Secrets of the Swarm—NIAID Mosquito Scientists Describe Their Research

NIAID Now | August 20, 2021

Mosquito sphere chamber used for swarming experiments. The black cloth mimics a ground swarming marker.

Credit: NIAID

Mosquito-borne illnesses sicken or kill millions of people around the world each year. Mosquitoes spread diseases like malaria, Zika, West Nile, dengue, and Chikungunya to humans, which can present significant health challenges to communities across the globe. The World Health Organization estimated that there were 229 million cases of malaria and over 400,000 malaria deaths in 2019 alone. NIAID supports research to discover new mechanisms for controlling mosquito populations and preventing mosquito-borne diseases. Dr. Joel Vega-Rodríguez and Dr. Tovi Lehmann are two researchers working in this area. Dr. Vega-Rodríguez is the Chief of the Molecular Parasitology and Entomology Unit in NIAID’s Laboratory of Malaria and Vector Research (LMVR). Dr. Lehmann is Facility Head of LMVR and works in the Mosquito Ecology and Malaria Culture and Insectary Unit. NIAID Now spoke with Dr. Vega-Rodriguez and Dr. Lehmann about their work and how their research on mosquito biology and mating is helping to develop much needed novel mosquito-control methods.

Why are you interested in looking into the genetic mechanisms of Anopheles mosquitoes?

Dr. Vega-Rodríguez: In the past 15 years, we have had a significant decrease in the number of malaria cases and malaria deaths, mostly driven by implementation of mosquito-control strategies such as insecticide-treated bed nets or indoor mosquito spraying. However, in the past two years, we have seen this decline has plateau, and now, in some countries, we are seeing an increase in malaria cases and deaths. This is largely caused by mosquitoes becoming resistant to insecticides. Therefore, there is a pressing need to identify biological pathways that could be targeted by new interventions to control and prevent mosquito-borne diseases. Such pathways can be identified by studying the genetic and molecular mechanisms coordinating essential mosquito behaviors, including swarming and mating.

Why did you choose to study mosquito swarming and mating?

Dr. Vega- Rodríguez: If you’ve experienced a group of mosquitoes flying above your head, don’t worry; they are swarming males looking for a mate and they don’t bite! Mating and swarming behaviors are essential to mosquito biology. To mate and reproduce, several mosquito species (including Anopheles mosquitoes, the vectors of malaria) form mating swarms as a pre-requisite for mating. Each day at dusk, male mosquitos gather together, flying and “dancing” in synchrony to draw virgin females to the swarm. Females enter the swarm, carefully select a fit male, and copulate while flying away from the swarm. Typically, each female will only mate once in her lifetime. This demonstrates how critical the mating process is. Females, once inseminated, undergo physiological changes that prevent further mating and stimulate the biting behavior needed to acquire the blood they require for egg laying.

Swarms are regulated by environmental factors including light and temperature fluctuations during the day and night cycles. However, the molecular mechanisms of mosquito swarming and their interplay with the environmental factors are not fully understood. This is why we began studying molecular mechanisms of mosquito swarming in collaboration with the Johns Hopkins Malaria Research Institute, the Shanghai Institute of Biological Sciences, and the Institut de Recherche en Science de la Santé (IRSS) in Burkina Faso. We want, first, to gain a deeper understanding of the genes coordinating this essential mosquito behavior; and, second, to utilize this knowledge to design new interventions to prevent mating or swarming or improve vector control strategies that rely on successful reproductive behavior, like the release of genetically modified mosquitoes.

What are the biggest challenges that you face in studying mosquito mating swarms?

Dr. Lehmann: The first challenge that I faced was locating malaria mosquito mating swarms! I spent many weekends searching around villages in Kenya and found many swarms of different insects, but I failed to find any swarms of malaria mosquitoes. It took years to find my own swarm, and it happened only after Dr. Abdoulaye Diabate, one of my colleagues who joined my group later, showed me several swarms. So simply locating malaria mosquito swarms is a huge challenge.

The greater challenge is observing the events and processes that are occurring in a swarm. These fast mosquitoes move in a dense horde, making identification of specific mating events and the actions that lead to them very difficult. Did the female mosquito reject other male mosquitoes? How long did the female stay in the swarm until she found her mate? Based on what criteria did the mates choose each other? Questions like these, which have great importance to mosquito biologists and vector-control researchers, are difficult to answer due to the complex nature of mosquito swarming and mating processes.

How does studying mosquito swarming behavior benefit public health?

Dr. Lehmann: One potential solution to help limit mosquito-borne diseases is to release genetically modified male mosquitoes into the wild with the hope that they will spread their selected characteristics throughout the population. For this to succeed, the released male mosquitoes must be able to out-compete wild male mosquitoes during the swarming and mating process. Research that can identify the characteristics of male mosquitoes that enable them to have greater mating success rates would allow for vector-control biologists to better ensure that the genetically altered mosquitoes are able to mate and spread the gene of interest. Additionally, studying mating swarms allows for the discovery of strategies for mating disruption. Several different tactics of mosquito control target the swarm and mating process itself, and further knowledge in this area will allow for more mating disruption methods to emerge. These are just some examples of how we can use the information resulting from this research to serve public health needs in different ways.

Read more about NIAID-supported research on mosquitoes and other disease vectors at https://www.niaid.nih.gov/research/vector-bio.

Read a recent paper about mosquito swarming by Dr. Vega-Rodriguez and colleagues.

 G Wang et al. Clock genes and environmental cues coordinate Anopheles pheromone synthesis, swarming, and matingScience. 2021;371(6527):411-415. doi:10.1126/science.abd4359

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