Behavioral dissection of Drosophila larval phototaxis

A behavior generally comprises multiple processes. Analyzing these processes helps to reveal more characteristics of the behavior. In this report, light/dark choice-based Drosophila larval phototaxis is analyzed with a simplistic mathematical model to reveal a fast phase and a slow phase response that are involved. Larvae of the strain w¹¹¹⁸, which is photophobic in phototaxis tests, prefer darkness to light in an immediate light/dark boundary passing test and demonstrate a significant reduction in motility in the dark condition during phototaxis tests. For tim⁰¹ larvae, which show neutral performance in phototaxis tests, larvae unexpectedly prefer light to darkness in the immediate light/dark boundary passing test and demonstrate no significant motility alteration in the dark condition. It is proposed that Drosophila larval phototaxis is determined by a fast phase immediate light/dark choice and an independent slow phase light/dark-induced motility alteration that follows.