Résultat de la recherche
Sensory and behavioural responses of the stable fly Stomoxys calcitrans to rumen volatiles
Analysis of volatiles from rumen digesta by gas chromatography linked antennogram recordings from Stomoxys calcitrans (L) (Diptera: Muscidae) antennal receptor cells revealed about 30 electrophysiologically active constituents, the most important of which is dimethyl trisulphide with a sensory threshold in the femtogram range. The behavioural responses of S. calcitrans to five chemostimulants (dimethyl trisulphide, butanoic acid, p-cresol, oct-1-en-3-ol and skatole) were tested in a wind tunnel where activation and attraction of hungry flies to rumen volatiles were recorded. Dimethyl trisulphide, butanoic acid and p-cresol were found to attract S. calcitrans. This sensitivity to rumen volatile constituents, that also occur in animal wastes used for oviposition by Stomoxys spp., as well as in flowers used by stable flies as sources of nectar is discussed in the context of the behavioural ecology of these flies.
Evaluating the Induced-Odour Emission of a Bt Maize and its Attractiveness to Parasitic Wasps
The current discussion on the safety of transgenic crops includes their effects on beneficial insects, such as parasitoids and predators of pest insects. One important plant trait to consider in this context is the emission of volatiles in response to herbivory. Natural enemies use the odours that result from these emissions as cues to locate their herbivorous prey and any significant change in these plant-provided signals may disrupt their search efficiency. There is a need for practical and reliable methods to evaluate transgenic crops for this and other important plant traits. Moreover, it is imperative that such evaluations are done in the context of variability for these traits among conventional genotypes of a crop. For maize and the induction of volatile emissions by caterpillar feeding this variability is known and realistic comparisons can therefore be made. Here we used a six-arm olfactometer that permits the simultaneous collection of volatiles emitted by multiple plants and testing of their attractiveness to insects. With this apparatus we measured the induced odour emissions of Bt maize (Bt11, N4640Bt) and its near-isogenic line (N4640) and the attractiveness of these odours to Cotesia marginiventris and Microplitis rufiventris, two important larval parasitoids of common lepidopteran pests. Both parasitoid species were strongly attracted to induced maize odour and neither wasp distinguished between the odours of the transgenic and the isogenic line. Also wasps that had previously experienced one of the odours during a successful oviposition divided their choices equally between the two odours. However, chemical analyses of collected odours revealed significant quantitative differences. The same 11 compounds dominated the blends of both genotypes, but the isogenic line released a larger amount of most of these. These differences may be due to altered resource allocation in the transgenic line, but it had no measurable effect on the wasps’ behaviour. All compounds identified here had been previously reported for maize and the differential quantities in which they were released fall well within the range of variability observed for other maize genotypes.
Chemostimuli implicated in selection of oviposition substrates by the stable fly Stomoxys calcitrans
Horse and cow dung were tested as substrates for oviposition by the stable fly Stomoxys calcitrans (L) (Diptera: Muscidae) in laboratory cages. Odour alone from either horse or cow dung was sufficient to attract flies for oviposition. This was confirmed in wind tunnel experiments, where both horse and cow dung were shown to attract gravid stable flies. However, when S. calcitrans was offered a choice between these two oviposition substrates, flies always chose horse dung over cow dung, both when allowed to contact the substrates and when relying on dung odour alone. Analyses of volatile compounds emanating from horse and cow dung by gas chromatography linked antennogram recordings from S. calcitrans antennae revealed no differences in the chemostimuli released from the two substrates. The predominant chemostimulant compounds in both substrates were carboxylic acids (butanoic acid), alcohols (oct-1-en-3-ol), aldehydes (decanal), ketones (octan-3-one), phenols (p-cresol), indoles (skatole), terpenes (β-caryophyllene) and sulphides (dimethyl trisulphide). Higher levels (20–40 p.p.m.) of carbon dioxide were recorded over horse dung compared with cow dung, a factor that may contribute to the preference exhibited by S. calcitrans for this substrate for oviposition.
The role of odour perception in the sensory ecology of the stable fly, Stomoxys calcitrans L.
Commune dans le monde entier, la mouche d'étable, Stomoxys calcitrans L., est un insecte nuisible du bétail. Males et femelles se nourrissent de sang et bien que la mouche d'étable s'attaque à un large éventail d'animaux, les grands herbivores comme les bovins et les équidés demeurent ses hôtes préférés. Pour la ponte, les femelles de la mouche d'étable utilisent toutes sortes de matériaux organiques en décomposition comme du foin fermenté, du compost et même des amas d'algues. Les déjections animales, et particulièrement lorsqu'elles sont mélangées à de la matière végétale en décomposition, sont également couramment exploitées par Stomoxys pour la ponte. Dans cette étude, l'haleine humaine et le CO2 se sont avérés être attractifs pour Stomoxys, qui est également activée par les composés volatils dégagés par la panse de vache et très probablement exhalés dans son haleine. La désorption thermique des constituants volatils de la panse en chromatographie gazeuse, couplée à des enregistrements électro-antennographiques, a permis la détection d'une trentaine de composés perçus par S. calcitrans, dont certains ont également été trouvés dans l'odeur dégagée par les poils de vache. Un seuil de détection très bas pour le dimethyl trisulfide, comparable à celui obtenu pour l'octénol, a été enregistré chez la mouche d'étable. De plus, le dimethyl trisulfide s'est avéré être attractif pour Stomoxys lors d'expériences en chambre de vol, de même que l'acide butanoïque et le p-crésol. Nous avons également démontré que S. calcitrans est capable de localiser un substrat potentiel de ponte, du crottin ou de la bouse dans notre cas, en se basant uniquement sur des indices olfactifs. L'analyse des composés volatils émis par le crottin et la bouse démontre que les composés perçus par S. calcitrans sont communément présents dans les deux substrats. Cependant, qu'elle ait un contact avec le substrat ou uniquement son odeur pour le localiser, la mouche d'étable démontre toujours une nette préférence de ponte pour le crottin de cheval par rapport à la bouse de vache. Le CO2 pourrait être en partie responsable de cette préférence pour le crottin de cheval, ce dernier dégageant plus de CO2 que la bouse de vache. D'une manière générale, ce travail montre que S. calcitrans se base sur un éventail de composés volatils communs aux différentes ressources qu'elle exploite. Pour ne citer que les plus importants d'entre eux, le dimethyl trisulfide, l'acide butanoïque, le p-crésol, le ?-caryophyllene et l'octénol, se retrouvent à la fois dans l'odeur des substrats de ponte et dans les effluves animales.
(1S,3S,7R)-3-methyl-α-himachalene from the male sandfly Lutzomyia longipalpis (Diptera: Psychodidae) induces neurophysiological responses and attracts both males and females
Lutzomyia longipalpis adult males form leks on or near hosts and release (1S,3S,7R)-3-methyl-α-himachalene from their tergal glands to lure females to the same site for mating and feeding. Here we have examined whether the male-produced attractant could also serve as a male aggregation stimulus. High resolution chiral capillary gas chromatography analysis of male tergal gland extracts, synthetic (1S,3S,7R)-3-methyl-α-himachalene, and a synthetic mixture of all isomers of 3-methyl-α-himachalene, was coupled to electrophysiological recordings from ascoid sensillum receptor cells in antennae of male and female sandflies. Receptor cells of both sexes responded only to the main component of the male tergal gland extract that eluted at the same retention time as (1S,3S,7R)-3-methyl-α-himachalene. Furthermore, of the eight 3-methyl-α-himachalene isomers in the synthetic mixture only the fraction containing (1S,3S,7R)-3-methyl-α-himachalene, co-eluting with an isomer of (1S*,3S*,7S*)-3-methyl-α-himachalene, elicited an electrophysiological response from male and female ascoid sensillum receptor cells. Both males and females flew upwind in a wind tunnel towards a filter paper disk treated with either 4–6 male equivalents of the tergal gland extract, pure (1S,3S,7R)-3-methyl-α-himachalene or the synthetic mixture of eight isomers. This indicates that (1S,3S,7R)-3-methyl-α-himachalene derived from L. longipalpis males may have a dual function in causing male aggregation as well as serving as a sex pheromone for females.