The year of the locust

TV Jayan | Updated on June 05, 2020 Published on June 05, 2020

City under siege: The locust invasion in Rajasthan several weeks before the monsoon has surprised farmers   -  PTI

The dreaded crop raiders have already paid an unscheduled visit, but experts warn that more insect invasions are in store

*A locust onslaught was expected with the monsoon, not in early May

* Locusts had visited the state last year too

When millions of buzzing locusts descended on parts of Rajasthan last month, the invasion evoked more surprise than fear among farmers. A locust onslaught was expected with the monsoon, not in early May. With the last of the grains harvested and safely stashed away, desert locusts — dreaded crop raiders that they are — could not wreak widespread damage, but still caused some harm.

“I had never seen locusts this early in Rajasthan,” says Churu farmer Chaganlal Choudhary, general secretary of the state unit of the All India Kisan Sabha. The insects destroyed newly sown crops in more than a dozen Churu villages before authorities controlled them by spraying insecticides, he adds.

Locusts had visited the state last year. too, but had arrived, as was expected, with the monsoon winds. The damage to the crops was limited as the Centre and the state governments of Rajasthan and Gujarat were prepared for the onslaught. But their appearance last year was a warning, for typical locust incursions are rarely one-off events. The last major locust invasion the country witnessed was in 1993.

Extreme weather events associated with climate change may be a reason for the unseasonal locust visits, experts hold. The three back-to-back severe cyclones that hit the region around the Arabian desert from May 2018 could have played a part too, they add. “The situation has been developing over the last two years as a result of a number of cyclones hitting Middle Eastern [West Asian] countries,” says Keith Cressman, senior locust forecasting officer, Food and Agriculture Organization (FAO).

Jyoti Kumar Sharma, head of the School of Natural Sciences at Shiv Nadar University and a noted plant pathologist, concurs. “Soil moisture helps pests breed,” he says, pointing out that West Asian countries used to be hit by a cyclone once in five years. “In 2018, the region had three severe cyclones, which led to the formation of many lakes in the desert,” Sharma says.

The rains triggered by the cyclones provided the ideal warm and wet conditions for desert locusts to breed and band undetected in remote regions. The hatched locusts slowly moved east and west, to Iran and Pakistan as well as to East Africa, for further breeding. East Africa is currently facing one of its worst locust invasions with swarms threatening food security across nine countries.

The locusts which moved east, to southern Iran and south-west Pakistan, found ideal conditions for breeding last spring, Cressman says. Smaller waves of locusts that arrived in Rajasthan and Gujarat last year came from these breeding areas. “Ideally, those locusts should have gone back to Pakistan and Iran at the end of the monsoon. But, because of the prolonged monsoon in Rajasthan last year, temperatures remained low, and they could not move all the way back. As a result, many were stuck in parts of Rajasthan, Punjab and the Indus Valley in Pakistan,” he explains.

This, he says, presented a seed population to start off the season this year. It also explains why Rajasthan experienced a locust attack in early May. More swarms flew in from Balochistan and south-west Pakistan as vegetation had dried up early and rapidly there. Significantly, those that had crossed over were found to be young ones. “These yet-to-be-adult locusts are voracious eaters as they need to store up energy for reproduction and flying,” Sharma says. A locust, weighing nearly 2g, can eat vegetation that equals its weight. Massive locust swarms are typically several kilometres long and wide, with each square kilometre containing 40-80 million insects. According to FAO, each square kilometre of these swarms devours in a single day crops enough to feed 35,000 people.

But this isn’t the end of the story. The next wave of locusts from southern Iran is expected by mid-June. Smaller swarms from northern Oman are also expected to cross the Arabian Sea — the passive flyers wait to ride the monsoon winds to get to Sindh, Rajasthan and Gujarat, Cressman warns. Locust swarms are capable of travelling up to 150km a day, if wind conditions are favourable.

If these threats weren’t enough, fresh locust invasions are expected from East Africa, too. “Once swarms are formed in East Africa — which would be in the second half of June — they would move northward. Swarms that get into the north-eastern parts of Somalia will fly across the Arabian Sea and come to Gujarat, southern Sindh and Rajasthan. This migration is expected to occur in early July,” the FAO expert says. He, however, adds that though there can be significant damage to crops in areas that lie in the path of the swarms, there is no cause for panic.

India has one of the oldest locust warning systems in the world, dating back to the 1930s. The authorities are seized of the matter, says Cressman, who was in India in January to take stock of the situation. Measures to tackle the events appear to be in place; even in this challenging time of the pandemic, locust control teams are on ground. “We have placed orders with a UK firm for 60 aerial sprayers (for spraying insecticide) that can be mounted on aircraft and drones,” says KL Gurjar, deputy director, Directorate of Plant Protection, Quarantine and Storage, Faridabad.

These locust swarms are expected to travel with the monsoon winds all the way to Bihar and Jharkhand, but ultimately return to Rajasthan and other desert regions. “They are not comfortable anywhere other than the desert,” Cressman says.

Sharma, meanwhile, bemoans the lack of research on locust control. “India has not experienced a locust plague for several decades. The last plague cycle was in the early ’60s. Even though pesticide use may be inevitable if there is widespread crop damage, a better option would be to destroy the breeding grounds of locusts. This may require trans-boundary operations,” he says.

Interestingly, scientists have already understood how a neurochemical — serotonin — helps the otherwise solitary insects form swarms. In the future, science might offer a way to block serotonin signalling in locusts and prevent them from swarming. But that will have to wait. Till then, pesticides may be the only effective way to limit crop damage. And looking out for the insect with an eagle eye.

TV Jayan

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Published on June 05, 2020
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