Could kind of flies or mosquitoes migrate and reproduce?

[kenny1999]

I know that some flies or mosquitoes some parts of Africa could spread serious or even fatal disease to human if bitten. I am wondering why it looks like they will not travel to other continents and reproduce there? Is it because they are not able to travel a long distance or because they are already satisfied with their current environment so they don't need to travel so they are mostly localized?

[CharonY]

Actually they do spread a fair bit (mostly mosquitos) and mosquitos are present in most parts of the world. The spread of disease depends a fair bit on the pathogens and human/animal reservoirs in which they reproduce. Since there is no human-to-human spread, travel does not factor in like it does e.g. with influenza or SARS-CoV-2.

However, it is very wrong to assume that those diseases are only found in Africa as a lot of mosquito-borne diseases are present on several continents.

Malaria which is caused by Plasmidium palcifarum is found in Africa, South America and throughout South Asia, for example. 

The Dengue virus has a similar distribution, but there are occasional outbreaks in the continental US (though often travel-related).

West Nile virus is found in Africa, Europe, Middle East and North America and West Asia. While most limited to the more Southern parts, due to global Warming their territory is creeping Northward.

Tropical climate does benefit mosquito life cycles and often provides abundant reservoirs for a given disease, but again, they