Locusta migratoria (Linnaeus 1758)
Systematic position: Class Insecta, order Orthoptera, family Acrididae, subfamily Acridinae, genus Locusta; In the concerned area (Caucasus and Central Asia), there are two sub-species Locusta migratoria migratoria (Linnaeus 1758) and L. m. rossica Uvarov & Zolotarevsky 1929. The latter is found in forest-steppes and in the south of forest zone of European Russia.
Synonyms of Locusta migratoria migratoria, the Asiatic Migratory Locust: Gryllus migratorius Linnaeus 1758; G. (L.) danicus Linnaeus 1767; Pachytylus australis Saussure 1884
Identification: Large size and absence of prosternal tubercule. Other distinctive characteristics concern the wings: smoky at the apex (radial sector) and black veins in the anal sector.
Biological group: Polyphagous insect pests
Migratory Locust has the largest world distribution area among all locusts and grasshoppers, comprising practically all temperate and tropical parts of the eastern hemisphere, i.e. Europe, Africa incl. Madagascar, Arabian and Indo-Pakistan peninsulas, Caucasus, Central and South-eastern Asia, Australia, Papua New Guinea and New-Zealand. The northern limit of this huge distribution area corresponds roughly with the southern edge of the coniferous forest zone of Europe and Asia. Southern extension reaches New-Zealand. The western limit corresponds to the Azores, in the Atlantic Ocean, and the eastern one to at least the Fiji, in the Pacific Ocean. The altitudinal distribution of the species is also amazingly wide, from sea-level to more than 4,000 m in Central Asian mountains. Therefore, the species is present in a wide range of habitats presenting very different climatic and environmental conditions; this results in different biological responses fitting with local conditions and a number of geographical subspecies.
This paragraph focuses on Locusta migratoria migratoria, the most important and widely distributed sub-species of Migratory Locust in Caucasus and Central Asia.
The Migratory Locust is a large insect, with body length varying from 35 to 50 mm for males and from 45 to 55 mm for females. Mandibles are blue. Elytra are shining and long: 43.5-56.0 (males), 49.0-61.0 mm (females), exceeding clearly the abdominal extremity. Wings are colourless, except smoky tint and black veins previously mentioned. The bottom of internal side of hind femora is brownish, bluish to black. The length of hind femur is of 22.0-26.0 mm (males) and 20.0-32.0 mm (females). Hind tibia is yellowish, beige or red. There is a dense pilosity of the inferior face of thorax. The colour can vary but is usually green, brown, yellowish-green or grey. In profile, the pronotum is curved for solitary adults and saddle-shaped for gregarious ones, with convex or straight to slightly concave median keel respectively. The transversal furrow is well marked for gregarious individuals. The hoppers also differ, being green in solitary phase but grey in the 1st instar, then darkening and becoming orange and black in the later instars when gregarizing.
This paragraph focuses on Locusta migratoria migratoria.
The Migratory Locust is univoltine in the considered area (but can have up to five generations per year in tropical zones under highly suitable conditions). Oviposition occurs in August-September and the eggs over winter. There are at least 1-3 egg pods per female (up to 5 in southern localities and with warm conditions) with an average of 60-80 eggs (from 40 to 120) per pod. Egg pod is large, slightly bent, 50-85 mm in length, 7-10 mm in diameter; eggs are 7-8 mm long. Light sandy soils are favourable for egg laying. Hatching takes place between early May and early June; it is quick, completed in 4-5 days in every station. There are 5 hopper instars and the hopper development lasts 35-40 days (i.e. 7-8 days for each instar). Adults appear from June to early July, remaining sometimes as late as November in the warmest parts. The copulation starts 2-4 weeks after fledging, and females start laying eggs 2-3 weeks later (usually at the end of July).
Ecology and behaviour
The Migratory Locust is mainly graminivorous, occupying the grass cover near the ground. River, lake and sea banks with plantings of reeds and sedges, particularly Phragmites communis, form its main habitat. Such regions are often surrounded by steppe and desert areas. Most outbreak areas are in the deltas of rivers flowing into the Black, Caspian and Aral Seas and into Lake Balkash, the Danube delta being the most westerly one for this sub-species. It is known to fly at night. Most migratory flights are local and oviposition takes place in same general area but occasionally, depending on weather conditions, massive movement of swarms occurs, spreading over hundreds of kilometres into the surrounding territories.
There are 7 permanent habitat areas of Migratory Locust in the Russian Federation and in Central Asia countries, and the most active are Balkhash-Alakol lakes, Amu Darya river and, more recently Northern Caspian and Dagestan regions. The Migratory Locust is a rather strict oligophagous, preferring wild grasses (e.g. reed, couch-grass).
During the few days after hatching, gregarious hoppers start forming groups, whose density can reach 80,000 hoppers/m² for 1st instar and 7,000 hoppers/m² for 5th instar. These groups can move on relatively long distances. Inside poor vegetation cover, 5th instar hoppers can march up to 3 km per day. Gregarious adults form swarms about 10 days after fledging. Despite its food preference, the Migratory Locust can eat plants of many families after leaving its outbreak areas or when its favourite grasses are missing. Each individual eats from 300 to 500 g of green forage during its life. Population dynamics is intimately connected to changes of water balance in breeding areas, alternation of seasonal floods and dry periods in reed beds causing reduction or spreading of food supply and oviposition sites.
Economic importance and useful plants attacked
Solitary hoppers and adults can damage various vegetable crops, rice, cotton, as well as plantations of volatile oil bearing plants in Tajikistan. During years of mass increases/outbreaks, grain and other crops are severely damaged as well as hayfields and pastures. It is also the case for many tree species. Gregarious hoppers and adults of Migratory Locust can strongly harm wheat, rye, barley, oat, maize, rice, Panicum, sorghum, millet, alfalfa, clover, peas, legumes, string bean, soja and other Fabaceous crops, red and sugar-beet, potato, tobacco, cabbage, rutabaga, cucumbers, watermelons, melons, and other cucurbits, sunflower, hop, buckwheat, althaea, cotton, flax, castor-oil plant, vegetable and other crops, young plants of many fruit, vines, fruit, forest and bush trees, haylands and pastures. Damage on trees concerns stem, fruit and branches broken by the weight of locusts.
A large number of natural enemies were recorded in former USSR as well as various birds and predators, especially the rose-coloured and common stralings (Pastor roseus L. and Sturnus vulgaris L.).
Some related references
Bei-Bienko G.Ya. 1932. A manual of locust survey. Leningrad: Upravlenie Sluzhby ucheta Gos. OBV Narkozema SSSR. 159 pp.
Bei-Bienko G.Ya., Mishchenko L.L. 1951. Locusts of the fauna of the USSR and adjacent countries. Keys to Fauna of USSR, N38, parts I & II. Moscow & Leningrad: AN SSSR. 668 pp.
Latchininsky A.V., Sergeev M.G., Childebaev M.K., Chernyakhovsky M.E., Lockwood J.A., Kambulin V.E., Gapparov F.A. 2002. Locusts of Kazakhstan, Central Asia and adjacent territories. Larami: Association for Applied Akridology International, University of Wyoming. 387 pp.
Mishchenko L.L. 1952. Locusts (Catantopinae). Fauna of the USSR. Orthopterous insects. Leningrad: AN SSSR. V. 4(2): 610.
Sergeev M.G. 1986. Regularities in distribution of orthopterous insects of Northern Asia. Novosibirsk: Nauka. 238 pp.
Tsyplenkov E.P. 1970. Locust pests in the USSR. Leningrad: Kolos. 272 pp.