I have nematode issues every year with my D. granti eggs if I don't pull them out soon enough. I only use standard topsoil as the egg-laying medium though, purchased from a garden store and while it looks rather like "clean" dirt, it seems to have nematodes at some stage...each year, because I see them later. I often dig up my eggs in batches of 30 or so, once every six weeks or so in the spring. The nematodes will attack healthy eggs in a large tank of rather sterile substrate. When your adult female dies, I recommend removing the eggs of anything you aren't trying to overwinter. I usually overwinter my D. granti eggs and if I wait to long to dig them up for incubation in the spring, they succumb to nematodes that eventually crawl right in and party for a month or two. Mites seem to only suck on them a little bit at most or just hang out on the surface, waiting for a ride somewhere, perhaps. I've not noticed mites to actually kill an egg, but they are very commonly found on the eggs. I've tested a few out that have been found with mites and even kept with mites and they all hatched w/o issue. Seems strange, but then again I suspect these are offspring of the mites that came in on the adult beetles. Anybody whose had adult WC D. granti has probably seen these mites. The egg mites will reproduce themselves somehow w/o having done damage to the eggs so they are feeding on something. They are quite large and white and seem not to be found anywhere else but in association with the adult beetles or eggs, neither of which do they seem to harm in my experience.
When you harvest your eggs, inspect them. Then move them to a sterile substrate like coconut fiber to incubate if they are good. Simple.
