Diazinon selective toxicity

Keizer, J., G. D Agostino, R. Nagel, T. Volpe, P. Gnemi and L. Vittozzi. Enzymological differences of AChE and diazinon hepatic metabolism correlation of in vitro data with the selective toxicity of diazinon to fish species. Sci. Total Environ. 171 213—220, 1995. 

The organophosphorons insecticides dimethoate and diazinon are mnch more toxic to insects (e.g., housefly) than they are to the rat or other mammals. A major factor responsible for this is rapid detoxication of the active oxon forms of these insecticides by A-esterases of mammals. Insects in general appear to have no A-esterase activity or, at best, low A-esterase activity (some earlier stndies confnsed A-esterase activity with B-esterase activity) (Walker 1994b). Diazinon also shows marked selectivity between birds and mammals, which has been explained on the gronnds of rapid detoxication by A-esterase in mammals, an activity that is absent from the blood of most species of birds (see Section 23.23). The related OP insecticides pirimiphos methyl and pirimiphos ethyl show similar selectivity between birds and mammals. Pyrethroid insecticides are highly selective between insects and mammals, and this has been attributed to faster metabolic detoxication by mammals and greater sensitivity of target (Na+ channel) in insects. 

Dimethoate also has an intrinsic selectivity, for it is far more toxic to insects than to mammals. This favourable effect was found, surprisingly, to depend little on differences in S O conversion (as in malathion and diazinon), but to rely mainly on preferential operation of mammalian amidase (Krueger, O Brien and Dauterman, 1960). This discovery introduced an expanded feeling of latitude in designing selective organophosphate insecticides. 

---