The flea beetle （Agasicles hygrophila） was imported to Florida, USA and then introduced from Florida into China in 1987 as a biological control agent for the invasive plant alligator weed （Alternanthera philoxeroides）. The initial beetle population was subsequently used for sequential introductions in other areas of China, but little is known about the genetic consequences of the introductions. In this study, the genetic diversity and population structure of five beetle populations, the source Florida population, three intentionally introduced China populations and one accidentally dispersed China population, were examined using amplified fragment length polymorphisms. The results showed a clear pattern of decreasing genetic diversity with the sequential introductions. The diversity was highest in the Florida population followed by the first introduction to Chongqing and then in Kunming and Fuzhou. The lowest diversity was found in the accidentally dispersed Guangzhou population that was first recorded in 1996. Both loci parameters and Nei＇s genetic diversity showed a high variation among these populations. Genetic differentiation among populations was further verified by the GST statistic （0.136–0.432）. Beetles in Kunming had the highest gene flow with those in Guangzhou, and therefore lowest differentiation and closest genetic distance. These data show that sequential introduction influenced the genetic diversity of populations in China. Genetic diversity should be considered in planning introduction and long-term maintenance of populations.
Rui-Yan MaXiao-Yun JiaWen-Zhong LiuRoger H. LaushmanLong-Long ZhaoDong JiaRen Wang
