Nepal | July 11, 2020

Locust swarms enter Nepal: What do we know?

Himalayan News Service
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Kathmandu, June 30

Amid the coronavirus pandemic, the swarms of locusts entering the country has added stress to farmers raising fear of famine amongst people.

The insects were seen in Nepal way back in 1962 when the swarms had attacked crops in Kathmandu, Nuwakot, Dhading and a few other districts causing huge damage.

And the current incoming of locusts from India has also drawn attention of many for the threat they possess due to eating everything available.

While India is witnessing its worst locust invasion in decades, Nepal is yet to see the impacts the swarms will cause here.

Swarms of locust have already been seen in Sindhuli, Bara, Parsa, Sarlahi and Rupandehi.

Understanding locusts

Locusts are part of a large group of insects called grasshoppers which have big hind legs for jumping.

Locusts belong to the family called Acrididae. The desert locust is one of about a dozen species of short-horned grasshoppers (Acridoidea) that are known to change their behaviour and form swarms of adults or bands of hoppers (wingless nymphs). The swarms that form can be dense and highly mobile. These swarms spread across regions, devouring crops and leaving serious agricultural damage in their wake.

Plagues of locusts have devastated societies since the Pharaohs led ancient Egypt, and they still wreak havoc today, according to National Geographic. Locusts are termed as the oldest migratory pests in the world by the Food and Agriculture Organisation (FAO), while the desert locusts are regarded as being the deadliest of them all.

Behaviour and swarming

Most of the time, locusts exist in their grasshopper phase — they lead solitary lives, they are green and pretty unremarkable, according to the NPR. And they can live alone for years. But when environmental conditions are right — usually when there’s a lot of rainfall and moisture — they increase in numbers and sense one another around them — known as the gregarious phase of the locust. They can become gregarious at any point in their lifecycle.

According to FAO, as desert locusts increase in number and become more crowded, they change their behaviour from that of acting as an individual (solitarious) insect to that of acting as part of a group (gregarious).

National Geographic adds that during the gregarious phase locusts can even change colour and body shape. Their endurance increases and even their brains get larger.

The gregarious locusts form bands of wingless nymphs which later become swarms of winged adults. Both the bands and the swarms move around and rapidly strip fields and cause damage to crops.

Locust swarms can vary from less than one square kilometre to several hundred square kilometres.

There can be at least 40 million and sometimes as many as 80 million locust adults in each square kilometre of swarm.

The adults are powerful fliers — they can travel great distances, consuming most of the green vegetation wherever the swarm settles.

They can cover vast distances — some species may travel 81 miles or more a day. They can stay in the air for long periods, regularly making nonstop trips. In 1954, a swarm flew from northwest Africa to Great Britain, while in 1988 another made the trek from West Africa to the Caribbean, a trip of more than 3,100 miles in just 10 days, as per the National Geographic.

Locust plague

According to FAO, there is no evidence that locust plagues occur after a specific number of years. Instead, plagues develop intermittently.

Plagues of locusts have been reported since the Pharaonic times in ancient Egypt. The ancient Egyptians carved them on their tombs and the insects are mentioned in the Iliad, the Mahabharata, the Bible and the Quran.

During this century, desert Locust plagues occurred in 1926-1934, 1940-1948, 1949-1963, 1967-1969 and 1986-1989.

Swarms have devastated crops and been a contributory cause of famines and human migrations.

The swarming behaviour decreased in the 20th Century, but despite modern surveillance and control methods, the potential for swarms to form is still present, and when suitable climatic conditions occur and vigilance lapses, plagues can still occur.

Desert locusts

Desert locust adult can consume roughly its own weight in fresh food per day, that is about two grams every day. A one square kilometre size swarm contains about 40 million locusts, which eat the same amount of food in one day as about 35,000 people. This is based on a person eating an average of 2.3 kg of food per day, according to the FAO.

A swarm the size of Niamey (Niger) or Bamako (Mali) eats the same amount of food in one day as half the respective country, as per the FAO. A swarm the size of Paris eats the same amount of food in one day as half the population of France; the size of New York City eats in one day the same as everyone in New York and California; the size of Rome eats the same of everyone in Kenya; the size of Sydney (Australia) eats the same amount of food in one day as Australia eats in 1.5 hours, adds FAO.

Found in Africa, the Middle East, and Asia, this species inhabits an area of about six million square miles, or 30 countries, during a quiet period. During a plague, when large swarms descend upon a region, however, these locusts can spread out across some 60 countries and cover a fifth of Earth’s land surface. Desert locust plagues threaten the economic livelihood of a tenth of humans.

Locust and ecology

When conditions are favourable for reproduction, locust numbers increase and when they are not, numbers decrease either by natural mortality or through migration.

For the desert locust, favourable conditions for breeding are — moist sandy or sand/clay soil to depths of 10-15 cm below the surface, some bare areas for egg-laying, and green vegetation for hopper development. Often favourable conditions may exist in the desert but there are no locusts present.

Therefore, the presence of moist soil and green vegetation does not automatically mean that there are locusts around. Weather patterns and historical locust records help experts predict where swarms might form. Once identified, an area is sprayed with chemicals to kill locusts.

According to the National Geographic some experts worry that locust plagues will worsen in a warming world. Rising sea temperatures are causing prolonged bouts of wet weather, including a surge of rare cyclones in eastern Africa and the Arabian Peninsula where desert locusts thrive.

Current upsurge

The current locust infestation in Africa, the Arabian Peninsula, South Asia and South America is an outbreak of desert locusts which is threatening the food supply across the region. The outbreak is the worst in 70 years in Kenya and the worst in 25 years in Ethiopia, Somalia and India. The plague began in June 2019 and has continued through 2020.

The current upsurge began to slowly develop two years ago as a result of two cyclones that brought heavy rains to the Empty Quarter in the Arabian Peninsula in May and October 2018, as per FAO. This allowed an unprecedented three generations of breeding to occur during a period of nine months that caused locust numbers to increase 8,000-fold.

In Spring 2019, swarms spread from these areas, and by June 2019, they spread north to Iran, Pakistan, India and south to East Africa, particularly the Horn of Africa. By the end of 2019, there were swarms in Ethiopia, Eritrea, Somalia, Kenya, Saudi Arabia, Yemen, Egypt, Oman, Iran, India, and Pakistan.

By June, another swarm appeared in South America, affecting Paraguay and Argentina as well.

— Compiled


A version of this article appears in e-paper on June 30, 2020, of The Himalayan Times.


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