Toxicity of extracts derived from different parts of cassava plant, Manihot esculenta Crantz to four major coleopteran pests of stored-products

Fumigant toxicity of insecticidal principles extracted from tuber rind, fresh leaf, fresh leaf with petiole, and dried leaf of cassava (var. M4) was studied against four major stored-product insect pests viz. Sitophilus oryzae (L.), Rhyzopertha dominica (F.), Tribolium castaneum (Herbst) and Callosobruchus chinensis (L.) under laboratory conditions (28±2ºC, Rh. 75±5%). Mortality of the test insects varied with respect to extracts collected from different parts of the plant, and time of exposure. Extract collected from cassava rind recorded the highest toxicity. Callosobruchus chinensis was highly susceptible and showed immediate knockdown effect to the active principles extracted from tuber rind, fresh leaf, fresh leaf with petiole, twig and semi-dried leaf. The extract collected from various parts of plant caused 100% mortality of R. dominica at 1 hour after treatment (HAT), but the same collected from tuber and dried leaves did not show any toxic effect. Mortality of S. oryzae was 100% at 1 HAT with tuber rind extract, but no response was observed from the extract collected from semi-dried leaf, twig, and leaf with petiole. No fumigant action was observed in all the four coleopteran pests exposed to the extract collected from dried leaves. The study revealed that fresh leaf and tuber rind are good sources for the extraction of biofumigant against major coleopteran pests, however dried leaves are unfit for same purpose.