Polytene chromosomes normal.
Newly laid eggs upshifted to the restrictive temperature and then returned to the permissive temperature on either the 3rd or 5th day give rise to larvae that do not reach the third instar and subsequently die. Early and late third instar larvae upshifted to the restrictive temperature fail to pupariate. Adults shifted to 29 pr 31.5oC at any age show almost 100% mortality after the third day of incubation.
Homozygotes and hemizygotes raised at the nonpermissive temperature exhibit a failure to pupariate, failure of head eversion and noneclosion of developed adults.
Hemizygotes reared at 27oC die during metamorphosis, usually at a late stage of adult differentiation. These uneclosed adults appear morphologically normal, and remain viable within the puparium for several days past the expected time of eclosion. Hemizygotes or homozygotes raised at 29oC fail to develop past the prepupal stage, and hemizygotes or homozygotes raised at 31oC die as larvae.
Temperature upshift at egg-laying causes lethality at the first or second instar. Temperature upshift at third instar and puparium formation cause lethality at larval and pharate adult stages respectively.
Mutagen was either ethyl methanesulfonate or γ ray.
Temperature shift experiments show that normal dre4 function is required late in larval development, during the period following the initiation of wandering behaviour. The dre4e55ts mutation causes an ecdysteroid deficiency at the time of pupariation.