From Peter Borst’s previous post:

“Host suicide is most profitable when the host is infected by a parasitoid. 
The parasitoid reduces the host's reproductive fitness to zero, so that the*
(added)* cost of the suicide is also zero.”

So in order for this mechanism to have evolved or otherwise been acquired 
by European honey bees it seems likely that there are, or would have been, 
parasitoids that they or their close ancestors have had to deal with for a 
long time. Aside from the very difficult task of determining if it is 
suicide or a pathogen that kills bees that leave and don’t return, some of 
the questions that need to be answered, it seems to me, include:  Are their 
any such ancient parasitoids known to be associated with honey bees?  Are 
Varroa and or TM parasitoids in the true sense, i.e. do they for certain 
reduce their host’s reproductive fitness to zero?  How does the fact that 
Apis melifera is a social insect, whose individuals are not all capable of 
reproducing, affect the way this mechanism would function for the benefit 
of the species?  In other words would we need to examine the virulence of 
the prospective parasitoid in terms of its impact on the reproductive 
fitness of the individuals or the colony as a whole?  Both individuals and 
colony can be thought of as host for the parasite in this situation, and a 
colony does embody some of the characteristics of an individual in this 
regard, so it gets a little more interesting.  It would seem that the 
reproductive fitness of the colony is what's at stake here, and yet it is 
the non-reproductive workers who would be committing suicide.  My head is 
spinning.  Like many host-parasite relationships this gets very complicated 
and nothing about it seems obvious to me.  I think that when anything 
involving behavior in the natural world starts to seem obvious, red flags 
should go up.  But the mind boggling complexity of nature is also what 
makes it fascinating and awe inspiring to me.

Steve Noble

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