"Commercial honeybee enterprises began feeding bees high-fructose corn syrup back in the 70's after research was conducted that indicated that doing so was safe. Since that time, new pesticides have been developed and put into use and over time it appears the bees' immunity response to such compounds may have become compromised.
"The researchers aren't suggesting that high-fructose corn syrup is itself toxic to bees, instead, they say their findings indicate that by eating the replacement food instead of honey, the bees are not being exposed to other chemicals that help the bees fight off toxins, such as those found in pesticides."
Read more at: http://phys.org/news/2013-04-high-fructose-corn-syrup-tied-worldwide.html#jCp
Something apparently we cannot blame on global warming or climate change.