The problem with that is flax is too unstable due to the high polyunsaturated fat content, once ground the flax seeds won’t last longer than a couple weeks, and the oils will go rancid. It would be better to leave the seeds whole, although the beetles and worms would have more trouble eating it.
This would not only be detrimental to the health of the mealworms, (due to their passive respiration system they are very vulnerable to oxidative damage, so any extra from rancid oils may impair their antioxidant status and effect their growth and survival rate in theory.
Additionally, the ground flax would cause off flavors in the meat and eggs of any animals that you feed the mealworms to, since the mealworms would accumulate such high levels of PUFA from a rancid substrate.
This is well known in animal agriculture, especially in pork production, there is a hard limit on the amount of flax or fish oil you can add to an animals diet, before off flavors can be detected in its edible products. This is something that happens because of the low oxidative stability of PUFA, and omega 3 fats especially. This is also one of the reasons fish spoils so rapidly. Feeding high levels of vitamin E to livestock can reduce the off flavors in their meat and eggs, but not completely if very high omega 3 diets are fed.
Ive thought about this as well, and decided it would be better to dehydrate a very low fat, starchy vegetable with a good omega 3/6 ratio, and grind it into a four to use as bedding, potatoes are a perfect option, and this could be combined with brewers yeast, and perhaps hay or dried weeds/green plants, and only a very small amount of freshly ground flax periodically, just enough to last one or to days at a time.
A second option is to make a high MUFA bedding using high oleic peanut flour, or some sort of high monounsaturated fat tree nut, like acorns, hazelnuts, macadamia, etc. acorns could be collected from the wild and cleaned, toasted, and turned into flour. Oleic acid is a healthy fat like omega 3, but far more stable.
