The colliding car and insect really do exert equal
While the car is moving along towards the point of impact, the engine is working against air resistance, the friction of the wheels and axels, and losses in the transmission and motor in order to keep the vehicle moving.
It may be moving at a constant velocity or accelerating or braking at the time. The energy expended by the car at this time is
Any of the actions above require a huge magnitude of energy compared to that needed by the insect to maintain its flight.
But it is exactly the flight energy
So at the time the collision takes place, the total energy needed by the car to maintain its motion will be
The resultant change in energy from