The inhibition kinetics on carboxylesterase (CarE) andacetylcholinesterase (AChE) of Liposcelis bostrychophila and Liposcelis entomophila of paraoxon andcarbosulfan were compared. The results showedthat L. entomophila exhibitedsignificantly greater specific activity of CarE than L. bostrychophila [0.045vs. 0.012lmol of a-naphthyl acetate (a-NA) hydrolysed/mg protein/min]. Moreover, L. entomophila showedhigher affinity (i.e. lower Km value) to the substrate a-NA than L. bostrychophila (0.29vs. 0.67mm). For AChE-specific activity andaffinity, no significant differences between the two species were observed. Based on the I50 values, AChE of L. bostrychophila was more sensitive to paraoxon andcarbosulfan than that of L. entomophila. According to inhibition kinetics, the results revealedthat AChE of L. bostrychophila was 3.8-foldmore sensitive to inhibition by paraoxon than that of L. entomophila, but L. entomophila was 1.5-foldmore susceptible to carbosulfan.