Longevity among blowfliesPhormia terraenovae R.D. kept in non-24-hour light-dark cycles

Summary From the day of hatching, groups of about 150 blowfliesPhormia terraenovae R.D. were continuously subjected to light-dark cycles (LD) of constant duration, ranging from 20 to 28 h (Zeitgeber period T), or to constant illumination (LL). Survival was determined by the number of days after which only 10% of the flies in each group were still alive, and expressed as percent of the survival of a control group kept in T=24 h. With T equal to 25, 26 or 27 h, survival was 100%; it was reduced to about 90% in T=23 or 28 h, to 85% in T=22 h, and to 70% in T=20 h. In LL, survival was between 52% and 75%, depending on light intensity. From records of locomotor activity, obtained from a few flies in each group, it can be concluded that in all the LD-conditions the activity rhythms were entrained by the Zeitgeber. Several possible explanations of the reduction of survival in the non-24-h days and in LL are discussed.Dedicated to Professor Colin S. Pittendrigh on the occasion of his 60th birthday