Preliminary characterisation of known pesticide resistance alleles in Spodoptera frugiperda (Lepidoptera: Noctuidae) in its invasive Australian range

Fall armyworm (Spodoptera frugiperda) has recently been detected in Australia. Globally, S. frugiperda is reported to be resistant to insecticides, including those permitted for its control by the Australian Pesticides and Veterinary Medicines Authority. Consequently, an understanding of the insecticide resistance status of newly migrated S. frugiperda into Australia, as well as an ability to accurately identify newly hatched larvae, would facilitate sustainable management. To aid identification, we developed a real-time polymerase chain reaction diagnostic assay that can identify S. frugiperda species, irrespective of life stage, and distinguish between the rice and corn strains. We then screened S. frugiperda individuals from Queensland, Western Australia, the Northern Territory and New South Wales for mutations causing target site insensitivity in the acetylcholinesterase (AChE) gene, the voltage-gated sodium channel gene and the ryanodine receptor gene. In the populations tested, we found that mutation at positions A210S and F290V in AChE were common. These mutations are known to be associated with carbamate and organophosphate resistance in S. frugiperda outside Australia. In contrast, no mutation was found in gene voltage-gated sodium channel causing pyrethroid resistance or the ryanodine receptor gene associated with diamide resistance. As S. frugiperda is new to Australia, the wide distribution of mutations in the AChE gene associated with organophosphate/carbamate resistance suggests that the original migrated S. frugiperda moths may have carried the mutations from outside Australia. As resistance genes have been detected, it is important to continue to monitor the resistance status of Australian S. frugiperda and further integrate complementary bioassay when available. Finally, as pesticide resistance is possible, it should be additionally considered when making pest management decisions and any spray failure should be followed by a pesticide from a different chemical group.

Automated summary

The fall armyworm has been detected in Australia, leading to the development of a real-time PCR diagnostic assay for identifying the species and detecting mutations related to insecticide resistance. Common mutations associated with carbamate and organophosphate resistance were found in the populations tested, suggesting that the original migrated moths may have carried these mutations from outside Australia. Monitoring the resistance status of Australian fall armyworm is important, as well as considering pesticide resistance in pest management decisions.