What potential effects could the Oxitec mosquito have on the ecosystems?

It’s very unlikely that our technology would have any major effects on the ecosystem of an area in which they were released because outside of Africa Aedes aegypti is an invasive species that has been spreading around the world in the last few hundred years, so reduction of this introduced pest would help restore the ecosystem. When a species has been recently introduced to a country, it is unlikely that any native species is substantially dependent on them, e.g. for food, especially where the species is an urban dweller living exclusively close to people. Aedes aegypti mosquitoes do not make up a significant proportion of the diet of their various predators.  So, although various things (fish, ants, spiders, etc.) can eat them if they find them, few if any actually depend on this one species, even where it is native. And eating an Oxitec mosquito would be the same as eating a wild one because the proteins from the two introduced genes are non-toxic and non-allergenic.

Our approach exclusively targets the Aedes aegypti mosquito. However other control tools such as insecticides are broad spectrum and will affect many insect species and their food chains.

Further reading:

USDA (2009). Use of Genetically Engineered Fruit Fly and Pink Bollworm in APHIS Plant Pest Control Programs: Record of Decision. U. S. D. o. Agriculture, Federal Register. 74: 21314 -21316.

Fang J. (2010). A world without mosquitoes. Nature 466: 432-434.