An amateur German group called the Krefeld Entomological Society has been monitoring insect numbers at 100 nature reserves in Western Europe since the 1980s. Although there were the annual fluctuations they discovered that by 2013 numbers began to plummet by nearly 80 per cent.
Most people likely see this as a huge loss, particularly animal advocates. Environmentalists will of course see this as a huge loss given the effects on many ecosystems.
There's a growing body of literature, however, that suggests a different reaction (for instance, see Simon Knutsson). Much of it is done by lay people, but I hope to be able to study this question academically before long. If insects do feel pleasure and pain, then their lives look pretty lousy. In the vast majority of cases, "being an insect" means being born and promptly starving, being eaten alive, or dying in another horrific way.
It seems too early to take much action on insect suffering (besides research), but it is thought-provoking to wonder whether this trend is instead a merciful one.