Synergistic control against Asian corn borer (ACB) by Trichogramma vectored Beauveria bassiana infection on survival larvae escaped from parasitism

Abstract

The combined application of natural enemies and entomopathogens as an alternative pest-control may act synergistically, additively or antagonistically. The objective of this study is to determine the efficacy of the combined application by parasitic Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae) carrying insect-pathogenic fungus Beauveria bassiana (Bals.) Vuill. (TCB) against Asian corn borer (ACB), Ostrinia furnacalis (Lepidoptera: Pyralidae). 0.1% (w/v) starch solution was selected from several adjuvants due to its highest ability to carry fungal conidia, over 3.60 × 104 conidia per wasp. The fungal conidia adsorbed on the surface of factitious host, Antheraea pernyi eggs, subsequently adhered on new emerged T. dendrolimi as a vector, which carried the conidia onto eggs’ surface of ACB. The B. bassiana had no influence on T. dendrolimi’s parasitic rate, whereas resulting in fungal conidia adhering on over 60.00% of hatched larvae, which consequently caused 27.00 ± 5.70% percent of muscardine cadaver rate of pest’s larvae in a screen house test. In field trial, it showed significantly lower incidence parameters regarded as number of damaged plants, wormholes, and living pests, per 100 plants in TCB treatment compared to that of sole T. dendrolimi release (non-TCB) and non-treatment as control, respectively, especially the number of muscardine cadaver per 100 plants was 6-fold amount higher than that of non-TCB treatment. In this study, the suitable adjuvant of cost-effective and safe to T. dendrolimi emergence was selected for fungal conidia adhering for TCB, and the fungal conidia transmitting process from host eggs to pest infection was visualized by fluorescence observation, on the basis, it was proved in both screen house and field experiments that the TCB was a synergistic ACB control program with labor saving, low cost and high efficient advantage compared to sole biocontrol agent application.