New publication | Fine-scale landscape genomics helps explain the slow spatial spread of Wolbachia through the Aedes aegypti population in Cairns, Australia

Author summary and figures by Tom Schmidt

Wolbachia is a bacterium that suppresses the capacity for arbovirus transmission in the mosquito Aedes aegypti, and can spread spatially through wild mosquito populations following local introductions. Recent introductions in Cairns, Australia have successfully established Wolbachia in the Ae. aegypti population, but the infection has spread more slowly than expected through the surrounding area. Potential reasons for this include: (i) barriers to Ae. aegypti dispersal; (ii) higher incidence of long-range dispersal; and (iii) intergenerational loss of Wolbachia. We investigated these three potential factors using highly informative molecular markers and an assay that tested for the presence of Wolbachia in 161 Ae. aegypti collected from Cairns in 2015. With these, we investigated spatial genetic structure and patterns of kinship, as well as the presence and absence of Wolbachia.

We detected a small but significant barrier effect of Cairns highways on Ae. aegypti dispersal. We also found a pair of full-siblings in ovitraps 1312 m apart, indicating long-distance female movement likely mediated by human transport. Finally, we found a pair of full-siblings of different infection status, indicating intergenerational loss of Wolbachia in the field. These three factors are all expected to contribute to the slow spread of Wolbachia through Ae. aegypti populations, though from our results it is unclear whether Wolbachia loss and long-distance movement are sufficiently common to reduce the speed of spatial spread appreciably.

These findings inform the strategic deployment of Wolbachia-infected mosquitoes during releases, and show how parameter estimates from laboratory studies may differ from those estimated using field data. Our landscape genomics approach can be extended to other host/symbiont systems that are being considered for biocontrol.