Abstract

Essential oils of aromatic plants with insecticidal properties are more and more considered as alternative insecticides to protect stored products. Many banned insecticides have high persistence which allow them to occur at several levels of trophic chains. The aim of the present work is to analyse the persistence of insecticidal activity of crude essential oil of three most used local aromatic plants : Annona senegalensis Pers. (Annonaceae), Hyptis spicigera L. (Lamiaceae) and Lippia rugosa L. (Verbenaceae) towards the four majors stored product insect pests: Sitophilus zeamais Motsch., Sitophilus oryzae L., Callosobruchus maculatusFab. and Tribolium castaneum Herbst. This research revealed that H. spicigera essential oil was the most active towards S. oryzae with a LD50 = 20.18ppm. T. castaneum was the less sensitive insect to the three essential oils tested. During a period of 24 hours L. rugosa essential oil was the most persistent, showing mortalities for S. zeamais of 80%, S. oryzae more than 60%, C. maculatus 100% and T. castaneum 50%. The two other oils tested were not as persistent as L. rugosa. This important persistence of the essential oil of L. rugosa could be explained by its high content of oxygenated compounds compared to that of the other oils. This most interesting essential oil is therefore a suitable one for popularisation in strategies of pest management in storage.

Key words: essential oils, aromatic plants, stored products, insect pests, persistence.