Antennal Electrophysiological Responses of Three Parasitic Wasps to Caterpillar-Induced Volatiles from Maize (<i>Zea mays mays</i>), Cotton (<i>Gossypium herbaceum</i>), and Cowpea (<i>Vigna unguiculata</i>)

Many parasitic wasps are attracted to volatiles that are released by plants when attacked by potential hosts. The attractiveness of these semiochemicals from damaged plants has been demonstrated in many tritrophic systems, but the physiological mechanisms underlying the insect responses are poorly understood. We recorded the antennal perception by three parasitoids (Cotesia marginiventris, Microplitis rufiventris, and Campoletis sonorensis) to volatiles emitted by maize, cowpea, and cotton plants after attack by the common caterpillar pest Spodoptera littoralis. Gas chromatography-electroantennography (GC-EAG) recordings showed that wasps responded to many, but not all, of the compounds present at the physiologically relevant levels tested. Interestingly, some minor compounds, still unidentified, elicited strong responses from the wasps. These results indicate that wasps are able to detect many odorant compounds released by the plants. It remains to be determined how this information is processed and leads to the specific behavior of the parasitoids

Individual learning ability and complex odor recognition in the honey bee, Apis mellifera L.

29 ref.International audienceIndividually restrained worker bees were trained to recognize complex odors in a conditioned proboscis extension assay. Three groups of bees were considered, based on the responses recorded during the experimental procedure: selective learners, nonselective learners, and nonlearners. For conditioning, three concentrations of two synthetic mixtures were used. The distribution of bees between groups was not significantly affected by the nature or by the concentration of the conditioning mixture. After conditioning, bees were tested with the individual compounds, and the responses were analyzed with respect to the three groups. Selective learners showed discriminative responses to a few key compounds, while nonselective learners responded to all the compounds, and nonlearners to none. These results showed that complex odor recognition is based on the recognition of key components and relies on the ability of bees to learn

Recognition of complex odors by restrained and free-flying honeybees, Apis mellifera

34 ref.International audienceComplex odor recognition in the honeybee was investigated using two behavioral assays: (1) the conditioning of the proboscis extension (CPE) with restrained individuals, and (2) the observation of foragers visiting an artificial feeder in a flight room. Nine compounds, previously identified as oilseed rape flower volatiles, were tested either individually or in mixtures. Different sets of experiments were done to determine: (1) the acquisition rate of the nine compounds in the CPE assay, and (2) the discrimination of the individual compounds after conditioning to a mixture, using the CPE assay and free-flying foragers. After conditioning to a complex mixture, honeybees established a hierarchy among the components, with some of them accounting for a major part of the behavioral activity of the mixture. Both behavioral assays led to the same classification of compounds, indicating good agreement between discriminating abilities of restrained individuals and of a population of foragers. The key compounds for recognition of these mixtures were those that were well learned when presented individually. However, the recognition of some compounds was affected by the other components of the mixture, with the activity of some compounds being either enhanced or reduced

Identification of human-derived volatile chemicals that interfere with attraction of the Scottish biting midge and their potential use as repellents.

The Scottish biting midge, Culicoides impunctatus (Diptera: Ceratopogonidae), is a major pest in Scotland, causing a significant impact to the Scottish tourist and forestry industries. C. impunctatus is a generalist feeder, preferring to feed on large mammals, and is notorious for its attacks on humans. Until now, there was anecdotal evidence for differential attraction of female host-seeking C. impunctatus to individual human hosts, and the mechanism for this phenomenon was unknown. Using extracts of human odor collected by air entrainment, electroantennogram recordings to identify the physiologically active components, followed by behavioral assays, we show, for the first time, the differential attraction of female C. impunctatus to human odors and the chemical basis for this phenomenon. Certain chemicals, found in greater amounts in extracts that cause low attractiveness to midges, elicit a repellent effect in laboratory assays and repellency trials in the field. Differences in the production of these natural human-derived compounds could help to explain differential "attractiveness" between different human hosts. A mixture of two compounds in particular, 6-methyl-5-hepten-2-one and geranylacetone [(E)-6,10-dimethylundeca-5,9-dien-2-one], showed significant repellency (87, 77.4, 74.2, and 31.6% at hours 0, 1, 2, and 3, respectively) in the field and have the potential to be developed as novel repellents

Protection in an ant-plant mutualism: an adaptation or a sensory trap?

Many traits of ant plants and their ant symbionts are thought to be coevolved, but there is little evidence for adaptation in these symbioses. We investigated the ant trait of worker attraction to, and consequent patrolling of, new plant shoots, and we tested two hypotheses to explain the maintenance of this trait. (1) New shoots chemically mimic ant brood or alarm pheromones (a ‘sensory trap’) and thereby elicit worker patrolling of vulnerable plant parts. (2) Worker attraction to new shoots is the result of selection on the ant to direct patrolling to the plant parts that maximize the capture of plant-provided rewards. As our model system, we used the ant plant Cordia nodosa and its protecting ant symbiont Allomerus octoarticulatus var. demerarae. Gas chromatography analyses suggested that compounds were shared between new leaves and Allomerus brood, and Allomerus workers were attracted to brood extracts of nonself colonies, findings that are consistent with the sensory trap hypothesis. However, patrolling Allomerus workers were attracted only to new leaves, whereas brood-tending workers collected from inside plant domatia (‘nurses’) were attracted to Allomerus brood rather than to new leaves. Only patrollers were attracted to new leaves significantly more than to mature leaves, and nurse workers were larger than patroller workers, which suggests that the behavioural differences reflect caste differentiation. Therefore, we reject the sensory trap hypothesis. Our results are consistent with the idea that worker attraction to new shoots is the result of selection

Identification of floral volatiles involved in recognition of oilseed rape flowers, Brassica napus by honeybees, Apis mellifera

2 tables 1 graph.International audienceVolatiles from oilseed rape, Brassica napus, flowers were sampled by air entrainment and their relevance to the natural odor profile of the flowers was confirmed by conditioned proboscis extension (CPE) assays with honeybee, Apis mellifera L., foragers. Coupled gas chromatography (GC)-CPE analysis of the air entrainment samples was used to locate key compounds involved in the recognition of B. napus flowers, and the compounds were then identified using coupled gas chromatography-mass spectrometry and comparison with authentic samples. Six regions of the gas chromatograms elicited CPE responses from bees previously conditioned to the total extract, and from these areas 16 compounds were identified that elicited CPE activity from conditioned bees when tested with synthetic samples. Eight of the 16, α-pinene, phenylacetaldehyde, p-cymene, α-terpinene, linalool, 2-phenyl-ethanol, (E,E)-α-farnesene, and 3-carene, gave the highest responses. When the bees were conditioned to the total extract of flower volatiles, a mixture of the eight components elicited responses from 83% of the individuals, suggesting that the eight-component mixture accounted for a major part of the CPE activity of the total extract. In addition, a mixture of the three most active compounds, phenylacetaldehyde, linalool, and (E,E,)-α-farnesene, evoked responses from 85% of the bees after the latter had been conditioned to the eight-component mixture. Thus, these three compounds appear to play a key role in the recognition of the eight component mixture and, by inference, of oilseed rape flowers

Identification of human-derived volatile chemicals that interfere with attraction of Aedes aegypti mosquitoes.

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