Tissue distribution, characterization and in vitro inhibition of B-esterases in the earwig Forficula auricularia

Abstract

Earwigs are important natural enemies of numerous pests in pome fruit orchards worldwide. Studying the effects of agricultural practices on these biological control agents is important for understanding its vulnerability in the field. The aim of this study was to characterize the B-esterase activities in the European earwig Forficula auricularia and to evaluate in vitro its sensitivity to organophosphate and carbamate pesticides. Acetylcholinesterase (AChE) activity was mainly measured with 1.5mM acetylthiocholine as the substrate in the microsomal fraction of earwig heads (70% of total AChE activity). Carboxylesterase (CbE) activities were measured with three substrates [5mM 4-nitrophenyl acetate (4-NPA), 1mM 4-nitrophenyl valerate (4-NPV), and 2mM α-naphtyl acetate (α-NA)] to examine different isoenzymes, which were present mainly in the cytosolic fraction (about 70–88% of total activities) of all earwig tissues. CbE activity was higher than AChE activity, especially with α-NA, then 4-NPA and lastly 4-NPV. Chlorpyrifos-oxon an organophosphate, and carbaryl a carbamate pesticide, inhibited AChE and CbE activities in a concentration-dependent manner. Earwig CbE activities showed a stronger sensitivity to organophosphate than AChE, with the strongest effect for chlorpyrifos-oxon on male carboxylesterase activities. CbE and AChE showed about the same sensitivity to carbamate pesticides regardless of sex. These results suggest that B-type esterases in the European earwig F.auricularia are suitable biomarkers of pesticide exposure.