I gave that a shot, and they didn't last. You'd be introducing them as a treat, not as a reproducing group. The surfaces of tanks are too small when there are fish predators. With Epiplatys killies, much smaller than your hungry Pantodon, they were gone in a minute, in a 4 foot 75.
Many diving beetles are fish predators.
As food, they could provide some enrichment, but I wouldn’t intentionally introduce unknown insects into a reef tank. You could end up adding contaminants, pesticides, or species that reproduce faster than expected. If they show up naturally, your butterflyfish may treat them like live snacks, but I’d leave the population alone rather than trying to culture them in the tank.
This isn't a reef tank situation. I regularly add insects from outside to my tanks, depending on the tank and the species. It takes a little research (a few minutes) when you meet a new one, but this is what my fish eat in the wild. I favour insectivorous fish. Mosquito, midge and fly larvae, ant eggs and larvae, swatted bugs, daphnia, cyclops - it's all great stuff. I avoid the predacious diving beetles and dragonfly larvae, although small dragon fly species have reached maturity unseen and unharmful in tanks here. I don't know if I accidentally introduced them or if they got in and laid eggs.
If you are in an urban centre or in a weird lawn mad suburb, then pesticides could be an issue. Otherwise, it's unlikely. At times of the year, insects are the staple here, allowing me to avoid processed fish foods. But the dream of a tank where insect species sustain themselves in the presence of a predatory fish species is just a dream. Tanks are too small and fish are just too good at their work.
Pantodon are large mouthed, and you could probably culture grubs used in the reptile hobby. They're too big for my fish, although I culture wingless fruit flies and white worms for my tanks. The aquarium are in an outbuilding 50 metres from the house, or my wife would kill me dead for all this!
