Associative learning reconfigures colour-guided behaviour in Drosophila larvae

Third-instar Drosophila melanogaster larvae learn to avoid the shock-paired colour, and choice tracks spectral identity rather than the dimmer intensity cue.

• Why it matters: Innate versus learned colour value assignment in a numerically simple nervous system is unresolved, limiting mechanistic links between sensory inputs and visual memory.
• What they did: Using an automated differential-conditioning assay, larvae were trained with blue and green light where one colour was paired with electric shock, then tested after cue intensity transfer; Rh5 and Rh6 photoreceptor pathways were disrupted and extracellular recordings were made.
• The result: Learned avoidance persisted after intensity transfer, and disrupting Rh5 or Rh6 weakened the training-induced behavioural shift (Rh5 mutants showed only a small residual shift), while recordings showed robust ultraviolet and broadband white responses but smaller, variable blue/green responses.