Insecticide Responses in the Collembola Pest, Sminthurus viridis (Collembola: Sminthuridae), in Australia.

Lucerne flea (Sminthurus viridis Linnaeus) is an important establishment pest of winter grain crops and pastures in Australia. Control of S. viridis largely relies on the application of insecticides through foliar sprays or seed treatments; however, in recent years, farmers have faced increasing difficulties managing this pest. This is likely due to their high inherent tolerance to certain chemicals, although there are increasing concerns around emerging resistance. Despite this, there have been no studies worldwide investigating insecticide sensitivity shifts on S. viridis. Further, there is currently no established method to test the response of S. viridis to neonicotinoids, which are now widely used to protect many crops attacked by this species. Here, we established a robust and sensitive bioassay methodology to test neonicotinoids against S. viridis. We also generated important sensitivity data for the first time across multiple S. viridis populations from geographically distinct regions in Australia to two commonly used insecticides, omethoate, and imidacloprid. While there was variation in responses between populations for both chemicals, there is no evidence to suggest insecticide resistance has evolved in the field. This study is an important step for future monitoring of insecticide resistance in S. viridis, particularly given the considerable selection pressure imposed on this pest in Australia and its purported high-risk of evolving resistance.