Persistent Toxicity of Botanical Insecticides against Castor Semilooper, Achaea Janata Linn.(Lepidoptera:Noctuidae)

Investigations were carried out on persistent toxicity of botanicals against castor semilooper, Achaea Janata Linn. Based on feeding and exposure period, promising botanicals like dust and cold alcohol extracts (CAE) of Clerodendrum inerme were compared with a commercial neem based botanical and a recommended chemical insecticide, methyl parathion for their persistence in the field. Feeding of treated leaves for 24h, irrespective of exposure (weathering) period after treatment, did not cause any mortality in all the plant products. Successive increase in feeding period increased the mortality, when leaves were exposed from 0–15 days. Maximum mortality was 84.4 per cent in C. inerme dust (15%) and C.inerme CAE(10%), followed by neemgaurd (77.8%), C.inerme CAE 5% (75.6%) and C. inerme 10% dust(71.1%) on 9th day of feeding. The effectiveness of all botanicals decreased with increase in exposure period at all intervals of feeding period. In all the strengths of botanicals tested, prolonged feeding up to 5–9 days was required to exhibit treatment effect. The longest persistence of eight days was recorded in C. inerme (CAE 10%) whereas, shortest period of five days in C. inerme (10%) dust with continuous feeding for nine days. In none of the botanicals the persistence was beyond three days to cause 75 per cent mortality. In contrast, methyl parathion which exhibited quick knockdown effect inducing 84.4 per cent mortality when fed at one hour after treatment for 24 h lost its effectiveness gradually to reach 6.7 per cent at 15th day of exposure. Similar trend in the depletion of effectiveness was evident at 2, 5, and 9 days feeding period intervals with initial mortality being highest (100%). The persistence period of methyl parathion was 15 days at shortest feeding period of one day.