Experimental evidence for a hormonal control of digestion in the tsetse fly, Glossina morsitans Westwood: A study of the larva, pupa, and teneral adult fly

Abstract

The pattern of midgut proteolytic enzyme activity in the larva, pupa, and newly emerged adult is the same for field flies as for first- and second-generation laboratory-hatched and -reared flies. Enzyme activity ceases with the formation of the definitive pupa and begins again towards the end of the pharate adult stage. During the 24 hr following eclosion the midgut proleolytic enzyme activity increases almost threefold and, since there is no change in the quantity or position of the midgut contents throughout this period, the increase in enzyme activity is attributed to the inflation of the crop with air which normally aids in the expansion of the fly. Inflation of the crop is prevented by puncturing the ptilinum at emergence and this also prevents the increase in enzyme activity. The level of enzyme activity achieved in the normal fly is not affected by causing the newly emerged adult to crawl through sand before expansion, nor is it affected by increasing or decreasing its flight activity after expansion. By ligaturing the head from the thorax protease activity is slightly decreased below the level it had reached before the ligature was applied. However, enzyme activity is increased in the ligatured fly by injecting extracts of brains from normal flies into its thorax 3 hr before assay. Severing the ventral nerve cord between the brain and the thoracic ganglion mass prevents an increase of enzyme activity, but in many cases the operated controls also fail to increase their protease activity normally and this supports the view that tsetse flies are more sensitive to surgical interference than many other insects. For this reason it is not possible to assess the effect of the operation completely. The increase in enzyme activity in the teneral adult fly is best explained in terms of a neuroendocrine control of midgut proteolytic enzyme activity, mediated through the stomatogastric nervous system responding to the inflation of the crop with air during expansion and hardening.