title: Toxicity of deltamethrin and cypermethrin to the larvae of the diamond-back moth, Plutella xylostella L.
abstract: Two photostable pyrethroids, deltamethrin and cypermethrin, were tested against fourth instar larvae of a susceptible (S) strain and a resistant (R) strain of Plutella xylostella L. by topical application. Both compounds were very effective against the S strain larvae (LD50 for deltamethrin = 0.0014 micrograms/larva, LD50 for cypermethrin = 0.0046 micrograms/larva, at 48 h). However, the R strain collected from the field was greater than 1600-fold resistant to deltamethrin and greater than 30 000-fold resistant to cypermethrin. Deltamethrin was poorly synergised with piperonyl butoxide in the S strain, but much stronger synergism was obtained in the R strain. The possible reasons for such high levels of resistance and the potential use of synergised pyrethroids in Plutella control programmes are discussed.
mesh_terms: D000818:Animals; D007305:Insecticide Resistance; D007814:Larva; D007915:Lepidoptera; D009036:Moths; D009570:Nitriles; D011722:Pyrethrins
chemical_list: D009570:Nitriles; D011722:Pyrethrins; C017160:cypermethrin; C017180:decamethrin