Susceptibility of diamondback moths (Lepidoptera: Plutellidae) resistant to conventional insecticides to chitin synthesis inhibitors

A simple bioassay, in which third-instar diamondback moths, Plutella xylostella (L.), were fed sprayed mustard seedlings, was used to determine the susceptibility of strains resistant to conventional insecticides to two benzoylphenyl ureas (BPU’s), teflubenzuron and chlorfluazuron. No significant cross-resistance between conventional insecticides and the two BPU’s was detected, although these strains showed low levels of tolerance to teflubenzuron as compared with a susceptible strain (maximal LC50 difference 3.5-fold). Teflubenzuron was slightly more toxic than chlorfluazuron to all seven strains tested.