The Biology of Ageing in Insects 255 



balance" operating against the attainment of the longevity 

 potential of a particular sex for a particular species, when the 

 diet is inadequate for the physiological needs of such animals. 

 Rockstein (1958) suggested that food reserve in the ovaries 

 might indeed be a factor important in higher female longevity 

 even during starvation. In this connexion, a paper by Grosch 

 (1950) has shown that starving female wasps, Habrohracon 

 juglandis (Ashmead), draw upon the reserves of the ovarioles, 

 as evidenced by the gradual resorption of ova from the ovari- 

 oles which is especially marked during the latter days of their 

 lives. Woke, Ally and Rosenberger (1956) further support 

 this idea of the ovaries as a source of nutrition in starvation 

 for the female mosquito, Aedes aegypti L., in the observations 

 that delaying the first blood meal or decreasing the size 

 thereof lowers total egg production markedly. In the Levant 

 housefly, Musca vicina Macq., Ascher and Levinson (1956) 

 have also found protein essential to the adult diet for ovi- 

 position and cited similar evidence for other species of muscoid 

 adults. However, the common housefly does lay eggs, albeit 

 much more spottily, even on a protein-free diet, but no 

 information is available as to the number and viability of such 

 eggs. 



V 



Longevity differences and sex 



In order to obtain further insight into the differences 

 between male and female longevities in the housefly, a study 

 on a much larger scale was undertaken. Fig. 2 (taken from 

 Rockstein and Lieberman, 1958) shows the survival curves 

 for about 8,500 flies of both sexes of the same NAIDM 

 strain extending over nine generations, reared and maintained 

 on a complete diet under the controlled laboratory conditions 

 described earlier. Both survival curves show a rectangular 

 character typical of animal populations manifesting sene- 

 scence, namely, a very low mortality rate during the early 

 days of the cohort's existence, and a middle period of rapid 

 dying off. However, during the final five to ten per cent of the 



