Submitted to: Society for Invertebrate Pathology Annual Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/15/2003
Publication Date: 8/15/2003
Citation: WRAIGHT, S.P., RAMOS, M., WILLIAMS, J.E., AVERY, P.B., JARONSKI, S., VANDENBERG, J.D. COMPARATIVE VIRULENCE AND HOST SPECIFICITY OF BEAUVERIA BASSIANA ISOLATES ASSAYED AGAINST LEPIDOPTERAN PESTS OF VEGETABLE CROPS. PROCEEDINGS OF THE ANNUAL MEETING OF THE SOCIETY FOR INVERTEBRATE PATHOLOGY. 2003. v. 36. p. 36.
Technical Abstract: Approximately 40 isolates of the entomopathogenic fungus Beauveria bassiana were screened against second-instar larvae of diamondback moth (Plutella xylostella) (DBM), European corn borer (Ostrinia nubilalis) (ECB), corn earworm (Helicoverpa zea) (CEW), and fall armyworm (Spodoptera frugiperda) (FAW), and 30 of these isolates were tested against beet armyworm (Spodoptera exigua) (BAW). Highly virulent isolates identified in the screening assays were also tested against black cutworm (Agrotis ipsilon) (BCW), and the top isolate was also assayed against imported cabbage worm (Pieris rapae) (ICW) and cabbage looper (Trichoplusia ni) (CL). B. bassiana was pathogenic against all lepidopteran species tested, and numerous highly virulent isolates were identified. Corn earworm and beet armyworm were most susceptible to fungal infection, and fall armyworm was least susceptible. Limited testing suggested low susceptibility also of black cutworm and cabbage looper. A unique isolate (strain BB1200) exhibited virulence against all pest species greater than or equal to the most important commercial strain of B. bassiana currently registered in the U.S. (strain GHA). In assays in which larvae were topically sprayed and maintained on the treated substrate for 24 h at 100% relative humidity, 6-day (25ºC) median lethal rates (LR50s) of this isolate against CEW, BAW, DBM, FAW, ICW, ECB, CL, and BCW were 4, 5, 7, 11, 12, 98, 125, and 273 conidia/mm2, respectively. The respective LR50s of commercial strain GHA against these pest species were 9, 67, 97, 1213, 29, 1668, 541, and 3504 conidia/mm2. Use of LR50 versus median lethal dose ratios (comparing LR50s of each isolate to a "standard" strain) generated similar rankings of isolate virulence.