Impact of Tomato spotted wilt virus (Family Bunyaviridae, Genus Tospovirus) On Western Flower Thrips ( Frankliniella occidentalis) Feeding Behaviors and Analysis of the Adult Salivary Gland Transcriptome

The interactions between parasites and their vectors can cause profound changes in vector behavior, including changes that can enhance parasite transmission and alter trophic interactions. Parasite driven modification of vector feeding behavior is of broad adaptive significance, as vector borne parasite fitness relies on passage to a new host through vector feeding. We report for the first time, that vector infection by a plant virus alters feeding behavior. Here we show that infection with Tomato spotted wilt virus (TSWV), (family Bunyaviridae, genus Tospovirus), alters both the plant feeding behaviors and predatory behaviors of its omnivorous thrips vector, Frankliniella occidentalis (Pergande). Interestingly, the behavioral alterations reported herein are sexually dimorphic. TSWV infection altered the plant feeding behavior of male but not female thrips, and altered the predatory behavior of female thrips to a greater extent than male thrips.;TSWV infection and cell-to-cell movement requires the inoculation of virus particles into a living, functional plant cell, therefore feeding behaviors that introduce virus particles into this type of environment are most likely to result in successful virus transmission. Male thrips infected with TSWV fed on plant material more than uninfected males, with the frequency of all feeding behaviors increasing by up to 3 fold. Importantly, infected males made almost 3 times more non-ingestion probes (probes in which they salivate, but leave cells largely undamaged), compared to uninfected males, thus increasing the probability of virus inoculation. F. occidentalis infected with TSWV also exhibited increased predatory behaviors and the presence and consumption of mite eggs as an alternative food source did not significantly alter vector plant feeding behaviors. Alteration to thrips predatory behavior is unlikely to be directly linked with increased virus transmission because increased predation did not affect plant feeding behaviors. Taken together these alterations to thrips feeding behaviors appear to be a compensatory response to alleviate detrimental effects of virus infection, as opposed to a direct manipulation of vector feeding behaviors to increase virus transmission. Furthermore, these finding shows an alternative pathway by which viruses can influence the structure of trophic interactions in food webs.;Saliva is known to play a crucial role in insect feeding behavior and virus transmission. Currently, very little is known about the salivary glands and saliva of thrips. As a first step towards characterizing thrips salivary gland functions, we sequenced the transcriptome of the primary salivary glands of F. occidentalis using short read sequencing (Illumina) technology. We found 32,566 high quality contig sequences with an average size of 605 bp. A high percentage (57.29%) of contigs had no protein or nucleotide hits, but 13,275 contigs had significant BLAST hits (E-value≤1.0E -6). We identified several genes that are likely to play a role in thrips feeding including: aldehyde dehydrogenases, metalloproteases, and glucose oxidase, which are likely to be involved in counteracting plant host defense responses; beta glucosidases and pectin lyases which are likely play a role in the extra-oral digestion of plant structural tissues; and &agr; amylase,and &agr; glucosidase while likely play a role in the extra-oral digestion of sugars. This is the first comprehensive study of a sialotranscriptome for any Thysanopteran species and provides a necessary tool to further our understanding of how thrips interact with their viruses and plant hosts.