Grasshoppers Used to Fight "Worst Water Weed"

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In the late 1960s, in South America, researchers discovered two weevils and a moth that destroy the water hyacinth. These creatures have been successfully released in more than 30 countries worldwide. In East Africa's Lake Victoria, for example, two weevil species reduced the coverage of waterhyacinth by 80 percent. (See related article.)

This conquest through biocontrol has spurred the search for other insects to match the range of climates where the water hyacinth thrives.

During the past six years, Center has led three expeditions to South America to find other natural enemies of the water hyacinth—insects and microbes that evolved over millions of years along with the plant and keep it in check.

Finding the Right Bug

Center and his colleagues have conducted surveys from Buenos Aires to northern Argentina, from Iquitos, Peru, to the tributaries of the Amazon, and in Ecuador.

"We tear the plants apart, and pull out all the larvae, and the adults, and see what damage they do," said Center.

Using sweep nets and aspirators the researchers collect insects and take them to a lab in Buenos Aires. There they test an insect to see whether it only has a taste for water hyacinth. Otherwise an introduction could threaten other indigenous species and some cash crops.

The researchers recently took another look at Cornops, rejected during the 1960s because grasshoppers were considered indiscriminate eaters.

For the past five years, Hill has been testing South African relatives of the water hyacinth—about 150 species in all—to see whether the grasshopper will deviate from its favorite food.

"South Africa has 22,000 indigenous plant species—we can't release insects that will eat other species," Hill said.

After five years in a secure lab, Cornops is now deemed safe for biocontrol use in South Africa. This year Hill expects to release several thousand of the insects into a water hyacinth-plagued body of water.

Researchers are looking for an effective, environmentally safe weapon against the water hyacinth in southeast Asia, higher-altitude regions of Africa and elsewhere.

In the U.S., though, Cornops doesn't work. The grasshopper has a taste for pickerel weed—an indigenous plant. The search for a magic bullet goes on.

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