Fungal Doom for Locusts and Grasshoppers

Preliminary trials show 96% success rate

1985-1989 were good years for locusts but bad years for farmers in northern and central Africa. Outbreaks of desert locusts traveled across the region in cloud-like swarms and descended on villages. They clung to almost any green living thing and ate until the green was gone. These swarms can destroy an entire field of crops in a matter of hours—leaving a family without food for the coming year.

During the last outbreak, millions of dollars were spent on aerial pesticide campaigns. Spray campaigns, however, have their drawbacks. In the most effective recorded aerial spray, 95% of the active material was wasted and only 5% hit the target. The wasted spray and contaminated locusts can have broad-reaching effects, killing other insects, entering the food chain, surface water, and threatening human health as well. Since 1990 researchers* have been working together in a collaborative effort towards a safer, more effective biological control. The results of preliminary field trials conducted on desert locust in Niger, in which 96% of the locust were killed, offer a strong indication that an effective solution may be close at hand.

Researchers at the International Institute of Biological Control (IIBC) have developed an oil-based formulation of an entomopathogenic fungi that destroys locusts and can survive high temperatures and low humidity, desert conditions. The fungus Metarhizium flavovoride is apparently widespread throughout Africa, and although its natural incidence is low, it is highly infectious, specific to acridids and can be readily grown on artificial substrates and formulated for application.

Modus operandi

Just how do fungal spores kill the locust? When a spore lands on a grasshopper, it breaks through to the inside using enzymes and mechanical force. It lives and reproduces in the insect, progressively digesting the grasshopper. Seven to ten days after infection the grasshopper dies.

When the insect is near death, the fungus attacks the grasshopper’s nervous system, altering its behavior, causing it to crawl to the top of a blade of grass or plant stalk, grasping it until it dies. The fungus then sends tubes out through the dead insect, which shoot out spores that either infect other grasshoppers, or over-winter in the dormant stage.

A procedure for large scale production of the Metarhizium flavovoride spores has been developed. Blastospore cultures are grown in a liquid medium containing yeast extract and sugar on a shaker. Three to four days later the blastospores are inoculated onto autoclave rice in plastic bags. This is incubated for 7 to 10 days. The conidia are harvested in kerosene and stored at 4°C. New isolates are being screened for pathogenicity to Schistocerca g.

Field tests were conducted with wild locust at a wadi called Anu-Makaren, 150km North of Agadez, Niger. Solitary locusts come from the Air Mountains to breed at the site every rainy season (July-September). Locusts were collected and sprayed in the field with a formulation containing 2 X 109 spores/ml. They were then recaptured for evaluation. 96% of the locusts sprayed were killed in 10 days. During that time temperatures rose to above 40°C and humidity dropped to 15%. The researchers tested the formulation when they returned from the trials and found that its viability was still just as good.

This method kills locusts without producing toxins, and appears to be a very powerful insecticide in comparison with the other locust control methods. This technique has potential for both high technology and intermediate technology formulation. The trials are preliminary and were done on a small scale, but their success will lead to full scale trials in 1992 .

Bateman, R. (1992). Controlled Droplet Application of Myco-insecticides: an Environmentally Friendly Way to Control Locust. Antenna, Vol. 16, No. 1.

Biorational control of locusts and grasshoppers, Biological Control Center for Africa, International Institute of Tropical Agriculture. Cotonou, Benin.

Excerpted from “The Farming World” Program, the BBC World Service.

*The International Control of Locusts and Grasshoppers is a collaborative research program implemented by IIBC, the International Institute of Tropical Agriculture (IITA) Biological Control Program in Contonou, Benin and the Departement de Formation en Protection des Vegetaux (DFPV) in Niamey, Niger.