ABSTRACT

Formulations are being developed for protecting entomopathogenic fungi from solar radiation to improve mycoinsecticide efficacy. Beauveria bassiana (GHA) spores were coated by spray drying with either water-soluble lignin or water-insoluble Ca²⁺-cross-linked lignin. These coated spores were suspended in either water (0.04% Silwet L77) or oil (Orchex 692) and compared with non-coated spores in water or oil to demonstrate the impact of the coating on spore survival under simulated solar radiation and pathogenicity to tarnished plant bug, Lygus lineolaris (Palisot de Beauvois). The rate of spore mortality under simulated solar radiation was approximately ten times lower for the three formulations in which spores in suspension remained coated with lignin (cross-linked lignin in water, lignin in oil, and cross-linked lignin in oil). The pathogenicity of the six formulation strategies did not differ significantly on the basis of LC₅₀ values for direct spray applications to L lineolaris adults. However, the three lignin coated formulations that provided the greatest UV protection were slower to kill L. lineolaris (higher LT₅₀ values). Adult L. lineolaris mortality was approximately 20 times lower when exposed to broccoli florets treated with B. bassiana formulations than when L. lineolaris was sprayed directly. In bioassays with treated broccoli florets, non-coated spores in 0.04% Silwet L77 were the most pathogenic. Under field conditions where solar radiation significantly impacts mycoinsecticide efficacy, the improved persistence of lignin coating formulations may outweigh the negative effects of reduced pathogenicity.