Invasive aquatic weeds influence abundances of larval mosquitoes and other invertebrates

Aquatic plants provide habitat structure that affects aquatic invertebrates. As invasive aquatic weeds, water hyacinth (Eichhornia crassipes) and Brazilian waterweed, aka egeria (Egeria densa) can modify and dominate aquatic habitats, altering natural ecosystems. Invasive aquatic vegetation could affect habitat quality for larval mosquitoes, a topic largely unexplored. Some aquatic weeds harbor mosquitoes, whereas others repress them. In this mesocosm study, we measured wild larval mosquito abundances and naturally recruited invertebrate predators and competitors in three aquatic habitat types: open water, water covered with water hyacinth, or water with egeria. Early in the development of weed populations (3 to 6 wk), we found more larval mosquitoes in open water than in other habitats. Abundance was 9-fold lower in water hyacinth and over 30-fold lower in egeria than in water tanks. Competitors were about five times more abundant in open water and egeria than in water hyacinth, and larvae of a representative competitor, Ceratopogonidae, had the same pattern but were over seven times more abundant. Later (Weeks 8 to 10), mosquitoes did not vary among treatments, whereas competitors were almost 3-fold lower in hyacinth than in open water. Predators were marginally lower with hyacinth both early and later (P , 0.07). Overall, healthy water hyacinth had comparatively low numbers of larval mosquitoes and competitors, and when compared to open water, egeria strongly suppressed mosquitoes but did not inhibit predators or competitors. The results have implications for targeting of sites for mosquito control in relation to aquatic weed invasions and integrating control strategies, according to One Health practices.