Occurrence of Cholinesterase in Tenebrio and Tribolium

Abstract

Lord and Potter have reported¹ that they could not obtain preparations of Tenebrio molitor larvæ or Tribolium castaneum adults which could hydrolyse acetyleholine. This failure is surprising in view of the supposed ubiquity of cholinesterase “in conductive tissue throughout the whole animal kingdom”², and is of importance because of its bearing on the question of the mode of action of organo-phosphorus insecticides. Since both insects are killed by low concentrations of tetraethyl pyrophosphate (TEPP), Lord and Potter's observations would indicate that the significance of its anti-cholinesterase effect is not as great as had been thought³. Although the authors stated that “no persistent attempt was made to prepare an extract hydrolysing ACh”, their work has been taken to show⁴ the absence of cholinesterase in these insects. In their principal preparation, the supernatant from their homogenates was treated with half its volume of ethyl alcohol. The inability of the resultant solution to hydrolyse acetylcholine is not surprising in view of the anti-cholinesterase activity of ethyl alcohol⁵. Furthermore, the brei was centrifuged at two stages, and the centrifugates rejected; Babers and Pratt⁶ have shown that, in the honey-bee, five-sixths of the cholinesterase is in the centrifugate of whole brei.