Characterization and genetic analysis of Drosophila melanogaster photobehavior during larval development.

In Drosophila melanogaster, during the mid third instar of development larvae cease foraging and commence a period of increased locomotor activity referred to as wandering behavior. In this study, we quantified the wild type larval response to light during the foraging (first, second, and early third instars) and wandering (late third instar) stages of development. Foraging larvae in the first, second and early third instars exhibited a robust and marked aversion to light (negative phototaxis). From the mid larval third instar larvae showed a decrease in photonegative behavior, until just before pupation when the response of wandering larvae to light became random. The photobehavior of several strains known to affect the adult visual system were also studied. All but four exhibited normal phototaxis in the foraging and wandering stages. gl mutant larvae failed to respond to light during the foraging stage likely due to lack of larval photoreceptors. Larvae carrying three different mutations in the rhodopsin RH1 gene continued to express negative phototaxis throughout both the foraging and wandering stages. These results suggest that the transition from negative phototaxis toward photoneutral behavior characteristic of the wandering third instar larva requires vision.