How do species, population and active ingredient influence insecticide susceptibility in Culicoides biting midges (Diptera: Ceratopogonidae) of veterinary importance?

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.

Insecticidal effects of deltamethrin in laboratory and field populations of Culicoides species: how effective are host-contact reduction methods in India?

“…In India, resistance could occur for the same reason in areas where intensive regimes of insecticide use are maintained against biting insects. Culicoides oxystoma is a suspected vector of BTV in India [ 4 ], and comparative studies of the other major putative vector species in this region would be useful in placing toxicity in context, particularly as they include C. imicola for which baseline data has already been collected from areas lacking sustained insecticide use [ 23 , 24 ].…”

Bluetongue: control, surveillance and safe movement of animals

“…In France,Venail et al. (, ) obtained high mortality (i.e. 100% after 1 h exposure 0.0025% deltamethrin) for either colony‐reared adults of C. nubeculosus and field‐collected adults of C. obsoletus and C. imicola to different concentrations of deltamethrin‐impregnated papers at 24 h after 1 h exposure.…”

“…The protocol basically consists on exposing adult Culicoides to insecticides-impregnated papers of different concentrations and therefore LD 50 and LD 90 could be estimated. In France, Venail et al (2011Venail et al ( , 2015 obtained high mortality (i.e. 100% after 1 h exposure 0.0025% deltamethrin) for either colony-reared adults of C. nubeculosus and field-collected adults of C. obsoletus and C. imicola to different concentrations of deltamethrinimpregnated papers at 24 h after 1 h exposure.…”

“…Several types of insecticides have been broadly tested in laboratory conditions against Culicoides in the last decade (EFSA (2008) and Table 9). In general, the great majority of works have shown a high killing effect of insecticides (usually 90-100% mortality after 1 h exposure) such as deltamethrin, cypermethrin, alphacypermethrin, lambda-cyhalothrin, fenvalerate, zeta-cypermethrin and permethrin when tested either on hair clippers (Liebisch and Liebisch, 2008;Schmahl et al, 2009a); Papadopoulos et al, 2009Papadopoulos et al, , 2010, WHO testing tubes contacting directly animal hair (Reeves et al, 2010;Venail et al, 2011Venail et al, , 2015Del Rio et al, 2014b;Onuike et al, 2015); or material substrates (see Section 3.6.2 for details) such as plates and nets (Schmahl et al, 2008). However, in some cases, interpretation and comparison among studies are difficult due to the lack of information about the efficacy, times and mode of exposure to insecticides of Culicoides in testing cages or tubes (Harrup et al, 2016).…”

“…One open question is to know if a protection up to 86% provided by pour-on insecticides would be sufficient to avoid BTV transmission or biting of BTV-infected Culicoides. According to scientific literature reviewed in this opinion, high level of efficacy of pour-on insecticides is difficult to achieve Venail et al (2011Venail et al ( , 2015 0.001% of deltamethrin and little information is available about the effect of reduction on the numbers of engorged Culicoides females in relation to BTV transmission. In fact, different methods for assessing insecticide performance may lead to different results when considering the effect on engorged females (Harrup et al, 2016).…”