NervousVersusNeurohormonal Control of Insect Heartbeat

Recording semi-isolated insect heartbeat at one time was an art only to be attempted by the most patient of research workers. Thanks to modern advances in biomedical instrumentation, insect heartbeat measurement by impedance conversion and contact thermography allows not only heartbeat recordings, but recording of accessory pulsatile organs and diaphragm movements. The characteristic heartbeat patterns as recorded from adult insects vary enormously from very regular in orthopteroids to highly irregular in Diptera. Pupal stages in holometabolous insects are characterized by a heartbeat which appears to have little or no nervous influence and is punctuated by cessation for periods up to several hours in some insects. The controversy over nervous and/or hormonal control of insect heartbeat has never been completely resolved. There is now a good deal of evidence for nervous control of the heartbeat of Dipteran adults, Lepidopteran adults, Orthopteran nymphs and adults, Dictyopteran nymphs and adults, and Hymenopteran adults. The evidence of hormonal control of heartbeat remains inferential, and is based mostly on the responses of semi-isolated heart preparations. One of the most important events in recent years in this field has been Brian Brown's elucidation of Proctolin in cooperation with Alvin Starratt in Canada. Proctolin is a suspected neurohormone or neurohumor of the proctodeum which may also be used to regulate heartbeat in insects.