An Investigation into Neuroendocrine Regulators of Excretory Organs in the Adult Disease-Vector Mosquito, Aedes aegypti

Maintenance of ionic and osmotic homeostasis in insects allows them to succeed in many ecological and environmental niches, while utilizing a variety of feeding strategies. When faced with extreme and variable conditions, most insects regulate the composition of their blood within narrow limits. Haematophagus insects, such as the female yellow fever mosquito, Aedes aegypti, ingest bloodmeals comparable to twice their body volume, resulting in considerable amounts of salts and water in excess, threatening the osmotic and ionic balance of their haemolymph. Like other insects, mosquitoes achieve strict regulation of their hydromineral balance through the neuroendocrine control of their excretory system, consisting of the Malpighian ‘renal’ tubules (MTs), which are responsible for formation of the primary urine, along with the hindgut, which functions as a primarily reabsorptive organ. While extensive studies have examined this process of hydromineral balance in A. aegypti focusing on diuretic regulation, the roles of anti-diuretic hormones remained largely elusive. This research sought to advance our understanding of the hormonal regulation of the excretory system in A. aegypti by (1) investigating the role of CAPA neuropeptides as anti-diuretic hormones in adult MTs; (2) identifying the signalling components leading to CAPA-induced inhibition of fluid secretion; and (3) elucidating the expression and putative functional roles of ITP and ITP-L neuropeptides. In adult MTs, AedaeCAPA-1 peptides elicit a selective anti-diuretic role, inhibiting DH31- and 5HT-stimulated secretion through the NOS/cGMP/PKG pathway. CAPA-mediated inhibition promotes V-type H+-ATPase (VA) disassembly, reducing the driving force of DH31-stimulated secretion. Post-blood feeding, DH31 peptides are immediately released into the female haemolymph to promote natriuresis and diuresis while CAPA peptides are released shortly after, hindering the effects of DH31. Lastly, examination of ITP and ITP-L neuropeptides in A. aegypti indicated enrichment of ITP in the brain and ITP-L in the abdominal ganglia. Novel observations of AedaeITP and AedaeITP-L in feeding/starvation, ionoregulation, and reproductive behaviour and success suggest a vital pleiotropic role for these neuropeptides. Together, these studies highlight the complexity of neuroendocrine control of excretory organs in adult A. aegypti mosquitoes, furthering our understanding of various diuretic and anti-diuretic signalling systems in this important human disease vector.