Busy Bees Get Workshy When Times are Good

The stereotypical image of the hard-working bumblebee has been shattered by new research published in the journal Behavioural Ecology and Social Biology.

Scientists from Queen Mary University London have found that bumblebees Bombus terrestris will only work if they absolutely have to – an evolved strategy to conserve energy in times of plenty.

Bees are known to respond to cues describing how full their food reserves are; successful foragers will reduce the number of runs to and from a nectar source, and fewer bees will engage in foraging trips. Molet and Raine, the lead authors of this study, investigated whether bees will respond to a third cue, that of recruitment pheromones.

To investigate this idea, the team attached minute radio transmitters (Radio Frequency Identification or RFIDs) to the bees, to determine the frequency of visits to pollen sites within the study area. The researchers created a concoction of chemicals that closely resembled bumblebees’ natural cue pheromone, and also used a single chemical cue, to examine recruitment response. The bouts were recorded in 30 minute intervals, and during each interval the researchers monitored how ‘full’ the honeypots were.

Although pheromones increased the number of foraging bouts and new recruits, the bees were far less likely to respond when food reserves were well stocked, effectively ignoring the invitation to forage for nectar.

Dr Raine described how the chemical cue given off by single foragers to collect more food was not always heeded:

“If there isn’t stuff to collect, a lot of them are pretty much on standby. They will be sitting around doing very little, or apparently so.”

In summary, the research shows that bees use a suite of complex cues, (recruitment pheromone, frequency of visits by other foraging bees, and food reserve fullness) to decide whether or not to bother going out and foraging for food. This is the first time bumblebees’ response to pheromones has been shown to be tempered by another cue, in this case – colony nutrition status.

The research has potential implications for commercial crop pollination. A healthy, well fed colony may be more reluctant to go out looking or food – and thus pollinating – if the incentive isn’t there. In the study the bumblebees were up to four times more responsive to the natural, 3-chemical pheromone mix than the single eucalyptus cue, therefore using the right chemical make-up when enticing bees is essential to motivating them.

However the bees reputation has not been completely tarnished. Dr Raine said that its not that the bumblebees are lazy, they have simply evolved an effective strategy to conserve energy when food is plentiful, and they are busy when there is work to be done.

Reference: Molet, M., Chittka, L., Stelzer, R.J., Streit, S., & Raine, N.E., 2008, Colony nutritional status modulates worker responses to foraging recruitment pheromone in the bumblebee Bombus terrestris, Behavioural Ecology and Sociobiology, 62:1919–1926, DOI 10.1007/s00265-008-0623-3