Heinrich Himmler, naughty Nazi, asked scientists in Dachau to test if mosquitoes could replace cyanide as an effective way of mass-murdering incarcerated Jews and if it worked then asked them to produce squadrons of the beasts so they could attack London!
Luckily, the experiment failed because mosquitoes hated the English weather; rain, cold, storms, etc, and were unable to fly against the strong North West winds that always seem to blow across the UK.
After realising that his stupid idea would not work, Himmler ordered the Doodlebug, but again it failed because the Allies were already beating the shit out of the Nazis in France, Holland and Belgium. Hitler then decided to swallow his own medicine and overdosed on cyanide because he was allergic to mosquito stings and could not stand the thought of looking swollen and red faced if the Russians found him.
Dachau Nazi scientists, when realising that the war was lost, stuck the rest of the killer mosquitoes in the gas chambers hoping to remove all evidence of their dastardly plan. Luckily a Jew on a motorbike escaped and died of malaria in the hands of the approaching allies shortly after proving to the world that the Nazis were just a bunch of nasty bug-gars!