Monitoring the Insecticide Resistance of Dendrolimus punctatus and the Synergism of Pyrethroids by SV_1

Fourth instar populations of Dendrolimus punctatus collected from 16 counties in Jiangxi Province were evaluated to study the susceptibility to deltamethrin, fenvalerate and cypermethrin. The results showed that the resistance of D. punctatus populations in Gao an and Guixi to deltamethrin was not very high. The resistance of all other populations tested to deltamethrin increased obviously. No resistance to fenvalerate or cypermethrin was observed. Binary mixture of 5 different ratios (0.5∶1,1∶1,3∶1,5∶1 and 10∶1) of SV 1 with deltamethrin or fenvalerate or cypermethrin was applied. Synergism was observed at any ratio of SV 1 plus the three pyrethroids. The higher the concentration of SV 1, the stronger the synergistic effect. Combinations of four pyrethroid insecticides plus SV 1 were tested in pine forest. The results showed that the combination of 2.5% deltamethrin plus SV 1 (1∶5), combination of 20% fenvalerate plus SV 1 (1∶3～1∶5), combination of 2.5% cyhalothrin plus SV 1 (1∶3～1∶5) and combination of 10% cypermethrin plus SV 1 (1∶5) got significant synergistic effects and could effectively bring the D. punctatus under control.