In terms of why some colonies succumb to AFB and others don't, I think it's more likely a lack of hygienic behavior and/or immunological responses rather than environmental factors related to sunlight or cold. Spivak reviewed the literature with a focus on Rothenbuhler's extensive work on the subject of AFB and hygienic behavior. Also, see Randy's article,  http://scientificbeekeeping.com/sick-bees-part-3-the-bee-immune-system/  for a more comprehensive explanation of immunity. 


>Spivak M, Gilliam M (1998) Hygienic behaviour of honey bees and its application for control of brood diseases and varroa Part I. Hygienic behaviour and resistance to American foulbrood. Bee Wld 79: 124–134.M

>https://tinyurl.com/y7ekus4g


Unfortunately, Rothenbuhler is behind a paywall:

>ROTHENBUHLER, W C; THOMPSON, V C (1956) Resistance to American foulbrood in
honey bees. I. Differential survival of larvae of different genetic lines. Journal of Economic
Entomology 49: 470–475.

Bill Hesbach
Cheshire CT. 

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