Attack, reproduction, and development of Ips calligraphus (Coleoptera: Scolytidae) in relation to temperature and slash ...

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Title:
Attack, reproduction, and development of Ips calligraphus (Coleoptera: Scolytidae) in relation to temperature and slash pine phloem thickness
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x, 178 leaves : ill. ; 28 cm.
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Haack, Robert Allen, 1952-
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Subjects / Keywords:
Bark beetles   ( lcsh )
Ips calligraphus   ( lcsh )
Pine -- Diseases and pests   ( lcsh )
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bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1984.
Bibliography:
Includes bibliographical references (leaves 166-177).
Statement of Responsibility:
by Robert Allen Haack.
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Typescript.
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Vita.

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University of Florida
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Full Text











ATTACK, REPRODUCTION, AND DEVELOPMENT OF
IPS CALLIGRAPHUS (COLEOPTERA: SCOLYTIDAE)
IN RELATION TO TEMPERATURE AND
SLASH PINE PHLOEM THICKNESS






BY


ROBERT ALLEN HAACK


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY



UNIVERSITY OF FLORIDA


1984














ACKNOWLEDGHENTS


I sincerely appreciate the time and guidance unselfishly

contributed to this study by my major advisor Professor

Robert C. Wilkinson, Jr. I am indebted to the other members

of my supervisory committee, Associate Professor George M.

Blakeslee, Jr., Associate Professor John L. Foltz, and

Assistant Professor Frank Slansky, Jr., for their guidance

and assistance throughout the course of these

investigations. Special thanks are extended to Dr. Jeffrey

A. Corneil for his assistance in field, laboratory, and

computer programming aspects of this study.

I as deeply indepted to my wife Sheridan for the sharing

of her thoughts, her time, and her smile.

Appreciation is extended to Ovens-Illinois Inc. for

allowing access to their slash pine plantations and to Mr.

G. William Schlitzkus, of Owens-Illinois, for his time and

efforts.

Thanks are also extended to the faculty and fellow

students of the Department of Entomology and Nematology for

advice, assistance, and a stimulating atmosphere in which to

learn.

This research was supported in part by the U.S.

Department of Agriculture under the program entitled "The








Integrated Pest Management RD&A Program for Bark Beetles of

Southern Pines" (Southern Forest Experiment Station

Cooperative Agreement 19-81-8 with the University of

Florida).


iii
















TABLE OF CONTENTS



PAGE

ACKNOWLEDGMENTS . ii

ABSTRACT .. a . .. viii


CHAPTER

I. INTRODUCTION . a .. 1

II. GALLERY CONSTRUCTION AND OVIPOSITION BY IPS
CALLIGRAPHUS (COLEOPTEBA: SCOLYTIDAE) IN
ELATION TO TEMPERATURE AND SLASH PINE PHLOEM
THICKNESS . . 3


Introduction a .a a
Methods and Materials a a a a a a
Bark slab preparation . .
Source of experimental beetles a a
Introduction of beetles into bark slabs


Data collection .
Analyses . .
Results a a a a a a a a
Beetle size . .
Oviposition rate (OR) a a a .
Gallery construction rate (GCR)
Initial egg-free gallery (PRE-EG)
Egg density (ED) a .
Depth of xylea-etching (DIE) .
Discussion a a a a .
Summary a .


III. LONGEVITY AND FECUNDITY OF IPS CALLIGRAPHUS
(COLEOPTEBA: SCOLYTIDAE) IN RELATION TO
SLASH PINE PHLOEM THICKNESS .

Introduction. a
Methods and Materials. .
Bolt preparation .
Source of experimental beetles a .
Introduction and transfer of beetles .
Data collection a a a .
Analyses . .


* a a 7
a a a a 8
* a a 9
. 9
. .. 10
a a 10
. .11
. 11
- 12
. a 17
. 20


. 22

. 22
. 23
. 23
. 24
. 25
. 26
. 28








Results . . 29
Female size . 29
Longevity . 29
Total gallery length (TGL) . 30
Gallery construction rate (GCR) 30
Realized fecundity a. 31
Oviposition rate (OR) a ... 31
Egg density (ED) a a a a a 0 8 32
Phloem water content (PWC) . 33
Discussion a . 42
Summary ... 44

IV. IPS CALLIGRAPHUS RE-EMERGENCE, BROOD DEVELOPMENT,
BROOD PRODUCTION PER PARENT FEMALE, AND
BROOD-ADULT EMERGENCE, PRONOTAL VIDTH, AND
SEX RATIO IN RELATION TO TEMPERATURE AND
SLASH PINE PHLOEM THICKNESS . 46

Introduction a a a a a a a a a 46
Methods and Materials . 47
Bolt and bark slab preparation .a 47
Source of experimental beetles .. 48
Introduction of beetles into bolts and
bark slabs . 49
Data collection .* a .a 50
Analyses . 51
Results a a a a a a a a a a 52
Re-emergence of parent adults a, a 52
Brood development 53
Brood adult production per parent female 53
Brood adult emergence .* 53
Brood adult pronotal width a 54
Brood adult sex ratio 54
Discussion .. . 67
Re-emergence of Parent Adults .a 67
Development and Brood Adult Characteristics 68
Summary . a a .. 76

V. SEASONAL DEVELOPMENT AND DIURNAL ACTIVITY PATTERNS OF
IPS CALLIGRAPHUS IN FLORIDA 78

Introduction . 78
Methods and Materials .80
Tree selection and treatment a .a 80
Brood adult collection .* 81
Generation synchronization .. 82
Data collection and analyses a 83
Day-degree accumulation a a a a a *. 84
Results . . 86
Voltinism, generation time, and brood
emergence . 86
Sex ratio and brood density a 87
Diurnal and seasonal activity patterns 87
Day-degree accumulation .. a a* 88








Discussion . . 100
Seasonal development . 100
Male and female emergence 101
Sex ratio . 102
Brood density ... 103
Diurnal activity patterns .. 104
Day-degree accumulation 107
Summary . 110

VI. FIELD STUDIES ON SPATIAL ATTACK PATTERN,
REPRODUCTION, AND BROOD DEVELOPMENT OF IPS
CALLIGRAPHUS IN RELATION TO SLASH PINE PHLOEM
THICKNESS . 112

Introduction 112
Methods and Materials a a 113
Tree selection *. 113
Bolt preparation 114
Male introduction into bolts 1. 14
Exposure of bolts on turntables 115
Bolt mapping a a 116
Installment of emergence traps on bolts 117
Data collection and analyses 118
Initial analyses 118
Spatial attack pattern . 119
I-delta of Morisita 120
The index R of Clark and Evans and of
Thompson a & a a a a a a a 120
Pielou's index of non-randoaness, I-alpha 121
The Hopkins and Skellam index A 122
Attack density . 122
Harem size a 123
Gallery density . 123
Egg density a. a 124
Time to 50% brood emergence 125
Brood density . 126
Egg-to-adult mortality a 126
Sex ratio . 126
Pronotal width .. a 126
Results . . 127
Spatial attack pattern .* 127
Attack density . 128
Harem size .. . 128
Gallery density . 129
Egg density *. .. 130
Time to 50% brood emergence 131
Brood density .. 131
Egg-to-adult mortality 132
Brood sex ratio a 132
Body size . 132
Discussion a .. .*. 147
Spatial attack pattern . 147
Attack density .., .. 150
Harem size . 152








Gallery density 153
Egg density . 154
Time to 50% brood emergence .. a 157
Brood density . 158
Egg-to-adult mortality ... .* 158
Sex ratio .. . 159
Body size . 159
Summary . 160

VII. CONCLUSIONS a a . 162

LITERATURE CITED . .. 166

BIOGRAPHICAL SKETCH a a . 178


vii














Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy



ATTACK, REPRODUCTION, AND DEVELOPMENT OF
IPS CALLIGRAPHUS (COLEOPTERA: SCOLYTIDAE)
IN RELATION TO TEMPERATURE AND
SLASH PINE PHLOEM THICKNESS


By


Robert Allen Haack


April 1984


Chairman: Dr. Robert C. Wilkinson
Major Department: Entomology and Nematology



Ips calligraphus (Germar) is the major scolytid pest of

typical slash pine, Pinus elliottii Engelmann var.

elliottii, the principal crop tree grown in Florida forests.

Field reports and rearing experience suggested that I.

calligraphus infestations and reproductive success were

greatest in slash pines with relatively thick phloem (inner

bark), but experimental evidence for such a relationship was

lacking.

Effects of temperature and slash pine phloem thickness on

I. calliqraphus attack, reproduction, and brood development


viii








were investigated in laboratory and field studies conducted

in north-central peninsular Florida. Adult females average

1.8 am in pronotal width and construct egg galleries

primarily in phloes at the phloea-xyles interface. For

experimental purposes, "thick" phloem (>beetle width)

generally ranged from 2.5-4.0 mm and "thin" phloem (
width) from 0.5-1.5 mm in thickness.

In laboratory studies, female longevity was 66% greater

and fecundity 104% greater in thick vs. thin phloem at 300C.

Gallery construction rate and parent-adult residence time

were temperature- (positively and negatively correlated,

respectively) but not phloem thickness-dependent at 200,

250, and 300C, Reproduction was best in thick phloem at

300C and poorest in thin phloem at 20oC.

In field studies, I. calliqraphus completed 9

generations/year in thick phloem. The distribution of male-

constructed nuptial chambers was regular regardless of

phloes thickness. Nuptial chambers/da2, egg gallery/dm2,

eggs/da2, brood/da2 and brood survival were all positively

correlated with phloes thickness.

In both laboratory and field studies, performance was

greater on thick vs. thin phloem considering mean eggs/ca of

gallery (38-49% greater), brood adults/parent female

(46-107%, laboratory), brood adults/dn2 of bark (194%,

field), and brood adult pronotal width (8% male, 6% female).

Time to 50% brood adult emergence occurred 3-4 days sooner

on thicker phloem.








Both temperature and phloea thickness were significant

factors in the population dynamics of I. calligraphus. This

has important implications for rearing, sampling, and

population modeling of this bark beetle.














CHAPTER I
INTRODUCTION


Ips calligra2hus (Germar) (Coleoptera: Scolytidae) is one

of the principal bark beetle pests of pines in the

southeastern USA (Wilkinson and Foltz 1980, 1982; Connor and

Wilkinson 1983), and of typical slash pine, Pinus elliottii

Engelmann var. elliottii, in particular (Fatzinger et al.

1983). In Florida, where slash pine is the most important

forest crop tree grown (Sheffield et al. 1983), 1.

calliqraphus has been associated with increased tree

mortality in slash pine plantations since 1960 (Chellman

1980).

Two historical points prefacing this study are that (1)

laboratory rearing experience indicated that 1. calligraphus

reproduced best in slash pine logs with relatively thick

phloem (inner bark), and (2) in north Florida, I.

calligraphus infestations have been greatest in plantations

of rapidly growing slash pine trees (G. W. Schlitzkus,'

personal communication), which typically have thicker

phloem. Phloem thickness is known to be a key factor in

adult reproduction and brood production of the mountain pine

beetle, Dendroctonus ponderosae Hopkins (Coleoptera:
-- ---e- -e


Forester, Owens-Illinois Inc. Hawthorne, Florida 32640.

1






2

Scolytidae), in the western USA (Amman 1972; Amman and Pace

1976; Amman and Cole 1983). The importance of phloem

thickness in the population dynamics of the mountain pine

beetle is well-recognized as indicated by its inclusion in

pest management guidelines (Amman et al. 1977) and risk

decision models (Berryman 1982).

The studies described herein were conducted in

conjunction with the research program entitled "Sampling and

Dynamics of Back-infesting Beetles in Slash Pine

Plantations," which was funded in part by the U.S.

Department of Agriculture under the program entitled "The

Integrated Pest Management RD&A Program for Bark Beetles of

Southern Pines." The specific objective of my research was

to investigate I. calligraphus attack, reproduction, and

development in relation to temperature and slash pine phloem

thickness under both laboratory and experimental field

conditions. If temperature and phloes thickness were found

to be significant factors in the population dynamics of this

bark beetle, the findings could be incorporated into future

sampling schemes and pest management guidelines for use in

the slash pine ecosystem.














CHAPTER II
GALLERY CONSTRUCTION AND OVIPOSITION BY IPS CALLIGRAPHUS
(COLEOPTERA: SCOLYTIDAE) IN RELATION TO TEMPERATURE AND
SLASH PINE PHLOEM THICKNESS



Introduction

Bark beetles (Coleoptera: Scolytidae) construct their egg

galleries primarily within the phloem (inner bark) tissue of

their hosts, at the phloem-xylem interface (Stark 1982).

The thickness of the phloem layer, relative to the beetle's

size, is important wAen considering the relative proportions

of phloem, xylem, and outer bark through which it tunnels.

Since Ips females walk on their tibiae and rotate along

their longitudinal axes when tunneling (Schmitz 1972; Gouger

et al. 1975), the maximal pronotal width (PW) can be

considered one measure of beetle size and serve as an

estimate of minimum egg-gallery diameter.

In the relatively large mountain pine beetle

(Dendroctonus ponderosae Hopkins; mean PW=2.5 am, estimated

from data in Wood 1982), reproduction was significantly

affected by phloem thickness over the range 1.6-4.8 mm in

lodgepole pine (Pinus contorta Douglas) (Amman 1972; Amman

and Pace 1976). However, for the much smaller southern pine

beetle (Dendroctonus frontalis Zimmermann; mean PW=1.2, mood

1982) no significant relationship was found between its








reproduction and phloes thickness in loblolly pine (Pinus

taeda L.) (Wagner et al. 1981a). In that study, phloes

thickness generally ranged from 1.1-1.6 am (T. L. Wagner,'

personal communication).

Ips calliqraphus (Germar) is a major pest of pines in the

southeastern USA (Wilkinson and Foltz 1980), and of typical

slash pine (Pinus elliottii Engelmann var. elliottii) in

particular (Chellaan 1980). No studies on the relationship

between phloes thickness and I. calligraphus reproductive

performance have been reported. This bark beetle is

relatively large (aean PW=1.8 ma, Wood 1982), and in slash

pine growing in Florida, phloem thickness commonly ranges

over 0.5-4.0 am (unpublished data). Thus a relationship

like that between D. ponderosae and P. contorta may exist

between I. calligraphus and P. elliottii. The objective of

this study was to quantify several measures of I.

calligraphus reproduction in relation to slash pine phloem

thickness, temperature, and season of year.
















1 Department of Entomology, Texas AS& University, College
Station, Texas 77843.






5

Methods and Materials


Bark slab preparation. Bark slabs were prepared from 20-

to 21-year-old, dominant and co-dominant slash pines growing

in a plantation with a site index of 58 ft (17.6 a) at 25

years, near Orange Heights, Alachua County, Florida. Five

trees for the fall study and 4 trees for the summer study

were felled on 30 September 1981 and 16 June 1982,

respectively. The selected trees had phloes thicknesses

ranging from 0.5-4.0 am. After felling, bolts (30-35 ca

long) were cut from the trunks between the first and fifth

meter, measured from groundline. The bolts were labelled,

end-dipped in a benoayl fungicide-water solution (1%), and

dried for 3-4 days at 40Oo and 40-50X relative humidity

(RH). Following drying, loose outer bark flakes were shaved

from each bolt, bark at the bolt ends was pared until

unstained phloea was detected, bolts were grooved on a table

saw, and bark slabs (29-33 cm long, 10-14 ca wide, 2-4 ca

thick) were cut away by splitting with ax and hammer. Each

slab was coated with paraffin on all cut edges to inhibit

contamination and desiccation.


Source of experimental beetles. The parent adults were

reared from 2 slash pines, naturally infested subsequent to

felling, having ca. 3-ra thick phloem; 1 was felled on 11

September 1981 and the other on 22 May 1982. When most of

the developing brood reached the pupal stage, infested trunk






6

sections were taken to the laboratory and stored in outdoor

emergence cages. Emerging brood adults were collected

several times daily, sexed according to the form of the

third elytral tooth (Hopping 1963), put into containers with

moist paper towels, and stored at 200C until used.


Introduction of beetles into bark slabs. Only mature,

non-injured adults that had been collected within 48 h prior

to the time of introduction were used. Because Amman (1972)

reported a direct relationship between beetle size and both

oviposition rate and egg density in D. ponderosae, the few

relatively large (PW>2.1 ma) or small (PW<1.5 an) adults

collected were not used. Following the methods of Wilkinson

(1964), a "starter hole" (3 mm diam.) was drilled obliquely

through the outer bark to the underlying phloem in the

center of each slab. A single adult male was placed into

the long section of a size 00 gelatin capsule that contained

a ring of paper for footing, and that had been pierced on

the end for ventilation. The capsule was secured over the

starter hole with a ring of Duxseal(R) sealing compound.

Males not actively boring within 1 h after introduction were

replaced. All males were allowed 24 h to construct a

nuptial chamber at 250C. Three females were then serially

introduced in the same manner into each nuptial chamber at

30-45 min intervals. Infested slabs were randomly assigned

to one of 3 temperature treatments: 200 (1), 250 (1), and

30oC (+1) (photoperiod 12L:12D; 55-70% RH). These








temperatures were selected because in Alachua County,

Florida, summer temperatures average near 300C, while in

spring and fall they average near 20oC (Dohrenwend 1978).

The infested slabs were held in ventilated rearing cans

except for about 30 min daily when radiographed (see below).

Each treatment was replicated 18 times in the fall study

(162 females) and 20 times in the summer study (180

females).


Data collection. l2s calliAraEhus egg gallery

construction, which tends to follow the wood grain

(Wilkinson et al. 1967), and concomitant oviposition (Gouger

let al.I 1975) were monitored by x-raying the slabs with a

Faxitron(R) X-ray unit and Kodak(B) AA film. Each infested

slab was radiographed within 1-2 h after introduction of the

females and daily thereafter until the egg galleries had

been extended to the slab ends. After the last radiograph,

the slabs were immediately frozen for 24 h to stop further

development and then stored at ca. 4oC in plastic bags. The

slabs were later dissected to recover the parent adults and

to expose the egg galleries and egg niches located on the

sides of the galleries. Recovered parent adults were stored

by slab and egg gallery number. An acetate tracing of each

slab was made to show the nuptial chamber, egg galleries,

and egg niches. The oviposition pattern was reconstructed

by identifying the daily increments of egg gallery on the

radiographs and marking them on the tracings; egg gallery








was measured in millimeters. In this way, oviposition and

gallery construction were recorded for each female, and

those values were used to calculate egg density (eggs/cm).

The average thickness of the phloem through which each

female tunneled was calculated from 3-4 phloem samples taken

from the sides of each egg gallery during the dissection

process. A dissecting microscope with ocular micrometer was

used to measure phloem thickness to the nearest 0.1 am. The

average depth to which each female etched the xylem was

calculated from two measurements (nearest 0.05 ma) taken

from slab sections cut at right angles to the egg gallery.


Analyses. Data were analyzed by the general linear

models procedures of the Statistical Analysis System (SAS),

version 1979.6. Analyses were based on the first 4 days of

egg gallery construction at 300, first 6 days at 250, and

first 8 days at 200C -- the times when most females were in

close proximity to the slab ends at each temperature. Only

those females that remained alive and constructed gallery

throughout the study were included (171 in summer; 138 in

fall). Mean sizes of parent adults, as determined by

elytral length (measured dorsally) and pronotal width

(measured dorsally at the widest point), was compared both

within and between studies with the Duncan's multiple-range

test. Begressions of oviposition rate (OR, eggs/day),

gallery construction rate (GCR, cm/day), length of initial

egg-free gallery (PRE-EG, am), egg density (ED, eggs/ca),








and depth of xylem-etching (DXE, mm) were each performed

over the entire data set, with phloes thickness (PT) as the

independent variable and season (S) and temperature (T) as

class variables. Significance of all main effects and

interactions was tested at the P<0.05 level. PBE-EG was

determined by measuring the length of gallery from where

each female began tunneling (as determined from the first

radiograph) to her first egg. Linear regression of ED with

PT was performed after log-log transformation of the data

(Steel and Torrie 1980), because of the curvilinear relation

observed between these 2 variables. Egg density was defined

as follows:

ED = total eggs / (total gallery length PRE-EG).


Results


Beetle size. Mean adult size for each sex did not differ

significantly (P>0.05) between studies, nor among

temperature treatments within each study. Therefore, beetle

size is not considered a factor in the response variable

differences noted below. For all recovered adults, mean

pronotal width and elytral length were 1.80 am (+0.09 SD)

and 2.52 (+0.13) for sales (N=100), and 1.71 (+0.08) and

2.50 (+0.12) for females (N=296), respectively. The

relationship between pronotal width (PM, am) and elytral

length (EL, am) by sex was PW = 0.531 + 0.503 EL (r2=0.527,

Sy.x=0.048, N=100) for males, and PW = 0.419 + 0.515 EL

(r2=0.528, Sy.x=0.028, N=296) for females.








Oviposition rate (OR). The number of eggs laid per

female per day was significantly related to season,

temperature, phloem thickness and 3 interactions between

these factors (Table 2-1). Temperature and phloem thickness

were the principal factors influencing OR. Oviposition rate

was positively correlated with temperature and phloem

thickness in both summer and fall (Fig. 2.1). Extremes of

individual oviposition rates ranged from 1.1 eggs/day (200C,

PT=0.8 am) to 20.3 (300C, 3.5 am) in the fall study, and

from 1.1 (200C, 0.6 ma) to 19.3 (300C, 3.6 am) in the summer

study.


Gallery construction rate (GCR). The length of gallery

constructed per female per day was significantly correlated

with season, temperature, phloem thickness, and 3

interactions between these factors (Table 2-1). Temperature

was the major factor affecting GCB; the 2 were positively

correlated. Mean GCR was 1.67 ca/day (+0.36) at 200 (N=96),

2.41 (+0.37) at 250 (N=108), and 3.34 (+0.73) at 30oC

(N=105). Because of the weak association of GCR with PT

(rz=0.014) predictive equations incorporating phloem

thickness were not considered. When the data sets for each

study were analyzed independently, GCE was significantly

(P<0.05) related to PT in the fall study only. Extremes of

individual gallery construction rates ranged from 0.9 cm/day

(200C, PT=0.7 an) to 5.7 (300C, 3.5 am) in the fall study,

and from 1.0 (200C, 3.0 am) to 4.9 (300C, 2.6 am) in the

summer study.






11

Initial eq-freegallery _(PRE-EG). The amount of gallery

between the nuptial chamber and the first egg was

significantly associated with season, temperature, and

phloem thickness (Table 2-1). Temperature was the principal

factor influencing PRE-EG; the 2 were negatively correlated.

Because PT explained only 1.7% of the model variation,

predictive equations incorporating phloem thickness were not

considered. Again, when the data sets for each study were

analyzed independently, PRE-EG was significantly (P<0.05)

related to PT in the fall study only. Mean distance to the

first egg was significantly (P<0.05) shorter in the summer

study than in the fall study at 250 and 300 but not at 200

(Table 2-2). Also, mean distance to the first egg tended to

shorten with increasing temperature in both studies.

Extremes of individual egg-free gallery lengths ranged from

6 am (300C, PT=0.6 am) to 57 (250C, 1.0 ma) in the fall

study, and from 7 (300C, 1.5 am) to 49 (200C, 2.5 am) in the

summer study.


Egg density (ED). The number of eggs laid per unit

length of gallery was significantly related to phloea

thickness, temperature, season, and 1 interaction term

(Table 2-1). Phloem thickness was the major factor

explaining the observed variation in ED. Egg density was

positively correlated with phloem thickness and temperature

in both the summer and fall studies (Fig. 2-2). Extremes of

individual egg densities ranged from 1.1 eggs/ca (200C,






12

PT=0.8 am) to 5.1 (300C, 3.4 an) in the fall study, and from

1.3 (200C, 0.6 am) to 11.0 (30oC, 3.5 am) in the summer

study.


Depth of xyle-etching_(DXE). The depth to which females

etched the xylem was significantly associated with season,

temperature, and phloem thickness (Table 2-1). Phloem

thickness was the principal factor affecting DXE; the 2 were

negatively correlated. Females tended to etch more xylem

than outer bark until phloem became less than ca. 0.8-am

thick, after which more outer bark was etched. Egg gallery

diameters and female pronotal widths ranged from 1.7-2.1 am

and 1.5-1.9 an, respectively. The overall regression

equation for DXE (am) with PT (ma) was

DXE = 0.503 0.119 PT (r=0.656, Sy.x=0.009, N=309).

Extremes of individual depths of xylem etching ranged from

0.7 mm (300C, PT=0.8 ma) to 0.05 (300C, 3.5 ma) in the fall

study, and from 0.7 (200, 0.7 an) to 0.05 (300, 3.3 am) in

the summer study.













18 300
SUMMER FALL
30*
14


>, / as /
^ 10 / 25* 25t


6 20". 20*


2

1 2 3 4 I 2 3 4
PHLOEM THICKNESS (MM)





Fig. 2-1. Ips calligraphus oviposition rate (OR; eggs/day)
at 3 temperatures in bark slabs from slash pines cut in fall
(F) 1981 and summer (S) 1982, and having phloem thicknesses
ranging from 0.5-4.0 am. Equations were based on first 8
days of oviposition at 200, first 6 days at 250, and first 4
days at 30oC, beginning at time of female introduction
(overall r2=0.86; overall Sy.x=0.24; N=309). Individual
equations of OR with PT are:


5,300(N=59) 38=7.88+2.54 PT
S,250(N=59) DR=5.16+1.28 PT
S,200(N=53) OR=2.87+0.78 PT


F,300(N=46) OR=2.50+3.30 PT
F,250(N=49) OR=2.17+2.04 PT
F,200(N=43) 0O=0.39+1.54 PT



























U'. ...
I 2 3 4 I 2 3 4
PHLOEM THICKNESS (MM)





Fig. 2-2. Ips calligraphus egg density (ED; eggs/ca) at 3
temperatures in bark slabs from slash pines cut in fall (F)
1981 and summer (S) 1982, and having phloea thicknesses
ranging from 0.5-4.0 aa. Equations were based on first 8
days of oviposition at 200, first 6 days at 250, and first 4
days at 300C, beginning at the first egg (overall rZ=0.73;
overall Sy.x=0.05; N=309). Individual equations of ED with
PT are:


S,300 (=59)
S,250(N=59)
S,200(N=53)


ED=3.01 PTO.5O
ED=2.76 PTO.4s
ED=2.44 PTa. 3


F,30o(N=46)
F,250(N=49)
F,200(N=43)


ED=2.34 PTO.so
ED=2.15 PTO.*s
ED=1.90 PTO.32








Table 2-1. Partial and overall coefficients of determination
(r2) and their corresponding significance levels for linear
regression model variables pertaining to Ips calliqraphus
oviposition rate (OR), gallery construction rate (GCR),
initial egg-free gallery (PRE-EG), egg density (ED), and
depth of xylem-etching (DXE), at 200, 250, and 300C in slash
pine bark slabs prepared during the fall (1981) and summer
(1982) seasons. Regression was performed using phloem
thickness (PT) as the independent variable and with season
(S) and temperature (T) as class variables.


Oviposition and Gallery Parameters

Model
Variable OR GCR PRE-EG ED' DIE


S 0.090**2 0.007* 0.050** 0.179** 0.011**

T 0.536** 0.631** 0.212** 0.152** 0.031**

PT 0.179** 0.014** 0.017** 0.397** 0.622**

SxT 0.022** 0.015** n.s. n.s. n.s.

SxPT 0.008** 0.046** n.s n.s. n.s.

TxPT 0.025** n.s. n.s. 0.006* n.s.

SxTxPT n.s. 0.023** n.s. n.s. n.s.


Overall 0.860** 0.736** 0.279** 0.734** 0.664**

N 309 309 309 309 309


'Linear regression of ED with
transformation of the data.


PT was performed after log-log


2n.s. = not significant at the P<0.05 level, = P<0.05,
** = P<0.01.








Table 2-2. Length (am) of Ips calligraphus initial egg-free
gallery (PRE-EG) at 200, 250, and 300C in slash pine bark
slabs that were prepared during the fall (1981) and summer
(1982) seasons.


Initial Egg-free Gallery Length (am)


200 250 300


Season X + SD (N) X + SD (8) I + SD (N)


Fall 24.2+7.7 alZ(43) 21.4+7.3 al (49) 17.7+6.1 a2 (46)

Summer 23.3+7.6 al (53) 17.1+5.0 b2 (59) 13.5+3.4 b3 (59)


'Initial egg-free gallery was measured from the point where
each female began tunneling to her first egg.

2Means followed by the same letter (within columns) or
number (within rows) are not significantly different at the
P<0.05 level (Duncan's multiple-range test).








Discussion

Several investigators have attributed observed variations

in beetle reproduction to changes in the quality of the

beetles themselves (Sahota and Thomson 1979; Wagner et al.

1981a). However, it may be changes in host quality that

offer the principal explanation for the variations noted in

this study. Ips calliqraphus adults are liquid-feeders,

obtaining nutrients from the tissues through which they

tunnel (Gouger et al. 1975). Thus, the observed variations

in I. calliqraphus reproductive performance are probably

related to the following points.

1. Physical and nutritional differences that exist among

xylem, phloes, and outer bark.

2. Seasonal changes that occur within these plant

tissues.

3. Differences in the relative proportions of these

tissues that are encountered when tunneling in thin

versus thick phloem.

The xylem in pines consists of mostly thick-walled,

highly lignified cells. The outer bark contains weakly

lignified, heavily suberized cells (suberin is a waxy

substance), and the phloem is mostly thin-walled,

unlignified and unsuberized cells (Howard 1971; Koch 1972).

Water content is usually higher in phloes than in either

xylem or outer bark, average values for slash pine being 69%

(Hartin 1969), 47% (Miller 1959), and 20% (Martin 1969),








respectively. In trees, water content is generally

inversely related to specific gravity, a measure of density

(Koch 1972). Seasonal changes are especially apparent in

xylem. In slash pine, the relatively thick-walled latewood

cells (nearest the paloem in the fall study) are 2-2.5 times

more dense than are earlywood cells (nearest the phloen in

the summer study) (Paul 1939; Ifju 1969). Thus, in

conducting xylem, water content would apparently be lower in

latewood than in earlywood. Also, the nutritional qualities

of xylem, phloem, and outer bark are quite different.

Concentrations of carbohydrates, lipids, and nitrogenous

compounds are generally highest in phloem, lover in xylem,

and lowest in outer bark (Kramer and Kozlowski 1979).

Considering these known differences in the tissues of

pines, tunneling in thin phloea most likely requires

additional energy because more of the adjacent xylem and

outer bark is etched. Furthermore, more energy is probably

expended when etching latewood as opposed to earlywood

xylem. Similarly, females would apparently obtain fever

nutrients per unit length of gallery when tunneling in thin

phloem. Consequently, the resources necessary for egg

production are obtained over longer distances in thinner

phloem, and thus, OR and ED tend to be lower in thinner

phloem. The overall greater reproductive performance by

females in the summer study may, in part, reflect the

relatively lower density and higher moisture content of






19

earlywood versus latewood xylem. The greater egg densities

at the higher temperatures shown in Fig. 2-2 may indicate

increased efficiencies of conversion and assimilation of

ingested food with increasing temperature (Sahota and

Thomson 1979; Scriber and Slansky 1981).

As was the case in our study, Amman (1972) reported no

strong correlation between phloem thickness and gallery

construction rate. A plausible explanation is that per ca

of gallery, females in thin phloem must spend relatively

more time tunneling than ovipositing, whereas females in

thick phloem spend more time ovipositing than tunneling. As

a result, gallery construction rate is similar over a wide

range of phloem thicknesses.

The inverse relationship between I. calliqraphus initial

egg-free gallery and temperature (Table 2-2) is similar to

that reported for several species of Dendroctonus (Sahota

and Thomson 1979; Wagner et al. 1981a). This relationship

probably reflects temperature-dependent processes that occur

in the flight muscles, fat body, reproductive organs, and

corpora allata (Reid 1958; Atkins and Farris 1962; Sahota

and Thomson 1979). Shorter distances to first oviposition

in the summer study at 250 and 300C may reflect the density

and moisture differences between earlywood and latewood.

The fact that I. calliqraphus oviposition rate and egg

density were positively correlated with phloem thickness

indicates that great care should be taken when selecting






20

host materials for biological studies of bark beetles. This

would be especially important when using tree species with

phloem thicknesses that bracket the range of adult sizes

found in the beetles under study. Phloem thickness and

reproduction may not have correlated in the southern pine

beetle study (Wagner et al. 1981a) because the phloem was

generally thick relative to beetle width. In contrast, in

the mountain pine beetle studies (Amman 1972; Amman and Pace

1976) and in our own work, where there are significant

changes, phloem thickness has ranged from thinner to thicker

than beetle width.



Summary

In summary, the following points can be made with respect

to I. call raphus gallery construction and reproduction in

relation to phloem thickness and temperature.

1. Gallery construction rate is positively correlated

with temperature, but apparently little affected by

phloem thickness.

2. Females etch deeper into the xylem as phloem becomes

thinner. Temperature has no apparent effect on depth

of xylem etching.

3. Oviposition rate and egg density (eggs/cm of gallery)

are positively correlated with both phloem thickness

and temperature. These measures of reproductive

performance were greatest with a combination of








thicker phloem (3-4 ma) and warmer temperature

(300C).

4. The length of gallery that females construct before

first oviposition is negatively correlated with

temperature, and apparently unaffected by phloea

thickness.

5. Under similar conditions of phloea thickness and

temperature, reproductive performance is greater when

earlywood is outermost in the current annual ring of

xylem (this was the case in the summer study) than

when latewood is outermost (fall study). Such a

finding demonstrates that seasonal variations in host

materials should be considered in biological studies

of phloea-dwelling insects, especially for

multivoltine species.

6. The above results indicate that phloem thickness

should be considered in population dynamics studies

of I. calligraphuus in slash pine, especially in

summer when warmer temperatures accentuate phloea

thickness effects on female reproduction.














CHAPTER III
LONGEVITY AND FECUNDITY OF IPS CALLIGRAPHUS (COLEOPTERA:
SCOLYTIDAE) IN RELATION TO SLASH PINE PHLOEM THICKNESS



Introduction

Bark beetles (Coleoptera: Scolytidae) tunnel and oviposit

primarily in the phloem (inner bark) tissue at the bark-wood

interface of the host tree (Stark 1982). Actual values of

bark beetle fecundity are difficult to obtain because parent

adults commonly re-emerge after establishment of their first

brood and go on to construct another egg gallery elsewhere

(Coulson et al. 1978). Thus, only a fraction of a female's

eggs are deposited in any one gallery. Nevertheless,

estimates do exist for a few species of bark beetles. Under

natural conditions, Reid (1962) found 263 eggs in a single

gallery of Dendroctonus ponderosae. In laboratory studies

terminated after 30 days, mean fecundity was 159 eggs for

Dendroctonus frontalis at 280C (Clarke et al. 1979); and

similarly, using females reared from natural populations, 77

for Ips avulsus (Eichhoff), 117 for Ip calliqraphus, and

108 for Ips grandicollis (Eichhoff) at 300C (Yearian et al.

1972). In a different study, at various temperatures,

maximum fecundity during a 30-day period was 109 for I.

avulsus, 274 for I. calligraphus, and 206 for I.

grandicollis (Dale 1967).






23

While constructing an egg gallery, females obtain liquid

nourishment from the host tissues through which they tunnel

(Gouger et al. 1975). The thickness of the phloem layer

with respect to the beetle's size affects the relative

proportions of xylem, phloem, and outer bark encountered

while tunneling. Amman (1972) reported that D. ponderosae

etched deeper into xylem as phloem became thinner, and that

oviposition rate (eggs/day) and egg density (eggs/cm of

gallery) were significantly lower in thinner phloem. I

reported similar correlations for I. calligraphas in typical

slash pine, Pinus elliottii, in chapter II. In that study,

phloea thickness effects on I. calligraphus oviposition rate

and egg density were greatest at 300C (see Figs. 2-1 and

2-2). However, at that temperature, oviposition was

monitored for only a 4-day period. Thus, the effects of

phloea thickness on overall female longevity and fecundity

were not observed. The objective of this study was to

record I. calliqraphus longevity and fecundity at 300C in

relation to slash pine phloem thickness.



Methods and Materials


Bolt preparation. Rearing bolts (35 cm long) were

prepared from 21-year-old slash pine trees growing in a

plantation with a site index of 58 ft (17.6 m) at 25 years,

near Orange Heights, Alachua County, Florida. Fifteen trees

were felled between 12 April and 16 June 1982 to ensure






24

having adequate numbers of rearing bolts available. Phloem

thickness at breast height (1.4 m) measured 1.0-1.5 am on 7

of these trees, and 2.5-3.5 mm on the other 8. These ranges

of phloea thickness were considered, respectively, "thin"

and "thick" relative to the size of I. calliqraphus adults

from Florida (about 1.5-2.1 am, see chapter II). After

felling, bolts were cut from the 2- to 6-a section of the

trunk, measured from groundline. The bolts were labelled

and dried for 3-4 days at 40oC and 40-50% RH. Following

drying, the loose outer bark was removed and the bolt ends

were pared back to unstained phloem. The bolt ends were

then dipped in a benomyl fungicide-water solution (1%) and

melted paraffin to inhibit contamination and desiccation.

The bolts were stored at 20oc until used.


Source of experimental beetles. The beetles used to

initiate the study were reared from a 21-year-old slash pine

tree with thick phloea that was naturally infested

subsequent to felling on 19 March 1982. When most of the

developing brood reached the pupal stage, infested sections

of trunk were returned to the laboratory and stored in

screen emergence-cages in an open-air insectary. Emerging

brood adults were collected several times daily, sexed

according to the form of the third elytral tooth (Hopping

1963), put iato containers with moist, brown paper towels,

and stored at 200C until used. To ensure a sufficient

number of males throughout the study, 2 additional pines






25

with thick phloes were felled and treated as above; felling

dates were 23 April and 22 May 1982.


Introduction and transfer of beetles. Only females

collected within 24 h, and sales within 48 h, prior to the

time of introduction were used as parent adults. Following

the methods of Wilkinson (1964), "starter holes" were made

through the outer bark along the bolt aid-line. From 2-6

starter holes were made per bolt with no 2 holes closer than

10 ca. A single adult sale was placed into the long section

of a size 00 gelatin capsule that contained a ring of paper

for footing, and that had been pierced at the end for

ventilation. The capsule was placed over the starter hole

and held there with a ring of Duxseal(B) sealing compound.

Hales were allowed 24 h at 30oC to construct their nuptial

chambers, after which time 1 female was introduced into each

chamber in similar fashion. A code number for each female

was written on the outer bark next to the nuptial chamber

she had entered. These bolts were placed into ventilated

rearing cans and maintained at 300C, 60-70% RH, and

photoperiod 12L:12D. Three days later, each gallery system

was dissected and the female removed and immediately

introduced into another nuptial chamber on a different bolt.

This period of time was chosen because after 3 days of

tunneling, females would be nearing either the top or bottom

of the bolt. These "new" nuptial chambers had been

constructed over the previous 24 h by recently emerged








males. In general, males were used to construct only a

single nuptial chamber, after which they were frozen. In

this manner, 40 females were transferred from one set of

males and bolts to another every 3 days until all females

had died. There were 4 treatments (N=10 each) with respect

to female transfer:

1. From thick phloem to thick phloem only (KK).

2. Alternating between thick and thin phloem, beginning

on thick (KN).

3. Alternating between thick and thin phloem, beginning

on thin (NK).

4. From thin phloem to thin phloem only (NN).


Data collection. Each female's ovipositional history was

recorded by making acetate tracings of all the egg galleries

that she made during her lifetime. Each tracing included

the nuptial chamber, the entire egg gallery, and the

location of all egg niches. Total number of eggs, total

gallery length (measured in am beginning at the first egg),

and longevity (days) were recorded for each female. Using

the above values, egg density (eggs/cm of gallery),

oviposition rate (eggs/day), and gallery construction rate

(am/day) were recorded. Additionally, for those females

switched between thick and thin phloem, numbers of eggs laid

in the first (beginning at the first egg) and last 2 cm of

each gallery were recorded.






27

For several females the exact day on which death occurred

was not certain. In such cases, the day was estimated by

comparing the length of that individual's final gallery to

the one she had constructed the previous 3 days, and by

comparing the developmental stage of her last eggs (if any)

to those of females that lived and oviposited the entire

3-day period.

Because a direct relationship between female size and

reproductive performance has been reported for other bark

beetles (Reid 1962; Amman 1972; Clarke et al. 1979), aean

size of the females used in this study was analyzed among

treatments. The maximal pronotal width was used as an

indicator of female size; it was measured dorsally to the

nearest 0.05 as using a dissecting microscope with ocular

micrometer.

The average thickness of phloem through which each female

had tunneled was calculated from 2-3 samples taken less than

1 cm from the sides of her egg gallery during bolt

dissection; samples were removed with a knife. Phloea

thickness was measured to the nearest 0.1 mm. The phloea

water content of each bolt was also calculated from 4-6

samples taken no less than 5 cm from an egg gallery during

bolt dissection. After removal, samples were immediately

weighed in milligrams, dried to no further weight change

(ca. 3 days) at 550C, and reweighed. Percent water content

(PWC) was recorded on a wet-weight basis:

PWC = 100 x (Fresh wt Dry wt) / Fresh wt.






28

Analyses. Data were analyzed with the t-test and general

linear models procedures of the Statistical Analysis System

(SAS), version 1982.3. Preliminary analyses, using the t-

test, indicated no significant differences (P>0.05) between

the KN and NK treatments as measured by mean longevity

(P>0.90), mean total gallery length (P>0.75), and mean

fecundity (P>0.73). Data from these 2 treatments were thus

pooled in all subsequent analyses, except where indicated

below.

Mean female prothoracic width, longevity, total gallery

length (TGL), gallery construction rate (GCR), fecundity,

oviposition rate (OR), and egg density (ED) were compared

among the 3 treatments (KK, KN+NK, NN) using Duncan's

multiple-range test. Additionally, mean TGL, fecundity, and

ED were compared by means of analysis of covariance using

"age" (i.e., longevity) as the covariate. Similarly, mean

GCR, OR, and ED were compared both within and among the 4

original treatments (KK, KN, NK, NN) for each 3-day

oviposition period, Regression analyses of longevity, TGL,

GCR, fecundity, OR, and ED were each performed separately

with female prothoracic width, after sorting by treatment.

Similarly, regressions were performed on female survival

(number alive at end of each 3-day period), GCR, OR, and ED,

using female age as the independent variable; data from each

3-day oviposition period were used in these analyses. For

those females switched between thick and thin phloes (KN and






29

NK), t-tests were used to compare (1) overall GCR, OR, and

ED while in thick phloem to that while in thin phloem, and

(2) ED over the first 2 ca of egg gallery to that over the

last 2 ca. In the latter analysis, only data from the

2nd-7th gallery (days 4-21) were used. Mean percent water

content was compared between thick- and thin-phloem bolts by

the t-test without transformation.



Results


Female size. Mean pronotal width of the parent females

did not differ significantly (P>0.97) among the 3 treatments

(KK, KN+NK, NN). Female size was thus not considered to be

a significant factor in the response variable differences

noted in the subsequent among-treatment comparisons. Mean

pronotal width was 1.77 am (+0.09 SD) for the 40 females,

and 1.84 (+0.10) for a sample (N=50) of the 321 males used

throughout the study. Pronotal widths ranged from 1.6-1.95

am for females and from 1.7-2.1 for males.


Longevity. Females lived significantly (P<0.05) longer

on KK than on NN (Table 3-1), averaging 66% longer on KK.

No significant linear relationship was found between

longevity and female pronotal width within any of the 3

treatments (P>0.82 KK; 0.56 KN+NK; 0.72 NN). The numbers of

females alive at the end of each 3-day oviposition period

are presented in Table 3-2 by treatment; the values given in








Table 3-2 are the "N" values for Tables 3-4 to 3-6.

Equations based on regression analyses of female

survivorship with female age are presented in Table 3-3.

Survival curves fo the treatments KK, KN+NK, and NN are

shown in Fig. 3-1.


Total _aller length (TGL). The total length of all

galleries constructed per female lifetime did not differ

significantly (P>0.10) among treatments (Table 3-1).

Similar results were obtained when mean TGL was compared

among treatments using female age as covariate. No

significant linear relationship was found between TGL and

female pronotal width within any of the 3 treatments (P>0.81

KK; 0.27 KN+NK; 0.42 NN).


Gallery construction rate (GCR). Females constructed

significantly (P<0.05) more gallery per day on KN+NK than on

KK (Table 3-1), averaging 24% more on KN+NK. Only in the NN

treatment was there a weakly significant (P<0.07 NN; >0.71

KK; >0.96 KN+NK) correlation between GCB and female pronotal

width (PW; mm): GCB = 79.9 26.8 Pw (r2=0.34; N=10). Mean

GCR values for each 3-day period are compared both within

and among treatments in Table 3-4. In general, GCB

decreased with female age; no distinct differences were

noted among treatments. Equations based on regression

analyses of GCR with female age are presented in Table 3-3;

in all treatments, a negative correlation exists between








these two variables. In a combined regression analysis,

using treatment as a class variable, both treatment and age

added significantly (P<0.01 for both) to the overall

equation; treatment accounted for 5% of the total variation

and age 46% (overall r2=0.51; N=311). For females switched

between thick and thin phloem, mean GCR while on thick

phloes did not differ significantly (P>0.19) from that while

on thin phloem; mean values were 30.6 as/day (+10.9, N=75

galleries) and 33.8 (+12.4, N=76), respectively.


Realized fecundity. The total number of eggs laid per

female lifetime was significantly (P<0.05) greater on KK

than on NN (Table 3-1), averaging 104% more on KK. Similar

results were obtained from the analysis of covariance using

female age as covariate. No significant linear relationship

was found between fecundity and female pronotal width within

any of the 3 treatments (P>0.80 KK; 0.34 KN+NK; 0.55 NN).


Oviposition rate (OB). Females laid significantly

(P<0.05) more eggs per day on KK than on NN (Table 3-1),

averaging 27% more on KK. No significant linear

relationship was found between OR and female pronotal width

for any of the 3 treatments (P>0.42 KK; 0.79 KN+NK; 0.27

NN). Mean OR values for each 3-day period are compared both

within and among treatments in Table 3-5. OR was generally

greater on thick phloem (KK) than on thin phloes (NN) during

days 6-15. Overall, OR decreased with age within each






32

treatment; regression equations of OR with female age are

presented in Table 3-3. The relatively low coefficient of

determination for the KN+NK treatment (r2=0.28) probably

reflects how OR fluctuated as a result of the females being

switched between thick and thin phloem. In a combined

regression analysis, using treatment as a class variable,

both treatment and age added significantly (P<0.01 for both)

to the equation; treatment accounted for 3% of the total

variance and age 41% (overall r2=0.44; N=311). For those

females alternating between thick and thin phloem, mean OR

on thick phloem was significantly (P<0.01) greater than that

on thin phloem; mean values were 13.2 (+5.2, N=75 galleries)

and 10.0 (+5.1, N=76), respectively.


Egg density (ED). Females laid significantly (P<0.01)

more eggs per cm of gallery on KK than on NN (Table 3-1),

averaging 49% more on KK. Similarly, ED averaged 25%

greater on KN+NK than on NN. A similar ranking of the means

was determined from an analysis of covariance using female

age as covariate. No significant linear relationship was

found between ED and female pronotal width for any of the 3

treatments (P>0.53 KK; 0.73 KN+VK; 0.69 NN). Mean ED values

for each 3-day period are compared both within and among

treatments in Table 3-6. In general, ED tended to decline

with female age in all treatments; equations based on

regression analyses of ED with female age are presented in

Table 3-3. Overall, ED was consistently greater for females






33

in thick phloea (KK) than in thin phloem (NN) over the first

21 days of oviposition. In the combined regression

analysis, using treatment as a class variable, both

treatment anJ female age added significantly (P<0.01 for

both) to the overall equation; treatment accounted for 8% of

the total variance and age 11% (overall r2=0.19; N=311).

The density of eggs laid by females repeatedly switched

between thick and thin phloem generally increased while on

thick phloes and decreased on thin phloes (Fig. 3-2).

Overall, ED was 4.3 (+1.2, N=75 galleries) eggs/ca on thick

phloem, and 2.8 (+1.1, N=76) on thin phloem. More

specifically, ED changed significantly (P<0.01) between the

beginning and end of the galleries. Females switched from

thin into thick phloem produced 3.8 (+1.1) eggs/ca in the

first 2 ca and 5.0 (+1.3) in the last 2 cm (N=46 galleries).

Females switched into thin phloem had egg densities decline

from 3.5 (+1.1) at the beginning of the gallery to 2.4

(+1.5) at the end (N=49).


Phloea water content (PWC). Average phloem water content

(%) did not differ significantly (P>0.83) between the 2

phloea thickness classes. Mean PVC was 68.6% (+4.3, N=40

bolts) for thick phloem, and 68.4% (3.4, N=44 bolts). For

individual bolts, PWC ranged from 60-76% in thick phloem,

and from 60-74% in thin phloem.















100 "I ""',n-
--too ,
S'* *-. KK




'S
so .\ \ o--- KN*NK
S\ 1 *---o NN

.j 60" *' W* *






% *%
20 *o* *
--. -"-~
I I I i nI ,
6 12 18 24 30 38 42 48 54
FEMALE AGE (DAYS)






Fig. 3-1. Survival curves (% alive) of Is calliqraphus
females in slash pine bolts at 300C by treatment; KK= 10
females maintained on thick (2.5-3.5) phloem only, KN+NK =
20 females switched between thick and thin (1.0-1.5 ma)
phloem at 3-day intervals, and NN = females maintained on
thin phloem only.























N oK
3 .* *
NK K
4 *
\/
3 0 N
3.
n
I *
N



6 12 18 24 30 36 42 48 54
DAY






Fig. 3-2. Egg density (eggs/ca of gallery) averaged over
3-day periods throughout the lives of Ips calliqraphus
females that were switched every 3 days between slash pine
bolts having either thick (K; 2.5-3.5 ma) or thin (N,
1,0-1.5 am) phloea at 300C. N = 10 females/treatment
initially; see Table 3-2 for "N" values pertaining to the
number of females alive on a given day.








Table 3-1. Longevity, total gallery length (TGL), gallery
construction rate (GCR), fecundity, oviposition rate (OR),
and egg density of Is calligraghus females maintained in
slash pine bolts at 30oC by treatment.


Treatment1


KK KN+NK NN


Parameter X + SD X + SD X + SD
(Range) (Range) (Range)


Longevity 29.1+12.3a2 23.0+14.0ab 17.5+7.9b
(days) (14 54) (9 54) (9 30)

TGL 75.8+20.4a 73.8+33.6a 55.8+25.0a
(ca) (44 113) (32 149) (24 101)

GCR 27.9+6.1b 34.6+6.2a 32.4+4.9ab
(am/day) (21 40) (24 44) (24 41)

Fecundity 326+104a 263+120a 160+70b
(eggs) (156 464) (80 572) (58 280)

OR 11.8+2.8a 12.4+2.7a 9.3+1.6b
(eggs/day) (9 17) (8 17) (6 11)

ED 4.3+0.8a 3.6+0.5b 2.9+0.3c
(eggs/cm) (3.5 5.9) (2.5 4.8) (2.2 3.2)


1KK=10 females maintained on thick (2.5-3.5 ma) phloem
only; KN+NK=20 females switched between thick and thin
(1.0-1.5 ma) phloem at 3-day intervals; and NN=10 females
maintained on thin phloem only.

2Means followed by the same letter (within rows) are not
significantly different at the P<0.05 level (P<0.01 for ED)
(Duncan's multiple-range test).








Table 3-2. Percent of Ips calliqraphus females that were
alive at the end of each 3-day oviposition period when
maintained in slash pine bolts at 30oc by treatment.


Percent Alive by Treatment1
Time
Periods KK KN NK NN
(Days) (N=10) (N=10) (N=10) (N=10)


1-3 100 100 100 100
4-6 100 100 100 100
7-9 100 100 100 100
10-12 100 100 70 60
13-15 100 70 70 60
16-18 90 60 60 60
19-21 60 60 50 30
22-24 50 30 30 20
25-27 50 20 30 20
28-30 50 20 30 10
31-33 50 20 20 0
34-36 20 20 20 0
37-39 10 10 20 0
40-42 10 10 20 0
43-45 10 10 20 0
46-48 10 10 10 0
49-51 10 10 10 0
52-54 10 0 10 0
55-57 0 0 0 0


1KK=females maintained on thick (2.5-3.5 an) phloem only;
KN=females switched between thick and thin (1.0-1.5 mm)
phloem at 3-day intervals beginning on thick phloem; NK=
females switched between thick and thin phloem at 3-day
intervals beginning on thin phloem; and NN=females main-
tained on thin phloem only.








Table 3-3. Linear equations, levels of significance (P),
and coefficients of determination (rz) for regression
analyses of Ips calliqraphus female survival (Ix; percent
alive at beginning of day x), gallery construction rate
(GCR; ma/day), oviposition rate (OR; eggs/day), and egg
density (ED; eggs/ca) with female age (D; days) at 30oC by
treatment and overall.


Treatment* N** Equation P< r2


Survival

KK 18 lx = 116 2.27 D 0.01 0.91
KN+NK 35 Ix = 101 2.07 D 0.01 0.86
NN 10 Ix = 118 3.76 D 0.01 0.93
Overall 63 Ix = 103 2.12 D 0.01 0.83

Gallery Construction Bate

KK 98 GCR = 42.03 0.87 D 0.01 0.65
KN+NK 151 GCR = 42.24 0.61 D 0.01 0.41
NN 62 GCR = 42.26 0.93 D 0.01 0.42
Overall 311 GCR = 41.72 0.72 D 0.01 0.47

Oviposition Rate

KK 98 OR = 20.00 0.48 D 0.01 0.64
KN+NK 151 OR = 15.29 0.24 D 0.01 0.28
NN 62 OR = 15.38 0.55 D 0.01 0.49
Overall 311 OR = 15.96 0.32 D 0.01 0.35

Egg Density

KK 98 ED = 5.55 0.10 D 0.01 0.32
KN+NK 151 ED = 3.72 0.02 D 0.11 0.02
NN 62 ED = 3.80 0.10 D 0.01 0.29
Overall 311 ED = 4.05 0.04 D 0.01 0.08


*KK=10 females maintained on thick (2.5-3.5 aa) phloem only;
KN+NK=20 females switched between thick and thin (1.0-1.5
am) phloem at 3-day intervals beginning on either thick
or thin phloea, respectively; and NN=10 females maintained
on thin phloem only.

**N for "Survival" = number of 3-day intervals during which
females were alive by treatment, and N for "GCR," "OR," and
"ED" = number of egg galleries on which observations were
made by treatment.








Table 3-4. Gallery construction rate (mn/day; mean + SD)
over 3-day periods throughout the lives of Ips callijqaphus
females in slash pine bolts at 300C by treatment.


Time Gallery Construction Rate by Treatment'
Periods
(Days) KK KN NK NN


1-3 35 + 5ab22 30 + 6abcd3 42 + 6a1 40 + 4ab12
4-6 40 + 4ab1 42 + 7al 38 +10al 41 6a1
7-9 42 a 5al 40 + 7ab1 42 + 9a1 33 + 8abc2
10-12 30 + 8abc2 35 + 8abcd12 40 + 6al 28 11bcd2
13-15 28 +lObcl 29 + 9abcdl 34 +1lab1 26 + 9cdl
16-18 27 +lObcdl 27 +14abcdl 29 +11abcl 27 + 9cdl
19-21 26 + 9bcd2 31 + 8abcd12 36 + 7ab1 16 + 5d3
22-24 17 + 7cdel 24 +16abcdel 25 +10abcdl 25 +12cdl
25-27 11 + 3e2 19 +10cdel2 28 + 6abcdl 26 + 8cdl
28-30 12 + 5e2 38 +12abcl 18 + 5bcd2 20 +12d2
31-33 9 + 3e 20 +11bcde 16 +16cd
34-36 11 + 3e 15 + 9de 17 + 9bcd -
37-39 8 e 28 abcd 18 + 4bcd
40-42 13 e 18 cde 16 + cd -
43-45 8 e 15 de 18 + Ibcd
46-48 5 e 6 e 17 bcd -
49-51 6 e 20 cde 13 cd
52-54 7 e 10 d -


*KK=10 females maintained on thick (2.5-3.5 mn) phloem only;
KN=10 females switched between thick and thin (1.0-1.5 am)
phloem at 3-day intervals beginning on thick phloem; NK= 10
females switched between thick and thin phloem at 3-day
intervals beginning on thin phloem; and NN=10 females
maintained on thin phloem only.

2Means followed by the same letter (within columns) or
number (within rows) are not significantly different at the
P<0.05 level (Duncan's multiple-range test).








Table 3-5. Oviposition rate (eggs/day; mean + SD) over
3-day periods throughout the lives of Ips calligraphus
females in slash pine bolts at 30oC by treatment.


Time Oviposition Rate by Treatment'
Periods
(days) KK KN NK NN


1-3 17 + 3a12 15 + 5ab1 15 + 2abl 16 + 2bcd1
4-6 19 + 2a1 13 + 3abc2 15 + 5a2 11 + 4ab2
7-9 18 + 3a1 16 + 3al 12 + 5abc2 9 + 5b2
10-12 14 + 5ab12 9 + 5abcd23 15 + 3al 7 + 5bc3
13-15 13 + 6abc12 16 + 3al 8 + 5abc23 7 + 4bcd3
16-18 11 + Sabcl 10 T 5abcdl 10 + 6abc1 8 + 5bcl
19-21 10 + 7abcdl 14 + Sabcl 9 + 3abcl 2 + 1cd2
22-24 7 + 5bcdel 9 + 7bcdl 11 + Sabcl 5 + 6bcdl
25-27 6 + 4bcdel 8 + Sabcdl 9 + 4abcl 2 + 3cd1
28-30 4 + 3cde2 13 + 2abcl 9 + 2abcl 1 7 1d2
31-33 2 + 2de 7 +lOabcd 3 + Sc
34-36 1 + 2de 4 + 5cd 8 + labc -
37-39 2 e 11 abcd 3 + 4c -
40-42 0 e 7 abcd 7 + labc
43-45 1 e 6 abcd 5 + 3c -
46-48 0 e 1 d 6 bc -
49-51 0 e 7 abcd 4 c
52-54 0 e 4 c -


tKK=10 females maintained on thick (2.5-3.5 ma) phloem only;
KN=10 females switched between thick and thin (1.0-1.5 am)
phloem at 3-day intervals beginning on thick phloem; NK=10
females switched between thick and thin phloem at 3-day
intervals beginning on thin phloes; and 11=10 females
maintained on thin phloem only.

2zeans followed by the same letter (within columns) or
number (within rows) are not significantly different at the
P<0.05 level (Duncan's multiple-range test).








Table 3-6. Egg density (eggs/ca of gallery beginning at the
first egg; mean + SD) over 3-day periods throughout the
lives of Ips calliqraphus females in slash pine bolts at
30oc by treatment.


Time Egg Density by Treatment'
Periods
(Days) KK KN NK NN


4.9+1.3al
4.8+0.5a 1
4.2+0.6abc1
4. 6+1.6abl
4.1+1.6abcl
4.3+:1.5abc1
3.7+2.2abc 12
3.5+1.9abcl
5.0+3. lal
3.6+2.2abc12
1.4+1.8abcd
1.1+1.3bcd
2.0 abcd
0.0 d
0.8 cd
0.0 d
0.0 d
0.0 d


5.0+1. 8abl
3.1+0.6abcd3
4.1+0.9abcdl
2.6+1.0bcd2
5.7+ 1. Oal
3.5+0.7abcdl2
4.4+1.1abcl
1.4+1.6d1
3.9+0.3abcdl
3.5+0.6abcd12
2.5+3.6bcd
1.8+2.5cd
3.9 abcd
3.8 abcd
4.0 abcd
1.7 cd
3.5 abcd


3.5+0.6abcd2
3.8+0.7abcd2
2.7+0.8bcde2
3.8.+0.4abcdl
2.3+1.1cde2
3.7+2.0abcdl2
2.4+0.7cde23
4.5+0.5abl
3.2+0.9bcdl
5.3+0.8a1
1.2+1.7e
4. 5+0. 2ab
2.0+2.8de
4. 1+1.1abc
3.0+1.9bcde
3.3 abcd
3.3 abcd
4.1 abc


4.*1+0.6a12
2.7+0.8abc3
2.6+1.labc2
2.1+1.4bc2
2.4+1.2abc2
2.6+1.3abc2
1.0+0.9cd3
3.0+3.7abl
1.0+1.4cdl
0.3+0.03d2


*KK=10 females maintained on thick (2.5-3.5 mm) phloea only;
KN=10 females switched between thick and thin (1.0-1.5 am)
phloem at 3-day intervals beginning on thick phloem; NK=10
females switched between thick and thin phloem at 3-day
intervals beginning on thin phloem; and NN=10 females
maintained on thin phloem only.

2Means followed by the same letter (within columns) or
number (within rows) are not significantly different at the
P<0.05 level (Duncan's multiple-range test).


1-3
4-6
7-9
10-12
13-15
16-18
19-21
22-24
25-27
28-30
31-33
34-36
37-39
40-42
43-45
46-48
49-51
51-54








Discussion

The observed variations in I. calliqraphus longevity and

fecundity are probably related to (1) differences in the

physical and nutritional nature of xylem, phloem, and outer

bark and, (2) differences in the relative proportions of

these tissues that are encountered when females tunnel in

thin versus thick phloem. As was discussed in chapter II,

xylem in pines consists mostly of thick-walled, heavily

lignified, nutrient-poor cells; outer bark consists mostly

of heavily suberized, slightly lignified, nutrient-poor

cells; and phloem consists mostly of thin-walled,

unlignified, unsuberized, nutrient-rich cells (Howard 1971;

Kramer and Kozlowski 1979). In slash pine, average water

content is 69% in phloem (Martin 1969), 47% in xylem (Miller

1959), and 20% in outer bark (Martin 1969). Similar values

were reported by Wagner et al. (1979) for uninfested

loblolly pine, Pinus taeda L.; being ca. 69% in phloem, 44%

in xylem, and 23% in outer bark.

Considering the above tissue characteristics and that I.

calliqraphus is a liquid-feeder (Gouger et al. 1975), it

appears likely that females would expend more energy and

obtain fewer nutrients per ca of gallery when tunneling in

thin phloes because they would be forced to mine more xylem

and outer bark. Females in thick phloea, however, would

probably acquire nutrients with relative ease, expend less

energy in egg production, and thus could allocate more total






43

resources to egg production. Indeed, Reid (1962) reported

that D. ponderosae oviposition rate dropped with declining

phloem water content (PWC), and that oviposition ceased when

PWC fell below ca. 51%. The above scenarios may partially

explain why I. calligraphus longevity, fecundity, OR, and ED

are lower for females in thin phloea.

The fact that females lay more eggs per ca of gallery

when switched from thin to thick phloes and then lay fewer

when moved back again (Fig. 3-2) indicates (1) that

reproduction is strongly influenced by host characteristics,

and (2) that changes in reproduction occur rapidly when a

different host environment is encountered. Also, the

decline in egg density along the length of the gallery when

females were switched from thick to thin phloes suggests

that nutrients are accumulated when in thick phloem and

subsequently used during initial oviposition when in thin

phloem. As a result, egg density decreases over time after

transfer to thin phloem. Similarly, initial reproduction in

thick phloem appears to be affected by the presumed physical

and nutritional constraints that are encountered in thin

phloem; that is, egg density increases over time after

females are transferred from thin to thick phloem.

Another point to consider is that very few galleries

contained any appreciable length of terminal egg-free

gallery; when it did occur the phloem thickness class in

which the gallery had been constructed was almost invariably








"thin." Thus, the OR and ED values presented in this

chapter probably approach the upper limits attainable by

this bark beetle species; that is, because females were

widely spaced and removed before reaching the bolt ends,

they did not encounter any apparent intraspecific

competition, associated microorganisms from other galleries,

or discolored phloes, all of which are known to lower

oviposition in bark beetles (McMullen and Atkins 1961;

Franklin 1970; Amman 1972; Yearian et al. 1972; Thomson and

Sahota 1981; Wagner et al. 1982). Because the above factors

were minimized by the experimental design of this study, it

seems logical that the differences in reproductive

performance observed in this study are best explained in

terms of the aforementioned nutritional and physical

constraints to boring in thin versus thick phloem.



Summary

In summary, the following points can be made with respect

to I. calligraphus longevity and fecundity in relation to

slash pine phloem thickness.

1. Females live longer when constructing egg gallery in

thicker phloem.

2. Total length of gallery constructed per female

lifetime is apparently little affected by phloem

thickness.

3. Realized fecundity is greater in thicker phloem.






45

4. The number of eggs laid per unit time as well as the

number laid per unit length of gallery is greater for

females in thicker phloem.

5. Female reproduction can apparently be modified by a

new host environment within a single day.

6. Such results demonstrate the potential influence the

host tree can have on biological parameters of

relatively large phloem-feeding insects such as I.

calligraphus. Great care should therefore be

exercised when selecting host materials for bark

beetles studies, especially if phloea thickness

ranges from thinner to thicker than the average width

of females used in a study.














CHAPTER IV
IPS CALLIGRAPHUS RE-EMERGENCE, BROOD DEVELOPMENT, BROOD
PRODUCTION PER PARENT FEMALE, AND BROOD-ADULT EMERGENCE,
PRONOTAL WIDTH, AND SEX RATIO IN RELATION TO TEMPERATURE AND
SLASH PINE PHLOEN THICKNESS



Introduction

The studies described in chapters II and III have shown

that slash pine phloem thickness has a profound effect on I.

calligraphus reproductive performance. The question as to

whether or not variation in phloem thickness also affects

parent adult re-eaergence, brood developmental time, brood

production per parent female, and brood adult emergence,

pronotal width (a measure of body size), and sex ratio

naturally followed.

Relatively little has been published on the re-emergence

process in Ifs bark beetles (Foltz et al. 1984). This is in

sharp contrast to the abundant information on re-emergence

by the southern pine beetle, Dendroctonus frontalis (Cooper

and Stephen 1978; Wagner et al. 1981a, 1981b; Gagne et al.

1982). Several accounts of I. calligraphus development are

found in the literature (Dale 1967; Yearian and Wilkinson

1967; Yearian et al. 1972; Ascencio 1979). Overall, these

studies described the effects of temperature, diet and/or

symbionts on rate of brood development. Data were presented








by Dale (1967) on brood production per parent female and

times to 50% brood emergence for I. calliqraphus reared at

several temperatures. He also reported average pronotal-

width values of 1.6-1.8 aa for brood adults. In several

studies a 1:1 sex ratio has been reported for I.

callijraphus brood adults (Wray 1951; Dale 1967; Cook et al.

1983).

Several laboratory studies were conducted during 1981 in

order to investigate the relationship between slash pine

phloem thickness and the above parent adult and brood

parameters. The results of these studies will be discussed

in this chapter.



Methods and Materials


Bolt and bark slab preparation. Rearing materials were

prepared from 20-year-old slash pine trees growing in a

plantation with a site index of 58 ft (17.6 a) at 25 years,

near Orange Heights, Alachua County, Florida. Sixteen trees

were felled between 12 April and 30 September 1981. Phloem

thickness along the trunk measured 0.5-1.5 mm on 7 of these

trees, and 2.5-3.5 an on the other 9 trees. These phloea-

thickness ranges were considered, respectively, "thin" and

"thick" relative to the average pronotal width of I.

calligraphus adults; average pronotal width for Florida

populations range between 1.7-1.8 ma (see chapter II).

After felling, bolts (30-35 ca long) were cut from the lower






48

trunk of each tree, end-dipped in a benoayl fungicide-water

solution (1%), and dried for 3-4 days at 40-420C and 40-50%

RH. Following drying, the loose outer-bark flakes were

removed and the bolt ends were pared back until unstained

phloem was detected. Those rearing materials that were used

as bolts were then end-dipped in melted paraffin. However,

in the case of bark slabs, a few of the bolts were

subsequently grooved on a table saw, with the bark slabs

(30-34 ca long, 10-14 cm wide, 2-4 cm thick) then cut away

by splitting with ax and hammer. Each slab was coated with

paraffin on all cut surfaces. Bolts and slabs were stored

at 200C until used.


Source of experimental beetles. Parent adults were

reared from 15- and 20-year-old slash pine trees having

thick phloem; 6 trees were cut in all. These trees were

felled throughout the period of study and allowed to undergo

natural infestation by I. calligraphus. When most of the

developing brood reached the pupal stage, infested sections

were taken to the laboratory and stored in outdoor emergence

cages. Emerging brood adults were collected several times

daily, sexed according to the form of the third elytral

tooth (Hopping 1963), put into containers with moist paper

towels, and stored at 200C until used.

In two studies, brood adults reared from thick- and thin-

phloem bolts at 300C (first filial generation = Fl), were

used as parent adults to produce the subsequent F2






49

generation. As above, the F1 brood adults were collected

and sexed daily, and stored at 20oC until used.


Introduction of beetles into bolts and bark slabs. Only

mature, non-injured adults that were collected within 48 h

prior to the time of introduction were used as parent

adults. Following the methods of Wilkinson (1964), "starter

holes" were drilled obliquely through the outer bark and

into the underlying phloem. Two starter holes were made on

opposing sides of each bolt along the aid-line. A single

adult male was placed into the long section of a size 00

gelatin capsule that had been pierced on the end for

ventilation and contained a ring of paper for footing. The

capsule was secured over the starter hole with a ring of

Duxseal(R) sealing compound. Hales not actively boring

within 1 h after introduction were replaced. Hales were

allowed about 24 h to construct a nuptial chamber at 300C.

Three females were serially introduced into each nuptial

chamber at 30-45 min intervals as described above. The

infested bolts and slabs were randomly assigned to 1 of 3

temperature treatments (200, 250, 300C), and stored in

ventilated rearing cans (photoperiod 12L:12D; 55-70% RH).

These temperatures were selected because in Alachua County,

Florida, summer temperatures can average near 300C, while in

spring and fall they average near 20oc (Dohrenwend 1978).

With respect to the FI-F2 study, F1 adults from the 300C

treatment that had been collected within 24 h prior to the








time of introduction were used as parent adults. The F1

adults were introduced into thick-phloea bolts using the

procedures and sex ratios described above, and held at 300C.


Data collection. Ips calliqraphus egg gallery

construction and brood development were monitored by x-

raying slabs with a Faxitron(R) X-ray unit and Kodak(R) AA

film. Infested slabs were radiographed at regular intervals

throughout the period of oviposition and subsequent brood

development. Re-emergence of parent adults was tallied

daily. The numbers of larvae, pupae, and young brood adults

observed on each radiograph were recorded on a per-slab and

per parent-female basis. Following the last day of

radiography, a portion of the slabs were frozen while the

others were left to allow for brood adult emergence. The

frozen slabs were later dissected to obtain values of

initial oviposition. An acetate tracing was made of each

dissected slab to show the nuptial chamber, egg galleries,

and egg niches. Brood adult emergence was tallied daily.

Developmental time was recorded in days starting from the

date of parent female introduction. Production of brood

adults was recorded on a per parent-female basis. Bolts and

slabs were dissected after brood emergence had ceased in

order to record the actual number of egg galleries and egg

niches from which the individuals had originated. This was

done to avoid counting those parent females that had either

re-eaerged or died before producing brood. All brood adults






51

were sexed, and from a sample of these adults, the pronotal

width was measured using a microscope with ocular

micrometer.

In the F1-F2 study, bolts were debarked when most of the

F2 brood reached the adult stage and all individuals were

collected. The pronotal width and sex of the F2 brood

adults were determined from samples of adults representing

each rearing bolt. The F2 sex ratio was expressed on a per-

bolt basis.


Analyses. Data were analyzed with the t-test and general

linear models procedures of the Statistical Analysis System

(SAS), version 1982.3. Preliminary analyses, using the t-

test, indicated no significant (P>0.05) differences between

experiments conducted in bolts and slabs of the same phloem

thickness with respect to parent adult re-emergence, brood

developmental time, and brood adult emergence time, pronotal

width, and sex ratio. These data were thus pooled in

subsequent analyses.

Re-emergence of parent adults was compared between sexes,

phloem thickness classes, and among temperature treatments,

using the t-test and Duncan's multiple-range test.

Regression analysis of re-emergence times was performed with

temperature for parent males and females separately. Brood

development in thick and thin phloem was analyzed within

each temperature treatment by comparing the proportions of

larvae, pupae, and brood adults found at various times








throughout their development. These data were analyzed

after arcsin transformation (Steel and Torrie 1980). Brood

production per parent female and times to 50% emergence of

the F1 brood adults were compared between phloem thickness

classes and among temperatures using the t-test and Duncan's

multiple-range test. Regression of average developmental

time was performed with temperature for thick and thin

phloem separately. Pronotal widths and sex ratios of the F1

and F2 brood adults were compared between sexes, phloem

thickness classes, and generations using the t-test. Sex

ratios were expressed as a percent and analyzed without

transformation by the t-test.



Results


Re-emergence of parent adults. The average number of

days to 50% re-emergence of parent males and females did not

differ significantly (P>0.10) between phloem thickness

classes, and thus these data were pooled within each sex.

On the average, parent males re-emerged about 1-2 days

earlier than parent females (Table 4-1). Overall, 90-100%

of the males and 89-100% of the females re-emerged from the

bolts and slabs used in the various studies. Average time

to 50% re-emergence decreased with increasing temperature

(Table 4-1). Regression equations of time to 50% re-

emergence (R, days) with temperature (oc) are R = 54.66 -

1.560C for males (r2=0.71, Sy.x=0.11, N=87 males), and R =








55.21 1.500C for females (r2=0.71, Sy.x=0.07, N=197

females).


Brood development. Brood developed faster in thick

phloem than in thin phloem at each of the 3 temperatures

tested (Table 4-2). The radiographs made late during

development revealed significantly (P<0.05) more individuals

in the pupal and adult stages in thick versus thin phloem.

Brood development in thick phloem is presented on a per

female-parent basis in Figs. 4-1 (200), 4-2 (250), and 4-3

(300C). In this particular study, cumulative oviposition

(%) at 20o, 250, and 300C was, respectively, 3, 8, and 15%

on day 1; 13, 27, and 37% on day 2; 40, 65, and 80% on day

4; and 71, 98, and 100% on day 8. Cumulative oviposition

reached 100% by day 16 at 250 and by day 24 at 200C. Egg

hatch occurred after about 6, 3, and 2 days at 200, 25o, and

300C, respectively, based on daily dissections of other

similarly-prepared bark slabs.


Brood adult production per parent female. More Fl brood

adults emerged per parent female from thick phloem than from

thin phloem (Table 4-3). Brood production was largest in

thick phloem at 30oc, and smallest in thin phloem at 20oC.


Brood adult emergence. Average time to 50% emergence of

brood adults was about 3-4 days sooner on thick versus thin

phloem (Table 4-4). Brood emergence, expressed as brood

adults/parent female/day, is presented in Tables 4-5 (200),






54

4-6 (250), and 4-7 (300C). Time to 50% adult emergence was

inversely correlated with temperature. Regression equations

for time to 50% brood emergence (E, days) with temperature

(oC) are E = 108.00 2.780o in thick phloem (r2=0.82,

Sy.x=0.02, N=3090 brood adults from 69 brood cohorts), and E

= 110.63 2.750C in thin phloem (r2=0.83, Sy.x=0.04, N=1006

and 42).


Brood adult pronotal width. Pronotal widths of F1 males

and females from thick phloem were 8 and 6% larger,

respectively, than those for the same sex from thin phloem

(Table 4-8). Hales were significantly (P<0.01) wider (ca.

5%) than females when reared from thick phloem. However,

when reared in thin phloem, males and females had similar

pronotal widths (P>0.49). With respect to the F2 brood

adults, who all developed in thick phloem, pronotal width

was not influenced by parental phloem thickness (Table 4-8).

That is, progeny of the thin-phloem reared F1 adults were as

large as progeny of thick-phloem reared F1 adults.


Brood adult sex ratio. The sex ratio was approximately

1:1 (males:females) for F1 brood adults reared from thick

phloem. In thin phloea, the sex ratio was skewed in favor

of females, being ca. 1:2 (Table 4-9). In the F2

generation, where all development occurred on thick phloem,

the sex ratio of progeny from both thick- and thin-phloem

reared adults was 1:1.


















40 a PUPAE
SIa LARVAE






2 10
-0 EGGS
S30
l.



01

i .-. .

0 4 8 12 IS 20 24 28 32 36 40
DAYS POST INTRODUCTION






Fig. 4-1. Is callilraphus brood stages (no. offspring per
parent female) through time at 200C in slash pine bark slabs
(N=7) with thick (2.5-3.5 ma) phloem. Life stages were
determined trom inspection of radiographs taken on various
days (after parent-female introduction) throughout the
period of brood development.



















W B ADULTS
IM PUPAE
2 40- a LARVAE
a. 0 EGGS

L 30


20
tL
010

0 U
0 2 4 6 8 10 12 14 16 18 20 22 24

DAYS POST INTRODUCTION






Fig. 4-2. Ips calligraphus brood stages (no. offspring per
parent female) through time at 250C in slash pine bark slabs
(N=7) with thick (2.5-3.5 am) phloem. Life stages were
determined from inspection of radiographs taken on various
days (after parent-female introduction) throughout the
period of brood development.















60
30*
m ADULTS
so0 PUPAE
LARVAE

40-

a. 30
30


a 20

10


0 2 4 8 8 10 12 14 16
DAYS POST INTRODUCTION






Fig. 4-3. I3 s calli.raphus brood stages (no. offspring per
parent female) through time at 300C in slash pine bark slabs
(N=7) with thick (2.5-3.5 mm) phloem. Life stages were
determined from inspection of radiographs taken on various
days (after parent-temale introduction) throughout the
period of brood development.








Table 4-1. Average number of days to 50% re-emergence of
Igs calljgraphus male and female parent adults, starting
from the time of parent female introduction, in slash pine
bolts and slabs and maintained at 200, 250, or 300C.


Re-emergence (Days)


Male Female


X + SDI X + SD
oC N (Range) N (Range)


200 28 24.3 + 5.4al 68 25.9 + 5.5al
(16 35) (18 37)

250 30 14.1 + 3.6b2 57 15.7 + 3.0bl
(8 20) (10 20)

300 29 8.6 + 2.4c2 72 10.9 + 2.4cl
(6 15) (6 15)


iMeans followed by the same letter (within columns) or
number (within rows) are not significantly different at
the P<0.05 level (Duncan's multiple range test).








Table 4-2. Percent of Ips calligraphus brood individ-
uals (I) found in the larval, pupal, and adult stages in
slash pine slabs with thick (TK, 2.5-3.5 an) or thin (TN,
0.5-1.5 am) phloem on various days after parent female
introduction at 20, 25, and 30oC.


P Life Stages (X)
h
1 NI Larval Pupal Adult

e
oC Day a I S X + SD2 X + SD I + SD


200
28 TK 158 3 51 + 19b 49 + 19a 0 a
TN 116 4 95 + 4a 5 + 4b 0 a

323 TK 533 7 18 + 11 80 + 11 3 + 3

35 TK 163 3 6 + 4b 32 + 13a 62 + 17a
101 4 52 + 36a 40 + 31a 8 + 9b

403 TK 507 7 2 + 2 9 + 4 89 + 4

250
16 TK 854 9 31 + 10b 63 + 12a 7 + 6a
TN 189 5 93 + 5a 6 + 4b 1 + lb

20 TK 824 9 4 + 4b 11 + 4b 85 + 6a
TN 188 5 49 + 21a 48 + 20a 3 + 3b

300
12 TK 1035 10 30 + 12b 66 + 10a 4 + 4a
TN 194 4 90 + 16a 10 + 16b 0 b

16 TK 981 11 3 + 2b 5 + 3b 92 + 4a
TN 185 4 63 + 24a 29 + 15a 9 + 14b


'I=number of individuals counted; S=number of slabs used.

2Means followed by the same letter (within columns, by
life stage and day) are not significantly different at
the P<0.05 level (Duncan's multiple-range test).

3Only slabs with thick phloea were radiographed on days
32 and 40 in the 200C treatment.








Table 4-3. Ips calligraphus brood adults (F1) per
parent female from slash pine bolts and slabs with thick
(2.5-3.5 mm) or thin (0.5-1.5 am) phloem and maintained
at 200, 250, or 30oc.


Brood Adults / Parent Female


Thick Phloem Thin Phloem
--------- -- ---
NI N

X + SD2 X + SD
oc FP P (Range) F1 P (Range)


200 607 18 33.7 + 10.9bl 158 9 17.6 + 2.9b2
(13 44) (15 21)

250 556 15 37.1 + 10.9bl 229 9 25.4 + 5.0a2
(22 55) (18 29)

300 1927 36 53.5 + 17.8a1 619 25 25.8 + 5.8a2
(22 74) (16 33)


ifl=number of brood adults that emerged; P=number of
parent females that constructed egg galleries and
oviposited.

2Means followed by the same letter (within columns) or
number (within rows) are not significantly different
at the P<0.05 level (Duncan's multiple-range test).








Table 4-4. Number of days to 50% emergence of Igs
calligjirahus brood adults (Fl) starting from the time
of parent female introduction, in slash pine bolts and
slabs with thick (2.5-3.5 mm) or thin (0.5-1.5 an)
phloem and maintained at 200, 250, or 300C.


Brood Emergence (Days)


Thick Phloem Thin Phloem

N' N

S+ SD X + SD
oc F1 S (Range) F1 S (Range)


200 607 7 55.0 + 5.1a2 158 3 58.5 + 4.5al
(47 68) (51 70)

250 556 7 33.1 + 5.6b2 229 3 37.9 + 4.8b1
(25 -50) (29 50)

300 1927 11 25.5 + 3.8c2 619 9 28.8 + 3.8c1
(17 37) (22 38)


'F1=number of brood adults that
bolts and/or slabs used.


emerged; S=number of


2Means followed by the same letter withinn columns) or
number withinn rows) are not significantly different
at the P<0.01 level (Duncan's multiple-range test).








Table 4-5. Average number of Ips calligraphus brood adults
per parent female per day that emerged from slash pine bolts
and slabs with thick (2.5-3.5 ma) or thin (0.5-1.5 am)
phloea at 200C.

Brood Adults / Parent Female' / Day at 20oc

Thick Phloem Thin Phloem


Day2 N3 X + SD* Ranges N X + SD Range


47 18 1.0 + 1.0 (0.0-2.3) 0
48 24 1.2 + 1.2 (0.0-2.7) 0
49 36 1.8 + 2.0 (0.0-5.3) 0
50 47 2.4 + 2.0 (1.0-6.0) 0
51 49 2.4 + 2.0 (0.0-5.7) 6 0.7 + 0.3 (0.5-1.0)
52 50 2.4 + 1.4 (0.0-4.0) 8 0.9 + 0.4 (0.5-1.3)
53 42 2.1 + 1.0 (0.0-3.0) 9 1.0 + 0.6 (0.5-1.7)
54 45 2.6 + 0.4 (2.0-3.0) 10 1.0 + 1.2 (0.0-2.3)
55 51 2.8 + 0.6 (2.0-4.0) 15 1.7 + 0.6 (1.3-2.3)
56 52 2.6 + 1.5 (1.0-5.3) 16 1.9 + 0.6 (1.3-2.3)
57 29 1.5 + 1.1 (0.7-4.0) 8 1.0 + 0.1 (0.8-1.0)
58 27 1.4 + 1.3 (0.0-4.0) 8 1.0 + 0.5 (0.7-1.5)
59 19 1.0 + 0.8 (0.0-2.3) 11 1.0 + 0.9 (0.0-1.8)
60 18 1.2 + 1.0 (0.3-3.0) 11 1.1 + 0.5 (0.5-1.5)
61 17 1.1 + 0.6 (0.3-2.0) 14 1.7 + 0.8 (1.0-2.5)
62 12 0.8 + 1.1 (0.0-3.0) 14 1.7 + 0.7 (1.3-2.5)
63 20 1.5 + 1.4 (0.0-4.0) 8 0.9 + 0.1 (0.8-1.0)
64 16 0.9 + 0.9 (0.0-2.0) 6 0.6 + 0.1 (0.5-0.8)
65 10 0.5 + 0.5 (0.0-1.0) 4 0.5 + 0.4 (0.3-1.0)
66 11 0.4 + 0.6 (0.0-1.5) 3 0.3 + 0.3 (0.0-0.5)
67 8 0.3 + 0.6 (0.0-1.5) 2 0.3 + 0.3 (0.0-0.5)
68 6 0.2 + 0.4 (0.0-1.0) 1 0.1 + 0.2 (0.0-0.3)
69 0 2 0.3 + 0.3 (0.0-0.5)
70 0 2 0.3 + 0.3 (0.0-0.5)


'There were 18 parent females in thick phloem and 9 in thin
phloem that constructed egg gallery and oviposited.

2Values represent the number of days after parent female
introduction.

3N=number of brood adults that emerged on the day indicated.

*Means were based on the combined data from 7 bolts and/or
slabs with thick phloem and 3 with thin phloem.

sValues represent the range of values for individual bolts
and/or slabs.








Table 4-6. Average number of Ips callig.ra2hus brood adults
per parent female per day that emerged from slash pine bolts
and slabs with thick (2.5-3.5 an) or thin (0.5-1.5 mm)
phloea at 250C.

Brood Adults / Parent Female' / Day at 25oC

Thick Phloem Thin Phloem


Day2 N3 x + SD4 Ranges N X + SD Range


(0.0-1.5)
(0.0-1.8)
(0.0-5.0)
(0.0-7.0)
(1.0-5.5)
(1.0-6.0)
(1.0-4. 0)
(0.5-4.0)
(0.5-4.0)
(0.0-4.0)
(0.0-4.5)
(0.0-3.5)
(0.0-4.0)
(0.0-7.0)
(0.0-5.0)
(0.0-4.0)
(0.0-3.5)
(0.0-3.0)
(0.0-3.0)
(0.0-3.0)
(0.0-0.5)
(0.0-3.0)
(0.0-3.0)
(0.0-1.0)
(0.0-0.5)
(0.0-1.0)


0.4
0.9
0.7
0.9
1.1
1.8
2. 1
1.9
1.3
1.8
2.2
1,7
1.4
0.9
1.1
1.0
0.6
0.8
0.6
0.4
0.3
0.3


0.8
1.2
0.9
1.0
0.6
0.8
1.5
1.7
0.8
0.6
0.8
0.8
0.3
0.7
0.6
0.5
0.3
0.6
0.3
0.5
0.3
0.6


(0.0-1.3)
(0.0-2,3)
(0.0-1.7)
(0.0-2.0)
(0.5-1.7)
(1.0-2.5)
(0.5-3.5)
(0.5-3.8)
(0.7-2.3)
(1.3-2.5)
(1.3-2.8)
(1.0-2.5)
(1.0-1.7)
(0.0-1.3)
(0.5-1.7)
(0.7-1.5)
(0.3-1.0)
(0.3-1.5)
(0.3-1.0)
(0.0-1.0)
(0.0-0.5)
(0.0-1.0)


IThere were 15 parent females in thick phloes and 9 in thin
phloem that constructed egg gallery and oviposited.

2Values represent the number of days after parent female
introduction.

3N=number of brood adults that emerged on the day indicated.

4Means were based on the combined data from 7 bolts and/or
slabs with thick phloem and 3 with thin phloem.

sYalues represent the range of values for individual bolts
and/or slabs.


0.4
0.8
2.5
3.9
3.4
3.4
2.9
2.0
2.1
1.9
1.6
1.3
1.4
2.1
1.6
1.3
1.0
0.5
0.7
0.7
0.1
0.5
0.5
0.4
0.1
0.2


0.6
0.7
2.1
2.4
1.3
1.5
1.0
1.3
1.2
1.6
1.6
1.5
1.6
2.6
1.8
1.5
1.4
1.1
1.1
1.1
0.2
1.1
1. 1
0.5
0.2
0.3








Table 4-7. Average number of Ips calligraphus brood adults
per parent female per day that emerged from slash pine bolts
and slabs having either thick (2.5-3.5 am) or thin (0.5-1.5
ra) phloem at 30oC.

Brood Adults / Parent Female' / Day at 300C

Thick Phloem Thin Phloem


DayZ N3 x + SD4 Ranges N I SD Range


17 5 0.2 + 0.5 (0.0-1.7) 0
18 19 1.0 + 1.9 (0.0-6.0) 0
19 52 1.8 + 2.2 (0.0-6.0) 0
20 85 2.8 + 2.7 (0.0-7.0) 0
21 131 4.0 + 2.6 (0.0-7.5) 0
22 172 4.3 + 2.7 (2.0-8.8) 4 0.1 + 0.2 (0.0-0.5)
23 187 5.1 + 3.9 (0.7-13.0) 17 0.7 + 1.0 (0.0-2.7)
24 203 5.5 + 4.6 (0.7-14.0) 59 2.0 + 1.6 (0.0-4.8)
25 134 3.0 + 2.9 (0.0-7.0) 63 2.2 + 1.8 (0.0-5.5)
26 152 3.0 + 3.0 (0.0-7.0) 53 2.1 + 1.2 (0.3-4.0)
27 211 4.2 + 4.8 (0.0-14.3) 72 3.0 + 1.8 (0.8-6.5)
28 146 2.8 + 3.8 (0.0-10.3) 40 1.4 + 0.8 (0.0-2.8)
29 135 2.6 + 3.4 (0.0-10.0) 47 1.9 + 0.6 (1.0-3.0)
30 98 1.9 + 2.4 (0.0-6.3) 73 2.7 + 1.1 (1.0-4.3)
31 64 1.3 + 1.8 (0.0-6.0) 42 1.6 + 1.3 (0.0-4.0)
32 57 1.1 + 1.9 (0.0-6.0) 42 1.7 1 1.5 (0.0-4.0)
33 24 0.5 + 0.7 (0.0-2.0) 31 1.1 + 0,7 (0.0-2.5)
34 23 0.4 + 0.7 (0.0-2.0) 26 1.1 + 0.4 (0.5-2.0)
35 10 0.2 + 0.3 (0.0-1.0) 10 0.5 + 0.6 (0.0-1.5)
36 10 0.2 + 0.4 (0.0-1.0) 11 0.6 + 0.4 (0.0-1.0)
37 9 0.2 + 0.2 (0.0-0.5) 21 0.8 + 0.5 (0.0-1.5)
38 0 8 0.2 + 0.3 (0.0-0.8)


'There were 36 parent females in thick phloem and 24 in thin
phloem that constructed egg gallery and oviposited.

2Values represent the number of days after parent female
introduction.

3N=number of brood adults that emerged on the day indicated.

*Means were based on the combined data from 11 bolts and/or
slabs with thick phloes and 9 with thin phloem.

sValues represent the range of values for individual bolts
and/or slabs.








Table 4-8. Pronotal width of Ips calliqraphus sale and
female brood adults reared in slash pine bolts having either
thick (TK, 2.5-3.5 am) or thin (TN, 0.5-1.5 an) phloen (F1
generation), and similarly, by using F1 adults reared at
300C from both thick and thin phloem as parents, the
pronotal width of the F2 brood adults that were reared in
thick-phloea bolts at 300C.


Pronotal Width (mm)

P
h F1 Brood Adults F1 to F2 F2 Brood Adults
1 Change
o in
e X + SD2 Phloea X + SD
a NM (Range) ____ N (Range)


Hales

TK 50 1.84 + 0.09a2 TK to TK 50 1.90 + 0.09al
(1.7 2.1) (1.7 2.1)

TN 50 1.70 + 0.14b2 TN to TK 50 1.89 + 0.09a1
(1.4 2.0) (1.7 2.1)

Females

TK 50 1.77 + 0.08a2 TK to TK 50 1.81 + 0.08al
(1.6 1.9) (1.7 2.0)

TN 50 1.69 + 0.08b2 TN to TK 50 1.78 + 0.08a1
(1.5 1.8) (1.5 1.9)


'Each sample consisted of 50 randomly-selected adults

2Means followed by the same letter (within columns by sex)
or number (within rows) are not significantly different at
the P<0.05 level (t-test).








Table 4-9. Hale proportion of Ips calligraphus brood adults
reared from bolts having either thick (TK, 2.5-3.5 an) or
thin (TN, 0.5-1.5) phloem (F1 generation), and similarly,
using F1 adults reared at 300C from both thick and thin
phloem as parents, the sale proportion of the F2 generation
when reared in bolts having thick phloes at 300C.


Percent Hales


P F1 Brood Adults F1 to F2 F2 Brood Adults
h Change
1 N' in N
o Phloes
e X + SD2 SD
a I B (Range)3 I B (Range)


TK 1223 12 49.9 + 4.2al TK to TK 1005 9 49.2 + 3.1al
(42 59) (45 54)

TN 280 5 33.7 + 5.5b2 TN to TK 764 9 50.3 + 3.4b1
(29 41) (46 56)


'I=number of brood adults collected; B=number of bolts used.

2zeans followed by the same letter (within columns) or
number (within rows) are not significantly different at the
P<0.05 level (t-test). Means were calculated on a per-bolt
basis.

3Values represent the range of percent from individual
bolts.








Discussion

Re-emergence of Parent Adults

The similarity in time to 50% re-emergence between the 2

phloem thickness classes at a given temperature is related

to the rate of gallery construction (GCB) by parent females.

Lines of evidence are (1) I. calligraphus constructs egg

galleries that follow the wood grain (Wilkinson et al.

1967), (2) GCR does not vary significantly with changes in

phloem thickness (see chapters II and III), and (3) females

in both thick and thin phloem reached the bolt and slab

extremes (which were similar in length between phloem

thickness classes) in about equal times. The radiographs

indicated that upon reaching the top or bottom of a slab,

females generally stopped ovipositing but continued to

construct gallery (terminal egg-free gallery). It was at

this time that the females probably changed from a

reproductive to a flying condition, and eventually re-

emerged. Such changes have been documented in the mountain

pine beetle, Dendroctonus ponderosae (Reid 1962). These

results indicate that re-emergence of I. calligraphus

parent-adults is strongly influenced by the contiguous

length of pine material available and suitable for

oviposition.

The close agreement between average times of male re-

emergence (Table 4-1) with cumulative 100% oviposition (see

"Brood development" section of this chapter) and earlier re-






68

emergence in males compared to females suggest that sales

may utilize cessation of oviposition as a signal for re-

emergence. Such behavior would maximize a male's

reproductive success assuming that he would be (1) guarding

and assisting those females with which he had Rated during

their period of active oviposition, and (2) allowing himself

sufficient time to re-emerge, locate other host material,

and construct a new nuptial chamber prior to peak female re-

emergence.



Development and Brood Adult Characteristics

The observed variations in I. calligraphus developmental

time, brood production, and brood adult emergence, pronotal

width, and sex ratio are probably related to (1) differences

in the physical and nutritional nature of xylem, phloem, and

outer bark and (2) differences in the relative proportions

of these tissues that are encountered by larvae when

tunneling in thin versus thick phloem. As was discussed in

chapter II, mostly thick-walled, nutrient-poor cells

constitute xylem and outer bark of pines, whereas mostly

thin-walled, nutrient-rich cells constitute phloem (Howard

1971; Kramer and Kozlowski 1979). In slash pine, water

content averages ca. 69% in phloem (Martin 1969), 44% in

xylem (Miller 1959), and 23% in outer bark (Martin 1969).

Thus, the larval environments afforded by host trees with

either thick or thin phloem are quite distinct. Larvae in








thin phloem (0.5-1.5 a) especially last (3rd) instars

whose head capsules alone measure ca. 1 am in width

(Wilkinson 1963), must excavate more of the adjacent xylem

and/or outer bark than their counterparts in thick phloem.

Larvae developing in thin phloem are thus presented with an

environment that offers fewer nutrients and water per unit

length of gallery constructed, and one that probably also

requires more energy to tunnel through. The foregoing

scenario explains the protracted development observed in

thin phloea, as well as delayed brood emergence. In other

studies, developmental time of Tribolium confusum Jacquelin

duVal (Coleoptera: Tenebrionidae) was lengthened when

larvae were reared on a low- compared to a high-lysine diet

(Lamb and Loschiavo 1981). Similarly, developmental time of

other Coleoptera is inversely correlated with nitrogen

content (Bletchly and Farmer 1959) and moisture content

(Cannon and Robinson 1981) of wood.

In thin phloem, I. calliqraphus larvae constructed

visually longer mines prior to pupation than did larvae in

thick phloea. Similar behavior was observed by R. C.

Wilkinson, (personal communication) in I. calligraphus

larvae reared on slash pine foliage-based diets. In diet

containing current year's foliage (believed to be of

relatively low nutritional quality), larval mines were

longer and developmental time was protracted compared to



i Department of Entomology & Neaatology, University of
Florida, Gainesville, Florida 32611.






70

larvae on diet containing previous year's foliage. Other

results from that study are reported in Richeson et al.

(1970). Dendroctonus ponderosae larvae in thin phloem mined

faster than those in thick phloem during the first 2 weeks

of larval life (Amman and Cole 1983).

Webb and Franklin (1978) reported that D. frontalis

produced long larval mines when phloem water content (PVC)

was relatively high. In my study, although PWC was not

measured in all rearing materials, PWC did not vary

significantly (P>0.10) between phloem thickness classes (ca.

70% in each). Similar results were reported in chapters II

and III. Webb and Franklin (1978) suggested that high PVC

was detrimental to the symbiotic bluestain fungus,

Ceratocystis minor (Hedgc), associated with D. frontalis,

and thereby indirectly influencing brood survivorship as was

shown to occur by Barras (1973). However, in the case of I.

calligraphus, Yearian et al. (1972) successfully reared this

species through 4 successive generations in fungus-free

slash pine logs. In my study, growth of Ceratocystis jps

(Rumbold) C. Noreau, the symbiotic bluestain fungus

associated with I. calligraphus, was apparently similar in

thick and thin phloem; C. ips perithecia were first observed

on the walls of the nuptial chamber on day 6, and along the

egg-gallery walls on day 8 following parent-female

introduction at 300C in both thick and thin phloem.

Therefore, the observed variations in brood development






71

recorded in the present study probably cannot be explained

in terms of either PWC or C. i2s.

Greater brood production/female in thick phloes is

probably best explained in terms of greater original egg

density (eggs/ca of gallery), than in terms of greater brood

survival in thick versus thin phloes. In this study, brood

mortality was similar between phloem thickness classes,

being ca. 35-50%. As discussed in chapter II, egg density

increased with both increasing phloem thickness and

temperature. Therefore, assuming equal survival of larvae

in thick and thin phloem, the above differences in final

brood production are a reflection of greater initial

oviposition in thicker phloem.

Dale (1967) reported I. calligraphus brood production

values of 15-18 brood adults/feaale when reared at

temperatures between 200-300C. He used 30-cm-long bolts

from various pine species and infested these at the rate of

2 sales and 4 females per bolt. These relatively low brood-

production values suggest that thin-phloem rearing materials

were used in his study. This very likely would have been

the case, because in general the southern pines have

relatively thin phloem, averaging about 1.5 am (Howard

1971).

Larvae in thin phloem had longer developmental times than

those reared in thick phloem, and the resulting thin-phloem

reared adults were smaller than those reared in thick






72

phloem. This probably occurred because in thin phloea, more

of the ingested food would have been used as an energy

source for tunneling and/or body maintenance, instead of

being utilized for growth. In the study by Dale (1967),

average time to 50% emergence and pronotal width of the

brood adults were ca. 45 days and 1.7 am at 250, and 29 days

and 1.6 am at 300C, respectively. Such results, in

comparison to the ones presented here, further indicate that

the host materials used in Dale's study had relatively thin

phloem. Similar results have been reported for D.

ponderosae when reared in thin phloem (Aaman and Pace 1976;

Amman and Cole 1983).

Great variation in adult size has been reported for

several wood-inhabiting Coleoptera. Andersen and Nilssen

(1983) suggest that such variation in adult size reflects

the inability of the wood-feeding larvae to choose and

determine their own nutritional situation. That is, adult

females may not be able to evaluate and choose the best

larval food, and thus by ovipositing on a given host they

may force their relatively immobile larvae to develop on

materials of low nutritional quality.

Although pronotal width of thick-phloem reared males and

females was only slightly larger than that of thin-phloem

reared males and females, such differences become magnified

when body volume is considered. This occurs because in a

cylinder, volume is related to the square of the diameter






73

(i.e., pronotal width). In another study (F. Slansky Jr.2

and R. A. Haack, unpublished data), dry weights of brood

adults from thick and thin phloes were, respectively, 3.2 ag

(+0.4 SD, n=30) and 2.1 (+0.5, n=34) for males, and 2.7

(+0.4, n=35) and 1.9 (+0.3, n=40) for females.

The relatively large size of males compared to females,

when reared in thick phloes, is probably associated with

differential development times for each sex. Hale larvae

seem to develop over a longer period of time as indicated by

the longer time to 50% emergence of brood males compared to

females for the same cohort, and thus they attain a larger

final size than do females. This finding was reported by

Dale (1967) and was also noted in my study of I.

calliqraphus voltinisa as detailed in chapter V. When

development occurs in thin phloem, males seem to be more

sensitive than females to the adverse conditions therein.

Male size is reduced to a greater extent than is female

size, so much that there is no significant difference in

final adult body size between the sexes. The importance of

phloem thickness is further indicated by the fact that the

small size of the thin-phloem reared F1 adults did not

affect the final size of their progeny when reared on thick-

phloem.






2 Department of Entomology & Nematology, University of
Florida, Gainesville, Florida 32611.






74
When considering the biology of I. calligraphus, at least

2 advantages in having males larger than females can be

postulated. A larger entry tunnel night enable females to

enter the male-constructed nuptial chamber more quickly and

thus avoid predators. Also, in those cases where a male has

constructed "starter tunnels" away from the nuptial chamber,

a female could probably begin oviposition sooner because she

would not need to re-bore that length of gallery.

The apparently longer developmental time of males may

contribute to the female-biased sex ratio observed in thin

phloem. Assuming that the initial sex ratio was 1:1, longer

male developmental time may have allowed for greater

mortality from cannibalism (by larvae and general adults)

and/or lower male survival under the adverse conditions of

thin phloem. Larvae may be relatively "crowded," in a

physical sense, when developing in thin phloem. The effects

of larval crowding in various insects include smaller adult

size, protracted development, lower survival, and changes

from the normal sex ratio (Klomp 1964; Peters and Barbosa

1977). Crowded conditions may also lead to a higher

incidence of infection by the bacterium, Serratia marcescens

Bizio, in I. calligraphus general adults (Jouvenaz and

Wilkinson 1970). Amman and Cole (1983) reported lower male

survival when D. ponderosae populations were stressed by

crowding, cold, thin phloem, and to drying of the host

tissues. A male-lethal factor has been suggested by Lanier






75

and Wood (1968) as an explanation for highly female-biased

broods in Dendroctonus jeffreyi Hopkins.

Alternately, the female-biased sex ratio in progeny from

thin phloem could have occurred if I. calligraphus parent

females were able to regulate the sex of their progeny.

Charnov (1982, p. 65) stated that there are few examples

where environmental control of sex development has been

documented in diploid insects; haplodiploidy has not been

reported in Ips bark beetles (Kirkendall 1983). Another

possible explanation for the skewed sex ratio is that there

may be more than 1 type of female as reported by Hopping

(1962, 1964) and Bakke (1968), for Ips tridens Hannerheim

and Ips acuminatus (Gyllenhal), respectively. They reported

that some females produce all-female broods while others

produce bisexual broods. It is of interest to note that

these species occur in northern North America and Europe,

respectively, and thus such findings may reflect adaptations

by these beetles to their harsh environment. Nevertheless,

I have no evidence to support the possibility of 2 types of

females in I. calligraphus because in all of my rearing

experiments with this bark beetle, I have never observed a

single all-female brood. Thus, these latter suggestions

probably do not explain the female-biased sex ratio observed

in this study when development occurred in thin phloem.








Summary

In summary the following points can be made with respect

to I. calligraphus development in thin and thick slash pine

phloea.

1. The average number of days to 50% re-emergence of

parent adults decreases with increasing temperature,

but apparently it is unaffected by phloes thickness.

2. The rate of brood development is positively

correlated with both temperature and phloem

thickness.

3. The number of F1 brood adults produced per parent

female increases with both increasing temperature and

phloem thickness.

4. The average number of days to 50% emergence of brood

adults decreases with both increasing temperature and

phloem thickness.

5. Pronotal width of thick-phloem reared brood adults is

greater than that of brood adults reared from thin

phloes. Male pronotal width is greater than that of

females when development occurs in thick phloem but

not when it occurs in thin phloem.

6. The sex ratio (male:female) of brood adults is 1:1

when reared in thick phloes and 1:2 when reared in

thin phloem.

7. The progeny of thin-phloem reared F1 adults are as

large and of the same sex ratio (1:1) as are the






77

progeny of thick-phloem reared F1 adults when all

development occurs in thick phloem.














CHAPTER V
SEASONAL DEVELOPMENT AND DIURNAL ACTIVITY PATTERNS OF IPS
CALLIGRAPHUS IN FLORIDA



Introduction

Little information is available on seasonal development

of the southern pine bark beetles. Thatcher (1960),

extrapolating from developmental rates reported in the

literature, predicted that in the southern USA at least 3

generations per year would be completed by Dendroctonus

frontalis, and similarly, at least 2 by Dendroctonus

terebrans (Olivier), 10 by Ips avulsus, and 6 by both Ips

calligraphus and Ips qrandicollis. A later study by

Thatcher and Pickard (1967) revealed that D. frontalis

completed 7 (and a partial 8th) consecutive generations

within a year's time in east Texas. ;Rs calliqraphus is

reported to complete 4 generations per year in California

(Wood and Stark 1968), and 12 generations per year in Mexico

(Ascencio 1979).

Many bark and ambrosia beetles show a bimodal pattern of

daily flight on warn summer days, with peaks occurring

during early morning and again as evening approaches

(Anderson 1948; Gara and Vite 1962; Rudinsky 1963; Budinsky

and Daterman 1964; Vite et al. 1964; Hertel et al. 1969).






79

During the summer in Florida, peak flight of I. calligraphus

occurs from 0600-0900 h and 1600-2000 h (Wilkinson 1964).

Few records exist on diurnal flight of bark beetles during

seasons other than summer. Spring flight often occurs as a

single peak during late afternoon (Rudinsky 1963; Rudinsky

and Daterman 1964). Kinn (1978) reported that during the

winter months in Louisiana, D. frontalis had a single, early

afternoon peak of emergence. He also reported similar daily

activity patterns for both males and females during the

different seasons.

Scolytid flight is influenced greatly by the prevailing

weather conditions. Flight activity is generally stimulated

by rising temperatures (Henson 1962; Moser and Dell 1979),

increasing light intensity (Mason 1969), and with cloudy

conditions and the onset of rainstorms (Vite et al. 1964),

but retarded by heavy rains (Moser and Dell 1979) and

excessive temperatures (Henson 1962). The possible

relationship between these meteorological phenomena and bark

beetle flight behavior has been reviewed by Chapman (1967).

For many scolytids in the southern USA, the threshold

temperature for flight ranges from 180-220C (Vite et al.

1964; Turnbow and Franklin 1980). Predictive equations for

D. frontalis developmental time have been established

utilizing the day-degree concept of Arnold (1959) and field-

collected temperature data (Mizell and Nebeker 1978).






80

The objectives of this study were (1) to determine the

seasonal development (voltinism) of I. calligraphus in

thick-phloem slash pines in north-central peninsular

Florida, (2) to record the diurnal activity pattern of male

and female I. calligraphus adults throughout the year, and

(3) to describe the above findings in regard to available

weather data for Gainesville, Florida.



Methods and materials


Tree selection and treatment. Apparently healthy,

dominant and co-dominant, 21- to 22-year-old slash pine

trees were used in this study. The trees were growing in a

plantation with a site index of 58 ft (17.6 m) at 25 years

near Orange Heights, Alachua County, Florida. Phloem

thickness along the trunk was generally greater than 2.5 mm

in all selected trees. Such a thickness was considered

"thick" relative to the pronotal width of I. calligraphus

adults which generally range from 1.5-2.1 am in Florida

populations (see chapters II and IV). After felling, the

trunks were supported off the ground and then left in the

field to undergo natural infestation by I. calliqraphus and

its associates. The trees were inspected every 2-5 days for

evidence of bark beetle attack, i.e., pitch tubes and boring

frass. During inspection, bark was removed from some

attacks along the length of the trunk to determine the

beetles' progress. Records were made on presence or absence








of completed nuptial chambers, parent females, eggs, and

larvae. Later inspections were made to determine the time

of pupation. When most individuals reached the pupal stage,

infested trunk sections (50-90 cm long) were cut, returned

to the laboratory (a distance of ca. 12 miles), and placed

into screen emergence cages (ca. 96 ca long, 71 cm wide, 82

cm high) in an open-air insectary (ca. 5.5 a long, 3.8 a

wide, 2.2 m high).


Brood adult collection. Emerging brood adults were

collected several times daily from the screen walls of the

cages. It was observed that I. calligraphus adults would

readily fly and/or walk from the pine logs to the screen

walls throughout the day when conditions were presumably

favorable for flight. However, when conditions were not

favorable, adults were found to remain on the bark of the

logs either walking or remaining motionless. Collecting

adults from the screen walls was thus considered an

appropriate means of approximating the natural diurnal

flight activity of I. calliqraphns adults. Whenever

possible, collections were made at 2-hour intervals from

early morning (0700-0900 h) until dusk (1700-2000 h, Eastern

Standard Time). Beetles were placed into containers

labelled by date and collection time, frozen, sexed

according to the form of the third elytral tooth (Hopping

1963), and returned to the freezer and there stored by

generation number. Numbers of emerging male and female






82

brood adults were recorded daily. Average time to 50% brood

emergence was calculated when emergence stopped for a given

cohort. In addition, length and diameter-inside-bark were

recorded for all bolts, and from these values the bark

surface area was calculated. The bark was then removed from

several of the bolts and the inner surfaces inspected for

bark beetles, associates, and extent of cerambycid grazing;

observations were recorded.


Generation synchronization. The time at which 50% brood

emergence occurred for a given generation was considered the

starting point for the subsequent generation. Because the

exact day on which 50% emergence was to occur was at first

unknown, several trees had to be felled in order to bracket

this occasion. This was done by felling 2-6 unifested slash

pines throughout the period of brood emergence at 3-7 day

intervals (Fig. 5-1). These newly felled trees were

inspected regularly as described above for signs of beetle

attack with dates and observations recorded. The tree

eventually selected as the "brood tree" for the following

generation was the one whose date of colonization most

closely matched the date of 50% emergence of the then

current generation. Overall, one generation was matched to

the next with apparently no more than a 1-2 day error. The

above procedures were carried out for one generation after

another beginning in March 1982 and going through May 1983.

The initial generation that developed was used mainly to






83

develop proper techniques. Then, starting from the date of

50% emergence for that generation, the study was conducted

for approximately one year's time.


Data collection and analyses. For each generation, the

daily counts of males and females were used to calculate

average times to 50% emergence for each sex separately and

combined. Means were compared between sexes and among

generations using the t-test and Duncan's multiple-range

test. Analyses were performed using the general linear

models procedures of the Statistical Analysis System (SAS),

version 1982.3. Significance was tested at the P<0.05

level. The duration of each generation (generation time)

was calculated as the number of days between dates of 50%

emergence for two consecutive generations. The sex ratio

was determined for each generation based on all adults

collected. The proportion of males in each generation as

well as for all generations combined was compared to 0.5

(the proportion expected in a 1:1 sex ratio) by the z-test

(two-tailed) (Freund 1960, p. 253). Similarly, the mean

male proportion (averaged over the 9 generations) was

compared to 0.5 using the t-test (Freund 1960, p. 222).

Brood adult density was calculated for each generation as

follows: Brood density = No. adults collected/bark surface

area. Data from the numerous daily collections were pooled

into 3 convenient diurnal periods: 0700-1000 h (AM),

1100-1400 h (MIDDAY), and 1500-2000 h EST (PM). This was








done because collections could not always be made at the

same times from day to day or from generation to generation.

The proportion of brood adults that emerged during each of

these periods was calculated on a daily basis using only

those days on which at least 5 beetles were collected and

collections were made at 2-hour intervals from dawn to dusk.

Means were compared among generations and the 3 collection

periods by Duncan's multiple-range test, after arcsin

transformation of the data (Steel and Torrie 1980).


Day-degree accumulation. The day-degree (OD)

accumulation for each generation was calculated summing over

all days between that generation's date of 50% emergence and

that of the generation preceding it. Three lower threshold

temperatures and two different methods were used. The

temperatures [500 (10.0oC), 550 (12.80C), and 60oF (15.6oC)]

were chosen to bracket the actual developmental threshold

temperature of I. calliqraphus, which probably lies within

these limits. Wilkinson and Foltz (1982) reported a base

temperature of about 590F for I. calliqraphus brood

development. Based on the 200 and 300C rearing data

presented in chapter IV, the threshold temperature' would be



I The threshold was calculated as shown by Kapler and
Benjamin (1960), where development in relation to
temperature is expressed as a constant in the equation K
= y(t-a), where "y" is the average number of days required
to complete development, "t" is the average daily mean
temperature, and "a" is the base temperature. In the
above calculations the threshold "a" was calculated by
simultaneously solving the equations using the 200 and
300C rearing data.






85

about 50.60 (10.30C) in thin phloem, and 52.50F (11.40C) in

thick phloem. In the mean-minus-threshold method (Pruess

1983), the formula used was OD = [ (HAXO MINO)/2] -

thresholdO; negative values were dropped. In the other

method, the above formula was employed when the daily

minimum temperature was equal to or greater than the

threshold. However, when the daily minimum temperature was

below the threshold, the following formula was used: OD =

1/2 [(MAXo thresholdO)2/(MAXO HINO) ]. The latter

formula allows for day-degree accumulation on many days when

the mean-minus-threshold method would give negative values

(Lindsey and Newman 1956; Arnold 1960). Daily maximum and

minimum air temperatures were obtained from the Official

Weather Data for Gainesville 3 WSW, Florida.2 The most

appropriate temperature/method combination was selected by

comparing their respective coefficients of variation as

described by Arnold (1959). This test statistic was

generated when the average number of day-degrees per

generation was calculated for each of the 6 combinations.













2 Published by the Department of Agronomy, University of
Florida, Gainesville, Florida 32611, in cooperation with
NOAA.








Results


Voltinism,_ generation time, and brood eaerqence. Igs

callig~Ephus completed 9 consecutive generations during a

1-year period (371 days) in north-central peninsular

Florida. Felling dates of brood trees and the overall

emergence data are presented in Table 5-1. The period of

brood emergence for a single generation ranged from as many

as 68 days (Gen. 1) in the winter to as few as 11 days (Gen.

7) in late summer. Similarly, generation time was 81 days

in duration for the 2 generations (Gens. 1-2) that developed

during the cooler months, and 27-28 days long for the 4

generations (Gens. 4-7) that developed during the warmer

months. Percent daily emergence for each of the 9

generations is depicted in Fig. 5-2.

Females tended to emerge before males of the same cohort

(Table 5-2). Average number of days to 50% female emergence

was significantly less than that of males in each

generation. Differences between male and female mean-times

to 50% emergence ranged from 8 days for the cohort that

emerged during the cooler months (Gen. 1), to 1-2 days for

those that emerged during the warmer months (Gens. 4-9).

Male and female cumulative percent daily-emergence is

presented on a seasonal basis in Fig. 5-3, and in tabular

form in Tables 5-3 (winter; Gen. 1), 5-4 (spring; Gen. 2),

and 5-5 (summer-fall; Gens. 3-9). These results clearly

demonstrate that female emergence was advanced over that of

males throughout the entire process of brood emergence.








Sex ratio and brood density. The sex ratio was

approximately 1:1 for 5 generations (Gens. 2,3,5,6,8), but in

the other 4 (Gens. 1,4,7,9), the proportion of brood males

was significantly different from the theoretical 0.5 (Table

5-2). In addition, the overall male proportion (0.45) of

all brood adults (N=7368) was significantly different from

0.5 when tested both as a proportion (z=8.76; two-tailed)

and as a mean (t=3.36; df=8; two-tailed).

Brood density varied from over 5 adults/da2 for the

generation that developed during the months of April-June

(Gen. 3), to fewer than 1 adult/da2 in the generations that

developed from January to May (Gen. 2) and from September to

October (Gen. 8) (Table 5-2). Brood density declined from

generation to generation throughout the summer (Gens. 3-7).


Diurnal aad seasonal activity patterns. In general, the

diurnal activity pattern of males and females did not differ

significantly within any generation. The data were thus

pooled with respect to sex. Similarly, the diurnal activity

pattern did not differ significantly among generations 4-7,

and thus these data were pooled. Consistent data with

respect to collection time were not available for

generations 3 (collection times had not yet been

standardized) and 9 (because the author was hospitalized).

The pattern of daily activity shifted from season to

season (Table 5-6). In spring (Gen. 2), two-thirds of the

adults were collected during the PH, with fewer recovered






88

near MIDDAY, and the fewest during the AM. As the spring

days became warmer, beetles were collected progressively

earlier during the day; beetles emerging in spring were

first collected at 1000 h on 8 May and at 0800 h on 16 May

1983. During the summer (Gens. 4-7), adult activity was

greatest in the PM, with the next most active period being

the AM. On several summer days no beetles were collected

during the MIDDAY period. In fall (Gen. 8), beetles were

most active during the MIDDAY and PH periods. During winter

(Gen. 1), nearly three-fourths of the adults were recovered

near MIDDAY, and of those remaining, most were collected at

PM. Adults were collected only once during the AM (at 1000

h on 30 January 1983) in winter. That day was unseasonably

warm for Gainesville; maximum and minimum air temperatures

were 780 and 50OF (25.60 and 10.0oC), respectively, compared

to the January 1983 monthly average of 65.20 and 420F (18.4o

and 5.60C). No beetles were collected later in the day than

1600 h until 6 March 1983, when some were recovered at 1700

h. With respect to the three collection periods, beetle

activity was greatest in the Am during summer, at MIDDAY

during winter, and in the PM during spring (Table 5-6).


Day-degree accumulation. Day-degree summations for each

of the 9 generations were quite similar (Table 5-7). There

was generally best agreement among the summer generations

(Gens. 3-8), regardless of the threshold temperature used.

However, for generations 1 and 9, fewer heat units were






89

accumulated when 550 and 60oF were used as threshold

temperatures. The smallest coefficient of variation (CV)

was associated with a threshold temperature of 50oF and the

mean-ainus-threshold method, suggesting that this

combination is the most appropriate of those tested.























W







DAYS





Fig. 5-1. Schematic representation of the field methods
employed in tae ps calligraphus vbltinism study. Depicted
are (1) emergence of brood adults for a given generation
through time and (2) the felling of thick-phloem pine trees
on various days throughout this period of brood emergence,
which were then allowed to undergo natural infestation. The
tree felled and infested nearest to the time of 50% brood
emergence was selected as the "brood" tree for the following
generation.