Selective Insecticidal Action of Isopropyl Parathion and Analogues

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Abstract
The comparative susceptibility of honey bees, Apis mellifera L., and house flies, Musca domestica L., to a series of substituted phenyl dialkyl phosphorothionates was investigated by topical applications. The p-nitrophenyl di-isopropyl phosphorothionate (isopropyl parathion) was only about 0.005 as toxic to the bee as to the fly, although the corresponding dimethyl, diethyl, and dipropyl analogues were nearly equitoxic to both species. Similar selectivity associated with isopropyl esters was demonstrated for several other series of phosphorothionate compounds. The biochemical basis for this selectivity was studied. The lowered activity of isopropyl parathion to the bee appears to be the overall result of a decreased rate of in vivo oxidation to the lethal p-nitrophenyl di-isopropyl phosphate together with a decreased affinity of this latter compound for bee cholinesterase.