Estimating the immigration source of rice planthoppers, Nilaparvata lugens (Stal) and Sogatella furcifera (Horvath) (Homoptera: Delphacidae), in Taiwan

Since overwintering populations of brown planthopper (Nilaparvata lugens) and white-backed planthopper (Sogatella furcifera) in Taiwan are very low based on field observations, immigrant planthoppers have become the most important source of serious damage to rice crops (Oryza sativa). Backward trajectory analysis was conducted using trap catch data from 1990 to 2005 to estimate the source of immigrant planthoppers, taking into account the emigration periods and weather conditions, and showed that southern China, Vietnam and the Philippines (Luzon Island) were possible source areas. Southern China was found to be the most important source of emigration. Of all the immigration cases tested, the sources from southern China were estimated to be about 77% in the first rice crop and 65% in the second rice crop. Vietnam came second with about 37% and 56% in the first and second rice crops, respectively. Typhoons were the most important weather factor, inducing mass emigrations from China and Vietnam. Since the population properties are known to differ among the emigration regions and Taiwan, careful monitoring of these insects in the emigration sources and Taiwan is needed in order to establish better pest management practices.