Comparative study of organophosphorus insecticide metabolizing enzymes in larvae and adults of the bollworm, Heliothis zea (Boddie), and the tobacco budworm, Heliothis virescens (F.)

Vita.Comparative in vitro measurements of ali-esterase (Ali-E), microsomal mixed-function oxidases (MFO), and glutathione-dependent S-aryl transferase activities, were conducted utilizing third- and fifth-instar and full grown larvae, and female and male moths of the bollworm and the budworm. In vitro assays were also conducted to investigate the effect of enzyme inhibitors upon larval Ali-E and cholinesterase (ChE) activities. In addition, rates of ChE activity in female and male moths were measured in vitro. Rates of Ali-E activity per. mg protein and per insect, and rates of MFO activity per insect, were greater in budworm larvae than in bollworm larvae. The greatest rates of MFO-mediated oxidative metabolixm of ¹⁴C-parathion in larvae, were achieved by alimentary canal microsomes. Microsomes from whole insects or fat body tissue possessed less oxidative activity. Total rates of Ali-E and MFO activity rapidly increased as the larvae grew older. Negligible differences between species were observed in the inhibition of larval ChE and Ali-E activities by esterase inhibitors. Therefore, quantitative differences in Ali-E and MFO activity, rather than qualitative differences in ChE enzymes, appear to be the cause of differential susceptibility to insecticides in these two Heliothis species. GSH-dependent S-aryltransferase activity was higher in bollworm than in budworm larvae. Apparently this activity decreases as the larvae grew older. Enzymatic activity was also variable between sexes and between species of Heliothis adult. Ali-E and ChE activities were higher in adult bollworms than in adult budworms. The opposite was observed with S-aryltransferase enzymes. No conclusive differences were obtained from MFO activity measurements.