[DEinspanjer]

I can't discuss how the rain interacts with the adults, but I have read scientific research that discusses how stagnant water is required for mosquitos to lay eggs and for the larvae to breathe. If the surface of the water ceases to be stagnant, the eggs cannot be laid and the larvae will suffocate.

I retrieved a link to an article last year that discusses a device that uses solar power to aerate ponds as a mosquito preventative [1].

A reasonable conclusions for the drop in population is therefore that two generations can be severely depopulated by a heavy rainstorm, leaving only the portion living in stagnant water that is sheltered from the rain and run-off to survive and repopulate.

1. http://www.wired.co.uk/news/archive/2014-05/19/mosquito-devi...