Abstract:Apanteles derogatae Watanabe is major larva endoparasitoid and plays an important role in controlling Sylepta derogata Fabricius. This paper studied the parasitic behavior of A.derogatae with the method of artificial inoculation under laboratory conditions. The results indicated the searching time of the parasitoid was 2.38min on average and the attacking time was 0.86min. A.derogatae preferred the 2nd instar larvae to other instar larvae. The death rate of the 1st instar larvae of host was 32%, while the parasitic rate was only 16%, the other 16% died because of puncturing. It can prolong the parasitism and puncturing time when the parasitoids were fed with honey water solution. The correlation showed a parabolic curve between the parasitic ability of parasitoid and the host density. When parasitoid density was 16/m3 female, the number of parasitized larvae increased as the increase of host density from 80/m3 to 320/m3, but the number of parasitized larvae gradually decreased when the host density increased over 320/m3.