Recent Status of Insecticide Resistance in Asian Rice Planthoppers

Since 2005, outbreaks of rice planthoppers have occurred in East-Asian countries such as Vietnam, China and Japan. These outbreaks are closely related to the development of insecticide resistance in these regions. The susceptibilities of the brown planthopper (BPH) and the whitebacked planthopper (WBPH) to four insecticides were evaluated by a topical application method on insects collected from Japan, China, Taiwan, Vietnam, and Philippines in 2006. Species-specific changes in insecticide susceptibility were found in Asian rice planthoppers: imidacloprid resistance in BPH and fipronil resistance in WBPH. Topical LD50 values for imidacloprid in the BPH strains from East Asia (Japan, China and Taiwan) and Vietnam were significantly higher than those from the Philippines, suggesting that resistance to imidacloprid has developed in BPH in East Asia and Indochina, but not in the Philippines. Almost all the WBPH populations collected had extremely large LD50 values for fipronil, suggesting that resistance to this insecticide is widespread in WBPH populations throughout East and Southeast Asia. Possible reasons for species-specific development of insecticide resistance are identified and discussed.