The toxicity of six insecticides, acephate, methomyl, ethofenprox, cartap, chlorfluazuron, and Bacillus thuringiensis (Bt) was tested on different developmental stages of the egg parasitoid, Trichogramma dendrolimi (Matsumura). Each of the insecticides tested showed different degrees of toxicity to the parasitoid, Ethofenprox showed the highest toxicity and cartap showed relatively higher toxicity compared with the other insecticides. The development of the parasitoids treated with these two insecticides was normal, similar to that of the control group. Only the emergence of adult wasps from host eggs was disturbed. Emergence of the host, Mamestra brassicae larva was reduced following treatment with ethofenprox, cartap and methomyl. However, adult female wasps, which emerged from host eggs treated with the insecticides had the ability to oviposit normally.

No abstract

Factitious hosts are needed for mass-propagation in crop pest management. Egg parasitoids are considered as effective biocontrol agents of lepidopterous pests because they kill host eggs and can usually be easily mass propagated on factitious hosts. However, previous studies indicated that parasitoids which had been reared on a factitious host changed host preference and did not parasitize the native host. In the present report, Trichogramma dendrolimi were collected from egg masses of Mamestra brassicae in cabbage fields maintained without insecticides. T. dendrolimi was maintained in the laboratory for 12 successive generations on Ephestia kuehniella. After the 12 successive generations, the parasitoid females still preferred M. brassicae to E. kuehniella for oviposition. T. dendrolimi, that emerged from M. brassicae eggs were larger in size and laid twice as many eggs as those from E. kuehniella during their lifetime. These results suggest that T. dendrolimi parasitizes the native host without losing host preference even after 12 successive generations on a factitious host.