Will give brainliest.
the town in which this forest ecosystem lies is afraid the moths will destroy the fir trees and want to use insecticides kill the moths. what may be some unintended consequence of that action?
-the bird population may increase
-rabbit population may increase stream becomes polluted
-fish population increases

The stream becomes polluted

Explanation:

In this case, the insecticides are being used as a measure of pest control i.e. to kill the moths and save the Douglas Fir trees. Intended purpose of spraying insecticides:

If the moths are eliminated, the Douglas Fir trees will prosper. Their needles will be intact and it would be more suitable for the birds to use the trees for nesting. With their competition eliminated, more birds will choose the trees for nesting which would result in an increase in their population.

Unintended Consequence:

Insecticides are chemical agents that kill insects or pests. These chemical compounds are toxic and a health hazard humans and animals. As the insecticides are sprayed on the trees, some quantity of them will reach the stream and pollute the water.