Role of acetylcholinesterase and glutathione S-transferase following exposure to nicosulfuron and diazinon in Helicoverpa zea

The acute toxicity of diazinon combined with the herbicide nicosulfuron was determined using the corn earworm, Helicoverpa zea. Nicosulfuron significantly increased toxicity of diazinon to H. zea compared to diazinon alone based on dip bioassays to evaluate acute contact toxicity. Diazinon, an organophosphorous insecticide, controls insects by inhibiting acetylcholinesterase in the nervous system. Acetylcholinesterase activity was significantly altered in corn earworms exposed to binary mixtures compared to those exposed to diazinon alone; however, the activity did not correspond consistently with toxicity. Glutathione S-transferase (GST), also known to be altered by organophosphorous insecticides, did not exhibit significant changes following exposures to diazinon, nicosulfuron, or binary mixtures. Our results suggest that nicosulfuron increases toxicity of diazinon but the mechanism of toxicity does not appear to be correlated with acetylcholinesterase or GST inhibition.