Quenching variability of Drosophila larval behavior using multi-sensory stimulation

The larvae of the common fruit fly (Drosophila melanogaster) are small, crawling animals that have a nervous system comprised of approximately 10,000 neurons. To navigate their environment, larvae execute computations that modify their behavioral outputs based on temporal changes in sensory input—for instance, by increasing their turn rate when detecting rising levels of aversive stimuli. However, the behavior of individual larva can vary when subjected to the same stimulus, revealing intrinsic variability in the neural computations underlying behavior.

To investigate this variability, we delivered increases and decreases in fictive odor concentration by optogenetically activating CO₂ (Gr21a) and odor (Or42a) receptor neurons, alone and in combination with increases in visual stimulation. Individual analyses revealed substantial variability: while some animals selectively responded to uni-sensory stimulation, combining light and CO₂ reliably amplified behavioral responses, suggesting downstream integration that boosts weakly encoded sensory signals. In contrast, combining a decrease in attractive odor with an increase in light did not significantly amplify responses, implying that odor-light and CO₂-light combinations may be processed by distinct pathways.