Effects of Imidacloprid on Two Parasitoids, Toxoneuron nigriceps and Campoletis sonorensis, of the Tobacco Budworm, Heliothis virescens, and High-throughput Sequencing of the Tobacco Thrips, Frankliniella fusca

TAYLOR, SALLY VANN. Effects of Imidacloprid on Two Parasitoids, Toxoneuron nigriceps and Campoletis sonorensis, of the Tobacco Budworm, Heliothis virescens, and High-throughput Sequencing of the Tobacco Thrips, Frankliniella fusca. (Under the direction of Dr. Clyde E. Sorenson and Dr. R. Michael Roe.) Toxoneuron nigriceps (Viereck) (Hymenoptera, Braconidae) and Campoletis sonorensis (Cameron) (Hymenoptera, Ichneumonidae) are parasitoids of the larval stage of the tobacco budworm Heliothis virescens (Fabricius) (Lepidoptera, Noctuidae). They species are valuable biological tools in controlling tobacco budworm populations in Southeastern US agricultural production systems. We calculated the topical LD50 of imidacloprid to C. sonorensis and to T. nigriceps to estimate the toxicity of imidacloprid to these beneficial species. The parasitoids in our study did not have a similar response to topical imidacloprid exposure. The topical LD50 value of imidacloprid for adult T. nigriceps was estimated to be 366-fold higher compared to the topical LD50 value for adult C. sonorensis. Field and greenhouse trials conducted from 2011-2014 compared parasitism rates and life span of parasitoids that developed inside H. virescens larvae which fed on tobacco plant tissue treated with and without imidacloprid. Residues of imidacloprid and its metabolites were detectable in the bodies of H. virescens larvae fed treated plants and T. nigriceps larvae and adults from H. virescens larvae fed treated plants. The two parasitoids in our study did not have similar responses to larvae fed with this insecticide-treated plant tissue. T. nigriceps had reduced parasitism and adult lifespan, but C. sonorensis parasitism rate and life span were unaffected. These findings suggest that there are ecological effects of imidacloprid use on multiple trophic levels, and that insecticide use may differentially affect natural enemies with similar feeding niches. The tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera, Thripidae), is a major agricultural pest in the southeastern United States for which there are increasingly limited management options. The identification of genes essential to growth, development and homeostasis of this insect provides potential targets for RNA interference (RNAi) transgene therapies. We sequenced whole-body transcriptomes of larval and adult F. fusca using Illumina ® high-throughput technology. The resulting 236 million 100 base pair reads were assembled, batch BLASTed, mapped, and annotated into over 25 thousand contiguous sequences per life stage, to be further analyzed to identify function. To illustrate the depth of contig information in our global, putative functional analysis, messages involved in the RNAi pathway, hormonal regulation of development, steps in juvenile hormone (JH) biosynthesis and degradation, known commercial insecticide targets, and enzymes involved in insecticide detoxification were characterized. We have identified putative proteins associated with reproduction in larval thrips, illustrating a need for species-specific and life stage-specific sequencing across insect taxa. The use of whole-body insects for sequencing yielded messages produced by bacteria, fungi and viruses associated with insects and plant hosts. Our data provide a critical first step in understanding the unique physiology of F. fusca and potential new approaches for their control. © Copyright 2015 Sally Vann Taylor All Rights Reserved Effects of Imidacloprid on Two Parasitoids, Toxoneuron nigriceps and Campoletis sonorensis, of the Tobacco Budworm, Heliothis virescens, and High-throughput Sequencing of the Tobacco Thrips, Frankliniella fusca by Sally Vann Taylor A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy