Treatments with Metarhizium brunneum BIPESCO5 and EAMa 01/58-Su strains (Ascomycota: Hypocreales) are low risk for the generalist predator Chrysoperla carnea

Abstract

Metarhizium spp. (Hypocreales: Clavicipitaceae) are used as alternatives to hazardous pesticides. During host infection, they secrete secondary metabolites such as destruxin A. Information on the fate of those secondary metabolites in the food chain and their risk to human and animal health is scarce. In the present work, predator–prey bioassays were performed to evaluate the behavior and survival of green lacewing Chrysoperla carnea (Neuroptera: Chrysopidae) larvae when presented with armyworm Spodoptera littoralis (Lepidoptera: Noctuidae) larvae treated with Metarhizium brunneum BIPESCO5 and EAMa 01/58-Su strains. Moreover, ecotoxicological studies were done using HPLC–MS to monitor the fate of destruxin A in the prey–predator system. HPLC–MS confirmed the presence of destruxin A at low concentrations in S. littoralis larvae infected with BIPESCO5 (approximately 0.014 μg/g) and EAMa 01/58-Su (approx 0.031 μg/g) strains, whereas the metabolite was not detected in C. carnea larvae consuming M. brunneum-treated S. littoralis larvae. Furthermore, C. carnea larvae preferentially fed on healthy prey versus M. brunneum-treated prey as revealed by both the higher predator ratio feeding on S. littoralis control larvae and the higher per capita number of control larvae consumed by the predator compared to M. brunneum-treated larvae. Moreover, this preference was inversely related to the post-inoculation period of S. littoralis larvae treated with M. brunneum. Furthermore, C. carnea larvae fed on healthy prey gained more weight than those fed on treated individuals. Both M. brunneum treatments used against S. littoralis larvae may be considered low risk to C. carnea due to the lack of fungus-related mortality in the predator and the lack of movement of destruxin A from the prey to the predator. However, further studies on other nontargets and with more strains of M. brunneum are needed to evaluate their possible simultaneous use in integrated pest management.