mites. starvation is easy to spot. every cell has a bee butt sticking out. ALL my hives have candy that is checked throughout the winter as weather permits.
I may be repeating myself but...1st I HATE using chemical treatments in my hives, yard, garden, or orchard. I use them it's a last resort. ex.-my wife gets poison ivy if she looks at the plant. I cut down the vine to where I can coil it up, spray it, & then cover the sprayed plants with an overturned 5 gallon bucket. this minimizes environmental exposure.
I originally would put mite drop boards on hives & the infested hives were treated & non-infested were not. then when the untreated hives died that winter the usda tests usually showed high mite counts in those hives. so MY take is that things can change within days or weeks so now I only test AFTER I treat ALL hives. the last 3 years I've been having 9-10% losses in the winter. my regimen has been to use oxalic acid drizzle in late march, apiguard in mid-late august, & oxalic acid vapor in October & November ( if it's warm enough ). I also did a test this January & vaporized 2 hives during a warm spell.