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There were 12 references to locusts in the Bible: and a lot more at a workshop organised by the International Fund for Agricultural Development (IFAD) in Rome in September on The Development of Environmentally Acceptable Control Systems for the Desert Locust-which heard "the most exciting development in locust control in seventy-five years." As the workshop closed, a plague warning was announced in Eritrea.
Swarms-where do they go?
The last locust upsurge was in the period
1986-89. After chemical treatments that included some 14 million kg of pesticide
dust and 16 million litres of liquid formulations the plague abated-but the
threat receded not because of the effectiveness of the chemicals but because the
locusts drifted on the wind out to sea off Morocco.
An
increasing body of opinion now argues that the effectiveness of pesticides and
the potential crop yield losses are almost impossible to quantify, and that
donor money would be better spent on insurance or other post-harvest pest
control areas1 rather than trying to locate and combat every single locust
upsurge.
...where do they come from?
Locusts are unique animals in that, given
sufficient rainfall and vegetation the population density increases to a
critical point. At this point phase change happens, altering behaviour, colour,
and body size-from a solitary state they become gregarious, and move and feed
as a body. Although phase change was suggested in the 1920s, it was not observed
in a single outbreak until 1967.
Dr Stewart
Simpson of Oxford University announced his discovery of the mechanism of phase
change. For up to one hour before the female lays her eggs, she is able to
transmit information to the new generation about the environment-and this
directly affects whether or not the emerging hopper will be solitary or
gregarious. The information is contained in the froth that surrounds the eggs,
and an elegant experiment showed that if a gregarising female lays eggs and the
froth is washed off, the hoppers are solitary. This discovery paves the way for
interference in the process of gregarisation, which could prevent swarming and
the long-distance threat to crops that the swarm poses.
...and what happens next?
Allegations of inefficiency combined with
lack of resources and lack of political interest in periods of locust recession
means that regional and umbrella locust control organisations in Africa have not
been able to maintain survey work, and continued political unrest in locust
upsurge areas has also prevented effective control.
The current
favoured strategy is a new FAO initiative, EMPRES (Emergency Prevention System
for Transboundary Animal and Plant Pests and Diseases). EMPRES will focus
initially on the Red Sea area, where most recent upsurges are thought to have
started-and where locust alerts are currently sounding.
In the
meantime, trials of insect growth regulators like diflubenzuron will take place
in Eritrea alongside current control measures with pyrethroid and OP pesticides
until the new control and forecasting techniques can contain the threats. (PB)
1. S. Krall, Desert Locusts in Africa-a Disaster? Disasters, Journal of Disaster Studies and Management, March 1995, 19:1-7.
[This
article first appeared in Pesticides News No. 30,
December 1995, page 19]