Problem statement: Floating water fern / fairy fern (Azolla filiculoides) has, for years, been a highly effective invasive species in South Africa, creating problems in inland waterways. These problems include increased flood risks, hindrance to recreational activities, threats to livestock and loss of aquatic biodiversity. Fragmentation of the weed fronds has made control by mechanical means virtually impossible, a problem compounded by the annual production of millions of tiny spores, which are released in autumn and grow into new plants in the following year.

Methods: Investigators sought to identify an effective biological agent for the eradication of the invasive aquatic fairy fern (A. filiculoides). The weevil, Stenopelmus rufinasus was found to feed only on species of Azolla, consuming large quantities of the plant.

Outcomes and Impacts: Since its release by South African scientists, the weevil has brought even the most heavily infested sites under control within a matter of months, without the need for chemicals or further control measures. Control of Azolla has lessened its impact on aquatic biodiversity and reduced its blockage of waterways and the associated problems of flooding, livestock loss and obstacles to the recreational use of waterways.

Lessons: Eradication of this invasive species is now possible without damage to fresh water biodiversity. Identification of an effective biological control agent for Azolla depended on expert taxonomic work.