Insects must be able to survive periods without water (desiccation) and periods of low temperature, both of which reduce the volume and osmolarity of insect blood (called hemolymph). Peptides encoded by capability (capa) activate the G protein–coupled receptor (GPCR) capaR present on the renal tubules (called Malpighian tubules) to promote diuresis, excretion of fluid from the renal tubules into the hemolymph. Terhzaz et al. found that the mRNA for capa was increased in several species of fruit flies and mosquitos exposed to desiccating or cold conditions. In Drosophila melanogaster, capa mRNA abundance decreased within a few hours after recovery from the stress. Immunofluorescence analysis in D. melanogaster of the abundance of the precursor of two capa peptides, capa-1 and capa-2, in ventral neuroendocrine cells showed that desiccated or cold-stressed flies had increased capa precursor in these cells and that during recovery the abundance decreased, suggesting that capa peptides were released during the recovery period, but not during the period of stress. RNAi-mediated silencing of capa in the ventral neuroendocrine cells resulted in reduced amounts of capa precursor, desiccated flies with larger abdomens, flies with reduced water loss following exposure to desiccating conditions, and increased length of time that the flies survived desiccating conditions. Flies in which capa was knocked down by RNAi and that were injected with an active stabilized peptide analog exhibited reduced desiccation tolerance compared with the knockdown flies injected with an inactive mutant version, and this difference correlated with the activity of the peptides to stimulate renal tubule secretion. Capa-knockdown flies also exhibited longer recovery time from exposure to cold compared with control flies. Injection of the active peptide reduced the cold recovery time in the capa-knockdown flies compared with the recovery time of knockdown flies injected with the inactive peptide. Consistent with the function of capa peptides as diuresis-promoting signals, which involves the vacuolar H+-ATPase and the Na+/H+ exchangers in the Malpighian tubules, mutations in genes encoding subunits of either of these transporters also delayed the time required for recovery from cold. Understanding the mechanisms by which adaption and recovery occur can provide new directions for insect control.
S. Terhzaz, N. M. Teets, P. Cabrero, L. Henderson, M. G. Ritchie, R. J. Nachman, J. A. T. Dow, D. L. Denlinger, S.-A. Davies, Insect capa neuropeptides impact desiccation and cold tolerance. Proc. Natl. Acad. Sci. U.S.A. 112, 2882–2887 (2015). [Abstract] [Full Text]