The chemical ecology involved in cuckoo bumlebee offspring survival in host nest

In social insects, the high energetic costs of brood care have promoted the evolution of social parasites that exploit worker force of conspecifics or heterospecifics. In bumblebees, all the species of the subgenus Psithyrus have lost their worker caste and are completely dependent on host workers to produce their offspring. One of the most striking challenges for these social parasites is to avoid the detection and aggression by their hosts. Many studies have shown how socially parasitic queens overcome host recognition systems to enter successfully into host colonies. However, once a social parasite has successfully usurped a host nest, its emerging offspring still face the same challenge of avoiding host recognition. This is especially the case for the young Psithyrus males who possess a strong chemical signature because of their early production of species specific sex pheromones. Therefore, host workers might be able to recognize them. We hypothesized that parasitic males should require a strategy to prevent host agonistic behaviors. This study presents how males of the cuckoo bumblebee Bombus vestalis fool Bombus terrestris workers during their intranidal life. Our results show that parasitic males produce an allomone that repel attacking host workers. This is the first example of an active exfiltration strategy in social parasites.