Sebastian Spiewok, Department of Zoology, Martin-Luther University Halle-Wittenberg, Hoher Weg 4, Halle (Saale), 06099, Germany and Peter Neumann, Swiss Federal Research Station for Animal Production and Dairy Products, Swiss Bee Research Centre, Agroscope Liebefeld-Posieux, Schwarzenburgstrasse 161, 3003, Bern, Switzerland.
Monogyny of honeybee colonies, Apis mellifera, is restored after swarming via lethal fights among multiple virgin queens. Fights are pheromonally released by physical contact to the dorsal abdominal surface. However, swarm mergers result in polygynous colonies with older and mated queens. Since monogyny is restored after such mergers, we also expect older, mated and laying queens to fight. To assess the fighting abilities of older queens, we conducted contests between paired individuals in Petri dishes: 20 virgins (= VQ, <7 days old), 16 recently mated ones (= MQ, 4 weeks old) and 20 older mated ones (= OQ, ~1 year old). The number of contacts, spraying behaviour (releasing faeces), attacks (bending of the abdomen, biting) and fights (aggressions lasting >10 s) were recorded for 10 min. In case of ongoing fights, observation time was extended for up to 1 hour. OQ showed no spraying behaviour, while spraying was observed in 25% of fights between MQ and in 70% of fights between VQ (χ2=11.50; p=0.003). Significant higher proportions of the encounters in VQ and MQ led to attacks or fights compared to the OQ (p<0.05). While all contests between VQ and 75% of those between MQ were lethal, this was only the case in 10% of the fights between OQ (χ2=17.94; p=0.001). Our results indicate that the abdominal releaser of queen stinging behaviour is still present in MQ and OQ, but the latter ones are less aggressive and less efficient in killing opponents than VQ or MQ. One underlying reason may be the high degree of ovary activation of laying queens in large, established colonies. Nevertheless, our observations clearly show that MQ and OQ also fight, which appears adaptive in light of mergers between honeybee colonies.
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