Utilization of Ruta graveolens and Azadirachta indica leaf powders and their binary combinations for the management of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) in stored maize in Sri Lanka

Abstract

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M aize w eevil (Sito p h ilu s zeam ais, M otsch.) is a ubiquitous and cosm opolitan field-to-store pest o f m aize o f econom ic im portance in tropical and subtropical regions o f the w orld. T he current renew ed interest to replace synthetic insecticides has served as the im petus for the evaluation and intensification o f eco-friendly anti-w eevil m easures such as the use o f plant based bioinsecticides. T his study w as therefore, designed to investigate the insecticidal and repellent potency o f leaf pow ders o f R uta graveolens and A zadirachta indica in single treatm ents and com binations o f various proportions under am bient laboratory conditions against Sitophilus zeam ais in both contact and vap o u r form s. For both plants, 100 g each o f m aize grains w ere m ixed w ith leaf pow ders at different doses o f 1.0, 3.0, 5.0, 7.0 and 10.0 g. T he bio-potential o f three com binations o f 1:1, 1:2 and 2:1 o f R. graveolens and A. indica le a f pow ders incorporating into the dosage level o f lO.Og w as also evaluated. M aize grains treated w ith R. graveolens leaf pow der caused 100 % contact and 68 % fum igation m ortalities w ithin 24 hours o f exposure w hilst repelling 97 % and 96 % w eevils w ithin an hour in both contact and vapour form s respectively. A. indica pow der w as less efficacious com pared to that o f R. graveolens causing significantly low er repellency w ithin an hour and m ortalities after 10 days o f storage. A pplication o f 2:1 com bination o f R. graveolens and A. indica produced respective levels o f 100 % and 73% contact and fum igation m ortalities w ithin 24 hours and highly significant repellent effects on S. zeam ais, offering greater potential for large-scale storage since such com binations are relatively cheaper than using either o f the botanicals singly. L ea f pow ders o f the tw o plants under present investigation revealed their im proved grain protecting capacity w hen used individually and in m ixtures as bio-rational leads in large-scale protection o f stored m aize.