You take a nature walk in Western New Mexico during the spring season and you notice several large, black yellow insects with shiny abdomens drilling through a piece of dead wood. Your bee radar is triggered and you identify them as valley carpenter bees! Now, you may be wondering why are these bees hard at work instead of enjoying the breeze. Well, the holes in the wood will serve as nests for the young carpenter bees and the adults build their nests surrounded by large aggregations of many other nests. A problem which arises as a result of this type of nesting behavior is that it hampers a bee’s ability to accurately identify its nest and to distinguish the same from amongst other nests.
In order to understand how these bees localize their nests in such a dense population, researchers, Madeleine Ostwald, Zachary Shaffer, Stephen Pratt and Jennifer Fewell manipulated visual or olfactory cues at several nest entrances. These nests were found on 4 logs of wood relocated from a nearby park to Arizona State University. Before beginning their experiments, they surrounded each log with curved rebar poles so that they could accurately measure the search time and the search error rate of the bees. Search time referred to how long a bee spent after passing through the poles till when they recognized their nest and search error rate was defined as how often they went in and out of a nest before settling on which was theirs. Since the bees were not marked, proper localization of a nest was determined by entering a nest and remaining there for at least 30 seconds without leaving to search nearby nests.
To solve the mystery of nest identification, they set up 4 observational experiments. The first was to rotate the log 180° along its vertical axis. This would clarify if positioning played a role in nest identification. The second was placing colored shapes (squares, circles, triangles and double triangles) close to the nest entrances. This was to investigate how close range visual features affect search time and search error rate. The third experiment involved applying cuticular hydrocarbon (CHC) extracts from foreign bees to nest entrances to test how adding new odors affected nest localization. The fourth experiment explored how removing chemical cues lining the inside of the nest entrance influenced a forager’s ability to find their nest. To test this, the researchers applied hexane to the inside of the nest entrance immediately after a bee left, and recorded search time when the bee returned. All the data gathered from the experimental logs were statistically (using three statistics tests) compared to data collected from undisturbed logs.
They found that rotating the log rotation significantly increased the search time for nests as the bees spent approximately eight times as long as they had in the undisturbed logs. Similarly, placing the shapes near nest entrances almost doubled the search time of the bees. However, the bees did not make any nest recognition errors in this experiment. Contrastingly, they found that addition of scents from foreign bees reduced the bee’s search time and no bee also made a nest recognition error.
All of these findings suggest that valley carpenter bees utilize a multi modal cue system to recognize their nests and in the absence of an olfactory cue, a visual cue might be sufficient for proper nest localization. It is also possible that carpenter bees have evolved to be cautious about entering the wrong nests and would not risk encountering aggressive behavior if they did enter; hence they were less likely to make nest recognition errors.
What a lesson that was. Now, you may continue on your walk. Thanks for pausing to listen!
References
Madeleine M. Ostwald, Zachary Shaffer, Stephen C. Pratt, Jennifer H. Fewell (2019). Multimodal cues facilitate nest recognition in carpenter bee aggregations. Animal Behaviour,
Volume 155, Pages 45-51, ISSN 0003-3472, https://doi.org/10.1016/j.anbehav.2019.06.023.
