Evidence for division of labor in the social caterpillar Eucheira socialis(Lepidoptera : Pieridae)

The caterpillars of Eucheira socialis westwoodi cooperatively spin and main tain a hollow silken nest and an elaborate network of silken foraging trail s on their host plant, madrone (Arbutus spp.: Ericaceae). Nests typically c ontain several hundred larvae. Two populations are known to harbor a sex ra tio distorter. The primary sex ratio in these two populations for four gene rations has been exceedingly male biased (64-79% male). Lepidoptera larvae are easily sexed using external morphology, allowing us to uniquely mark ma le and female larvae and to assemble larval groups of particular sex ratios . We report here the results of experiments on sex-specific larval behavior and physiology and the effect of colony sex ratio on individual behavior. We found that male larvae spent more time spinning silk on the nest and les s time feeding than female larvae. Males were the first to emerge from the nest and the first to venture out along trails to feed. Male-biased nests h ad a significantly greater amount of silk deposited on their surfaces than female-biased nests. In the field, male-biased nests produced heavier male and female pupae than female-biased nests. Male and female larvae in 75% ma le nests became active earlier than males and females in other sex ratio tr eatments.