Terrestrial vegetation and aquatic chemistry influence larval mosquito abundance in catch basins, Chicago, USA

• Main Authors: Gardner Allison M, Anderson Tavis K, Hamer Gabriel L, Johnson Dana E, Varela Kate E, Walker Edward D, Ruiz Marilyn O
• Format: Article
• Language: English
• Published: BMC 2013-01-01
• Series: Parasites & Vectors
• Subjects: <it>Culex</it> mosquitoes; Larval habitat; Landscape ecology; Vegetation; Aquatic chemistry; Geographic information science; West Nile virus
• Online Access: http://www.parasitesandvectors.com/content/6/1/9

<p>Abstract</p> <p>Background</p> <p>An important determinant of mosquito-borne pathogen transmission is the spatial distribution of vectors. The primary vectors of West Nile virus (WNV) in Illinois are <it>Culex pipiens</it> Linnaeus (Diptera: Culicidae) and <it>Culex restuans</it> Theobald. In urban environments, these mosquitoes commonly oviposit in roadside storm water catch basins. However, use of this habitat is inconsistent, with abundance of larvae varying significantly across catch basins at a fine spatial scale.</p> <p>Methods</p> <p>We tested the hypothesis that attributes of the biotic and abiotic environment contribute to spatial and temporal variation in production of mosquito vectors, characterizing the relationship between terrestrial vegetation and aquatic chemistry and <it>Culex</it> abundance in Chicago, Illinois. Larvae were sampled from 60 catch basins from June 14 to October 3, 2009. Density of shrubs and 14 tree genera surrounding the basins were quantified, as well as aquatic chemistry content of each basin.</p> <p>Results</p> <p>We demonstrate that the spatial pattern of <it>Culex</it> abundance in catch basins is strongly influenced by environmental characteristics, resulting in significant variation across the urban landscape. Using regression and machine learning techniques, we described landscape features and microhabitat characteristics of four Chicago neighborhoods and examined the implications of these measures for larval abundance in adjacent catch basins. The important positive predictors of high larval abundance were aquatic ammonia, nitrates, and area of shrubs of height <1 m surrounding the catch basins, whereas pH and area of flowering shrub were negatively correlated with larval abundance. Tree density, particularly of arborvitae, maple, and pear, also positively influenced the distribution of <it>Culex</it> during the fruit-bearing periods and early senescent periods in August and September.</p> <p>Conclusions</p> <p>This study identifies environmental predictors of mosquito production in urban environments. Because an abundance of adult <it>Culex</it> is integral to efficient WNV transmission and mosquitoes are found in especially high densities near larval habitats, identifying aquatic sites for <it>Culex</it> and landscape features that promote larval production are important in predicting the spatial pattern of cases of human and veterinary illness. Thus, these data enable accurate assessment of regions at risk for exposure to WNV and aid in the prevention of vector-borne disease transmission.</p>