Role of cuticle-degrading enzymes of Beauveria bassiana and Metarhizium anisopliae in virulence on Plodia interpunctella (Lepidoptera, Pyralidae) larvae

Entomopathogenic fungi (EPF) are important biological control agents in pest management programs in agro-ecosystems against insect pests. EPF such as Beauveria bassiana (Bals.) Vuillemin and Metarhizium anisopliae (Metchn.) Sorokin produce a wide range of extracellular enzymes involved in disturbance of the first barrier in the insect cuticle comprising proteins, chitin, and lipids. Realizing relationships between the expression of these enzymes and fungal virulence might aid in development of effective mycoinsecticides. The virulence of B. bassiana (isolates TV and OZ1) and M. anisopliae (isolate CS1) were investigated on Plodia interpunctella (Hubner) larvae in this study. The third instar larvae were immersed in a suspension containing 1 x 108 conidia mL-1 of fungal conidial inoculum. The results revealed that all three fungal isolates caused mortality in larvae, but there was a considerable variation in their virulence. Total proteinase, exochitinase and lipase assays were done for these isolates. The TV isolate with the highest mortality with 41.7%, had the highest level of specific activity of exochitinase, protease, and lipase with 0.148, 0.654, and 0.190 U. mg-1 protein, respectively. In the current study, a positive correlation was determined between the virulence of fungal isolates and the activities of protease and lipase, but this link was not significant for exochitinase. Our results demonstrated that extracellular enzymes, particularly protease and lipase, may play a crucial role in the virulence of these fungal isolates against P. interpunctella larvae.

Automated summary

Entomopathogenic fungi play an important role in pest management by producing enzymes that disrupt insect cuticles. In this study, the virulence of different isolates of two EPF species was evaluated against Plodia interpunctella larvae. The results showed that protease and lipase activities were positively correlated with the virulence of the fungal isolates.