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.