Adler's study finds natural plant chemicals reduce bee parasites
https://www.cns.umass.edu/about/newsletter/april-2015/adler-finds-natural-plant-chemicals-reduce-bee-parasites
The second article has Heather Mattila at Wellesley College showing the importance of nutrition on honey bee development.
Honey Bee Workers That Are Pollen Stressed as Larvae Become Poor Foragers and Waggle Dancers as Adults
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0121731
One of the easiest and best things we can do to help our bees is to simply plant more diverse flowers in our gardens. Not only do we aid the little pollinators, we also make our environment cheerier!