Abstract

The Asian corn borer (ACB), Ostrinia furnacalis, is a serious maize pest in Southeast Asia, responsible for substantial economic losses to the maize crop every year. To establish insect biocontrol programmes, it is crucial to determine the ideal numbers and developmental stage of natural enemies to release. The purpose of the present study was to assess the parasitism ability of Trichogramma dendrolimi and Trichogramma ostriniae, which are the most promising biocontrol agents of the ACB, under two different methods of inundative release in maize fields. A total of 10,000 wasps of both species were released using two different methods, i.e. wasps at the same developmental stage (SDS) and wasps at different developmental stages (DDS). The results showed that T. dendrolimi wasps exhibited significantly higher parasitism of ACB eggs when they were released with the DDS method than when they were released with the SDS method. In the SDS release method, T. dendrolimi parasitized ACB eggs for only 3 days after release, while in the DDS release method, parasitism of ACB eggs occurred for 6 days. However, the two release methods had no significant impact on the performance of T. ostriniae in maize fields. In both release methods, T. ostriniae parasitized a high percentage of ACB eggs. The results of the present study clearly indicate that the poor field performance of T. dendrolimi due to the host-age factor can be improved using the DDS release method.