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)-␤-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 ␣-tubulin isoform.

The roots of most land plants are colonised by mycorrhizal fungi that provide mineral nutrients in exchange for carbon. Here, we show that mycorrhizal mycelia can also act as a conduit for signalling between plants, acting as an early warning system for herbivore attack. Insect herbivory causes systemic changes in the production of plant volatiles, particularly methyl salicylate, making bean plants, Vicia faba, repellent to aphids but attractive to aphid enemies such as parasitoids. We demonstrate that these effects can also occur in aphid-free plants but only when they are connected to aphid-infested plants via a common mycorrhizal mycelial network. This underground messaging system allows neighbouring plants to invoke herbivore defences before attack. Our findings demonstrate that common mycorrhizal mycelial networks can determine the outcome of multitrophic interactions by communicating information on herbivore attack between plants, thereby influencing the behaviour of both herbivores and their natural enemies.

It is known that human individuals show different levels of attractiveness to mosquitoes. In this study, we investigated the chemical basis for low attractiveness. We recorded behaviors of Aedes aegypti toward the hands of human volunteers and toward the volatile chemicals produced by their bodies. Some individuals, and their corresponding volatiles, elicited low upwind flight, relative attraction, and probing activity. Analyzing the components by gas chromatography coupled to electrophysiological recordings from the antennae of Aedes aegypti, enabled the location of 33 physiologically relevant compounds. The results indicated that higher levels of specific compounds may be responsible for decreased "attractiveness." In behavioral experiments, five of the compounds caused a significant reduction in upwind flight of Aedes aegypti to attractive human hands. Thus, unattractiveness of individuals may result from a repellent, or attractant "masking," mechanism.

Natural enemies respond to herbivore-induced plant volatiles (HIPVs), but an often overlooked aspect is that there may be genotypic variation in these 'indirect' plant defence traits within plant species. We found that egg deposition by stemborer moths (Chilo partellus) on maize landrace varieties caused emission of HIPVs that attract parasitic wasps. Notably, however, the oviposition-induced release of parasitoid attractants was completely absent in commercial hybrid maize varieties. In the landraces, not only were egg parasitoids (Trichogramma bournieri) attracted but also larval parasitoids (Cotesia sesamiae). This implies a sophisticated defence strategy whereby parasitoids are recruited in anticipation of egg hatching. The effect was systemic and caused by an elicitor, which could be extracted from egg materials associated with attachment to leaves. Our findings suggest that indirect plant defence traits may have become lost during crop breeding and could be valuable in new resistance breeding for sustainable agriculture.

The alarm pheromone for many species of aphids, which causes dispersion in response to attack by predators or parasitoids, consists of the sesquiterpene (E)-␤-farnesene (E␤f). We used high levels of expression in Arabidopsis thaliana plants of an E␤f synthase gene cloned from Mentha ؋ piperita to cause emission of pure E␤f. These plants elicited potent effects on behavior of the aphid Myzus persicae (alarm and repellent responses) and its parasitoid Diaeretiella rapae (an arrestant response). Here, we report the transformation of a plant to produce an insect pheromone and demonstrate that the resulting emission affects behavioral responses at two trophic levels.Diaeretiella rapae ͉ Myzus persicae ͉ semiochemical ͉ volatile ͉ farnesene