ENHANCED TOXICITY OF BROWN ALGAL SEAWEED Sargassum wightii GREVILLE WITH ORGANIC INPUTS AGAINST RICE LEAF FOLDER Cnaphalocrocis medinalis GUENEE (LEPIDOPTERA: CRAMBIDAE) UNDER LABORATORY CONDITIONS

Abstract

Rice leaf folder (Cnaphalocrocis medinalis Guenee) as a key pest have imparted extensive leaf damage during the tillering stage of the crop and has been reported to cause more than 15% damage. The experiment was conducted to evaluate the enhanced insecticidal and IGR activity of solvent extracts (Acetone) of brown algal seaweed Sargassum wightii Greville in combination with organic inputs (Neem Leaf Extracts 3% and 5%) against rice leaf folder C. medinalis in the Seaweed Laboratory, Department of Entomology, Faculty of Agriculture, Annamalai University, Tamil Nadu, India during 2021-2022. The seaweed Extracts @ 6, 7 and 8 per cent alone and in combination of seaweed 6, 7, 8 percent with Neem Leaf Extracts 3 and 5 per cent concentrations were investigated for their enhanced toxicity (larvicidal and Insect Growth Regulator activity) against rice leaf folder compared with standard checks (Neem Leaf Extracts 3% and 5%). The highest mortality (66.66%) was observed in the combination treatment S. wightii seaweed extract 8 per cent + Neem Leaf Extract 5 per cent followed by S. wightii seaweed extract 8% with Neem Leaf Extract 3% which exerted 60.00 per cent mortality. The larva to adult conversion ratio of 1:0.13 in S. wightii seaweed extract 8% with Neem Leaf Extract 5% was the least when compared with other treatments whereas S. wightii seaweed extract 8% with Neem Leaf Extract 3% was the effective treatment in the second experiment with a larval and adult conversion ratio of 1:0.20 meanwhile no mortality was observed in both untreated controls in both the experiments. The combination effect of S. wightii seaweed extract 8% with Neem Leaf Extract 5% was superior than other treatments in reducing the larval vitality, pupation and also influenced insect growth regulator activity in the pupal and adult stages of insect which would be recommended for the future IPM programmes.