Toxicity of Some Plant Products to Selected Insect-Pests, and its Enhancement by Combinations

Different plant products including oils have been examined singly and in combinations against a broad cross-section of insect pests/vectors: mosquitoes, termites, stored grain pests and a crop pest. The results suggest widespread entomopathic potential of plant products, pinpointing one of the latter viz. calamus oil, exhibiting highest toxicity showing lowest LC₅₀ 46.00 ppm against Culex quinquefasciatus mosquito larvae and 0.45 m/cm² against the adults of stored grain pests viz. Callosobruchus chinensis. Remarkably, activity of calamus oil itself was enhanced when mixed with inactive oils or other derivatives. In these mixtures, each constituent was only one-half and l/3^rd in double and triple combinations, respectively. In such a 1:1 combination of calamus oil with karanja oil, LC₅₀ of 45.87 ppm was elicited against Culex larvae, whereas in combination with capric acid, LC₅₀ of 0.51 mg/cm² was elicited against C. chinensis adults. Similar triple combination (1:1:1) of calamus oil, terpineol and capric acid showed LC₅₀ of 62.82 ppm against Culex larvae and 0.93 mg/cm² against C. chinensis adults. Enhancement of activity in combinations could be thus traced to the presence of calamus oil, hinting possible synergistic action.