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PRI's Environmental News Magazine

Mite Makes Right: Biological Insect Control in Benin

Air Date: Week of June 9, 1995

A tiny insect has saved Benin, Africa from possible famine. Scientists discovered and then imported a natural predator wasp to kill off mealy-bugs that were devastating the nation’s staple cassava harvest. David Baron of member station WBUR reports.

Transcript

CURWOOD: Chemical pesticides have contributed to tremendous growth in food production in this century, but not without causing other serious problems, including contaminated groundwater, decimated wildlife, and human illness. Today, many farmers are trying to use pesticides more sparingly and are looking increasingly to natural solutions. In Africa, scientists say they are on the verge of winning the war against 2 devastating crop pests that put millions in danger of starvation. And they're doing it without using a drop of poisonous spray.
Instead, they're helping farmers use nature's way to hold pests in check. David Baron of member station WBUR recently traveled to Benin and prepared our report.

(Footfalls, a machete digging)

BARON: Emil Nuessu, a farmer in the tiny West African nation of Benin, uses a machete to cut into the hard-baked soil. It's the dry season and the small farms of cotton and corn and oil palms are brown. But there is food hidden underground. Nuessu digs up chunks of dirt around a spindly plant about 5 feet tall topped by fans of greenish brown leaves. This is cassava, a staple crop for more than 200 million Africans. Nuessu is harvesting the plant's roots.

(Hubert Creassu speaks as digging continues.)

BARON: Nuessu's cousin, Hubert Creassu, explains his family eats cassava every day. The root, which looks like an elongated potato, can be boiled or grilled. It can be processed into flour and made into cakes. In the United States, cassava is known primarily as the source of tapioca. What makes cassava especially important is its reliability. During the dry season and during years of terrible drought, the plant can survive, storing energy, calories, in its roots. Cassava is often the last buffer against famine, but 20 years ago this buffer began to vanish.

(Creassu speaks)

BARON: Creassu shows a cassava leaf that's malformed, kind of bunched up: evidence of mealy bug damage. Creassu says mealy bugs in large numbers can destroy his crop. The mealy bug is one of 2 devastating cassava pests that arrived in Africa in the early 1970s and quickly spread across the continent, wiping out cassava fields across an area larger than the United States. Around 1980 a team of international scientists began assembling in Africa to address the mealy bug emergency. Swiss entomologist Hans Herren headed the effort.

HERREN: We needed really to have, like a Marshall Plan to deal with this, because the cassava's dying out.

BARON: The story of how Herren and his team controlled the mealy bug has gained almost legendary status in African agriculture. When the mealy bug first appeared in Africa some farmers tried insecticides. But the chemicals didn't work very well, and few farmers in Africa could afford them anyway. Herren had a different idea. If he could find the natural habitat of the mealy bug, he could probably find a natural enemy to keep it in check. Cassava was brought to Africa 4 centuries ago from South America, so Herren figured the mealy bug, which was adapted to eating cassava, must also have come from somewhere in the Americas.

HERREN: Anywhere between Southern California and Northern Argentina. This was the range, so we had a very hard time even to pinpoint where are we looking for this mealy bug.

BARON: After an exhaustive, year-long search, Herren and his team found the mealy bug living in Paraguay, where no one was aware of its existence.

HERREN: It's amazing, that people who have worked on cassava in Paraguay for years, they've never seen this thing, because it was, there were very few and nobody found this to be any problem.

BARON: It appeared Herren's intuition was correct. The mealy bug wasn't a problem in the Americas, so it must have its own natural enemies, its own pests, that keep it under control. Herren's team found a tiny wasp, no bigger than the tip of a pencil, that lays its eggs in the mealy bugs, killing them. After conducting field tests to make sure the wasp wouldn't cause any problems if introduced to Africa, Herren decided to rear thousands upon thousands of the insects in a laboratory, and then to shoot them out of the back of an airplane crisscrossing Africa, spreading the wasp from Senegal to Mozambique.

HERREN: A lot of people thought I was a bit out of my mind to do this: Basically it won't work.

BARON: But it did work, remarkably well.

HERREN: It established itself, and brought the mealy bug under control in let's say 95% of the cases.

BARON: It's estimated that within 20 years, for every dollar spent controlling the mealy bug, farmers will have saved $150 in crop losses. The project may end up saving the world billions of dollars in food aid. But controlling the mealy bug was only half the battle; the second devastating cassava pest, a tiny mite, continued to spread. In fact, with the mealy bug under control, the mite problem grew worse. American biologist Steve Yaninek now wants to do to the mite what Hans Herren did to the mealy bug.

YANINEK: See those mites there?

BARON: Yaninek stands in a field of cassava at the International Institute of Tropical Agriculture, just outside the city of Cotonou in Benin. He is peering through a magnifying glass at tiny green 8-legged animals on the underside of a leaf. The plants look sickly; their green leaves are covered with yellow spots.

YANINEK: See the spots where the green chlorophyll has actually been sucked out of the plant by the mites.

BARON: Yaninek and his colleagues, who also worked on the mealy bug effort, believe they can find a similar non-chemical solution to the green mite. Retracing the same steps over the course of a decade, the scientists have found a Brazilian bug they believe fits the bill. It's another mite that eats the cassava green mite. Yaninek has been testing this predatory mite on some of the plants in his field.

YANINEK: Overall, you can see that the foliage is much more lush. And all the plants have nice, big, healthy shoot tips. That's because of the predators that are in there.

BARON: Yaninek says the predatory mite has been tested successfully in Ghana, Sierra Leone, Cameroon, Uganda, Burundi, and Zambia. He hopes soon to have a large-scale distribution effort up and running to spread the bugs to farmers' fields across Africa's cassava growing belt. Peter Neuenschwander, who heads the agricultural research station where Yaninek works, says the threat to Africa's cassava crop may largely be over in a few years. And the feat will have been accomplished using methods appropriate for Africa, a continent with little infrastructure.

NEUENSCHWANDER: You don't need foreign currency, foreign exchange, to import things. You do not need machinery, you do not need water and so on. This offers sustainable solutions.

BARON: International agricultural experts are well aware of the cassava pest control effort in Africa and widely praise it. But few farmers or biologists in the developed world are familiar with the project. Cornell University entomologist Edward Glass hopes to see that change.

GLASS: I think it's a spectacular success. This method of plant protection ought to be taught and practiced to a wider extent.

BARON: Glass says biological control isn't appropriate for every pest, but the cassava story shows sometimes the best solution includes leaving pesticides on the shelf. In Africa, he points out, biological control saved millions of people from potential famine, while saving money and the environment as well. For Living on Earth, I'm David Baron reporting.

 

 

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