The Biology of Ageing in Insects 259 



some interesting data on differences in longevity between the 

 sexes for over 2,000 males and females of a 15-year inbred 

 strain of normal houseflies, originating from a wild strain 

 collected in the Sacramento, California, area, and reared and 

 maintained on a Peet-Grady medium at 80° f. For male 

 houseflies, he obtained a 50 per cent mortality at 11 days (as 

 opposed to our values of 16 days) and for females at 29 • 5 days 

 (very much like our own data for females). Thirty-day 

 mortalities of 98 per cent for males and 52 per cent for females 

 corresponded very closely to those obtained for our own 

 NAIDM strain. For the Levant house-fly, Musca vicina 

 Macq., however, Feldman-Muhsam (1944) and Ascher and 

 Levinson (1956) found no significant difference in longevity 

 between the two sexes. 



Parental age 



In an attempt to establish the possible effect of parental 

 age of houseflies at oviposition upon the longevity of the 

 offspring, a preliminary investigation was made according to 

 the procedure of Lansing (1947, 1948, 1954). For standard 

 breeding and in all previous studies, eggs were collected from 

 parents at the youngest possible age (at the fourth to fifth 

 day after emergence). In this series of experiments, however, 

 225 eggs each were collected at the fourth, sixth, ninth, 15th, 

 23rd and 27th days and the offspring otherwise reared and 

 maintained as before on complete diets. Table III shows that 

 the female offspring longevity is progressively diminished 

 with advancing age of the parents at the time of oviposition ; 

 e.g. survival, as expressed as 30-day mortality for female 

 offspring, falls from 50 per cent mortality for eggs from young 

 parents, to 92 per cent mortality for eggs laid at 27 days of 

 parental life. The 30-day mortality data for male offspring, 

 on the contrary, were interpreted as meaning that male 

 offspring longevity was unaffected by increasing parental age. 

 Values also included in Table III show corresponding declines 

 in average longevities for females from about 32 days for 



