Cardiac activity changes in response to external sensory stimulation have been described as a sensitive mean for testing the responsiveness of several species of adult insects. In the present research study we have examined if cardiac responses to odour delivery could be detected in blowfly pupae as well, thus helping in evaluating their responsiveness to the chemical properties of the external environment. To this end we studied the regular activity of heart pupae and its variations following odour delivery.
Electrocardiograms were recorded on Protophormia terraenovae blowflies, 48 to 24 hours before adult emergence. Effects of odour application were tested by delivering air-containing vapours of ammonia or 1-hexanol on single pupae by means of a standard olfactometer.
Regular heart activity consisted of the alternation of two phases of activity, easily distinguishable on the basis of opposite polarity and different amplitude and frequency of electric signals. Odour delivery induced a constant pattern of heart activity changes, consisting of an immediate arrest of the phase at a higher signal frequency, the Fast phase, and a premature setting in of the phase at a lower signal frequency, the Slow phase. Odour delivery was ineffective on the activity pattern of specimens on which functional ablation had been performed of olfactory organs, i.e. the antennae and maxillary palps. Results show that the cardiac response is an effective indicator of olfactory reception in blowfly pupae, thus representing a useful tool for testing the biological importance of the chemical environment during insect development.
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