Invasives Blog

Edited by Washington Otieno, Roger Day and Matthew Cock.

Larva

Figure 1. Spodoptera eridania (southern armyworm); final instar larva. Laboratory specimen. Public Domain – Released by the USGS Bee Inventory & Monitoring Lab.

The International Institute of Tropical Agriculture (IITA) has confirmed that caterpillar and adult moth samples from West and Central Africa are southern armyworm, Spodoptera eridania.

SAW-2

Figure 2. Spodoptera eridania (southern armyworm); final instar larva. Close-up of head capsule and anterior region. Laboratory specimen. Public Domain – Released by the USGS Bee Inventory & Monitoring Lab.

These samples were collected in cassava fields in Nigeria in 2016 and Bénin in 2017. Samples were further obtained from a tomato field in Cameroon and from the University of Masuku in Gabon (more information can be found in IITA’s factsheet).

Southern armyworm is native to the tropical Americas where it feeds on a wide range of vegetables, fruits and grasses. In recent years, it has been reported as a significant pest of cotton, soybean and tomato in its native range (Efrom et al., 2013). In Africa, the IITA has reported that it can be found on amaranth and maize, in addition to cassava and tomato.

Identifying the caterpillar of southern armyworm is particularly challenging since it looks very similar to other Spodoptera species, including S. littoralis, S. litura, S. exigua and S. frugiperda (identification information regarding these species can be found in EPPO’s Spodoptera diagnostics bulletin). Therefore, laboratory analysis is recommended in order to accurately identify these Spodoptera caterpillars. The adult moth of southern armyworm can look distinct from the moths of other Spodoptera species but individual variation can still complicate diagnosis.

Colour phases

Figure 3. Spodoptera eridania (southern armyworm); late instar colour phases, on a cotton leaf (Gossypium hirsutum). USA. ©Ronald Smith/Auburn University/Bugwood.org – CC BY 3.0 US

As of yet, it is not clear whether southern armyworm has had, or will have, a significant long-term impact on crops in Africa, nor how wide its distribution is or will be. If ecological conditions in Africa prove to be as conducive to the pest as those in the Americas, it may spread just as quickly as S. frugiperda (fall armyworm) has done. It is not known how long it has been in Africa or how it was introduced.

CABI is monitoring the situation through networks of plant clinics in Africa. Plant doctors (extension workers) record pest diagnoses at the plant clinics and can send suspected samples of southern armyworm for identification. If southern armyworm becomes a major threat, farmers will need immediate advice on what to do, so factsheets are also being developed. At the same time, research to test and adapt known control methods will be required.

You can find out more about southern armyworm by reading CABI’s ISC datasheet.

1 Comment

  1. JOPESTKIL KENYA on 26th July 2018 at 12:13 pm

    Army worms, this destructive garden pest gets its name because it travels in small insect armies and consumes just about everything in its path. There’s a number of species of armyworm caterpillars, many with a distinct taste for a particular plant or vegetable. But some will eat anything green or red or yellow. They’re most active at night and hide in plants and under garden debris during the day.
    In their larval stage, army worms attack a variety of crops as well as grasses, sometime moving in masses to new areas in a way that brings to mind, as its name suggest. The assault is mostly aerial, with the gray moths usually arriving under cover of darkness to lay eggs. The biggest invasion of army worms usually occurs after a cool, wet spring.

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