Abstract
Acetylcholinesterase (AChE) activity in homogenates of KCM strain western flower thrips, Frankliniella occidentalis (Pergande), was chiefly membrane bound, sensitive to eserine, and insensitive to diisopropyl phosphorofluoridate (DFP). The rate of substrate hydrolysis decreased in the order acetylthiocholine (ASCh)→ propionylthiocholine→ acetyl-β-methylthiocholine (MeSCh)→ butyrylthiocholine (BuSCh). Inhibition by excess substrate was not observed at concentrations up to 8.0 mM. Inhibition by BW 284C51 indicated the presence of two components with different sensitivity to this compound. Butyrylcholinesterase (BuChE) activity, which was considerably higher than AChE activity, was chiefly soluble and sensitive to eserine and DFP and insensitive to BW 284C51. The sulfhydryl reagents p-hydroxymercuribenzoic acid and 5,5′dithiobis-2-nitrobenzoic acid inhibited AChE and BuChE activities. Several organophosphates and carbamates were potent inhibitors of ASCh and BuSCh hydrolysis with the organophosphates being especially active against BuSCh. Substrate specificity and inhibitor sensitivity of AChE and BuChE from UMC strain thrips were similar but not identical to that of KCM thrips. It was suggested that BuChE in western flower thrips might function as a scavenger enzyme to protect AChE from anticholinesterase insecticides. Similarities between the properties of western flower thrips cholinesterases and those reported previously for aphids were striking.
Published Version
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