2
6.41 4.5 41.5 45.5 54.0 36.4
n=2 n=3 n=4 n=2
12.80 4.5 52.2 72.0 55.2 46.0
n=2 n=3 n=5 n-Z
19.23 5.8 39.0 44.5 59.0 37.1
n=2 n=2 n=2 n=2
25.64 2.5 31.8 56.7 ---- 30.3
n=2 n=3 n=10
38.46 0.5 24.5 ---- ---- 12.5
n=2 n=2
Grand
Mean 3.4 36.2 54.5 55.1

 

 

(a)

(b)

96 Nitrogen x 6.25

‘76 Survival

37

29

21

13,

Figure

16

 

245% N

 

 

T T T T T I
3.55 8.4T I 2.80 18.23 25.84 38.48

96 Dry Weight Sugar

 

A

v
A

 

/J'
A

 

 

 

l
l
.\

 

 

96 Dry Weight Sugar

1. Combined male and female larval survival
to the pupal stage (%) in relationship to
dietary levels of sugars and nitrogen (% dw).

17

Pupal Height

Female pupal weights were clearly dependent on
both dietary nitrogen and sugar levels. Pupal weight was
significantly lower at the 1.38% nitrogen level than at all
other higher nitrogen levels (Tables 2,3 and Figures 2,3).
0n the lowest nitrogen diets, weights ranged from 66.7 mg
(38.46% sugar) to 84.4 mg (19.23% sugar). 0n diets
containing twice as much nitrogen (2.45%), weights increased
about 30%, ranging from 87.8 mg (3.55% sugar) to 108.2 mg
(19.23 % sugar). At the next highest nitrogen level (4.90%)
weights were only about 10% higher, ranging from 98.8 mg
(3.55% sugar) to 114.1 mg (6.41 and 12.80% sugar). The
latter (114.1 mg) was the highest mean female pupal fresh
weight for any sugar/nitrogen combination. At the highest
nitrogen level (6.41%), weights declined slightly, ranging
from a low of 99.9 mg (6.41% sugar) to a high of 107.0 mg
(12.80% sugary

Adult Height

Female adult weight, as was true for pupal weight, was
clearly dependent on both dietary sugar and nitrogen levels
(Tables 4,5 and Figures 4,5). Adult weights were again lower
at 1.38% nitrogen than at all other higher nitrogen levels.
On these diets, weights ranged from 12.5 mg (3.55% sugar) to

16.0 mg (19.23% sugar). 0n diets containing twice as much

18

 

 

 

 

Table 2. Female pupal fresh weight (mg) I standard error
and number of insects surviving per treatment.
Nitrogen % Dry Height
Sugar Grand
% dw 1.38 2.45 4.90 6.41 Mean
3.55 74.6+4.1 87.8+4.0 98.8+1.8 102.2+2.6 98.2
n=4 n=34 n=162 n=91 (3)
(C.1)* (b.c.4) (a.b.3) NA)
6.41 78.0+4.1 98.6+3.1 114.1+2.2 99.9+2.4 105.2
n=8 n=57 n=128 n=T04 (2)
(CA) (b.2.3) (a.1) (b,1)
12.80 75.9+4.7 107.0+2.1 114.1+1.4 107.0+2.7 109.5
n=T3 n=91 n=202 n=102 (1)
(C.1) (b.1) (6.1) (b.1)
19.23 84.4+4.6 108.2+3.2 106.2+2.4 100.5+2.5 103.6
n=Tl n=64 n=99 n=TO9 (2)
(b.1) (6.1) (6.2) (6.1)
25.64 72.3+2.5 105.2+2.9 113.7+1.1 ------ 112.4
n=4 n=53 n=422 (1)
(C.1) (13.1.2) (a.1)
38.46 66.7+13.6 88.7+4.1 ------------ 87.3
n=2 n=30 (3)
(b,1) (a,3,4)
Grand
Mean 77.6 101.8 110.7 102.3
(d) (C) (a) (b)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range testL

 

 

 

(a) ’5, HS —
E llD -
V
.5 I05 -
. m 100 2
0 95 ~
:5 SD —
9 as ~
Q) 80 ...
3: 75-
2 7O —
g 55 _. 1.35% N
0 EU I T T T T r l
“- 3.55 8.4l IZBD 19.23 25.54 38.48
96 Dry Weight Sugar
(b)

 

  

96 Nitrogen x 6.25

    

A ’ \L/‘_/_/_\__// 0 ..
13>\ °M //_—_——/—/\—
bit:\’\".

96 4Dry Weighot Sugarz

 

 

 

32 38

Figure 2. Female pupal fresh weight (mg) in relationship to
dietary levels of sugars and nitrogen (% dw).

20

Table 3. Male pupal fresh weight (mg) I standard error and
number of insects surviving per treatment.

 

 

Nitrogen % Dry Heighfi

 

 

Sugar Grand
% dw 1.38 2.45 4.90 6.41 Mean
3.55 43.3+3.9 63.0+1.9 68.4+1.0 67.6+1.4 66.8
n=6 n=56 n=183 n=TO4 (3,4)
(C.1.2)* (b.2l (a.4) (a.1)
6.41 46.7+2.5 67.0+1.9 74.8+1.2 66.3+1.6 69.2
=18 n=87 n=T71 n=T26 (2,3)
(c,1,2) (b,1,2) (a,2) (b,1)
12.80 52.4+3.7 70.6+1.2 78.1+1.0 69.0+1.4 73.5
n=18 n=T40 n=296 n=122 (1)
(C.1) (b.1) (8.1) (b,1)
19.23 50.1+1.9 65.5+1.8 66.3+1.5 68.3+1.6 65.6
=31 n=79 n=99 n=157 (4)
WM (6.2) MA) («3.1)
25.64 43.8+3.4 67.2+1.4 71.8+0.8 ------ 70.5
n=T4 n=85 n=542 (2)
(C.1.2) (b.1.2) (a.3)
38.46 36.5+5.8 48.5+2.2 ------------ 47.0
n=6 n=42 (5)
(b.2) (3.3)
Grand
Mean 47.6 65.8 72.7 67.8
(d) (C) (a) (b)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range test).

’5?
V

a)

(B
I

m - W99” N
85 - \ .
BU _ 341/. N \

Male Weight Gain (mg)
UT
UT
1

 

 

jg - \W A

40 J

35 _ L381 N

30 T T T T T ‘ l T
3.55 8.41 IZOD l8.23 25.84 38.48

96 Dry Weight Sugar

 

(b) - - . , 2 - - - - 2 -,
37A /
(/,//””’————‘\\3

(7’

21’

96 Nitrogen x 6.25

13 42M

\3T\—\/————4“

N 2 rt"
8 14 20

96 Dry Weight Sugar

l

 

 

 

 

 

 

 

Figure 3. Male pupal fresh weight (mg) in relationship to
dietary levels of sugars and nitrogen (% dw).

Table 4.

22

Female adult weight (mg) I standard error and
number of insects surviving per treatment.

 

 

Nitrogen % Dry Height

 

 

Sugar Grand
% dw 1.38 2.45 4.90 6.41 Mean
3.55 12.5+1.2 14.7+1.1 17.4+0.6 19.9+0.6 18.1
n=4 n=22 n=62 n=78 (5)
(d.2)* (C.d.3) (b.d.3) (6.1)
6.41 12.6+1.9 18.6+0.6 20.0+0.5 19.8+0 6 19.4
n=5 n=79 n=111 n=95 (4)
(b.2) (a.2) (6.2) (6.1)
12.80 15.3+1.4 20.7+0.5 23.8+0.5 21.1+0 6 21.9
n=9 n=96 n=T31 n=85 (2)
(C.2) (b.1) (a.1) (b.1)
19.23 16.0+1.1 21.1+0.8 21.3+O.6 20.3+0 6 20.7
n=TO n=54 n=89 n=8 (3)
(b.2) (a.1) (a.2) (a.1)
25.64 12.7+1.1 20.8+0.7 23.5+0.3 ------ 22.9
n=T n=67 n=358 (1)
(C.2) (b.1) (6.1)
38.46 16.1+0.0 17.0+1.0 ------------ 17.0
n=T n=26 (5)
(b,1) (a,2,3)
Grand
Mean 14.5 19.6 22.3 20.2
(c) (b) (a) (b)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range test).

23

 

 

 

 

(a) ’5, 25 -
E 488% N
V
.3 29 ‘ Afi
(D 245% N
c .
.9, 138/ N
o m ._
3
2
m 55'
6
LL 0 T T T T F r 1
3.55 8.41 12.80 18.23 25.84 38.48
96 Dry Weight Sugar
(b)
37 ’

 

.3

“N

96 Nitrogen x 6 25

  
  

 

/\—/'/

   

 

 

 

 

1., In ".J“ ;
8 14 20 26 32 38

96 Dry Weight Sugar

Figure 4. Female adult dry weight (mg) in relationship to
dietary levels of sugars and nitrogen (% dw).

24

Table 5. Male adult weight (mg) I standard error and number
of insects surviving per treatment.

 

 

Nitrogen % Dry Height

 

 

Sugar Grand
% dw 1.38 2.45 4.90 6.41 Mean
3.55 5.2+0.5 8.2+0.3 8.7+0.3 10.0+0.2 9.1
=6 n=34 n=43 n=90 (3)
(6.3)* (b.2) (b.41 (6.1)
6.41 7.7+0.4 8.9+0.3 10.1+0.2 9.8+O.2 9.6
n=T =87 n=T6O n=TO4 (2,3)
(b.2) (b.21 (6.3) (6.1)
12.80 8.8+1.1 10.1+0.3 11.4+0.2 10.5+O.3 10.7
n=9 n=Tl7 n=TZ5 n=9 (1)
(b.2) (b,1) (a.1) (b.1)
19.23 7.5+0.4 9.9+0.3 10.1+0.3 10.2+0.3 10.0
n=T3 n=59 n=89 n=121 (2)
(b.2) (6.1) (a.3) (a.1)
25.64 5.6+0.8 10.5+O.3 10.9+O.1 ------ 10.8
n=6 n=68 n=472 (1)
(b.3) (a,1) (a,2)
38.46 8.0+0.0 7.9+0.4 ------------ 7.9
n=T n=28 (4)
(a.1) (a.2)
Grand
Mean 7.3 9.6 10.6 10.1
(d) (C) (a) (b)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range testL

25

 

 

 

 

 

 

 

 

 

 

(a) ... 12 —
g 8.41% W450}: N
V 10 _
.E //\
8 B - --2.4SX N
f; 5 ‘ 1.38% N
o
3 4-
2
m 2-—
2
D T T T T f 1 1
3.85 5.41 12.88 18.23 25.84 38.48
96 Dry Weight Sugar
(b) 2 ' / -
‘95
to
9!
co
x
c:
o
o:
e ..
'2 21:
89 (\u
13 \ ‘fl/ d_4oo/ l
f/A/ [ $2 - l
8 14 32 38
96 Dry Weighot Sugar
Figure 5. Male adult dry weight (mg) in relationship to

dietary levels of sugars and nitrogen (% dw).

26

nitrogen (2.45%), mean weights increased about 35%, ranging
from a low of 14.7 mg (3.55% sugar) to a high of 21.1 mg
(19.23% sugar). Adult weights were still higher at 4.90%
nitrogen, ranging from a low of 17.4 mg (3.55% sugar) to a
high of 23.8 mg (12.80% sugar). The latter (23.8 mg) was the
highest mean female adult weight for any sugar/nitrogen
combination. At the highest nitrogen level (6.41%), female
adult weights no longer increased and were relatively
uniform across all sugar levels, ranging from 19.8 mg (6.41%

sugar) to 21.1 mg (12.80% sugar).

Pupal Growth Rate

Female pupal growth rate (pupal weight divided by the
number of days to reach the pupal stage) is equivalent to
biomass accumulated per day.As expected, growth rates for
females were significantly lower at 1.38% nitrogen than at
all other nitrogen levels (Tables 6,7 and Figures 6,7L
Growth rates at this nitrogen level ranged from a low of
1.35 mg/da (38.46% sugar) to a high of 1.94 mg/da (19.23%
sugar). 0n diets containing twice as much nitrogen (2.45%),
growth rates increased about 65%, ranging from 2.19 mg/da
(38.46% sugar) to 3.28 mg/da (12.80% sugar). At 4.90%
nitrogen, growth rates were still larger, ranging from 3.18
mg/da (3.55% sugar) to 4.03 mg/da (12.80% sugar). The latter
(4.03 mg/da) was the highest mean female pupal growth rate

for any sugar/nitrogen combination. At the highest nitrogen

27

Table 6. Female pupal growth rate (mg/da) 1 standard error
and number of insects surviving per treatment.

 

 

Nitrogen % Dry Weight

 

 

Sugar Grand
% dw 1.38 2.45 4.90 6.41 Mean
3.55 1.68+0.15 .43+0.13 .18+0.08 .23+0.11 3.09
n=4 n=34 n=162 n=91 (3)
(b.1)* (b.3) (3.3) (6.1)
6.41 1.83+0.10 .94+0.12 .85+0.11 .28+0.01 3.42
n=8 n=§7 n=128 n=TO4 (2)
(C.1) (b.2) (6.2) (b.1)
12.80 1.73+0.13 .28+0.08 .03+0.07 .51+0.12 3.66
n=TB n=91 n=202 =TOZ (1)
(CM NM) NM) (b.1)
19.23 1.94+0.13 .96+0.11 .42+0.01 .30+0.10 3.21
n=T1 n=64 n=99 n=TO9 (3)
(C.1) (b.2) (a.3) (a.1)
25.64 1.59+0.09 .85+0.10 .65+0.05 ------ 3.55
n=4 n=33 n=422 (2)
(c,1) (b,2) NJ)
38.46 1.35+0.29 .19+0.12 ------------ 2.14
n=2 n=30 (4)
(b.1) (6.3)
Grand
Mean 1.77 2.90 3.65 3.33
(d) (C) (a) (b)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range test).

4.5 -
4.0 ~
3.5 d
3.0 -
2.5
2.0 -
1.5 d

(a)

1

0.5 -‘

 

28

2.45% N

 

0.0

Female Growth Rate mg/da

I

i T I T I
3.55 5.41 12.80 13.23 25.54 38.45

96 Dry Weight Sugar

 

(b)

96 Nitrogen x 6.25

 

 

 

 

 

 

 

 

 

8 14 20 ' 2 32 38

Figure 6.

96 Dry Weight Sugar

Female pupal growth rate (mg/da) in
relationship to dietary levels of sugars and
nitrogen (2 dw). ‘

29

 

 

 

 

Table 7. Male pupal growth rate (mg/da) I standard error
and number of insects surviving per treatment.
Nitrogen % Dry Weight
Sugar Grand
Zdw 1.38 2.45 4.90 6.41 Mean
3.55 1.03+0.09 .83+0.07 .44+0.05 .30+0.06 2.27
n=6 =36 n=183 n=TO4 (3)
(c.1.2)* (b.21 (a.3) (a.1)
6.41 1.11+0.07 .21+0.08 .80+0.07 .38+0.07 2.46
n=18 n=87 n=T71 n=TZ6 (2)
(C.1.2) (b.1) (6.2) (b,1)
12.80 1.26+0.09 .35+0.05 .98+0.05 .45+0.06 2.66
n=18 n=T40 n=296 n=122 (1)
(6.1) (b.1) (a.1) (b,1)
19.23 1.24+0.06 .87+0.07 .29+0.07 .38+0.07 2.15
n=31 n=79 n=99 n=Ts7 (4)
(C.1) (b.2) (6.3) (6.1)
25.64 0.99+0.09 .01+0.05 .44+0.04 ------ 2.35
n=T4 n=85 =542 (3)
(C.2) (b.2) (6.3)
38.46 0.80+0.16 .28+0.07 ------------ 1.22
n=6 =12 (5)
(b.21 (6.3)
Grand
Mean 1.14 2.04 2.60 2.38
(d) (C) (a) (b)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range test).

(a) 3.130 —

2.75 -
2.50 - 4.901 N

225 ‘ 8.41% N
2.00 —

1.75 -
|.50 -

|.25 - 2.45% N
075 _ LSBX N

050

 

Male Growth Rate mglda

 

T

3.55 8.4 | i 2.80 l8.23 25.84 38.48

96 Dry Weight Sugar

 

(b)

 

 

96 Nitrogen x 6.25

 

 

 

 

 

 

 

 

96 Dry Weight Sugar

Figure 7. Male pupal growth rate (mglda) in relationship
to dietary levels of sugars and nitrogen (:
dw).

31

level (6.41%), growth rates no longer increased but in fact
declined slightly. Values ranged from 3.23 mg/da (3.55%
sugar) to 3.51 mg/da (12.80% sugar).

Adult Growth Rates

Female adult growth rate (adult dry weight divided by
the number of days to adult eclosion) was lowest at 1.38%
nitrogen, ranging from 0.237 mglda (3.55% sugar) to 0.309
mg/da (19.23% sugar) (Tables 8,9 and Figures 8,9). With
twice as much nitrogen (2.45%) in the diet, growth rates
increased about 54%, ranging from 0.327 mglda (3.55% sugar)
to 0.468/da (12.80% sugar). 0n diets containing 4.90%
nitrogen, growth rates were still higher, ranging from
0.405 mglda (3.55% sugar) to 0.617 mglda (12.80% sugar). The
latter (0.617 mglda) was the highest mean female adult
growth rate for any sugar/nitrogen combination. At the
highest nitrogen level (6.41%), growth rates declined
slightly, ranging from 0.494 mglda (3.55% sugar) to 0.538
mg/da(12.80% sugar).

Pupal Devel0pment Rate

Female pupal development rate (100 divided by the
number of days to the pupal stage), is equivalent to percent
development per day. As expected, female development rates

were significantly lower at 1.38% nitrogen than at all other

Table 8. Female adult growth rate
and number of insects surviving per treatment.

32

(mglda) 1

standard error

 

 

 

 

Nitrogen % Dry Weight

Sugar Grand

% dw 1.38 2.45 4.90 6.41 Mean

3.55 .237+0.02 0.327+0.03 .405+0.02 0.494+0.02 0.432
n=4 n=22 n=62 n=78 (4)
(C.2)* (C.3) (b.41 (6.1)

6.41 .259+0.05 0.409+0.02 .491+0.01 0.512+0.02 0.472
n=5 =79 n=111 n=§5 (3)
(C.2) (b.2) (a.3) (6.1)

12.80 .301+0.03 0.468+0.01 .617+0.01 0.538+0.02 0.543
n=9 n=96 n=131 n=85 (1)
(4.2) (C.1) (6.1) (b,1)

19.23 .309+0.03 0.466+0.02 .550+0.02 0.526+0.02 0.512
n=TO n=54 n=89 =89 (2)
(c.2) (b.11 (6.2) (a.1)

25.64 .236+0.03 0.443+0.02 .588+0.01 ------ 0.562
n=4 n=67 n=358 (1)
(6.2) (b.1.2) (a.1)

38.46 .268+0.00 0.346+0.02 ------------ 0.343
n=T =26 (5)
(b,1) (8.3)

Grand

Mean 0.280 0.431 0.559 0.518
(d) (C) (a) (b)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range testL

 

 

 

— 4.902 N
_ 5.412 N
.1 \
2.452 N
_ ’/——_\1.382 N '
T T F I T I T
3.55 5.41 12.80 19.23 25.54 38.46

96 Dry Weight Sugar

 

(a) g 0.70
B:
E 0.130
2 0.50
(U
m 0.40
5
3 0.30
2
o 0.20
2
m [MD
5
u_ 13.00
(b)

96 Nitrogen x 6.25

 

 

 

 

 

 

 

Figure

 

96 Dry Weight Sugar

8. Female adult growth rate (mglda) in
relationship to dietary levels of sugars and
nitrogen(% de

34

Table 9. Male adult growth rate (mglda) I standard error
and number of insects surviving per treatment.

 

 

Nitrogen % Dry Weight

 

 

Sugar Grand
% dw 1.38 2.45 4.90 6.41 Mean
3.55 0.103+o.01 0.189+0.01 o.225+0.01 0.266+0.01 0.235
n=5 n=34 n=43 n=90 (4)
(d.3)* (C.3.4) (b.4) (a.2)
6.41 0.156+0.01 0.204+0.01 0.269+0.01 0.272+0.01 0.250
=13 n=87 n=160 n=TO4 (3,4)
(C.2) (b.31 (a.3) (a.1.2)
12.80 .171+0.02 .248+0.01 .319+0.01 .292+0.01 0.284
n=9 n=Tl7 n=125 n=§8 (1)
(d.2) (C.1) (a.1) (b,1)
19.23 .157+0.01 .227+o.01 .273+o.01 .276+0.01 0.258
n=T3 n=69 =89 n=T21 (3)
(c,2) (b,1,2) (a,2,3) (a,1,2)
25.64 .108+0.02 .241+0.01 .286+0.01 ------ 0.279
n=6 n=68 n=472 (2)
(C.3) (b.1.2) (a.2)
38.46 .163+0.00 .172+0.01 ------------ 0.172
n=T n=28 (5)
(b,1) (a.4)
Grand
Mean 0.147 0.223 0.284 0.276
(C) (b) (a) (a)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range test).

A
8

085
080
025
020
015
010
005

Male Growth Rate mglda

000

(b)

35

 

 

 

3.55 8.41 12.80 18.28 25.84 88.48
96 Dry Weight Sugar

 

 

96 Nitrogen x 6.25

 

 

 

 

 

Figure 9.

 

96 Dry Weight Sugar2

.Male adult growth rate (mglda) in relationship

to dietary levels of sugars and nitrogen (%
dw).

36

nitrogen levels (Tables 10,11 and Figures 10,11). Growth
rates at this nitrogen level ranged from a low of 2.02%lda
(38.46% sugar) to a high of 2.35%lda (6.41% sugar). 0n
diets containing twice as much nitrogen (2.45%),
development rates were about 22% faster ranging from
2.45%/da (38.46% sugar) to 2.91%/da (12.80% sugar). 0n diets
containing 4.9% nitrogen, development rates were still
faster, rangingfrom 3.18%lda (3.55 and 38.46% sugar) to
3.47%/da (12.80 % sugar). The latter (3.47%lda) was the
highest mean female pupal development rate for any
sugar/nitrogen combination.At the highest nitrogen level
(6.41%), development rates no longer increased
significantly, ranging from 3.12%lda (3.55% sugar) to
3.26%/da (6.41% sugar)

Adult Development Rate

Female adult development, as was true for female pupae,
was much slower on diets containing 1.38% nitrogen, ranging
from 1.67%/da (38.46% sugar) to 1.94%lda (12.80% sugar),
(Tables 12,13 and Figures 12,13). 0n diets containing twice
as much nitrogen (2.45%), development rates increased about
14%, ranging from 2.01%lda (38.46% sugar) to 2.25%/da
(12.80% sugar). Development rates on diets containing 4.90%
nitrogen were even faster, ranging from 2.30%lda (3.55%
sugar) to 2.59%lda (12.80% sugar). The latter (2.59%/da)

was the highest mean female adult develpment rate for any

37

Table 10. Female pupal development rate (%/da) + standard

 

 

 

 

error and number of insects surviving per
treatment.
Nitrogen % Dry Weight
Sugar Grand
% dw 1.38 2.45 4.90 6.41 Mean
3.55 .25:0.18 .73:0.06 .18:0.03 3.12:0.04 3.10
n=4 n=34 n=162 n=91 (2)
(C.1)* (b,2,3) (6.3) (6.2)
6.41 .35:0.08 .81:0.04 .30:0.04 3.26:0.04 3.13
n=8 n=110 n=167 n=104 (2)
(CM (b.2) (a,2) (6.1)
12.80 .27:0.05 .91:0.03 .47:0.02 3.23:0.04 3.25
n=13 n=143 n=285 n=102 (1)
(d.1) (C.1) (a.1) (13.1)
19.23 .30:0.07 .71:0.05 .20:0.04 3.25:0.04 3.07
n=11 n=64 n=99 n=109 (1)
(c,1) (b,2,3) (a,2,3) (a,1)
25.64 .19:0.07 .62:0.03 .18:0.02 ------ 3.09
n=4 n=85 n=480 (2)
(C.1) (b.31 (6.3)
38.46 .02:0.02 .45:0.05 ------------ 2.42
n=2 n=30 (3)
(b,1) (6.4)
Grand
Mean 2.27 2.76 3.27 3.22
(d) (C) (a) (b)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range test).

 

 

 

 

 

 

as
'o
a \ . _
( ) as 880
2 3.40 4 /\
c0 —— 8.41% N
m 3.20 - / R—4.802 N
E 3.00 A
a:
E 2.80 3
a
2 2.50 4
g 2.40 _ 2.457 N
g 2.20 -‘ /\/\
- . X
E 2.00 T T T f T 1' 38 N1
q, 3.55 8.41 12.80 18.23 25.84 38.48
1.1.
96 Dry Weight Sugar
(b) { ‘J 5 '
1//
1
to L
9! 1‘
co
X
c
o
o:
2
.2.
ae

 

 

 

 

 

8 14 20 26 32 38
96 Dry Weight Sugar

 

Figure 10. Female pupal development rate (%lda) in
relationship to dietary levels of sugars and
nitrogen (% dw).

39

 

 

 

 

Table 11. Male pupal development rate (%lda) :; standard
error and number of insects surviving per
treatment.

Nitrogen % Dry Weight
Sugar Grand
% dw 1.38 2.45 4.90 6.41 Mean
3.55 2.40:0.13 2.88:0.05 3.52:0.03 3.37:0.04 3.35
n=6 n=56 n=183 n=104 (2)
(d.1.2)* (C.3) (6.3) (13.2)
6.41 2.37:0.06 3.08:0.04 3.64:0.04 3.52:0.04 3.41
n=18 n=147 n=238 n=126 (2)
(d.1.2) (C.2) (6.2) (13.1)
12.80 2.42:0.08 3.17:0.03 3.78:0.03 3.52:0.04 3.53
n=18 n=188 n=364 n=122 (1)
(11.1.2) (C.1) (3.1) (b,1)
19.23 2.47:0.05 2.82:0.05 3.41:0.05 3.42:0.03 3.21
n=31 n=79 n=99 n=157 (3)
(c,1) (b,3) (a,3,4) (8,1,2)
25.64 2.24:0.05 2.91:0.03 3.35:0.02 ------ 3.27
n=14 n=107 n=622 (3)
(c,2) (b,3) (6.4)
38.46 2.15:0.08 2.60:0.06 ------------ 2.54
n=6 n=42 (4)
(13.2) (a.3)
Grand
Mean 2.38 2.99 3.52 3.46
(d) (C) (a) (b)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range test).

(a) 3.50 —
3.40 -
3.20 -
3.00 -
2.50 -

2.50 — \2452 N

2.40 -‘ \/\
Z-ZD ‘ 1.88% N

2.00

 

 

 

I I

T I I I I
3.55 8.41 12.80 18.23 25.84 38.48

Male Development Rate %/da

96 Dry Weight Sugar

37 ) ‘
. » s

 

 

 

96 Nitrogen x 6 25

 

 

 

 

 

 

\ f
/ \ - g - - 1m- -/

8 ‘14 20 26 32 38
96 Dry Weight Sugar

Figure 11. Male pupal development rate (%lda) in
relationshp to dietary levels of sugars and
nitrogen (% dw). ‘

41

 

 

 

 

Table 12. Female adult development rate (%lda) 1 standard
error and number of insects surviving per
treatment.

Nitrogen % Dry Weight

Sugar Grand

% dw 1.38 2.45 4.90 6.41 Mean

3.55 1.89+0.13 2.19+0.05 .30+0.03 .44+0.03 2.34
n=1 n=22 n=52 n=79 (2)
(C.2)* (b.1.2) (b.3) (6.2)

6.41 2.02+0.07 2.19+0.02 .44+0.02 .57+0.03 2.40

n=5 n=79 =T11 n=95 (1)
(C.2) (C.1) (11.2) (61.1)

12.80 1.94+0.06 2.25+0.02 .59+0.02 .52+0.03 2.45
n=8 n=§6 n=T31 n=85 (1)
(d.2) (C.1) (6.1) (b.1)

19.23 1.91+0.06 2.19+0.03 .56+0.03 .55+0.03 2.45
n=T0 n=54 n=89 =89 (1)
(C.2) (b.1.2) (6.1) (6.1)

25.64 1.84+0.06 2.11+0.02 .48+0.01 ------ 2.42
n=1 n=57 n=359 (1)
(C.2) (b.2) (6.2)

38.46 1.67:0.00 2.01+0.04 ------------ 1.99
":1 n=2; (3)
(b,1) (6.3)

Grand

Mean 1.92 2.18 2.49 2.52

(d) (C) (b) (a)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range test).

42

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

to
'o
(a) a} 2.50 —
#3 2.50-
‘1 5.412 N 4.302 N
o— 2.40 ‘
c
o
E 2.20-
o.
2 245/ N
g 2.88 - . ...
o
D 1.80-
o .
a 180 135/. N
E - I I I T I j 1
to: 3.55 8.41 12.88 18.28 25.84 88.48
96 Dry Weight Sugar
(b)
1.0
9!
to
X
c
o
c»
8
.2
a2
96 Dry Weight Sugar
Figure 12. Female adult development rate (%lda) in

relationship to dietary levels of sugars and
nitrogen (% dw).

43

 

 

 

 

Table 13. Male adult development rate (%lda) + standard
error and number of insects surviving per
treatment.

Nitrogen % Dry Weight
Sugar Grand
% dw 1.38 2.45 4.90 6.41 Mean
3.55 1.99 0.10 2.29 0.04 2.56 0.04 .64 0.03 2.53
n=6 n=34 n=43 n=90 (2)
(C.2)* (b.2.3) (3.2) (6.2)
6.41 2.03+0.04 2.28+0.03 2.66+0.02 .74+0.03 2.57
n=T3 n=87 n=T60 n=104 (2)
(d.2) (C.2) (b.2) (6.1)
12.80 1.93+0.08 2.42+0.03 2.77+0.02 .76+0.03 2.63
n=8 n=Tl7 n=125 n=98 (1)
(C.2) (b.1) (6.1) (6.1)
19.23 2.10+0.05 2.27+0.03 2.67+0.04 .67+0.02 2.55
=13 n=89 n=89 n=121 (2)
(C.2) (b.2.3) (4.2) (a.2)
25.64 1.92+0.05 2.29+0.03 2.60+0.02 ------ 2.55
n=5 n=58 n=475 (2)
(C.2) (b.21 (6.2)
38.46 2.04+0.00 2.16+0.05 ------------ 2.16
n=T =28 (3)
(b,1) (a.3)
Grand
Mean 2.01 2.31 2.64 2.70
(d) (C) (b) (a)

 

 

* Means followed by the same letter (within rows) or number
(within columns) are not significantly different at the p <
0.05 level (Ducans multiple range test).

44

(a) 2.50 —

2.80 - 4.80% N

2'20 2 2.457 N
2.00 _ /\/\/1.357 N

 

 

Male Development Rate 96lda

 

1.80-
1.80 fl 1 1 1 1 1 1
3.55 5.41. 12.80 18.28 25.54 35.45
96 Dry Weight Sugar
(b) - - - 3 2 3 - -
LV

 

 

 

96 Nitrogen x 6.25

 

pA—un\/\J 0‘0
13 (Rue: Hm. u‘°/\1
\4/7:/—~\/—/
X - -/ ‘9'» - - 2 - a K
8 14 20 26 32 38
96 Dry Weight Sugar

 

 

 

Figure 13. Male adult development rate (%lda) in
relationship to dietary levels of sugars and
nitrogen (% dw).

45

sugar/nitrogen combination. At the highest nitrogen level
(6.41%), development rates decreased only slightly ranging
from 2.44%/da (3.55% sugar) to 2.57%lda (6.41% sugar).

Optimal Ratios of Sugar to Nitrogen
at Different Nitrogen Levels

As before, performance of male and female budworm
followed similar patterns among all treatments.Hence, to
avoid unneccessary discussion only female responses will be
presented for the following parameters; pupal fresh weight
gain, pupal growth rate (mglda) and pupal development rate
(%lda). Data for all sexes and all parameters are, however,
demonstrated in the tables and figures. Optimal ranges were
determined using Duncans multiple range test. Ranges on
diets containing 1.38% nitrogen were very broad. This was
due in part to the small sample size which resulted because
of poor survival on these diets. For example, data from
diets containing 1.38% nitrogen and 38.46% sugar were not

included because sample size was so small (n=2 survivors).

£9221 £5822 921901

On diets containing 1.38% nitrogen, optimal
sugar/nitrogen ratios ranged from 2.59/1 to 18.67/1
(midpoint 10.63/1) (Figure 14). On diets containing twice as
much nitrogen (2.45%), the range for optimal sugar/nitrogen

ratios was from 5.24/1 to 10.49/1 (midpoint 7.87/1). 0n

46

 

 

 

 

 

20
Female Pupal Fresh Weight
.9
7.3 18 -
c:
1:
8
o 12 -
.b
\
8 8 —
a1
:1
m
.E 4 ‘
'6
:1
0 1

 

I I I
1.88 2.45 4.80 8.41
X Drg Weight Nitrogen

Figure 14. Optimal ratios of sugar to nitrogen at different
nitrogen levels in relationship to female pupal
weight (mg).

47

diets containing 4.90% nitrogen, the optimal ratio ranged
from 1.31/1 to 5.23/1 (midpoint 3.27/1). At the highest
level of nitrogen (6.41%), the range of optimal ratios was

smallest, extending from 0.55/1 to 3.0/1 (midpoint 1.78/1L

Pupal Growth Rate (mglda)

 

Female pupal growth rates followed a pattern similar to
that for female pupal fresh weight (Figure 15). On diets
containing 1.38% nitrogen, the Optimal sugar/nitrogen ratio
extended from 2.59/1 to 18.67/1 (midpoint 10.63). On diets
containing 2.45% nitrogen, the optimal sugar/nitrogen
ratio was a single point (5.24/1), just as it was for diets
containing 4.90% nitrogen (2.61/1). At the highest level of
nitrogen (6.41%), optimal ratios extended from 0.55/1 to
3.0/1 (midpoint 1.78/1).

Pupal Development Rate (%lda)

 

Female pupal development rates followed patterns that
were very similar to both pupal weight and pupal growth rate
(Figure 16). On diets containing 1.38% nitrogen, the optimal
sugar to nitrogen ratio extended from 2.59/1 to 18.67/1
(midpoint 10.63/1). On diets with the next highest nitrogen
content (2.45%), the optimal sugar/nitrogen ratio was again
a single point (5.24/1), just as it was for diets containing

4.90% nitrogen(2.61/1L,At the highest level of nitrogen

48

 

 

 

 

20
Female Puoel Growth Fiate [mg/dal

.9

75 18 3

II

C

81

o 12 -

.:

ii

\1.

m 8 -

CD

I)

U)

.8 4 -

‘8

D

D I 7 I 1
1.88 2.45 4.80 8.41
X 0rg Weight Nitrogen

Figure 15. Optimal ratios of sugar to nitrogen at

different nitrogen levels in relationship to
female pupal growth rate (mg/da).

 

49

 

 

 

 

20
0 Female Puoal Development Rate [Zda]
'73 18 -
II
C
81
0 12 =
.b
32
\t
m 8 -
01
Zl
U)
E 4 .1
'8
Cl
0 I I I I
1.38 2.45 4.80 8.41
X 0rg Weight Nitrogen
Figure 16. Optimal ratios of sugar to nitrogen at

different nitrogen levels in relationship to
female pupal development rate (%/da).

 

50

(6.41%), optimal ratios extended from 1.0/1 to 3.0/1
(midpoint2.0/1L

Regression Relationships Between Insect Performance and

Dietary Sugar and Nitrogen Concentrations

In order to find a likely mathematical relationship
between budworm performance and the various levels of
nitrogen and sugar in it's diet, I regressed the seven
measures of performance (survival, pupal weight, adult
weight, pupal growth rate, adult growth rate, pupal
development rate, and adult development rate) on the linear,
log and the squared measures of these two nutrients (Table
14). I used the log and squared values because it was
evident from the figures (1-13) that performance was
probably not linear with respect to these nutrients but was
some type of dome-shaped function.

The results of the regression analyses (Table 14)
showed a rather clear and consistent pattern. Sugar and
nitrogen entered into regression equations only as their log
or their squared concentrations. The most general patterns
were for insect performance variables to be a function of
all four variables; log N, log S, -N2 and -S2 (4 cases) or a
binary subset of them: log N, log S (4 cases) and log N, -N
(2 cases). In just two cases, only one variable (log N) was

significant, whereas in one case, three variables (log N,
2

log S, -S ) were. For any given performance variable (e.g.

51

Table 14. Regression relationshps between insect
performance variables and dietary nitrogen
and sugar (p 5.05).

 

 

Coefficients for diet nutrient Variables

 

 

Performance1 2 2 2
Variable Log N N Log 5 S R
Survival Rate 60.88 -1.12 .90
Pupal Neight(F) 49.05 -1.25 .82
Pupal Neight(M) 35.91 -0.94 6.03 -0.18 .95
Adult Height(F) 9.04 -0.20 4.49 -O.24 .85
Adult Neight(M) 2.02 .55
P.Growth Rate(F) 2.33 -0.51 0.38 -O.89 .96
P.Growth Rate(M) 1.82 -0.41 0.23 -0.73 .94
A.Growth Rate(F) 0.18 0.34 . .82
A.Growth Rate(M) 0.92 .80
P.Dev.Rate(F) 1.25 0.23 .93
P.Dev.Rate(M) 1.43 0.25 .91
A.Dev.Rate(F) 0.32 0.14 -0.14 .93
A.Dev.Rate(M) 0.48 .94
1

(F)= Female, (M)= Male, P. = Pupal, A. = Adult

52

pupal weight), the equations for males and females were
usually not exactly alike. This implies that both sexes are
not equally responsive to these two nutrients. However, it
is clear that insects respond in a nonlinear manner to
changing levels of these two classes of nutrients. If the
general performance (P) of the budworm is a function of all
four variables such that P= a logN - b N2 + a logS - b 52
then the Optimal performance fhr one nutrient,2holding the
other constant can be described by taking the partial
derivative of this equation with respect to the variable

nutrient (V) and then setting it equal to zero and solving

for V. The result is the fol lowing:

V = a /2b
opt i i

The equation says that the optimal value for the nutrient
(V) will be equal in) the square root of it's "a “
i
coefficient divided by two times it's “b " coefficient.
1

Concentration of Sugars Remaining In Budworm Frass

Budworm frass was analyzed for soluble sugar content
(HPLC analysis). Soluble sugars found in frass were
in the form of fructose and glucose. At the very highest
sugar level (38.46%) budworm frass contained about 8% dw

sugar at both nitrogen levels (Figure 17). At sugar levels

53

 

 

 

 

l0

m 7. Dry Weight Sugar in Frass
m

m 8 -

L

LL

.8

5 5 "

01

:1

m

z 4 7

.Q'

o

3:

31 2 ‘

L

:1

x

D /

I I I j I I
8.55 8.41 12.80 18.28 25.84 88.48
7. Org Weight Sugar in Diet

Figure 17. Percent dry weight sugar left in frass in

relationship to percent dry weight sugar in
artificial diet.

 

54

less than or equal to 25.64%, budworm frass contained only
1% sugar or less at all nitrogen levels. Frass from diets
containing 6.41% sugar or less at all nitrogen levels

contained virtually no soluble sugars at all.

Addition of Fatty Acids to Low Level Nitrogen Diets

Fatty acid were added to diets containing 2.45% nitrogen
in the form of either wheat germ oil or indivdually
(linoleic and linolenic acids). These oils were added via an
acetone solvent to the casein portion of the diet media.
Oils were added in ammounts which compensated for the loss
of fatty acids when nitrogen levels were reduced from 4.91%
to 2.45% by reducing the wheat germ content of the diet.
Female pupal weights were significantly higher for all sugar
levels on control diets (2.45% nitrogen with no added oils)
than on diets containing 2.45% nitrogen with added wheat

germ oil or added linoleic and linolenic acids (Table 15).

55

 

 

 

 

 

 

Table 15. Female pupal weight (mg) on diets containing
2.45% nitrogen, 2.45% nitrogen with linoleic and
linolenic acids and 2.45% nitrogen with wheat
germ oil. Levels where blanks (----) occur
indicate zero percent survival.

. , . 1
Nitrogen A Dry Weight
Sugar % dry
weight 2.45% 2.45 w/fa 2.45% w/oil
3.55 87.8+4.0 ------------
n=34
6.41 98.6+3.1 a 89.6+3.7 76.5+4.2 c
n=57 n=T6
12.80 107.0+2.1 a 88.6+2.9 81.7+5.1 b
=91 =37 n=Ts
19.23 108.2+3.2 a 94.9+4.6 95.6+3.8 b
n=54 n=21 n=23
25.64 105.2+2.9 a 90.5+3.9 92.1+5.2 b
n=53 =T9 n=20
38.46 88.7+4.1 a 57.7+2.5 69.5+2.8 b
n=30 n=29 n=T6
Grand
Mean 101.8 84.2 83.3
Means followed by the same letters across rows are not

significantly different at the p
multiple range test).

<

.05

level

(Duncans

56

Field Studies

 

Balsam Fir and White Spruce Foliar Sugar and Nitrogen
0
Concentrations in Relation to ( D) Accumulations

Three major sugars were found in current year foliage of
balsam fir and white spruce throughout the entire time of
budworm feeding: fructose, glucose and sucrose. Hereafter,
sugar concentrations refer to the sum total of these three
sugars.

Balsam fir foliar sugar concentration was about 5.2% dwt
just after budworm emergence and during needle mining (220
00; see 00 estimation technique in Mattsonet al. 1983)
(Figure 18).Foliar sugar concentration declined slightly
and then gradually increased to a maximum oftL2% dwt (630
00) when budworm were sixth instars. Ninety percent of
budworm feeding occurs while they are fifth and sixth
instars. Minimum foliar sugar concentration was 3.0% dwt
(300 0D).

For white spruce, foliar sugar concentrations followed
a pattern like that of fir but were much more variable,
ranging from 6.1% dwt (220 00) during budworm needle
mining, increasing to a high of about 20.2% and then
declining to 10.1% dwt (630 00) when budworm were in the
sixth instar (Figure 18). Minimum concentration was 5.0%

o
dwt (300 D) and maximum concentration was 20.8% dwt (480

S7

 

24

18"

151-

121-

% Sugar: Dry Weight

 

I I I I

   
  
    
 

b.epruce ebw ebw ebw
budbreelt 51h 0th pupee
w spruce

budbmlt

I

hflr
budbreek

the: mining
1 your needles

 

 

wWhite Spruce

   

Balsam Fir

 

1 I ' J J J 1 1 J 4

 

Figure 18.

100 200 300 400 500 600 700 800 900

De 9 ree Days

Balsam fir and white spruce foliar sugar
concentration in relation to degree day

accumulaton.

58

D).

In contrast, balsam fir and white spruce foliar
nitrogen concentrations showed a: steady exponential decay

throughout the growing season (Figure 19L.F0r balsam fir,
0
there was a maximum concentration of 5.5% dw (220 0) just
0
after budworm emergence and 1.7% dw (630 0) when budworm

were sixth instars. For white spruce, there was a maximum
0
concentration of 6.6%1hv(220 D) at budworm emergence and
o
1.1% dw (630 0) when budworms were sixth instars.

Balsam fir foliar sugar/nitrogen ratios ranged from

o o
0.95/1 (220 0) to 4.13/1 (700 D). White spruce foliar
o
sugar/nitrogen ratios ranged from 0.94/1 (220 D) to 13.0/1
o
(480 0).

Concentrations of Nitrogen and Sugars During

Fifth and Sixth Larval Stages

Northern Minnesota

 

Mean foliar nitrogen concentrations of balsam fir
during thebudworm's fifth and sixth larval stages between
1981 and 1984 ranged from 1.30% dw (1981) to 1.86% dw
(1984), (Tables 16,17). Mean total foliar sugar values
ranged from 2.88% dw (1981) to 8.12% dw (1983). Mean
sugar/nitrogen ratios extended from a low of 1.92/1 in 1981
to a high of 5.76/1 in 1983. Black spruce trees in 1981 and
1982 had mean foliar nitrogen values of 0.75% dw (1981) and

59

 

 

 

 

 

 

 

 

 

 

7 I '1 j j T 1 j f
6 " White Spruce a '
Balsam Fir I
5 " u
U)
9 4 - q
:9:
2
‘_ “in mining
5 3 - 1year needles -
8 inr
(D
D. 2 1- budbraak -
mapruce
budbraak
1 )- q
5. ruce lbw .bw
bu break 5th 0th pupae
o I y I 1___J
O 100 200 300 400 500 600 700 800 900
Degree Days
Figure 19. Balsam fir and white spruce foliar nitrogen

concentration in relation to degree day
accumulation.

60

Table 16. Grand mean values 1 standard error for nitrogen,
sugar and sugar/nitrogen ratios for field studies
performed from 1981-1982. n= number of trees per

 

 

study.

Study Area/Yr/Tree Sp.1 N Mean S Mean S/N Mean

1. Falls 1981 B.F. 1.55:0.04 2.88:0.16 1.92:0.14
n=31 n=31

1. Falls 1982 B.F. l.30+0.03 4.l7+0.51 3.24:0.40
n=30 n=30

1. Falls 1981 N.S. 1.24+0.04 3.32+0.23 2.70:0.18
n=T8 n=18

1. Falls 1982 N.S. 1.20+0.03 3.67+0.44 3.03:0.33
n=20 n=20

Cromwell 1981 Bk.S. 0.75+0.04 3.50+O.33 4.84:0.53
n=T6 n=T6

Cromwell 1982 Bk.S. 0.85+0.02 3.92+0.40 4.64:0.49
n=T5 =T5

 

 

I.= International, BJH= balsam fir,1LS.= white spruce,
Bk.S. = black spruce

61

Table 17. Grand mean values I standard error for nitrogen,
sugarand sugar/nitrogen ratios for field studies
performed from 1983-1984. n= number of trees per

 

 

study.

Study Area/Yr/Tree Sp.1 N Mean S Mean S/N Mean

Kellogg 1983 B.F. 1.60+0.02 5.42+0.86 3.34:0.48
n=20 n=20

Kellogg 1984 B.F. 1.90+0.05 4.20+0.52 2.32:0.30
n=34 .n=§4

I. Falls 1983 B.F. 1.41+0.04 8.12+0.46 5.76:0.24
n=T0 n=10

1. Falls 1984 B.F. 1.86+0.04 7.64+0.29 4.12:0.14
n=T4 n=T4

Antigo 1984 B.F. 2.84+0.11 6.86+0.60 2.60:0.26
n=28 n=28

Kellogg 1983 ”.5. 1.38+0.03 9.63+0.80 6.95:0.52
n=33 n=33

Kellogg 1984 N.S. 1.80+0.05 3.25+0.42 1.85:0.27
n=32 n=32

Hellston 1984 H.S. 2.24+0.05 7.13+0.42 3.23:0.20
n=34 =34

 

 

B.Ffi‘ balsam fir, N.SJ= white spruce.

62

0.85% dw (1982) and mean total sugar values of 3.5% dw
(1981) and 3.92% dw (1982) (Table 16). Mean sugar/nitrogen
ratios were 4.84/1 in 1981 and 4.64/1 in 1982. Nhite spruce
trees in 1981 and 1982 had mean foliar nitrogen values of
1.24% dw (1981) and 1.20% dw (1982) and mean total sugar
values of 3.32% dw (1981) and 3.67% dw (1982) (Table 16).
Mean sugar/nitrogen ratios ranged from 2.7/l in 1981 to

3.03/1 in 1982.

Lower Michigan/Wisconsin

 

Mean foliar nitrogen levels in balsam fir trees at
Kellogg Forest, Michigan in 1983 and 1984 were 1.60% dw
(1983) and 1.90% dw (1984) (Table 17). Mean total sugar
values were 4.20% dw (1984) and 5.42% dw (1983), while mean
sugar/nitrogen ratios were 2.32/1 in 1984 and 3.34/1 in
1983. Foliar nitrogen levels in Kellogg white spruce trees
were 1.38% dw (1983) and 1.80% dw (1984) (Table 17). Mean
total sugar values were 3.25% dw (1984) and 9.63% dw (1983),
while mean sugar/nitrogen ratios ranged from 1.85/1 in 1984
to 6.95/1 in 1983. White spruce at Hellston, Michigan in
1984 had a mean foliar nitrogen value of 2.24% dw, mean
total sugar value of 2.13% dw and a mean sugar/nitrogen
ratio of 3.23/1 (Table 17). Balsam fir trees at Antigo,
Wisconsin in 1984 had a mean nitrogen value of 2.84% dw,
mean total sugar value of 6.86% dw and a mean sugar/nitrogen

ratio of 2.6/1 (Table 17).

63

Insect Performance

Northern Minnesota

 

Insect performance clearly varied by host tree species.
Performance variables which were measured included; combined
male and female percent survival to the adult stage and male
and female adult dry weight (Table 18L.Balsam fir was by
far the most suitable host with an overall grand mean female
adult dry weight of 19.3 mg compared to 16.2 mg on white
spruce and 10.6 mg on black spruce. Males showed the same
pattern between species. There were little or no differences
between years on the same host species, at least with
respect to adult weight. This was not true for survival.
For example, on balsam fir, survival ranged from a low of
12.4% (1984) to 30.4% (1981). On white spruce it ranged from
a low of 21.3% (1981) to 34.9% (1982). On black spruce
survival was 9.7% in 1981 but increased to 26.9% in 1982.

Lower Michiggngisconsin

 

 

Differences existing among host species from
International Falls were not so evident from comparable
field studies in Lower Michigan and Wisconsin (Tables 19,
20). Mean female and male weights on balsam fir were
similar to those on white spruce.As before, there were no

apparent differences between years on the same host species

64

Table 18. Grand mean values + standard error for insect
performance variabTes on a per tree basis. n=
number of trees per study.

 

 

Performance Variables1

StudyArea/Yr/TreeSp.2 % Surv Fwt th
I.Falls 1981 B.F. 30.410.02 19.810.48 9.810.17
n=31 n=31 n=31
I.Falls 1982 B.F. 27.5:0.02 20.810.59 12.3:0.37
n=30 n=30 n=30
I.Falls 1981 W.S. 21.310.02 15.5:O.7l 7.8:O.36
n=18 n=18 n=18
I.Falls 1982 W.S. 34.910.02 16.910.84 9.810.43
n=20 n=20 n=20
Cromwell 1981 Bk.S. 9.710.01 10.711.10 5.810.51
n=16 n=16 n=16

Cromwell 1982 Bk.S. 26.930.02 10.510.45 6.510.29
n=15 n=15 n=15

 

 

% surv= combined male and female % survival to the adult
stage, fwt= female adult dry weight, mwt= male adult dry
weight.

2 I.= International, BJK= balsam fir,1LS.= white spruce,
Bk.S.= black spruce

65

 

 

 

 

 

Table 19. Grand mean values + standard error for insect
performance variabTes on a per tree basis. n=
number of trees per study.

Study Area lyear/tree species1

Performance2 Kellogg Kellogg I.Falls Antigo

Variables 99 9999 99 3.1 99 99:. 99 9.9-

% Surv 24.810.02 37.7:0.02 12.4:0.02 19 310.01
n=20 n=34 n=ll n=28

Fwt 20.210.86 21.2:0.74 19.1:0.66 20 510.69
n=20 n=34 n=ll n=28

th 10.4:0.40 10.610.23 10.0:0.48 10.7:0.27
n=20 n=34 n=11 n=28

Fagt 0.42:0.02 0.46:0.02 0.41:0.02 0.44:0.02
n=20 n=34 n=11 n=28

Magt 0.2210.01 0.23:0.01 0.22:0.01 0.23:0.01
n=20 n=34 n=11 n=28

Fadt 2.09:0.02 2.17:0.01 2.15:0.02 2.15:0.01
n=20 n=34 n=ll n=28

Madt 2.13:0.02 2.19:0.01 2.16:0.01 2.17:0.01
n=20 n=34 n=11 n=28

1

B.F.= balsam fir, I.= International

% Surv= combined male and female % survival to the adult
stage, fwt= female adult dry weight, mwt= male adult dry
weight, fagt= female adult growth rate (mglda), magt= male
adult growth rate (mglda), fadt= female adult deve10pment
rate (%lda), madt= male adult development rate (%/da).

66

 

 

 

 

 

Table 20. Grand mean values + standard error for insect
performance variables on a per tree basis. n=
number of trees per study.

Study Area lyear/tree species1
Performance2 Kellogg Kellogg Wellston
Variables 99 9.9. 999999 99 9999
% Surv 26.830.02 43.5:0.02 47.4:0.02
n=33 n=32 n=34
Fwt 21.0:0.63 20.010.58 18.810.71
n=33 n=32 n=34
th 11.530.32 10.110.23 10.010.27
n=33 n=32 n=34
Fagt 0.44:0.01 0.45:0.01 0.44:0.02
n=33 n=32 n=34
Magt 0.25:0.01 0.23:0.01 0.24:0.01
n=33 n=32 n=34
Fadt 2.09:0.01 2.24:0.01 2.32:0.01
n=33 n=32 n=34
Madt 2.16:0.01 2.23:0.01 2.35:0.01
n=33 n=32 n=34
1

W.Su= white spruce

% Surv= combined male and female % survival to the adult
stage, fwt= female adult dry weight, mwt= male adult dry
weight, fagt= female adult growth rate (mglda), magt= male
adult growth rate (mglda), fadt= female adult development
rate (%lda), madt= male adult development rate (%ldaL

67

for adult weight. Survival, however, did vary between
years. On balsam fir trees, it ranged from a low of 19.3%
(1984 Antigo) to 37.7% (1984 Kellogg). On white spruce,
survival ranged from a low of 26.8% (1983 Kellogg) to 47.4%
(1984 Wellston).

Regression Relationships Between Insect Performance

and Foliar Sugar and Nitrogen

Northern Minnesota

 

Foliar sugar and nitrogen levels apparently had little
effect on tree to tree variation in budworm survival rates.
Regression analyses indicated that in only two of six cases
(Table 21) were either sugars (+G) or nitrogen (+Log N2)
linked to survival. Female weight was positively linked to
nitrogen levels (N2, LogNz) in three of six cases and in one
case to levels of glucose. Male weight was positively linked
to nitrogen in one case (N , LogN ) and to sugars (+F,-G,-

S/N) in another.

Lower Michigan lNorthern Wisconsin

 

 

As before, foliar sugar and nitrogen levels apparently
had little effect on tree to tree variations in budworm
survival. The regression analyses indicated that in only two

of seven cases were either sugars (+G) or nitrogen (+LogN)

68

Table 21. Regression relationships between insect
performance variables and selected host plant
nutrients. (+) or (-) indicates significant
(p <.05) positive or negative correlation
coefficients.

 

 

Performance Variables1

StudyArea/Yr/TreeSp.2 % Surv Fwt th
I.Falls 1981 B.F. +LogN2 +F-G-S/N
I.Falls 1982 B.F. +LogN2
I.Falls 1981 W.S. +G +LogN2
I.Falls 1982 W.S. +8

2 2 2
Cromwell 1981 Bk.S. +N +N +LogN

Cromwell 1982 Bk.S.

 

 

% surv= combined male and female % survival to the adult
stage, fwt= female adult dry weight, mwt= male adult dry
weight, F= fructose, G= glucose, N= nitrogen, S= total
sugar, S/N= sugar/nitrogen ratio

2 (S)=small, (M)= medium and mature,

1. International,
B.F.= balsam fir, W.Sa= white spruce, Bk.S.

black spruce

69

linked to survival (Tables 22,23). Female weight was linked
to sugars in two cases (+F, -S/N) while male weight was
linked to sugars in three cases (+F, +52, -S/N). The mean
number of days to adult eclosion for females was linked to
either sugars(+SZ, -LogS)cH'nitrogen(-LogN, -N2,-LogN2)
in four out of seven cases. Number of days to adult eclosion
was positively linked to sugar in only one case (+52).
Female adult growth rate was linked to sugars only (+F,
-LogS)in three of seven cases while male adult growth rate
was linked to sugars in four cases.(+F, -Sz, -LogS) and to
nitrogen in one case (+N L.Female adult development rate
was positively linked to nitrogen in two cases (+LogN, +N2)
and to sugars in two cases (-52, +LogS). Male adult
development rate was positively linked to sugars in one case
only (-SZ).

For both areas in which experiments using balsam fir
were performed (Northern Minnesota and Lower
Michigan/Wisconsin) there were no clear, consistant nitrogen
and sugar effects on budworm performance between years.
There were, however, some consistant patterns within a
single year at one experimental site. For example, on
balsam fir trees at Kellogg in 1984, sugar levels (fructose)
showed a clear pattern of positive consistent linkage to
budworm growth (male and female adult weight and male and
female adult growth rates). The same was true on balsam fir
trees at Antigo in 1984 where sugars ($2, LogS) were

consistently linked to rates of growth and development (male

70

Table 22. Regression relationships between insect
performance variables and selected host
plant nutrients. (+) or (-) indicates
significant (p < .05) positive or negative
correlation coeTficients.

 

 

Study Area lyear/tree species1

 

 

 

Performance2 Kellogg Kellogg I.Falls Antigo
Variables 83 835; 85 83:; 83 8.5- 85 835;
% Surv +LogN
Fwt +F
th +F
Fd -LogN+F -LogN2 +Sz-LogS
Md +S2
Fagt +F
Magt +F +N2 -S2
Fadt +LogN-F -SZ+L0gS
Madt -S2
1

B.Fn= balsam fir, F= fructose, N= nitrogen, S= total
sugar

% Surv= combined male and female % survival to the adult
stage, fwt= female adult dry weight, mwt= male adult dry
weight, Fd= days to female adult development, Md= days to
male adult development, fagt= female adult growth rate
(mglda), magt= male adult growth rate (mglda), fadt= female
adult development rate (%lda), madt= male adult development
rate (%lda).

71

Table 23. Regression relationships between insect
performance variables and selected host
plants nutrients. (+) or (-) indicates
significant U3< .05) positive or negative
correlation coefficients.

 

 

Study Area lyear/tree species1

 

Performance2 Kellogg Kellogg Wellston
1111151.. 99 9999 99 9999 99 999.
% Surv +G

Fwt +F-S/N
th +52 +F-S/N
Fd -N2

Md

Fagt +F-LogS
Magt +F +F-LogS
Fadt +N2

Madt

 

 

1 WJL= white spruce, F= fructose, N= nitrogen, G= glucose,
S= total sugar, S/N= sugar/nitrogen ratios

% Surv= combined male and female % survival to the adult
stage, fwt= female adult dry weight, mwt= male adult dry
weight, fd= days to female adult devel0pment, md= days to
male adult development, fagt= female adult growth rate
(mglda), magt= male adult growth rate (mglda), fadt= female
adult deve10pment rate (%lda), madt= male adult development
rate (%lda).

72

and female days to adult eclosion, male and female adult
development rates and male adult growth rateL White spruce,
like balsam fir, also showed no consistent nitrogen or sugar
effects on budworm performance between years or study areas.
There were, however, some consistent patterns within a year
for the same experimental site. For example, on white spruce
trees at Wellston in 1984, sugars (+F, +G, -LogS,) were
linked to budworm growth and survival with five positive
correlations (% survival, male and female adult weight and
male and female adult growth rate) and two negative

correlations (male and female adult growth rateL

Discussion

Quantities of soluble sugars and nitrogen as well as
the relative proportions of these nutrients play important
roles in the growth and development of the spruce budworm.
This agrees in part with the work of Harvey (1974), who
evaluated budworm performance on artificial diets with
sugar/nitrogen ratios ranging from 1.10/1 to 8.82/1. He
found that female spruce budworm pupal weight increased to a
maximum (114.9, mg n=43) on diets containing roughly 4%
nitrogen and a sugar/nitrogen ratio of 8.82/1. In tme
present study, maximum female pupal weight (106.2 mg, n=99

to 114.1 mg, n=128) occurred on diets containing 4.9%

73

nitrogen with sugar/nitrogen ratios between 1.31/1 and
2.61/1 (Figure 14). On diets containing one half the
ammount of nitrogen (2.45%), maximum female pupal weight
(105.0 n=53 to 107.0 n=9l) occurred on a larger and broader
sugar/nitrogen range (5.24/1 to 10.49/1) (Figure 14). Harvey
(1974) further found that female larval survival to the
pupal stage was positively correlated with increasing
sugar/nitrogen ratios. He found that on diets containing 4%
nitrogen, survival was poorest (29.6%) at a sugar/nitrogen
ratio of 1.10/1 and highest (46.6%) at a ratio of 1.98/1. 0n
diets containing 4.9% nitrogen 'hi the present study,
maximum male and female survival (72.0%) occurred at a
sugar/nitrogen ratio of 2.61/1 whereas minimum survival
(45.5%) occurred at a: sugar/nitrogen ratio of 1.31/1 (Table
1 and Figure 1).0n diets containing one half that amount
of nitrogen (2.45%), maximum survival (52.2%) occurred at a
ratio of 5.24/1 whereas minimum survival (24.5%) occurred at
a ratio of 15.73/1 (Table 1 and Figure 1). Harvey (1974)
also measured pupal development rate (%lda). He found that
on diets containing 4% nitrogen, female pupal development
rate generally increased with increasing sugar/nitrogen
ratios. The slowest development (3.70%lda, n=15) occurred at
a sugar/nitrogen ratio of 1.98/1 and fastest development
(4.35%lda, n=43) at a sugar/nitrogen ratio of 8.82/1. The
present study measured development rates for females on
diets containing 4.9% nitrogen and found that slowest rates

(3.18%lda, n=480, and n=162) occurred at two sugar/nitrogen

74

ratios; 3.93/1 and 0.73/1 and fastest rates (3.47%/da,
n=285) occurred at a ratio of 2.61/1 (Table 10 and Figure
10). On diets containing 2.45% nitrogen, the slowest
development rate (2.45%/da, n=30) occurred at a
sugar/nitrogen ratio of 15.73/1 and the fastest development
rate (2.91%lda, n=43) at a ratio of 5.24/1.

Although the study of Harvey (1974) and the present
study do not always agree on specific values, it is obvious
that both studies demonstrate that there is an optimal
sugar/nitrogen ratio, and that this optimal ratio seems to
be most dependent upon the level of nitrogen in the diet.

The present study included experiments with diets
containing 1.38% nitrogen, which had sugar/nitrogen ratios
ranging from 2.59/1 (3.55% sugar) to 28.0/1 (38.46% sugar).
Here, peak performance occurred across a broad
sugar/nitrogen range, extending from 2.59/1 to 18.67/1. This
probably occurred partly because of small sample sizes but
also was due to the increased importance of soluble sugars
at such low levels of nitrogen.

It should be pointed out that the low level nitrogen
diets (1.38 and 2.45%) contained reduced levels of wheat
germ, the source of the budworm's fattyacids. Commercial
wheat germ1is made up of approximately 10.8% lipid (Hlynka
1964). Roughly 84% of the fatty acids contained within this
lipid portion are in the unsaturated form, mostly linoleic
a, linoleic b and oleic acids. The major saturated fatty

acids in wheat germ are palmitic and stearic acids. Most

.75

insects display an absolute requirement for polyunsaturated
fatty acids whereas saturated and monosaturated fatty acids
may be synthesized from non-lipid precursors (Downer 1978).
To study the significance of this loss, I prepared two sets
of diets containing 2.45% nitrogen to which fatty acids were
applied. In these experiments one ml each of linoleic and
linolenic acids or twatnlscfliwheat germ oil were added to
the casein portion of the diet media via an acetone solvent.
Female pupal weights on diets containing added fatty acids
or added wheat germ oil were significantly lower (Duncans
multiple range test, (p 5 .05) than the equivalent diets
containing no added oils (Table 15). Thus, it would seem
that the reduction in fatty acids at the 2.45% level of
nitrogen was not a significant factor affecting growth.
Whether this reduction in fatty acids was in some way
responsible for the poor response of the budworm at the
lowest nitrogen level (1.38%) remains unknown from the
results of this study.

In addition to fatty acids, wheat germ is also an
important source of minerals for the budworm in artificial
diets. Minerals such as manganese, phosphorous and potassium
at appr0priate levels have positive effects on fecundity and
growth (House 1965). Because minerals can be important in
trace amounts, and are often present in trace amounts in
various components of artificial diets, itis often very
difficult to formulate diets of a known mineral content

(Fraenkel 1958). Indeed, this was a problem in this study

76

because in reducing nitrogen levels by manipulation of
wheat germ content, mineral levels were also reduced.
Whether this reduction in mineral levels was in some way
responsible for the poor performance of the budworm at low
nitrogen level diets(flq38) cannot be ascertained from the
results of these experiments.

At the very highest sugar level (38.46%) budworm frass
contained about 8% dw sugar, demonstrating that sugar levels
were far beyond that which could be fully utilized (Figure
17). Increasing nitrogen while maintaining the same sugar
level (38.46%), did not change the amount of sugars
occurring in budworm frass. Sugars in frass were exclusively
in the form of fructose and glucose whereas the diet
contained almost exclusively sucrose (HPLC analysis). Thus
it would seem to be a very costly process for spruce budworm
to ingest and break down sucrose into its component parts
and then not utilize them for energy.At.sugar levels less
than or equal to 25.64%, budworm frasscontained only 1%
sugar or less at all nitrogen levels (Figure 17). Moreover,
at levels less than or equal to 6.41% sugar at all nitrogen
levels, frass contained virtually no soluble sugars at all.
It appears then, that budworms can metabolize nearly all the
sugars occurring in it's diet provided sugars do not exceed
about 25% dw.

This study utilized diets containing 6.41% nitrogen in
an effort to exceed the budworm's optimal level of dietary

nitrogen. These diets had sugar/nitrogen ratios extending

77

from 0.55/1 to 3.0/1. For most performance measures there
were little or no differences between sugar levels. Most
growth measurements were only slightly below values recorded
on diets containing the next lowest level of dietary
nitrogen (4.90%). Thus, it would seem that the budworm is
generally less sensitive to the deleterious effects of supra
optimal levels of dietary nitrogen compared to supra optimal
levels of dietary sugar.

Albert et al. (1982) found that the behavioral
threshold for sucrose was between 0.0001 and 0.001 M. My
study utilized diets which had molar concentrations of
sucrose well above this threshold (0.02 M, 3.55% sugar to
0.20 M, 38.46% sugar). Diets at sugar levels of 3.55 and
6.41% sugar (0.02 and 0.03 M) fel 1 into the range of optimal
feeding response1(0.01 to 0.05 M; Albert et al. 1982). The
remaining sugar levels; 12.80% (0.06 M), 19.23% (0.09M),
25.64% (0.12 M) and 38.46% (0.20M), exceeded the optimal
range. The highest level of sugar (38.46%, 0.20 M) may in
fact have served as a feeding deterrent rather than as a
feeding stimulant.

Soluble sugars have been shown to be an important
component of spruce budworm diet. Harvey (1974) reared
budworm on artificial diets containing no soluble sugars and
about 6.3% nitrogen. On these diets there were low pupal
weights, long development times and poor survival (19%)
although some were able to survive and lay fertile eggs.

This study demonstrates that sugars become more important as

78

nitrogen becomes limiting and that the budworm is generally
far more sensitive to changing nitrogen levels than to

changing sugar levels in artificial diets.

Field Studies

 

Balsam fir was the most suitable host plant in terms
of budworm performance followed by white and black spruce.
Mean nitrogen and sugar levels were not consistently
different between species from year to year except for black
spruce, which had consistantly low nitrogen levels. Mean
foliar nitrogen levels were relatively uniform within
species across all years. Mean total sugar levels, however,
from balsam fir trees at International Falls, Minnesota
increased yearly from 1981 (2.88%) to 1983 (8.12%) after
which they declined slightly in l984(7.64%L.The reasons
for this upward trend are not known. However, it is of
interest to note that mean rainfall recorded at the
International Falls weather station for the 21 day period
prior to foliage collection followed a similar upward trend
(NOAA 1981-1984) and when regressed on mean total sugars
showed a positive relationship (r2=.91, significant at p
<.05). Mean temperature for 21 days prior to foliage
collection was variable between years and showed no
significant (p >.05) trend. More work is needed, however, to
determine if rainfall has an immediate effect on foliar

sugar levels.

79

Balsa01fir and white spruce foliar sugar and nitrogen
levels varied considerably throughout the period of budworm
larval development as well as from year to year. The ratios
of these two nutrients were highly variable within and
between years. The budworm must therefore be able to adjust
to these changes during it's lifetime as well as from
generation to generation.

Nitrogen and sugar effects did not appear to be
consistantly related to budworm performance in the field
studies. This may have occurred because the budworm can
compensate for fairly wide variations in these nutrients so
that their effects on budworm 'fitness" are minimized. For
example, larvae of other insects confronted with
nutritionally poor foliage have been found to increase
their rate of consumption or improve their digestive
efficiency (Slansky and Scriber 1985). Conducting more field
and laboratory studies such as those described in this
thesis, along with studies of feeding behavior and digestive
physiology would further clarify the relationships between

this insect and it's host plants.

80

CONCLUSIONS

Diet Matrix Study

 

. The optimal sugar/nitrogen ratio for all growth

variables at every sugar and nitrogen level was 2.61/1
(4.90% nitrogen and 12.80% sugar)

. The optimal ratio of dietary sugar/nitrogen varied

according to the level of nitrogen in the diet, but
generally increased when dietary levels of nitrogen were
low. This demonstrated an increased importance of sugar
when dietary nitrogen was low.

Supra optimal levels of dietary sugar (> 30% dw)were
deleterious to spruce budworm growth and development.

Supra optimal levels of dietary nitrogen reduced growth
slightly but were not as deleterious as supra optimal
levels of sugar.

Reductions in fatty acid and mineral levels may be an

important factor in the poor response of the budworm at
the lowest level of nitrogen (1.38%).

Field Studies

 

1. Balsam fir was the most suitable host plant in terms of

2.

budworm performance followed by white and black spruce.

Levels of balsam fir and white spruce foliar sugar and
nitrogen varied considerably throughout the life cycle
of the budworm.

Levels of foliar sugar and nitrogen were variable from
year to year and may have been dependent on such factors
as precipitation and temperature.

The ratios of these two nutrients from year to year and
within the same year were therefore highly dynamic. The
budworm must be able to adjust and accomodate to such
changes between and within generations.

81

Nitrogen and sugar effects did not appear to be
consistantly related to budworm performance. This may be
due to the fact that budworms may behaviorally or
physiologically compensate for fairly wide variations in
these nutrients so that their effect on budworm
"fitness" is minimized.

REFERENCES CITED

82

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