Global insect declines: Why aren't we all dead yet?

(Epistemic status: not much domain knowledge here, working off of first principles and off the top of my head.)

I had a conversation about roughly this topic (specifically it was about the ecological effects of killing all the mosquitoes with CRISPR) with Critch once and I quite liked his reply, which was, roughly and as best as I can recall: ecosystems have many negative feedback loops in them making them much more resilient to this sort of shock than a naive analysis would suggest. If a bunch of insects die, whatever food sources they were relying on can proliferate, which means other organisms (insects or otherwise) have an easier time eating them, and can in turn can be eaten by whatever predators were preying on the insects earlier.

There's also a big difference between the effect of suddenly killing off 75% of the insects and the update you make after observing that 75% of the insects have died. The latter could just be a new equilibrium ecosystems have settled into in response to a more fundamental shock, e.g. global warming or pesticides or whatever else.

Random speculative ideas:

I think my general answer is that we are seeing really massive changes to the ecosystem, it's just that humans don't really need to worry that much about the health of the ecosystem. By and large, and taking into account human industrial scale efforts and ingenuity, the only thing that we really need is fresh water and oxygen, and as long as those exist we can probably adjust our crop production somehow to make things work. There is a good chance we can colonize mars, which doesn't have a healthy ecosystem at all, because we have such a massive ability to reshape our environments to our needs.

What kind of observations would you expect to see in a world in which the biosphere has exploded and humans were able to reshape their environments as much as I think they can?

Some speculation

The original article mentions few reasons what may be going on in Germany - industrial scale use of pesticides or the increase in farms dedicated to a single crop. The same factors plus better crops and fertilizers allowed for 10x increase in crop productivity (check this truly amazing graph https://www.agry.purdue.edu/ext/corn/news/timeless/images/CornYieldTrend_US.gif)

Industrial farming is progressively more decoupled from ecosystems and does not need rich ecosystems (imagine hydroponic indoor farms growing vegetables just from water, artificial nutrients, and under LED light)

Also my guess would be you are overestimating importance of insects (copared eg to bacteria)

[Epistemic status: high confidence grounded in empirical observables, no domain expertise]

In fact, those shockwaves up the trophic chain are already being observed: https://www.theguardian.com/world/2018/mar/21/catastrophe-as-frances-bird-population-collapses-due-to-pesticides

The reason we aren't all dead is that humans exist atop a mostly separate food chain from wild animals. If all wild insects die, there will be collapse of wild ecosystems, but crop yields will be the same, if not better due to the lack of pests. Most pollination of commercial scale crops which need active pollination is done with rented beehives, these days. See https://en.wikipedia.org/wiki/Pollination_management

I haven't read this in detail yet, but this new article feels like substantial evidence against the basic observation of "global insect populations are drastically declining": 

https://www.nature.com/articles/s41559-020-1269-4

Quotes: 

Recent reports of dramatic declines in insect abundance suggest grave consequences for global ecosystems and human society. Most evidence comes from Europe, however, leaving uncertainty about insect population trends worldwide. We used >5,300 time series for insects and other arthropods, collected over 4–36 years at monitoring sites representing 68 different natural and managed areas, to search for evidence of declines across the United States. Some taxa and sites showed decreases in abundance and diversity while others increased or were unchanged, yielding net abundance and biodiversity trends generally indistinguishable from zero. This lack of overall increase or decline was consistent across arthropod feeding groups and was similar for heavily disturbed versus relatively natural sites. The apparent robustness of US arthropod populations is reassuring. Yet, this result does not diminish the need for continued monitoring and could mask subtler changes in species composition that nonetheless endanger insect-provided ecosystem services.

Not an expert; I think a better question would be not "why aren't we dying" but "what we can actually see if...". We're not dying on "this" scale due to very many reasons. Here's just some thoughts I had, all "weak hypotheses".

So, maybe:

1) we need better studies, and simply cannot say anything from "undifferentiated insect biomass" (seriously, what part of it was pollinators, what part - predators, etc?)

2) due to some weird thing, most of the effect is happening in the sea, not on land (how much organic matter is washed out now, and how it compares to 50 years before?)

3) it's not extinction we should be looking out for, but rapid evolution of other organisms that are going to occupy the freed niches (since the one rule of biology says "it will be consumed" :); an especially interesting problem here is evolution of communities, not of species. Think drier plains & Artemisia, Atriplex, etc -based herbaceous layer instead of the usual "full-blooded Poaceae-Fabaceae seesaw"? Dunno when desertification will catch up, but if Ambrosia is going to be typical of the new coenoses, pollinators are gonna sell out.

(that's just off the top of my head)

From the link:

The study is the result of a collaboration with the Entomological Society of Krefeld – essentially made up of members of the public

This decreases my confidence in the robustness of the results of this particular study. Unfortunately I'm fairly unversed this area so I don't know whether this is a widely repeated result or an outlier.

Many crops have been engineered to be wind or self pollinated so do not rely on insects directly. Some very resilient crop seeds have pesticides engineered right into them. For now they will do ok, though increasing drought and flooding are already starting to have an effect. Humans (1st world especially) are highly adaptable in our manipulation of the environment, but there is no doubt we depend on a healthy ecosystems in the long run.

just an idea - most of the biosphere is in the ocean and ocean ecosystems are in pretty bad shape, but we don't "see" this happening so it doesn't seem like as big a deal as it actually is.

This suggests that nature isn't a Rube Goldberg machine that some imagine. It seems that most of the commenters are also in the "life finds a way" camp, so I don't have much to add.

The interesting questions instead need to be answered by you. If I had told you 27 years ago, that insect populations would fall by 75%, what specific effects would you have predicted? I myself would have guessed that some insect eating animal populations would shrink (presumably they have), maybe get outcompeted by plant eating populations. And maybe that some plants pollinated by insects would be outcompeted by other more independent species. But I don't really see what should lead to catastrophe, especially not the kind that would hurt trees themselves. On the other hand, I could even imagine some forests becoming healthier due to reduction in parasites.

Non-expert, but high confidence:

Almost all claims exaggerate the importance and sensitivity of ecosystems and the biosphere. Professors of entomology have clear incentive to exaggerate the importance of their field. Other people hold nature on a pedestal and will happily believe strong claims uncritically. They'll read how the extinction of cockroaches might mean that red-cockaded woodpeckers lose 50% of their natural diet, and think this is a global catastrophe.

The real worst case scenarios of insect extinction and other ecosystem disturbances, are probably more like scenarios where cucumbers get really expensive, rather than anything close to global catastrophe. This is evidence of that. If a 75% reduction in insects doesn't have almost any effect, I'm not sure what would be needed for catastrophic results.

Human male sperm count failed 60 per cent since 1970s, so the effect is almost the same. Something is killing small things! Seriously, may be there is unidentified toxin which slowly affects both sperm and insects?

https://www.researchgate.net/blog/post/sperm-counts-in-the-western-world-have-declined-nearly-60-percent-since-the-1970s