A high incidence of imposex in Pomacea apple snails in Taiwan: A decade after triphenyltin was banned

The South American apple snails Pomacea canaliculata and P. scalaris were intentionally introduced into Taiwan in the 1980s. Subsequently, P. canaliculata has become a serious pest to aquatic crops, and triphenyltin (TPT) was the major control agent. We conducted a nationwide survey on the imposex status of P. canaliculata and P. scalaris to evaluate the effectiveness of the ban on TPT use in agriculture since 1999. Pomacea canaliculata was distributed island-wide, but P. scalaris was only distributed in southern Taiwan, sympatrically with P. canaliculata. The imposex condition was found in snails from all collecting sites of the 2 species. Based on vas deferens sequence (VDS) indices, P. scalaris and P. canaliculata have the same susceptibility. Additionally, imposex-affected individuals of P. canaliculata were found in all types of freshwater habitats, i.e., crop drainage, reservoirs, and wastewater drainage, with respective VDS indices ranging 1.02-1.40, 0.75-2.00, and 1.00-1.88. Based on these survey results, the illegal use of TPT in agriculture has likely continued, and extra control actions are urgently needed.