Searching for a sign of exotic Aedes albopictus (Culicidae) introduction in major international seaports on Kyushu Island, Japan

Abstract

Background: The Asian tiger mosquito, Aedes albopictus, has spread around the world. The migration was mainly mediated by maritime transportations. This species is known as an efficient vector for arboviruses, and it was responsible for the recent dengue outbreak in Tokyo, Japan. As the vector competence varies among geographical populations, and insecticide resistant populations have emerged, it is important to reveal their movements. The present study uses molecular techniques to search for a sign of introduction of an exotic population in three major international seaports on Kyushu Island.

Methodology/principal findings: Adults of Ae. albopictus were sampled around the international seaports of Fukuoka, Kitakyushu, and Nagasaki. Pairwise fixation indexes were estimated between the sampled populations based on 13 microsatellite markers. There was no clear genetic differentiation between distant and port populations in Kitakyushu and Nagasaki. However, the analysis found one distinct group near the container terminal in Fukuoka, which handles international freight containers mainly from adjacent countries. DNA samples were also obtained from Goto, Tsushima, Honshu, Ryukyu, Thailand, and the Philippines; and a cluster analysis and discriminant analysis revealed that the distinct group in Fukuoka did not belong to these groups. Combined with the results of phylogenetic analysis based on CO1, these results implied that this group originated from one Asian temperate region outside of Japan. Neutrality test and mismatch distribution analysis suggested that the establishment of this group was not recent.

Conclusions/significance: The present study found a sign of Ae. albopictus introduction from a temperate region of Asia through maritime freight container transportation. The genetically distinct group found in Fukuoka likely originated from a temperate region outside of Japan. Maritime container transportation may introduce to Japan mosquitoes with greater vector competence/insecticide resistance. This is the first study to describe the spatial population structure of Ae. albopictus in Japan using molecular techniques.

Fig 1. Collection sites of Ae. albopictus in Kyushu.

Created by processing Free vector and raster map data @ naturalearthdata.com and National Land Numerical Information (Administrative Area Data) @ Ministry of Land, Infrastructure, Transport and Tourism, Japan (https://nlftp.mlit.go.jp/ksj/gml/datalist/KsjTmplt-N03-v3_0.html).

Fig 2. Bayesian membership assignment of Ae. albopictus individuals from Japan.

Only results supported by Evanno’s best K are shown. (A) indicates the cluster assignment with K = 2, red: cluster 1; orange: cluster 2. (B) shows the cluster assignment with K = 6, red: cluster 1; orange: cluster 2; yellow: cluster 3; green: cluster 4; blue: cluster 5; and purple: cluster 6.

Fig 3. Bayesian membership assignment of Ae. albopictus populations in Japan with K = 6.

Red: cluster 1; orange: cluster 2; yellow: cluster 3; green: cluster 4; blue: cluster 5; and purple: cluster 6. Fukuoka A is enclosed in dashed line. Created by processing Free vector and raster map data @ naturalearthdata.com and National Land Numerical Information (Administrative Area Data) @ Ministry of Land, Infrastructure, Transport and Tourism, Japan (https://nlftp.mlit.go.jp/ksj/gml/datalist/KsjTmplt-N03-v3_0.html).

Fig 4. Discriminant analysis of principal components for the Ae. albopictus populations in Japan.

1–6: Fukuoka A colored by maroon; 7–18: Fukuoka B colored by red; 19–25: KK1-KK7 colored by orange; 26–36: NG1-NG11 colored by yellow; 37–38: GT1-GT2 colored by green; 39–46: TS1-TS8 colored by light blue; 47–50: RK1-RK4 colored by navy blue; and 51–53: HS1-HS3 colored by purple.

Fig 5. Cluster analysis using F_st in ten Ae. albopictus groups consisting of Kyushu, Honshu, and two tropic populations.

Fig 6. CO1 genetic relationships among ten Aedes albopictus groups.

Fig 7. Observed and expected mismatch distribution of the Fukuoka A group.

Fig 8. Phylogenetic tree of Ae. albopictus (total 108 taxa).

Taxa are labeled with accession numbers and countries or haplotype name (H1-H84) and countries, and colored by haplogroups as defined by Battaglia et al. [60]. Areas which had identical sequences are listed after a colon symbol. Figures in parentheses show the number of identical sequences found in the 524 sequences. Support values above the branches indicate posterior probabilities (>50) of Bayesian Inference with MCMC. Haplotypes found in Fukuoka A are highlighted (enclosed in boxes).