Evaluation of dry powder of certain chilli cultivars with emphasis on capsaicin against Sitophilus oryzae (Coleoptera: Curculionidae) on wheat

The weevil, Sitophilus oryzae is considered the most important primary pest of stored wheat. Secondary metabolites like capsaicinoids extracted from chilli can be used in insect pests control as a potential alternative to synthetic insecticides. Therefore, the present study aimed to test the contact and fumigation repellency test of capsaicin from different chilli cultivars viz., Kashmiri, Guntur Sannam (S4), Jwala, Bullet and Bhut Jolokia collected from various zones of India. For this a modified cup bioassay apparatus was designed by altering the structural features of cup bioassay apparatus without changing its core principle, Consisting of outer big and inner small polyacrylic box with 2 mm perforations at the inner box on all four sides and bottom side, this can hold test grains up to 500 g. capacity. The repellency bioassay was also conducted using the area preference method. The results revealed that the treatments with the chilli cultivar Bhut Jolokia at a concentration 0.50 % (w/w basis), concentration at 10 ml and 5 g proved to be effective against all treatments and control under contact and fumigation repellency test of capsaicin respectively. And the percentage repellency was noted to be the highest in the treatments with Bhut Jolokia at a concentration of 5 ml (63.33 %). Therefore, capsaicin from the Bhut Jolokia chilli cultivar in its dry powder, ethanol extract and crude form performed well in repelling the maximum number of the test insects that it may be employed as the grain protectant against S. oryzae. Future research efforts may be made to focus on the evaluation of these molecules in specific trap tests to evaluate their efficacy in increasing pheromone trap captures.