African armyworm

Definition

A highly migratory noctuid moth (Spodoptera exempta) whose larvae are major agricultural pests in sub-Saharan Africa and parts of the Middle East, Australia, and the Pacific. The species exhibits density-dependent polyphenism: solitary larvae (solitaria phase) are green and develop slowly, while crowded larvae (gregaria phase) turn black, become highly active, and march in coordinated groups—hence 'armyworm'—devastating cereal crops, pasture grasses, and sugarcane within weeks.

Etymology

From 'army' for the coordinated marching behavior of gregarious larvae, plus 'worm' (archaic for caterpillar); 'African' denotes primary distribution.

Example

During the 2016 East African outbreak, gregaria-phase African armyworm larvae marched across maize fields in Tanzania at densities exceeding 1,000 per square meter, stripping plants to stems within 48 hours.

Synonyms

• okalombo
• kommandowurm
• nutgrass armyworm
• Spodoptera exempta

Related Terms

• Armyworm
• density-dependent polyphenism
• gregaria
• solitaria
• Noctuidae
• Fall armyworm
• Migratory locust
• outbreak pest

Usage Notes

Distinguished from the fall armyworm (Spodoptera frugiperda) by distribution and host range; the latter is invasive in Africa and has largely displaced S. exempta in some regions. Outbreaks follow drought-rain patterns, with populations crashing to undetectable levels in dry seasons. The phase polyphenism parallels that of locusts but is less extreme and reversible.