The effect of piperonyl butoxide on pyrethroid‐resistance‐associated esterases in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Pyrethroid resistance in field populations of Australian Helicoverpa armigera (Hübner) is primarily a consequence of the overproduction of esterase isoenzymes which metabolise and sequester pyrethroid insecticides. Biochemical studies have shown that pyrethroid‐resistance‐associated esterases in H armigera are inhibited by the insecticide synergist piperonyl butoxide (PBO). Esterase inhibition by PBO did not occur immediately after dosing, but exhibited maximum inhibition 3–4 h after dosage. Esterase activity subsequently recovered until full activity was restored by 24 h. Topical bioassays using a pre‐treatment of PBO showed that maximum H armigera mortality was achieved with pre‐treatment times corresponding to maximum esterase inhibition. These results demonstrated that, with correct temporal application, PBO can restore pyrethroid efficacy against H armigera . It would also be expected that restoration of efficacy with other conventional insecticides, currently compromised by esterase‐based resistance mechanisms, would occur. Copyright © 2005 Society of Chemical Industry