DOSE-RESPONSE AND AGE-RELATED AND TEMPERATURE-RELATED SUSCEPTIBILITY OF THE DIAMONDBACK MOTH (LEPIDOPTERA, PLUTELLIDAE) TO 2 ISOLATES OF BEAUVERIA-BASSIANA (HYPHOMYCETES, MONILIACEAE)

Two isolates of Beauveria bassiana (Balsamo) Vuillemin were used in bi oassays against the diamondback moth, Plutella xylostella (L.). One is olate, ARSEF 4543, originated from a dia mondback moth larva collected in New York and the other, Mycotech GHA, is the active ingredient in Mycotrol, a product registered for control of insect species belonging to several orders. Dose response assays of suspended spores sprayed o n larvae resulted in similar LD(50)s (518 and 614 spores per square ce ntimeter for ARSEF 4543 and Mycotech GHA, respectively) but different slopes for the probit regression lines (0.64 and 0.89). Survival times for larvae inoculated at a range of dosages were variable for ARSEF 4 543 but decreased with increasing dosages for Mycotech GHA. Third and 4th instars were more susceptible than 2nd instars, although survival times varied between the 2 isolates for different instars. Larvae inoc ulated early in the 2nd or 3rd instar had. shorter survival times than those inoculated later in each instar. Spores of B. bassiana were rea dily detected on exuviae from inoculated larvae using fluorescence mic roscopy, indicating the significance of molting as a means of avoiding infection. The isolates did not differ significantly in their activit ies over a range of temperatures. Highest mortality and lowest surviva l times were observed at 25 degrees C; mortality decreased and surviva l time increased at temperatures both above and below 25 degrees C. Th ese Endings provide baseline information on the susceptiblity of P, xy lostella to B, bassiana and they indicate the potential utility of a c ommercial preparation of B. bassiana for use against PI xylostella in the field.