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Abstract. Equine encephalosis virus (EEV) is widespread and prevalent in southern Africa. In this study, the oral susceptibility of Culicoides (Avaritia) imicola Kieffer (Diptera: Ceratopogonidae) to EEV was confirmed. In addition, C. (A.) bolitinos Meiswinkel, collected in the high-lying eastern Free State, South Africa, was systemically infected with the Bryanston serotype of EEV after feeding through a membrane on artificially infected equine blood containing 4.7 log 10 PFU/mL of EEV. The mean infectivity of Bryanston virus in C. bolitinos increased from 1.2 log 10 PFU/midge, in midges assayed for virus immediately after feeding on the blood-virus mixture, to 3.1 log 10 PFU/midge in midges assayed after 10 days' incubation at 23.5 C. Elevated virus infectivity titres, found in individual infected C. bolitinos, suggested that this Culicoides species is a vector of EEV. This bovine dung-breeding Culicoides species may play an important role in transmitting EEV in the cooler parts of southern Africa, where it can be the most abundant Culicoides species collected near livestock. In the present study the prevalence of infection obtained for C. bolitinos (2.2%) with the Bryanston serotype of EEV was significantly lower than that of C. imicola (18.4%). After incubation, the Bryanston serotype of EEV was also isolated from one of 110 C. onderstepoortensis Fiedler assayed. However, the virus titre in this midge was 1.2 log 10 PFU/ midge, which is not different from the titre that would be expected immediately after feeding on the blood-virus mixture. Culicoides species that survived the incubation period and that were negative for the presence of Bryanston virus were C. magnus ColacË o (96), C. bedfordi Ingram & Macfie (95) and C. pycnostictus Ingram & Macfie (45).

Awareness of all potential vectors of the viruses of bluetongue and African horse sickness is crucial for the implementation of integrated control measures, risk analysis and disease manage­ment. The primary monitoring tools used for the collection of Culicoides midges are various models of suction light traps. In order to facilitate comparison of data between laboratories, the efficiency of the Onderstepoort, Rieb, mini-CDC, Pirbright and BG-sentinel, used at present and during the past in Europe, was compared in the field in South Africa. In a separate series of comparisons, the influence of trap height, the presence of hosts and the addition of octenol to the trap on species composition and number of Culicoides midges collected were determined. Comparisons were done in an appropriate number of replicates of a randomized Latin square design. The Onderstepoort trap collected significantly more Culicoides midges in summer and in winter than the other traps. It was found that relatively small vari­ations in the height at which the trap is deployed can have a sig­nificant influence on the number of midges collected. Although these results seem to indicate a height preference for C. imicola it needs to be determined to what extent environmental fac­tors, the presence of nearby structures, other light sources and hosts near the trap might have on the height at which Culicoides midges will fly. Significant differences were found in the num­ber of Culicoides and especially C. imicola numbers collected at various distances from host animals. Statistically significant higher numbers and proportions of C. imicola were collected immediately next to the animals compare to collections made 5 to 30 m away from animals. The addition of 1-octen-3-ol (9.1 mg/h) and 4-methylphenol (15.5 mg/h) did not have any significant influence on the number of Culicoides collected with the Onderstepoort trap. Relatively small but statistically signifi­cant differences were found in the species composition, parous rates, sex ratios as well as the ratio of Culicoides midges to other insects, as determined by the different collection regimes. Despite a great variety of factors that can influence light trap results, it remains the most reliable and practical way to deter­mine species richness and abundance in an area. The results of this study highlighted a few factors that may influence the num­bers of Culicoides midges collected and the problems involved in the reliable comparison of light trap data between different collection sites. It emphasized the need for the standardization of techniques for measuring the variables of vectorial capacity