A common manifestation of it is to find lethargic insects. Bodily fully intact and seeming healthy, yet barely able to move. Insects normally skittish that you can simply pick up. I'm not talking about insects at the end of their life cycle or them being very cold. There's something very wrong with these individuals, I believe studies suggest their brains are messed up from the pesticides.
Big if true. Sounds like it working as designed.
Maybe people like you should experience what a world without insects would look like. I can save you the time. There will be no world.
Even this can cause a collapse by removing a food source from other predators.
> I can save you the time. There will be no world.
This is true. Insects are food for a huge number of predators, and insect larvae are a really important component of having soil capable of growing plants.
"First they ignore you, then they laugh at you..."
The topic seems to come up here ever few months, and there's always a significant percentage of the discussion devoted to aerodynamic effects, or changes in insect distribution specific to roadside habitats. Those converstations often feel like "middlebrow dismissal": people who think the fact they can come up with a plausible explaination alternate explaination for the data given a few seconds thought means it's likely that the studies are totally flawed and can be ignored.
Meanwhile if you dig in to the actual evidence, the studies based on vehicle data show a small negative correlation between vehicle age and number of impacted flying insects (i.e. older cars have slightly fewer splats, not more). More importantly, the general trends of declining biomass of (especially, but not only) flying insects reproduce over a wide range of methodologies and habitats. For skeptical readers, there are some links to studies in a previous comment I made on a previous thread on this same general topic [1].
Having said that, I think you've missed one of the big factors that's likely to contribute to the decline: the widespread use of insecticides (especially) and herbicides in industrial agriculture. Studies on bees show that even insects exposed to something much lower than the LD50 of certain insecticides experience behavioural changes that dramatically decrease their survival rates. And because "pest" insects typicaly have short lifecycles and rapid reproduction rates, they're often best placed to evolve tolerances for the insecticides, so there's pressure on farmers to use more and more to get the same effect.
For anyone who's interested in an introduction to this topic aimed at the general public (like me!), but written by a Professor of Entomology, I can recommend Slient Earth [2].
[1] https://news.ycombinator.com/item?id=31278206 [2] https://bookshop.org/p/books/silent-earth-averting-the-insec...