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.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.

Human biting mosquitoes and implications for West Nile virus transmission.

BACKGROUND: West Nile virus (WNV), primarily vectored by mosquitoes of the genus Culex, is the most important mosquito-borne pathogen in North America, having infected thousands of humans and countless wildlife since its arrival in the USA in 1999. In locations with dedicated mosquito control programs, surveillance methods often rely on frequent testing of mosquitoes collected in a network of gravid traps (GTs) and CO2-baited light traps (LTs). Traps specifically targeting oviposition-seeking (e.g. GTs) and host-seeking (e.g. LTs) mosquitoes are vulnerable to trap bias, and captured specimens are often damaged, making morphological identification difficult. METHODS: This study leverages an alternative mosquito collection method, the human landing catch (HLC), as a means to compare sampling of potential WNV vectors to traditional trapping methods. Human collectors exposed one limb for 15 min at crepuscular periods (5:00-8:30 am and 6:00-9:30 pm daily, the time when Culex species are most actively host-seeking) at each of 55 study sites in suburban Chicago, Illinois, for two summers (2018 and 2019). RESULTS: A total of 223 human-seeking mosquitoes were caught by HLC, of which 46 (20.6%) were mosquitoes of genus Culex. Of these 46 collected Culex specimens, 34 (73.9%) were Cx. salinarius, a potential WNV vector species not thought to be highly abundant in upper Midwest USA. Per trapping effort, GTs and LTs collected > 7.5-fold the number of individual Culex specimens than HLC efforts. CONCLUSIONS: The less commonly used HLC method provides important insight into the complement of human-biting mosquitoes in a region with consistent WNV epidemics. This study underscores the value of the HLC collection method as a complementary tool for surveillance to aid in WNV vector species characterization. However, given the added risk to the collector, novel mitigation methods or alternative approaches must be explored to incorporate HLC collections safely and strategically into control programs.

Paved Paradise: Belowground Parking Structures Sustain Urban Mosquito Populations in Washington, DC.

After notification of mosquitoes within federal buildings in Washington, DC, we surveyed belowground levels of nearby parking structures for mosquitoes and standing water in the summer months of 2018 and 2019. Aedes aegypti, Ae. albopictus, and members of the Culex pipiens Assemblage were found. Genotyping revealed pipiens, molestus, and quinquefasciatus ancestry among Cx. pipiens Assemblage mosquitoes, and allele frequency comparisons indicated a stable, resident population. Winter and spring aboveground temperatures ranged from -11°C to 35°C, while belowground temperatures never dropped below 5°C or exceeded 30°C, and winter temperatures were significantly higher belowground compared with aboveground. Moderated winter conditions suggest that belowground urban structures could act as refugia for warmer-climate species, like Ae. aegypti and Cx. quinquefasciatus, allowing them to overcome assumed thermal barriers. Surveys of parking structures should be incorporated into integrated vector management programs in urban areas.

Mulching as a cultural control strategy for Drosophila suzukii in blueberry.

BACKGROUND: Fruit growers largely depend on chemical control to reduce populations of the economically damaging invasive fly, Drosophila suzukii (Matsumura). Drosophila suzukii is susceptible to high temperatures and low humidity; therefore, it may be possible to implement cultural control practices that create microclimates unfavorable for its development and survival. In addition to other fruit production benefits, in-row mulches may impede the development of D. suzukii immatures when larvae leave the fruit to pupate in the soil. This study compared the effects of different mulches (black polypropylene fabric weedmats, sawdust, and wood chips) on temperature and relative humidity (RH), and on adult emergence of D. suzukii from larvae in blueberries and pupae, both above and below the ground surface in blueberry plantings (Vaccinium corymbosum L.). RESULTS: Across regions, both lower larval survival and longer periods with high suboptimal temperatures occurred above the ground in comparison to buried below the ground, regardless of mulch type. Fewer D. suzukii adults emerged from larvae on weedmat mulch at one site, but there was no effect of mulch type on temperature, RH, or D. suzukii emergence at most sites. The relationships between temperature, RH, and the emergence of adults from larvae and pupae varied by region. Natural infestation by D. suzukii in blueberries was lower over weedmat compared to wood-based mulches at one site. Greenhouse experiments showed that larvae burrowed to pupate underneath sawdust mulch, but were unable to pupate underneath a weedmat mulch. CONCLUSIONS: Although weedmats may not modify temperatures or RH enough to consistently affect D. suzukii emergence, they can reduce field suitability for D. suzukii by providing a barrier that prevents larvae from reaching favorable pupation microhabitats underground. © 2019 Society of Chemical Industry.