Key facts
Credits:FAO, CABI,Infonet
Fall Armyworm is an insect native to tropical and subtropical regions of the Americas
It was first detected in Central and Western Africa in early 2016 and has now spread across Sub-Saharan Africa and recently reached Yemen and India
In the larval stage, the insect causes damage to crops, feeding on more than 80 plant species
FAW primarily affects maize, but also rice and sorghum as well as cotton and some vegetables
The moth can fly up to 100 km per night and the female moth can lay up to a total of 1000 eggs in her lifetime
In the Americas, farmers have been managing FAW in their crops for many centuries and researches have been studying it for decades
Sustainable management practices that are used in the Americas need to be to be adapted to countries’ socio-economic-environmental contexts.
Recognizing FAW is the first step for management. The pest is new to Africa, and farmers need to be able to recognize FAW, and distinguish it from other pests. Below are pictures of the different development stages of FAW, from egg to larvae, pupae and adults.
Eggs are pale green or white at the beginning, get covered in scales, and turn clear brown to brown before hatching. They hatch within 2-3 days.
There are 6 larvae stages. Young larvae are pale colored. They become brown to pale green, then turn darker at the latest stages. The larvae stages last 12 to 20 days (depending on ambient temperature and other environmental conditions).
Half-grown or fully grown caterpillars are the easiest to identify. The larvae are generally characterized by
3 yellow stripes on the back, followed by a black, then a yellow stripe on the side. Look out for four dark spots forming a square on the second to last segment (photo). Each spot has a short bristle (hair). The head is dark; it shows a typical upside down Y-shaped pale marking on the front.
The pupa is dark brown and hides in the soil, more rarely in the stalk. Pupa lives 12-14 days before an adult emerges.
The moth is 3 to 4 cm wide. Its front wings are dark brown while the rear wings are grey white. It will live 2 to 3 weeks before dying
The Fall Armyworm lifecycle includes egg, 6 growth stages of caterpillar development (instars), pupa and moth.
This diagram illustrates the lifecycle, showing where the Fall Armyworm is usually found on maize plants at any given stage.
Day 1-3
100-200 eggs are generally laid on the underside of the leaves typically near the base of the plant, close to the junction of the leaf and the stem. These are covered in protective scales rubbed off from the moths abdomen after laying.
When populations are high then the eggs may be laid higher up the plants or on nearby vegetation.
Day 3-6
GROWTH STAGES 1-3
After hatching the young caterpillars feed superficially, usually on the undersides of leaves. Feeding results in semitransparent patches on the leaves called windows.
Young caterpillars can spin silken threads which catch the wind and transport the caterpillars to a new plant.
The leaf whorl is preferred in young plants, whereas the leaves around the cob silks are attractive in older plants.
Feeding is more active during the night.
Day 6-14
GROWTH STAGES 4-6
By stage 3-6 it will have reached the protective region of the whorl, where it does the most damage, resulting in ragged holes in the leaves.
Feeding on young plants can kill the growing point resulting in no new leaves or cobs developing.
Often only 1 or 2 caterpillars found in each whorl, as they become cannibalistic when larger and will eat each other to reduce competition for food. Large quantities of frass (caterpillar poo) present. When this dries it resembles sawdust.
If the plant is older and has already developed
cobs then the caterpillar will eat its way through
the protective leaf bracts into the side of the cob where it begins to feed on the developing
kernels (seeds). After approximately 14 days the fully grown caterpillar will drop to the ground.
The caterpillar will then burrow 2-8 cm into the soil before pupating.
The loose silk oval shape cocoon is 20-30 mm in length.
If the soil is too hard then the caterpillar will cover itself in leaf debris before pupating. After approximately 8-9 days the adult moth emerges to restart the cycle.
Under warm conditions, a female moth can lay 6 to 10 egg masses of 100 to 300 eggs each, giving a maximum of 1 500 to 2 000 eggs in her lifetime of 2-3 weeks. As for other pests, most eggs will not develop into adults due to mortality in different parts of the lifecycle.
In tropical America, FAW is an established pest, and outbreaks in which populations reach densities that can cause important damage are rare. Natural enemies keep FAW populations at low levels under normal circumstances, and smallholder farmers have learnt to manage the pest. However, FAW populations do increase rapidly when area of maize cultivation expand. This is what the FAW population mostly respond to.
In Africa, FAW infestations are occurring in “outbreak” style in many maize-production areas – i.e. large populations of the pest are found in the fields and cause damage. As the pest is new to Africa, natural enemies are still rare, though some local species seem to be able to feed on FAW and reduce its populations. It is possible that FAW is now reaching “peak” levels in Africa. Within a few years, as natural enemy populations catch up and spread, a lower equilibrium population of FAW could be present in Africa. It is therefore important to preserve and enhance natural enemy populations in Africa. Unlike FAW in the Americas, or the African Armyworm (AAW), FAW in sub-Saharan Africa may not develop a migratory pattern. Most likely, given our understanding ofthe pest in the Americas, we expect that FAW populations will be resident over much of Sub-Saharan Africa, surviving on maize and on other plants during periods without maize; but in some cooler or drier areas, it may become migratory. We just don’t know for now.
Feeding behaviour and damage: In the lifecycle graph on the next page, more information is provided on the different stages of FAW, and where to find them on the plant.
Although FAW larvae can feed on more than 80 species of plants, they prefer maize, as well as, rice, cotton, groundnut, sorghum and vegetables.
The favourite spot of the caterpillar stage of the FAW is curled up in the whorl of a maize plant, where it feels protected and chews and grows on its favourite food – tender, young maize leaves. As they chew away, the leaves continue to grow out, leaving ragged, half-chewed leaves that are typical of FAW- infested maize fields.
Sometimes, but much less often, FAW can act as a young plant cuter, if high populations of the caterpillar are present on weeds or other host plants in fields adjacent to newly- planted maize fields. This Armyworm-like action by FAW is rare, but can occur. At very high population levels FAW can also penetrate maize ears, causing direct damage to the harvest. But again, this is rarer than the typical behaviour of burrowing down into the whorl to eat leaves.
8 to 14 days old larvae can cause severe damage to maize plants, especially when the growing points of young plants are eaten. Early vegetative-stage FAW infestation can cause more leaf damage and yield losses than late vegetative stage infestation. Fortunately, maize plants can significantly recover (compensate) from early growth stage damage on leaves and short duration defoliation. When the FAW population is high on a plant, the adult larvae might occasionally move to the tassel and the ears, reducing the quality of the produce at harvest.
Heavy rains can wash young larvae off leaves, and drown those in the whorl.