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Ravaged by a caterpillar: on the armyworm invasion in India

More than a handful: Armyworm larvae in various stages of their lifecycle.   | Photo Credit: Sudhakara Jain

It is a hot day in September, and two men are prising open the leaves of maize in a field in Karnataka’s Chikkaballapur district. The crop is two months away from being harvested, but the leaves look diseased. Some have streaks of white on them, while others are peppered with holes. Soon, one of the men, entomologist Arakalagud Nanjundaiah Shylesha, spies the culprit behind these holes — a small greenish-brown worm with dark lines along its length and an inverted ‘Y’ on its head. It looks like any of the thousands of pests that infest fields in India each year, but this one is special.

It is the fall armyworm (Spodoptera frugiperda), a native of the Americas, which was first seen in Asia five months ago. Since its identification in the State’s Shivamogga district in May, the pest has reached as far as West Bengal and Gujarat.

Shylesha shakes half-a-dozen of the caterpillars into his hand. They are of different sizes, which means that they are at different stages, or instars, of the larval life cycle. There are six such instars in the fall armyworm’s life, and between the first and the last, its appetite changes dramatically. Within days, it turns from a light feeder into a voracious eater that can wipe out farms. After pupation, adult moths emerge. As Nanjundaiah carefully transfers the specimens into a plastic bottle, his colleague, Sampath Kumar, remarks, “Not even a single plant is without damage. Oh my god!”

Ravaged by a caterpillar: on the armyworm invasion in India

Nanjundiah and Kumar, who are researchers at the the National Bureau of Agricultural Insect Resources (NBAIR), in Bengaluru, are a worried lot. Karnataka is one of the largest maize producers in India, and maize is the third most widely produced cereal in the country. This isn’t the first time a foreign visitor is poised to wreak havoc on Indian farms. In 2008, the papaya mealybug, a central American native, entered the country and destroyed plantations in several States. Then, in 2014, the tomato pinworm, or Tuta absoluta, a South American moth, was spotted in Karnataka. Within a couple of years, it had reached Maharashtra, Gujarat, Delhi and other regions, where it caused widespread damage to tomato crop.

Such alien species which migrate to a new geography from their native lands can be a huge risk to both agriculture and wildlife. They could be insects, trees, weeds or viruses. Many of them tend to die out in new environments. Some become naturalised, like a few eucalyptus species have in India. Naturalised aliens maintain their population and do not pose a great risk to biodiversity.

But a small percentage of aliens, like the fall armyworm, turn invasive, which means they spread uncontrollably. The absence of natural predators from their original homes allows them to disrupt ecosystems and cause massive economic losses. In 2016, a paper published in Nature Communications, titled ‘Massive yet grossly underestimated global costs of invasive insects’, calculated that such attacks cost the world around $70 billion a year.

Such destruction is why countries take strong measures to prevent the entry of these pests. The first line of defence is a quarantine system, under which imports of grains and plants that can host such insects are inspected at shipping ports, airports and land border crossings. In India, this responsibility lies with the Directorate of Plant Protection, Quarantine & Storage, with its headquarters in Faridabad, Haryana. Unfortunately, many agriculture researchers say, the directorate is failing in its task of policing Indian borders. It is short-staffed and hamstrung by the lack of a strong legislation.

Voracious pests

The earliest published reports of widespread destruction by the fall armyworm come from Georgia, U.S. in the 18th century. One of the worst attacks occurred in 1912, and a farmer’s bulletin of the time describes it thus: “The pest swept almost the entire U.S. east of the Rocky Mountains, utterly destroyed the corn and millet in the southern U.S., severely injured cotton and truck crops, and destroyed grass on lawns in cities as if by magic.” The fall armyworm was known as a particularly voracious pest. Though it preferred maize, it ate nearly 80 other plants. Even today, when farmers have learnt to check damage with integrated pest management and genetically modified crops, it continues to be a major cereal pest in both North and South America.


So, nobody was particularly pleased when, in 2016, the pest turned up in the west African country of Nigeria. Initially, farmers confused it with another Spodoptera species native to the region. But as the situation grew worse, the alien visitor was identified. Today, two years later, the pest has spread to 43 countries on the continent. Nearly 200 million people here depend on maize for nutrition, and they are all at risk from the little brown caterpillar.

It is proving expensive to control. In June, the Food and Agriculture Organisation of the United Nations said it had invested $20 million in controlling the pest in Africa, and was looking for another $23 million. There are several reasons why the armyworm is thriving: it reproduces rapidly, and the continent’s tropical and sub-tropical climates allow it to feed all year round. In contrast, fall armyworms die in Canada’s frigid winters. So, each summer, new populations of the moth migrate to Southern Canada from warmer states in the U.S. like Texas. Such migration isn’t hard for them; the Spodoptera moth is known to be able to fly around 1,400 km. This is another reason why it spread so quickly to new countries after it landed on African shores.

But how did the armyworm get to Africa in the first place? Nobody knows. Researchers speculate that it might have hitched a ride in cargo containers on commercial aircraft or in someone’s cabin baggage. There is enough evidence that the pest is capable of this. According to the European Union Notification System for Plant Health Interceptions, Spodoptera frugiperda was intercepted 14 times by EU quarantine officers in 2017. It was caught piggybacking on all kinds of organic material — flowers from Kenya, bonnet peppers from Mexico, and cucurbits from Suriname, to name a few.

India’s quarantine system

To get into India, the fall armyworm would have either had to fly here, or make it past India’s plant quarantine system. This system is built around the Plant Quarantine (Regulation of Import into India) Order of 2003. The order, in turn, is notified under an Act that is over a century old: The Destructive Insects and Pests Act of 1914.


Under the Plant Quarantine Order, grains or plant material can come to India only through notified points of entry. These include 44 sea ports, 23 airports, 19 land frontier stations, as well as foreign post offices and container depots. Imports at each of these points is to be inspected by officers from the Directorate of Plant Protection. But this system isn’t watertight. The first problem is that the directorate lacks key experts at some of these ports, says Celia Challam Vasimalla, a biosecurity researcher at New Delhi’s National Bureau of Plant Genetic Resources (NBPGR). Some quarantine stations do not have nematologists (scientists who study roundworms) while others are missing virologists. When virologists are present, they may not have equipment such as ELISA testing kits for detecting viruses. This makes it likely that they will miss key pests.

There are also gaps in regulating the import of plant materials by individual passengers. Under the Quarantine order, around 2 kg of cut flowers and dry fruits are exempt, but any seeds or larger quantities of flowers must be accompanied by a certificate declaring that they are free of pests and microbes. If not, passengers arriving at international airports are required to declare them. Says Shylesha of the NBAIR, “99% of the people don’t do that. If they do, they will have to stand in line, and time is wasted.”

In 2012, in the wake of the papaya mealybug infestations across India, the then Director of NBAIR, N.K. Krishna Kumar, wrote to the Chief Secretary of Karnataka asking for quarantine systems to be strengthened at the internationals airports in the State (Bengaluru and Mangaluru). The letter asked for prominent signboards in airports warning passengers of the dangers of bringing exotic fruits and flowers into the country. It also asked for better training of plant quarantine officers and for providing them with equipment to detect dangerous species. Much of this hasn’t happened yet.

Not all airport quarantines systems are as ineffective as India’s though. The Australian Quarantine and Inspection Service (AQIS), for example, employs sniffer dogs to detect agricultural material on passengers. It also has scanners that can detect organic material such as seeds in baggage. Several Indian airports do not have this, says Vasimalla. When such items are found, stringent penalties are necessary. In 2002, Indian cricketers Harbhajan Singh and Saurav Ganguly famously paid fines of NZ $200 at Auckland airport in New Zealand for not declaring mud on their footwear. India would do well to adopt some of these practices, says Kavita Gupta, a biosecurity researcher, also from the NBPGR: “If other countries have done it, why can’t we?”

Time for a new law?

To be fair, however, Indian legislation is a stumbling block for quarantine officers. Because the Destructive Insects and Pests Act is subsidiary to the Customs Act, 1962, quarantine officers must wait for customs officers to flag suspicious goods before they can check them. In other words, quarantine officials do not have the power to search and seize in India. “But the customs officer may not suspect anything, because what they are looking for is entirely different. Their focus is on items such as gold and narcotic drugs. This is completely different from what a quarantine officer wants to examine,” Gupta points out.

As the pest spreads across the world, it is proving expensive to control it.

As the pest spreads across the world, it is proving expensive to control it.   | Photo Credit: Sudhakara Jain


In 2013, after widespread recognition of the lapses in the current quarantine system, a new Bill called the Agricultural Biosecurity Bill was tabled in the Lok Sabha. The Bill borrowed from some of the most stringent quarantine regimes in the world, such as the U.S., Australia and New Zealand. Unlike India’s Directorate of Plant Protection, Quarantine and Storage which comes under the Ministry of Agriculture, the U.S.’s Animal and Plant Health Inspection Service (APHIS) and AQIS are autonomous bodies. The Bill envisaged setting up a similar body in India, called the Agricultural Biosafety Authority of India. Quarantine officers would have wider powers under this Bill. And the authority could even penalise States for not following its directions in controlling an invasive species outbreak. But as of today, this Bill has lapsed.

Could a stronger quarantine system have prevented the fall armyworm from entering India? It is hard to say, because no system can stop the entry of new species with cent per cent effectiveness. The question is whether the risk of introduction is as low as possible. In response to this question, D.D.K. Sharma, plant security adviser, who heads the Directorate of Plant Protection, Quarantine and Storage told The Hindu that at least in the fall armyworm’s case, there wasn’t much that the Directorate could have done. According to him, the pest cannot survive in shipments of grains, because it needs fresh plant material to survive. “We hardly import any such material,” he said.

But Sharma’s statements contradict what other entomologists say. According to C.M. Kalleshwara Swamy from the University of Agricultural and Horticultural Sciences, at Shivamogga in Karnataka, this caterpillar has several stages in its life cycle, during which it does not need food to survive. Out of these stages, the pupal and adult moth stages can survive for days without food. Such pupae or moths could easily have hitched a ride on maize shipments into India, argues Swamy.

In 2018 alone, India imported 500 million tonnes of maize. Further, the experience of the European Union shows that armyworms can survive on fresh fruits and vegetables too. India’s imports of fresh fruits and vegetables are not high, but they are not non-existent either. According to the data from the Ministry of Food Processing Industries, in 2016-17, India’s imports of edible vegetables were worth $1,371 million.

The rise in invasives

Some researchers have argued that India has traditionally been extra vulnerable to invasive species because of its history of political invasions. From the Mughals to the British and the Portuguese, everyone brought their share of noxious weeds, insects and trees. Consider the case of the Lantana species, camara, which was first introduced by the British as an ornamental hedge in the 19th century. Today, it is widespread across India and threatens biodiversity by taking over forest understorey and grabbing resources from other species. Another invasive, congress grass, is thought to have piggybacked via wheat shipments from the U.S. under the 1950s PL-480 Food for Peace program.

But the entry of invasives has been rising the world over in the last few decades, and one likely reason is increased trade. Several studies have explored the link between the two. A 2007 analysis of invasive species present in 227 countries found that out of several factors such as a country’s population density and amount of cropland, it was the degree of international trade that best predicted the number of invasives.

In India, data from NBAIR list the entry of several invasive species since 2001: Australia’s eucalyptus gall wasp, Sri Lanka’s sapota seed borer, the South American tomato pinworm, and the papaya mealybug.

The papaya mealybug is among the most destructive. First reported in Coimbatore in 2008 by researchers from the U.S.’s Integrated Pest Management Collaborative Research Support Program, the bug spread all over the country quickly. In papayas, it caused a white cottony coating on the fruit and killed papaya trees. But it also survived on over 80 other plants, including mulberry, tapioca, hibiscus and several fruits. “You name the crop, and the mealybug was attacking it,” says Shylesha.

Within two years, the pest spread to over 50 hectares of mulberry in Tamil Nadu, the crop on which silkworms feed. According to one report, the Tamil Nadu silk industry saw cocoon productivity drop by over 60%. At first, farmers turned to chemical insecticides to control the pest. But the insect had a thick, waxy coating on its body, which resisted sprays. Worse, the insecticides were killing the handful of natural enemies the pest had in India, such as ladybird beetles.

Stung by the attack, the Central Silk Board began exploring the idea of classical biological control, which would require importing natural predators of the species from its native country. In this case, the country was Mexico. Eventually, together with the NBAIR, they imported three parasitoids, or insects whose larvae kill the mealybug. After experiments to test whether these parasitoids attacked other beneficial species in India, such as the mulberry silk worm and honeybees, researchers chose one of the three: a wasp called Acerophagus papayae.

Today, says Shylesha, the mealybug is mostly under control. But it did cause damage worth ₹1,500 crore every year to farmers during the early days. “And this doesn’t include the damage to the environment due to pesticide sprays.” There were things the Directorate of Plant Protection, Quarantine and Storage could have done to prevent the pest from spreading to other States after initial reports, such as imposing restrictions on the movement of plant material from Tamil Nadu. But such a “domestic quarantine” wasn’t imposed, he says.

In August this year, the directorate issued an advisory to the agricultural departments of the States affected by the fall armyworm. It called for extensive surveys to track the pest’s spread. It also named a parasitoid that could be released to kill the eggs of the caterpillar. Further, it also suggested pesticides against the armyworm, such as Lambda cyhalothrin, but cautioned that they shouldn’t be used simultaneously with the parasitoid.

But it is already too late for some farmers. One of them is S. Raghavendra, a 35-year-old, whose extended family owns the fields in Chikkaballapur that Shylesha and his team have been surveying. Very few maize stalks in the field are armyworm-free today.

When the caterpillar first showed up, Raghavendra visited an insecticide store and the shopkeeper suggested a few pesticides. “But every time I sprayed them, the pest would come back in a week,” Raghavendra said. Now, he fears that he might lose most of his income from his five acre maize farm. I ask him if he knows whether the caterpillar in his fields is a foreign visitor, never seen before in India.

He says he doesn’t, but has a question for me in return. “If this is a new pest, how long will it stay?” As I begin to answer, however, he completes the sentence — “probably forever.”

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Printable version | May 8, 2021 12:00:00 PM |

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