Could you say more about the epistemic status of agricultural pesticides as the largest item in this category, e.g. what chance that in 3 years you would say another item (maybe missing from this list) is larger?
(Probabilities are ballpark guesses, not rigorous)
Just in terms of insects impacted because trying to estimate nematodes or other microscopic animals gets really tricky:
Today: >99% agricultural pesticides are the largest direct cause of insect mortality
3 years: >98% agricultural pesticides are the largest direct cause of insect mortality
20 years: >95% likely agricultural pesticides are the largest direct cause of insect mortality
The one possible category I could imagine overtaking agricultural pesticides are insects raised for animal feed. I think it is fairly unlikely farming insects for human food will grow substantially, but much more likely that insects raised for poultry feed will grow in number a lot, and even more likely that insects raised for fish feed will grow a lot. There is a lot of venture capital going into raising insects for animal feed right now, so it seems at least somewhat likely some of those projects will take off (though there are cost hurdles they haven’t cleared yet compared to other animal feeds. Replacing fishmeal with insects seems even more likely because fishmeal is already a lot more expensive than grain feed.
Replacing ~40% of fishmeal with black soldier flies would put insect deaths from farming at the lower end of my current estimate for the scale of impact from agricultural pesticides. So I guess if estimates of agricultural pesticide impact are too high for an unknown reason (maybe insect populations collapse in the near future or something), there is a definite possibility, but not a big one, that insect farming could overtake pesticides in terms of deaths caused.
And what ratio do you see between agricultural pesticides and other issues you excluded from the category (like climate change and partially naturogenic outcomes)?
I am very uncertain about this. Brian Tomasik estimates the global terrestrial arthropod population to be 10^17 to 10^19 individuals, which would be 10 to 100,000 times the animals impacted by pesticides. Plausibly basically all of them could be impacted by climate change, but it’s hard to know whether or not the sign of those impacts will be negative. I imagine that most the impact from climate change, for example, would come from populations shifting—e.g. there suddenly are far fewer of an animals with survival strategy X, and a lot more of insects with survival strategy Y, and that change leads to a lot more positive or negative welfare. That being said, I think we possibly should expect ecosystems changing rapidly to be on average bad for the animals who live through that change or are born after it, at least in the short term.
I think one other excluded area I excluded that could be huge is nematodes and other microscopic invertebrates. There are obviously questions that ought to be raised about their likelihood of having valenced experiences, but as of writing I can purchase 250 million nematodes for biological control on Amazon for $135 USD. Nematodes are widely used in agriculture, and some agricultural pesticides possibly impact nematodes, implying that they’d possibly kill wild nematodes. So it seems like there is some possibility that nematodes impacted by agricultural pesticides outweigh insects impacted by them.