Potential for classical biological control of Crassula helmsii and Hydrocotyle ranunculoides
Crassula helsmii (Crassulaceae, EPPO A2 List) and Hydrocotyle ranunculoides (Apiaceae, EPPO A2 List) are invasive alien aquatic plants which are very difficult to manage as the use of herbicides is tightly regulated in waterbodies. Research into biological control for these two species has been funded by the UK Government as a long-term sustainable solution for their management. Surveys in each of the plants’ native range have revealed many natural enemies which have been narrowed down to a small subset that have the potential to act as biological control agents. Hydrellia perplexa (Insecta: Diptera), Aculus sp. (Arachnida: Eriophydae) and Colletotrichum sp. (Pezizomycotina: Glomerellaceae) have been found to cause significant damage to C. helmsii in Australia and are currently being safely tested under quarantine conditions.
Similar testing is underway on Listronotus elongatus (Insecta: Coleoptera), Eugaurax sp. (Diptera: Chloropidae) and Puccinia hydrocotyles (Basidiomycotina: Pucciniaceae) to be potentially used as biological control agents against H. ranunculoides.
Wood S, Varia S, Djeddour D, Jones K, Seier M, Shaw R (2014) Potential for classical biological control of two non-native aquatic weeds in Europe: Crassula helmsii (Kirk) Cockayne and Hydrocotyle ranunculoides L.f. Abstract of the 4th International Symposium on Environmental Weeds and Invasive Plants, Montpellier (FR), 2014-06-19-23.