Management of Potato Leafhopper and Maple Spider Mite on Nursery Grown Maples Julia Prado Beltran Purdue University

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Fall 2013 Management of Potato Leafhopper and Maple Spider Mite on Nursery Grown Maples Julia Prado Beltran Purdue University

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This document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact [email protected] for additional information. Graduate School ETD Form 9 (Revised 12/07) PURDUE UNIVERSITY GRADUATE SCHOOL Thesis/Dissertation Acceptance

This is to certify that the thesis/dissertation prepared

By Julia Karina Prado Beltran

Entitled Management of Potato Leafhopper and Maple Spider Mite on Nursery Grown Maples

Doctor of Philosophy For the degree of

Is approved by the final examining committee: Roberto G. Lopez Clifford S. Sadof Chair Ricky E. Foster

Ian Kaplan

Michael V. Mickelbart

To the best of my knowledge and as understood by the student in the Research Integrity and Copyright Disclaimer (Graduate School Form 20), this thesis/dissertation adheres to the provisions of Purdue University’s “Policy on Integrity in Research” and the use of copyrighted material.

Approved by Major Professor(s): ______Clifford S. Sadof ______

Approved by: Steve Yaninek 11/15/2013 Head of the Graduate Program Date

MANAGEMENT OF POTATO LEAFHOPPER AND MAPLE SPIDER MITE ON NURSERY GROWN MAPLES

A Dissertation

Submitted to the Faculty

Purdue University

Julia K. Prado

In Partial Fulfillment of the

Requirements for the Degree

Doctor of Philosophy

December 2013

Purdue University

West Lafayette, Indiana

ACKNOWLEDGEMENTS

I would like to thank Dr. Cliff Sadof for being an excellent advisor, for his dedication, confidence, patience, and support during my studies at Purdue University.

Thanks to his wife, Linda for her love and support throughout my career. I would also like to thank my committee members Dr. Ian Kaplan, Dr. Rick Foster, Dr. Michael

Mickelbart and Dr. Roberto Lopez for sharing their knowledge and their valuable collaboration in my professional training. In addition, I would like to thank to my labmates for their great effort and contribution during the field season, and make possible the culmination of this project. To Purdue University and the Department of Entomology for give me the opportunity to improve my scientific background in Entomology and my capacity to conduct research. Thanks to proffesors, staff, and graduate students for their kindness and help me when I needed.

I want to thank my dear friends for their time, love, and company, for help me to move forward and inconditional friendship. I would like to thank specially to my parents for being the unconditional support in every new opportunity, for teaching me to be my best self and for being an inspiration in my career. I want to thank to my amazing sisters for always being supportative throughout these past years, for their encouragement, affection, and patience.

iii

TABLE OF CONTENTS

Page LIST OF TABLES ...... vi

LIST OF FIGURES ...... vii

ABSTRACT ...... x

CHAPTER 1. INTRODUCTION ...... 1

1.1 Introduction ...... 1

1.2 Fertilization Practices and Pest Outbreaks ...... 2

1.3 Potato Leafhopper ...... 3

1.4 Spider mites ...... 8

1.5 Objectives ...... 13

1.6 Literature Cited ...... 15

CHAPTER 2. EFFECTS OF PESTICIDE APPLICATION ON ARTHROPOD PESTS

OF NURSERY GROWN MAPLES ...... 27

2.1 Abstract ...... 27

2.2 Introduction ...... 28

2.3 Materials and Methods ...... 30

2.4 Results ...... 34

2.5 Discussion ...... 40

Page

2.6 Literature Cited ...... 44

Appendix A Survey ...... 56

CHAPTER 3. EFFECTS OF FERTILIZATION ON ARTHROPOD PESTS OF

NURSERY GROWN MAPLES ...... 57

3.1 Abstract ...... 57

3.2 Introduction ...... 58

3.3 Materials and Methods ...... 60

3.4 Results ...... 64

3.5 Discussion ...... 66

3.6 Literature Cited ...... 70

Appendix B Impacts of Soil Fertilization on Characteristics of Red Sunset and

Autumn Blaze Maples ...... 81

CHAPTER 4. INTRAGUILD PREDATION MEDIATES HOST PLANT

RESISTANCE TO Oligonychus aceris (Shimer) ON MAPLE CULTIVAR RED

SUNSET (Acer rubrum) ...... 86

4.1 Abstract ...... 86

4.2 Introduction ...... 87

4.3 Materials and Methods ...... 89

4.4 Results ...... 91

4.5 Discussion ...... 93

Page

4.6 Literature Cited ...... 96

CHAPTER 5. SUMMARY ...... 106

5.1 Literature Cited ...... 110

VITA ...... 112

LIST OF TABLES

Table ...... Page Table 1.1 Damage by maple spider mite on maple cultivars in North Carolina nurseries and the abundance of leaf domatia (Steve Frank not published) ...... 26

Table 2.1 Percentage of the most common insecticide used by Indiana growers to control

E. fabae on maple trees in 2008...... 49

Table 2.2 Effects of early season and threshold on number of applications of different insecticides to control E. fabae on Red Sunset red maple trees in 2009 ...... 49

Table 2.3 Effects of threshold level of potato leafhopper on number of bifenthrin applications per tree to control E. fabae on maple trees in 2010...... 50

Table 2.4 Percentage of maple trees treated with bifenthrin to control E. fabae in 2010. 50

Table 4.1 Mite species and life stages used in experiments to assess the capacity of N. fallacis and Z. mali to feed on prey in Petri dish studies using Autumn Blaze and Red

Sunset maple trees as host plant substrates. Only one kind of prey was tested during each

24 hr period...... 101

vii

LIST OF FIGURES

Figure ...... Page Figure 2.1 Average density (±SE) of E. fabae per branch in five terminal nodes (A) and average of damaged tips (B) by E. fabae (±SE) on maple trees treated with different insecticides early in the season (ES) or at threshold level of one leafhopper (TH) during

2009 field studies ...... 51

Figure 2.2 Average density (±SE) of O. aceris (A), phytoseiid predatory mites (B), and Z. mali (C) per cm2 of leaf on maple trees treated with different insecticides early in the season (ES) or at threshold level of one leafhopper (TH) during 2009 field studies ...... 52

Figure 2.3 Average density (±SE) of E. fabae per branch in five terminal nodes (A) and average of damaged tips (B) by E. fabae (±SE) on maple trees treated with bifenthrin at threshold level of one, three and six leafhoppers (PLH) per branch during 2010 field studies ...... 53

Figure 2.4 Average density (±SE) of O. aceris (A), predatory mites phytoseiids (B), and

Z. mali (C) per cm2 of leaf on maple trees treated with bifenthrin at threshold level of one, three and six leafhopper (PLH) per branch during 2010 field studies...... 54

Figure 2.5 Percentage of trees that reached the threshold of one leafhopper and percentage of damaged tips by E. fabae on maple trees (A), and average density (±SE) of

E. fabae per branch and caught on sticky card on maple trees during 2010 field studies. 55

viii

Figure Page

Figure 3.1 Leaf domatia rank. Scored on a scale of 0 to 4 based on the presence of pubescence along a hierarchical scale of leaf veins...... 75

Figure 3.2 Average density (±SE) of damaged tips by E. fabae on maple trees treated with different fertilization treatment (A) and the relation between percentage of nitrogen on leaves and number of damaged tips by E. fabae during 2009 and 2010 field studies in

Lafayette, IN ...... 76

Figure 3.3 Average density (±SE) of O. aceris (A) and phyotseiid predatory mites (B) and Z. mali (C) per cm2 of leaf on Red Sunset (RS) and Autumn Blaze (AB) maple trees treated with 0, 20,40 g N during 2009 and 2010 field studies in lafayette, IN ...... 77

Figure 3.4 The relation between nitrogen content of leaves and the number of potato leafhopper per branch on Red Sunset red maple and Autumn Blaze Freeman maple during 2009 and 2010...... 78

Figure 3.5 The relation between nitrogen content of leaves and number of cumulative maple spider mites per cm2 on Red Sunset red maple and Autumn Blaze Freeman maple leaves during 2009 and 2010...... 79

Figure 3.6 Effects of nitrogen application rates on the averages (±SE) of the percentage nitrogen in Red Sunset red maple and Autumn Blaze Freeman maple leaves during 2009 and 2010...... 80

Figure 4.1 Leaf domatia rank scored on a scale of 0 to 4 based on the presence of pubescence along a hierarchical scale of leaf veins...... 102

Figure 4.2 Proportion of maximum leaf domatia (=Leaf domatia rank/4) on Red Sunset red maple and Autumn Blaze Freeman maple...... 103

Figure Page

Figure 4.3 Abundance of predatory mites on Red Sunset red maple and Autumn Blaze

Freeman maple...... 103

Figure 4.4 The relation between leaf domatia index and the number of Z. mali on Red

Sunset red maple and Autumn Blaze Freeman maple in 24 h...... 104

Figure 4.5 Predation on eggs, nymphs and adults of O. aceris by adult Z. mali and N. fallacis predatory mites on Red Sunset red maple and Autumn Blaze Freeman maple in

24 h...... 105

Figure 4.6 Intraguild predation on protonymph and adult Z.mali and N. fallacis on Red

Sunset red maple and Autumn Blaze Freeman maple in 24 h. Adult Z. mali and N. fallacis did not consume any adult predators during this assay...... 105

Appendix Figure ...... Page Figure B 1 Effects of nitrogen application rates on the averages (±SE) of the following maple leaf characteristics: chlorophyll content (A) and specific leaf weight (B) during

2009 and 2010 field studies ...... 85

ABSTRACT

Prado, Julia K. Ph.D., Purdue University, December 2013. Management of Potato Leafhopper and Maple Spider Mite on Nursery Grown Maples. Major Professor: Clifford S. Sadof.

Potato leafhopper Empoasca fabae (Harris) (Homoptera: Cicadellidae) and maple spider mite Oligonychus aceris (Shimer) (Acarina: Tetranychidae) are important pests of maple trees. Investigations determined how insecticide use and fertilization impacted the abundance of E. fabae and O. aceris on ‘Red Sunset’ red maple and ‘Autumn Blaze’

Freeman maples. Bifenthrin applications directed against leafhoppers reduced damage to both cultivars, but increased O. aceris on Autumn Blaze. Using a threshold of one leafhopper per branch to trigger pesticide applications protected Red Sunset maples from leafhopper injury. It also prevented outbreaks of O. aceris on Autumn Blaze because few trees reached this density. Two phytoseiid mites, Neoseiulus fallacis (Garman) and

Typhlodromus caudiglans (Schuster) (Acarina: Phytoseiidae), and one stigmaeid,

Zetzellia mali (Ewing) (Acarina: Stigmaeidae) were identified as predators of O. aceris on maple leaves. Populations of Z. mali were higher in both years on Red Sunset than

Autumn Blaze.

Fertilizer applications on field grown maples increased populations of leafhoppers and spider mites. More damage by E. fabae was observed on fertilized Red Sunset than on fertilized Autumn Blaze trees. O. aceris populations were higher on fertilized Autumn

Blaze than fertilized Red Sunset trees. O. aceris populations were positively correlated with nitrogen content in the leaves in both cultivars. Mite populations increased at a lower rate with increasing concentration of nitrogen in the leaves of Red Sunset than on those of Autumn Blaze maples. Differences may be explained by a greater abundance of

Z. mali (Ewing) on Red Sunset maples.

In laboratory experiments N. fallacis consumed significantly more protonymphs and adults of O. aceris, whereas Z. mali consumed more eggs. N. fallacis consumed more Z. mali on Autumn Blaze than on Red Sunset maple. Z. mali consumed fewer N. fallacis on both maple cultivars than O. aceris. Leaf domatia on Red Sunset leaves provide refugia for Z. mali predators. Absence of leaf domatia on Autumn Blaze left Z. mali no place to hide from N. fallacis and diminished their contribution to O. aceris mortality Thus, differential susceptibility of these cultivars to spider mites is mediated by the capacity of leaf domatia to influence intraguild predation among phtyoseiid and stigmaeid predators.

CHAPTER 1. INTRODUCTION

1.1 Introduction

Red maples (Acer rubrum Linnaeus) are one of the most widely grown species of landscape trees (Kielbaso 1990, Oliver et al. 2009). This popular tree is used for its environmental adaptability, attractive form, and red autumn foliage (Townsend and

McIntosh 1993). Numerous cultivars have been developed for superior growth, leaf characteristics, insect resistance, and other plant qualities (Townsend and Douglass 1998).

About 55 distinct cultivars of red maple are available in the nursery industry

(Sibley et al. 1998). Some cultivars have been developed from crosses and backcrosses between red maple and silver maple (Acer saccharinum L.) (Sibley et al. 1996).These hybrids are known as Acer freemanii E. Murray (Freeman maple) (Santamour 1993).

A recent survey of 12 large cities in Eastern North America indicates that the genus Acer is the most common genus, comprising 15% to 57% of the street trees. Over the last few years, maple trees have become even more popular because they can serve as replacements for ash trees killed by emerald ash borer, Agrilus planipennis Fairmaire.

The introduction of this and other exotic pests have captured the attention of urban foresters and reinforced recommendations to increase the diversity of urban forests

(Raupp et al. 2006).

Many red maple cultivars, however, are susceptible to damage caused by the potato leafhopper (Empoasca fabae Harris) (Bentz and Townsend 1999). Control of this pest usually requires several insecticide treatments (Potter and Spicer 1993, Bentz and

Townsend 2005, Oliver et al. 2009). Susceptibility of red maple to feeding injury by the potato leafhopper varies significantly among cultivars. In particular red maple clones and

Freeman maple cultivars differ in their susceptibility to potato leafhopper feeding injury

(Towsend 1989, Townsend and McIntosh 1993, Bentz and Towsend 1999, Bentz and

Townsend 1997, Bentz and Townsend 2003). Although this leafhopper causes severe economic damage to red maple in nurseries and landscape settings, Freeman maple cultivars are relatively resistant to leafhoppers, but are susceptible to spider mites (Potter and Spicer 1993, Seagraves et al. 2013, Frank et al. 2013).

1.2 Fertilization Practices and Pest Outbreaks

Plant nutrient concentration can influence interactions between herbivorous arthropods and plants (Kytö et al. 1996). Historically, growers have thought that fertilizer application can enhance pest resistance (Herms 2002). A growing body of evidence suggests that high rates of fertilization can decrease plant resistance because it improves the nutritive quality of the host plant making it more susceptible to arthropod injury

(Crafts-Brandner 2002, Opit et al. 2005, Zehnder and Hunter 2009, Raupp et al. 2010,

England et al. 2011).

Insect herbivores are considered nutrient limited, because they have a higher concentration of nitrogen and phosphorous than their host plants (Ayres et al. 2000,

Bentz and Townsend 2001, Huberty and Denno 2006, Awmack and Leather 2002).

Addition of nitrogenous fertilizer has been linked to increased susceptibility to insect pests due to reduced development time, increased survival rates, body mass, and fecundity (Zehnder and Hunter 2009, Denno and Fagan 2003). Plant nitrogen also influences phythophagous insects indirectly through effects on the production of plant secondary metabolites (Kytö et al. 1996). Such compounds often help protect plants by reducing insect growth and survival (Harborne 1993).

Bryan et al. (1983) suggested the Carbon/Nutrient Balance (CNB) hypothesis to explain the effects of fertilization on phenotypic variation in secondary metabolites. The

CNB hypothesis predicts that concentration of carbon based secondary metabolites will be positively correlated with the carbon/nutrient (C/N) ratio of the plant. In contrast, concentrations of nitrogen-based secondary metabolites are expected to be inversely correlated with the C/N ratio of the plant. Fertilization has been shown to increase concentrations of N-based secondary metabolites and decrease concentrations of C-based secondary metabolites that can be used for plant defense (Herms and Mattson 1992).

1.3 Potato Leafhopper

Distribution and Host Range. The potato leafhopper, Empoasca fabae (Harris)

(Homoptera: Cicadellidae), is an important migrant pest of red maple, Acer rubrum L., causing severe economic damage in nurseries and landscape settings (Potter and Spicer

1993). This polyphagous insect has been recognized as an economic pest of nearly 220 kinds of plants including forage legumes, vegetable crops, and deciduous nursery stock in the midwestern and eastern United States (Lamp et al. 1994).

Leguminous hosts are preferred, followed by potatoes and other species of the genus Solanum (Bullas et al. 2003). Maple trees are the most economically important ornamental crop of nurseries and landscapes affected by E. fabae. Potato leafhopper could cause significant economic losses because of its capacity to extend production time for maple seedlings in nursery production and reduce market value by detracting from plant appearance (Oliver et al. 2009).

In North America, the known overwintering area of E. fabae extends across much of the southern pine region from Texas to the Florida panhandle, (Carlson et al. 1992,

Taylor and Shield 1995). Populations build in this region from February through April and are blown north to the Midwest and Northeast United States during spring storms from April through June (Lamp and Liewehr 1995). Based on systematic surveys of leafhopper abundance in alfalfa, the migration is likely to occur in Indiana during the month of May (Carlson et al. 1992).

Biology and development. Empoasca fabae have three or four generations during the growing season after they arrive in Indiana during the spring. The adults are 1/8 inch

(3.2 mm) long, wedge shaped and pale green. The nymphs appear similar to adults but they do not have wings (Bullas et al. 2003). Eggs are transparent to pale yellow and measure about 1 mm long. Potato leafhopper females produce 200-300 eggs. The adult female can survive about 30 days. Eggs are inserted into the veins and petioles of leaves and hatch in about 6 to 10 days in continuously high summer temperatures. Hatching occurs over a range of 7 to 20 days (Munyaneza and Henne 2013). Nymphs mature to adults in approximately 8 to 25 days, depending on the temperature. Adults mate two days after emergence, and the pre-oviposition period is 3 to 8 days. Development of

5 leafhoppers takes from 20 to 30 days during midsummer with two to six overlapping generations (Bentz and Towsend 2004). The lower temperature threshold for development is estimated to be 8.4C and the upper threshold to be 29C. Adult longevity is usually 30 to 60 days (Munyaneza and Henne 2013).

Feeding habitats and damage. Nymphs and adults feed on host plants by making lacerations into vascular tissue of a stem, petiole, or leaf vein and sucking sap through a stylet (Backus et al. 2005). The leafhopper feeds by repeatedly injecting its stylet into the vascular tissue to ingest fluids from the mesophyll and the phloem (Backus and Hunter

1989). Through a combination of mechanical and salivary stimuli, potato leafhopper feeding causes the vascular tissue around the feeding site to degrade (Ecale and Backus

1995). Feeding activity on new shoots and leaf growth interrupts the movement of plant food through the phloem (Flinn et al. 1990, Bentz and Townsend 1999, Nielsen et al.

1990) Thus, leafhopper feeding initiates a sequence of changes that produce a characteristic yellowing of leaves. The leaves become deformed and chlorotic and the edges turn black to brown (Backus et al. 2005). This syndrome of delayed plant maturity reduced plant nutrition, stunted growth, and reduced yield in agronomic crops like alfalfa is called hopper burn (Lamp et al. 2004).

Factors that contribute to damage and population abundance. Ornamental landscapes are commonly fertilized (Smiley 2007). Several studies show that feeding injury and performance of the potato leafhopper on field-grown maple trees are related to leaf phenology and to the leaf nutrient content of the host plant, which varies among cultivars (Bentz and Towsend 1997, 1999, 2001).

Leafhoppers respond to the mineral nitrogen content of their host, by increasing rates of oviposition based on the level of fertilizer (Roltsch and Gage 1990). This is likely because as piercing-sucking herbivores, potato leafhoppers can respond to small difference in sugar and nitrogen distribution within a plant (Lamp et al. 2001, Bullas et al.

2003, Backus et al. 2005).

Bryant et al. (1983) suggest that plants with increased nitrogenous fertilization have a low C/N ratio that causes higher susceptibility to leafhopper feeding. The surplus

C would result in accumulation of carbon-based secondary substances that defend the plants against herbivory (Bentz and Towsend 2003). Bentz and Townsend (2003) postulated that the C to N ratio could explain the susceptibility to leafhopper attack under different growing conditions. Bentz and Towsend (1997) demonstrated that maples responded to nitrogen fertilization by prolonging the production of tender elongating shoots that are susceptible to leafhoppers.

Susceptibility of red maple to feeding injury by the potato leafhopper varies significantly among half-sib progenies (Towsend 1989), full sib progenies (Townsend and McIntosh 1993), and clones (Bentz and Towsend 1999). Clones with more red maple characteristics are more susceptibile than clones with silver maple characteristics. Known as Freeman maples (A freemanii E. murray) these crosses between red and silver maples

(A. saccharinum L.) are resistant to feeding injury by this insect (Towsend and Douglas

1998).

Differences between the susceptibility of maple clones are consistent with what is known about leafhopper biology. There is a strong relationship between the time of leaf initiation, morphological and chemical factors, and nutrient content of a particular maple

7 clone or progeny group (Bentz and Towsend 1997, 2003). Red maple clones most tolerant to potato leafhopper are generally those that initiated growth earliest in the spring.

The early leaf-flushing genotypes would have less succulent stem tissue because they would be fully developed, tougher and leathery by the time the leafhopper arrived.

Management of Potato Leafhopper. Preventive strategies for managing potato leafhopper need to consider the relationship between arrival times, weather and pest status (Maredia et al. 1998). Although several techniques have been explored for monitoring potato leafhopper, including in situ counts, sweep netting, pan traps, D-vac sampling, and the use of yellow sticky traps, few of these methods are sensitive enough for making management decisions (DeGooyer et al. 1998). Nymphs are preferred for monitoring because adults are highly mobile, and eggs are not visible unless leaf tissue has been cleared.

Insecticides are the primary means of control for potato leafhopper. These include organophosphate insecticides such as dimethoate and phorate; pyrethroids such as bifenthrin, permethrin and ß-Cyfluthrin; carbamates such as carbaryl; and neonicotinoids such as imidacloprid, thiamethoxam and clothianidin (Bullas et al. 2003, Potter and

Spicer 1993, Bentz & Townsend 2005, Kaplan et al. 2008, Oliver et al. 2009). Chemical control should be implemented before symptoms occur because plants do not recover well once the vascular system has been damaged (Davis and Fick 1995).

The distinct preferences of phytophagous insects for particular varieties or growth stages of host plants may be exploited by modifying crop management practices.

Intercropping systems provide a diversity of host and nonhost vegetation that result in substantially lower pest populations when compared with monocultures (Brewer and

Schmidt 1995). A soybean-wheat cropping system contains smaller population of female potato leafhoppers compared with a uniform planting of soybean (Miklasiewicz and

Hammond 2001). Similar results were observed when alfalfa is intercropped with grassy weeds, forage grasses or oats (Lamp 1991, Roda et al. 1997a,b). Alternatives to blanket insecticide applications are likely to include use of sampling based thresholds based on trap-crops, biological control and host plant resistance.

1.4 Spider mites

The common name spider mite applies only to mite species in the family

Tetranychidae, belongs to the order Acarina. Spider mites comprise a large group of phytophagous mites that are serious pests in many cropping systems, including ornamental plant systems where they attack a variety of woody and herbaceous plants.

The genus Oligonychus includes a large number of species (Jeppson et al. 1975,

Weidhaas 1979, Johnson and Lyon 1991, Zhang 2003, Hoy 2011).

The maple spider mite, O. aceris (Shimer), is closely related to the southern red mite (O. ilicis). O. aceris occurs on maple and feeds on the undersides of the leaves. This spider mite has been reported wherever maples are grown in the US (Johnson and Lyon

1991, Frank and Sadof 2011, Seagraves et al. 2013, Frank et al. 2013). The southern red mite, Oligonychus ilicis (McGregor), is the most important, widespread, and destructive spider mite on broad-leaved evergreens, especially Japanese hollies, camellia, and azalea

(Johnson and Lyon 1991).

Biology. Maple mites overwinter as bright red eggs on the bark. The typical developmental stages for spider mites include a round, usually flattened egg, a 6-legged

"larva," an 8-legged protonymph, an 8-legged deutonymph, and an 8-legged female and male adult (Weidhaas 1979).

The generalized life cycle of these mites is as follows: Time from egg hatch to adult can be from 4 to 6 days, with adult females laying several hundred eggs over a period of 2-3 weeks. There are many overlapping generations during the summer months

(Potter 2008). Populations can increase rapidly and cause extensive plant damage in a very short time (Weidhaas 1979).

Feeding habitats and damage. O. aceris is an important pest of nursery-grown maples, especially Freeman maples (Seagraves et al. 2013). Spider mites have needle-like mouthparts and feed by piercing the leaves of host plants and sucking out the fluids from individual plant cells (Jeppson et al. 1975, Shrewsbury and Hardin 2004). This causes the leaves to have a stippled or flecked appearance, with chlorotic dots where the cellular contents have been removed (Hoffland et al. 2000). Prolonged, heavy infestations cause leaf scarification, yellowing or bronzing of the foliage, sometimes accompanied by extensive foliage webbing with silk (Johnson and Lyon 1991, Perumalsamy 2010,

Seagraves et al. 2013).

Factors that contribute to damage and population abundance. Prior to the extensive use of synthetic organic pesticides, spider mites (Acari: Tetranychidae) were minor pests for agricultural crops (Penman and Chapman 1988). This pest has become problematic due to cultural and chemical practices that stimulate spider mite populations or/and eliminate their natural enemies. In addition, spider mites rapidly have generated resistance to several pesticides in different production systems where pesticides are

10 broadly used (Croft and Van De Baan 1988, Thwaite 1991, Knowles 1997, Stumpf and

Nauen 2001, Pree et al. 2002, Zhang 2003).

One of the cultural practices that could increase mite populations is fertilization.

Trees are commonly fertilized in production and container nurseries to stimulate growth and improve appearance (Stubbs et al. 1997, Smiley 2007, Raupp et al. 2008). Several studies however, have shown that adding fertilizers can increase the abundance of mites.

Hoffland et al. (2000) demonstrated that nitrogen levels in leaf tissue of tomato are positively correlated with rates of mite development and fecundity.

Dust on foliage can contribute to spider mite outbreaks because interferes with the effectiveness of spider mite predators. Increasing irrigation to remove dust can reduce stresses caused by drought that have also been associated with spider mite outbreaks

(English-Loeb 1990). Cover crops can also be planted in nurseries to reduce the amount of dust. In addition, these crops provide shelter, alternative prey or hosts, and nectar for predators as well as retain them in the crops (Hoy 2011).

Biological control of spider mites. Biological control of mites is achieved primarily by predators that include lacewings, lady beetles, thrips and syrphids and predatory mites. The most important predators include mites in the families Phytoseiidae and Stigmaeidae (Hoy 2011, Gerson et al. 2003). These predatory mites have been studied extensively because they regulate populations of the genus Tetranychus in certain agro-ecosystems (Jones and Parella 1983, Clements and Harmsen 1990, Croft and

MacRae 1993, Sato 2001). These predators interact through competition for prey or by feeding on each other (MacRae and Croft 1996). Abad-Moyano et al. (2010) suggest that phytoseiids are superior in terms of field efficacy, prey consumption per predator and

11 intrinsic rate of increase. Some of the characteristics that contribute to the efficacy of phytoseiids include their ability to survive for long periods without prey by feeding on pollen, conspecifics and other phytoseiid species. Phytoseiids also show a numerical response to spider mite populations via aggregation and increased reproduction

(McMurtry and Croft 1997).

The family Stigmaeidae also includes potentially important predaceous mites, especially the genera Agistemus and Zetzellia (Khodayari et al. 2008). These predators are able to act on their own or supplement control provided by phytoseiids (Santos and

Laing 1985, Croft and MacRae 1993). The life cycle of stigmaeids appears to be longer than that of phytoseiids, which could limit their ability to respond to spider mite population increase. However, they might survive on a variety of alternative foods and persist for long periods without prey and eventually reach densities capable of controlling pest mites (Jamali et al. 2001, Khodayari et al. 2008). Zetzellia mali (Ewing) is considered a predator of tetranychid eggs and is a source of intraguild predation on phytoseiids (Clements and Harmsen 1990, Zahedi-Golpayegani et al. 2007). Clements and Harmsen (1992, 1993) suggested that groups of stigmaeids and phytoseiids have greater efficacy than either predator alone over a wide range of prey densities.

The performance of these predators however is often interrupted by pesticide use leading to outbreaks of spider mites (Sato et al. 2001, Gerson et al. 2003, Frank and

Sadof 2011). The concept of secondary pest outbreaks was originated from studying how spider mite abundance increased when differential mortality removed the biological controls of the spider mite population without killing spider mites (McMurtry et al. 1970,

Penman and Chapman 1988, Hill and Foster 1998, Lester et al. 1999, Pratt and Croft

2000, Hoy 2011). Currently, this has been associated with the application of pyrethroids and neonicotinoid insecticides (Bowie et al. 1999, James and Vogele 2001). Pesticides might directly and indirectly affect predatory mites by killing them or by changing their behaviour. Irritability and dispersion are the main behaviour responses which have been shown due to sublethal residues of many pesticides (Li and Harmsen 1992, Bowie et al.

2001, Sato et al. 2001, James 2003). Some phytoseiids are resistant to organophosphates insecticides, which makes them a good fit for integrated pest management. However,

Environmental Protection Agency (EPA) is gradually removing organophosphates form the market (Strickler et al. 1987, Croft and Slone 1998)

The effects of pesticides on spider mites become more complex when the interaction of both predators is interrupted. Sato et al. (2001) suggested that the deleterious effect of chemicals on the phytoseiids could force them to prey on more readily available stigmaeids, and allow spider mite populations to increase. Adding Z. mali to the predator diversity would lower the overall levels of spider mites. The ability of this stigmaeid to persist at low prey densities on alternative foods and its superior competitive abilities over phytoseiids at low prey densities may enable it to contribute significantly to biological control of pest mites (Croft and MacRae 1993, Croft and Slone

1997).

The dynamics between predator and prey and the interaction among predatory mites also might be influenced by host plant traits (O’Dowd and Pemberton 1998, Roda et al. 2001). Leaf surface characteristics such as pubescence and domatia have been shown to affect predation and predator survival and fitness. Domatia consist of small hair tufts, pockets, or invaginations in the major vein junctions on the undersides of the leaf

(O’Dowd and Wilson 1989, Pemberton and Turner 1989, Wilson 1991). Recent studies have documented that plants with these structures are better protected against phytophagous mites (Walter and O’Dowd 1992, O’Dowd 1994, Norton et al. 2000).

Agrawal et al. 2000 observed that on leaves with domatia, each of the predators was found inside the domatia two to three times more often than outside the domatia. Norton et al. (2000) suggest that domatia reduce the effects of predator-predator interactions on beneficial mite abundance by providng them a place to hide.

Morphologies of domatia vary greatly among plant species and even within individual plants, and thus the adaptive significance of domatia may differ according to their morphology (Nishida et al 2005). Several studies have demonstrated that predatory mites were consistently more abundant on plants with leaf domatia, especially

Phytoseiidae and Stigmaeidae (Duso 1992, Karban et al. 1995, Walter and O’Dowd 1992,

Walter 1996, Norton et al. 2000, Roda et al. 2000). Preliminary data of the abundance of

O. aceris on maple varieties suggest that leaf domatia may be involved in conferring differences between red maple and freeman maple cultivars on maple spider mite abundance (Steve Frank not published) (Table 1.1).

1.5 Objectives

The purpose of my research was to develop an integrated approach to manage the maple pest complex based on understanding the influence of fertilization and pesticides on pest abundance and damage. To reach this objective I will test the following three hypotheses:

1. Maple spider mite populations respond positively to early season application

of insecticide to control potato leafhopper on Autumn Blaze maple cultivars

more than on Red Sunset maple cultivars (Chapter 2).

2. Potato leafhopper and maple spider mite populations respond positively to

elevated rates of fertilizer on Red Sunset and Autumn Blaze maple cultivars

(Chapter 3).

3. Leaf domatia influence on maple spider mite population and the interaction

with predatory mites on Red Sunset and Autumn Blaze (Chapter 4)

The goal of my research is to develop tools for managing these two groups of maples in ways that protect their health and value without causing spider mite outbreaks.

1.6 Literature Cited

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Table 1.1 Damage by maple spider mite on maple cultivars in North Carolina nurseries and the abundance of leaf domatia (Steve Frank not published)

% Cultivar Phytoseiids/cm2 Domatia/ midvein mite damage/leaf

Autumn Blaze 35.4 b 0.005 c 0.09 c

October Glory 20.4 a 0.012 b 1.31 b

Red Sunset 17.0 a* 0.125 a 2.20 a

F2,97=7.3; P=0.001 F2,81=140.1; P<0.001 F2,81=48.1; P<0.001

CHAPTER 2. EFFECTS OF PESTICIDE APPLICATION ON ARTHROPOD PESTS OF NURSERY GROWN MAPLES

2.1 Abstract

Field studies were conducted to determine how the use of insecticides to control

Empoasca fabae (Harris) (Homoptera: Cicadellidae) affects Oligonychus aceris (Shimer)

(Acarina: Tetranychidae) populations on ‘Red Sunset’ red maple and ‘Autumn Blaze’

Freeman maple. Two experiments were carried out on field grown nursery trees. One examined the effects of early season pesticide applications during 2009. The other experiment compared effects of using threshold levels of one, three, or six leafhoppers per branch to time applications in 2010. Pesticide applications directed against leafhoppers reduced their abundance and damage in both cultivars, but caused an increase in O. aceris on ‘Autumn Blaze’ during 2009. In contrast, Red Sunset, populations of O. aceris did not increase after applications were made. In 2010, insecticide applications did not increase abundance of O. aceris on Autumn Blaze because I used a threshold to manage leafhoppers and fewer trees of this cultivar were treated. Two phytoseiid mites,

Neoseiulus fallacis (Garman) and Typhlodromus caudiglans (Schuster), and one stigmaeid, Zetzellia mali (Ewing) were identified as the principle predators of O. aceris on maple leaves. Insecticide applications had no significant effects on the total abundance of predatory mites on either Red Sunset or Autumn Blaze maples in 2009 or 2010.

However, populations of the predator Z. mali were higher in both years on Red

Sunset than Autumn Blaze. These results suggest the need for developing pest management approaches that considers the susceptibility of these two maple cultivars to specific pests.

2.2 Introduction

Red maples (Acer rubrum Linnaeus) are one of the most widely grown species of landscape trees (Oliver et al. 2009). This popular tree is used for its environmental adaptability, attractive form, and leaf color (Townsend and McIntosh 1993). A recent survey of 12 large cities in Eastern North America indicate that the genus Acer is the most common genus, comprising 15% to 57% of the street trees (Raupp et al. 2006).

Over the last few years, maple trees have become even more popular because they can serve as replacements for ash trees killed by emerald ash borer, Agrilus planipennis

(Fairmaire).

Numerous cultivars have been developed for superior growth, leaf characteristics, insect resistance, and other plant qualities (Townsend and Douglass 1998). Some popular cultivars have been developed from red (Acer rubrum) and silver maple (Acer saccharinum L.). (Sibley et al. 1996). These hybrids are known as Acer freemanii E.

Murray (Freeman maple) (Santamour 1993). Unfortunately, some popular cultivars are susceptible to damage caused by the potato leafhopper (Empoasca fabae Harris) (Bentz and Townsend 1999). The potato leafhopper, Empoasca fabae (Harris) (Homoptera:

Cicadellidae), is a serious pest of maple trees, causing severe economic damage in nurseries and landscape settings (Potter and Spicer 1993, Oliver et al. 2009). Nymphs and

29 adults feed on host plants by making lacerations into the vascular tissue of a stem, petiole, or leaf vein and sucking sap through a stylet (Backus and Hunter 1989, Backus et al.

2005). Thus, leafhopper feeding initiates a sequence of changes that produce a characteristic yellowing of leaves called hopper burn (Lamp et al. 2004).

Control of this pest is usually obtained by several insecticide treatments (Potter and Spicer 1993, Bentz and Townsend 2005, Oliver et al. 2009, Frank et al. 2013). These applications can destroy natural enemies and enable the development of injurious secondary pests such as mites and scales, which have the potential to cause high levels of damage to maples and, therefore, are of great concern to growers (Hill and Foster 1998,

Seagraves et al. 2013). In particular, Freeman maple cultivars are relatively resistant to potato leafhopper but are susceptible to the maple spider mite, Tetranychidae:

Oligonychus aceris (Shimer) (Potter and Spicer 1993, Townsend and Douglass 1998). A recent investigation of cultivar resistance indicated that Red Sunset red maples were most susceptible to potato leafhoppers and least susceptible to maple spider mites (Seagraves et al. 2013). In the same study, Autumn Blaze freeman maples were found to be most resistant to potato leafhopper and most susceptible to maple spider mites during midsummer.

Applications of pesticides on the canopy of maple trees have been shown to be responsible for outbreaks of spider mites (Frank and Sadof 2011). I have observed phytoseiid and stigmaeid mites in the genera Typhlodromus, Neoseiulus and Zetzellia to be common on maple trees. Mites in these families have been studied extensively because they regulate populations of their tetranychid prey in certain agro-ecosystems (Jones and

Parrella 1983, McMurtry and Croft 1997, Sato et al. 2001). They interact interspecifically through competition for prey or by feeding on each other (MacRae and Croft 1996).

The goal of this study was to develop an integrated approach to managing leafhoppers and spider mites on Autumn Blaze and Red Sunset maple cultivars.

Specifically, I examined the relative capacity of commonly used insecticides to control leafhoppers. Then, using the most effective insecticide for leafhoppers, I determined a threshold density for potato leafhoppers that could effectively reduce the damage caused by this pest on each maple cultivar. Impacts of these pesticide applications on maple spider mite populations were also assessed.

2.3 Materials and Methods

Grower Survey. During the spring of 2008, nursery inspection reports from the

Indiana Department of Natural Resources were examined to identify nurseries with a history of spider mite problems on maple trees. Nursery producers were surveyed

(Appendix 2.1) to obtain detailed information on the maple cultivars grown, insecticides and fertilizer used, and frequency of application. The purpose of the survey was to look for potential relationships between cultural practices and spider mite outbreaks that could be explored in future experimentation.

Insecticide Studies. Experiments were conducted at Bellinger’s Nursery near

Lafayette, IN, during the 2009 and 2010 growing season to evaluate effects of commonly used foliar insecticides on populations of potato leafhopper and maple spider mites on

Acer rubrum cultivar ‘Red Sunset’ and Acer freemanii cultivar ‘Autumn Blaze’. The main field plot consisted of 84 trees planted 2 m apart in rows that were separated by 3.5

31 m. The average diameters of Red Sunset and Autumn Blaze maples measured 10 cm above the soil line were respectively 5.57±0.15 and 8.63±0.72 cm.

2009 Studies. In 2009, the main objective was to determine the relative effectiveness of insecticides commonly used by growers to control E. fabae. For this reason, most of the treatments were on Red Sunset maples because of grower concerns about their susceptibility to E. fabae. Three insecticides, 0.13 ml ai/l bifenthrin (Talstar®S

7.9EC, FMC Corporation Agricultural Products Group, Philadelphia, PA), 0.56 ml ai/l buprofezin (Talus 40SC, SePRO Corporation, Carmel, IN), and 0.96 ml ai/l imidacloprid

(Marathon® 60WP, OHP, Inc. Mainland, PA) were applied to Red Sunset trees either on

29 May or when the density of leafhoppers reach a specified threshold density.

Treatments were arranged in a randomized complete block design with the six insecticide treatments plus a water control with 10 replications. Each treatment was applied with a

Solo 425® backpack sprayer (Newport News, VA) using a hollow cone nozzle until runoff.

During insecticide applications, a 1.5 3.5 m styrofoam board was placed behind each tree to prevent spray drift between trees. Due to availability of fewer Autumn Blaze trees at the nursery, only bifenthrin was tested when applied early in the season and compared it to control with seven replications.

Abundance of E. fabae on each plant was determined weekly from 29 May until 4

August. One branch from each of the four cardinal directions from the lower 2 m of the tree was selected for visual inspection of the first five leaf nodes from the branch terminal.

Numbers of E. fabae and nodes deformed by leafhoppers were recorded for each branch to estimate pest density and injury. Weekly counts of E. fabae on branches were used to determine when the threshold treatments were applied. A second estimate of injury to

32 each tree was made by examining 10 shoot tips in the upper canopy and recording the proportion of distorted shoots.

At the same time, leaves were collected every three weeks from 6 July until 7

September to evaluate the abundant maple spider mite and their predators. Samples consisted of a total of 12 leaves, three chosen from four branches in each cardinal direction. The leaves were placed in labeled paper bags. All paper bags were placed in a cooler with freezer packs until they were taken to the laboratory for processing. There, leaves were removed from each bag and immediately processed through a mite brushing machine (Leedom Engineering, Twain Harte, CA) to transfer the mites to labeled Petri dishes that were coated with a thin layer of vegetable oil. All samples were transferred to

Petri dishes on the same day that leaves were collected. Petri dishes were stored in a 10ºC refrigerator until all the samples were processed (no more than 2 weeks). Adult and nymphal stages of spider mites and predators present in the Petri dishes were counted.

2010 Studies. In 2010, the main purpose was to study the effect of different thresholds for E. fabae using bifenthrin on red and Freeman maples. Bifenthrin was determined in 2009 to be the most effective insecticide to reduce their damage and is one of the most widely-used insecticides by nursery producers. The 2009 data also suggested that there was a link between early season use of bifenthrin (Talstar S) against E. fabae and the occurrence of O. aceris problems later in the season. The impact of these pesticide applications and the thresholds for leafhopper on the maple spider mite population and their predatory mites was also assessed.

This study was conducted at Bellinger’s Nursery in Lafayette, Indiana with separate plantings of Red Sunset and Autumn Blaze maples. The treatments consisted of

33 an untreated control and an application of 0.13 ml ai/l bifenthrin (Talstar®S 7.9EC, FMC

Corporation Agricultural Products Group, Philadelphia, PA) when densities of E. fabae exceeded one, three or six leafhoppers per branch. Longevity of control provided by each spray was estimated for each threshold as the average number of weeks until the density on a tree returned to the threshold. The upper threshold of six per branch approximates the average density of leafhoppers on untreated susceptible Red Sunset cultivars in preliminary studies. There were 10 replications of each treatment in the planting of Red

Sunset and five replications in the planting of Autumn Blaze. Abundance of leafhoppers and damage on each plant was determined weekly from 15 April until 29 July as described previously. Maple spider mite populations were assessed by collecting leaves from trees every month from 29 June until 16 September using methods described for

2009.

Timing counts of E. fabae. To facilitate adaptation of this type of threshold, growers need a tool to simplify the procedure. Yellow sticky cards can be used to indicate when growers should start inspecting trees in order to determine the threshold densities are reached. For this reason, a 6 10 cm yellow sticky card was placed on a stick five cm from the stem and at the base of the canopy before leaf bud breaks (13 April, 2010) and examined weekly. We plotted the weekly number of leafhoppers in the sticky cards and per branch over time to compare the relative usefulness of this measure to trigger either threshold sprays or the initiation of monitoring activity.

Statistical Analysis. Results are presented on the figures as arithmetic means ± standard error for each treatment for E. fabae and O. aceris. For evaluation of the effect of early insecticide application and the threshold level on leafhopper and maple spider

34 mite density we conducted a repeated measures analysis using PROC GLIMMIX for

Generalized Linear Mixed Models (SAS® 9.3 Institute Inc., Cary, NC). The GLIMMIX procedure selected a regression model based on the distribution of each response variable using a Laplace maximum likelihood estimation method. Distribution of E. fabae density was best explained by the negative binomial distribution, whereas damage tips and damaged nodes were described with beta distribution and spider mite density was best described by a Poisson distribution. I used the compound symmetry option to approximate constant variance and covariance at each sample date over time. LSMEANS were separated using Tukey’s HSD Test at an -level of 0.05 to compare insecticide applications to control leafhopper. Differences among number of insecticide applications to control E. fabae were analyzed by Analysis of variance (ANOVA) using a randomized complete block using PROC GLM for general linear models (SAS® 9.3 Institute Inc.,

Cary, NC).

The correlation between number of damaged nodes and number of damaged tips caused by potato leafhopper per tree were determined via Pearsons correlation using

PROC CORR (SAS® 9.3 Institute Inc., Cary, NC) for each cultivar. Similarly, the correlation between density of E. fabae per card and their abundance per tree were determined via Pearson’s correlation on Red Sunset and Freeman maples.

2.4 Results

Grower Survey. A total of 48 of the 150 licensed nursery producers responded to the survey. Most of producers (91%) grew trees in the ground. The rest (9%) grew trees in containers. Although many maple cultivars were grown in the nurseries, 83% of

35 producers grew Red Sunset and Autumn Blaze. The top four arthropod pests in order of importance were potato leafhopper (58.3%), maple spider mite (45.8%), cottony maple scale (18.8%) and aphids (6.2%).

In order to associate control strategies with self-reported pest problems, growers were categorized as those using or not using insecticides. Growers who used insecticides tended to apply pesticides to control E. fabae and had more maple spider mite problems than those who did not use insecticides. Pyrethroids were the most commonly used insecticide followed by neonicotinoids. Use of either insecticide class was associated with spider mite problems (Table 2.1).

Effect of early insecticide application on Red Sunset red maples on E. fabae and

O. aceris populations. The number of Red Sunset maple trees reaching threshold levels over the course of the season differed among insecticide treatments (F = 39.99; df = 6, 63;

P < 0.0001). Trees that reached the threshold of one leafhopper per branch received the most applications when buprofezin was used, followed by those treated with imidacloprid and bifenthrin (Table 2.2). Time (F = 82.04; df = 7, 441; P < 0.0001) and insecticide treatment (F = 28.98; df = 6, 54; P < 0.0001) significantly affected E. fabae density during 2009 (Fig. 2.1A). Insecticide treatments caused the greatest reductions in E. fabae from mid-May through June. At this time all treatments had fewer E. fabae than the untreated control. Later in the season as the abundance of E. fabae declined no treatment effects on densities were detected.

Damaged nodes per shoot and damaged tips per plant were highly correlated

(Pearson’s r = 0.71; P < 0.0001). Damage caused by potato leafhopper differed significantly among treatments (nodes, F = 30.53; df = 6, 54; P < 0.0001; tips, F = 15.16;

36 df = 6, 54; P < 0.0001) and over the course of the season (nodes, F = 32.58; df = 14, 882;

P < 0.0001; tips, F = 6.31; df = 13, 819; P < 0.0001) (Fig. 2.1B-C). The damage was considerably lower in trees with either bifenthrin treatment than in those treated with buprofezin or imidacloprid. The most heavily damaged trees during the season were those that did not receive any insecticide applications during 2009 field studies, followed by those treated with buprofezin at the beginning of the season.

Oligonychus aceris populations did not differ among treatments (F = 1.20; df = 6,

54; P = 0.3228) on Red Sunset trees. However, there was a significant effect of time (F =

5.43; df = 3, 189; P = 0.0013) during 2009 (Fig. 2.3A). Two phytoseiid mites, Neoseiulus fallacis (Garman) and Typhlodromus caudiglans (Schuster), and one stigmaeid, Zetzellia mali (Ewing) were the predatory mites found in maple trees. The abundance of phytoseiids did not differ among treatments throughout the season on Red Sunset maple cultivar (F = 0.02; df = 6, 54; P = 0.9900), nor was there a significant effect of time (F =

0.08; df = 3, 189; P = 0.9700) (Fig 2.3B). Similarly, Z. mali density did not differ significantly among treatments (F = 0.12; df = 6, 54; P = 0.9930) nor time (F = 1.24; df =

3, 189; P = 0.2982) (Fig. 2.3C).

Effect of early insecticide application on Autumn Blaze Freeman maples on E. fabae and O. aceris populations. During the 2009 field studies, the density of E. fabae did not differ among trees treated with insecticide and the untreated control (F = 0.79; df

= 1, 6; P = 0.4079), but there was a significant effect of time on E. fabae density (F =

48.83; df = 3, 36; P < 0.0001) (Fig. 2.1A). Insecticide use also failed to reduce damage caused by E. fabae on Autumn Blaze maples (nodes, F = 2.20; df = 1, 6; P = 0.1887; tips,

F = 2.63; df = 1, 6; P = 0.1560). The damage did not differ significantly over the course

37 of the season (nodes, F = 0.19; df = 12, 144; P = 0.9987; tips, F = 0.35; df = 10, 120; P =

0.9639) (Fig 2.1B-C).

During the 2009 field studies, O. aceris populations differed significantly among treatments (F = 9.31; df = 1. 6; P = 0.0225), but did not vary considerably over the course of the season (F = 0.02; df = 3, 36; P = 0.9964) (Fig. 2.3A). Autumn Blaze maple trees treated with bifenthrin early in the season had the higher populations of O. aceris and this trend of higher abundance persisted throughout the season. In contrast, the abundance of the predatory mites was too low to detect effects of treatment (phytoseiids, F = 0.09; df =

1, 6; P = 0.7783; stigmaeids, F = 0.09; df = 1, 6; P = 0.7783) or time (phytoseiids, F =

0.16; df = 3, 36; P = 0.9220; stigmaeids, F = 0.16; df = 3, 36; P = 0.9220) (Fig. 2.3B-C).

Effect of threshold levels on E. fabae and O. aceris populations on Red Sunset red maples. There were no significant differences in numbers of potato leafhopper per branch among trees treated at threshold densities and the untreated control (F = 0.01; df = 3, 27;

P = 0.9999) (Fig. 2.4A). Density of E. fabae varied significantly over time during 2010 with the peak occurring on 27 May (F = 9.65; df = 3, 108; P < 0.0001). The number of trees reaching threshold levels over the course of the season differed among threshold treatments (F = 11.67; df = 3, 36; P < 0.0002). Trees treated with bifenthrin at threshold level of one leafhopper per branch received more applications followed by those with three and six leafhoppers per branch (Table 2.3).

Damage caused by E. fabae on red maple trees differed significantly among threshold levels (nodes, F = 16.37; df = 3, 27; P < 0.0001; tips, F = 6.46; df = 3, 27; P =

0.0019) throughout the season. Trees treated with bifenthrin at threshold level of one leafhopper per branch had the lowest level of damage among the threshold levels

38 followed by a threshold level of three per branch (Fig. 2.4B). Damage to trees treated at a threshold of six leafhoppers per branch was not significantly different from the control.

These findings were consistent throughout the season (nodes, F = 0.17; df = 9, 324; P =

0.9999; tips, F = 1.70; df=10, 396; P = 0.0784).

Insecticide treatments (F = 0.03; df = 3, 27; P = 0.9935) and time (F = 0.21; df =

4, 144; P = 0.9319) had no significant effect on O. aceris density (Fig. 2.5A). Three predatory mites N. fallacis, T. caudiglans and Z. mali were present on maple trees.

Combined populations of phytoseiid (N. fallacis and T. caudiglans) mites were not significantly affected by threshold treatments (F = 0.08; df = 3, 27; P = 0.9686) or time

(F = 0.04; df = 4, 144; P = 0.9965) (Fig. 2.5B). Similarly, Z. mali was not affected by insecticide application (F = 0.29; df = 3, 27; P = 0.8322) or time (F = 0.06; df = 4, 144; P

= 0.9933) (Fig. 2.5C).

Effect of threshold levels on E. fabae and O. aceris populations on Autumn Blaze

Freeman maples. In 2010, E. fabae density did not differ significantly among threshold treatments (F = 1.11; df = 3, 12; P = 0.3819) on Autumn Blaze maples (Fig. 2.4A). In contrast, E. fabae density varied significantly over time (F = 11.30; df = 15, 60; P <

0.0001) with a peak observed on 27 May. Trees with the threshold treatment of one leafhopper per branch had the most applications over the course of the season (F = 16.00; df = 3, 16; P = 0.0001). However, fewer Autumn Blaze trees received insecticide than

Red Sunset. Thresholds of three or more leafhoppers per branch were not reached by

Autumn Blaze maple trees during 2010 (Table 2.3). Damage caused by E. fabae on trees treated with bifenthrin at any threshold level did not differ from those that did not receive insecticide applications overall (nodes, F = 0.02; df = 7, 112; P = 0.9999; tips, F = 0.31;

39 df = 7, 112; P = 0.8159) or at any time over the season (nodes, F = 1.14; df = 3, 12; P =

0.3711; tips, F = 0.03; df = 7, 112; P = 0.9999).

Insecticide treatments (F = 1.30; df = 3, 12; P = 0.3186) and time of collection (F

= 0.30; df = 4, 64; P = 0.8750) did not significantly affect O. aceris populations on

Autumn Blaze maples during 2010 (Fig. 2.5A). Similarly, there were no differences in phytoseiid densities (F = 0.03; df = 3, 12; P = 0.9912), or Z. mali in any of the trees (F =

0.06; df = 3, 12; P = 0.9790) (Fig 2.5B) or at any time (F = 0.01; df = 4, 64; P = 0.9997;

F = 0.05; df = 4, 64; P = 0.9958) over the season (Fig 2.4C). Numbers of maple spider mites per cm2 were significantly lower in 2010 than 2009 (Figs. 2.3A and 2.5A).

Sticky cards as monitoring indicator for E. fabae on maple cultivars. Density of potato leafhopper per branch and numbers of E. fabae per sticky card accounted for only

13% of the variation of the population on Red Sunset (r = 0.36; df = 638; P < 0.0001), and 10% on Autumn Blaze maple tree branches (r = 0.32; df = 318; P < 0.0001) (Fig

2.6A). Leafhoppers were first detected in sticky cards on 22 April in the Red Sunset planting, two weeks before they were detected in the trees (Fig. 2.6A). The first trees reached the threshold density of one leafhopper per branch on 20 May, a full month after the first detection of leafhoppers in sticky cards (Fig. 2.6B). Damage by E. fabae was not detected until 20 May when > 50% of the trees reached the threshold density of one leafhopper per branch (Fig. 2.6A). E. fabae on Autumn Blaze were first detected in sticky cards one week after Red Sunset on 29 April (Fig. 2.6A). The first Autumn Blaze trees reached the threshold density of one leafhopper per branch on 27 May when < 40% of trees reached that threshold (Fig. 2.6B). Autumn Blaze maple trees that reached this threshold were less severely damaged than Red Sunset red maple (Fig 2.6B).

2.5 Discussion

Problems reported by nursery growers with spider mites on maples are related to insecticide use. Growers who treated for potato leafhoppers with pyrethroids or neonicotinoids reported having more spider mite problems than those who did not use these insecticides. Our research identified how specific strategies for controlling potato leafhopper can lead to outbreaks of spider mites in some maple cultivars. These findings are consistent with previous studies in which outbreaks of spider mites were associated with insecticides (Trichilo and Wilson 1993, Hill and Foster 1998, Sclar et al. 1998,

Raupp et al. 2004, Cloyd and Bethke 2011, Frank and Sadof, 2011, Szczepaniec et al.

2011, Szczepaniec and Raupp 2012).

Our comparisons of insecticide efficacy suggest that bifenthrin applications reduced leafhopper damage on Red Sunset red maple better than the other products tested.

This is consistent with the high levels of efficacy demonstrated by pyrethroids against leafhoppers in a variety of crops (Cheng and Roy 1985, Kaplan et al. 2008, Frank et al.

2013). Although not as effective as bifenthrin, foliar applications of imidacloprid significantly reduced damage of potato leafhopper compared to the control. This is consistent with Oliver et al. 2009, who determined that early season applications of neonicotinoid insecticides provided effective control of E. fabae. Studies on grape vines had similar results with foliar and soil applications of neonicotinoids providing adequate control of potato leafhopper (Van Timmeren et al. 2011). In contrast, buprofezin did not reduce the potato leafhopper damage in Red Sunset red maple. Although some studies have reported that buprofezin kills leafhoppers, its action was limited to molting stages of insects (Heinrichs et al. 1984, Mas’ud and Moeh 1987, Konno 1990).

Using a threshold of one leafhopper per branch to trigger bifenthrin treatments can reduce damage to Red Sunset maples. In 2010 using a threshold of one, three, or six leafhoppers per branch to time bifenthrin applications resulted in 18%, 54% and 88% respectively of the tips showing damage. During this year, the threshold strategy was implemented before any leafhoppers were detected on sticky cards or in tree branches.

Interestingly, in 2009, only 29% of the tips were damaged when the threshold of one leafhopper per branch was implemented after trees had an average density of 5.17+0.60 leafhoppers per branch. Trees that were treated only once with bifenthrin without follow up monitoring and treatment had an average of 20% of their tips damaged. Clearly, trees can benefit from sustained monitoring and treatment. Lack of correlation between the abundance of leafhoppers in trees and on sticky cards suggests that visual inspection of trees is needed to time applications. Growers seeking to reduce their scouting efforts may want to place sticky cards out in the field and begin scouting after leafhoppers are found on cards.

Red Sunset maples are more susceptible to injury from E. fabae than Autumn

Blaze trees. Nearly 100% of shoot tips were damaged on untreated Red Sunset in both years whereas on Autumn Blaze < 15% of tips were damaged. In contrast only 40%

Autumn Blaze maples reached the threshold of one potato leafhopper per branch. The use of bifenthrin did not significantly improve the management of E. fabae on Autumn Blaze because of the high level of resistance. This finding supports previous research which suggests that maple cultivars differ in their susceptibility to potato leafhopper (Potter and

Spicer 1993, Seagraves 2006, Seagraves et al. 2013). Another important difference between Red Sunset and Autumn Blaze maples is their susceptibility to maple spider

42 mites outbreaks. In Red Sunset, populations of O. aceris did not increase after applications of bifenthrin were made. In contrast, bifenthrin applications made in 2009 caused outbreaks of maple spider mites on Autumn Blaze. In 2010, bifenthrin application did not increase abundance of O. aceris on Autumn Blaze because I used a threshold to manage E. fabae and only 20% of these were treated (Table 2.4).

The response of spider mite populations on Autumn Blaze maples to bifenthrin is consistent with other studies that attribute outbreaks of spider mites to the negative effects that pyrethroids can have on predatory mites (Penman and Chapman 1988, Gerson and Cohen 1989, Li et al. 1992, Hermans 1996, Li and Harmsen 1992, Hill and Foster

1998, Bowie et al. 1999, Hardman et al. 2007). Lester (1998) found that Z. mali did not appear to be affected by the pyrethroid spray as was T. caudiglans. Strickler et al. (1987) and Croft and Slone (1998) suggested that Z. mali was affected less by pesticides than were phytoseiids. Our data do not show any significant effects of bifenthrin on predatory mites on either Red Sunset or Autumn Blaze maples in 2009 or 2010. However, they do show that populations of the predator Z. mali were higher in both years on Red Sunset than Autumn Blaze regardless of insecticide treatment. Although our observed response of predators to insecticides does not correspond to other studies on the impact of pyrethroids on predators, they do point to a qualitative difference between the ability of these cultivars to harbor spider mite predators in the presence or absence of insecticides. I investigated cultivar differences in leaf morphology such as how the presence of leaf domatia could harbor predators and influence in population dynamics (O’Dowd and

Pemberton 1998, Agrawal et al. 2000, Pratt and Croft 2000, Norton et al. 2001) in chapter

In conclusion, pest problems on maple trees can be avoided when varietal differences in susceptibility are considered. Susceptible cultivars of red maples must be managed for potato leafhopper, whereas resistant cultivars like Autumn Blaze do not require management for this pest. On Red Sunset, a cultivar susceptible to potato leafhopper, threshold densities of one potato leafhopper per branch could be used to avoid damage by potato leafhopper. Modification of maple management in nurseries to avoid outbreaks of spider mites can be advantageous to growers. Management for

Autumn Blaze maples should concentrate on conserving natural enemies to avoid maple spider mite outbreaks, through avoiding early season insecticide sprays for E. fabae.

2.6 Literature Cited

Agrawal, A.A., R. Karban, and R.G. Colfer. 2000. How leaf domatia and induced plant resistance affect herbivores, natural enemies and plant performance. Oikos 89: 70- 80. Backus, E.A. and W.B. Hunter. 1989. Comparison of feeding behavior of the potato leafhopper Empoasca fabae (Homoptera: Cicadellidae) on alfalfa and broad bean leaves. Environ. Entomol. 18(3): 473-480. Backus, E.A., M.S. Serrano, and C.M. Ranger. 2005. Mechanisms of hopperburn: an overview of insect taxonomy, behavior, and physiology. Annu. Rev. Entomol. 50: 125-151. Bentz, J. and A.M. Townsend. 1999. Feeding injury, oviposition, and nymphal survivorship of the potato leafhopper on red maple and Freeman maple clones. Environ. Entomol. 28(3): 456-460. Bentz, J. and A.M. Townsend. 2005. Diversity and abundance of leafhopper species (Homoptera: Cicadellidae) among red maple clones. J. Insect Conserv. 9: 29-39. Bowie, M.H., S.D. Worner, and R.B. Chapman. 1999. The use of image analysis to study the effects of residues of esfenvalerate on the locomotory behaviour of Panonychus ulmi and Typhlodromus pyri (Acari: Tetranychidae, Phytoseiidae). Exp. Appl. Acarol 23: 1-9. Cheng, H. H. and R.C. Roy. 1985. Field evaluation of insecticides for suppression of potato leafhopper (Homoptera: Cicadellidae) on peanuts in Ontario. Peanut Science 12(1): 1-4. Cloyd, R.A. and J.A. Bethke. 2011. Impact of neonicotinoid insecticides on natural enemies in greenhouse and interiorscape environments. Pest Manag. Sci. 67(1): 3- 9. Croft B.A. and D.H. Slone. 1998. Perturbation of regulated apple mites: Immigration and pesticide effects on outbreaks of Panonychus ulmi and associated mites (Acari: Tetranychidae, Eriophyidae, Phytoseiidae and Stigmaeidae). Environ. Entomol. 27(6): 1548-1556.

Frank, S.D. and C.S. Sadof. 2011. Reducing insecticide volume and nontarget effects of ambrosia beetle management in nurseries. J. Econ. Entomol. 104(6): 1960-1968 Frank, S.D. W.W.E. Klingeman, S.A. White, and A. Fulcher. 2013. Biology, injury, and management of maple tree pests in nurseries and urban landscapes. J. Integ. Pest Mngmt. 4(1): B1-B14 Gerson, U. and E. Cohen. 1989. Resurgences of spider mites (Acari: Tetranychidae) induced by synthetic pyrethroids. Exp. Appl. Acarol. 6: 29-46. Hardman, J.M., J.L. Franklin, F. Bealieu, N.J. Bostanian. 2007. Effects of acaricides, pyrethroids and predator distributions on populations of Tetranychus urticae in apple orchards. Exp. Appl. Acarol. 43: 235-253 Heinrichs, E.A., R.P. Basilio, and S.L. Valencia. 1984. Buprofezin, a selective insecticide for the management of rice planthoppers (Homoptera: Delphacidae) and leafhoppers (Homoptera: Cicadellidae). Environ. Entomol. 12(2): 515-521. Hermans, S. 1996. Integrated control of the European red mite, Panonychus ulmi, by the predatory mite Amblyseius fallacis: the role of timing and unsprayed refuges. BSc dissertation. Quee’s University, Kingston, Ontario, Canada. Hill, T.A. and R.E. Foster. 1998. Influence of selective insecticides on population dynamics of European red mite (Acari: Tetranychidae), apple rust mite (Acari: Eriophyidae), and their predator Amblyseius fallacis (Acari: Phytoseiidae) in apple. J. Econ. Entomol. 91(1): 191-199. Jones, V.P. and M.P. Parrella. 1983. Compatibility of six citrus pesticides with Euseius stipulates (Acari: Phytoseiidae) populations in Southern California. J. Econ. Entomol. 76: 942-944. Kaplan, I., P. Dively, and R.F. Denno. 2008. Variation in tolerance and resistance to the leafhopper Empoasca fabae (Hemiptera: Cicadellidae) among potato cultivars: implications for action thresholds. J. Econ. Entomol. 101(3): 959-968 Konno, T. 1990. Buprofezin; a reliable IGR for the control of rice pests. In Pest Management in Rice, B.T. Grayson, M.B. Green, and L.G. Copping (eds). Elsevier Applied Science, NY. p 210-222.

Lamp, W.O., G.R. Nielsen, C.B. Fuentes, and B. Quebedeaux. 2004. Feeding site preference of potato leafhopper (Homoptera: Cicadellidae) on alfalfa and its effect on photosynthesis. J. Agric. Urban Entomol. 21(1): 25-38. Lester, P.J., H.M.A. Thistlewood and R. Harmsen. 1998. The effects of refuge size and number on acarine predator-prey dynamics in a pesticide-disturbed apple orchard. J. Appl. Ecol. 35: 323-331.

Li, S.Y. and R. Harmsen. 1992. Effects of low application rates of the pyrethroid PP321 on the apple orchard mite complex (Acari) in Ontario. Can. Entomol. 124:381-390 Li, S.Y., R. Harmsen, and H.M.A. Thistlewood. 1992. The effect of pyrethroid lambdacyhalothrin applications on the spatial distribution of phytophagous and predatory mites in apple orchards. Exp. Appl. Acarol 15: 259-269 Mas'ud, S., and S. Moeh. 1987. Effect of buprofezin in controlling green leafhopper (GLH) and tungro (RTV) incidence. International Rice Research Newsletter 12(3): 36-37. MacRae, I.V. and B.A. Croft. 1996. Differential impact of egg predation by Zetzellia mali (Acari: Stigmaeidae) on Metaseiulus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae). Exp. Appl. Acarol. 20: 143–154. McMurtry, J.A. and B.A. Croft. 1997. Life-styles of phytoseiid mites and their roles in biological control. Annu. Rev. Entomol. 42: 291-321. Norton, A.P., G. English-Loeb, and E. Belden. 2001. Host plant manipulation of natural enemies: leaf domatia protect beneficial mites from insect predators. Oecologia 126: 535-542. O’Dowd, J. and R.W. Pemberton. 1998. Leaf domatia and foliar mite abundance in broadleaf deciduous forest of North Asia. Am. J. Bot. 85(1): 70-78. Oliver, J.B., D.C. Fare, N. Youssef, M.A. Halcomb, M.E. Reding, and C.M. Ranger. 2009. Evaluation of systemic insecticides for potato leafhopper control in field- grown red maple. J. Environ. Hort. 27(1): 17-23 Penman, D.R. and R.B. Chapman. 1988. Pesticide-induced mite outbreaks: pyrethroids and spider mites. Exp. Appl. Acarol. 4: 265-276

Potter, D.A. and P.G. Spicer. 1993. Seasonal phenology, management, and host preferences of potato leafhopper on nursery-grown maples. J. Environ. Hort. 11(3): 101-106 Pratt, P.D. and B.A. Croft. 2000. Toxicity of pesticides registered for use in landscape nurseries to the acarine biological control agent, Neoseiulus fallacis. J. Environ. Hort. 18(4): 197-201. Raupp, M.J., R. Webb, A. Szczepaniec, D. Booth, and R. Ahern. 2004. Incidence, abundance and severity of mites on hemlocks following applications of imidacloprid. J. Arboric. 30:108–113. Raupp, M.J., A.B. Cumming, and E.C. Raupp. 2006. Street tree diversity in Eastern North America and its potential for tree loss to exotic borers. Arboriculture & Urban Forestry 32(6): 297-304. Santamour, F.S. Jr. 1993. Freeman maple – illusion and truth. J. Arboric. 19(4): 195-200. SAS Institute. 2013. SAS user’s guide: Statistics. Version 9.3 ed. SAS Inst., Cary, N.C. Sato, M.E., A. Raga, L.C. Cerávolo, M.F. De Souza F., A.C. Rossi, and G.J. De Morales. 2001. Effect of insecticides and fungicides on the interaction between members of the mite families Phytoseiidae and Stigmaeidae on citrus. Exp. Appl. Acarol. 25: 809-818. Sclar, D.C., D. Gerace, and W.S. Cranshaw. 1998. Observations of population increases and injury by spider mites (Acari : Tetranychidae) on ornamental plants treated with imidacloprid. J. Econ. Entomol. 91: 250–255. Seagraves, B.L. 2006. Relative resistance of nursery-grown maples to multiple insect pests and seasonal biology of the maple shoot borer, Proteoteras aesculana Riley. MS Thesis, University of Kentucky, Lexington, KY. Seagraves, B.L., C.T. Redmond, and D.A. Potter. 2013. Relative resistance or susceptibility of maple (Acer) species, hybrids and cultivars to six arthropod pests of production nurseries. Pest Manag. Sci. 69(1): 112-119. Sibley, J.L., D.J. Eakes, C.H. Gilliam, G.J. Keever, W.A. Dozier Jr., and D.G. Himelrick. 1996. Foliar SPAD-502 meter values, nitrogen levels, and extractable chlorophyll for red maple selections. HortScience 31(3): 468-470.

Strickler K., N. Cushing, M. Whalon, and B.A. Croft. 1987. Mite (Acari) species composition in Michigan apple orchards. Environ. Entomol. 16: 30-36 Szczepaniec, A., S.F. Creary, K.L. Laskowski, J.P. Nyrop, and M.J. Raupp. 2011. Neonicotinoid insecticide imidacloprid causes outbreaks of spider mites on elm trees in urban landscapes. PLoS ONE 6(5): 1-10 Szczepaniec, A. and M.J. Raupp. 2012. Effects of imidacloprid on spider mite (Acari: Tetranychidae) abundance and associated injury to boxwood (Buxus spp.). Arboriculture & Urban Forestry 38(2): 37-40. Townsend, A.M. and M.S. McIntosh. 1993. Variation among full-sib progenies of red maple in growth, autumn leaf color, and leafhopper injury. J. Environ. Hort. 11(2): 72-75. Townsend, A.M. and L.W. Douglass. 1998. Evaluation of various traits of 40 selections and cultivars of red maple and freeman maple growing in Maryland. J. Environ. Hort. 16(4): 189-194. Trichilo, P.J. and L.T. Wilson. 1993. An ecosystem analysis of spider mite outbreaks: physiological stimulation of natural enemy suppression. Exp. Appl. Acarol 17: 291-314 Van Timmeren, S., J.C. Wise, C. VanderVoort, and R. Isaacs. 2011. Comparison of foliar and soil formulations of neonicotinoid insecticides for control of potato leafhopper, Empoasca fabae (Homoptera: Cicadellidae), in wine grapes. Pest Manag. Sci. 67 560-567.

Table 2.1 Percentage of the most common insecticide used by Indiana growers to control E. fabae on maple trees in 2008.

% % % Insecticide Class Growers Potato Leafhopper Maple Spider Mite

Pyrethroids (Bifenthrin, ß- 35 94 71 Cyfluthrin, Permethrin)

Neonicotinoids (Imidacloprid, 27 84 62 Thiamethoxam)

None 37 22 22

Table 2.2 Effects of early season and threshold on number of applications of different insecticides to control E. fabae on Red Sunset red maple trees in 2009

Treatment # insecticide application

Bifenthrin early season 1.0b1

Bifenthrin threshold level 1.40±0.22b Buprofezin early season 1.0b Buprofezin threshold level 4.0±0.42d Imidacloprid early season 1.0b Imidacloprid threshold level 3.20±0.39c Untreated 0.0a

Source of variation

Treatment F (6,63)= 36.99, p<0.0001 Contrast early season vs. threshold F (1,63)= 96.85, p<0.0001

Table 2.3 Effects of threshold level of potato leafhopper on number of bifenthrin applications per tree to control E. fabae on maple trees in 2010.

Applications per tree Applications per tree Treatment Red Sunset trees Autumn Blaze trees

1 Potato leafhopper/branch 1.1±0.23b1 0.80±0.20b1

3 Potato leafhopper/branch 0.80±0.13b 0.0a

6 Potato leafhopper/branch 0.2±0.13a 0.0a

Untreated 0.0a 0.0a

Source of variation

Treatment F (3,36)= 11.667, p=0.0002 F (3,16)= 16.000, p=0.0004

Table 2.4 Percentage of maple trees treated with bifenthrin to control E. fabae in 2010.

% % Treatment Red Sunset trees Autumn Blaze trees 1 Potato leafhopper/branch 90 20

3 Potato leafhopper/branch 80 0

6 Potato leafhopper/branch 20 0

Untreated 0 0

10 10 RED SUNSET AUTUMN BLAZE

8 8

BIFENTHRIN ES 6 BIFENTHRIN TH 6 UNTREATED May June July August September BUPROFEZINMay June ES July August September BIFENTHRIN ES MayMay JuneJune JulyJuly AugustAugust SeptemberSeptember BUPROFEZINMaMayy THJuneJune JulJulyy AuAugustgust SeSeptemberptember 4 IMIDACLOPRID ES 4 IMIDACLOPRID TH UNTREATED 2 2 # LEAFHOPPERS PER BRANCH PER # LEAFHOPPERS BRANCH PER # LEAFHOPPERS 0 0

(A)

0.6 1.0 RED SUNSET AUTUMN BLAZE 0.5 0.8 0.4 0.6 0.3 0.4 0.2

0.1 0.2

0.0 0.0 PROPORTION OF DAMAGED NODES PROPORTION OF DAMAGED PROPORTION OF DAMAGED NODES NODES PROPORTION OF DAMAGED (B)

1.0 RED SUNSET 1.0 AUTUMN BLAZE 0.8 0.8

0.6 0.6

0.4 0.4

0.2 0.2 PROPORTION OF DAMAGED TIPS PROPORTION OF DAMAGED PROPORTION OF DAMAGED TIPS PROPORTION OF DAMAGED 0.0 0.0 (C)

Figure 2.1 Average density (±SE) of E. fabae per branch in five terminal nodes (A) and average of damaged tips (B) by E. fabae (±SE) on maple trees treated with different insecticides early in the season (ES) or at threshold level of one leafhopper (TH) during 2009 field studies

2.5 2.5 RED SUNSET AUTUMN BLAZE 2 2

2.0 BIFENTHRIN ES 2.0 UNTREATED BIFENTHRIN TH BIFENTHRIN ES BUPROFEZIN ES 1.5 BUPROFEZIN TH 1.5 IMIDACLOPRID ES IMIDACLOPRID TH 1.0 UNTREATED 1.0

0.5 0.5 # MAPLE SPIDER MITE/cm SPIDER # MAPLE # MAPLE SPIDER MITES/cm SPIDER # MAPLE 0.0 0.0 July 6 July 27 Aug 17 Sept 7 July 6 July 27 Aug 17 Sept 7

(A)

0.4 0.4 RED SUNSET AUTUMN BLAZE

2 0.3 2 0.3

0.2 0.2

0.1 0.1 # PHYTOSEIIDS/cm # PHYTOSEIIDS/cm

0.0 0.0 July 6 July 27 Aug 17 Sept 7 July 6 July 27 Aug 17 Sept 7

(B)

0.4 0.4 RED SUNSET AUTUMN BLAZE 2 2 0.3 0.3 /cm /cm

0.2 0.2 # Zetzellia mali # Zetzellia # Zetzellia mali # Zetzellia 0.1 0.1

0.0 0.0 July 6 July 27 Aug 17 Sept 7 July 6 July 27 Aug 17 Sept 7

(C)

10 10 RED SUNSET AUTUMN BLAZE 8 8

6 1 PLH 6 1 PLH April May June July April3 PLH May June July April May June July April May June July 3 PLH April May June July 6April PLH May June July 6 PLH 4 UNTREATED 4 UNTREATED

2 2 # LEAFHOPPERS PER BRANCH PER # LEAFHOPPERS BRANCH PER # LEAFHOPPERS 0 0

(A)

1.0 1.0 RED SUNSET AUTUMN BLAZE 0.8 0.8

0.6 0.6

0.4 0.4

0.2 0.2

0.0 0.0 PROPORTION OF DAMAGED NODES PROPORTION OF DAMAGED NODES PROPORTION OF DAMAGED

(C)

1.0 1.0 RED SUNSET AUTUMN BLAZE

0.8 0.8

0.6 0.6

0.4 0.4

0.2 0.2 PROPORTION OF DAMAGED TIPS PROPORTION OF DAMAGED PROPORTION OF DAMAGED TIPS PROPORTION OF DAMAGED 0.0 0.0 (B)

2.5 2.5 RED SUNSET AUTUMN BLAZE 2 2 2.0 2.0 1 PLH 1 PLH 3 PLH 3 PLH 1.5 6 PLH 1.5 6 PLH UNTREATED UNTREATED 1.0 1.0

0.5 0.5 # MAPLE SPIDER MITE/cm SPIDER # MAPLE MITE/cm SPIDER # MAPLE

0.0 0.0 Jun 29 July 16 Aug 9 Aug 25 Sept 15 Jun 29 July 16 Aug 9 Aug 25 Sept 15 (A)

0.4 0.4 RED SUNSET AUTUMN BLAZE

2 0.3 2 0.3

0.2 0.2

0.1 0.1 # PHYTOSEIIDS/cm # PHYTOSEIIDS/cm

0.0 0.0 Jun 29 July 16 Aug 9 Aug 25 Sept 15 Jun 29 July 16 Aug 9 Aug 25 Sept 15

(B)

0.4 0.4 RED SUNSET AUTUMN BLAZE 2 0.3 2 0.3 /cm /cm

0.2 0.2 # Zetzellia mali Zetzellia # 0.1 mali # Zetzellia 0.1

0.0 0.0 Jun 29 July 16 Aug 9 Aug 25 Sept 15 Jun 29 July 16 Aug 9 Aug 25 Sept 15

(C)

Figure 2.4 Average density (±SE) of O. aceris (A), predatory mites phytoseiids (B), and Z. mali (C) per cm2 of leaf on maple trees treated with bifenthrin at threshold level of one, three and six leafhopper (PLH) per branch during 2010 field studies.

25 25 RED SUNSET AUTUMN BLAZE

20 20 April May June April May JunePer Branch April May June April May June Sticky Card 15 15

10 10 # LEAFHOPPER # LEAFHOPPER # LEAFHOPPER 5 5

0 0

(A)

100 100 RED SUNSET AUTUMN BLAZE

80 80

TREES 1 PLH 60 60 DAMAGED TIPS UNTREATED

40 40 PERCENTAGE PERCENTAGE 20 20

0 0

(B)

Figure 2.5 Percentage of trees that reached the threshold of one leafhopper and percentage of damaged tips by E. fabae on maple trees (A), and average density (±SE) of E. fabae per branch and caught on sticky card on maple trees during 2010 field studies.

Appendix A Survey

Grower: ______1. What proportion of your production is in the field or container? Field______Container______Greenhouse liner production______Which varieties of maple tree do you have? Red Sunset _____ Autumn Blaze ______Others ______2. What kind of pest do you have? Potato Leafhopper______Mites______Cottony maple scale ______3. What kind of pesticide do you apply? Imidacloprid______Marathon______Talstar_____ Talus______Others______How often do you apply pesticide? ______4. Do you use overhead or drip irrigation? ______How do you control irrigation system?______5. How is your fertilization? Field Container Type of fertilizer Rate Frequency

Do you keep records?______6. What kind of weed program do you have? ______

CHAPTER 3. EFFECTS OF FERTILIZATION ON ARTHROPOD PESTS OF NURSERY GROWN MAPLES

3.1 Abstract

Potato leafhopper Empoasca fabae (Harris) (Homoptera: Cicadellidae) and maple spider mite Oligonychus aceris (Shimer) (Acarina: Tetranychidae) are important pests of maple trees. I conducted studies to determine how rates of fertilization and tree species contributed to E. fabae and O. aceris populations on ‘Red Sunset’ red maple (Acer rubrum) and ‘Autumn Blaze’ Freeman maple (Acer x fremanii) in 2009 and 2010.

Fertilizer applications on field grown maples increased populations of both pests, but to a different extent on each variety. More damage by E. fabae was observed on fertilized Red

Sunset than on Autumn Blaze. O. aceris populations were higher on fertilized Autumn

Blaze than Red Sunset trees. O. aceris populations were positively correlated with nitrogen content in the leaves in both cultivars. Analysis of covariance indicated that mite populations increased at a lower rate with increasing content of nitrogen in the leaves of

Red Sunset than on those of Autumn Blaze maples. Differences may be explained by the relative abundance of two phytoseiid mites, Neoseiulus fallacis (Garman) and

Typhlodromus caudiglans (Schuster), and one stigmaeid mite predator, Zetzellia mali

(Ewing) on each maple. Populations of the predator Z. mali were higher in both years on

Red Sunset than Autumn Blaze. Examination of leaf morphology suggest that this

58 difference and the relative resistance of Red Sunset maples to O. aceri may be due to the increased abundance of leaf domatia.

3.2 Introduction

Trees are commonly fertilized in production and container nurseries to stimulate growth and improve appearance (Stubbs et al. 1997, Smiley 2007). Increased rates of growth can shorten production schedules and increase plant value (Larimer and Struve

2002, Lloyd et al. 2006). Nitrogen is the most common soil supplement in ornamental plant production because it is relatively inexpensive and strongly associated with increased growth (Larimer and Struve 2002, Wilson et al. 2010). Nitrate-N is usually formulated as a soluble or controlled-release product (Wilson et al. 2010). Although water soluble fertilizers can be easily delivered through irrigation systems, growers often apply controlled-release fertilizer to avoid high initial salt levels and reduce nutrient leaching losses (Cox 1993, Cabrera 1997, Rose et al. 1999, Erickson et al. 2001, Taylor et al. 2006).

Plant nutrient concentration can also influence interactions between herbivorous arthropods and plants (Kytö et al. 1996, Awmack and Leather 2002). Historically, growers have thought that fertilizer application can enhance pest resistance (Herms 2002).

A growing body of evidence suggests that high rates of fertilization can decrease plant resistance because it improves the nutritive quality of arthropod host-plants making them more susceptible to injury (Herms and Mattson 1992, Crafts-Brandner 2002, Opit et al.

2005, Zehnder and Hunter 2009, Raupp et al. 2010, England et al. 2011).

Maples (Sapindales: Aceraceae) are one of the most widely grown genera of landscape trees because of their environmental adaptability, attractive form, and foliage color (Townsend and McIntosh 1993, Oliver et al. 2009, Raupp et al. 2010). Numerous cultivars of Acer rubrum, A. saccharinum and their Freeman maple hybrids have been developed for superior growth, leaf characteristics, and insect resistance (Townsend and

Douglass 1998). Two of the principle foliar pests in nursery production are the potato leafhopper Empoasca fabae and maple spider mite, Oligonychus aceris. Red maple clones and Freeman maple cultivars differ in their susceptibility to potato leafhopper feeding injury (Towsend 1989, Townsend and McIntosh 1993, Bentz and Towsend 1997,

1999, 2003, Chapter 2). Although this leafhopper can cause severe economic damage to red maple in nurseries and landscape settings, Freeman maple cultivars are relatively resistant. In contrast, Freeman maple cultivars are susceptible to spider mites and resistant to E. fabae (Potter and Spicer 1993, Townsend and Douglass 1998, Seagraves et al. 2013, Chapter 2). The mechanism for spider mite resistance in maples has yet to be described, although the presence of leaf domatia has been associated with the presence of predatory mites and their capacity to reduce spider mite populations. Leaf domatia are

“structures restricted to vein axils that are inhabited by predators” (Walter 1996).

Several studies have shown that adding fertilizers can increase the abundance of phytophagous pests attacking maples. Bentz and Townsend (2001) found higher rates of oviposition by potato leafhopper on leaves with higher nitrogen content. Although there have been no studies linking fertilization to increase abundance of O. aceris on maples, numerous studies have demonstrated that fertilizing plants can increase the population of

60 spider mites on other plants (Löyttyniemi and Heliövaara 1991, Walde 1995, Wilson

1994, Chen et al. 2007).

Nursery producers need fertilization programs to grow marketable plants without increasing susceptibility to pests. In this study, I worked with red maples because of their wide use and susceptibility to potato leafhopper and spider mites. The objective of this research was to determine the relative effect of commonly used fertilizer rates on susceptibility of maple cultivar to arthropod pest populations.

3.3 Materials and Methods

Field studies. Experiments were conducted during the 2009 and 2010 growing season at Purdue Meigs Farm, Lafayette, IN, a Purdue Agricultural Research Center to evaluate the effects of fertilizer on Empoasca fabae (Harris) and maple spider mites,

Oligonychus aceris (Shimer) on Acer rubrum cultivar ‘Red Sunset’ and Acer freemanii cultivar ‘Autumn Blaze’. Acer freemanii, commonly called Freeman maple, is a hybrid of a red maple (A. rubrum) and silver maple (A. saccharium). The main plot consisted of

24 trees of Red Sunset and 24 of Autumn Blaze cultivars. Trees were planted in 2006 and arranged in rows 2 m apart separated by 2 m. The average diameters of Red Sunset and

Autumn Blaze maple stems measured 10 cm above the soil line were 2.24±0.14 and

3.53±0.11 cm respectively.

To determine the effects of fertilization on arthropod populations and cultivar susceptibility, controlled-release fertilizer Osmocote® (Scott-Sierra, Marysville, OH) 12-

12-12 was used as a source of nutrients and the application rates were 0, 20 and 40 g of N per tree. Every year, trees received half of this fertilizer during each of two applications

61 three weeks apart in April and May. Plants were arranged in randomized complete block split-plot experimental design, where Autumn Blaze and Red Sunset cultivars were assigned at random to the whole plot, and three levels of fertilization were assigned to subplots in eight replicate blocks.

Abundance of E. fabae on each plant was determined weekly starting on 29 May until 4 August in 2009 and from 16 April to 30 July in 2010. Four branches from the lower 2 m of the tree were then selected for visual inspection of the first five leaf nodes from the branch terminal from each of the four cardinal directions. Injury by E. fabae to maple trees was assessed by examining 10 shoot tips in the upper canopy of each plant to determine the percent of shoots showing deformation. In previous studies we have found this measure of injury to be highly correlated with damage caused by leafhoppers measured in the lower canopy (Chapter 2).

The abundance of maple spider mites and their predators on each tree was evaluated by collecting leaves from the middle of tree branchesevery three weeks from 6

July until 7 September in 2009 and from 29 Jun to 16 September in 2010. Samples consisted of a total of 12 leaves per tree, three chosen from one branch located in each of the four cardinal directions. The leaves were placed in labeled paper bags. All paper bags were placed in a cooler with freezer packs until they were taken to the laboratory for processing. Leaves were removed from each bag and immediately processed through a mite brushing machine (Leedom Engineering, Twain Harte, CA) to transfer the mites to labeled Petri dishes that were coated with a thin layer of vegetable oil. All samples were transferred to Petri dishes on the same day that leaves were collected. Petri dishes were stored in a 10º C refrigerator until all the samples were processed (no more than 2 weeks).

Adult and nymphal stages of spider mites and predators present in the Petri dishes were also counted.

To test effects of fertilizer applications and cultivar on mite populations and damage by potato leafhopper, I conducted a repeated measures analysis using PROC

GLIMMIX for Generalized Linear Mixed Models (SAS® 9.3 Institute Inc., Cary, NC).

The GLIMMIX procedure selected a regression model based on the distribution of each response variable using a Laplace maximum likelihood estimation method. Distribution of E. fabae damage was best explained by the binomial distribution, whereas populations of O. aceris and predatory mites were best described by a Poisson distribution. I used the compound symmetry option to approximate constant variance and covariance at each sample date over time. LSMEANS were separated using Tukey’s HSD Test at an -level of 0.05 to compare fertilization levels.

Effects of N concentration on leaves of Red Sunset and Autumn Blaze maples on populations of E. fabae per branch and the cumulative abundance of O. aceris, were determined with an analysis of covariance (SAS® 9.3 Institute Inc., Cary, NC) where the covariate was the percentage of foliar nitrogen. Cumulative density of O. aceris and predators were determined for each tree. The equation for calculating was as follows:

Cumulative density (mite days) = [((S1+S2)/2*D))+((S2+S3)/2*D))+((S3+S4)/2)*D))],

Where S is the consecutive samples and D is the number of days between samplings. Mite-days are the average of the number of maple spider mites per cm2 between each pair of consecutive observations multiplied by the number of days between samplings (Atawi et al. 2007).

Leaf nitrogen content. Approximately 20 leaf samples were taken on August 2009 and on June 2010 from each tree to analyze foliar nitrogen concentration. The leaves were gently washed to remove debris and dried at 80C until a constant weight then ground to have at least 5 g plant biomass in each sample. Ground leaf tissue was sent to

A & L Great Lakes Laboratories, Inc (Fort Wayne, IN). For total leaf nitrogen, the

Dumas Method (Nitrogen by Combustion or Nitrogen by thermal conductance) was used.

Effects of fertilization levels on foliar nutrient concentration were tested using

PROC MIXED (SAS® 9.3 Institute Inc., Cary, NC). Means of these response variables for each fertilization level were separated by Tukey’s HSD Test at an -level of 0.05.

Leaf domatia. In 29 August 2010, I collected leaves to determine the abundance of leaf domatia on each maple cultivar. A total of 12 leaves from each tree was collected; three were chosen from one branch in each of four cardinal directions. Leaves were observed under the microscope and scored on a scale of 0 to 4 based on the presence of pubescence along a hierarchical scale of leaf veins (Fig 3.1). Assessments were started at the primary petiole-leaf blade vein branch and continued to secondary, tertiary and quaternary branching. Leaves lacking domatia were given a score of 0. Differences in the leaf domatia score were determined using PROC GLIMMIX for Generalized Linear

Mixed Models (SAS® 9.3 Institute Inc., Cary, NC). The GLIMMIX procedure selected a regression model based on the distribution of each response variable using a beta distribution for proportion of maximum possible domatia score. LSMEANS were separated using Tukey’s HSD Test at an -level of 0.05 to compare fertilization levels.

3.4 Results

Effect of fertilization treatment on E. fabae and O. aceris populations on Autumn

Blaze and Red Sunset maple cultivars. At the end of the season damage caused by E. fabae in both years differed among fertilizer treatments (F = 4.71; df = 2, 14; P = 0.0272) and cultivar (F = 9.56; df = 1, 7; P = 0.0175) (Fig. 3.2). Damage caused by E. fabae did not differ between 2009 and 2010 field studies (F = 0.02; df = 1, 49; P = 0.8781).

Interaction between fertilizer treatment and cultivar did not affect the proportion of damaged shoots by E. fabae (F = 1.09; df = 2, 49; P = 0.3432). Damage caused by potato leafhopper was lowest on trees that did not receive any fertilization in Red Sunset red maple and Autumn Blaze Freeman maple. The most heavily damaged trees were those treated with 40 g N in both cultivars at the end of the season during 2009 and 2010. Red

Sunset had more than twice the proportion of damaged tips than Autumn Blaze (Fig. 3.2).

Oligonychus aceris populations did not differ among fertilizer treatments (F =

1.01; df = 2, 14; P = 0.3876) (Fig. 3.3A). However, there was a significant effect of cultivar (F = 26.14; df = 1, 7; P = 0.0014) and sampling year (F = 18.71; df = 1, 337; P <

0.001). Interaction between fertilizer treatment and cultivar did not affect O. aceris populations (F = 0.09; df = 2, 337; P = 0.9166). Maple spider mite populations in

Autumn Blaze were considerably higher than Red Sunset in both years (Fig. 3.3A).

Two phytoseiid mites, Neoseiulus fallacis (Garman) and Typhlodromus caudiglans (Schuster), and one stigmaeid mite, Zetzellia mali (Ewing) were found in both maple tree cultivars. The abundance of phytoseiids did not differ among fertilizer treatments throughout the season (F = 0.11; df = 2, 14; P = 0.8959), cultivar (F = 1.23; df

= 1, 7; P = 0.3040) and year (F = 2.24; df = 1, 337; P = 0.1354). There was no significant

65 interaction between fertilizer treatment and cultivar effects (F = 0.42; df = 2, 337; P =

0.6602) (Fig. 3.3B). Similarly, Z. mali density did not differ significantly among treatments (F = 0.01; df = 2, 14; P = 0.9899) nor year (F = 0.50; df = 1, 337; P = 0.4810).

However, cultivar significantly affected the abundance of Z. mali collected (F = 7.40; df

= 1, 7; P = 0.0298). Red Sunset had a significantly higher mean of Z. mali populations than Autumn Blaze during both years (Fig. 3.3C). There was no significant interaction between fertilizer treatment and cultivar effects (F = 0.01; df = 2, 337; P = 0.9960).

Effect of foliar nitrogen on damage from E. fabae and abundance of O. aceris.

Numbers of potato leafhopper per branch were correlated with the percentage of nitrogen on leaves for both Red Sunset (r = 0.55; P = 0.0005) and Autumn (r = 0.42; P = 0.0042)

Blaze. Although, the numbers of E. fabae did not differ by cultivar (F = 0.52; df = 1, 77;

P = 0.4722). The N concentration in leaves were significantly different (F = 22.88; df = 1,

77; P < 0.0001), but there was not an interaction between N concentration and cultivar (F

= 0.79; df = 1, 77; P = 0.7860). Covariance analysis of number of E. fabae per branch and leaf N indicated that foliar increases in nitrogen content causes a greater increase in E. fabae abundance on Red Sunset than on Autumn Blaze maples (Fig. 3.4). Similarly, numbers of cumulative mites at the end of the season and percentage of nitrogen on leaves were highly correlated for both Red Sunset (r = 0.87; P < 0.0001) and Autumn

Blaze (r = 0.75; P < 0.0001). The N concentration in leaves were significantly different

(F = 113.51; df = 1, 77; P < 0.0001) and there was an interaction between N concentration and cultivar (F = 6.93; df = 1, 77; P = 0.0102). Covariance analysis of cumulative mites and leaf N indicated that foliar increases in nitrogen content causes a

66 greater increase in O. aceris abundance on Autumn Blaze than on Red Sunset maples

(Fig. 3.5).

Effect of fertilization rate on foliar nitrogen concentration. Application of fertilizer treatment significantly affected foliar levels of N on trees (F = 5.72; df = 2, 88;

P = 0.0046) and differed among years (F = 63.60; df = 2, 88; P < 0.0001). The greatest foliar nitrogen concentrations occurred on trees fertilized with either 20 or 40 g N (Fig

3.6). No differences were found between the foliar N in the two maple cultivars (F = 2.47; df = 1, 7; P = 0.1626). Foliar concentration was not affected by interaction between cultivar and fertilization treatment (F = 0.77; df = 2, 88; P = 0.4647) nor interaction between fertilization treatment and year (F = 1.96; df = 4, 86; P = 0.1078).

Effect of fertilization rate on leaf domatia of maple cultivars. Proportions of the maximum rank of leaf domatia were not affected by fertilizer treatments (F = 0.04; df = 2,

30; P = 0.9601). However, leaf domatia rank varied significantly between maple cultivars

(F = 13.79; df = 1, 30; P = 0.0008). On Red Sunset, the average domatia ranking on leaves was 0.73±0.02 of the maximum and on Autumn Blaze it was 0.08±0.01. Domatia ranking was not affected by interaction between fertilizer treatment and cultivar (F = 0.01; df = 2, 30; P = 0.9899).

3.5 Discussion

The addition of nitrogenous fertilizer has been linked with the increased feeding, oviposition, survival and development of a wide variety of arthropods (Zehnder and

Hunter 2009, Denno and Fagan 2003). The positive relationship that I found between fertilization treatments and E. fabae injury on maple trees is also consistent with this

67 body of literature. Our data supports Bentz and Townsend (1999, 2001, 2003) who found fertilization to increase oviposition, survival and development by E. fabae on clones of red maple.

Our results show that levels of injury on both Red Sunset red maples and Autumn

Blaze Freeman maples increased with fertilization treatments. However, the proportions of injured shoots on Red Sunset maples were much higher than on Autumn Blaze. Nearly

100% of Red Sunset shoot tips were damaged when 40 g N were applied and less than 40% of tips on Autumn Blaze. This finding supports previous research which suggests that red maple cultivars are more suitable or preferred for leafhoppers (Potter and Spicer 1993,

Bentz and Townsend 1997, 1999, 2001, 2003, Seagraves 2006, Seagraves et al. 2013).

Although the foliar N level was significantly higher for fertilized trees, there was no relation between percentages of foliar N and the amount of injury by E. fabae. Bentz and Towsend (2001) suggest lack of correlation between the degrees of susceptibility to nitrogen concentration in maple leaves is indicative to non-nutritive mechanisms of host resistance against E. fabae. In contrast to E. fabae, the abundance of O. aceris was not influenced by rates of soil fertilization. Spider mite populations were more influenced by cultivar, with Autumn Blaze having more O. aceris than Red Sunset maples. This finding supports previous research which suggests that maple cultivars differ in their susceptibility to spider mites (Potter and Spicer 1993, Seagraves 2006, Seagraves et al.

2013, Chapter 2).

Interestingly, I found a positive relationship between concentration of N in leaves and O. aceris populations for both cultivars. This is also consistent with reported findings

68 of accelerated development and increased fecundity of other spider mites in response to foliar nitrogen (Wilson 1994, Löyttyniemi and Heliövaara 1991, Opit et al. 2005).

Differences between the responses of O. aceris abundance to foliar nitrogen in each cultivar are probably related to their relative capacity to harbor predatory mites. In this study, populations of the predator Z. mali were higher in both years on Red Sunset than Autumn Blaze. My data on leaf domatia suggest that the increased abundance of Z. mali on Red Sunset maples may be due to the greater number of leaf domatia. This would be consistent with other studies that show how the presence of leaf domatia can harbor predators and influence in population dynamics of tetranychid mites (O’Dowd and

Pemberton 1998, Agrawal et al. 2000, Norton et al. 2001). No differences were observed between the abundance of phytoseiid mites on each maple cultivar.

I postulate that Z. mali becomes well established in the domatia of Red Sunset maples because the domatia help them avoid predation by phytoseiids. Clements and

Harmsen (1990, 1993) found that Z. mali often form dense clusters along a leaf vein on apples due of their lack of mobility, in contrast to phytoseiids which usually form a less contiguous distribution. Some studies suggest that Z. mali hide in domatia created by the midrib, veins and hairs of apple leaves and their aggregation is not affected by predation because phytoseiids in general do not prey upon them to any great extent (MacRae and

Croft 1996, Slone and Croft 1998, 2001).

In summary, this study documents differences in susceptibility and resistance of maple cultivars to E. fabae and O.aceris. The data clearly shows E. fabae to be the more important pest of Red Sunset red maple while O. aceris is more important on Autumn

Blaze Freeman maple. This study also suggests that the relative resistance of Red Sunset

69 maples could be mediated by leaf domatia which has the potential to protect predatory mites from intraguild predation.

3.6 Literature Cited

Agrawal, A.A., R. Karban and R.G. Colfer. 2000. How leaf domatia and induced plant resistance affect herbivores, natural enemies and plant performance. Oikos 89: 70- 80. Awmack, C.S. and Leather, S.R. 2002. Host plant quality and fecundity in herbivorous insects. Annu. Rev. Entomol. 47: 817–44. Bentz, J. and A.M. Townsend. 1997. Variation in adult populations of the potato leafhopper (Homoptera: Cicadellidae) and feeding injury among clones of red maple. Environ. Entomol. 26(5): 1091-1095. Bentz, J. and A.M. Townsend. 1999. Feeding injury, oviposition, and nymphal survivorship of the potato leafhopper on red maple and Freeman maple clones. Environ. Entomol. 28(3): 456-460. Bentz, J. and A.M. Townsend. 2001. Leaf element content and utilization of maple and elm as hosts by the potato leafhopper (Homoptera: Cicadellidae). Environ. Entomol. 30(3): 533-539. Bentz, J. and A.M. Townsend. 2003. Nitrogen fertilization and use of container-grown maple selections as hosts by the potato leafhopper. J. Amer.Soc. Hort. Sci. 128(6): 821-826. Cabrera, R.I. 1997. Comparative evaluation of nitrogen release patterns from controlled- release fertilizers by nitrogen leaching analysis. HortScience 32(4): 669-673. Chen, Y., G.P. Opit, V.M. Jonas, K.A. Williams, J.R. Nechols and D.C. Margolies. 2007. Twospotted spider mite population level, distribution, and damage on ivy geranium in response to different nitrogen and phosphorous fertilization regimes. J. Econ. Entomol. 100(6): 1821-1830. Clements, D. R., and R. Harmsen. 1990. Predatory behaviour and prey-stage preferences of stigmaeid and phytoseiid mites and their potential compatibility in biological control. Can. Entomol. 122: 321-328. Clements, D. R., and R. Harmsen. 1993. Prey preferences of adult and immature Zetzellia mali Ewing (Acari: Stigmaeidae) and Typhlodromus caudiglans Schuster (Acari: Phytoseiidae). Can. Entomol. 125: 967-969.

Cox, D.A. 1993. Reducing nitrogen leaching-losses from containerized plants: The effectiveness of controlled-release fertilizers. J. Plant Nutrition 16: 533-545. Crafts-Brandner, S.J. 2002. Plant nitrogen status rapidly alters amino acid metabolism and excretion in Bemisia tabaci. J. Insect Phys. 48: 33-41. Denno, R.F. and W. F. Fagan. 2003. Might nitrogen limitations promote omnivory among carnivorous arthropods? Ecology 84(10): 2522–2531. England, K.M., C.F. Sadof, L.A. Canas, C.H. Kuniyoshi, and R.G. Lopez. 2011. Effects of selected fertilizers on the life history of Bemicia tabaci (Hemiptera: Aleyrodidae) biotype B. J. Econ. Entomol. 104(2): 548-554. Erickson, J.E., J.L. Cisar, J.C. Volin and G.H. Snyder. 2001. Comparing nitrogen runoff and leaching between newly established St. Augustine grass turf and alternative residential landscape. Crop Sci. 41: 1889-1895. Herms, D.A. and W.J. Mattson. 1992. The dilemma of plants: to grow or defend. Q. Rev. Biol. 67(3): 283-335. Herms, D.A. 2002. Effects of fertilization on insect resistance of woody ornamental plants: reassessing an entrenched paradigm. Environ. Entomol. 31(6): 923-933. Hoffmann, W.A. and H. Poorter. 2002. Avoiding bias in calculations of relative growth rate. Ann. Bot.-London 80: 37-42. Kytö, M., P. Niemelä, and S. Larsson. 1996. Insects on trees: population and individual response to fertilization. Oikos 75(2): 148-159. Larimer, J. and D. Struve. 2002. Growth, dry weight and nitrogen distribution of Red Oak and Autumn Flame red maple under different fertility levels. J. Environ. Hort. 20(1): 28-35. Lloyd, J.E., D.A. Herms, M.A. Rose, and J. Van Wagoner. 2006. Fertilization rate and irrigation scheduling in the nursery influence growth, insect performance, and stress tolerance of “Sutyzam” crabapple in the landscape. HortScience 41(2): 442- 445. Löyttyniemi K. and K. Heliövaara. 1991. Effect of forest fertilization on the spruce spider mite Oligonychus ununguis (Jacobi) (Acarina, Tetranychidae). Acarologia 32(2): 139-143.

MacRae, I. V., and B. A, Croft. 1996. Differential impact of egg predation by Zetzellia mali (Acari: Stigmaeidae) on Metaseiulus occidental and Typhlodromus pyri (Acari: Phytoseiidae). Exp. Appl. Acarol. 20: 143-154. Norton, A.P., G. English-Loeb, and E. Belden. 2001. Host plant manipulation of natural enemies: leaf domatia protect beneficial mites from insect predators. Oecologia 126: 535-542. O’Dowd, D.J. and R.W. Pemberton. 1998. Leaf domatia and foliar mite abundance in broadleaf deciduous forest of North Asia. Am. J. Bot. 85(1): 70-78. Oliver, J.B., D.C. Fare, N. Youssef, M.A. Halcomb, M.E. Reding, and C.M. Ranger. 2009. Evaluation of systemic insecticides for potato leafhopper control in field- grown red maple. J. Environ. Hort. 27(1): 17-23. Opit, G.P., Y. Chen, K.A. Williams, J.R. Nechols, and D.C. Margolies. 2005. Plant age, fertilization, and biological control affect damage caused by twospotted spider mites on ivy geranium: development of an action threshold. J. Amer. Sco. Hort. Sci. 130(2):159-166. Potter, D.A. and P.G. Spicer. 1993. Seasonal phenology, management, and host preferences of potato leafhopper on nursery-grown maples. J. Environ. Hort. 11(3): 101-106 Raupp, M.J., P.M. Shrewsbury, and D.A. Herms. 2010. Ecology of herbivorous arthropods in urban landscapes. Annu. Rev. Entomol. 55: 19-38. Rose, M.A. M. Rose, and H. Wang. 1999. Fertilizer concentration and moisture tension affect growth and foliar N, P, and K contents of two woody ornamentals. HortScience 34(2): 246-250. Seagraves B.L. 2006. Relative resistance of nursery-grown maples to multiple insect pests and seasonal biology of the maple shoot borer, Proteoteras aesculana Riley. MS Thesis, University of Kentucky, Lexington, KY. SAS Institute. 2013. SAS user’s guide: Statistics. Version 9.3 ed. SAS Inst., Cary, N.C. Seagraves, B.L., C.T. Redmond, and D.A. Potter. 2013. Relative resistance or susceptibility of maple (Acer) species, hybrids and cultivars to six arthropod pests of production nurseries. Pest Manag. Sci. 69(1): 112-119.

Sibley, J., D.J. Eakes, C.H. Gilliam, G.J. Keever. W. A. Dozier, Jr., and D.G. Himlrick. 1996. Foliar SPAD-502 meter values, nitrogen levels, and extractable chlorophyll for red maple selections. HortScience 31(3): 468-470. Slone, D.H. and B.A. Croft. 1998. Spatial aggregation of apple mites (Acari: Phytoseiidae, Stigmaeidae, Tetranychidae) as measured by a binomial model: effects of life, stage, reproduction, competition, and predation. Environ. Entomol. 27(4): 918-925. Slone, D.H. and B.A. Croft. 2001. Species association among predaceous and phytophagous apple mites (Acari: Eriophyidae, Phytoseiidae, Stigmaeidae, Tetranychidae). Exp. Appl. Acarol. 25: 109-126.

Smiley, E.T. 2007. Fertilization Rx. American Nurseryman 205(7): 38-40 Stubbs, H.L., S.L. Warren, F.A. Blazich, and T.G. Ranney. 1997. Nitrogen nutrition of containerized Cupressus arizonica var. glabra “Carolina Sapphire”. J. Environ. Hort. 15(2): 80-83. Taylor, M.D., S.A. White, S.L. Chandler, S.J. Klaine, and T. Whitwell. 2006. Nutrient management of nursery runoff water using constructed wetland systems. HortTechnology 16(4): 610-614. Townsend, A.M. 1989. Evaluation of potato leafhopper injury among Acer rubrum progenies. J. Environ. Hort. 7(2); 50-52 Townsend, A.M. and M.S. McIntosh. 1993. Variation among full-sib progenies of red maple in growth, autumn leaf color, and leafhopper injury. J. Environ. Hort. 11(2): 72-75. Townsend, A.M. and L.W. Douglass. 1998. Evaluation of various traits of 40 selections and cultivars of red maple and Freeman maple growing in Maryland. J. Environ. Hort. 16(4): 189-194. Walter, D.E. 1996. Living on leaves: mites, tomenta, and leaf domatia. Annu. Rev. Entomol. 41: 101-114. Wilson, L.J. 1994. Plant-quality effect on life-history parameters of the twospotted spider mite (Acari: Tetranychidae) on cotton. J. Econ. Entomol. 87(6): 1665-1673.

Wilson, C., J. Albano, M. Mozdzen, and C. Riiska. 2010. Irrigation water and nitrate- nitrogen loss characterization in Southern Florida nurseries: cumulative volumes, runoff rates, nitrate-nitrogen concentrations and loadings, and implications for management. HorTechnology 20(2): 325-330. Walde, S.J. 1995. How quality of host plant affects a predator-prey interaction in biological control. Ecology 76(4): 1206-1219. Zehnder, C.B. and M.D. Hunter. 2009. More is not necessarily better: the impact of limiting and excessive nutrients on herbivore population growth rates. Ecological Entomology 34: 535–543.

3 2 4

Figure 3.1 Leaf domatia rank. Scored on a scale of 0 to 4 based on the presence of pubescence along a hierarchical scale of leaf veins.

8 0 g N 20 g N 40 g N 6

# DAMAGED TIPS BY LEAFHOPPERS TIPS BY # DAMAGED 0 Autumn Blaze Red Sunset

2.0 2.0

2 2009 2010

RS 0 g N 1.5 1.5 RS 20 g N RS 40 g N AB 0 g N 1.0 1.0 AB 20 g N AB 40 g N

0.5 0.5 # MAPLE SPIDER MITES/cm SPIDER # MAPLE

0.0 0.0 July 7 July 28 Aug 18 Sept 8 June 29 July 17 Aug 10 Aug 26 Sept 16 (A)

0.05 0.05 2010 2009 0.04

2 0.04 RS 0 g N 0.03 RS 20 g N 0.03 RS 40 g N AB 0 g N 0.02 AB 20 g N 0.02 AB 40 g N

# PHYTOSEIIDS/cm 0.01 0.01

0.00 0.00 July 7 July 28 Aug 18 Sep 8 June 29 July 17 Aug 10 Aug 26 Sep 16 (B)

0.30 0.30 2009 2010 0.25 0.25 2

0.20 0.20 RS 0 g N RS 20 g N 0.15 0.15 RS 40 g N AB 0 g N AB 20 g N 0.10 0.10 AB 40 g N # Zetzellia mali/cm Zetzellia # 0.05 0.05

0.00 0.00 July 7 July 28 Aug 18 Sep 8 June 29 July 17 Aug 10 Aug 26 Sep 16 (C) Figure 3.3 Average density (±SE) of O. aceris (A) and phyotseiid predatory mites (B) and Z. mali (C) per cm2 of leaf on Red Sunset (RS) and Autumn Blaze (AB) maple trees treated with 0, 20,40 g N during 2009 and 2010 field studies in lafayette, IN

Figure 3.4 The relation between nitrogen content of leaves and the number of potato leafhopper per branch on Red Sunset red maple and Autumn Blaze Freeman maple during 2009 and 2010.

Figure 3.5 The relation between nitrogen content of leaves and number of cumulative maple spider mites per cm2 on Red Sunset red maple and Autumn Blaze Freeman maple leaves during 2009 and 2010.

b b a 80 b ab a

3.0 3.0 2009 2010 2.5 2.5

2.0 2.0

1.5 1.5

1.0 1.0

PERCENTAGE NITROGEN PERCENTAGE 0.5 0.5

0.0 0.0 02040 02040 NITROGEN (g) ADDED PER YEAR PER TREE NITROGEN (g) ADDED PER YEAR PER TREE

Figure 3.6 Effects of nitrogen application rates on the averages (±SE) of the percentage nitrogen in Red Sunset red maple and Autumn Blaze Freeman maple leaves during 2009 and 2010.

Appendix B Impacts of Soil Fertilization on Characteristics of Red Sunset and Autumn

Blaze Maples

Experimental Design: Experiments were conducted during the 2009 and 2010 growing season at Purdue Meigs Farm, Lafayette, IN, a Purdue Agricultural Research

Center to evaluate the effects of fertilizer on Empoasca fabae (Harris) and maple spider mites, Oligonychus aceris (Shimer) on Acer rubrum cultivar ‘Red Sunset’ and Acer x freemanii cultivar ‘Autumn Blaze’. Acer x freemanii, commonly called Freeman maple, is a hybrid of a red maple (A. rubrum) and silver maple (A. saccharium). The main plot consisted of 24 trees of Red Sunset and 24 of Autumn Blaze cultivars. Trees were planted in 2006 and arranged in rows 2 m apart separated by 2 m. At this time, the average diameters of Red Sunset and Autumn Blaze maples measured 10 cm above the soil line were 2.24±0.14 and 3.53±0.11 cm respectively.

To determine the effects of fertilization on growth and other plant characteristic a controlled-release fertilizer Osmocote ® (Scott-Sierra, Marysville, OH) 12-12-12 was used as source of nutrients and the application rates were 0, 20 and 40 g of N per tree.

Every year, trees received half of this fertilizer during each of two applications three weeks apart in April and May. Treatments were arranged in a split-plot design with the cultivar as the main effect and the fertilizer as the subplot with eight replications.

Growth parameters. Effects of fertilization were evaluated on the following tree characteristics: caliper, height, leaf area, and the chlorophyll content of leaves. Caliper of the main trunk on each tree was measured 10 cm above the soil line using a 6” Harbor

Freight Digital Caliper (Camarillo, CA) measuring tool. Height was estimated on each

82 tree from the ground level to the top of the canopy using a rigid tape measure.

Measurements were taken in May and October of 2009 and 2010. I sampled leaves from each tree taking the first fully expanded leaf, located four to five nodes from the branch apex in June and September of 2009 and 2010 to measure leaf area with a LI-COR 3100

Model Leaf Area Meters Equipment (Lincoln, NE), and chlorophyll with a SPAD-502 chlorophyll meter (Ramsey, NJ). Triplicate SPAD readings were recorded and averaged per tree (Sibley et al. 1996). I adapted standard relative growth rate (RGR) equation (r =

(ln(H2)-ln(H1))/(t2-t1) to measure how individual changes in size in response to the effect of fertilization treatments on caliper and height (Hoffmann and Poorter 2002). I chose to measure time in years because growth was measured at the end of each season.

Effects of fertilization levels on growth parameters and leaf characteristics were tested using PROC MIXED (SAS® 9.3 Institute Inc., Cary, NC). Means of these response variables for each fertilization level were separated by Tukey’s HSD Test at an

-level of 0.05.

Results: No differences in chlorophyll content were found among fertilizer treatments (F

= 2.29; df = 2,105; P = 0.1340). Chlorophyll content was significantly different among years (F = 83.29; df = 2,105; P < 0.0001) and between cultivars (F = 22.59; df = 1,105; P

= 0.0014). Chlorophyll content was affected by interaction between cultivar and fertilization treatment (F = 5.59; df = 2,105; P = 0.0055) and interaction between cultivar and year (F = 18.63; df = 2,105; P < 0.0001). In general, chlorophyll content was higher for Red Sunset (Fig. 2.7A). Chlorophyll content in Red Sunset trees with 40 g N had the highest values, but Autumn Blaze maple trees did not differ in chlorophyll content. No

83 differences were found by interaction between fertilizer treatment and year (F = 1.27; df

= 4,105; P = 0.2895).

Specific leaf weight was not significantly affected by fertilizer treatment (F =

0.33; df = 2,105; P = 0.7219). However, specific leaf weight differed across years (F =

93.29; df = 2,105; P < 0.0001) and cultivars (F = 4.66; df = 1,105; P = 0.0336). Specific leaf weight was not affected by interaction between cultivar and fertilizer treatment (F =

1.79; df = 2,105; P = 0.1726) nor interaction between fertilizer treatment and year (F =

0.81; df = 4,105; P = 0.5252). In contrast, there was a significant interaction between cultivar and year on specific leaf weight (F = 4.94; df = 2,105; P = 0.0095). Red Sunset had the greatest specific leaf weight (Fig. 2.7B).

No significant differences in surface area were found among fertilizer treatments

(F = 1.22; df = 2,105; P = 0.2993) and years (F = 1.97; df = 2,105; P = 0.1454). However, surface leaf area differed significantly between cultivars (F = 67.11; df = 1,105; P <

0.0001). Autumn Blaze (45 cm2) had larger leaves compared with Red Sunset (23 cm2) maple cultivars. Surface leaf area was not affected by interaction between fertilizer treatment and cultivar (F = 2.37; df = 2,105; P = 0.0996) nor interaction between fertilizer treatment and year (F = 0.62; df = 4,105; P = 0.6488).

Fertilizer treatments had no effect on tree growth measurements. Relative caliper increase was not affected by fertilizer treatment (F = 1.25; df = 2,40; P = 0.2997), nor was a significant effect on relative height increase (F = 0.5601; df = 2,40; P = 0.5601).

However, there was a significant response of both caliper (F = 6.45; df = 1,40; P =

0.0163) and height (F = 122.31; df = 1,40; P < 0.0001) to cultivar. Autumn Blaze

Freeman maple grew accumulative greater caliper (15%) and height (77%) than Red

Sunset red maple.

a ba a b 85 b a

50 50 2009 2010

40 40

30 30

20 20 SPAD-502 VALUES SPAD-502 10 10

0 0 Autumn Blaze Red Sunset Autumn Blaze Red Sunset

(A)

12 12 2009 2010 10 10

8 8

6 6

4 4

2 2 SPECIFIC LEAF WEIGHT (g/cm2) 0 0 Autumn Blaze Red Sunset Autumn Blaze Red Sunset

(B)

Figure B 1 Effects of nitrogen application rates on the averages (±SE) of the following maple leaf characteristics: chlorophyll content (A) and specific leaf weight (B) during 2009 and 2010 field studies

CHAPTER 4. INTRAGUILD PREDATION MEDIATES HOST PLANT RESISTANCE TO Oligonychus aceris (Shimer) ON MAPLE CULTIVAR RED SUNSET (Acer rubrum)

4.1 Abstract

The predatory mites Neoseiulus fallacis (Garman) (Acarina: Phytoseiidae) and

Zetzellia mali (Ewing) (Acarina: Stigmaeidae) have the potential to moderate populations of Oligonychus aceris (Shimer) (Acarina: Tetranychidae) on maple cultivars. Relative resistance of ‘Red Sunset’ red maple (Acer rubrum) to O. aceris compared to ‘Autumn

Blaze’ Freeman maple (Acer fremanii) has been associated with a greater incidence of leaf domatia. Laboratory experiments were conducted to determine how leaf domatia could alter rates of predation of O. aceris and intraguild predation between N. fallacis and

Z. mali. N. fallacis consumed significantly more protonymphs and adults of O. aceris, whereas Z. mali consumed more eggs. This trend was consistent between the two cultivars of maples used in this study. Rates of intraguild predation between phytoseiids and stigmaeids were significantly influenced by maple host cultivar. N. fallacis consumed more immature stages of Z. mali on Autumn Blaze than on Red Sunset maple. Z. mali consumed fewer immature N. fallacis on both cultivars. Presence of leaf domatia on Red

Sunset leaves could provide refugia required by Z. mali, and thereby explain lower number of O. aceri present. In contrast, absence of leaf domatia left Z. mali no place to hide from N. fallacis and diminished their capacity to contribute to the mortality of O.

87 aceris on Autumn Blaze maples. Thus, differential susceptibility of these cultivars to spider mites is mediated by the capacity of leaf domatia to influence rates of intraguild predation among phtyoseiid and stigmaeid predators.

4.2 Introduction

Predatory mites in the family Phytoseiidae and Stigmaeidae have been studied extensively because they regulate populations of their tetranychid prey in certain agro- ecosystems (McMurtry et al 1970, Jones and Parella 1983, Croft et al. 1992, Duso 1992,

Sato et al. 2001). Several studies have documented that Neoseiulus and Typhlodromus species feed on and regulate Oligonychus species (McMurtry and Croft 1997, Croft et al.

1998, Shrewsbury and Hardin 2003, Pratt and Croft 2000). Maple spider mite

Oligonychus aceris (Shimer) (Acarina: Tetranychidae) are important pests of nursery grown maples. Studies of susceptibility to O. aceris among cultivars showed ‘Red Sunset’ red maple (Acer rubrum) to be less susceptible than ‘Autumn Blaze’ Freeman maple

(Acer x fremanii) (Potter and Spicer 1993, Seagraves et al. 2013, Chapter 2-3). I propose that this relative resistance to O. aceri is due to varietal differences in the relative abundances of leaf domatia that can provide refugia for the predatory mites we have found on these varieties. These include two phytoseiids Neoseiulus fallacis (Garman) and

Typhlodromus caudiglans (Schuster), and one stigmaeid, Zetzellia mali (Ewing). Red

Sunset maples have far more leaf domatia and higher populations of Z. mali than Autumn

Blaze. Although, these two species of phytoseiids have been found in both varieties, previous studies failed to find significant differences in their abundance on each variety

(Chapter 3).

Leaf domatia, or acarodomatia, are small cavities formed by tissue at the juncture of the vein axils on the underside of leaves. Their most common shapes are pit

(invaginations of leaf surface that reach the mesophyll), pocket (cavities beneath expanded veins), dense hair-tufts, or an association between hair-tufts and pits or pockets

(O’Dowd and Willson 1991, Nishida et al. 2005). The main inhabitants of leaf domatia are mites especially predators in the families Phytoseiidae and Stigmaeidae (Walde 1995,

Agrawal et al. 2000, Lester et al. 2000, Kreiter et al. 2002). Recent studies indicated that domatia modulate the predator-prey interaction by altering predatory mite distribution and abundance (Pemberton and Turner 1989, O’Dowd and Wilson 1989, Walter 1996,

Walter and O’Dowd 1992, Norton et al. 2001, Loughner et al. 2008). Several studies indicate that leaves with domatia have lower numbers of spider mites because they contain more predaceous mites (Walter and O’Dowd 1992, Duso 1992, English-Loeb et al. 2002, Karban et al. 1995, Loughner et al. 2008). Some studies suggest that Z. mali hide in domatia and due to lack of mobility forms dense groups along the vein where the domatia are lacking (MacRae and Croft 1996, Slone and Croft 1998, 2001). In contrast, phytoseiid predatory mites disperse around leaves and have high ambulatory and aerial mobility (Duso and Vettorazzo 1999, Clements and Harmsen 1992).

Phytoseid and stigmaeid predators interact through competition for prey or by feeding on each other (Clements and Harmsen 1990, Croft and MacRae 1993, MacRae and Croft 1996). Although the coexistence of two or more predators can enhance the control of spider mites, intraguild predation may disrupt biological control (Croft and

McRae 1993, Rosenheim et al. 1995). Some studies suggest that phytoseiids do not

89 consume stigmaeids, but may alter their populations through competition for prey

(Clements and Harmsen 1993, MacRae and Croft 1996, Slone and Croft 1998).

To better understand Autumn Blaze Freeman maple is more susceptible to O. aceris than Red Sunset red maple, I determined how the presence of leaf domatia affectedthe interactions between stigmaeids, phytoseiids and spider mites on these two cultivars.

4.3 Materials and Methods

Leaf domatia. Autumn Blaze and Red Sunset maple trees grown at the Purdue

Meigs Farm, in Lafayette were used for this study (Chapter 3). On 29, August 2010, samed aged leaves were collected from 24 trees of each variety. A total of 12 leaves from each tree were collected from one branch located in each of four cardinal directions.

Leaves were observed under the microscope and scored on a scale of 0 to 4 based on the presence of pubescence along a hierarchical scale of leaf veins (Fig 4.1). Assessments were started at the primary petiole-leaf blade vein branch and continued to secondary, tertiary and quaternary branching. Leaves lacking domatia were given a score of 0. Adult and nymphal stages of spider mites and predators present in the leaf were also counted when leaf domatia was scored.

Differences in the leaf domatia score were determined using PROC GLIMMIX for

Generalized Linear Mixed Models (SAS® 9.3 Institute Inc., Cary, NC). The GLIMMIX procedure selected a regression model based on the distribution of each response variable using a beta distribution for proportion of maximum possible domatia score. The relationship between the total number of predatory mites and the average domatia index

90 per tree were determined via Pearson correlation using PROC CORR (SAS® 9.3 Institute

Inc., Cary, NC) analysis for each cultivar.

Intraguild predation. In order to determine prey and intraguild consumption, I investigated the capacity of each Neoseiulus fallacis (Garman) and Zetzellia mali (Ewing) predatory mite to feed on different stages of O. aceris and on each other on leaves of

Acer rubrum cultivar ‘Red Sunset’ and Acer x freemanii cultivar ‘Autumn Blaze’. The lab experiments were conducted between July and August 2011 in a series of Petri dish experiments using prey listed in table 4.1. Mites were collected from Red Sunset and

Autumn Blaze maple trees located at Purdue Meigs Farm, Lafayette, IN.

In each Petri dish, one leaf of either Red Sunset or Autumn Blaze were placed with a known number of prey that was at least twice the number consumed by a single adult predator in our preliminary experiment. One adult predator was placed in each Petri dish and the number of prey consumed in 24 hrs was measured. Leaves used in the study were collected from a planting of Autumn Blaze and Red Sunset located at the Purdue

Meigs Farm. Each excised leaf was placed on wet cotton in a 14.5 cm diameter and 2.5 cm deep Petri dish that was loosely covered with a Petri dish top and maintained in a growth chamber at 25°C at 16: 8 L:D. All adult female N. fallacis and Z. mali assayed were starved by isolating them on individual leaves for 24 hours prior to each experiment.

To determine consumption rate of mobile mite prey I collected mites from infested leaves at Purdue Meigs Farm and transferred them with a camel’s hair brush to the experimental leaves in the Petri dish. Twelve mobile prey were delivered to each leaf and the number remaining were counted after 24 hr. To determine the number of maple spider mite eggs consumed I collected leaves from Purdue Meigs Farm and removed all

91 but the maple spider mite eggs. Then five adult female O. aceris were placed on each leaf to supplement the numbers of eggs available for consumption. After 24 hours, maple spider mite adults were removed and the number of eggs was counted.

To monitor consumption rate of mobile predators as prey I used the same procedure described for mite prey. Twelve mobile prey of Z. mali were delivered to each leaf and one adult of N. fallacis was placed to evaluate intraguild predation by N. fallacis.

Conversely, intraguild predation by Z. mali was measured by placing twelve mobile prey of N. fallacis on each leaf and one adult of Z. mali.

Experiments were conducted using a completely randomized design to determine effects of predator and host plant cultivar on the attack rate of a given type of prey. Only one prey stage was evaluated for each predator in a 24 hour period for each cultivar and predator. Thus, 40 assays were conducted each day for each prey species and stage.

Effects of host plant and cultivar were analyzed using PROC GLM for Generalized

Linear Models (SAS® 9.3 Institute Inc., Cary, NC) with a two way ANOVA. Both the

Levine and Bartlett tests were used to check assumptions of constant variance and a log transformation to the data was applied to correct for non-normality.

4.4 Results

Leaf domatia by maple cultivars. Proportions of maximum rank of leaf domatia varied significantly between maple cultivars (F = 823.10; df = 1, 37; P < 0.0001). On

Red Sunset, the average domatia ranking on leaves was 0.73±0.02 of the maximum and on Autumn Blaze it was 0.08±0.01 (Fig. 4.2). There are more predatory mites on Red

Sunset than Autumn Blaze (F = 39.11; df = 1, 37; P < 0.0001). There were more Z. mali

92 on Red sunset than Autumn Blaze (F = 46.43; df = 1, 37; P < 0.0001). There was no significant difference between the number of phytoseiid mites on the two maple varieties

(F = 2.45; df = 1, 37; P = 0.1323). (Fig. 4.3).

Numbers of phytoseiids per cm2 were not correlated with domatia on maple leaves either for Red Sunset (r = -0.05; P = 0.8395) or for Autumn Blaze (r = -0.05; P =

0.8083). However, number of Z.mali per cm2 were highly correlated with domatia on leaves of Red Sunset (r = 0.65; P = 0.0006) but not for Autumn Blaze maples (r = 0.09; P

= 0.6852) (Fig.4.4).

Prey-predator interactions: Consumption of O. aceris eggs, nymphs and adults by predatory mite adults differed significantly among predators (F = 80.37; df = 1, 36; P

< 0.001; F = 37.13; df = 1, 36; P < 0.0001; F = 35.93; df = 1, 36; P < 0.0001, respectively)

(Fig. 4.5). On average adult Z. mali consumed 11.3±0.90 O. aceris eggs which was almost three times the 3.95±0.26 consumed by N. fallacis. In contrast, the number of protonymphs and adults consumed by N. fallacis was twice of the number attacked by Z. mali (Fig. 4.5). Maple cultivar did not affect consumption of eggs, nymphs, or adults by each predator (F = 0.01; df = 1, 36; P = 0.9630, F = 0.55; df = 1, 36; P = 0.4632; F = 0.69; df = 1, 36; P = 0.4126; respectively). There was no significant interaction between cultivar and predatory mite on the O. aceri eggs, nymphs or adults consumed (F = 3.82; df = 1, 36; P = 0.0586; F = 2.14; df = 1, 36; P = 0.1521; F = 1.51; df = 1, 36; P = 0.2269; respectively).

Predator-predator interaction: Consumption of protonymphs of Z. mali by adult

N. fallacis and consumption of protonymphs of N. fallacis by adult Z. mali was significantly affected by maple cultivar (F = 67.21; df = 1, 36; P < 0.0001) and predator

93 mite species (F = 58.09; df = 1, 36; P < 0.0001). N. fallacis adults consumed an average of 8.6±0.82 Z. mali proptonymphs on Autumn Blaze cultivar which was near four times the 2.3±0.30 consumed by N. fallacis adults on Red Sunset. In contrast, the number of N. fallacis protonymphs consumed by Z. mali adults was almost the same in both cultivars

(Fig. 4.6). This resulted in a significant interaction between predator mite species and cultivar (F = 40.52; df = 1, 36; P < 0.0001). Adult Z. mali and N. fallacis did not consume any adult predators during this assay (Fig. 4.6).

4.5 Discussion

Three predators, N. fallacis, T. caudiglans (Phytoseidae) and Z. mali (Stigmaeidae) were found in our maple study system. Both Stigmaeidae and Phytoseiidae have a long history of reducing phytophagous mites in cropping systems. In many agricultural ecosystems, these predators compete for the same spider mite prey and prey on each other (Schausberger 1999, Schausberger and Croft 2000). These interactions, called intraguild predation are defined as the attack between predators in the same system

(Schausberger 1999, Schausberger and Croft 2000, Arim and Marquet 2004). Phytoseiid predators are often seen as more agressive and are important at high pest densities, but stigmaeids are more efficient at maintaining low prey numbers (Rosenheim and Harmon

2006).

N. fallacis and Z. mali differed significantly in number and stage of tetranychid prey consumed. N. fallacis attacked more protonymphs and adults, whereas Z. mali consumed more eggs. Interestingly, this trend was consistent between the two cultivars of maples used in this study. This finding supports previous research which suggests that Z.

94 mali feeds on the eggs and immature stages of tetranychids, because they are too slow to attack mobile prey. Due to this consumption strategy Z. mali has the capacity to survive in systems where spider mites populations are low (Santos and Laing 1985, Clements and

Harmsen 1992, 1993, Croft 1994). Similarly, these findings are also consistent with other studies that characterize phytoseiids as predators with a much stronger preference for mobile stages of prey than eggs (Clements and Harmsen 1992, Duso et al. 2004).

In contrast to predation on spider mites, rates of intraguild predation between phytoseiids and stigmaeids were profoundly influenced by maple host cultivar. N. fallacis consumed nearly four times the number of immature Z. mali on Autumn Blaze than on

Red Sunset maple. Z. mali consumed the same number of immature N. fallacis on both maple cultivars. This rate of consumption was similar the number of Z. mali consumed by

N. fallacis on Red Sunset. This finding is unique in that previous studies failed to report stigmaeid consumption by phytoseiids (Clements and Harmsen 1992, 1993, MacRae and

Croft 1996, Slone and Croft 1998).

The capacity of phytoseiid mites to consume both eggs and nymphal stages of Z. mali emphasizes the importance of refugia for Z. mali survival and their capacity to contribute to the mortality of O. aceris prey beyond that provided by N. fallacis alone.

Thus, the presence of more domatia on Red Sunset leaves could provide the refugia required by Z. mali, and thereby explain the lower number of O. aceri on this cultivar. On

Autumn Blaze, the absence of leaf domatia leave Z. mali with no place to hide and could explain why fewer Z. mali were present compared to Red Sunset Maples (Chapter 3).

Pubescence within the leaf domatia of Red Sunset could explain the coexistence of phytoseiids and stigmaeid mite on their leaves. Several studies showed that

95 pubescence in leaf domatia could reduce the capacity of some predators for searching and finding prey (Krips et al. 1999, Roda et al. 2000, Kreiter et al. 2002, Croft et al. 2004,

Duso et al. 2004). This phenomenon has been used to suggest that N. fallacis lay their eggs in these domatia to guard against cannibalism (Slone and Croft 1998, 2001). On

Autumn Blaze maples where few domatia are present, N. fallacis can forage for prey easily, and with few places to hide, few Z. mali remain on the leaves. In contrast, on Red

Sunset maples, where domatia are abundant, this favors Z. mali over N. fallacis. Here, both Z. mali and A. fallacis lay eggs in the domatia, where Z. mali can hide from N. fallacis and eat the occasional N. fallacis egg. Nevertheless, studies of other Z. mali indicate a preference for tetranychid over phytoseiid eggs (Clements and Harmsen 1990,

1992, 1993).

In conclusion, this study strongly suggests that the observed resistance of Red Sunset maples to O. aceri is mediated by the presence of leaf domatia that alters intraguild predation at the higher trophic levels. This finding underscores the importance of accounting for predator-predator as well as predator prey interactions when determining the role of beneficial organisms in agroecosytems.

4.6 Literature Cited

Agrawal, A.A., R. Karban, and R.G. Colfer. 2000. How leaf domatia and induced plant resistance affect herbivores, natural enemies and plant performance. Oikos 89: 70- 80. Arim, M. and P.A. Marquet. 2004. Intraguild predation: a widespread interaction related to species biology. Ecology Letters 7: 557-564. Clements, D.R. and R. Harmsen. 1990. Predatory behaviour and prey-stage preferences of stigmaeid and phytoseiid mites and their potential compatibility in biological control. Can. Ent. 122: 321-328. Clements, D.R. and R. Harmsen. 1992. Stigmaeid-phytoseiid interactions and the impact of natural enemy complexes on plant-inhabiting mites. Exp. Appl. Acarol. 14: 327-341. Clements, D.R. and R. Harmsen. 1993. Prey preferences of adult and immature Zetzellia mali Ewing (Acari: Stigmaeidae) and Typhlodromus caudigalns Schuster (Acari: Phytoseiidae). Can. Entomol. 125: 967-969. Croft, B.A., I.V. MacRae, and K.G. Currans. 1992. Factors affecting biological control of apple mites by mixed populations of Metaseiulus occidentalis and Typhlodromus pyri. Exp. Appl. Acarol. 14: 343-355. Croft, B.A. and I.V. MacRae. 1993. Biological control of apple mites: impact of Zetzellia mali (Acari: Stigmaeidae) on Typhlodromus pyri and Metaseiulus occidentalis (Acari: Phytoseiidae). Environ. Entomol. 22(4): 865-873. Croft, B.A. 1994. Biological control of apple mites by a phytoseiid mite complex and Zetzellia mali (Acari: Stigmaeidae): long-term effects and impact of azinphosmethyl on colonization by Amblyseius andersoni (Acari: Phytoseiidae). Environ. Entomol. 23(5): 1317-1325. Croft, B.A., J.A. Murtry, and H.K. Luh. 1998. Do literature records of predation reflect food specialization and predation types among phytoseiid mites (Acari: Phytoseiidae)? Exp. Appl. Acarol. 22: 467-480. Croft, B.A., J.S. Blackwood, and J.A. McMurtry. 2004. Classifying life-style types of phytoseiid mites: diagnostic traits. Exp. Appl. Acarol. 33: 247-260.

Duso, C. 1992. Role of Amblyseius aberrans (Oud.), Typhlodromus pyri (Scheuten) and Amblyseius andersoni (Chant) (Acari: Phytoseiidae) in vineyards. J. Appl. Ent. 114: 455-462. Duso, C. and E. Vettorazzo. 1999. Mite population dynamics on different grape varieties with or without phytoseiids released (Acari: Phytoseiidae). Exp. Appl. Acarol. 23: 741-763. Duso, C., V. Malagnini, A. Paganelli, L. Aldegheri, M. Bottini, and S. Otto. 2004. Pollen availability and abundance of predatory phytoseiid mites on natural and secondary hedgerows. BioControl 49: 397-415. English-loeb, G., A.P. Norton, and A. Walter. 2002. Behavioral and population consequences of acarodomatia in grapes on phytoseiid mites (Mesostigmata) and implications for plant breeding. Entomol. Exp. Appl.104: 307-319. Jones, V.P. and M.P. Parrella. 1983. Compatibility of six citrus pesticides with Euseius stipulates (Acari: Phytoseiidae) populations in Southern California. J. Econ. Entomol. 76: 942-944. Karban, R., English-Loeb, G., Walker, M.A., and J. Thaler. 1995. Abundance of phytoseiid mites on vitis species: effects of leaf hairs, domatia, prey abundance and plant phylogeny? Exp. Appl. Acarol. 19: 189–197. Kreiter, S., M.S. Tixier, B.A. Croft, P. Auger, and D. Barret. 2002. Plants and leaf characteristics influencing the predaceous mite Kampimodromus aberrans (Acari:Phytoseiidae) in habitats surrounding vineyards. Environ. Entomol. 31(4): 648-660. Krips, O.E., P.W. Kleijn, P.E.L. Willems., G.J.Z. Gols, and M. Dicke. 1999. Leaf hairs influence searching efficiency and predation rate of the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae). Exp. Appl. Acarol. 23: 119-131. Lester, P.J., H.M.A. Thistlewood, and R. Harmsen. 2000. Some effects of pre-release host-plant on the biological control of Panonychus ulmi by the predatory mite Amblyseius fallacis. Exp. Appl. Acarol. 24: 19-33.

Loughner, R., K. Goldman, G. Loeb, and J. Nyrop. 2008. Influence of leaf trichomes on predatory mite (Typhlodromus pyri) abundance in grape varieties. Exp. Appl. Acarol. 45: 111-122. MacRae, I.V. and B.A. Croft. 1996. Differential impact of egg predation by Zetzellia mali (Acari: Stigmaeidae) on Metaseiulus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae). Exp. Appl. Acarol. 20: 143-154. McMurtry, J. A., C. B. Huffaker, and M. van de Vrie. 1970. Ecology of tetranychid mites and their natural enemies: A review. I. Tetranychid enemies: their biological characters and the impact of spray practices. Hilgardia 40: 33 1-390. McMurtry, J.A. and B.A. Croft. 1997. Life-styles of phytoseiid mites and their roles in biological control. Annu. Rev. Entomol. 42:291-321. Nishida, S., A. Naiki, and T. Nishida. 2005. Morphological variation in leaf domatia enables coexistence of antagonistic mites in Cinnamomum camphora. Can. J. Bot. 83:93-101. Norton, A.P., G. English-Loeb, and E. Belden. 2001. Host plant manipulation of natural enemies: leaf domatia protect beneficial mites from insect predators. Oecologia 126: 535-542. O’Dowd, D.J. and M.F. Willson. 1989. Leaf domatia and mites on Australasian plants: ecological and evolutionary implications. Biol. J. Linn. Soc. 37: 191-236. O’Dowd D.J. and M.F. Willson. 1991. Associations between mites and leaf domatia. Tree 6(6): 179-182. Pemberton, R.W. and C.E. Turner. 1989. Occurrence of predatory and fungivorous mites in leaf domatia. Am. J. Bot. 76(1): 105-112. Potter, D.A. and P.G. Spicer. 1993. Seasonal phenology, management, and host preferences of potato leafhopper on nursery-grown maples. J. Environ. Hort. 11(3): 101-106. Pratt, P.D. and B.A. Croft. 2000. Screening of predatory mites as potential control agents of pest mites in landscape plant nurseries of the Pacific Northwest. J. Environ. Hort. 18(4): 218-223.

Roda, A., J. Nyrop, M. Dicke, and G. English-Loeb. 2000. Trichomes and spider-mite webbing protect predatory mite eggs from intraguild predation. Oecologia 125:428-435. Rosenheim, J.A., H.K. Kaya. L.E. Ehler, J.J. Marois, and B.A. Jaffee. 1995. Intraguild predation among biological-control agents: theory and evidence. Biol. Control 5: 303-335. Rosenheim, J.A. and J.P. Harmon. 2006. The influence of intraguild predation on the suppression of a shared prey population: an empirical reassessment. pp. 1-20 In Brodeur J. and G. Boivin (eds), Trophic and Guild Interactions in Biological Control. Springer, Davis, CA. Santos, M.A. and J.E. Laing. 1985. Stigmaeid predators. pp. 197-203 in Helle, W. and M.W. Sabelis (eds). Spider Mites: Their Biology, Natural Enemies and Control. Vol. 1B. Elsevier, Amsterdam, The Netherlands. SAS Institute. 2013. SAS user’s guide: Statistics. Version 9.3 ed. SAS Inst., Cary, N.C. Sato, M.E., A. Raga, L.C. Ceravolo, M.F. De Souza Filho, A.C. Rossi, and G.J. De Morales. 2001. Effect of insecticides and fungicides on the interaction between members of the mite families Phytoseiidae and Stigmaeidae on citrus. Exp. Appl. Acarol. 25: 809-818. Schausberger, P. 1999. Predation preference of Typhlodromus pyri and Kampimodromus aberrans (Acari; Phytoseiidae) when offered con- and heterospecific immature life stages. Exp. Appl. Acarol. 23: 389-398. Schausberger, P. and B.A. Croft. 2000. Nutritional benefits of intraguild predation and cannibalism among generalist and specialist phytoseiid mites. Ecol. Entomol. 25: 473-480. Seagraves, B.L., C.T. Redmond, and D.A. Potter. 2013. Relative resistance or susceptibility of maple (Acer) species, hybrids and cultivars to six arthropod pests of production nurseries. Pest Manag. Sci. 69(1): 112-119. Shrewsbury, P.M. and M.R. Hardin. 2003. Evaluation of predatory mite (Acari: Phytoseiidae) releases to suppress spruce spider mites, Oligonychus ununguis (Acari: Tetranychidae), on juniper. J. Econ. Entomol. 96(6): 1675-1684.

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Slone, D.H. and B.A. Croft. 1998. Spatial aggregation of apple mites (Acari: Phytoseiidae, Stigmaeidae, Tetranychidae) as measured by a binomial model: effects of life stage, reproduction, competition, and predation. Environ. Entomol. 27(4): 918-925. Slone, D.H. and B.A. Croft. 2001. Species association among predaceous and phytophagous apple mites (Acari: Eriophyidae, Phytoseiidae, Stigmaeidae, Tetranychidae). Exp. Appl. Acarol. 25: 109-126. Walde, S.J. 1995. How quality of host plant affects a predator-prey interaction in biological control. Ecology 76(4): 1206-1219. Walter, D.E. and D.J. O’Dowd. 1992. Leaves with domatia have more mites. Ecology 73(4): 1514-1518. Walter, D.E. 1996. Living on leaves: mites, tomenta, and leaf domatia. Annu. Rev. Entomol. 41: 101-114.

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Table 4.1 Mite species and life stages used in experiments to assess the capacity of N. fallacis and Z. mali to feed on prey in Petri dish studies using Autumn Blaze and Red Sunset maple trees as host plant substrates. Only one kind of prey was tested during each 24 hr period.

Predatory mites Prey Stage (Adult)

N. fallacis O. aceris Eggs Z. mali

N. fallacis Nymph Z. mali

N. fallacis Adult Z. mali

N. fallacis Nymph Z. mali

Adult Z. mali

Z. mali Nymph N. fallacis

Adult N. fallacis

102

3 2 4

Figure 4.1 Leaf domatia rank scored on a scale of 0 to 4 based on the presence of pubescence along a hierarchical scale of leaf veins.

103

1.0

0.8

0.6

0.4

0.2

PROPORTION OF MAXIMUM DOMATIA OF MAXIMUM PROPORTION 0.0 RED SUNSET AUTUMN BLAZE

Figure 4.2 Proportion of maximum leaf domatia (=Leaf domatia rank/4) on Red Sunset red maple and Autumn Blaze Freeman maple.

0.4 2

0.3 Z. mali Phytoseiids

0.2

0.1 # PREDATORY MITES/cm # PREDATORY

0.0 RED SUNSET AUTUMN BLAZE

Figure 4.3 Abundance of predatory mites on Red Sunset red maple and Autumn Blaze Freeman maple.

104

PROPORTION OF MAXIMUM DOMATIA

Figure 4.4 The relation between leaf domatia index and the number of Z. mali on Red Sunset red maple and Autumn Blaze Freeman maple in 24 h.

105

14 Neoseiulus fallacis 14 Zetzellia mali 12 EGGS 12 PROTONYMPH 10 ADULTS 10 8 8 6 6

4 4 # CONSUMED PREY # CONSUMED PREY 2 2

0 0 RED SUNSET AUTUMN BLAZE RED SUNSET AUTUMN BLAZE

Figure 4.5 Predation on eggs, nymphs and adults of O. aceris by adult Z. mali and N. fallacis predatory mites on Red Sunset red maple and Autumn Blaze Freeman maple in 24 h.

10 Zetzellia mali 10 Neoseiulus fallacis 8 8 consumed 6 PROTONYMPH consumed 6 ADULTS

4 4

2 2 # Zetzellia mali mali # Zetzellia # Neoseiulus fallacis 0 0 RED SUNSET AUTUMN BLAZE RED SUNSET AUTUMN BLAZE

Figure 4.6 Intraguild predation on protonymph and adult Z.mali and N. fallacis on Red Sunset red maple and Autumn Blaze Freeman maple in 24 h. Adult Z. mali and N. fallacis did not consume any adult predators during this assay.

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CHAPTER 5. SUMMARY

Many red maple cultivars are susceptible to damage caused by potato leafhopper.

Control of this pest is usually obtained by insecticide treatments (Oliver et al. 2009,

Frank et al. 2013). Based on the nursery inspector reports, maple spider mite problems have been increasing in Indiana. Spider mites in the family Tetranychidae, have been reported as problems in a wide range of crops (Nyalala and Grout 2007, Prischmann et al.

2002, Opit et al. 2005, Bynum et al. 2004). Several studies have shown that pesticide use and fertilization applications contribute to outbreaks of this pest (Wilson 1994, Walde

1995, Hill and Foster 1998, Shrewsbury and Hardin 2003, Szczepaniec et al. 2011).

In the spring of 2009, I worked with the Indiana Department of Natural Resources to identify nurseries growing maples that had a problem with maple spider mites; most of them reported using bifenthrin early in the season to control E. fabae. This data suggests a link between early season use of bifenthrin against E. fabae and the occurrence of maple spider mite problems later in the season. Insecticide application had the potential to destroy natural enemies and cause outbreaks of secondary pests such as maple spider mites which have the potential to cause high levels of damage to maples and, therefore, are of great concern to growers.

I conducted two field studies to determine how pesticides and fertilizer applications affect the abundance of E. fabae and O. aceris in two maple cultivars, Red

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Sunset red maple and Autumn Blaze Freeman maple. Preliminary studies have shown that red maple clones and Freeman maple cultivars differ in their susceptibility to E. fabae and O. aceris feeding injury. Although this leafhopper causes severe economic damage to red maples in nurseries, Freeman maple cultivars are relatively resistant.

However, Freeman maple cultivars are susceptible to maple spider mites (Potter and

Spicer 1993, Oliver et al. 2009, Seagraves et al. 2013).

The pesticide study suggests that damage by E. fabae is considerably lower in trees treated with bifenthrin compared to those treated with other early-applied foliar insecticides on Red Sunset red maple. On Autumn Blaze Freeman cultivar, bifenthrin did not provide added protection from E. fabae, because it was already tolerant to this pest.

However, O. aceris populations increased after applications of bifenthrin were made on

Autumn Blaze, but not on Red Sunset. One remarkable finding is that use of these products to control E. fabae on maples is only warranted on varieties that are susceptible to this pest. Establishing threshold levels can provide a useful tool to help them identify varieties that require treatment. When bifenthrin treatments were applied based on our established threshold, fewer applications were needed for E. fabae management on

Autumn Blaze. This resulted in lower populations of O. aceris. Reduction of pesticide use associated with this can have the added advantage of reducing spider mite outbreaks on some cultivars by conserving spider mite predators. Our data does not show any significant affects of bifenthrin on predatory mites, Neoseiulus fallacis (Garman) and

Typhlodromus caudiglans (Schuster), Zetzellia mali (Erwing) on either Red Sunset or

Autumn Blaze maples. However, they do show that populations of the predator Z. mali were higher on Red Sunset than Autumn Blaze regardless of insecticide treatment. The

108 ability of Red Sunset to harbor more predatory mites suggests that O. aceris populations are regulated in this cultivar by predator populations, not by insecticide applications.

I observed that damage caused by E. fabae and O. aceris populations increases when fertilization is applied. The response of each pest differs between cultivars. The greatest damage caused by E. fabae was on Red Sunset maple cultivar when trees received high rates of fertilizer. In contrast, O aceris populations in Autumn Blaze were considerably higher than Red Sunset when fertilizer was applied. Interestingly, cumulative mites at the end of the season and percentage of nitrogen on leaves were highly correlated in both cultivars. Variation in mite populations in both cultivars are correlated with nitrogen suggesting that morphological differences such as leaf domatia between them could improve the capacity of predatory mites to regulate O. aceris populations on Red Sunset. In this study, Red Sunset maple cultivar has more leaf domatia than Autumn Blaze. Our data suggests that differences on the presence of leaf domatia influence predator population dynamics with O. aceris.

Effects of leaf domatia on predation rates of O. aceris and intraguild predation were tested in a series of laboratory experiments with excised leaves. On leaves from both cultivars, Z. mali prefer O. aceris eggs over adults and protonymphs, whereas N. fallacis consume more mobile stages of O. aceris. Rates of intraguild predation were influenced by maple host cultivar. N. fallacis adults consumed more immature Z. mali on

Autumn Blaze than on Red Sunset maple. Z. mali adults consumed the same number of immature N. fallacis on both maple cultivars. This rate of consumption was similar to the number of Z. mali immatures consumed by N. fallacis adults on Red Sunset.

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I can conclude that leaf domatia enhance levels of beneficial mites through reducing intraguild predation. In Red Sunset red maple cultivar, leaf domatia provides a hiding place for Z. mali where phytoseiids cannot consume them. In this way, Z. mali and phytoseiids have an additive effect in their predation of O. aceris density. In Autumn

Blaze Freeman maple cultivar, there is no place for Z. mali to hide and phytoseiids are able to consume them. This can potentially reduce top-down regulation from both Z. mali and phytoseiid mites. Phytoseiids alone are not able to reduce O. aceris density. When growers use insecticide to control E. fabae on both cultivars, leaf domatia allow to predators to hide on Red Sunset. The absence of domatia increases exposure of both predators to the pesticides, reducing their abundance and facilitating outbreaks of O. aceris.

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5.1 Literature Cited

Bynum, E.D., W. Xu, and T.L. Archer. 2004. Potential efficacy of spider mite-resistance genes in maize testerosses. Crop Prot. 23: 625-634. Frank, S.D., W.W.E. Klingeman, S.A. White, and A. Fulcher. 2013. Biology, injury, and management of maple tree pests in nurseries and urban landscapes. J. Integ. Pest Mngmt. 4(1): B1-B14. Hill, T.A. and R.E. Foster. 1998. Influence of selective insecticides on population dynamics of european red mite (Acari: Tetranychidae), apple rust mite (Acari: Eriophyidae), and their predator Amblyseius fallacis (Acari: Phytoseiidae) in apple. J. Econ. Entomol. 91(1): 191-199. Nyalala, S. and G. Brian. 2007. African spider flower (Cleome ginandra L./Gynandropsis ginandra (L.) Briq.) as red spider mite (Tetranychus urticae Koch) repellent in cut flower rose (Rosa hybrida L.) cultivation. Scientia Horticulturae 114: 194-198. Oliver, J.B., D.C. Fare, N. Youssef, M.A. Halcomb, M.E. Reding, and C.M. Ranger. 2009. Evaluation of systemic insecticides for potato leafhopper control in field- grown red maple. J. Environ. Hort. 27(1): 17-23. Opit, G.P., Y. Chen, K.A. Williams, J.R. Nechols, and D.C. Margolies. 2005. Plant age, fertilization, and biological control affect damage caused by twospotted spider mites on ivy geranium: development of an action threshold. J. Amer. Sco. Hort. Sci. 130(2):159-166. Potter, D.A. and P.G. Spicer. 1993. Seasonal phenology, management, and host preferences of potato leafhopper on nursery-grown maples. J. Environ. Hort. 11(3): 101-106. Prischmann, D.A., B.A. Croft, and H.K. Luh. 2002. Biological control of spider mites on grape by phytoseiid mites (Acari: Tetranychidae, Phytoseiidae): emphasis on regional aspects. J. Econ. Entomol. 95(2): 340-347. Seavagres, B.L., C.T. Redmond, and D.A. Potter. 2013. Relative resistance or susceptibility of maple (Acer) species, hybrids and cultivars to six arthropod pests of production nurseries. Pest Manag. Sci. 69(1): 112-119.

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Shrewsbury P.M. and M.R. Hardin. 2003. Evaluation of predatory mite (Acari: Phytoseiidae) releases to suppress spruce spider mites, Oligonychus ununguis (Acari: Tetranychidae), on juniper. J. Econ. Entomol. 96(6): 1675-1684. Szczepaniec, A., S.F. Creary, K.L. Laskowski, J.P. Nyrop, and M.J. Raupp. 2011. Neonicotinoid insecticide imidacloprid causes outbreaks of spider mites on elm trees in urban landscapes. PLoS ONE 6(5): 1-10 Walde S.J. 1995. How quality of host plant affects a predator-prey interaction in biological control. Ecology 76(4): 1206-1219. Wilson, L.J. 1994. Plant-quality effect on life-history parameters of the twospotted spider mite (Acari: Tetranychidae) on cotton. J. Econ. Entomol. 87(6): 1665-1673.

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VITA

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VITA

My interest in studying entomology began while I was working for ornamental exporting farms in Ecuador (the last one Esmeralda-Ecuador). Insects are one of the most important factors that influence in ornamentals production. During my four years in those companies, I was able to develop professionally and become an IPM Supervisor

(Integrated Management of Pests). This job consisted of overseeing insects and diseases management through the process of sampling and decisions making. Other responsibilities included the implementation of a strategic plan to bring our production practices up to an International Standard (ISSO 9000), which allowed free export for our products. I have always been interested in doing research on developing new alternatives that would help pest managers to avoid economic lost and ensure the profitability of their businesses.

To continue my training, I enrolled myself in a Master’s Degree in Agro Ecology at CATIE, in Costa Rica. As part of the training there, I conducted an investigation of sampling protocols for pests of quarantine importance in Dracaena and studied the relation between their abundance and growing practices. My deep interest in scientific and ecological approaches to pest management had led me to pursue my studies at Purdue

University. Purdue University provided me the tools to deal with production practices which will help me to have a better understanding of integrated pest management. I will

113 develop a career in education, research, and extension in Ecuador; therefore I will help growers to meet the changing demands of domestic and international market.