Following your nose into the swarm

“I couldn’t imagine the scale until I saw it with my own eyes,” reports Einat Couzin-Fuchs.

When a plague of locusts broke out in Kenya four years ago, she and her team were in the field: “Some areas were just fully infested, with only toxic plants left behind after the locusts had moved through.”

Back at their workplace, the University of Konstanz, they planned experiments and models based on the data collected in the field. Their mission: to unravel the mysteries of locust plagues, a global threat that affects one in ten people on the planet. The Food and Agriculture Organization of the United Nations (FAO) estimates that a swarm of one billion locusts devours around 1,500 tons of food in a single day, equivalent to the daily food needs of 2,500 people. These staggering figures highlight the urgency and importance of their research.

Substantial differences between solitary and gregarious animals
It is important to note that locusts are not always swarming. Locusts are grasshoppers that can switch between a solitary (living alone) and gregarious (living in a swarm) state within a few hours. This change of state has a large impact on behaviour, development, physiology and reproduction. Changes are also exhibited in the nervous system and body colour, which changes from camouflage green to a striking yellow-black.

“This extreme change in lifestyle impacts how animals search for food as well as the availability of information animals have at their disposal when foraging”, says doctoral student Inga Petelski. Therefore, she conducted behavioural experiments to monitor foraging decisions in the lab by exposing solitary and gregarious animals. Food choices could be perceived either visually or olfactorily or in combination. Her colleague Yannick Günzel uses the data obtained to develop a decision-making model. “Based on the behavioural experiments and the decision-making model, we found that the sense of smell is extremely important in gregarious animals when searching for food,” says the neurobiologist.

Key in the olfactory system of animals
Therefore, the research team knew that a central key lies in the olfactory system. Consequently, they took a closer look at the area of the brain responsible for smell processing using an in vivo calcium imaging technique. This procedure visualizes information processing across entire regions of the brain.

The apparent result: “If you pair food and grasshopper scent, you get a synergistic effect: the brain activity is significantly more pronounced than you would expect from pure addition. We only found this effect in the gregarious grasshopper,” says Inga Petelski. This means that locusts adapt their sense of smell when they switch to the gregarious lifestyle. Their olfactory system now appears to be specialized to better detect food odours in the swarm’s odour cocktail. Her colleague Yannick Günzel concludes: “This is the reason why food can still be sensibly perceived by locusts in a swarm.”

“Combining calcium imaging experiments and computational analyses, our team has succeeded in gaining a better understanding of how locusts adapt to new environmental conditions,” says group leader Einat Couzin-Fuchs. “We now have a better mechanistic understanding of the neural changes happening in the transition to swarming.” She is certain that future research and method development will advance our ability to understand, and therefore predict, and manage future outbreaks.

 

Fact Overview   Publication: Petelski, I., Günzel, Y., Sayin, S. et al. Synergistic olfactory processing for social plasticity in desert locusts. Nat Commun 15, 5476 (2024). Link: Yannick Günzel and Inga Petelski are doing their doctorates at the University of Konstanz. They are both also members of the international Max Planck Graduate School QBEE. Einat Couzin-Fuchs is a group leader at the Cluster of Excellence Centre for the Advanced Study of Collective Behaviour at the University of Konstanz. Researchers from the Cluster of Excellence Centre for the Advanced Study of Collective Behaviour are conducting several studies on the formation of locust swarms, for example experiments with 10,000 locusts in the swam laboratory, the Imaging Hangar. The Cluster of Excellence Centre for the Advanced Study of Collective Behaviour at the University of Konstanz is a world-leading research centre for the study of swarm behaviour. It tackles pressing questions across species and organizational levels in an interdisciplinary manner, from neuronal mechanisms to individual perception and preferences to collective behaviour in groups or entire socities.

 

Note to editors:

You can download images and a video here:
 

1. Interactive graphic of the processes in the locust’s brain:

You can download the graphic here:

• With text:
• Without text:
  Copyright: Inga Petelski, Yannick Günzel, Cluster of Excellence Collective Behaviour
• 2. Video:

Description: Confocal scan throughout a locust’s right antennal lobe with an anatomical backfill staining of projection neurons (antennal lobe output neurons). The video starts at the surface of the antennal lobe, clearly showing individual cell bodies. Deeper in the antennal lobe, microglomeruli (functional units of the antennal lobe) become apparent, with projection neuron axons leaving the antennal lobe through the medial tract. The antennal nerve enters the antennal lobe from the left. Image coordinates: right, medial; top, dorsal.
Copyright: Yannick Günzel, Cluster of Excellence Collective Behaviour

 

1. Solitary and gregarious locust:

Caption: Locusts can switch between a solitary (living alone) and gregarious (living in a swarm) state within a few hours. This change of state has a large impact on behaviour, development, physiology and reproduction. Changes are also exhibited in the nervous system and body colour, which changes from camouflage green to a striking yellow-black.
Copyright: Inga Petelski, Cluster of Excellence Collective Behaviour

 

1. Locust swarm:
   Caption: Locust plague in Kenya
   Copyright: Einat Couzin-Fuchs, Cluster of Excellence Collective Behaviour

 

 

 

 

 

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