Octopamine, the hypertrehalosemic peptides HT-I and HT-II and the calcium ionophore A23187 elevate intracellular calcium levels in cultured haemocytes of Malaeosoma disstria (Lepidoptera: Lasiocampidae). The octopamine-mediated response is dose-dependent and the magnitude of the response is influenced by the concentration of calcium in the incubation medium. Mianserin, an inhibitor of octopamine-mediated elevation of cyclic AMP production, blocks the octopamine-mediated increase in intracellular calcium but has no effect on the HT-I-and HT-II-mediated responses. The results indicate that some effects of octopamine are mediated through agonist-dependent calcium gating whereas others are expressed through receptors coupled to adenylate cyclase. The study also confirms previous suggestions that HT-I and HT-II elevate intracellular calcium concentrations.

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