Performance of Trichogramma japonicum as a vector of Beauveria bassiana for parasitizing eggs of rice striped stem borer, Chilo suppressalis

The rice striped stem borer (RSSB), Chilo suppressalis Walker, is a major pest of rice causing significant yield loss worldwide. Although biological control plays a key role in RSSB management, the use of a sole biocontrol agent is not always sufficient for enabling effective control. Other management methods are therefore required for developing effective integrated pest management strategies. In the present study under laboratory conditions, we estimated the pathogenicity of Beauveria bassiana solution (1x108 conidia mL-1) on various RSSB larval instars (1st to 6th) and assessed the ability of Trichogramma japonicum Ashmead infected by B. bassiana to parasitize RSSB eggs. We also evaluated the quantity of B. bassiana spores vectored by T. japonicum and the quantity deposited on RSSB eggs during parasitism. The impact of B. bassiana on T. japonicum biological parameters when developing in RSSB eggs of various ages (0-, 2-, and 4-days old) was also studied. We demonstrated that T. japonicum vectored B. bassiana and the number of spores deposited on RSSB eggs was sufficient to induce high mortality in hatching larvae. There was no major impact of B. bassiana on T. japonicum biological traits. Nonetheless, B. bassiana reduced the egg to adult duration and increased the parasitism rate of 2-day old RSSB eggs. Beauveria bassiana conidia were shown to proliferate on parasitoid adult bodies and host egg masses, potentially enhancing biocontrol services when both agents were combined. Therefore, T. japonicum vectoring B. bassiana may provide a means to improve biological control programs targeting RSSB in rice crops.