Know your armyworm species

Effective control of armyworm begins with being able to differentiate between the various species. South African crop farmers need to learn and apply this skill, Dr Annemie Erasmus of the Agricultural Research Council’s Grain Crops Institute told Annelie Coleman.

- Annelie Coleman.

Three armyworm species occur in South Africa: the fall armyworm (Spodoptera frugiperda), the African armyworm (S. exempta), and the lesser armyworm (S. exigua). These insects’ life cycles, behaviour and ecologies differ, and they feed on different crops, says Dr Annemie Erasmus, a senior researcher of entomology at the Agricultural Research Council’s (ARC) Grain Crops Institute.

The lesser armyworm, for example, survives on broadleaved plants, while the African armyworm feeds on grass species such as maize.

“It is essential for crop producers to familiarise themselves with the different species of armyworm to ensure correct classification and effective control should an outbreak occur,” says Erasmus.

Fall Armyworm

Fall armyworm (FAW) larvae were first collected in South Africa in 2017, mainly on maize lands. The pest can cause great devastation to a number of different crops.

Its life cycle varies between 24 and 30 days, depending on prevailing temperature and humidity, and the number of generations that appears in an area is determined by the number of dispersing moths.

FAW does not have a diapause (overwintering) stage. The moths lay eggs, which are domeshaped, have a flat base and curve upwards to a broadly round point, in batches on foliage. Up to 200 eggs in a batch have been recorded, and a moth can lay more than 1 000 eggs in her lifespan.

The female deposits a layer of furry-looking, greyish scales over the egg batch. The egg stage lasts two to three days.