Rise of male individuals in stingless bees colonies leads to queen's death

August 30, 2017

Queens of stingless bee species (Meliponini) face a reproductive dilemma. If they mate with males with which they turn out to share the same sex determination gene, half of their offspring will consist of males, and the colony's workforce will fall by half, given that effectively only the females are workers.

In addition, males with both paternal and maternal (diploid) genetic material as a result of this unfortunate choice by the queen only consume the resources collected by workers and are usually sterile, contributing to diminished reproductive chances for the colony. A research project supported by the São Paulo Research Foundation (FAPESP) involving a team of scientists in universities of Brazil, Belgium, and the United Kingdom shows that the emergence of diploid males from this type of mating also leads to the death of the queen in colonies of the stingless bee species Scaptotrigona depilis.

According to Ayrton Vollet-Neto, first author of the study, the results suggest that this behavior may be common to all stingless bee species because it occurs in phylogenetically distant genera.

One possible explanation for the death of a queen that doesn't comply with the role of maintaining a proportional rate of worker bees in the colony is that a replacement daughter queen will be able to mate and ensure the colony's survival. Otherwise, the most probable outcome would be the death of the colony. "If the queen is killed quickly, she can be replaced by a daughter that will have a chance to mate with a male that doesn't have the same sex allele," Vollet-Neto said.

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Stingless bees have their nests protected by soldiers

Date: February 23, 2017

Source: Universität Mainz

Although stingless bees do not have a sting to fend off enemies, they are nonetheless able to defend their hives against attacks. Only four years ago it was discovered that a Brazilian bee species, the Jatai bee, has a soldier caste. The slightly larger fighters guard the entrance to the nest and grip intruders with their powerful mandibles in the event of an attack. Working in collaboration with Brazilian researchers at the University of Sao Paulo and Embrapa in Belém, biologists at Johannes Gutenberg University Mainz (JGU) managed to identify four further species which produce a special soldier caste to defend their nests. "This is therefore not a solitary case, as it seems there is an astounding variety of social organization among other stingless honey bees," said Dr. Christoph Grüter of Mainz University. The scientists had examined a total of 28 different species from entirely different habitats in Brazil.

There are more than 500 species of stingless honey bees worldwide, 400 of them in Brazil alone. They form highly social societies with a queen and collect pollen in the same way as European honeybees. Many of the stingless bee species, however, are helplessly exposed to attacks by robbers. These robber bees, which also belong to the stingless bees, have given up foraging for pollen or nectar themselves. Instead, they invade the nests of other bees and steal their honey and pollen, even wax and brood food. In 2012, however, Dr. Christoph Grüter and his colleagues discovered for the first time that parasitic robbers encounter difficulties when they assault a Jatai bee (Tetragonisca angustula) colony. The nest entrance is protected by guard bees which are larger than the hive's other worker bees.

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