A shut‐down in expression of an insulin‐like peptide, ILP‐1, halts ovarian maturation during the overwintering diapause of the mosquito Culex pipiens

Short day‐length is used to programme adult diapause in the mosquito, Culex pipiens. The downstream endocrine event that halts ovarian maturation is a shut‐down in juvenile hormone (JH) production, and recent evidence suggests that the insulin signalling pathway may be a key upstream player in executing this developmental arrest. Genes encoding insulin‐like peptides‐1, ‐2 and ‐5 were identified in C. pipiens, and we report that transcript levels of insulin‐like peptides‐1 and ‐5 were significantly lower in diapausing females than in their nondiapausing counterparts. Genes encoding both insulin‐like peptides‐1 and ‐5 were suppressed using RNA interference in mosquitoes programmed for nondiapause, and ovarian maturation was monitored. Knocking down insulin‐like peptide‐1 with RNAi in nondiapausing mosquitoes resulted in a cessation of ovarian development akin to diapause, and this arrest in development could be reversed with an application of JH. Knocking down insulin‐like peptide‐5 did not alter ovarian development. These results are consistent with a role for insulin‐like peptide‐1 in the signalling pathway leading from the perception of short day‐lengths to the shut‐down in JH production that characterizes adult diapause in C. pipiens.

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