Which of the following is a common forest pest that affects hardwood trees?

The gypsy moth is a common forest pest that significantly affects hardwood trees. This pest is notorious for its caterpillars, which feed on the leaves of a variety of hardwood species, including oaks, maples, and aspens. The feeding habits of gypsy moth caterpillars can lead to defoliation, weakening trees and making them more susceptible to diseases and other pests. In severe infestations, prolonged defoliation can even result in tree mortality.

In contrast, the rice weevil primarily targets stored grains and is not a threat to forest trees. The European corn borer mainly affects corn and other grasses, making it irrelevant to hardwood trees. Lastly, while western flower thrips can cause damage to a variety of plants, including some crops and ornamental plants, they do not specifically target hardwood trees in forest settings. Thus, the gypsy moth stands out as the significant forest pest that directly impacts hardwood trees.