Controlled-release ofBacillus thurigiensisformulations encapsulated in light-resistant colloidosomal microcapsules for the management of lepidopteran pests ofBrassicacrops

Abstract

Bacillus thuringiensis(B. t.) based formulations have been widely used to control lepidopteran pests in agriculture and forestry. One of their weaknesses is their short residual activity when sprayed in the field. Using Pickering emulsions, mixtures of spores and crystals from threeB. t.serovars were successfully encapsulated in colloïdosomal microparticles (50 μm) using innocuous chemicals (acrylic particles, sunflower oil, iron oxide nanoparticles, ethanol and water). A pH trigger mechanism was incorporated within the particles so thatB. t.release occurred only at pH > 8.5 which corresponds to the midgut pH of the target pests. Laboratory assays performed onTrichoplusia ni(T. ni) larvae demonstrated that the microencapsulation process did not impairB. t.bioactivity. The best formulations were field-tested on three key lepidopteran pests that attackBrassicacrops, i.e., the imported cabbageworm, the cabbage looper and the diamondback moth. After 12 days, the mean number of larvae was significantly lower in microencapsulated formulations than in a commercialB. t.formulation, and the effect of microencapsulated formulations was comparable to a chemical pesticide (lambda-cyhalothrin). Therefore, colloïdosomal microcapsule formulations successfully extend the bioactivity ofB. t.for the management of lepidopteran pests ofBrassicacrops.