ASSESSMENT OF BEAUVERIA-BASSIANA SPRAYS FOR CONTROL OF DIAMONDBACK MOTH (LEPIDOPTERA, PLUTELLIDAE) ON CRUCIFERS

Evaluations of the efficacy and persistence of Beauveria bassiana (Bal samo) Vuillemin for control of the diamondback moth, Plutella xylostel la (L.),on crucifers were done in growth chambers, the greenhouse, and the field. In growth chamber studies done at 21 or 26 degrees C and 6 0 or 90% RH, neither temperature nor humidity affected the survival of larvae, but treatment with fungal spores always provided significantl y greater mortality than the control. In 2 greenhouse trials, 1 applic ation of B. bassiana spores suspended in water or oil significantly re duced larval populations compared to controls. In a field trial, both treatment and insect stage at treatment (2nd and 3rd to 4th instars) s ignificantly affected larval survival. The fungus, formulated as a wet table powder at 2 rates and as an emulsifiable suspension at a high ra te, provided significant reductions in larval counts. Two applications of the wettable powder at the higher rate resulted in lower larval co unts than did a single application. Two applications (but not 1) of we ttable powder at the lower rate resulted in significantly lower counts of 2nd instars but not 3rd to 4th instars. Both treatment and time af fected both the persistence of viable B. bassiana spores on leaves and the retention of efficacy of treated leaves for P. xylostella larvae. These trials indicate the potential for including B, bassiana in an o verall management program for P. xylostella.