Is mass killing of animals 'just' okay?

Let’s say a university organisation tells us that we can kill one million dogs, or cats, or geese.
Probably there would be outrage over it.
Last week a Dutch insectologist,connected to the Wageningen University, warned the people that in the coming days there is going to be a mosquito plague, due to a warm and wet summer.
The larvae are supposed to house in puddles, streams and on (waterfilled) saucers under the plant pots in your garden.
So he suggested to turn the saucers around which effectively would kill them.
Is it okay to mass kill mosquitoes/-larvae?
Are they not animals, just like dogs or cows or sparrows, too?