Biological Control Conquers Biblical Plague

By Andrew Darby

CANBERRA, Australia, January 10, 2001 (ENS) - The plague locust is being halted in its devastating path. Evidence is emerging of successful biocontrol of the insects that have been the scourge of farmers and agro-industrialists since biblical times.

In its first large scale operational trial, the fungal pesticide Metarhizium has successfully killed Australian plague locusts in the outback of the state of New South Wales after about 10 days exposure.

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Researcher holds an Australian plague locust. The arrow points to the dark spot on its hind wing that distinguishes the Australian species from all others. (Photos courtesy Australian Plague Locust Commission)
The program had been so successful that inspectors who examined treated areas said they compared with eradication rates achieved by conventional chemical insecticides, a spokesman for the Australian Plague Locust Commission said.

A representative of the United Nations Food and Agriculture Organization (FAO), Dr. Clive Elliott, said the success could encourage the FAO to conduct similar trials in sub-Saharan Africa.

"Some of these countries have very sensitive areas which may be important for ecological reasons," Dr. Elliott said. "They have large national parks which can't be treated under present circumstances if the locusts go in. These would be the areas targeted for use of metarhizium. It could also be used for broad scale prevention control in outbreak areas."

Locust plagues occur after successive seasons of good rainfall in dryland areas stimulate good grass growth and allow the insects to complete three to four generations of their life cycle in a year.

A large swarm of adult locusts can consume several tons of plant material every day, quickly devastating crops or pastures in their path. Numbers only decline to background levels when there is a prolonged dry period again.

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Adult locust
Fungal spores of the naturally occurring Metarhizium anisopliae var. acridium are suspended in mineral or vegetable oil and sprayed onto the locusts. According to the Australian Plague Locust Commission, the fungus only attacks locusts and grasshoppers, and is harmless to all other kinds of organisms.

This contrasts with other locust control chemicals, mainly an organophosphorous insecticide, fenitrothion. National regulations such as Australia's forbid the insecticide from being sprayed near homesteads, vehicles, dams, or within five kilometers (three miles) of beehives or the crops that they are pollinating.

In New South Wales, cattle farmers have been warned to withhold their animals from slaughter for 14 days after spraying fenitrothion to avoid the presence of chemical residues in the meat.

Locust plagues have been threatening crops in several Australian states for the past six months. In what it said was a highly successful spring campaign in late December, the Australian Plague Locust Commission controlled a total of 331 band and swarm aggregations of locusts that were infesting around 1,789 square kilometers.

Adult Australian plague locusts can gather in bands that may extend over several kilometers or swarms consisting of many millions of individuals that may cover an area of several square kilometers. They are capable of migrating 500 kilometers (300 miles) in 24 hours aided by prevailing winds, leading to their sudden appearance overnight in areas that were previously without any infestation.

In its latest advice to farmers, the Australian Plague Locust Commission said another significant infestation of locusts has erupted in the outback around the New South Wales - Queensland border after widespread breeding in early summer. It said chemical control is not possible due partly to the presence of floodwaters.

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The fungal pesticide Metarhizium is sprayed on African locusts. (Photo courtesy Green Muscle)
The FAO is currently helping to coordinate locust management in the central Asian country of Kazakhstan and the African island nation of Madagascar, and the insects remain a recurring concern in sub-Saharan Africa where they have caused famine and dislocation of population since ancient times.

FAO experts have argued that conventional pesticides should be discontinued, because of their unavoidable negative environmental effect. But through the 1990s these pesticides had been the only available tactic.

Development of the fungal pesticide metarhizium first began in Britain, West Africa and the United States about 10 years ago as a method to treat African locusts, and it remains available only in limited quantities. To report locust activity, visit: Australian Plague Locust Commission