Gypsy moths kill trees by destroying their leaves.
burrowing into and weakening the roots.
building heavy nests that weaken branches.
separating the bark from the rest of the tree.

The correct answer is - destroying their leaves.

Explanation:

Gypsy moths are the most important moth species as their caterpillar defoliate the leaves of the trees, shrubs, and other plants and ultimately kills them.

These moths destroy most of the leaves or separate the leaves from the trees. These moths lay their egg on the leaves of the trees and plants and their caterpillar eat these leaves for food and nutrition.