Fumigant toxicity of citruspeel oils against adult and immature stages of storage insect pests.
The biological action of citrus peel oils was shown to depend on a strong fumigant action. Bioassays conducted in airtight glass chambers showed that all the 6 citrus oils tested had vapour toxicity to adults of Callosobruchus maculatus, Sitophilus zeamais and Dermestes maculatus. The 24-h LC50 value of lime peel oil (a typical citrus oil) vapour against C. maculatus was 7.99 μl/litre which made it 1.5 and 1.6 times less toxic to the smaller S. zeamais and the larger D. maculatus adults, resp. When immature stages were fumigated, lime peel oil vapour had 24-h LC50s of 7.8 and 21.5 μl/litre against eggs of C. maculatus and D. maculatus, resp., and 9.1, 17.8, 23.1, 23.9 μlitre/litre against early larvae and pupae of C. maculatus and late larvae and pupae of D. maculatus, resp. X-ray studies showed that fumigated C. maculatus larvae within cowpea grains died immediately without further development. The bioactivities of 5 other citrus peel oils were similar to that of lime peel oil. Bioassays showed that sorption of citrus peel oil fumes occurred in the presence of cereal grains or strips of dried fish, and that this tended to reduce the amount available for fumigant action outside the materials. The problems presented by sorption may hinder the development of citrus oils into practical fumigants for large-scale treatments of stored commodities.