Can resistance management strategies recover insecticide susceptibility in pests?: a case study with cotton aphid Aphis gossypii (Aphididae: Hemiptera) in Australian cotton

Cotton pest management in the Australian cotton industry was highly pesticide reliant from its inception in the early 1960s until the late 1990s. Aphids were controlled effectively over this period either co-incidentally by compounds applied against Helicoverpa spp. or by targeted applications of dimethoate/omethoate or pirimicarb in the late 1990s. By cotton season 1999-2000, after this prolonged period of selection, the cotton aphid Aphis gossypii Glover showed resistance to pirimicarb and cross resistance to dimethoate/omethoate as well as resistance to older organophosphates (profenofos, chlorpyrifos-methyl, chlorpyrifos-ethyl) targeted against Helicoverpa spp.. No new chemical controls were available so effective control required development of an insecticide resistance management (IRM) strategy incorporated with integrated pest management (IPM) strategies designed to maximalise any known selective disadvantage for resistant individuals. The IRM component emphasised rotation between insecticide mode of action (MOA) groups and limited the number of applications of any MOA. The IPM component incorporated farm hygiene to reduce overwinter hosts for resistant aphids, conserved natural enemies and incorporated effective use of pest sampling and thresholds. The aphid management strategy was fluid, evolving and adapting as new knowledge, new resistance and further IPM or IRM tactics became available. For instance, in 2007-2008 resistance was detected in aphids to the neonicotinoids resulting in field failures. Detection of neonicotinoid resistance required modifications to the aphid management strategy to address prolonged selection by both neonicotinoid seed treatments and foliar applications. The strategy also considered the need to manage concurrent pest species to mitigate the risk that insecticides sprayed against those pests would coincidently cause aphid outbreaks or select for resistance in aphids. The integrated strategy has now almost completely recovered susceptibility to IPM friendly pirimicarb and resistance to neonicotinoid insecticides has declined dramatically.