The Modified Pharaoh Approach: Stingless bees mummify beetle parasites alive

Abstract

Social insect colonies usually live in nests, which are often invaded by parasitic species. Workers from these colonies use different defence strategies to combat invaders. Nevertheless, some parasitic species are able to bypass primary colony defences due to their morphology and behaviour. 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 destructive nest parasites Aethina tumida alive, 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 parasite advancements and removes their ability to reproduce. The convergent evolution of live mummification by stingless bees and social encapsulation by honeybees suggests that colonies of social bees generally rely on, secondary defence mechanisms when harmful nest intruders cannot be killed or ejected easily. This process is analogous to immune responses in animals.