Volatile compounds present in essential plant oils are known to influence insect behaviour. They are generally of low molecular weight, highly volatile, have a unique mode of action and are sometimes of low toxicity to non-target organisms. One example of a volatile compound extracted from a plant is methyl salicylate which is being used to reduce aphid infestation on barley in some European countries. The use of such volatile compounds was therefore considered as an alternate control option to be included in the control programme of Diuraphis noxia (Kurd.) after plant resistance-breaking biotypes started to develop in South Africa. The aim of this study was to test the response of alate D. noxia to plant extracts from four plant species in a four-arm olfactometer. Aqueous and light mineral oil extracts of Artemisia afra (Jacq.), Datura stramonium (L.), Tagetes minuta (L.) and Tulbaghia violacea (Harv.), which grow naturally in some dryland wheat production regions of South Africa, were tested. These plants were chosen based on possible insect repelling properties known to occur in other species of the same genera. Aphids were strongly repelled by the oil extract of T. violacea and the aqueous extract of A. afra. The oil extract of A. afra, both T. minuta extracts and T. violacea aqueous extract were less repellent but still elicited an exceptional repelling response. Aphids were not repelled by D. stramonium extracts. The effectiveness of these basic extracts in repelling D. noxia should, however, be tested under field conditions before they can be recommended as a control option.
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Vol. 22 • No. 4