Using transcriptomics to uncover seasonal responses in male mosquitoes

Females of the Northern house mosquito, Culex pipiens, are the major vectors of West Nile Virus and overwinter as adults in a reproductive diapause. Diapausing females fail to take a blood meal and keep sperm viable until they terminate diapause ~3-6 months later. The short daylengths of late summer and early fall are the cues that females of Cx. pipiens use to anticipate winter’s arrival. However, we do not know whether male mosquitoes, that do not enter diapause, alter their accessory gland proteins in response to short daylengths to inhibit blood-feeding and promote sperm storage in females. Our RNAseq results reveal that male mosquitoes of Cx. pipiens differentially regulate their accessory gland proteins in response to photoperiod. Specifically, several genes that promote host-seeking, blood meal-processing and egg maturation are down-regulated in short-day reared males of Cx. pipiens, while genes involved in protecting sperm and enhancing immune responses are upregulated. Additionally, behavioral assays show that females who mate with long-day reared males are more likely to blood feed and lay more eggs than females that mate with short day-reared males. Further, RNA interference directed against a protease in males of Cx. pipiens inhibited blood-feeding in long-day reared females that had mated with dsRNA-treated males. Together, these results suggest that daylength induces changes in male mosquito reproductive physiology that have significant impacts on seasonal differences in female blood feeding, fecundity and sperm storage, and reveal the power of using transcriptomics to uncover the molecular mechanisms of insect overwintering.