How do Varroa Mites know when to leave a hive?

Varroa mites are one of the single most detrimental stressors to honey bees.  Living off the blood of young bees and replicating alongside the capped, young honey bee larvae, they also rapidly spread viruses to the colony.  If the bite from the mites don't cause the bees' death, the viruses usually do.

Varroa mite on a bee.  Photo by Alex Wild  www.AlexanderWild.com

But, if you are a living organism that is constantly killing your host, how do you survive?

Researchers in Italy may have answer to this question. The results of their study are published in the Journal of Experimental Biology.  It suggests that varroa mites will stay within a hive with low levels of mite infestation.  There, they ride on the backs of the nurse bees which rarely venture far from the hive.  They can distinguish them from older foraging bees by the difference in their 'smell' - presumably by the chemical make-up contained in the wax coating in their backs. However, as the mite level increases, the odor differences become less and less distinguishable.  This allows the mites to attach to foragers where they can leave the hive on a regular basis.  Once outside the hive, these hitch hikers have a better chance of ending up in a neighboring hive as bees naturally drift between colonies.

So, now that we know the chemical odor that attracts varroa mites, my question is:  Could we make a trap for them baited with this odor?  Or, would it befoul the delicate balance of natural volatilized chemical compounds found within the hive?

Read more:
http://jeb.biologists.org/content/217/17/2998.abstract
http://entomologytoday.org/2014/08/29/how-do-varroa-mites-know-when-to-leave-honey-bee-hives-its-all-in-the-bees-wax/

Drone production starts when colony size is right

Researchers at  Cornell University recently published the results online of a study entitled

"A critical number of workers in a honeybee colony triggers investment in reproduction". 

Abstract:  "Social insect colonies, like individual organisms, must decide as they develop how to allocate optimally their resources among survival, growth, and reproduction. Only when colonies reach a certain state do they switch from investing purely in survival and growth to investing also in reproduction. But how do worker bees within a colony detect that their colony has reached the state where it is adaptive to begin investing in reproduction? Previous work has shown that larger honeybee colonies invest more in reproduction (i.e., the production of drones and queens), however, the term ‘larger’ encompasses multiple colony parameters including number of adult workers, size of the nest, amount of brood, and size of the honey stores. These colony parameters were independently increased in this study to test which one(s) would increase a colony’s investment in reproduction via males. This was assayed by measuring the construction of drone comb, the special type of comb in which drones are reared. Only an increase in the number of workers stimulated construction of drone comb. Colonies with over 4,000 workers began building drone comb, independent of the other colony parameters. These results show that attaining a critical number of workers is the key parameter for honeybee colonies to start to shift resources towards reproduction. These findings are relevant to other social systems in which a group’s members must adjust their behavior as a function of the group’s size. "

Frame with drone brood on the bottm

See the full text  of the study