In 1992, Newsweek had written it on the cover: "Malaria returns with a vengeance." When you would think (or, hope, without thinking) that the bug would not be bugging any more, or an illness of it was finally curable, it has been coming back surging, massively, and it goes on, and on, thus.
They have been adapting to the chemicals which target their genetic vulnerabilities.
Throughout history, the success against mosquitoes have been mostly by drying up wetlands.
They need water (whether finding it in a broken bottle, or pond), for laying eggs there.
No water around? Mosquitoes have resilience to live through dryness, too. Their eggs will wait there, until some water (rain, etc) splashes there to make floods, or minimal-ponds.[1] Perhaps not all of the now-known subspecies, may stick through dry periods, but if a flexibility is there in the genome of a species, it would not be surprising to find that the same type of persistence-to-dryness, may occur, in other subspecies, too.
Ironically, people who were writing about mosquitoes, more than a century ago, had written of our human experiences that, when some mosquito sound pierces the night (that is, surging), how aggravating that is, how people perceive that as alarm, to fight back against that mosquito. Next, throughout the 20th century, witnessing the cases of mosquitoes surging back as a species.
Thus, surging both individually and as a species. The scale is important, though. A single mosquito which interrupts your leisure or work, wastes your effort, while mosquitoes colonizing a geography massively, have been capable of inhibiting the (economical, etc.) development of that geography, because of the illnesses they carry.
As of 2000s, mosquitoes have not been getting away, but surge toward new grounds.
WHO is reporting about Dengue fever that, "Before 1970 only nine countries had experienced DHF epidemics, a number that had increased more than four-fold by 1995.
Not only is the number of cases increasing as the disease is spreading to new areas, but explosive outbreaks are occurring. In 2007, Venezuela reported over 80 000 cases, including more than 6 000 cases of DHF." [2]
[1] Emerson Yorke Studios (mid-20th century). "The Life Cycle of the Mosquito" Retrieved (video) through http://www.archive.org/details/life_cycle_of_the_mosquito, on April 6, 2010.
[2] WHO (March 2009). "WHO | Dengue and dengue haemorrhagic fever" Retrieved from http://www.who.int/mediacentre/factsheets/fs117/en/, on March 22, 2010.
listing mosquito-characteristics (mnemonic "sercan")
MosquitoCharacteristics1: Unisex Target
MosquitoCharacteristics2: Sucks Not Only Human Blood, But Animals, Too
MosquitoCharacteristics3: Surging
Why mosquitoes? Reflecting about the purposes of Allah, in creating those.