Abstract
Here we explored the potential for host shift from honeybee, Apis mellifera, colonies to bumblebee, Bombus impatiens, colonies by the small hive beetle, a nest parasite/scavenger native to sub-Saharan Africa. We investigated small hive beetle host choice, bumblebee colony defence as well as individual defensive behaviour of honeybee and bumblebee workers. Our findings show that in its new range in North America, bumblebees are potential alternate hosts for the small hive beetle. We found that small hive beetles do invade bumblebee colonies and readily oviposit there. Honeybee colonies are not preferred over bumblebee colonies. But even though bumblebees lack a co-evolutionary history with the small hive beetle, they are able to defend their colonies against this nest intruder by removal of beetle eggs and larvae and stinging of the latter. Hence, the observed behavioural mechanisms must be part of a generalistic defence system suitable for defence against multiple attackers. Nevertheless, there are quantitative (worker force) and qualitative differences (hygienic behaviour) between A. mellifera and B. impatiens.