Abstract

The brown planthopper, Nilaparvata lugens Stål (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 six isolates ofBeauveria to N. lugens egg were tested in the laboratory. Different stage eggs were sprayed with a standard concentration of 1.0×10⁸ conidia/ml. During a 12 day observation period after spray, the infected eggs shrunk in shape, then turned orange-brown forBeauveria, 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 theBeauveria infection followed by the 2, and 3 day old. Only two B. brongniartii Bbr03, and Bbr09 isolates killed >50% of the eggs. Both isolates were further bioassayed against the eggs with sprays of 1×10⁶, 1×10⁷, and 1×10⁸ 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 Bbr09 with an LC₅₀ of 1.40×10⁷ conidia/ml was highly infectious to N. lugens eggs, followed by B. brongniartiiBbr03 (2.97×10⁷ 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.

Key words: Beauveria bassiana, Beauveria brongniartii, Metarhizium anisopliae,Nilaparvata lugens, ovicidal activity, microbial control.