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Pest Profile - Fall Armyworm

Fall armyworm, Spodoptera frugiperda

If unremarkable in appearance, the fall armyworm (FAW) is capable of extraordinary feats. Caterpillar hordes devastate crops overnight, and the adult moth is capable of crossing oceans on stormfronts. Its appetite for our favourite vegetables could leave our supermarkets bare, but our vigilance can help stop them in their tracks.

Native range:

FAW originate across Central and South America, and in the warmer parts of North America. They prefer it tropical, and perish in the freezing cold.

Arrival in Aotearoa:

FAW only recently landed in Aotearoa, around February, 2022.

The global spread began in 2013, when it was detected in the island city of São Tomé, of São Tomé and Príncipe. From there, the armyworm invasion continued across the African continent, into Asia and Europe, Australia . . . now here.

Many counties have attempted eradication, but none have yet found success.

The fall armyworm effect:

It’s said that the fluttering of a butterfly’s wings in the Amazon can cause a hurricane in Texas. While the fall armyworm invasion isn’t whipping up weather events, the adult moth is said to ride storm fronts, helping enable the global spread.

The moth is an excellent flyer, traveling up to 100km in a night. It migrates before laying eggs, sometimes to distances of 500km. The larval stage also knows how to move, with hordes of caterpillars marching between adjacent crops.

They’re driven by their stomachs, and they have similar tastes to us . . .

Crops at risk:

Corn and maize (the caterpillar's favorite!)

The Solanaceae family, or nightshades, including potatoes, tomatoes, and capsicum

Brassica species, like broccoli and bok choy

Asparagus, beetroot, beans, peas . . . and many more.

Native and endemic plants may also become targets.

Identifying Fall Armywom

What keeps the fall armyworm in check in its natural range?

Of special interest to those looking to halt the march of the worms, are the parasitic wasps and flies that target caterpillars as hosts (think Ridley Scott’s Alien). As we know, biological controls are risky and have to be rigorously tested.

As you might expect, the caterpillars and moths don’t lack predators, and are in fact preyed on by many, including bats, birds, beetles and other insects. Restoring healthy ecosystems supports healthy predator populations, which can in turn help keep FAW populations in check. The fall armyworm’s main defense against predation is multiplying to unconquerable numbers, and migrating ahead of the seasonal conditions when their predators are most active.

Critical mass!

Armyworms go on the march when their local population reaches critical mass – that is, when they reach numbers beyond which can be supported in their current location. That’s when things get serious.

Luckily for Aotearoa, this level of reproduction requires year-round warm weather, with our cold snaps putting a real dent in the FAW mission.

However, in the balmy North, the armyworms are likely to garner a foothold, surviving winters to come. Additionally, weather events favourable to FAW, like El Niño, could still tip the scale and cause disaster.

Action stations: Catch it. Snap it. Report it.

Vigilance is key is meeting the FAW threat.

Farmers and growers are keeping their eyes peeled for any sign of the FAW, including investigating crop damage for signs of FAW, and laying traps.

Anyone can help in this effort, by familiarizing themselves with the signature looks of the FAW caterpillars and moths. Notably, the caterpillar has an inverted Y-shaped mark on its head, and four dark dots in square arrangement on its back.

If you find a caterpillar: Catch it. Take a photo. Report it on Find-a-Pest.

Article written by Kerry Donovan-Brown for Find-A-Pest


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