Riding on the wind: volatile compounds dictate selection of grassland seedlings by snails.

Background and Aims: Seedling herbivory is an important selective filter in many plant communities. The removal of preferred food plants by both vertebrate and, more commonly, invertebrate herbivores can destroy entire seedling cohorts, and consequently dictate plant community assembly. Nevertheless, our understanding of how and why some seedlings are more prone to herbivore attack than their neighbours remains limited. For seedlings, where even minor tissue damage is fatal, avoiding contact with herbivores is probably advantageous and, on this basis, volatile organic compounds (VOCs) are strong candidates to fulfil a primary defensive role. Methods: We quantified seedling selection by snails (Cornu aspersum) for 14 common, European grassland species. Seedling acceptability was subsequently compared with species-specific expression of constitutive secondary defence metabolites (CSDMs), and VOCs to determine their relative influence on seedling selection. Results: We found no relationship between seedling acceptability and CSDMs, but seedling selection was strongly associated with VOC profiles. Monoterpenes (specifically β-ocimene) were identified as likely attractants, while green leaf volatiles (GLVs) (3-hexen-1-ol acetate) were strongly associated with low seedling acceptability. Conclusions: By elucidating a relationship between VOCs and seedling acceptability, we contradict a long-held, but poorly tested, assumption that seedling selection by herbivores in (semi-)natural plant communities centres on CSDMs. Instead, our results corroborate recent work showing how GLVs, including 3-hexen-1-ol acetate, deter crop seedling selection by molluscs. Although our failure to establish any early-ontogenetic relationship between VOCs and CSDMs also suggests that the former do not 'advertise' possession of the latter, we nevertheless reveal the role that VOCs play in defending seedlings against herbivory before lethal damage occurs

Behavioural responses of the aphid parasitoid Diaeretiella rapae to volatiles from Arabidopsis thaliana induced by Myzus persicae

In response to herbivory by insects, several plant species have been shown to produce volatiles that attract the natural enemies of those herbivores. Using a Y-tube olfactometer, we investigated responses of the aphid parasitoid Diaeretiella rapae Macintosh (Hymenoptera: Aphidiidae) to volatiles from Arabidopsis thaliana Columbia (Brassicaceae) plants that were either undamaged, infested by the peach-potato aphid, Myzus persicae Sulzer (Homoptera: Aphididae), or mechanically damaged, as well as to volatiles from just the aphid or its honeydew. In dual-choice experiments, female D. rapae given oviposition experience on A. thaliana infested with M. persicae were significantly attracted to volatiles from A. thaliana infested with M. persicae over volatiles from undamaged A. thaliana and similarly were significantly attracted to plants that had been previously infested by M. persicae, but from which the aphids were removed, over undamaged plants. Diaeretiella rapae did not respond to volatiles from M. persicae alone, their honeydew, or plants mechanically damaged with either a pin or scissors. We conclude that an interaction between the plant and the aphid induces A. thaliana to produce volatiles, which D. rapae can learn and respond to. Poor responses of D. rapae to volatiles from an A. thaliana plant that had two leaves infested with M. persicae, with the two infested leaves being removed before testing, suggested the possibility that, at this stage of infestation, the majority of volatile production induced by M. persicae may be localized to the infested tissues of the plant. We conclude that this tritrophic interaction is a suitable model system for future investigations of the biochemical pathways involved in the production of aphid-induced volatiles attractive to natural enemie

Analysis of ecosystem services provision in the Colombian Amazon using participatory research and mapping techniques

Over the last two decades indigenous peoples in the lower Caquetá River basin in Colombia have experienced detrimental changes in the provision of important ecosystem services in ways that have significant implications for the maintenance of their traditional livelihoods. To assess these changes we conducted eight participatory mapping activities and convened 22 focus group discussions. We focused the analysis on two types of change: (1) changes in the location of ecosystem services provisioning areas and (2) changes in the stock of ecosystem services. The focal ecosystem services include services such as provision of food, raw materials and medicinal resources. Results from the study show that in the past two decades the demand for food and raw materials has intensified and, as a result, locations of provisioning areas and the stocks of ecosystem services have changed. We found anecdotal evidence that these changes correlate well with socio-economic factors such as greater need for income generation, change in livelihood practices and consumption patterns. We discuss the use of participatory mapping techniques in the context of marginalized and data-poor regions. We also show how this kind of information can strengthen existing ecosystem-based management strategies used by indigenous peoples in the Colombian Amazon

Effects of Bt maize on the herbivore Spodoptera littoralis (Lepidoptera: Noctuidae) and the parasitoid Cotesia marginiventris (Hymenoptera: Braconidae)

Recent studies have shown that transgenic insect resistant plants can have negative effects on non-target herbivores as well as on beneficial insects. The studyof tritrophic interactions gives insight into the complex mechanisms of food webs in the field and can easily be incorporated into a tiered risk assessment framework. We investigated the effects of transgenic maize (Zea mays) expressing insecticidal proteins derived from Bacillus thuringiensis (Bt maize) on Spodoptera littoralis, a non-target herbivore, and on the hymenopteran parasitoid Cotesia marginiventris. In a laboratory study, S. littoralis larvae were reared for their whole lifespan on a mixture of leaves and stems from 2–4-week old Bt maize plants. S. littoralis survival, developmental times and larval weights were significantly affected by Bt maize diet. However, adult moths, which survived development on Bt maize, were the same size as the adults from the control group. C. marginiventris survival, developmental times and cocoon weights were significantly negatively affected if their S. littoralis host larva had been fed Bt maize. ELISA tests confirmed that S. littoralis larvae ingest high amounts of Cry1A(b) toxin while feeding on Bt maize. In S. littoralis pupae and in C. marginiventris cocoon silk, only traces of the toxin could be detected. No toxin was found in S. littoralis and C. marginiventris adults. Thus the toxin is not accumulating in the trophic levels and in fact appears to be excreted. Our results suggest that the effects on C. marginiventris when developing in susceptible S. littoralis larvae are indirect (host mediated). The biological relevance of those results and the significance of this study in risk assessment are discussed

New roles for cis-jasmone as an insect semiochemical and in plant defense.

cis-jasmone, or (Z)-jasmone, is well known as a component of plant volatiles, and its release can be induced by damage, for example during insect herbivory. Using the olfactory system of the lettuce aphid to investigate volatiles from plants avoided by this insect, (Z)-jasmone was found to be electrophysiologically active and also to be repellent in laboratory choice tests. In field studies, repellency from traps was demonstrated for the damson-hop aphid, and with cereal aphids numbers were reduced in plots of winter wheat treated with (Z)-jasmone. In contrast, attractant activity was found in laboratory and wind tunnel tests for insects acting antagonistically to aphids, namely the seven-spot ladybird and an aphid parasitoid. When applied in the vapor phase to intact bean plants, (Z)-jasmone induced the production of volatile compounds, including the monoterpene (E)-beta-ocimene, which affect plant defense, for example by stimulating the activity of parasitic insects. These plants were more attractive to the aphid parasitoid in the wind tunnel when tested 48 h after exposure to (Z)-jasmone had ceased. This possible signaling role of (Z)-jasmone is qualitatively different from that of the biosynthetically related methyl jasmonate and gives a long-lasting effect after removal of the stimulus. Differential display was used to compare mRNA populations in bean leaves exposed to the vapor of (Z)-jasmone and methyl jasmonate. One differentially displayed fragment was cloned and shown by Northern blotting to be up-regulated in leaf tissue by (Z)-jasmone. This sequence was identified by homology as being derived from a gene encoding an alpha-tubulin isoform