Workers from social insect colonies use different defence strategies to combat invaders. Nevertheless, some parasitic species are able to bypass colony defences. In particular, some beetle nest invaders cannot be killed or removed by workers of social bees, thus creating the need for alternative social defence strategies to ensure colony survival. Here we show, using diagnostic radioentomology, that stingless bee workers (Trigona carbonaria) immediately mummify invading adult small hive beetles (Aethina tumida) alive by coating them with a mixture of resin, wax and mud, thereby preventing severe damage to the colony. In sharp contrast to the responses of honeybee and bumblebee colonies, the rapid live mummification strategy of T. carbonaria effectively prevents beetle advancements and removes their ability to reproduce. The convergent evolution of mummification in stingless bees and encapsulation in honeybees is another striking example of co-evolution between insect societies and their parasites.

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.

The eYcacy of bottom board traps and CheckMite + strips using Coumaphos, for small hive beetle (SHB) diagnosis and control was studied in Australia. Colonies in three apiaries (N = 10 each) were surveyed for SHB. In two apiaries, colonies received bottom board traps (cardboard or plastic) with CheckMite + strips and in the control apiary, traps without strips. After 5 days, all colonies were surveyed again, killed and dissected to quantify non-detected SHB. SigniWcant diVerences in the number of live SHB were found between apiaries after treatment, supporting the fact that Coumaphos traps are eYcient (trap mortality: 94.73 § 0.06% cardboard and 99.53 § 0.01% plastic). However, mortality assessment at the colony level (53.29 § 31.30%), showed that only a limited SHB proportion was aVected. Post mortem colony inspections revealed that 14.06 § 10.53% SHB were undetected, which should be considered for quantitative diagnosis. Bottom board traps provided a Wrst estimate of infestation levels (43.03 § 27.02%).

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