Crossing continents: First record and evidence of establishment of the Australian backyard mosquito Aedes notoscriptus (Diptera: Culicidae) in Europe, Bosnia and Herzegovina

Mosquitoes are more than just summer nuisances; they are some of the most effective travelers on the planet, capable of carrying diseases across vast distances. While many species are tied to specific climates, a few have proven remarkably adaptable, learning to breed in the small, artificial pools of water created by human activity, such as discarded tires or flower pots. These "container-breeding" mosquitoes can survive dry spells by laying eggs that wait out the drought, hatching only when rain returns. This ability, combined with global trade and travel, allows them to hitch rides far from their native homes, sometimes establishing new populations in regions where they have never existed before. When a mosquito species arrives in a new continent, it brings with it a new set of ecological rules and potential risks to local wildlife and human health, making the discovery of such an arrival a critical moment for scientists who track these invisible invaders.

In the southern region of Bosnia and Herzegovina, a team of researchers has documented the first confirmed arrival of a mosquito species that was previously unknown to Europe. The insect in question is Aedes notoscriptus, commonly known as the Australian backyard mosquito. Native to Australia and nearby islands, this species had never been recorded as an established population in Europe or the broader Palearctic region until now. The discovery was made in the city of Mostar, where scientists found not just a single stray insect, but a thriving, reproducing community. The evidence points to a population that has successfully adapted to the local environment, laying eggs, hatching larvae, and surviving through multiple seasons, marking a significant expansion of the species' global range.

The journey to this discovery began in September 2024, when researchers were conducting a routine survey of mosquito populations in Herzegovina. Using traps baited with carbon dioxide to attract adult mosquitoes, they captured a specimen in the historic center of Mostar that did not match any of the known European species. Because the insect looked unlike anything in the local identification guides, the team turned to genetic analysis to solve the mystery. They extracted DNA from the mosquito and sequenced a specific genetic marker, a molecular barcode used to identify species. The results were definitive: the insect was Aedes notoscriptus. This initial finding was just the beginning. Over the next two years, through 2025 and 2026, the team returned to the same site and expanded their search to surrounding neighborhoods. They found the mosquito repeatedly, confirming that it was not a one-time visitor blown in by the wind, but a resident.

To prove that the mosquito had truly established itself, the researchers needed to find evidence of a new generation. In June 2026, they located larvae in a water-filled container in a private garden near the original capture site. The container, shaded by a pomegranate tree and filled with decomposing leaves, provided the perfect nursery for the young mosquitoes. Finding these larvae was crucial, as it demonstrated that the population was not just surviving but actively breeding in the wild. In total, the team collected 86 specimens from eight different locations in and around Mostar. They also captured larvae, further solidifying the case for a local, self-sustaining population. The genetic analysis of nine of these specimens confirmed they all belonged to the same species and shared a very close genetic relationship with mosquitoes found in Australia and New Zealand.

The genetic data revealed that the Bosnian mosquitoes were remarkably similar to their Australian cousins, sharing specific genetic signatures that linked them directly to populations in the Southern Hemisphere. The researchers found two slightly different genetic versions, or haplotypes, among the local mosquitoes, both of which were already known from Australia and New Zealand. This close genetic match suggests that the mosquitoes likely arrived from one of these regions, perhaps hidden inside a shipment of goods or on a vehicle, though the exact path of their arrival remains a mystery. The genetic diversity was low, which is typical for a new population that has just started to grow from a small number of founding individuals.

The discovery in Mostar is significant because the local climate, with its hot, dry summers and mild, wet winters, appears to be suitable for this species. The mosquito is known for its ability to thrive in urban and suburban environments, using artificial containers to breed. In Mostar, the researchers found the insects in gardens with fruit trees and ornamental plants, environments that mirror the "backyard" habitats the species is famous for in its native Australia. The fact that the population has persisted through two winters suggests that the mosquitoes have found a way to survive the cooler months, possibly by overwintering as larvae or adults, or by relying on their tough, drought-resistant eggs.

This finding raises important questions about the future spread of the species and its potential impact. Aedes notoscriptus is known to carry diseases that affect both humans and animals, including viruses that cause fever and a parasite that causes heartworm in dogs. Since heartworm is already present in dogs in Bosnia and Herzegovina, the arrival of a mosquito capable of transmitting it adds a new layer of concern for veterinary health. The researchers emphasize that while the mosquito is now established in Mostar, its full range within Europe is unknown. Continued monitoring is essential to track how far it spreads and to understand how it interacts with local ecosystems.

The story of the Australian backyard mosquito in Europe is a reminder of how quickly the biological landscape can change. Through the combination of global movement and ecological adaptability, a species can cross continents and take root in a new home. The work of the researchers in Bosnia and Herzegovina provides the first concrete proof of this event, moving the species from a theoretical possibility to a documented reality. As they continue to study the population, the focus will be on understanding its habits, its limits, and its potential risks, ensuring that the scientific community is prepared for whatever changes this new arrival might bring to the region.