Group feeding as a strategy for exploiting food resources in the burnet moth Pryeria sinica

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Abstract
Pryeria sinica (Zygaenidae) larvae feed on young and growing leaves of Euonymus japonicus in groups. The larvae often defoliate their host plant. Hence, the larvae are occasionally subject to serious shortage in food resources. We hypothesize that larval aggregation is an adaptation for the economical utilization of limited food resources. To test this hypothesis, the patterns of resource utilization were studied on larvae settled on shoots of host plant in various group sizes. The amount of food resources in a shoot was affected by the following three factors; (1) shoot growth, (2) food consumption of larvae, and (3) inhibition of growth or degeneration of shoot by larval activity on it. These factors were measured and the efficiency in resource utilization was compared among groups of varied sizes. The loss in resources caused by the third factor was found to be decreased with group size, i.e., the larger the group size, the larvae utilized the food resources more economically. The advantages of group feeding in survival and reproduction of this species were discussed using a simple graphical model.