Roles of adjuvants in aphicidal activity of enzymes from Beauveria bassiana (Ascomycota: Hypocreales) SFB-205 supernatant

Enzymes from Hypocrealean entomopathogenic fungi often encounter unfavorable abiotic and biotic factors during pathogenesis. The present work describes the roles of adjuvants, such as corn oil and polyoxyethylene-(3)-isotridecyl ether (TDE-3), in promoting aphicidal activity of enzyme precipitate from Beauveria bassiana SFB-205 supernatant. Supernatant enzymes including chitinase and proteases were lyophilized by attagel-mediated protein precipitation to produce attagel-mediated enzyme powder (AMEP). Corn oil-based AMEP + TDE-3 suspension showed 96.3% control efficacy against cotton aphids, Aphis gossypii Glover (Hemiptera: Aphididae), in glasshouse conditions at 2 days post-application, whereas water-based AMEP + TDE-3 suspension or TDE-3 alone showed < 20% efficacy. Corn oil-based AMEP + TDE-3 suspension was superior in degrading chitinase-specific substrate (p-nitrophenyl-β-d-acetylglucosaminide) under a drying condition compared to water-based AMEP + TDE-3 suspension. TDE-3 made supernatant, a source material of AMEP, degraded more cotton aphid proteins than supernatant alone in SDS-polyacrylamide gel electrophoresis; supernatant was used to clearly show the degradation without interfering with other proteins such as AMEP. These results suggest that 1) corn oil can slow down the evaporation of the diluted suspension drop and provide more time for enzymes from AMEP to degrade more cuticles at the time of application and 2) TDE-3 can disrupt chitin–protein matrixes within procuticle and facilitate enzymes from AMEP in degrading proteins which increases the exposure of chitin fibers to the attack of chitinases. This approach can provide another strategy in developing biopesticides using entomopathogenic fungi.