Effect of sub-lethal and lethal concentrations of the entomopathogenic fungus Metarhizium anisopliae Sorokin on detoxification enzymes and demographic parameters of Mythimna separata (Walker)

Abstract

The maize armyworm, Mythimna separata (Walker) (Lepidoptera: Noctuidae), is a polyphagous, destructive, and migratory pest. Improper pesticide application induced resistance may be an alternative mechanism for pest resurgence. In this study, the efficacy of Metarhizium anisopliae (Sorokin) was estimated, while focusing on sub-lethal (LC15) and lethal (LC50) concentration treatments on the F0 and F1 generations of laboratory-reared M. separata. The results indicated an LC50 value of 2.2 × 106 conidia mL−1 against M. separata larvae after infection with M. anisopliae. The sub-lethal and lethal concentrations and trans-generational effects on demographic parameters were estimated using the age-stage, two-sex life table. After treatment with LC15 (2.1 × 105conidia mL−1) and LC50 (2.2 × 106 conidia mL−1) concentrations, the progeny of M. separata exhibited reduced fecundity, larval duration and adult male and female longevity as compared to the control. Subsequently, population growth parameters such as mean generation time (T) and net reproductive rates (Ro) were reduced in these concentrations. Furthermore, activities of the detoxification enzymes glutathione S-transferases (GST), acetylcholinesterase (AChE) and esterases (EST) were significantly different at the LC50 as compared to LC15 and the control. These findings showed pathogenicity of M. anisopliae even at sub-lethal concentration, with negative effects on the fecundity, biological parameters and also altered the detoxifying enzymes of M. separata which enhanced its potential use as a management tool in eco-friendly and long-lasting management programs.