Northern range expansion of the Asian tiger mosquito (Aedes albopictus): Analysis of mosquito data from Connecticut, USA

Abstract

Background: The Asian tiger mosquito (Aedes albopictus) is an invasive species and important arbovirus vector that was introduced into the U.S. in the 1980's where it continues to expand its range. Winter temperature is an important constraint to its northward expansion, with potential range limits located between the 0° and -5°C mean cold month isotherm. Connecticut is located within this climatic zone and therefore, Ae. albopictus was monitored statewide to assess its northern range expansion and to delineate where populations can stably persist.

Methodology/principal findings: Ae. albopictus females were monitored at fixed trapping sites throughout Connecticut from June-October over a 20-year period, 1997-2016. In addition, Ae. albopictus larvae and pupae were collected from tire habitats and tires were retrieved from the field in the spring and flooded to evaluate overwintering success of hatching larvae. Ae. albopictus was first detected during statewide surveillance when a single adult female was collected in 2006. This species was not collected again until 2010 and was subsequently detected each successive year with increasing abundance and distribution except following the unusually cold winters of 2014 and 2015. Ae. albopictus mosquitoes were most abundant in urban and suburban locations along the southwestern shoreline of Connecticut; however, single specimens were occasionally detected in central parts of the state. Field-collected females were also screened for arbovirus infection yielding two isolations of Cache Valley virus and one isolation of West Nile virus, highlighting the threat posed by this mosquito. Ae. albopictus overwintered in Connecticut under mild winter conditions as shown by recovery of hatched larvae from field collected tires in spring and by early season detection of larvae and pupae.

Conclusions/significance: This study documents the establishment and expansion of Ae. albopictus at the northern boundary of its range in the northeastern U.S. and provides a baseline for monitoring the future spread of this species anticipated under climate change.

Fig 1. County map of Connecticut showing geographic distribution of mosquito trapping sites and land use characteristics.

Black circles indicate locations where Ae. albopictus were collected from 2006–2016 and are scaled according to numbers collected at each site. Red arrow indicates location of the Stratford site. Inset map of northeastern U.S. shows approximate location of the 0°C and -5°C cold month isotherm.

Fig 2. Connecticut map showing geographic locations where Ae. albopictus were collected by year.

Open circles indicate location of all mosquito trapping sites and black circles depict trapping sites positive for Ae. albopictus. Number of Ae. albopictus collected is indicated for each year.

Fig 3. Mean monthly temperatures recorded at weather stations in Bridgeport, New Haven, Stamford, and Stratford, Connecticut.

Fig 4. Weekly collection of juvenile (larvae and pupae) and adult (females) Ae. albopictus from Stratford, CT.