Larvae develop a brain tumour at 29oC and die around the time of puparium formation. The invasive tumour consists of adult optic neuroblasts and optic ganglion mother cells. The temperature-sensitive period for tumour formation spans the embryonic, first and second larval instar stages. During this time, brain tumour development is reversible upon shifting animals down to 22oC, but during the third larval instar stage the brain tumour becomes irreversibly established. Shifting to the restrictive temperature after the temperature-sensitive phase for tumour formation and during adult life causes female sterility. The defects in oogenesis correlate with the developmental time of the shift to the restrictive temperature. In the earliest temperature shifts, oogenesis is arrested at the stem cell stage, while germaria shifted at later stages show fused egg chambers. Ovaries that have differentiated germaria at the time of the temperature shift form individualised egg chambers, but the eggs are short and incapable of further development. About 25% of eggs from late shifted females develop into segmented embryos, most of which have head defects. About half of these embryos also have thoracic and abdominal segment abnormalities.