>> [Hu] and Dickerson constructed a flight arena consisting of a small acrylic cage covered with mesh to contain the mosquitoes but permit entry of water drops. The researchers used a water jet to simulate rain stream velocity while observing six mosquitoes flying into the stream. Amazingly, all the mosquitoes lived.
The researchers used simulated rain drops on six mosquitoes. There are more than six species of mosquitoes. They controlled for wind effects (which are part and parcel of rain). So they excluded horizontally travelling raindrops. My immediate reaction to the conclusion that mosquitoes can fly in rain was "Really? Not always". Here is a methodologically lacking and wholly unscientific anecdote: I have lived in Johannesburg my entire life, where mosquitoes are quite prevalent during the summer months. When it is raining heavily (it is usually quite windy as well), the local species of mosquito that feeds of humans do not present a problem as the number of airborne mosquitoes tends to zero.