Ret^LM1 homozygous larvae as well as Ret^LM1/Ret^LM2 and Ret^LM1/Ret^LM3 transheterozygous larvae hatch normally hatch normally but show a range of feeding defects, as compared to controls: a foraging phenotype in which larvae move away from a central food source; accumulation of food in the oesophagus; reduced/absence of food in the midguts and absence of food in the oesophagus. In agreement, Ret^LM1 homozygous larvae show a similar frequency of proventricular contractions, but the wave of peristalsis is mostly absent. Ret^LM1 homozygous larvae are frequently immobile or sluggish in response to touch, as compared to controls.

Ret^LM1 homozygous embryos frequently exhibit missing or shortened frontal nerves as well as disrupted frontal ganglia and esophageal ganglia that do not migrate as far as in the control; axons enervating the larval midgut are tightly fasciculated crossing the proventriculus, but rapidly start branching on encountering the anterior midgut and do not project very far into the midgut.