The extermination of insects needs more than just the fact that they suffer, but
They suffer so much that their existence is not outweighed by other positive things (e.g. their happiness, their contribution to the welfare of other beings, their intrinsic value).
There is no easier/more valuable method for relieving their suffering while keeping other goods.
The suffering outweighs other goods at every “margin”, i.e. there is no amount of insects for which it isn’t better to reduce their population.
(Being nitpicky)
The extermination of insects needs more than just the fact that they suffer, but
They suffer so much that their existence is not outweighed by other positive things (e.g. their happiness, their contribution to the welfare of other beings, their intrinsic value).
There is no easier/more valuable method for relieving their suffering while keeping other goods.
The suffering outweighs other goods at every “margin”, i.e. there is no amount of insects for which it isn’t better to reduce their population.