ADAPTIVE SIGNIFICANCE OF DENSITY-DEPENDENT BALLOONING BY BAGWORM LARVAE, METISA-PLANA (WALKER) (LEPIDOPTERA, PSYCHIDAE)

Experiments conducted in a plantation of oil palms, Elaeis guineensis (Jacquin), infested with bagworms, Metisa plana (Walker), tested the h ypotheses that crowding enhances the incidence of larval ballooning an d negatively affects the size attained by pupae. Proportions of balloo ning larvae increased with increasing densities of larvae per palm. Th e lengths of bags (and pupal cases) decreased with increasing numbers of bagworms per leaf. Ballooning of larvae from crowded palms is likel y adaptive because individuals attaining large size at pupation have p roportionately greatest survival, mating success, and fecundity.