APPLYING THE INTRA-TREE DISTRIBUTION AND FORAGING BEHAVIOUR OF THE ELM SPANWORM, SUBSIGNARIA, ON MATURE SYCAMORE MAPLE TO MANAGEMENT PRACTICES DURING AN URBAN OUTBREAK

by

Heidi Rosanna Clarice Fry

Bachelor of Science (Honours), Biology, Memorial University of Newfoundland (2005)

A Thesis Submitted in Partial Fulfillment of

the Requirements for the Degree of

Master of Science

In the Graduate Academic Unit of Biology

Supervisor(s): Dan T. Quiring, PhD, Biology, UNB Krista L. Ryall, PhD, Forestry and Environmental Management, UNB

Examining Board: Dr. Les Cwynar, PhD, Biology, UNB, Chair Dr. Graham Forbes, PhD, Biology, UNB Dr. Graham Thurston, PhD, Forestry and Environmental Management, UNB

This thesis is accepted by the Dean of Graduate Studies

THE UNIVERSITY OF NEW BRUNSWICK

October, 2007

© Heidi R. C. Fry, 2007 Library and Archives Bibliotheque et 1*1 Canada Archives Canada Published Heritage Direction du Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington Ottawa ON K1A 0N4 Ottawa ON K1A0N4 Canada Canada

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1+1 Canada Dedicated to my parents, Mollie and Frank, and my sister, Sarah

11 ABSTRACT

Ennomos subsignaria laid most eggs on the lower bole of mature sycamore

maple. Egg hatch was synchronized with the availability of the most suitable leaves for

development on proximal branches of the lower crown, the location where most

larvae initiated feeding. Intra-tree larval and pupal distribution was not influenced by

variable natural enemy activity or foliage quality within the crown. This is the first

evidence of a restricted phenologjcal window of foliage suitability for an early-season

caterpillar feeding on leaves that have expanded past bud scales. Monitoring egg masses

on the lower bole and early-instars in the lower crown provided a reliable forecast of end

of season defoliation and therefore can assist pest managers when deciding to use (or not

to use) suppression methods. Two-thirds of the manufacturer recommended dose of bole-implanted acephate (AceCap® 97) significantly reduced E. subsignaria density and

defoliation during the treatment year.

Key words: , elm spanworm, sycamore maple, intra-tree variation, phenology, egg hatch, foraging behaviour, pest management, acephate

in PREFACE

The three main chapters presented in this thesis are independent but related

manuscripts that have been prepared for publication in Ecological Entomology (Chapter

2), Forest Ecology and Management (Chapter 3) and the Journal of Economic

Entomology (Chapter 4). The authorship of all publications will be:

Heidi R. C. Fry1, Dan T. Quiring1,2, Krista L. Ryall2'3 and Peggy L. Dixon2'4

'Population Ecology Group, Department of Biology, University of New Brunswick,

Fredericton, New Brunswick, Canada, E3B 5P7

Population Ecology Group, Faculty of Forestry and Environmental Management,

University of New Brunswick, Fredericton, New Brunswick, Canada, E3B 5P7

3Natural Resources Canada, Canadian Forest Service - Atlantic Forestry Centre, P.O.

Box 960, Corner Brook, Newfoundland and Labrador, Canada, A2H 6J3

4Agriculture and Agri-Food Canada, Atlantic Cool Climate Crop Research Centre, P.O.

Box 39088, St. John's, Newfoundland and Labrador, Canada, A1E 5Y7

During the development of these manuscripts, I was primarily responsible for the design

and organization of experiments, the preparation and presentation of the initial research proposal, collecting and analyzing data, and writing the manuscripts. Dan Quiring was

involved in all aspects of this research. Many of the ideas presented in this thesis reflect

the essential advice and guidance given by Dan. Krista Ryall provided important

feedback on experimental design as well as valuable information during the

iv development of these manuscripts. Peggy Dixon provided logistical support throughout the study, good suggestions on sampling and rearing, and provided valuable comments

and suggestions during the preparation of these manuscripts.

v ACKNOWLEDGMENTS

I sincerely thank my supervisor, Dr. Dan Quiring, for the guidance and

encouragement that he provided starting from our first conversation. Dan's excellent

academic feedback coupled with his friendly nature made my graduate studies at the

University of New Brunswick very enjoyable. Also, my co-supervisor, Dr. Krista Ryall,

provided me with important comments regarding the design of experiments and content

of manuscripts.

Thanks to my committee member Dr. Peggy Dixon, who provided valuable

comments on manuscripts, laboratory space during my field seasons and helped with

fieldwork. I also thank my committee member Dr. Yvan Pelletier who provided

important feedback during committee meetings and on manuscripts, as well as

committee member Dr. Tillmann Benfey, who also provided important comments on manuscripts. I thank Dr. Mike Duffy who provided me a teaching assistantship position

as well as Linda Allen, Rose Comeau and Bonny Morrison, who were all very helpful

during my graduate studies.

I thank my lab mates, including Drew Carleton, Leah Flaherty, Roger Graves,

Rob Johns, Jonathan Leggo, Andrew Morrison, Lauren Pinault and Kate Van Rooyen,

who were always supportive and provided feedback on presentations.

Thanks to everyone who helped me in the field and processing samples in the lab but I especially thank Ryan Pugh for his dedication and humour. During my field

seasons it was a pleasure to work out of the Atlantic Cool Climate Crop Research Centre

in St. John's where the staff was always friendly and helpful. In particular I thank

members of the Dixon entomology lab, including Robyn Auld, Janet Coombes, Nancy

vi Hudson and Carolyn Parsons, for their support and friendship. I also thank Dave Evans and the field crew working for the Department of Parks and Services in St. John's for access to my field sites. I thank the Canadian Forest Service, the University of New

Brunswick and the Canadian Tree Fund for providing financial support during my graduate studies.

This work would not have been completed without the continuous encouragement, support and understanding given by my parents, Frank and Mollie, and sister, Sarah. I was fortunate to be able to carry out my research in my hometown, St.

John's, where local enthusiasm for elm spanworm research made my field seasons even more enjoyable.

vn TABLE OF CONTENTS

ABSTRACT iii PREFACE iv ACKNOWLEDGEMENTS vi LIST OF TABLES x LIST OF FIGURES xi CHAPTER 1: GENERAL INTRODUCTION 1 References 6

CHAPTER 2: INFLUENCE OF INTRA-TREE VARIATION IN PHENOLOGY AND OVIPOSITION SITE ON THE DISTRIBUTION AND PERFORMANCE OF ENNOMOS SUBSIGNARIA ON MATURE SYCAMORE MAPLE 13 Abstract 13 Introduction 14 Methods 17 Study insect and plant 17 Study sites 17 Intra-tree distribution, parasitism and herbivory 18 Description of sycamore maple bud and leaf development 21 Effect of host phenological stage on insect performance 21 Synchrony between budburst and egg hatch 23 Statistical analyses 24 Results 25 Intra-tree distribution, parasitism and herbivory. 25 Effect of host phenological stage on insect performance 27 Synchrony between budburst and egg hatch 28 Discussion 29 Acknowledgements 33 References 34

CHAPTER 3: RELATIONSHIPS BETWEEN ELM SPANWORM, ENNOMOS SUBSIGNARIA, DENSITY AND DEFOLIATION ON MATURE SYCAMORE MAPLE IN AN URBAN ENVIRONMENT 48 Abstract 48 Introduction 49 Methods 52 Description of study insect 52 Study sites 52 Estimating defoliation 53 Predictive density-defoliation relationships 53 Statistical analyses 56 Results 56 Estimating defoliation 56 Predictive density-defoliation relationships 57

Vlll Discussion 57 Acknowledgements 60 References 60

CHAPTER 4: SUPPRESSION OF ENNOMOS SUBSIGNARIA ( : GEOMETRIDAE) ON ACER PSEUDOPLATANUS (ACERACEAE) IN AN URBAN FOREST USING BOLE-IMPLANTED ACEPHATE 69 Abstract 69 Introduction 70 Materials and Methods 71 Study insect 71 Study site and experimental design 72 Application of implants 73 Evaluation of efficacy in treatment year 73 Evaluation of efficacy in post-treatment year 75 Statistical analyses 76 Results 77 Evaluation of efficacy in treatment year 77 Evaluation of efficacy in post-treatment year 78 Discussion 78 Acknowledgements 82 References cited 82

CHAPTER 5: GENERAL DISCUSSION 90 References 94

CIRRICULUM VITAE

IX LIST OF TABLES

Table 3.1. Summary of linear regression analyses evaluating relationships between

mean early and late instar densities of E. subsignaria and mean defoliation on

twenty mature sycamore maples in 2006. Both insect density and defoliation

were measured in the lower, mid and upper crown but are expressed as the mean

per tree (i.e., mean of the three crown levels) or as the mean in the lower crown.

Density and defoliation data were subjected to a square root and arcsine square

root transformation, respectively, prior to analysis

(

x LIST OF FIGURES

Figure 2.1. Mean (± SE) of E. subsignaria: egg masses (a); early-instars (b); late-instars

(c); and pupae (d) on mature sycamore maple. Mean egg mass density on the

lower bole is represented by (•). Black and white bars represent proximal and

distal branches within each crown level,

respectively 42

Figure 2.2. Temporal pattern of mean (± SE) defoliation within the crown of sycamore

maple attributable to herbivoryby£. subsignaria when caterpillars were early-

instars (a), late-instars (b) or when all caterpillars had finished feeding(c). Black

and white bars represent proximal and distal branches within each crown level,

respectively 43

Figure 2.3. The influence of sycamore maple phenological stage on mean (± SE)

survival of E. subsignaria. Phenological stages of: 1, bud cap tight; 7, two pairs

of leaves expanded and; 9, three pairs of leaves expanded were

evaluated 44

Figure 2.4. Mean (± SE) percent budburst on proximal (black bars) and distal (white

bars) branches of sycamore maple in St. John's, NL, on 16 May 2006. Black and

white bars represent proximal and distal branches within each crown level,

respectively 45

Figure 2.5. Temporal pattern of Ennomos subsignaria cumulative egg hatch and

sycamore maple budburst in St. John's in 2006. Mean (± SE) egg hatch and %

budburst are indicated by dotted and solid lines, respectively. 46

Figure 2.6. Mean (± SE) proportion of most suitable leaves (i.e., phenological stage 9)

XI on proximal (-•-) and distal (-o-) branches in the upper (a), mid (b) and lower (c)

crown of fifteen randomly selected sycamore maples in Larch Park, St. John's,

NL. The non-cumulative mean proportion of hatched eggs on the same trees is

indicated by the shaded area 47

Figure 3.1. Relationships between tree level and upper (a), mid (b) and lower (c) crown

level defoliation estimates for twenty mature sycamore maples in St. John's, NL

in 2006. Crown level percent defoliation was averaged to obtain mean tree

defoliation. Raw data are presented in figure but were subjected to an arcsine

square-root transformation prior to analyses 66

Figure 3.2. Relationships between E. subsignaria mean mid crown egg (a), egg mass (b)

and late-instar (c) density and end of season mean mid crown defoliation on

thirty mature sycamore maples in 2005. Data from the 5 sites were pooled prior

to analyses. Raw data are presented but density data were subjected to a square

root transformation and defoliation data were subjected to an arcsine square-root

transformation prior to analysis 67

Figure 3.3. Relationships between E. subsignaria mean egg (a), egg mass (b), early

-instar (c) and late-instar (d) density and end of season mean tree level

defoliation on twenty mature sycamore maples in 2006. Densities of all

developmental stages were assessed in the lower crown except egg mass density,

which was assessed on the lower bole. Mean tree level defoliation was calculated

by averaging crown level defoliation for each tree. Raw data are presented but

density and defoliation data were subjected to a square root and arcsine square-

root transformation, respectively, prior to analysis 68

xii Figure 4.1. Comparison of the destructive individual-leaf defoliation assessment method

(y-axis) and non-destructive visual crown-level defoliation assessment method

(x-axis) used to estimate E. subsignaria defoliation on 40 sycamore maples in St.

John's, NL in July 2005 86

Figure 4.2. Mean (± SE) E. subsignaria: (a) egg mass density on bole and branches of

40 sycamore maples that were randomly assigned to one of four treatments:

FULL = full dose of AceCap® 97; 2/3 = two thirds of the full treatment of

AceCap® 97; 1/3 one third of the full treatment of AceCap® 97; or CONTROL -

untreated in St. John's, NL in spring 2005 before acephate implantation; (b)

larval and pupal densities in July 2005; and (c) percentage defoliation in July

2005. * Indicates that treatment is significantly different from control (Dunnett's

test P< 0.05) 87

Figure 4.3. Mean (± SE) percentage defoliation attributable to E. subsignaria in the

lower, mid, and upper crown of 40 sycamore maples, regardless of treatment, in

St. John's, NL in July 2005. Different letters above bars indicate a significant

difference between crown levels (Tukey's test P < 0.001) 88

Figure 4.4. The effect of bole-implanted acephate on mean (± 1 SE) percentage

defoliation attributable to E. subsignaria during the post-treatment year (2006)

on 40 sycamore maples in St. John's, NL. FULL = full dose of AceCap® 97; 2/3

= two thirds of the full treatment of AceCap® 97; 1/3 one third of the full

treatment of AceCap® 97; CONTROL = untreated 89

xin CHAPTER 1: GENERAL INTRODUCTION

Insect herbivores and their host plants have co-existed for millions of years (Gillott,

2005). Over this time, plants have adopted numerous ways of defending themselves

against insect herbivory. For example, at the spatial scale of a leaf, a caterpillar is likely

to encounter a very heterogeneous and potentially dangerous environment (Hagen and

Chabot, 1986). Trichomes (i.e., leaf hairs) on the leaf surface can physically interfere

with herbivory while glandular trichomes have the ability to secrete feeding repellent

compounds (Levin, 1973). Once a caterpillar has established a feeding site on a leaf, it

has to then contend with an array of constitutive or induced defensive toxins that may

not be uniformly distributed throughout a leaf (Levin, 1976; McKey, 1979; Karban and

Myers, 1989; Wittstock and Gershenzon, 2002). Furthermore, once feeding is initiated,

the plant may release volatile compounds, luring parasitoids or predators to the insect

(Turlings et al., 1995; Kessler and Baldwin, 2001).

Only in recent years have ecologists and entomologists recognized that

individual plants are highly dynamic habitats for insect herbivores and that this

heterogeneity may be an adaptive defence strategy (Denno and McClure, 1983). Intra- plant heterogeneity has been attributed to intrinsic factors, such as the availability of newly-burst foliage (i.e., host phenology) (Quiring, 1993), foliage quality (Carroll and

Quiring, 1994; Murakami and Wada, 1997; Fortin and Mauffette, 2002; Johns, 2007)

and plant architecture (Alonso and Herrera, 1996), as well as to extrinsic factors, such as

natural enemy activity (Williams et al., 2001; Kessler and Baldwin, 2002) and microclimate (Alonso, 1997; Kessler and Baldwin, 2002). This intra-plant heterogeneity

1 provides insect herbivores with an assortment of variable feeding sites, making it difficult for herbivores to adapt to all aspects of the plant at once (Whitman, 1983).

Insect herbivores have responded to this intra-plant heterogeneity by evolving oviposition and foraging behaviours that allow them to utilize fitness-maximizing feeding locations within their host plant (Karban and Agrawal, 2002). In turn, the distribution of many insect herbivores is clumped on conifers (West, 1990; Wallin and

Raffa, 1998; Anstey et al, 2002; Straw et al., 2006; Johns 2007), hardwoods (Teulon and Cameron, 1995; Brown et al., 1997; Wardhaugh et al., 2006), shrubs (Ide, 2006) and crops (Naranjo and Flint, 1995; Duffield and Chappie, 2001).

A critical time in the life of an insect herbivore is when eggs hatch and feeding is initiated. In the spring, rapidly flushing foliage is a nutritious but highly ephemeral food source for newly emerged larvae (Hunter and Lechowicz, 1992). To take advantage of this succulent resource, the phenology of many spring-feeding caterpillars is closely synchronized with host budburst. Phenological asynchrony has been demonstrated to result in high levels of juvenile mortality (Ostaff and Quiring, 2000; van Asch and

Visser, 2007). If egg hatch is early, larvae may risk starvation whereas if egg hatch is delayed, larvae may not be able to establish on tougher, less nutritious foliage.

Therefore, for many early-season caterpillars, there is a restricted phenological window of opportunity to feed on suitable foliage (Hunter and Lechowicz, 1992; Quiring, 1992;

Lawrence et al., 1997; Hunter and Elkinton, 2000; Jones and Despland, 2006).

Lepidopteran species that begin feeding in the spring are more likely to reach outbreak densities than species that initiate feeding later in the summer (Hunter, 1991).

This trend has been attributed to variable synchrony between spring folivore phenology

2 and host phenology, resulting in greater variation in spring feeder population sizes compared to summer feeders (Hunter, 1991; Hunter and Elkinton, 2000). When reach outbreak densities, and the insect is considered to be a pest, the ability to forecast end of season plant damage can greatly aid management programs. These predictive relationships can be used to develop economic (Pedigo et al., 1986) and aesthetic

(Coffelt and Schultz, 1990) injury levels that aid pest managers when deciding to apply

(or not to apply) pest suppression tactics (Binns and Nyrop, 1992). These tactics can then be limited to individual trees forecasted to have high levels of defoliation. In turn, this should reduce pesticide use. An understanding of insect intra-tree distribution and foraging ecology should enhance the efficacy of these management tactics.

Study Insect

Native to North America, the elm spanworm, Ennomos subsignaria (Hiibner)

(Lepidoptera: Geometridae) is a reported pest of forest, shade and orchard trees and has periodically reached outbreak densities in the northeastern United States (Ciesla, 1964).

In the urban forest of St. John's, Newfoundland and Labrador (NL), E. subsignaria has maintained outbreak densities over the past 5 years. This is the first recorded outbreak of

E. subsignaria in this province, where it had previously been classified as a rare insect

(Morris, 1980).

During the spring and summer, larvae feed mainly on the foliage of mature sycamore maple, Acer pseudoplatanus L. (Aceraceae), Norway maple. A. platanoides L.

(Aceraceae), and linden, Tilia americana L (Malvaceae), but many other tree species are also attacked in St. John's. Completely defoliated trees often refoliate in the late

3 summer (personal observation) but can die after two or more successive seasons of

complete defoliation by E. subsignaria larvae (Fedde, 1964). Ennomos subsignaria is a

considerable nuisance and sometimes a safety hazard for citizens because masses of

larvae, as well as their silk strands and frass, can sometimes cover houses, sidewalks,

driveways and cars. In addition, this outbreak may negatively affect the tourism industry

as many historic city parks are infested at the peak of the summer season.

Egg hatch of this univoltine insect occurs early in the spring and in St. John's

larvae are usually present in the field from early June to late July. After developing

through 5 instars, larvae pupate in loose cocoons between foliage or in bark crevices.

Adult usually emerge in early August and mated females lay eggs in masses that

overwinter on the underside of branches and on the tree bole (Ciesla, 1964; Kaya and

Anderson, 1973; Talerico, 1979). Descriptions of juvenile and adult developmental

stages are provided by Ciesla (1964) and Guenee (1857), respectively.

Thesis Objectives

This thesis investigated the influence of intra-tree heterogeneity on the intra-tree

distribution and performance of the elm spanworm, Ennomos subsignaria (Hubner)

(Lepidoptera: Geometridae) on mature sycamore maple and as well as the selective pressures shaping that distribution. This knowledge was then applied while developing insect density - defoliation predictive relationships and evaluating a suppression method

for this defoliator.

Preliminary observations suggested that E. subsignaria early instar density and resultant defoliation was highest in the lower crown of mature sycamore maple. Based

4 on these observations and the assumption that host plant phenological stage influences the performance of juvenile E. subsignaria, in Chapter 2 I tested the following three alternate hypotheses that attribute variation in the intra-tree distribution of E. subsignaria on mature sycamore maple to: heterogeneous natural enemy activity within the crown (natural enemy hypothesis); foliage quality varying within the crown independent of intra-tree variation in leaf development (foliar quality hypothesis); or variations in intra-tree host phenology (i.e., acropetal bud burst and subsequent leaf development) (phenology hypothesis). These hypotheses are not mutually exclusive. For example, if both the phenology and natural enemy hypotheses are true, then natural selection should favour individuals that emerge when the best phenological stage (for development) is present in the location of the tree where mortality by natural enemies is lowest. These hypotheses and the assumption regarding the influence of host phenology were evaluated by carrying out field surveys and a manipulative experiment to determine: 1) the intra-tree distribution of E. subsignaria juvenile developmental stages on sycamore maple; 2) the pattern of intra-tree herbivory attributable to E. subsignaria on sycamore maple; 3) the phenological window of foliage suitability for E. subsignaria development; and 4) the degree of synchrony between E. subsignaria egg hatch and sycamore maple phenological development.

Urban trees are highly valued for many reasons (Raupp et al., 1992). Their aesthetic appeal, as well as their ability to improve air quality, provide shade and increase property value, justify the need for urban forest pest management strategies

(Coffelt and Schultz, 1990). Currently, there are no established relationships relating E. subsignaria juvenile stage population density to end of season defoliation. In Chapter 3,

5 I describe the development of a sampling plan for assessing defoliation of mature

sycamore maple and the evaluation of the relationships between densities of E.

subsignaria eggs, egg masses and early- and late-instar larvae and resultant lower crown

and tree level (i.e., mean of all crown levels) defoliation on mature sycamore maple.

By identifying trees that will experience high levels of defoliation, control tactics

can be limited to individual trees and therefore insecticide use can be reduced, which is

especially important in an urban environment. In Chapter 4 I describe the evaluation of

the efficacy of three doses of bole-implanted acephate (AceCap® 97) for reducing

densities and associated defoliation of E. subsignaria on sycamore maple during the

treatment and post-treatment year. This systemic insecticide is translocated acropetally

and therefore its efficacy may be influenced by the distribution of larvae within host trees. Overall, the research presented in this thesis attempts to apply ecological knowledge of E. subsignaria while developing practical and effective monitoring and

suppression practices during an urban outbreak of this polyphagous defoliator.

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Quiring, D. T. 1992. Rapid change of white spruce for a specialist herbivore, Zeiraphera

canadensis, as a function of leaf age. Canadian Journal of Zoology, 70, 2132-

2138.

Quiring, D. T. 1993. Influence of intra-tree variation in time of budburst of white spruce

on herbivory and the behaviour and survivorship of Zeiraphera canadensis.

Ecological Entomology, 18, 353-364.

Raupp, M. J., Koehler, C. S. and Davidson, J. A. 1992. Advances in implementing

10 integrated pest management for woody landscape plants. Annual Review of

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Straw, N., Fielding, N., Green, G. and Price, J. 2006. Seasonal changes in the

distribution of green spruce aphid Elatobium abietinum (Walker) (Homoptera:

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8, 139-154.

Talerico, R. L. 1979. Elm spanworm oviposition locations on northern red and white

oak. Journal of Georgia Entomological Society, 14, 24-31.

Teulon, D. and Cameron, E. A. 1995. Within-tree distribution of pear thrips

(Thysanoptera: Thripidae) in sugar maple. Environmental Entomology, 24, 233-

238.

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12 CHAPTER 2: INFLUENCE OF INTRA-TREE VARIATION IN PHENOLOGY AND

OVIPOSITION SITE ON THE DISTRIBUTION AND PERFORMANCE OF

ENNOMOS SUBSIGNARIA ON MATURE SYCAMORE MAPLE

Abstract. We conducted field surveys and a manipulative experiment to examine the hypotheses that intra-tree heterogeneity in natural enemy activity, foliar quality

(independent of phenology), or phenology influence the intra-tree distribution and performance of Ennomos subsignaria (Hubner) (Lepidoptera: Geometridae) on mature sycamore maple, Acerpseudoplatanus L. (Aceraceae). Ennomos subsignaria intra-tree distribution was distinctly clumped. Egg mass density was 85% higher on the lower bole than in the crown. Most early-instars were found on lower crown proximal branches while most late-instars and pupae were found on lower crown distal branches. This resulted in high levels of defoliation in the lower crown, especially on proximal branches. No parasitoids were reared from eggs or late-instar larvae and only one pupa was parasitized, suggesting that preference for the bole and lower crown was not in response to parasitism. Similarly, E. subsignaria performance was not influenced by variable foliage quality (independent of phenology) within the crown. However, sycamore maple phenology had a large influence on E. subsignaria survival. More than

90% of newly emerged larvae survived to adult when they fed on foliage with three pairs of leaves expanded per bud (i.e., phenologjcal stage 9) whereas survival on younger foliage was reduced by > 45%. The peak period of E. subsignaria egg hatch was approximately 2 weeks after the peak period of sycamore maple budburst, which occurred acropetally. Egg hatch was closely synchronized with the availability of most

13 suitable leaves for insect development on proximal branches of the lower crown, the

location where most larvae initiated feeding. Our results support the phenology hypothesis and suggest that intra-tree variation in oviposition site and host phenological

development influence the intra-tree distribution and performance of this generalist herbivore.

Key words. Ennomos subsignaria, elm spanworm, sycamore maple, intra-tree

distribution, phenology, intra-tree heterogeneity

Introduction

The intra-plant distribution of many insect herbivores is clumped on conifers (West,

1990; Wallin and Raffa; 1998; Anstey et al, 2002; Straw et al, 2006; Johns 2007), hardwoods (Teulon and Cameron, 1995; Brown et al, 1997; Wardhaugh et al., 2006),

shrubs (Ide, 2006) and crops (Naranjo and Flint, 1995; Duffield and Chappie, 2001), presumably in response to intra-plant variations that influence their fitness. This plant variability has been attributed to intrinsic factors, such as the availability of newly-burst

foliage (i.e., host phenology) (Quiring, 1993), foliage quality (Murakami and Wada,

1997; Fortin and Mauffette, 2002; Johns, 2007) and plant architecture (Alonso and

Herrera, 1996), as well as to extrinsic factors, such as natural enemy activity (Weseloh,

1972; Williams et al, 2001; Kessler and Baldwin, 2002) and microclimate (Alonso,

1997; Kessler and Baldwin, 2002).

The degree of temporal synchrony between an insect herbivore and its host phenology can have a considerable influence on insect performance (Feeny, 1970; Wint,

1983; Quiring, 1992; Jones and Despland, 2006) and on the distribution of juveniles

14 within trees (Quiring, 1993; Carroll and Quiring, 1994). This influence has been attributed to the well-documented relationship between foliage age and foliage quality

(Rhodes and Cates, 1976; Schultz et al, 1982; Mauffette and Oechel, 1989). Generally, young expanding foliage is soft and contains high amounts of nitrogen, water and defensive toxins while mature, expanded foliage is usually tougher and less nutritious for insects (Mattson and Scriber, 1987; Scriber and Slansky, 1981; Lill and Marquis,

2001; Brenes-Arguedas et al, 2006). The rapidly changing biochemical profile of flushing leaves presents many early-season insect herbivores with a restricted phenological window of foliage suitability (Aide and Londono, 1989; Hunter and

Lechowicz, 1992; Mattel and Kause, 2002).

Phenological asynchrony between insect herbivores and their hosts can cause high levels of juvenile mortality (Ostaff and Quiring, 2000; van Asch and Visser, 2007).

If egg hatch is early, larvae may risk starvation whereas if egg hatch is delayed, larvae may not be able to establish on tougher, less nutritious foliage. Previous studies investigating the influence of this foraging constraint on Lepidopteran species have focused on species feeding on very young foliage (Quiring, 1992; Lawrence et al., 1997;

Hunter and Elkinton, 2000; Jones and Despland, 2006). To our knowledge, a phenological window of suitable foliage has only been described for one caterpillar species feeding on a post-budburst phenological stage (Stoyenoff et al, 1994).

The elm spanworm, Ennomos subsignaria (Hiibner) (Lepidoptera: Geometridae) is a highly polyphagous defoliator of hardwood trees (Ciesla 1964). In the urban forest of St. John's, Newfoundland and Labrador (NL), this insect has maintained outbreak densities over the past 5 years. In St. John's, E. subsignaria larvae feed mainly on the

15 foliage of mature sycamore maple, Acer pseudoplatanus L. (Aceraceae), Norway maple.

A. platanoides L. (Aceraceae), and linden, Tilia americana L (Malvaceae) but many

other tree species are also attacked. This urban outbreak provided an opportunity to

study the intra-tree distribution of E. subsignaria as well as the selective pressures that

influence the distribution.

Preliminary data suggested that E. subsignaria early-instar density and resultant

defoliation was highest in the lower crown of mature sycamore maple. Based on these

observations and the assumption that host plant phenology influences the performance of juvenile E. subsignaria, we tested the following three alternate hypotheses that attribute

variation in the intra-tree distribution of E. subsignaria on mature sycamore maple to:

variations in foliage quality that are independent of intra-tree variation in the time of budburst (foliar quality hypothesis); variations in natural enemy activity within the

crown (natural enemy hypothesis); or variations in intra-tree host phenology (phenology

hypothesis). The hypotheses are not necessarily independent. For example, if both the

phenology and natural enemy hypotheses are true, then natural selection should favour

individuals that time egg hatch to correspond to the time when the best phenological

stage (for development) is present in the location of the tree where mortality by natural

enemies is lowest. These hypotheses and the assumption regarding the influence of host

phenology were evaluated by carrying out field surveys and a manipulative experiment

to determine: 1) the intra-tree distribution and parasitism of E. subsignaria juvenile

developmental stages on sycamore maple; 2) the pattern of intra-tree herbivory

attributable to E. subsignaria on sycamore maple; 3) the phenological window of foliage

16 suitability for E. subsignaria development; and 4) the degree of synchrony between E. subsignaria egg hatch and sycamore maple phenologjcal development.

Materials and Methods

Study insect and plant

Native to North America, E. subsignaria is a reported pest of forest, shade and orchard trees and has periodically reached outbreak proportions in the northeastern United States

(Ciesla, 1964). Egg hatch of this univoltine insect occurs early in the spring and in St.

John's larvae are usually present in the field from early June to late July. After developing through 5 instars, larvae pupate in a loose cocoon between foliage or in bark crevices. Adult moths usually emerge in early August and mated females lay eggs in masses that overwinter on the underside of branches and on the tree bole (Ciesla, 1964;

Kaya and Anderson, 1973; Talerico, 1979). Descriptions of juvenile and adult developmental stages are provided by Ciesla (1964) and Guenee (1857), respectively.

The most heavily attacked tree by E. subsignaria in St. John's is sycamore maple. This hardwood species is found in North America and Europe and, although is it not native to the former, its distributional range in North America (USDA, 2007) overlaps with the range of E. subsignaria and includes areas where outbreaks of this defoliator have occurred (Ciesla, 1964; Kaya and Anderson, 1973). Furthermore, plantings of this tree species in St. John's started in the early 1800's, indicating that E. subsignaria may have had > 200 years to adapt to sycamore maple intra-tree variation.

Study sites

17 Studies were carried out in 2006 in Larch Park and on the campus of Memorial

University of Newfoundland in St. John's, Newfoundland and Labrador (47° 33'N, 52°

40'E). Larch Park was dominated by open-grown 50-60 year old sycamore maple with a

few Norway maple and linden. Archips sp. larvae and adults (Lepidoptera: Tortricidae)

were the only other insect herbivore observed on study trees and they were present at

negligible densities. Leucoma salicis (L.) (Lepidoptera: Lymantriidae) larvae and adults

were observed in the area but not on study trees. The area of Memorial University

campus utilized for this study was dominated by open-grown 20-30 year old sycamore

maple. Ground vegetation in both sites consisted of the common grass mixture of 40%

Kentucky blue grass, Poa pratensis L. (Poaceae), 40% creeping red fescue, Festuca

rubra L. (Poaceae) and 20% perennial rye, Loliumperenne L. (Poaceae).

Intratree distribution, parasitism and herbivory

The intratree distribution, parasitism and feeding pattern of E. subsignaria on mature sycamore maple was assessed by carrying out field surveys on twenty randomly

selected trees in Larch Park. Mean bole diameter at breast height (i.e., 1.37 m above the

ground) was 40.20 ±2.53 cm. Insect densities were assessed on four sample dates when most juveniles were eggs, early-instars, late-instars or pupae, respectively. One proximal and one distal branch growing from the same southerly-facing first order branch were cut using pole pruners from the lower, mid and upper crown of each tree.

Branches were individually placed in labelled, clear, plastic bags and stored at 5°C until they were processed. On each sampled branch the number of egg masses, eggs per egg mass, larvae and pupae were counted and E. subsignaria density was expressed as mean

18 egg, egg mass, early-instar, late-instar or pupal density per branch surface area. Branch

surface area (excluding the leaves) was calculated using the formula for the lateral

surface area of a cone, where surface area = (rcXradius of branch base)(length of branch).

All shoots growing from the main branch that had a base diameter > 1 cm were also

included in this calculation. The mean area of sampled branches was 1.86 ±0.04 m

(N=480).

When assessing egg density, each sampled branch was carefully examined for

new egg masses. Old eggs (from a previous generation) do not have an operculum

(Talerico, 1979) and when free of debris are light brown in colour while new eggs that have overwintered only once are brown with a white opercular rim. Each new egg mass

was carefully removed from its branch by cutting and removing the section of bark

where the egg mass was attached. Each egg mass (still attached to bark) was individually

placed in a 30 ml clear, plastic cup that contained a piece of damp filter paper in the bottom. Egg masses were then immediately placed in a controlled environment at 20°C,

16 L: 8 D, and 70% RH to determine percent egg hatch and parasitism. As well, upon removal from branches, egg masses were inspected for evidence of predation.

Egg mass density was also assessed on the lower bole. A 0.5 m wide band of bark was measured on each bole from 1.37- 1.87m above ground level and the number of egg masses within the band, expressed as the number of egg masses per band surface

area, was recorded with respect to cardinal direction.

To determine the mean larval instar present in the field when sampling early and

late instar larvae, five larvae were systematically collected from each sampled branch

from five randomly selected study trees. There were several instances when less than

19 five larvae were collected per branch due to low larval density. Larvae were stored in

glass vials containing 70% ethanol until head capsules were measured. The widest point

of the dorsal aspect of the head capsules was measured using a dissecting microscope

with a calibrated micrometer. The mean head capsule widths for early-instars in the

lower, mid and upper crown were 0.66±0.05 (N=37), 0.70±0.07 (N=21) and 0.65±0.05

(N=22) mm, respectively, all falling in the range of widths for second-instars. The mean

head capsule widths for late-instars in the lower, mid and upper crown were 2.91±0.05

(N=46), 2.97±0.05 (N=33) and 2.89±0.09 (N=37) mm, respectively, all falling in the

range of widths for fifth-instars (Ciesla, 1964).

To determine late-instar parasitism rate, ten larvae were haphazardly selected

from one sampled branch in the lower crown of each study tree and reared in the

laboratory at room temperature (approximately 20°C). To determine pupal parasitism rate and adult sex ratio, five pupae were haphazardly selected from one branch in the

lower and one branch in the upper crown of each tree and pupae were reared in the

laboratory at room temperature. The sex of surviving adults was easily determined by

distinguishing adults with plumose (male) from those with filiform (female) antennae.

Intra-tree herbivory by E. subsignaria was assessed destructively by

systematically selecting ten leaves from each sampled branch. Leaves from each branch

were wrapped in paper towels, placed in labelled freezer bags and stored at 0°C until

processed. Percent defoliation of each leaf was visually estimated using defoliation

classes of 0, 1-10, 11-20, 21-40, 41-60, 61-80, 81-99, and 100% (Chapter 3).

20 Description of sycamore maple bud and leaf development

Bud and leaf phenological development was categorized as follows: 1, bud cap is tight (i.e., no foliage visible); 2, bud beginning to burst (i.e., bud cap is broken and foliage is visible but individual leaves are not distinguishable and the last pair of bud scales have not separated from each other); 3, last pair of bud scales has separated but individual leaves are still not distinguishable; 4, first pair of leaves are distinguishable from each other but have not expanded (i.e., leaf lobes are not distinguishable); 5, first pair of leaves are expanded; 6, second pair of leaves are visible but individual leaves are not distinguishable; 7, second pair of leaves are expanded; 8, third pair of leaves are visible but individual leaves are not distinguishable; 9, third pair of leaves are expanded;

10, fourth pair of leaves are visible but individual leaves are not distinguishable; 11, fourth pair of leaves are expanded.

Effect of host phenological stage on insect performance

To assess the effect of host phenological stage on E. subsignaria performance, newly emerged larvae (<24h old) were placed on leaves in phenological stage 1, 7 or 9 on each of 6 sycamore maples that were randomly selected on campus. To obtain newly emerged larvae at different times, eggs were collected from a separate site within St.

John's (Lion's Park) on 15 May and held at 5-20°C for various periods of time. Newly emerged larvae were placed on foliage in phenological stage 1 starting 20 May 2006, phenological stage 7 starting 30 May 2006 and on leaves in phenological stage 9 starting

21 6 June 2006. Unfortunately, few eggs held at low temperatures hatched after 6 June,

precluding the incorporation of later phenological stages (10 and 11) in this study.

Each phenological stage was replicated twice on lower crown proximal branches

and twice on mid crown distal locations of each tree. Three newly emerged larvae were

placed on each study branch (i.e., 3 larvae/branch x 6 branches/crown level x 2 crown

levels/tree x 6 trees = 216 larvae). Before larvae were transferred, branches were

carefully inspected to verify that there were no other insects on the branch. Because

newly emerged larvae are positively phototaxic, they could be easily removed from

rearing cup lids. To ensure larvae were not damaged by the transfer, each individual

larva was allowed to walk onto a pair of forceps and then walk onto a leaf of the study branch. Once transferred, larvae moved from the upperside of the leaf, where they were placed, to the underside of the leaf (personal observation). Study branches had the potential to provide more than enough food for three E. subsignaria larvae. Each study branch was enclosed by a white, nylon mesh cage to eliminate the effects of natural

enemies and to ensure that larvae fed only on the leaves of the selected branch. Caged

and uncaged leaves were observed throughout the experiment to assess whether the cage

influenced bud and leaf development. The presence of the cage did not seem to

obviously influence the timing of bud burst, leaf expansion or shoot elongation.

Furthermore, previous studies have demonstrated that sleeve cages did not influence branch or caterpillar development, or leaf chemistry (Rossiter et al., 1988; Quiring,

1993; Carroll and Quiring, 1994; Parsons et al., 2005).

At the end of larval development, study branches, still enclosed by sleeve cages, were cut and transported to the laboratory. Sleeve cages were removed and the number

22 of pupae on each branch was recorded. Pupal length and maximum width was recorded and pupae were individually placed in 30 ml labelled, clear, plastic cups that contained a piece of damp filter paper in the bottom. Pupae were reared in a controlled environment at 20°C, 16 L: 8 D and 70% RH and moth emergence was subsequently recorded to determine E. subsignaria survival. The sex and maximum length (i.e., from wing base to apex) of the right forewing of the surviving adults was also recorded. Insect performance was assessed using the indices of survival (to adult), pupal size and wing length.

Synchrony between budburst and egg hatch

Sycamore maple phenological development was evaluated on five sample dates within a 28-day period from mid May to mid June on fifteen randomly selected trees in

Larch Park. The mean bole diameter at breast height of the fifteen trees was 38.07 ± 1.87 cm. One proximal and one distal branch growing from the same southerly-facing first order branch were cut using pole pruners from the lower, mid and upper crown of each study tree on each sample date. Once branches were cut they were transported to the laboratory immediately for processing. As bud phenology did not vary along a branch, the phenological stage of the terminal bud on each sampled branch was recorded using the phenological stages previously described.

To evaluate the relationship between the time of sycamore maple budburst and the time of E. subsignaria egg hatch, one egg mass was observed on the southern half of the lower bole of each study tree on each of the five sample dates. Using a 1 OX hand lens, the number of hatched eggs on each sample date was recorded. The same egg mass was observed on each study tree for the duration of the study.

23 Statistical Analyses

A repeated measures ANOVA was employed to evaluate the influence of crown level, branch location and developmental stage (repeated factor: early-instars, late- instars and pupae) on E. subsignaria density and defoliation. The random factor of tree was included in both models. Egg density was not included in the model as a repeated factor because most eggs were oviposited on the lower bole and not within the crown

(see Results). To determine if larvae dispersed upward and outward within the crown because of foliage depletion in lower, proximal areas, study trees were divided into two groups based on the level of larval density and defoliation and a repeated measures analysis was carried out for each group (i.e., groupl > 44% defoliation; group 2 < 44% defoliation where mean study tree defoliation was 44%; larval density and defoliation were highly correlated (Chapter 3)). All density and defoliation data were subjected to square root and arcsine square root transformations, respectively, before analyses to correct problems with homogeneity and/or normality of residuals (Zar, 1984). Intra-tree variation in egg mass density was assessed using a one-way ANOVA with intra-tree position (lower bole, lower, mid and upper crown) and tree as model factors. Intra-tree variation in egg density was assessed using a one-way ANOVA with crown level (lower, mid and upper), branch location and tree as model factors. Egg and egg mass densities were subjected to square root transformations prior to analysis to meet the model assumption of homogeneity of residuals (Zar, 1984). One-way ANOV As were used to assess intra-tree variation in the number of eggs per egg mass, percent egg hatch per egg mass as well as the influence of cardinal direction on lower bole egg mass density. The

24 influence of phenological stage on E. subsignaria performance was evaluated using

analyses of variance. A repeated measures ANOVA was used to evaluate the influence

of crown level, branch position and time (repeated factor: 16 May, 26 May, 1 June, 7

June, 13 June) on the time of bud burst and presence of most suitable leaves for E.

subsignaria development. All repeated measures analyses were completed using SAS

statistical software (SAS Institute Inc., 1999). All other analyses were completed using

Minitab® statistical software (Minitab Inc., 2000).

Results

Intra-tree distribution, parasitism and herbivory

Egg mass density varied significantly within the tree ^3,117=8.93, P<0.001), and

was more than 7 times higher on the lower bole than in the crown (Fig. 2.1a). Egg mass

density on the lower bole did not differ significantly with cardinal direction (F3,57=0.77,

P=0.516), although >34% of egg masses were oviposited on the northwest quadrant. Egg

density did not vary significantly between (F2,95=2.08, P=0.131) or within (i.e., on

proximal versus distal branches) crown levels (Fi,95=0.01, P=0.913). The mean (± SE)

number of eggs per egg mass (64.48±6.31, N=61) did not vary significantly between

(F2;55=0.83, P=0.441) or within crown levels (FU5=0.90, P=0.346). There was no

significant difference in mean percent egg hatch per egg mass (88.46±2.10%, N=61) between (F2,55=2.15, P=0.127) or within crown levels (Fii55=2.60, P=0.113).

Early-instar density was significantly influenced by crown level (F2,97=26.38,

PO.001) and branch location (Fi,97=23.94, P<0.001), where most early-instars were

found on proximal branches of the lower crown (Fig. 2.1b). Late-instar and pupal

25 density were not significantly influenced by crown level (F2,97=0.97, P=0.383;

F2,97=0.53, P=0.591) but densities differed with branch location (¥u91=1.94, P=0.006;

Fi,97=7.65, PO.007). Most late instars and pupae were found on distal branches of the lower crown (Fig. 2.1c and d).

The intra-tree distribution of E. subsignaria varied significantly with crown level

(F2,97=7.53, P<0.001) and developmental stage (F2,]94=20.49, P<0.001). As larvae matured, many dispersed to outer areas of the crown while some dispersed upwards (Fig.

2.1b and c). This movement resulted in significant interactions between branch location and developmental stage (F2,i94=16.71, P<0.001) and between crown level and developmental stage ^4,194=3.10, P=0.017). The crown level and developmental stage interaction was only evident on trees with high density and high defoliation (low,

F4,94=1.04, P=0.390; high, F4,94=2.59, P=0.041) but the branch location and developmental stage interaction was evident regardless of the level of larval density and defoliation (low, F2,94=5.81, P=0.004; high, F2;94=l 1.06, PO.001). Crown level did not influence the percentage of E. subsignaria adults that were females (59.56 ± 5.27%).

No parasitoids emerged from E. subsignaria eggs or late-instar larvae. One parasitoid, Apechthis Ontario (Cresson) (Hymenoptera: Ichneumonidae), emerged from one E. subsignaria pupa that was collected from the lower crown. There were no obvious signs of egg mass predation. The few eggs that did not hatch were atypically dark or yellow. These eggs did not have parasitoid exit holes and, upon dissection, had no evidence of larval development.

Defoliation of sycamore maple by E. subsignaria was significantly influenced by crown level (F2,97=33.76, PO.001), branch position (Fi,97=31.00, PO.001) and insect

26 developmental stage (F2J94=378.28, P<0.001) (Fig. 2.2). Defoliation was highest in the

lower crown, especially on proximal branches, and consistently decreased with higher

crown levels. Small variations in the influence of crown level for different

developmental stages resulted in a significant crown level and developmental stage

interaction (F4,i94=4.44, P=0.001).

Effect of host phenological stage on insect performance

Sycamore maple phenological stage significantly influenced E. subsignaria

survival (F2,6i=60.34, P<0.001) (Fig. 2.3). More than 90% of newly emerged larvae

survived to adult when reared on stage 9 foliage but < 5% survived when placed on branches with unburst buds. Phenological stage did not influence pupal length

(F2,6i=1.09, P=0.352), pupal width (F2,6i=0.12, P=0.890) or wing length (F2,6i=0.98,

P=0.389). Crown level did not influence survival (Fi>6i=0.22, P=0.642), pupal length

(Fi>27=2.04, P=0.164), pupal width (F1>27=1.82, P=0.188) or wing length (Fu28=3.92,

P=0.058).

Female pupae and adults were significantly larger than male pupae and adults

(pupal length, Fi;93=64.51, PO.001; pupal width, Fi,93=59.04, P<0.001; wing length,

FU93=49.89, P<0.001). Female and male pupae were 2.07±0.02 (N=60) and 1.84±0.02

cm (N=35) long, respectively, and 0.57±0.01 (N=60) and 0.49±0.01 cm (N=35) wide.

Mean female and male wing lengths were 2.11±0.02 (N=61) and 1.9±0.02 cm (N=37),

respectively.

27 Synchrony between budburst and egg hatch

Due to acropetal budburst, the proportion of burst buds varied significantly by

crown level (F2,72=l 1-85, P<0.001), branch position (Fij72=7.22, P=0.009) and date

(F4,288=285.61, P<0.001). Buds burst first on proximal branches in the lower crown and

burst last on distal branches in the upper crown (Fig. 2.4). Because buds flushed first in

the lower crown, variation in the proportion of burst buds between crown levels was

high when sampling began. This variation decreased over time as buds flushed in the

mid and upper crown, resulting in an interaction between date and crown level

(F8,288=3.96, P<0.001). There was also a significant variation in the time of budburst

between trees (Fi4,72= 14.33, PO.001).

Ennomos subsignaria egg hatch was not closely synchronized with sycamore

maple budburst. The peak period of budburst occurred between 16 and 26 May but the

peak period of egg hatch occurred approximately two weeks later (Fig. 2.5). Instead, egg hatch was closely synchronized with the period when the highest proportion of leaves

was in phenological stage 9, the stage giving the highest survival. This synchrony was

greatest for proximal branches in the lower crown (Fig. 2.6).

The mean proportion of most suitable leaves (i.e., stage 9) for E. subsignaria

development increased more rapidly in the lower crown than in the mid and upper

crown, resulting in a significant interaction between date and crown level (Fg,288=2.57,

P=0.0364). Similarly, due to acropetal leaf development, the mean proportion of most

suitable leaves increased more rapidly on proximal than on distal branches, resulting in a

= significant interaction between date and branch location (F4;288 6.40, P=0.001).

28 Discussion

The intra-tree distribution of E. subsignaria on mature sycamore maple was

clumped in the lower crown, apparently in response to intra-tree variation in foliar phenology. Egg mass density was considerably higher on the lower bole than in the

crown. Most early-instars were found on lower crown proximal branches and most late

instars were found on lower crown distal branches, leading to high levels of defoliation

in the lower crown.

It is intriguing that egg mass density was higher on the lower bole rather than in the lower crown, where newly emerged larvae would be closer to foliage. Oviposition

site preference for the lower bole may have resulted due to differential costs of dispersal

for female moths and newly emerged larvae. Most larvae pupate in the lower crown and when moths emerge, many drop to the ground under the tree where they expand and dry their wings (H. Fry, personal observation). Results from an independent study (H. Fry, unpublished data) demonstrated that more moths mate on the ground and on the lower bole than in the lower crown. Although both male and female moths can fly, females are more sluggish than males. Perhaps the cost of dispersal for mated female moths, from the ground or lower bole to the lower crown, is greater than that for newly emerged larvae dispersing from the lower bole to lower crown. Therefore, E. subsignaria females may have evolved dispersal and oviposition behaviours that allow them to minimize predation risk by decreasing their dispersal distance. The lower bole may also be more suitable for egg development due to increased shading or snow cover.

The peak period of E. subsignaria egg hatch was approximately two weeks after the peak period of budburst. Evidence from our manipulative experiment indicated that

29 E. subsignaria has a restricted period of time to initiate feeding on sycamore maple. If

egg hatch occurs before the phenological window of most suitable foliage, E.

subsignaria survival is drastically reduced. Lower survival on younger foliage may be

attributable to the inability of E. subsignaria larvae to penetrate swollen buds, refusal to

eat younger foliage, or the inability of young larvae to detoxify poisonous compounds in

very young foliage. The most suitable phenological stage for E. subsignaria

development was stage 9, indicating that these leaves were the most nutritious for this

insect while being soft enough for newly emerged larvae to establish a feeding site.

Unfortunately, due to low egg hatch in the laboratory, we do not know how E.

subsignaria would perform on foliage older on than stage 9. However, because the peak

period of egg hatch occurred over a restricted period of < 7 days we speculate thati?. subsignaria performance would decline rapidly on older foliage. Furthermore, Drooz

(1970) demonstrated that E. subsignaria individuals reared on old foliage of pignut

hickory, Carya glabra (Mill.) (Juglandaceae), had lower fecundity than individuals

reared on juvenile foliage.

Previous studies investigating the influence of a phenological window of foliage

suitability for caterpillars have focused on species feeding on newly flushed foliage

(Quiring, 1992; Lawrence et al, 1997; Hunter and Elkinton, 2000; Jones and Despland,

2006). Although Stoyenoff et al. (1994) demonstrated that gypsy moth, Lymantria

dispar (L.) (Lepidoptera: Lymantriidae), performance was higher on slightly more mature foliage (i.e., most of foliage expanded past bud scales) than on foliage that had just broken through the tip of the bud or on swollen buds, the stages investigated were

still very young in comparison to foliage in phenological stage 9 in the present study.

30 Therefore, to our knowledge, our study provides the first evidence for a restricted

phenological window for an early-season caterpillar feeding on leaves that have

expanded past bud scales. Our study suggests that the performance of early-season insect

herbivores that initiate feeding on leaves that are almost expanded can be influenced by

changes in foliar quality as foliage matures to the same extent as insects initiating

feeding on newly burst buds (e.g., Quiring, 1992).

Ennomos subsignaria egg hatch on the lower bole was closely synchronized with

the proportion of most suitable leaves for E. subsignaria development on lower crown

proximal branches. Not surprisingly, this was the intra-tree location where most early

instar larvae fed. It is not known if the few eggs oviposited in the upper crown hatched

later to account for acropetal leaf development. However, when early instars were

sampled, instar development did not vary between crown levels, suggesting that egg hatch is not delayed in upper regions of the crown.

Our manipulative experiment demonstrated that E. subsignaria performance is not enhanced by feeding on lower crown foliage compared to mid crown foliage in the

same phenological stage. This suggests that possible variations in foliage quality between crown levels are not influencing E. subsignaria intra-tree distribution (foliar

quality hypothesis). Similarly, results from field surveys suggest that variable natural

enemy activity within the tree may not be a strong selective pressure shaping intra-tree

distribution (natural enemy hypothesis). Independent data collected during the past three

years support this conclusion as egg parasitism was 0% and larval and pupal parasitism was <15% (Fry, 2004; unpublished data). However, it is possible that natural enemy populations are not sustained in an urban environment. In a forested environment natural

31 enemies may have a greater influence on the population and on the intra-tree distribution. Interestingly, Anderson and Kaya (1973) reported that the incidence of E. subsignaria egg parasitism by Ooencyrtus ennomophagus Yoshimoto (Hymenoptera:

Encyrtidae) was greatest in upper areas of the canopy while parasitism by Telenomous droozi (Muesebeck) (Hymenoptera: Scelionidae) did not vary between canopy levels in a forested setting.

There are at least two reasons, which were not evaluated, that could explain why

E. subsignaria egg hatch has evolved to synchronize with the availability of stage 9 foliage in the lower crown. First, the cost of dispersal, both in terms of time, energy and exposure to natural enemies, by newly emerged larvae from the lower bole to the lower crown may be less than the cost of dispersing from the lower bole to mid or upper crown

(Bergelson and Lawton, 1988). Second, the more shaded and humid microenvironment of the proximal lower crown maybe more suitable for small, newly emerged larvae that might desiccate in upper distal areas of the crown (Bernays and Chapman, 1994; Zalucki et al, 2002).

As larvae matured, many dispersed acropetally (sensu Quiring, 1993) to distal areas of the crown while some dispersed upwards. Our data suggest that upward dispersal occurred only under the conditions of high larval density, when most of the foliage was consumed in the lower crown. In contrast, larvae appeared to disperse to distal areas of the crown regardless of the level of larval density or foliage consumption.

Carroll and Quiring (1994) demonstrated that acropetal dispersal by the spruce bud moth

Zeiraphera canadensis (Mutt. & Free.) (Lepidoptera: Tortricidae) was an adaptive response to acropetal budburst in juvenile white spruce, Picea glauca Moench (Voss.)

32 (Pinaceae) (Quiring, 1993), that allowed larvae to feed twice on newly burst buds, the optimal phenological stage for their development. However, defoliation byE. subsignaria was higher on proximal than distal branches, suggesting that larvae did not disperse to distal, exposed areas in the crown to feed on stage 9 foliage twice. Intra-tree defoliation data suggest that larvae spend most of their time feeding on proximal branches. It is possible that late instars disperse to distal, exposed areas of the crown to bask during the day. As E. subsignaria larvae mature, their colour changes from light green to black, and studies have demonstrated that basking behaviour is more advantageous for dark pigmented insects (Watt, 1968; Rawlins, 1980; Porter, 1982).

Porter (1982) reported that only the jet-black late instars of Euphydryas aurinia Rott.

(Lepidoptera: Nymphalidae) displayed basking behaviour.

Intra-tree variability in bud and leaf development can greatly influence the distribution and performance of herbivorous insects. As leaves start to flush their biochemical and physical properties rapidly change and caterpillars are confronted with a phenological window of foliage suitability that restricts their foraging behaviour. Our study provides the first evidence that the performance of a spring-feeding caterpillar foraging on a post-budburst leaf stage can also be influenced by a restricted phenological window of opportunity.

Acknowledgments

I would like to thank B. Butler, J. Coombes and R. Pugh for excellent technical assistance in the field and laboratory. I also thank D. Evans and the Department of Parks and Services in St. John's, NL for access to my field site on city property and C. Baird

33 for access to my field site on MUN property. Financial support was provided by the

Canadian Forest Service and the University of New Brunswick.

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41 egg masses ia)

i i

early instars {t»

n in JZ•L

late instars

1 ill • i pupae(d)

LlloweLr l mid i upper crown level

Fig. 2.1. Mean (± SE) of E. subsignaria: egg masses (a); early instars (b); late instars

(c); and pupae (d) on mature sycamore maple. Mean egg mass density on the lower bole is represented by (•). Black and white bars represent proximal and distal branches within each crown level, respectively.

42 early instar (a) 60 4

40

20 j

n late instar (b) 60

= 40 .2 .*2 jo X -a 20

final (c) 60

40 I

20 i

lower mid upper

crown level

Fig. 2.2. Temporal pattern of mean (± SE) defoliation within the crown of sycamore

maple attributable to herbivory by E. subsignaria when caterpillars were early instars

(a), late instars (b) or when all caterpillars had finished feeding(c). Black and white bars represent proximal and distal branches within each crown level, respectively.

43 100

80 4

60

40 4

20 4

IL 1 7 9

phenological stage

Fig. 2.3. The influence of sycamore maple phenological stage on mean (± SE) survival of E. subsignaria. Phenological stages of: 1, bud cap tight; 7, two pairs of leaves expanded and; 9, three pairs of leaves expanded were evaluated.

44 Lower Mid Upper crown level

Fig. 2.4. Mean (± SE) percent budburst on proximal (black bars) and distal (white bars) branches of sycamore maple in St. John's, NL, on 16 May 2006. Black and white bars represent proximal and distal branches within each crown level, respectively.

45 100 -| t • 3» r —. 80 - i i i o i IS i J= 60 - i o> i D> 0) i i ^ 40-

W nqp i [i J • ^3 / * 20- / J / /

0 - ••> i i i May 16 May 26 June 1 June 7 June 13

date

Fig. 2.5. Temporal pattern oiEnnomos subsignaria egg hatch and sycamore maple budburst in St. John's in 2006. Mean (± SE) egg hatch and % budburst are indicated by

dotted and solid lines, respectively.

46 {a/

.--"OK 0.0 1.0

J! 06 4

£ 0.4 A

00 1 0

' ... \ Jf

May 16 May 26 -June 1 ..lun« ? June 13

date

Fig. 2.6. Mean (± SE) proportion of most suitable leaves (i.e., phenological stage 9) on proximal (-•-) and distal (-o-) branches in the upper (a), mid (b) and lower (c) crown of fifteen randomly selected sycamore maples in Larch Park, St. John's, NL. The non- cumulative mean proportion of hatched eggs on the same trees is indicated by the shaded area.

47 CHAPTER 3: RELATIONSHIPS BETWEEN ELM SPANWORM, ENNOMOS

SUBSIGNARIA, DENSITY AND DEFOLIATION ON MATURE SYCAMORE

MAPLE IN AN URBAN ENVIRONMENT

Abstract

Using field surveys, we established sampling procedures for estimating defoliation resulting from elm spanworm, Ennomos subsignaria (Hiibner) (Lepidoptera:

Geometridae), feeding on mature sycamore maple, Acerpseudoplatanus L. (Aceraceae), in St. John's, Newfoundland and Labrador. We also determined whether densities of E. subsignaria eggs, egg masses, or early- or late-instar larvae could predict the amount of defoliation at the end of the larval feeding period. Defoliation estimates acquired by sampling branches from only the lower, mid or upper crown explained more than 80% of the variation in tree level defoliation, suggesting that density-defoliation relationships established using defoliation data from any crown level would also be useful for predicting tree level defoliation. Egg and egg mass densities explained <20% of variation in defoliation and thus only provide a crude relative estimate of the amount of defoliation that will occur. Early- and late-instar density in the lower crown explained 53 and 29%, respectively, of the variation in defoliation in the lower crown, where defoliation levels were highest. Thus monitoring early-instar density in the lower crown should provide pest managers with reliable information for decisions regarding whether to apply suppression tactics while allowing enough time to implement these tactics, if necessary.

48 Key words: Ennomos subsignaria; elm spanworm; sycamore maple; density- defoliation relationship; integrated pest management; within-tree distribution

1. Introduction

The ability to predict future damage to a host plant by sampling early season insect density is a fundamental component of integrated pest management. Studies often compare insect egg and/or larval densities to end of season defoliation (Gansner et al.,

1985; Lysyk, 1990; Williams et al., 1991; Carroll and Quiring, 1993; Coffelt and

Schultz, 1993a; Liebhold et al., 1993; Nealis et al., 1997; Parsons et al., 2005; Johns et al., 2006a) while others compare adult densities (Johns et al., 2006a) or frass production

(Coffelt and Schultz, 1993b) to subsequent defoliation. These predictive relationships can be used to develop economic (Pedigo et al., 1986) and aesthetic (Coffelt and

Schultz, 1990) injury levels that aid pest managers when deciding whether to apply pest suppression tactics (Binns and Nyrop, 1992).

The development of robust insect density-defoliation relationships can be complicated by several factors. Variations in juvenile mortality (Lysyk, 1990), foliage age preference (Parsons et al., 2005), and distribution and behaviour of juveniles foraging within a tree (Ticehurst and Yendol, 1989; Carroll and Quiring, 1993; Rowe and Potter, 1996; Johns et al., 2006a and b), as well as complex plant architecture

(Southwood, 1978), can all influence the relationship between early season insect density and end of season defoliation. For example, during an urban outbreak of the orangestriped oakworm, Anisota senatoria (J. E. Smith) (Lepidoptera: Saturniidae), in

Virginia, Coffelt and Schultz (1994) determined that most eggs and early-instars were

49 found in the lower crown and subsequently recommended that pest managers only monitor the lower crown for these developmental stages and only apply insecticide sprays in this area.

In the urban environment of St. John's, Newfoundland and Labrador (NL), the elm spanworm, Ennomos subsignaria (Hubner) (Lepidoptera: Geometridae), has maintained outbreak densities during the past 5 years. This is the first recorded outbreak of this highly polyphagous defoliator (Ciesla 1964) in this province, where it had previously been classified as a rare insect (Morris, 1980). During the summer, larvae feed mainly on the foliage of sycamore maple, Acer pseudoplatanus L. (Aceraceae),

Norway maple, Acerplatanoides L. (Aceraceae), and linden, Tilia americana L.

(Malvaceae), but several other species are also defoliated. Completely defoliated trees often refoliate in late summer (H. Fry, pers. obs.) but can die after two or more successive seasons of complete defoliation by E. subsignaria larvae (Fedde, 1964).

Ennomos subsignaria is a considerable nuisance and sometimes a safety hazard for citizens because masses of larvae, as well as their silk strands and frass, can sometimes cover houses, sidewalks, driveways and cars. In addition, this outbreak may negatively affect the tourism industry as many historic city parks are infested at the peak of the summer season. Currently there is no urban management plan for this defoliator.

Urban trees are highly valued for many reasons (Raupp et al., 1992). Their aesthetic appeal, as well as their ability to improve air quality, provide shade and increase property value, justify the need for urban forest pest management programs

(Coffelt and Schultz, 1990). Currently, the only registered insecticides for E. subsignaria in Newfoundland is Bacillus thuringiensis subsp. kurstaki (Btk) (registered Btk products

50 include: Dipel WP, Thuricide-Hpc High Potency Aqueous Concentrate, Thuricide 48LV

Aqueous Concentrate, Dipel 2X DF Biological Insecticide, Bioprotec Aqueous

Biological Insecticide, Bioprotec CAF Aqueous Biological Insecticide, Bioprotec Eco)

and phosmet (Imidan). The authors recently demonstrated that bole-implanted acephate

is also effective in reducing E. subsignaria density and defoliation (Chapter 4). Both

suppression tactics could potentially be limited to trees that have been forecasted to have

high levels of defoliation, thereby minimizing pesticide use, which is especially

important in an urban area.

Female E. subsignaria moths preferentially oviposit on the lower bole of

sycamore maple and most newly emerged larvae feed on the underside of leaves within

the lower crown (Chapter 2). This distribution and foraging behaviour produces a

distinctly clumped within-tree pattern of defoliation where most defoliation occurs in the

lower crown. Severe lower crown defoliation may not affect tree health as much as upper crown defoliation could (Elliott et al., 1993) but represents an aesthetic concern

for citizens. Because of this, predicting defoliation in the lower crown as well as at the tree level would be a useful component of an urban management plan for this insect.

There are few publications describing sampling procedures to determine the relative

abundance of shade tree insects (Fettig, 2005) and there are currently no established

relationships relating E. subsignaria juvenile stage population density to end of season

defoliation. The objectives of this study were: 1) to establish a sampling plan for

assessing defoliation of mature sycamore maple; and 2) to evaluate the relationships between densities of E. subsignaria eggs, egg masses and early- and late-instar larvae

51 and resultant lower crown and tree level (i.e., mean of all crown levels) defoliation on mature sycamore maple, the most frequently attacked tree in the outbreak area.

2. Methods

2.1. Description of study insect

Native to North America, E. subsignaria is a reported pest of forest, shade and orchard trees and has periodically reached outbreak proportions in the northeastern

United States (Ciesla, 1964). Egg hatch of this univoltine insect occurs early in the spring; in St. John's larvae are usually present in the field from early June to late July.

After developing through five instars, larvae pupate in a loose cocoon on or between foliage or in bark crevices. Adult moths usually emerge in early August and mated females lay eggs in masses on the underside of branches and on the tree bole, where they overwinter (Ciesla, 1964; Kaya and Anderson, 1973; Talerico, 1979). Ciesla (1964) describes the immature developmental stages of E. subsignaria and Guenee (1857) describes the adult stage.

2.2 Study sites

In 2005, five sites were chosen with varying E. subsignaria densities on public property in St. John's, Newfoundland and Labrador (47° 33'N, 52° 40'E). Only one of these five sites was used for studies in 2006. All sites were dominated by open-grown

50-60 year-old sycamore maple with a few Norway maple and linden. Ground

52 vegetation consisted of the common grass mixture of 40% Kentucky blue grass, Poa pratensis L. (Poaceae), 40% creeping red fescue, Festuca rubra L. (Poaceae), and 20%

perennial rye, Lolium perenne L. (Poaceae). Archips sp. larvae and adults (Lepidoptera:

Tortricidae) were the only other insect herbivore observed on study trees. They were

present at negligible densities at two of the five sites in 2005. Leucoma salicis (L.)

(Lepidoptera: Lymantriidae) larvae and adults were observed in 2006 but individuals

were not observed on study trees.

2.3. Estimating defoliation

To develop a general sampling method for assessing defoliation attributable to E.

subsignaria feeding within the crown of mature sycamore maple, twenty trees were

randomly selected at one site in 2006. The mean (±S.E.) bole diameter at breast height

(i.e., 1.37 m above the ground) of the twenty trees was 40.20 ± 2.53 cm. Sampling

commenced once the majority of larvae had pupated. One proximal and one distal

branch growing from the same southerly-growing first order branch were cut using pole

pruners from the lower, mid and upper crown of each tree. Defoliation hyE. subsignaria

at the branch-level was assessed destructively by systematically sampling ten leaves

from each sampled branch. Leaves from each branch were wrapped in paper towels,

placed in labelled freezer bags and stored at 0°C until processed. Percent defoliation of

each leaf was visually estimated using defoliation classes of 0, 1-10, 11-20, 21-40, 41-

60, 61-80, 81-99, and 100% (Piene et al., 1981). Proximal and distal branch defoliation

was averaged to obtain mean crown level defoliation for each study tree. Lower, mid

and upper crown defoliation was averaged to obtain mean tree percent defoliation.

53 2.4. Predictive density-defoliation relationships

In 2005, the relationships between mid crown defoliation and E. subsignaria mid

crown egg, egg mass and late-instar density were evaluated. Six sycamore maples were

randomly selected at each of the five sites prior to budburst. The mean bole diameter at

breast height of the thirty trees was 38.62 ± 3.56 cm. Trees were sampled on two dates

when: 1) eggs; and 2) late-instar larvae were present in the field. To assess the density of

each developmental stage, two distal mid crown branches were destructively sampled

from each tree using pole pruners. Branches were individually placed in labelled, clear,

plastic bags and stored at 5°C until they were processed. The mean surface area of

sampled branches was 1.32 ± 0.07 m2 (N=180). Branch surface area (excluding the

leaves) was calculated using the formula for the lateral surface area of a cone, where

surface area = (7tXradius of branch base)(length of branch). All shoots growing from the main branch that had a base diameter > 1 cm were also included in this calculation. For

each sampled branch, the number of eggs per mass, egg masses, and late-instar larvae

were counted and E. subsignaria density was expressed as mean egg, egg mass, or late-

instar larval density per branch surface area. Mean insect developmental stage density

per tree was calculated by averaging the densities of the two sampled branches per tree.

Mid crown branch level defoliation was assessed as described under Estimating

defoliation.

Ennomos subsignaria eggs from the previous seasons remain attached to tree

bark. Because of this, it is important to distinguish between old and new eggs to prevent

overestimation of egg or egg mass density. When larvae emerge they destroy the egg

54 opercula and therefore old eggs do not have an operculum (Talerico, 1979). Also, old

eggs (that are free of debris) are light beige in colour while new eggs, that have

overwintered, are brown with a white opercular rim. Old egg masses also tend to be

more brittle compared to new egg masses.

An independent study carried out by the authors in 2005 indicated that most E. subsignaria larvae fed in the lower crown of mature sycamore maple and that the majority of defoliation subsequently occurred there (Chapter 2). Consequently, in 2006

we investigated the most appropriate: 1) within-tree sampling location; and 2) E. subsignaria developmental stage to sample to predict lower crown and tree level end of

season defoliation. Twenty sycamore maples were randomly selected at one site (see

Estimating defoliation section). Trees were sampled over three dates when most juveniles were eggs, early instars or late instars. On each date, one proximal and one

distal branch growing from the same southerly-growing first order branch were cut using pole pruners from the lower, mid and upper crown of each tree. The mean branch size

sampled was 1.86 ± 0.04 m2 (N=360). Branches were individually placed in labelled,

clear, plastic bags that were carefully sealed and stored at 5°C until examined. On each

sampled branch the number of eggs per mass, egg masses and larvae were counted.

Ennomos subsignaria density was expressed as mean egg, egg mass, early-instar or late-

instar per branch surface area. Ennomos subsignaria densities on proximal and distal branches for each life stage were averaged to obtain mean insect developmental stage density per crown level for each study tree. Lower, mid and upper crown density for

each developmental stage was averaged to obtain density estimates at the tree level.

55 Egg mass density was also assessed on the lower bole in 2006. A 0.5 m wide band of bark was measured on each bole from 1.37-1.87 m above ground level and the number of egg masses within the band was recorded with respect to cardinal direction.

Egg mass density was calculated as the number of egg masses per band surface area, the latter of which was calculated by multiplying bole circumference by 0.5 m.

To determine the mean larval instar present in the field when sampling early- and late-instar larvae, five larvae were systematically sampled from each sampled branch from five randomly selected study trees. Larvae were stored in glass vials containing

70% ethanol until head capsules were measured. The widest point of the dorsal aspect of each head capsule was measured using a binocular microscope with a calibrated micrometer. The mean head capsule width for the early- and late-instar sampling periods was 0.67 ± 0.03 mm and 2.92 ± 0.04 mm, which falls in the range of head capsule widths for second- and fifth-instar larvae, respectively(Ciesla, 1964).

Defoliation resulting from E. subsignaria feeding in the lower, mid and upper crown was assessed at the branch level as described under Estimating defoliation.

2.5. Statistical analyses

Linear regression was used to evaluate the relationships between crown level and tree level defoliation as well as E. subsignaria density and end of season defoliation. All defoliation data were subjected to an arcsine square root transformation and all density data were subjected to a square root transformation prior to analyses to correct problems with homogeneity and/or normality of residuals (Zar, 1984). All analyses were completed using Minitab® statistical software (Minitab Inc., 2000).

56 3. Results

3.1. Estimating defoliation

Sampling branches from the lower (FU8=99.10, PO.001), mid (Fu8=98.23,

= PO.001) or upper (Fi;is 73.41, P<0.001) crown provided very robust predictions of tree level defoliation that resulted from E. subsignaria feeding each explaining over 80% of the variation (Fig. 3.1).

3.2. Predictive density-defoliation relationships

Mid crown egg, egg mass and late-instar density all significantly predicted end of season mid crown defoliation in 2005 {F\^% > 7.05, P < 0.013) (Fig. 3.2). Mid crown egg and egg mass density explained 20% of the variation in defoliation of the mid crown while mid crown late-instar density explained 44% of this variation. Analyses produced similar results when repeated without the outlier.

In contrast, neither egg nor egg mass density explained a significant proportion of the variation in defoliation of trees at the one site studied in 2006, regardless of whether regressions were carried out at the within-crown or tree level (Fi,ig<2.03, P

>0.171)(Fig. 3.3a). Using lower bole egg mass density as a predictor of lower crown and tree level defoliation only marginally improved r2 values (F\^^<0.S2, F>0.377) (Fig.

3.3b). However, early- and late-instar density in the lower crown explained > 39% of the variation in mean defoliation per tree (Table 3.1, Fig. 3.3c,d).

4. Discussion

57 Defoliation resulting from E. subsignaria feeding in the lower, mid or upper crown is highly related to tree level defoliation. This suggests that E. subsignaria density-defoliation relationships established using defoliation data from any crown level would also be useful predicting tree level defoliation.

Egg and egg mass densities within the crown were not consistent predictors of end of season defoliation but could be used as a crude forecasting tool when complemented by other tools (i.e., early-instar density). Egg and egg mass densities predicted subsequent defoliation in 2005 but not in 2006. These inconsistent relationships may be due to differences in sample sizes among years (five sites in 2006 versus only one in 2006) or because of high dispersal rates of larvae. Larvae are very mobile and probably often move among trees. Newly emerged larvae can disperse by ballooning (Fedde, 1964) and later instars may disperse by looping across the ground

(Fedde, 1971; H. Fry pers. obs.). The sides of buildings and many sidewalks in St.

John's were covered by E. subsignaria during this study, suggesting that dispersal among trees occurred frequently. Inconsistent relationships probably did not result from differential egg mortality in 2005 and 2006, as mean egg hatch for both years was >88%

(unpubl. data).

Lower bole egg mass density could serve as a quick, non-destructive, crude predictor of end of season defoliation. The within-tree egg mass distribution on sycamore maple is clumped on the lower bole (Chapter 2) and monitoring egg mass density in this region could be particularly useful for identifying sites with a high potential for extensive defoliation. Once these sites are identified, individual trees within

58 these sites could be monitored for early-instars in the lower crown and subsequently suppression methods could be limited to individual, high value trees.

Field surveys in 2005 demonstrated that mid crown late-instar larval density is significantly related to mid crown defoliation while surveys conducted in 2006 established that early- and late-instar density from all crown levels can significantly predict lower crown and tree level defoliation. Even though mean tree early- and late- instar density explained more variation in lower crown defoliation than lower crown densities, this increase was only by 5 and 10%, respectively. Sampling upper crown branches from mature deciduous trees is challenging and the small increase in prediction precision may not be worth the extra effort.

Early-instar density in the lower crown explained a larger proportion of the variation in lower crown and tree level defoliation than lower crown late-instar density, presumably due to the high dispersal rates of older larvae. Sampling early-instars in the lower crown would provide pest managers with reliable forecasts of end of season defoliation and would give them enough time to implement suppression tactics, if needed.

Density - defoliation relationships that take into account large variations in the distribution of juvenile insects within trees have been previously established for several pests of hardwoods and conifers. Similar to E. subsignaria, A. senatoria early-instars are clumped in the lower crown of pin oak, Quercus palustris Muench. (Fagaceae) (Coffelt and Schultz, 1994). Consequently, Coffelt and Schultz (1994) recommended that only the lower crown should be monitored for young larvae. Both the yellow-headed spruce sawfly, Pikonema alaskensis (Roh.) (Hymenoptera: Tenthredinidae), on black spruce,

59 Picea mariana (Mills.) B.S.P. (Pinaceae), and the spruce bud moth, Zeiraphera canadensis Mutt. & Free. (Lepidoptera: Tortricidae), on white spruce, Picea glauca

Moench. (Pinaceae), disperse acropetally (sensu Quiring, 1993) from lower to upper regions of the crown, and thus egg or larval densities in the mid or lower crown were used to predict defoliation in the upper crown (Carroll and Quiring, 1993; Johns et al.,

2006a).

In conclusion, we suggest that lower bole egg mass density could be used to complement lower crown early-instar density to predict lower crown and tree level defoliation by E. subsignaria in an urban environment. Suppression tactics could then be restricted to individual trees that are forecasted to have high levels of defoliation.

Acknowledgements

We thank B. Butler, J. Coombes, C. Parsons and R. Pugh for excellent technical assistance in the field and laboratory and D. Evans and the Department of Parks and

Services in St. John's, NL for access to field sites. Financial support was provided by the

Canadian Forest Service, the University of New Brunswick and the Canadian Tree Fund.

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64 Table 3.1. Summary of linear regression analyses evaluating relationships between mean early and late instar densities of E. subsignaria and mean defoliation on twenty mature sycamore maples in 2006. Both insect density and defoliation were measured in the lower, mid and upper crown but are expressed as the mean per tree (i.e., mean of the three crown levels) or as the mean in the lower crown. Density and defoliation data were subjected to a square root and arcsine square root transformation, respectively, prior to analysis (a=0.05).

2 Defoliation Predictor Slope Intercept df F P r

Lower crown Early Instar Lower crown 13.2 13.7 1,18 20.35 <0.001 0.53 Mid crown 14.3 18.7 1,18 11.75 0.003 0.40 Upper crown 1.16 11.4 1,18 22.67 <0.001 0.56 Tree 19.7 6.68 1,18 25.1 <0.001 0.58

Lower crown Late Instar Lower crown 9.91 14.4 1,18 7.49 0.014 0.29 Mid crown 12.4 16 1,18 7.05 0.016 0.28 Upper crown 10.7 24.6 1,18 7.79 0.012 0.30 Tree 2.69 26.1 1,18 11.38 0.003 0.39

Tree Early Instar Lower crown 8.95 17 1,18 16.36 0.001 0.48 Mid crown 9.75 20.3 1,18 10.09 0.005 0.36 Upper crown 21.3 11.5 1,18 25.2 <0.001 0.58 Tree 13.9 11.1 1,18 23.73 <0.001 0.57

Tree Late Instar Lower crown 8.12 12.7 1,18 11.26 0.004 0.39 Mid crown 11.9 9.6 1,18 18.03 <0.001 0.50 Upper crown 0.99 8.74 1,18 73.41 <0.001 0.80 Tree 2.34 21.1 1,18 24.26 O.001 0.57

65 (a) upper crown y so

60 •

40 • :y

20 - y y=0.99x+8.47 • r"=0.80 n ,. uu - sh) mid crown /'* SO - * • X .5 60 - y' • ~o y • • /* • 40 - •

20 - / y y=0.73x+9.84 yfm ^=0.65 fi­ • , „, —, -T , uu - (c) lower crown •

50- •

60 ,s*'

40 - /.«' • -'1' 20 - y=0.66x+8.69 • ,-'' r'=0.85 n - / 0 20 40 60 SO 100 mean crown level defoliation (%)

Fig. 3.1. Relationships between tree-level and upper (a), mid (b) and lower (c) crown level defoliation estimates for twenty mature sycamore maples in St. John's, NL in

2006. Crown level percent defoliation was averaged to obtain mean tree defoliation.

Raw data are presented in figure but were subjected to an arcsine square-root transformation prior to analyses.

66 JO- , .. ,^- *' • • • ^' eggs

i> m • ^^

10- • »

0- ' • • * y=1.27x+40.3 '* r2=0.20 0 - 200 JJIXl 1030 1200

ib) egg masses •D

y=14.7x+30.7 r=0.20

late instars

«•,

y=3.5x+23.4 r2=0.44

100 200 300

mean mid crown density

Fig. 3.2. Relationships between E. subsignaria mean mid crown egg (a), egg mass (b) and late instar (c) density (number/m2) and end of season mean mid crown defoliation on thirty mature sycamore maples in 2005. Data from the 5 sites were pooled prior to analyses. Raw data are presented but density data were subjected to a square root transformation and defoliation data were subjected to an arcsine square-root transformation prior to analysis.

67 (a i eggs

y=0.85x+46.9 f-'=0.004

egg masses (lower bole)

y=2.9x+34.8 ("=0.04

(C) early instars

y=8.95x+17 rJ=0.48

(d) late instars

y=S.12*.+12.7 rJ=0.39

mean lower crown density

Fig. 3.3. Relationships between E. subsignaria mean egg (a), egg mass (b), early instar

(c) and late instar (d) density (number/m2) and end of season mean tree-level defoliation on twenty mature sycamore maples in 2006. Densities of all developmental stage were assessed in the lower crown except egg mass density, which was assessed on the lower bole. Mean tree-level defoliation was calculated by averaging crown level defoliation for each tree. Raw data are presented but density and defoliation data were subjected to a square root and arcsine square-root transformation, respectively, prior to analysis.

68 CHAPTER 4: SUPPRESSION OF ENNOMOS SUBSIGNARIA (LEPIDOPTERA :

GEOMETRIDAE) ON ACER PSEUDOPLATANUS (ACERACEAE) IN AN URBAN

FOREST USING BOLE-IMPLANTED ACEPHATE

Abstract. Trees in an urban forest are highly valued because they have aesthetic appeal, provide shade, and improve air quality. During the past 5 years (2002-2006) in St.

John's, Newfoundland and Labrador, the elm spanworm, Ennomos subsignaria

(Hubner) (Lepidoptera: Geometridae), has reached outbreak densities. Each year hundreds of trees have been completely defoliated, and many more trees have been partially defoliated. Adding to this problem, the larvae, their silk strands, and their frass are a considerable nuisance to property owners in areas of high larval densities. In this study, we evaluated the efficacy of three doses of bole-implanted acephate (AceCap®

97) for reducing densities and associated defoliation of E. subsignaria on sycamore maple, Acerpseudoplatanus L. (Aceraceae). During the treatment year (2005), all three doses significantly reduced E. subsignaria density; both full and two-thirds doses significantly reduced defoliation compared with control trees. During the post-treatment year (2006), bole-implanted acephate did not affect E. subsignaria mortality or defoliation. Bole-implanted acephate is an effective and practical way of suppressing E. subsignaria densities and herbivory in an urban forest where the protection of high- value trees and the reduction of environmental contamination is of utmost importance.

Key Words: elm spanworm, Ennomos subsignaria, Acer pseudoplatanus, acephate

69 The elm spanworm, Ennomos subsignaria (Hiibner) (Lepidoptera: Geometridae),

can cause high levels of defoliation in hardwood trees (Ciesla 1964). Native to North

America, this highly polyphagous species has reached outbreak densities during the past

5 years (2002-2006) in St. John's, Newfoundland and Labrador (NL). This is the first

recorded outbreak of E. subsignaria in this province, where it had previously been

classified as a rare insect (Morris 1980). Large numbers of deciduous trees in St. John's, including sycamore maple, Acer pseudoplatanus L. (Aceraceae), Norway maple, Acer platanoides L. (Aceraceae), and linden, Tilia americana L (Malvaceae), have been

completely defoliated during this outbreak. It is not known how long the trees can tolerate complete defoliation before experiencing significant growth loss or mortality.

Fedde (1964) observed that two or more successive seasons of complete defoliation would usually kill a tree. Ennomos subsignaria larvae as well as their silk strands and

frass sometimes cover houses, sidewalks, driveways, and vehicles representing a

significant nuisance and safety hazard in urban areas of high population density. In

addition, this outbreak may negatively affect local economies as many historic city parks

are infested with larvae during peak tourist season.

It is desirable to protect urban trees from insect defoliators because they have high aesthetic value, provide shade, and improve air quality. Currently, the only

registered insecticides for E. subsignaria in NL is Bacillus thuringiensis subsp. kurstakii

(registered Btk products include: Dipel WP, Thuricide-Hpc High Potency Aqueous

Concentrate, Thuricide 48LV Aqueous Concentrate, Dipel 2X DF Biological

Insecticide, Bioprotec Aqueous Biological Insecticide, Bioprotec CAF Aqueous

Biological Insecticide, Bioprotec Eco) and phosmet (Imidan). Ground spray application

70 of insecticides is impractical in the urban area of St. John's, as most trees are mature,

making full crown coverage difficult. Efficacy of this type of treatment is further limited

by frequent wind and rain. Systemic bole implantation of insecticides pose lower risk to

human and environmental health than ground spray application because products are

delivered directly to the tree, and thus exposure is limited to organisms feeding on tree

tissues. Systemic insecticide implants to control this pest would be particularly

advantageous in an urban setting such as St. John's.

Acephate systemic bole implants (Acecap® 97 manufactured by Creative Sales,

Inc., Fremont, NE) have been effective in reducing damage in a variety of conifer-insect

herbivore systems (Reardon and Haskett 1981, Stein et al. 1988, West and Sundaram

1992, Stein and Mori 1994, Roques et al. 1996, Flanagan 2003) as well as in a few

deciduous-insect herbivore systems (e.g., Webb et al. 1988; Fleischer et al. 1989; Fox et

al. 1995). When insect herbivores consume foliage from a tree that has been treated

systemically with acephate, they ingest acephate and its toxic metabolite,

methamidophos (Magee 1982), which leads to cholinesterase inhibition. The xylem of

the tree acropetally transfers acephate (Crisp et al. 1978) to foliage of the lower crown, before it is translocated to foliage of the mid and upper crown. As most E. subsignaria

larvae begin feeding in the lower crown (Chapter 2), bole-implanted acephate could

cause high levels of mortality of newly emerged larvae, thereby minimizing damage to

the tree.

In this study, we evaluated the efficacy of three doses of bole-implanted acephate

(Acecap® 97) to determine the lowest effective dose for reducing E. subsignaria

71 densities and associated herbivory on sycamore maple during the treatment and post-

treatment year.

Materials and Methods

Study Insect. Ennomos subsignaria has a univoltine life cycle. In spring, larval

emergence is synchronized with bud burst (Ciesla 1964). Most first-instar larvae begin

feeding on leaves of proximal branches in the lower crown, whereas most late-instar

larvae feed on leaves of distal branches in the lower and mid crown (Chapter 2). h St.

John's, larvae are usually present in the field from early June to late July. Larvae pupate in a loose cocoon on foliage or in bark crevices. Adult moths usually emerge in early

August, and mated females lay eggs in masses that overwinter on the underside of branches and on the tree bole. Ciesla (1964) describes the immature developmental

stages of E. subsignaria and Guenee (1857) describes the adult stage.

Study site and experimental design. This study was carried out in 2005 and

2006 in Victoria Park, St. John's, NL (47° 33'N, 52° 40'E). The site was dominated by open-grown, 60- to 70-year-old sycamore maple, Norway maple, and linden. These trees, which are not native to Newfoundland, had experienced moderate to heavy defoliation by E. subsignaria larvae during the previous 4-5 years (H. Fry, personal observation).

In the spring of 2005, before budburst and egg hatch, each sycamore maple in the park was assigned a number and 40 trees (43.58 ± 2.53 cm diameter at breast height

[1.37 m]; mean ± SE) were randomly selected for this study. Sycamore maple was

chosen because it is the most abundant tree species in St. John's and has been heavily attacked by E. subsignaria. Study trees in close proximity were arbitrarily assigned into

72 groups of four, and one tree within each group was randomly assigned to one of the following treatments: 1) 0.28 g/cm dbh of acephate, the dose recommended by the manufacturer of AceCap 97 to protect trees from other defoliating insects (hereafter referred to as "full" treatment); 2) two thirds of the full treatment of AceCap® 97; 3) one third of the full treatment of AceCap® 97; or 4) control (not treated with AceCap® 97).

Therefore, treatment trees and control trees were spatially intermixed and each treatment was replicated 10 times.

Application of implants. On 30 and 31 May 2005, capsules were implanted following the methods outlined by the manufacturer. This was done when buds had started to burst on the study trees, but before E. subsignaria larval emergence. Capsules were implanted into pre-drilled holes (approximately 1 cm wide and 3 cm deep) that spiralled up and around the lower bole, starting approximately 15 cm from soil level and spaced every 10 cm (full treatment, i.e., recommended spacing interval), every 15 cm

(two thirds treatment), and every 30 cm (one third treatment).

Evaluation of efficacy in treatment year. On 29 May 2005, before trees were treated with acephate, egg mass density was assessed using two measurements to determine initial E. subsignaria density on each study tree. Egg mass density was assessed on the lower bole and in the mid crown because these are the areas of highest

E. subsignaria egg mass density (Chapter 2). First, the number of egg masses was recorded in a 0.5 m wide band of tree bark around each bole from 1.37-1.87 m above ground level. Egg mass density was calculated as the number of egg masses per band surface area, which was calculated by multiplying bole circumference by 0.5 m. Second, pole pruners were used to collect one distal branch from the mid crown of each tree to

73 estimate egg mass densities in the crown. The mean (± 1 SE) branch area sampled was

1.1 ±5.94 m2. The number of egg masses on each branch was recorded, and egg mass density was expressed as the number of egg masses per unit branch surface area. Branch surface area (excluding the leaves) was calculated using the formula for the lateral surface area of a cone, where surface area = (rcXradius of branch base)(length of branch).

All shoots growing from the main branch that had a base diameter >1 cm were also included in this calculation. Egg mass densities on the bole and branch of each tree were averaged to obtain mean egg mass density for each tree.

To evaluate the efficacy of acephate in reducing E. subsignaria densities and herbivory, study trees were sampled on 26 July 2005, at the end of larval development.

Two distal branches were cut with pole pruners from the lower, mid, and upper crown of each tree. Branches were individually placed in labelled, clear plastic bags and stored at

5°C until they were processed. The mean branch area sampled was 1.7 ±5.47 m2. The number of larvae and pupae were counted on each branch and E. subsignaria density was expressed as mean larval and pupal density per branch surface area. Archips sp. larvae (Lepidoptera: Tortricidae) were the only other insect herbivore observed at the study site, and they were present at negligible densities. Mean larval and pupal density per branch per tree was calculated by averaging the mean larval and pupal densities per crown level.

Ennomos subsignaria herbivory at the branch level was assessed destructively by systematically sampling 10 leaves from each sampled branch. Percentage defoliation of each leaf was visually categorized, using defoliation classes of: 0, 1-10, 11-20, 21-40,

41-60, 61-80, 81-99, and 100% (Piene et al. 1981).

74 On 27 July 2005, defoliation of the lower, mid, and upper crown of each tree was estimated non-destructively using the defoliation classes previously mentioned. Two people visually observed each crown level (using binoculars when needed) by circling the tree both close to the bole and from approximately 15-20 m away. When classifications differed between the two observers, the mean of the two observations was used. For both the destructive and non-destructive methods of assessing defoliation, mean percentage defoliation per tree was calculated by averaging percentage defoliation estimated for the lower, mid, and upper crown.

The destructive and non-destructive methods of defoliation assessment used in

2005 were compared using a regression analysis (Fig. 4.1). The destructive method gave higher defoliation estimates than the non-destructive method, but the two methods were highly related and thus the non-destructive method was used in 2006.

Evaluation of efficacy in post-treatment year. To evaluate the efficacy of acephate in decreasing E. subsignaria egg mass densities the year following implantation, egg mass density was assessed on 27 May 2006, following the same procedure used in 2005.

To determine if acephate had carry-over effects on E. subsignaria survival 1 year after implantation, five replicate trees of each treatment were selected in spring2006.

All study trees were not tested due to logistic reasons. On 20 June 2006, six second- instar larvae, collected from a nearby (<2 km) site where trees had not been treated, were placed on two distal branches (three larvae per branch) in the lower crown of each tree to complete development. Branches were carefully observed before larvae were transferred to verify that there were no other larvae on the branch. To ensure larvae were

75 not damaged by the transfer, each individual larva was allowed to walk onto a pair of forceps and then walk onto a leaf of the haphazardly selected branch. A white, nylon sleeve cage was placed over each study branch to prevent parasitoids or predators from attacking larvae and to ensure that larvae fed only on the leaves of the selected branch.

Each branch provided more than enough foliage for the development of three larvae. In mid July, when surviving larvae had pupated, the number of pupae on each branch was recorded, and pupae were collected and individually placed in 30-ml clear plastic cups that contained a piece of damp filter paper in the bottom. In the laboratory, moth emergence was subsequently recorded to determine E. subsignaria survival.

On 20 July 2006, non-destructive visual crown defoliation estimates were conducted using the same protocol as in 2005 to determine if bole-implanted acephate was effective 1 year following implantation in reducing defoliation attributed to E. subsignaria herbivory.

Statistical analyses. Differences in E. subsignaria egg mass density between treatments before acephate implantation were evaluated using a one-way analysis of variance (ANOVA). To evaluate the effect of bole-implanted acephate on larval and pupal densities and on defoliation, an analysis of covariance was employed using treatment and crown level as fixed model factors, tree as a random factor, and egg mass density as a covariate. This was followed by Dunnett's test to evaluate differences in density and defoliation between control and treatment trees. Differences in crown level defoliation were evaluated using Tukey's test. A comparison of egg mass densities in

2005 with egg mass densities on the same trees in 2006 was completed using a paired t- test. Ennomos subsignaria mortality in the post treatment year was analyzed using a

76 one-way ANOVA. Egg density (2005 and 2006) and larval and pupal density data were subjected to a square-root transformation, and defoliation data (2005) were subjected to an arcsine square-root transformation before analysis to correct problems with normality and/or variance. All analyses were completed using Minitab® statistical software

(Minitab Inc., 2000).

Results

Evaluation of efficacy in treatment year. Before acephate was implanted in

2005, E. subsignaria egg mass density on control trees was lower than that on treatment trees, although differences were not significant (F = 1.67, df = 3, 36, P = 0.191) (Fig. 4.2 a).

Bole-implanted acephate significantly reduced E. subsignaria densities on sycamore maple (F = 9.55, df = 3, 192, P < 0.001) (Fig. 4.2 b). One third of the recommended amount of acephate resulted in densities more than 45% lower than on control trees, whereas the two thirds and full recommended doses of acephate resulted in densities 61 and 76% lower than the control, respectively. Ennomos subsignaria density at the end of larval development was not related to initial egg mass density (F =

0.0089, df = 1, 192, P = 0.924) and was not significantly influenced by a crown level and treatment interaction (F = 1.05, df = 6, 192, P = 0.394).

Bole-implanted acephate significantly reduced defoliation attributable to E. subsignaria (F = 16.22, df = 3, 72, P < 0.001) (Fig. 4.2 c). Two thirds of the recommended dose of acephate and the full concentration of acephate reduced defoliation by 46 and 50%, respectively, compared with the control. One third of the

77 recommended dose of acephate did not significantly reduce defoliation (Fig. 4.2 c).

Defoliation was not related to initial egg mass density (F = 0.31, df = 1, 72, P = 0.579).

The amount of defoliation on sycamore maple varied among crown levels (F =

6.43, df = 2, 72, P = 0.002) (Fig. 4.3). Percentage defoliation was highest in the lower crown and lowest in the upper crown. Defoliation was not significantly influenced by a crown level and treatment interaction (F = 1.46, df = 6, 72, P = 0.201), although differences in intra-tree crown level defoliation were slightly greater in control trees than in full treatment trees.

Evaluation of Efficacy in Post-treatment Year. Egg mass densities on study trees in 2006 were 30% lower than in 2005 (before treatment), but this reduction was not significant (t = 1.13, P = 0.197). Treatment egg mass density in 2006 ranged from 0.25 ±

0.04 to 0.93 ± 0.42 egg masses per square meter, but there were no significant differences in egg mass densities among treatments (F = 0.93, df = 3, 36, P = 0.435).

Similarly, treating sycamore maples with bole-implanted acephate in 2005 did not reduce E. subsignaria survival in 2006 (F = 0.13, df = 3, 36, P = 0.941). Survival on all treatments ranged from 76-80%. Not surprisingly, given the above results, there were no significant differences in percentage defoliation between treatment and control trees at the end of larval feeding in 2006 (Fig. 4.4) (F = 0.79, df = 3, 72, P = 0.507).

Discussion

Bole-implanted acephate was effective in suppressing densities of, and defoliation by, E. subsignaria on sycamore maple. Three different doses of acephate were evaluated, and all significantly decreased larval/pupal density compared with control trees; furthermore, the full and two-thirds (of manufacturer recommended dose)

78 treatments significantly reduced defoliation compared with control trees. Most literature evaluating the efficacy of bole-implanted acephate to decrease insect densities and/or defoliation has been carried out with insect pests on conifers (Reardon and Haskett

1981; Stein et al. 1988, West and Sundaram 1992, Stein and Mori 1994, Roques et al.

1996, Flanagan 2003), but only a few studies have evaluated this suppression technique with insects feeding on deciduous trees (Webb et al. 1988, Fleischer et al. 1989, Fox et al. 1995). Webb et al. (1988) observed that the recommended dose of bole-implanted acephate significantly reduced defoliation by gypsy moth, Lymantria dispar L.

(Lepidoptera: Lymantriidae), on red oak, Quercus rubra L. (Fagaceae), and white oak,

Q. alba L. (Fagaceae), by 77 and 74%, respectively. Fox et al. (1995) reported that bole- implanted acephate significantly reduced defoliation by Brachys tesselatus F.

(Coleoptera: Buprestidae) on turkey oak, Quercus laevis Walter (Fagaceae), by 50 and

20% (at two sites), and that it significantly reduced the mean number of mines per leaf by 38 and 28%. In contrast, bole-implanted acephate has not been effective in reducing densities of some insect species that do not feed directly on tree tissues that contain acephate, such as the spruce beetle, Dendroctonus rufipennis (Kirby) (Coleoptera:

Scolytidae) (Shea et al. 1991), as well as the cone scale midge, Resseliella skuhravyorum Skrz. (Diptera: Cecidomyiidae), (Roques et al. 1996) and Ips engraver beetles (Coleoptera: Scolytidae) (DeGomez et al. 2006). The current study clearly demonstrates that bole-implanted acephate can be an effective tool for suppressing^. subsignaria densities and defoliation on sycamore maple.

To our knowledge, no previous studies have evaluated the efficacy of different doses of bole-implanted acephate in reducing insect densities and defoliation on

79 hardwoods. Fogal and Lopushanski (1989) attempted to investigate the influence of spacing acephate implants in a conifer-insect herbivore system, but the authors were unable to compare insect damage to cones on treated vs. control trees during the treatment year because they lacked enough cones for assessment. Reardon et al. (1985) manipulated acephate dosage by decreasing the space between injections, thereby increasing the dosage of injected acephate, in an effort to improve acephate distribution within the tree crown and subsequently increase seed and cone insect mortality on

Douglas fir, Pseudotsuga menziesii (Mirbel) Franco var. glauca (Beissn.) (Pinaceae).

They showed that both the recommended and higher dosage of injected acephate significantly reduced Lepidopteran larval damage to cone seeds by 42 and 79%, respectively, although acephate dose did not significantly influence the mean number of damaged seeds. Application of the higher dose also did not significantly reduce the density of western spruce budworm, Choristoneura occidentalis Freeman (Lepidoptera:

Tortricidae), larvae more than the application of the recommended dose, h contrast, our objective was to determine the lowest effective dose of implanted acephate for reducing

E. subsignaria densities and defoliation by increasing the space between implanted capsules. Our data indicate that a 62% reduction in E. subsignaria larval/pupal densities and 46% reduction in defoliation by E. subsignaria on sycamore maple can be obtained by implanting two-thirds of the Acecaps recommended by the manufacturer.

The foraging behaviour of E. subsignaria may contribute to the observed suppression provided by bole-implanted acephate. Most E. subsignaria larvae begin feeding on leaves on proximal branches in the lower crown, whereas most late-instar larvae disperse to distal branches in the lower and mid crown to finish feeding (Chapter

80 2). This larval foraging pattern mimics the acropetal translocation of acephate in the primary xylem (Crisp et al. 1978), and probably results in most of the first-instar larvae ingesting a lethal dose of acephate.

While several studies have determined that bole-implanted acephate can reduce insect densities and damage on conifers the year following treatment (Sandquist and

Erickson 1991, West and Sundaram 1992, Stein and Mori 1994), this is only the second study to investigate it in hardwoods (Reardon and Webb, 1990). West and Sundaram

(1992) found that residual levels of acephate were high enough the year following treatment to reduce cone insect damage on black spruce, Picea mariana (Mill.) B.S.P

(Pinaceae), whereas Stein and Mori (1994) found bole-implanted acephate reduced defoliation of the Douglas-fir tussock moth, Orgyia pseudotsugata McDunnough

(Lepidoptera: Lymantriidae), on white fir, Abies concolor (Gordon & Glendinning)

Lindley ex Hildebrand (Pinaceae), the year following treatment. In our study, E. subsignaria survival and defoliation did not differ significantly between treatment and control trees during the post-treatment year (2006). This may have resulted due to rapid chemical breakdown during the treatment year (Campana 1979). Additionally, hardwood species generally have a faster uptake rate of solutions than conifers (Sanchez-Zamora and Escobar 2000) due to differences in xylem anatomy (Taiz and Zeiger 2002). Thus, all acephate powder in implanted capsules may have dissolved and subsequently been translocated during the treatment year (2005). Furthermore, there maybe a negligible delay in insecticide movement in sycamore maple. For example, when acephate is translocated in tree species that display carryover effects, acephate may become fixed to

81 walls of xylem cells by chemical binding or physical adhesion, temporarily delaying its upward movement (Campana 1979).

In conclusion, bole-implanted acephate was effective in significantly reducing densities of, and defoliation by, E. subsignaria on sycamore maple during the treatment year. Bole-implanted acephate was not effective during the post-treatment year, and, therefore, re-treatment of heavily infested trees maybe necessary. Caution should be used when re-treating trees, as the repeated drilling of holes in the bole may harm the tree. However, the presumed rapid breakdown of the active ingredient is a favourable feature when using this pesticide in an urban environment. This method of control is a safe, practical, and effective way of managing E. subsignaria during an urban outbreak.

Acknowledgments

We would like to thank J. Coombes, M. Faulkner, A. Penney, and R. Pugh for excellent technical assistance in the field and laboratory. P. DeGroot, C. Simpson, J.

Sweeney as well as two anonymous reviewers provided helpful comments on earlier versions of the manuscript. We also thank D. Evans and the Department of Parks and

Services in St. John's, NL for access to our field site and assistance with implanting capsules. Acecap®97 was donated by Creative Sales, Inc., and financial assistance was provided by the Canadian Tree Fund, the Canadian Forest Service, and the University of

New Brunswick.

References Cited

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J. J. Kielbaso, H. Davidson, J. Hart, A. Jones, and M. K. Kennedy (eds.), Proceedings,

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Entomol. Soc. Am. 57: 591-596.

Crisp, C. E., T. W. Koerber, C. E. Richmond, and B. H. Rottgering. 1978. Acropetal translocation of acephate into terminal shoot of Jeffery pine for the chemical control of western pine shoot borer. In J. J. Kielbaso, H. Davidson, J. Hart, A. Jones, and M. K.

Kennedy (eds.), Proceedings, Symposium on Systemic Chemical Treatments in Tree

Culture: 9-11 October 1978, East Lansing, MI. Braun-Brumfield, Inc., Ann Arbor, MI.

DeGomez, T. E., C. J. Hayes, J. A. Anhold, J. D. McMillin, K. M. Clancy, and P. P.

Bosu. 2006. Evaluation of insecticides for protecting southwestern Ponderosa pines from attack by engraver beetle (Coleoptera: Curculionidae: Scolytinae). J. Econ.

Entomol. 99: 393-400.

Fedde, G. F. 1964. Elm spanworm, a pest of hardwood forests in the southern

Appalachians. J. For. 62: 102-106.

Flanagan, P. T. 2003. Efficacy of systemic insecticide in reducing populations of black pineleaf scale (Nuculaspis californicd). J. Arboric. 29: 303-305.

Fleischer, S. J., D. Delorme, F. W. Ravlin, and R. J. Stipes. 1989. Implantation of acephate and injection of microbial insecticides into pin oaks for control of gypsy moth: time and efficacy comparisons. J. Arboric. 15: 153-158.

Fogal, W. H., and S. M. Lopushanski. 1989. Stem incorporation of systemic insecticides to protect white spruce seed trees. For. Chron. 65: 359-364.

83 Fox, C. W., K. J. Waddell, K. D. White, S. H. Faeth, and T. A. Mousseau. 1995.

Suppression of leafminer (Coleoptera: Buprestidae) populations on turkey oak

(Fagaceae) using implants of acephate. Environ. Entomol. 24: 1548-1556.

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Paris, France.

Magee, P.S. 1982. Structure-activity relationships in phosphoramidates. pp. 101-162.

In J. R. Coats (ed.), Insecticide Mode of Action. Academic Press, New York, NY.

Minitab Inc. 2000. Minitab user's guide 2: Data analysis and quality tools, Release 13

for Windows. Minitab Inc. State College, PA.

Morris, R. F. 1980. Butterflies and moths of Newfoundland and Labrador: the

Macrolepidoptera. Research Branch, Agriculture Canada. Publication 1691, Hull,

Quebec.

Piene, H., D. A. MacLean, and R. E. Wall. 1981. Effects of spruce budworm-caused defoliation on the growth of balsam fir. experimental design and methodology

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Atlantic Forestry Centre, Fredericton, New Brunswick.

Reardon, R. C, and M. J. Haskett. 1981. Effect of orthene medicaps on populations of western spruce budworm on grand fir and Douglas fir. J. Econ. Entomol. 74: 266-270.

Reardon, R. C, L. J. Barrett, T. W. Koerber, L. E. Stipe, and J. E. Dewey. 1985.

Implantation and injection of systemics to suppress seed and cone insects in Douglas fir in Montana. Can. Entomol. 117: 961-969.

84 Reardon, R. C. and R. E. Webb. 1990. Systemic treatment with acephate for gypsy

moth management: population suppression and wound response. J. Arboric. 16: 174-

178.

Roques, A., J. Sun, X. Zhang, G. Philippe, and J. Raimbault. 1996. Effectiveness of

trunk-implanted acephate for the protection of cones and seeds from insect damage in

France and China. Can. Entomol. 128: 391^-06.

Sanchez-Zamora, M. A., and R. F. Escobar. 2000. Injector-size and the time of

application affects uptake of tree trunk-injected solutions. Sci. Hortic. 4: 163-177.

Sandquist, R. E., and V. J. Erickson. 1991. Carry-over effects of trunk-implanted

acephate for protecting Douglas fir from western-spruce budworm defoliation. For. Ecol.

and Manage. 40: 87-91.

Shea, P. J., Holsten, E. H., and J. Hard. 1991. Bole implantation of systemic

insecticides does not protect trees from spruce beetle attack. West. J. Appl. For. 6: 4-7.

Stein, J. D., T. W. Koerber, and C. L. Frank. 1988. Trunk-implanted acephate to protect Douglas-fir seed crops on individual trees in northern California. J. Econ.

Entomol. 81: 1668-1671.

Stein, J. D., and S. R. Mori. 1994. Systemic insecticide implants for protection of white

fir scionwood from Douglas-fir tussock moth (Lepidoptera: Lymantriidae). J. Econ.

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Sunderland, MA.

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Argauer. 1988. Suppression of gypsy moth (Lepidoptera: Lymantriidae) populations on

85 oak using implants or injections of acephate and methamidophos. J. Econ. Entomol. 81:

573-577.

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86 100 T

% defoliation

Figure 4.1. Comparison of the destructive individual-leaf defoliation assessment method

(y-axis) and non-destructive visual crown-level defoliation assessment method (x-axis) used to estimate E. subsignaria defoliation on 40 sycamore maples in St. John's, NL in

July 2005.

87 a)

« 0.6 \

b)

d> a. it m 0.06 8. •cO 0.04 <0

30 - c) 25 • T

1 20 I 15 • 1 1 1 s-s 10

5 •

n full 713 1/3 control

Figure 4.2. Mean (± SE) E. subsignaria: (a) egg mass density on bole and branches of

40 sycamore maples that were randomly assigned to one of four treatments: Full = full dose of AceCap® 97; 2/3 = two thirds of the full treatment of AceCap® 97; 1/3 one third of the full treatment of AceCap® 97; or Control = untreated in St. John's, NL in spring

2005 before acephate implantation; (b) larval and pupal densities in July 2005; and (c) percentage defoliation in July 2005. * Indicates that treatment is significantly different from control (Dunnett's test P < 0.05).

88 30 - a T

o 20 - b I T

c 10 I

I i 1 1 lower mid upper crown level

Figure 4.3. Mean (± SE) percentage defoliation attributable to E. subsignaria in the lower, mid, and upper crown of 40 sycamore maples, regardless of treatment, in St.

John's, NL in July 2005. Different letters above bars indicate a significant difference between crown levels (Tukey's test P < 0.001).

89 t>0 •

40 •

10 • T T

20 •

10 •

0 - i 1 1 full 2/3 1/3 control

Figure 4.4. The effect of bole-implanted acephate on mean (± 1 SE) percentage defoliation attributable to E. subsignaria during the post-treatment year (2006) on 40 sycamore maples in St. John's, NL. Full = full dose of AceCap® 97; 2/3 = two thirds of the full treatment of AceCap® 97; 1/3 one third of the full treatment of AceCap® 97;

Control = untreated.

90 CHAPTER 5: GENERAL DISCUSSION

The overall aim of the research presented in this thesis was to investigate the

intra-tree distribution of E. subsignaria on mature sycamore maple, as well as the

selective pressures influencing this distribution, while applying this information towards

developing management strategies during an urban outbreak of this defoliator. Results

reported in Chapter 2 demonstrated that the intra-tree distribution and feeding pattern of

E. subsignaria on sycamore maple is clumped in the lower crown, apparently in response to intra-tree variation in foliar phenology and oviposition site. The majority of

egg masses were found on the lower bole and most larvae were found in the lower

crown, resulting in extensive lower crown defoliation. By manipulating the time of egg hatch, it was determined that sycamore maple phenological stage significantly influences

E. subsignaria survival. Survival was greatest on the oldest phenological stage (i.e.,

stage 9) assessed while field surveys demonstrated that E. subsignaria egg hatch is most

closely synchronized with the availability of this phenological stage in proximal areas of the lower crown. This evidence indicates that E. subsignaria has a restricted period of

time to initiate feeding on sycamore maple and egg hatch outside of this phenological

window can have deleterious affects on insect survival. Results from Chapter 3

suggested that lower bole egg mass density could serve as a quick, non-destructive,

crude predictor of end of season defoliation but should be coupled with lower crown

early instar density when identifying trees with a high potential for extensive defoliation.

Chapter 4 demonstrated that bole-implanted acephate is effective in reducing^. subsignaria density and herbivory. In addition to the toxicity of acephate to the insect, the efficacy of this suppression method could be attributed to the acropetal translocation

91 of acephate. Acephate reaches leaves of the proximal lower crown first, where most larvae initiate feeding.

Many studies have investigated the influence of variation between plants on herbivore preference and performance while few have questioned the effect of variability within plants (Denno and McClure, 1983). Mature trees, especially, could potentially provide herbivores with a variety of varying feeding sites. This intra-plant variation may put selective pressure on herbivores that subsequently adopt oviposition or feeding behaviours that allow them to utilize fitness-maximizing feeding locations within their host plants (Whitman, 1983; Karban and Agrawal, 2002). It seems that E. subsignaria has adapted to intra-tree variation in phenology in sycamore maple by synchronizing the timing of egg hatch with the time when the proportion of most suitable leaves (i.e., phenological stage 9) for insect development on proximal branches of the lower crown is highest and subsequently this was where most larvae initiated feeding.

As larvae matured, some dispersed acropetally upwards in the crown, while many dispersed outwards in the crown. Upward dispersal appeared to be primarily influenced by foliage depletion in the lower crown. However, this did not seem to be the driving force behind outward movement. Larvae may move to distal, exposed areas of the crown to bask during the day. This behaviour may be particularly advantageous due to their black colour, which larvae acquire as they mature. In order to determine if this dispersal behaviour is adaptive, a study manipulating the dispersal behaviour of larvae is required.

92 Interestingly, while sycamore maple phenological stage influenced E. subsignaria survival, it did not influence E. subsignaria pupal size or wing length.

Drooz (1965) demonstrated that E. subsignaria pupal weight was highly related to egg potential and in Chapter 2 we assumed that pupal size was related to potential fecundity.

Pupal weight was not used an indicator of performance because pupae lose weight as they develop and it is often difficult to determine exactly when larvae pupate. Some studies evaluating insect herbivore performance have used developmental time to assess performance (Carroll and Quiring, 1994). Measurements of insect developmental time may have been helpful in determining why E. subsignaria egg hatch on the lower bole is synchronized with the most suitable phenological stage in proximal areas of the lower crown rather than the mid or upper crown (i.e., perhaps individuals develop faster when feeding in lower, proximal areas compared to other areas of the crown).

Most pest management programs incorporate the practice of sampling early season insect density to predict plant damage at the end of the season. These predictive relationships can be used to develop economic (Pedigo et al., 1986) and aesthetic

(Coffelt and Schultz, 1990) injury levels that assist pest managers when deciding to implement pest suppression tactics (Binns and Nyrop, 1992). In an urban forest, woody landscape plants are grown for aesthetic reasons, not for economic profit. In this environment, management decisions are usually based on aesthetic injury levels (Raupp et al., 1992). During the urban outbreak of the orangestriped oakworm, Anisota senatoria (J. E. Smith) (Lepidoptera: Saturniidae), in Norfolk, Virginia, Coffelt and

Schultz (1990) established an aesthetic injury level by determining: 1) how much defoliation citizens would accept; 2) and the level of defoliation at which tree vigor

93 would not be affected. They suggested that suppression tactics would be justified if

ornamental oaks were > 25% defoliated. Once implemented, this aesthetic injury level reduced pesticide use by >80%. Similarly, an aesthetic injury level should be developed

for future urban outbreaks of E. subsignaria to aid pest managers in decision-making processes regarding the use of suppression tactics.

Knowledge of the intra-tree distribution and foraging behaviour of insect herbivores should greatly benefit the establishment of robust and practical predictive relationships (e.g., Johns et al., 2006). Results in Chapter 2 demonstrated that egg mass

density is considerably higher on the lower bole than in the crown of mature sycamore maple and that most larvae initiate feeding in the lower crown. In Chapter 3 it was

established that lower bole egg mass density, complimented with lower crown early instar density, should be an accurate and practical indicator of end of season defoliation.

If pest managers monitor these developmental stages they should be able to forecast which trees will have high levels of defoliation while having enough time to apply

suppression tactics, if necessary. Even though late instar density is a reliable indicator of resultant defoliation at this time in the season, it is likely too late for control tactics to be useful. Prior to this study, sampling techniques and density-defoliation predictive relationships had not been established for E. subsignaria. Hopefully this information

will help pest managers decide if the use of control tactics is necessary and this should result in reduced insecticide use.

Not only are urban trees aesthetically appealing but they also recycle oxygen and provide shade (Raupp et al., 1992). All of these features justify the need for urban forest pest management strategies (Coffelt and Schultz, 1990). To protect mature sycamore

94 maples in the urban forest of St. John's from intensive feeding by E. subsignaria, I evaluated the efficacy of three doses of bole-implanted acephate (Chapter 3). Two-thirds of the recommended dose of acephate was effective in significantly reducing E. subsignaria density and defoliation during the treatment year but not during the post- treatment year. Efficacy during the treatment year may be attributed to the acropetal translocation of acephate. Acephate reaches proximal areas of the lower crown first, where most larvae initiate feeding. Currently there are no systemic insecticides registered for use against E. subsignaria, however systemic bole implantation of insecticides is considered to pose lower risk to human and environmental health than ground spray application because products are delivered directly to the tree, thus limiting potential exposure only to applicators or to other organisms feeding on tree tissues. To my knowledge, this is the first study to manipulate acephate dosage by increasing the spacing interval between acephate implants on hardwoods.

Ultimately, the research presented in this thesis demonstrates the importance of considering individual trees as dynamic environments for insect herbivores and demonstrates how this information could be applied to management strategies.

References

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decision making. Annual Review of Entomology, 37, 427-453.

Carroll, A. L. and Quiring, D. T. 1994. Intratree variation in foliage development

influences the foraging strategy of a caterpillar. Ecology, 75, 1978-1990.

Coffelt, M. A. and Schultz, P. B. 1990. Development of an aesthetic injury level to

95 decrease pesticide use against orangestriped oakworm (Lepidoptera: Saturniidae)

in an urban pest management project. Journal of Economic Entomology, 83,

2044-2049.

Denno, R. F. and McClure, M. S. 1983. Variable plants and herbivores in natural and

managed systems. Academic Press, New York.

Drooz, A. T. 1965. Some relationships between host, egg potential, and pupal weight of

the elm spanworm, Ennomos subsignarius (Lepidoptera: Geometridae). Annals

of the Entomological Society of America, 58, 243-245.

Johns, R., Ostaff, D. and Quiring, D. 2006. Relationships between yellowheaded spruce

sawfly, Pikonema alaskensis, density and defoliation on juvenile black spruce.

Forest Ecology and Management, 228, 51 -60.

Karban, R. and Agrawal, A. A. 2002. Herbivore offense. Annual Review of Ecology and

Systematics, 33, 641-664.

Pedigo, L. P., Hutchins, S. H. and Higley, L. G. 1986. Economic injury levels in theory

and practice. Annual Review of Entomology, 31, 341-368.

Raupp, M. J., Koehler, C. S. and Davidson, J. A. 1992. Advances in implementing

integrated pest management for woody landscape plants. Annual Review of

Entomology, 37, 561-585.

Whitham, T. G. 1983. Host manipulation of parasites: within-plant variation as a

defence against rapidly evolving pests. In: Variable plants and herbivores in

natural and managed systems (ed. By R. F. Denno and M. S. McClure).

Academic Press, New York.

96 CURRICULUM VITAE

Candidate's full name: Heidi Rosanna Clarice Fry

Universities attended: Memorial University of Newfoundland, St. John's

Newfoundland; Bachelor of Science (Honours) (Biology, Entomology/Parasitology

Focus); 2001-2005

Publications:

Fry, H. R. C, Quiring, D. T., Ryall, K. L. and Dixon, P. 2007. Suppression of Ennomos subsignaria (Lepidoptera: Geometridae) on Acerpseudoplatanus (Aceraceae) in an

urban forest using bole-implanted acephate. Journal of Economic Entomology.

Tentatively accepted pending minor revision, resubmitted on October 5, 2007.

Fry, H. R. C, Quiring, D. T., Ryall, K. L. and Dixon, P. 2007. Relationships between

elm spanworm, Ennomos subsignaria, density and defoliation on mature sycamore maple in an urban environment. Forest Ecology and Management. Tentatively accepted pending minor revision.

Fry, H. R. C, Quiring, D. T., Ryall, K. L. and Dixon, P. 2007. Influence of intra-tree

variation in phenology and oviposition site on the distribution and performance of

Ennomos subsignaria on mature sycamore maple. In preparation.

Fry, H. R. C, Quiring, D. T., Ryall, K. L. and Dixon, P. 2007. Diel activity rhythm of

the moth, Ennomos subsignaria. In preparation. Fry, H. R. C, Quiring, D. T., Ryall, K. L. and Dixon, P. 2007. Influence of defoliation by Ennomos subsignaria on sycamore maple budburst the following year. In preparation.

Presentations:

Fry, H. R. C. 2007. Effect of intra-tree variation on elm spanworm distribution and performance. The 15th annual University of New Brunswick Graduate Student

Association Conference. Fredericton, NB.

Fry, H. R. C. 2007. Development of a sampling program and density-defoliation relationships for elm spanworm on sycamore maple in St. John's. Forest Entomology

Workshop. Canadian Forest Service. Corner Brook, NL.

Fry, H. R. C. 2006. Management of the elm spanworm with the systemic insecticide

Ace-Cap 97. The 14th annual University of New Brunswick Graduate Student

Association Conference. Fredericton, NB.

Ryall, K.L., Dixon, P. L, and Fry, H. R. C. 2005. Survival and fecundity of elm

spanworm, Ennomos subsignaria (Lepidoptera, Geometridae), reared on different host tree species. Joint annual meeting of the Alberta and Canadian Entomological Societies.

Canmore, Alberta (Poster)

Fry, H. R. C, Dixon, P. L., and J. Finney-Crawley. 2004. An urban epidemic: the elm spanworm, Ennomos subsignaria (Hiibner) (Lepidoptera: Geometridae) in St. John's,

Newfoundland. Joint annual meeting of the Acadian and Canadian Entomological

Societies. Charlottetown, P.E.I. (Poster) Media Coverage of B.Sc. (Hons.) and M.Sc. Research:

Fry, H. R. C. Interview for radio segment on CBC "The Morning Show", 13 July 2005.

Jeff Gilhooly, host.

Fry, H. R. C. Media release for Memorial University, 28 June 2005, "Student uses trees on Memorial University's campus for elm spanworm research", Deborah Inkpen, MUN communications

Fry, H. R. C. Interview for TV segment on CBC evening news hour, 29 July 2004.

Glenn Dier, reporter.

Fry, H. R. C. Interview (live) for radio segment on CBC "The Morning Show", 20 July

2004. Jeff Gilhooly, host and reporter.