By comparing the diapause responses between locally hibernating species, C. pipiens pallens, and C. tritaeniorhynchus the overwintering way of which is yet unknown, we found the relative identities of these 2 species in their ovarian diapause criteria, change of the mid-gut and the behaviour of refusing blood feeding. The increases in body weight and fatty contents in the dispersed tritaeniorhynchus were much less than those in diapause pipiens species. Moreover, their ability to resist low temperature was also found significantly weaker. In Shanghai area, the date of the critical photoperiod for C. tritaeniorhynchus was found around the 25th of September with a daylight exposure length (including twilight) of about 13 hours and 43 minutes, being 20 days earlier than that of the locally hibernating species C. pipiens pallens. The gonotrophic dissociation during critical photoperiod occurred more frequently in tritaeniorhynchus than in pipiens mosquitoes. In contrast to pipiens species, it is extremely difficult to obtain diapause tritaeniorhynchus in nature post critical photoperiod. The possibility of a seasonal migratory behaviour of C. tritaeniorhynchus was discussed.