Observing mosquitoes mating may seem a particularly bizarre activity, but it is proving essential in the development of new strategies to combat malaria. Female Anopheles gambiae mosquitoes transmits the malaria plasmodium, which is responsible for hundreds of thousands of deaths each year. The techniques developed in recent years to combat this disease are based on a very simple principle: fewer mosquitoes, fewer vectors of transmission, and fewer deaths. The use of insecticide-impregnated mosquito nets has proved very effective over the last 20 years. But this is not enough. Mosquitoes have developed resistance to insecticides, so after an initial reduction, the number of annual infections is now increasing.

The scientific imperative is therefore to identify new strategies, to be used in conjunction with current control methods. A 'gene drive' approach attempts to use mosquito mating to spread genetic modifications that make mosquitoes sterile or unable to transmit the malaria parasite. "To assess the effectiveness of these innovative techniques, it is necessary to have a thorough understanding of the mating mechanism", says Roberta Spaccapelo, of the University of Perugia, "we know that these insects mate in flight and that the males associate in groups, swarms of hundreds of individuals, to be more visible and attractive to females. But we don't know much more than that. Do the females that enter the swarm choose which male to mate with? How do they make this choice? Are there traits that make some males more attractive than others?”

The article "Characterization of lab-based swarms of Anopheles gambiae mosquitoes using 3D-video tracking", just published in Scientific Reports, the result of a strong interdisciplinary collaboration between the Department of Medicine and Surgery of the University of Perugia, the CoBBS (Collective Behavior in Biological Systems) group of Sapienza's Department of Physics and the Institute for Complex Systems of the CNR, takes the first steps towards answering these questions. "Reproducing swarms of Anopheles in the controlled environment of the laboratory was a very complicated task. We chose to study these swarms in very large cages to be able to analyse the flight dynamics of the mosquitoes while avoiding potential behavioural effects due to the confined space of small cages", says Irene Giardina of Sapienza University.

"We filmed swarms of hundreds of mosquitoes using a stereometric camera system that allowed us to reconstruct the trajectories of each mosquito in the group in three-dimensional space. By analysing these data, we could verify that the swarms reconstructed in the laboratory have characteristics compatible with those observed in the natural environment", says Stefania Melillo, a researcher at the CNR's Institute for Complex Systems. "The main novelty presented in the paper is that we were able to document different mating events: pairs of mosquitoes flying together for up to 15 seconds. But the most amazing thing is that we observed and documented mating competition. Several males competing to mate with the same female at the same time”.

The article, therefore, represents a first step in understanding the mating dynamics of mosquitoes and provides an important benchmark for the international scientific community to assess the effectiveness of new technologies in reducing the population of such dangerous insects to humans.

Further developments of this study, both from an experimental and modelling point of view, are the subject of the project entitled: Demystifying mosquito sex: unravelling MOsquito SWARMs with lab-based 3D video tracking (acronym: MoSwarm), jointly presented by the University of Perugia and the CNR, which has just been funded by the MUR under the PRIN 2022 projects.

References:

Characterization of lab‐based swarms of Anopheles gambiae mosquitoes using 3D‐video tracking - Andrea Cavagna, Irene Giardina, Michela Anna Gucciardino, Gloria Iacomelli, Max Lombardi, Stefania Melillo, Giulia Monacchia, Leonardo Parisi, Matthew J. Peirce & Roberta Spaccapelo – Scientific Reports https://doi.org/10.1038/s41598-023-34842-0 

Further Information

Irene Giardina
Department of Physics
irene.giardina@uniroma1.it