Response of Starch-Encapsulated Bacillus thuringiensis Containing Ultraviolet Screens to Sunlight

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Abstract
Formulations of Bacillus thuringiensis Berliner spores and crystals, encapsulated together within a starch matrix containing no ultraviolet screens, lost all spore viability and insecticidal activity against the European corn borer, Ostrinia nubilalis (Hübner), within 4 d. Encapsulated crystals and spores with Congo red or folic acid as screens exhibited moderate spore viability and retained at least 50% of their original toxicity after 12 d. Congo red was the most effective protectant, followed by folic acid and para amino benzoic acid. Because Bacillus thuringiensis is likely sensitive to the entire ultraviolet-component in sunlight, ability to provide broad-band ultraviolet protection is required to prolong insecticidal activity effectively.