Effect of antifeedants on the diamondback moth (Plutella xylostella) and its parasitoid Cotesia plutellae

Two neem preparations and the bitter-tasting synthetic chemical denatonium benzoate were tested in the laboratory as antifeedants against the diamondb ack moth, Plutella xylostella L. The effects of the three materials on Cote sia plutellae (Kurdjumov), a hymenopteran parasitoid of P xylostella, were also recorded. All three materials significantly reduced the food consumpti on of P xylostella larvae. Parasitoid cocoons were formed on approximately half of those larvae which had been exposed to female C plutellae, regardle ss of antifeedant treatment, but emergence of adult parasitoids from the co coons was significantly reduced by antifeedant treatment. In terms of food consumption and mortality of unparasitised P xylostella larvae, and emergen ce of adult C plutellae, the effect of each antifeedant preparation was dir ectly related to the concentration of material used, but the effects of the neem preparations were greater than those of denatonium benzoate. However, no adult P xylostella emerged on any antifeedant treatment, therefore some of the parasitoids survived antifeedant treatments which were fatal to the unparasitised hosts. (C) 2000 Society of Chemical Industry.