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ROLE OF PREDATORS IN SUPPRESSION OF

THE EUROPEAN CORN BORER, OSTRINIA NUBILALIS (HUBNER), ON SWEET CORN.

DISSERTATION

Presented in Partial Fulfillment of the Requirement for the

Degree of Doctor of Philosophy in the Graduate School of the

Ohio State University

By

Sandra Alcaraz, M.S.

The Ohio State University

1996

Dissertation Commitree: Approved by

C. Welty

R. Hall

R. Lindquist

R. Williams Adviser

Department of Entomology

Co-Advisor

Department of Entomology UMI Number; 9710517

UMI Microform 9710517 Copyright 1997, by UMI Company. All rights reserved.

This microform edition is protected against unauthorized copying under Title 17, United States Code.

UMI 300 North Zeeb Road Ann Arbor, MI 48103 Copyright by Sandra Alcaraz 1996 ABSTRACT

Four experiments were conducted to study the role of predators in

the control of European corn borer {Ostrinla nubllalis (Hûbner)) on sweet

c o m and possible methods for enhancing predator activity. A commercial

predator food attractant was used in combination with different

formulations of conventional and microbial insecticides in a field

experiment with early and late plantings of sweet corn in 19 93, 1994, and

1995. The predator food attractant alone or combined with Bacillus

thuringiensis treatment did not consistently affect density of coccinellid

or anthocorid predators or ear quality at harvest.

The types of functional response from predators to varying densities

of eggs and first instars of European corn borer were studied in a

laboratory experiment. With few exceptions, the predators Coleomegilla

maculaca (DeGeer) , Orius insidiosus (Say) , and Chrysoperla camea Stephens

had a type II functional response to both eggs and first instars.

Releases of C. maculata and O. insidiosus either alone or together on individually caged sweet corn plants were evaluated to determine their

ability to search for and consume eggs and first instars of European corn borer. Results showed that C. Maculata has more potential than O.

insidiosus for further studies on inundative releases for control of

European corn borer.

C. camea eggs and larvae were field released on sweet corn to

11 evaluate its potential as a biological control agent. Adequate control was not achieved with any of various rates and timings tested.

Potential use of C. maculata for commercial releases will depend on improvements in mass rearing and in predator release technology, and basic field studies for control of the European corn borer.

Ill To mv ramilv

IV ACKNOWLEDGMENTS

I am indebted to my major adviser. Dr. Celeste Welty, for her support not only as an academic adviser but also as a friend through difficult times. Without her guidance and patience, this work would not have been completed. I want to thank all the members of my Graduate

Advisory Committee, Drs. Richard Hall, Richard Lindquist, and Roger

Williams for their comm.ents on my dissertation. I appreciate the advice given by Dr. S. Juliano on functional response. I thank Dr. J. Cbrycki for providing me with Coleomegilla maculata specimens and Ms. Jean Dyar for supplying me with European corn borer egg masses. I want to acknowledge Rhône-Poulenc, Abbott, and FI4C for donation of products used in this study.

I thank Ken Scaife and Mark Schmittgen for maintaining fields and applying treatments. I also thank Karen Magnuson for her assistance with field work and her friendship. I would like to acknowledge the help given by the students that worked with me during the last three years in the field and the laboratory. Finally, I would like to thank my husband, for his continued support and love, and my daughters Juliana and Marcela who have been understanding of my work and for whom I am finishing this chapter of my life. VITA

May 6, 1961...... Born Armero, Colombia

1984 ...... B.S., Pontificia Universidad Javeriana Bogota, Colombia

1992...... M. S., The Ohio State University, Columbus,Ohio

1992 - present...... Graduate Research Associate, Department of Entomology, The Ohio State University, Columbus, Ohio

FIELD OF STUDY

Major field: Entomology

VI TABLE OF CONTENTS

ABSTRACT...... ii

DEDICATION...... iv

ACKNOWLEDGMENTS...... v

VITA...... Vi

TABLE OF CONTENTS...... vii

LIST OF TABLES...... ix

LIST OF FIGURES...... xi

INTRODUCTION...... 1

CHAPTER I. PREDATOR CONSERVATION AND AUGMENTATION PRACTICES FOR SWEET CORN PEST MANAGEMENT...... 4

Introduction...... 4 Materials and Methods...... 6 Results...... 13 Discussion...... 24

II. FUNCTIONAL RESPONSE OF Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae), Orius insidiosus (Say) (Hemiptera: Anthocoridae), AND Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) TO EGGS AND FIRST INSTARS of Ostrinia nubilalis Hübner (Lepidoptera: Pyralidae)...... 4 9

Introduction...... 49 Materials and Methods...... 51 Results...... 57 Discussion...... 63

III. CAGE RELEASES OF Coleomegilla maculata (Coleoptera: Coccinellidae) AND Orius insidiosus (Hemiptera: Anthocoridae) FOR CONTROL OF Ostrinia nubilalis (Lepidoptera: Pyralidae)...... 84

Introduction...... 84 Materials and Methods...... 85 Results...... 85 Discussion...... 87

IV. FIELD RELEASES OF Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) EGGS AND LARVAE FOR PREDATION ON Ostrinia nubilalis (Lepidoptera: Pyralidae) ON SWEET CORN...... 91

V I 1 Introduction...... 91 Materials and Methods...... 92 Results...... 94 Discussion...... 97

BIBLIOGRAPHY...... 103

v i n LIST OF TABLES

TABLE PAGE

1.1. Effect of treatments on beneficial arthropod (mean number per plant) populations on sweet corn at Columbus and Fremont Ohio in early sweet corn plantings in 1993, 1994, and 1995...... 29

1.2. Effect of treatments on beneficial arthropod (mean number per plant) populations on sweet corn at Columbus and Fremont Ohio in late sweet corn plantings in 1993, 1994, and 1995...... 31

1.3. Percentage marketable ears (strict and liberal standards) and percentage ears infested with European corn borer (ECB), corn earworm (CEW), and fall armyworm (FAWj at harvest of early sweet corn plantings in 1993, 1994, and 1995...... 33

1.4. Percentage marketable ears (strict and liberal standards) and percentage ears infested with European corn borer (ECB), corn earworm (CEW), and fall armyworm (FAW) at harvest of late sweet corn plantings in 1993, 1994, and 1995...... 35

1.5. Interaction of location by treatment for percentage marketable ears (strict and liberal standards) and percentage ears infested with European corn borer (ECB), corn earworm (CEW), and fall armyworm (FAW) at harvest of early sweet corn plantings in 1993, 1994, and 1995...... 35

1.5. Interaction of location by treatment for percentage marketable ears (strict and liberal standards) and percentage ears infested with European corn borer (ECB), corn earworm (CEW), and fall armyworm (FAW) at harvest time of late sweet corn plantings in 1993, 1994, and 1995...... 38

1.7. Treatment means for marketable ears and P values (in parenthesis) of significant interactions of location by treatment by attractant at harvest for early and late sweet corn plantings in Columbus and Fremont, Ohio, 1993-1995...... 39

2.1. Logistic regression results for Coleomegilla maculata consuming eggs and first instars of European corn borer based on the logistic equation...... 57

2.2. Coleomegilla maculata parameters of the functional response to eggs and first instars of European corn borer, based on Rogers' type II functional response equation...... 58

2.3. Logistic regression results for Chrysoperla carnea consuming eggs and first instars of European corn borer based on the logistic equation...... 59

2.4. Chrysoperla carnea parameters of the functional response to eggs and first instars of European corn borer, based on Rogers' type II functional response equation...... 70

ix 2.5. Logistic regression results for Orius insidiosus consuming eggs of European corn borer based on the logistic equation...... 71

2.6. Orius insidiosus parameters of the functional response to eggs of European corn borer, based on Rogers' type II functional response equation...... 72

2.7. Logistic regression results for Orius insidiosus consuming first instars of European corn borer based on the logistic equation. 73

2.8. Orius insidiosus parameters of the functional response to first instars of European corn borer, based on Rogers' type II functional response equation...... 74

2.9. Logistic regression results for Orius insidiosus consuming eggs of European corn borer based on the logistic equation...... 75

2.10. Orius insidiosus parameters of the functional response to eggs of European corn borer, based on Rogers' type II functional response equation...... 76

2.11. Logistic regression results for Orius insidiosus consuming first instars of European corn borer based on the logistic rearession ...... r...... 77

2.12. Orius insidiosus parameters of the functional response to first instars of European corn borer, based on type I functional response...... 77

3.1. Percentage emergence of Ostrinia nubilalis from egg masses exposed to predation by Coleomegilla maculaca and/or Orius insidiosus...... 89

4.1. Percentage of sweet corn ears with and without kernel damage and with European c o m borer (ECB), fall armyworm (FAW), and corn earworm (CEW) present at harvest of an early planting in Fremont, 1993, after treatment with C. carnea eggs and larvae; non- orthogonal contrasts of ore-planned comoarisons of factor effects ...... ' ...... ‘ ...... 99

4.2. Percentage of sweet corn ears with and without kernel damage and with European corn borer (ECB), fall armyworm (FAW), and corn earworm (CEW) present at harvest of an early planting in Columbus, 1993, after treatment with c.carnea eggs and larvae; non orthoaonal contrasts of pre-planned comparisons of factor effects

' 100

4.3. Percentage of sweet corn ears with and without kernel damage and with European corn borer (ECB), fall armyworm (FAW), and corn earworm (CEW) present at harvest of a late planting in Columbus, 1993, after treatment with C.carnea eggs and larvae; non orthogonal contrasts of pre-planned comparisons of factor effects 101 4.4. Percentage of sweet corn ears with and without kernel damage and with European corn borer (ECB), fall armyworm (FAW), and corn earworm (CEW) present at harvest of a late planting in Fremont, 1993, after treatment with c.carnea eggs and larvae; non orthogonal contrasts of pre-planned comparisons of factor effects 102 LIST OF FIGURES

FIGURE PAGE

1.1. Mean number of Coleomegilla maculata per plant for early sweet corn plantings in 1993, 1994 (mean of 5-7 evaluation dates), and 1995 (mean of 2 evaluation dates)...... 41

1.2. Mean number of orius insidiosus per plant for early sweet corn plantings in 1993, 1994 (average of 5-7 evaluation dates), and 1995 (average of 2 evaluation dates)...... 42

1.3. Coleomegilla maculata abundance in untreated plots throughout early sweet corn plantings in Columbus and Fremont, Ohio, 1994 and 1995...... 43

1.4. Orius insidiosus abundance in untreated plots throughout early sweet corn olantings in Columbus and Fremont, Ohio, 1993 to 1995...... '...... 44

1.5. Mean number of Coccinellidae per plant for sweet corn plantings in 1993, 1994 (average of 5-7 evaluation dates), and 1995 (average of 2 evaluation dates)...... 45

1.6. Mean number of orius insidiosus per plant for late sweet corn plantings in 1993, 1994 (average of 5-7 evaluation dates), and 1995 (average of 2 evaluation dates)...... 46

1.7. Coleomegilla maculata abundance in untreated plots throughout late sweet corn plantings in Columbus and Fremont, Ohio, 1993 to 1995...... 47 1.8. Orius insidiosus abundance in untreated plots throughout late sweet corn plantings in Columbus and Fremont, Ohio, 1993 to 1995...... 48

2.1. Logistic regression curves and functional response curves for Coleomegilla maculata consuming eggs and first instars of European corn borer with prey replenishment...... 78

2.2. Logistic regression curves and functional response curves for Coleomegilla maculata consuming eggs and first instars of European corn borer without prey replenishment...... 79

2.3. Logistic regression curves and functional response curves for Chrysoperla carnea consuming eggs and first instars of European corn borer with prey replenishment...... 80

2.4. Logistic regression curves and functional response curves for Chrysoperla carnea consuming eggs and first instars of European corn borer without prey replenishment...... 81

2.5. Logistic regression curves and functional response curves for Orius insidiosus consuming eggs and first instars of European corn borer with prey replenishment...... 82

xi 2.6. Logistic regression curves and functional response curves for Orius insidiosus consuming eggs and first instars of European corn borer without prey replenishment...... 83

3.1 Cages where releases of Coleomegilla maculata and Orius insidiosus were made on 3 September 1995...... 90

Xll INTRODUCTION

Sweet corn (Zea mays L.) is an important vegetable crop in the midwestern United States. In Ohio, it is grown mainly for the fresh market, which has low tolerance for insect damage. Fresh market sweet corn planted in Ohio in 1994 totalled 15,900 acres and production from those acres was valued at $19.2 million (Ohio Agric. Stat. Service

1995). Three lepidopteran species are the three key insect pests with the highest impact on sweet corn production in the area; Ostrinia nubilalis (Hübner) (European corn borer), Halicoverpa zea (Boddie) (corn earworm), and Spodoptera frugiparda (J. E. Smith) (fall armyworm).

Sweet corn is reported as the vegetable crop with the second highest amount of insecticides applied in Ohio (Waldron et al. 1992).

Integrated pest management (1PM) has been developed and implemented for

Ohio-grown sweet corn during the past five years; however, the focus has been based mainly on appropriate timing of insecticide applications in order to reduce total number of applications (Welty 1991). Although many authors have recognized and identified predators, parasites, and diseases capable of attacking these key pests, biological control has not been implemented as a main component of an IPM program.

To determine the variety of indigenous predarors in sweer corn, a survey was conducted in 1992 (Welty, 1992). This survey found

Colaomagilla maculata (DeGeer)(Coleoptera: Coccinellidae) and Orius insidiosus (Say) (Hemiptera: Anthocoridae) as the most abundant natural enemies in insecticide treated and untreated sweet corn. Although c. maculata prefers aphids and pollen, and O. insidiosus prefers thrips, both eat eggs and small larvae of caterpillars such as the three key sweet corn pests. It is unlikely that predation from these indigenous natural enemies can suppress pest population to an acceptable level, but it is unknown whether the conservation of the generalist predators combined with other control measures may provide acceptable control.

Microbial insecticides such as Bacillus thuringiensis var. kurstaki Berliner are used to selectively kill caterpillars, but B. thuringiensis products have produced variable results when evaluated on sweet corn in the midwestern and mid-Atlantic states in the USA. It appears that B. thuringiensis is most promising for control of whorl- feeding European corn borer and fall armyworm, moderately promising for corn borer in silks, and least promising for corn earworm in silks

(Bartels & Hutchison 1991) . B. thuringiensis products are not highly effective for controlling pests in silking corn due to the short time that these caterpillars feed in exposed locations. Mo information is available on how B. thuringiensis interacts with predator food attractants. It is not knovm if this combination could improve the role of the indigenous natural enemies and how performance of the B. thuringiensis products compares to that of the commonly used conventional synthetic insecticides.

Release of commercially reared parasitoids and predators is a practice that has emerged as an alternative to chemical control, but little experimental information is available on their use to control sweet corn pests. Larvae of Chrysopidae are known to be potentially good predators of corn borer eggs and small larvae, however no field data are available for sweet corn.

In my dissertation research, I conducted field experiments to determine how microbial and conventional insecticides control the lepidopteran complex with and without the use of supplemental food for predators, and how these different treatments affect natural enemy abundance. Emphasis was given to observations on European corn borer.

Field releases of eggs and larvae of Chrysoperla carnea were evaluated for control of the lepidopteran complex. Laboratory experiments were conducted to study functional response of C. maculata adults, c. carnea

first instars, and o. insidiosus adults, to varying densities of eggs and first instars of O. nubilalis. A caging experiment was conducted in

the field to determine efficacy of C. maculata and O. insidiosus on searching and destroying eggs of O. nubilalis. Chapter- I

Predator Conservation and Augmentation Practices

for Sweet C o m Pest Management

INTRODUCTION

Sweet corn {Zea mays L.) is an important vegetable crop in the midwestern United States. In Ohio, it is grown mainly for the fresh market, which has low tolerance for insect damage. Fresh market sweet corn planted in Ohio in 1994 totalled 15,900 acres and production from those acres was valued at $19.2 million (Ohio Agric. Stat. Service

1995). Three lepidopteran species are the key insect pests on sweet corn production in the area: Ostrinia nubilalis (Hübner) (European corn borer), Helicoverpa zea (Boddie) (corn earworm), and Spodoptera frugiparda (J. E. Smith) (fall armyworm).

Among vegetable crops in Ohio, sweet corn is the second highest in total amount of insecticides used (Waldron et al. 1992). Integrated pest management (IPM) has been implemented for Ohio-grown sweet corn during the past five years with a focus on appropriate timing of insecticide applications in order to reduce total number of applications

(Welty 1991).

Of the three key pests, European corn borer is the most consistently troublesome to growers due to feeding damage on ears.

First generation larvae of European corn borer can cause severe damage to early planted sweet corn when the later instars start to feed in leaves, stalks, and young ears. Second generation larvae emerge from egg masses laid on leaves above or below the ear zone, the ear leaf, or the husk and usually start feeding directly on the ears. Parasitoids were first introduced for classical biological control

of European corn borer in the U. S. in 1919 (Baker et al. 1949). Poor

rate of success has been attributed to lack of life cycle

synchronization between parasitoids and the borer and inadequate local

conditions (Lewis 1982) . Some research has been conducted to determine

the efficacy of releasing Trichogramma nubilalis for control of European corn borer on sweet corn (Losey et al. 1995), but their use has not been

implemented as part of a pest management program. Many indigenous predators are known to prey on European corn borer eggs and larvae

(Showers et al. 1989). Coleomegilla maculata (DeGeer) (Coleoptera:

Coccinellidae) and Orius insidiosus (Say) (Hemiptera: Anthocoridae) have been identified as the most abundant insect predators in sweet corn

(Coll & Bottrell 1988). It is unlikely that predation from these natural enemies can suppress pest populations so that the percentage of damage-free ears ranges between 95 and 100-, which is the acceptable level for sweet corn grown for fresh market (Straub 1983). It is unknown whether the conservation of the generalist predators combined with other control measures may provide adequate control.

Supplemental foods can retain, attract, or increase fecundity of entomophagous insects. They could be useful when higher numbers of indigenous enemies are needed to prevent pests from increasing to damaging levels (Hagen 1986). Retaining or arresting can be achieved by providing a source of food to prevent natural enemies from leaving the crop when food sources are low or the target pest is not yet present.

In corn, there are a few cases where supplemental foods have been used experimentally to attract and retain natural enemies. Ewert and Chiang

(1966) reported an increase in total number of adults of three coccinellid species when a sucrose solution was sprayed in corn plants.

Schiefelbein and Chiang (1966) found that sucrose sprayed on corn plants concentrated populations of coccinellid and chrysopid adults which led to suppression of Rhopalosiphum maidis (Fitch) (Homopthera: Aphidae) populations. Increases in adult chrysopids and coccinellids were related to a decrease in European corn borer numbers when sugar and molasses were sprayed on corn plants (Carlson & Chiang 1973).

Attractants such as tryptophan have been added to supplementary foods to provide cues to predators or parasitoids that are attracted and then arrested in a crop that was otherwise unattractive (Hagen 1986). No studies were found that reported use of predator food attractants in combination with insecticides.

Microbial insecticides such as Bacillus thuringiensis var. kurstaki Berliner are used to selectively kill caterpillars, but these products have produced variable results when evaluated on sweet corn

(Raun 1963, McWorther et al. 1972, Lynch et al. 1977a, Lynch et al.

1977b, Dunkle £ Shasha 1988, McGuire et al. 1990). S. thuringiensis is more promising for control of fall armyworm and first generation

European corn borer, moderately promising for European corn borer in silks, and least promising for corn earworm (Bartels and Hutchison

1991). B. thuringiensis is not highly effective for controlling pests in silking corn due to the short time that these larvae feed in locations exposed to B. thuringiensis.

The objective of this study was to determine how the use of a predator food attractant affected abundance of indigenous predatory insects alone and when combined with B. thuringiensis products as well as conventional insecticides.

MATERIALS AND METHODS

Locations and Plantings.

Experiments were conducted in 1993, 1994, and 1995 at Ohio State

University research farms at Columbus (central Ohio) and at Fremont

(northern Ohio). Two plantings of sweet corn were established each year. The hybrid 'Seneca Horizon' was used for early plantings and the hybrid 'Lancelot' was used for late plantings. Early plantings were seeded as soon as soil was dry enough to be plowed. Late plantings were scheduled so that plants were likely to reach the silking stage during the time that second generation European corn borer was active. At Columbus, early plantings were seeded on 11

May 1993, 18 April 1994, and 19 April 1995; late plantings were seeded in 24 June 1993, 5 July 1994, and 14 June 1995. At Fremont, early plantings were seeded on 3 May 1993, 23 April 1994, and 16 May 1995; late plantings were seeded on 24 June 1993, 16 June 1994, and 22 June

1995.

Experimental Design and Treatments.

Presence or abscence of a predator food attractant were used as main plots in all trials. The main plots were always planted at least

153 meters apart so that the effect of the predator food attractant was isolated. In 1993 there were two medium-rate applications one week apart. In 1994 and 1995 low-rate sprays were delivered weekly. The increase in frequency was expected to provide a constant supply of food which would cause the predators to stay longer even if plants were not in the attractive stage of pollen shedding. For all years and plantings, food attractant sprays started within one week of when the first European corn borer egg mass was observed on the plants. For 1994 and 1995, sprays were stopped when fresh silk was present in 50 - or more of the plants.

Granular applications of permethrin and s. thuringiensis to whorl- stage corn, as well as thiodicarb sprays to silking corn, were common to all early plantings. Early plantings in 1994 and 1995 were identical and had more treatments than 1993. All late plantings had B. thuringiensis and thiodicarb spray treatments directed to the silks.

Late plantings in 1993 and 1994 had granular treatments of S. thurlnlglensls and permethrin granules in combination with the spray treatments. Treatments in early plantings, 1993. For the early planting, a

split-split plot design was used with two main plot treatments

replicated two times. Main plot replications were Columbus and Fremont,

and main plot treatments were presence or absence of the food

attractant, and presence or absence of carbofuran. Carbofuran is

commonly used by sweet corn growers for control of Chaetocnama

pulicularia Melsheimer (corn flea beetle), which vectors bacterial wilt.

A randomized complete block design was used to lay out four replications

of four subplot treatments within each main plot. Treatments were

granular B. thuringiensis in whorls, granular permethrin in whorls,

thiodicarb sprays during silking, and an untreated control. Sub-plot

size at Columbus was 7 m by 6 m with eight rows spaced 0.8 m apart; at

Fremont, plot size was 7 m by 9 m with 10 rows spaced 0.9 m apart.

Granular products were applied once on 23 June at Columbus and 24 June

at Fremont, and thiodicarb sprays were applied four times at Columbus

and two times at Fremont. Number of sprays was different at the two

locations due to higher European corn borer pressure at Columbus than at

Fremont.

Treatments in late plantings, 1993. Late plantings had a split

plot design with two main plot treatments replicated two times. Main

plot replications were Columbus and Fremont and main plot treatments

were presence or absence of the food attractant. Subplot treatments

and plot sizes were the same as those of the early planting. Granular

products were applied once on 3 August at Fremont and 9 August at

Columbus, and thiodicarb sprays were applied four times at Columbus and

five times at Fremont; differences in the number of applications were based on higher pest pressure at Fremont than at Columbus.

Treatments in early plantings, 1994 and 1995. A split plot design was used with two main plots replicated two times each. Main plot

replications were Columbus and Fremont, and main plot treatments were presence or absence of the food attractant. A randomized complete block design was used to lay out four replications of seven subplot treatments within each main plot. Treatments were granular B. thuringiensis to whorls, granular permethrin to whorls, thiodicarb sprays during silking, S. thuringiensis sprays during silking, 3. thuringiensis granules in whorls plus B. thuringiensis sprays during silking, permethrin granules in whorls plus thiodicarb sprays during silking, and an untreated control.

Plot size for both locations, years, and plantings was 7 m by 6 m with eight rows spaced 0.8 m apart at Columbus and 0.5 m at Fremont.

There was a 1.5 meter bare ground buffer between plots.

For early plantings, the predator food attractant was sprayed four times in 1994 and twice in 1995 for Columbus, and three times at Fremont in 1994 and two times in 1995. Differences in applications between locations and years were due to rain that prevented the delivery of the product on the planned schedule of first application within one week of first detection of egg masses and then weekly up to early silking. In

1994, granular products were applied once on 22 June at Columbus and 21

June at Fremont; in 1995 they were applied on 20 June at Fremont and 22

June at Columbus. Thiodicarb and B. thuringiensis were sprayed three times at both locations in 1994 and 1995.

Treatments in late plantings, 1994 and 1995. The late plantings also used a split plot design but with only three subplot treatments: B. thuringiensis sprays to silks, thiodicarb sprays to silks, and an untreated control. In 1994 B. thuringiensis granules and permethrin granules were applied in combination with B. thuringiensis sprays and thiodicarb sprays respectively. In 1995 granules were not applied because fall armyworm presence did not warrant their application.

The predator food attractant was sprayed five times in 1994 and twice in 1995 at Columbus; it was sprayed three times at Fremont for both years. Granular products were applied once in 1994, and were not applied in late plantings of 1995. In 1994 thiodicarb and B. thuringiensis sprays were applied four times at Columbus and six times at Fremont; in 1995 these products were applied three times at Columbus and four times at Fremont. Differences in the number of applications between Columbus and Fremont for both years were due to differences in pest pressure between the two locations, and heavy rains at Columbus that prevented application of products in a timely fashion.

Plot size for both locations, years, and plantings was 7 m by 6 m with eight rows spaced 0.8 m apart at Columbus and 0.9 m at Fremont.

There was a 1.5 meter bare ground buffer between plots.

Food attractemt and insecticides.

The food attractant used was Pred-Feed IPM6 (Custom Chemicides,

Fresno, California). Product ingredients are sucrose, lactose, alkyl aryl sulfonate, sodium ligno sulfonate, and cotton seed. Rates specified on the label are 4.5 to 11.25 kg/ha. Application rates were

7.8 kg/ha in 1993 and 4.5 kg/ha in 1994 and 1995. Because this product washes away with water, it was reapplied if it rained within 24 hours of application. The attractant was applied on the crop canopy at both locations with a hydraulic boom sprayer with flat fan nozzles (XR TeeJet

8008, Spraying Systems Co., Wheaton, XL) at a pressure of 0.043 kg/cm’.

Granular products applied to whorl-stage corn were permethrin

(Pounce 1.5G [granular], FMC Corp., Philadelphia, PA) at a rate of 12.2 kg/ha and Bacillus thuringiensis var. kurstaki Berliner (Dipel lOG,

Abbott Laboratories, North Chicago, XL) at a rate of 11.2 kg/ha. Foliar sprays used were thiodicarb (Larvin 80 OF [dry flowable], Rhone Poulenc

Ag Co., Research Triangle Park, NC) at a rate of 0.67 kg Al/ha (0.84 kg product/ha) and B. thuringiensis var. kurstaki (Dipel ES [emulsifiable solution], Abbott Laboratories) at a rate of 1.17 liters/ha. Carbofuran

(Furadan 15G) was applied to the soil at planting time at a rate of 9.7 kg/ha for flea beetle control but was used only on the early plantings of 1993.

10 Granular products were applied manually in the whorls when

European corn oorer egg masses were hatching in early plantings or when

fall armyworm damage to the whorl was first detected in late plantings.

Scheduling of thiodicarb and B. thuringiensis sprays during silking was based on guidelines used for control of European corn borer in Ohio.

These indicate a 5-7 day schedule if only European corn borer is present; if corn earworm is also present, then a 3-5 day schedule is used (Welty 1991) . Sprays were directed to the ears when fresh silk was observed in 50- or more of the plants. Sprays were delivered at

Columbus with a backpack sprayer (SOLO w Model 425, Urbana, IL) set at a pressure of 0.043 kg/cm2 and a hollow cone nozzle (TeeJet D3-23,

Spraying Systems Co., Wheaton, IL). Sprays at Fremont were applied with a hydraulic boom sprayer with drop pipes and four hollow cone nozzles

(TeeJet D3-25, Spraying Systems Co., Wheaton, IL) per row and a pressure of 0.043 kg/cm2.

Evaluations and statistical analysis. Pests and natural enemies were monitored weekly in 1993 and 1994 and twice per planting in 1995.

Direct observations were made on 10 plants randomly selected from the four middle rows of each plot. Natural enemies were counted on the entire plant throughout the season. Total numbers of o. insidiosus, c. maculata, and other coccinellid adults were added and averaged over two to seven sampling dates per planting to determine treatment differences.

Seasonal trends were also compared in untreated plots with and without the use of the food attractant.

Evaluation of European corn borer egg mass presence and damage by early instars was done by direct observation of the entire plant until the ears showed first silk. After silking began, damage was evaluated only in the ear area. Pheromone traps and blacklight traps were used for monitoring flight activity of European corn borer and corn earworm in order to determine the frequency of insecticide application during silking. At each location and for each species, three pheromone traps

11 were located at the borders of the sweet corn fields. One blacklight trap was used at each location.

Twenty five ears per plot were harvested and evaluated for damage and presence of key pest species. At Columbus, early plantings were harvested on 29 July 1993, 16 July 1994, and 18 July 1995; late plantings were harvested on 4 October 1993, 23 September 1994, and 22

August 1995. At Fremont, early plantings were harvested on 19 July

1993, 14 July 1994, and 27 July 1995; late plantings were harvested on

31 August 1993, 1 September 1994, and 22 August 1995. For 1993 early and late plantings, ears with any damage to kernels were considered not marketable. For the other two years, the standards were modified as follows to allow more flexibility in damage evaluation. Ear quality was categorized as marketable under liberal standards and marketable under strict standards. Strict standards would apply to sweet corn grown for the wholesale fresh market, while liberal standards would apply to processing corn and many retail farm markets. Ears considered as marketable by liberal standards were those that had kernel damage less than 2.5 cm from the tip of the ear and those with clean kernels but some damage to husks, silks, and/or shank. Ears considered not marketable were those with kernel damage more than 2.5 cm from the tip, ears with any damaged kernels in the middle or bottom of the ear, or ears in which a large caterpillar was found when ear husks were removed.

Ears considered as marketable by strict standards were only those ears with undamaged kernels, husks, silks, and shanks. Presence of European corn borer, corn earworm, fall armyworm, or sap beetle larvae was recorded.

Harvest data were subjected to analysis of variance, and a priori comparisons were made using mean comparisons with t statistics from a pooled error term. Least significant difference t tests were used for multiple mean comparison of data. Students' t test was used for the scouting data to determine differences between treatments with and

12 without use of the attractant. Data in percentages were transformed

using arcsin transformation (Steel & Torrie 1980). Analysis was done using the SAS statistical package (SAS Institute Inc. 1991).

RESULTS

Predator monitoring and seasoned, trends

During the three year study, the most commonly observed predatory insects were coccinellids, particularly C. maculata. In 1993, Scymnus

tarminatus (Blackburn) was frequently observed on tassels and silks, but its abundance in 1994 and 1995 was very low. Other coccinellid species found included Hippadamia convergens Guerin-Meneville and Coccinella septempunctata L. O. insidiosus was present in sweet corn plantings during the three years of this study; this predator was usually observed in the leaf axils and on the silks. Other groups occasionally observed include nabids, chrysopids, cantharids, and araneids.

O. insidiosus was more abundant in the late plantings than in the early ones. It started colonizing sweet corn crops in the early June and peak populations occurred just as corn was silking and pollen was being shed. For the late plantings, the peaks occurred late August, which was the same time at which second flight of corn borer was ending.

C. maculata was scarce in the early planting of 1993 at Columbus and Fremont. For the early plantings in 1994 and 1995, C. maculata peaked in early summer. For the late plantings populations were abundant at late summer time, when the second-generation corn borer egg masses and small larvae were reaching their peak.

Treatment effects on predators, early plantings.

Main plot factors. Analysis of variance showed that there was a significant attractant effect on C. maculata {P = 0.01; df = 1,111, F =

4.1) in the early planting of 1994. However, there was not a significant attractant effect on any of the other coccinellids (adults or larvae) or in o. insidiosus (Table 1.1) for either 1993 or 1995.

13 Sub-plot factors. Few significant differences were observed at the sub-plot level for some of the predators observed in the early plantings. No differences were observed in 1993.

In the early 1994 plantings (Table 1.1) differences were observed between sub-plots with the combination permethrin granules with thiodicarb sprays. Significantly less coccinellids and o. insidiosus adults were observed in these sub-plots than in the untreated controls.

Additionally, less coccinellid adults were observed in sub-plots that had received the combination of permethrin granules with thiodicarb sprays than in those that received B. thuringiensis granules. Likewise, less o. insidiosus adults were observed in plots that received the combination of permethrin and thiodicarb than in plots that received the combination ofB. thuringiensis or those that received the B. thuringiensis sprays alone (Table 1.1).

In the early 1995 plantings, the only differences observed were for O. insidiosus adults. Significantly lower numbers were found in sub-plots that received the combination permethrin-thiodicarb, than in those chat were left untreated, received S. thuringiensis granules, or the combination of S. thuringiensis formulations.

Two way interactions among factors.

Location by treatment Pre-planned comparisons of the interaction of location by treatment for early 1993 plantings showed some significant differences among treatments. Plots that received B. thuringiensis granules had significantly more C. maculata at Columbus (B

= 0.04), other coccinellid adults (P = 0.0001) at Fremont, coccinellid larvae (B = 0.02) at Columbus, and o. insidiosus at Columbus (B =

0.0001) and (B = 0.04) at both locations than plots that received thiodicarb sprays.

When the interaction of location by treatment was considered for the early plantings in 1994, there were no significant treatment differences at either location for coccinellid larvae, spiders, and

14 soldier beetles; no significant differences were found for O. insidiosus at Fremont. Significantly more c. maculata were present at Fremont in plots to which B. thuringiensis granules plus sprays were applied than in plots that received thiodicarb sprays (P = 0.041 or permethrin granules plus thiodicarb sprays (P = 0.0009). Same was true for O. insidiosus at Columbus which was present in significantly higher numbers in plots that received the combination B. thuringiensis granules plus sprays than in those that received thiodicarb sprays (P = 0.0001) or permethrin granules plus thiodicarb sprays (P = 0.0001). No significant differences were observed in 1995.

Three way interactions. For the three years of the study, pre­ planned comparisons of interactions of location by attractant by treatment were carried out to evaluate treatment differences with and without the use of the attractant. There were no significant (P s 0.05) differences in mean nut±ier of C. maculata per plant (Fig. 1.1) for treatments with and without the predator food attractant at the different locations for the first two years. However, in 1995 at

Columbus significantly more c. maculata were found in untreated plots that had received attractant applications than in untreated plots that had not iFig. 1.1).

For the early 1993 planting at Columbus, significantly more O. insidiosus were found in plots treated with 3. thuringiensis granules or permethrin granules without the attractant than in plots with the attractant (Fig. 1.2); no differences were observed at Fremont.

For the early plantings in 1994 and 1995 at Columbus, o. insidiosus was significantly more abundant in plots where B. thuringiensis granules, B. thuringiensis sprays (only 1994), or the combination of both, were applied along with the attractant, than in plots that had received the same treatments but no attractant

(Fig. 1.2). o. insidiosus abundance was lowest in plots where

15 thiodicarb sprays and the combination of permethrin granules with

thiodicarb sprays were applied.

Attractant effects on untreated subplots. Untreated controls in

subplots with versus without attractant were compared for presence of C.

maculata and o. insidiosus for the early plantings at both locations

(Figs. 1.3 and 1.4). Few were the statistically significant differences

observed. For c. maculata the only difference was observed on 18 June

1995, when significantly more c. maculata per plant (t = -2.1; df = 78;

P = 0.04) were observed at Columbus in subplots that received the

attractant than in those that did not (Fig. 1.3). Significantly more

(t= -2.2; df = 78;P = 0.03) O. insidiosus were observed at Fremont on 8

July 1993 in untreated subplots that had received the attractant than in

those that had not (Fig. 1.4).

Treatment effects on predators, late plantings.

Main plot factors. Analysis of variance indicated that there was

not a significant (P < 0.05) effect of attractant or location for any of

the beneficial arthropods monitored in this study in late plantings

(Table 1.2).

Sub-plot factors. As in the early plantings, few were the

significant differences observed at the sub-plot level. In 1993,

significantly less C. maculata were observed in plots where permethrin

granules had been applied than in those where B. thuringiensis granules

were applied or in plots that were left untreated (Table 1.2).

Additionally, less coccinellids were observed in plots where thiodicarb was sprayed than in untreated plots or plots where B. thuringiesis

granules were used. No differences were observed in 1994. In 1995,

significantly less C. maculata adults, coccinellids, and O. insidiosus

were observed in plots sprayed with thiodicarb than in plots treated with S. thuringiensis granules (Table 1.2).

16 Two way interaction among factors.

Location by attractant. No differences were observed for 1993 and

1994. In 1995, when the interaction of location by attractant was considered, the late planting at Columbus had significantly {P s 0.01) more coccinellids in plots where the attractant had been sprayed over those where it had not. No significant differences were found for o. insidiosus at either location.

Location by treatment. For the late planting of 1993 at Columbus,

C. maculata was significantly more abundant in plots that received B. thuringiensis granules than in plots that received permethrin granules

(P = 0.0001) or plots that received thiodicarb sprays (P = 0.001). At

Fremont coccinellid adults other than c. maculata were significantly more abundant in B. thuringiensis granules plots than in thiodicarb sprays (P = 0.04) or the permethrin granule (P = 0.04) plots. The same vias observed for coccinellid larvae which were significantly more abundant in B. thuringiensis plots than in thiodicarb sprays (P =

0.0001) or permethrin granule (P = 0.0004) plots. O. insidiosus abundance at Fremont was significantly (P = 0.02) higher in plots

treated with B. thuringiensis granules than in plots sprayed with thiodicarb.

For the late planting in 1994, significantly (P = 0.008) fewer coccinellids were present at Columbus in plots that had been treated with permethrin granules plus thiodicarb sprays than those treated with

B. thuringiensis granules plus sprays. The same was true for coccinellid larvae at Fremont (P = 0.02) and O. insidiosus at Columbus

(P = 0.0001) .

For the late 1995 plantings at both Columbus and Fremont, significantly (P s 0.05) less coccinellids and O. insidiosus were found in plots where thiodicarb sprays were used than in plots treated with B. thuringiensis sprays or left untreated.

17 Three way interactions. When the interactions of location by

attractant by treatment were compared a few differences were found. For

the late plantings no significant differences were observed in mean

number of C. maculata per plant (Fig. 1.5) between treatments with or

without the attractant.

For the late 1994 planting at Columbus, significantly (P s 0.05)

more coccinellids were found in plots that had used permethrin granules

with the attractant than in plots without the attractant. For the late

planting at Columbus, O. insidiosus was present in significantly higher

numbers in untreated plots that had received the attractant than in

those that had not (Fig. 1.6), but in significantly lower numbers in

plots that had used 8. thuringiensis granules and sprays with the

attractant than in those that had not (Fig. 1.6).

Attractant effects on untreated subplots. Untreated controls in

subplots with versus without attractant were compared for presence of C. maculata (Fig. 1.7) or O. insidiosus (Fig. 1.8) for the late plantings

at both locations. In the late 1994 plantings, the trend was to have more c. maculata on those plots that had received the attractant chan on plots that had not (Fig. 1.7); however, no significant differences were

observed. O. insidiosus was significantly (t = -2.6; df = 78; P = 0.01) more abundant only on 18 August in the late 1994 planting at Columbus

(Fig. 1.8) in plots that had received the attractant than in chose Chac

had noC. For Che late 1995 planting at Columbus, significantly

(t = -3.2; df = 78; P = Ü.UÜ3) more C. maculata were observed on 10

August in untreated plots that received applications of the food

attractant than in those that had not (Fig. 1.7).

Pest monitoring.

Traps. Blacklight and pheromone traps were useful in detecting

flight activity for European corn borer. These traps showed that for

the three years, European corn borer population density was higher at

Fremont than at Columbus. This is likely due to higher concentration of

18 corn fields in northern Ohio, whereas traps at Columbus were in a more urban environment. For the three years, first trap catches were observed mid to late May, and peaks for first generation moths were usually observed in early to mid June. Second generation usually peaked in mid August. In 1993 and 1995 a third generation developed; the third peak was observed in mid-September for both locations.

Pheromone traps detected corn earworm activity which usually peaked in early to mid September.

Scouting. One of the serious concerns raised when predator food attractants are used is the possibility of increasing numbers of pests such as nitidulids, chrysomelids and cicadellids (C. Ahrendes, unpublished data, Clovis, California), as well as the adults of the lepidopteran pests that attack sweet corn. Mo significant increases were found when numbers of the first three groups were compared between plots where treatments were applied in combination with the attractant and those where no attractant had been used. However, when presence of

European corn borer egg masses as well as leaf and tassel damage was documented over the five to seven weeks before silking, there were few cases in which significant differences existed between untreated plots that had received the attractant and those that had not. Although differences were statistically insignificant the general trend was of more pests or damage in plots that had received the attractant than in those that had not.

Treatment effects at haxvest, early plantings.

Main plot factors. The predator food attractant did not have a significant effect on ear quality at harvest time (Table 1.3) for any year whether strict or liberal standards of marketability were used.

For the 1993 early planting, there was no carbofuran or location effect on the percentage of marketable ears under either liberal or strict standards (Table 1.3). In the early 1994 planting, significantly (P s

0.05) more marketable ears were harvested at Columbus than at Fremont

19 (Table 1.3). For 1995, the percentage of marketable ears was significantly higher at Fremont.

Sub-plot factors. In the early planting of 1993, when using strict standards for marketability, there were no significant differences between permethrin granules and thiodicarb sprays. In this planting, significantly fewer marketable ears were harvested from untreated subplots and subplots where 3. thuringiensis granules were applied than from those where the thiodicarb sprays were used (Table

1.3). When using the liberal standards, subplots with thiodicarb sprays had significantly more marketable ears than any of the other treatments

(Table 1.3). For early plantings in 1994 there were no significant treatment differences when strict standards were used. However, when liberal standards were used, thiodicarb sprays had a significancly higher percentage of marketable ears than the uncreated control. For the early plantings in 1995 combinations of permethrin granules with thiodicarb sprays rendered significantly more marketable ears than the untreated control under both standards of marketability (Table 1.3).

Two way interaction among factors.

Treatment by attractant. None of the treatments provided significantly better control wnen useo in comoination witn the attractant than when used without it.

Treatment by locality. There were differences within each locality for percentage of marketable ears under strict and/or liberal standards. For the early 1993 planting at Columbus, the thiodicarb spray treatment had significantly more marketable ears than the B. thuringiensis granules treatment for both liberal and strict standards, but was not significantly different from the untreated treatment (Table

1.5). Under the liberal standard, more marketable ears were harvested from plots where thiodicarb sprays were applied than from plots where permethrin granules were applied (Table 1.5). For the early 1993 planting at Fremont, more marketable ears were harvested from

20 thiodicarb spray plots than from any of the other treatments plots, when the liberal standards were used. When strict standards were used, no differences were observed among thiodicarb sprays, permethrin granules, or B. thuringiensis granules (Table 1.5).

For early 1994 plantings, there were no significant treatment differences at Columbus. At Fremont, significantly more marketable ears were harvested from thiodicarb spray plots than from B. thuringiensis spray plots and untreated control plots when using liberal or strict marketability standards; when using strict standards these plots were also significantly different from the permethrin granule plots (Table

1.5) .

For the early 1995 planting, no significant differences were observed among treatments at Fremont (Table 1.5). At Columbus, significantly fewer marketable ears were harvested from B. thuringiensis spray plots and thiodicarb spray plots than from plots where either permethrin or S. thuringiensis granules had been used, or plots where the combination B. thuringiensis granules and sprays or permethrin granules and thiodicarb sprays had been used (Table 1.5); this could be due to lack of control of early instars of the first generation whorl feeding European corn borer larvae.

Location by attractant. Mo significant differences were observed in

1993 and 1994. In 1995, significantly fewer marketable ears were harvested at Fremont from plots that received the attractant than from those that had not.

Three way interactions.

Location by treatment by attractant Due to differences in pest pressure at both localities, pre-planned comparisons were carried out for the interaction of location by treatment by attractant, which allowed comparison of treatment performance with and without the use of the attractant within each locality. Reported are only those categories for which significant differences were observed (Table 1.7), For the

21 early 1993 planting at Columbus, significantly more marketable ears

(liberal standards) were harvested from plots that had received

thiodicarb sprays alone than from those that had received it combined

with the attractant (Table 1.7}. For the early planting in 1994 at

Fremont, using strict marketability standards, significantly more

marketable ears were harvested where treatments were used alone, than

when the same treatments were used in combination with the attractant

for thiodicarb sprays, combination of B. thuringiensis granules plus

sprays, and combination permethrin granules and thiodicarb sprays

(Table 1.7).

For the early planting in 1995 significantly more marketable ears

(strict standards) were harvested at Columbus when B. thuringiensis

granules and sprays were combined with the attractant than when they

were not. The opposite occurred at Fremont where fewer marketable ears were harvested from plots that had used B. thuringiensis and sprays in

combination with the attractant than from plots that had not used the

attractant (Table 1.7); the same was observed for thiodicarb spray plots and the untreated control.

Treatment effects at hairvest, late plantings.

Main plot factors. .A.S in the early plantings, the predator food

attractant did not have a significant effect on ear quality at harvest

time (Table 1.4) for any year. There was no significant location effect

for 1993. For the late planting of 1994 significantly (P < 0.05) more

marketable ears were harvested at Fremont than at Columbus, due mainly

to significantly higher density of fall armyworm and corn earworm at

Columbus (Table 1.4). For 1995, percentage of marketable ears was

significantly higher at Fremont (Table 1.4). Damage in the late

planting was due mainly to European corn borer (Table 1.4) which was

found in significantly higher numbers in ears harvested from plots that

had been sprayed with the attractant than from those that had not.

22 Sub-plot factors. In the late planting of 1993, significantly

more marketable ears were harvested from subplots treated with

thiodicarb sprays than from any of the other subplots. The late

planting in 1994 showed no significant difference among treatments, but

there was a large numerical difference, in which 93% of ears harvested

from subplots where the conventional insecticides were used were clean, as compared with only 68% of ears harvested from subplots where the

combination of B. zhuringiansis products was used (Table 1.4).

Significantly more marketable ears were harvested in 1994 from Fremont

than from Columbus, and low numbers of damaged ears at Fremont widened the margin to detect statistical differences among treatments. For the

1595 late planting, when treatments included sprays at silking but no granules in whorls, significantly more marketable ears were harvested

from subplots treated with thiodicarb sprays or with S. thuringiensis sprays than from subplots left untreated (Table 1.4). Significantly more European corn borer larvae were found in ears harvested from B.

thuringiensis subplots than in ears harvested from thiodicarb plots.

Although not significantly different, 20 - fewer marketable ears were harvested from B. thuringiensis plots than from thiodicarb sprays plots

(Table 1.4).

Two way interactions among factors.

Treatment by attractant. As in the early plantings, none of the treatments provided better control when used in combination with the attractant than when used without it.

Treatment by locality. For late 1993 plantings at Columbus and

Fremont, more marketable ears were harvested from plots where thiodicarb sprays had been applied than from any of the other treatments (Table

1.6). For the late planting in 1954 at Columbus, significantly (P s

0.05) more marketable ears were harvested from plots where the combination of permethrin granules and thiodicarb sprays had been used than from the untreated plots and the combination B. thuringiensis

23 granules and sprays plots (Table 1.6); B. thuringiensis granules plots also had significantly more marketable ears than the untreated plots.

At Fremont, no significant differences were observed for the late planting in 1994 when comparing the conventional with the microbiological controls (Table 1.6).

For the late planting in 1995, there were no significant differences between thiodicarb sprays or B. thuringiensis sprays at

Columbus. At Fremont, more marketable ears were harvested from B. thuringiensis plots than from untreated plots. On the other hand, less marketable ears were harvested from the B. thuringiensis plots than from the thiodicarb spray plots.

Location by attractant. For the late planting in 1993, there was a significant interaction of location by attractant for the percentage of marketable ears using strict standards, and it was found that at

Fremont there were significantly (PsO.05) more clean ears harvested from plots that had not received the attractant than from plots that had. In contrast, significantly (P<0.01) fewer marketable ears were harvested at

Columbus from plots that had not received the attractant than from those that had.

Three way interactions among factors. Significantly more marketable ears (liberal standards) were harvested at Columbus from plots that had received the combination B. thuringiensis treatment with the attractant than from those that had received the combination without the attractant (Table 1.7). The same was true for the untreated plots.

DISCUSSION

Supplementary foods and predator attractants have been long regarded as key factors in enhancement of the effectiveness of biological control agents (Hagen 1950, Hagen 1986). Previous reports have shown significant increases in number of adults of predatory insects when these products have been used in crops such as soybeans, potatoes, and corn (Carlson & Chiang 1973, Hagen & Bishop 1979).

24 Schiefelbein and Chiang (1956) and Carlson and Chiang (1973) showed that there was an increase in the chrysopid population when 10* sucrose sprays were used on sweet corn and that there was an increase in coccinellids, although not significant. In my experiments, there was a trend towards higher density of C. maculata and other coccinellids in plots that received applications of the food attractant. However, the numbers of natural enemies were still low, and their density did not increase to a level at which they could provide commercially acceptable levels of control of European corn borer. Sparks et al. (1966) found that predators can be very effective at consuming European corn borer egg masses and small larvae, but can not be relied on to affect borer numbers from year to year. While my study addressed how predators were affected by the use of different insecticidal products, no direct measurement of predation was obtained. Rather, the cumulative impact of the natural enemies was determined at harvest time, when cleaner ears in plots treated with the attractant would have been assumed to be related to predator performance. In the 1995 early planting at Fremont (Table

1.7), 94 * marketable ears (strict standards) were harvested from plots that used the attractant in combination with B. thuringiensis granules and sprays, whereas only 79- marketable ears were harvested from plots that had used s. thuringiensis granules and sprays without the attractant. Similar results were obtained for the 1994 late planting at Columbus, where 55 - marketable ears (liberal standards) were harvested from plots that had use the combination of 8. thuringiensis granules and sprays with the attractant, while only 25t marketable ears were harvested from plots that had used the same combination without the attractant. In contrast, some of the treatments in the early 1994 and early 1995 plantings at Columbus had significantly fewer marketable ears when combined with the attractant than when applied alone (Table 1.7).

Different rates of the attractant could affect the number of predatory insects in the field as well as their rate of egg deposition

25 {Hagen 1976). Differential effects of rates of the predator food attractant on predator populations were not studied within this experiment. However, further research would be useful on optimal use of this product. Because the attractant slightly increased pest presence and damage at certain crop stages, increased rates of the attractant could enhance this negative effect.

O. insidiosus overwinters as an adult and colonizes corn fields in late spring or early summer; its peak nymph population has been reported to occur just as corn is silking and pollen is being shed, which in my late plantings was the same time at which second flight of

European corn borer was ending. Because it prefers young silking corn

(Barber 1936, Coll & Bottrell 1991) it has been suggested that its impact as a predator is higher on consumption of corn earworm eggs than of European corn borer. In contrast, Reid (1991) determined that a density of 12 adults per plant can cause a mortality of 16- (on ears) and 80' (on leaves) of European corn borer when plants were caged and other predators eliminated. During 1995, there were much higher numbers of O. insidiosus per plant than in prior years; density reached an average of 9 per plant when corn was silking. This naturally high density must have an impact on the borer population, but further experimentation is needed to determine the impact of this predator on

European corn borer populations under field conditions.

According to Andow (1990), C. maculata is the most important predator of European corn borer egg masses in Minnesota. This coccinellid was most abundant from late June to mid-August, when the second generation corn borer egg masses and small larvae reach their peak, making it an ideal candidate for conservation and augmentation practices. In this experiment it was found that its density was usually numerically higher in plots that used the attractant than in those that did not; this was true as well for all other Coccinellidae observed.

This species is particularly suitable for manipulation by predator food

26 attractants because it is able to use pollen as a food source for up to

50^ of its diet (Hoffman £ Frodsham 1993).

Because sweet corn in Ohio is produced mainly for the fresh market, tolerance to any damage is very low. If predator conservation tactics are to be part of a pest management program, it is critical to determine which insecticidal products can provide acceptable pest control and have the least impact on the beneficial arthropods. A combination of B. thuringiensis granules and sprays provided adequate control of early generation European corn borer. Permethrin granules also gave adequate control and did not adversely affect the numbers of natural enemies as much as thiodicarb sprays did. Because silk treatments alone have proven not to be enough to reach a desirable 95 - to 100' damage-free ears for the fresh market (Straub 1977), granular insecticides applied to the whorl show more promise than sprays applied during silking for effective control of first generation European corn borer (Straub 1983). For second generation, the level of control of the combination B. thuringiensis granules in the whorl and sprays to the silks was intermediate between the conventional insecticide and the untreated control. For this generacion, che best control still lies with a conventional product, which is also the harshest on the natural enemy population. In my experiments, there were no significant differences between the use of combined permethrin granules and thiodicarb sprays and the use of thiodicarb alone to the silks. Second generation corn borers are usually controlled only at the silking stage because oviposition occurs as pollination begins and larvae usually start feeding in the ear region.

In conclusion, the use of S. thuringiensis granules and sprays for conservation of natural enemies appears to be a fair alternative for control of first generation European corn borer. Conventional products such as thiodicarb sprays are presently the best control measure for second generation of European corn borer. The potential for better

27 performance of B. thuringiensis products may change with different formulation types, or on the use of transgenic corn, where the B. thuringiensis toxins are already incorporated into the plant. The conservation and augmentation of predatory arthropods with the predator food attractant was not achieved at the intensity tested and did not contribute to higher levels of biological control.

28 Table 1.1. Effect of treatments on beneficial arthropods (mean number per plant averaged over all sampl ing dates ) in early sweet corn plantings at Columbus and Fremont, Ohio in 1993, 1994, and 199Ï Treatment ColeomegiJJa Other Total adult Coccinellidae Orius waculsta Coccinellidae Coccinellidae larvae insidiosus adults (A) adults (B) (A + B) adults 1993 Main plot Attractant 0.004a 0.1a 0. la 0.004a 0.06a No Attractant 0.004a 0.08a 0.08a 0.005a 0.08a Main plot Carbofuran 0.003a 0.09a 0. la 0.003a 0.06a No Carbofuran 0.005a 0.09a 0.09a 0.006a 0.08a Sub-plot Untreated control 0.004a 0. la 0.1a 0.007a 0.09a B. thuringiensis 0.006a 0.1a 0. la 0.007a 0.09a granules Permethrin granules 0.004a 0.08a 0.08a 0.002a 0.06a Thiodicarb sprays 0.001a 0.03a 0.03a 0.001a 0.02a Location Columbus 0.004a 0.02a 0.02a 0.006a 0.08a Fremont 0.004a 0.2a 0.2a 0.003a 0.05a 1994 Main plot Attractant 0.05a 0.02a 0.07a 0.001a 0.13a No Attractant 0.04b 0.01a 0.05a 0.003a 0.09a Sub-plot Untreated control 0.05ab 0.03a 0.08a 0.002ab 0.16a B. thuringiensis 0.06ab 0.02ab 0.08a 0.0b 0.14ab granules Permethrin granules 0.03ab 0.006b 0.04ab 0.0b 0.09ab B. thuringiensis sprays 0.05ab O.Olab 0.06ab 0.01a 0.16a Thiodicarb sprays 0.04ab 0.02ab 0.05ab 0.002ab 0.06ab B. thuringiensis 0.07a O.Olab 0.08a 0.002ab 0.15a granules tsprays Permethrin granules + 0.02b O.Olab 0.03b O.OOlab 0.03b thiodicarb sprays Location Columbus 0.04b 0.01a 0.06a 0.001a 0.18a Fremont 0.05a 0.01a 0.07a 0.004a 0.04a Table l.l.(cont.)* Effect of treatments on beneficial arthropods (mean number per plant averaged over all sampling dates ^) in early sweet corn plantings at Columbus and Fremont, Ohio in 1993, 1994, and 1995.______Treatment Coleomegilla Other Total adult Coccinellidae O n u s maculata Coccinellidae Coccinellidae larvae insidiosus adults (A) adults (B) (A + B) adults 1995 Main plot Attractant 0.01a 0.02a 0.04a 0.004a 0.12a No Attractant 0.01a 0.01a 0.03a 0.005a 0.11a Sub-plot Untreated control 0.03a 0.04a 0.07a 0.03a O.lGab B. thuringiensis 0.025a 0.02a 0.04abc 0.0a 0.15ab granules Permethrin granules 0.003a 0.003a O.OOeic 0.0a 0.04c B. thuringiensis 0.025a 0.02a 0.04abc 0.006a 0.13abc sprays Thiodicarb sprays 0.009a 0.04a 0.05ab 0.0a O.llbc B. thuringiensis 0.0a 0.009a 0.009bc 0.0a 0.22a w granules +sprays o Permethrin granules + 0.0a 0.003a 0.003c 0.0a 0.03c thiodicarb sprays Location Columbus 0.02a 0.01a 0.04a 0.01a 0.15a Fremont 0.005a 0.02a 0.03a 0.0a 0.09a ^Within each column, means are separated by main plot, sub-plot, and location; for each of these, means followed by different letters are significantly different from each other (PsO.05), by least significant difference t test. Table 1,2. Effect of treatments on beneficial arthropods (mean number per plant averaged over all " ings at Columbus and Fremont, Ohio in 1993, 1994, and 1995. Treatment Coleomegilla Other Total adult Coccinellidae Orius maculata Coccinellidae Coccinellidae larvae insidiosus adults (A) adults (B) (A + B) adults 1993 Main plot Attractant 0.07a 0.08a 0.2a 0.04a 0. 5a No Attractant 0.07a 0.07a 0.1a 0.08a 0. 4a Sub-plot Untreated control 0.11a 0. 07a 0.2a 0.07a 0.4a B. thuringiensis granules 0.09a 0.09a 0.2a 0.09a 0. 5a Permethrin granules 0.02b 0.07a 0.09b 0.04a 0.5a Thiodicarb sprays 0.04ab 0.07a 0. lb 0.03a 0. 4a Location Columbus 0. la 0.07a 0.2a 0.04a 0. 4a Fremont 0. la 0.08a 0.1a 0.08a 0.5a 1994 Main plot to Attractant 0.04a 0.02a 0.07a 0.03a 0.39a No Attractant 0.04a 0.02a 0.06a 0.02a 0.38a Sub-plot Untreated control 0.05a 0.03a 0.08a 0.05a 0. 5a B. thuringiensis granules 0.04a 0.01a 0.07a 0.03a 0.5a tsprays Permethrin granules + 0.03a 0.03a 0.04a 0.004a 0.1a thiodicarb sprays Location Columbus 0.06a 0.04a 0.1a 0.02a 0. 6a Fremont 0.02b 0.01a 0.03b 0.03a 0.2b Table 1.2. Effect of treatments on beneficial arthropods (mean number per plant averaged over all sampling dates in late sweet corn plantings at Columbus and Fremont, Ohio in 1993, 1994, and 1995. Treatment Coleomegilla Other Total adult Coccinellidae Orius macula ta Coccinellidae Coccinellidae larvae insidiosus adults (A) adults (B) (A + B) adults 1995 Main plot Attractant 0.3a 0.3a 0.6a 0.2a 3. 6a No Attractant 0.2a 0. la 0.3a 0. la 3.5a Sub-plot Untreated control 0.3a 0.2ab 0. 5ab 0.2a 3.9a B. thuringiensis sprays 0.3a 0.3a 0. 6a 0.2a 3.9a Thiodicarb sprays 0.2a 0. lb 0.4b 0.1a 3.0b Location Columbus 0.3a 0.3a 0. 6a 0. Oa 3.9a ^Fremont 0.2a 0.1a 0.3a 0.3a 3.3a

followed by different letters are significantly different from each other (PsO.05), by least significant difference t test. w Table 1.3. Percentage marketable ears by strict and Jiberal standards, and percentage of ears infested with European corn borer (ECB) , corn earworm (CEW) , and fall armyworm (FAW) at harvest in early sweet corn plantings in 1993, 1994, and 1995. Treatment • Market'.able ears t Infe sted ears Strict Liberal ECB CEW FAW standards standards 1993 Main plot Attractant 83.5a 86. 6a 0.05a 2.5a 0 No Attractant 84.9a 87.8a 0.04a 3.7a 0 Main plot Carbofuran 85.3a 88. Oa 0.03a 3.9a 0 No Carbofuran 83.0a 86. 5a 0.07a 2.4a 0 Sub-plot Untreated control 82.2b 86.7a 0.1a 2.6ab 0 B. thuringiensis granules 81.2b 83.8a 0.05a 4.2a 0 Permethrin granules 84.6ab 85. 6a 0.003a 5. 6a 0 Thiodicarb sprays 88.3a 92.9b 0.06a 1.1b 0 Location w 00 Columbus 84.8a 86.2a 0,01a 1.7a 0 Fremont 83.6a 88.2a 0.1a 4.9a 0 1994 Main plot Attractant 93.8a 97. 7a 0.5a 0. 8a 0.04a No Attractant 97.7a 98.6a 0.3a 0.5a 0. Oa Sub-plot Untreated control 92.4a 94.8b 1.7a 2.9a 0.01a B. thuringiensis granules 95.6a 98.4ab 0. 7ab 1. lab 0. Oa Permethrin granules 97.0a 98.7ab 0, lab 0.1b 0.01a B. thuringiensis sprays 93.0a 97.6ab 1. Oab 0.1b 0.03a Thiodicarb sprays 99.1a 99.6a 0.06b 1.2ab 0.01a B. thuringiensis granules t sprays 95.0a 98.6ab 0, 4ab 0. 8ab 0. Oa Permethrin granules + thiodicarb sprays 97.4a 98.2ab 0.01b 0.02b 0.0a Location Columbus 99.0a 99. 4a 0.08b 2,1a 0.0a Fremont 91.0b 96.4b 1.0a 0.02b 0.04a Table 1.3 (cont.). Percentage marketable ears by strict, and liberal standards, and percentage ears infested with European corn borer (ECB) , corn earwocm (CEW), and fall armyworm (FAW) at harvest in early sweet corn plantings in 1993, 1994, and 1995. Treatment ' Marketable ears 'I Infested ears Strict Liberal ECB CEW E’AW standards standards 1995 Main plot Attractant 90.0a 95.2a 0. 8a 2.9a 0 No Attractant 94.1a 93.2a 0.5a 0.1b 0 Sub-plot Untreated control 84.7b 84.7b 2.9a 1.9a 0 B. thuringiensis granules 92.Gab 94.2ab 1. lab 1. la 0 Permethrin granules 96.5ab 97.1a 0.1b 1.3a 0 B. thuringiensis sprays 92.lab 92.lab 0.1b 0.7a 0 Thiodicarb sprays 93.Oab 93.Oab 1.2ab 1. 5a 0 B. thuringiensis granules + sprays 94.2ab 95.3ab 0. Bab 1.0a 0 Permethrin granules + thiodicarb sprays 93.1a 98.7a 0.02b 0.4a 0 Location w Columbus 83.6b 86.7b 2.1a 1.6a 0 Fremont 97.7a 98.7a 0.02b 0.7b 0 Within each column means are separated by main plot, sub-plot, and location; for each of these, means followed by different letters are significantly different from each other (P s 0.05), by least significant difference t test. Table 1.4. Percentage marketable; e;ars by strict and liberal standards, and percentage ears infested with European corn borer (ECB), corn earworm (CEW), and fall armyworm (FAW) at harvest of late sweet corn plantings in 1993, 1994, and 1995. Treatment r Marketable ears r. Infested ears Strict Liberal ECB CEW FAW standards standards 1993 Main plot Attractant 20.8a 24.8a 21.2a 10.6a 2.3a No Attractant 18.4a 20.7a 26.6a 4. 3a 3.2a Sub-plot Untreated control 10.3b 12.7b 37.0a 9.4a 4. la B. thuringiensis granules 6.7b 9.6b 25.6ab 9.8a 4.9a Permethrin granules 9.9b 12.4b 28.2ab 11.3a 2.9a Thiodicarb sprays 64. 4a 66. 6a 8.0b 1. 5a 0. 5a Location Columbus 29.2a 36.0a 39.3a 0.5b 0.2a Fremont 10.7a 10.7a 9.5a 23.3a 8.8a 1994 w en Main plot Attractant 72.5a 88.3a 5.4a 2.8a 9.9a No Attractant 70.1a 79.9a 4.2a 1.3a 13.3a Sub-plot Untreated control 45.9a 66,2a 19.0a 3.8a 19.2a B. thuringiensis granules + sprays 67.7a 81.5a 2.4b 3.0a 19.0a Permethrin granules + thiodicarb sprays 93.1a 97.6a 0.3b 0.3a 1.9a Location ColuiTibus 30.4b 50.0b 3.6a 7.3a 36.6a Fremont 98.0a 99.9a 6.2a 0.01b 0.2b 1995 Main plot Attractant 41.2a 57.0a 40.7a 0.6a 0.2a No Attractant 44.9a 57.1a 33.7b 2.1a 0. Oa Sub-plot Untreated control 16.6b 27.6b 66.9a 2.4a 0.1a B. thuringiensis sprays 47.3a 61.2a 38.0a 1.2ab 0.06a Thiodicarb sprays 67.7a 80. 8a 11.4b 0.5b 0.02a Location Columbus 19.5b 35.8b 51.8a 2.8a 0.01a Fremont 68.3a 77.0a 23.7b 0.3b 0.2a within each column means are separated by main plot. sub-plot, and location ; for each of the followed by different letters are significantly different from each other (P <. 0.05) , means by least significant difference t: test. Table 1.5. Interaction of location by t reatment for percentage marketable ears and percentage ears infested with European corn borer (ECB), corn earworm (CEW) , and fall armyworm (FAVJ) at harvest of early sweet corn in 1993, 1594, and 199 5. Treatment - Marketable ears Infested ears Strict Liberal ECB CEW FAW standards standards 1993 Columbus Untreated control 8 4. 3al:' 86.lab 0.02a 1.0a 0 B. thuringiensis granules 81.1b 81.1b 0.0a 3. 5a 0 Permethrin granules 83.8ab 84.9b 0. Oa 3.0a 0 Thiodicarb sprays 89.4a 91.8a 0.06a 0.4b 0 Fremont Untreated control 79.9b 85.3b 0.2a 5. Oab 0 B. thuringiensis granules 81.3ab 86.3b 0.18ab 4, 9ab 0 Permethrin granules 85.4ab 86.3b 0.02b 8. 8a 0 Thiodicarb sprays 87.3a 93.9a 0.06ab 2.0b 0 1994 Columbus w CTi Untreated control 98.1a 98.4a 0.9a 0 98.1a B. thuringiensis granules 97.8a 99.7a 0.06ab 0 97.8a Permethrin granules 99.6a 99.6a 0.06ab 0 99.6a B. thuringiensis sprays 97. 6a 99.0a 0.06ab 0 97.6a Thiodicarb sprays 98.9a 98.9a 0.06ab 0 98.9a B. thuringiensis granules + sprays 99.7a 99.7a 0.0b 0 99.7a Permethrin granules + thiodicarb sprays 99.7a 99.7a 0.0b 0 99.7a Fremont Untreated control 83.2b 89.1b 2.7a 0 83.2b B. thuringiensis granules 92.7ab 96.2ab 2.1a 0 92.7ab Permethrin granules 91.9b 97.3ab 0.25b 0 91.9b B. thuringiensis sprays 86.0b 95.7b 2.9a 0 86.0b Thiodicarb sprays 99.3a 99.9a 0.06bc 0 99.3a B. thuringiensis granules + sprays 85.1b 96.5ab 1. 5ab 0 85.1b Permethrin granules + thiodicarb sprays 92.Bab 95.2b 0.06bc 0 92.Bab Table 1.5 (cont.). Interaction of location by treatment for percentage marketable ears and percentage ears infested with European corn borer (ECB), corn earworm (CEW), and fall armyworm (FAW) at harvest of early sweet corn plantings in 1993, 1994, and 1995. Treatment ^ Marketable ears ï Infested ears Strict Liberal ECB CEW FAW standards standards 1995 Columbus Untreated control 61.4c 67.4c 6. 9a 3.1a 0 B. thuringiensis granules 84.lab 88.6ab 3.2a 2.1a 0 Permethrin granules 94.0a 95.0a 0.6b 1. 5a 0 B. thuringiensis sprays 14.0bc 80.5b 0.5b 1.2a 0 Thiodicarb sprays 76.Ibc 81.1b 4. 8a 1. 6a 0 B. thuringiensis granules + sprays 88.lab 89.lab 3. la 0.7a 0 Permethrin granules + thiodicarb sprays 95.4a 96.0a 0.06b 1.1a 0 Fremont Untreated control 92. 3a 96.2a 0. 6a 0.9a 0 B. thuringiensis granules 98.0a 93.0a 0.06a 0. 5a 0 Permethrin granules 98.4a 93.5a Oa 1.0a 0 00 B. thuringiensis sprays 97. 4a 93.8a Oa 0. 4a 0 Thiodicarb sprays 97. 6a 99.3a Oa 1. 4a 0 B. thuringiensis granules + sprays 98.2a 93.8a Oa 1.2a 0 Permethrin granules + thiodicarb sprays 99.6a 99.9a Oa 0.06a 0

letters are significantly different from each other (/> s0.05), means differences based on t statistics from a pooled error term. Table 1.6. Interaction of location by treatment for percentage marketable ears and percentage ears infested with European corn borer (ECB), corn earworm (CEW), and fall armyworm (FAVJ) at harvest time of late sweet corn plantings in 1993, 1994, and 1995, Marketable ears s Infested ears Strict Liberal ECB CEW FAW standards standards 1993 Columbus Untreated control 14.0b 19.3b 60. 6a 0. la 0 B. thuringiensis granules 20.1b 23.7b 43.4b 0. 5a 0 Permethrin granules 21.3b 27.9b 44.8b 1,3a 0 Thiodicarb sprays 66. Oa 70.6a 12.7c 0. 6a 0 Fremont Untreated control 6.2b 6.2b 13.6a 34.3a 0 B. thuringiensis granules 0.06c 0. Ic 9. lab 32.0a 0 Permethrin granules 1. 6bc 1. 6bc 13. la 32.6a 0 Thiodicarb sprays 61.0a 63.1a 4.0b 2.7b 0 1994 Columbus w 00 Untreated control 7.8c 16.3c 13.8a 13.0a 54.6a B. thuringiensis granules + sprays 17.5b 39.7b 1.7b 11.9a 55. 4a Permethrin granules + thiodicarb sprays 74.2a 90.7a 0.4b 1,0b 7.5b Fremont Untreated control 87.3b 99.3a 24.9a 0.06a 0.6a B. thuringiensis granules + sprays 99.5a 100.Oa 3.3b 0.0a 0. 4a Permethrin granules + thiodicarb sprays 100.0a 100.0a 0.3b 0.0a 0. Oa 1995 Columbus Untreated control 1.8b 9.7b 84.0a 3.8a 0. Oa B. thuringiensis sprays 28.1a 44.4a 49.0b 2.7a 0.06a Thiodicarb sprays 39.2a 59.4a 21.0c 1.8a 0. Oa Fremont Untreated control 41.8c 50. 5c 46.9a 1.2a 0.5a B. thuringiensis sprays 66.9b 76.7b 27.6b 0.3a 0.06a Thiodicarb sprays 90.5a 95.4a 4. 5c 0. Oa 0.06a within each column means are separated by location; for each location, means followed by different letters are significantly different from each other (B s0.05), means differences based on t statisti from a pooled error term. Table 1.7. Treatment means for marketable ears and P values (in parenthesis) of significant interactions of location by treatment by attractant for early and late sweet corn plantings at Columbus and Fremont, Ohio, 1993-1995 Year/ Treatment Attractant • Marketable ears Infested ears Planting/ strict liberal Locality standards standards ECB CEW FAW 1993 Thiodicarb With - 86.5 1Û.2 - - Early sprays Without 96.8 2.2 Columbus (0.02) (0.01) _ 1993 Permethrin With - 0.25 35.7 -- Late granules Without 0.02 54.2 Columbus (0.04) (0.05) Untreated With - - - 5.1 20.0 control Without 0.0 7,2 (0.05) (0.02) 1994 Thiodicarb with 73.0 81.6 - - - Early sprays Without 95.0 100. 0 Fremont (0.027) (0.0006) w B. thuringiensis With 70.9 -- - - ID granules+sprays Without 95.1 (0.016) Permethrin + Witli 81.6 --- - Thiodicarb Without 99.0 (0.017) 1994 B, thuringiensis With - 55.1 - -" Late granules+sprays Without 25.4 Columbus (0.0008) Permethrin + With --- 2.9 - Thiodicarb Without 13.9 (0.017) Untreated With - 27.6 - -- control Without 7.5 (0.002) " Table 1.7. (cont.) Treatment means for marketable ears and p values (in parenthesis) of significant interactions of location by treatment: by attractant for early and late sweet corn plantings at Columbus and Fremont, Ohio, 1993-1995. Year/ Treatment Attractant r Marke table ears 5 Infested ears Planting/ Locality strict liberal standards standards ECB CEW FAW 1995 B. thuringiensis With - - 5.62 8.2 - Early granules Without 1.48 0.0 — Columbus (0.05) (0.0003) Thiodicarb With -- 1.9 -- sprays Without 0.0 -- (0.02) B. thuringiensis With -- 9.9 4.1 - sprays Without 1.5 0.25 - (0.001) (0.05) B. thuringiensis With 94.7 --- - granules+sprays Without 79.3 — - (0.017) o Untreated With -- 6.3 - - control Without 1.0 - - (0.05) Fremont Thiodicarb With 93.3 - 1.9 - - sprays Without 99.8 0.0 — (0.036) (0.003) S. thuringiensis With 93.1 95.1 4.9 - - granules+sprays Without 100.0 100.0 0.0 — — (0.008) (0.024) (0.005) Untreated With 85.5 -- 3.6 - control Without 97.0 0.0 (0.03) (0.016) 1905 Untreated With -- - 1.0 - Late control Without 8.4 Columbus (0.02)

Fremcnt Thiodicarb With 9.1 sprays Without 1.5 —— (0.05) Untreated With - - - 0 1.9 control Without 4.9 0.0 (0.009) (0.0 Columbus Fremont

0.014 0.01 1993 1993 0.012 0.008 0.01 0.008 0.006 0.006 0.004 0.004 0.002 0.002

0 0.1 1994 0.08

0.06 rp 0.04 fy

0.02

> 0

0.12 0.03 1995 1995 0.1 0.025

0.08 0.02

0.06 0.015

0.04 0.01

0.02 0.005

0 1 2 3 4 5 6 7

No attractant

Attractant -i-i- Treatment Figure 1.1. Mean number of Coleomegilla maculata per plant for early sweet com plantings in 1993, 1994 (average of 5-7 evaluation dates), and 1995 (average of 2 evaluation dates). When present, different letters indicate significant differences {P < 0.05) within each pair of columns for the interaction location by attractant by treatment. 1993 Treatments: 1. Bacillus thuringiensis granules; 2. permethrin granules; 3. thiodicarb sprays; 4. untreated control. 1994 and 1995 Treatments: 1. B. thuringiensis 2. permethrin granules; 3. B. thuringiensis sprays; 4. thiodicarb sprays; 5.B. thuringiensis granules + sprays; 6. permethrin granules + thiodicarb sprays; 7. untreated control. 41 Columbus Fremont

K.\\\\sVx^

0.4 0.2 1995 0.35 1995 0.3 0.15 0.25 0.2 0.1 0.15 0.1 0.05 0.05 I 7 0 1 2 3 5 6 74

No Attractant Treatment Figure 1.2. Mean number o fOrius insidiosiis per plant for early sweet com plantings in 1993, 1994 (average of 5-7 evaluation dates), and 1995 (average of 2 evaluation dates). When presen different letters indicate significant differences (P < 0.05) within each pair of columns for the interaction location by attractant by treatment. 1993 Treatments: 1. Bacillus /‘/n/rzwgrensrs granules; 2. permethrin granules; 3. thiodicarb sprays; 4. untreated control. 1994 and 1995 Treatments: 1. B. thuringiensis ÿcaraA&s, 2. permethrin granules; 3. B. thuringiensis sprays; 4. thiodicarb sprays; 5.B. thuringiensis granules + sprays; 6. permethrin granules + thiodicarb sprays; 7. untreated control. 42 Columbus Fremont

O 0.25 1994 (Pred-Feed on 6/8, 6/15, 1994 (Pred-Feed on 6/8, 6/11, II 0.2 6/20,6/23, 6/28) 6/14, 6/23)

S 0.15

g 0.1 g 0.05

a 0 k 6/4 6/10 6/20 5/17 5/31 6/7 6/15 6/21 6/28 7/12

A 0.16 1995 (Pred-Feed on k 0.14 1995 (Pred-Feed on 7/3 6/9, 6/13, 6/29) 0.12 p f i 0.1 s 0.08 g 0.05 g 0.04 P=0.04 Ÿ// / / / / g 0.02 g 6/20 7/11 0 ^ 6/18 7/2 No attractant Evaluation date Attractant

Figure 1.3. Coleomegilla maculata abundance in untreated plots for early sweet com plantings in Columbus and Fremont, Ohio, 1994 and 1995.

43 Columbus Fremont

0.4 1993 (Pred-Feed applied on PM).03 5/16, 6/23) pi 0.3 No attractant O Attractant 0.2 I

II 0.1

S 5/20 5/27 6/7 6/15 6/22 6/29 7/8 4-» c 0.35 CQ 1994 (Pred-Feed applied on 0.3 6/8, 6/15, 6/20, 6/23, 6/28) on6/8, 6/11,6/14, 6/23) 0.25 0.2 a 0.15 u 0.1 0.06 pfi 0 S 5/17 5/31 6/7 6/15 6/21 6/28 7/12 6/10 6/20 6/30

q 1995 (Pred-Feed applied on 1995 (Pred-Feed applied on 6/9, 6/13, 6/29) 7/3, 7/7) c 9 3

6/20 7/11 Evaluation date Figure 1.4. Orius insidtosus abundance in untreated plots for early sweet com plantings in Columbus and Fremont, Ohio, 1993 to 1995.

44 Columbus Fremont

9 3 0.4

m m

No attractant Attractant C % , y Treatment Figure 1.5. Mean number of Coleomegilla maculata per plant for late sweet com plantings in 1993, 1994 (average o f 5-7 evaluation dates), and 1995 (average o f 2 evaluation dates). No significant differences were observed for the interaction location by attractant by treatment. 1993 Treatments: 1. B. thuringiensis 2. permethrin granules; 3. thiodicarb sprays; 4. untreated control. 1994 Treatments: 1. jB. tAHnngiewsw granules + sprays; 2. permethrin granules + thiodicarb sprays; 3. untreated control. 1995 Treatments: 1. B. thuringiensis sprays; 2. thiodicarb sprays ; 3. untreated control.

45 Columbus Fremont 0.7 0.6 1993 0.6 0.5 0.5 0.4 0.4 0.3 0.3 0.2 0.2 S3 0.1 'VV 0.1 c s 0 1.2 0.25 1994 1994 U 0.2 0.8 A 0.15 0.6 u .'V 0.1 o 0.4 p J S ■A- s 0.2 0.05 I g 31 2 3 S3 5 5 1995 1995 S3 4 4 0 : 3 3

§ 2 2

1 1

0 0 1 2 3 1 2 3

No attractant Attractant / / / / Treatment Figure 1.6. Mean number of Orius insidiosus per plant for late sweet com plantings in 1993, 1994 (average of 5-7 evaluation dates), and 1995 (average of 2 evaluation dates). When presen different letters indicate significant differences (P < 0.05) within each pair of columns for the interaction location by attractant by treatment. 1993 Treatments: 1. B. thuringiensis granules; 2. permethrin granules; 3. thiodicarb sprays; 4. untreated control. 1994 Treatments: 1. B. thuringiensis granuies +sprays; permethrin2. granules + thiodicarb sprays; 3. untreated control. 1995 Treatments: 1. B. thuringiensis sprays; 2. thiodicarb sprays ; 3. untreated control. 46 Columbus Fremont

1993 (Pred-Feed on 8/27, 9/1) 1993 (Pred-Feed on 8/5, 8/11)

8/5 8/13 8/20 8/26 9/8 9/14 0 7/13

(Pred-Feed on 7/26, 8/1, 1994 (Pred-Feed on 7/22, 7/25, 8/& 8/ 15, 8/22) 8/9, 8/22)

k 0.05

8/18 8/25 7/12 7/20 7/26 8/2 8/6 8/16 8/23

1995 (Pred-Feed on 7/25, 8/1) 1995 (Pred-Feed on 7/26, 7/31,

P=O.OOS

«%:

No attractant Evaluation date Attractant

Figure 1.7. Coleomegilla maculata abundance in untreated plots for late sweet com plantings in Columbus and Fremont, Ohio, 1993 to 1995.

47 Columbus Fremont

1.6 1993 (Pred-Feed on 1993 (Pred-Feed on 8/5, 8/11) 1.4 8/27, 9/1) 1.2 o I 0.8 II 0.6 e g 0.4 ^ 0 . 2 0 8/5 8/13 8/20 8/26 9/8 9/14 a 2.5 1994 (Pred-Feed on 7/26, 8/1, ^ 1994 (Pred-Feed on 7/22, 7/25,, 8/9, 8/15, 8/22) 8/9, 8/22)

PN).Ol I 7/12 7/20 7/26 8/2 8/6 8/16 8/23

1995 (Pred-Feed on 7/25, 8/1) 1995 (Pred-Feed on 7/26, 7/31, 8/7

7/21 8/10 No attractant Evaluation date Attractant

Figure 1.8. Orius insidiosus abundance in untreated plots for late sweet com plantings in Columbus and Fremont, Ohio, 1993 to 1995.

48 Chapter II

Functional Response of Coleomegilla maculata (DeGeer) (Coleoptera:

Coccinellidae) , Orius insidiosus (Say) (Hemiptera :Anthocoridae) , and

Cbrysoperla camea Stephens (Neuroptera: Chrysopidae) to Eggs and First

Instars of Ostrinia nubilalis Hubner (Lepidoptera: Pyralidae).

INTRODUCTION

Since European corn borer {Ostrinia nubilalis Hubner) was first

found in the United States in 1917, the main approaches taken to

implement its biological control have been importation of parasitoids,

enhancement and augmentation of native parasitoids, as well as research

on microbiological control. Many indigenous predators prey on European

corn borer eggs and larvae (Showers et al. 1989). Coleomegilla maculata

(DeGeer) is an important predator of European corn borer eggs and early

instars (Conrad 1959). Chrysopids {Chrysopecla carnea Stephens) and

anthocorids {Orius insidiosus (Say)) have been observed preying on this pest (Sparks et al. 1966). Reid (1991) reported that a density of 12

0. insidiosus adults caused egg mortality of 16% (on ears), and 80% (on

leaves) on single caged plants where other predators and alternate prey

had been eliminated. Lacewing larvae have been reported to eat up to

377 0.nubilalis eggs per individual during larval development in the

laboratory (Obrycki et al. 1989) .

Functional response studies have been useful in determining the potential of a predator or parasitoid as a possible biological control

agent. Success of such an agent is dependent upon its ability to change

its attack rate in response to changes in prey density (Hassell 1978).

Functional response curves have been described as three different types:

type I functional response is a linear increase to a plateau, type II is

49 a decelerating increase to a plateau (curvilinear rise), and type III is

a sigmoid increase to a plateau (sigmoid rise)(Trexler et al. 1988).

While different types of functional responses to hosts or prey have been

found among insects, the most commonly found type among predatory arthropods is type II, which is described by the disk equation of

Moiling (1959):

Ng = aTN/1 + aT^N

where = number of prey eaten, a = attack rate (which is constant),

N = prey density, T = total time prey is available to predator, and = handling time per prey. This model assumes constant prey density (N) exists and no depletion of prey. Rogers (1972) developed a model, the

"random predator equation", which accounts for the change in prey density (prey depletion):

Ng = Ng (1-exp[a(Th N^-T)]}, where Nq is the number of prey initially offered and is the prey eaten. For the type III functional response, Hassell (1978) developed a model in which a (attack rate) is a function of the offered density, where :

a = d + bN/l+cN, when a is replaced in Rolling's equation, then:

Na = No (1 - exp[(d + b N ^ ) ( T^ Na - T)/(l + c Ng)]}, b, c, and d are constants whose value can be zero.

O. insidiosus exhibits a type II functional response to

Sericothrips variabilis (Beach)(Thysanoptera: Thripidae) (Isenhour &

Yeargan 1981), Panonychus ulmi (Koch)(Acari: Tetranychidae)(McCaffrey &

Horsburgh 1986), Caliothrips phaseoli (Thysanoptera: Thripidae)(Saucedo-

Gonzalez & Reyes-Villanueva 1987), and to Frankliniella occidentalis

(Thysanoptera: Thripidae)(Coll & Ridgway 1995). No similar studies have been published for European corn borer.

Multiple studies have been conducted on predation by C. maculata

(Andow & Risch 1985, Hazzard & Ferro 1991, Giroux et al. 1995). Only

50 Hazzard & Ferro (1991) dealt directly with the functional response of

C. maculata. In their experiments, C. maculata exhibited a type II functional response to eggs of Leptinotarsa decemlineata (Say)

(Coleoptera: Chrysomelidae) (Hazzard & Ferro 1991) .

Among the predators available from commercial insectaries, one of the most common is a green lacewing, C. carnea, which has been reported as an important predator of corn pests (Sparks et al. 1966, Ridgway &

Jones 1968, Carlson & Chiang 1973) . Yüksel & Gôçmen (1992) described a type II functional response of C. carnea to varying densities of Aphis gossypii Glover (Homoptera: Aphididae), but they did not use either

Holling's or Rogers' model to quantify the response.

Learning about the functional response of predators is a basic step in predicting performance of a predator on a particular prey. In this study, I conducted laboratory experiments to determine the functional response of C. maculata adults, 0. insidiosus adults, and C. carnea first instars to different densities of European corn borer eggs and first instars.

MATERIALS AND METHODS

Experiments were conducted at the Ohio State University. A growth chamber with a temperature of 25°C and a photoperiod of 15:9 (L:D) h. was used to conduct all studies. Each experiment was conducted on a separate day. There were a total of six non-replenishment experiments and six replenishment experiments. Non-replenishment experiments were conducted in September, and replenishment experiments were conducted in

November to December 1995. A completely randomized design with six replications was used for all experiments.

0. nubilalis egg masses were obtained from a laboratory colony at the Department of Entomology, Iowa State University (Ames, Iowa). First instars were obtained by placing eggs in the growth chamber and allowing them to develop.

51 Source of predators and pre-trial handling procedures. Non-replenishment esqperiments.

Orius insidiosus: Adults of 0. insidiosus were field collected

from sweet corn in Columbus, Ohio. Adults were provided with a surplus

of egg masses of European corn borer for 24 hours. They were then

sexed, placed in individual containers with cotton wicks saturated with

water, and starved for 24 hours.

Coleomegilla maculata: Adults of C. maculata were field

collected on sweet corn plants in Columbus, Ohio in September 1995. The

same procedures as for o. insidiosus were followed.

Chrysoperla carnea: C. carnea eggs were obtained from Rincon

Vitova Insectaries Inc. (Fresno, California). Eggs were allowed to

hatch and removed soon after hatching, placed in individual containers with a cotton wick saturated with water, and starved for 24 hours. Replenishment experiments.

Orius insidiosus: Adults of O. insidiosus were obtained from the

Green Spot in Barrington, New Hampshire. Because these adults had already been pre-fed with frozen moth eggs, they were immediately sexed, placed in individual containers with a cotton wick saturated with water,

and starved for 24 hours.

Chrysoperla carnea: C. carnea eggs were obtained from Rincon

Vitova Insectaries Inc. (Fresno, California). They were kept in the

growth chamber until eclosion of first instars.

Coleomegilla maculata: Overwintering adults were obtained from J.

Obrycki, Iowa State University, who collected them on 4 December 1995 in

Roland, Iowa. They were placed in a growth chamber at 25"C and a photoperiod of 15:9 (L:D) h., and fed European corn borer eggs and a mixture of honey and water. When adults started feeding and laying eggs, individuals were placed in containers with a cotton wick saturated with water, and starved for 24 hours.

52 Experimental procedures. Non-replenishment experiments

Orius insidiosus: Males and females were placed in individual 59 ml plastic containers with 10, 20, 30, and 40 European corn borer eggs or 10, 20, 30, and 40 European corn borer first instars. Eggs were attached to waxed paper and pieces were cut so that the target number of eggs was obtained. Water was applied to the walls of the containers with a fine brush. The cups were placed on a tray in the growth chamber. Total consumption was measured after 12 hours.

Chrysoperla carnea: First instar larvae were transferred to the individual containers with the experimental prey. The same densities and procedures as those used for O. insidiosus were used for this predator.

Coleomegilla maculata: The same procedures as for 0. insidiosus were followed, but egg and larval densities were 50, 75, 100, and 125 per container, and they were not sexed. Replenishment esqperiments

Orius insidiosus: Individual females and males were placed in containers with 2, 4, 6, 8, 10, and 12 eggs or 10, 20, 30, 40, or 50 larvae. Experiments lasted 12 hours, and individuals were transferred to a new container with the initial density every two hours.

Immediately after each transfer, old containers were checked for egg and larval consumption.

Chrysoperla carnea: The same procedures and densities as those used for 0. insidiosus were used for this predator.

Coleomegilla maculata: Individuals were transferred to containers with 25, 50, 75, 100, or 125 eggs or larvae. Experiments lasted twelve hours, and individuals were transferred to a new container with the initial density every two hours. Old containers were checked for egg or larval consumption.

53 Evaluation procedure.

When evaluating predation, eggs were considered to be consumed by

C. maculata if they had a partially or completely chewed chorion. Eggs

which had been sucked completely were considered to be consumed by 0.

insidiosus and C. carnea. First instars killed by C. maculata were

easily recognized because only the head capsule remained. First instars

killed by O. insidiosus and C. carnea had shriveled bodies. Those

killed but not sucked dry were completely motionless after probing with

a pin. Analysis of Data.

Functional response analysis was done in two steps as recommended

by Juliano (1993) . The first step was determination of the type of

functional response. Logistic regression (proc CATMOD in SAS (SAS

Institute Inc., 1991)) was used to determine the shape of the functional

response. This statistical technique allows for identification of

regions of negative, positive, or no density dependence, and is used

when the dependent variable is binary or dichotomous and the independent

variables are continuous (Neter et al. 1989). For functional response,

the outcome of the experiment was Y=0 or Y=1 for individual prey left

alive or dead. With this technique, the proportion of prey eaten

(Ng/Ng) was regressed on the number of prey offered (N^) and the

parameters of the logistic model were obtained. Also obtained were a

chi-square test of significance for each parameter and a maximum

likelihood ratio test. These tests evaluated for statistically

significant evidence of a lack of fit for the model, thus maximized the probability that observed values were arising from the parameters. The

objective was to find a polynomial function that described the relation between the proportion of prey eaten and the number of prey offered

(Juliano 1993). The parameters were then used to calculate the predicted values for the proportion of prey eaten, which were plotted versus the number of prey offered, to determine the type of

54 relationship. This graph identified the type of the functional response. The sign of the linear parameter identified the slope of the curve in the region close to the origin; if it were positive (initially increasing) , negative (initially decreasing), or flat, this indicated that the functional response was of type III, II, or I, respectively.

The second step in analysis was to estimate the parameters of the functional response. Hypothesis testing that involved the use of non­ linear least-squares regression of number of prey eaten versus number of prey offered was used as recommended by Williams and Juliano (1985) and

Juliano (1993). Non-linear regression (proc NONLIN in SAS with the DOD procedure)(SAS Institute Inc. 1991) was used to estimate the parameters of the functional response model. This procedure yielded the estimation of the parameters, their asymptotic standard error, and an asymptotic

95% confidence interval.

For experiments where prey were replenished every two hours, attack rate (a) and handling time (T^) of Holling's disk equation

(Rolling 1959) were estimated using the least-squares non-linear regression of number of prey eaten versus number of prey offered. This was done to evaluate possible effects of prey depletion or change in prey density when parameters were compared with those obtained by using using the random predator equation of Rogers (1972). For the three species, values were different, with a larger handling time when the disk equation was used. This indicated that there was an effect of prey depletion (Juliano 1996, personal communication), consequently,

Rogers random predator equation was used.

In the case of O. insidiosus, a classification variable was used to determine if there were statistical differences between males and females for the estimated parameters (Juliano 1993, Neter et al. 1989) .

The classification variable allowed measurement of the difference between attack rates (da) and handling time (dT^) of males and females.

The results of the least-squares non-linear regression with the

55 classification variable showed that the differences between the estimated parameters of attack rate and handling time were not statistically significant as the 95% asymptotic confidence interval includes zero. Because there were not statistically significant differences between male and female of 0. insidiosus in prey consumption based on the estimated parameters of attack rate and handling time , it was justified to pool the data for males and female and to estimate new parameters of attack rate and handling time for the pooled data.

SAS least-squares non-linear regression procedure was used to evaluate the least squares assumptions of normally and homogeneity distributed error. Graphic analysis and descriptive statistics were obtained. For the graphic analysis, the residuals of the non-linear least squares regression were plotted against the independent variable

(Nq ) and the predicted value of number of prey eaten (Predicted N^/Nq ) to study possible trends (Neter et al. 1989). Descriptive statistics and the variance of the residuals were obtained using proc MEANS in SAS

(SAS Institute Inc. 1991). The variance of the residuals was used as a weight to correct for the non-normally distributed errors (Judge et al.

1988) if the graphic analysis, and the value of the variance of the residuals, indicated non-homogeneity of the error term across the levels of the independent variable. The standard deviation of the residuals at each level of the independent variable was used as a weight for the observations at each respective level, and parameters of the functional response were re-calculated using a weighted least squares non-linear regression. Graphical analysis and descriptive statistics were again performed to re-evaluate for normality and homogeneity in the the distribution of the residuals by plotting them versus the predicted values of number of prey eaten.

When type I functional responses were found, after the logistic regression indicated a constant proportion of prey eaten, the procedure proc REG in SAS (SAS Institute Inc. 1991) with the SPEC option was used

56 to estimate the parameters of the linear equation. The SPEC option evaluated the hypothesis of non-homogeneous distributed error and tested it with a Chi-square distribution (SAS Institute Inc. 1991). If the hypothesis of non-normality were rejected, a weight would be needed and the procedure described above could be used to estimate parameters of the Type I functional response using a weighted least squares linear regression. There was no need to use weights in my data sets for type I functional response because the non-normality test was statistically non-significant. RESULTS Analysis of Variance

In both egg and larval consumption, C. maculata had the highest feeding rates of the three species considered, for both the replenishment and no replenishment studies. No replenishment studies

For the no replenishment experiment, there were no significant effects of European corn borer egg density on consumption. Of the three species used, C. maculata consumed the most eggs at the end of the 12 h period; average consumption was 45 eggs by those offered 125 eggs, and

26 eggs by those offered 50 eggs.

There was a significant prey density effect for C. carnea

(P =4.6, P = 0.01, df = 3,23) consuming first instars, with average consumption of 13.3 when offered 40 first instars. There was a significant effect of prey density (F = 7.34, P = 0.0017, df = 3,23) on

C. maculata. At the density of 125 first instars, C. maculata consumed an average of 77, significantly (P <: 0.05) more than those offered 50 first instars which consumed an average of 38. Significant density effects (F = 55.9, P = 0.0001, df = 3,23) were observed for O. insidiosus, for which all treatments were significantly different than one another (P s 0.05) . Maximum consumption was 31 first instars by O. insidiosus offered a density of 40, and minimum was 8 first instars by

57 those offered a density of 10.

Replenishment studies

There were only two cases out of eight in which there were significant differences in prey consumption as a function of time: C. maculata consuming eggs (F = 7.28, P = 0.0001, df = 5,125) and O. insidiosus consuming first instars (F = 2.2, P = 0.006, df = 15,200).

There were no significant treatment effects for c. carnea consuming eggs at any of the two hour periods except the last one

(F = 4.83, P = 0.002, df = 5,35) where those offered four eggs consumed significantly more (2.3 eggs) than the other groups (ranging from 1 to

0.2). For c. carnea consuming first instars, there was a significant

(F = 0.0001) treatment effect for all two hours periods. For all periods, those offered 50 European corn borer eggs had the highest consumption ranging from 19 eggs at 4 hours up to 31 eggs at the 8 hour period.

There was a significant treatment effect for all 2 hour periods for C. maculata consuming eggs and first instars of European corn borer.

Egg consumption was highest after two hours (47 eggs) for those offered

125 eggs, and lowest (10) after 12 hours for those offered 25 eggs. c. maculata consumption was always highest in the plots that had 125 first instars offered. Maximum predation was reached in the last period (12 h) when an average of 64 larvae were consumed in two hours.

There were no significant sex or treatment effects observed for O. insidiosus consuming European corn borer eggs. There was an average consumption of three eggs per two hours when offered 12 eggs.

Significant treatment effects were observed for consumption of European corn borer first instars, with a maximum consumption of four first instars per two hours for those offered 50 first instars.

Functlonctl response

Coleomegilla macalata with prey replenishment

After fitting the logistic regression equation, the parameter of

58 the linear term Nq was -0.021 (P = 0.073) for eggs and -0.040 (P =

0.0001) for first instars. The probability of the maximum likelihood

ratio test was not significant for eggs and first instars, indicating a

non-significant lack of fit for the polynomial logistic model (Table

2.1). The plot of the predicted values of proportion of prey eaten

(N^/Nq ) versus density of prey offered (Nq ) showed a monotonie declining

curve indicating a type II functional response (Fig. 2.1.A, 2.1.D).

Rogers' type II functional response equation was fit to the data for

eggs (Fig. 2.1.B) and first instars (Fig. 2.1.E) using weights, and eggs

(Fig. 2.I.e.; Table 2.1) and first instars (Fig. 2.1.F) not using

weights. The attack rate was statistically significant with and without

weights, but the handling time was significant only when weights were

used (Table 2.2).

Coleomeg±lla. ma.cvila.ta. without prey replenishment

After fitting the logistic regression equation, the value of the

parameter of the linear term was -0.037 (P = 0.056) for eggs and

-0.040 (P = 0.053) for first instars. The probability of the maximum

likelihood ratio rest was statistically significant for eggs and first

instars (Table 2.1), which indicated a significant lack of fit for the

polynomial logistic model. The plot of predicted values of proportion

of prey eaten (Ng/Mg) versus density of prey offered (N^) did not show a monoconic declining curve, indicating that this was not a type II

functional response (Fig. 2.2.A , 2.2.D). This could be due to too few data points at low prey density to obtain a good fit for the model.

Because the parameters of the linear term were negative and the proportion of prey eaten decreased, Rogers' type II functional response

equation was fit to these data (Figs. 2.2.B.,2.2.C.,2.2.E.,2.2.F; Table

2.2). The parameters for eggs and first instars were not significantly different than zero with and without weights.

Chrysoperla camea with prey replenishment

After fitting the logistic regression equation, the linear term Nq

59 was -0.5022 (P = 0.0729) for eggs and 0.00658 (P = 0.214) for first instars. The probability of the maximum likelihood ratio test was not statistically significant for eggs and first instars, indicating a non­ significant lack of fit for the polynomial logistic model (Table 2.3).

The plot of predicted values of proportion of prey eaten (N^/Nq ) versus density of prey offered (N^) showed a monotonie declining curve indicating a type II functional response for eggs (Fig. 2.3.A) and a positive increasing line indicating a type I functional response for first instars (Fig. 2.3.D). Rogers' type II functional response was fit to the egg consumption data using weights (Fig. 2.3.B) and without weights (Fig. 2.3.C; Table 2.4). After fitting a type I linear functional response model for the first instars data, the linear equation was Ne = -1.16 + 0.501*Mq with an adjusted r^ of 0.887 (Fig.

2.E; Table 2.4).

Chzysoperla camea without prey replenishment

After fitting the logistic regression equation, the linear term N^ was -0.1588 (P = 0.044) for eggs and -0.089 ( P = 0.081) for first instars. The probability of the maximum likelihood ratio test was statistically significant for eggs and first instars, which indicated a significant lack of fit for the polynomial logistic model (Table 2.3).

The plot of predicted values of proportion of prey eaten (N^/N^) versus density of prey offered (Nq ) showed a monotonie declining curve indicating a type II functional response for eggs (Fig. 2.4.A) and a non-monotonic declining curve for first instars (Fig. 2.4.D), which could be due to high variability in the data. Rogers' type II functional response equation was fit to the data for egg consumption

(Figs. 2.4.B, 2.4.C; Table 2.4) and larval consumption (Figs. 2.4.E,

2.4.F). The attack rate was not significantly different from zero, but the handling time was (Table 2.4).

Orlvis ±ns±d±osus with eggs and prey replenishment

After fitting the logistic regression equation, the linear term Nq

60 was 0.0445 for males and -0.316 for females. The probability of the maximum likelihood ratio test was not statistically significant for males or females, indicating a non-significant lack of fit for the polynomial logistic model (Table 2.5). The plot of the predicted values of proportion of prey eaten (N^/Nq ) versus density of prey offered (N^) showed monotonie declining curves for males and females indicating type

II functional responses. Rogers' type II functional response was fit for both females (a = 0.55 and T^ = 0.4480) and males (a = 0.29 and T^ =

0.66)(Table 2.6) without using weights. The differences between the estimated parameters between males and females using a classification variable showed no significant difference, for da (attack rate difference) = 0.4096 or dT^ (handling time difference) =

-0.0365 (Table 2.6). The plot of predicted values for proportion of prey eaten (N^/Nq ) versus density of prey offered (Nq ) for the pooled data of females and males showed a monotonie declining curve indicating a type II functional response (Fig. 2.5.A) Rogers' equation was fit for the pooled data without using weights (Fig. 2.5.B); both attack rate and handling time were statistically significant (Table 2.6).

Orlvis iasidiosus with first instars and prey replenishment

After fitting the logistic regression equation, the linear term Nq was -0.037 {P = 0.57) for males and -0.120 [P = 0.07) for females. The probability of the maximum likelihood ratio test was not significant for males or females, indicating a non-significant lack of fit for the polynomial logistic model (Table 2.7). The plot of predicted values of proportion of prey eaten (N^/Nq) versus density of prey offered (Nq) showed monotonie declining curves, indicating a type II functional response for males and females. Rogers' type II functional response equation was fit for both females (a = 0.09 and T^ = 0.14) and males (a

= 0.13 and T^ = 0.23) (Table 2.8). The differences between the estimated parameters between males and females using a classification variable indicated there was not a significant difference in da (attack

61 rate difference) = 0.0355 or dT^ (handling time difference) = 0.084

(Table 2.8). The plot of predicted values for proportion of prey eaten

(Na/No) versus density of prey offered (Nq ) for the pooled data of males and females showed monotonie declining curves indicating a type II functional response (Fig. 2.5.C). Rogers' equation was fit for the pooled data without using weights (Fig. 2.5.D). Attack rate and handling time were statistically significant (Table 2.8)

Orlus insldiousus with eggs and. no prey replenishment

After fitting the logistic regression equation, the linear term Nq was -0.005 {P = 0.94) for males and -0.101 (P = 0.21) for females, with a value of -0.049 (P = 0.37) for the pooled file. The probability of the maximum likelihood ratio test was not statistically significant for males, females, or the pooled data for males and females, indicating a significant lack of fit for the polynomial logistic model (Table 2.9).

The data were also fit using a third order polynomial equation, and the lack of fit of the model along with the estimated parameters were not statistically significant. The plot of predicted values of proportion of prey eaten (N^/Nq ) versus density of prey offered (Nq ) did not show a monotonie declining curve for males, but the plot for females and rhe pooled data I Fig. 2.7.A) more closely indicated a type II functional response. Therefore, Rogers' type II functional response equation was fit for males with (a = 0.04 and T^ = 4.4)) and without weights (a = 0.04 and T^ = 2.6), as well as for females with (a = 0.04 and T[^ = 4.9) and without weights (a = 0.01 and T^ = 0.9) (Table 2.10).

There was not a significant difference in parameters between males and females when using a classification variable da (attack rate difference)

= 0.0268 and dT^ (handling time difference) = 1.597 (Table 22). Rogers' equation was fit for pooled data without weights (Fig. 2.6.D; Table

2.10); only the handling time was statistically significant (Table

2 .10).

62 Orius insidiosns with first Instars and no prey replenishment

After fitting the logistic regression equation, the linear term Nq was -0.028 [P = 0.00) for males and 0.0133 (f = 0.15) for females. The probability of the maximum likelihood ratio test was not statistically significant for males and females, indicating a significant lack of fit for the polynomial logistic model (Table 2.11). The plot of the predicted values of proportion of prey eaten (N^/Nq) versus density of prey offered (Nq) showed a positive increasing line indicating a type I functional response for both males and females, as well as for the pooled data (Fig. 2.6.C).

After fitting a type I linear functional response model the linear equations were N^ = -1.25 + 0.802*No (adjusted r~ = 0.81) for females and Ng = 2.25 + 0.657*No (adjusted r^ = 0.78) for males. N^ = 0.73 -r

0.73*No (adjusted r~ = 0.84) was the equation obtained for the pooled data (Fig. 2.6.D)(Table 2.12).

DISCUSSION

With few exceptions C. maculaza, O. insidiosus, and C. carnea showed type II functional responses to eggs and first instars of

European corn borer. Of rhe chree species, C. maculaca was the most efficient at preying upon both stages of this pest. Consumption values for C. maculaca were similar ro those obtained by Conrad (1959), who studied one individual feeding on European corn borer eggs in a leaf cage on sweer corn. I found that one O. insidiosus could consume an average of 3.3 o. nubilalis eggs in a 12-hour period, when offered a density of 40 eggs, which is close to the results of Reid (1991) who worked with caged corn plants. Treacy et al. (1987) reported

Chrysaperla rufilahris first instars consumed an average of 1.2 eggs of

H. zea in a 12-hour period. This is close to the numbers of o. nubilalis eggs consumed at the different densities in a 12 hour period for both replenishment and no-replenishment experiments with C. carnea.

63 Determination of the functional response is a first step in evaluating the potential of a predator. Many studies have been published that have used Rolling's disk equation (Rolling 1966) to determine functional response, but many of these studies did not address the issue that prey must be replenished instantaneously to be able to use this equation (Juliano 1993); if prey are not replenished, parameters obtained with this equation are not to be trusted. Rogers'

"random predator" equation for type II functional response (Rogers 1972) addressed depletion by incorporating it into the statistical analysis.

While there has been criticism of this technique (Livdahl & Steven 1983;

Williams & Juliano 1985) due to use of linearization of the equation, use of nonlinear least squares has been effective for parameter estimation and comparison (Juliano 1993). Trexler et al. (1988) suggested use of logistic regression to distinguish among the different curves of predation.

Several problems arise when studying functional response under laboratory conditions, such as the high natural biological variability that increases as prey density increases (Juliano 1993, Trexler et al.

1988, Fan & Petit 1995) . When this high variability occurs, weights are sometimes necessary to obtain statistically significant parameters through the homogenization of variance across levels of prey density.

By using weights, predicted values of predation can be different from predicted values without the weight. This occurred in my experiment with data from predation of C. macula ta on European corn borer first instars (Table 2.2). Use of weights might therefore prevent a true biological interpretation of the observed data because weights move outlier values closer to the average, which lowers the attack rate and increases the handling time (Wiedemann & O'Neil 1991) . When considering the potential for predation, it may be necessary to use the true unweighted parameters in spite of lack of significance.

Non-significance of the parameters is usually caused by lack of

64 observations and not by a model that does not fit the data. This is particularly obvious when one has a statistically significant logistic regression determining a type II functional response and a non­ significant nonlinear least squares regression. This was the case in my data with 0. insidiosus where the logistic regression of males consuming

European corn borer eggs was statistically significant for a type II functional response (Table 2.5). However, after fitting the data through Rogers' equation for this type of response, the attack rate was not statistically different from zero. Once more data points were obtained by pooling male and female data, handling time became statistically different than zero (Table 2.6).

Under laboratory conditions, exogenous factors do not affect predatory behavior, particularly searching time. Searching time is reduced to zero or almost zero when predators and prey are contained, and this could lead to heightened values of attack rate and consequently total predator consumption.

In this experiment, I determined the impact of adding prey while determining functional response, and found that attack rate was much higher and handling time lower when new prey was introduced in the arena every two hours than when the insects were left with the same initial density offered. Based on the information gathered in these experiments, I suggest not using any prey replenishment so that parameters can be estimated under conditions closer to those in the field.

I conclude that use of functional response can be useful in estimating the potential of a predator as a biological control agent.

Based on information obtained in these experiments, C. maculata is the most likely candidate for further studies, such as determination of functional response under field conditions. In the field, other food

65 sources, increased searching time, and environmental factors could affect its performance as a predator of European corn borer eggs and young larvae.

66 Table 2.1. Logistic regression results for Coleomegillà maculata consuming eggs and first instars of European corn borer based on the logistic equation. Prey Prey Estimated Standard Chi- Probability Probability of Type Replenishment Parameters Error square likelihood ratio Eggs yes Pi= -0.021 0.007310 7.19 0.0073 0.1492 P2=0.001 0.000047 4.54 0.0313 no Pi= -0.037 0.0135 7.67 0.0056 0.0000 P?=0.000 0.000074 5.34 0.0208 First yes P,= -0.040 0.007750 27.23 0.0000 0.1387 instars P2=0.000 0.000046 23.03 0.0000 no Pi= -0.040 0.0146 7.77 0.0053 0.0000 P2=0.000 0.000079 4.95 0.0261 Table 2.2. Coleomegilla maculata parameters of the functional response to eggs and first instars of European corn borer, based on Rogers' type II functional response equation.

Prey Type Prey Weight Estimated Asymptotic Asymptotic Replenishment Used Parameter Standard 95 % Confidence Error Interval First yes yes a=0.9618 0.3169 0.3126:1.6110 instars T,^=0.1936 0.C262 0.1398:0.2475 no a=0.2856 0.0466 0.1900:0.3812 Th=0.0032 0.0070 -0.0112:0.0176 c n no yes a=0.35l2 0.5718 -0.8346:1.5371 00 Th=2.1696 1.2395 -0.4010:4.7303 no a=0.1392 0.0568 0.0170:0.2613 Th=0.ü719 0.0464 -0.0242:0.1682 Eggs yes yes a=0.5145 0.1557 0.1954:0.8336 T[^=0.1913 0.0406 0.1081:0.2745 no a=0.2702 0.0435 0.18103:0.3595 Th=0.CQ52 0.0071 0.00057:0.0299 no yes a=0.08 0.0505 -0.0243:0.1856 Th=2.58 1.9367 -0.4525:6.6276 no a=0.û933 0.0825 -0.0789:0.2655 Th=0.1474 0.1254 -0.1142:0.4091 Table 2.3. Logistic regression results for Chrysoperla carnea consuming eggs and first instars of European corn borer based on the logistic equation. Prey Prey Estimated Standard Chi- Probability Probability of Type Replenishment Pa rameters Error Square likelihood ratio Eggs yes Pi= -0.50220 0.28000 3.22 0.0729 1.00 m P2=0.02180 0.01860 1.38 0.2400 VO no Pi= -0.15880 0.05580 8.10 0.0044 0.0092 Po= 0.00209 0.00108 3.73 0.0534 First yes Pl=0.00660 0.00538 1.54 0.2146 0.7720 instars no Pi= -0.08900 0.05090 3.06 0.0810 0.0002 P,= 0.00088 0.00092 0.91 0.3400 Table 2.4. Chrysoperla carnea parameters of the functional response to eggs and first instars of European corn borer, based on Rogers' type II functional response equation. Prey Prey Weight Estimated Asymptotic As ymptotic Type Replenishment Used Parameter Standard 95 i Confidence Error Interval

First no yes a==0.1(392 0.1480 -0.1177:0.4961 instars Th==2. 5(35(3 0.7299 1.0720:4.0996 no a-0.1:373 0.0683 -0.0043:0.2790 o Th==0. 6597 0.1663 0.3147:1.0047 Eggs yes yes a==l. 0335 0.6833 -0.3567:2.4237 Th=0.5525 0.0519 0.4467:0.6583 no a==1.2125 1.0743 -0.0970:3.3957 Th=1.5939 0.1707 1.2469:1.9409 no yes a-0.0807 0.0537 -0.0290:0.1905 Th=4.3180 0.6395 3.0119:5.6240 no a=0.2157 0.4667 -0.7373:1.1689 Tj,=3.4904 0.6439 2.1752:4.8056 Table 2.5. Logistic regression results for Orius insidiosus consuming eggs of European corn borer based on the logistic equation. Sex Estimated Standard Chi- Probability Probability of Parameters Error Square likelihood ratio Male P.= -0.445 0.256 3.01 0.08 0.9957 P?= 0.028 0.016 1.88 0.17 Female no=-0.316 0.239 1.75 0.18 0.9294 no2=0.012 0.015 0.71 0.40 Table 2.6. Orius insidiosus parameters of the functional response to eggs of European corn borer, based on Rogers' t- vnp, TT fimnt i nnal rasnnnRA AniiAfinn. Sex Estimated Asymptotic Asymptotic 95 ; parameters Standard Error confidence interval Male a=0.2936 0.1495 -0.1019:0.5974 Th =0.6557 0.2399 0.1681:1.1433 -J K> Female a=0.5522 0.2586 0.0267:1.0778 Th=0.4480 0.1263 0.1912:0.7048 Compared dal=0.4096 0.2736 -0.1362:0.9556 dThl=-0.0365 0.1990 -0.4337:0.3607 Pooled a=0.4116 0.1551 0.1022:0.7210 data Th=0.5294 0.1315 0.2671:0.7916

using a classification variable Table 2.7. Logistic regression results for Orius insidiosus consuming first instars of European corn borer based on the logistic equation. Sex Estimated Standard Chi- Probability Probability Parameter error square Likelihood ratio w Male Pi=-0.037 0.0676 0.31 0.57 0.9997 P? =0.000 0.0012 0.09 0.76 Female Pi=-0.120 0.0683 3.13 0.07 0.9362 Pp =0.001 0.0012 2.40 0.12 Pooled Pi=-0.078 0.0480 2.68 0.10 0.9947 data P? =0.001 0.0008 1.69 0.19 Table 2.8. Orius insidiosus parameters of the functional response to first instars of European corn borer, based on Rogers' type II functional response equation. Se:: Estimated Asymptotic Asymptotic 95 ^ Parameters Standard Error Confidence Interval

Male a=0.1260 0.0323 0.0588:0.1932 -J Tv,=0.2277 0.0725 0.0773:0.3781 Female a=0.0903 0.0315 0.0248:0.1558 Th=0.1424 0.1232 -0.1236:0.4084 Compare dal=0.0355 0.0483 -.0619:0.1330 dThl=0.084 0.1425 -0,2024:0.3719 Pooled a=0.1087 0.0235 0.0613:0.1561 data Tv,=0.1948 0.0686 0.0555:0.3331

using a classification variable Table 2.9. Logistic regression results for Orius insidios us consuming eggs of corn borer based on the logistic equation. Sex Estimate Standard Chi- Probability Probability Parameter Error Square likelihood ratio e n Male Pi=-0.005 0.075 0.01 0.94 0.0010 P?=0.000 0.001 0.03 0.85 Female Pi=-0.101 0.081 1.55 0.21 0.0202 P?=O.OOG 0.001 1.21 0.27 Pooled Pn=-0.049 0.055 0.79 0.37 0.0020 data P?=0.000 0.001 0.37 0.54 Table 2.10. Orius insidiosus parameters of the functional response to eggs of European corn borer, based on Rogers' type II functional response equation. Sex Weight Estimated Asymptotic Asymptotic 95 t parameters Standard Error Confidence Interval Male no a=0.0388 0.0447 -0.0550:0.1328 T,,= 2 . 5897 1.2163 0.0342:5.1452 Female a=0.0120 0.0067 -0.0022:0.0263 Th=0.9887 1.6169 -2.408:4.3856 Compare dal=0.0268 0.0405 -0.0553:0.1090 (Tl dTh^=1.597 2.1878 -2.839:6.0342 Pooled a=0.0210 0.0118 -0.0028:0.0449 data Th==1.9952 0.9692 0.0330:3.957 4 Male yes a-O.037 0.0347 -0.0350:0.1101 Th=4.394 1.1914 0.3684:8.4203 Female a=0.035 0.0642 -0.0983:0.1715 Th=4.989 3.2132 -1.176:11.740 Pooled a=0.026 0.0168 -0.0079:0.0604 data Th==3. 998 1.7540 0.4474:7.5489

using a classification variable. Table 2.11. Logistic regression results for Orius insidiosus consuming eggs and first instars of European corn borer bcised on the logistic equation. Sex Estimated Standard Chi- Probability Probability Parameter error square Likelihood ratio Male no=-0.028 0.0107 7.13 0.00 0.0000 Female no=0.0133 0.0092 2.06 0.15 0.0000

Table 2. 12 Orius insidiosus parameters of the functional response to first in European corn borer, based on type I functional response equation. Sex Estimated Standard T-ratio prob R-square adjusted Parameters Deviation Male Bo=2.250 2.098 1.07 0.29 78.0 Î 61=0.697 0.070 9.09 0.00 -~J Female Bo=-1.25 2.190 0,57 0.57 81.2 \ 61=0.801 0.079 10.3 0.00 Joint 60=0.739 0.78 0.88 0.38 83.6 File 61=0.738 0.075 15.5 0.00 Eggs First instars 0.5- 0.65

8 0.45- 2 0.55- OJ- ■S 0.4- SO.45- 0 J5 - I .... £ 0 .3 5 - g 0.3-

0.25 0.25 0 25 37 50 62 75 »5 ICO 115 125 0 12 25 30 50 65 75 85 100 Number of eggs ofitrcd Meio Number of Larvae O&red

a = 0.27 a = 0.28 Th = 0.015 Th = 0.003

0 30- 1 25 50 75 100 Mean number of eg;s ofTcfed 0 25 50 100 12575 Mein Number ofLarvae Offered

a = 0.51 a = 0.96 5 Th = 0.19 5 Th = 0.19 â I B1I

z I S

0 25 50 75 100 125 0 25 so 75 100 125 Mean Number ofEggs OfTered Mean Number of Lam e OfTered Figure 2.1. Logistic regression curves and functional response curves for Coleomegilla maculata consuming eggs and first instars of European com borer with prey replenishment. ------indicates predicted values, ■ — «------indicates observed mean. A and D. Logistic regression for egg and larval consumption respectively. B and E. Functional response type II to eggs and fîrst instars respectively, based on unweighted non-linear least squares regression. C and F. Functional response type II to eggs and first instars respectively, based on weighted non-linear least squares regression. 78 Eggs First instars 0.6 1.2

a 0.S- O.S g 0.6- 80

5 0.1- 0.2

0 25 SO 65 7S «S 100 US 125 0 25 SO 65 75 S5 too 115 125 M m Number ofEggs Ofiered Mcaa Number of Lsrvae Offered

a = 0.09 g 60- a = 0.13 Th = 0.14 Tb = 0.07

o 40-

Z 20- Z 10-

0 2S SO 6S 75 85 100 115 I2S 25 50 65 75 85 ICO 115 125 Mcan Number of Eggs Offered Mean Number ofLuvae Offered

2.5 4.5 a = 0.08 5 4 - Th = 2.58 s

w 1.5- %I 2.5- I 2- w 0.5- a = 0.35 S 0.5- Th = 2.16

0 75 100 12550 0 Z5 so 65 75 85 100 115 125 Mean cumber of eggs offered Mean Number of Larvae Offered Figure 2.2. Logistic regression curves and functional response curves for Coleomegilla maculata consuming eggs and first instars of European com borer without prey replenishment. ------indicates predicted values,------# ------indicates observed mean. A and D. Logistic regression for egg and larval consumption respectively. B and E. Functional response type II to eggs and fîrst instars respectively, based on unweighted non-linear least squares regression. C and F. Functional response type II to eggs and first instars respectively, based on weighted non-linear least squares regression.

79 Eggs First instars

0.6 a 0.5

0.4 OJ

S 0.1-

0 5 10 15 20 25 30 35 40 45 SO M«tn Number ofEggs Offered Mean Proportion of Larvae Offered

a = 1.03 R- sqr = 0.88 .3 3.5- Th = 0.55

2 0 -

"5 15-

0 2 4 6 S 10 12 0 10 20 30 40 50 Mean Number of Eggs Offered Mean Number ofLaivae Ofiered

1 .6 a =1.21 . Ç gl4- iS 1.2- Th = 1.59 I I / II “I0.6- / / S 0'*- SO.2- I”*"/ 1 T 1 r I "1 I r i I " "1 0 12 3 4 5 6 7 S 9 10 11 12 Mcan Number of Eggj OSocd Figure 2.3. Logistic regression curves and functional response curves for Chrysoperla cornea consuming eggs and first instars of European com borer with prey replenishment. ------indicates predicted values, indicates observed mean. A and D. Logistic regression for egg and larval consumption respectively. B. Functional response type II to eggs based on unweighted non-linear least squares regression. C. Functional response type II to eggs based on weighted non-linear least squares regression. E. Functional response type I to first instars, based on a linear equation. 80 Eggs First instars O.t 'S OJ ’ JO.6- loj- g 0.15- I- | 0 J - K a i- I 0.2-

0 10 20 30 40 0 to 20 30 40 Mean Number Of Eq0s Offered Mean Number o f Prey Offerod

a = 0.21 a =0.13 4 - Th = 3.49 ' Th = 0.65

5 2- 6- Z Î

0 10 20 30 40 0 10 20 30 40 Mean Number ofEggs O&red Mean Number ofLarvae OOBsed

3 a = 0.18 F I 25 V-Th = 2.65 / a = 0.08 i ’- i05 / Th = 4.31 r - z 0- —'-T-----1----- 1----- 1------1------1------1----- 1----- 0 5 10 15 20 25 30 35 40 20 30 40 M as Kimber ofEggs Ofltnd Mean Number ofLarvae Offered Figure 2.4. Logistic regression curves and functional response curves forChrysoperla carnea consuming eggs and first instars of European com borer without prey replenishment. ------indicates predicted values, • indicates observed mean. A and D. Logistic regression for egg and larval consumption respectively. B and E. Functional response type II to eggs and first instars respectively, based on unweighted non-linear least squares regression. C and F. Functional response type II to eggs and first instars respectively based on weighted non-linear least squares regression.

81 Eggs First instars

0 .6-1 0.25 g 0.55-

0 4 5 -

E 0 J 5 - I 0.3- e 0.25- I 0 .2 - 0.15- 0 Z 4 6 g 10 12 Mean Number ofEggs OfTered Mean Number o f Larvae Offered

a = 0.10 c 3 5- Th = 0.53 Th = 0.19 4-

1 5 -

S 0.5-

0 2 4 6 % to 12 0 5 to 15 20 25 30 35 40 Mean Number ofEggs Offered Mean Number of Larvae Offered

Figure 2.5. Logistic regression curves and functional response curves for Orius insidiosus consuming eggs and first instars of European corn borer with prey replenishment. ------indicates predicted values, # ------indicates observed mean. A and C. Logistic regression for egg and larval consumption respectively. B and D. Functional response type II to eggs and first instars respectively, based on unweighted non-linear least squares regression.

82 Eggs First instars 0.16-, S O.H- I 0.9- “ 0*- a 0.12- i c 06- ° 0.5-

9.0.06- #0.4- |o . 3 - % 0.2- ,S 0.02-

0 10 20 JO 40 0 10 20 30 40 Mean M uoberof^lp Ofiered Number ofLaivaeQSesti

a = 0.021 R-sqr = 0.83 “ 30- Th = 1.99 I

nJ 20- 0 1 IS-

Z 10-

Z 0.5- I-

0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35 40 Mon Number of Eggs Ofiered Mean Number ofL irvie Offered

Figure 2.6. Logistic regression curves and functional response curves for Orius insidiosus consuming eggs and first instars of European com borer without prey replenishment. ------indicates predicted values, # ------indicates observed mean. A and C. Logistic regression for egg and larval consumption respectively. B. Functional response type II to eggs, based on unweighted non-linear least squares regression. D. Functional response type I to first instars, based on a linear equation.

83 Chapter III Cage Releases of Coleomegilla maculata (Coleoptera: Cocclnellidae) and Orius insidiosus (Hemiptera: Anthocoridae) for Control of Ostrinia nubilalis (Lepidoptera : Pyralxdae) . INTRODUCTION

When evaluating the influence of general predation on European corn borer {Ostrinia nubilalis Hubner) populations, Sparks et al. (1966) found that predators can be effective at consuming corn borer eggs and small larvae, but can not be relied on to affect borer numbers from year to year. Both Coleomegilla maculata (DeGeer) and Orius insidiosus (Say) have been reported as predators of European corn borer eggs and small larvae. Reid (1991) determined that a density of 12 0. insidiosus adults on sweet corn caused European corn borer egg mortality of 16% (on ears) and 80% (on leaves) on single caged plants where predators had been eliminated. Conrad (1959) reported that one C. maculata adult could consume an average of 59 O. nubilalis eggs per day when caged on a corn leaf and in absence of other food. Because of inconsistency in predator numbers from year to year, augmentation could enhance the role of predation in European corn borer control. Because these two predators are important factors in natural mortality of this pest, they are likely candidates for inundative releases for controlling European corn borer.

In this experiment, I studied the ability of 0. insidiosus and

C. maculata to search for and consume 0. nubilalis egg masses in caged sweet corn plants and in the absence of other prey. I also observed the effect of competition for the same food source in the consumption of O. nubilalis eggs by these two species.

84 MATERIALS AND METHODS

The experiment was established on 3 September 1995 at the Ohio

State University Horticulture Research Farm at Columbus, Ohio. The

sweet corn hybrid 'Lancelot' was used for this experiment. Cages were

placed over individual sweet corn plants early in the pollen shedding

stage. Tubular cages were constructed of sheer nylon tricot (Checker

Distributors, Maumee, Ohio) and structured with three rings of plastic

tubing 1.2 cm (outside diameter) by 0.9 cm (inside diameter). Cages measured 1.83 m high and 0.9m diameter. They were draped over the plants and tied at the top and bottom to a traverse wire running above and at the base of each corn row (Fig. 3.1) . Cages were easily opened at the bottom to access the plant for release of predators. Plants were sprayed with pyrethrins (Safer® Ringer Corp., Eden Prairie, Minnesota) to kill any predators or prey immediately before cages were placed over plants. Predators were released inside the cages 24 hours after plants were sprayed and caged.

Female adults of o. insidiosus and unsexed adults of C. maculata were field collected from sweet corn, placed in containers with cotton wicks saturated with water, and starved 24 hours before release. 0. nubilalis egg masses on a waxed paper substrate were obtained from a laboratory colony from the Department of Entomology, at Iowa State

University, Ames, Iowa. Three egg masses per plant were placed at positions commonly found in natural infestations. One was placed on the ear husk close to the tip, one on the bottom surface of the leaf immediately above the primary ear, and one on the bottom surface of the leaf immediately below the primary ear. Insect pins were used to attach egg masses to leaves. Egg masses had an average of 20 eggs.

Four replications of a three by four factorial were used. The three species treatments were 0. insidiosus, C. maculata, and a combination of 0. insidiosus and C. ma c u l a t a . The four density treatments were 0, 4, 8, and 12 O. insidiosus per plant; 0, 1, 3, and 5

85 c. maculata per plant; and a combination of both. Predator density

levels were chosen based on the range at which these species had been

found under natural conditions in plots where no chemical treatments had

been applied. Treatments with density of 0 were considered controls.

Twenty four hours after predators were released at the bottom of the

cages, egg masses were collected and held for 48 hours in a growth

chamber at 25°C until emergence was completed. Percentages of larval

emergence were assessed rather than percentages of eggs preyed upon,

because of difficulty in distinguishing which eggs were desiccated or

which eggs had been fed upon by O. insidiosus. In the case of C.

maculata there were egg masses in which only a small bite was taken from

one egg. In these cases, it was not clear at the time the eggs were

retrieved whether emergence of the larva had been affected.

Data were subjected to analysis of variance (ANOVA) using SAS's

general linear models procedure (SAS Institute 1991) to determine

effects of egg mass placement on the plant, percentage emergence at

different predator densities, and interactions between predators. Means

were separated by a Least Significant Difference means comparison test

(Steel & Torrie 1980) and non-orthogonal contrasts conducted to

determine species differences. RESULTS

There were no differences between percentage of emergence from egg masses located at the ear and those located above or below the ear (F =

0.07; p = 0.94/ df =2,105). Data for the three positions (above the

ear, below the ear, and at the ear) thus were pooled for the analysis of

variance. There was a significant (F = 3.8; df = 11,48; P = 0.001)

treatment effect on the percentage emergence.

There were no significant differences among densities of 0.

insidiosus or when compared with controls (Table 3.1); there were no

significant differences among densities of C. maculata either. When compared with the controls, the densities of three and five C. maculata

86 per plant had significantly lower percentage emergence (Table 3.1).

Emergence from plots with an intermediate density of eight O. insidiosus was not significantly different from emergence from plots with a combination of three C. maculata with eight O. insidiosus. The densities of 4 and 12 0. insidiosus had significantly (P i 0.05) higher percentage emergence than those in which the same densities of O. insidiosus were combined with 1 and 5 C. maculata respectively (Table

3.1). Significantly more emergence was observed when C. maculata density was one per plant than when one C. maculata adult was combined with four 0. insidiosus adults per plant. No differences were observed between plots in which three or five C. maculata were released, and those in which the same densities of C. maculata were combined with eight or 12 O, insidiosus. The treatment that had the least emergence,

6.3%, was that in which 12 O. insidiosus and five C. maculata were released. Non-orthogonal contrasts showed there were significant (P =

0.04) differences between the two species, with a higher percentage emergence where O. insidiosus had been released that where C. maculata had been released. DISCUSSION

C. maculata caused significant mortality to European corn borer egg masses in the absence of any other predators or prey. 0. insidiosus on the other hand did not. I believe that the 56% emergence obtained with the intermediate density of 8 o, insidiosus per plant, was more an aberrant result of natural mortality by factors such as desiccation and unfertilized eggs than of predation. Reid (1991) found that 0. insidiosus favored leaves over ears when searching for European corn borer egg masses; this was not found in my study, where no preferences for any of the three locations was detected. In Reid's experiments, 12

0. insidiosus adults caused 80% mortality of a mean of 90.7 eggs offered. I found that for the density of 12 adults per plant, a percentage emergence of 82.5 % (about 18% mortality) was observed, which

87 was not significantly different from any of the untreated controls.

Environmental changes can easily affect coccinellid predatory behavior (Smith 1971, Sparks et al. 1966). Even small disturbances such

as wind, can alter the feeding behavior in this family. Caged plants

can enhance predation because the insects do not have to fly around the

field searching for the particular prey, thus searching time decreases, and the ability to consume increases (Luck et al. 1988) .

It appears that O. insidiosus can search for and consume European

corn borer eggs; however, the number of eggs it can consume is very low.

These results are corroborated by functional response studies (Chapter

II) where this anthocorid exhibited a type II functional response to

European corn borer eggs with an average consumption of 3.2 eggs per 12 hours when prey density was 40 eggs. The same studies showed that C. maculata also exhibited a type II functional response to European corn borer eggs but the average consumption was 26 eggs per 12 hours when prey density was 50 eggs. Although an apparent enhancing effect occurred when C. maculata and O. insidiosus were used in combination, these results reflect mostly the effects of predation by C. maculata.

Mortality in most of the eggs was caused by chewing rather than by sucking or drying of the eggs. It has been reported that the favorite foods of 0. insidiosus in sweet corn are thrips and pollen (Dicke &

Jarvis 1962) and that C. maculata can derive up to a 50% of its diet from corn pollen (Hoffman & Frodsham 1993).

In conclusion, I propose that C. maculata alone rather than O. insidiosus should be considered for inundative releases for control of

European corn borer. Further studies should be conducted on the complex set of interactions with other prey and predators, shedding of pollen, and environmental conditions, to better understand how this coccinellid may be used as a biological control agent.

88 Table 3.1. Percentage emergence of Ostrinia nubilalis from egg masses exposed to predation by Coleomegilla maculata and/or Orlus insidiosus on caged sweet corn plants. Treatment Percentage emergence ^ (Density per plant)

Coleomegilla maculata Orius insidiosus 0 0 81.7 a 1 0 66.8 ab 3 0 35.1 bed 5 0 39.0 bed 0 0 84.9 a 0 4 81.3 a 0 8 56.4 abc 0 12 82.5 a 0 0 81.2 a 1 4 22.8 cd 3 8 33.8 bed 5 12 6.3 d different (PsO.05), least significant difference multiple means comparison t test.

89 Figure 3.1. Cages where releases of Coleomegilla maculata and Orius insidiosus were made on 3 September 1995.

90 Chapter IV Field Releases of Cbrysopexla. camea Stephens (Neuroptera: Chrysopidae) Eggs and First Instars for Predation on Ostrinia nubilalis Hübner (Lepldopter a : Pyralldae) on Sweet Com. INTRODUCTION

European corn borer {Ostrinia nubilalis Hubner) is a key pest of sweet corn in the midwestern United States. It damages the ear, reducing yields and lowering crop value. Although this pest on large commercial farms is most commonly controlled by insecticides, there is interest particularly from small-scale farmers on the use of biological control as an alternative. Predators and parasitoids can reduce the density of this pest but do not provide commercially acceptable levels of control because of their low density in natural populations.

Releasing commercially reared parasitioids and predators is a practice that has been emerging as a mechanism for enhancing the role of natural enemies (Hudon et al. 1989). Among the commercially available predators, one of the most common is the green lacewing Chrysoperla carnea Stephens, which has been reported as an important predator of corn pests (Sparks et al. 1966, Ridgway & Jones 1968, Carlson & Chiang

1973) . The inclusion of C. carnea as a component of a pest management program could be ideal because it has high tolerance for several insecticidal compounds such as pyrethroids (Bartlett 1964, Bashir &

Crowder 1983), and some organophosphates and carbamates (Free et al.

1989). Free et al. (1989) showed the existence of resistant strains within the species, which would further increase its value as a biological control agent. Other characteristics that make green lacewings good candidates are ease of rearing, polyphagy, and widespread

91 distribution (New 1975). A major drawback in the use of green lacewings

is the high cost.

In spite of the potential of C. carnea, there are few reports on

inundative and augmentative releases in the field. Experiments have

been conducted on cotton (Ridgway & Jones 1968, 1969), apples (Hagley

1989), peaches (Hagley & Miles 1987), and potatoes (Shands et al. 1972),

which report partial to high success in control of several pest species.

In this study, I evaluated field releases of different densities of C.

carnea eggs and larvae for control of European corn borer on sweet corn.

MATERIALS AND METHODS.

Field studies were conducted at two research farms at Columbus and

Fremont, Ohio. Two planting times (early and late) were selected so

that sweet corn plants were at their most attractive stage to be

infested by first and second generation European corn borer.

Early sweet com. Sweet corn [Zea mays L.) of the variety 'Seneca

Horizon' was planted on 11 May 1993 and 3 May 1993 at Columbus and

Fremont respectively. Four factors were evaluated: predator growth

stage (egg versus pre-fed larva); timing of release relative to crop phenology (whorl versus silk); rate of release (low versus high);

frequency of applications (one versus two). A randomized complete block design was used, with 6 replications of 17 treatments. Eight

treatments applied when corn was in the whorl stage were: 2 lacewing

eggs per plant, single release; 2 eggs per plant, double release; 5 eggs per plant, single release; 5 eggs per plant, double release; 1 lacewing

larva per plant, single release; 1 larva per plant, double release; 2

larvae per plant, single release; 2 larvae per plant, double release.

The same eight treatments were applied when corn was in the early

silking stage. Treatment 17 was a control where no releases were made.

In treatments with double releases, the specified number of lacewings was applied in each of the two releases. Densities of two lacewing eggs

92 or two larvae per plant were equivalent of 210,000 eggs or larvae per hectare; five eggs per plant were equivalent to 500,000 eggs per hectare; one larva per plant was equivalent to 105,000 larvae per hectare.

Plot size was 2.1 iti by 0.91 ra with 2 rows per plot and 0.2 m between plants. There were two guard rows on each side of the field and replicate blocks had bare ground between them. Plots were separated by

2.1 m of bare ground within each replication. No insecticides were used.

Lacewings were purchased from Rincon Vitova in Ventura,

California. Eggs were counted and placed by twos and fives in individual 3 ml vials to be released in the field. Eggs were released when their color was grey (close to hatching) so that larvae would be emerging within 24 hours of their release. Larvae came in corrugated cardboard cells and they were released by small groups in a large plastic container and then transferred with a camel-hair brush and placed in the whorl or on the silk. Releases were made in the morning hours, when some dew was still on the plants. Releases in Columbus were made on 23 June and 3 July 1993 (plots with two releases). Releases for

Fremont were made on 17 June and 24 June 1993 (plots with two releases).

Scouting evaluations once per week for 6 weeks determined presence and damage of the target pest as well as presence of natural enemies on

5 whole plants per plot. Ten ears per plot were harvested at Fremont on

15 July 1993. Plots at Columbus had uneven maturation, and only 5 ears per plot were harvested on 27 July 1993. Ears were evaluated for presence and/or damage of the lepidopteran complex that attacks sweet corn, which includes Ostrinia nubilalis (Hübner) (European corn borer),

Helicoverpa zea (Boddie) (corn earworm), and Spodoptera frugiperda (J.E.

Smith)(fall armyworm). When signs of larval feeding on the kernels were observed, the ear was rated as having kernel damage; when no damage or caterpillars were found in the kernels, husks, silks, and shank, the ear

93 was rated as clean; when damage was found in silks, shank, or husks, the

ear was rated as having husk/silk/shank damage.

Late sweet corn. The same procedures that were followed for early sweet

corn were followed for late sweet corn with some exceptions. The

variety 'Lancelot' was planted on 24 June for Fremont and 9 July for

Columbus. Lacewing larvae were released only during the early silk

stage, aimed at second generation European corn borer. Releases in

Columbus were made on 26 August and 2 September 1993 (plots with two

releases). Releases for Fremont were made on 12 August and 18 August

1993 (plots with two releases). A randomized complete block design was

used, with six replications of nine treatments. Single releases were:

two lacewing eggs per plant, five eggs per plant, one lacewing larva per

plant, two larvae per plant. Double releases were two eggs per plant,

five eggs per plant, one larva per plant, two larvae per plant.

Treatment nine was a control where no releases were made. Plot size and

evaluation were the same as for the early sweet corn. Ten ears per plot

were harvested at Fremont on 31 August 1993. Plots at Columbus had poor stands and all ears available, from two to 10 ears per plot, were

harvested on 21 September 1993. Ears were evaluated for damage by the

lepidopteran complex, and the same categories used for the early planting were used for the late planting.

Statistical Analysis. Data were subjected to an analysis of variance

(ANOVA) using SAS's general linear models procedure (SAS Institute,

1991) and means separated by a Least Significant Difference means

comparison test (Steel & Torrie 1980) . Pre-planned comparisons were performed with single degree of freedom non-orthogonal contrasts.

RESULTS

When weekly scouting data were analyzed to determine treatment effects on infestation from European corn borer, no significant differences were found for any of the individual dates at Columbus or

Fremont, in either early or late plantings. Fall armyworm larvae were

94 found feeding in the whorl of plants at Columbus' late planting.

Lacewings were rarely seen; usually the stages found were eggs or adults, few larvae were encountered. Natural enemies such as O.

insidiosus, C. maculata, and other Coccinellidae were commonly seen on plants, and could have reduced the European corn borer population.

Mortality due to released lacewings versus indigenous predators was not determined in this experiment.

For the early planting in Fremont, significantly fewer ears with kernel damage were harvested from plots that received double releases of two larvae per plant in the whorl than those harvested from untreated controls or from five other treatments (Table 4.2). No significant differences in the percentage of clean ears harvested were observed among treatments. Some differences were observed in the percentage of ears infested with European corn borer: significantly fewer infested ears were harvested from plots that received single releases of five eggs per plant in the whorl, double releases of two larvae per plant in the whorl, and single or double releases of two larvae per plant on the silks, than from plots where single and double releases of five eggs per plant on the silks, or single releases of one larva per plant in the whorl were made (Table 4.1). Non-orthogonal contrasts showed significant differences in the total percentage of ears with kernel damage between plots that received one larva and those that received two larvae per plant. Differences in percentage of clean ears were found between treatments in the whorl and in the silk. Percentage of ears infested with European corn borer was significantly different between plots that received one larva and those that received two larvae (Table

4.1)

At Columbus, a low percentage of lepidopteran larvae were found in harvested ears for all treatments (Table 4.2). Lack of European corn borer was apparently due to a late planting date. There were no significant treatment effects on the total percentage of ears with

95 kernel damage. The lowest percentage of ears with kernels damaged

(0.6%) was harvested from plots that received the double release of one

larva per plant at silking. Significantly fewer clean ears were

harvested from plots that received double releases of two lacewing eggs per plant at the whorl stage than from those that received the single

release.

For the late planting at Columbus, plots that received single

releases of five eggs per plant and plots that received double releases of two larvae per plant were the only ones that had significantly lower percentage of ears with kernel damage than the untreated control (Table

4.3). Significantly more clean ears were harvested from plots that

received the single release of five eggs per plant than from plots that

received single or double releases of two eggs per plant, double

releases of one larva per plant, single release of two larvae per plant, and the untreated control (Table 4.3). Non-orthogonal contrasts showed that the percentages of ears infested with European corn borer and fall armyworm were significantly different between plots thatreceived single releases of larvae and those that received two releases. Likewise, for percentage of ears infested with European corn borer and fall armyworm, differences were found between plots that received one larva and those that received two larvae, and between plots that received eggs and plots that received larvae.

The late planting at Fremont did not have any significant treatment differences for the percentage of ears with kernel damage or percentage of clean ears. Non-orthogonal contrasts did not show any significant differences either (Table 4.4). However, in this planting presence of corn earworm and fall armyworm was low, and better determination of treatment effects on European corn borer damage or presence could be assessed.

96 DISCUSSION

The harvest results showed that eggs and larvae of C. carnea released at 105,000 to 1,050,000 per hectare provided some control of

European corn borer, particularly in the early plantings. C. carnea larvae have been reported as efficient predators of eggs and first instars of H. zea and H. virescens eggs in caged cotton plants when released at a rate of 250,000 larvae per hectare {Lopez et al. 1976).

Ridgway and Jones (1968) reported a 99% reduction of H. virescens and H. zea larvae on cotton when field-cage releases of 1,000,000 C. carnea larvae per hectare were used. In the early planting at Fremont, significantly less kernel damaged ears (1.2%) were harvested from plots that had received a double release of 210,000 larvae per hectare at the whorl stage than from plots that had received no releases (15.6%); this showed there is potential for use of larvae for control of European corn borer. Likewise, double releases at silking of 210,000 larvae per hectare, significantly reduced the percentage of ears (43.4%) with kernel damage when compared with the control (82.8%) for the late planting at Columbus.

European corn borer egg masses are exposed for a short time after being laid. Hatching occurs within three to seven days for the first generation and within three to five days for the second generation

(Showers et al. 1989). It is very important to time releases with the day on which the majority of egg masses are hatching to provide the lacewing larvae the chance to search for and attack its prey. Changes in chorion toughness can affect the acceptability of certain eggs, with older eggs being less acceptable (New 1975). Added complications with lacewing releases come from temperature and predator to prey ratios. On the other hand, sweet corn whorls or silks are release sites more likely to retain lacewing eggs or larvae compared to other crops; whorls due to the architecture of the plant and silks due to the somewhat moist sticky

97 texture. Hagley (1989) found that populations of Aphis pomi DeGeer were efficiently reduced when the ratio was 1 to 10, but aphid numbers were not reduced when the ratio was 1 to 25. This was noticeable in our experiments, where pressure of European corn borer was higher in the late planting attacked by the second generation of borers, which are known to cause more severe damage to the ears.

Although egg releases are the most commonly used for C. carnea, I believe that the most efficient releases would be those of larvae because they can be more easily timed with the peak of egg mass abundance. The results of this experiment show highest potential for larval releases for first generation European corn borer. Even if c. carnea releases were highly effective, both egg and larval releases are hampered by wind and humidity, are labor intensive and costly. Further studies on higher release rates, methods of mechanized release, rates determined by ratio to prey, interactions with indigenous natural enemies, and possibilities of using the releases in combination with microbial insecticides could generate more information needed prior to incorporating this predator into a pest management program.

98 Table 4.1. Percentage of sweet corn ears with and without kernel damage and with European corn borer (ECB), fall armyworm (FAW), and corn earworm (CEW) present at harvest of an early planting in Fremont, 1993, after treatment with C. carnea eggs and larvae; and non orthogonal contrasts of pre-planned comparisons of factor effects.

Treatment Kernel Clean kernels, ECB FAW CEW damage husk, silk

IN WHORL 2 eggs/plant,single 10.1 a 86.1 a 1.1 ab 2.6 a 0 b double 13.6 ab 66.2 a 4.5 ab 1.1 a 0 b 5 eggs/plant,single 12.3 ab 80.8 a 0.3 b 3.4 a 0 b double 11.5 ab 87.2 a 1.1 ab 1.1 a 0 b 1 larva/plant,single 13.6 ab 79.1 a 7.9 a 1.7 a 0 b double 13.6 ab 80.7 a 3.4 ab 0.3 a 0 b 2 larvae/plant,single 8.8 ab 88.8 a 1.7 ab 0.3 a 0 b double 1.2 b 37.7 a 0.3 b 1.1 a 0 b IN SILKS 2 eggs/plant,single 15.6 a 69.4 a 1.7 ab 1.7 a 0 b double 10.3 ab 81.7 a 3.4 ab 0 a 0 b 5 eggs/plant,single 14.8 a 68.1 a 8.8 a 0 a 0 b double 15.3 a 69.4 a 5.1 a 1.1 a 0 b 1 larva/plant, single 15.3 a 65.4 a 3.4 ab 0.3 a 0.3 b double 21.4 a 70.8 a 5.6 ab 1.7 a 0 b 2 larva/plant, single 6.2 ab 69.4 a 0.3 b 0 a 0 b double 5.1 ab 83.8 a 0.3 b 0.3 a 0 b CONTROL No releases 15.6 a 73.3 a 1.7 ab 1.7 a 0 b NON-ORTHOGONAL CONTRASTS B P PPP Eggs vs. larva 0.5 0.6 0.7 0.4 0.3 Whorl vs. silk 0.6 0.03 0.5 0.1 0.3 Single vs. double-Egg 0.6 1.0 0.5 0.4 1.0 Single vs. double-Larva 0.6 0.5 0.6 0.6 0.2 2 eggs vs. 5 eggs 0.5 0.9 0.8 1.0 1.0 1 larva vs. 2 larva 0.01 0.2 0.009 0.4 0.2 5 eggs vs. 2 larva-Double 0.04 0.4 0.2 0.7 1.0 Within each column prior to contrasts, means followed by same letter are not significantly different (PsO.05), least significant difference t test.

99 Table 4.2. Percentage of sweet corn ears with and without kernel damage and with European corn borer (ECB), fall armyworm (FAW), and corn earworm (CEW) present at harvest of an early planting in Columbus, 1993, after treatment with C. carnea eggs and larvae; and non orthogonal contrasts of pre-planned comparisons of factor effects.

Treatment Kernel Clean kernels, ECB FAW CEW damage husk, silk

IN WHORL 2 eggs/plant,single 1.3 a 98.7 a 0 b 0 6 a Q b double 10.8 a 68.5 b 0 b 0 a 0.6 a 5 eggs/plant,single 13.2 a 86.8 ab 0 b 0 a 0 b double 17.1 a 82.9 ab 0 b 0.6 a 0 b 1 larva/plant,single 11.5 a 8 6.3 ab 0 b 0.6 b 0 b double 4.0 a 95.6 ab 0 b 0 a 0 b 2 larvae/plant, single 4.6 a 95.4 ab 0 b 0 a 0 b double 16.9 a 83.1 ab 0 b 0.5 a 0 b

IN SILKS 2 eggs/plant,single 19.2 a 80.8 ab 0 b 0 a 0 b double 16.3 a 77.6 ab 0 b 0 a 0 b 5 eggs/plant,single 5.3 a 94.7 ab G b 0 a 0 b double 16.6 a S3.4 ab 0 b 0.6 a 0 b 1 larva/plant,single 2.4 a 97.6 ab 0 b 0 a 0 b double 0.6 a 97.6 ab 0 b 0 a 0 b 2 larva/plant,single 1.0 a 87.3 ab 0 b 0 a 0 b double 8.6 a 91.3 ab 0.6 a 0.6 a b 0 b

CONTROL No releases 14.6 a 85.4 ab 0 b 1.3 a 0 b

NON-ORTHOGONAL CONTRASTS PPPP P Eggs vs. larva 0.1 0.2 0.3 0.3 1.0 Whorl vs. silk 0.6 0.8 0.3 0.3 0.5 Single vs. double - Egg 0.3 0.009 1.0 0.2 0.6 Single vs. double - Larva 0.6 0.9 0.2 1.0 0.6 2 eggs vs. 5 eggs 0.7 0.6 1.0 0.2 0.6 1 larva vs. 2 larva 0.5 0.4 0.2 1.0 0.6 5 eggs vs. 2 larva-Double 0.7 0.7 0.04 1.0 1.0 Within each column prior to contrasts, means followed by same letter are not significantly different (fsO.05), least significant difference t test.

100 Table 4.3. Percentage of sweet corn ears with and without kernel damage and with European corn borer (ECB), fall armyworm (FAW), and corn earworm (CEW) present at harvest of a late planting in Columbus, 1993, after treatment with c. carnea eggs and larvae; and non orthogonal contrasts of pre-planned comparisons of factor effects.

Treatment Kernel Clean ECB FAW CEW damage kernels, husk, silk IN SILKS 2 eggs/plant, single 81.4 abc 18.6 be 11.7 be 10.5 be 16.3 a double 70.6 abed 19.6 be 17.4 b 26.7 b 2.4 a 5 eggs/plant, single 46.2 cd 61.7 a 2.7 c 4.8 ,c 4.1 a double 75.0 abed 25.0 abc 15.4 be 11.2 be 9.1 a 1 larva/plant, single 56.0 bed 53.7 ab 19.8 b 17.9 be 5.3 a double 92.4 a 7.6 c 56.6 a 59.9 a 18.3 a 2 larva/plant,single 86.5 ab 13.5 c 10.5 be 16.5 be 14.5 a double 43.4 cd 56.6 ab 16.0 be 17.5 be 2.2 a CONTROL No releases 82.8 ab 17.2 be 17.3 b 8.7 be 12.5 a

NON-ORTHOGONAL CONTRASTS P P P P P Eggs vs. larva 0.6 1.0 0.008 0.01 0.7 Single vs. double - Egg 0.4 0.2 0.08 0. 0.5 Single vs. double - Larva 0.9 0.82 0.01 0.02 0.9 2 eggs vs. 5 eggs 0.2 0.09 0.2 0.1 0.8 1 larva vs. 2 larva 0.5 0.7 0.003 0.02 0.55 5 eaos vs. 2 larva-Double 0.1 0.1 0.9 0.5 0.3 Within each column prior to contrasts. means followed by same lette r are not significantly different (fsO.05), least significant difference t test.

101 Table 4.4. Percentage of sweet corn ears with and without kernel damage and with European corn borer (ECB), fall armyworm (FAW), and corn earworm (CEW) present at harvest of a late planting in Fremont, 1993, after treatment with C. carnea eggs and larvae; and non orthogonal contrasts of pre-planned comparisons of factor effects.

Treatment Kernel Clean ECB FAW CEW damage kernels, husk, silk IN SILKS 2 eggs/plant,single 92.3 a 1.7 a 63.6 a 0 b 6.7 a double 94.7 a 4.3 a 74.2 a 0 b 0.3 be 5 eggs/plant,single 98.3 a 0.9 a 75.0 a 0.3 a 0 c double 91.0 a 6.7 a 77.9 a 0 b 4.5 ab 1 larva/plant,single 95.5 a 2.6 a 51.7 a 0 b 1.7 abc double 92.3 a 5.6 a 68.4 a 0 b 2.6 abc 2 larva/plant,single 96.6 a 1.2 a 71.1 a 0 b 0.3 be double 95.7 a 2.4 a 57.7 a 0 b 2.0 abc CONTROL No releases 88.5 a 7.4 a 65.7 a 0 b 0.3 be

NON-ORTHOGONAL CONTRASTS P PP P P Eggs vs. larva 0.8 0.9 0.1 0.3 0.8 Single vs. double - Egg 0.5 0.1 0.5 0.1 1.0 Single vs. double - Larva 0.6 0.4 0.9 1.0 0.4 2 eggs vs. 5 eggs 0.7 0.9 0.4 0.1 0.5 1 larva vs. 2 larva 0.6 0.4 0.7 1.0 5.0 5 eggs vs. 2 larva 0.5 0.3 0.2 1.0 0.5 Double Wichin each column prior to contrasts, means followed by same letter are not significantly different (PsO.05), least significant difference t test.

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