I read this blurb in the New Scientist about a PNAS paper (subscription required for next 6 months) on how hive beetles (Aethina tumida) are able to infest bee hives by throwing off the bees because they are producing isopentyl acetate which is thought to be produced and used by bees to signal an alarm. So the increased levels of the pheromone disorients the bees allowing beetles to continue infecting. European bees appear to be susceptible to this attack while the African bees have apparently evolved to better handle the beetle infestation. I’m not clear if the African bees have a different behavior or if they have different biochemical pathways/receptors to not be fooled by the cheap perfume of the invaders.
The fungus part here is that the beetles are carrying a hemiascomycete yeast, Kodamaea ohmeri in the Saccharomyces clade (see Suh and Blackwell 2005 for more details), which produces the isopentyl acetate pheromone. So it is a sort of auto-immune hive reaction where the defense mechanism is being short-circuited and harming the host.
Another very cool multi-level co-evolutionary story where a fungus is playing a role. I think there are a lot of further molecular evolution stories to follow up on here to dive deeper into the evolution of the pheromone biosynthesis pathway in both the bees and the fungus. I wonder how long the fungus and beetles have been in contact and whether it is specific to these beetles only. Maybe there has also been selection to increase the production in the yeast somehow through cultivation by the beetle or is this just all a lucky move by the beetle to get the right fungus on it? The advantage for the fungus is a better place to reproduce and dispersal, so it would make sense that there is some selection to produce the compound, although I wonder if the beetles themselves are able to sense or is selection acting most strongly on the beetles success in the hive?
Also I wonder if any of the expression analysis that is being done on behavior (like in Charlie Whitfield’s lab) could also tell if the African bees are responding differently to the pheromone. The research in this paper shows that aspects of domestication of european honeybees is partly responsible for the different outcomes of a beetle infestation.