Swarm Prediction

On June 6, 2007, the Food and Agriculture Organization's Locust Watch program issued an alert on its web site stating the desert locust situation in Yemen had become "extremely serious." The warnings have helped agencies on the ground implement control measures to prevent destructive swarms from taking to the air and threatening the agriculture of the region. Powering these alerts are IRI's vegetation and rainfall monitoring tools, designed to help decision makers quickly assess the risk levels of the insect pests.

The desert locust (Schistocerca gregaria, Forskal 1775) lives in remote desert zones that extend from North Africa to Southwest Asia. These habitats are generally far from populated centers and difficult to access.

As it turns out, the locust populations are quite sensitive to environmental and climatic conditions. The insects need moist soils for laying eggs and plenty of green vegetation to sustain the 'hoppers', or non-flying juveniles. If these conditions persist, the hoppers increase in number and their behavior changes-- from that of acting as an individual (solitarious) insect to that of acting as part of a group (gregarious). They then morph into flying adult locusts, and a swarm is born.

A mature locust can eat its own weight in vegetation every day. A typical swarm can be miles across and contain a billion members. If the wind conditions are right, the swarms can travel thousands of miles and can threaten the food security and livelihoods of up to a fifth of the world's population. Recent plagues that occurred between 2003 and 2005, for example, cost an estimated $400 million and affected 8.4 million people, according to the FAO.

Controlling locust populations before they can swarm is a difficult endeavor.

"The potential breeding sites are spread of vast, unpopulated areas that are typically difficult to access," says IRI scientist Pietro Ceccato.

Countries with limited resources and infrastructure can't possibly track all the areas in a systematic way, and conducting searches by guesswork is very inefficient, he says.

Instead, Ceccato exploited the fact that locusts need certain environmental requirements to thrive. He developed a set of mapping and monitoring tools to help locust-control workers pinpoint areas where conditions are favorable to locust breeding. The tools allow for an early-warning system of sorts, says Ceccato, because the locusts can be located and controlled before their populations grow to full-scale plagues. In the time since FAO issued the alert for Yemen, for example, ground teams have treated more than 19,000 hectares.

A swarm of desert locusts. Photo: FAO

Users can monitor satellite-derived daily rainfall on a map of the entire desert locust region. Clicking on any point on the map displays charts of historical precipitation for that area. They can also download free high-resolution TERRA-MODIS satellite images to monitor changes in vegetation and water bodies. These images are updated every 16 days and can be downloaded automatically into Geographic Information System (GIS) software.

Mani Tanko, a desert-locust officer in Niger's Ministry of Agriculture, uses the images for his field assessments. "They are very precise and provide many details on the vegetation," he recently wrote Ceccato from his station in Agadez, in the Sahara desert.

Tanko is just one of many control workers who rely on the IRI's monitoring tools to assist them in their work. The FAO's alerts are read by 23 ministries of agriculture.

Keith Cressman, who runs the desert-locust forecasting program at FAO, says the organization's ability to monitor developments has "improved dramatically" thanks to the IRI's new tools. "We are now able to have a much better estimate of where rain may have fallen and where vegetation may be green in desert-locust habitats. Up until recently, it was impossible to accurately monitor these vast areas that extend from West Africa to India and account for nearly 20% of the Earth's land surface, including some of the remotest places on the planet."