EFFECTS OF SUNLIGHT AND SIMULATED RAIN ON RESIDUAL ACTIVITY OF BACILLUS-THURINGIENSIS FORMULATIONS

The effect of sunlight and simulated rain on the residual insecticidal activity of Bacillus thuringiensis subsp. Kurstaki formulations appli ed to field grown cabbage were measured. Leaf samples were collected 1 , 2, 4 and 7 d after treatment and assayed against neonate cabbage loo per, Trichoplusia ni (Hubner). Simulated rain applied Lv a sprinkler i rrigation system washed B. thuringiensis from the plants, causing on a verage 20% reduction in insecticidal activity across all treatments. S unlight intensity was manipulated by applying degrees of shade treatme nts consisting of no cover, clear plastic covers, and black plastic co vers. Black plastic provided protection from sunlight degradation for 7 d, whereas both clear plastic and no cover treatments lost insectici dal activity equally beginning 2 d after application of B. thuringiens is. There was no interaction between simulated rain and shade treatmen ts and thus no synergistic loss of insecticidal activity by the combin ation of both environmental factors. Formulations of B. thuringiensis differed in their ability to resist wash-off by simulated min and degr adation by sunlight. Formulations consisting of 1% wt:vol gluten or 0. 5% wt:vol casein resisted wash-off better than flour/sucrose (2% wt:vo l) and Dipel 2X. Resistance to sunlight degradation was greatest with the gluten formulation and progressively less for casein, flour/sucros e and Dipel 2X formulations. Half-life of insecticidal activity in res ponse to sunlight was calculated to be 7.1, 5.7, 4.8, and 4.3 d for gl uten. casein. flour/sucrose and Dipel 2X formulations, respectively.