Positive effect of environmentally friendly farming on paddy field odonate assemblages at a small landscape scale

Abstract

Odonata species can be used to indicate the effects of anthropogenic disturbance on agrobiodiversity. In Japan, populations of some odonate species inhabiting rice paddy fields have decreased strongly owing to their high susceptibility to insecticides, and they therefore need to be conserved. To identify effective conservation strategies, we investigated how agricultural practices (conventional vs. environmentally friendly: EF) and surrounding landscape (area of forest at three spatial scales, namely 50, 100 and 200 m from the edge of the paddy field) influenced the abundance of odonates in rice paddies in Tochigi Prefecture, Japan. Generalized linear mixed-effect models revealed that EF farming increased the abundance of odonate adults and the number of nymphal exuviae, suggesting a strong negative effect of insecticides. The influence of forest area at the local scale on the numbers of odonate adults and nymphal exuviae was small, with the exception of a strong negative influence on adult Sympetrum infuscatum: the presence of a large area of forest within 200 m of the edge of the paddy field reduced their abundance, probably reflecting this dragonfly’s oviposition site preference. Our results suggest that EF farming could generally support the conservation and recovery of local populations of odonates, but its effectiveness potentially varies depending on the ecological aspects of each species.