Fiona F. Hunter

A population of Aedes ( Stegomyia ) albopictus (Skuse) (Diptera: Culicidae), a vector of chikungunya, dengue, yellow fever, and Zika and West Nile viruses, has been detected in Windsor, Ontario, Canada from 2016 onwards. Here, we describe its seasonal distribution, as well as the various aquatic habitats from which this species was collected and its larval co‐habitation. We collected immatures from tires, treeholes, extruded polystyrene foam containers, discarded plastic cups, old recycling bins and oviposition traps. Aedes albopictus larvae were collected with Aedes japonicus (Theobald), Anopheles punctipennis (Say), Culex pipiens Linnaeus, Ochlerotatus hendersoni (Cockerell), Ochlerotatus triseriatus (Say) and Orthopodomyia signifera (Coquillett). Adult female and male specimens were collected from Biogents sentinel traps (Biogents AG, Regensburg, Germany), as well as Centers for Disease Control and Prevention miniature light traps (CDC, Atlanta, GA, U.S.A.), and also as they alighted on the investigators. Peak adult collections occurred in September during epidemiological week 37. We also collected Aedes ( Stegomyia ) aegypti (Linnaeus), a new record for Canada, in 2016 and from two new collection sites in 2017. The 2017 collections were 3.5 km north and 19.4 km south of the index site. The present study adds to the increasing number of studies reporting range expansions of these mosquito species.

The purpose of this study was to establish geospatial and seasonal distributions of West Nile virus vectors in southern Ontario, Canada using historical surveillance data from 2002 to 2014. We set out to produce mosquito abundance prediction surfaces for each of Ontario’s thirteen West Nile virus vectors. We also set out to determine whether elevation and proximity to conservation areas and provincial parks, wetlands, and population centres could be used to improve our model. Our results indicated that the data sets for Anopheles quadrimaculatus, Anopheles punctipennis, Anopheles walkeri, Culex salinarius, Culex tarsalis, Ochlerotatus stimulans, and Ochlerotatus triseriatus were not suitable for geospatial modelling because they are randomly distributed throughout Ontario. Spatial prediction surfaces were created for Aedes japonicus and proximity to wetlands, Aedes vexans and proximity to population centres, Culex pipiens/restuans and proximity to population centres, Ochlerotatus canadensis and elevation, and Ochlerotatus trivittatus and proximity to population centres using kriging. Seasonal distributions are presented for all thirteen species. We have identified both when and where vector species are most abundant in southern Ontario. These data have the potential to contribute to a more efficient and focused larvicide program and West Nile virus awareness campaigns.

West Nile Virus (WNV) first arrived in Ontario, Canada in 2001 and has since spread throughout most of the province, causing disease in humans. The provincial government established a province-wide surveillance program to monitor WNV transmission throughout the 36 regional health units. Here we have acquired records of WNV human and mosquito surveillance from 2002 to 2013 to describe seasonal and geographic trends in WNV activity in southern Ontario. Additionally, we obtained climate data from seven municipalities to investigate how temperature and precipitation affect WNV transmission dynamics. We identified a strong quadratic relationship between the number of confirmed human cases and positive Culex mosquito pools recorded at the end of each year (R² = 0.9783, p < 0.001). Using Spearman rank correlation tests, we identified that the minimum infection rate of Culex pipiens/restuans pools are the strongest predictor of human cases at a 1 week lag period. We also identified positive correlations between minimum infection rates, temperature, vector abundance, and cumulative precipitation. Global Moran’s I index indicates strong positive autocorrelation and clustering of positive Culex pool counts in southern Ontario. Local indicators of spatial association tests revealed a total of 44 high-high and 1 high-low trap locations (n = 680). In the current work we have identified when and where hot spots of WNV activity have occurred in southern Ontario. The municipalities surrounding the western shore of the Lake Ontario and Windsor-Essex County have the largest records of positive mosquitoes and human cases. We identified that positive mosquitoes are a strong indicator of human cases to follow in the coming weeks. An epidemic action threshold of cumulative positive Culex pools was established, allowing Ontario public health officials to predict an epidemic at epidemiological week 34 (rho = 0.90, p < 0.001). These data have the potential to contribute to more efficient larvicide programs and awareness campaigns for the public.

Linking Only Aedes aegypti with Zika Virus Has World-Wide Public Health Implications

Ceratopogonidae (Diptera) were collected on sheep farms in southern Ontario to establish whether Culicoides spp. pose a threat to the livestock industry. Specimens were collected in modified CO₂-baited Centers for Disease Control and Prevention light traps, returned to the laboratory, freeze-killed, and identified to species under a microscope. In addition to Culicoides variipennis (Coquillet), we found that Culicoides sonorensis Wirth & Jones occurred on a number of farms over a 2-yr period. These records represent a significant departure from C. sonorensis’ previously known geographical distribution. We present spatial and temporal distribution data for both species, with an emphasis on C. sonorensis. DNA sequence information is presented so that researchers lacking the necessary taxonomic skills can determine whether C. sonorensis is present in their collections. To differentiate C. sonorensis from C. variipennis, taxonomically reliable and informative traits were found in EF1α and, to a lesser extent, in ITS1, whereas the universal barcode region of cytochrome oxidase subunit 1 (CO1) was unsuitable.

Culex (Melanoconion) erraticus (Dyar and Knab) is now established in southern Ontario, Canada. This species was first discovered in 2002 during a province-wide adult mosquito surveillance program for West Nile virus. Using CO₂-baited CDC miniature light traps, a few Cx. erraticus were collected from 2002 to 2011, but the total number increased during the 2012 and 2013 seasons. The number of Ontario Public Health Units with records for Cx. erraticus has also increased since 2002, demonstrating that the geographic distribution of this species is expanding northward. Cx. erraticus is a potential arboviral bridge vector for a number of pathogens and its establishment in Ontario should be considered a potential public health concern.

We tested whether the known bird-biting mosquito, Culex pipiens Linnaeus (Diptera: Culicidae), is attracted to human hosts by placing humans at ground level (∼1.5 m) or in the forest canopy (∼5 m) in a Niagara woodlot. Modified Centers for Disease Control (CDC) miniature light traps (no light, no CO2) were placed next to the human hosts to capture the attracted mosquitoes. The human-baited traps were compared with control traps (standard CDC miniature light traps with CO2, but no light). As expected from previous research, there were more C. pipiens captured at the higher elevation than at ground level. Generally, they were attracted to control traps more than to human-baited traps at 5 m, whereas at 1.5 m there was no difference between the two trap types. As a comparison, most Aedes vexans (Meigen) mosquitoes were captured at the 1.5 m elevation but there were significantly more captured in the control traps than the human-baited traps during all periods. Because C. pipiens is attracted to humans throughout the entire season at the 1.5 m height (where they might encounter humans), it is likely that C. pipiens can serve as a bridge vector of West Nile virus (WNV). Nous avons vérifié si le moustique piqueur d'oiseaux bien connu, Culex pipiens Linnaeus (Diptera: Culicidae), est attiré par les hôtes humains au niveau du sol (∼1,5 m) et au niveau de la canopée (∼5 m) dans une terre boisée de Niagara. Nous avons placé des pièges lumineux miniatures de type CDC (Centres de contrôle des maladies), sans lumière, ni CO2, près des hôtes humains pour capturer les moustiques attirés. Les pièges avec appâts humains ont été comparés à des pièges témoins (des pièges miniatures CDC standard avec CO2, mais sans lumière). Tel que le laissaient prévoir les recherches antérieures, il y a plus de C. pipiens au point plus élevé qu'au niveau du sol. Généralement, ils sont plus attirés par les pièges témoins que par les pièges avec appât humain à 5 m, alors qu’à 1,5 m il n'y a pas de différence entre les deux types de pièges. Par comparaison, la plupart des moustiques Aedes vexans (Meigen) ont été capturés à la hauteur de 1,5 m, mais il y avait significativement plus de captures dans les pièges témoins que dans les pièges avec appât humain durant toutes les périodes. Parce que C. pipiens est attiré par les humains durant toute la saison à la hauteur de 1,5 m (là où il risque de rencontrer des humains), il est vraisemblable que C. pipiens puisse servir de vecteur-pont pour le virus du Nil occidental (WNV).

We studied Culex pipiens L. in the Niagara Region of Ontario, Canada, to establish whether or not these mosquitoes are attracted to hosts other than birds at different elevations or as the season progresses. Guinea-pigs and chickens were used as representative mammalian and avian hosts, respectively. Bait animals were placed next to modified CDC miniature light traps (no light and no CO2) hung 1.5 or 5 m above ground in a Niagara woodlot. The season was divided into three 6-week periods (early, middle, and late). Significantly more C. pipiens were captured at the 5 m than at the 1.5 m elevation. In general, chicken-baited traps were preferred over control and guinea-pig-baited traps, with one important exception: there was no significant difference among traps during the late period at 1.5 m elevation. The potential role of C. pipiens as a bridging vector of West Nile virus to humans is discussed. Nous avons étudié des Culex pipiens L. dans la région de Niagara en Ontario, Canada, afin de déterminer si ces moustiques sont attirés par des hôtes autres que des oiseaux en fonction de la hauteur et au cours de la saison. Des cobayes et des poulets ont servi d'hôtes représentatifs, respectivement des mammifères et des oiseaux. Les animaux appâts ont été placés près de pièges lumineux CDC miniatures modifiés (sans lumière, ni CO2) pendus à 1,5 et à 5 m au-dessus du sol dans une région boisée de Niagara. La saison a été divisée en trois périodes de 6 semaines (précoce, médiane et tardive). Il y a eu significativement plus de captures de C. pipiens à la hauteur de 5 m qu’à 1,5 m. En général, les pièges munis d'un poulet sont choisis de préférence aux pièges témoins et à ceux qui contiennent un cobaye, sauf qu’exceptionnellement il n’y a pas eu de différence significative entre les pièges durant la période tardive à la hauteur de 1,5 m. Le rôle de C. pipiens comme vecteur-pont potentiel du virus du Nil occidental chez les humains fait l'objet d'une discussion. [Traduit par la Rédaction]

The original Centers for Disease Control and Prevention (CDC) gravid trap, with its mesh collection bag, can cause considerable damage to the captured mosquitoes. In an effort to reduce this damage and keep costs at a minimum, we modified our existing CDC gravid traps to accept a collection cup from a CDC light trap. This modification allowed for easier transport, freezing, storage, and removal of the mosquitoes. Modifying the CDC gravid traps takes little expertise or resources and can be completed quickly.