Excess rainfall in March, April and early May, along with north westerly winds due to Super cyclone Amphan carried locusts to areas they did not usually impact
The recent locust attacks in Rajasthan, Madhya Pradesh, Uttar Pradesh, parts of Gujarat and Haryana might be the result of excess rainfall in March, April and the first half of May, along with the prevalence of north westerly winds in the wake of Super cyclone Amphan.
For Madhya Pradesh and Uttar Pradesh, this has happened for the first time in 27 years. Super cyclone Amphan, that hit the West Bengal coast on May 20, 2020, changed the direction of winds over India because of its anti-clockwise circulation of winds and resulted in heat waves in northwest, central and peninsular India, according to the India Meteorological Department (IMD).
“Locusts are a genetic phase of the grass hopper which prevail under favourable environmental conditions. They emerge from the soil when there is rainfall as the eggs are laid there,” AK Chakravarthy, entomologist and former head of Indian Institute of Horticulural Research of the Indian Council of Agricultural Research in Bengaluru, said.
“Then, they move towards areas with green cover. The continued rainfall might have created these green patches along with cultivated farmlands in the regions which are now witnessing the swarms,” he added.
If there are winds in a specific direction, they will move along them and devour any green patches they find in their path. The north westerly winds might have brought them from Pakistan, which is facing one of its worst locust crisis, to Rajasthan and then to Madhya Pradesh and Uttar Pradesh.
The wind and rainfall have combined to provide the conditions for the movement of the locusts into areas that usually do not get impacted by them.
According to data from the IMD, Rajasthan has 25 districts with large excess rainfall (more than 60 per cent excess rainfall) from March 1 to May 25 while Madhya Pradesh has 39 districts with large excess rainfall.
These numbers for Uttar Pradesh and Haryana are 71 and 19 respectively. These constitute more than 90 per cent districts in these states.
“They generally prefer new tender leaves over old and drying leaves and plants as they contain proteins and carbohydrates that are easily digestible,” Chakravarthy said. The locusts are finding such young leaves wherever they are moving.
The Food and Agricultural Organization of the United Nations in its latest locust bulletin on May 21 said the insects’ spring breeding has continued in Iran and southwest Pakistan and that they will be moving to the India-Pakistan border till at least early July.
The FAO bulletin also says that rainfall in early June along the India-Pakistan border will aid in egg laying of the locusts. This, it pointed out, will limit the further eastward spread of the locusts that has not happened as the swarms have moved further east.
The rising heat and heat waves in the affected regions will also not impact the locusts as they can survive in hot and water scarce conditions.
“This is because locusts store energy in the form of lipids which contain water. They can depend upon water released when lipids get digested to tide over water stressed conditions that can result from higher temperatures,” Chakravarthy said.
Their rate of metabolism (rate at which they digest food) also increases with increasing temperatures, making them even more dangerous. This also means that rising temperatures and global warming can make locusts much more potent.
Half a million locusts can weigh approximately one tonne and these can eat as much food in one day as about 10 elephants, 25 camels or 2,500 people. A large locust swarm can range up to 150 million per square kilometre. A one square kilometre swarm is capable of eating the food of 7,50,000 people or 3,000 elephants in a day.
From December 2019 to February 2020, locusts had attacked many parts of Rajasthan, Gujarat and Punjab mainly because of an elongated and intense southwest monsoon season till October and even early November. Unseasonal rainfall in Rajasthan in May 2019 might have aided their arrival in India from Iran via Afghanistan and Pakistan.
The locusts had travelled to Iran from the Arabian peninsula where they had grown to large numbers due to an unusual cyclone season in 2018. The cycle seems to be never ending and deadly.
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