Abstract: To identify the resistance risk and the resistance mechanism of avermectin against Dendrolimus punctatus, we examined the cross-resistance of avermectin resistance population (AV) to multiple tested insecticides and the synergism of piperonyl butoxide (PBO), triphenyl phosphate (TPP) and diethyl maleate (DEM) to AV, Qin-ling Jieguanting (JGT) and susceptible (S) popultions, by leaf dipping method. The activities of carboxylesterase (CarE), glutathione S-transferases (GST) and mixed-functional oxidases (MFOs) in AV, JGT and S populations of D. punctatus was measured with spectrophotometry. The results showed that the AV population of D. punctatus had medium level of cross-resistance to emamectin benzoate (resistance ratio, RR₅₀=25.0), chlorpyrifos (RR₅₀=19.0), and cyhalothrin (RR₅₀=15.4), and low level of cross-resistance to chlorfenapyr (RR₅₀=8.1), but no cross-resistance to spinetoram, spinosad and chlorantraniliprole. Both PBO and TPP had significant synergism of avermectin to AV, JGT, and S populations, while DEM had no synergism to all the three populations. Compared with the S population, the AV population had higher content of MFOs cytochromes P₄₅₀(3.5-fold) and b₅(3.1-fold) and the activities of O-demethylase (4.1-fold) and CarE (2.2-fold). There was no significant difference in the activities of GST between AV and S populations. The increasing mixed-functional oxidases and CarE played an important role in the resistance of D. punctatus to avermectin. Spinetoram, spinosad, chlorantraniliprole, and avermectin were recommended to control D. punctatus.

Key words: Dendrolimus punctatus, avermectin, spinosad, cross-resistance, resistance mechanism.