Reed, an invasive alien plant that is abundant on the banks of many rivers, ponds and canals, can encourage the growth of common mosquito populations in the absence of natural predators. When the plant’s litter accumulates, the chemical properties of the water and the composition of the biological communities in the environment change radically, and this facilitates the development of mosquito larvae in freshwater ecosystems.
This is one of the conclusions of a study published in the journal NeoBiota and led by Professor Alberto Maceda-Veiga, a member of the FORESTREAM Research Group at the Faculty of Biology and the Biodiversity Research Institute (IRBio) at the University of Barcelona.
The study, whose lead author is Oriol Cano-Rocabayera, involved collaboration from experts at the Institute for Agri-Food Research and Technology (IRTA-UAB), the Mosquito Control Service (SCM) of El Baix Llobregat Regional Council, the University of Seville, the Doñana Biological Station (EBD-CSIC), the Goethe University (Frankfurt, Germany), the University of Florida (United States) and the universities of Cardiff and Chester (United Kingdom).
More mosquitoes if the invasive reed is present
The ecological impacts of invasive riparian plants at the ecosystem level are not yet fully understood, beyond their impact on specific groups of organisms or on environmental conditions. In addition to altering biodiversity and the composition of the natural environment, exotic and invasive riparian vegetation can affect human well-being.
In the study, the team used experimental aquariums (microcosms) to analyse the ecological impact of replacing native common reed (Phragmites australis) with giant reed (Arundo donax), a species classified as invasive and similar in appearance.
In the presence of A. donax, the mosquito larvae survived longer and grew larger and faster. Behind this increase lies the proportion of A. donax leaf litter, which altered the water’s physicochemical properties and the composition of populations of organisms known as microeukaryotes — protozoa, fungi and other microscopic organisms — which are essential to the functioning of the ecosystem.
The study highlights a dramatic ecological effect, even at low concentrations of A. donax compared with P. australis. “This effect was catalysed by changes in water quality and in the abundance of certain groups of microeukaryotes, such as flagellates and amoebae, which form part of the microbial food webs on which the larvae of the common mosquito Culex pipiens feed,” says Professor Alberto Maceda-Veiga, from the UB’s Department of Evolutionary Biology, Ecology and Environmental Sciences.
“It is important to remember — he continues — that the common mosquito can act as a vector for diseases of medical and veterinary significance. Identifying which plants encourage the proliferation of mosquitoes helps us to understand the complex relationships that species form in nature and, in turn, helps pest control services to predict where they are most likely to find larvae and to apply control measures, where necessary, due to the risk to human health.”
Improving environmental management along river courses
The reed, which can withstand high summer temperatures, typically produces a large amount of biomass and is even being used to generate alternative energy sources. Interestingly, in previous studies, the team had described the potential positive effects of the species, as it provides shelter and protection for native fish in rivers with typically poor coverage of riparian vegetation (Science of The Total Environment, 2025).
Now, the findings of this study shed light on an unexpected aspect of the ecological impact of this invasive plant in riparian areas. “In freshwater ecosystems most severely affected by chemical pollution, the natural aquatic predators of the larvae — such as fish and dragonflies — are often absent. Many larvae mean many adult mosquitoes, which can cause nuisance to humans and even pose health risks.”
In light of these new findings, the authors suggest prioritizing the initial eradication of A. donax in infested areas and restoring these sites with native vegetation such as P. australis, as well as encouraging future studies to determine the breeding preferences of mosquitoes in these habitats and their interactions with their natural predators.
“When the eradication of an invasive species is not feasible, we turn to mitigation measures to reduce its impact. In the case of mosquitoes, we must not give in to alarmism. Firstly, we must remember that in nature, mosquitoes have many predators, as they are a natural part of food webs. Secondly, we have some fantastic mosquito control services, such as the Baix Llobregat SCM participating in this study, which ensure that mosquitoes do not become a problem in areas with high human traffic, such as cities and the marshes of peri-urban environments,” concludes Maceda-Veiga.