Several factors effecting on hatching of Aedes albopictus eggs

Abstract

Hatching of Aedes albopictus eggs were investigated to clarify their hatching stimuli and manner of their adaptation to environment. Eggs hatched at a higher rate in water containing Chlorella or at a low concentration of dissolved oxygen (DO) than in distilled water or water containing high DO. However, the eggs laid by adults, which had been exposed to shorter photoperiod (8 hours light) and/or delyed their blood-feeding, hatched at a lower rate in the same hatching media. Most of eggs kept wet for shorter than six hours after deposition, were killed with subsequent seven day egg-drying. Whereas eggs kept wet for longer than 24 hours, were not malformed but entered to quiescence by egg-drying. When those eggs were submerged in tap water or water containing a high DO, they hatched at a lower rate of no more than 20 percent, but the majority hatched after subsequent submergence in water containing Chlorella or a low DO. Thus, egg hatching response is determined by mainly concentration of DO, and by photoperiod and duration from emergence to blood-feeding at adult stage before egg-laying. Egg-drying after completion of embryonic development lowers the egg-hatching rates. We consider, the hatching response to DO concentration enables eggs to adjust their hatching to food quantity, and the lowered hatching response of eggs laid by delyed blood-feeding mosquitoes may imply their adaptation for avoiding increase of futile adult population when animal hosts are very few. The lowering effect of shorter photoperiod and egg-drying on egg-hatching response are considered their adaptation to overwinter at egg stage and that to prevent most of eggs from hatching just after a passing recovery of water level in their habitat according to a temporary rainfall, respectively.