The oil of garlic, allium sativum L. (Amaryllidaceae), as a potential grain protectant against Tribolium castaneum (Herbst) and Sitophilus zeamais motsch.

Abstract

Fresh garlic cloves were steam-distilled to obtain the essential oil. The garlic oil was tested for toxicity against the eggs, larvae and adults of Tribolium castaneum and adults of Sitophilus zeamais. T. castaneum egg mortality increased with garlic oil concentration, complete kill of eggs being achieved at 4.4 mg/cm2, using the filter paper impregnation bioassay. The eggs were the most susceptible stage, followed by adults, 10-day old larvae and older larvae. T. castaneum adults were more susceptible to garlic oil than S. zeamais adults, with KD50 values of 1.32 mg/cm2 and 7.65 mg/cm2, respectively. When rice and wheat were treated with garlic oil, eggs that were laid in the media failed to produce F1 progeny at concentrations of >2000 ppm in rice for T. castaneum and 5000 ppm in wheat for S. zeamais. The weights of F1 adults of T. castaneum and S. zeamais in treated media were not significantly different (P > 0.05) from those of the controls. The potential of garlic oil, and the bioactive compounds therein, as an effective grain protectant is discussed.