Innovative biological control of invasive aquatic plants

Invasive aquatic weeds threaten South African aquatic ecosystems and both the quantity and quality of potable water. It’s essential to understand the ecology and management of these weeds and that’s just what the Biological Control Research Group (BCRG) at the department of zoology and entomology at Rhodes University has been doing since 2007.

“It costs the government millions of rands to control invasive aquatic weeds,” says Professor Martin Hill, head of entomology at Rhodes University and director of the BCRG. He is considered Africa’s foremost authority on the biological control of these weeds. 

Biocontrol for management

The BCRG develops cost-effective biological control methods for invasive aquatic plants, with practical implementation in mind. “It’s a particularly appealing solution to use host-specific natural enemies as they’re not toxic, don’t harm non-target organisms and are self-perpetuating,” says Hill. 

In South Africa, several floating problematic aquatic plants have been successfully suppressed through biological control. However, water hyacinth is considered the world’s worst aquatic weed and needs special attention. 

Water hyacinth accounts for up to 40% water loss through evapotranspiration (the sum of evaporation and plant transpiration from the earth’s land and ocean surface to the atmosphere) and threatens aquatic biodiversity. 

It also negatively affects the livelihoods of people who depend on freshwater waterways for food, transport and clean water. The dense, impenetrable mats created by water hyacinth affect irrigation canals, hydroelectric programmes and even tourism.

The BCRG’s studies have shown that high water nutrient status is critical for water hyacinth growth — not good news for South Africa, since the country has some of the most eutrophic (nutrient-loaded) aquatic systems in the world. 

Hill says that one of the BCRG’s most significant research contributions is unravelling the role and impact of eutrophication in aquatic ecosystems. 

It shows that investing in biological control and herbicides for aquatic weeds is not a final solution, because the weeds are symptoms of a far bigger problem.

In 2008, the BCRG established a biological control agent mass-rearing programme at Rhodes University. “The programme has successfully reared and released approximately one million biological agents, assisting in control of the country’s five worst invasive floating aquatic weeds, including water hyacinth, water lettuce, Salvinia, parrot’s feather and red water fern,” says Hill.

Stringent safety procedures

Biological control is considered an environmentally sound solution to invasive aquatic species and the most cost-effective method. Furthermore, it is safe. Before release, extensive research is undertaken to ensure the agent only targets the identified weed. This includes consulting available literature, stringent testing in quarantine, and applications to national departments for release permission. The process takes three to five years. 

“South Africa has been using biological control for over 100 years and, to date, over 100 species of agents have been released and no non-target effects have been reported,” says Hill. 

The BCRG developed a training course in biological control in 2013, targeted at people with disabilities This was done in collaboration with a nongovernmental organisation to create employment opportunities for people with disabilities, of whom seven are currently employed in the programme. A similar programme has now been set up in Cape Town with the BCRG’s assistance.

The BCRG sees research and implementation as intricately connected; thus, knowledge transfer is crucial if biological control is to be used in aquatic weed management plans. This is done through courses, workshops and literature.

The outcomes of the research conducted at the BCRG have also seen an increased capacity in weed biological control, from high school learners to university students, as well as through community engagement. The research-intensive group has also published and presented widely.

In 2009, the Biology Internship Programme (BIP) was developed with Victoria Girls High School (VGHS). It has successfully encouraged environmental stewardship and an interest in science. The programme now includes Graeme College and Ntsika Secondary School. 

A mass-rearing programme for biological control agents for water hyacinth has also been started at Ntsika. The BCRG aims to roll this out to schools nationally. Hoërskool Warrenvale in the Northern Cape is already part of the programme, having started in 2010. 

Through funding from the department of environmental affairs’ Working for Water initiative, the BCRG has continued to grow and have an impact as an internationally leading institute for biological control. 

Its success in reducing aquatic weed invasion and recovering aquatic ecosystems is unprecedented worldwide. 

The team now comprises two professors, a senior research officer, two research officers, an instrument scientist, one project manager, two technical officers, two research technicians, six lab assistants (from the programme aimed at people with disabilities), two postdoctoral fellows, six PhD students and seven MSc students.

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