Abstract
BackgroundCulicoides biting midges are biological vectors of internationally important arboviruses of livestock and equines. Insecticides are often employed against Culicoides as a part of vector control measures, but systematic assessments of their efficacy have rarely been attempted. The objective of the present study is to determine baseline susceptibility of multiple Culicoides vector species and populations in Europe and Africa to the most commonly used insecticide active ingredients. Six active ingredients are tested: three that are based on synthetic pyrethroids (alpha-cypermethrin, deltamethrin and permethrin) and three on organophosphates (phoxim, diazinon and chlorpyrifos-methyl).MethodsSusceptibility tests were conducted on 29,064 field-collected individuals of Culicoides obsoletus Meigen, Culicoides imicola Kieffer and a laboratory-reared Culicoides nubeculosus Meigen strain using a modified World Health Organization assay. Populations of Culicoides were tested from seven locations in four different countries (France, Spain, Senegal and South Africa) and at least four concentrations of laboratory grade active ingredients were assessed for each population.ResultsThe study revealed that insecticide susceptibility varied at both a species and population level, but that broad conclusions could be drawn regarding the efficacy of active ingredients. Synthetic pyrethroid insecticides were found to inflict greater mortality than organophosphate active ingredients and the colony strain of C. nubeculosus was significantly more susceptible than field populations. Among the synthetic pyrethroids, deltamethrin was found to be the most toxic active ingredient for all species and populations.ConclusionsThe data presented represent the first parallel and systematic assessment of Culicoides insecticide susceptibility across several countries. As such, they are an important baseline reference to monitor the susceptibility status of Culicoides to current insecticides and also to assess the toxicity of new active ingredients with practical implications for vector control strategies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-1042-8) contains supplementary material, which is available to authorized users.
Highlights
Culicoides biting midges are biological vectors of internationally important arboviruses of livestock and equines
This study aims to assess the susceptibility of multiple populations of Culicoides species in different countries to the most frequently used insecticide active ingredients in Europe (SP: alpha-cypermethrin, deltamethrin and permethrin; OP: diazinon/dimpylate and phoxim) and Africa/Latin America (OP: chlorpyrifosmethyl)
Amongst the 4,973 individuals from Obsoletus group collected in Corrèze, France; 4,815 (96.8 %) were identified as C. obsoletus, 149 (3.0 %) as C. scoticus and 9 (0.2 %) were unidentified; from the 543 individuals collected in Mallorca Island, Spain, 513 (94.5 %) were identified as C. obsoletus, 3 (0.5 %) as C. scoticus and 27 (5.0 %) were not identified
Summary
Culicoides biting midges are biological vectors of internationally important arboviruses of livestock and equines. Culicoides Latreille (Diptera: Ceratopogonidae) are small haematophagous insects implicated worldwide as primary biological vectors of arboviruses causing important diseases of livestock [1]. These arboviruses include bluetongue (BTV), African horse sickness (AHSV), epizootic haemorrhagic disease (EHDV) and Schmallenberg (SBV) viruses [2]. In attempts to control Culicoides-borne arboviruses such as BTV and AHSV outside of their endemic range, compulsory vaccination campaigns and livestock movement restrictions are usually employed as the most effective way of controlling outbreaks [8]. The use of insecticide residual spraying within stables and during transport when livestock is moved outside a restricted movement zone has been recommended in protecting animals with high economic value (e.g. prize rams and racehorses). Additional physical measures have been suggested to reduce Culicoides populations such as the mechanical removal and/or reduction of larval breeding sites on farms and housing livestock during periods of high Culicoides activity [9]
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