Desert locust
| Desert locust | ||||||||||||
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Desert locust ( Schistocerca gregaria ), female laying eggs in sandy soil |
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| Schistocerca gregaria | ||||||||||||
| ( Forsskål , 1775) |
The desert locust ( Schistocerca gregaria ) is one of the species known as migratory locusts . It is an imposing short-feeler terrestrial that is noticeable in motion . At times these animals are able to migrate in flocks of up to 50 million individuals.
features
The desert locust is a very large species of field locust, females reach a body length of 70 to 90 millimeters, males 60 to 75 millimeters. The very long wings protrude above the end of the abdomen and the rear knees. As is typical of the relationship, the thread-like antennae are rather short, shorter than the head and pronotum combined. Outside of the migration phases, in the solitary phase, the animals are quite uniformly yellow-gray to ocher in color with dark spots on the semi-transparent tegmina (the forewings), but never with distinct dark transverse bands. Mature individuals in the migration phase are colored bright yellow. Immature , freshly skinned individuals are initially tinted pink; if the environmental conditions deteriorate during this phase, they can sometimes alternatively take on a strong red-brown coloration, so that swarms of yellow and red-brown individuals can be mixed. However, the pronotum never bears distinct yellow spots (as in the genus Kraussaria and Cataloipus ), black lines and bands (as in Hieroglyphus daganensis ) or dark longitudinal bands (as in Cyrtacanthacris and Nomadacris ). The hind wings, which are hidden under the tegmina when they are at rest , are usually crystal clear, hyaline, without dark bands or red bases. In older individuals, they can have a pale pink or yellowish tint at the base. As with a number of related species, the complex eyes are strikingly streaked. It differs from the very similar genus Anacridium , among other things, by the lack of conspicuous white thorns on the rear half of the pronotum. The rear rails are brownish to yellowish in the species, not colored as in a number of related species.
The species is the only representative of the genus Schistocerca in the Old World and can therefore be distinguished on the basis of its generic characteristics. The cone-shaped protrusion on the front breast (Prosternum), characteristic of the representatives of the subfamily Cyrtacanthacridinae, is cylindrical and weak, but curved forward. The tip of the head in front of the complex eyes (called fastigium) is trapezoidal with an indistinct longitudinal impression. The pronotum is divided by transverse constrictions into three transverse bulges, called sulci, which also interrupt the longitudinal central keel, which is low in the species and indistinct to the front. Side keels are not pronounced, the rear edge of the pronotum is rounded when viewed from above. In the male sex, the subgenital plate, drawn out in two corners and incised in the middle, is typical of the genus. In the species, the cerci are also short with a rectangular outline. In females, the ovipositor consists of four recognizable valves, these are short, robust and rounded at the tip. The lower valve has a blunt protrusion on the outside.
Polyphenism
The life of the animals can take place in two different phases, the solitary phase (“single phase”) and the gregarious phase (“swarm phase”). In the solitary phase, all animals, like other grasshopper species, are tied to one place. If the conditions are particularly good for a generation, it can happen that so many larvae develop that it becomes too cramped for the entire population in the current habitat and the locusts first join together in sociable groups and then begin to migrate. In this gregarious phase or migration phase, the animals completely adapt their behavior to one another, so that the migration direction of the swarm no longer changes. The change in behavior precedes the morphological change.
Not only the winged adults, but also the nymphs ( called hopper in English ) show swarming behavior. They move toward areas of denser vegetation where they merge. Densities of up to 30,000 individuals per square meter can be achieved in the first nymph stage, in the last (fifth) it is more likely 50 to 100. The animals alternate between resting phases and wandering phases, moving in long, closed marching columns. You can cover about 200 to 1700 meters per day. When they are resting, they climb plants to eat.
The imaginal swarms usually move forward in leaps, whereby about 30 meters are covered in the flight phase. If necessary, however, they are persistent fliers who can fly hundreds of kilometers. Depending on the wind conditions, swarms can extend up to a height of about 1500 meters like clouds, but mostly they form flatter swarms close to the ground. The average density within a swarm is estimated to be around 50 million individuals per square kilometer (which corresponds to around 50 animals per square meter). Swarms fly during the day (while solitary desert locusts tend to fly at night), the flight phase is nine to ten hours a day. The animals move with the wind, so that the swarm is kept together even if the individual animals move in different directions. When there is no wind, they reach a flight speed of around three to four meters per second. Usually numerous animals always land, so the swarm moves more slowly than wind speed.
The gregarious phase is triggered by the high density of individuals in the nymphs' habitat, which means that it is overexploited and that food becomes scarce. The direct trigger is the mechanical contact stimulus when the numerous nymphs constantly come into body contact, the only triggering being the touch of the thighs of the hind legs. Frequent contact with the hind legs triggers the production of the hormone serotonin , which apparently means that solitary nymphs can go into the gregarious phase within a few hours. The transition from isolated-reared grasshoppers back to the solitary phase, on the other hand, takes place slowly, within one or more generations. The female influences the phase of her offspring via a chemical signal, so that individuals of the fermented or solitary phase can arise directly.
The nymphs of the gregary phase can be easily distinguished from those of the solitary phase by their coloration. The solitary nymphs are colored green, in the last two of the five nymph stages sometimes partly brown, always without black spots. The gregary nymphs are black in the first two stages, later yellow or yellow-orange with black markings. The eyes and a spot on the back of the head are red.
Life cycle
After the egg phase, desert locusts go through five nymph stages (occasionally a sixth in solitary individuals) before they molt into a sexually mature imago . The egg phase lasts about 10 to 65 days. The nymph stages are completed in 24 to 95 days, on average in 36 days. Adults have a lifespan of 2.5 to 5 months.
Copulation takes place after a sexually mature male has jumped onto the back of a female, whose body has been clasped with his legs and the end of his body has reached her gonopodia along the side of her abdomen. The sperm packet is transferred from the top of her abdomen into the female's abdomen, where it is stored. The process can take a few hours. One mating is sufficient for several egg clutches. Females lay the eggs about 5 to 10 centimeters deep in the ground, digging a hole with the mobile valves of their ovipositors. The eggs are deposited in oothecae that are about 3 to 4 centimeters long, these are encased in a foam-like secretion that later hardens. Each ootheca contains around 90 to 160 eggs in the solitary phase and less than 80 eggs in the migrating phase. Around three quarters of the females create a second, around a quarter a third, and only extremely few create another clutch. The success of the clutch depends heavily on the soil moisture; under favorable conditions, 16 to 20 successful offspring per female is not uncommon.
Newly hatched adults need about 10 days for the wings to harden sufficiently for their first flight. They are then not immediately sexually mature, but remain in an immature intermediate state until they encounter favorable environmental conditions that trigger maturity. In their arid habitats, these are phases of rain. When swarms reach a region in which it is raining or has rained shortly before, all individuals in the swarm reach sexual maturity in a synchronized manner in this way collectively in a short time. Under dry conditions, they can remain in the immature state for up to six months.
distribution
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The desert locust lives in the zone of the tropic deserts in North Africa and the Near and Middle East, east to Pakistan and the west of India in the area of the Indopakistani desert Thar . In North Africa the distribution area mainly includes the Sahel zone . In many years the animals move from these regions as summer habitats to adjacent areas as winter habitats, where the conditions, especially the precipitation and the night temperatures, enable survival in winter but not in summer. In North Africa these winter habitats are north of the Sahel, in the Sahara, on the Horn of Africa and along the west coast of the Arabian Peninsula to the Red Sea, but in favorable years they can spread to the mountains in the interior of the Arabian Desert. Due to the economic importance of the species, the distribution and swarming is closely monitored so that control measures can be started in good time. The Food and Agriculture Organization of the United Nations maintains the Locust Watch program for this purpose. It also publishes the monthly online magazine Desert Locust Bulletin .
Apart from the rest of the distribution area and separated from it by a broad disjunction , the desert locust occurs in arid habitats in South Africa. The animals in this region never form migrating flocks.
Habitat
Permanently, in the solitary phase, the desert locust colonizes arid areas with open vegetation, with steppe or shrub steppe up to semi-desert vegetation. These are areas with irregular but occasionally heavy rainfall in the winter months. A typical vegetation consists of annual grasses, especially millets of the genera Panicum , Pennisetum and Sorghum , in Arabia Dipterygium glaucum , especially on sandy soils. They can also occur in cultivated millet fields and become harmful here. Swarms can occur in all kinds of vegetation, the species is known to accept numerous plant species as food ( polyphagous ), but is by no means indiscriminate. In North Africa, for example, they prefer vegetation with Tribulus spp., Heliotropium species and the cruciferous Schouwia purpurea . Outside the cultivated land, on the other hand, many plant species have protected themselves from being eaten by the desert locust by secondary plant substances or are even poisonous for them, including species of the genera Calotropis , Peganum harmala , the neem tree Azadirachta indica and the oleander ( Nerium oleander ).
Antagonists
Occasional swarms of locusts are used as food by Duméril's fringed lizard . However, some locusts, such as the desert locust, prefer plants such as Egyptian henbane , which contain toxins that are non-toxic to them and which sequester the locusts in their bodies and subsequently develop an aposematism that intensifies their coloration. Duméril's fringed lizards then avoid desert locusts with such warning colors .
Taxonomy
The genus Schistocerca comprises about 50 species, all of which, with the exception of the desert locust, live in the New World. According to genetic data, the desert locust's sister group is the rest of the genus put together. This can best be explained by the fact that the species of the New World can be traced back to immigrants from Africa, presumably a swarm that had drifted across the Atlantic, and only then split into numerous new species. Direct observation has shown that such swarms can reach America.
The species is a type of the genus Schistocerca . In addition to the nominate form , a subspecies is recognized within the species :
- Schistocerca gregaria flaviventris (Burmeister, 1838). It occurs in South Africa.
literature
- Stanley Baron: The eighth plague. The desert locust, the world's largest pest (OT: The desert locust ). Parey, Hamburg / Berlin 1975, ISBN 3-490-00418-3 .
- PM Symmons, K. Cressman: Desert Locust Guidelines 1. Biology and behavior. 2nd edition, 2009. FAO Food and Agriculture Organization of the United Nations, Rome, 2001.
- JFDuranton, M. Lecoq: Le Criquet Pélerin au Sahel. Collection Acridologie Opérationnelle no.6. Permanent Inter-États de Lutte contre la Sécheresse dans le Sahel (CILSS). Ministère des Affaires Étrangères des Pays-Bas et CIRAD / PRIFAS (France). 1990. ISBN 2-87614-033-0 .
Web links
- Schistocerca gregaria in Fauna Europaea. Retrieved February 28, 2010
Individual evidence
- ↑ Rashid Nayeem & Kamil Usmani (2012): Taxonomy and field observations of grasshopper and locust fauna (Orthoptera: Acridoidea) of Jharkhand, India. Munis Entomology & Zoology 7 (1): 391-417.
- ↑ FAO Food and Agriculture Organization of the United Nations: Locust Handbook: identification key (download)
- ↑ Schistocerca Information site, by Hojun Song: Taxonomic Identification Key to Schistocerca species . accessed on June 6, 2019.
- ↑ Les Criquets Ravageurs. Pest Locusts: Schistocerca gregaria (Forskål, 1775) CIRAD Center de coopération internationale en recherche agronomique pour le développement, accessed on June 6, 2019.
- ^ SJ Simpson, E. Despland, BF Hägele, T. Dodgson (2001): Gregarious behavior in desert locusts is evoked by touching their back legs. PNAS Proceedings of the National Academy of Sciences USA 98 (7): 3895-3897.
- ↑ Michael L. Anstey et al .: Serotonin Mediates Behavioral Gregarization Underlying Swarm Formation in Desert Locusts . In: Science . tape 323 , January 30, 2009, ISSN 1095-9203 , p. 627–630 , doi : 10.1126 / science.1165939 ( sciencemag.org [PDF; accessed January 16, 2019]).
- ↑ Gabriel A. Miller, M. Saiful Islam, Timothy DW Claridge, Tim Dodgson, Stephen J. Simpson: Swarm formation in the desert locust Schistocerca gregaria: isolation and NMR analysis of the primary maternal gregarizing agent . In: Journal of Experimental Biology . tape 211 , no. 3 , February 1, 2008, ISSN 0022-0949 , p. 370–376 , doi : 10.1242 / jeb.013458 , PMID 18203992 ( biologists.org [accessed December 1, 2017]).
- ↑ a b P.M. Symmons, K. Cressman: Desert Locust Guidelines 1. Biology and behavior. 2nd edition, 2009. FAO Food and Agriculture Organization of the United Nations, Rome, 2001.
- ↑ Locust handbook: 2. Desert Locust-Schistocerca gregaria: Life cycle. Retrieved December 1, 2017 .
- ↑ Locust Watch: Desert Locust
- ^ Wopke van der Werf, Gebremedhin Woldewahid, Arold van Huis, Munir Butrous, Karle Sykora (2005): Plant communities can predict the distribution of solitarious desert locust Schistocerca gregaria. Journal of Applied Ecology 42: 989-997.
- ↑ M. Bagari, A. Bouhaimi, S. Gaout, J. Chihrane (2013): The toxic effects of Nerium oleander on larvae of the desert locust Schistocerca gregaria (Forskål, 1775) (Orthoptera, Acrididae). Zoologica baetica 24: 193-203.
- ^ Gregory A. Sword, Stephen J. Simpson, Ould Taleb M. El Hadi, Hans Wilps: Density-dependent aposematism in the desert locust. In: Proceedings of the Royal Society of London B: Biological Sciences 267, No. 1438, 2000, pp. 63-68, doi: 10.1098 / rspb.2000.0967 (full text).
- ^ NR Lovejoy, SP Mullen, GA Sword, RF Chapman, RG Harrison (2006): Ancient trans-Atlantic flight explains locust biogeography: molecular phylogenetics of Schistocerca. Proceedings of the Royal Society London Series B 273: 767-774 doi: 10.1098 / rspb.2005.3381
- ↑ Schistocerca gregaria flaviventris. Orthoptera Species File (Version 5.0 / 5.0)
- ^ Marie Pierre Chapuis, Corinna S. Bazelet, Laurence Blondin, Antoine Foucart, Renaud Vitalis, Michael J. Samways (2016): Subspecific taxonomy of the desert locust, Schistocerca gregaria (Orthoptera: Acrididae), based on molecular and morphological characters. Systematic Entomology 41 (3): pp. 516-530. doi: 10.1111 / syen.12171