Pests cost thousands of millions of
dollars annually in lost agricultural
production, and at least 10 percent of the
world's harvest is destroyed, mainly by rodents
and insects, while in storage. In 1970, disease
devastated one-sixth of the United States' maize
crop. Later that decade, Java lost 70 percent of
its rice crop to brown planthoppers, while a
1976 outbreak of New World screwworm in Texas
cost US$375 million. The world's potato farmers
spend some US$1 600 million annually to combat
the fungus that caused the Irish potato famine
of the 1840s. Rinderpest, a killer disease that
in the 1890s wiped out 80 to 90 percent of all
cattle in sub-Saharan Africa, is now the target
of a coordinated Pan-African eradication
campaign.
Pesticides help. Their use multiplied by a
factor of 32 between 1950 and 1986, with
developing countries now accounting for a
quarter of the world's pesticide use. But
inappropriate and excessive use can cause
contamination of both food and environment and,
in some cases, damage the health of farmers.
Pesticides also kill the natural enemies of
pests, allowing them to multiply; meanwhile the
number of pest species with resistance to
pesticides has increased from a handful 50 years
ago to over 700 now.
Biological controls, such as the use of
pests' natural enemies, are useful. In West
Africa, the introduction of a wasp has brought
about a spectacular control of the mealybug,
thereby saving cassava, the basic food crop for
millions of Africans. In India the seeds of the
neem tree, Azadirachta indica, are used
as a natural insecticide to protect crops and
stored grain. Researchers have found that the
active compounds can control over 200 pest
species, including major pests such as locusts,
maize borers and rice weevils, yet do not harm
birds, mammals or beneficial insects such as
bees.
Scientists have developed new varieties of
plants, often using genes from wild varieties
with inbuilt disease resistance. Genes from the
wild have been used to protect Brazil's coffee
plantations; while a Mexican wild maize confers
resistance to seven major diseases.
Both pesticides and biological controls can
be expensive: pests become increasingly
resistant to chemicals, and the genetic
resistance of plants to pests needs to be
renewed regularly by the plant breeder.
Integrated pest management (IPM), now the
basis of FAO
plant
protection activities, combines a variety of
controls, including the conservation of existing
natural enemies, crop rotation, intercropping
and the use of pest-resistant varieties.
Pesticides may still continue to be used
selectively but in much smaller quantities.
