Field Release of the Parasitoid Microplitis mediator (Hymenoptera: Braconidae) for Control of Helicoverpa armigera (Lepidoptera: Noctuidae) in Cotton Fields in Northwestern China’s Xinjiang Province

Field experiments and surveyswere conducted in 2003 and2004 to evaluate theefÞcacy of using the parasitoidMicroplitis mediator (Haliday) to control populations of Helicoverpa armigera (Hübner) in cotton Þelds in Northwestern ChinaÕs Xinjiang Province. The population levels of the second generation of H. armigera in southern Xinjiang in 2003 and 2004 were 20Ð60% above the economic threshold of this pest. The longevity of Þeld-released female andmale parasitoids was 7.6 0.4 and 3.9 0.4 d, respectively. Field tests showed that the number of parasitized H. armigera increasedwith an increasing number ofM.mediator cocoons released in the Þeld. The release of 2,250 or 15,000 laboratory-reared M. mediator cocoons per hectare in cotton Þelds resulted in 38Ð61% parasitismofH.armigera in 2003 and35Ð66%parasitism in2004.TheefÞciencyof theparasitoids varied considerablywith different numbers of parasitoid cocoons andwith the frequency and sites of release. However, the highest damage reduction in these studies was obtainedwith a single release of cocoons and the highest number of release sites. Large-area releases of M. mediator in cotton Þelds of Shufu, Shule, and Shache counties resulted in 60% parasitism and an 80% decrease in cotton boll and bud damage comparedwith the control Þelds. The above results indicated that Þeld release ofM.mediator could be used effectively in managing H. armigera in cotton in Xinjiang.