Treatment of horses with cypermethrin against the biting flies Culicoides nubeculosus, Aedes aegypti and Culex quinquefasciatus E. Papadopoulos a, *, M. Rowlinson b , D. Bartram c , S. Carpenter d , P. Mellor d , R. Wall b a Laboratory of Parasitology and Parasitic Diseases, Faculty of Veterinary Medicine, Aristotle University of Thessaloniki, University Campus, 54120 Thessaloniki, Greece b Veterinary Parasitology & Ecology Group, School of Biological Sciences, University of Bristol, UK c Fort Dodge Animal Health, Southampton, UK d Institute for Animal Health, Pirbright, Woking, Surrey, UK 1. Introduction The blood-feeding activity of biting flies has a significant detrimental effect on horses worldwide, both as a result of the hypersensitivity reactions they can induce and in their role in the transmission of pathogens. Culicoides biting midges (Diptera: Ceratopogonidae), are among the most important groups in this regard and have been implicated in both roles. These insects can occur in extremely large numbers on horses and their bites have been linked to an immediate-type hypersensitivity reac- tion which causes a chronic skin disease, known colloqui- ally as ‘sweet-itch’ (Mellor and McCaig, 1974; Anderson et al., 1991). Clinical signs of sweet-itch include pruritus, crusting and alopecia of the face, ears, withers, mane, rump and tail and, lesions are exacerbated by self-trauma and scratching which often results in hyperpigmentation and skin thickening. This is one of the most common allergic skin diseases recorded in horses and the tendency to develop a hypersensitivity reaction appears to have a Veterinary Parasitology 169 (2010) 165–171 ARTICLE INFO Article history: Received 19 May 2009 Received in revised form 1 December 2009 Accepted 16 December 2009 Keywords: Biting flies Horses Midge Mosquito Insecticide Pyrethroid ABSTRACT An in vitro assay was used to assess the efficacy of the proprietary pyrethroid insecticide cypermethrin applied to horses (Deosect spray, 5.0%, w/v Fort Dodge Animal Health) against the biting midge Culicoides nubeculosus (Meigen) (Diptera: Ceratopogonidae) and the mosquitoes Aedes aegypti Linneaus and Culex quinquefasciatus Say (Diptera: Culicidae). Hair was collected from the back, belly and legs of the horses immediately prior to treatment and 7, 14, 21, 28 and 35 days after treatment, and also from untreated controls. In laboratory assays groups of 10 adult female C. nubeculosus, Ae. aegypti or C. quinquefasciatus were exposed to 0.5 g of hair for 3 min. In all cases, little or no mortality was observed in insects kept in contact with the pre-treatment samples or the untreated controls. With post-treatment samples for C. nubeculosus, mortality was close to 80% 7 days after treatment and then declined gradually; mean mortality was still at around 50% for hair collected 35 days after treatment. In general, Ae. aegypti and C. quinquefasciatus appeared to be less susceptible to cypermethrin than C. nubeculosus and the attenuation of the toxic effect declined more quickly with time after treatment. There were differences in the toxicity of hair from different body regions, with hair from the back consistently inducing the highest mortality and hair from the legs the lowest; this effect was more pronounced for C. nubeculosus than Ae. aegypti or C. quinquefasciatus. The results demonstrate the potential for topical insecticide treatment to offer protection to horses against biting flies; but highlight the major differences that exist in susceptibility between different insect species. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +30 2310 999926; fax: +30 2310 999947. E-mail address: eliaspap@vet.auth.gr (E. Papadopoulos). Contents lists available at ScienceDirect Veterinary Parasitology journal homepage: www.elsevier.com/locate/vetpar 0304-4017/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.vetpar.2009.12.023