Certain species of insects introduced accidentally in a forest are destroying all the Douglas fir trees in that forest. The wood of these trees is extensively used for construction. In order to control the damage caused by these insects, the forestry department decided to introduce the moth caterpillar in the forest. These caterpillars are natural predators of the insects. Which method did the forestry department implement to control the invasive species?

The forestry department implemented a(n) _______ control method.