So far, areas of Rajasthan, Madhya Pradesh, Maharashtra and Uttar Pradesh have witnessed the ravages of desert locust swarms. Reports say that the swarms may head towards the national capital of New Delhi. Usually, desert locusts are seen in western Rajasthan and Gujarat between June and November. However, this year, unusually, these insects were seen as early as April, as reported by Locust Warning Organization (LWO), which falls under the Ministry of Agriculture & Farmers' Welfare. What is also cause for concern is that the desert locust are generally alone or in small groups.
The current swarms are unusual and are alarming, because locust swarms can cause serious threat to food crops. These swarms can devour on crops that is enough to feed roughly 2,500 people a year, according to the United Nations’ Food and Agriculture Organisation (FAO).
How locust swarms are formed
Locusts are grasshoppers from the Acrididae family. These insects usually exist as solitary species or in small groups. But, if breeding conditions are favorable, they can multiply and also change their behaviour. From solitary pests, they turn into gregarious hordes.
The swarm behaviour of this insect species is purely related to overcrowding. When the desert locusts meet, their nervous system release a special type of hormone known as serotonin which causes them to get mutually attracted. This is a prerequisite for the formation of huge swarms. Not only do they exhibit behavioral changes that are observable in overcrowding, morphological changes also occur. They change their body color as well.
Swarms of locusts can be formed by as many as ten billion individuals and can stretch over hundreds of kilometers. The metamorphosis of locusts from solitary to gregarious also make them nomadic, and they can cover as much as 200 kilometers a day. On their way, they make halts in areas of green cover and can devour a variety of crops, including food crops, thus devastating swathes. They have been called one of the most dangerous migratory pests in the world.
Climate change a cause for swarms?
The current swarms in India may be traced back to the devastating swarms in East Africa that have ravaged the region over the last couple of years. The cyclonic storms that hit Oman and Yemen in 2018 facilitated locust breeding, since a lot of rain water was dumped in the desert of Oman. The infestation that occurred in the Arabian Peninsula invaded Eastern Africa and the concomitant heavy rains in these parts further facilitated their breeding. From there, they invaded Iran and Pakistan in 2019.
Keith Cressman, senior locust forecasting officer of the FAO, told Reuters: “We know that cyclones are the originators of swarms – and in the past 10 years, there’s been an increase in the frequency of cyclones in the Indian Ocean Normally there’s none, or maybe one. So this is very unusual. It’s difficult to attribute to climate change directly, but if this trend of increased frequency of cyclones in Indian Ocean continues, then certainly that’s going to translate to an increase in locust swarms in the Horn of Africa.” There were two cyclones in the year 2018 and nine in 2019.
The increased cyclones are attributable to a phenomenon called “The Indian Ocean Dipole” (IOD). A result of this phenomenon is an irregular oscillation of sea surface temperature. The western Indian Ocean becomes warmer than average and results in greater precipitation. This is accompanied by a corresponding cooling observed in the eastern Indian Ocean. This phase oscillates; opposite cycles of warming and cooling in the western and eastern parts takes place.
The IOD caused droughts in the land areas adjacent to the ocean during the cooling phase in these areas. Australia and Indonesia witnessed droughts due to the IOD. The IOD also caused higher than average rainfall in East Africa during the positive phase of the IOD. A positive phase means greater than average sea surface temperature and greater rainfall. In fact, the devastating bush fires in Australia in 2019 and the terrible flood in East Africa is linked to the phenomenon.
The IOD phenomenon is said to be happening on a more frequent basis and adopting a more extreme form. Global warming has super-charged such activity in the Indian Ocean.
Global warming has caused a serious threat to climates. Though the ravaging locust swarms in many places of the world is not directly linked to global warming. But, it has surely helped these swarms gather momentum and expanse.