Inferring feeding habits of Carabidae (Coleoptera) larvae based on mandible morphology: Case studies of Lesticus magnus and Chlaenius costiger

In the beetle family Carabidae, feeding habits are important life history traits that determine their role in ecosystems and suitability as bioindicators. However, they have not been elucidated for most species, especially in the larval stages. Using laboratory-rearing experiments, this study examined the larval feeding habits of two large carabid species: Lesticus magnus (tribe Pterostichini) and Chlaenius costiger (tribe Chlaeniini). Although previous studies failed to rear these larvae on insect larva diets, the mandible morphology of the first instars described in those studies, together with subsequently obtained knowledge of the relationship between mandible morphology and feeding habits in other carabid larvae, suggests that they are earthworm feeders. Rearing experiments with three types of animal diet (insect larvae, mixed snail and slug, and earthworm diets) showed that as expected, their larvae are earthworm feeders. In L. magnus, although the larvae accepted the mixed snail and slug diet and the earthworm diet, only larvae reared on the earthworm diet reached adulthood. In C. costiger, the larvae accepted only the earthworm diet and reached adulthood. This is the first report of earthworm feeding during the larval stage for the genus Lesticus (tribe Pterostichini) and tribe Chlaeniini. The importance of these results is discussed from ecological and evolutionary perspectives.