1st Place: D3019: Spatiotemporal variation in black fly (Simulium sp.) species during and after a vesicular stomatitis virus outbreak in southern New Mexico

Vesicular stomatitis virus (VSV), a vector-borne pathogen of livestock, emerges periodically in the western United States. In New Mexico (NM) most cases occur close to the Rio Grande after dams are opened, implicating black flies (Simulium sp.) as a vector. In 2020, VS cases were reported in NM from April to May. The brevity of VSV circulation in NM is puzzling, as our 2020 surveillance showed that black fly abundance remained high from April to August. We hypothesize that VSV transmission depends on the abundance of key black fly species rather than total black fly abundance. To test this, we randomly sub-sampled individual black flies collected along the Rio Grande during the outbreak and post-outbreak period from traps placed upstream or downstream of Leasburg dam; river flows are substantially higher upstream . DNA barcoding revealed four species: S. meridionale (n= 106), S. mediovittatum (n=39), S. robynae (n=21), and S. griseum/notatum (n=1); the latter was excluded from analysis. Relative abundance of S. robynae was significantly higher and relative abundance of S. mediovittatum was significantly lower downstream of the dam (chi-squared = 20.8, p= < 0.0001), where the majority of VS cases were detected. Sample size for the post-outbreak period is currently too small for statistical analysis, however differences in relative abundance of S. robynae between outbreak and post-outbreak periods upstream (0% vs. 0%, respectively) and downstream (21.4% vs. 0%, respectively) of the dam suggest that the spatiotemporal dynamics of particular Simulium species may shape VSV transmission.