IN the late 1980s, swarms of locusts and grasshoppers swept simultaneously across Africa with a ferocity not seen in 50 years. Then, almost as suddenly, much of the insect plague dissipated - and pesticide warfare financed by Western aid may not have been the main reason. Results from chemical-control efforts were disappointing, according to a new United States government study of the African locust problem. Weather was the big factor in the bugs' demise. Moreover, the popular Western conception that locusts threaten Africans with damage of Biblical proportions may be overdrawn.
``The link between famine or food shortages and locusts and grasshoppers is questionable,'' says the new report, prepared by the Congressional Office of Technology Assessment (OTA).
On a local basis insect damage can be devastating. But the plagues are like tornadoes, the OTA report says, destroying small swaths while leaving other areas untouched. Overall, at the height of infestation in 1986 insects apparently caused a crop loss of less than 1 percent in the nine most affected African nations.
The Striga weed and the army worm probably cause more crop loss, and drought is a far more deadly plant killer. Insect outbreaks are only one more adverse factor in a stew of problems that includes drought, deforestation, civil war, and economic stagnation, the OTA says.
The worst of the African insect pests, the desert locust, erupted in seven different plagues during the years 1860 to 1972. In 1985, after rains ended a multiyear drought, young plants provided Desert Locusts with the environment to rise again. At the plague's 1988 height, desert locust swarms could be found in a belt stretching across northern Africa from the Atlantic to the Red Sea.
Mobilized by the crisis, public and private Western aid donors contributed $275 million for insect control in 23 countries from 1986 until '89. The US provided about $60 million of this total, mostly in aircraft, chemicals, and technical help.
Given the pressing nature of the problem, control, of necessity, focused on widespread pesticide application. In 1988 alone, 13 million liters (3.4 million gallons) of insecticide were used, mainly against desert locusts in Northwest Africa.
Despite concerns that it would continue for years, the Desert Locust infestation ended in late 1989. Some experts pointed to this as evidence of the wisdom of intensive chemical control. But the OTA notes that a number of other experts feel that the efficacy of control programs is unproved, and that cold weather and winds may have ended the swarms.
``While insecticides can protect standing crops, their ability to end or prevent plagues is not clear,'' says the OTA.
In the nine most affected countries, the cost of insect control was just about equal to the value of the crops saved. Much of the pesticide was poorly applied, at the wrong time. Environmental problems ranged from accidentally poisoned sheep in Tunisia to people in Niger eating chemically killed locusts.
In the face of what it judges ``disappointing'' control results in the '80s African Locust Plagues, the OTA recommends several ways to do better next time:
More prevention by mapping seasonal insect breeding grounds and concentrating long-term control efforts there.
More research on new control approaches such as natural pesticides derived from microbes and viruses.
More multipest strategies. Locust species often appear similar, while requiring different types of insecticide for control.