As with all methods of controlling insects, there is always a small chance that resistance could develop. But the chance is much smaller with our solution than conventional pesticides. That’s because when pesticides are sprayed in the wild, mosquitoes will be subject to different dose levels and sub lethal doses will encourage resistance. Any mosquitoes which are resistant to insecticides will pass on their resistance gene, so over time more insects become resistant – this is sometimes called selection pressure. Our modified mosquitoes are reared in a laboratory where they can remain alive and healthy due to a chemical repressor, tetracycline, so there’s no selection pressure for them to develop resistance to the gene we’ve introduced. As a result, we’ve not observed any sign of resistance developing in our mosquitoes, despite rearing them over more than 100 generations (in human terms that number would take us back to the time of the Vikings!).
It’s also important to remember that our technology would be used in conjunction with other existing methods of control, and that will minimise the chances of resistance developing. In addition, we are always investigating new advances and modifications of our approach to reduce still further the risk of resistance. The colour marker carried by Oxitec insects is one of the methods of control that allows us to assess their performance.