STUDIES TO ELUCIDATE THE EFFECT OF MONOTERPENES ON ACETYLCHOLINESTERASE IN TWO STORED-PRODUCT INSECTS

The possible involvement of acetylcholinesterase in the susceptibility of two stored-product insects to terpenes was examined.
Five monoterpenes were tested and found to have different activities as fumigants on Rhizopertha dominica and Tribolium confusum. SEM76, an unidentified terpene, was the most effective compound against both insect species.
ZP51, another unidentified terpene, and terpinen-4-ol showed less but still marked toxicity. 1,8-cineole showed slightly lower activity on R. dominica, and was much less effective on T. confusum. When evaluated as acetylcholinesterase inhibitors SEM76, showed again the highest inhibitory effect on both electric eel acetylcholinesterase and that of R. dominica. ZP51, terpinen-4-ol and 1,8-cineole also inhibited the enzyme activity from both sources.
On the other hand, d-limonene had no fumigant toxicity against these two insects and did not inhibit either of the enzymes.
The specific activity of acetylcholinesterase extracted from T. confusum was very low compared with that of R. dominica, which made it difficult to access the inhibitory effect of the enzyme in this insect.

All compounds were competitive inhibitors for both enzymes, but at relatively high concentrations of the terpenes.
These results are consistent with the in vivo studies in which the enzyme activity was affected only slightly by treatment with the various terpenes.
The failure of the biologically active monoterpenes to produce strong enzyme inhibition leads to the postulate that acetylcholinesterase is not the main site of action of the monoterpenes.

International Symposium on Medicinal and Aromatic Plants

Sima H. Greenberg-Levy, M. Kostjukovsky, U. Ravid, E. Shaaya

https://doi.org/10.17660/ActaHortic.1993.344.17