Entomopathogenic Potential of Cuticle-Degrading Enzymes From Bacillus velezensis CE100 in the Biocontrol of Pine Aphid (Eulachnus thunbergii Wilson)

Pine aphids are notoriously destructive sap-sucking pests of pine trees worldwide. We investigated the biocontrol efficacy of Bacillus velezensis CE100 through cuticle-degrading enzymes, which degrade the cuticular structure of insect pests. During its growth, CE100 produced protease, chitinase, and lipase activities up to 17 units/mL, 83 units/mL, and 27.5 units/mL, respectively. Treating aphid nymphs with bacterial broth culture and bacterial crude enzyme fraction of CE100 caused several lethal effects under laboratory conditions with up to 92% and 93% mortality rates, respectively, 30 h post-treatment. The median lethal time (ET50) of bacterial broth culture and crude enzyme fraction against aphid nymphs was 10 h, 36 min, and 5 h, 16 min, respectively. The aphids from the treatment groups exhibited severe fissures and disintegration of the cuticle, exposing internal tissues, and causing substantial loss of setae. The degradation of the wax layer, chitin, and glycoprotein polymers by the cuticle-degrading enzymes caused a high rate of aphid mortality, and thus, CE100 could effectively control aphid population and should be further studied as a potential component of integrated pest management strategies in pine forests.