Related Experiment Video
Updated: May 2, 2026
Drosophila Passive Avoidance Behavior as a New Paradigm to Study Associative Aversive Learning
Published on: October 15, 2021
Fruit flies learn to avoid odours associated with virulent infection
Aurélie Babin1, Sylvain Kolly, Franziska Schneider
1Department of Ecology and Evolution, University of Lausanne, , CH 1015 Lausanne, Switzerland.
Abstract:
While learning to avoid toxic food is common in mammals and occurs in some insects, learning to avoid cues associated with infectious pathogens has received little attention. We demonstrate that Drosophila melanogaster show olfactory learning in response to infection with their virulent intestinal pathogen Pseudomonas entomophila. This pathogen was not aversive to taste when added to food. Nonetheless, flies exposed for 3 h to food laced with P. entomophila, and scented with an odorant, became subsequently less likely to choose this odorant than flies exposed to pathogen-laced food scented with another odorant. No such effect occurred after an otherwise identical treatment with an avirulent mutant of P. entomophila, indicating that the response is mediated by pathogen virulence. These results demonstrate that a virulent pathogen infection can act as an aversive unconditioned stimulus which flies can associate with food odours, and thus become less attracted to pathogen-contaminated food.
Insights
Fruit flies (Drosophila melanogaster) can learn to avoid food odors associated with virulent pathogens. This learned avoidance is linked to pathogen virulence, not just taste aversion.
Area of Science:
- Animal behavior
- Pathogen-host interactions
- Neuroethology
Background:
- Learning to avoid toxic substances is common in many animals.
- However, the ability of animals to learn to avoid cues linked to infectious diseases is less understood.
- This study investigates pathogen-associated olfactory learning in insects.
Purpose of the Study:
- To determine if Drosophila melanogaster can learn to avoid olfactory cues associated with a virulent intestinal pathogen.
- To investigate if this learned avoidance is dependent on pathogen virulence.
Main Methods:
- Drosophila melanogaster were exposed to food containing a virulent pathogen (Pseudomonas entomophila) scented with a specific odorant.
- A control group was exposed to pathogen-laced food with a different odorant or an avirulent pathogen mutant.
- Subsequent olfactory preference tests were conducted to assess learned avoidance.
Main Results:
- Flies exposed to virulent P. entomophila associated the odorant with infection and subsequently avoided it.
- This learned avoidance was not observed when flies were exposed to an avirulent mutant of P. entomophila.
- The pathogen itself was not aversive to taste when directly added to food.
Conclusions:
- A virulent pathogen infection can serve as an aversive stimulus, enabling associative learning in flies.
- Drosophila can learn to associate food odors with pathogen contamination and reduce attraction to contaminated food.
- This demonstrates a novel mechanism for pathogen avoidance in insects mediated by learned olfactory cues.
