Insecticidal effects of essential oils of Pelargonium graveolens and Cymbopogon citratus on Sitophilus zeamais (Motsch.)

Abstract

The evaluation of the effect of essential oils of Pelargonium graveolens andCymbopogon citratus on maize weevil (Sitophilus zeamais) has assigned the most significant insecticidal activity against it with a maximum mortality rate of 100%. The essential oils were found to have high contact and ingestion toxicity than fumigant / respiratory poison. This is evident from 90% mortality of weevils that come in contact or ingest contaminated food and only 40% when inhaled. This observation clarifies that the non volatile active components are more efficient than the volatile compounds of these essential oils. The insecticidal activity was more intense but short for higher concentrations of these oils and low and long-lasting for average concentrations. In fact, insecticidal activity decreased with the concentration of essential oils and varnishes with very small concentrations (from a dilution of 1/80 in our case) while it decreased with an increase in contact distance. The statistical results showed that the difference between the insecticidal activity of essential oils of P. graveolens (geranium) and C. citratus (lemongrass) was not significant in the three tests. Given that the weevil is the most devastating insect of maize (post-harvest), this study showed that these essential oils can serve, in one way or another, as a means of conserving maize corns for a longer time. Key words: Cymbopogon citratus, Pelargonium graveolens, essential oils, insecticidal activity, Sitophilus zeamais.