Experiments exposing Aedes aegypti to winter conditions were conducted at Narita International Airport, Japan during December 2012 to March 2013 to evaluate the possible overwintering of the species. Four and 2 study sites were selected inside and outside the terminal buildings, respectively, and air temperature and relative humidity were recorded hourly at each site. Eggs were placed for 91 or 63 days at each study site, respectively, and the hatching rate and adult emergence rate were examined in March 2013. Under outdoor conditions (daily average of 5.2°C and 57.3%R.H.), 6% of the exposed eggs hatched but no adults emerged. Eggs exposed to indoor conditions (daily average of 14.3–19.4°C and 34.3–36.8%R.H.) showed 2 to 8% adult emergence. Exposure experiments using larvae were conducted for 1 week every month, and their development and survival rate were observed. Under outdoor conditions in January and February 2013, all the exposed larvae died within a week. Larvae placed inside the terminal building developed well and the threshold temperature for larval development was estimated as 10.6°C and 11.6°C for hatched larvae and 4-day-old larvae, respectively.
