Potential Research:

Another Viewpoint: Taste Aversion as a Product of Roost-Interactions 

There is also the possibility that taste aversion in generalist bats in comparison to vampire bats comes about through continuous learned associations with other bats.  While vampire bats form roost sites with other vampire bats, food associations between vampire bats are usually between mothers and their offspring (Wilkinson, 1984) wheras fruitivirous bats are believed to glean information about food from any potential roost mate by smell (Ratcliffe et. al., 2005).  This brings up the question of whether taste aversion can or cannot be learned through direct mother-offspring interactions or continual processes of indrect roost interactions.  Indirect roost interactions between fruitivirous bats who have eaten unripe, toxic fruits may act as the stimulus by which other bats will learn to be adverse to unripe and toxic fruits.  In vampire bats, however, mother's usually directly feed or lead their offspring to blood, which may suggest that vampire bat offspring do not have the opportunity to learn or distinguish between different blood sources.  

roosting bats @ http://www.conservationcentre.org/images/vamclose.jpg

A roost of vampire bats.

Photo found at http://www.conservationcentre.org/images/vamclose.jpg

Phylogenetic Investigation

It is not currently known if there is a genetic mechanism for taste aversion in bats, however a phylogenetic study of bats may reveal if there is such a mechanism and if it has been lost twice or gained many times.  Many of the papers concerning taste aversion in bats appear to assume that taste aversion is a trait that was lost in vampire bats since taste aversion is a mechanism that is assumed to be necessary for animals that have a widely varying diet.  A comparative study of various species of bat , looking at taste aversion as well as other behavioral and non-behavioral phenotypes, could answer this question.