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Jatai forager bee (left) and the larger Jatai guard

Sussex scientists working with researchers in Brazil have identified the first example of a ‘soldier’ bee.

The discovery was made by a team including Professor Francis Ratnieks and Dr Christoph Grueter from Sussex's Laboratory of Apiculture and Social Insects, working with scientists from the University of São Paulo .

The team studied a common tropical stingless bee Tetragonisca angustula in São Paulo State in Brazil where it is known locally as Jataí. It nests in tree and wall cavities. Each nest has one queen and up to 10,000 workers.

Insect societies such as the Jataí’s are defined by cooperative and altruistic behaviour, with the workers caring for the nest and the queen’s offspring. This lifestyle also includes the division of labour among workers.

The research, published yesterday (Monday 9 January 2012) in the journal Proceedings of the National Academy of Sciences (PNAS) states that:

Jataí guard bees are 30 per cent heavier than their forager nestmates;

• they differ slightly in shape from foragers, with disproportionately larger legs and smaller heads;
• approximately one per cent of workers bees reared in a colony are soldier-sized;
• Jataí soldiers stand on the nest entrance tube and also hover near the entrance where they provide “early warning” detection of enemy attack

Like other social insects, Jataí use guard workers to protect the nest. A previous study by the team had shown that these guards were specialists who performed guarding duties for far longer (up to three weeks) than other types of worker bee, such as the honey bee, who spend just one day guarding the nest, progressing to other tasks as they get older.

The new research shows that Jataí guards, unlike their honey bee counterparts, are morphologically (physically) specialised to perform a particular task, being consistently larger than their nest mates.

Having larger-bodied guards is important for nest-defence, as they are better at fighting one of Jataí’s main enemies – the robber bee Lestrimelitta limao, which can kill off many colonies when raiding nests for food. These guards, then, are more like the ‘soldier’ workers found in some ant and termite colonies.

Even though the Jataí guard lacks a sting and is eventually killed, it can clamp its head onto the wing of a robber bee, preventing it from flying.

The discovery is significant in terms of the evolution of advanced insect societies. Large-bodied soldier workers have long been known in ants and termites, but this is the first evidence of a soldier bee – a worker physically designed for active defence of the nest.

Professor Ratnieks says: “Stingless bees are not defenceless. Jataí is one of the most common bees found in Brazil, but its sophisticated defences make it one of the most amazing.”