Crowding-triggered phenotypic responses alleviate consequences of crowding inEpirrita autumnata (Lep., Geometridae)

CrowdedEpirrita larvae had shorter larval periods than, and similar pupal masses to, their solitary siblings when reared on low quality diets. When fed on high quality diets, pupal masses of crowded larvae were lower than in singletons, and there was no difference in larval period. Because changes in food availability (absolute shortage, induced resistance in foliage) are caused by high larval densities in the field, crowding-triggered phenotypic changes may helpEpirrita to overcome detrimental consequences of high larval density. Pupal period was longer in crowded larvae than in singletons and crowded adults emerged later than their solitary siblings. Eggs of late emerging moths eclosed late in the ensuing spring, which coincides with delayed leaf flush in the year after defoliation. The reason for the faster growth of crowded individuals on poor diets was higher intake albeit less thorough processing of food in crowded, but not in solitary, larvae. On good diets solitary individuals tended to consume more than crowded larvae but there was no difference in processing. Predicted differences of host plant use between stealthy and opportunistic types of herbivores (sensu Rhoades 1985) were generally found between solitary and aggregated larvae on poor but not on good diets. The group response could not be explained by benefits to the group although the assumptions of Wilson's model of group selection were satisfied.