I've seen that happen in species bulbs that are susceptible to too much moisture. On the scales, the rot always starts from the proximal (the part closest to the central stem) end and progresses outward. In my case, I've never found insects to be the cause, but they are an impetus for bulb rot in many situations. If the insects appear round (think teeny-tiny itsy-bitsy spiders) rather than oblong, they are likely bulb mites. If they are in the shape of an aphid, that's lprobably what they are.
