Could this effect be caused, or enhanced, by the aerodynamics of the modern cars?

Could also be that insects evolved to avoid long black patches of ground.

That doesn’t look likely, but also not impossible. That’s why we need the study.

Also, predator-prey systems (https://en.wikipedia.org/wiki/Lotka–Volterra_equations) can have fairly large cycles with huge population swings. That makes verifying that there really is a decline not _that_ easy. You can’t just repeat an insect count done 30 years ago and compare the numbers.

You can see the effect on the very same car very clearly. We have been traveling with a camping car from germany to romania. In germany we did not need to clean the windscreen at all. In romania we did it almost every day.

Your anecdote is very interesting, thank you!

> The research included vintage cars up to 70 years old to see if their less aerodynamic shape meant they killed more bugs, but it found that modern cars actually hit slightly more insects

https://www.theguardian.com/environment/2020/feb/12/car-spla...

Ironically I removed my mention of the windscreen evidence. There are some citizen science surveys documenting the decline (e.g. a UK study found a 60% decline over 20 years, or something like that). But it's a good example of a strong indicator but not the greatest quality evidence - geographically limited, concerns low flying population only, might be confounded by changes in car aerodynamics, verge / hedgerow maintenance etc.

2020, from The Guardian: https://www.theguardian.com/environment/2020/feb/12/car-spla...

> The survey of insects hitting car windscreens in rural Denmark used data collected every summer from 1997 to 2017 and found an 80% decline in abundance. It also found a parallel decline in the number of swallows and martins, birds that live on insects