In vivo and in vitro evaluation of Beauveria bassiana pathogenicity for western flower thrips, Frankliniella occidentalis [MSc Dissertation]

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  • Western flower thrips, Frankliniella occidentalis, are major pests in greenhouses. The fungus Beauveria bassiana is a safer alternative to use of chemical insecticides against this insect; and evaluating isolates for high virulence has usually involved in vivo studies. My approach examines in vitro properties of B. bassiana in relation to F. occidentalis in vivo virulence. I developed in vitro tools based on colony growth and metabolite analyses to identify isolates for biocontrol potential. Six characteristics were developed and assessed against LT50 data. My results indicated that 3 combined characteristics (harvest quality, mycelial fragments and degree of submerged mycelia) can be used to predict virulence. Oosporein production was also examined by photo-exposure. Results indicated that all 4 isolates tested, exhibiting low to high virulence, produced oosporein thereby disassociating it from whole animal virulence. Instead, oosporein may function as a photo-protectant. Beauvericin production was also evaluated by HPLC and was produced by all 5 isolates tested. Beauvericin production and whole animal virulence appear to be uncoupled although my results do suggest a weak correlation. The toxicity of beauvericin was evaluated on a whitefly embryonic cell line and was found to be sensitive in a dose- and time-dependent fashion. I demonstrated the CC50 after 48 h incubation to be comparable to that of other researchers using different cell lines. These analyses will help reduce processing time and labour intensity required for in vivo studies when screening isolates. This approach contributes to a greater understanding of pathology and supports microbial control registration for commercial use.

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    Attribution 3.0 International