Ground beetles (Coleoptera: Carabidae) and other insect predators overwintering in arable and fallow fields in central Japan

Abstract To clarify assemblage patterns of overwintering ground beetles (Coleoptera: Carabidae) and other insect predators in farmland habitats for the purpose of proper land management to enhance beneficial predators, we collected carabid and other insect predators at eight plots including arable and fallow rice and vegetable fields and a bank of an adjacent irrigation pond in central Japan. In total, 159 adults and 268 larvae of 33 carabid species, and 178 individuals of at least 17 species of other insect predators were collected by the quadrat sampling method. In rice fields, both the number of species and no. of individuals of overwintering carabid beetles increased as the soil became dry and vegetational succession proceeded, whereas in fallow vegetable fields carabids decreased according to succession. Similar trends were confirmed in other insect predators. Variations of carabid species richness and abundances among the plots might be attributed to soil water content, vegetation and prey availability. In early-successional fallow vegetable fields, the larvae of the carabid genus Harpalus overwintered with high density; this appeared to be because the fingergrass Digitaria ciliaris (Poaceae), whose seeds were a potential food for Harpalus, were densely vegetated there. In a dry fallow rice field and early-successional vegetable fields, beneficial predators such as Dolichus halensis (Coleoptera: Carabidae), Agrypnus binodulus (Coleoptera: Elateridae), and soldier beetle (Coleoptera: Cantharidae) larvae hibernated with high densities. For proper farmland management to augment insect predators, it is desirable to maintain fallow rice and vegetable fields as relatively dry habitats and at early successional stages. Ploughing fallow fields in winter may reduce overwintering predacious insect larvae.