Bioefficacy of Insecticides Against White Grub, Leucopholis lepidophora Blanch Infesting Arecanut Palm

The root infesting scarabaeid white grub, Leucopholis lepidophora Blanch is a major pest on arecanut in Western ghats area of Karnataka. In an attempt to identify an insecticide with enhanced bioaction against L. lepidophora, four insecticides viz., carbosulfan, tefluthrin, chlorpyriphos and phorate (standard insecticide) were screened for their toxicity in the laboratory and in the field. In laboratory bioassay studies, the order of toxicity observed was carbosulfan > tefluthrin > chlorpyriphos > phorate. On relative toxicity, carbosulfan was 4.2 times more toxic as compared to phorate followed by tefluthrin (2.8) and chlorpyriphos (1.9) in the case of II instar grubs. In III instar grubs carbosulfan was 13 times more toxic than phorate whereas, tefluthrin and chlorpyriphos were 12.5 and 2.7 times more toxic than phorate, respectively. A replicated field trial was taken up at arecanut gardens in Sringeri (Karnataka) for two years and the treatments were imposed during post monsoon season (1999 and 2000). Carbosulfan @ 20 g/palm during first and second years effected a mean reduction in grub population to a tune of 80.6% and 66%, respectively. Chlorpyriphos @ 8 ml/palm and carbosulfan @ 10 g/palm caused > 60% reduction in grub population during both the years of study. The standard insecticide phorate @ 10 g/palm caused a mean reduction of 36.43% and 44% during the respective years.