Abstract: At present there still lacks ideal commercial microbial insecticides to control the brown planthopper (BPH), Nilaparvata lugens (Stal), an important pest of rice in Asia. Entomopathogenic fungi can penetrate the cuticle of insect hosts and thus have the advantage of controlling sucking pests. In this study, laboratory bioassays were carried out on 12 isolates of three entomopathogenic fungal species, Metarhizium anisopliae, Metarhizium flavoviride and Beauveria bassiana, which were originally obtained from various hosts and geographic origins, for their virulence against BPH adults. The results showed that at the concentration of 1 100 conidia/mm², the strain Mf82 had the highest virulence to adults with the corrected mortality reaching 83.5% within 10 d after treatment and the LT₅₀ value 4.65 d. The pathogenicity of Mf82 to adults, nymphs at different instars and eggs of BPH were further assessed at a series of conidial concentrations. This strain was most virulent to adults, moderately virulent to old nymphs, and least virulent to young nymphs. It was also found that Mf82 could infect both oviposition marks and eggs in rice seedlings, with the infection rates of 66.7% and 51.2%, respectively, at 10 d after treatment. The younger the eggs, the higher the infection rate, with the 0.5 d-old eggs to be the most easily vulnerable. The results suggest that Mf82 is a promising biocontrol agent for BPH.

Key words: Nilaparvata lugens, Metarhizium anisopliae, Metarhizium flavoviride, Beauveria bassiana, toxicity, pathogenicity, infection rate