Abstract
The total glycoalkaloid fraction (TGA) and the two glycoalkaloids, alpha-chaconine and alpha-solanine of potato, Solanum tuberosum, were isolated. Their toxic and antifeedant activities against the Khapra beetle, Trogoderma granarium Everts were investigated. Results indicated considerable toxicity, especially when adults were topically treated with the glycoalkaloids. The TGA fraction was the most toxic with LC50's of 16.7 and 11.9 mu g/mg insect, 48 and 96 h post treatment, respectively. LC50's of alpha-chaconine and alpha-solanine 96 h post treatment were 18.1 and 22.5 mu g/mg insect, respectively. Moderate toxicities were recorded when insects were confined on dry-film residues of botanicals with LC50's ranging between 26.1 and 56.6, and 19.4 and 45.7, mu g/cm(2) 48 and 96 h post treatment, respectively. Nutritional studies using the flour disc bioassay revealed significant reduction in the growth rate (RGR), food consumption rate (RCR) and food utilization (ECI) by T. granarium at concentrations ranging between 20 and 30 mg g(-1) food with feeding deterrent indices reaching 82.4% with the TGA fraction. When tested as binary or crude alkaloidal mixtures, toxic and antifeedant activities of glycoalkaloids were increased, indicating some additive interaction among these botanicals. There is potential for use of such compounds to protect stored grains from insect infestation. (C) 2011 Elsevier Ltd. All rights reserved.