Chemicals Responsible for Bee Scouting Behavior Elucidated

As a hobbyist beekeeper, I'm always excited to come across papers on bee biology. Bees are fascinating to me largely because of their eusociality, meaning that most bees never reproduce but instead assist a fertile queen to do so. As I said in a previous post, this behavior challenges our mental picture of what consitutes an organism. Is a worker bee an organism, or is the entire hive an organism? Is ability to reproduce more or less important than being a product of a single embryological event in our definition of an organism? While these questions are certainly interesting, I would like to draw your attention to a recent paper published in Science¹ that tackles a particular question about bee behavior: scouting.

The survival of a hive depends on a constant influx of food during the nectar flow, the part of the year where flowers are paying bees with nectar for their pollination services.This requires constant scouting for new nectar sources within the hive's 2-mile foraging radius. However, bees don't wander aimlessly looking for nectar rich flowers. Once the hive finds a lucrative source, it pays to send many bees back and forth until the source is exhausted. This behavior is coordinated by the famous bee dances, which were decoded in a series of brilliant experiments that won Karl von Frisch the Nobel Prize. Finding food sources, however, relies on scouting behavior, what the authors of this study also call "novelty-seeking behavior."

Scouting comes into play in another part of the bee lifecycle as well. When a hive becomes overcrowded, the workers rear a new queen (or several, which fight to the death!). The old queen flies away with about half of the bees, leaving the daugher queen to care for the home she's left behind. If you've ever seen a swarm of bees, you know that they tend to hang in a big clump on objects like branches. With the queen safely inside, scout bees search for potential nesting locations

The authors of this study wanted to understand the neurochemical basis of scouting behavior. Determining whether a bee is actively scouting, as opposed to being directed to or incidentally finding a food source, is no easy task. The authors used a combined approach, first by moving the hive and looking for the first bees to return with food, and second by enclosing a hive in a screened area and selecting bees that repeatedly sought out novel feeders introduced to the enclosure. Interestingly, nest scout bees were much more likely to act as food scouts than their non-scout sisters

To understand this novelty-seeking behavior from a neurochemical perspective, the team used microarray analysis to understand the differences in gene expression between scout and non-scout bees. They identified several genes already known for their role in novelty-seeking behavior in humans and other vertebrates, including personality differences in humans! One of the genes is involved with neurochemical signalling that relies on the amino acid glutamate. The researchers fed non-scout bees glutamate, and found that they were significantly more likely to adopt scouting behavior when compared to the control. Further, if the glutamate was administered with an antagonist, the effect was cancelled as this model would predict.

In the end, the authors concluded that this novelty-seeking system in bees is probably convergent with that of humans, suggesting that it represents a "basic tool kit" that has arisen in the course of the evolution of animal behavior. I was a bit surprised by this conclusion (my intuition was that such a complicated system would be ancestral), but I'm not very familiar with the chemical basis of animal behavior. Regardless, I found these experiments very clever and the results intriguing. Plus, as a beekeeper, it's nice to know a little bit more about the intricacies of a hive.

Image Credit: muslef (via Wikimedia)

Reference:

1. Liang, Z. S. et al. Molecular Determinants of Scouting Behavior in Honey Bees. Science 335, 1225–1228 (2012).