How Fruit Flies Follow a Scent

Biological Strategy

Common fruit fly

Sam Stier

Image: Ant Cooper / Shutterstock / Some rights reserved

Sense Chemicals (Odor, Taste, etc.) From the Environment

Chemicals are important for signaling and communication among living systems, either intentionally (such as when two living systems try to find one another) or unintentionally (such as when a plant emits a chemical signal that an herbivore can use to find a tasty bite). They are also important for other uses, such as navigating or finding sources for minerals. But chemical signals are often relatively weak and disperse when moving through water or gases. Therefore, detecting them requires specialized abilities, including a way to determine where they are coming from. A well known example of sensing chemicals can be seen in ants following a pheromone trail laid down by others in their colony to locate a quality and abundant food source.

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Navigate Through Air

Although free from many of the physical obstructions found on land and in water, organisms that move through the air must still avoid hitting each other and objects in their flight path, such as trees and mountains. They also need to navigate from one place to another, which presents a different challenge. They use one strategy to navigate around obstructions and another to move towards their destination. For example, bats use echolocation to detect both obstacles and prey. To navigate during migration, bats also use vision, sun orientation, and likely other strategies.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Insects use an alternating pattern of searches and surges to make sense of an inconsistent trail.

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Introduction

There may be in your home right now a creature that is the marvel and envy of aeronautical engineers and computer scientists alike. Place a blueberry anywhere in your kitchen, and you will likely soon find the diminutive and intrepid fruit fly (Drosophila melanogaster) hovering nearby. Move the blueberry and turn on a rotating room fan, or try the experiment outside on a windy day. The fly will still find the treasure. How do these insects track odors to their source in a complicated and ever-changing environment?

The Strategy

Insects like fruit flies initially determine the location of a food source using olfactory information. The plumes of odor that emanate from a food source do not typically flow out in a cartoonish stream. Air currents and turbulence break up the plume into smaller, more short-lived filaments. An insect then must infer the food source location amidst a background of many other unrelated smells.

Insects follow a characteristic set of behaviors to help them use this sporadic olfactory information to locate a food source. Upon first detecting a filament of odor, they turn and move upwind, toward the source. When the odor filament ends, they begin moving laterally, across the direction of wind flow. Once they detect another filament, they move upwind again, homing in whiff by whiff. In this way, they use an accumulation of small experiences to build towards an ultimate determination of the food source.

The Potential

Working with incomplete information is the norm in the real world. Creating computational programs that effectively model navigation by insects could have far-ranging applications in human technologies that aim to navigate in similarly-constrained situations. For example, this could be helpful in rescue operations, or searching for sources of pollution, where information is incomplete and time is critical.

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Innovation: Academia

Machine Learning Model Inspired by Insects’ Nervous Systems

University of Cologne

A network model from the University of Cologne integrates fast, parallel processing with recognition of experience to enable an artificial agent to learn more efficiently.

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Last Updated November 30, 2021

References

“Foraging is a vital behavioral task for living organisms… We focus on cast and surge strategies employed by flying insects when foraging within turbulent odor plumes. Using a spike-based plasticity rule, the model rapidly learns to associate individual olfactory sensory cues paired with food in a classical conditioning paradigm… Our work successfully combines biological computational principles with spike-based machine learning. It shows how knowledge transfer from static to arbitrary complex dynamic conditions can be achieved by foraging insects and may serve as inspiration for agent-based machine learning.” (Rapp and Nawrot 2020: 28412)

Journal article

A spiking neural program for sensorimotor control during foraging in flying insects.

PNAS | 2020 | Rapp, H. and Nawrot, M.P.

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