Duration of repellency of selected agents against Culicoides species when applied to polyester mesh

Abstract

Culicoides biting midges (Diptera: Ceratopogonidae) are of economic and veterinary significance worldwide. Of principal importance to equids in sub-Saharan Africa are Culicoides (Avaritia) imicola Kieffer and Culicoides (Avaritia) bolitinos Meiswinkel which have been implicated in the transmission of African horse sickness virus (AHSV) and equine encephalosis virus (EEV). Various species of Culicoides are associated with equine insect hypersensitivity, a common equine skin allergy. Recommended measures to prevent diseases associated with Culicoides in equids include vaccination for African horse sickness (AHS), stabling at night, meshing of stables, and application of insect repellents both to the animal and its stable environment. The effects of repellents against Culicoides on humans have been documented, with most studies reporting the repellency of compounds against that of N,N-diethyl-3-methylbenzamide (DEET). DEET is registered for human use in South Africa, whilst citronella oil and cypermethrin are included in topical ectoparasiticides registered for use on horses. The aim of this study was to determine and compare repellent efficacy of 15% DEET, 0.6% citronella oil, and 0.3% á-cyanocypermethrin against Culicoides species when applied to polyester mesh under South African conditions. The repellent efficacy against Culicoides species was compared in three 5 X 5 Latin squares (15 replicates). DEET, citronella oil or á-cyano-cypermethrin was applied to polyester meshes that were fitted to down-draught suction 220 V ultraviolet (UV) light traps which were operated overnight. A total of 107,204 Culicoides midges was collected in hourly light-trap collections made over 15 nights from five light traps operated simultaneously. Of 34 Culicoides species collected C. Imicola was the most abundant and comprised 79.1% of midges collected, followed by C. Bolitinos which comprised 5.3%. The mean number of Culicoides midges as well as the mean number of C. Imicola collected hourly with DEET was significantly (P < 0.05) lower than for all other treatments at all times except the first (19h00) and the last (06h00) sampling points. The study concluded that DEET had a significant repellent effect against Culicoides species, including C. Imicola, for all catches made from after sunset to before sunrise, when applied to polyester mesh as tested with a down-draught suction light trap. No significant repellent effect against Culicoides was found for the citronella oil or the á-cyano-cypermethrin treatments. Copyright