Why do insects rebound after an insecticide is sprayed?

Question

Other than developing a resistance to the insecticide, could you tell me why this happens?

Answer 1

If the insecticide doesn't kill *all* (100%) of the insects, then the survivors will repopulate. Even if you kill 99% of the insects, the surviving 1% will repopulate ... it's what organisms do ... they make babies.

Now if those surviving 1% survived because they were lucky enough to have some mutation that made them a little more resistant to the insecticide than the other 99% who died ... then the next generation of insects are the descendants of those survivors ... and thus are more likely to have that lucky mutation in much higher numbers.

That's basic natural selection.

Answer 2

I am not sure what you mean by "rebound". Some insects are just knocked down by the force of the spray, and regain their original stance after the spray has ended.