Yeah, even if there are no obligate mosquivores, we're perturbing a chaotic system, which is defined by sensitive dependence on initial conditions. Any action we take (including none at all) is going to have some arbitrarily large (or small) effect on the future state of the system.

If it works exactly as described, the 'only male offspring' modification should be nice and side-effect-free. But then, evolution is a big-numbers statistical game. Who knows what interesting variations we'll see..