Modelling factors that affect the presence of larval mosquitoes (Diptera: Culicidae) in stormwater drainage systems to improve the efficacy of control programmes

Abstract

Stormwater catch basins form part of artificial drainage systems in urban areas and can provide larval habitat for mosquito vector species of West Nile virus (WNv), such as Culex pipiens Linnaeus (Diptera: Culicidae). We evaluated the impact of management techniques and targeted applications of larvicide on larval populations of this potential WNv mosquito vector species in catch basins from the Lower Mainland of Vancouver and on Vancouver Island of British Columbia, Canada. A mixed effects logistic regression model described the relationship between larval presence and larvicide treatment while controlling for other parameters. Parameter estimates showed that larvicide treatment reduced the odds of larvae presence by a factor of ,7.23. The model also revealed relationships between larval presence and water temperature and adjacent land use but larvicide treatment consistently reduced the presence of larvae regardless of these other factors. This knowledge can now be used to prioritise and target control efforts to most efficiently reduce WNv mosquito vector populations, and most effectively reduce the risk of WNv transmission to humans. A similar research strategy could be applied to emerging threats from other potential mosquito vectors of disease around the world, to help lower the incidence of mosquito-borne disease.Résumé-Les réseaux artificiels de drainage dans les zones urbaines comprennent des bassins de captage des eaux pluviales qui peuvent servir d'habitats pour les larves de moustiques vecteurs du virus du Nil occidental (WNv), tels que Culex pipiens Linnaeus (Diptera: Culicidae). Nous évaluons les impacts des techniques d'aménagement et des épandages ciblés de larvicide sur les populations de larves de cette espèce, un moustique vecteur potentiel du WNv, dans des bassins de captage dans les basses terres de la région de Vancouver et sur l'île de Vancouver en Colombie-Britannique, Canada. Un modèle de régression logistique à effets mixtes permet de décrire la relation entre la présence de larves et le traitement au larvicide, tout en tenant compte des autres variables. Les estimations des variables montrent que le traitement au larvicide réduit la probabilité de présence de larves par un facteur de l'ordre de 7,23. Le modèle montre aussi une relation entre la présence de larves, d'une part, et la température de l'eau et l'utilisation des terres adjacentes, d'autre part; cependant, le traitement au larvicide réduit toujours la présence des larves, quels que soient les autres facteurs. Ces informations peuvent servir à établir des priorités et fixer des cibles dans les programmes de lutte pour réduire le plus efficacement possible les populations de moustiques vecteurs du WNv et diminuer ainsi le risque de transmission du WNv aux humains. On pourrait utiliser une stratégie de recherche similaire pour étudier les nouvelles menaces que représentent d'autres moustiques vecteurs potentiels de maladies sur la planète afin de diminuer l'incidence des maladies transmises par les moustiques.

Small-Scale Trials Suggest Increasing Applications of Natular™ XRT and Natular™ T30 Larvicide Tablets May Not Improve Mosquito Reduction in Some Catch Basins

“…Stormwater catch basins are common sources of permanent or semipermanent standing water that are routinely targeted for mosquito larvicide applications by local mosquito control programs to reduce local mosquito populations and incidence of mosquito-borne diseases. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] A common practice is to treat the stagnant water in all or most of the tens of thousands or sometimes hundreds of thousands of basins that can exist in an agency's operational area with at least one application of an extended-release larvicide formulated to last up to 150-180 days. Since the mid-1990s, extended-release larvicides (eg, Altosid® XR, FourStar®, and Natular™ XRT) have been used by the North Shore Mosquito Abatement District (NSMAD), a publicly funded mosquito control agency serving the northeast Chicago metropolitan area, to reduce mosquitoes in ∼50,000 catch basins each season.…”

Observed Loss and Ineffectiveness of Mosquito Larvicides Applied to Catch Basins in the Northern Suburbs of Chicago IL, 2014

“…As part of efforts to decrease local vector populations of West Nile virus (WNV) and other mosquito-borne diseases, stormwater catch basins are often targeted for routine larvicide applications in urban areas around the world. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The North Shore Mosquito Abatement District (NSMAD) treats approximately 50,000 catch basins each season in the District's 207 sq km (80 sq mi) located in the northeastern greater Chicago IL metropolitan area. Treatment is with extended-release, 180-day larvicides, and the specific objective is to reduce local populations of the local WNV vectors Culex pipiens and Cx.…”

Identification of Larvicide-Resistant Catch Basins from Three Years of Larvicide Trials in a Suburb of Chicago, IL

“…In urbanized areas throughout the world, catch basins (subsurface vaults designed to capture urban storm water runoff) are common habitats for the aquatically confined immature stages of vector mosquito species. [1][2][3][4][5][6][7] In the United States, West Nile virus (WNV) vector species in the Culex pipiens complex are found consistently within these structures, making catch basins an important focus of local vector control programs. [8][9][10][11] In some urbanized regions, including the Chicago metropolitan area, these structures may even be the most prevalent source of these species.…”

“…For example, larger rainfall events or catch basins prone to higher volumes and/or intensity of runoff may "flush" mosquitoes out of basins resulting in decreased larval abundance in the following days. [17][18][19] Jackson et al 4 found catch basins surrounded predominately by pavement were less likely to hold larvae than those with nearby trees or grassy areas. Indeed, Gardner et al 20 observed certain environmental features, including ammonia and nitrates in basin water, and the area of all shrubs of height ,1 m surrounding the catch basins were positively associated of high larval abundance, whereas pH and area of flowering shrub were negatively associated with larvae.…”