African armyworm

African armyworm
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Lepidoptera
Family: Noctuidae
Genus: Spodoptera
Species: S. exempta
Binomial name
Spodoptera exempta
(Walker, 1856)
Synonyms
  • Agrotis exempta Walker, 1856
  • Prodenia bipars Walker, 1857
  • Prodenia ingloria Walker, 1858
  • Laphygma exempta

The African armyworm (Spodoptera exempta) also called okalombo, kommandowurm, or nutgrass armyworm, is an African moth. It is a very deleterious pest, capable of destroying entire crops in a matter of weeks. The larvae feed on all types of grasses, early stages of cereal crops (e.g., corn, rice, wheat, millet, sorghum), sugar cane, and occasionally on coconut.[1][2] The armyworm gets its name from its habit of "marching" in large numbers from grasslands into crops. African armyworms tend to occur at very high densities during the rainy season, especially after periods of prolonged drought.[3][4] During the long dry season in eastern Africa, population densities are very low. Because outbreaks are never observed during the dry season, it is called the "off-season" by those who monitor African armyworms.[5]

The species also occurs in Yemen, some Pacific islands, and parts of Australia.[6]

Life cycle

S. exempta moths live about 10 days. The female can lay a maximum of about 1000 eggs in her lifetime. The ivory-coloured eggs of the African armyworm are laid in clusters on leaves. Eggs hatch in 2–5 days. Six larval (caterpillar) instars are completed in 2–3 weeks. Caterpillars occur in two morphologically distinct forms: a "gregarious" form, which is black with yellow stripes, and a solitary form, which is green or brown. The morphological form is determined by density — becoming "gregarious" at higher densities; it is these "gregarious" forms that cause outbreaks. However, the African armyworms do not exhibit the true gregarious behavior of locusts. Generally, African armyworms are not noticed by farmers until the caterpillars are 10 days old and change from green to black.[7] In the last instar, larvae burrow 2–3 cm into the ground to pupate. Adults emerge in 7 to 10 days.[8] The moths probably migrate over tens, and probably over hundreds, of kilometers between their emergence sites and their oviposition sites,[9] causing outbreaks to occur suddenly in areas that were free of the pests for several months.[10]

Infestations

In mid-April 1999, an African armyworm infestation started in southern Ethiopia, spreading into the north the following month and into the Jubba valley of Somalia in early May. Similar outbreaks affected the Rift Valley Province of Kenya and parts of Uganda at the same time. While Ethiopian officials had stocks of pesticides to treat 350,000 hectares of affected land, neither Kenyan nor Ugandan officials had sufficient supplies to combat the insect and no central government was present to respond to the emergency in Somalia.[11]

STAR radio in Liberia reported in January 2009 that Zota District in Bong County had been invaded by African armyworms, which had consumed vegetation, polluted creeks and running water,[12] and were moving toward Guinea and Sierra Leone.[13] On 28 January 2009, the President of Liberia declared a state of emergency to deal with the infestation of army worms in the country.[14]

African armyworms marching along a road in Tanzania

December 2009 had an infestation of ten regions of Tanzania. The infested regions include three of the five main grain-producing regions. The other two major grain-producing regions are at risk of infestation. Tanzania has trained farmers in fighting armyworms since 2007, and responded to forecasts of the late 2009 infestation by sending out hundreds of liters of pesticides to rural farmers. The first infestation was reported on 22 December and quickly spread to surrounding regions. The previous growing season had Tanzania produce 10.872 million tons of grain; after 10.337 million tons of domestic consumption, the remaining 0.534 million tons were exported. By 31 December almost 1,400 acres (5.7 km2) of grain had been destroyed by armyworms.[15]

In January 2015 armyworm outbreaks were reported in Zimbabwe.[16] In November 2015 armyworm outbreaks were reported in Botswana.[17]

In 2016 fall armyworm (Spodoptera frugiperda, a species of American origin that behaves similarly) invaded maize crops in Zambia.[18] By 3 January 2017 about 90,000 hectares were affected, according to reports released by the Zambian government's Disaster Management and Mitigation Unit (DMMU).[19] The Zambia national farmers union (ZNFU) indicated that some farms were completely wiped out. The Zambian president directed the air force to help airlift pesticides to fight the outbreak.[19]

in 2017 infestations of fall armyworm were detected in further African countries, such as Zimbabwe and South Africa.[20]

See also

References

  1. ↑ Odiyo, P. O. 1984. A guide to seasonal changes in the distribution of armyworm infestations in East Africa. Insect Sci. Applic. 5: 107–119.
  2. ↑ Yarrow, J. G. Otindo, B. L., Gatehouse, A. G., and Lubega, M. C. 1981. Dwarf variety of coconut, Cocos nucifera (Palmae), a host plant for the African armyworm, Spodoptera exempta (Walk.) (Lepidoptera, Noctuidae). Insect Science and its Application 1: 361–362.
  3. ↑ Haggis, M. J. 1984. Distribution, frequency of attack and seasonal incidence of the African armyworm, Spodoptera exempta (Walk.) (Lepidoptera: Noctuidae), with particular reference to Africa and south-western Arabia. Tropical Development Research Institute, London, Report No. L69, pp. 116.
  4. ↑ Haggis, M. J. 1986. Distribution of the African armyworm, Spodoptera exempta (Walker) (Lepidoptera: Noctuidae), and the frequency of larval outbreaks in Africa and Arabia. Bulletin of Entomological Research 76: 151–170.
  5. ↑ Odiyo, P.O. 1981. Development of the first outbreaks of the African armyworm Spodoptera exempta (Walk.), between Kenya and Tanzania during the 'off-season' months of July to December. Insect Science and its Application 1: 305–318.
  6. ↑ Rose, D. J. W., Dewhurst, C.F. and Page, W. W. 2000. The African Armyworm Handbook (2nd Edn). NRI, Chatham, UK, 304 pp ISBN 978-0859545235
  7. ↑ Brown, E. S. 1972. Armyworm control. Pest Articles and News Summaries.
  8. ↑ Dewhurst, C. F. 1985. The African armyworm (Spodoptera exempta) — the East African story outlined from 1962. Antenna 9: 12–18.
  9. ↑ Riley, J. R., Reynolds, D. R. and Farmery, M. J. 1983. Observations of the flight behaviour of the armyworm moth Spodoptera exempta, at an emergence site using radar and infra-red optical techniques. Ecological Entomology 8: 395–418.
  10. ↑ Jahn, G.C. 1995. Environmental assessment for armyworm control in Ethiopia. USAID, Washington, DC.
  11. ↑ Judith Achieng for Inter Press Service News Agency. May 25, 1999 Army worm Invasion Poses Threat To Main Crop
  12. ↑ STAR radio Liberia: Caterpillar invasion: Government declares Zota District emergency zone Archived July 22, 2011, at the Wayback Machine.
  13. ↑ "Liberia worms trigger emergency". BBC. 27 January 2009. Archived from the original on 28 January 2009. Retrieved 2009-01-27.
  14. ↑ AOL.com: Caterpillars Trigger Emergency in Liberia
  15. ↑ "Armyworm Scourge Spreads to Ten Regions". allAfrica.com. Archived from the original on 2 January 2010. Retrieved 2009-12-31.
  16. ↑ Zivengwa, Petros (2015-01-01). "Zimbabwe: Govt Reacts to Armyworm Outbreak". allAfrica.com. Retrieved 2015-11-29.
  17. ↑ "Mmegi Online :: African Armyworm outbreak reaches Botswana". Mmegi.bw. 2013-01-10. Retrieved 2015-11-29.
  18. ↑ Editor, Support. "Zambia : Army worms invade four districts on the Copperbelt". Retrieved 2016-12-29.
  19. 1 2 "Zambia Battles Armyworms That Are Decimating Corn Fields". Bloomberg.com. 2017-01-03. Retrieved 2017-01-05.
  20. ↑ (www.dw.com), Deutsche Welle. "'Fall armyworm' attacks southern African crops | Africa | DW.COM | 07.02.2017". DW.COM. Retrieved 2017-02-07.
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