Migratory locust

The migratory locust (Locusta migratoria) is the most widespread locust species. It occurs throughout Africa, Asia, Australia and New Zealand. It used to be common in Europe but has now become rare there. Because of the vast geographic area it occupies, which comprises many different ecological zones, numerous subspecies have been described. However, not all experts agree on the validity of some of these subspecies. The main ones are:

Locusta migratoria migratoria (West and Central Asia, eastern Europe)
Locusta migratoria migratorioides (mainland Africa and Atlantic islands)
Locusta migratoria capito (Madagascar)
Locusta migratoria manilensis (eastern Asia)

A polyphenic insect

They transform enormously behaviourally and physically under the effect of population density and are thus called polyphenic insects, or locust. There are two main phases:

The solitary phase
The gregarious phase

As the density of the population increases the locust transforms progressively from the solitary phase towards the gregarious phase with intermediate phases:

Solitaire = solitary phase → transiens congregans (intermediate form) → gregarious phase → transiens dissocians (intermediate form) → solitaire = solitary phase.

Other common locust are Schistocerca gregaria and Nomadacris septemfasciata

Pigmentation and size of the migratory locust

Pigmentation and size of the migratory locust vary according to its state (gregarious or solitary or intermediate form) and its age (larva, mature or immature adult).

Gregarious larvae have a yellow to orange covering with black spots. Solitary larvae are green or brown.

The gregarious adult is brownish with yellow, the latter colour becoming more intense and extensive on maturation. The solitary adult is brown with varying extent of green colour depending on the colour of the vegetation. Gregarious adults vary in size between 40 and 60 mm according to the sex. They are smaller than the solitary adults.

Often confused with the desert locust, there are some major differences between the migratory and desert locust.

A Devastating Insect

Locusts are highly mobile, and usually fly with the wind at a speed of about 15-20 km/h. Swarms can travel about 5-130 km or more in a day.

Locust swarms can vary from less than one square kilometre to several hundred square kilometres with 40 to 80 million locust per square kilometre.

An adult locust can consume its own weight (about 2 grams) in fresh food per day. For every million locusts, one ton of food is eaten.

Still a major threat?

In Africa, the last serious widespread plague of Locusta m. migratorioides occurred from 1928 to 1942. Since then, environmental transformations have made the development of swarms from the migratory locust unlikely. However, the desert locust which is very similar to the African migratory locust remains a major threat.

Nevertheless potential outbreaks are constantly monitored as plagues can be devastating.

Locust survey and control are primarily the responsibility of the Ministry of Agriculture in locust-affected countries and are operations undertaken by national locust units.

The Food and Agriculture Organization (FAO) of the United Nations provides information on the general locust situation to all interested countries and gives warnings and forecasts to those countries in danger of invasion.