I have been noticing this for several decades, actually.  I recall that when we used to go on a day trip, even to the desert, the car window and front grills had an abundance of smashed insects.  When is the last time you noticed this?  It's been years.

The Monarch butterfly is probably at risk for extinction in a few decades, if not sooner. 

We have sprayed so many areas, most roadsides, and urban growth has swallowed up  land.  It's not just a pretty thing - the Monarch is the strikingly beautiful "canary in the coal mine" for our natural environment, an easy to see example of the insect world.  Climate change and urban development, large scale farming is killing many insects, many whose important roles in the ecosystem are still unknown to most people..  They are an important key species for other animals in the natural food chain. 

Have you noticed as I have, that there are fewer song birds also?  Still plenty of crows and pigeons though.

We need to be much more mindful of our actions while we try to wipe out "pests".  We may be wiping out forever, the natural balances that are part of our world.

Read more about this in linked Bug Squad article, "Insect Apocalypse: Where Have All the Insects Gone?"