Rain in the desert can be a mixed blessing. In four countries of Northwest Africa - Mauritania, Morocco, Algeria, and Tunisia - the unusually heavy rains of several weeks ago have spawned swarms of hungry locusts, flying over huge tracts of land in search of something green to eat.
Across southern Algeria, for example, a wide, ``green dam'' of trees planted in the 1970s to halt the advance of the desert is being attacked. In Morocco, a staff of 1,500 has been assigned to pest-control programs.
A report from the United States Agency for International Development (AID) says that a swarm estimated at 20 billion insects, measuring 150 square miles, crossed from Algeria into Tunisia in the last few weeks.
Locust plagues in Africa are a perennial scourge. International aid agencies have stepped in to try to halt the insect onslaught by applying hundreds of thousands of liters of pesticides.
These liberal applications of pesticides, which have sparked some controversy, are donated mainly by Western Europe, the US, and, to a lesser degree, the Soviet Union. Donations of pesticides and equipment to combat locusts totaled $90 million for 1986 and 1987, according to the UN Food and Agriculture Organization, which acts as liaison between the affected nations and donor governments.
Environmentalists and many others are concerned about the danger posed by chemical pesticides to other forms of wildlife - and to humans.
The good news this year is that the three main pesticides being used - malathion, fenitrothion, and, in smaller amounts, carbaryl - are generally considered safer to the environment than the three leading pesticides used against locusts in Africa last year. They have all been approved by the US Environmental Protection Agency (EPA).
The bad news comes in two parts. First, FAO consultant Nick Raymond says the three pesticides being used this year could prove to be less than effective.
``We consider them so safe that FAO is raising the question of whether we need to go to a more powerful pesticide - dieldrin - which everybody agrees has more severe environmental side effects,'' says Mr. Raymond. Dieldrin, a type of DDT, is one of the highly-criticized chemicals used during a locust infestation in Africa nations last year. It is said to cause cancer and is banned in the US.
Second, the three pesticides being used may be safer than in the past, but according to environmental monitoring groups, even these can not be considered ``safe.''
``It's a step forward, but it's only a baby step,'' says Diane Baxter of the National Coalition Against the Misuse of Pesticides in Washington. ``These are less toxic pesticides, but it's like choosing between Satan and Beelzebub. And their effects are not permanent. It's a stop-gap solution, and it's harsh. It can kill beneficial insects.
``We can't just substitute pesticide for pesticide. Any permanent solution would have to take into account the life style of this pest.''
Does such a ``permanent solution'' exist? Baxter thinks it may, under the name of nocima locustae, a biologically produced parasite that attacks locusts - and only locusts.
Nocima Locustae is marketed under the name of Nolobait by Evans Biocontrol in Broomfield, Colorado. Director John Evans will be meeting with FAO officials in Rome this week, and then traveling to Africa to discuss the application of Nolobait to the current locust problem.
Nolobait kills only from 50 to 60 percent of targeted insects. But females pass it on through the egg into the third and fourth generation. (There can be several generations in one year in Africa.)
Mr. Evans admits nocima is a long-term, rather than quick, solution to be used in emergencies. ``Once there are swarms of adult locusts coming across the desert, nocima is not going to work,'' he says, but adds that it does reduce the amount of eating a locust can do.
A number of experts are more guarded in their endorsement of Nocima for use in Africa. ``An integrated approach is the best approach to take,'' says Jerry Fowler, director of the Grasshopper Integrated Test Management Project of the US Department of Agriculture in Boise, Idaho. ``In environmentally sensitive areas, nocima works particularly well on very young grasshoppers in localized areas. ... In certain situations it's not the best choice, but it must be a part of the arsenal we are using. ...''
Jeremy Roffey, head of FAO's locust division, is skeptical. ``It's not being used in Africa.'' he says. ``Some field trials were undertaken in Senegal but the general feeling was these trials were not very satisfactory. It was more effective when mixed with a chemical pesticide. ...''