Spray-dried microencapsulated Bacillus thuringiensis formulations for the control of Epilachna varivestis mulsant

A new sprayable microgranule formulation of Bacillus thuringiensis subsp. kumomatoensis (strain C-9) was evaluated for the control of the Mexican bean beetle Epilachna varivestis Mulsant. Strain C-9 was isolated from dead E. varivestis in a Phaseolus vulgaris L. field in Durango, Mexico. A spore and crystal complex of the C-9 strain were active against E. varivestis larvae in bioassays using treated bean plants (LC₅₀ of 642 μg/ml), and against Trichoplusia ni (Hubner) larvae using artificial diets (LC₅₀ of 219 μg/ml). The sprayable powder (microgranule formulation), consisting of cornstarch (CS), nixtamalized corn flour (NCF), vegetable oil, powdered sugar, 2-propanol, malachite green, and formaldehyde, was prepared using a spray-dry process. Shelf life of formulated B. thuringiensis maintained over 90% of its original activity after 24 months of storage. A field test demonstrated that treatments of formulated B. thuringiensis controlled E. varivestis significantly better than treatments with unformulated B. thuringiensis. This study demonstrated that B. thuringiensis can potentially be formulated by spray drying, based on ingredients, which would help to improve its activity as a biopesticide under field conditions.