Insecticide resistance in Australian populations of the serpentine leaf miner Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae)

Serpentine leaf miner, Liriomyza huidobrensis, invaded New South Wales and Queensland late 2020. Overseas, L. huidobrensis has a history of developing insecticide resistance and, since its Australian discovery, has caused significant control issues in Australian horticultural industries. Here, we developed bioassay methods to test the response of L. huidobrensis larvae to spirotetramat and L. huidobrensis adults to dimethoate, imidacloprid and chlorantraniliprole. Against two New South Wales and one Queensland collected strains, we found a 33-fold elevated response against dimethoate and 200-fold more against imidacloprid than the field-recommended field rates. Furthermore, we found that a maximum rate of 64-fold the field-recommended rate of chlorantraniliprole controlled only 94% of one tested population. Similarly, the maximum rate of spirotetramat tested (64-fold the field-recommended rate) only achieved 84%-94% mortality for the same populations. Prior to our study, the efficacy of chlorantraniliprole and spirotetramat against Liriomyza was poorly studied, with only a few reports with chlorantraniliprole against Liriomyza trifolii. Consequently, none of the tested insecticides in this study will likely control Australian invasive L. huidobrensis at the field-recommended rates. Our results presented here highlight the need to identify and study alternative chemical and biological products and natural enemies for the control of L. huidobrensis in Australian horticulture.