Aposematism in Archips cerasivoranus not linked to the sequestration of host-derived cyanide.

This study addressed the question of how caterpillars of Archips cerasivoranus feeding upon Prunus virginiana cope with the cyanogenic compounds of their food. Analysis by ion chromatography showed that young and aged leaves of P. virginiana consumed by the caterpillars during spring have hydrogen cyanide potentials (HCN-ps) of 2,473 +/- 130 ppm and 1,058 +/- 98 ppm, respectively. Although less than 3% of the cyanide released as the caterpillars feed escapes into the atmosphere, the larva's bright-yellow aposematic coloration and conspicuous activity can not be attributed to the sequestration of cyanide. Only six of 25 samples of the caterpillars' defensive regurgitants collected from 12 field colonies contained cyanide (17.6 +/- 6.54 ppm), less than 5% of the quantity previously reported to occur in the regurgitant of the tent caterpillar M. americanum. Only seven of 13 caterpillars assayed had detectable quantities of cyanide in their bodies (3.9 +/- 0.9 ppm). The fecal pellets that encase the cocoon contained no cyanide, nor did the frass that litters the leaf shelters. The small quantities of cyanide that occur in the caterpillar compared to the HCN-p of ingested plant material appear attributable to paced bouts of feeding and the maintenance of a highly alkaline foregut that inhibits cyanogenesis.