I'm sure many of us have observed this over the past two decades. 20 years ago I could drive to California from Arizona and by the time I got to San Jose my windshield would be smothered in insects. Not so much now, just a few on the whole trip. I recently drove to Albuquerque and noticed one hit my windshield on the way back. One. Which I tried getting off with the wipers, but it was stubborn (must have been a big one) so I ended up squeegeeing it off at a gas station. There definitely has been a reduction in insect population here in the southwest.