Economy of food utilization in a gregarious sawfly, Arge nigrinodosa Motschulsky (Hymenoptera: Argidae): Relative abundance of food in the natural habitat and behavioral pattern of larval feeding

Summary Relative abundance of natural food resource, leaves of wild rose, of Arge migrinodosa was evaluated by comparing the food quantity which the larvae composing a colony utilized throughout the larval stage with that which is available in the habitat. In this connection, behavioral pattern of larval feeding was also observed under natural conditions, and its ecological significance was discussed. It was quantitatively clarified that the larvae faced the severe shortage of food and had to disperse to other shoots with the expense of probably high risk. Under pressures of such insufficient supply of food, the larvae follow the most efficient pattern of feeding behavior that they move to the tip of shoot at first and feed regularly downward thereafter. Though individual larvae behaved completely independently of each other, the aggregation appeared to be formed and maintained because all the larvae from the same egg mass follow this fixed feeding pattern.