BackgroundCulicoidesLatreille (Diptera: Ceratopogonidae) is a genus of hematophagous midges feeding on various vertebrate hosts and serving as a vector for numerous pathogens important to livestock and wildlife health. North American pathogens include bluetongue (BT) and epizootic hemorrhagic disease (EHD) viruses. Little is known aboutCulicoidesspp. distribution and abundance and species composition in Ontario, Canada, despite bordering numerous U.S. states with documentedCulicoidesspp. and BT and EHD virus activity. We sought to characterizeCulicoidesspp. distribution and abundance and to investigate whether select meteorological and ecological risk factors influenced the abundance ofCulicoides biguttatus,C. stellifer, and the subgenusAvaritiatrapped throughout southern Ontario.MethodsFrom June to October of 2017 to 2018, CDC-type LED light suction traps were placed on twelve livestock-associated sites across southern Ontario.Culicoidesspp. collected were morphologically identified to the species level when possible. Associations were examined using negative binomial regression amongC. biguttatus,C. stellifer, and subgenusAvaritiaabundance, and select factors: ambient temperature, rainfall, primary livestock species, latitude, and habitat type.ResultsIn total, 33,905Culicoidesspp. midges were collected, encompassing 14 species from seven subgenera and one species group.Culicoides sonorensiswas collected from three sites during both years. Within Ontario, the northern trapping locations had a pattern of seasonal peak abundance in August (2017) and July (2018), and the southern locations had abundance peaks in June for both years.Culicoides biguttatus,C. stellifer, and subgenusAvaritiawere significantly more abundant if ovine was the primary livestock species at trapping sites (compared to bovine).Culicoides stelliferand subgenusAvaritiawere significantly more abundant at mid- to high-temperature ranges on trap days (i.e., 17.3–20.2 and 20.3–31.0 °C compared to 9.5–17.2 °C). Additionally, subgenusAvaritiawere significantly more abundant if rainfall 4 weeks prior was between 2.7 and 20.1 mm compared to 0.0 mm and if rainfall 8 weeks prior was between 0.1 and 2.1 mm compared to 0.0 mm.ConclusionsResults from our study describeCulicoidesspp. distribution in southern Ontario, the potential for spread and maintenance of EHD and BT viruses, and concurrent health risks to livestock and wildlife in southern Ontario in reference to certain meteorological and ecological risk factors. We identified thatCulicoidesspp. are diverse in this province, and appear to be distinctly distributed spatially and temporally. The livestock species present, temperature, and rainfall appear to have an impact on the abundance ofC. biguttatus,C. stellifer, and subgenusAvaritiatrapped. These findings could help inform targeted surveillance, control measures, and the development of management guides forCulicoidesspp. and EHD and BT viruses in southern Ontario, Canada.Graphical Abstract