Intestinal flow and digestive parameters of Lutzomyia longipalpis larvae.

Lutzomyia longipalpis Lutz & Neiva, 1912 (Diptera, Psychodidae), is the primary vector of Leishmania infantum Nicole, 1908, the etiological agent of American visceral leishmaniasis. During their development, sandfly larvae pass through four instars, consuming soil particles enriched with microorganisms and decomposing organic material. In numerous insect species, the intestinal epithelium not only secretes digestive enzymes and absorbs digested nutrients but also carries out additional functions, such as regulating luminal pH and facilitating the absorption or secretion of ions and water. The transport of ions and water plays a crucial role in the establishment of a countercurrent flow responsible for recycling soluble digestive enzymes. This study aimed to explore specific aspects of digestion in L. longipalpis larvae that remain poorly understood. We measured the intestinal flow within the endoperitrophic space, which varied depending on the type of diet offered to the larvae, with an average total time of 191 min. Additionally, we demonstrated the countercurrent flow in L. longipalpis larvae. Finally, we showed that the production of digestive enzymes can be modulated by nutrient availability, particularly by the amino acids in the larval diet. The higher the amino acids concentration, the higher the trypsin activity. On the other hand, the aminopeptidase activity was poorly influenced by the amino acids concentration.