Tracking genetic invasions: genome-wide SNPs reveal the source of pyrethroid-resistant Aedes aegypti (yellow fever mosquito) incursions at international ports

Biological invasions are increasing globally in number and extent despite concerted efforts to restrict their spread. Knowledge of incursion pathways is necessary to prevent new invasions and to design more effective biosecurity protocols at source and recipient locations. In this study, we use genome-wide single-nucleotide polymorphisms (SNPs) and reference mosquitoes from 15 locations to determine the origin of 115 incursive Aedes aegypti (yellow fever mosquito) detected at international ports in Australia and New Zealand. We also genotyped mosquitoes at three point mutations in the voltage-sensitive sodium channel (Vssc) gene. These mutations confer knockdown resistance to synthetic pyrethroid insecticides, which are widely used for controlling invertebrate pests. We first delineated reference populations using a set of 188 unrelated Ae. aegypti collected from Southeast and East Asia, South America, Australia and the Pacific Islands. Incursives were assigned to these populations using discriminant analysis of principal components (DAPC) and an assignment test with a support vector machine predictive model, which showed strong agreement in assignment. We found that Bali, Indonesia, was the most common origin of Ae. aegypti detected at international ports in Australia, while Ae. aegypti detected at international ports in New Zealand originated from Pacific Islands such as Fiji. Most incursives detected at Australian ports had the same allelic genotype across the three point mutations at the Vssc gene. This genotype can confer strong resistance to synthetic pyrethroids, the only insecticide class used in current aircraft disinsection protocols. This was the only genotype found in mosquitoes from Bali and was also present in other reference mosquitoes across Southeast Asia and the Pacific Islands. This research highlights the need for current disinsection protocols endorsed by the World Health Organisation (WHO) to consider insecticide resistance for preventing introductions of Ae. aegypti, while demonstrating the utility of genomic datasets for managing global biosecurity objectives. Author Summary Invasive species are a growing global threat. To help control their spread, it is necessary to identify where invasive species are coming from and how current protocols to prevent them could be improved. Here, we used genomic markers to identify the incursion pathways of 115 Aedes aegypti (yellow fever mosquito) detected at borders in Australia and New Zealand. We also screened these mosquitoes for three mutations that confer resistance to insecticides commonly used to suppress insect pests. We found that Aedes aegypti detected in Australia and New Zealand came from different global regions, with those detected in Australia coming from Southeast Asia, South America, and domestically within Australia, while those detected in New Zealand came from Pacific Islands such as Fiji. We found that all intercepted Aedes aegypti that arrived on international flights had mutations associated with resistance to pyrethroid insecticides, which are the only class of insecticide currently endorsed for aircraft disinsection by the World Health Organisation (WHO). These mutations are not found in Australian Aedes aegypti populations. Our results show that using single classes of insecticides may not be effective for stopping movement of resistant insect pests, and that genomics is a useful tool for improving biosecurity strategies.