The effects of invasive alien aquatic plants on larval mosquito abundances and predation

Abstract

Invasive alien aquatic plants (IAAPs) pose significant threats to biodiversity by forming dense surface mats that limit light penetration, reduce species diversity, and impede water movement, adversely affecting freshwater ecosystems and the communities reliant on them. Climate change exacerbates these threats by facilitating the range expansion of IAAPs, amplifying their ecological and economic impacts globally. Despite extensive research on their broader effects, the role of IAAPs in facilitating mosquito proliferation is underexplored, particularly in South Africa, where conditions are ideal for both invasions and mosquito survival. Given the role of mosquitoes as vectors of various human, livestock and wildlife diseases, this represents a critical knowledge gap. This study investigated the relationship between IAAPs and mosquito population dynamics through two experimental components. The first was a 42-day outdoor mesocosm experiment evaluating whether the IAAPs Pontederia crassipes (water hyacinth), Pistia stratiotes (water lettuce), Azolla filiculoides (red water fern), Myriophyllum aquaticum (parrot's feather), and Salvinia molesta (giant salvinia) differentially facilitate aquatic insect communities, with an emphasis on mosquito colonization. The second component comprised laboratory-based experiments testing predator-prey interactions between larvae of the mosquito, Culex pipiens and the predatory backswimmer Anisops debilis in the presence of IAAPs Azolla filiculoides, M. aquaticum, Po. crassipes and a native plant control, Lemna minor. Specifically, the first part of this component investigated the prey consumption rates under 100% cover of the IAAPs. The second part investigated the predator behaviour under the different treatment scenarios. Results from the first component revealed that mosquitoes respond significantly differently to IAAPs, but that Po. crassipes and M. aquaticum facilitate the highest mosquito densities, while also having significant implications for predation and competition dynamics. Results from the second component showed that IAAPs significantly impede predation with Po. crassipes and M. aquaticum conferring the greatest mosquito prey risk reduction. Results from this second component also showed that the aquatic predator An. debilis adjusts its behaviour depending on the nature of the IAAP and that M. aquaticum in particular seems to be avoided, with implications for predator-prey encounter rates. These findings highlight the potential for specific IAAPs to exacerbate mosquito proliferation, posing risks for biodiversity and public health. This research underscores the need for targeted IAAP management strategies and opens avenues for future studies on mitigating mosquito-borne diseases in IAAP-invaded freshwater systems.