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The effects of yeheb (Cordeauxia edulis Hemsl.) leaf extract on feeding and oviposition by diamondback moth (DBM) (Plutella xylostella L.) and the behavior of DBM parasitoid, Cotesia vestalis (Haliday), were studied. Volatile organic compounds (VOCs) from the headspace of intact and DBMdamaged broccoli plants sprayed with yeheb extracts (YE) were also analyzed. Larval feeding and growth, and oviposition by adult DBM were strongly inhibited by the extract. Cotesia vestalis were attracted to volatile blends from intact or DBM-damaged broccoli plants sprayed with YE over intact plants sprayed with water or methanol. Analyses of VOCs in the headspace of broccoli plants revealed that both intact and DBM-damaged plants sprayed with YE showed remarkable differences in sesquiterpene compounds compared to intact control treatments. These combined negative effects of YE on DBM fitness together with positive effects on the parasitoid show that yeheb is a potential source of compounds for use in integrated pest management to control damage caused by DBM.

The use of plant-based compounds to control insect pests is an alternative to the use of synthetic pesticides. We evaluated the repellent and antifeedant effects of Cordeauxia edulis Hemsley (Fabaceae) and Rhododendron tomentosum Harmaja (Ericaceae) extracts against Hylobius abietis L. (Coleoptera: Curculionidae) and Phyllodecta laticollis Suffrian (Coleoptera: Chrysomelidae). Repellent properties were evaluated by monitoring responses of adult insects toward the odor from extracts or extraction solvents (controls) in a Y-tube olfactometer, and choice or no-choice feeding tests were conducted by applying extracts or extraction solvents on stems of Scots pine [Pinus sylvestris L. (Pinaceae)] and European aspen [Populus tremula L. (Salicaceae)], host plants of H. abietis and P. laticollis, respectively. Extracts of R. tomentosum repelled adults of both insect species effectively. However, extracts of C. edulis did not repel H. abietis although its ethyl acetate extract showed repellence against the adults of P. laticollis. Feeding by H. abietis was significantly reduced by a methanol extract of C. edulis, and methanol and hexane extracts of R. tomentosum. Feeding by the adults and larvae of P. laticollis was significantly reduced by extracts from both plant species. Concomitant with less feeding, larval growth was retarded by ethyl acetate extracts of both plant species. Gas chromatography-mass spectrometry analyses of the volatile components of the extracts showed that extracts from both plant species were mixtures of various terpene and non-terpene compounds, which showed quantitative and ⁄ or qualitative variations between plant species and extraction solvents. This experiment showed that extracts from both plant species effectively manipulated the orientation and ⁄ or feeding behavior of the two beetle species. Hence, they may be considered as potential alternatives to synthetic chemical pesticides.

Yeheb is a shrub endemic to the Horn of Africa. It is adapted to hot and xeric environments and known to be resistant to insect herbivores. We analysed volatile organic compounds (VOCs) from the headspace of vegetative branches (VBs) and fl owering branches (FBs), stored terpenoids from leaf and bark extracts and foliar total phenolics. Isoprene was the dominant compound in the headspace. In total, 66 VOCs were identifi ed, but only a few stored terpenes were detected. Isoprene and monoterpene emissions from FBs were at levels of 24.0 and 5.12 μg/g dw (dry weight)/h, respectively. A total of 30 compounds were emitted at signifi cantly higher rates from FBs than from VBs. The emission of large quantities of a diverse range of VOCs and the presence of high levels of total phenolics in this plant may be attributed to its defence strategy against both abiotic and biotic stresses in arid environments.

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