Does reproductive investment change with age in tsetse flies, <i>Glossina morsitans morsitans</i> (Diptera: Glossinidae)?

1. Viviparous insects such as tsetse ( Glossina spp.) provide unusual opportunities to compare age‐related changes in the proportion of maternal resources transferred to offspring. 2. In laboratory populations of Glossina morsitans morsitans the survival of females was high for the first 60 days of adult life but declined rapidly thereafter. 3. Average longevity did not differ significantly between mated and unmated females (93·6 and 90 days, respectively). 4. Nutritional state in terms of fat content and residual dry mass did not decline with adult female age. 5. The fecundity of mated females was constant for the first 60 days of adult life and declined only slightly thereafter. 6. Offspring size did not change towards the end of the adult female lifespan and there was no evidence of an increase in the allocation of resources to reproduction in older females. 7. Results contrast with those obtained recently for vertebrates and may indicate that age‐related changes in offspring size in Glossina are not adaptive, or that so few females reach old age under natural conditions that there is no selection for a strategy of terminal investment.