The continuous monitoring of mosquitoes in the Doñana National and Natural Park in 2023 allowed the identification of 14 different mosquito species belonging to the genera Aedes, Anopheles, Culex, and Culiseta. In this area, mosquito monitoring has been routinely conducted since 2003 [12]; however, the presence of the invasive species Ae. albopictus in this highly protected natural area has not been reported until now.
The passive transport of Ae. albopictus by cars has been demonstrated in Spain [13], which may also explain its introduction in Doñana. Adult mosquitoes could be transported in vehicles from surrounding areas where this species is already established. According to the citizen science platform Mosquito Alert (https://www.mosquitoalert.com), there was a significant increase in Ae. albopictus reports rising from 19 in 2022 to 200 in 2023 in the surrounding provinces of Sevilla and Huelva. Another possible explanation is the local transport of material (i.e., containers, pots, or other goods) harboring the eggs or immature stages of Ae. albopictus. Eggs of Ae. albopictus are highly resistant to desiccation and shipping, allowing the viability of specimens transported from one site to another. Although we did not detect Ae. albopictus larvae, suitable habitats for the development of the larvae of this species mostly include artificial water containers, although Ae. albopictus can also use natural breeding sites [14]. Aedes albopictus females feed on blood from a wide range of vertebrates, although mammals, including humans, dominate their diet [15]. Humans are present in the areas where Ae. albopictus mosquitoes were found in Doñana, especially during the day when the species reaches its maximum activity. The potential role of this mosquito species in the local transmission of pathogens in the studied area, including zoonotic ones, merits further investigation. This includes Dirofilaria immitis, which may circulate in Doñana and affect highly endangered species, such as the Iberian lynx Lynx pardinus [16]. West Nile and Usutu viruses also circulate in the area [17] and could be transmitted by Ae. albopictus [14], although the role of this species in the transmission of avian pathogens is likely low owing to its highly mammal-biased blood-feeding pattern [15, 18].
Because Ae. albopictus colonization of the area monitored in this study should be at an initial stage, local authorities authorized an urgent control program to prevent or minimize spread. In our study, we applied Bti in water-holding containers at two time points to inhibit the development of mosquito larvae in artificial containers used as potential larval sites. Although in this study we collected mosquitoes until September, additional captures done in the Palacio de Doñana station using Center for Disease Control (CDC) traps supplemented with CO2 in September and October did not detect the presence of Ae. albopictus. While these actions may have contributed to limiting the establishment of Ae. albopictus in the area where Ae. albopictus was found, future reintroductions should be considered. Therefore, it is necessary to define future monitoring recommendations and control measures to reduce the chances of establishment. For example, it is important to clean and sterilize any container introduced in the area that can retain water using diluted bleach, and to cover all the tanks used for microcosm experiments with water with mosquito screens. However, the main routes of Ae. albopictus introduction into the Doñana National and Natural Park are probably the vehicles used by researchers, workers, and park visitors, making extremely difficult to reduce this source of introduction. A possible solution for minimizing the impact of this kind of importation would be the spraying of commercial insecticides inside vehicles before displacements, especially during the months of peak activity of Ae. albopictus. This may help minimizing this form of introduction.
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