Comparison of the Head Acetylcholinesterase Sensitivity to Insecticides between Two Honeybee Populations

The sensitivities of acetylcholinesterase (AChE) from heads of Apis cerana cerana Fabricius and Apis mellifera ligustica Spinola to organophosphorus and carbamate insecticides were investigated by determining the inhibiting kinetic constants (K/em>i, K2, Ka and K3) and the time-course curve of inhibition. The time-course curve of inhibition indicated that the sensitivities of AChE from head of A. mellifera ligustica to eserine, methomyl and dichlorovos were higher than that from head of A. cerana cerana. However, there was no significant difference of the AChE sensitivities to propoxur, thiodicarb, methamidophos and monocrotophos between both bees. The bimolecular reaction constants (Ki) of AChEs from A. mellifera ligustica and A. cerana cerana were 4.003×106 and 3.403×106 (mol/L)-1 ·min-1 for eserine, 5.744×104 and 4.633×104 (mol/L)-1 · min-1 for propoxur, 5.249×104 and 4.233×104 (mol/L)-1 · min-1 for thiodicarb, 4.872×104 and 10.408×104 (mol/L)-1 · min-1for methomyl, 1.986×106 and 1.262×106 (mol/L)-1 · min-1 for carbofuran,and 5.492×104 and 5.072×104 (mol/L)-1 · min-1 for carb osulfan, respectively. However, methomyl was more potentially inhibiting AChE from A. cerana cerana than that from A. mellifera ligustica. The value of Ki was 10.408×104 and 4.872×104 (mol/L)-1 · min-1 in A. cerana cerana and in A. mellifera ligustica, respectively. The reactivation rates of AChE inhibited by eserine and methomyl were higher in A. cerana cerana than in A. mellifera ligustica, however, when inhibited by propoxur, thiodicarb, carbofuran and carbosulfan, the former was lower than the latter.