AN ABSTRACT OF THE THESIS OF Diane M. Sether for the degree of Master of Science in Entomology presented on September 10, 1991. Title: Transmission Efficiency and Life Table Parameters of Western Flower Thrips, Frankliniella occidentalis (Pergande) Exposed to Tomato Spotted Wilt Virus-Impatiens Serotype Abstract approved:Redacted for Privacy Peppermint, Mentha piperita 'Black Mitcham' was established as a host for tomato spotted wilt virus-impatiens serotype (TSWV-I). TSWV-I infection of peppermint, initially observed in a research greenhouse (Corvallis, OR), included stunting and downward curling of leaves accompanied by bronzing, and occasionally tip necrosis. Young leaves appeared either symptomless, deformed, or pale even under high nitrogen conditions. Older leaves had sunken, brownish-grey lesions. Bright yellow mottling was observed on newly mature deep green leaves. A begonia isolate of TSWV-I was transmitted to peppermint both mechanically and by western flower thrips, Frankliniella occidentalis (Pergande). Symptoms of TSWV-I infection were similar although only a faint yellow mottling was produced and only under cool temperatures (15°C). ELISA detection of virus distribution throughout the plant indicated infection was systemic. Bulked groups of thrips (5 thrips/sample) also tested positive for TSWV-I using ELISA. Transmission efficiency of 4, 6, 8, and 10 day old thrips adults given acquisition sources during the entire nymphal stage varied from 0-40% for thrips tested in pairs and 0-20% for single thrips (based on a 12 hour access feeding period). Adults 2 days old failed to transmit the virus. Western flower thrips exposed to TSWV-I had reduced survival and reproductive potential and slower development rates than unexposed thrips. Virus- exposed thrips were 1.4 times as likely to die than unexposed thrips on a given day. Both individual and population reproductive potentials were significantly lower. Preoviposition period was extended in virus-exposed thrips. Development time from second instar to adult was 15% longer for virus-exposed thrips. This is the first report of altered population parameters in western flower thrips exposed to TSWV-I. Transmission Efficiency and Life Table Parameters of Western Flower Thrips, Frankliniella occidentalis (Pergande) Exposed to Tomato Spotted Wilt Virus-Impatiens Serotype by Diane M. Sether A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Completed September 10, 1991 Commencement June 1992 APPROVED: Redacted for Privacy Assistant Professor of intomology in charge of major Redacted for Privacy Associate Pro4-s-sor of Entomologi/n charge of major Redacted for Privacy Head of Department of Entomology Redacted for Privacy LCilll 1J1 ttallitItC U. Date thesis is presented September 10, 1991 Typed by Diane Sether Acknowledgements A heartfelt thanks is owed to my co-major professors, Dr. Jack DeAngelis and Dr. Phil Rossignol. Without their encouragement, financial support and constructive criticisms this thesis may never have come to be. Also, I thank Dr. Ken Johnson for his review of my manuscripts and participation on my committee and Dr. Darrell Ross who made sure I jumped through the proper hoops during my oral examination. Dr. Ralph Berry is also owed thanks for his fortunate (or unfortunate) placement of peppermint cuttings in the greenhouse used in my virus/vector research. And last, but certainly not least, I wish to thank Mr. Dick Samson and Dr. Tom Allen whom provided a seemingly endless supply of TSWV-I infected plants. This work was funded in part by a grant from NIAID, NIH, a grant from the Oregon Department of Agriculture, the Oregon Mint Commission, the Nursery Advisory Council, and the Oregon Association of Nurserymen. Table of Contents 1. Introduction 1 Literature Review Virus symptomology and virion identification 3 Thrips identification and biology 7 Vector and virus relationship 13 Objectives and Rationale 15 2. Western flower thrips, Frankliniella occidentalis (Pergande) transmission of tomato spotted wilt virus-impatiens serotype in peppermint, Mentha piperita L. 'Black Mitcham' 16 Abstract 17 Introduction 18 Methods and Materials 20 Results 26 Discussion 37 References Cited 40 3. Decreased survival and reproductive potential and slower development rate in western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) exposed to tomato spotted wilt virus-impatiens serotype 42 Abstract 43 Introduction 44 Methods and Materials 46 Results 51 Discussion 61 References Cited 63 4. General Conclusions 65 Bibliography 69 Appendices Appendix 1: Tomato spotted wilt virus host list 80 References Cited 90 Appendix 2: Families of tomato spotted wilt virus hosts 96 List of Figures Figure 1.1. Adult female western flower thrips, Frankliniella occidentalis (Pergande). 8 Figure 1.2. Life stages of western flower thrips, Frankliniella occidentalis (Pergande). 10 Figure 2.1. Symptomatic peppermint plant, Mentha piperita L. 'Black Mitcham' from original TSWV-I infection in a research greenhouse (Corvallis, OR). 27 Figure 2.2. Leaf of 'Black Mitcham' peppermint showing symptoms of TSWV-I. 28 Figure 2.3. Comparison of leaves of equal rank and age from healthy 'Black Mitcham' peppermint plants (bottom row) and plants infected with a begonia isolate of TSWV-I (top row). 32 Figure 3.1. Survival curves of TSWV-I exposed and unexposed Frankliniella occidentalis (Pergande) replicates. 53 Figure 3.2. Survival curves and development time for TSWV-I exposed and unexposed Frankliniella occidentalis (Pergande). 56 Figure 3.3. Cumulative reproductive potential for TSWV-I exposed and unexposed Frankliniella occidentalis (Pergande) populations. 59 Figure 4.1. Components of the disease pyramid for vector-borne diseases. 68 List of Tables Table 2.1. ELISA analysis for distribution of TSWV-I in symptomatic peppermint, Mentha piperita L. 'Black Mitcham'. 29 Table 2.2. ELISA analysis for distribution of TSWV-I in symptomatic peppermint, Mentha piperita L. 'Black Mitcham'. 30 Table 2.3. Transmission efficiencies of western flower thrips given 12 hour feeding access on 'Black Mitcham' peppermint. 34 Table 3.1. Mean development times (days ± standard error) at 26°C for TSWV-I exposed and unexposed Frankliniella occidentalis (Pergande). 52 Table 3.2. Logrank test results for survival differences both between replicates and for pooled replicates of TSWV-I exposed and unexposed Frankliniella occidentalis (Pergande). 55 Transmission Efficiency and Life Table Parameters of Western Flower Thrips, Frankliniella occidentalis (Pergande), Exposed to Tomato Spotted Wilt Virus-Impatiens Serotype Chapter 1 Introduction Tomato spotted wilt is a persistent and debilitating vector-borne plant virus first reported on tomato in 1919 (Brittlebank, 1919). Since then, over 560 plant species (appendix 1), including both monocots and dicots representing 62 families (appendix 2) have been confirmed as hosts. At present, six species of phytophagous thrips, in three genera, are known vectors of TSWV, namely, western flower thrips (WFT), Frankliniella occidentalis (Pergande); tobacco thrips, F. fusca (Hinds); common blossom thrips, F. schultzei (Trybom); onion thrips, Thrips tabaci Lindeman; T. setosus Moultan; and chile thrips, Scirtothrips dorsalis Hood (Allen & Broadbent, 1986). Of these, western flower thrips is becoming increasingly important as a virus vector because of broad host range and widespread resistance to insecticides commonly used for its control in greenhouses (Robb et al., 1988). Understanding how to control many vector-borne diseases has been aided by modeling of dynamics of the vector population. Vector parameters paramount in such models include transmission efficiency, longevity, fecundity, and development time. A serotype of TSWV known as TSWV-I is prevalent in greenhouses where WFT are a common problem. Up until now it has been assumed, although not documented that WFT can vector the impatiens serotype of TSWV. If this is indeed true, the occurrence of both 2 potential vector and virus in greenhouse situations where vector and virus parameters can be manipulated make the WFT-TSWV-I-plant host system a prime candidate for epidemiological modeling. 3 Literature Review Virus svmptomolokv and virion identification In recent years, TSWV has accounted for 50-90% of summer crop losses of crisphead and romaine lettuce in Hawaii, losses in peanuts exceeding five million dollars in Texas, and heavy losses of ornamental and bedding plants in commercial greenhouses throughout the U.S. and Canada (Cho et al., 1986; Halliwell & Barnes, 1987; MacDonald et al., 1989; Stewart et al., 1989; Tehrani et al., 1990). Onions, tobacco, pineapple, watermelon, tomatoes, and peppers have incurred major economic damage from TSWV as well, and the list continues to expand (Amin et al., 1981; Iwaki et al., 1984; Dintenfass, 1987; Broadbent et al., 1987; Pitblado et al., 1990). The extensive host range of the virus includes weeds as well as crop species further complicating control. In addition, TSWV is easily confused with certain fungal and bacterial diseases such as those caused be species of Botrytis, Nectria, Pseudornonas, Mycospherella, and Colletotrichum spp. (Matteoni et al., 1988). Virus tolerance and symptom expression is dependent on host species or cultivar, environment, age of plant, and virus strain. Tolerance generally increases with age of plant. Young plants are very susceptible and may die quickly whereas older