Depletion of host-derived cyanide in the gut of the eastern tent caterpillar, Malacosoma americanum.

Using a colorimetric procedure, we assessed the HCN-p of black cherry leaves (Prunus serotina) ingested by the eastern tent caterpillar, Malacosoma americanum, and the cyanide content of the bolus as it passed thorough the caterpillar's digestive tract and into the detritus pool. The mean HCN-p of leaves in our study area was 1902 +/- 174 (SE) ppm. Young leaves found at the tips of growing branches, which the caterpillars preferred, had a significantly higher HCN-p (3032 +/- 258 ppm) than older leaves found at the middle (1542 +/- 243 ppm) or base of the shoot (1131 +/- 159 ppm). Following a bout of overnight feeding on young leaves, the cyanide content of the foregut and midgut boluses of early sixth-instar caterpillars averaged 631 +/- 161 ppm, and 14 +/- 3 ppm, respectively, indicating that host-derived cyanide is rapidly depleted as the bolus transits the gut. Some cyanide, however, remains. In three studies, the mean cyanide content of fresh fecal pellets ranged from approximately 20 to 38 ppm, while the dried, compacted pellets ranged from 63 to 85 ppm. Food in the foreguts of mature caterpillars dispersing over the ground in search of pupation sites had 417 +/- 99 ppm cyanide. The potential impact of this egested and caterpillar-transported cyanide on the consumer and detritivore communities is discussed.