Genetic analysis of invasive Aedes albopictus populations in Los Angeles County, California and its potential public health impact

Abstract

The Asian tiger mosquito, Aedes albopictus, is an anthropophilic aggressive daytime-biting nuisance and an efficient vector of certain arboviruses and filarial nematodes. Over the last 30 years, this species has spread rapidly through human travel and commerce from its native tropical forests of Asia to every continent except Antarctica. In 2011, a population of Asian tiger mosquito (Aedes albopictus) was discovered in Los Angeles (LA) County, California. To determine the probable origin of this invasive species, the genetic structure of the population was compared against 11 populations from the United States and abroad, as well as preserved specimens from a 2001 introduction into California using the mitochondrial cytochrome c oxidase 1 (CO1) gene. A total of 66 haplotypes were detected among samples and were divided into three main groups. Aedes albopictus collected in 2001 and 2011 from LA County were genetically related and similar to those from Asia but distinct from those collected in the eastern and southeastern United States. In view of the high genetic similarities between the 2001 and 2011 LA samples, it is possible that the 2011 population represents in part the descendants of the 2001 introduction. There remains an imperative need for improved surveillance and control strategies for this species.

Figure 1. Phylogenetic network of 66 mitochondrial haplotypes of CO1 gene in Aedes albopictus from 11 localities.

Localities are indicated by different color (bottom-right) and samples of LA01 and LA11 are labeled by crosses and asterisks, respectively. Sizes of circles are approximately proportional to the number of individuals with the given haplotype. GZ: Guangzhou; XM: Xiamen; JS: Jiangsu; TW: Taiwan; JP: Japan; SG: Singapore; IT: Italy; LA01: Los Angeles 2001; LA11: Los Angeles 2011; NJ: New Jersey; TX: Texas; and HW: Hawai’i.

Figure 2. Bayesian cluster analysis using STUCTURE program.

A) Pie charts showing the composition of proportional membership coefficient of Aedes albopictus individuals within the 6 clusters identified by the Bayesian analyses; and B) color code of respective clusters and membership coefficient values for the Aedes albopictus populations studied. The coefficient values above 0.20 are highlighted in bold. GZ: Guangzhou; XM: Xiamen; JS: Jiangsu; TW: Taiwan; JP: Japan; SG: Singapore; IT: Italy; LA01: Los Angeles 2001; LA11: Los Angeles 2011; NJ: New Jersey; TX: Texas; and HW: Hawai’i.

Figure 3. Observed and expected mismatch distributions showing the frequencies of pairwise differences.

The observed distributions (blue bars) are compared for their goodness-of-fit to a Poisson distribution under a model of sudden expansion illustrated by the overlaid curve (red dots and solid lines).