Sprayable self-encapsulating starch formulations for Bacillus thuringiensis

Under glasshouse conditions, various cornstarches and adjuvants were examined as encapsulating agents in sprayable formulations for Bacillus thuringiensis subsp. kurstaki Berliner. When these materials were suspended in water and tested for physical factors such as viscosity, clumping, and retention on plant surfaces, a range of responses was observed. All formulations tested had acceptable viscosity, but some formulations clumped. When applied to cotton leaves, certain formulations remained less than 4 d, whereas others remained greater than 2 wk. One of these formulations containing equal parts of Mira-sperse (a commercially available pregelatinized cornstarch) and sucrose (6% total solids) was selected for testing persistence of B. thuringiensis insecticidal activity against Ostrinia nubilalis Hübner neonate larvae. When encapsulating agents were present, insecticidal activity decreased over a 2-wk period significantly more slowly than when encapsulating agents were absent. This indicates an enhanced persistence of B. thuringiensis under glasshouse conditions. Implications of a sprayable self-encapsulating formulation for B. thuringiensis are discussed.