Cape honeybee, Apis mellifera capensis, workers can be social parasites and host colonies can defend
themselves by rejection of such workers. Using the pseudo-clonal obligate parasitic lineage of A. m.
capensis and wild-type A. m. capensis workers, which are facultative parasites, we show that host
colonies significantly increase their defence behaviour towards social parasites upon secondary
exposure. Most obligate and facultative social parasites were rejected before they could even produce
significant amounts of the queen-like mandibular gland pheromone secretion or activate their ovaries.
This suggests that other signals, like cuticular hydrocarbons, could be used by host colonies to identify
potential invaders. Honeybee colonies seem to be able to utilise these potential cues, learn from
their initial exposure to hive intruders and enable them to improve their defensive behaviour during
subsequent infestations, resulting in increased removal rates of parasites.