Abstract: Tests of the toxicity of several chitin synthesis inhibitors to the fourth instar larvae of diamondback moth, Plutella xylostella, were carried out in the laboratory. The results indicated that toxicities of XRD-473, CME-134, Cascade and IKI-7899were markedly higher than those of Dimilin and Alsystin, and toxicities of all these chitin synthesis inhibitors were significantly higher than those of the conventional insecticides DDVP, Cypermethrin and Dimehypo. Stomach poisoning was found to be the main mode of action, and contact poisoning was also important for IKI-7899 to the larvae. When adults were fed with the solutions of IKI-7899 or Cascade at 50 ppm, life spans of the female and male moths were shortened by 1 and 4 days respec- tively, number of eggs laid was only about 1/3 that of the untreated moth and the rates of egg hatching were reduced to 5.35% and 0, respectively. Temperature showed significant effect on the action of IKI-7899 in the speed of causing larval mortality, and the higher the temperature, the higher the mortality rate within the same period.

Key words: Plutella xylostella——chitin synthesis inhibitor——insecticidal activity