No homozygous adult flies are recovered at 18-27^oC, however, at 29-30^oC homozygous adults are obtained. These homozygous flies can then be maintained at 29^oC or 27^oC and have a comparable viability to the parent strain at these temperatures. Matings between first generation homozygotes generally fail to produce any adult progeny at 20^oC, but after a few generations of growing at 27^oC, mating between homozygotes generates a few viable offspring at 20^oC. The temperature-sensitive period is between early embryogenesis and the third larval instar stage. Adult homozygotes reared at 29-30^oC, and then maintained at 27^oC show severe defects in movement and phototactic behaviour, and are bang sensitive. These flies show defects in negative geotactic behaviour, with the severity of the phenotype increasing as the temperature decreases. Homozygotes show increased tolerance to high temperature compared to wild-type.