Locust

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This article is about the insects. For the plants with the same name, see Robinia. For other uses, see Locust (disambiguation).
Millions of swarming Australian plague locusts on the move

Locusts are the swarming phase of certain species of short-horned grasshoppers in the family Acrididae. In the solitary phase these grasshoppers are innocuous, their numbers are low and they cause little economic threat to agriculture. However, under suitable conditions of drought followed by rapid vegetation growth, serotonin in their brains triggers a dramatic set of changes: they start to breed abundantly, becoming gregarious and nomadic (loosely described as migratory) when their populations become dense enough. They form bands of wingless nymphs which later become swarms of winged adults. Both the bands and the swarms move around and rapidly strip fields and cause damage to crops. The adults are powerful fliers; they can travel great distances, consuming most of the green vegetation wherever the swarm settles.

Locusts have formed plagues since prehistory. The Ancient Egyptians carved them on their tombs and the insects are mentioned in the Bible and the Quran. Swarms have devastated crops and been a contributory cause of famines and human migrations. More recently, changes in agricultural practices and better surveillance of locations where swarms tend to originate, have meant that control measures can be used at an early stage. The traditional means of control are based on the use of insecticides from the ground or the air, but other methods using biological control are proving effective. Swarming behaviour has decreased in the twentieth century, but despite modern surveillance and control methods, the potential for swarming behaviour is still present, and when suitable climatic conditions occur and vigilance lapses, plagues can still occur.

Locusts are edible insects; they have been eaten throughout history and are considered a delicacy in many countries. The word "locust" is derived from the Vulgar Latin locusta.[1]

Swarming grasshoppers[edit]

Main articles: Grasshopper and Swarm behaviour
A desert locust ovipositing in sand

Locusts are the swarming phase of certain species of short-horned grasshoppers in the family Acrididae; see those articles for details of their general biology and taxonomy. These insects are usually solitary, but under certain circumstances become more abundant and change their behaviour and habits, becoming gregarious.[2][3][4]

Desert locusts in copulation

There is no taxonomic distinction between locust and grasshopper species; the basis for the definition is whether a species forms swarms under intermittently suitable conditions. In English the term "locust" is used for grasshopper species that change morphologically and behaviourally on crowding, forming swarms that develop from bands of immature stages called hoppers. These changes are examples of phase polymorphism; they were first analysed and described by Boris Uvarov who was instrumental in setting up the Anti-Locust Research Centre.[5] He made his discoveries during his studies of the desert locust, whose solitary and gregarious phases had previously been thought to be separate species. He designated the two phases as solitaria and gregaria.[6] These are also referred to as statary and migratory morphs, though strictly speaking their swarms are nomadic rather than migratory. Charles Valentine Riley and Norman Criddle were also involved in achieving the understanding and control of locusts.[7][8]

Swarming behaviour is a response to overcrowding. Increased tactile stimulation of the hind legs causes an increase in levels of serotonin.[9] This causes the locust to change colour, eat much more, and breed much more easily. The transformation of the locust to the swarming form is induced by several contacts per minute over a four-hour period.[10] A large swarm can consist of billions of locusts spread out over an area of thousands of square kilometres, with a population of up to eighty million individuals per square kilometre (two hundred million per square mile).[11] It has been shown that when desert locusts meet, their nervous systems release serotonin, which causes them to become mutually attracted, a prerequisite for swarming.[12][13]

The initial bands of gregarious hoppers are known as "outbreaks" and when these join together into larger groups it is known as an "upsurge". Continuing agglomerations of upsurges on a regional level originating from a number of entirely separate breeding locations are known as "plagues".[14] During outbreaks and the early stages of upsurges, only part of the locust population becomes gregarious, with scattered bands of hoppers spread out over a large area. As time goes by, the insects become more cohesive and the bands become concentrated in a smaller area. In the desert locust plague in Africa, the Middle East and Asia that lasted from 1966 to 1969, the number of locusts increased from two to thirty billion over two generations but the area covered decreased from over 100,000 square kilometres (39,000 sq mi) to 5,000 square kilometres (1,900 sq mi).[15]

Solitary and gregarious phases[edit]

Solitaria (grasshopper) and gregaria (swarming) phases of the desert locust

The greatest difference between the solitary and gregarious phases is behavioural. The gregaria nymphs are attracted to each other, this being seen as early as the second instar. They soon form bands of many thousands of individuals. These groups behave like cohesive units and move across the landscape, mostly downhill, but making their way round barriers and merging with other bands. The attraction between the insects seems to be largely visual, but also involves olfactory cues, and the band seem to navigate using the sun. They pause to feed at intervals before resuming their march, and may cover tens of kilometres over a few weeks.[6] There are also differences in morphology and development. In the desert locust and the migratory locust for example, the gregaria nymphs become darker with strongly contrasting yellow and black markings, they grow larger and have a longer developmental period. The adults are larger with different body proportions, less sexual dimorphism and a higher metabolic rate. They mature more rapidly and start reproducing earlier but have a lower level of fecundity.[6]

The mutual attraction between individual insects continues into adulthood and they continue to act as a cohesive group. Individuals that get detached from a swarm fly back into the mass. Others that get left behind after feeding, take-off to rejoin the swarm when it passes overhead. When individuals at the front of the swarm settle to feed, others fly past overhead and settle in their turn, the whole swarm acting like a rolling unit with an ever-changing leading edge. The locusts spend much time on the ground feeding and resting, moving on when the vegetation is exhausted. They may then fly a considerable distance before settling in a location where transitory rainfall has caused a green flush of new growth.[6]

Species diversity[edit]

Several species of grasshopper, including especially the following, swarm as locusts:[16]

In addition, species such as the Senegalese grasshopper (Oedaleus senegalensis), and the African rice grasshopper (Hieroglyphus daganensis), both from the Sahel, often display locust-like behaviour and change morphologically on crowding.

History[edit]

Locust detail from a hunt mural in the grave-chamber of Horemhab. Ancient Egypt, c. 1422–1411 BC

The Ancient Egyptians carved locusts on tombs in the period 2470 to 2220 BC, and a devastating plague is mentioned in the Book of Exodus in the Bible, as taking place in Egypt around 1300 BC.[15][19] Plagues of locusts also appear in the Quran.[11] The Bombay locust (Nomadacris succincta) was a major pest in India and southeastern Asia in the eighteenth and nineteenth centuries, but has seldom swarmed since the last plague in 1908.[20]

The extinction of the Rocky Mountain locust has been a source of puzzlement. Recent research suggests the breeding grounds of this insect in the valleys of the Rocky Mountains came under sustained agricultural development during the large influx of gold miners,[21] destroying the underground eggs of the locust.[22][23]

Interaction with humans[edit]

Monitoring[edit]

Eugenio Morales Agacino on expedition monitoring locusts in the desert of Spanish Sahara, 1942

Early intervention is a more successful means of dealing with locusts than later action when swarms have already built up. The technology to control locust populations is now available, but the organisational, financial and political problems may be difficult to overcome. Monitoring is the key to reducing damage, with the early detection and eradication of nymphal bands being the objective. Ideally a sufficient proportion of nomadic bands can be treated with insecticide before the swarming phase is reached. Reaching this objective may be possible in richer countries like Morocco and Saudi Arabia, but neighbouring poorer countries lack the resources and may act as a source of locust swarms that threaten the whole region.[11]

Several organizations around the world monitor the threat from locusts. They provide forecasts detailing regions likely to suffer from locust plagues in the near future. In Australia this service is provided by the Australian Plague Locust Commission.[24] It has been very successful with dealing with developing outbreaks but has the great advantage of having a defined area to monitor and defend without locust invasions from elsewhere.[25] In Central and Southern Africa the service is provided by the International Locust Control Organization for Central and Southern Africa (IRLCO-CSA).[26] In West and Northwest Africa the service is co-ordinated by the Food and Agriculture Organization's Commission for Controlling the Desert Locust in the Western Region (CLCPRO), and executed by locust control agencies belonging to each country concerned.[27] The FAO also monitors the situation in the Caucasus and Central Asia, where over twenty-five million hectares of cultivated land are under threat.[28]

Control[edit]

Preparing to flame locusts in Palestine, 1915

Historically there was little that people could do to protect their crops from being devastated by locusts, although eating the insects themselves may have been some consolation. By the early twentieth century, efforts were being made to disrupt the development of the insects by cultivating the soil where eggs were laid, collecting hoppers with catching machines, killing them with flame-throwers, trapping them in ditches, crushing them with rollers and other mechanical methods.[15] By the 1950s, the organochloride Dieldrin was found to be an extremely effective insecticide but it was later banned from use in most countries because of its persistence in the environment and its bioaccumulation in the food chain.[15]

Cessna of the International Red Locust Control Organization spraying red locusts in Iku Katavi National Park, Tanzania, 2009

In years when locust control is needed, the hoppers are targeted in spring by applying water-based, contact pesticides using tractor-based sprayers. This is effective but slow and labour-intensive and it is preferable, where possible, to spray concentrated insecticide solutions from aircraft over the insects or the vegetation on which they feed.[29] The use of ultra-low volume spraying of contact pesticides from aircraft in overlapping swathes is effective against nomadic bands and can be used to treat large areas of land swiftly.[25] Other modern technologies used for planning locust control include GPS, GIS tools and satellite imagery, and computers provide rapid data management and analysis.[30]

Locusts killed by the naturally-occurring fungus Metarhizium, an environmentally friendly means of biological control. CSIRO, 2005[31]

A biological pesticide to control locusts was tested across Africa by a multinational team in 1997.[32] Dried fungal spores of a Metarhizium species sprayed in breeding areas pierce the locust exoskeleton on germination and invade the body cavity, causing death.[33] The fungus is passed from insect to insect and persists in the area, making repeated treatments unnecessary.[34] This approach to locust control was used in Tanzania in 2009 to treat around 10,000 hectares in the Iku-Katavi National Park infested with adult locusts. The outbreak was contained and the elephants, hippopotamuses and giraffes present in the area were unharmed.[26]

The ultimate goal in locust control is the use of preventative and proactive methods that disrupt the environment to the least possible extent. This would make agricultural production easier and more secure in the many regions where growing crops is of vital importance to the survival of the local people.[14]

As experimental models[edit]

The locust is used as an experimental model in biological research.[35] It is a suitable school laboratory animal because of its robustness and the ease with which it can be grown.[36]

As food[edit]

See also: Kosher locust
Skewered locusts in Beijing, China

Several cultures throughout the world consume insects, and locusts are considered a delicacy and eaten in many African, Middle Eastern and Asian countries. They have been used as food throughout history.[37] They can be cooked in many ways but are often fried, smoked or dried.[38] It is recorded in the Bible that John the Baptist ate locusts and wild honey (Greek: ἀκρίδες καὶ μέλι ἄγριον, akrides kai meli agrion) while living in the wilderness;[39] attempts have been made to explain the locusts as suitably ascetic vegetarian food such as carob beans, but the plain meaning of ἀκρίδες is the insects.[40][41] The Torah, although disallowing the use of most insects as food, permits the consumption of certain locusts; specifically, the red, the yellow, the spotted grey and the white are considered permissible.[42][43] In Islamic jurisprudence, eating locusts is considered halal.[44]

Locusts yield about five times as much edible protein per unit of fodder as cattle, and produce lower levels of greenhouse gases in the process.[45] The feed conversion rate of orthopterans is 1.7 kg/kg,[46] while for beef it is typically about 10 kg/kg.[47] The protein content in fresh weight is between 13–28 g/100g for adult locust, 14–18 g/100g for larvae, as compared to 19–26 g/100g for beef.[48][49] The calculated protein efficiency ratio is however low, with 1.69 for locust protein compared to 2.5 for standard casein.[50] 100 g of desert locust provides 11.5 g of fat, 53.5% of which is unsaturated, and 286 mg of cholesterol.[50] Among the fatty acids, palmitoleic, oleic and linolenic acids were found to be the most abundant. Varying amounts of potassium, sodium, phosphorus, calcium, magnesium, iron and zinc were present.[50]

See also[edit]

References[edit]

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  2. ^ Simpson, Stephen J.; Sword, Gregory A. (2008). "Locusts". Current Biology 18:r364-366. doi:10.1016/j.cub.2008.02.029open access publication - free to read
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  4. ^ "Grasshoppers". Animal Corner. Retrieved 1 April 2015. 
  5. ^ Reed Business Information (20 April 1972). New Scientist. Reed Business Information. p. 156. ISSN 02624079. 
  6. ^ a b c d Dingle, Hugh (1996). Migration : The Biology of Life on the Move. Oxford University Press. pp. 273–274. ISBN 978-0-19-535827-8. 
  7. ^ "Riley, Charles Valentine". The Encyclopedia Americana. Retrieved 16 April 2015. 
  8. ^ Holliday, N.J. (1 February 2006). "Norman Criddle: Pioneer Entomologist of the Prairies". Manitoba History. Manitoba Historical Society. Retrieved 16 April 2015. 
  9. ^ James Morgan (January 29, 2009). "Locust swarms 'high' on serotonin". BBC News. Archived from the original on October 10, 2013. Retrieved March 4, 2014. 
  10. ^ Stephen M. Rogers, Thomas Matheson, Emma Despland, Timothy Dodgson, Malcolm Burrows & Stephen J. Simpson (2003). "Mechanosensory-induced behavioral gregarization in the desert locust Schistocerca gregaria" (PDF). Journal of Experimental Biology 206 (22): 3991–4002. doi:10.1242/jeb.00648. PMID 14555739. open access publication - free to read
  11. ^ a b c Showler, Allan T. (2008). "Desert locust, Schistocerca gregaria Forskål (Orthoptera: Acrididae) plagues". In John L. Capinera. Encyclopedia of Entomology. Springer. pp. 1181–1186. ISBN 978-1-4020-6242-1. 
  12. ^ P. A. Stevenson (January 2009). "The key to Pandora's box". Science 323 (5914): 594–595. doi:10.1126/science.1169280. PMID 19179520. 
  13. ^ Ewen Callaway (January 29, 2009). "Blocking 'happiness' chemical may prevent locust plagues". New scientist. Retrieved January 31, 2009. 
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  15. ^ a b c d Krall, S.; Peveling, R.; Diallo,B.D. (1997). New Strategies in Locust Control. Springer Science & Business Media. pp. 453–454. ISBN 978-3-7643-5442-8. 
  16. ^ a b c Harmon, Katherine (30 January 2009). "When Grasshoppers Go Biblical: Serotonin Causes Locusts to Swarm". Scientific American. Retrieved 7 April 2015. 
  17. ^ Alexandra M. Wagner (Winter 2008). "Grasshoppered: America's response to the 1874 Rocky Mountain locust invasion". Nebraska History 89 (4): 154–167. 
  18. ^ Yoon, Carol Kaesuk (23 April 2002). "Looking Back at the Days of the Locust". The New York Times. Retrieved 1 April 2015. 
  19. ^ Book of Exodus. pp. 10: 13–15. And Moses stretched forth his rod over the land of Egypt, and the Lord brought an east wind upon the land all that day, and all that night; and when it was morning, the east wind brought the locusts. 14 And the locust went up over all the land of Egypt, and rested in all the coasts of Egypt: very grievous were they; before them there were no such locusts as they, neither after them shall be such. 15 For they covered the face of the whole earth, so that the land was darkened; and they did eat every herb of the land, and all the fruit of the trees which the hail had left: and there remained not any green thing in the trees, or in the herbs of the field, through all the land of Egypt. 
  20. ^ "Bombay locust - Nomadacris succincta". Locust Handbook. Humanity Development Library. Retrieved 3 April 2015. 
  21. ^ Encarta Reference Library Premium 2005 DVD. Rocky Mountain Locust.
  22. ^ Ryckman, Lisa Levitt (22 June 1999). "The great locust mystery". Rocky Mountain News. Archived from the original on February 28, 2007. Retrieved 20 May 2007. 
  23. ^ Jeffrey A. Lockwood (2005). Locust: the Devastating Rise and Mysterious Disappearance of the Insect that Shaped the American Frontier. Basic Books. ISBN 978-0-465-04167-1. 
  24. ^ "Role of the Australian Plague Locust Commission". Department of Agriculture, Forestry and Fisheries. Commonwealth of Australia. 14 June 2011. Retrieved 2 April 2015. 
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  26. ^ a b "Red Locust disaster in Eastern Africa prevented". Food and Agriculture Organization. 24 June 2009. Retrieved 1 April 2015. 
  27. ^ "Countries take responsibility for regional desert locust control". FAO. 2015. Retrieved 2 April 2015. 
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  33. ^ Bateman, R., Carey, M., Moore, D., Prior, C. (1993). "The enhanced infectivity of Metarhizium flavoviride in oil formulations to desert locusts at low humidities". Annals of Applied Biology 122: 145–152. doi:10.1111/j.1744-7348.1993.tb04022.x. 
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  36. ^ Scott, Jon (March 2005). "The locust jump: an integrated laboratory investigation". Advances in Physiology Education 29 (1): 21–26. doi:10.1152/advan.00037.2004. The relative size and robustness of the locust make it simple to handle and ideal for such investigations. 
  37. ^ Fromme, Alison (2005). "Edible Insects". Smithsonian Zoogoer (Smithsonian Institution) 34 (4). Archived from the original on November 11, 2005. Retrieved 26 April 2015. 
  38. ^ Dubois, Sirah (24 October 2011). "The Nutritional Value of Locusts". Livestrong.com. Retrieved 12 April 2015. 
  39. ^ Gospel of Mark Mark 1:6; Gospel of Matthew 3:4
  40. ^ Brock, Sebastian. "St John the Baptist’s diet - according to some early Eastern Christian sources" (PDF). St John's College, Oxford. Retrieved 4 May 2015. 
  41. ^ Kelhoffer, James A. (2004). "Did John The Baptist Eat Like A Former Essene? Locust-Eating In The Ancient Near East And At Qumran". Dead Sea Discoveries 11 (3): 293–314. There is no reason, however, to question the plausibility of Mark 1:6c, that John regularly ate these foods while in the wilderness. 
  42. ^ "Are locusts really Kosher?! « Ask The Rabbi « Ohr Somayach". Ohr.edu. Retrieved 12 April 2015. 
  43. ^ Hebblethwaite, Cordelia (21 March 2013). "Eating locusts: The crunchy, kosher snack taking Israel by swarm". BBC News: Magazine. Retrieved 12 April 2015. 
  44. ^ "The Fiqh of Halal and Haram Animals". Shariahprogram.ca. Retrieved 12 April 2015. 
  45. ^ Global Steak – Demain nos enfants mangeront des criquets (2010 French documentary).
  46. ^ A., Collavo; Glew, R. H.; Huang, Y. S.; Chuang, L. T.; Bosse, R.; Paoletti, M. G. (2005). "House cricket small-scale farming". In Paoletti, M. G. Ecological implications of minilivestock: potential of insects, rodents, frogs and snails. New Hampshire: Science Publishers. pp. 519–544. 
  47. ^ Smil, V. (2002). "Worldwide transformation of diets, burdens of meat production and opportunities for novel food proteins". Enzyme and Microbial Technology (30): 305–311. 
  48. ^ "Composition database for Biodiversity Version 2, BioFoodComp2". FAO. 2013-01-10. Retrieved 2015-04-01. 
  49. ^ "nutritional value of insects for human consumption" (PDF). FAO. Retrieved 1 April 2015. 
  50. ^ a b c Abul-Tarboush, Hamza M.; Al-Kahtani, Hassan A.; Aldryhim, Yousif N.; Asif, Mohammed (2010-12-16). "Desert Locust (Schistocercsa gregaria): Proximate Composition, Physiochemcial Characteristics of Lipids, Fatty Acids and Cholesterol Contents and Nutritional Value of Protein" (ARTICLE). College of Foods And Agricultural Science (King Saud University). Retrieved 2015-01-21. 

External links[edit]