Effects of the botanical insecticide thymol on biology of a braconid,Cotesia plutellae(Kurdjumov), parasitizing the diamondback moth,Plutella xylostellaL.

Terpenes and biogenically related phenols commonly found in plant essential oils are known to be toxic to insect pests. Accordingly thymol was tested for acute toxicity via topical application to diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae) and its parasitoid, Cotesia plutellae (Kurdjunov) (Hymenoptera: Braconidae under laboratory conditions. Topical application to adult female parasitoids versus second instars of P. xylostella showed that thymol was about 62 times less toxic to the parasitoid than to the host larvae with 24 h LD50 of 0.052 and 0.0008M, respectively. Although thymol was less toxic to the parasitoid, some biological parameters of the progeny at sublethal doses of surviving parasitoids were impaired such as rate of emergence and development time of larvae and pupae. The impact on detoxification enzymes was also studied and there was no significant induction in cytochrome P450 and carboxylesterase activities in both treated male and female wasps. Results obtained suggest that parasitoid is able to withstand the impact of thymol significantly.