Assessment of vector/host contact: comparison of animal-baited traps and UV-light/suction trap for collecting Culicoides biting midges (Diptera: Ceratopogonidae), vectors of Orbiviruses

<p>Abstract</p> <p>Background</p> <p>The emergence and massive spread of bluetongue in Western Europe during 2006-2008 had disastrous consequences for sheep and cattle production and confirmed the ability of Palaearctic <it>Culicoides </it>(Diptera: Ceratopogonidae) to transmit the virus. Some aspects of <it>Culicoides </it>ecology, especially host-seeking and feeding behaviors, remain insufficiently described due to the difficulty of collecting them directly on a bait animal, the most reliable method to evaluate biting rates.</p> <p>Our aim was to compare typical animal-baited traps (drop trap and direct aspiration) to both a new sticky cover trap and a UV-light/suction trap (the most commonly used method to collect <it>Culicoides</it>).</p> <p>Methods/results</p> <p>Collections were made from 1.45 hours before sunset to 1.45 hours after sunset in June/July 2009 at an experimental sheep farm (INRA, Nouzilly, Western France), with 3 replicates of a 4 sites × 4 traps randomized Latin square using one sheep per site. Collected <it>Culicoides </it>individuals were sorted morphologically to species, sex and physiological stages for females. Sibling species were identified using a molecular assay. A total of 534 <it>Culicoides </it>belonging to 17 species was collected. Abundance was maximal in the drop trap (232 females and 4 males from 10 species) whereas the diversity was the highest in the UV-light/suction trap (136 females and 5 males from 15 species). Significant between-trap differences abundance and parity rates were observed.</p> <p>Conclusions</p> <p>Only the direct aspiration collected exclusively host-seeking females, despite a concern that human manipulation may influence estimation of the biting rate. The sticky cover trap assessed accurately the biting rate of abundant species even if it might act as an interception trap. The drop trap collected the highest abundance of <it>Culicoides </it>and may have caught individuals not attracted by sheep but by its structure. Finally, abundances obtained using the UV-light/suction trap did not estimate accurately <it>Culicoides </it>biting rate.</p

The tree that hides the forest: cryptic diversity and phylogenetic relationships in the Palaearctic vector Obsoletus/Scoticus Complex (Diptera: Ceratopogonidae) at the European level

Abstract Background Culicoides obsoletus is an abundant and widely distributed Holarctic biting midge species, involved in the transmission of bluetongue virus (BTV) and Schmallenberg virus (SBV) to wild and domestic ruminants. Females of this vector species are often reported jointly with two morphologically very close species, C. scoticus and C. montanus, forming the Obsoletus/Scoticus Complex. Recently, cryptic diversity within C. obsoletus was reported in geographically distant sites. Clear delineation of species and characterization of genetic variability is mandatory to revise their taxonomic status and assess the vector role of each taxonomic entity. Our objectives were to characterize and map the cryptic diversity within the Obsoletus/Scoticus Complex. Methods Portion of the cox1 mitochondrial gene of 3763 individuals belonging to the Obsoletus/Scoticus Complex was sequenced. Populations from 20 countries along a Palaearctic Mediterranean transect covering Scandinavia to Canary islands (North to South) and Canary islands to Turkey (West to East) were included. Genetic diversity based on cox1 barcoding was supported by 16S rDNA mitochondrial gene sequences and a gene coding for ribosomal 28S rDNA. Species delimitation using a multi-marker methodology was used to revise the current taxonomic scheme of the Obsoletus/Scoticus Complex. Results Our analysis showed the existence of three phylogenetic clades (C. obsoletus clade O2, C. obsoletus clade dark and one not yet named and identified) within C. obsoletus. These analyses also revealed two intra-specific clades within C. scoticus and raised questions about the taxonomic status of C. montanus. Conclusions To our knowledge, our study provides the first genetic characterization of the Obsoletus/Scoticus Complex on a large geographical scale and allows a revision of the current taxonomic classification for an important group of vector species of livestock viruses in the Palaearctic region

Correction to: The tree that hides the forest : cryptic diversity and phylogenetic relationships in the Palaearctic vector Obsoletus/Scoticus complex (Diptera: Ceratopogonidae) at the European level

An amendment to this paper has been published and can be accessed via the original article

The tree that hides the forest: Cryptic diversity and phylogenetic relationships in the Palaearctic vector Obsoletus/Scoticus Complex (Diptera: Ceratopogonidae) at the European level

Background: Culicoides obsoletus is an abundant and widely distributed Holarctic biting midge species, involved in the transmission of bluetongue virus (BTV) and Schmallenberg virus (SBV) to wild and domestic ruminants. Females of this vector species are often reported jointly with two morphologically very close species, C. scoticus and C. montanus, forming the Obsoletus/Scoticus Complex. Recently, cryptic diversity within C. obsoletus was reported in geographically distant sites. Clear delineation of species and characterization of genetic variability is mandatory to revise their taxonomic status and assess the vector role of each taxonomic entity. Our objectives were to characterize and map the cryptic diversity within the Obsoletus/Scoticus Complex. Methods: Portion of the cox1 mitochondrial gene of 3763 individuals belonging to the Obsoletus/Scoticus Complex was sequenced. Populations from 20 countries along a Palaearctic Mediterranean transect covering Scandinavia to Canary islands (North to South) and Canary islands to Turkey (West to East) were included. Genetic diversity based on cox1 barcoding was supported by 16S rDNA mitochondrial gene sequences and a gene coding for ribosomal 28S rDNA. Species delimitation using a multi-marker methodology was used to revise the current taxonomic scheme of the Obsoletus/Scoticus Complex. Results: Our analysis showed the existence of three phylogenetic clades (C. obsoletus clade O2, C. obsoletus clade dark and one not yet named and identified) within C. obsoletus. These analyses also revealed two intra-specific clades within C. scoticus and raised questions about the taxonomic status of C. montanus. Conclusions: To our knowledge, our study provides the first genetic characterization of the Obsoletus/Scoticus Complex on a large geographical scale and allows a revision of the current taxonomic classification for an important group of vector species of livestock viruses in the Palaearctic region.[Figure not available: See fulltext.

Action des radicaux OH• ou [math] sur la N-acétylcystéine

L'action des radicaux OH• ou [math] sur la N-acétylcystéine (RSH) a été étudiée en solution aqueuse à pH 7 par radiolyse à l'état stationnaire. Les rendements initiaux de disparition de RSH ont été déterminés pour une gamme de concentration de RSH comprise entre 3 x 10-5 et 10-3mol. l-1. Les radicaux OH• ou [math] réagissent stoechiométriquement avec la N- acétylcystéine. Un mécanisme réactionnel est proposé

Double chambre d'ionisation alpha avec passeur d'échantillons

This device is designed to measure successively the alpha activity of eight samples, two of them being counted simultaneously.Cet ensemble permet de mesurer successivement l'activité alpha de huit sources, deux d'entre elles étant comptées simultanément

Double chambre d'ionisation alpha avec passeur d'échantillons

Cet ensemble permet de mesurer successivement l'activité alpha de huit sources, deux d'entre elles étant comptées simultanément

Inactivation de la catalase par des radicaux libres dérivés de l’oxygène par radiolyse γ

L’inactivation de la catalase 10-5mol.l-1 par les radicaux libres OH• ou OH•/[math] à pH 7.4, a été étudiée par radiolyse γ (doses de 0 à 9000 Gy). Les valeurs maximales des rendements initiaux d’inactivation sont : G [math] = (1,25 ± 0,25).10-8 mol.J-1 et G [math] = (1,4 ± 0,2).10-8 mol.J-1 (valeurs très inférieures à celles des radicaux produits par radiolyse). Les courbes d’inactivation, en fonction de la dose d’irradiation, sont biphasiques: rapides (de 0 à ~ 500 Gy) puis lentes (de ~ 500 à 9000 Gy). L’addition d’eau oxygénée au début des irradiations diminue le rendement d’inactivation par les radicaux OH•, ce qui pourrait être dû à une moindre sensibilité du composé-I (catalase-H2O2) vis-à-vis de ces radicaux

Effect of pH on the system I

The reaction mechanism involved in the iodide anion oxidation initiated by hydrogen peroxide is relatively well known although several elementary steps are not well defined. Particularly, the two reverse steps of iodine hydrolysis and the reaction of hydrogen peroxide with hypoiodous acid had to be determined. New experimental kinetic data have been obtained concerning I-/H2O2 ([I-]0 = 10-2 to 5 x 10-1M, [H2O2]0 = 0.9 x 10-5 to 7.4 x 10-4 M) at different pH (4.7, 7,8 and 9), and I-/I3-/H2O2 ([I-]0= 10-1M, [H2O1]0 = 1.1 to 7.4 x 10-4M, [I3-]0 = 3 x 10-4M) at pH 8. According to these data, we have established(1) the important reactivity of the basic forms (HO2- and/or IO-), even at pH values less than the corresponding pKa's (10.6- 11.2), (2) that the two reverse reactions of iodine hydrolysis equilibrium are competitive with the other usual reations of the mechanism (this competitivity had not before been taken into consideration). By computation of all the experimental curves we have determined the following rate constants: k(I2+OH-) = (7 ± 0.5) x 107 M-1 s-1, k(I-+IOH) = (7.5 ± 0.5) x 105 M-1 s-1 (K(I2 hydrolysis) = 93), and k(IOH+HO2-) = (1 ± 0.2) x 108 M-1 S-1