Larvae of the fall webworm, Hyphantria cunea, inhibit cyanogenesis in Prunus serotina

The larvae of the fall webworm, Hyphantria cunea (Dru.), though vulnerable to cyanide poisoning, consume the cyanogenic leaves of black cherry, Prunus serotina, without apparent harm. The cyanide contents of leaves, defensive regurgitant, the bolus, and frass were assayed by ion chromatography to determine the fate of the toxin in the caterpillar. Leaves collected in September, when the caterpillars were feeding, contained 1592+/-276 p.p.m. cyanide. Samples of dried frass obtained from caterpillars fed these leaves yielded 2868+/-552 p.p.m. cyanide. Frass extracted directly in NaOH yielded approximately five percent of the cyanide obtained from frass ground in buffer and distilled in Warburg flasks, indicating that cyanogenesis is largely inhibited as the bolus traverses the gut. This inhibition is attributable to the ability of the caterpillar to maintain a foregut environment in the presence of the bolus that is sufficiently alkaline to suppress the conversion of the plant cyanogen to cyanide. Although a number of caterpillars feed without harm on cyanogenic plants, this it the first shown to inhibit cyanogenesis in this manner.