Mutants show hypersensitivity to hyperoxia (100% oxygen), showing 100% mortality in 1 day (control flies show a mean survival of 6.9 +/- 0.1 days under hyperoxia). Under normoxia, homozygotes flies show a twitching phenotype a few days after eclosion and then begin to die. All the homozygotes are dead within 2 weeks, and the mean survival is only 8.4 +/- 3.5 days. Heterozygous flies have a normal lifespan. At 2 days of age, hys¹ flies do not display major defects in the flight muscle mitochondria, but by 7 days after eclosion, the mitochondria throughout the flight muscle accumulate swirls of cristae. At 7 days of age, hys¹ flies show a 31% decrease in CO₂ production compared to controls, consistent with severe mitochondrial dysfunction. 2 day old hys¹ flies show a severe defect in flight capacity.