The neuropeptide RhoprCCHamide2 inhibits serotonin-stimulated transcellular Na+ transport across the anterior midgut of the vector of Chagas disease, Rhodnius prolixus

Water fluxes and nutrient absorption along the midgut of three hemipterans, Mahanarva fimbriolata, Dysdercus peruvianus, and Rhodnius prolixus

Hemiptera Order comprises insect species adapted to different diets regarding water and nutrient content and availability, thus suggesting different combinations of proteins to ensure their absorption. To find out whether hemipterans use the same or distinct set of proteins and whether these differences are related to the phylogeny or the diet, RNAseq analyses were conducted in gut sections of three hemipterans, M. fimbriolata, D. peruvianus, and R. prolixus, with remarkable distinct diet. Since only a few of the selected proteins were functionally characterized, the coded putative proteins were manually curated by bioinformatics to infer their physiological function. The results suggest a relationship between gene expression patterns and water and nutrient dietary content and availability. In contrast, putative gene expansions and deletions are related to phylogeny, corresponding to evolutionary adaptations of ancestral forms to feed on xylem, cotton seeds, and blood, resulting in more resemblances between D. peruvianus and R. prolixus than M. fimbriolata. M. fimbriolata absorbs water through aquaporins Drip and Prip in the filtration chamber by passive diffusion, with a higher contribution of water-selective Drip. D. peruvianus water absorption involves Drip and Prip, but Prip contribution appears to be higher, and they probably cooperate with water-ion cotransporters in the posterior midgut. R. prolixus absorbs water in the anterior midgut involving a sodium transporter and a putative water-urea Prip. Sugars, amino acids, and lipids might be absorbed along the midgut in the three species, with a higher contribution of the posterior midgut for amino acid and lipid absorption in M. fimbriolata and D. peruvianus and the middle midgut in R. prolixus.

Integrating water balance mechanisms into predictions of insect responses to climate change

Efficient water balance is key to insect success. However, the hygric environment is changing with climate change; although there are compelling models of thermal vulnerability, water balance is often neglected in predictions. Insects survive desiccating conditions by reducing water loss, increasing their total amount of water (and replenishing it) and increasing their tolerance of dehydration. The physiology underlying these traits is reasonably well understood, as are the sources of variation and phenotypic plasticity. However, water balance and thermal tolerance intersect at high temperatures, such that mortality is sometimes determined by dehydration, rather than heat (especially during long exposures in dry conditions). Furthermore, water balance and thermal tolerance sometimes interact to determine survival. In this Commentary, we propose identifying a threshold where the cause of mortality shifts between dehydration and temperature, and that it should be possible to predict this threshold from trait measurements (and perhaps eventually a priori from physiological or -omic markers).

CCHamide-2 Signaling Regulates Food Intake and Metabolism in Gryllus bimaculatus

Neuropeptides play vital roles in energy homeostasis in insects and other animals. Although the importance of the regulatory network of neuropeptides in feeding and metabolism has been illuminated, a complete understanding of the mechanisms has not been addressed as many factors are involved in the regulation. CCHamide-2 is a newly identified brain-gut neuropeptide that regulates feeding behavior in several insect species including Drosophila melanogaster. However, little is known about the mechanisms controlling the feeding-related behavior and metabolic functions modulated by CCHamide-2 in other insects. In this study, we addressed the functions of CCHamide-2 in the two-spotted cricket, Gryllus bimaculatus, which was used as the experimental material to research the mechanisms of feeding and metabolism in this omnivorous insect species. Knockdown crickets by RNA interference against GbCCHamide-2R increased the amount of food intake, while injection of chemically synthetic GbCCHamide-2 peptide reduced the amount of food intake. Further, knockdown and peptide injection experiments revealed that GbCCHamide-2 signaling increased the concentrations of circulating lipids and carbohydrates, and the carbohydrate-rich diet increased the transcript levels of GbCCHa-2R. Moreover, GbCCHa-2 injection decreased the transcript level of Gbilp. By contrast, GbCCHamide-2 signaling did not affect nymphal growth or the transcript level of GbAKH, as well as feeding preferences. Taken together, CCHamide-2 signaling in G. bimaculatus regulates food intake associated with alterations in lipid and carbohydrate levels in hemolymph.

Fluid Secretion by Malpighian Tubules of Rhodnius prolixus: Neuroendocrine Control With New Insights From a Transcriptome Analysis

Rhodnius prolixus (the kissing bug and a major vector of Chagas disease) is an obligate blood feeder that in the case of the fifth instar consumes up to 10 times its unfed body weight in a single 20-minute feed. A post-prandial diuresis is initiated, within minutes of the start of gorging, in order to lower the mass and concentrate the nutrients of the meal. Thus, R. prolixus rapidly excretes a fluid that is high in NaCl content and hypo-osmotic to the hemolymph, thereby eliminating 50% of the volume of the blood meal within 3 hours of gorging. In R. prolixus, as with other insects, the Malpighian tubules play a critical role in diuresis. Malpighian tubules are not innervated, and their fine control comes under the influence of the neuroendocrine system that releases amines and neuropeptides as diuretic or antidiuretic hormones. These hormones act upon the Malpighian tubules via a variety of G protein-coupled receptors linked to second messenger systems that influence ion transporters and aquaporins; thereby regulating fluid secretion. Much has been discovered about the control of diuresis in R. prolixus, and other model insects, using classical endocrinological studies. The post-genomic era, however, has brought new insights, identifying novel diuretic and antidiuretic hormone-signaling pathways whilst also validating many of the classical discoveries. This paper will focus on recent discoveries into the neuroendocrine control of the rapid post-prandial diuresis in R. prolixus, in order to emphasize new insights from a transcriptome analysis of Malpighian tubules taken from unfed and fed bugs.