Even if [Oxitec's] transgenic mosquitoes can be proven to reduce dengue or Zika infections, it is possible that natural selection could reduce their effectiveness. Females could develop a preference for wild-type A. aegypti males — stopping the company's currently furthest-developed lineage of GM insects (called OX513A) from spreading in the wild.At best this means a lot of money for Oxitec and little value for the payors. At worst, Zika virus adapts and the mosquitoes become useless.
Someone once said that "Life... finds a way".