Acetylcholinesterase inhibition by nootkatone and carvacrol in arthropods

The essential oils from many botanicals have been screened for insecticidal activity. Two constituents of the Alaskan yellow cedar tree, the monoterpenoid carvacrol and the sesquiterpenoid nootkatone, both are toxic against several arthropods. The mode of action through which nootkatone and carvacrol exert their insecticidal activity remains uncertain. It has been hypothesized that they may inhibit acetylcholinesterase enzyme activity. The degree of acetylcholinesterase inhibition of carvacrol and nootkatone was compared to that of carbaryl, a known acetylcholinesterase inhibitor, in the house fly (Musca domestica), yellow fever mosquito (Aedes aegypti), American dog tick (Dermacentor variabilis) and American cockroach (Periplaneta americana). The concentration of carbaryl, at which 50% of the acetylcholinesterase activity was inhibited (IC50), was less than 2 μM in all four arthropod models. Carvacrol was observed to cause slight inhibition of the acetylcholinesterase enzyme in house flies, ticks and cockroaches, but it did not inhibit the mosquito acetylcholinesterase enzyme. Nootkatone did not inhibit the acetylcholinesterase enzyme in any of the four arthropod models tested. From this study, we conclude that the acetylcholinesterase inhibition is not likely the primary mode of action for insecticidal activity by nootkatone or carvacrol.

Graphical abstractConcentration of carbaryl, carvacrol and nootkatone for 50% inhibition of the acetylcholinesterase enzyme extracted from house flies, American dog tick, American cockroach, and yellow fever mosquito.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlight► Carvacrol and nootkatone are toxic against several arthropods. ► Their mode of action remains unknown. ► Carvacrol slightly inhibited acetylcholinesterase (AChE) in three arthropods. ► Nootkatone did not inhibit AChE. ► AChE inhibition is not likely the primary mode of action for insecticidal activity.