Submitted to: International Colloquium on Invertebrate Pathology and Microbial Control Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: August 18, 2002
Publication Date: September 1, 2002
Citation: UGINE, T.A., WRAIGHT, S.P., SANDERSON, J.P., BROWNBRIDGE, M. Dose acquisition by second-instar and adult female western flower thrips exposed to leaf disks and impatiens plants treated with Beauveria bassiana. International Colloquium on Invertebrate Pathology and Microbial Control Proceedings. 2002. v. 8. p. 93.
Bioassays were conducted against western flower thrips using three preparations of Beauveria bassiana: an unformulated powder (UP), a wettable powder (WP), and an oil-based emulsifiable suspension (ES). Sixty second-instar nymphs and 30 adults were exposed to each of four rates of fungus applied to bean leaf disks; assays were replicated four times. Mortality was assessed after 5 days. The conidia acquisition profile (distribution of conidia on specific body regions) was determined for each formulation on nymphs and for the WP on adults. Thrips were collected 24 h post-treatment, and conidia were counted at 400x magnification. Thrips on potted impatiens plants were also sprayed with the WP at a concentration of 5 x 107 conidia/ml. Conidia were counted on second-instar nymphs and adult females after 24 h. Formulation had no effect on numbers of conidia on the whole insect or on specific body regions. Nymphs treated with UP, WP and ES had LD50's of 42, 50, and 50 conidia/insect and LC50's of 74, 178, and 112 conidia/mm2, respectively. Conidia acquired after 24 h caused no significant increase in mycosis among nymphs. Adult females were more susceptible than nymphs, with an LC50 of 19 conidia/mm2. The dose on adults after 24 h indicated an LD50 of only 5 conidia/insect. Acquisition efficiency (conidia/insect divided by conidia/mm2 of leaf substrate) decreased with increasing application rate. Greatest numbers of conidia were found on the legs of both nymphs and adults (32% and 46% of total conidia acquired), on the abdomens of nymphs (31%), and on the thoraces (wings and legs excluded) of adults (26%). Nymphs collected from foliage and open flowers of treated plants had 115 and 452 conidia/insect, respectively; the respective doses on adults were 255 and 204.