Abstract
BACKGROUND: Anticoagulant rodenticides (ARs) are used globally to manage pest rodent populations. However, resistance to ARs in target rodent populations challenges pest control efforts and can increase risks to nontarget species. Resistance is frequently associated with nonsynonymous single nucleotide polymorphisms (nsSNPs) in the Vkorc1 gene, and this study carried out the first Vkorc1 survey of introduced rats on the Australian mainland. RESULTS: We identified three species of introduced rat using the cytochrome b gene across Brisbane, Melbourne, Perth and Sydney: Rattus rattus (Linnaeus 1758) (Lineage I); Rattus norvegicus (Berkenhout 1769); and Rattus tanezumi (Temminck 1844) (Lineage II). Three nsSNPs were detected in the Vkorc1 gene: Tyr25Phe, Trp59Arg and Phe55Ile. The mutation Tyr25Phe, which is associated with resistance to ARs, was identified in 58 of 108 R. rattus (53.7%) and one of 31 R. tanezumi (3.2%). It has been suggested that the mutation Trp59Arg (detected in two R. rattus) can increase susceptibility to haemorrhage, whereas the mutation Phe55Ile (identified in only one R. rattus) has not been reported previously. No nsSNPs were identified in R. norvegicus. CONCLUSION: This is the first update to the resistance status of introduced rats on the Australian mainland since the 1970s and the first to employ genetic screening. The widespread occurrence of Tyr25Phe in urbanized areas of Australia suggests potential resistance to ARs is common in R. rattus. However, practical resistance conferred by Tyr25Phe needs further investigation as does the role of hybridization in the transfer of resistance from the R. rattus to the R. tanezumi nuclear genome. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.