Desert locust
Plagues of the desert locust (Schistocerca gregaria) have threatened
agricultural production in Africa, the Middle East and Asia for
centuries. The livelihood of at least one-tenth of the worlds
human population can be affected by this hungry insect. The 2004
desert locust plague is predicted to cause significant crop losses
in West Africa and have a negative impact food security in the
region.
Desert locust ecology
The desert locust lives a solitary life, until it rains. Rain
causes vegetation growth and spurs the development of eggs that
have been laid in the sandy soil. The new vegetation provides food
for the newly hatched locusts and provides them with shelter as
they develop into winged adults.
When vegetation is distributed in such a way that the locusts have
to congregate to feed, and there has been sufficient rain for a lot
of eggs to hatch, forced physical contact causes the insect's hind
legs to bump up against one another. This triggers a cascade of
metabolic and behavioral changes that signal the insects
transformation from solitary behaviour to gregarious behavior. When the locusts
become gregarious they change from green coloured to yellow and
black, their bodies become shorter, and they give off a hormone
that causes them all to be attracted to the same location,
enhancing swarm formation.
Solitary (top) and gregarious
(bottom) desert locusts, Schistocerca
gregaria
During quiet periods, called recessions, locusts are confined to a
16-million-square-kilometer belt that extends through the Sahara
Desert in northern Africa, across the Arabian Peninsula, and into
northwest India. When conditions are right swarms invade countries
on all sides of the recession area, as far north as Spain and
Russia and as far east as India and southwest Asia. As many as 60
countries can be affected.
Swarms regularly cross the Red Sea between Africa and the Arabian
Peninsula and are even reported to have crossed the Atlantic Ocean
from Africa to the Caribbean. A single swarm can cover 1,200 square
kilometers and can contain between 40 and 80 million locusts per
square kilometer. The locust can live between three to six months,
and there is a tenfold increase in locust numbers from one
generation to the next.
Crop loss
Desert locusts can consume the approximate equivalent of their body
mass each day (2 g) in green vegetation: leaves, flowers, bark,
stems, fruit, and seeds. Nearly all crops, and non crop plants, are
at risk, including millet, rice, maize, sorghum, sugarcane, barley,
cotton, fruit trees, date palm, vegetables, rangeland grasses,
acacia, pines, and banana.
Desert locusts
feeding
Crop loss from locusts was noted in the Bible and Qur'an. During
the twentieth century, Desert Locust plagues occurred in 1926-1934,
1940-1948, 1949-1963, 1967-1969 and 1986-1989. The significant crop
losses caused by swarming desert locusts, exacerbate problems of
food shortage, and are a threat to food security.
Control
NASA has developed methods for detecting conditions and regions
likely to give rise to swarms by satellite. Satellite data,
combined with weather information and ground surveys, are used by
the FAOs Desert Locust Information Service to produce forecasts
published on the Web and in regular locust bulletins. They also
provide information and training to affected countries and arrange
for funding from donor agencies in case of major upsurges and
plagues.
The desert locust is a difficult pest to control, and control
measures are made more difficult by the large and often remote
areas (16-30 million sq. km) where locusts can be found.
Undeveloped basic infrastructure in some affected countries,
limited resources for locust monitoring and control and political
turmoil within and between affected countries further reduce the
capacity of a country to prevent swarms.
At present the primary method of controlling desert locust swarms
is with organophosphate insecticides applied in small concentrated
doses by vehicle-mounted and aerial sprayers. The insecticide must
be applied directly to the insect. Control is undertaken by
government agencies in locust affected countries or by specialised
organisations like the Desert Locust Control Organisation for East
Africa (DLCO-EA).
A biological control product has been available since the late
nineties. It is based on a naturally occurring entomopathogenic
(i.e. infecting insects) fungus, Metarhizium anisopliae var.
acridum. The species
M. anisopliae is
widespread throughout the world infecting many groups of insects,
but it is harmless to humans and other mammals and birds. The
variety acridum has
specialised on short-horned grasshoppers, to which group locusts
belong, and has therefore been chosen as the active ingredient of
the product.
The product is available under different names in Africa and
Australia. It is applied in the same way as chemical insecticides
but does not kill as quickly. At recommended doses, the fungus
typically takes two to three weeks to kill up to 90% of the
locusts. For that reason, it is recommended for use mainly against
hoppers, the wingless early stages of locusts. These are mostly
found in the desert, far from cropping areas, where the delay in
death does not result in damage. The advantage of the product is
that it affects only grasshoppers, which makes it much safer than
chemical insecticides. Specifically, it allows the natural enemies
of locusts and grasshoppers to continue their beneficial work.
These include birds, parasitoid and predatory wasps, parasitoid
flies and certain species of beetles. Though they cannot always
prevent plagues, they can limit the frequency of outbreaks and
contribute to their control.
2004 Desert locust swarm
In 2004 West Africa faces the largest desert locust plague in 15
years. The costs of fighting the swarm are estmiated by the FAO to
reach US$122 million and harvest losses are valued at up to US$2.5
billion which will have disastrous effects on the food security
situation in West Africa.
The countries affected by the 2004 plague are Algeria, Benin,
Burkina Faso, the Canary Islands, Cape Verde, Chad, Egypt, Gambia,
Guinea, Libyan Arab Jamahiriya, Mali, Mauritania, Morocco, Niger,
Nigeria, Saudi Arabia, Senegal, Sudan, Tunisia and Yemen.
Recently, large swarms of locusts traveled from Egypt into Jordan
and Israel. It was reported that millions have reached the Gulf of
Aqaba and the surrounding regions. Israel's Ministry of Agriculture
reported sightings of individual insects as far north as Jerusalem
and Tel-Aviv.
Large scale control efforts are underway, but most countries face
serious shortages of pesticides and aircraft.
Issue #88
