Negative effects on the development of Chrysodeixis includens and Spodoptera cosmioides fed by peanut plants inoculated with entomopathogenic fungi

Abstract

Recent studies have shown that entomopathogenic fungi, as endophytes, can have beneficial effects on plants, protecting them from defoliating insects. The potential of endophytic association by entomopathogenic fungi with the peanut crop has been little explored. In our study, we conducted experiments by inoculation of peanut seeds through a soil drench method with nine strains/species of entomopathogenic fungi of the genera Metarhizium, Beauveria and Cordyceps, subsequently these plants were consumed by two larval pests, Chrysodeixis includens and Spodoptera cosmioides. The parameters of larval growth rates, mortality, foliar consumption and larval period were observed during the development of larvae. In addition, the endophytic capacity of these fungi in peanut plants and their persistence in soil were investigated. In two replicate greenhouse trials for each larva, peanut plants were inoculated with fungi by the soil-drench method. We evaluated the performance of C. includens and S. cosmioides feeding on inoculated peanut plants starting at the 2nd larval instar. The larval and pupal weights of C. includens and S. cosmioides were significantly different among the fungal treatment groups, where insects feeding on control plants exhibited higher larval and pupal weights than insects feeding on treated plants. The differences in larval period showed that Control larvae pupated faster than the larvae fed on fungal-inoculated plants, fungal treatments had a larval period of 3 to 5 days more than the control. The mortality rates of C. includens and S. cosmioides were significantly different among the fungal treatment groups, insects fed on Control plants exhibited higher survival than insects fed on fungal-inoculated plants. The persistence of all Metarhizium fungi was higher in the soil compared to other fungi, and only Metarhizium and B. bassiana IBCB215 emerged from the phyllosphere of peanut plants. Although the fungus Cordyceps presented the worst performance among the fungal treatments. Overall, our results demonstrate the negative effects on the development of C. includens and S. cosmioides that were fed on fungal-inoculated peanut plants, the best results recorded were for Metarhizium strains and the fungus B. bassiana IBCB215.

Keywords: Lepidoptera; biological control (CB); entomopathogen; groundnut (A. hypogaea L.); hypocreales.