The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform

Pascal Steullet - One of the best experts on this subject based on the ideXlab platform.

  • Identification of vertebrate volatiles stimulating olfactory receptors on tarsus I of the tick Amblyomma variegatum Fabricius (Ixodidae)
    Journal of Comparative Physiology A, 1994
    Co-Authors: Pascal Steullet, P. M. Guerin
    Abstract:

    Gas chromatography-coupled electrophysiological recordings (GC-EL) from olfactory sensilla within the capsule of Haller's organ of the tick Amblyomma variegatum indicate the presence of a number of stimulants in rabbit and bovine odours, and in steer skin wash. Some of these stimulants were fully identified by gas chromatography-mass spectrometry analysis and by matching electrophysiological activity of synthetic analogues as: 1) hexanal, 2-heptenal, nonanal, furfural, benzaldehyde, and 2-hydroxybenzaldehyde (in all extracts); 2) heptanal, 2-, 3-, and 4-methylbenzaldehyde, and γ-valerolactone (only in bovine and rabbit odour). Careful examination of the electrophysiological responses permit characterization of 6 receptor types: 1) a benzaldehyde receptor, 2) a 2-hydroxybenzaldehyde receptor, 3) three types of receptors responding differently to aliphatic aldehydes, and 4) a lactone receptor.

  • Identification of vertebrate volatiles stimulating olfactory receptors on tarsus I of the tick Amblyomma variegatum Fabricius (Ixodidae)
    Journal of Comparative Physiology A, 1994
    Co-Authors: Pascal Steullet, P. M. Gnerin
    Abstract:

    Bovine odour excites olfactory receptor(s) in a wall-pore olfactory sensillum on the anterior pit of Haller's organ in Amblyomma variegatum . Gas chromatography-coupled electrophysiology recordings from this sensillum reveal the presence of 4 active compounds in bovine odour. The two strongest stimulants were identified as 2-nitrophenol and 4-methyl-2-nitrophenol by gas chromatography-coupled mass spectrometry, and by matching electrophysiological activity of synthetic analogues. Synthetic analogues of known vertebrate-associated volatiles also stimulate other olfactory receptors in sensilla on the surface of tarsus I: a lactone receptor responding to γ-valerolactone and 6-caprolactone; different fatty acid receptor types responding best to either pentanoic acid, 2-methylpropanoic acid or to butanoic acid; three receptors responding to NH_3; and one receptor responding to 3-pentanone. Gas chromatography-coupled mass spectrometry analysis of vertebrate volatiles revealed presence of a number of these olfactory stimulants in concentrates of rabbit and steer odour, i.e. 2-methylpropanoic acid, butanoic acid, 3-methylbutanoic acid, pentanoic acid, and γ-valerolactone.

  • Perception of breath components by the tropical bont tick, Amblyomma variegatum Fabricius (Ixodidae)
    Journal of Comparative Physiology A, 1992
    Co-Authors: Pascal Steullet, Patrick M. Guerin
    Abstract:

    Wall-pore olfactory sensilla located in the capsule of Haller's organ on the tarsus of Amblyomma variegatum ticks bear cells responding to vertebrate breath: one of these sensilla contains a CO_2-excited receptor and a second sensillum has a CO_2- inhibited receptor. Each of these antagonistic CO_2-receptors, which display typical phasic-tonic responses, monitors a different CO_2-concentration range. The CO_2-inhibited receptor is very sensitive to small concentration changes between 0 and ca. 0.2%, but variations of 0.01% around ambient (ca. 0.04%) induce the strongest frequency modulation of this receptor. An increase of just 0.001–0.002% (10–20 ppm) above a zero CO_2-level already inhibits this receptor. By contrast, the CO_2-excited receptor is not so sensitive to small CO_2 shifts around ambient, but best monitors changes in CO_2 concentrations above 0.1%. This receptor is characterized by a steep dose-response curve and a fast inactivation even at high CO_2-concentrations (>2%). In a wind-tunnel, Amblyomma variegatum is activated from the resting state and attracted by CO_2 concentrations of 0.04 to ca. 1%, which corresponds to the sensitivity range of its CO_2-receptors. The task of perceiving the whole concentration range to which this tick is attracted would thus appear to be divided between two receptors, one sensitive to small changes around ambient and the other sensitive to the higher concentrations normally encountered when approaching a vertebrate host.

  • Perception of breath components by the tropical bont tick, Amblyomma variegatum Fabricius (Ixodidae)
    Journal of Comparative Physiology A, 1992
    Co-Authors: Pascal Steullet, Patrick M. Guerin
    Abstract:

    Wall-pore sensilla in the capsule of Haller's organ on foreleg tarsi of the tick, Amblyomma variegatum , show multicellular responses upon stimulation with human and bovine breath. Filtering breath through charcoal removes the stimulant for some of these receptors. Analysis by gas chromatography coupled with olfactory sensillum electrophysiological recordings indicates that an ethanol extract of the breath components trapped on charcoal contains a major stimulant eluting at the same retention time as H_2S. Two types of H_2S-sensitive receptors have been identified. They are housed in separate sensilla, and are called sulfide-receptor 1 and 2. Although, both receptor types are characterized by a high sensitivity to H_2S with an estimated threshold of ca. 0.1 ppb and a response range covering 5–6 log orders of magnitude, their overall response to sulfides and mercaptans is nevertheless dissimilar. The type 1 receptor fires slightly more upon stimulations with H_2S than type 2, whereas ethylmercaptan induces a stronger response from type 2, and dimethyl sulfide activates only receptor 2. In a bioassay, H_2S tested at concentrations of ca. 0.02 ppm and 1 ppm equally arouses 60% of resting ticks. Two-thirds of these ticks quest the air with their first pair of legs, and the remainder start active search. By contrast, H_2S at ca. l ppm in a mixture with CO_2 severely diminishes the locomotor stimulating effect of CO_2.

  • Perception of breath components by the tropical bont tick, Amblyomma variegatum fabricius (Ixodidae). I : CO2-excited and CO2-inhibited receptors
    Journal of comparative physiology. A Sensory neural and behavioral physiology, 1992
    Co-Authors: Pascal Steullet, Patrick M. Guerin
    Abstract:

    Wall-pore olfactory sensilla located in the capsule of Haller's organ on the tarsus of Amblyomma variegatum ticks bear cells responding to vertebrate breath: one of these sensilla contains a CO2-excited receptor and a second sensillum has a CO2- inhibited receptor. Each of these antagonistic CO2-receptors, which display typical phasic-tonic responses, monitors a different CO2-concentration range. The CO2-inhibited receptor is very sensitive to small concentration changes between 0 and ca. 0.2%, but variations of 0.01% around ambient (ca. 0.04%) induce the strongest frequency modulation of this receptor. An increase of just 0.001–0.002% (10–20 ppm) above a zero CO2-level already inhibits this receptor. By contrast, the CO2-excited receptor is not so sensitive to small CO2 shifts around ambient, but best monitors changes in CO2 concentrations above 0.1%. This receptor is characterized by a steep dose-response curve and a fast inactivation even at high CO2-concentrations (>2%). In a wind-tunnel, Amblyomma variegatum is activated from the resting state and attracted by CO2 concentrations of 0.04 to ca. 1%, which corresponds to the sensitivity range of its CO2-receptors. The task of perceiving the whole concentration range to which this tick is attracted would thus appear to be divided between two receptors, one sensitive to small changes around ambient and the other sensitive to the higher concentrations normally encountered when approaching a vertebrate host.

Nicolas Barré - One of the best experts on this subject based on the ideXlab platform.

  • Repeatability of the level of infestation by Amblyomma variegatum ticks on Creole cattle.
    Annals of the New York Academy of Sciences, 1998
    Co-Authors: Michel Naves, Nicolas Barré, M. Fargetton, Rosalie Aprelon
    Abstract:

    En Guadeloupe, #Amblyomma variegatum# est une tique endemique dans les elevages de bovins. La mise en place d'une politique adequate de lutte contre ce parasite est importante dans l'optique d'une amelioration de la productivite des animaux. En effet, #Amblyomma variegatum# est present dans les Caraibes et en Amerique depuis un siecle ou il est toujours associe aux maladies majeures qui touchent les elevages. Il existe plusieurs techniques permettant de limiter l'infestation par ce parasite. Mais les possibilites d'utiliser les mecanismes de resistance genetique ou la sensibilite des hotes sont peu connues. Plusieurs etudes demontrent la difference de resistance des especes bovines aux tiques (#Boophilus microplus, Rhipicephalus appendiculatus#). Cette etude fait le point sur la resistance des bovins guadeloupeens a la tique tropicale #Amblyomma variegatum#

  • Efficacy of tags impregnated with pheromone and acaricide for control of Amblyomma variegatum
    Medical and veterinary entomology, 1998
    Co-Authors: Sandra A. Allan, Nicolas Barré, Daniel E. Sonenshine, M.j. Burridge
    Abstract:

    The efficacy of tags impregnated with pheromone and acaricide for control of #Amblyomma variegatum# on cattle in Guadeloupe was determined for a 13-week trial. Comparisons were made between untreated cattle and cattle with tags containing either pheromones alone (o-nitrophenol, methyl salicylate, 2,6-dichlorophenol and phenylacetaldehyde), pheromones plus acaricide (cyfluthrin or deltamethrin), or acaricide alone. Tags were fastened to cattle both on collars on the neck and with adhesive to tail hairs, with over 98 and 90% of tags retained, respectively, during the trial. By the end of the trial, tick infestations increased on untreated cattle (311.7%) and cattle with pheromone tags (154.8%) but decreased on cattle with pheromone/cyfluthrin (-45.0%), cyfluthrin (-42.8%), pheromone/deltamethrin (-68.7%) and deltamethrin tags (-87.6%). Cattle with pheromone tags had greater proportions of ticks on the hind regions (81%) compared to untreated cattle (62.5%) and on the front regions (18.2%) compared to untreated cattle (8.2%) indicating that ticks aggregated in response to pheromones. Analysis of hair samples by gas chromatography indicated that, within 2 days of placement, cyfluthrin spread rapidly over the body from the tags. Both cyfluthrin and deltamethrin were present in detectable levels on all eight body regions examined throughout the trial. Analysis of the tags indicated that they all still contained pheromone components after 13 weeks under field conditions. (Resume d'auteur)

  • Factors of variation of Amblyomma variegatum infestation on Creole cattle in Guadeloupe.
    Annals of the New York Academy of Sciences, 1996
    Co-Authors: Michel Naves, Nicolas Barré, M. Fargetton, Rosalie Aprelon, Christian Sheikboudou
    Abstract:

    The level of infestation of "Creole" beef cattle of Guadeloupe by the tick #Amblyomma variegatum# was recorded during a long-term survey in an experimental 61 steers and 83 cows were distributed in different lots according to sex and management. They grazed continuously either on irrigated #Digitaria decumbens# pastures or on dry native savannahs. Tick numbers as well as animal weights were registered monthly. Climatic data were also recorded. Different acaricide treatments were tested during the survey. But in order to minimize their effect in the data analysis, only tick counts over an average of 5 adult ticks per cattle were taken into account. The level of infestation is analyzed with respect to environmental factors (season, management) and individual factors (sex, weight, physiological stage, genetic effect).The effects of f these factors are discussed with regard to altemative tick-control methods, such as the selection of resistant hosts. (Resume d'auteur)

  • Propagation of the tick Amblyomma variegatum in the Caribbean.
    Revue scientifique et technique (International Office of Epizootics), 1995
    Co-Authors: Nicolas Barré, Glen I. Garris, Emmanuel Camus
    Abstract:

    Summary: The tropical bont tick, Amblyomma variegatum, is an African tick species which infests livestock and wildlife. It was probably introduced in the central eastern islands of the Caribbean during the 18th or 19th century, with cattle shipped from Senegal. In Africa and the Caribbean, this tick is a vector of heartwater (a rickettsial disease of ruminants) and is associated with acute dermatophilosis (a bacterial skin disease of animals). Until 1948, only Guadeloupe and the neighbouring islands of Marie Galante and Antigua were infested with this tick species. Following increased agricultural commerce between Guadeloupe and Martinique, the latter became infested in 1948. Between 1967 (when the tick was identified in St Croix) and 1988 (when a male tick was reported in St Vincent), fourteen new islands were reached by this tick. Most of the dissemination of the tick to new islands cannot be explained by legal or illegal movements of livestock. Recently-determined circumstantial evidence strongly links the increase in populations of the cattle egret (Bubulcus ibis), a migrating bird established in the Caribbean circa 7960, with increased colonisation of new islands by A. variegatum. Considering the wide range of areas currently occupied by this bird species in the Greater Antilles and on the American mainland, there is a high probability that the tick will also expand its range and invade new areas. Eradication of A. variegatum from the Caribbean and thus from the western hemisphere, and the strengthening of measures to prevent inter-island movements of livestock, would be the only effective means of preventing this threat.

  • Kinetics of male pheromone production by Amblyomma variegatum (Acari: Ixodidae).
    Journal of medical entomology, 1993
    Co-Authors: Claude Pavis, Nicolas Barré
    Abstract:

    Males of Amblyomma variegatum (F.), when attached on their host, produce a pheromonal blend composed of methyl salicylate, ortho-nitrophenol, and nonanoic acid, which acts as an aggregation-attachment pheromone. Using olfactometry assays, assays on hosts, and quantification of the compounds by capillary gas chromatography, the kinetics of pheromone production has been studied. Males engorged for at least 10 d elicit attachment from most of the tested females. Attractiveness of males for females is significant only between days 14 and 23 of engorgement. Before 10 d of attachment, the amounts of pheromones detected in hexanic male body extracts are very low (< 10 ng); they then increase to a maximum of 2 micrograms for the major compound per male. Large amounts can be detected until 80 d of engorgement. The inter-individual variation is very large throughout the engorgement period. The interest and the limitations of the different techniques used are discussed.

N. Barre - One of the best experts on this subject based on the ideXlab platform.

  • Attempts to feed Amblyomma variegatum ticks on artificial membranes.
    Annals of the New York Academy of Sciences, 1998
    Co-Authors: N. Barre, R. Aprelon, Maguy Eugène
    Abstract:

    Feeding jars were used to feed nymphs of Amblyomma variegatum on blood of goats or cattle. Sterile blood was collected daily or weekly (kept at 4°C or frozen until use), with addition either of heparin alone or of heparin and antibiotics/fungicide or of heparin, adenosine triphosphate and glutathione. Membranes were made of a thin (0.12-0.32 mm) film of silicone mastic. Blood in the jars was replaced twice a day, and reached a temperature of 39°C in a waterbath before it became available to the ticks. Attachment of nymphs was stimulated by dropping on the membrane fresh goat hair and squamae collected close to prefed males, skin washing and natural pheromone extracts. Using these devices, attachment of nymphs is rapid and intense (68%). Their body mass when engorged and the molting success, were lower than that of naturally fed ticks. Furthermore, the proportion of engorging ticks was usually much less and the length of the blood meal was much longer than of naturally fed ticks. The best results were obtained with fresh goat blood or cattle blood with antibiotics. Further developments are needed before this method can be used routinely. (Resume d'auteur)

  • Attempts to feed Amblyomma variegatum ticks on artificial membranes
    Annals of the New York Academy of Sciences, 1998
    Co-Authors: N. Barre, R. Aprelon, Maguy Eugène
    Abstract:

    Feeding jars were used to feed nymphs of Amblyomma variegatum on blood of goats or cattle. Sterile blood was collected daily or weekly (kept at 4 degrees C or frozen until use), with addition either of heparin alone or of heparin and antibiotics/fungicide or of heparin, adenosine triphosphate and glutathione. Membranes were made of a thin (0.12-0.32 mm) film of silicone mastic. Blood in the jars was replaced twice a day, and reached a temperature of 39 degrees C in a waterbath before it became available to the ticks. Attachment of nymphs was stimulated by dropping on the membrane fresh goat hair and squamae collected close to prefed males, skin washing and natural pheromone extracts. Using these devices, attachment of nymphs is rapid and intense (68%). Their body mass when engorged and the molting success, were lower than that of naturally fed ticks. Furthermore, the proportion of engorging ticks was usually much less and the length of the blood meal was much longer than of naturally fed ticks. The best results were obtained with fresh goat blood or cattle blood with antibiotics. Further developments are needed before this method can be used routinely.

  • Dermal gland secretions of tropical bont tick,Amblyomma variegatum (Acarina: Ixodidae): Biological activity on predators and pathogens
    Journal of Chemical Ecology, 1994
    Co-Authors: C. Pavis, H. Mauleon, N. Barre, M. Maibeche
    Abstract:

    When they are mechanically disturbed, all instars of the tropical bont tick Amblyomma variegatum exude droplets of a liquid on the dorsal, lateral, and ventral cuticle. These spread out and quickly evaporate. In this study, the possible role of these secretions was investigated in relation to predators and pathogens. In laboratory bioassays, it was demonstrated that the secretions from engorged larvae, nymphs, and females have an antibiotic activity against the bacteria species Bacillus thuringiensis and Serratia marcescens , combined with a repellent effect on a potential predator, the fire-ant Solenopsis geminata .

  • Landsat-TM identification of Amblyomma variegatum (Acari: Ixodidae) habitats in Guadeloupe
    1992
    Co-Authors: M. Hugh-jones, N. Barre, G. Nelson, K. Wehnes, J. Warner, James B. Garvin, Glen I. Garris
    Abstract:

    The feasibility of identifying specific habitats of the African bont tick, Amblyomma variegatum, from Landsat-TM images was investigated by comparing remotely sensed images of visible farms in Grande Terre (Guadeloupe) with field observations made in the same period of time (1986-1987). The different tick habitates could be separated using principal component analysis. The analysis clustered the sites by large and small variance of band values, and by vegetation and moisture indexes. It was found that herds in heterogeneous sites with large variances had more ticks than those in homogeneous or low variance sites. Within the heterogeneous sites, those with high vegetation and moisture indexes had more ticks than those with low values.

  • Landsat-TM identification of Amblyomma variegatum (Acari : Ixodidae) habitats in Guadeloupe
    Remote Sensing of Environment, 1992
    Co-Authors: M. Hugh-jones, N. Barre, G. Nelson, K. Wehnes, J. Warner, James B. Garvin, G. Garris
    Abstract:

    Abstract The objective of this study in 1986–1987 was to determine whether it was possible to remotely identify the specific habitat or habitats of the African bont tick, Amblyomma variegatum , using Landsat-TM imagery data. An unsupervised classification of the April 1986 image was carried out using LAS KMEANS and SPCSRT. The predictability of the landcover classes was determined by visiting random preselected sites within wetlands, woodlands, canefields, and grazing. On a second visit adult ticks were counted in over 103 herds and the habitats recorded. Descriminant analysis indicated that there were a limited number of tick habitats. The tick counts for the herds within these habitats indicate that each habitat probably has a characteristic tick density. The visible farms in Grande Terre, representing four habitats, were then compared with the landcover classes found in a 5 × 5 pixel array at each farm site in the classified image. The habitats could be separated using principal component analysis. Divisive clustering analysis was applied to the band values and derived indices for a similar sized array for each farm site visible in the original unclassified image of Guadeloupe. This analysis clustered the sites by large and small variance of band values, and by vegetation and moisture indices. Herds in heterogeneous sites with large variances had more ticks than those in homogeneous or low variance sites. Within the heterogeneous sites, those with high vegetation and moisture indices had more ticks than those with low values.

Frédéric Stachurski - One of the best experts on this subject based on the ideXlab platform.

  • Poor inheritance of low attractiveness for Amblyomma variegatum in cattle.
    Veterinary Parasitology, 2007
    Co-Authors: Frédéric Stachurski
    Abstract:

    Abstract Because of the high variability of cattle infestation, selective breeding has been proposed to control three-host ticks in Africa in the same way as it has been implemented to control the one-host tick Boophilus microplus in Australia. Interbreeding (divergent selection experiment) between Gudali zebu cattle was performed at the Wakwa Research Centre, Adamawa, Cameroon to assess the feasibility and impact of such a selective breeding programme. Fifty cows (chosen out of 129) and 2 bulls (chosen out of 10) were selected according to their greater or lesser attractiveness for the tick Amblyomma variegatum , assessed by their infestation degree (ID, ratio between individual animal infestation and mean herd infestation). Half of the animals displayed a high ID (H) and the remainder a low ID (L). The presence of a suckling calf had a significant effect on the infestation of its dam, the udder of lactating cows being significantly less infested ( P P P P  = 0.03), but the difference was much less than that observed between the dams (0.35 versus 2.30, P  = 7 × 10 −9 ). A positive correlation between dam ID and calf ID was found when only these 20 cows were taken into consideration ( r  = 0.57, P A. variegatum would be uncertain but that a more drastic selection of the breeders than that implemented in the present study may perhaps have some positive impact.

  • Attachment kinetics of the adult tick Amblyomma variegatum to cattle.
    Medical and veterinary entomology, 2006
    Co-Authors: Frédéric Stachurski
    Abstract:

    At the beginning of the 1999 rainy season, three traditional cattle herds were monitored for 48 days while grazing in the bushy savannah of southwestern Burkina Faso. Cattle in each herd were caught on several occasions each day and the attached ticks were counted. This confirmed that Amblyomma variegatum Fabricius (Acari: Ixodidae) adults picked up in the pastures mainly attach to the interdigital areas (87% of the 791 ticks captured), and reach the predilection sites later (chest and udder/inguinal area) when the animals lie down. As many females as males attached to the hosts, but the seasonal distribution was very heterogeneous, with only a few females attaching as long as the humidity rate remained low. It is suggested that this prevents eggs from being laid when conditions are not optimal for their survival and that of the larvae. Ticks attached all day but the number picked up hourly and daily varied greatly according to their density on the pasture. As a general trend, confirmed by another study carried out in 2005, the number of ticks picked up daily increased from less than one tick/animal/day, before the onset of the rainy season, to 6.5 (+/- 1.5) ticks/animal/day on average during the infestation peak, which lasted 6-8 weeks, until early or mid-July. The number then decreased to less than one tick/animal/day from the end of July onwards. The infestation on the predilection sites followed the same trend, with a daily tick burden increase of three to five A. variegatum adults, depending on herd and year, during the infestation peak.

  • Invasion of West African cattle by the tick Amblyomma variegatum.
    Medical and Veterinary Entomology, 2000
    Co-Authors: Frédéric Stachurski
    Abstract:

    Studies in Cameroon and Burkina Faso examined the invasion process of cattle by adult Amblyomma variegatum Fabricius (Acari: Ixodidae) ticks. Nearly all the ticks picked up in the pasture during grazing were found on the limb ends, near the hooves, where they temporarily attached. Then when the cattle lay down, the ticks moved from the feet towards the predilection sites, where they attached definitively. Many ticks disappeared during this displacement. All the female ticks and approximately 70% of the males were thus unable to attach to the predilection sites as long as the pioneer males had not attached and started to produce attraction-aggregation-attachment pheromones. Nevertheless, A. variegatum females and males attached to the feet in similar numbers during grazing, whether the cattle were already infested or not, indicating that stimuli originating from the hosts are powerful enough to attract both sexes. After attachment of the pioneer males, the number of ticks that successfully reached the predilection sites increased. However, even on infested animals, 40-50% of A. variegatum ticks found near the hooves after the grazing periods disappeared during the night following their capture. When moving from the temporary attachment sites towards the final ones, one-third of the ticks changed the individual host. Considering this two-stage infestation process, it is suggested that a targeted tick control, using a foot-bath, might greatly reduce cattle infestation. In particular, it could be effective in traditional herds, with animals grazing permanently during the day, lying down only once back in the night pen.

  • Variability of cattle infestation by Amblyomma variegatum and its possible utilisation for tick control.
    Revue d'elevage et de medecine veterinaire des pays tropicaux, 1993
    Co-Authors: Frédéric Stachurski
    Abstract:

    A great variability of the individual infestation by Amblyomma variegatum adults was observed on naturally infested Gudali zebus. Some of the animals (called "attractive for A. variegatum") had a tick burden 10 to 16 times higher than that of the least parasitized cattle of the herd (called "non-attractive"). Ranking of the animals based on A. variegatum infestation was correlated for successive tick counts. Experiments were designed to determine if the "non-attractive" cattle remained lightly infested when the "attractive" ones are removed from the herd. When these two types of cattle grazed separately, it was observed that the "non-attractive" animals had a lower tick burden and that their infestation occurred more slowly than that of the "attractive" ones. The difference between the two groups was nevertheless smaller than that existing when the animals were in the same herd. The selection of the "non-attractive" cattle, on which a tick control programme should not exclusively be based, could however be used as a component of a tick control strategy, if this characteristic is hereditary. An experiment in progress will study the question.

Patrick M. Guerin - One of the best experts on this subject based on the ideXlab platform.

  • Perception of breath components by the tropical bont tick, Amblyomma variegatum Fabricius (Ixodidae)
    Journal of Comparative Physiology A, 1992
    Co-Authors: Pascal Steullet, Patrick M. Guerin
    Abstract:

    Wall-pore olfactory sensilla located in the capsule of Haller's organ on the tarsus of Amblyomma variegatum ticks bear cells responding to vertebrate breath: one of these sensilla contains a CO_2-excited receptor and a second sensillum has a CO_2- inhibited receptor. Each of these antagonistic CO_2-receptors, which display typical phasic-tonic responses, monitors a different CO_2-concentration range. The CO_2-inhibited receptor is very sensitive to small concentration changes between 0 and ca. 0.2%, but variations of 0.01% around ambient (ca. 0.04%) induce the strongest frequency modulation of this receptor. An increase of just 0.001–0.002% (10–20 ppm) above a zero CO_2-level already inhibits this receptor. By contrast, the CO_2-excited receptor is not so sensitive to small CO_2 shifts around ambient, but best monitors changes in CO_2 concentrations above 0.1%. This receptor is characterized by a steep dose-response curve and a fast inactivation even at high CO_2-concentrations (>2%). In a wind-tunnel, Amblyomma variegatum is activated from the resting state and attracted by CO_2 concentrations of 0.04 to ca. 1%, which corresponds to the sensitivity range of its CO_2-receptors. The task of perceiving the whole concentration range to which this tick is attracted would thus appear to be divided between two receptors, one sensitive to small changes around ambient and the other sensitive to the higher concentrations normally encountered when approaching a vertebrate host.

  • Perception of breath components by the tropical bont tick, Amblyomma variegatum Fabricius (Ixodidae)
    Journal of Comparative Physiology A, 1992
    Co-Authors: Pascal Steullet, Patrick M. Guerin
    Abstract:

    Wall-pore sensilla in the capsule of Haller's organ on foreleg tarsi of the tick, Amblyomma variegatum , show multicellular responses upon stimulation with human and bovine breath. Filtering breath through charcoal removes the stimulant for some of these receptors. Analysis by gas chromatography coupled with olfactory sensillum electrophysiological recordings indicates that an ethanol extract of the breath components trapped on charcoal contains a major stimulant eluting at the same retention time as H_2S. Two types of H_2S-sensitive receptors have been identified. They are housed in separate sensilla, and are called sulfide-receptor 1 and 2. Although, both receptor types are characterized by a high sensitivity to H_2S with an estimated threshold of ca. 0.1 ppb and a response range covering 5–6 log orders of magnitude, their overall response to sulfides and mercaptans is nevertheless dissimilar. The type 1 receptor fires slightly more upon stimulations with H_2S than type 2, whereas ethylmercaptan induces a stronger response from type 2, and dimethyl sulfide activates only receptor 2. In a bioassay, H_2S tested at concentrations of ca. 0.02 ppm and 1 ppm equally arouses 60% of resting ticks. Two-thirds of these ticks quest the air with their first pair of legs, and the remainder start active search. By contrast, H_2S at ca. l ppm in a mixture with CO_2 severely diminishes the locomotor stimulating effect of CO_2.

  • Perception of breath components by the tropical bont tick, Amblyomma variegatum fabricius (Ixodidae). I : CO2-excited and CO2-inhibited receptors
    Journal of comparative physiology. A Sensory neural and behavioral physiology, 1992
    Co-Authors: Pascal Steullet, Patrick M. Guerin
    Abstract:

    Wall-pore olfactory sensilla located in the capsule of Haller's organ on the tarsus of Amblyomma variegatum ticks bear cells responding to vertebrate breath: one of these sensilla contains a CO2-excited receptor and a second sensillum has a CO2- inhibited receptor. Each of these antagonistic CO2-receptors, which display typical phasic-tonic responses, monitors a different CO2-concentration range. The CO2-inhibited receptor is very sensitive to small concentration changes between 0 and ca. 0.2%, but variations of 0.01% around ambient (ca. 0.04%) induce the strongest frequency modulation of this receptor. An increase of just 0.001–0.002% (10–20 ppm) above a zero CO2-level already inhibits this receptor. By contrast, the CO2-excited receptor is not so sensitive to small CO2 shifts around ambient, but best monitors changes in CO2 concentrations above 0.1%. This receptor is characterized by a steep dose-response curve and a fast inactivation even at high CO2-concentrations (>2%). In a wind-tunnel, Amblyomma variegatum is activated from the resting state and attracted by CO2 concentrations of 0.04 to ca. 1%, which corresponds to the sensitivity range of its CO2-receptors. The task of perceiving the whole concentration range to which this tick is attracted would thus appear to be divided between two receptors, one sensitive to small changes around ambient and the other sensitive to the higher concentrations normally encountered when approaching a vertebrate host.