Methods of estimating physiological age and its relationship to calendar age in the female housefly, Musica domestica L.

Methods of determining physiological age of females of many bloodsucking insects put forward by Kuzina (1942; quoted in Miller and Treece, 1968), Detinova (1945; quoted in Detinova, 1962) and Polovodova (1947, 1949; both quoted in Detinova, 1962) were investigated for their application to the housefly, Musca domestica L. In addition to these methods, depletion of pupal fat body was also studied. These methods were useful in distinguishing nulliparous, uniparous and biparous females but usually did not give clear results beyond triparous individuals because the yellow bodies became compact and dilatations broke easily. Depletion of fat body had little relation to the completion of the first gonotrophic cycle but was dependent on temperature, food and time. Each ovarian cycle could be divided into five stages and thus the life-time into seventeen physiological ages. Estimates of the age of each female on the completion of each gonotrophic cycle, duration of each gonotrophic cycle, and number of gonotrophic cycles completed during the life-time were determined for three geographic strains at four temperatures. Longevity of each strain increased with a decrease in temperature. There were highly significant differences among the longevities of the three strains and temperature affected the longevities of the three strains differently. Cumulative percentage mortality per gonotrophic cycle increased with a decrease in temperature and thus temperature increased the mean as well as the maximum number of gonotrophic cycles completed during the life-time. The number of gonotrophic cycles completed during the life-time did not differ significantly among the three strains but differed with temperature. Temperature affected the egg development differently in the three strains. There was an almost linear increase in the mean age at the completion of various gonotrophic cycles yielding a linear regression equation for each combination of strain and temperature to be used in estimating the mean age of a female housefly from the number of gonotrophic cycles. Study of age distribution in a natural population indicated that nulliparous females always formed the majority of the sample, while females having completed 3+ gonotrophic cycles constituted only a small portion. This data, coupled with observations regarding decrease in activity with age, wing breakage, and increase in weight with gravidity, suggests that most females in nature do not live long enough to complete more than three gonotrophic cycles.