I have observed a great many local declines in insects and other animals in my area. I can say that there was a noticeable change from 2017 to 2018 in my immediate location, a mile north of Detroit, Michigan, USA.
I have a modest area of backyard surrounding a worn-out asphalt parking area. What remains of the grass, etc. is about a fringe of 10 ft. (3.3meters) to the east, and what is called locally, the easement to the north of about 12 ft. (4 meters). On the west, likewise, is a fringe of grass about 10 ft. (3.3 meters), also. In this meager area I never use chemicals, and try to encourage wildflowers to grow in the north easement by seeding regularly.
Every year I noted June bugs (brown beetles) in fairly large numbers emerge in late June. I observed large black crickets emerge in late August. I heard a loud, shrill cacophony of cricket calls every late summer. I also observed yellow jackets (a variety of wasp) throughout my backyard with a menacing presence. I would see fireflies in large numbers in June and July. Whenever I turned my back light on in the evening for a few hours, there were often large numbers of moths and other insects swarming around it.
I have birdfeeders hung by my north window, where I observed, among the many sparrows, juncos, black capped chickadees, occasional woodpeckers, and other wild birds in the winter.
It's not my imagination. I'm not in the habit of exaggerating.
Since 2017, I see almost NO beetles, NO crickets (I don't hear them chirping in chorus), NO yellow jackets, only TWO wild birds (perhaps third and fourth) in the last year. (I do see blue jays, but rarely any crows.)
I also no longer see earthworms or nightcrawlers in the massive numbers on the street and sidewalks after a rain. Mosquitos are rare. I say this while acknowledging the complete absence of amphibians I saw and heard in tremendous numbers as a child.