World Health Organisation test applied on Culicoides: a multicentric study

The aim of this work is to organize a multicentric assay to compare susceptibilities of Culicoides populations to insecticides (i.e. C. imicola and C. obsoletus sensu stricto). The base line of the World Health Organisation test kit (WHO/VBC81.805) is to expose mosquitoes to papers impregnated with insecticides to detect the resistance of Anopheles (paludism vector) in the field. In a novel approach, the WHO test can be used on Culicoides to assess midges' susceptibility to insecticides. Information on the intrinsic susceptibilities to insecticides is required to assess correctly the existing (or new) formulations of insecticide. This multicentric assay will improve our capacity to experiment by networking and assess the population variability by comparing susceptibilities between different populations of Culicoides. Field-collected midges are trapped alive using an ultraviolet light trap (OVI model, South Africa) and replacing the collection jar with a fine mesh cage. To prevent desiccation, cages are covered with wet papers, wrapped in aluminium foil and retrieved at dawn. It is important to choose the site and period with abundant target species to improve robustness with more individuals. Experiments should be carried out in an insecticide-free environment with constant temperature and humidity, and started a few hours after collection. Insecticide-impregnated papers are rolled and fastened into the WHO kit test tube. About 30 Culicoides (approximately 20 nulliparous females) are collected and transferred to the tube. Tubes are maintained horizontally for an hour (exposure to insecticide). Mortalities are recorded 1 h and 24 h after exposure. One control is performed without insecticide to validate the test. Mortalities are analysed by probit regression to obtain LC50 and LC90 for each population. The test has to be run at least with four concentrations of insecticide, one control and four replicates with samples from the same population. Only nulliparous females are recorded. Insecticide concentrations are given in percentages (WHO standard). In this WHO test, the target species are C. imicola and C. obsoletus s.s., and the active ingredient used is deltamethrin at doses 0.005, 0.001, 0.0005 and 0.0001%. Data will be centralized and analysed by EID-Méditerranée (France), and results will be given back to the partners and published. Future studies could focus on comparing the four deltamethrin concentrations on other species and testing Culicoides susceptibility to other components. (Texte intégral

Acercamiento a la estructura y composición de la comunidad íctica arrecifal de la Isla de Malpelo, utilizando el censo visual rápido (RVC) en el mes de marzo de 2002

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Host-Seeking Activity of Bluetongue Virus Vectors: Endo/Exophagy and Circadian Rhythm of Culicoides in Western Europe

Feeding success of free-living hematophagous insects depends on their ability to be active when hosts are available and to reach places where hosts are accessible. When the hematophagous insect is a vector of pathogens, determining the components of host-seeking behavior is of primary interest for the assessment of transmission risk. Our aim was to describe endo/exophagy and circadian host-seeking activity of Palaearctic Culicoides species, which are major biting pests and arbovirus vectors, using drop traps and suction traps baited with four sheep, as bluetongue virus hosts. Collections were carried out in the field, a largely-open stable and an enclosed stable during six collection periods of 24 hours in April/May, in late June and in September/October 2010 in western France. A total of 986 Culicoides belonging to 13 species, mainly C. brunnicans and C. obsoletus, was collected on animal baits. Culicoides brunnicans was clearly exophagic, whereas C. obsoletus was able to enter stables. Culicoides brunnicans exhibited a bimodal pattern of host-seeking activity with peaks just after sunrise and sunset. Culicoides obsoletus was active before sunset in spring and autumn and after sunset in summer, thus illustrating influence of other parameters than light, especially temperature. Description of host-seeking behaviors allowed us to discuss control strategies for transmission of Culicoides-borne pathogens, such as bluetongue virus. However, practical vector-control recommendations are difficult to provide because of the variation in the degree of endophagy and time of host-seeking activity.This study was funded by CIRAD, by the Ministe`re de l’agriculture, de l’alimentation, de la peˆche, de la ruralite´ et de l’ame´nagement du terroire and by the EU FP7-HEALTH-2010-single-stage grant 261504 EDENext. This paper is catalogued by the EDENext Steering Committee as EDENext032 (http://www.edenext. eu). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding received for this study