Monitoring Desert Locusts in the Middle East: An Overview

Desert Locusts, Schistocerca gregaria (Forskal), are the most dangerous of locust species. Under favorable environmental conditions, a few solitary individuals can dramatically multiply, form large swarms able to migrate great distances, and threaten agriculture over a large part of Africa, the Middle East and Southwest Asia. There have been six plagues of Desert Locusts this century, one of which lasted almost 13 years. Initial Desert Locust control efforts were largely curative; the trend in the twentieth century has been toward preventing such plagues from occurring. Affected countries have assumed ever more responsibility for monitoring locust breeding areas and treating infestations before they increase in size and number. Five of the 18 countries which currently undertake comprensive surveys for, and control efforts against locusts, are in the Middle East. Most recently, Saudi Arabia completed large scale control operations to prevent a sudden outbreak of locusts from becoming a plague. Over the years, our knowledge of the Desert Locust has evolved along with our ability to manage locust plagues. The challenge in the future lies in the implementation of control strategies that insure food security with minimal environmental consequences. INTRODUCTION Locusts are part of a large group of insects commonly called grasshoppers belonging to the family Acrididae. The Desert Locust, Schistocerca gregaria (Forskal), is one of about a dozen species of short-horned grasshoppers (Acridoidea) that are known to change their behavior and physiology in response to changes in population density by forming swarms of adults or bands of wingless nymphs called hoppers. Swarms may contain billions of individuals behaving in unison; they can migrate over hundreds or even thousands of kilometers. Bands can contain a similar number of non-flying nymphs which also act as a cohesive unit. True grasshoppers form neither bands nor proper swarms. However, the distinction between locusts and grasshoppers is not entirely clear-cut. There are some species, such as Oedaleus senegalensis, which occasionally form small loose swarms. Locusts such as the Tree Locust (Anacridium sp.) rarely form bands. Some locust species, such as the Australian Plague Locust (Chortoicetes terminifera), do not change shape and color in response to changes in density. DESERT LOCUST LIFE CYCLE The Desert Locust poses the greatest threat of all locusts to humans because hopper bands and adult swarms can rapidly arise and migrate, potentially threatening food security in some 60 countries in Africa, the Middle East and Asia. A desert locust lives three to five months although this is extremely variable and depends on weather and ecological conditions. The life cycle comprises three stages: egg, hopper, and adult (Figure 1). 1 For the purposes of this paper, the Middle East is defined as those countries that extend from Egypt to Turkey eastwards to Iran, including the entire Arabian Peninsula.