An insecticide baseline study of Australian broadacre aphids

Abstract

Brevicoryne brassicae (Linnaeus), Lipaphis pseudobrassicae (Davis), Acyrthosiphon kondoi (Shinji), Aphis craccivora (Koch) and Rhopalosiphum padi (Linnaeus) are among the most important aphid pests in Australian broadacre systems. In this study a leaf-dip method was used to assay pirimicarb, dimethoate, α-cypermethrin and imidacloprid against field populations collected from Victoria, New South Wales, South Australia, Western Australia and Queensland. This research established toxicity baseline data that will be important for future monitoring of insecticide responses in broadacre crops. It also provided an opportunity to identify any chemical tolerance that may be evolving in these pests. Acyrthosiphon craccivora populations showed differences in their responses to dimethoate, pirimicarb and imidacloprid (but not to α-cypermethrin), indicating possible shifts in field sensitivity to these three chemicals. Rhopalosiphum padi had the lowest sensitivity to all insecticides tested, with two populations (collected from South Australia and Queensland) showing less than 100% mortality when tested at the field rate of α-cypermethrin. There were few differences in insecticide responses between populations of the other three species. Continued screening of A. craccivora and R. padi populations is needed to fully assess the current status of tolerance among field populations and to strengthen resistance management tactics.