Resistance Of Plutella Xylostella To Avermectin

Diamondback moth,Plutella xylostella L.,a cosmopolitan pest of crucifers ,had shown resistance to more than 50 insecticides which had brought large difficulties in chemical control of pests. Avermectin , a kind of antibiotic insecticides,had better effect to control many agricultural pests mites and animal parasite pests. Since it was introduced and separated in the late 1980s, avermectin had become a major pesticide against Plutella xylostella in china. In this paper, the stomach poisoning of avermectin to the second instar larva of Plutella xylostella,contract poisoning to egg , the effect of avermectin on adult lifespan and on mean number of eggs , and the effect of temperature on avermectin toxicity were determined. The studies on the biological activity of avermectin to Plutella xylostella showed that field population of Plutella xylostella were more sensitive to avermectin than to certain insecticides used commonly.Avermeetin has no contract poisoning toxicity to eggs and no effect on adult lifespan and mean number of eggs of Plutella xylostella .Temperature showed significant effect on the toxicity of avermectin to the second instar larva of Plutella xylostella.The toxicity become greater as temperature ranged from 15 -~-- 32 C . At 15 C ~?32 ~C ,the toxicity of avermectin to the larva of Plutella xylostella increased 32.35 times. An avermectin resistant strain of Plutella xylostella was 31 obtained by laboratory selection of fifteen generations with avermectin from a field population collected from Fuzhou,which exhibited about 66.44 times resistance to avermectin as compared with the field population. The resistant strain had no cross-resistance to cypermethrin~ malathion~ methomyl and chlorfluazuron. The studies on synergism of esterases inhibitor TPP and MFO inhibitor Pb to avermectin-resistant strain showed that TPP and Pb exhibited 1.61 and 1 .38 times synergism to avermectin respectively. Life tables of avermectin-resistant strain and avermectin-susceptible strain were constructed to evaluate their developmental and reproductive characteristics.The results indicated that there was no significant difference between R-strain and S-strain in hatchability and in developmental duration of the egg~ larva and pupa stages.However, the mean number of eggs per female laid by R-strain decreased 15.8% compared with S-strain.The R-strain was calculated to have a fitness value of 0.85 relative to the S-strain.