Imidacloprid resistance in Thrips tabaci (Thys. Thripidae) populations collected from onion fields in Isfahan

Onion thrips, Thrips tabaci, is the most important pest of onion in Isfahan. Onion growers often rely on the pesticide spraying. Imidacloprid is frequently used against this pest. To investigate the thrips resistance to this insecticide, 10 onion-growing regions of Isfahan were selected. After their laboratory rearing, certain concentrations of imidacloprid were applied to these populations, using a leaf dip bioassay method. LC50 values of field populations were compared to Harand population as a susceptible reference strain. Different levels of resistance were observed in most populations. To investigate the resistance mechanisms, populations were pre-treated with two synergists namely PBO (piperonyl butoxide) and DEM (diethyl maleate) as inhibitors of monooxygenases and glutathione-S-transferases, respectively. Based on the results, theses enzymes do not seem to play a substantial role in the resistance. The results also indicated that there is no high level of cross resistance in most imidacloprid-resistant populations against acetamiprid, another neonicotinoids insecticide.