Locusts, together with grasshoppers, belong to a large family of insects called Acridids (Acrididae) –order Orthoptera- which have big jumping hind legs and short antennae. Locusts differ from grasshoppers in that they have the ability to change their behaviour, appearance, physiology and habits depending on population density (this shift is called “phase change”) and that they can form marching hopper bands and flying swarms of adults migrating over large distances and settle a wide range of habitats. See also “More about locusts”.
According to the binomial nomenclature, which was developed in the second half of the 18th century, any species has a Latin name made of a genus name (with a cap) and a specific name. The genus name is unique; the specific one refers usually to a geographical origin or specific habitats, describes a morphologic or behavioural characteristic or derives from a family name (descriptor of the species, homage paid to an entomologist, etc.). After the binomial name, the author’s name (of the first description or of a revision) and the related year are indicated.
The acronyms of CIT, DMA and LMI are created with the first letter of the genus name and the two first letters of the species name for easy use. They correspond to: Calliptamus italicus (Linnaeus 1758), Dociostaurus maroccanus (Thunberg 1815) and Locusta migratoria migratoria (Linnaeus 1758). These names are italicized or underlined to indicate that they are Latin words.
In CCA, the common features of the three species are: the number of generation per year (i.e. they are univoltine species, meaning only one annual generation), the period of presence and their polyphagy in gregarious phase.
Hatching occurs generally in early spring and nymphs develop during spring. Adults are usually present from spring to the end of summer or early autumn and the females lay over-wintering eggs.
The three species can eat a wide range of natural and cultivated plants and their hopper bands and adult swarms are therefore devastating for agriculture and forestry. The three species differ by their preferred habitats: CIT can be considered as the locust of fallows and waste lands and DMA of arid steppe and semi-desert while LMI is mainly found on river and lake banks.
The three species are present in a lot of countries throughout the Old World (in Europe and Asia for the three species and also in Africa for DMA and LMI). The distribution areas of CIT and DMA cover about 40 countries of which one third can be affected by outbreaks. LMI distribution area is much bigger and covers about 100 countries with damage reported from two thirds of them. See also distribution maps for CIT, DMA AND LMI.
Similarly to all heterometabolous insects (whose development has no pupal stage between the young and adult stages), locusts and grasshoppers have three successive stages during their life: egg, nymph (also called hopper or larva) and adult. In CCA, at the end of summer, over-wintering eggs protected by egg-pod are laid inside the ground (according to species, one to six egg-pods containing each 20 to 120 eggs are laid by females). Hatching occurs generally in early spring and is followed by hopper development which last several weeks; hoppers look like small adults without wings and usually five or six instars are needed to reach the adult stage (between each instar, there is a moult allowing growth in size and weight; the growth cannot be continuous because of the external skeleton). Young and still soft adults (fledglings) appear after the last moult (called fledging); they have wings and genitalia, the first becoming operational in a few hours, after drying out, the latter after maturation.
Individuals of CIT, DMA and LMI live a maximum of six months from hatching (nymph appearance, in spring) to adults’ death (in autumn, after laying of over-wintering eggs). Within CCA, exact periods of appearance and disappearance depend on latitude and altitude as well as, to a lesser extent, on weather and ecological conditions. It should be noted that some (mostly non-swarming) species exhibit a different life strategy, with egg-laying in early summer, hatching in late summer, and over-wintering hoppers or adults.
Under suitable ecological conditions, locust number increase as well as their density; this results in a change of behaviour (grouping of individuals) and later in a phase change, from solitary to gregarious. Insects do no more behave as individuals but as a group, roosting, feeding, moving, copulating and laying eggs all together; hoppers form bands and adults form swarms, both devastating for agriculture. These changes of behaviour come together with some other changes in appearance (shape, size, colour and pattern), ecology (high adaptability to a wide range of habitats), biology and physiology. Changes are so spectacular that until 1921, it was thought that these so-called phases corresponded to two different species of locust.
Successive years with seasonal conditions suitable for breeding and egg survival eventually result in an outbreak.
Suitable weather and ecological conditions allow more successful breeding (during spring and summer) as well as decrease of natural mortality (mainly for over-wintering eggs). More egg-pods are laid close to each other and in high density (up to 10,000/square meter for CIT, 8,000 for DMA and 2,500 for LMI) in areas called egg-beds. Next hatching, which occurs during the following spring, gives rise to nymphs in high density that quickly form groups and bands and usually feed in natural vegetation. After fledging (the last moult), the newly appeared adults form groups and swarms able to fly towards better habitats, in terms of food and potential laying areas. As natural vegetation often dries out during the few weeks of the nymph development, flying adults invade cultivations, whose greenness last longer. It takes usually several generations (i.e. several years for these univoltine species) to reach levels of locust population able to devastate crops and pastures.
There is no evidence that outbreaks occur after a specific number of years but reference is sometimes made to sun cycles to explain apparent periodicity.
The distance flown per day or during the entire life of the locust depends on the species and of related flight ability.
CIT adults fly in loose swarms downwind 20-30 km/day, covering distances up to 200-300 km during their entire life.
DMA swarm flights are not as long as for most other locusts: the distance covered by swarms ranges from four to 10 km per day. During the entire adult life, which lasts about 50 days, swarms can fly from 25 to 100 km with a maximum of about 250 km.
LMI is an excellent flyer. In the past (1967 and other years), swarm migrations of LMI from the Aral Sea breeding areas over the Caspian Sea into Daghestan (over 1,000 km) were documented.
Hoppers can also move; DMA hoppers marching in dense bands cover usually 50 to 70 m (2nd instar) and up to 600 m (5th instar) per day. The total distance covered by a hopper band during its nymphal development can reach 5 km.
Locust swarms can vary from a few hectares to several hundred square kilometres. There can be up to 80 million locust adults in each square kilometre of swarm. For example, the size of a landed swarm of LMI can reach 120 by 10 km (120,000 ha). Adult density in such swarm could reach 2,000 to 3,000 per square meter.
Swarm of Migratory Locust, Kazakdarya, Karakalpakstan, Uzbekistan, July 2007 (A.V.Latchininsky)
The potential impacts of climate change are under investigation. However, locusts being very opportunistic, it can be anticipated that they can quickly take advantage of any suitable weather conditions. With more exceptional meteorological events, number of locust issues is expected to increase.
Locust pests IN CCA eat a huge variety of natural and cultivated herbs and grasses as well as bushes and trees. The preferred plants and crops are a bit different for CIT, DMA and LMI but all three species can cause severe damage to grain crops and trees (mainly DMA & LMI), forage, hayfields and pasture (mainly CIT) as well as a lot of other plants.
It is generally admitted that locust adults can eat their own weight every day, i.e. one to two grams of fresh vegetation per day. In other words, a small part of an average swarm (or about one ton of locusts) eats the same amount of food in one day as about 10 elephants or 25 camels or 2,500 people.
Locusts can attack leaves, stalk/stem, fruit and grain. Branches can also be broken by the weight of locust swarms. Over 25 million ha of cultivated areas are potentially at risk in Caucasus and Central Asia. Natural vegetation in which locusts develop before it dries out can also be severely damaged.
The most affected populations are the rural communities living in locust outbreak and invasion areas, who are also the most vulnerable ones. In addition to crop losses, rural populations are exposed to negative impacts of locust control operations on their health and environment. At least 20 million people are at risk in CCA.
Locusts do not attack people or animals. There is no evidence that locusts carry diseases that could harm humans.
Preventive approach enables to reduce occurrence and intensity of locust outbreaks and to prevent their development into major upsurges. It consists in appropriate monitoring of locust habitats in order to allow early detection of locust increase and behaviour change, thus early warning and early reaction.
Preventive approach lays upon: monitoring and related early detection; timely reporting of field data; early warning; early reaction; information and forecasting; preparedness for risk reduction, incl. through contingency planning; capacity-building; promotion of up-to-date and environmentally sound survey/control methods and technologies; close cooperation between all stakeholders.
Preventive approach is the only sustainable solution possible. It offers invaluable comparative advantages in terms of (a) reduced damage on crops and rangeland and therefore on food security and livelihood of highly vulnerable rural communities; (b) reduced negative impact on human health and the environment; and (c) reduced financial costs.
In CCA, countries’ geographical configuration largely complicates locust issues as locust permanent breeding areas are often located along borders. In these conditions, any sustainable preventive approach must include both national and regional levels. FAO sustains countries’ efforts in developing regional cooperation. A two-year project, funded by the Technical Cooperation Programme (TCP) of the Organization, is being implemented in this regard (2009-11) and a Five-year Programme, aiming at developing an effective regional preventive approach, is currently being submitted to donors for funding and further implementation. It is inspired by the EMPRES approach (see below).
Although movements of locust populations are rare between these two neighbouring regions, Caucasus and Central Asia are affected by the same locust species. Both have large borders with the Russian Federation and can use the same language. Gathering the two regions in a single approach allows each region to benefit from the experience of the other and to participate in events of interest for both (training, etc.).
The Director-General of FAO launched the Programme ‘Emergency Prevention System for Transboundary Animal and Plant Pests and Diseases” (EMPRES) in 1994 to in order to minimize the risk of such emergencies and promote preventive control (http://www.fao.org/EMPRES/default.htm). The Desert Locust Component of the Programme was implemented around the Red Sea (in the so-called Central Region of the Desert Locust distribution area) from 1997 to 2006 and was extended to West and Northwest Africa (the Western Region) from 2006. It has contributed to strengthen national Desert Locust control capacities (early warning, rapid reaction, preparedness, environmentally safer control techniques, etc.) and to prevent major upsurges.
For the time being, no civil weather or other satellites used to monitor the environment are able to detect locust individuals or swarms. Only military satellites have this capacity but it is unlikely that national and international locust organizations would have the ability to interpret the hundreds of images that would be produced on a daily basis.
Locusts are important elements of food chains, in particular in sensitive habitats with scarce food for vertebrates such as birds, reptiles or small mammals. Therefore, the purpose is not to eradicate locusts but to keep their populations under levels threatening for crops (usually referred as “Economic Injury Threshold” -EIT), or, more generally, under densities that could lead to the development of outbreaks and upsurges.
In CCA, spraying of chemical pesticides against hopper bands is the predominant locust control method. The chemicals belong mainly to the organophosphate and synthetic pyrethroid chemical families and are in water-based (EC) formulation. They are applied by hand-held and vehicle-mounted sprayers and, if needed, by aircraft. Also around the world, the primary method for controlling locusts relies on chemicals. However, other methods less harmful for human health and the environment are emerging using Insect Growth Regulators and biopesticides.
Most of the time, locust monitoring and control are supervised and managed by the same national body, which is a department, division or service of the Ministry of Agriculture (MoA). However, different solutions are adopted concerning implementation of the control operations, which can be carried out by the regional representations of the relevant MoA body, by private companies following public tenders or by both public service and private companies.
During times of major outbreaks, other partners can be involved if external assistance from the donor community and international organizations is required.
As control focuses on nymphs in CCA, spraying operations are mainly carried out during spring. They can be extended in summer to combat swarms of adults. Sometimes, egg-bed destruction is undertaken to facilitate or complement hopper control; in that case, mechanical control is organized in autumn or early spring.
The impact can be the poisoning of staff involved in control operations, of rural populations living in the locust infested areas and of non-target fauna as well as the pollution of the treated areas and adjacent ones. This impact results from unnecessary exposure to chemical pesticides during spraying operations and pesticide handling.
Tremendous progress was made over the past decade concerning biological control of locusts, mainly focusing on pathogens. During recent FAO emergency projects, operational use of biopesticides formulated with the spores of the fungus Metarhizium anisopliae var. acridum demonstrated their efficiency to control locust outbreaks (against Migratory Locust Locusta migratoria sp. in 2007 in Timor-Leste, and against the Red Locust Nomadacris septemfasciata in 2009 in Tanzania). Research is on-going.
Control by natural predators (birds, reptiles, small mammals, spiders, etc.) and parasites is limited since locusts multiple much quicker than their natural enemies and can also quickly migrate away from them.
In Caucasus and Central Asia, people do not eat locusts. However, in other regions or countries around the world (Sahelian countries, Indonesia, Madagascar, etc.), locusts and grasshoppers are cooked to be eaten immediately (stir-fried, roasted or boiled) or later (dried). They are also used to feed poultry (in Madagascar and Peru, for example).
Locust as food: Indonesia (Migratory Locust) and Madagascar (Red Locust), 2007 (A.Monard)
As mentioned previously, locusts as protein source are used to feed people or poultry. However, eating locusts do not correspond to Caucasian and Central Asian food habits. In addition, it is very difficult to rely on locust for any sustainable economic activity as insects multiplication does not occur on a regular basis.
- Desert Locust, Schistocerca gregaria (Forskål 1775) in Africa, Middle-East, South-West Asia
- Other Migratory Locust sub-species, such as Locusta migratoria migratorioides in Africa; Locusta migratoria manilensis in South-East Asia; Locusta migratoria capito in Madagascar, etc.
- Red Locust, Nomadacris septemfasciata (Serville 1838) in Southern and astern Africa, Madagascar
- Brown Locust Locustana pardalina (Walker 1870) in Southern Africa
- Australian Plague Locust Chortoicetes terminifera (Walker 1870) in Australia
- Tree Locusts (Anacridium sp.) in Africa, Near East and around the Mediterranean Sea
- South-American species of Schistocerca and in particular Schistocerca interrita Scudder 1899 in Peru