Perennial emergent macrophytes as the main determinant of Hydrochara affinis inhabitation

Due to the increasing mosquito activity and the risks associated with them, mosquito control has become a global issue. In particular, biological control using the natural enemies of mosquitoes has attracted great attention. Hydrochara affinis, an aquatic beetle, has recently been identified as a biological control agent for mosquitoes. It is necessary to explore the environmental characteristics of its natural habitats for successful mosquito control. Therefore, we surveyed the environmental characteristics of its natural habitats (dwelling sites, DS), former habitats (former dwelling sites, FDS), and non-habitats located near its natural habitats or with a similar landscape (non-dwelling sites, NDS). Perennial emergent macrophytes accounted for 85.5% of the total plant cover in the DS, while they accounted for 44.2% and 43.0% in FDS and NDS, respectively. The environmental characteristics, such as electrical conductivity and cation concentration of the water, in the 3 categories (DS, FDS, and NDS) were significantly different. The ranges of these values in the DS were wide. Based on these results, we concluded that perennial emergent macrophyte communities can be a determinant for H. affinis habitat selection. It is, therefore, important to maintain a proper environment in which macrophyte communities, that can serve as habitats for H. affinis, can proliferate.