Cardiac activity of intact Protophormia terraenovae flies and its taste- and feeding-induced variations were analysed by electrocardiogram recording either simultaneously with nervous spike discharge from stimulated labellar taste sensilla, or during feeding. Results indicate that the cardiac response to taste stimulation consists of the inhibition of fast beating activity and the premature setting in of tachicardiac slow beating activity. Although the response was evoked by taste stimulation with solutions of sucrose or NaCl, the former were far more effective than the latter. During feeding, variations in cardiac activity consisted of a sharp reduction in the duration of periods of fast and slow activity, that continued for 20 minutes after the end of feeding. Variations in haemolymphatic circulatory dynamics which, in all likelihood, are consequent to taste- and feeding-induced cardiac changes may influence haemolymphatic volume and pressure in extracardiac compartments. The hypothesis is advanced that the biological meaning of variations in cardiac activity and thus in haemolymphatic pressure, is that of creating conditions favourable to the behaviour the insect has to manifest, in particular as concerns the ingestion of food.
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