the effect of piperonyl butoxide on susceptibility of the common pistachio psyllid, agonoscena pistaciae burkhardt and lauterer to amitraz and specific activity of esterase enzyme

amitraz is one of the pesticides which is used in a vast area for controlling of the common pistachio psyllid, agonoscena pistaciae (hem.: aphalaridae). in this study the synergistic effect of piperonyl butoxide (pbo) on the toxicity of amitraz on adults of rafsanjan population of common pistachio psyllid was evaluated by residual contact vial (rcv) in laboratory conditions. the results showed that lc50 values of amitraz when use alone and with pbo together in the summer form of common pistachio psyllid were 213.7 and 151.8 mg l-1, respectively. synergistic ratio of these results obtained 1.3 fold. lc50 values for amitraz alone and with pbo together in the winter form of a. pistaciae were 351.6 and 95.3 mg l-1 that according to the statistic measurements, there is a significant difference in the winter form when used amitraz alone and with pbo together and the synergism ratio obtained 3.6 for this form. results of this study showed that susceptibility of the winter form of pistachio psyllid to amitraz was less than summer form and pbo has a synergistic effect on amitraz toxicity. indeed determination of esterase activity showed that there is significant difference between summer and winter forms. it seems that one of the reasons of less susceptibility of the winter form to amitraz pesticide is related to the increase esterase activity.