Effects of diapause on the excretory physiology of the northern house mosquito, Culex pipiens

Diapause is a condition where insects undergo a series of physiological changes to survive cold harsh temperatures and/or dessication. The northern house mosquito Culex pipiens, a vector of West Nile virus, overwinters as an adult female. An important component to its survival during diapause is water conservation. Previous studies by the Denlinger laboratory have shown that C. pipiens conserve water during diapause by suppressing cuticular water loss, but it is unknown whether corresponding alterations occur in the renal system to conserve water. Malpighian tubules are the insect’s primary renal tissue; they are functionally analogous to the kidneys of mammals. The tubules produce urine by the transepithelial secretion of salts and water from the hemolymph to the tubule lumen.  The present study tests the hypothesis that Malpighian tubules of diapausing mosquitoes facilitate water conservation by suppressing their urine production, thereby limiting excretory water loss.  We find that the excretory capacity of C. pipiens progressively decreases as they enter diapause, which suggests that their Malpighian tubules enter a quiescent state during diapause.  This may not only serve a role in water conservation but also in conserving energy during diapause because Malpighian tubules house energetically ‘expensive’ active transport mechanisms.