Abstract: Laboratory studies were conducted to determine the pathogenicity of the entomopathogenic fungus Metarhizium anisopliae var. acridum Driver et Milner on paddyfield spiders Pirata subpiraticus Bsenberg et Strand and Ummeliata insecticeps Bsenberg et Strand, to evaluate the effects of the fungus on the predating efficiency of the spiders on the brown planthopper, Nilaparvata lugens Stal. The results indicated that Metarhizium anisopliae var. acridum had no pathogenicity on both Pirata subpiraticus and Ummelita insecticeps. However, the activity of brown planthoppers decreased apparently after being infected with conidia of Metarhizium anisopliae var. acridum, that caused increase of the predating efficiency of the paddyfield spiders. At oncentrations of 10⁶, 10⁷, 10⁸ conidia/mL of Metarhizium anisopliae var. acridum, the mean predating efficiency of Pirata subpiraticus on brown plathoppers were 10.5 heads/d, 11.1 heads/d and 11.4 heads/d respectively; for Ummeliata insecticeps, the mean predating efficiency on plan thoppers were 3.8 heads/d, 4.3 hoppers/d and 4.7 hoppers/d respectively. Statistical analysis indicated that the differences between the treatments and control were significant. The predating efficiency of the spiders on planthopper increased slightly with the increasing of conidia concentrations of Metarhizium aniso pliae var. acridum.

Key words: Pirata subpiraticus, Ummeliata insecticeps, Metarhizium anisopliae var. acridum, Nilaparvata lugens, predating efficiency