Asklemmy

Hard to say. Mosquitos, is probably not one of them because even as much as we hate them, many animals prey on them, so unless other insect replaces them as a food source for those animals, them disappearing would probably affect many other species and subsequently, other species that may feed or depend in some form on those that feed on mosquitos.

My answer would probably be ticks, since I don't think there's many animals that feed on them and their only usefulness is population control, which should be doable by other species either way.

Edit: bed bugs as well, since it was mentioned by other commenters, I hate those fuckers and last I checked they weren't any animal's primary food source.

The bats would miss them.

Any change to the biodiversity on our planet will have a negative effect. What is a pest to you is food for another species, or a pollinator, or any of dozens of valuable purposes.

Ticks and botflies. We don't need maggots making a home in our skin. Even worse is what they do to animals like sheep.

Mosquitos are mainly an annoyance to me and I can deal with them.

The poisonous (not venomous) grasshoppers that eat plants to death but nothing eats them.

Really it is people, though.

Parasitic worms

I haven't vomited in years, but the concept of those things makes me feel like I'm gonna

Mosquitos. Also bedbugs. Any insect that feeds on blood really

Mosquitos are the largest killer of people in history. Getting rid of them would have a massive positive effect.

Same for me, mosquitoes. Those pesky little buggers!

Whatever shit's been preserved in the permafrost that's bound to come back.

cattle.

Australians would say emus

Disease carrying mosquito species

I feel like a reasonable but controversial answer to this is cows