Biological control of Pontederia crassipes in South Africa
Pontederia crassipes (Pontederiaceae: EPPO A2 List) is one of the world’s most invasive aquatic plants. Native to South America, P. crassipes has been introduced into the EPPO region where it can cause significant negative impacts including blocking water channels, degrading biological diversity, and providing breeding grounds for mosquitoes. Although nine biological control agents have been released against P. crassipes in South Africa, populations of the species remain above a tolerable level. Despite the large suite of introduced natural enemies, classical biological control of P. crassipes is constrained by cooler temperatures experienced in the more temperate areas of South Africa. Megamelus scutellaris (Hemiptera: Delphacidae) is a phloem-feeding bug which was released in South Africa in 2013 and causes a reduction in the photosynthetic efficiency of the plant. Although it is usually used as a classical biological control agent, inundative releases have been conducted, in which large numbers of M. scutellaris are released regularly. This has resulted in excellent establishment along with a significant reduction in P. crassipes cover in areas where, historically, biological control seemed unlikely due to excessive eutrophication. This study has shown that inundative releases of biological control agents over multiple seasons results in the most effective control of P. crassipes, especially at cool temperatures and eutrophic sites.
Sources
Miller B, Coetzee JA, Hill MP (2023) Evaluating the establishment of a new water hyacinth biological control agent in South Africa. African Entomology 30, e15613. https://doi.org/10.17159/2254-8854/2023/a15613