Prediapause migration of Culex tritaeniorhynchus reported one year previously was observed again in the autumn of 2008 in the same park in urban Tokyo. The time course of prediapause migration in 2007 and 2008 was similar starting in mid-/late September, peaking in mid-October and ending in December. The density of Cx. tritaeniorhynchus that migrated was higher in 2008 than 2007 throughout the study period with a peak density of 3,740 per 1 hr of sweeping, 3.5 times higher than in 2007. A total of 16,892 and 29,188 Cx. tritaeniorhynchus resting on vegetation were collected by sweeping from April to December in 2007 and 2008, respectively, with 99.9% collected during September to December in both years. Dissection showed that 96.5% (222/230) of these females in 2008 were in reproductive diapause with an ovariole stage of N or I and a primary to secondary follicular ratio of ≤1.5. In addition to Cx. tritaeniorhynchus, 11 mosquito species were collected in this study from September to December and 6 species were breeding in the park. The remaining 3 species were rice field mosquitoes and appeared in the autumn, coinciding with the appearance of Cx. tritaeniorhynchus. Mosquito collections were made in 2 additional study sites in mid-October 2008 to check for the occurrence and density of Cx. tritaeniorhynchus, and the average density of Cx. tritaeniorhynchus was significantly different between study sites. Hourly changes in direction and velocity of the wind during September to October indicated that a large part of the migrating Cx. tritaeniorhynchus originated from north to north-northwest areas of the study park. A total of 211 overwintered Cx. tritaeniorhynchus females including 4 blood-fed females were collected at the study site during March to early May 2009, indicating the presence of hibernacula for Cx. tritaeniorhynchus near the study site. Blood-meal identification by PCR using primers based on the cytochrome b gene and the 16S-rDNA region of vertebrate hosts showed that two blood meals were human-derived, one was cat-derived and the remaining meal showed no amplification.
2010 The Japan Society of Medical Entomology and Zoology