Human beings like to think that they are the dominant species on Planet Earth. But that domination has been challenged quite often. And most effectively by some of the smallest critters around. One of them is the Fall Armyworm Moth (Spodoptera frugiperda). There are some really remarkable facts about this drab member of the Order Lepidoptera. All of which add up to make it a terrifying destroyer of the very basis of human civilization – agriculture. In fact, the species’ scientific name is an apt reminder of its destructive potential – Spodoptera frugiperda. The term frugiperda comes from Latin and means ‘lost fruit’, a reference to the havoc the species’ caterpillars inflict on farms. In fact, the family to which it belongs, the Noctuidae, is also famous as the family of ‘cutworms’, caterpillars that damage plants by cutting their stems or roots.
The adults are between 25-40 mm long. They are native to the tropical and subtropical regions of the Americas. Vulnerable to low temperatures, they wait for summer to migrate along the Atlantic coast, as far north as southern Canada. In this region, they are notorious pests of maize, cotton, tobacco, peanuts, rice, and even fruits. The first time they were mentioned in American records as inflicting heavy damage was in the southeastern state of Georgia, in 1797. With the ability to target as many as 80 species and a tendency to lay waste to entire fields, the Fall Armyworm is a serious threat to farmers across the globe. Females can mate and lay as many as 100-200 eggs at a time, with as many as 1,500 eggs laid on average during an entire lifespan.
The eggs hatch after two to three days, and the larvae take between one (during summer) to two (during spring or fall) months to complete their development. They are small to begin with and increase in size, feeding rapidly on the host plants’ foliage. While feeding they can damage the leaves, buds and seeds. Heavy destruction can be inflicted within a very short period of time to the standing crop. Since they feed on such a wide variety of crops and weeds, they are capable of proliferating at astonishing rates. Entomologists have noted the cannibalistic tendencies of Fall Armyworm larvae, with larger larvae devouring smaller ones in times of food shortage. Having completed their six instars, the larvae pupate underground, for one week to a month, at a depth of two to eight cm in the soil.
The adults live for one to three weeks. Apart from laying eggs, they act as bridgeheads for the advance of the Fall Armyworm invasion. Scientists speculate that the moths use prevailing winds to travel vast distances. One generation of moths can leapfrog a distance of 300 km. This is how they make their way to southern Canada by September, having appeared in southeastern USA around July. But the manner in which they made their way across the Atlantic Ocean to wreak havoc in Africa (where, within a short span of two years, after their first appearance in Nigeria (or Sao Tome, according to the FAO) in 2016, they had covered as many as 28 countries) is still not clear. They reached the continent most probably as stowaways in grain consignments from the Western Hemisphere. Or were simply blown over thousands of kilometers of ocean by strong winds (a not altogether impossible scenario). Whatever the means of transportation, their debut in Africa was a terrifyingly successful one. Given below is an article -‘Why it’s hard to control the Fall armyworm in southern Africa’ in ‘The Conversation’ (by Kerstin Kruger, dated February 14, 2017) explaining its unstoppable advance:
The native range of the Fall armyworm – Spodoptera frugiperda – is in South and North America. But it’s rapidly spreading across southern Africa. This follows the first reports of its arrival on the African continent in Nigeria in January 2016. Within a year it spread, reaching South Africa by January 2017. The Fall armyworm is adding to the devastation already caused by the native African armyworm, Spodoptera exempta.
The Fall armyworm problem has massive implications for people in the region. The moth is a severe pest of maize and other grass family crops such as sorghum. It poses a serious threat to African agriculture and food security as well as international trade through quarantine restrictions. Its arrival is a particularly heavy blow for southern Africa which is just recovering from a severe drought. There are 208 million people dependent on maize for food security in sub-Saharan Africa. Maize also provides crucial income for small-holder farmers in the region.
Understanding how armyworms breed, travel and feed is critical to managing the devastation they can cause. They have a number of characteristics that make them particularly hard to control. This includes the fact that the moths are strong flyers, the fact that they breed at an astonishingly high rate and that their larvae can feed on a particularly wide range of host plants. In addition, they tend to develop resistance to pesticides.
Biological invasions like these threaten biodiversity, the functioning of natural and agricultural ecosystems, and ultimately food security. Sub-Saharan Africa is considered to be particularly vulnerable to invasive species due to its high dependence on agriculture. Usually the expansion of the geographical range of a species is hampered by barriers like oceans and mountain ranges. But an increase in international trade and travel has greatly facilitated biological invasions in recent decades. The larger grain borer, Prostephanus truncatus, another native of the Americas, was accidentally introduced into Tanzania in the 1970s. The beetle spread rapidly through infested consignments of maize and dried cassava. The species has invaded numerous countries since its first introduction into Africa.
There’s disagreement about how the Fall armyworm arrived in Africa. One suggested avenue is that it arrived on foodstuffs imported from the Americas. This is feasible as insects can readily cross borders with infested plant material. The species has been intercepted on shipments destined for Europe on several occasions. It’s also possible that the Fall armyworm arrived over the Atlantic through wind currents. This is because wind-borne adult insects can move over vast distances. The Fall armyworm wouldn’t be the first insect species crossing the Atlantic in this way. The most famous example is the monarch butterfly, Danaus plexippus, crossing the Atlantic from America to the British Isles.
Whichever way the Fall armyworm arrived, its rapid spread across the African continent attests to its high dispersal ability. As strong flyers adult moths cross borders with ease. In the US the species has long been known to use jet streams for adult dispersal. The scientific name, Spodoptera frugiperda, refers to the grey-patterned wings of the moths and the fruit destroying habits of the caterpillars. The common name, Fall armyworm, is based on the habit of mass movements of the caterpillars in autumn.
The Fall armyworm has several characteristics that make it difficult to control. Apart from being a strong flyer, adult females are highly fertile, laying in excess of 1000 eggs during their lifetime. The Fall armyworm has a large host plant range that spans nearly 100 plant species in 27 families. Although polyphagous – the ability to feed on many plant species – the preferred hosts are grass based plants such as maize, sorghum, millet, rice, and sugarcane. The most damaging reports from its native range are for maize.
Another reason the Fall armyworm is difficult to manage is because of its tendency to build up resistance to pesticides. There have been efforts to curb its devastating effect by planting BT-maize. But this remains highly contested territory in many African countries. The Fall armyworm has been reported to cause annual losses of US$600 million in Brazil alone. Caterpillars also feed on other important crops, such as cowpea, potato, and soybean. At this stage we know little about the potential impact on crops in Africa. But the fear is that it could be devastating.
Given the severe economic threat that the Fall armyworm poses, governments and international bodies are putting in place emergency plans. These include monitoring with pheromone traps to determine the spread of the Fall armyworm, road shows to increase public awareness and emergency registration of pesticides. Eradication of the Fall armyworm at this stage is unlikely. Control of the pest will be best achieved if managed on an international scale with southern African countries coordinating their efforts.
As is amply evident from the extract above, the Fall Armyworm is no ordinary insect. One of the measures taken to combat it in southern Africa, where it unleashed havoc on an transnational scale was the mobilization of the Zambian Air Force in December 2016. As many as 124,000 hectares of cropland had been devastated. Hit hard by the infestation, the country put pilots in charge of the pest control exercise. Given below is a FAO report , ‘Fall army worm outbreak, a blow to prospects of recovery for southern Africa’ examining in detail the aftermath of the ‘plague’ (dated February 3, 2017):
A fall armyworm outbreak, the first emergence of the pest in southern Africa, is causing considerable crop damage in some countries. If the pest damage aggravates, it could dampen prospects for good crop harvests that is anticipated in the current farming season. Maize, a staple food in the region has been the most affected, as well as other cereals including sorghum, millet and wheat. Southern Africa is reeling from the effects of two consecutive years of El Nino-induced drought that affected over 40 million people, reduced food availability by 15 percent and caused a cereal deficit of 9 million tonnes.
The FAO Subregional Coordinator for southern Africa, David Phiri, said that the situation was constantly evolving. “The situation remains fluid. Preliminary reports indicate possible presence (of the pest) in Malawi, Mozambique, Namibia, South Africa, Zambia and Zimbabwe. Zimbabwe has positively identified the presence of the pest while the rest are expected to release test results soon,” he said. In Zambia, the Government has already spent US$ 3 million in an attempt to control the pest that has affected approximately 130 000 hectares of crops. However, the full extent of the damage in the country and other affected countries, is yet to be established. The pest which primarily spreads through wind dispersal and host plant products, is reported to be still active. The affected countries are also in different stages of assessing the damage to the crops because the outbreaks did not occur simultaneously.
Fall armyworm is a relatively new pest from the Americas, whose presence on the African continent was first reported in Sao Tome and Principe around January 2016. The pest is known to cause extensive crop losses of up to 73 percent depending on existing conditions and is difficult to control with a single type of pesticide, especially when it has reached an advanced larval development stage. FAO, in partnership with the Southern African Development Committee (SADC) and the International Red Locust Control Organization for Central and Southern Africa (IRLCO-CSA), is organizing an Emergency Regional Meeting of key stakeholders from 14 to 16 February 2017 in Harare, Zimbabwe.
Image Attribution: The image above, sourced from Wikimedia Commons, shows a female Fall Armyworm Moth. It was uploaded by Andy Reago and Chrissy McClarren.
- ‘Why it’s hard to control the Fall armyworm in southern Africa’, ‘The Conversation’ (by Kerstin Kruger, dated February 14, 2017)
- ‘Fall army worm outbreak, a blow to prospects of recovery for southern Africa’, FAO (dated February 3, 2017)
- ‘Fall armyworm’ attacks southern African crops’, DW, (by Thuso Khumalo, dated February 7, 2017)
- Bug Guide