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Since agriculture was first practiced, the DesertLocust has been a major pest of semi-arid crops.
Until the early 1940s crop protection measures were organized on a national basis but as the Desert Locust often breeds in remote, sparsely populated areas and swarms frequently cross national boundaries, it was difficult for these organizatións to cope with unexpected Desert Locust invasions from neighbouring regions.
A major development in the fight against the Desert Locust was the recognition that, to be effective, antilocust measures had to be internationally coordinated so that locust organizations in affected countries could be informed of the latest developments and prepare accordingly.
A key factor in the efficient control of locusts is the reporting of them whenever they are seen.
Locust control organizations in affected countries need reports about Desert Locusts in their respective areas so that they can organize surveys or control operations. These reports are also sent to regional Desert Locust information centres where summaries of the current situation and forecasts of likely developments are prepared and sent to all interested governments or organizations.
In addition, the Emergency Centre for Locust Operations (ECLO) of the Food and Agriculture Organization of the United Nations (FAO) in Rome has the responsibility of maintaining a complete record of all locust reports for research purposes, and of preparing special situation summaries.
In the past, locusts have been reported by a wide range of people, for example, desert travellers, truck drivers, oil prospectors, pilots and ships' captains, as well as locust officers.
It is still vitally important that accurate reports of all sightings of Desert Locusts are passed on to locust organizations as soon as possible, and this pocket book will help you make these reports.
In the first part of the book, the distribution and appearance of the Desert Locust during the different stages of its life cycle are described and illustrated.
The second part concerns the actual reporting of Desert
Locusts:
WHAT WAS SEEN?
WHEN WAS IT SEEN?
WHERE WAS IT SEEN?
WHO SAW IT?
There is a summary of Points to check when you think you have found a Desert Locust on the last page of this pocket book.
Your help will be greatly appreciated
The third and final part deals with emergency control measures which may need to be undertaken in the absence of specialist locust control officers.
FIGURE
Figure
The Desert Locust is one of about twelve species of grasshopper which are able to change their habits and behaviour when their populations become large. When their numbers increase, they become gregarious and migrate in dense groups. These groups are called swarms when they are composed of winged adults, and bands when they consist of the young wingless stages, often called 'hoppers'.
Crops on every continent, except Antarctica, are subject to depredation by locusts, but the areas most heavily infested usually have warmer climates. Areas where the Desert Locust may be found are shown on the map in Figure 3.
Figure 4 This map shows the major
seasonal breeding areas of the Desert Locust during plagues and
recession
As with many other animals, the number of locusts fluctuates. Sometimes there are periods, which may last several years, when there are large numbers of swarms and hopper bands in many countries. It is during these periods, which are called plagues, that locusts cause greatest damage to crops. The longest plague on record lasted thirteen years.
The intervals between plagues are called recessions and may last several years' During recessions the number of locusts is much smaller; there are few, if any, swarms or bands, and most locusts are found thinly scattered and can be mistaken for large grasshoppers. Even when there are few locusts, however, they should still be reported because it is from them that new plagues arise.
The presence of small swarms or hopper bands in a recession may be one of the early signs of an approaching plague. National and regional locust organizations and the Emergency Centre for Locust Operations are interested in information about such populations.
Figure 5 The life cycle of the
Desert Locust showing the relative sizes of each
instar
There are three stages in the life cycle of locusts: egg, hopper, adult.
In order to breed, the Desert Locust must lay its eggs in damp soil. Breeding therefore occurs in the rainy season. The main breeding areas and seasons of the Desert Locust are shown on the map in Figure 4. In recessions the migrations are more restricted and the breeding areas do not extend so far north and south as they do during plagues.
When the eggs, which are difficult to find, have been in the ground long enough to complete development (this is variable depending on the temperature, between 10 and 70 days), hatching occurs. When they hatch, young locusts have no wings and are commonly called hoppers. As they grow older they moult, that is, they shed their skins, five or, occasionally, six times (Figure 5). After the fifth or sixth moult they become adults with fully grown wings. This is their final shape and it is in this stage that they migrate to new breeding areas. You may therefore find adults far from breeding areas where they were hatched or where they will lay.
Figure 6 Size of
hoppers
Between the time when the eggs hatch and the appearance of winged adults there are usually five hopper instars or stages as shown in Figure 5. Each instar is larger than the one before, so size gives an indication of how old the hoppers are, how long ago hatching occurred, and how soon adults may be produced.
If you find a Desert Locust hopper, it helps the locust control organizations and the Emergency Centre for Locust Operations if you can tell them to which instar it belongs. The simplest method of doing this is to compare the hopper with the diagram in Figure 6, even though hoppers of the same instar do vary in size.
In the fourth and fifth instars, the developing wings can be seen clearly. They are 2- 3 mm long in the fourth and about 6-8 mm in the fifth instar.
Desert Locust hoppers vary greatly in colour as shown in Figure 7. In general, their colour and pattern depend upon the density at which they have been living.
If there are few and they are living apart, they are usually green, but larger ones may be yellowish or pale brown; the exact colour often resembles that of the surrounding plants.
In dense hoppers bands, produced as a result of laying by a swarm, the young hoppers are black, but as they get older the black markings become proportionately smaller and a yellow background colour develops.
FIGURE Figure 8 The tip of the
abdomen of a female and a male Desert Locust, greatly
enlarged
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