The distribution and function of serotonin in the large milkweed bug, Oncopeltus fasciatus - A comparative study with the blood-feeding bug, Rhodniusprolixus

The blood-feeding hemipteran, Rhodnius prolixus, ingests a large blood meal at the end of each larval stage. To accommodate and process this meal, its cuticle undergoes plasticisation, and its gut and Malpighian tubules respe ctively absorb and secrete a large volume of water and salts for rapid diur esis. Serotonin has been found to be integral to the feeding process in thi s animal, along with a diuretic peptide(s). The large milkweed bug, Oncopel tus fasciatus, tends to feed in a more continuous and abstemious manner, an d therefore may have different physiological requirements than the blood fe eder. Unlike R. prolixus, O. fasciatus is lacking serotonin-like immunoreac tive dorsal unpaired median neurons in the mesothoracic ganglionic mass, an d lacks serotonin-like immunoreactive neurohaemal areas and processes on th e abdominal nerves, integument, salivary glands, and anterior junction of t he foregut and crop. The salivary glands and crop do, however, respond to s erotonin with increased levels of cAMP, while the integument and Malpighian tubules do not. In addition, 0. fasciatus Malpighian tubules respond to bo th O. fasciatus and R. prolixus partially purified CNS extracts, which are likely to contain any native diuretic peptides. Thus, while serotonin and d iuretic peptides may be involved in tubule control in R. prolixus, the latt er may be of greater importance in O. fasciatus. (C) 1999 Elsevier Science Ltd. All rights reserved.