Both the force of windshield on the bug and that of the bug on the windshield are equal but in opposite direction.
EXPLANATION:
When the vehicle is moving forwards and air flows around it, and it also causes the flying bugs to hit the windshield. This impact causes a force that is imparted on both the bug and the windshield.
Thus both the bug and the windshield experience equal and opposite reactions result in Newton's Third law of motion. According to this law, it states that there will be an equal and opposite reaction for every reaction.
