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Abstract
The brown planthopper, Nilaparvata lugens Stal (Homopera: Delphacidae), is an important pest of rice. Although current research indicates that the fungus can infect the adult and nymph, there is no information on the efficacy of entomopathogenic fungi against the egg. In this study, the virulence of two isolates of Metarhizium anisopliae, and four isolates of Beauveria to N. lugens egg were tested in the laboratory. Different stage eggs were sprayed with a standard concentration of 1.0x108 conidia/ml. During a 12 day observation period after spray, the infected eggs shrunk in shape, then turned orange-brown for Beauveria, and eventually had outgrowths of the sprayed fungus when maintained under the condition of RH > 95%. The 1 day old of N. lugens egg was the most sensitive to the Beauveria infection followed by the 2, and 3 day old. Only two B. brongniartii Bb5, and Bb8 isolates killed >50% of the eggs. Both isolates were further bioassayed against the eggs with sprays of 1x106, 1x107, and 1x10s conidia/ml with 4 replicates at each concentration. Based on the LC50 estimates determined by the concentration-mortality relationships of two isolates from probit analysis, B. brongniartii Bb8 with an LC50 of 1.20x107 conidia/ml was highly infectious to N. lugens eggs, followed by B. brongniartii Bb5 (2.58x107 conidia/ml). The results confirmed the ovicidal activity of the two fungal species and suggested the feasibility to search for more ovicidal isolates from fungal species that may serve as biocontrol agents against N. lugens.