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Bugs to fight water weeds

12 January 2011 - 00:20 By ADRIENNE CARLISLE

A team of Rhodes University scientists has been awarded a R9-million contract by Working for Water to research biological ways to control invasive aquatic weeds.

The team from the university's zoology and entomology department has enlisted pupils, disabled people and even a former prisoner to breed and release millions of insects that munch the alien pests hogging water resources, clogging waterways and destroying indigenous plant life.

South Africa loses 9% of its invaluable water runoff to alien invasive species such as the water hyacinth, parrot's feather, salvinia, water lettuce and red water fern, according to Rhodes entomology professor Martin Hill, who heads the project.

The plants, especially the water hyacinth, thrive in often polluted waterways that provide them with high levels of phosphorous and other plant nutrients.

Water hyacinth is originally from South America but has spread throughout the world. It can take over huge expanses of water quickly, doubling the area it occupies in seven days.

"So if it occupies a hectare of water today, in a week's time it would have taken over 2ha," said Hill.

Herbicides had a limited effect, often affecting indigenous insects, fish and other plant life. The answer was to use the plant's natural insect enemies from their region of origin, he said.

Hill has spent many years doing this. He introduced insects with such success in waterways around a Ugandan village that the local chief wanted to reward him with a house and wife.

He said weevils, moths and bugs were quarantined and studied for at least five years before release. It had to be ascertained they fed only on targeted weeds.

"These insects are totally safe and pose no threat to indigenous or economic plant species."

Alicedale's New Year's Dam was almost completely cleared of water hyacinth.

Hill said the insects would not eliminate the weed altogether but reduce it to an acceptable level.

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