Hemizygous male and homozygous female adults become sluggish in behaviour a few days after eclosion and then begin to die (most flies are dead within 2 weeks of eclosion) when kept at 29^oC after eclosion (after being raised at 25^oC until eclosion). Lifespan is normal if flies are kept at 25^oC after eclosion. Embryos and larvae raised at 29^oC show severe lethality. The brains of adults kept at 29^oC after eclosion appear normal when young, but with age, vacuoles develop in the optic lobes, first in the medulla, and then in the lamina and lobula. The central brain remains relatively unaffected. Axon terminals in the optic lobe neuropil become inflated. In some cases, groups of axons coalesce to form figures divided internally by membranes.