Abundance, diversity, and seasonal population dynamics of aquatic Coleoptera and Heteroptera in rice fields: effects of direct seeding management.

Recent introduction of modern drainage systems has produced intensely dry conditions in rice farmlands and has degraded habitats for aquatic animals. In this study, we compared water beetle (Coleoptera) and water bug (Heteroptera) communities within rice fields cultivated under different management regimes: V-furrow no-till direct-seeding (DS) and conventional regimes. In DS fields, rice is sown in well-drained fields, and flooding is performed a month later than in conventional rice fields. DS fields are then continuously flooded until harvesting; unlike in conventional fields, where midseason drainage is performed in summer. We observed that DS fields supported higher densities of water beetles and water bugs than conventional fields, probably because of the high compatibility between the flooding period and the reproductive season of the insects. The species richness of water beetles was higher in DS fields than in conventional fields. Overall, DS fields showed higher water beetle and water bug abundance, but the effect was variable for individual species: seven species were more abundant in DS than in conventional fields, whereas two species showed opposite tendencies. Considering the differential responses among species to the management regimes, a mosaic of DS and conventional fields is preferable to either field alone for the conservation of aquatic insects in rice agroecosystems.