Honeybees may have a unique system for accepting migrants. “Drifting” bees that wander into a neighbouring hive may be allowed to stay – if the guard bees see fit.
Honeybee drift is common in apiaries, where hives are placed closer together. A bee that drifts essentially migrates from its own hive to another, something thought to be unintentional.
Morgane Nouvian and her team at the University of Queensland in Brisbane, Australia, reviewed 161 papers on defensive behaviour in honeybees to get a comprehensive overview of the phenomenon.
They reported that 10 to 15 per cent of honeybees take on nest-guarding roles when they are 2 to 3 weeks old. Their main role involves detecting and dealing with predators, but they are also the first point of contact when drifting honeybees arrive.
In an inspection that can last half a minute, the guards check out chemical cues on the newcomer – typically hydrocarbons – that depend on hive-specific genetic factors and comb wax. If this profile matches or nearly matches that of their own hive, the guards will let the drifter in.
Around 30 per cent of drifting bees are allowed to stay, experiments show.
The guards also have to identify marauding bees that aim to steal honey. “We know now that these robber bees are detected by their flight patterns and speed,” says Nouvian. “Guards can detect an incoming robber and sting it before it even reaches the nest.”
Guided by resources
There are other factors that influence whether a newcomer is allowed in, the main one being the availability of resources both inside and outside the hive.
“It’s interesting that when there are enough resources, for instance nectar near the hive, and fewer empty combs, guards allow in more non-nestmates,” Nouvian says. There may not even be guards at the nest entrance in these circ*mstances, Nouvian adds.
These “open borders” can shut down quickly in situations of food scarcity. Guards not only reject newcomer bees in these cases, but may even kill them. Nouvian adds that combs with no stored honey may make guards more aggressive.
Experiments by Francis Ratnieks at the University of Sussex, UK, show that once accepted into a new hive, migrant bees eventually blend in chemically, too. He “fostered” young non-nestmate worker honeybees by placing them straight into the hive, bypassing the guards. The young bees took on the comb wax of the new hive and were just as likely to be accepted by the guards later on as the native bees were.
“This shows that the chemicals on their body surface by which they are recognised as nestmates are acquired from the colony they are in,” Ratnieks says.
Other work by Ratnieks shows that guard bees are extremely good at detecting predators like wasps.
“In experiments in which we introduce either a wasp or a non-nestmate honeybee to the hive entrance, we found the guards never mix up wasps with honeybees,” he says. “They are quite obviously detected as ‘different’ to the guards, which is important as wasps prey on larvae and worker bees in the hive.”
Journal of Experimental Biology DOI: 10.1242/jeb.143016
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