Uh, no. Mosquitos have killed around 50% of humans that have ever lived through malaria.
But even if it is, it's certainly not the case today.
It's not in the top-10 causes of death at the moment. If we limit the scope to developing nations only, it's #9, which is huge, but still killing less than half the number that heart disease does.
Furthermore, most mosquitoes don't carry malaria, but all sugary foods are capable of causing heart disease if consumed in excess.
So it's not unfair to say that sugary foods are more dangerous to humans than mosquitoes.
0: http://factmyth.com/factoids/malaria-killed-half-the-people-...
From the abstract of this paper: https://www.ncbi.nlm.nih.gov/pubmed/16250876