Fall Armyworm

Spodoptera frugiperda

Family: Noctuidae

Order: Lepidoptera

Other Names:

Frugiperda is Latin for “lost fruit”, because of its ability to destroy crops.

Summary:

The adult moths are 32 to 40 mm wing tip to wing tip, with a brown or grey forewing, and a white hind wing. Male fall armyworms have more patterns and a distinct white spot on each of their forewings (i.e. some sexual dimorphism). During the development stage, the larva is light coloured with a larger dark head. As they develop, they become browner with white lengthwise lines and a Y shaped line on the head. They also develop dark spots with spines.

Description:

Adult -

Colour - Grey

Body -

Wings - 32 to 40 mm wing tip to wing tip, with a brown or grey forewing, and a white hind wing. There is a pale brown line around the pale hind wings. Males have a distinct white spot on each forewing.

Mouthparts - Will sip nectar.

Antennae -

Legs - 6

Head -

Thorax -

Abdomen -

Habits - Adults are nocturnal and most active during warm and humid nights.

Caterpillar -

6 instars with slightly varying physical appearance and pattern.

Colour - Light tan to nearly black. The larvae have a distinctive inverted Y suture on the forehead. The first larval instar is light coloured with a larger dark head. As they develop through instars, they become browner with white lengthwise lines (or three thin light yellow lines down the back) and dark spots with spines. There is also a wider dark stripe and a wavy yellow red splotched stripe on each side or a pinkish line down the side. The head has a reticulate pattern

Body - The mature caterpillar is about 38-51 mm (1.5-2.0 inches) in length.

Mouthparts - chewing.

Antennae -

Legs -

Head - larger than body.

Thorax -

Abdomen -

Habits - Feed above ground. Active during the day.

Pupa - 14-18 mm long cocoon of soil and silk. Reddish.

Eggs - Dome-shaped, and measures around 0.4 mm in diameter and 0.3 mm in height. Tend to be on the underside of leaves in batches of 100-200.

Key Characters:

The larvae have a distinctive inverted Y suture on the forehead.

Reticulate pattern on head.

Collar is the same colour as the head.

Lack dark dorsal patches (even dark band down back)

With a hand lens, sclerotic rings at head and tail of larva can be seen.

Trapezoidal or square pattern of dots on larva rump.

Larvae of fall armyworms vary from light tan to nearly black with three thin light yellow lines down the back. There is also a wider dark stripe and a wavy yellow red splotched stripe on each side. Fall armyworms resemble both armyworms and corn earworms. Fall armyworms, though, have a prominent inverted "Y" mark on the front of the head.

The fall armyworm also can be distinguished from true armyworms by the time of year they appear and their habit of remaining and feeding on the plant during the day.

The moth has a pale brown line around the pale hind wings.

The male has a white dot on each dark fore wing.

Male genitalia and DNA used for identification.

Biology:

It appears to be diverging into two species. These two strains have major genetic differences that are connected to the plants they feed on, even though both still exist in the same area (sympatric speciation). These two strains can be loosely categorized into a rice strain and a corn strain. This separation is occurring because of differences in habitat (preferred host plant), and differences in reproductive behaviour. The reproductive differences can be divided into two causes: difference in the timing of mating at night, and difference in female sex pheromones.

The larva are cannibals.

The larva cannot enter into diapause and therefore cannot survive cold temperatures. The activity threshold is around 10 degrees C.

Adult moths sip nectar from flowers.

The insects do not burrow in the ground, but will hide under residue and do pupate underground.

Adults are capable of flying long distances. Their migration rate is remarkably fast, estimated at almost 500 kilometres per generation. They can also spread through people movement. It believed that their arrival in Africa was via a passenger flight.

Life Cycle:

Females prefer to lay eggs on the underside of leaves, but in high populations they will lay them just about anywhere. In warm weather, the eggs will hatch into larvae within a few days.

The larva process lasts from 14 to 30 days, again depending on temperatures. This is the most destructive life stage as the larvae have biting mouth parts. Young larvae may drop from leaves on silk threads and be blown around by the wind (ballooning) to infest neighbouring crops.

The larva then pupates underground for 7 to 37 days in a cocoon they form from soil and silk. Duration and survival of the pupal stage depend on the temperature of the environment.

Once emerged, the adults live for about 10 days, and sometimes up to 21 days, with the female laying most of her eggs early in life.

Adults are nocturnal and fare best during warm and humid nights.

The fall armyworm's life cycle is completed within 30 days during summer, and 60 days during the spring and autumn seasons; during the winter, these caterpillars' life cycle lasts about 80 to 90 days. The number of generations a moth will have in a year varies based on climate, but in her life span a female will typically lay about 1,500 eggs. Fall armyworms have from one generation a year in northern areas of the US to 5-10 generations a year in southern Florida.

Habitats:

Warm grassy areas.

Origin and History:

Native to tropical and sub-tropical areas of America. Initial detection in Africa in 2016 saw the fall armyworm spread to more than 30 countries over 3 years. In 2018, it was detected in India and Sri Lanka. In 2019 it has spread to Asian countries.

It was detected on northern Torres Strait islands and on the tip of Cape York in 2020 and moves to eradicate it were abandoned within weeks of arrival in Australia.

Distribution:

Almost everywhere with warm climates or no freezing conditions.

Significance:

The fall armyworm larva is known to eat more than 350 plant species, many of which are relied upon by humans.

Destruction of crops can happen almost overnight, because the first stages of a larva's life require very little food, and the later stages require about 50 times more. Because of this rapid change in food consumption, the presence of larva will not be noticed until they have destroyed almost everything in as little as a night.

Examples of targeted crops include cotton, tobacco, sweet corn, rice, wheat peanuts, and fruits including apples, oranges, grapes and many more. The list of possible food sources for the larvae is extensive. Because the larva eats so much of the plant, they are extremely detrimental to crop survival and yield.

The armyworm is expected to hit China's Northeast wheat belt in 2020. A report issued by the Ministry of Agriculture and Rural Affairs rates the situation as "very grave".

Each larva will produce about the same damage as Helicoverpa or cluster caterpillar in Australia.

Beneficial:


Detrimental:

Damages many economically important grain and fruit crops.

Legislation:

In Australia, officially declared ineradicable within weeks of discovery.

Management and Control:

Fly and wasp parasitoids target the fall armyworm, most commonly Archytas marmoratus, Cotesia marginiventris, and Chelonus texanus. The armyworm is also vulnerable to additional parasitoids, varying with location.

In South Africa, farmers are using pheromone lures with a combination of Dichlorvos blocks to trap and eliminate male armyworms with the intention of disrupting mating cycles.

Helicoverpa NPV (Vivus Max) has no activity on fall armyworm.

A range of insecticides will provide control in susceptible populations. However, the larva tends to entrench and most products require contact and have low residual which means control may be difficult.

Symptoms:

Windowing of leaves going to shot holes.

Yong larvae hanging by threads form leaves.

Leaves cut off.

Frass in the leaf whorls with fresh dark frass or lighter old frass.

Larvae may climb up to corn tassels.

Thresholds:

Suspect insects should be identified.

Thresholds tend to be around 20% of plants with larvae and 3 or more larvae per plant.

Related Species:

Fall armyworms resemble both armyworms (Spodoptera exigua) and corn earworms. Fall armyworms have a prominent inverted "Y" mark on the front of the head.

Cluster Caterpillar (Spodoptera litura)

False armyworm (Leucania loreyi)

Lawn Armyworm (Spodoptera mauritia, Spodoptera hydralis)

Mythimna species.

Similar Species:

Biocontrol:

Ants, minute pirate bugs, earwigs, assassin bugs, spiders, lacewings and others.

Trichogramma species are reared and released for control.

References:

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 for more information.