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Vector control plays a key role in prevention and control of major vector-borne diseases and often constitutes the first line of activity in case of epidemics of vector-borne diseases, and particularly, malaria. Chemical control (use of pesticides) is still the most important element in the integrated approach to vector control. But they are non-selective and harmful to other beneficial organisms. Some of the insecticides are carcinogenic agents and are positively dangerous and even carried through the food chain which in turn affects the non-target organism. In view of the above, the uses of biologically-active plant materials with anti-mosquitocidal properties and ecofriendly-biopesticides are attracted in recent years, because of their biodegradable nature and being relatively safer to human and other non-target organism in the environment. The present paper is to investigate on the larvicidal, pupicidal, smoke repellency effect of neem products against malarial vector, Anopheles stephensi. Six neem limonoids (purity>99%), namely azadiractin, salannin, deacetylgedunin, gedunin, 17-hydroxyazadiradione and deacetylnimbin were sent from Central Research Laboratories, Taiyo Kagaku Co Ltd., Japan. Larvicidal bioassays were conducted at the laboratory with neem limonoids the lethal concentrations (LC50, LC90) were worked out by Abottts’ formula. Repellency bioassay was done by human volunteers by using neem oil which was procured from the Local Neem Oil Mill, Kalverrampalayam, Coimbatore-641 046, India. Smoke toxicity was performed on the adult female mosquitoes at the laboratory by using neem seed kernel power and it was collected from the Bharathiar University Campus, Coimbaotore-641 046, India. The neem products also had significant larvicidal activity. The larval mortality was dose dependant. The LC50 and LC90values of Azadirachtin treatment at 0.50, 1.0 and 1.5 ppm concentrations was 0.299% and 1.061%, respectively. After treatment of neem oil at 0.50, 1.0 and 1.5 ppm concentrations were 0.503 and 1.324, respectively. After the treatment of salanin, 17-Hydroxyazadiradione, Deacetyl gedunin, Gedunin and Dacetyl nimbin the LC50 and LC90 values were increased when compare to Azadirachtin. There was significant repellent activity after the treatment of neem products at three different concentrations (0.2, 0.4, and 0.6). Neem oil had higher repellent activity (<300 minutes at 0.6 concentration), followed by Gedunin which showed less activity (<200 minutes at 0.6 concentration). However, the ethanol applied arm served as control which provided maximum 7.0 minutes repellency. The leaves and pods were also tested smoke repellency bioassay. Smoke emerged from the leaves and pods greater knock down effect were evident and percentage of repellency on leaf 59%, pod 53% and with commercial coil as positive control which showed 65% repellency. Moreover, smoke exposed larvae laid minimum number of eggs and hatchability also affected. From this study it has been concluded that based on the larvicidal, smoke repellent properties neem products showed mosquitocidal properties. Hence, it can be concluded that neem as effective biopesticides for the Integrated Vector Control Program. Moreover, neem is indigenous, medicinal importance and much of social relevance to people and traditional knowledge of our country.
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Author(s): K Murugan G James Pitchai P Madhiyazhagan T NatarajA Nareshkumar JiangShiou Hwang R Chandrasekar M NicolettiA AmsathRanjeet Bhagooli
Neem products, larvicide, repellent, smoke toxicity, malarial vector, physiology, cell and molecular biology, genetics, biochemistry, biotechnology, bioinformatics, microbiology, immunology, parasitology