What's a queen bee to do?
After hatching, a new queen leaves her colony to take off on her nuptial flight. She finds an area where drones (male bees) congregate and mates with many of them. Once mated, she needs a colony of her own over which to rule.
Honeybees solve this in an orderly way. First, very few new queens are born. Workers control whether a particular female will blossom into a queen with the quantity and quality of food they feed her. New queens are created if the reigning queen is near death, so a daughter can take her place. Alternatively, if the colony gets large enough, a new queen will be born and she will set off with some of the workers to start a new colony (a phenomenon called swarming).
Stingless bees of the genus Melipona are different. Queens are seemingly overproduced, with up to 20 percent of all females developing into queens. What happens to all those queens?
A recent genetic analysis suggested a surprising answer. It showed unrelated queens frequently invading and taking over colonies in which the reigning queen happened to die. This finding called into question the assumption that new colonies were only established through swarming or an old queen passing the torch to a daughter queen.
Ina new study, researchers from the Universities of São Paulo, Brazil and Leuven, Belgium, took a closer look at the situation. They observed eight colonies of Melipona scutellaris, half of which had their queens removed. The researchers collected the colonies' queens as they were born and marked each one with a radio frequency identification (RFID) tag.
The results confirmed that foreign queen takeovers are common occurrences. Interestingly, queen bees never attempted to take over a colony that had a queen in place. The queens were selectively seeking out colonies without queens in which to establish themselves.
The researchers also noticed that all takeover attempts took place in the evening around sunset. This happened to be the time of day that colony entrance guards were least efficient. Passing the guards is the trickiest part of infiltrating a colony, as they play the major role in rejecting and attacking intruders. Once a bee is inside the colony, she is home-free. Foreign queens seemed to be taking advantage of the letup in guard vigilance around sunset to sneak in to the colonies.
It's not entirely clear how foreign queens know which colonies lack queens. Previous observations of Melipona bees have revealed queenless colonies to be more "restless and irritable" than colonies with queens. This could be explained by the absence of queen-specific pheromones, which appear to have a calming effect on colony behavior. Invading queens might decide whether or not to enter a colony based on its collective behavior, or they could use the lack of queen-specific pheromones as a cue.
Whatever signals they use, queen bees are experts at taking advantage of the changes in guarding vigilance throughout the day. For newly mated queens in search of a colony in which to settle down and lay their eggs, sneakiness pays off.
References:
Van Oystaeyen, A., Alves, D. A., Oliveira, R. C., do Nascimento, D. L., do Nascimento, F. S., Billen, J. and Wenseleers, T. (2013). Sneaky queens in Melipona bees selectively detect and infiltrate queenless colonies. Animal Behaviour epub July 30, 2013. doi: 10.1016/j.anbehav.2013.07.001.
Wenseleers, T., Alves, D. A., Francoy, T. M., Billen, J. and Imperatriz-Fonseca, V. L. (2011). Intraspecific queen parasitism in a highly eusocial bee. Biology Letters 7: 173-176. doi: 10.1098/rsbl.2010.0819.
