I also think it’s important to put it into context.
1. These insects weren’t really robust to begin with. Take the monarch butterfly in the North America. They actually needed primarily milkweed to survive. A single point of failure (milkweed) can cause the population to collapse. When we put up houses and converted land to farms, you’re correct we killed many of the native species, but those species were HIGHLY tuned to a particular niche. In 100-200 years it’s likely the insects that survived will re-occupy new niches.
2. Insects typically need a much smaller range to survive, so hikes in the same woods as when you were a kid doesn’t add up. Unless there was another massive environmental issue - such as pesticides or chemicals like DDT which have a secondary impact. Personally, that bird egg analogy sounds exactly like what the US saw with DDT and the collapse of the eagle population.
3. In the 1950s in the Midwest there had already been farmland all over for 50+ years. Same with Ireland (for hundreds). The insect populations have only noticeably declined in the last few decades. Unfortunately, we don’t have enough historical data to confirm what it is exactly. Even in the 1970s you’d have solid layers of bugs on windshields driving between cornfields. Now, nothing.
https://en.m.wikipedia.org/wiki/Decline_in_insect_population...
To me, this indicates a chemical or set there of, as the most likely culprits.
EDIT: DET -> DDT