|SHASHA BARUCH S|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/1996
Publication Date: N/A
Interpretive Summary: The use of chemicals to control insect and weed pests of crops, for a variety of reasons is declining and tools to replace these control agents are under investigation. One type of tool is a group of natural agents called microbial pesticides that are safe to use, relatively specific in activity and very effective. However, microbial pesticides lose activity quickly after application. This paper reports on materials that can be used to extend the activity of microbial pesticides under field conditions. Cornstarch and corn flour can be easily modified to produce water soluble products. When modified starch or flour ismixed with powdered sugar and then added to spray tanks containing microbial pesticides, the resulting spray deposit dries and forms a film entrapping the active ingredient. Our tests demonstrated in two field experiments retention of insecticidal activity of Bacillus thuringiensis, one type of microbial pesticide, for up to eight days on cabbage under rainy conditions. A commercial product with B. thuringiensis as the active ingredient, lost activity after 3-4 days. These experiments should lead to an understanding of the factors responsible for microbial pesticide breakdown. On a practical basis, the materials used in the experiments can be incorporated into formulations of microbial pesticides, or used as spray adjuvants when added directly to a spray tank.
Technical Abstract: Microbial pesticides such as those based on Bacillus thuringiensis Berliner, exhibit short residual activity when applied as foliar sprays. We report on the use of pregelatinized cornstarch and corn flour as formulation ingredients for sprayable B. thuringiensis preparations to extend residual activities. In two field tests, residual activity was measured by feeding treated leaves to diamondback moth larvae. In the first test (1989) pregelatinized starch, when mixed with equal amounts of sucrose and tank mixed at a total of 4% solids (4 g/100 ml), provided protection of B. thuringiensis on cabbage leaves for up to 5 d under sunny field conditions. A commercial B. thuringiensis product lost activity after 3 d. In the second study (1991), pregelatinized flour, when mixed with sucrose, also provided protection in the presence of rainfall. In this study, 1, 2, and 4% solids were used to test the effects of amounts of formulation materials required to achieve protection of B. thuringiensis. In the presence of rain, 4% solids was required for optimum protection. Treatments that included 1 or 2% solids did not provide protection as measured against a commercial product. provide protection as measured against a commercial product. Laboratory tests demonstrated the protective effects of the flour formulations against artificial sunlight but did not support field results on rainfastness. These experiments, together reinforce the proposition that formulation ingredients such as corn flour can increase residual activity of B. thuringiensis.