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  • Publication
    AccĆØs libre
    Plant volatile compounds shorten reaction time and enhance attraction of the codling moth (Cydia pomonella) to codlemone
    (2012)
    Schmera, D.
    ;
    BACKGROUND: The codling moth is the most serious pest of deciduous tree fruit (apples, pears, crabapples, walnuts, quince) worldwide. The high frequency of insecticide treatments per season has resulted in breakdown of codling moth control owing to insecticide resistance. As an alternative, integrated pest management includes mating disruption to achieve population suppression in orchards. Under this scheme, the sex pheromone of the codling moth, (E, E)-8,10-dodecadien-1-ol (codlemone), is released from dispensers in crops to hinder mating by luring males. Increasing the attractiveness of codlemone formulations to codling moth males can be regarded as a key to increasing the efficacy of mating disruption. With this aim, the effects of adding plant volatiles on the behavioural responses of codling moth males to codlemone were tested. RESULTS: Adding R(+)-limonene, linalool, (E)-beta-farnesene or ethyl (E, Z)-2,4-decadienoate to codlemone significantly increases the proportion of males flying to the pheromone source in a wind tunnel. The response level is equivalent to that of males responding to females releasing codlemone. Using real-time recordings, it is shown how these four plant products also shorten the response time of males to codlemone under the behavioural criteria time to activation, time till upwind flight is induced and time to pheromone source contact. CONCLUSION: Shortening the response time and increasing source location by males of dispensers releasing codlemone with R(+)-limonene, linalool, (E)-beta-farnesene or ethyl (E, Z)-2,4-decadienoate added would enhance mating disruption through better engagement ofmales with dispensers, to the detriment of females. (C) 2011 Society of Chemical Industry
  • Publication
    AccĆØs libre
    Tsetse fly responses to volatile plant compounds
    (2012)
    Joris, Caroline
    ;
    Les glossines (Diptera, Glossinidae) constituent 31 espĆØces et sous-espĆØces rĆ©parties en trois sous-genres. Elles sont actuellement limitĆ©es Ć  lā€™Afrique sub-saharienne et prĆ©fĆØrent trois habitats: la savane, les zones riveraines et la forĆŖt. Les deux sexes sont strictement hĆ©matophages et peuvent transmettre la trypanosomiase au cours de leur repas de sang qui provoque la maladie du sommeil chez les humains et le nagana chez des animaux. Environ 60 millions de personnes et 50 millions de bovins dans 20 pays africains risquent continuellement lā€™infection, ce qui provoque des pertes Ć©conomiques Ć©normes.
    Les mouches tsĆ©-tsĆ© dĆ©tectent les hĆ“tes Ć  proximitĆ© Ć  lā€™aide de repĆØres visuels, dont le contraste, la forme et la couleur, et de signaux olfactifs Ć  distance. Comme elles sont ovovivipares, la dynamique de population des mouches tsĆ©-tsĆ© est caractĆ©risĆ©e par un taux de croissance faible. Des piĆØges et cibles appĆ¢tĆ©s peuvent ainsi Ć©puiser une population en quelques annĆ©es seulement. Les stimulants olfactifs principalement utilisĆ©s dans les piĆØges sur le terrain contre les mouches tsĆ©-tsĆ© sont lā€™1-octĆØne-3-ol, le 3-n-propylephĆ©nol, le p-crĆ©sol et de lā€™acĆ©tone.
    Les plantes fournissent aux mouches tsĆ©-tsĆ© non seulement habitat et refuge, mais en plus elles offrent des endroits protĆ©gĆ©s du soleil pour la larviposition aux femelles. La facultĆ© naturelle des mouches pour trouver une couverture adaptĆ©e sous la vĆ©gĆ©tation nā€™a attirĆ© que peu dā€™attention. Tenant compte du rĆ“le des sites de repos pĆ©ridomestiques, il est important de considĆ©rer les produits chimiques volatils dĆ©rivĆ©s de plantes pour le dĆ©veloppement de nouveaux piĆØges appĆ¢tĆ©s pour attirer toutes les tsĆ©-tsĆ© des 3 sous-genres. Il est possible que les mouches tsĆ©-tsĆ© font un usage parcimonieux de chimiostimuli (par exemple 1-octĆØne-3-ol qui est prĆ©sent dans les odeurs dā€™hĆ“te autant que les substances volatiles de plantes) pour trouver hĆ“te ou abris sous les plantes.
    En utilisant lā€™electroantennographie, les rĆ©ponses sensorielles aux produits volatils couramment trouvĆ©s dans les plantes ainsi quā€™aux odeurs dā€™hĆ“tes ont Ć©tĆ© enregistrĆ©es chez des mouches tsĆ©-tsĆ© des trois habitats africains. Les produits comprennent des monoterpĆØnes, des sesquiterpĆØnes et des C6-alcohols et aldehydes (GLVs). Nous avons dĆ©montrĆ© que les espĆØces de glossines des trois habitats africains perƧoivent les composants vĆ©gĆ©taux volatils dā€™une maniĆØre similaire, dont plusieurs Ć  des seuils de dĆ©tection similaires Ć  lā€™1-octĆØne-3-ol. Pour les Ć©tudes comportementales, la L-tĆ©rĆ©benthine est particuliĆØrement interĆ©ssante, car il sā€™agit dā€™un mĆ©lange de terpĆØnes simples avec un seuil de dĆ©tection bas, avec le limonĆØne et lā€™Ī±-pinĆØne comme composants principaux, accompagnĆ©s de monoterpĆØne ocimĆØne et dā€™aromatiques p-cymĆØne. La L-tĆ©rĆ©benthine est relativement facile Ć  obtenir, peu coĆ»teuse et peut ĆŖtre produite directement en Afrique.
    Les mouches tsĆ©-tsĆ© ayant un vol rapide, nous avons filmĆ© les rĆ©actions des G. pallidipes, G. brevipalpis et G. swynnertoni dans une soufflerie en utilisant un systĆØme dā€™enregistrement 3D. En combinant lā€™effet de sensibilisation du CO2 avec les composĆ©s dā€™essai, nous avons pu augmenter le nombre de mouches activĆ©es par dix et donc dĆ©tecter des diffĆ©rences dans les rĆ©ponses comportementales des mouches tsĆ©-tsĆ© aux traitements. Nos rĆ©sultats montrent que les mouches tsĆ©-tsĆ© rĆ©pondent Ć  une sĆ©rie de composants vĆ©gĆ©taux simples et Ć  leurs mĆ©langes. Les composants de plantes individuels avec le meilleur potentiel dā€™activation parmi les composants testĆ©s Ć©taient le S-(-)-limonĆØne et le p-cymĆØne. Les meilleurs rĆ©sultats ont Ć©tĆ© obtenus avec un mĆ©lange monoterpĆØne comprenant la L-tĆ©rĆ©benthine montrant un trĆØs bon effet activateur sur G. pallidipes, G. swynnertoni et G. brevipalpis induisant Ć©galement beaucoup de mouches Ć  effectuer une recherche locale Ć  lā€™extrĆ©mitĆ© de la chambre de vol. ƀ la dose optimale testĆ©e (10 Ī¼g /min), la L-tĆ©rĆ©benthine Ć©tait comparable Ć  lā€™haleine humaine en termes dā€™activation et dā€™induction de comportement de recherche locale par G. pallidipes et G. swynnertoni. Dans notre Ć©tude, nous nā€™avons constatĆ© aucune diffĆ©rence entre les rĆ©actions comportementales des mĆ¢les et des femelles G. pallidipes Ć  lā€™haleine humaine, le CO2 prĆ©sentĆ© seul et au lā€™1-octĆØne-3-ol, des produits gĆ©nĆ©ralement associĆ©s Ć  des hĆ“tes, mais nous pouvions dĆ©tecter des diffĆ©rences entre les rĆ©actions comportementales des mĆ¢les et des femelles Ć  des composants volatils de plantes (limonĆØne, le p-cymĆØne et L-tĆ©rĆ©benthine). Comme les G. brevipalpis sur le part de pondre rĆ©pondaient seulement Ć  la L-tĆ©rĆ©benthine mais pas Ć  lā€™haleine humaine on pourrait spĆ©culer que les composants volatils de plantes non seulement transportent des informations sur les hĆ“tes, mais indiquent aussi des sites de larviposition ou de repos, qui sont dā€™une importance plus grande pour les femelles en raison de leur plus grands besoins Ć©nergĆ©tiques en vol comparĆ© aux mĆ¢les.
    Pour Ć©valuer si les composants volatils de plantes pouvaient ĆŖtre utiles sur le terrain, Ć  savoir accroĆ®tre lā€™attractivitĆ© des piĆØges ou des cibles, nous avons testĆ© si les composants de plantes attiraient les mouches tsĆ©-tsĆ© vers une cible visuelle et nous avons donc introduit une sphĆØre bleue phthalogĆØne dans la soufflerie pour tester Ć  la fois des stimuli visuels et olfactifs. Nous avons montrĆ© que la L-tĆ©rĆ©benthine en prĆ©sence de CO2 augmente le temps et la distance passĆ©s en vol autour dā€™une cible et affecte Ć©galement la hauteur relative de vol vers la cible et lors de la recherche locale autour dā€™elle. En prĆ©sence de L-tĆ©rĆ©benthine, le vol vers la cible a Ć©tĆ© plus orientĆ© quā€™ avec le CO2 seul et la recherche locale a eu lieu Ć  une plus faible altitude.
    Les rĆ©sultats prĆ©sentĆ©s dans cette thĆØse montrent que les mouches tsĆ©-tsĆ© non seulement perƧoivent des composants volatils de plantes, mais que ces vecteurs de maladie, en particulier les femelles, sont attirĆ©s par les terpĆØnes et les mĆ©langes de terpĆØnes simples prĆ©sentĆ©s avec et sans cible visuelle Ć  des concentrations de 1000 Ć  10ā€™000 fois infĆ©rieures au niveau de CO2 naturel. De maniĆØre gĆ©nĆ©rale, ce travail suggĆØre que les composants volatils de plantes sont prometteurs quant Ć© leur intĆ©gration dans les techniques de contrĆ“les sĆ©miochimiques pour les mouches tsĆ©-tsĆ©., Tsetse flies (Diptera, Glossinidae) constitute 31 species and subspecies divided into three subgenera. They are currently confined in sub-Saharan Africa and occupy three preferred habitats: savannah, riverine zones and forest. Both sexes are strictly haematophagous and can transmit during their blood meal trypanosomiasis which causes sleeping sickness in humans and Nagana in animals. It is estimated that about 60 million people and 50 million cattle are continuously at risk in 20 African countries resulting in enormous economic losses.
    Tsetse flies locate hosts using visual cues including contrast, shape and colour at short range, and olfactory cues at a distance. Tsetse fly population dynamic is characterised by a slow intrinsic growth rate as they are ovoviviparous, so visual baited traps and targets can deplete a population in only a few years. The major olfactory stimulants used in field traps to control tsetse flies are 1-octen-3-ol, 3-n-propylphenol, p-cresol and acetone.
    Plants not only provide the habitat and shelter for tsetse flies but also provide females with sunlight-protected places for larviposition. Little attention has been paid to the fliesā€™ propensity for finding suitable cover under vegetation. Keeping in mind the role of peridomestic resting sites, it is important to consider volatile chemicals derived from plants for the development of new odour-baited traps to attract tsetse from all 3 subgenera. It is possible that the tsetse flies make parsimonious use of chemostimuli (e.g. 1-octen-3-ol present in both host odours and plant volatiles) for host finding and shelter under plants.
    Sensory responses of tsetse flies from all three African habitats to volatile products commonly found in plants as well as host odours were recorded using the electroantennogram techniques. Products included monoterpenes, sesquiterpenes and green-leaf volatiles. We have shown, that tsetse species from all three African habitats perceive volatile plant compounds in a similar manner, several at detection thresholds similar to 1-octen-3-ol. Of main interest for behavioural studies is L-turpentine, as it is a simple terpene mixture with a low detection threshold, with limonene and Ī±-pinene as main components , along with the monoterpene ocimene and aromatic p-cymene, and it is relatively easily obtained, inexpensive and can be produced directly in Africa.
    Tsetse flies are fast flyers, so we filmed the responses of G. pallidipes, G. brevipalpis and G. swynnertoni in the wind tunnel using a 3D recording system. By combining the sensitising effect of CO2 with the test compounds we were able to increase the number of activated flies by tenfold and were therefore able to detect differences in the behavioural responses of tsetse flies to treatments. Our results show that tsetse flies respond to a series of single plant compounds and their mixtures. The single plant compounds tested with the best activation potential were S-(-)-limonene and p-cymene. The best results were achieved with the monoterpene mixture comprising L-turpentine showing a very good activating effect on G. pallidipes, G. swynnertoni and G. brevipalpis and also inducing many flies to perform a local search at the upwind end of the wind tunnel. At the optimal dose tested (10Ī¼g/min) L-turpentine was comparable to human breath in terms of activating and inducing local search behaviour by G. pallidipes and G. swynnertoni. In our study we found no differences in behavioural responses of male and female G. pallidipes to human breath, CO2 alone and 1-octen-3-ol, products usually associated with hosts, but we could detect differences in behavioural responses of males and females to volatile plant compounds (limonene, p-cymene and L-turpentine). As pregnant G. brevipalpis responded only to L-turpentine but not human breath one could speculate that volatile plant compounds not only carry information about hosts, but also indicate larviposition or resting sites, both of which are of greater importance for females due to the higher energy demands of flying than for males.
    To assess whether volatile plant compounds could be of use in the flied, i.e. increasing trap and target encounters, we tested if plant compounds attract tsetse flies to a target and therefore introduced a phthalogen blue sphere into the wind tunnel to test combined visual and olfactory stimuli. We showed that L-turpentine in the presence of CO2 increases the time and distance spent flying around a target and also affects the relative hight of flight to the target and of the local search at the target. With L-turpentine presented, flight to the target was more directed than with CO2 alone and the local search around the sphere was lower in elevation.
    The results presented in this thesis show that tsetse flies not only perceive volatile plant compounds, but that these vectors of disease, especially females, are attracted by terpenes and simple terpene mixtures presented with and without a visual target at amounts 1000 to 10ā€™000 times lower than background CO2 levels. Overall this work suggests that volatile plant compounds hold promise for integration into semiochemicalbased control techniques for tsetse flies., Tsetse-Fliegen (Diptera, Glossinidae) unterteilen sich in 31 Arten und Unterarten, welche in drei Untergattungen eingeteilt werden. Ihre Verbreitung ist zur Zeit auf ein Gebiet sĆ¼dlich der Sahara begrenzt, wo sie drei bevorzugte Habitate besiedeln: Savanne, Uferzonen von FlĆ¼ssen und Seen sowie Waldregionen. Beide Geschlechter sind rein haematophag und kƶnnen wƤhrend ihrer Blutmahlzeit Trypanosomen Ć¼bertragen, welche bei Menschen die Schlafkrankheit und bei Tieren Nagana auslƶsen. GeschƤtzte 60 Millionen Menschen und 50 Millionen Tiere sind in den 20 betroffenen afrikanischen LƤndern stƤndig in Infektionsgefahr, was zu enormen ƶkonomischen Verlusten fĆ¼hrt.
    Auf kurze Distanz finden Tsetse-Fliegen ihre Wirte durch visuelle Signale wie Kontrast, Form und Farbe und auf lƤngere Distanz durch olfaktorische Stimuli. Bedingt durch ihren Ovoviviparismus ist die Populationsdynamik der Tsetse-Fliegen durch ein langsames intrinsisches Wachstum charakterisiert, wodurch Kontrollmassnahmen eine Population in wenigen Jahren auslƶschen kƶnnen. Die wichtigsten in Fallen verwendeten Kƶder sind 1-Octen-3-ol, 3-n-Propylphenol, p-Cresol und Aceton.
    Pflanzen stellen nicht nur die LebensrƤume und Verstecke fĆ¼r die Tsetse-Fliegen, sondern dienen den Weibchen auch als sonnengeschĆ¼tzte AblageplƤtze fĆ¼r ihre Larven. Bisher wurde der FƤhigkeit der Fliegen UnterschlĆ¼pfe unter der Vegatation zu finden, wenig Beachtung entgegengebracht. BerĆ¼cksichtigt man die Rolle der hausnahen RuheplƤtze, mĆ¼ssen flĆ¼chtige Pflanzenstoffe fĆ¼r die Entwicklung neuer Kƶder zum Anlocken der Tsetse-Arten aus allen drei Untergattungen betrachtet werden. Mƶglicherweise erlaubt die sparsame Benutzung von Chemostimuli (wie z. B. 1-Octen-3-ol, welches Bestandteil von Wirt- und PflanzendĆ¼ften ist) den Tsetse-Fliegen Wirte wie auch Verstecke unter Pflanzen zu finden.
    Anhand von Elektroantennogrammen wurden die sensoriellen Antworten auf flĆ¼chtige Produkte, welche Ć¼blicherweise in Pflanzen und Wirten vorhanden sind, bei Tsetse- Fliegen aus allen drei Habitatstypen gemessen. Zu den Produkten gehƶrten Monoterpene, Sesquiterpene und GrĆ¼n-Blattduftstoffe (GLVs). Wir konnten zeigen, dass Tsetse- Arten aus allen afrikanischen Habitaten flĆ¼chtige Pflanzenstoffe in ƤhnlicherWeise wahrnehmen. Einige dieser Produkte weisen eine Ƥhnlich tiefe Detektionsschwelle auf wie 1-Octen-3-ol. Von speziellem Interesse fĆ¼r die Verhaltensstudien ist L-Terpentin, eine einfache Mischung aus Terpenen mit einer niedrigen Detektionsschwelle. Seine Hauptbestandteile sind Limonen und Ī±-Pinen mit dem Monoterpen Ocimen und dem Aromaten p-Cymen. Zu seinen Vorteilen gehƶrt, dass es relativ einfach und gĆ¼nstig direkt in Afrika produziert werden kann.
    Da Tsetse-Fliegen sehr schnelle Flieger sind, filmten wir das Verhalten von G. pallidipes, G. brevipalpis und G. swynnertoni mit einem 3D-Aufnahmeverfahren in einem Windkanal. Indem wir den Sensibilisierungseffekt von CO2 mit den Testprodukten kombinierten, konnten wir die Anzahl der aktivierten Fliegen um ein zehnfaches erhƶhen, und so Unterschiede in ihrem Verhalten auf Behandlungen feststellen. Unsere Resultate zeigen, dass Tsetse-Fliegen auf eine Reihe von flĆ¼chtigen Pflanzenstoffen sowie ihren Mischungen reagieren. Die einfachen Pflanzenprokdukte mit dem grƶssten Aktivierungspotential waren S-(-)-Limonen und p-Cymen. Die besten Resultate in Bezug auf Aktivierung, Flug- und Suchverhalten am Ende desWindkanals von G. pallidipes, G. brevipalpis und G. swynnertoni wurden mit der Monoterpenmischung L-Terpentin erhalten. Die Wirkung von L-Terpentin in seiner optimalen getesteten Dosis (10Ī¼g /min) war in Bezug auf sein Aktivierungspotential und als Auslƶser des Suchverhaltens am Ende des Windkanals von G. pallidipes und G. swynnertoni vergleichbar mit der Wirkung menschlichen Atems.
    In unserer Untersuchung wurden keine Unterschiede im Verhalten von mƤnnlichen und weiblichen Fliegen bei menschlichem Atem, CO2 und 1-Octen-3-ol, also Produkten, die normalerweise mit denWirten in Verbindung gebracht werden, festgestellt. Jedoch konnten Unterschiede in ihrem Verhalten zu flĆ¼chtigen Pflanzenstoffen (Limonen, p-Cymen und L-Terpentin) festgestellt werden. Da tragende G. brevipalpis auf L-Terpentin, nicht jedoch auf menschlichen Atem reagierten, kƶnnte spekuliert werden, dass flĆ¼chtige Pflanzenstoffe nicht nur Informationen zu Wirten, sondern auch zu Larvablege- und RuheplƤtzen tragen. Diese beiden Informationen sind fĆ¼r tragende Weibchen aufgrund ihres grƶsseren Energieverbrauchs beim Fliegen von grƶsserer Bedeutung als fĆ¼r MƤnnchen.
    Zum evaluieren, ob flĆ¼chtige Pflanzenstoffe im Feld von Nutze sein kƶnnten, z. B. zum Erhƶhen der AttraktivitƤt der Fallen, testeten wir, ob diese Pflanzenprodukte die Fliegen zusƤtzlich zu einem visuellen Signal anziehen kƶnnten. Dazu fĆ¼hrten wir eine enzianblaue Kugel in den Windkanal ein und konnten so die Kombination von visuellen und olfaktorischen Stimuli testen. Wir konnten zeigen, dass L-Terpentin in Kombination mit CO2 nicht nur die Zeit und die Flugdistanz vergrƶsserten, die die Fliegen um die Kugel herum verbrachten, sondern auch die relative Flughƶhe und die Hƶhe des Suchverhaltens um die Kugel herum beeinflussten. Im Beisein vom L-Terpentin waren die FlĆ¼ge und die Hƶhe des Suchverhaltens, verglichen mit CO2 alleine, tiefer.
    Die Resultate dieser Doktorarbeit zeigen, dass Tsetse-Fliegen nicht nur flĆ¼chtige Pflanzenstoffe wahrnehmen, sondern dass insbesondere die Weibchen, von Terpenen und einfachen Terpenmischungen angezogen werden, und dies sowohl im Beisein von visuellen Stimuli wie auch ohne. Sie reagieren auf diese Stoffe schon in Mengen, die 1000 bis 10ā€™000 mal kleiner sind als die natĆ¼rlichen CO2 -Mengen. Schliesslich zeigt diese Arbeit eine Mƶglichkeit zur Integration der flĆ¼chtigen Pflanzenstoffe in die bestehenden Tsetse-Kontrolltechniken auf.
  • Publication
    AccĆØs libre
    Darkness induces mobility, and saturation deficit limits questing duration, in the tick Ixodes ricinus
    The behaviour of Ixodes ricinus nymphs was recorded in 10-day experiments using computer-assisted video-tracking, in the absence of any host stimuli. These ticks switch spontaneously from questing in a desiccating atmosphere to quiescence in a water-saturated atmosphere after dark. Quantification of both questing and quiescence duration demonstrates that questing duration is inversely related to saturation deficit whereas quiescence duration is not. Distance walked after quiescence increased with desiccating conditions, while the distance walked after questing remained unchanged. Almost all locomotor activities of I. ricinus occurred during darkness under either a 14 h:10 h L:D or a 8 h:4 h L:D cycle. We established that all life stages of I. ricinus are equipped to sense shifts in light intensity with bilaterally placed strings of photoreceptors. This permits I. ricinus to use onset of darkness to trigger mobility when desiccation risk is reduced in nature.
  • Publication
    AccĆØs libre
    Olfactory and behavioural responses of the blood-sucking bug Triatoma infestans to odours of vertebrate hosts
    (2001)
    Guerenstein, Pablo G.
    ;
    Olfactory receptors in basiconic and grooved-peg sensilla on the antenna of fifth-instar Triatoma infestans nymphs respond to host odours. Gas chromatography analyses of host odour extracts coupled to electrophysiological recordings from basiconic sensillum receptors indicate that nonanal is a constituent of sheep wool and chicken feather odour that stimulates one of the receptors in this type of sensillum. Similar analyses revealed isobutyric acid in rabbit odour to be a chemostimulant for one of the receptors in grooved-peg sensilla. The response of the aldehyde receptor was higher to heptanal, octanal and nonanal than to other aliphatic aldehydes, and the response of the acid receptor was higher to isobutyric acid than to other short-chain branched and unbranched acids. The behavioural responses of fifth-instar T. infestans nymphs to nonanal and isobutyric acid in an air-stream on a servosphere indicate that, whereas nonanal causes activation of the bugs, isobutyric acid induces an increase in upwind displacement, i.e. odour-conditioned anemotaxis. Binary mixtures of these compounds did not improve the attraction obtained with isobutyric acid alone. A comparison of the behavioural and electrophysiological responses of the bugs to different amounts of isobutyric acid in air suggests that attraction is obtained at concentrations that causes low-to-moderate increases in the firing rate of the acid-excited receptor in the grooved-peg sensilla, whereas at a dose that evokes relatively high firing rates (>40 Hz) no attraction is obtained.
  • Publication
    AccĆØs libre
    Influence of Dose and Ratio of Mixtures of Pheronome Components on the Attraction of the Tropical Bont Tick, Amblyomma Variegatum
    (2000)
    McMahon, Conor
    ;
    The responses of A. variegatum adults to constituents ot 'their aggregation-attraction pheromone presented in an air stream were studied using a locomotion compensator. The responses to vapours from two mixtures were compared, the first a 1:1 mixture of o-nitrophenol and methyl salicylale, the second a four component mixture Ā® containing o-nitrophenol, methyl salicylale, 2,6 dichlorophenol and phenyl acetaldehyde in the ratio 10:10:2:1, respectively. No difference was found between the kineses responses of A. variegatum adults for either mixture: both elicited an increase in angular velocity and a reduction in speed. Moreover, attraction to vapours of either mixture was reduced significantly as the source dose was increased: both mixtures were good attractants at a source dose of 10 Ī¼g of the main components, but were not attractive at source doses 100 times higher. As with many other arthropods, A. variegatum adults arc responsive to the ratio, as well as to the dose, of constituents in an attractant mix. We suggest that the quantity and ratios of compounds in attractive mixtures released from commercial dispensers should be measured before use in any control programme.
  • Publication
    AccĆØs libre
    Ixodid ticks avoid contact with liquid water
    (1999)
    Thomas Krƶber
    ;
    Larvae of the cattle tick Boophilus microplus and all life stages of the European sheep tick Ixodes ricinus avoid walking on a wet membrane surface surrounding a dry patch. Of 170 reactions made at a border with liquid water by 22 B. microplus larvae, 40% consisted of immediate turns to the opposite side to bring all the legs back onto a dry patch, 41% were walks along the border, during which the ticks maintained contact with both the dry and wet zones, and 19% were returns to the dry patch after a short excursion onto the wet surround. Since contact with one front leg tip was sufficient to cause return reactions from the wet surface in most of the border contacts, the water receptor(s) that enable ticks to perceive the wet surface are probably located in terminal pore sensilla on the first-leg tarsi. Observations on the return reactions of ticks with different groups of chemosensilla masked confirmed this. Ticks have an ambiguous relationship with water: they appear to avoid direct contact with it, but they need a high humidity to compensate for any deficit in body water.
  • Publication
    AccĆØs libre
    Behavioural and electrophysiological responses of the phlebotomine sandfly Lutzomyia longipalpis (Diptera: Psychodidae) when exposed to canid host odour kairomones
    (Wiley, 1999)
    Dougherty, M. J.
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    Ward, R.D.
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    Hamiltion, J.G.C.
    Compounds from the odour-producing glands of the fox Vulpes vulpes were collected. This complex mixture of compounds was used to stimulate the 'ascoid' olfactory organs of female sandflies in single sensillum and gas chromatography-linked single sensillum recordings. Sixteen of these compounds were identified using gas chromatography-linked mass spectrometry and amounts present were determined. The compounds fell into four organic classes: ketones, carboxylic acids, alcohols and aldehydes. Specific neurones present in the ascoid sensillum that responded to each of these classes of compound were characterized.
    A bioassay chamber was developed that gave female sandflies the choice of two odour sources. Female sandflies were attracted upwind by fox odour and were trapped in closer proximity to the fox odour port than the control port. Synthetic compounds were recombined in appropriate quantities to mimic the fox odour. In this bioassay, the synthetic blend attracted sandflies upwind, and again they were caught closer to the test port than the control port. Furthermore, the synthetic fox odour induced an electrophysiological response from neurones in the ascoid sensillum that was very similar to that induced by natural fox odour. No synthetic compound alone induced the same behavioural response from sandflies as did whole fox odour. However, benzaldehyde, 4-hydroxy-4-methyl-2-pentanone and 4-methyl-2-pentanone alone did cause sandflies to fly upwind and to be caught closer to the test port than the control.