Size-dependent reproductive output of female bagworms (Lepidoptera: Psychidae): Implications for inter-generational variations of population density

Abstract

The unusual life history of bagworms, Metisa plana (Lepidoptera: Psychidae), with females completing all reproductive activity within a bag they construct as larvae, makes them ideal subjects to quantify intraspecific variations of reproductive success. This study investigated the relationship between body size and reproductive output of females, and tested the hypothesis that size-dependent variations of fecundity affect inter-generational variations of population density. Body size attained by female larvae at pupation (assessed by measuring the length of the pupal bag) was positively correlated with several parameters of reproductive output, including weight of pupae, weight and potential fecundity of calling female, as well as weight and realized fecundity of mated females. Our results further suggest that females allocate about two thirds of the resources they accumulate as larvae into egg production, and that a significant proportion of eggs are cannibalized by sibling neonates. In cage experiments, density of larvae in offspring generations on individual nursery palms was not affected by the size of females in parental generations. This result suggests that body size of females may not affect inter-generational variations of population density when potential resource depletion of host plants promotes a high incidence of dispersal among neonates.