Combined effects of some insecticides and different isolates of Beauveria bassiana and Metarhizium anisopliae on mortality and immune responses of Chilo suppressalis Walker (Lepidoptera: Crambidae)

Abstract

The combined use of microbial agents and chemical insecticides is an effective strategy against insect pests in agroecosystems. This study evaluates the effects of four insecticides-permethrin, fenitrothion, trichlorfon, and tebufenozide-together with four isolates of the entomopathogenic fungus Beauveria bassiana and two isolates of Metarhizium anisopliae on the fourth instar larvae of Chilo suppressalis. In the first experiment, treatment with fungal isolates induced the activities of general esterases and glutathione S-transferases (GST) in the larvae. Field concentrations of insecticides increased larval mortality in both control and fungus-treated groups, except for BBLN2, which showed no significant difference. In the second experiment, conidia cultured in control and insecticide-treated media were exposed to field concentrations of insecticides on C. suppressalis larvae. This resulted in a significant decrease in larval mortality when treated with conidia cultured with insecticides. In the third experiment, larvae treated with permethrin exhibited the highest total hemocyte counts among those injected with BBLN1 and BBLN2, whereas larvae treated with fenitrothion and trichlorfon showed similar results after injection with BBAL1. All insecticide and fungal isolate treatments increased phenoloxidase activity compared to control larvae. These results underscore the importance of screening for optimal combinations of insecticides and entomopathogenic fungi to enhance control measures, which depend on the specific fungal isolate and type of insecticide.