Entomotoxigenic Potential of Wild and Domesticated Yellow-Green Aspergilli: Toxicity to Corn Earworm and Fall Armyworm Larvae

Abstract

Corn earworm (Heliothis zea) and fall armyworm (Spodoptera frugiperda) larvae were fed on diets consisting of maize kernels fermented (8 da; 28 C) with individual strains of “wild” or domesticated yellow-green aspergini (e.g., wild isolates = Aspergillus flavus var. flavus, A. flavus var. parasiticus; domesticated, non-aflatoxigenic koji molds = A. flavus var. oryzae, A. flavus var. sojae). Kernels fermented with individual strains of var. sojae were less toxic to larvae than kernels fermented with isolates of the related wild variety parasiticus. Likewise, kernels fermented with isolates of var. flavus were, with one exception (NRRL 6513), more toxic to fall armyworm larvae than kernels fermented with isolates of the related domesticated variety oryzae. As a group, strains of var. oryzae were no less toxic to corn earworm larvae than the var. flavus strains that were tested. Toxic fungal metabolities are believed to be the direct cause of larval mortality because dead larvae were not colonized by fungal hyphae. This is consistent with the hypothesis that wild strains of A. flavus produce a suite of defensive entomotoxic metabolites having no adaptive value in a koji environment. We suggest that koji molds used in food fermentations be screened by means of insect bioassays as a relevant test of the toxigenic potential of individual domesticated strains.