LAUSR

Freshwater ecosystems tend to have the highest proportion of species threatened with extinction. Paddy fields provide alternative habitats for many species inhabiting wet hinterlands of rivers. This study examined the susceptibilities of three hydrometrid species, Hydrometra procera Horváth (Hemiptera: Hydrometridae), H. albolineata (Scott) (Hemiptera: Hydrometridae), and H. okinawana Drake (Hemiptera: Hydrometridae), inhabiting paddy fields in Japan to seven insecticides that were frequently applied to paddy fields, and evaluated the effect of each insecticide according to the hazard assessment classes by the International Organization for Biological Control and Integrated Control of Noxious Animals and Plants/West Palearctic Regional Section. Etofenprox, imidacloprid, and fenobucarb were found to be seriously harmful to the third instar nymphs of the three hydrometrid species. Buprofezin (an insect growth regulator) was also evaluated as seriously harmful based on the mortality at the third instar of the three species before the completion of molting to the fourth instar. Etofenprox, imidacloprid, and buprofezin were particularly harmful even at low concentrations to H. procera. Some of these insecticides have been heavily used in paddy fields since the 1950s or 1960s. It was around this time when the endangered species, H. albolineata populations began to decline drastically. Our results suggested that heavy use of these insecticides is one of the factors that caused the decline in H. albolineata populations.