Prospects for Integrating Augmentative and Conservation Biological Control of Leaffolders and Stemborers in Rice

Possibilities to combine augmentative biological control using Trichogramma spp. egg parasitoids and conservation biological control through habitat manipulation, for the management of rice leaffolder and rice stemborer pests have received only cursory mention in the literature. We reviewed information on the use of Trichogramma releases and on habitat manipulation to manage leaffolders and stemborers in rice. Stemborers have become a priority for biological control since the 1990s with research focusing mainly on Chilo suppressalis in China and Iran, Scirpophaga incertulas in South and Southeast Asia, and Chilo agamemnon in Egypt. In most cases, 100 K wasps (T. japonicum or T. chilonis) released over 30-100 release points ha(-1) at least once during early crop stages, resulted in good control (>50% reduction in damage). Despite positive results accumulated over decades, larger scale releases in rice have only been conducted very recently. Research on conservation biological control of stemborers has focused on manipulating rice field habitat, particularly along rice bunds (levees). Several studies reported higher Trichogramma densities or greater egg parasitism in rice fields with flowering plants on bunds compared to control fields (without bund vegetation and usually with insecticides). These trends have mainly been attributed to nectar as a supplementary food for the adult wasps, although evidence for this mechanism is weak. Trap plants, such as vetiver grass (Chrysopogon zizanioides) attract ovipositing stemborers, but suppress larval development. Repellent and banker plants have not yet been identified for rice stemborers or leaffolders. We outline the opportunities and challenges for combining augmentative and conservation biological control of leaffolders and stemborers in rice.

Automated summary

The possibilities of combining augmentative biological control using Trichogramma spp. egg parasitoids with conservation biological control through habitat manipulation for rice leaffolder and rice stemborer pests have not been extensively studied. The research mainly focuses on releasing Trichogramma wasps and manipulating habitat in rice fields to manage stemborers, with positive results observed. However, larger scale releases of Trichogramma in rice fields have only recently been conducted. The manipulation of habitat, particularly planting flowering plants along rice bunds, has shown potential in attracting Trichogramma wasps, but the evidence for nectar as a supplementary food source is weak.