Dynamics of the pregnancy cycle in the tsetse Glossina morsitans

A normal pregnancy in tsetse involves the successful integration of larval development with maternal activity. At 25°C, ovulation in Glossina morsitans occurs 1 hr after the previous larviposition, the egg hatches on day 3·8 (1·57 mm length, 0·09 mg dry wt.), ecdysis to second instar occurs on day 4·9 (2·3 mm, 0·30 mg), the third instar cuticle is formed on day 6·8 (4·5 mm, 5·0 mg), and parturition occurs on day 9·0 (6·0 mm, 10·0 mg). Melanization of the in utero third instar follows a regular sequence over a 2 day period. Parturition follows a circadian pattern with a peak 9 hr after lights on (12 hr daily photophase). All instars receive nutriment from the female's milk gland. During early pregnancy the rate of milk synthesis is greater than rate of uptake by the larva, thus causing expansion of the secretory reservoirs. After day 6, the volume of the secretory reservoirs decreases, but as is indicated by nuclear volume and larval growth the rate of synthesis remains high until day 8. Feeding activity of the adult female is maximal on day 1, levels off at 60 per cent up to day 6, and then declines sharply towards the end of pregnancy. Oöcyte development proceeds in phase with larval development and thus minimizes a lag period between successive pregnancies.