Utilization of U-14C amino acids or U-14C protein by adult Glossina morsitans during in utero development of larva

Administration of U¹⁴C protein hydrolysate in the diet of adult female Glossina morsitans at different times throughout the second reproductive cycle was followed by analysis of the distribution of radioactivity between the adult flies, their excreta, and the fully grown third instar larvae produced by these flies. A constant proportion of the total administered label was recoverable independently of the time lapse between administration and assay. Peak incorporation of labelled material occurred in the larva between the seventh and eighth day of a 9 or 10 day interlarval period, indicating that the larva feeds avidly on recently synthesized maternal uterine gland secretion at this time. Haemocoelic injection of U¹⁴C protein hydrolysate into similar adult females, between feeds, resulted in continued incorporation of labelled material by the larva to within 12 hr of parturition. Results are consistent with the hypothesis that uterine gland secretion and larval feeding continue throughout the intrauterine life of the larva.A constant and low proportion of detectable label remained in the adult fly while increased incorporation by the larva was paralleled by a reduction of detectable label in the adult excreta. This indicates direct competition between the uterine gland cells and those of the Malpighian tubules for free amino acids in the haemolymph.Administration of U¹⁴C protein in the adult diet did not result in incorporation of label by the developing larva, and the bulk was excreted as protein by the adult fly. Apparently the midgut trypsin of G. morsitans is incapable of splitting this labelled protein.Analysis of urine and haemolymph samples from flies in early pregnancy, recently fed on a diet containing U¹⁴C protein hydrolysate or U¹⁴C protein, shows that free labelled amino acids in the diet enter the adult haemolymph almost immediately after feeding, and are excreted along with dietary water during initial diuresis. The labelled protein used in these experiments was not taken up by the haemolymph and consequently did not appear in the urine.Implications are that the adult female G. morsitans possesses little storage capacity for substances in the diet which are destined to provide nutrients for the developing larva. Assuming a 48 hr digestion time, the digestive products of a blood meal ingested on day 5 or 6 of a 9 day interlarval period will provide the bulk of nutrients for larval growth. It is therefore significant that blood meals ingested at this time are larger than those ingested earlier or later in the cycle.