Since the introduction of Bt-cotton secondary pests such as aphids, mites and bugs have become more prominent requiring targeted insecticide control. These sprays have lead to resistance in some pest species that have caused the chemical control to fail. Spray failures increase grower costs and the likely hood of unforseen environmental consequences but very importantly can permanently tarnish Australia’s reputation for producing high quality lint if 2

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failures cause ‘sticky cotton’. Recently in Australian cotton, there has been control failure against aphids with chemicals belonging to the group known as neonicotinoids. This group includes the mainstay cotton seed treatment thiamethoxam (Cruiser®) and the cost effective foliar spray clothianidin (Shield®). The neonicotinoid insecticides control several problematic pest species in cotton including aphids and mirids and their loss due to resistance puts increased pressure on remaining control products by severely limiting control options. In the 2007-2008 cotton season neonicotinoid resistance was detected for the first time in cotton aphid but control failures were not experienced. During the following 2008-2009 season neonicotinoid resistance increased in both level and abundance (82% of the stains tested) and for the first time neonicotinoid resistance caused control failures and cross resistance to other neonicotinoid products was additionally implicated. Interestingly, the proportion of strains showing neonicotinoid resistance in 2009-2010 remained approximately static at 78% but for season 2010-2011 the frequency of strains showing resistance increased to an extreme 96% of strains tested. Such resistance makes the neonicotinoids unreliable for cotton aphid control and growers may well be better off using alternative foliar products for aphid control if neonicotinoid seed dressings have been used. It is noteworthy that Integrated Pest Management friendly pirimicarb (Pirimor®) is currently resistance free so it would be a good first choice for an aphid specific foliar spray. Other alternatives are also available including, diafenthiuron (Pegusus®), spirotetramat (Movento®), pymetrozine (Chess®) an OP or spray oil. If foliar neonicotinoids are to be used against aphids I recommend the following to help manage resistance. Try to limit in-season use of foliar neonicotinoids for aphid control if they have been used as a seed treatment. If foliar sprays are required for aphid control and neonicotinoid seed treatments have been used it is most important that the first foliar spray is not from the neonicotinoid chemical group. Finally, consider the implications of coincident aphids if spraying neonicotinoids against other pests such as mirids. Aphids will develop resistance even if the sprays are not targeted directly against them and control failures could result.