He defines hedonium/dolorium as the maximum positive/negative utility you can generate with a certain amount of energy:

"For example, I think a given amount of dolorium/dystopia (say, the amount that can be created with 100 joules of energy) is far larger in absolute moral expected value than hedonium/utopia made with the same resources."

See responses to this post on /r/badeconomics.

The closest is probably Wild-Animal Suffering Research, since they have published (on their website) a few papers on invertebrate welfare (e.g., Which Invertebrate Species Feel Pain?, An Analysis of Lethal Methods of Wild Animal Population Control: Invertebrates). However, their work doesn't focus exclusively on invertebrates, as they have published some articles that either apply to all animals (e.g., “Fit and Happy”: How Do We Measure Wild-Animal Suffering?), or only apply to vertebrates (e.g., An Analysis of Lethal Methods of Wild Animal Population Control: Vertebrates).

Animal Ethics and Utility Farm also work on issues relating to wild animal suffering. My impression is that AE mostly focuses on outreach (e.g., About Us, leaflets, FB page), and UF mostly focuses on advocacy and social change research (e.g., Study: Effective Communication Strategies For Addressing Wild Animal Suffering, Reviewing 2017 and Looking to 2018), although AE also claims to do some research (mainly moral philosophy literature reviews?). Again, these organizations don't only focus on invertebrates. In fact, AE doesn't even focus solely on wild animals, as they seem to spend significant resources on traditional animal advocacy (farm animals, veganism) as well.

I don't know of any insect-specific charities, although some may exist. Unfortunately, the Society for the Prevention of Cruelty to Insects is only satire. If we widen the scope a bit and include invertebrate-specific charities, I know only of Crustacean Compassion, but there may be others. There was also at one point a website called Invertebrate Considerations that seemed to be EA-aligned, but it's gone now and I don't think it was ever anything more than just a mockup.

Humane insecticides might be a promising area for future work.

According to this reddit thread:

The EA Hub team had to take down a few sites because of a CPU overuse error. Until they work out what the problem is and an alternative, some sites will have to stay offline. An archive has been retained.