Sprayable granule formulations for Bacillus thuringiensis

Spray-dried Bacillus thuringiensis subsp. kurstaki formulations, composed of citric or lactic acid, pregelatinized corn flour, cornstarch, isopropyl alcohol, sugar, and corn oil, were used in leaf and diet incorporation bioassays to determine the effects of solar radiation and rain on insecticidal activity. In diet incorporation tests against Helicoverpa zea (Boddie), Trichoplusia ni (Hubner), Heliothis virescens (F.), and Spodoptera exigua (Cramer), insecticidal activity of spray-dried B. thuringiensis did not decrease when compared with unformulated technical B. thuringiensis. Cotton leaf bioassay tests using Ostrinia nubilalis (Hubner) showed that insecticidal activity of formulations exposed to 8 h of artificial solar radiation was significantly higher than technical B. thuringiensis exposed to solar radiation, suggesting that the formulations provided protection against solar radiation. In cotton leaf bioassays, when 5 different starches were used individually in the formulations, insecticidal activity was significantly reduced in only 1 case after exposure to solar radiation. Cotton leaf bioassays also showed a reduction in insecticidal activity caused by exposure to solar radiation as the amount of active ingredient (wt:wt) in the formulation increased. Throughout all tests, rainfastness of formulations was not consistently better than technical B. thuringiensis alone.