This investigation was concerned with determining the relationships of Culicoides to poultry in Virginie while studying their role as potential vectors of infectious synovitis. In addition, a survey of Culicoides in Virginia was made to study their distribution, bionomics and life histories. The insects were trapped in the field, collected as larvae, and reared in the laboratory. Using light traps in chicken coops at Ferrum, Virginia in 1959, it was found that the following species of Culicoides were present; arboricola, crepuscularis, debilipalpis, guttipennis, haematopotus, obsoletus (most abundant), ousairani, stellifer, travisi, variipennis, venustus, and villosipennis. During the same summer, traps at Poplar Camp took many of the above species plus biguttatus and the piliferus group. That same year a single specimen of C. paraensis was taken while biting the author. Light trapping in 1960 was done at Blacksburg about three nights a week for six months. Other trapping was done at Elkton, Newport and Saltville. At Blacksburg and Elkton traps were operated both in the woods and in poultry houses. The 1960 trapping activities revealed the following species were present: arboricola, baueri, biguttatus, crepuscularis, chiopterus, debilipalpis, guttipennis, haematopotus, obsoletus, ousairani, piliferus group, snowi, spinosus, stellifer, travisi, variipennis, venustus, and villosipennis. All but chiopterus, debilipalpis, snowi, and spinosus have been taken in poultry houses. In 1960 crepuscularis was the most abundant species taken in poultry houses and travisi was the most numerous species in the woods. It was found that more Culicoides were taken in poultry houses located near a woods than in ones farther from a woods. Trapping revealed that Culicoides were most abundant at Blacksburg in June, with May being the next most favorable month. The following species were found every month: haematopotus, obsoletus, stellifer, and variipennis. All specimens were preserved in 70 per cent ethyl alcohol and latex mounted in phenol-balsam on microscope slides. Apparently the weather had little influence on the trapping results. During 1959 and 1960 larvae were collected in a number of situations, but mostly from rot hole: in trees and soft mud. Tree-hole collections produced specimens of C. arboricola, guttipennis, and namis. Mud and muddy water produced C. variipennis. The latter were extremely abundant in saline mud at Saltville, there being found as many as 2000 larvae per 500 cc. of mud. These were used in the infectious synovitis transmission experiments. The larvae were reared in pans and crocks containing their original substrate. After emergence they were held in cages fashioned from round ice cream cartons, and kept in an incubator at 75° F. and approximately 40 per cent relative humidity. Under these conditions the adults lived an average of 27.7 days after emergence with the longest time being 96 days. The adults emerged in largest numbers four to eight days after collection. In 1959 attempts were made to transmit infectious synovitis to healthy chickens by injecting them with macerated, engorge. Culicoides which had been live-trapped in poultry houses containing chickens infected with the disease. These attempts were unsuccessful. In 1960 specimens of C. variipennis were induced to feed upon chickens injected with the agent of infectious synovitis. These were later macerated at varying intervals and injected into healthy chickens. No transmission was demonstrated. It was found that the insects fed most readily on the heads of chickens when the insects were two to four days old. / Ph. D.