Although mosquitoes are very annoying and carry diseases the mosquitoes are really important to the earth and environment.
Mosquitoes provide food for fish and other animals on earth and the mosquito larvae are very important in aquatic ecology.
Many other insects and small fish feed on the mosquitoes as well and the loss of that food source for them would be bad.
Because any animals, fish etc that feed on mosquitoes would suffer without the food source.
Although we could probably get by without mosquitoes if the fish and other animals had other food sources other than mosquitoes.
But it's best to not make mosquitoes go fully extinct although at times we wish they would.
You still should get rid of mosquitoes in your yard or other areas especially around your pond etc.