Imprecise excision of the P{EPgy2}TrehEY06982 progenitor insertion, resulting in a deletion of approximately 860bp of the Treh second intron.
Homozygotes die at the late third larval instar or pupal stages, with 2% escaping to adulthood.
The outer proliferation center neuroepithelium is partly disintegrated in the brains of late third instar homozygous larvae, and the neuroepithelial cells have an abnormal rounded morphology.