Outcomes and mechanisms of interspecific competition between invasive Aedes vectors
Professor L. Philip Lounibos, University of Florida, USA
Aedes aegypti and Aedes albopictus are not only the most important vectors of dengue, chikungunya, and Zika viruses but also the world’s most invasive mosquito species. Because of their widespread distributions and similar ecological requirements, the two species frequently encounter one another, leading to potential competitive interactions. Despite this, most predictive spatial distribution models do not account for the effects of such interspecific competition. Outcomes of interactions depend on both local environments and the genotypes of competitors. In the common circumstances where invasions result in their co-existence, habitat segregation favours the predominance of domesticated A. aegypti in urban areas and of A. albopictus in vegetated zones. Examples of competitive displacements of A. albopictus by A. aegypti are confined to urbanised environments. Massive competitive displacements that led to local extinctions of A. aegypti by A. albopictus have been documented in southeastern USA and Bermuda. These rapid displacements are believed to be caused by asymmetric reproductive interference, known as satyrization. Larval resource competition favouring A. albopictus may act synergistically with satyrisation, or alone to achieve slower outcomes, such as habitat segregation during co-existence. Resistance to satyrisation evolves rapidly in A. aegypti and is retained in all Florida populations of this species in sympatry with A. albopictus. Different outcomes may prevail in other co-existence contexts, e.g., where A. aegypti are represented by the feral ssp. formosus, or where male A. albopictus are inefficient satyrs. Genetic control planning should include awareness of the potentials for competitive displacements and the evolution of antagonistic phenotypes.
Key factors in mosquito-borne pathogen transmission and control: what can models tell us?
Dr Cynthia Lord, University of Florida, USA
Ecological factors are likely to be critical in successful application of genetic control strategies, including movement dynamics and use of the landscape, and factors affecting population dynamics such as mortality rates and competitive interactions. Models provide tools for integrating the effects of many factors, but it is not feasible to include all factors in every model. Models focusing on genetic control strategies may not include ecological details, while models focusing on pathogen transmission, other control strategies, or population dynamics likely do not include genetic control strategies. However, many types of models can be useful in the discussion about genetic strategies. Considering the factors included, available data, and effects on the outcomes of different models can provide information about important ecological aspects that may influence outcomes of genetic control strategies, and highlight areas requiring additional data for parameter estimation. Models of mosquito-borne viruses will be used to illustrate how differences between mosquito species can influence transmission dynamics and need to be considered in developing control strategies. Mosquito movement across a landscape likely influences the success of control strategies. Models of mosquito movement in simplified landscapes will illustrate how landscapes affect spatial distribution and potential efficacy of different control strategies.
Ignoring the gaps in understanding the ecology of Anopheles gambiae: implications for malaria control
Dr Tovi Lehmann, National Institute of Allergy and Infectious Diseases, National Institutes of Health, USA
Nearly 20 years into a successful global campaign against malaria, the disease still costs over 400,000 lives a year. As the campaign’s primary weapon was aimed against the mosquito, it is also a testimony for the resilience of this vectorial system. The genetic mosquito control promises to overcome limitations of our conventional measures of vector control by recruiting the vector reproductive drive as a weapon against itself. Trusting the mosquito to do its part might be naïve even without undesirable results. The complexity of the real world is not represented in a cage (even if named malaria-sphere), where the mosquito manifests only a fraction of its multi-faceted biology and personalities. Our knowledge of mosquitoes outside the lab is full of major unknowns, multiplying the uncertainty in predicting the spread of introduced genes within and between populations. Nobody has followed a single wild mosquito through a full night. We only guess where they take their sugar meals, mate, rest, how far they fly, how they persist though the months-long dry season? Current knowledge of the deme’s effective size, geographical dimensions, its boundaries, and the geneflow connecting different demes–are all questionable. Further, we don't know how fast they would counter our actions by mutation(s) in the introduced gene or in other genes whose function alters the outcome. Because we will never know all the answers, we could test the success of the genetic approach on a distant island or in a ‘developed country’ targeting a local vector, while at the same time, seek answers to high priority questions. Moreover, demonstrating a capacity to ‘recall’ an introduced gene and restore the previous genetic makeup would be key.
Ecological dynamics of population suppression
Professor Charles Godfray CBE FRS, University of Oxford, UK
Gene-editing and gene-drive techniques offer the possibility of imposing a genetic load on a mosquito vector population that reduces its density to a level at which it can no longer support disease transmission or itself goes extinct. The possibility of extinction distinguishes this form of vector control from most other interventions. This talk will consider the potential ecological consequences of removing a species from a community or driving its population to very low densities, with a particular focus on the African vectors of malaria. It will consider the possibility of relaxed competition leading to super-competent vectors or population rebound, and the risks of an empty niche being filled by other potentially more powerful vectors. It will also explore the possibility that removing a species from an ecological web will cause a perturbation that affects other members of community. The talk will finish by exploring how such eventualities should be considered in risk assessment and by regulators examining proposed releases of modified mosquitoes.