Identification of a bacterium isolated from the diseased brown planthopper and determination of its insecticidal activity

Abstract

ABSTRACTThe brown planthopper, Nilaparvata lugens, is one of the most harmful insect pests of rice crops in Asian countries. To find an effective biological control agent against this pest, we investigated the bacterial flora of field N. lugens collected from Jiangsu Province, China, in 2012 and tested its insecticidal activity. A novel bacterium strain, S-JS1, was isolated from N. lugens nymphs and adults and showed a high level of insecticidal activity. Based on its phenotypic, physiological and biochemical properties, and its 16S rRNA gene phylogeny, the isolate was assigned to Serratia marcescens; the name S. marcescens S-JS1 is proposed. The pathogenicity of S-JS1 against the third-instar nymphs, and the macropterous and the brachypterous adults of N. lugens were compared. The median lethal concentration (LC50) values of S-JS1 against the brachypterous adult were the lowest (LC50, 1.53 × 108 colony forming units (cfu)/ml), followed against the macropterous adult (LC50, 1.65 × 109 cfu/ml) and third-instar nymphs (LC50, 1.86 × 109 cfu/ml) at 5 days post-infection. The median lethal time values of 8 × 108 cfu/ml S. marcescens S-JS1 against the brachypterous adult, macropterous adult, and third-instar nymph were 4.5, 5.5, and 5.7 days, respectively. These results indicate that the S-JS1 isolate appears to be a promising S. marcescens strain with strong biocontrol potential against N. lugens.