Organophosphate insecticides are valuable insecticides used to control Helicoverpa armigera on cotton in Australia. Organophosphates most commonly used for Helicoverpa spp. control, are profenofos, methyl parathion and chiorpyrifos. However, there is an emerging organophosphate resistance threat in Australian H. armigera, which is compounded by cross resistance between profenofos and methyl parathion. An insensitive acetylcholinesterase has been identified as the common resistance mechanism. No resistance to chlorpyrifos has been detected and acetylcholinesterase remains fully sensitive to chlorpyrifos and its oxon