Winter Activity and Diapause of Aedes albopictus (Diptera: Culicidae) in Hanoi, Northern Vietnam.

We studied the winter activity of Aedes albopictus (Skuse) from November 2008 to April 2009 in Bat Trang village of Hanoi, Vietnam. We selected 12 houses and collected: 1) adults with BG sentinel traps, 2) pupae from household water containers, and 3) eggs with ovitraps. Aedes albopictus adults, pupae, and eggs were not collected from early January to early February. Though the egg hatching probability tended to be initially high at longer day length, the maximum probability gradually shifted to shorter day length, as the observation period elapsed. When females were reared under long day length and their eggs were immersed 1 or 5 wk after oviposition, >50% of eggs hatched within 20 days. However, when females were reared under short day length and their eggs were immersed after 1 wk, hatching was suppressed for 60 days. When females were reared under short day length, the median hatching day occurred earlier in eggs kept dry for 5 and 10 wk after oviposition than in those dried for only 1 wk. This indicates that the extended dry periods accelerate egg hatching. Our results showed that hatchability gradually changed with day length, suggesting that selection for overwintering is not as strong relative to Ae. albopictus living in the temperate zone, where winter conditions are less favorable than in tropical and subtropical areas.