WASHINGTON, D.C.—After more than 15 years of research, scientists from three leading
agricultural research centers announced today that they have identified a predatory mite
that controls one of the world's most devastating cassava pests. The starchy root
crop—cassava—is a major food source for close to half a billion people
worldwide, some 200 million of them living in Africa's poorest countries. First released
in 1993 in Benin, Africa, the predatory mite has reduced populations of cassava green
mites by up to 90 percent in field tests without the use of dangerous pesticides. The
beneficial mite is now established in 12 African countries over more than 400,000 square
kilometers.According to the centers sponsoring the research—the
Nigeria-based International Institute of Tropical Agriculture (IITA), the Colombia-based International
Center for Tropical Agriculture (CIAT), and the Brazilian Agricultural Research Enterprise
(Embrapa)—use of the natural
enemy boosts cassava production by at least one-third. An external assessment of the
program's early impact on half of the cassava-growing zones in Benin, Cameroon, Ghana, and
Nigeria estimated that the resulting increase in production is worth about US$60 million a
year. As scientists spread the predator to the rest of the continent, the benefits should
be 3 to 5 times greater. The project receives financial support from a number of donors,
including the United Nations Development Programme (UNDP), the International Fund for Agricultural Development (IFAD), and the governments of Denmark and
Germany.
"The economic benefits of this research will be enormous for poor
African farmers, because we can now protect cassava against one of its most important
enemies—the cassava green mite," said Lincoln Smith, an entomologist from CIAT.
"The tiny, but destructive mite was ravaging cassava crops in 27 African nations. The
humble crop, cassava, is one of the world's most important food crops; it is a vital
staple for one out of ten of the world's citizens."
According to IITA entomologist Steve Yaninek, who started the biological
control project in 1983, "this is the first time anywhere that a mite pest on a field
crop is being controlled on a continental scale using classical biological control—a
method that does not require the use of pesticides and is as old as plants
themselves." Biological control is the introduction of natural control agents, with
safeguards, into areas where they did not occur before.
The pest mite (Mononychellus tanajoa) is akin to the spider mites
that prey on potted plants in the U.S. and Europe. Cassava is known as the poor person's
staff of life because of its ability to grow under drought and other harsh conditions. The
cassava green mite predator (Typhlodromalus aripo) is 90 percent effective in
protecting cassava in the dry season, when pest populations are usually high. In the wet
season, pest attacks are less severe, and, therefore, the reduction in mite populations is
less dramatic.
Most all plants have evolved with natural defenses, including beneficial
insects that attack harmful pests. But when a food crop is moved from its home territory,
as cassava was when Portuguese traders carried it from Latin America to Africa several
centuries ago, it often leaves behind both its pests and natural protectors. In Africa,
the plant thrived for hundreds of years in the absence of its Latin American enemies. But
when the cassava green mite arrived in Uganda in the early 1970s, it spread rapidly across
Africa.
"In the absence of natural controls, the mite swept through Africa's
cassava belt, destroying from a third to more than half of the crop," said Yaninek
from IITA, "depending on weather, soil, and other conditions."
Researchers from IITA and CIAT began their search for a nonchemical cure
for cassava green mites by looking for potential mite predators in cassava's center of
origin: Latin America. Northeast Brazil's climate most closely resembles that of the
African regions where mite damage was worst. After evaluating many species of predatory
mites over a 10-year period, IITA, CIAT, and EMBRAPA found several species of mites that
can survive in Africa. The most successful does not feed on cassava itself, can be easily
reared by local growers, and spreads rapidly.
"By reestablishing the natural balance between the cassava green mite
and its predators, this approach provides a self-sustaining, environmentally sound
solution to the pest problem," said Smith from CIAT.
IITA and CIAT are nonprofit, nongovernment research organizations
dedicated to alleviating hunger and poverty and to protecting natural resources in the
tropics. They are among 16 centers sponsored by the Consultative Group on International
Agricultural Research (CGIAR). EMBRAPA
leads Brazil's national agricultural research system, placing science and technology at
the service of the country's agriculture and agroindustry.
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