Tritrophic interactions involving fall armyworm, parasitoid wasp and grasses releasing cyanide

Oviposition tendency and subsequent development of the parasitoid wasp Euplectrus platyhypenae Howard was compared using the corn and rice host strains of Spodoptera frugiperda (J. E. Smith) fed corn (Zea mays, ‘Truckers Favorite’) or stargrass (Cynodon nlemfuensis Vanderyst var. nlemfuensis, ‘Florona’ grass). In no-choice and two-choice experiments using newly molted fourth instar hosts female wasps preferred to oviposit on corn strain larvae fed corn plants.  Rice strain larvae were parasitized when fed corn plants, but only after the host had reached an optimal size.  When female wasps were given a choice between corn and rice strain larvae, they always produced more female offspring on the corn strain than the rice strain larvae, irrespective of the host plant the larvae fed upon.  Among rice strain hosts, those fed corn hosted more female offspring than those fed grass.  The data also show that host quality had a direct effect on parasitoid size, since significantly larger parasitoid offspring resulted from largest host fed corn plants, and smaller offspring resulted from the smallest hosts, rice strain larvae fed stargrass. Furthermore, E. platyhypenae larval mortality occurred in hosts of both strains fed stargrass, which may indicate that stargrass allelochemicals might not be appropriate for this parasitoid.