Granular Insecticides Against the Incidence of Rice Blue Beetle, Leptispa pygmaea

Experiments were conducted at the Regional Agricultural Research Station, Pattambi, Kerala Agricultural University during Kharif and Rabi seasons in 2004 and 2005 for assessing the efficacy and persistent toxicity of five granular insecticides viz., cartap hydrochloride 4 G @ 1000 g a.i./ha, carbosulfan 6 G @ 1000 g a.i./ha, fipronil 0.3 G @ 100 g a.i./ha, phosphamidon 10G @ 1000 g a.i./ha and carbofuran 3G @ 1000 g a.i./ha as nursery application against rice blue beetle Leptispa pygmaea Baly(Coleoptera:Chrysomelidae). The incidence of blue beetle damage was higher in Rabi ranging from 7.7 to 27.5 per cent than in Kharif season (12.5 to 16.8 per cent). Highest damage was observed at 20 days after transplanting in the main field. Cartap hydrochloride@ 1000 g a.i./ha was found to be the most significantly effective treatment in reducing the leaf damage by L. pygmaea. It was significantly superior to control by bringing about 51.4 and 40.9 per cent reduction of leaf damage over control during 2004 and 2005, respectively at 20 days after transplanting. The efficacy of the tested granular insecticides in the descending order was cartap hydrochloride, carbofuran, carbosulfan, phosphamidon and fipronil. Persistent toxicity study of the granular insecticides showed that carbofuran was the most persistent insecticide with highest PT value followed by carbosulfan, phosphamidon, cartap hydrochloride and fipronil against L. pygmaea in the rice field. Carbofuran showed 100 per cent mortality while cartap hydrochloride caused 60 per cent mortality to rice. Fipronil was found to be the least effective insecticide with lowest persistent toxicity against L. pygmaea.