Spatiotemporal variation in abundance and genetic structure in an urban-rural landscape: Aedes albopictus (Skuse, 1894) (Diptera: Culicidae) in Wake County, NC

Abstract

Since its invasion of the United States in the 1980s, Aedes albopictus (Skuse, 1894) has become a major pest and a significant public health threat in the Southeastern United States. Despite its importance, we know little about its population genetics at fine spatial scales that correspond to the level of management units. To remedy this lack of information, we analyzed Ae. albopictus spatial variation in mosquito abundance and genetic structure in an urban-rural landscape over 2 years (2016 and 2018) in Wake County, NC, United States. We used a reduced representation sequencing method to generate between 1,100 and 30,000 single-nucleotide polymorphisms for population genetic analyses. We found spatial variation in both the abundance and genetic diversity, and significant differences in genetic divergence among sites that varied between the 2 years. The year-to-year variation in the population genetic patterns at the within-county scale suggests a dynamic system that requires extensive geographic, temporal, and genomic sampling to resolve.

Keywords: Aedes albopictus; ddRAD seq; mosquitoes; population genetics; urban landscapes.

Graphical Abstract

Fig. 1.

Delineation of zones for Wake County, which act as proxies for the overall pattern of urbanization. In order from most to least urbanized: the Inner Zone is defined as inside the Interstate 440 beltline, the Outer Zone is between the Interstate 540 beltline and I-440, and the Outside Zone is the remainder of the county.

Fig. 2.

Wake County sampling locations. (A) sites and site names from 2016; all have genetic data for a portion of collected individuals (note we limit the number of individuals per ovitrap). There are four sites in the Inner Zone, five in the Outer Zone, and six in the Outside Zone. (B) Sampled sites from 2018; points overlaid with asterisks are sites that also have genetic data for mosquitoes. The number of sites in each Zone (and number of sites used in population genetic analyses in parentheses) are as follows. Inner Zone: six (four); Outer Zone: 18 (14); Outside Zone: 37 (24).

Fig. 3.

Average A. albopictus abundance in Wake County. (A) Average egg abundance per week in 2016, larger points indicate higher average egg abundance. Aedes albopictus eggs were found at all sampling locations, and average count ranged from 10.75 to −213.59 per ovitrap per week. There were no significant differences in mean abundance between Zones. Sites in the Inner Zone are shown in red, those in the Outer Zone in gray, and in the Outside Zone, blue. (B) Average adult abundance per light-hour in Wake County 2018, at 61 locations. Larger points indicate higher average adult abundance. Aedes albopictus adults were found at 59/61 sites, and average abundance ranged from 0.02 to 10.31 adults per light-hour. There were no significant differences in mean abundance between zones. Sites in the Inner Zone are shown in red, those in the Outer Zone in gray, and in the Outside Zone in blue.

Fig. 4.

DAPC scatterplots for all sample sites. (A) 15 sites sampled in Wake County 2016, with the first two discriminant functions (DAs) on the x and y axes. Cross-validation retained 50 principal components, which produced a correct assignment rate of 0.807. (B) for the 42 sites sampled in Wake County 2018, with the first two discriminant functions (DAs) on the x and y axes. Cross-validation retained 60 principal components, which produced a correct assignment rate of 0.62.