Environmental correlates of abundances of mosquito species and stages in discarded vehicle tires

Abstract

Discarded vehicle tires are a common habitat for container mosquito larvae, although the environmental factors that may control their presence or abundance within a tire are largely unknown. We sampled discarded vehicle tires in six sites located within four counties of central Illinois during the spring and summer of 2006 to determine associations between a suite of environmental factors and community composition of container mosquitoes. Our goal was to find patterns of association between environmental factors and abundances of early and late instars. We hypothesized that environmental factors correlated with early instars would be indicative of oviposition cues, whereas environmental factors correlated with late instars would be those important for larval survival. We collected 13 species of mosquitoes, with six species (Culex restuans, Cx. pipiens, Aedes albopictus, Cx. salinarius, Ae. atropalpus, and Ae. triseriatus) accounting for r95% of all larvae. There were similar associations between congenerics and environmental factors, with Aedes associated with detritus type (fine detritus, leaves, seeds) and Culex associated with factors related to the surrounding habitat (human population density, canopy cover, tire size) or microorganisms (bacteria, protozoans). Although there was some consistency in factors that were important for early and late instar abundance, there were few significant associations between early and late instars for individual species. Lack of correspondence between factors that explain variation in early versus late instars, most notable for Culex, suggests a difference between environmental determinants of oviposition and survival within tires. Environmental factors associated with discarded tires are important for accurate predictions of mosquito occurrence at the generic level.

Fig. 1

CCA biplots for mosquito species and stages and the environmental factors measured in tires in spring (May–June) 2006 for six sites within central Illinois (n = 59 tires). For each axis, the amount of variation explained by each axis is shown. Arrows indicate the direction and relative importance of the environmental factors (Detritus category: Fine, Leaf, Seed [including fruit]); Habitat category (Tiresize – Tire size, Cover – Canopy cover, Human – Human density); Microorganism category (ProN – Protozoan abundance, PS – Bacterial productivity via protein synthesis). Species (a – Aedes albopictus, o – Ae. atropalpus, t – Ae. triseriatus, p – Culex pipiens, r – Cx. restuans, s – Cx. salinarius) and stages (E – early instars, L – late instars) are indicated within symbols. For clarity, Aedes are enclosed in squares, and Culex in circles.

Fig. 2

CCA biplots for mosquito species and stages and the environmental factors measured in tires in summer (July–August) 2006 for six sites within central Illinois (n = 65 tires). For each axis, the amount of variation explained as a part of the total variation in the model is shown. Arrows indicate the direction and relative importance of the environmental factors (Detritus category: Fine, Leaf, Seed [including fruit]); Habitat category (Tiresize – Tire size, Cover – Canopy cover, Human – Human density); Microorganism category (ProN – Protozoan abundance, PS – Bacterial productivity via protein synthesis). Species (a – Aedes albopictus, o – Ae. atropalpus, t – Ae. triseriatus, p – Culex pipiens, r – Cx. restuans, s – Cx. salinarius) and stages (E – early instars, L – late instars) are indicated within symbols. For clarity, Aedes are enclosed in squares, and Culex in circles.