Mosquitoes under the magnifying glass – how we learn to monitor the world’s most dangerous insects

Inconspicuous, yet one of the world’s deadliest animals – mosquitoes also remain a mystery in Polish cities. With more than 50 species, different habitat preferences, and the ability to transmit viruses such as West Nile fever and Zika, scientists are looking more and more closely at these insects. Kamil Slomczynski, a biologist and co-coordinator of the study, talks about the behind-the-scenes of Poland’s first systematic monitoring project of mosquito populations, funded by the Ministry of Science and Higher Education.

Water Matters: Is it true that mosquitoes are more conducive to small, dirty puddles than clean, open reservoirs? Where do mosquitoes live best today – in urban realities? And from a biologist’s point of view, can you pinpoint their favorite aquatic habitats?

Kamil Slomczynski: In Poland we have more than 50 species of mosquitoes, which have different habitat preferences. Some of them prefer permanent reservoirs, others – periodic ones. We have species that choose reservoirs with a lot of organic matter and those where there is less of it. Consequently, specific mosquito species have specific preferences for choosing where to lay their eggs. Therefore, we cannot generalize. In urban realities, in addition to natural aquatic habitats, we can find mosquito larvae in rainwater buckets, watering cans, ashtrays, abandoned toys or pots in the garden. It is worth noting that in order for mosquitoes to colonize such ephemeral anthropogenic habitats, rainfall is necessary, which is unfortunately lacking in Poland.

WS: We are increasingly promoting local water storage: retention tanks, rain gardens, rain barrels. Do we think just as often about how to prevent them from becoming colonized by mosquitoes? What does biology say, and what does practice say?

KS: Rainwater retention is a very important initiative and should absolutely not be abandoned because of the risk of creating homes for mosquito larvae. Of course, mosquitoes will be happy to use such infrastructure, but it is enough to properly secure buckets or rainwater barrels, such as with a dense net or tight lid, to minimize the chances of laying eggs. We can also regularly monitor the water in our garden tanks and mechanically remove mosquito larvae. However, from my experience I can say that this is rather rare practice. It is also worth mentioning that small tanks of this type will heat up much faster in hot weather than lakes or ponds, and the higher temperature has a positive effect on the rate of development of mosquito larvae.

WS: Invasive species – such as Aedes japonicus – move with remarkable ease today. Are our cities becoming ports of transfer for exotic mosquitoes, and thus the site of a potential epidemiological threat?

KS: With increasing globalization, some species manage to travel very far in a short period of time, beyond their natural range, and an example of this is Aedes japonicus. It is believed that this is a species that came to Europe with the help of man, through the transportation of tires, which contained the larvae of this species. Due to the fact that Ae. japonicus has found its way to our climatic conditions, it can be assumed that other foreign mosquito species will also establish themselves in Poland, if they make their way here. Since non-European mosquito species such as Aedes japonicus, Aedes albopictus and Aedes aegypti are vectors of various viral diseases, we can expect them to contribute to local epidemics once the pathogen arrives in the country. All of this is possible, while at this point the risk is difficult to assess.

WS: Your project is investigating mosquitoes as potential disease vectors. What viruses are being considered? Do we have a real risk of mosquitoes transmitting pathogens such as West Nile fever or Zika in Poland?

KS: We are focusing on four viruses in our project – these are dengue virus, Zika virus, West Nile virus and the virus that causes yellow fever. At the moment in Poland we are dealing with Aedes japonicus, which is the vector of West Nile fever, and it is the genetic material of this virus that is most likely to be detected during our research. In Poland, there was an endemic case of West Nile fever in the previous year, as well as a case of raven fever in Warsaw caused by the same virus.

WS: Mosquitoes evade some, others are perpetually bitten. What really determines how attractive we become to a mosquito? Body chemistry, skin temperature, metabolism – does it all come together?

KS: Female mosquitoes are guided by three main factors to find a host: exhaled carbon dioxide, body heat and the chemical composition of sweat. Of course, the intensity of these factors varies. For example, people with an elevated metabolic rate (e.g., during physical activity) who exhale more carbon dioxide will be more vulnerable to mosquito attacks. The chemical composition of sweat also determines whether these insects will take an interest in us. At this point, many different chemical components of human sweat have been identified, so mosquitoes have a lot to choose from. This factor is also highly variable at the individual level. There are studies that suggest a preference of some species for certain blood types, while there is a lot of doubt on this issue and the topic is still under study. In short, the food choices of mosquitoes is a complex issue with many questions still to be answered.

WS: For us smog, for them – a jungle of smells. How do mosquitoes find their way in a complex urban space? What do they follow when looking for a food source? Because, after all, it’s not always about blood.

KS: The urban jungle is certainly quite a challenge for mosquitoes. The high density of the human population in cities creates a great mix of carbon dioxide, substances in human sweat and pollutants, but mosquitoes nevertheless thrive in it. It seems that body heat and the chemistry of human sweat may be the key homing factors. Of course, female mosquitoes feed on blood (males feed on nectar from flowers, including those of balconies), but they also need sugar substances from nectar with which to get energy for flight, so they also dine in the same places as males.

WS: In the public space, mosquitoes appear mainly as a flying problem. Is it possible to do solid research on them, not fall into the trap of anthropocentrism and see that the mosquito is also part of the ecosystem, not just a seasonal enemy?

KS: It’s worth remembering that mosquitoes are part of an ecosystem that has existed on Earth far longer than humans. They are a very important part of trophic chains – adults are food for birds and bats, and larvae for fish and amphibians. They should not be feared, but viewed with appropriate respect and awareness. Globally, mosquito-borne diseases are responsible for about 800,000 deaths a year, although there are statistics that say as many as 1 million deaths a year. Therefore, it is important to remember that mosquitoes are a significant epidemiological threat and it is necessary to protect oneself from them by applying repellents or using mosquito nets. The key to sustainable coexistence with mosquitoes is to know them as well as possible, understand their ecology and monitor them systematically. Certainly, multi-area spraying should not be used, as it also kills other insect species, including pollinators, and destabilizes local ecosystems.

Project financed from state budget funds, granted by the Minister of Science and Higher Education within the framework of the Program “Student Scientific Circles Create Innovations”

MAIN PHOTO: Erik Kartis/Unsplash