No abstract

Brown planthopper (BPH), Nilaparvata lugens Stål, is a serious insect pest of rice. The invasion of BPH causes heavy losses in rice production, both quality and quantity. The objective of this research was to search for Metarhizium spp., a genus of entomopathogenic fungi in the Clavicipitaceae family, from forest soil in three districts of Phetchabun Province, Thailand: Khao Kho, Lom Kao and Nam Nao to control BPH. Metarhizium spp. fungi were isolated by soil dilution plate technique and determined their efficacy using conidia suspension at the concentration of 1X108 conidia/mL on BPH at the 2-3th instar nymph fed on seedlings of susceptible rice cultivars, Taichung Native 1 (TN1). The most effective Metarhizium sp. isolate was identified using the ITS region of 18S rDNA sequencing, Basic Local Alignment Search Tool (BLAST) and evolutionary history. The result showed that 126 isolates of Metarhizium spp. were found and coded as PB-01 to PB-126. All isolates infected BPH nymph with 26.7 to 100% mortality within 6 days after contacting conidia suspension. The isolate of PB-75 showed the highest efficacy (100% BPH mortality) with the lethal times of 50% mortality (LT50) within 2.9 days. The species identification showed that the DNA sequence of Metarhizium sp. isolate, PB-75, was 98.6% similar to M. anisopliae Genbank ID JQ889704.1. Evolutionary history based on phylogenetic analysis using neighbor-joining and maximum parsimony methods confirmed that PB-75 formed the same phylogenetic clade with M. anisopliae Genbank ID JQ889704.1 and M. anisopliae var. anisopliae.