SUBSTRATE-SPECIFICITY AND INHIBITOR SENSITIVITY OF CHOLINESTERASES INHOMOGENATES OF WESTERN FLOWER THRIPS

Acetylcholinesterase (AChE) activity in homogenates of KCM strain west ern flower thrips, Frankliniella occidentalis (Pergande), was chiefly membrane bound, sensitive to eserine, and insensitive to diisopropyl p hosphorofluoridate (DFP). The rate of substrate hydrolysis decreased i n the order acetylthiocholine (ASCh)--> propionylthiocholine--> acetyl -beta-methylthiocholine (MeSCh)--> butyrylthiocholine (BuSCh). Inhibit ion by excess substrate was not observed at concentrations up to 8.0 m M. Inhibition by BW 284C51 indicated the presence of two components wi th different sensitivity to this compound. Butyrylcholinesterase (BuCh E) activity, which was considerably higher than AChE activity, was chi efly soluble and sensitive to eserine and DFP and insensitive to BW 28 4C51. The sulfhydryl reagents p-hydroxymercuribenzoic acid and 5,5'dit hiobis-2-nitrobenzoic acid inhibited AChE and BuChE activities. Severa l organophosphates and carbamates were potent inhibitors of ASCh and B uSCh hydrolysis with the organophosphates being especially active agai nst BuSCh. Substrate specificity and inhibitor sensitivity of AChE and BuChE from UMC strain thrips were similar but not identical to that o f KCM thrips. It was suggested that BuChE in western flower thrips mig ht function as a scavenger enzyme to protect AChE from anticholinester ase insecticides. Similarities between the properties of western flowe r thrips cholinesterases and those reported previously for aphids were striking. (C) 1994 Academic Press, Inc.