POST TIME: 24 January, 2019 00:00 00 AM / LAST MODIFIED: 23 January, 2019 11:56:45 PM
Armyworm set to swarm croplands
Insect spotted in 16 districts
Anisur Rahman Khan, Dhaka

Armyworm set to swarm croplands

A new destructive worm, aptly called ‘fall armyworm’, is posing a big threat to farmers in Bangladesh and may even cause a famine-like situation, leaving farmers without any grain because of its massive destructive power. Scientists have identified the presence of this worm in 36 upazilas of 16 districts in the country.

The districts are Rajshahi, Chapainawabganj, Naogaon, Pabna, Kurigram, Lalmonirhat, Nilphamari, Rangpur, Gaibandha, Bogura, Sirajganj, Manikganj, Chuadanga, Jessore, Jhinedah and Moulvibazar.

The fall armyworm cannot be killed with chemical pesticides. They can only be controlled by applying bio-pesticides, but cannot be eradicated fully, scientists told The Independent yesterday.

The fall armyworm, the scientific name of which is Spodoptera frugiperada, is widely spread in many Asian countries like India, Sri Lanka, Nepal, Thailand and Myanmar. Bangladesh will face an epidemic if the spread of this pest is not controlled at an early stage.

The scientists said that the damage caused by the fall armyworm was very high. They can destroy crops overnight.

If not well controlled, the fall armyworm can cause significant damage to crops in its larvae stage. It prefers maize, but can feed on more than 80 additional species of plants including rice, sorghum, millet, sugarcane, vegetables, and cotton.

The researchers found that it can damage up to 350 species of plants.

In Bangladesh, over 100 parasitoid species have been recorded from pests of different horticultural plants, agricultural crops, including rice, jute, and sugarcane, as well as from stored product insects.

Insects like stem borer, maize earworm, black cutworm, maize aphid, maize pink stem borer, rice weevil, maize weevil, mayfly, wasp, dragonfly, butterfly, waters strider, scarab, beetle grasshopper, termite, housefly and silverfish are harmful to crops and damage production.

More than 208 different types of crops are cultivated in Bangladesh.

“It can fly a hundred kilometres from its birthplace every night. It can even fly 400–500km in favourable high winds,” Syed Nurul Alam, director of the entomology division at the Bangladesh Agricultural Research Institute (BARI), told The Independent yesterday.

Such worms could cause famine if not controlled, he said, adding, “We have already informed the Department of Agricultural Extension (DaE) for taking pre-cautionary measures against the devastating worm. We are discouraging farmers from using chemical pesticides as they are ineffective. Rather, farmers can use bio-pesticides.”

He said BARI has already supplied technology to the DaE including the pheromone trap. “Crop fields should be kept clean. Farmers have to continue irrigation activities in their fields. Besides, they can use pheromone traps to collect the worm,” he added.

He also said the government was aware of the presence of the worm. “The massive destructive fall armyworm has been identified for the first time in Bangladesh. We have already organised several awareness workshops across the country. We are also working to make special pheromone traps so that the worm gets attracted to them,” he added.

The female moth can lay up to 2,000 eggs in her lifetime, he said. “The destructive worm loves to eat maize and lay their eggs under the leaves of plants. It can lay at least 200-400 eggs at a time,” he added.

Alam warned that this worm could pose a risk to Bangladesh, if timely steps were not taken. “A massive attack by this worm would be disastrous. So, input supply lines should be set up instantly,” the BARI researcher observed.

According to Alam, seven states of India, including Karnataka, Tamil Nadu, Odisha and West Bengal, have already been attacked by this insect. The pest has invaded 70 per cent of the maize fields, resulting in a 20 per cent drop in crop yields in these regions.

The matured worm is more destructive, the BARI scientist said, adding, “Many African countries were affected in 2017 by the fall armyworm, which caused for famine due to a huge damage of crops.”

Fearing a possible spread of the pest, the DAE has already issued an alert and asked farmers to remain vigilant, Zakia Begum, deputy director of the DAE’s plant protection wing, told this correspondent.

“The worm can be a cause for famine as it destroys all plants in a crop field overnight, leaving the farmers as total losers,” she said.

The DAE has organised workshops and courtyard meetings in 14 regions to create awareness regarding the destructive pest, she added.

She said they advised farmers to use the hand-pick method and destroy the leaves of plants on which the pest lays its eggs.

The fall armyworm was a strong flier, and travelled long distances annually during the summer months, she observed.

“All plant quarantine offices under the DAE have been alerted. Our officials are regularly monitoring the situation. We have already received 500 pheromone traps from the BARI; these have been distributed in pest-identified areas,” she said in reply to a query.

Zakia also said that regular observation was needed regarding the worm and any lapse could prove disastrous. “We have also told farmers to spray bio-pesticides SNPV (Nuclear Polyhedrosis Virus) on the worm-affected plants after mixing it with water,” she added. According to the DAE, maize production and cultivation doubled in Bangladesh over the last seven years. The country produced 15.52 lakh tonnes of maize in 2010–11. The production rose to 35.16 lakh tonnes in 2016–17.

According to an estimate, 85 per cent maize produced in the country is used in the poultry sector, 10 per cent in fish feed and the remaining 5 per cent is used for fodder and human consumption.

The country’s annual demand for maize is five million tonnes. However, the country can only produce 70 per cent of its total demand. Around 1.2–1.5 million tonnes are imported from India, Egypt, and other countries, according to DaE sources.

The fall armyworm is native to the tropical regions of the western hemisphere from the United States to Argentina.

The fall armyworm is a prime noctuid pest of maize on the American continents, where it has remained confined despite occasional interceptions by European quarantine services in recent years.

The pest has currently become a new invasive species in West and Central Africa, where outbreaks were recorded for the first time in early 2016. The presence of at least two distinct haplotypes within samples collected on maize in Nigeria and São Tomé suggests multiple introductions into the African continent.

Another feature that makes it an incredibly successful invasive species is its ability to spread and reproduce quickly. The lifecycle of the fall armyworm, which includes eggs, six growth stages of caterpillar development (instars), pupa and adult moth.

Day 1–3.

About 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. When populations are high, the eggs may be laid higher up the plants or on nearby vegetation.

Day 3–6

Growth stages 1–3: After hatching, young caterpillars are feed superficially, usually on the undersides of leaves. Feeding results in semitransparent patches or “windows” on the leaves. Young caterpillars can spin silken threads that 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. If the plant 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. Feeding is more active during the night.

Day 6–14

Growth stages 4–6: By stages 4–6, the fall armyworm 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. Often only one or two caterpillars are found in each whorl as they become cannibalistic when they become larger. They will eat each other to reduce competition for food. Large quantities of frass (caterpillar poo), which resembles sawdust, will be present.

Day 14–23

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, the caterpillar will cover itself in leaf debris before pupating. After approximately eight to nine days, the adult moth emerges to restart the cycle.