Residual activity of powders and oils of Pimpinella anisum, Citrus aurantium and Origanum majorana as grain protectants against Callosobruchus maculatus (F.) and Sitphilus oryzae (L.)

The cowpea weevil, Callosobruchus maculatus (F.) and the rice weevil, Sitphilus oryzae (L.) are destructive insects attacking cowpea seeds and rice grains causing weight loss and reduced nutrition values. Laboratory experiments were conducted to evaluate the insecticidal toxicity of three plant oils and powders of anise (Pimpinella anisum), Bitter orange (Citrus aurantium) and Sweet marjoram (Origanum majorana ) as grain protectants on the mortality of C. maculatus and S. oryzae. The results showed that marjoram and anise in oil forms were highly toxic on C. maculatus with LC50 values of 0.69 and 1.09 ppm, respectively and on S. oryzae with LC50 values of 0.533 and 0.515 ppm, respectively. Furthermore, the residual toxicity of the tested materials was evaluated through three months of storage against adult and progeny of the two insects. The tested materials significantly increased the mortality percentages and reduced the fecundity of the two insects depending on the dosage, the exposure time and storage periods compared with control. Malathion had the highest effect against both insects compared to the plant products. The plant oils showed more efficacy than the powders against the two insects in initial time storage while, the plant powders were more effective at the end of storage periods. The identification of chemical composition of tested plant oils was done by using GC-MS analysis. Considering the results of the current study, it could be suggested that the three plant oils and powders especially, anise and marjoram may have potential to be used as an alternative to synthetic insecticides in an integrated pest management program for protecting stored grains.