1. The development of genetically modified mosquitoes and their subsequent field release offers innovative and cost-effective approaches to reduce mosquito-borne diseases, such as malaria. A sex-distorting autosomal transgene has been developed recently in G3 mosquitoes, a lab strain of the malaria vector Anopheles gambiae s.l. The transgene expresses an endonuclease called I-PpoI during spermatogenesis, which selectively cleaves the X chromosome to result in ~95% male progeny. Following the World Health Organization Guidance Framework for the testing of genetically modified mosquitoes, we assessed the dynamics of this transgene in large cages using a joint experimental-modelling approach.

2. We performed a four-month experiment in indoor large cages to study the population genetics of the transgene. The cages were set up to mimic a simple tropical environment with a diurnal light-cycle, constant temperature, and constant humidity. We allowed the generations to overlap to engender a stable age structure in the populations. We constructed a model to mimic the experiments, and used the experimental data to infer the key model parameters.

3. We identified two fitness costs associated to the transgene. First, transgenic adult males have reduced fertility and, second, their female progeny have reduced pupal survival rates. Our results demonstrate that the transgene is likely to disappear in less than three years under our confined conditions. Model predictions suggest this will be true over a wide range of background population sizes and transgene introduction rates.

4. Synthesis and applications: Our semi-field indoor cage experiments are in line with WHO guidance recommendations in regards to the development and testing of self-limiting technologies. Since the transgenic strain (Ag(PMB)1) has been considered for genetic vector control of malaria, our results are fundamentally important for determining expectations on the persistence of the transgene post-release. Our results provide a demonstration of the self-limiting nature of the transgene, and indicate that longevity will be further reduced by fitness costs that were not previously identified. Finally, our study has showcased an alternative and effective method for characterising the phenotypic expression of a transgene in an insect pest population.

In LargeCageType1_rawdata.xlsx file, we reported raw data (number of eggs) from large type-1 cages related to "Establishment of stable age-distributed wildtype populations".

In LargeCageType2_rawdata.xlsx file, we reported raw data (number of eggs, hatching rate, larval mortality, pupal mortality,  and frequencies of transgenic pupae among progenies) from large type-2 cages related to "Large cage populations comprising both wildtype and Ag(PMB)1 mosquitoes".

In LifeHistoryParameters_rawdata.xlsx file we reported raw data (larval mortality, pupal mortality, and adult survival in large cage type 2) related to "Additional survival measurements of wildtype and Ag(PMB)1 for model parametrization".