Insecticidal activity of four essential oils on the survival and oviposition of two sympatric bruchid species: Callosobruchus maculatus F. and Callosobruchus subinnotatus PIC. (Coleoptera: Chrysomelidea: Bruchinae)

Callosobruchus maculatus F. and Callosobruchus subinnotatus Pic. are two pest species of stored cowpeas and bambara groundnuts. Methods of controlling their populations remain the use of chemical insecticides that have ecotoxicological effects. The aim of this work is to look for alternative methods using essential oils extracted from four aromatic plants (Bidens borianiana, Chromolaena odorata, Cymbopogon giganteus and Cymbopogon nardus) to control these pests. Essential oils GC/MS analysis revealed differences in their composition. The major components of the essential oils of the two congeneric Poaceae species C. giganteus and C. nardus are totally different. Limonene (23.03%), cis-p-mentha-2, 8-dien-1-ol (14.26%) and p-mentha-1(7), 8-dien-2-ol isomer (14.06%) were the main compounds in C. giganteus oil whereas citronellal (30.58%) and geraniol (23.93%) were identified in C. nardus oil. In the essential oils of the other two plants, the major components are respectively geyrene (19.44%), α-pinene (15.96%), and germacrene D (14.03%) for Chromolaena odorata essential oil and trans-β-ocimene (31.58%) for Bidens borianiana essential oil. Toxicity tests were performed by fumigation on adult survival and female oviposition in C. maculatus and C. subinnotatus by evaluating the LD10; LD50 and LD90 of the four essential oils. These tests showed that only essential oils extracted from Cymbopogon species are efficient. The essential oil of C. giganteus was the most toxic to adults of both bruchid species. The LD50 were 20.06 and 34.62 µL/L, respectively for C. maculatus and C. subinnotatus while C. nardus essential oil showed the best ovicidal activity with female oviposition reduction in both bruchid species of more than 80% at a lower concentration (10 µL/L). C. giganteus and C. nardus essential oils can thus be used in stocks of cowpea and bambara groundnuts for adult control and prevent female oviposition.   Key words: Callosobruchus maculatus, Callosobruchus subinnotatus, Cymbopogon giganteus, Cymbopogon nardus, Bidens borianiana, Chromolaena odorata, essential oils, survival, oviposition