COMPARISON OF MOTOR PATTERNS IN LARVAL AND ADULT STAGE OF A BEETLE, ZOPHOBAS-MORIO

For a holometabolous insect, the beetle Zophobas morio, several motor patterns were recorded, using EMGs, for several homologous metathoraci c muscles of the larval and adult stage. In the larva, most muscles ar e employed during walking, while in the adult, only the remoter coxae muscle (M119) will be activated during leg movements. Segmental bendin gs of the larva are mainly due to contractions of the dorsal longitudi nal muscles. For adults, the myogenically driven thoracic flight muscl es display a phase preference within the wing-beat cycle, resulting in not only a functional but also activity-dependent classification of w ing depressor and elevator muscles. Time interval histograms of the ex citatory junctional potentials (ejp's) show several peaks separated by about 20 ms, representing the wing-beat period. Application of chlord imeform (CDM), an agonist of the neuromodulator octopamine, elicits in adults longer ''flight'' sequences without wing movement. During such sequences the 20 ms modulation of the ejp intervals is missing. This points to wing-beat dependent afferences involved in patterning of the output during normal flight. Application of CDM in the larva results in a tonic activation, which shows several similarities with the adult ''flight'' without wing-beat. This finding suggests that the basic ne uronal circuitry underlying the image's flight is present precociously , before the dramatic reorganization of the animal during metamorphosi s. (C) 1993 Wiley-Liss, Inc.