Migration analysis of Nilaparvata lugens (Hemiptera: Delphacidae) from the Philippines to Taiwan under typhoon-induced windy conditions

The population of Nilaparvata lugens (StAyenl) in Taiwan is believed to belong to the East Asian population of the species, which has low susceptibility to the insecticide imidacloprid. The population in the Philippines belongs to the Southeast Asian population, which has high susceptibility to imidacloprid. In this study, long-winged adults of N. lugens collected in paddy fields in Taitung, southeastern Taiwan, just after a typhoon, were tested for imidacloprid susceptibility after rearing for 4-17 generations. The migration source was also estimated by backward trajectory analysis. Our findings were, first, that its curved dosage-mortality plots for imidacloprid suggested that the Taitung population is heterogeneous in its susceptibility to the insecticide. Source estimation found areas on Luzon Island of the Philippines, mainly, and southern China, partially, as possible sources. Before the typhoon approached, however, light trap monitoring data indicated some local populations might have occurred in the survey area. Therefore, with other pieces of circumstantial evidence, this study suggested that migration of N. lugens to Taiwan from the Philippines, and, simultaneously, possibly southern China occurred because of the typhoon, with the insects partly crossing the boundary of the Asian populations, and that a mixture of individuals with different susceptibility to the insecticide happened to form the Taitung population at the time of collection.