Mosquito bites are such a nuisance every summer that it would seem we are the only ones they eat. However, these insects do not feed solely on our blood: they also like that of other animals. This is a key point that explains why mosquitoes are responsible for millions of infections and hundreds of …
Mosquito bites are such a nuisance every summer that it would seem we are the only ones they eat. However, these insects do not feed solely on our blood: they also like that of other animals. This is a key point that explains why mosquitoes are responsible for millions of infections and hundreds of thousands of deaths of people every year. But what animals do they prefer to feed on? And those preferences, do they depend on the environment or evolutionary history? These are key questions to understand how pathogens circulate between animal species, including humans. Their bite is a key factor in the transmission of pathogens
Diseases transmitted by mosquitoes, such as malaria, pose a global challenge for public and animal health. In Spain, the West Nile virus has gained prominence in recent years due to outbreaks in 2020 and 2024 in Andalusia and Extremadura. Also in 2024, indigenous cases of dengue were detected in Spain, until recently a disease that did not circulate in our environment. In addition to feeding on sugary secretions from plants, female mosquitoes require blood to complete the development of their eggs. That bite can represent the first contact of the insect with a pathogen that causes a disease. When a female mosquito bites an infected animal it can ingest the pathogen along with the host's blood. If this mosquito is a competent vector, the pathogen will be able to multiply inside it, reach its salivary glands and be transmitted to a new host with the next bite. Competent and accidental hosts
In general, pathogens transmitted by mosquitoes require at least two blood meals: one first for mosquitoes to acquire them and another, later, to transmit them to a new host. Like mosquitoes, not all animal hosts are equally competent for each pathogen. In the case of the West Nile virus birds act as a reservoir, since only in them does the virus replicate enough for a mosquito to become infected with the bite. When an infected insect bites a person or a horse, it can transmit the virus. In some cases this can cause severe symptoms and, infrequently, death. However, humans and horses are accidental hosts. In them the virus does not reach sufficient levels to infect new mosquitoes and continue the transmission cycle. In other words, the disease cannot be transmitted between humans and horses. Patterns of mosquito feeding
It would seem logical to think that the availability of hosts is one of the main factors that determines who the mosquito bites. Those living near farms will tend to feed on cattle, while those found in urban environments will be more likely to feed on humans. This is known as opportunistic feeding. However, not all mosquitoes are opportunistic. There are species that preferentially feed on certain animal groups, even when other hosts are more abundant in the area. These mosquitoes are known as specialists. For example, Culex hortensis and Uranotaenia lowii feed on reptiles and amphibians, respectively. The common mosquito Culex pipiens usually feeds on birds and occasionally on humans.
This, combined with its competitiveness as a vector, allows it to be one of the main transmitters of West Nile virus. Together, this makes us think of the existence of internal factors that influence the feeding preferences of mosquitoes, such as the evolutionary history of each species. The mosquito tribe determines its preferences
In a study led from the Doñana Biological Station, we analyzed to what extent the evolutionary history of mosquitoes influences their feeding preferences. To check it out, we obtained 765 feeding records of mosquitoes worldwide that included humans, other mammals, birds, reptiles and amphibians. This analysis allowed us to describe the feeding preferences at the level of tribe (a taxonomic category that groups evolutionarily related mosquito species). The results showed that tribes Aedini (to which the genus Aedes belongs), Anophelini (Anopheles), Mansoniini (Mansonia) and Sabethini (Sabethes) feed mainly on mammals. Culisetini (Culiseta) prefers birds and Uranotaeniini (Uranotaenia), amphibians. In addition, we found that the most closely related species tend to feed on similar groups of vertebrates. This is known as 'phylogenetic inertia', a concept that describes how certain traits tend to be conserved over evolution. The highest values of phylogenetic inertia appeared in mosquitoes that feed on amphibians. These differences could be due to the evolution of these insects' sensory systems, responsible for detecting their hosts through chemical, visual and acoustic signals. For example, Ur. macfarlanei, specialized in frogs, locates its hosts through acoustic stimuli. We also found an intermediate phylogenetic inertia in mosquitoes that feed on mammals and humans, which shows that many different species are capable of feeding on them. Probably, other ecological factors come into play to determine the host selection. Phylogeny is not the only factor
The study also showed that the country in which the mosquitoes were shown to influence the feeding patterns. It could be due to geographical and temporal variation in the presence and abundance of hosts and mosquitoes. All this influences their encounter probability. This gives rise to different scenarios in each location, with specific mosquito species facing different combinations of hosts. As a result, different feeding patterns are generated. Feeding preferences and disease transmission
Our results help us better understand a fundamental aspect of mosquito biology: their feeding preferences are not completely random, but are conditioned by their evolutionary history and ecological context. And this matters more than it seems. In a global change context, the emergence of zoonotic diseases, whose reservoirs are animals and which can infect humans, is increasing, driven by factors such as climate change and habitat alteration. Understanding what animals mosquitoes prefer to bite can help us better anticipate how pathogens circulate and which diseases have a greater probability of emerging or expanding.
This article has been co-authored by Alazne Díez Fernández, who at the time of writing this article was conducting her research at the University of Extremadura. Paula Parra, Ecology of parasitism, Doñana Biological Station (EBD-CSIC); Jessica Jiménez Peñuela, Postdoctoral researcher in urban ecology and vector-borne diseases, University of Granada; Jordi Figuerola Borras, Research Professor, Doñana Biological Station (EBD-CSIC); Josué Martínez de la Puente, Senior Scientist, Doñana Biological Station (EBD-CSIC); Martina Ferraguti, Ramón y Cajal Researcher, Doñana Biological Station (EBD-CSIC); Rafael Gutiérrez López, Postdoctoral researcher, Doñana Biological Station (EBD-CSIC) and Sergio Magallanes Argany, Postdoctoral researcher in the Department of Conservation Biology and Global Change, Doñana Biological Station (EBD-CSIC). This article was originally published in The Conversation. Read the original.
