Behavioral variability of Drosophila larva under uni- and multi-sensory stimulation*

Drosophila larva is a small crawling animal with about 10,000 neurons. Despite this simplicity, the larva carries out information-processing behaviors, including navigation which is enacted through a sequence of forward runs and reorienting turns. Larvae on average turn more often when facing increases in aversive stimuli, such as light or CO₂. However, larva’s behaviors are variable and not all larvae respond to same stimulus presentations in the same way. Moreover, a single larva may not respond with the same fidelity to different sensory modalities, and this intrinsic variability may reflect the differences in the neural implementation of its navigational algorithms to a range of sensory modalities. To study the larva’s information-processing algorithms, we present blue light to stimulate larva’s visual system and red light to optogenetically activate CO₂ receptor neurons. By studying responses to sensory stimuli alone and in combination, we categorize the variability of larva’s behavioral responses to light and fictive odors and determine the conditions under which their combination provides a more reliable response. These approaches allow us to hypothesize the basic underlying mechanisms that larvae engage in response to a combination of sensory cues.