Spatiotemporal organization of cryptic North American Culex species along an urbanization gradient

Landscape heterogeneity creates diverse habitat and resources for mosquito
vectors of disease. A consequence may be varied distribution and abundance
of vector species over space and time dependent on niche requirements. We
tested the hypothesis that landscape heterogeneity driven by urbanization
influences the distribution and relative abundance of Culex pipiens , Cx.
restuans, and Cx. quinquefasciatus, three vectors of West Nile virus (WNv)
in the eastern North American landscape. We collected 9,803 cryptic Culex
from urban, suburban, and rural sites in metropolitan Washington, District
of Columbia, during the months of June-October, 2019-2021. In 2021, we
also collected mosquitoes in April and May to measure early-season
abundance and distribution. Molecular techniques were used to identify a
subset of collected Culex to species (n = 2,461). Ecological correlates of
the spatiotemporal distribution of these cryptic Culex were examined using
constrained and unconstrained ordination. Seasonality was not associated
with Culex community composition in June-October over three years but
introducing April and May data revealed seasonal shifts in community
composition in the final year of our study. Culex pipiens were dominant
across site types, while Cx. quinquefasciatus were associated with urban
environments, and Cx. restuans were associated with rural and suburban
sites. All three species rarely coexisted. Synthesis and applications: Our
work demonstrates that human-mediated land-use changes influence the
distribution and relative abundance of Culex vectors of WNv, even on fine
geospatial scales. Site classification, percent impervious surface,
distance to city center, and longitude predicted Culex community
composition. We documented active Culex months before vector surveillance
typically commences in this region, with Culex restuans being most
abundant during April and May. Active suppression of Cx. restuans in April
and May could reduce early enzootic transmission, delay the seasonal
spread of WNv, and thereby reduce overall WNv burden. By June, the highest
risk of epizootic spillover of WNv to human hosts may be in suburban areas
with high human population density and mixed Culex  assemblages
that can transmit WNv between birds and humans. Focusing management
efforts there may further reduce human disease burden.