African armyworm
| African armyworm | |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Lepidoptera |
| Family: | Noctuidae |
| Genus: | Spodoptera |
| Species: | S. exempta |
| Binomial name | |
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Spodoptera exempta (Walker, 1856) |
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| Synonyms | |
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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. 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. 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.
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. However, the African armyworms do not exhibit the true gregarious behavior of locusts. The "gregarious" forms of AAW cause outbreaks. Generally, African armyworms are not noticed by farmers until the caterpillars are 10 days old and change from green to black. In the last instar, larvae burrow 2–3 cm into the ground to pupate. Adults emerge in 7 to 10 days. The moths migrate over tens, and probably over hundreds, of kilometers between their emergence sites and their oviposition sites. The observation that African armyworm outbreaks can suddenly occur in areas that were free of the pests for several months has led to the hypothesis that the moths migrate hundreds of kilometres.
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Wikipedia