The 2008 overseas mass migration of the small brown planthopper, Laodelphax striatellus, and subsequent outbreak of rice [Oryza sativa] stripe disease in western Japan

The small brown planthopper, Laodelphax striatellus (Fallén), is one of the major insect pests of rice in East Asia. This species is known as a vector insect of Rice stripe virus, and has been believed to show strong indigenousness, unlike other migratory rice planthoppers, the brown planthopper and the whitebacked planthopper. Large trap catches of L. striatellus with high viruliferous rates were recorded in western Japan on a windy day in early June 2008, and subsequently, rice stripe diseases spread in these regions. The migration source was estimated using backward trajectory analysis, and found to be Jiangsu Province, China. Laodelphax striatellus with high viruliferous rates and rice stripe diseases has occurred markedly throughout Jiangsu Province since 2004, and early June is the wheat harvest season, which could serve as a stimulus for planthopper emigration. Insecticide susceptibility of populations collected in rice fields both in western Japan and Jiangsu were compared by a topical application method. Both Chinese and immigrant populations showed resistance only against imidacloprid, whereas Japanese local populations showed resistance only against fipronil. Collectively, this evidence suggested that the overseas migration of viruliferous L. striatellus from China to western Japan occurred and subsequently caused rice stripe diseases in the areas to which insects immigrated.