The soft bodies and aquatic habitats of mosquito larvae pose a challenge for applying standard RNA-interference techniques to silence expression of target genes. Here we describe a novel technique for delivering double-stranded RNA into mosquito larvae by exploiting the larva's dehydration tolerance. Larvae were dehydrated in a NaCl solution and then rehydrated in water containing double-stranded RNA. Using larvae of Culex pipiens (L.) we demonstrated the principle by knocking down expression of the gene encoding heat shock protein 90. The knockdown persisted through the pupal stage and into adulthood, with a knockdown of ≈77% still evident on the third day of adult life. We anticipate that this relatively simple procedure will prove useful for knocking down expression of other genes as well, in larvae of this mosquito and in others.