Feeding electrograms of Hyalomma aegyptium ticks at different temperatures.

The conductivity of a low voltage electrical current passed through Hyalomma ( Hyalommasta ) aegyptium (L.) nymphs feeding on tortoises at 15°, 20°, 25°, 30° and 35°C was measured on an oscilloscope and changes in the pharyngeal sucking action and in the secretion of saliva were recorded photographically. Comparable observations were made on a nymph on the belly of a rabbit at 35°C and for another nymph towards the tip of the ear of the same host where the surface skin temperature was 25°C. The standard components making up a single feeding complex were the same for the nymphs regardless of the type of host. These consisted of a period of inactivity, pharyngeal pumping activity, salivary ejection, inactive open salivarium, and a period of flexing of the salivarium. Some flexing of the salivarium was also sometimes apparent during the pharyngeal period, particularly just before the ejection of saliva. Other electrical pulse patterns were observed but their significance in feeding was too tenuous to interpret seriously. Nymphs completed their engorgement at 20°C and above. A single feeding complex at 20°C and above took about 1 min. with the exception of the nymph on the abdomen of the rabbit at 35°C which took less than 1/2 minute. This was primarily attributable to a short period for the flexing of the salivarium. Both the rate of pharyngeal sucking and the rate of flexing of the salivarium increased with temperature even though their periods remained more or less unchanged. At 15°C the nymphs were unable to complete their engorgement, not because of a qualitative change in feeding dynamics, but because the feeding process was lowered to such a slow rate that death ensued before sufficient time had elapsed to permit complete engorgement.