by Allison Bray | BS/MS Candidate | SQ Vol. 10 (2012-2013)
The risk of predation can affect foraging by honey bees (Apis mellifera) even when predators do not succeed in killing the bee, through a non-consumptive effect. Bees can alter their behavior in response to a perceived risk, which can reduce foraging efficiency, potentially affecting hive fitness and plant pollination, a key ecosystem service. To better understand these effects it is important to understand how bees detect and react to the presence of a predator.
We tested if honey bees, given a choice between a food source with a predator, the praying mantis (Tenodera sinensis), and one without, would avoid the predator. We also tested to see if the introduction of a predator to a feeder would decrease waggle dancing (recruitment) among the bees visiting that feeder.
To test bee avoidance of food sources containing predators, we trained bees to a feeder, and then gave them a choice between a safe feeder, and a feeder with a live tethered predator, a mantis. We used live mantises of varying sizes, measured by instar (mantis growth stage). We recorded the number of bees that fed at each feeder (each bee was captured and marked). Bees did not avoid younger and smaller 4th and 5th instar mantises, but significantly avoided the larger 6th (73% chose the mantis-free feeder, n=172, p<0.01), 7th (63%, n=149, p<0.01), and 8th (adult) (67, n=161, p<0.01) instars. Bees may perceive larger mantises as being more risky, likely because larger mantises are more capable of successfully capturing a bee.
To determine if the bees were using visual or olfactory cues to detect predator, we conducted trials with a plastic mantis (visual cues only) and with a hexane extract obtained from mantis exoskeletons on filter paper (olfactory cues only). Bees significantly avoided the plastic mantis (67% chose the mantis-free feeder, n=262, p<0.01) and the mantis extract (74%, n=121, p<0.01). Thus, honey bees are capable of using either type of cue, and most likely use a combination of both.
Foraging behavior could also be affected if the bees altered their communication in response to a predator. Honey bees recruit nest mates to profitable food sources through a dance that communicates the location and quality of a food source. The more dance circuits, the higher the quality of the nectar. The presence of a predator may decrease the perceived profitability of a food source, decreasing dancing and recruitment for that source. To test the effect of a predator on recruitment communication, we trained bees from an observation hive to a feeder and marked them. We then recorded the number dance circuits for each returning bee. We then introduced a mantis to the feeder and recorded the number of dance circuits for each bee again (provided that it continued to visit the feeder), and compared dancing using a paired t-test.
Dancing decreased significantly after the introduction of the predator according to a two tailed paired t-test (t=2.68, df=67, p=0.009, Fig. 1), showing that bees do alter their recruitment communication in response to perceived predation risk.