Direct and Indirect Infection Effects of Four Potent Fungal Isolates on the Survival and Performance of Fall Armyworm Larval Parasitoid Cotesia icipe

Abstract

Fall armyworm (FAW), Spodoptera frugiperda, has recently invaded Africa where it is seriously threatening food security. Current management methods rely heavily on synthetic insecticides which are harmful to humans, the environment, and non-target beneficial insects. Cotesia icipe was recently identified as a major FAW-associated indigenous parasitoid causing a high parasitism rate on the pest in Kenya. Previous studies have demonstrated the efficacy of Metarhizium anisopliae ICIPE 7, ICIPE 41, ICIPE 78, and Beauveria bassiana ICIPE 621 against FAW. However, limited information is available on the interactions between these potent isolates and C. icipe. This study therefore assessed direct and indirect infection effects of these fungal isolates on C. icipe, induced 2nd instar FAW mortality, and parasitism rates of the infected C. icipe. Results showed that when C. icipe were directly exposed to dry conidia of the fungal isolates, ICIPE 7 and ICIPE 41 caused the highest (100%) C. icipe adult mortality seven days post-exposure. Both isolates also induced the highest FAW larval mortality of 55% and 53%, respectively. ICIPE 78 recorded the highest parasitism rates after direct infection. In the indirect exposure (fungal-infected FAW larvae exposed to the parasitoid), 1 × 109 conidia mL−1 recorded high C. icipe adult and FAW 2nd instar mortalities for all fungal isolates. This study provides an important baseline for effective fungal-based biopesticides development that could also be used in augmentative biological control. However, further studies are warranted to assess the performance of C. icipe in combination with these potent biopesticides in the field.