Mapping Neural Projections In The Bumblebee Brain


Bumblebees forage widely for pollen and nectar from flowers, sometimes travelling kilometers away from their nest, but they can somehow always find their way home in a nearly straight line. These insects have been known to return to their nest from new locations almost 10 kilometers away.

This homing ability is a complex neurological feat and requires the brain to combine several processes, including observing the external world, controlling bodily movements and drawing on memory.

While the navigational behavior of bees has been well-studied1, the neuronal circuitry behind it has not. Unfortunately, most of what is known about insects’ brain activity comes from studies in species such as locusts or fruit flies2.

The Central Complex

In these species, a region of the brain known as the central complex has been shown to have an essential role in homing behaviors. However, it is unknown how similar the central complex of bumblebees might be to fruit flies’ or locusts’, or how these differences may affect navigational abilities.

Marcel Sayre and colleagues obtained images of thin slices of the bumblebee central complex using a technique called block-face electron microscopy, which produces high-resolution image volumes. These images were used to obtain a three-dimensional map of over 1300 neurons.

This cellular atlas showed that key aspects of the central complex are nearly identical between flies and bumblebees, including the internal compass that monitors what direction the insect is travelling in.

bumblebee central complex
General structure of the bumblebee central complex. Credit: Marcel Sayre; CC-BY

However, hundreds of millions of years of independent evolution have resulted in certain differences.

Vector Memory Circuits

These differences were found in neurons possibly involved in forming memories of the directions and lengths of travelled paths, and in the circuits that use such vector memories to steer the insects towards their targets. Sayre et al. propose3 that these changes underlie bees’ impressive ability to navigate.

The results of this work help explain how the structure of insects’ brains can determine homing abilities. The insights gained could be used to develop efficient autonomous navigation systems, which are challenging to build and require a lot more processing power than offered by a small part of an insect brain.

  1. Loukola OJ, Solvi C, Coscos L, Chittka L (2017). Bumblebees show cognitive flexibility by improving on an observed complex behavior. Science 355:833–836. ↩︎
  2. Anna Honkanen, Andrea Adden, Josiane da Silva Freitas, Stanley Heinze, Basil el Jundi, Almut Kelber, Barbara Webb (2019). The insect central complex and the neural basis of navigational strategies. J Exp Biol 222 (Suppl_1): jeb188854. ↩︎
  3. Marcel Ethan Sayre et al. A projectome of the bumblebee central complex. eLife 2021;10:e68911 ↩︎

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Last Updated on December 8, 2022