Sounds like the temperature change caused whatever the bugs were to hatch. I have had this happen several times with various bugs when I bring a plant in the house. It is important to watch a plant carefully whenever it changes locale and to spray with some sort of organic pesticide as much as possible at the first sign of infestation.
All that said: That is too bad what happened to you. But don't linger too long on this. I think your cleaned-off babies should do just fine provided you didn't replant them in the exact same spot. If you did, the remaining eggs may still be dormant in the dirt and you should keep an eye on them next spring and be looking for the same pest again.

I don't know if I stated it clearly enough, but I am pretty sure your mealy pests traveled via the dirt which is laden with eggs. And I am also pretty sure that same dirt patch is still probably holding more eggs. That said: there are a lot of factors outside which can thwart pests. Ground beetles are a good one for eating this sort of pest. I suggest researching your pest because it is still out there and may or may not pose a problem in the spring. (It may not with plenty of natural predators present). But PLEASE find an organic solution if you do take an action based upon your findings.

Got it - bugs may still be there, and erhem, yes, bulbs went back in same bed. No choice there, unfortunately. So. Bugs. What would an organic treatment BE?

I have heard of both Bacillus popilliae (aka Milky Spore Disease) and predatory nematodes both being successful treatments for ground grubs. One is a disease on the grubs and the other is a parasite of the grubs. The grubs may not be a problem at all, but if you want to err on the safe side and do something preemptively then that is up to you. The Bp treatment (B. popilliae) is probably the easier of the two. You won't want to do it until the spring when the grubs are hatching/hatched. I have used Bt (a different species of bacteria) on moth larva/loopers with great success so I am guessing that the Bp will work similarly well.

How would I know when they hatch, aside from digging them up? I have a bed of dirt, with bulbs in one area, bearded iris in another, my Cl Cecile Brunner, and some lilies.

What signs should I look for? Keeping in mind that I did not see any buglife on the bulbs when I dug them up in the first place.

Honestly -> I don't know. I have told you all that I do know. Seek more guidance elsewhere or just experiment come spring. There is always the possibility that Mother Nature will just take care of it since the bugs won't be in isolation without all of the other critters (like they were in your garage). Best of luck to you! (I hope I was at least somewhat helpful)

Ya know what. I overlooked something very obvious: How long were the bulbs in your shed for??? Rereading your original post it seems like they may have been there for a while. Where they in the summer heat? They may simply have started to rot on their own and attracted flies. I may have overthought this whole thing.

They were in a garden shed that is WELL shaded, so it never gets more than warm in there, for a few months at most. I dug them up well after the leaves had dried up. I would think if flies had come in and gone after the rotting bulbs, I'd have found mealies in both saucers of bulbs, but they were ONLY in one saucer. So, I think I must have brought it in with them even if I didn't see it. And these were not maggots, they were mealy bugs, leaving little white webs where ever they squirmed. Some of my bulbs had dessicated, but none had rotted. There was no 'rot stink' going on. I may call or go visit my favorite local nursery and ask what they recommend for treating the mealies and when. They would tell me organic if I stipulated that.

Oh, and I failed to mention - there's no any lawn here. At all. There is some lawn in the area, but not much of it, as there's generally too much shade unless the trees have been cleared. I'm in a coastal band of redwoods just outside of San Francisco. My sunniest space is gravel driveway, and then there's ONE sunny bed for gardening in out front, and it looses the sun early afternoon. 6 hours max. Back yard is even worse for sun, and I have a septic I need to not plant on top of, once somebody tells me precisely where the thing IS....

Radiant Poppy - no overthinking. All info is good!