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  • Publication
    AccĆØs libre
    Respiratory physiology and anthropophilic behavioural traits of the main malaria vector "Anopheles gambiae" Giles (Diptera: Culicidae)
    (2018)
    Frei, JƩrƓme
    ;
    La vie adulte des moustiques est marquĆ©e par la rĆ©pĆ©tition de sĆ©quences comportementales incluant: la recherche dā€™un partenaire sexuel, la recherche de ressources (repas sanguin sur un hĆ“te ou sucre dā€™origine vĆ©gĆ©tale) et la recherche dā€™un site de ponte ; ces sĆ©quences comportementales Ć©tant intercalĆ©es de pĆ©riodes plus ou moins longues de repos. Lā€™entreprise de lā€™un ou lā€™autre de ces comportements typiques est influencĆ©e par des facteurs aussi bien internes (comme par exemple le bagage gĆ©nĆ©tique ou lā€™Ć©tat physiologique) quā€™externes (comme les conditions environnementales ou les signaux Ć©mis par lā€™hĆ“te). Dans ce contexte, le principal vecteur de la malaria, Anopheles gambiae Giles (An. gambiae), se distingue dā€™autres moustiques en plusieurs points : il commence sa vie adulte avec peu de rĆ©serves mĆ©taboliques, il concentre ses repas sanguins et doit souvent mĆŖme les multiplier, afin de pouvoir pondre. Ce moustique est endophage, endophile et dĆ©montre un comportement anthropophile (prĆ©fĆ©rence Ć  piquer des ĆŖtres humains Ć  par rapport Ć  dā€™autres vertĆ©brĆ©s) dictĆ© principalement par la signature olfactive de lā€™homme. Dans cette thĆØse, je me suis donc intĆ©ressĆ© Ć  la physiologie respiratoire et Ć  lā€™identification de signaux chimiques potentiels typiques Ć  lā€™homme qui rĆ©gulent la vie adulte de ce moustique.
    Comprendre comment ce moustique Ć©change les gaz respiratoires avec son environnement ou quel schĆ©ma respiratoire (SR) il utilise est fondamental, car on en sait trĆØs peu sur la physiologie respiratoire des insectes de petite taille. En tant que petit ectotherme et sachant que ce moustique est particuliĆØrement dĆ©pendant de lā€™hĆ©matophagie pour rĆ©pondre Ć  ses besoins mĆ©taboliques de base, une meilleure comprĆ©hension des variations de son SR en fonction de sa taille et de la tempĆ©rature est Ć©galement importante. Pour ce faire, un systĆØme de respiromĆ©trie Ć  flux continu a Ć©tĆ© poussĆ© vers ses limites en termes de prĆ©cision et de rĆ©solution temporelle, afin de rĆ©soudre le SR utilisĆ© par An. gambiae. Au repos, le SR de An. gambiae est caractĆ©risĆ© par la rĆ©pĆ©tition cyclique dā€™Ć©vĆ©nements excrĆ©toires de CO2 marquĆ©s, suivis de pĆ©riodes dā€™Ć©mission plus basses. Les composantes sous-jacentes constituant le SR ont pu ĆŖtre identifiĆ©es et quantifiĆ©es. Ces derniĆØres incluent : le taux mĆ©tabolique au repos reprĆ©sente par le taux de production standard de CO2 au repos (sVĢ‡CO2), la durĆ©e (Pint) et le taux dā€™Ć©mission de CO2 (iVĢ‡CO2) entre les Ć©vĆ©nements excrĆ©toires de CO2 marquĆ©s, ainsi que la frĆ©quence (F), le volume (Vb), lā€™amplitude (A) et la durĆ©e (Pb) de ces derniers. Sur lā€™intervalle de taille et de tempĆ©rature expĆ©rimentĆ©s, sVĢ‡CO2 varie dā€™un facteur de 10 (20 Ć  32Ā°C, 0.9 Ć  2.3 mg, 0.6 Ć  6 Ī¼l CO2/heure). Une analyse par rĆ©gressions multiples dĆ©montre une relation positive et isomĆ©trique de sVĢ‡CO2 avec la taille et un Q10 apparent de 2.13 (pour une augmentation de 10Ā°C, sVĢ‡CO2 est plus que doublĆ©). Sachant quā€™un taux mĆ©tabolique plus Ć©levĆ© imposĆ© par lā€™environnement pourrait provoquer une recherche de ressources nutritionnelles accrue, voire un contact plus frĆ©quent avec lā€™hĆ“te, cette relation est un fondement important pour toute tentative de modĆ©lisation bottom-up des maladies transmises par les moustiques. La comparaison entre deux groupes dā€™Ć¢ges distincts dĆ©montre un sVĢ‡CO2 plus bas et mieux maĆ®trisĆ© chez les An. gambiae plus Ć¢gĆ©s (6 jours), suggĆ©rant ainsi un Ć¢ge optimal pour le contrĆ“le du mĆ©tabolisme. Les individus prĆ©sentant un sVĢ‡CO2 particuliĆØrement bas, en plus de respirer de maniĆØre cyclique, respirent aussi de maniĆØre discontinue (Ć©changes de gaz proche de 0 durant la pĆ©riode de basse Ć©mission). En activitĆ©, An. gambiae utilise un SR continu. Il est conclu que ce petit insecte est capable dā€™utiliser les 3 SR dĆ©crits Ć  ce jour dans la littĆ©rature chez les insectes (SR continu, cyclique et cyclique/discontinu). Lors dā€™une augmentation de tempĆ©rature, il est dĆ©montrĆ© que F module fortement le taux dā€™Ć©changes gazeux en augmentant plus vite que le taux mĆ©tabolique au repos. Ce dĆ©couplage est compensĆ© par une diminution de Vb, suggĆ©rant ainsi une diminution de la capacitĆ© tampon pour le CO2 dans lā€™hĆ©molymphe lorsque la tempĆ©rature augmente. F varie indĆ©pendamment de la masse corporelle, alors que Vb augmente de maniĆØre disproportionnĆ©e avec cette derniĆØre, suggĆ©rant ainsi un volume trachĆ©al relativement plus Ć©levĆ© chez les individus de plus grande taille. Si lā€™on tient compte de leur taille et de la variĆ©tĆ© de comportements que les moustiques sont capables dā€™entreprendre durant leur vie adulte, il est suggĆ©rĆ© que la capacitĆ© dā€™utiliser divers SR peut ĆŖtre un avantage, afin dā€™adapter le schĆ©ma respiratoire Ć  la demande mĆ©tabolique imposĆ©e selon les circonstances rencontrĆ©es durant la vie adulte.
    An. gambiae, en plus dā€™ĆŖtre anthropophile, montre mĆŖme une prĆ©fĆ©rence pour certains types dā€™humains. Il est connu que le mĆ©canisme derriĆØre ce comportement sĆ©lectif est mĆ©diĆ© par lā€™odeur Ć©mise par lā€™hĆ“te. La seconde partie de cette thĆØse sā€™est donc concentrĆ©e sur lā€™identification de signaux chimiques Ć©mis par lā€™hĆ“te potentiellement impliquĆ©s dans ce comportement sĆ©lectif. Pour ce faire, un paradigme expĆ©rimental intĆ©grant une bonne Ć©valuation du comportement dans des conditions expĆ©rimentales optimales a Ć©tĆ© dĆ©veloppĆ© et utilisĆ©. Ce dernier comprend : i) une population test de moustiques adultes spĆ©cialement Ć©levĆ©e et prĆŖte Ć  rechercher un hĆ“te, ii) un olfactomĆØtre amĆ©liorĆ© Ć  deux ports permettant de mesurer lā€™intensitĆ© de la rĆ©ponse chimioanĆ©motaxique du moustique et sa capacitĆ© discriminative en redirigeant son vol vers lā€™une des deux odeurs sources prĆ©sentĆ©es, iii) la prĆ©sence inhĆ©rente de fluctuations de CO2 contrĆ“lĆ©es afin de simuler la prĆ©sence de deux hĆ“tes potentiels et augmenter la sensitivitĆ© des moustiques et iv) des conditions de vol optimales (tempĆ©rature, humiditĆ© et vitesse du vent).
    Les fluctuations de CO2 ont pu ĆŖtre mesurĆ©es et reproduites de maniĆØre consistante dans les deux ports de lā€™olfactomĆØtre. Cette stimulation a augmentĆ© la rĆ©ceptivitĆ© des moustiques Ć  rĆ©pondre Ć  des odeurs. Des expĆ©riences conduites avec lā€™ajout dā€™acide lactique (une signature olfactive humaine dā€™origine eccrine) dans un des ports de lā€™olfactomĆØtre confirment que ce compose volatile nā€™intensifie pas la rĆ©ponse chimioanĆ©motaxique de An. gambiae mais influence son comportement discriminant. AprĆØs avoir validĆ© le paradigme expĆ©rimental avec lā€™acide lactique, ce dernier a Ć©tĆ© utilise pour Ć©valuer la rĆ©ponse du vecteur Ć  des odeurs provenant de lā€™incubation de sueur mĆ¢le et femelle avec 3 espĆØces de bactĆ©ries peuplant lā€™aisselle humaine. Staphylococcus epidermidis a Ć©tĆ© choisi car il produit une odeur moins intense, alors que Corynebacterium jeikeium et Staphylococcus haemolyticus ont Ć©tĆ© choisi pour leurs contributions biologiques importantes dans la production dā€™une odeur axillaire intense. Ces deux derniĆØres bactĆ©ries, par le biais dā€™une activitĆ© enzymatique spĆ©cifique et prononcĆ©e, libĆØrent respectivement des acides carboxyliques dont notamment le (R)/(S)-3-hydroxy-3-methylhexanoique acide (HMHA) et des composĆ©s volatiles soufrĆ©s tel que le (R)/(S)-3-methyl-3-sulfanylhexane-1-ol (MSH). Les expĆ©riences avec lā€™olfactomĆØtre dĆ©montrent que les trois bactĆ©ries, de par leur action sur la sueur mĆ¢le ou femelle, libĆØrent des composĆ©s volatiles influenƧant le comportement aussi bien chimioanĆ©motaxique que discriminant de An. gambiae. Si le vecteur nā€™a pas pu distinguer la sueur mĆ¢le de la sueur femelle stĆ©rile, lā€™action de chaque bactĆ©rie a rendu la sueur mĆ¢le plus attractive de maniĆØre consistante. Lā€™action de Corynebacterium jeikeium a gĆ©nĆ©rĆ© la rĆ©ponse chimionanĆ©motaxique la plus intense et a engendrĆ© la prĆ©fĆ©rence la plus forte pour la sueur mĆ¢le. Les composĆ©s volatiles HMHA et MSH sont suspectĆ©s dā€™ĆŖtre propres Ć  lā€™odeur humaine mais aucun des deux composĆ©s volatiles nā€™a gĆ©nĆ©rĆ© de prĆ©fĆ©rence telle que celle observĆ©e pour lā€™acide lactique. Il nā€™est cependant pas exclu que ces deux signaux chimiques influencent le comportement du moustique au moment oĆ¹ il approche lā€™hĆ“te ou encore engendre une activation suivie dā€™un vol soutenu en direction de lā€™hĆ“te Ć  des distances plus Ć©loignĆ©es., Anopheles gambiae Giles (An. gambiae) is the main vector of malaria. To fulfil metabolic demand An. gambiae is particularly dependent on blood feeding which is an important driving force of its strong vectorial capacity. It is therefore important to better understand how its metabolism scales with body size and, as an ectotherm, evaluate the thermal sensitivity of its metabolism. Meanwhile, understanding how respiratory gases are exchanged, which gas exchange pattern (GEP) is employed by An. gambiae is also of broader importance as little is known about the respiratory physiology of smaller insects. For this purpose a flow-through respirometer system was pushed to its limit in terms of both its precision and temporal resolution in order to fully resolve the GEP of resting female An. gambiae. The underlying components constituting the GEP could be identified and quantified, including: the standard CO2 production rate of resting An. gambiae (sVĢ‡CO2) as a proxy for resting metabolic rate, the inter-burst CO2 emission rate (iVĢ‡CO2) and duration (Pint), and CO2 burst frequency (F), duration (Pb), amplitude (A) and volume (Vb). Over the temperatures and body size ranges tested, sVĢ‡CO2 varied over a 10-fold range (20 to 32Ā°C, 0.9 to 2.3 mg, 0.6 to 6 Ī¼l CO2/hour). Multiple regression analysis demonstrates a positive and almost isometric scaling with living body mass and an apparent Q10 of 2.13, i.e. for a 10Ā°C increment sVĢ‡CO2 is more than doubled. Comparison of two age groups reveals lower and more controlled sVĢ‡CO2 by older (6 days) An. gambiae, suggesting the existence of an optimum age for metabolic control. Considering that a higher metabolic demand imposed by the environment may enhance foraging and contact to hosts, these relationships provide an important foundation for bottomup modelling for diseases transmitted by mosquitoes.
    At rest, the GEP of An. gambiae can be characterised by the cyclic repetition of CO2 bursts intercalated with inter-burst periods with a lower CO2 emission rate. Individuals presenting particularly low sVĢ‡CO2 values exchange respiratory gases not only cyclically but also discontinuously (gas exchange is negligible during inter-burst periods). Disturbed An. gambiae presented a continuous GEP. It is concluded that An. gambiae uses all three GEPs described so far in the literature. With increasing temperature it is shown that F strongly modulates the gas exchange rate by increasing faster than sVĢ‡CO2. This discrepancy is almost compensated by lower Vb values at higher temperature suggesting a decrease in the haemolymph buffering capacity for CO2 with increasing temperature. F is independent of body mass whereas Vb scales out of proportion with body size suggesting a relatively larger tracheal volume in bigger mosquitoes. Considering mosquito size and the wide panel of behaviours undertaken during adult life, it is suggested that the ability to employ various GEPs and modulating its components might be an advantage to adapt the respiratory gas exchange pattern used (discontinuous and cyclic to only cyclic and eventually to continuous) to metabolic demand depending on the situation encountered in adult life.
    Another major contributor to the vectorial capacity of An. gambiae is its odour-mediated preference to bite humans over other vertebrate host and certain human types over others. The second part of the thesis focuses on the identification of potential infochemicals that may explain this odour-mediated anthropophilic and discriminative host seeking behaviour of An. gambiae. For this purpose an experimental paradigm integrating both a sound behavioural evaluation concepts and an appropriate testing environment is used. An improved dual-choice olfactometer that tests the host seeking behaviour of An. gambiae in the presence of continuous well-controlled intermittent CO2 stimulation is presented in both arm is developed. This background stimulation simulates the presence of two potential hosts whilst acting as a releaser of odour perception. Olfactometer tests with lactic acid, a human eccrine signature, added on one arm in the presence of CO2 pulses as sensitizer, confirm earlier findings that this infochemical not necessarily augments anemochemotactic upwind flight of the insect vector but influences the mosquitoā€™s discriminative behaviour. After confirming the validity of the experimental paradigm it is used to evaluate the responses of An. gambiae to odours from human male and female axillary sweat incubated with 3 human axilla bacteria species. Staphylococcus epidermidis was selected for its low odour-producing pattern, Corynebacterium jeikeium for its strong NĪ±-acylglutamine aminoacylase activity liberating carboxylic acids including (R)/(S)-3-hydroxy-3-methylhexanoic acid (HMHA), and Staphylococcus haemolyticus for its capacity to liberate sulfur-containing compounds including (R)/(S)-3-methyl-3-sulfanylhexan-1-ol (MSH). It is demonstrated that An. gambiae is able to discriminate for the olfactometer arm conveying odour generated by incubating any of the three bacteria species with either male or female sweat. Whereas An. gambiae cannot discriminate between male and female sterile sweat samples in the olfactometer, the mosquito consistently shows a preference for male sweat over female sweat incubated with the same bacterium, independent of the species used as inoculum. Axillary sweat incubated with C. jeikeium rendered An. gambiae particularly responsive and this substrate elicited the strongest preference for male over female sweat. HMHA and MSH are suspected to be unique to human odour. It is shown that when tested on their own, neither HMHA nor MSH elicited a clear discriminating response but may affect human host approach by An. gambiae or enhance activation followed by sustained upwind flight over longer distances.
  • Publication
    AccĆØs libre
    Investigations on resting site preferences by the tsetse fly Glossina pallidipes (Diptera, Glossinidae) as a means of improving the efficacy of visual baits for tsetse population control
    (NeuchĆ¢tel : UniversitĆ© de NeuchĆ¢tel, 2016)
    Emmanuel Kamba Mebourou
    ;
    RĆ©sumĆ© Les mouches tsĆ©tsĆ©s sont des insectes hĆ©matophages quā€™on trouve en Afrique subsaharienne et dont les espĆØces sont classifiĆ©es en trois principaux groupes Ć©cologiques (riverain, savane et forĆŖt). Les mouches tsĆ©tsĆ©s riveraines et de savane sont les vecteurs potentiels des trypanosomes, parasites qui causent la trypanosomiase (maladie du sommeil), Ć  lā€™Homme et au bĆ©tail Ć  travers leurs piqĆ»res au cours leur repas sanguin. La trypanosomiase est une maladie tropicale nĆ©gligĆ©e qui affecte la santĆ© humaine et cause dā€™importantes pertes Ć©conomiques. La rĆ©duction de la population des mouches tsĆ©tsĆ©s par lā€™utilisation des Ć©crans visuels imprĆ©gnĆ©s dā€™insecticide (tissus bleus, noirs ou bleuā€noir) reste lā€™un des moyens efficaces pour lutter contre la maladie. La rĆ©duction des Ć©crans visuels standards (1 m x 1 m) aux Ć©crans de petites tailles (25 cm x 25 cm) sont des moyens effaces et bon marchĆ© pour contrĆ“ler la population des mouches tsĆ©tsĆ©s riveraines. Une telle rĆ©duction de taille des Ć©crans visuels est inefficace contre les tsĆ©tsĆ©s de savane. Lā€™objectif principal de cette thĆØse Ć©tait de dĆ©velopper des appĆ¢ts visuels efficaces, bon marchĆ© et standardisĆ©s qui permettent de contrĆ“ler les populations des mouches tsĆ©tsĆ©s. Le control et lā€™Ć©radication des mouches tsĆ©tsĆ©s requiĆØrent une solide connaissance de leur comportement et de leur Ć©cologie. Jā€™ai dā€™abord explorĆ© au laboratoire le comportement au repos de Glossina pallidipes qui est une mouche tsĆ©tsĆ© de savane (groupe Morsitans). Jā€™ai montrĆ© que (1) le fait de trouver une perche auā€dessus du sol est un comportement fondamental de survie chez G. pallidipes qui est capable de voler vers des sites de repos dans l'obscuritĆ© estimĆ©e Ć  10 fois plus bas que l'illumination pendant une nuit Ć  ciel couvert et (2) le choix des sites de repos diurnes par les mouches est liĆ© Ć  leur rĆ©solution visuelle dĆ©terminĆ©e par leurs rĆ©ponses optomotrices et par Ć©lectrorĆ©tinographie. Ensuite, j'ai travaillĆ© suivant l'hypothĆØse que les sites de repos horizontaux des mouches tsĆ©tsĆ©s (branches horizontales dans la nature) pourraient ĆŖtre des substrats d'atterrissage efficaces de ces mouches lorsqu'ils sont associĆ©s Ć  des Ć©crans visuels. Le comportement en vol et l'atterrissage de G. pallidipes sur des Ć©crans visuels bidimensionnels et tridimensionnels dans une arĆØne circulaire de vol libre et dans une chambre de vol confirment que G. pallidipes sā€™approche d'un objet visuel par le dessous et explore l'objet en volant autour de la partie infĆ©rieure de celuiā€ci. Une barre en bois de 1.5 cm de diamĆØtre recouverte d'un tissu mat noir et placĆ© horizontalement Ć  la base d'un Ć©cran carrĆ© bleu (25 cm x 25 cm) augmente les atterrissages de G. pallidipes de facteur 2 sur lā€™Ć©cran comparĆ© Ć  lā€™Ć©cran tout bleu dans la chambre de vol. Lā€™Ć©cran bleu incorporant une barre noire Ć  la base est prometteur dā€™un dispositif rentable Ć  utiliser comme appĆ¢ts visuels imprĆ©gnĆ©s d'insecticide pour contrĆ“ler la population des mouches tsĆ©tsĆ©s. Enfin, la question de la persistance de deltamĆ©thrine, un insecticide de la classe des pyrĆ©throĆÆdes actuellement utilisĆ© pour le contrĆ“le des tsĆ©tsĆ©s, a Ć©tĆ© traitĆ©e. L'effet de lā€™exposition dans les conditions naturelles (Lambwe Valley, Kenya) sur la capacitĆ© de quatre diffĆ©rents textiles contenant des proportions croissantes (0, 35, 65 et 100%) de polyester et imprĆ©gnĆ©s de deltamĆ©thrine a Ć©tĆ© Ć©valuĆ©. Ces textiles ont Ć©tĆ© saturĆ©s d'une solution aqueuse de deltamĆ©thrine Ć  1000 mg/m2 et ont Ć©tĆ© exposĆ©s au champ durant 18 mois. La toxicitĆ© sur G. pallidipes de ces textiles imprĆ©gnĆ©s de deltamĆ©thrine et exposĆ©s au champ a Ć©tĆ© Ć©valuĆ©e sur 24 heures aprĆØs 45 secondes de contact de ces textiles avec les mouches. Seuls les textiles constituĆ©s de polyester Ć  65% et 100% Ć©taient capables de tuer respectivement 47 et 67% de G. pallidipes aprĆØs 9 mois d'exposition dans les conditions naturelles. Le textile Ć  100% polyester Ć©tait encore capable de paralyser toutes les mouches aprĆØs 18 mois dā€™exposition au champ. La dose lĆ©tale de deltamĆ©thrine pour tuer 50% (DL50) de G. pallidipes Ć©tait estimĆ©e Ć  30 mg/m2 sur du papier buvard tandis que Le textile Ć  100% polyester conservait 17 mg/m2 aprĆØs 9 mois dā€™exposition au champ et causait une mortalitĆ© de 67% chez les mouches soulignant l'influence du type de matĆ©riel sur la disponibilitĆ© de lā€™insecticide aux mouches tsĆ©tsĆ©s. Sur la base de l'ensemble des rĆ©sultats de cette thĆØse, une perspective de recherche a Ć©tĆ© proposĆ©e pour la RĆ©publique centrafricaine qui abrite quatre foyers de trypanosomiase oĆ¹ la lutte contre les mouches tsĆ©tsĆ©s a longtemps Ć©tĆ© nĆ©gligĆ©e.
  • Publication
    AccĆØs libre
    Quinine and artesunate inhibit feeding in the African malaria mosquito Anopheles gambiae: the role of gustatory organs within the mouthparts
    (2014) ;
    GonzƔlez, Julia
    ;
    ;
    Glauser, GaƩtan
    ;
    A membrane feeding assay in which the effects of the antimalarial drugs quinine and artesunate are tested on Anopheles gambiae Giles sensu stricto is described. In the present study, 87% of female A. gambiae are shown to feed on whole defibrinated bovine blood alone, whereas only 47% and 43.5% feed on saline and on salineā€‰+ā€‰bovine serum albumin (BSA) solutions, respectively, suggesting that additional components in the blood stimulate mosquito feeding. The addition of 1ā€‰mm quinine or artesunate to the BSA solution results in a significant reduction in percentage engorgement to 16.2% and 14.1%, respectively. However, the feeding rate is higher when 1ā€‰mm artesunate and quinine are mixed in the blood because 67.8% and 78.4% of females engorge on these solutions respectively. Artesunate (10ā€‰mm) in the blood reduces percentage engorgement to 20%. Because circulating doses of quinine and artesunate affecting Plasmodium in humans are much lower than those affecting feeding by A. gambiae in the in vitro assay, these two antimalarial drugs should have no effect, or only a minor effect, on the infection rate of mosquitoes feeding on treated patients. Because only the stylets penetrate the membrane and not the labellar lobes, the results of the present study suggest that both blood phagostimulants and feeding deterrents are detected by internal gustatory organs in A. gambiae, namely sensory cells in the apical and subapical labral pegs, in sensilla on the inner face of the labellar lobes, or by cibarial receptor cells. The neuroanatomy of gustatory sensilla on the apical and subapical labral pegs and on the inner face of the labellar lobes of female A. gambiae is described in the present study.
  • Publication
    AccĆØs libre
    Standardising Visual Control Devices for Tsetse Flies: Central and West African Species Glossina palpalis palpalis
    (2014-1)
    Kaba, Dramane
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    Zacarie, Tusevo
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    Makumyaviri Mā€™Pondi, Alexis
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    Njiokou, Flobert
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    Bosson-Vanga, Henriette
    ;
    ; ;
    Mihok, Steve
    ;
    Background: Glossina palpalis palpalis (G. p. palpalis) is one of the principal vectors of sleeping sickness and nagana in Africa with a geographical range stretching from Liberia in West Africa to Angola in Central Africa. It inhabits tropical rain forest but has also adapted to urban settlements. We set out to standardize a long-lasting, practical and cost-effective visually attractive device that would induce the strongest landing response by G. p. palpalis for future use as an insecticideimpregnated tool in area-wide population suppression of this fly across its range. Methodology/Principal Findings: Trials were conducted in wet and dry seasons in the Ivory Coast, Cameroon, the Democratic Republic of Congo and Angola to measure the performance of traps (biconical, monoconical and pyramidal) and targets of different sizes and colours, with and without chemical baits, at different population densities and under different environmental conditions. Adhesive film was used as a practical enumerator at these remote locations to compare landing efficiencies of devices. Independent of season and country, both phthalogen blue-black and blue-black-blue 1 m2 targets covered with adhesive film proved to be as good as traps in phthalogen blue or turquoise blue for capturing G. p. palpalis. Trap efficiency varied (8ā€“51%). There was no difference between the performance of blue-black and blue-blackblue 1 m2 targets. Baiting with chemicals augmented the overall performance of targets relative to traps. Landings on smaller phthalogen blue-black 0.25 m2 square targets were not significantly different from either 1 m2 blue-black-blue or blue-black square targets. Three times more flies were captured per unit area on the smaller device. Conclusions/Significance: Blue-black 0.25 m2 cloth targets show promise as simple cost effective devices for management of G. p. palpalis as they can be used for both control when impregnated with insecticide and for population sampling when covered with adhesive film.
  • Publication
    MƩtadonnƩes seulement
    Standardizing Visual Control Devices for Tsetse Flies: East African Species Glossina swynnertoni
    (2013-2)
    Mramba, Furaha
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    Oloo, Francis
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    Byamungu, Mechtilda
    ;
    ; ; ;
    Mihok, Steve
    Background: Here we set out to standardize long-lasting, visually-attractive devices for Glossina swynnertoni, a vector of both human and animal trypanosomiasis in open savannah in Tanzania and Kenya, and in neighbouring conservation areas used by pastoralists. The goal was to determine the most practical device/material that would induce the strongest landing response in G. swynnertoni for use in area-wide population suppression of this fly with insecticide-impregnated devices. Methods and Findings: Trials were conducted in wet and dry seasons in the Serengeti and Maasai Mara to measure the performance of traps and targets of different sizes and colours, with and without chemical baits, at different population densities and under different environmental conditions. Adhesive film was used as a simple enumerator at these remote locations to compare trapping efficiencies of devices. Independent of season or presence of chemical baits, targets in phthalogen blue or turquoise blue cloth with adhesive film were the best devices for capturing G. swynnertoni in all situations, catching up to 19 times more flies than pyramidal traps. Baiting with chemicals did not affect the relative performance of devices. Fly landings were two times higher on 1 m2 blue-black targets as on pyramidal traps when equivalent areas of both were covered with adhesive film. Landings on 1 m2 blue-black targets were compared to those on smaller phthalogen blue 0.5 m2 all-blue or blue-black-blue cloth targets, and to landings on all-blue plastic 0.32ā€“0.47 m2 leg panels painted in phthalogen blue. These smaller targets and leg panels captured equivalent numbers of G. swynnertoni per unit area as bigger targets. Conclusions: Leg panels and 0.5 m2 cloth targets show promise as cost effective devices for management of G. swynnertoni as they can be used for both control (insecticide-impregnated cloth) and for sampling (rigid plastic with insect glue or adhesive film) of populations.
  • Publication
    AccĆØs libre
    A standardised in vivo and in vitro test method for evaluating tick repellents
    (2013)
    Krƶber, Thomas
    ;
    ;
    The threat of transmission of Lyme borelliosis and tick-borne encephalitis by ixodid ticks has resulted in an increasing number of tick repellents coming onto the market. To allow proper evaluation of the efficacy of different types of compounds and their formulations, there is a need for standardised methods for testing ticks repellents. Ticks show a marked negative geotactic response following contact with a potential host, i.e., they climb up in order to locate attachment and feeding sites, whereas exposing ticks to repellents induces positive geotaxis, i.e., ticks walk downwards or drop off the treated host or substrate. We describe here complementary tests that employ these geotactic responses to evaluate repellents: one in vitro on a warm glass plate and the other on the lower human leg (shin). The compounds tested were DEET, EBAAP, icaridin, capric acid, lauric acid, geraniol, citriodiol, citronella essential oil and lavender essential oil, all non-proprietary ingredients of widely distributed tick repellent formulations.

    In controls on both the warm glass plate and the human leg, the majority of Ixodes ricinus nymphs walk upwards. By contrast, in both the in vitro and in vivo tests, effective doses of repellents cause ticks to either walk downwards or fall off the substrates, termed here ā€œaffected ticksā€. The ED75 values for affected ticks on the human leg indicate that the test products can be divided into three groups: (1) icaridin, EBAAP, DEET and capric acid with values between 0.013 and 0.020 mg/cm2, (2) citriodiol and lauric acid with values between 0.035 and 0.058 mg/cm2, and (3) geraniol, citronella oil and lavender essential oil with values between 0.131 and 1.58 mg/cm2. The latter three products can be considered as less effective repellents. The tests on the warm glass plate resulted in very similar efficacy rankings for the products tested in vivo, and the ticksā€™ behavioural responses also corresponded closely to those observed on the treated human leg. The ED75 values on the glass plate ranged from half to one sixth needed on the leg. The warm glass plate test thus provides a reliable alternative to human subjects for an initial evaluation of new repellents, and is particularly appropriate for testing products with still to be determined human toxicity and dermatological effects.
  • Publication
    MƩtadonnƩes seulement
    The sugar meal of the African malaria mosquito Anopheles gambiae and how deterrent compounds interfere with it: a behavioural and neurophysiological study
    In this study, we show that female African malaria mosquitoes Anopheles gambiae starved for 3-5 h start to engorge on sucrose at concentrations between 50 and 75 mmol l(-1). Half of the feeding response (ED50) is reached at 111 mmol l(-1) and the maximum response (0.4. mg) occurs at 250 mmol l(-1). Two receptor cells in a trichoid sensillum of the labellum, called the 'sucrose' and 'water' neurones, are activated by sucrose and water, respectively. The electrophysiological response of the sucrose receptor cell starts well below the level of sugar necessary to induce engorgement. The sugar receptor cell is most sensitive to small increments in sucrose concentration up to 10 mmol l(-1) with a response plateau from 25 mmol l(-1). Fructose has a mild phagostimulatory effect on A. gambiae, whereas no significant differences in meal sizes between water and glucose were found. However, when 146 mmol. l(-1) fructose plus glucose are mixed, the same engorgement as on 146 mmol l(-1) sucrose is observed. Likewise, even though the sucrose receptor cell is not activated by either fructose or glucose alone, equimolar solutions of fructose plus glucose activate the neurone. We conclude that there is a behavioural and neurophysiological synergism between fructose and glucose, the two hexose sugars of sucrose. We show that some bitter-tasting products for humans have a deterrent effect on feeding in A. gambiae. When 1 mmol l(-1) quinidine, quinine or denatonium benzoate is added to 146 mmol l(-1) sucrose, feeding is almost totally inhibited. The effect of berberine is lower and no significant inhibition on engorgement occurs for caffeine. The deterrent effect depends on the concentration for both quinine and quinidine. Capillary feeding experiments show that contact chemosensilla on the mouthparts are sufficient for the detection of sucrose and bitter products. The feeding assay findings with deterrents correlate with the neurophysiological responses of the sucrose and water labellar neurones, which are both inhibited by the bitter compounds denatonium benzoate, quinine and berberine between 0.01 and 1 mmol l(-1), but not by the same concentrations of caffeine. In conclusion, sucrose stimulates feeding and activates the labellar sucrose neurone, whereas feeding deterrents inhibit both the sucrose and water neurones. This study provides an initial understanding of the physiological mechanisms involved in sugar feeding in A. gambiae and shows how some bitter products interfere with it.
  • Publication
    MƩtadonnƩes seulement
    A standardised in vivo and in vitro test method for evaluating tick repellents
    The threat of transmission of Lyme borelliosis and tick-borne encephalitis by ixodid ticks has resulted in an increasing number of tick repellents coming onto the market. To allow proper evaluation of the efficacy of different types of compounds and their formulations, there is a need for standardised methods for testing ticks repellents. Ticks show a marked negative geotactic response following contact with a potential host, i.e., they climb up in order to locate attachment and feeding sites, whereas exposing ticks to repellents induces positive geotaxis, i.e., ticks walk downwards or drop off the treated host or substrate. We describe here complementary tests that employ these geotactic responses to evaluate repellents: one in vitro on a warm glass plate and the other on the lower human leg (shin). The compounds tested were DEET, EBAAP, icaridin, capric acid, lauric acid, geraniol, citriodiol, citronella essential oil and lavender essential oil, all non-proprietary ingredients of widely distributed tick repellent formulations. In controls on both the warm glass plate and the human leg, the majority of Nodes ricinus nymphs walk upwards. By contrast, in both the in vitro and in vivo tests, effective doses of repellents cause ticks to either walk downwards or fall off the substrates, termed here "affected ticks". The ED75 values for affected ticks on the human leg indicate that the test products can be divided into three groups: (1) icaridin, EBAAP, DEET and capric acid with values between 0.013 and 0.020 mg/cm(2), (2) citriodiol and lauric acid with values between 0.035 and 0.058 mg/cm(2), and (3) geraniol, citronella oil and lavender essential oil with values between 0.131 and 1.58 mg/cm2. The latter three products can be considered as less effective repellents. The tests on the warm glass plate resulted in very similar efficacy rankings for the products tested in vivo, and the ticks' behavioural responses also corresponded closely to those observed on the treated human leg. The ED75 values on the glass plate ranged from half to one sixth needed on the leg. The warm glass plate test thus provides a reliable alternative to human subjects for an initial evaluation of new repellents, and is particularly appropriate for testing products with still to be determined human toxicity and dermatological effects. (C) 2013 Elsevier Inc. All rights reserved.
  • Publication
    AccĆØs libre
    The behaviour of the tsetse fly Glossina pallidipes (Diptera, Glossinidae):: from host seeking to biting
    (2013)
    Chappuis, Charles
    ;
    Les tsĆ©-tsĆ© sont les principaux vecteurs des trypanosomes africains qui causent la maladie du sommeil chez lā€™humain et le nagana chez les bovins. Ces maladies reprĆ©sentent un lourd fardeau en ce qui concerne la santĆ© et la prospĆ©ritĆ© humaine. Une faƧon de lutter contre ces trypanosomes est de sā€™attaquer au vecteur en contrĆ“lant sa population Ć  lā€™aide de piĆØges qui le trompent par des moyens visuels et olfactifs. Par consĆ©quent, une meilleure comprĆ©hension de la maniĆØre dont une mouche tsĆ©-tsĆ© utilise les indices olfactifs et visuels laissĆ©s par lā€™hĆ“te peut aider Ć  dĆ©velopper des mĆ©thodes de captures plus efficaces encore. Et cā€™est dans ce contexte que nous avons Ć©tudiĆ© les phases critiques du comportement de recherche dā€™hĆ“te de G. pallidipes, telles que lā€™activation, lā€™anĆ©motaxie optomotrice, lā€™approche dā€™une stimulation visuelle forte, la recherche locale autour dā€™elle, lā€™atterrissage et finalement, la piqĆ»re.
    Nous nous sommes intĆ©ressĆ©s plus particuliĆØrement Ć  savoir comment lā€™haleine intervient dans le comportement de G. pallidipes. En effet, lā€™haleine est un mĆ©lange complexe de plus de 200 composĆ©s organiques volatiles (COV) qui proviennent en partie des Ć©changes dans les poumons entre lā€™air inspirĆ© et le sang. En quantifiant des phases comportementales aussi critiques que lā€™activation, lā€™anĆ©motaxie optomotrice, la recherche locale autour dā€™une stimulation visuelle forte, nous montrons comment G. pallidipes rĆ©pond Ć  lā€™haleine dans une chambre de vol. De plus, nous dĆ©montrons que le CO2, une molĆ©cule constituante de lā€™haleine et connue pour attirer les mouches tsĆ©-tsĆ© ainsi que dā€™autres insectes haematophages, nā€™est pas entiĆØrement responsable des rĆ©ponses comportementales obtenues avec lā€™haleine. En effet, cā€™est la combinaison du CO2 avec les COVs de lā€™haleine qui induit le comportement de recherche dā€™hĆ“te chez les tsĆ©-tsĆ©. Nos enregistrements dā€™Ć©lectroantennogramme (EAG) et nos donnĆ©es comportementales rĆ©vĆØlent que les constituants de lā€™haleine tels que lā€™acĆ©tone, les alcanes de C5-C10, lā€™isoprĆØne et le geranylacĆ©tone, jouent un rĆ“le dans le comportement de recherche de lā€™hĆ“te chez G. pallidipes.
    Nous dĆ©montrons en chambre de vol quā€™une barre noire coiffĆ©e dā€™une sphĆØre bleue est un stimulus dĆ©clenchant lā€™atterrissage chez G. pallidipes. De plus, le comportement dā€™atterrissage peut ĆŖtre modulĆ© en changeant la taille de la barre et la taille ou la forme de lā€™objet qui coiffe la barre.
    Finalement, nous dĆ©montrons que le systĆØme de refroidissement des mammifĆØres induit la piqĆ»re chez les tsĆ©-tsĆ©. En effet, lā€™humiditĆ© et la chaleur agissent dā€™une faƧon synergique pour induire la piqĆ»re et influencent le temps de latence, la persistance Ć  piquer et la dynamique dā€™un comportement aussi essentiel que la piqĆ»re. En plus, nous avons pour la premiĆØre fois identifiĆ© chez les tsĆ©-tsĆ© des neurones dĆ©montrant des propriĆ©tĆ©s hygrorĆ©ceptives dans les sensilles basiconiques des palpes maxillaires., Tsetse flies are major vectors of African trypanosomes causing sleeping sickness in humans and nagana in cattle. These diseases are substantial burdens on human health and prosperity. One way to break the trypanosomes life-cycle is the control of tsetse populations using visual odour-baited trapping devices. A better understanding of how tsetse use visual and chemical cues to locate hosts could help to design even more efficient trapping devices. It is in this context that critical host seeking behaviours of G. pallidipes were investigated in a wind tunnel. These behaviours include fly activation, optomotor anemotaxis, approach flights to a visual target, local search flights around a visual stimulus, landing responses of the fly and its biting response.
    I was interested in how a host odour emanation such as human breath intervenes in the host-seeking behaviour of G. pallidipes. Breath is a complex blend of more than 200 volatile organic compounds (VOCs) originating in part, from the exchange between air and blood in lungs. Quantifying critical behaviours such as activation, optomotor anemotaxis and local search flights around a blue sphere with a 3D tracking system in a wind tunnel allows us to understand how G. pallidipes responds to breath as an olfactory stimulus. Furthermore, I demonstrate how CO2, a constituent of breath known to attract tsetse and other blood-sucking insects, is not responsible on its own for the behavioural responses recorded for G. pallidipes to breath in the wind tunnel. In fact, CO2 combines with VOCs present in breath to elicit host-seeking behaviours in tsetse. Electroantennogram (EAG) recordings and the wind tunnel behavioural experiments reveal that breath constituents such as acetone, C5-C10 alkanes, isoprene and geranylacetone play a role in the host-seeking behaviour of G. pallidipes.
    I demonstrate in the wind tunnel that an object such as a black column supporting a blue sphere can serve as a landing stimulus for G. pallidipes and that the flyā€™s landing behaviour can be modulated by changing the width of the column and the size or shape of the object it supports.
    The manner in which tsetse exploit the cooling system of mammals to elicit their biting response was studied in a specially designed experimental set up. In this manner it could be demonstrated that simultaneous increases in the humidity and temperature of air act synergistically to induce biting in G. pallidipes. These combined physical stimuli influence the biting response latency, biting persistence and the dynamics of this fundamental behaviour. In addition, I report on neurones with hygroreceptive properties present in wall-pore sensilla on the maxillary palps of G. pallidipes that are probably implicated in biting behaviours.
  • Publication
    AccĆØs libre
    The sugar meal of the African malaria mosquito Anopheles gambiae and how deterrent compounds interfere with it: a behavioural and neurophysiological study
    In this study, we show that female African malaria mosquitoes Anopheles gambiae starved for 3ā€“5 h start to engorge on sucrose at concentrations between 50 and 75 mmol lāˆ’1. Half of the feeding response (ED50) is reached at 111 mmol lāˆ’1 and the maximum response (0.4 mg) occurs at 250 mmol lāˆ’1. Two receptor cells in a trichoid sensillum of the labellum, called the ā€˜sucroseā€™ and ā€˜waterā€™ neurones, are activated by sucrose and water, respectively. The electrophysiological response of the sucrose receptor cell starts well below the level of sugar necessary to induce engorgement. The sugar receptor cell is most sensitive to small increments in sucrose concentration up to 10 mmol lāˆ’1 with a response plateau from 25 mmol lāˆ’1. Fructose has a mild phagostimulatory effect on A. gambiae, whereas no significant differences in meal sizes between water and glucose were found. However, when 146 mmol lāˆ’1 fructose plus glucose are mixed, the same engorgement as on 146 mmol lāˆ’1 sucrose is observed. Likewise, even though the sucrose receptor cell is not activated by either fructose or glucose alone, equimolar solutions of fructose plus glucose activate the neurone. We conclude that there is a behavioural and neurophysiological synergism between fructose and glucose, the two hexose sugars of sucrose. We show that some bitter-tasting products for humans have a deterrent effect on feeding in A. gambiae. When 1 mmol lāˆ’1 quinidine, quinine or denatonium benzoate is added to 146 mmol lāˆ’1 sucrose, feeding is almost totally inhibited. The effect of berberine is lower and no significant inhibition on engorgement occurs for caffeine. The deterrent effect depends on the concentration for both quinine and quinidine. Capillary feeding experiments show that contact chemosensilla on the mouthparts are sufficient for the detection of sucrose and bitter products. The feeding assay findings with deterrents correlate with the neurophysiological responses of the sucrose and water labellar neurones, which are both inhibited by the bitter compounds denatonium benzoate, quinine and berberine between 0.01 and 1 mmol lāˆ’1, but not by the same concentrations of caffeine. In conclusion, sucrose stimulates feeding and activates the labellar sucrose neurone, whereas feeding deterrents inhibit both the sucrose and water neurones. This study provides an initial understanding of the physiological mechanisms involved in sugar feeding in A. gambiae and shows how some bitter products interfere with it.