Fumigation Action of Four Plant Oils Against Eggs of Callosobruchus chinensis (L.) (Coleoptera: Bruchidae)

The fumigant action of four plant oils viz., garlic (Allium sutivum L.), clove [Syzygium aromaticum (L.) Merr. & Perry], attarasa [Litsea cubeba (Lour.) Pers.] and coriander (Coriandrum sativum L.) oils, was tested against eggs of Callosobruchus chinensis (L.). After 72 h of exposure, garlic oil exhibited the highest fumigant toxicity against eggs of C. chinensis, which was followed by clove, attarasa and coriander oils, with LC50 values of 0.34, 1.12, 3.78 and 5.29 mu L/L air, respectively. Binary mixtures of clove/coriander oil and clove/attarasa oil showed significant synergism with the co-toxicity factor of 241.77 and 114.15, respectively, while other combinations did not show any synergism. Optimal volume proportions of these synergistic combinations were 24: 76 for clove/coriander oil and 41: 59 for clove/attarasa oil, which were screened out with the toxicity index and were further confirmed by the co-toxicity coefficient. GC-MS analysis of these oils showed that eugenol, aceteugenol and beta-caryophyllene were major components of clove oil, linalool, a-pinene, camphor, geranyl acetate and gamma-terpinolene of coriander oil, alpha-citral, beta-citral, D-limonene, linalool and sulcatone of attarasa oil, and sulphur compounds of garlic oil. Based on high toxicity against C. chinensis eggs and synergistic action of plant oil mixtures, clove oil can be used as another potential grain fumigant for the management of stored legume pests.