ABSTRACT
The rate of pumping and total number of pump strokes was recorded whilst Rhodnius prolixus fed on measured amounts of artificial diets.
Increasing the viscosity of the diet caused a decline in both the frequency with which the pharyngeal pump operates and the average stroke volume of the pump.
In 5th-instar Rhodnius, the stroke volume tends toward a maximum value of about 60 nl at viscosities lower than about 3 cP.
Feeding rates (volume per unit time) agree with Poiseuille’s law at high viscosities, but are less than predicted at low viscosities.
The maximum power output of the pump occurs at a viscosity between i and 3 cP, which is probably the range of the effective viscosity of blood in tubes with the dimensions of Rhodnius stylets.
These results are inconsistent with a hypothesis of a central nervous system ‘oscillator’ controlling the pump muscle, independent of feedback, but are consistent with a model involving peripheral feedback from stretch receptors, with an appropriate delay.
