Temperature shift experiments demonstrate the latest temperature-sensitive period for the requirement of phl during development is at the late pupal stage. Downshift experiment shows that embryos never hatch even when they were transferred to 17oC at 3 hours AEL at 28oC. The temperature-sensitive period for maternal phl function is 60 minutes AEL at 28oC and 260 minutes AEL at 17oC. Temperature shift up to 28oC within three days after puparium formation causes a failure to develop to mature adult within the pupal case, a raise in temperature after this period allows development to mature adult but individuals exhibit an eclosion defect. Mitotic clones demonstrate a proliferation defect, imaginal discs exhibit growth retardation. At 28oC the cell cycle is arrested at a phase or phases other than the M-phase.