Organisms manipulated as biological control agents of disease vectors should tolerate ranges of developmental conditions exploited by their target species. Furthermore, they should reduce numbers of host-seeking vector adults without providing fitness benefits to larval survivors developing among fewer competitors. We studied electrochemistry in rat-chewed coconuts, an important developmental habitat used by Aedes polynesiensis, a vector of lymphatic filariasis. We also studied the effects of larval density and predation by the mosquito Toxorhynchites amboinensis as predators of Ae. polynesiensis. The predators significantly reduced survival rates of Ae. polynesiensis and numbers of males and females developing in coconut husks. Adults from cohorts of Ae. polynesiensis exposed to predators emerged at the same time and were equal in size to adults emerging from predator-free cohorts. No differences were detected in the numbers or sizes of Ae. polynesiensis reaching adulthood among the densities tested. At least for this common natural habitat, Tx. amboinensis gave a good level of biological control of the vector Ae. polynesiensis.