Exploration of the microbial world of Frankliniella occidentalis (Pergande), the western flower thrips

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) are major insect pests of agricultural and ornamental plants. Thrips cause damage by vectoring devastating plant viruses and by feeding directly on plant leaves and flowers. Bacteria were found in thrips regardless of the age or diet of the host. Some bacterial symbionts have been known to dramatically affect host biology and evolution. The study of these bacteria will provide a more thorough understanding of the factors that influence the biology of this important pest. This dissertation aims to characterize these bacteria and better understand their prevalence in thrips populations, effect on their host, and interaction with biotic factors that have already established a relationship with Western flower thrips.Thus, the symbiosis between F. occidentalis and two unique microbes can be impacted by external forces and may impact the thrips-TSWV relationship.This dissertation has 3 parts: (1) Characterization of bacterial symbionts in Frankliniella occidentalis (Pergande), the Western flower thrips. F. occidentalis from around the world have a consistent microflora comprised of two unique bacteria. This association is widespread and meets the definition of a symbiosis. One thrips bacterial group may have a shared ancestry with Erwinia, whereas the second group had no supported phylogenetic relative. (2) Distribution and Ecology of Frankliniella occidentalis Bacterial Symbionts. F. occidentalis bacterial symbionts, BFo-1 and BFo-2, were detected in wild F. occidentalis populations from diverse California environments. No other bacteria consistently infected F. occidentalis. Regional differences in bacterial prevalence and infection suggested bacterial infection is associated with environmental conditions. (3) Triangle of Associations: Bacterial Symbionts, Tomato spotted wilt virus, and Western flower thrips. Thrips hatched from antibiotic-treated eggs (aposymbiotic thrips), followed by exposure to BFo-2, had significantly higher Tomato spotted wilt virus (TSWV) transmission success and frequency compared to untreated controls, although none of the aposymbiotic treatments were significantly different from one another. Gender studies showed BFo-1, BFo-2, and bacteria-free treatments were significantly male-skewed. Thrips infected with both symbionts were slightly less male-biased than the other treatments, but were not considered significantly different from untreated thrips.