[gus_massa]

Assuming they are like some flies that has been eradicated https://en.wikipedia.org/wiki/Sterile_insect_technique , the population would bounce back in a few years. You must repeat the treatment next year lower the population to the 5% of the initial population, and repeat the treatment the next year to reduce it to the 1% and repeat it a few years to reduce each time the population until it is completely eradicated. And then a few times to be sure.

And later implement some kind of check to avoid the reintroduction. Some countries that have a nice natural barrier have checks to avoid the introduction of fruit that may have flies larva. With mosquito, I'm not sure how the larva can travel from one country to another...

[cimmanom]

In the bilge of a ship, since they lay eggs in water?

[soperj]

Pretty sure mosquito eggs don't survive in salt water.

[samatman]

Bilge water isn't consistently salty.

A ship which unloaded in the St. Lawrence Seaway would fill the bilge tanks with fresh water.

[cimmanom]

Good point. I could still imagine puddles of fresh water from rain or from washing the decks languishing on in some corner of a ship.