Edited by Washington Otieno, Roger Day and Matthew Cock.
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.
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.
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.