Agents sans frontiers: cross-border aquatic weed biological control in the rivers of southern Mozambique

Biological control is an effective ways of controlling aquatic plants, especially in South Africa. Release of biological control agents has been limited to Mozambique, where water hyacinth (Eichhornia crassipes (Mart.) Solms-Laubach (Pontederiaceae)), water lettuce (Pistia stratiotes L. (Araceae)), red water ferns (Azolla spp. (Azollaceae)) and salvinia (Salvinia molesta DS Mitch. (Salviniaceae)) are significant weeds in the south of the country. In 2009, we assessed the status of these weeds in seven rivers across southern Mozambique and recorded whether any biocontrol agents were present. The weevils Neochetina eichhorniae Warner (Coleoptera: Curculionidae) and N. bruchi Hustache (Coleoptera: Curculionidae) were on water hyacinth, along with the pathogen Acremonium zonatum (Sawada) W. Gams (Hypocreales) and the mite Orthogalumna terebrantis Wallwork (Acarina: Sarcoptiformes: Galumnidae). Pistia stratiotes supported small numbers of the weevil Neohydronomus affinis Hustache (Coleoptera: Curculionidae). The red water fern in the rivers was A. cristata Kaulfuss (Azollaceae) not the more widely recorded A. filiculoides Lam. (Azollaceae), and it supported small numbers of the weevil Stenopelmus rufinasus Gyllenhal (Coleoptera: Curculionidae). No agents were present on S. molesta. Most of these agents are likely to have dispersed from South Africa, and the rivers of southern Mozambique are likely to be benefitting from the transnational dispersal of these agents.