Transgenic Aedes aegypti were engineered to express a virus-derived, inverted repeat (IR) RNA in the mosquito midgut to trigger RNA interference (RNAi) and generate resistance to dengue virus type 2 (DENV2) in the vector. Here we characterize genotypic and phenotypic stabilities of one line, Carb77, between generations G(9) and G(17). The anti-DENV2 transgene was integrated at a single site within a noncoding region of the mosquito genome. The virus resistance phenotype was strong until G(13) and suppressed replication of different DENV2 genotypes. From G(14)-G(17) the resistance phenotype to DENV2 became weaker and eventually was lost. Although the sequence of the transgene was not mutated, expression of the IR effector RNA was not detected and the Carb77 G(17) mosquitoes lost their ability to silence the DENV2 genome.