India is currently facing its worst locust attack of the last 27 years. States like Rajasthan, Punjab, Haryana, and Madhya Pradesh are all facing crop damage due to the early arrival of desert locust swarms. It is speculated that the 2019 cyclones in countries like Kenya, Somalia, Ethiopia, and Sudan causing widespread rainfall led to the early breeding of locusts.
Locust is the name given to the swarming phase of certain short horned grasshoppers. These locusts are generally solitary, but suitable climatic conditions and other factors cause them to become more abundant and alter their behavior and habits to enter the gregarious phase. Meaning, the term locust is used to refer those grasshopper species that under certain conditions have behavioural and morphological changes and enter swarming, crowding etc.
Locusts can form large groups known as swarms. These swarms tend to migrate and feed on available vegetation in a specific area. One of the major differences between solitary and gregarious locust is their behaviour.
Watch a report by CRUX on the recent Locust attack.
Solitary locusts, as the name suggests, reside on their own, try to avoid each other and fly at night. Also, the solitary locusts are green in colour. The changes that can be noted in locusts that are about to swarm is their behavior and their growth patterns (i.e. if they are still nymphs, they grow differently). These adults are multi-coloured, e.g. with black, pink and yellow areas. They are called gregarious forms. The adults in this case are larger, have different body proportions and mature more rapidly, reproducing earlier. The offspring of a gregarious mother may be solitary or gregarious. This decision is made by the mother. A protective foam around the eggs may make the eggs into gregarious nymphs.
Locust swarms act as cohesive groups. Even if one of them is left out of the group, it flies back into the swarm. They spend most of their time feeding and resting. Even through adulthood they remain together, moving from one vegetation to another. Farmers are the ones who suffer the most. A locust attack could easily destroy acres of vegetation.
WHY DO LOCUSTS SWARM ?
Swarming, as discussed earlier, is a behavioral change that occurs in the locust. Any change requires a stimulus. The stimulus could be touch, smell or sight. According to the scientists of Oxford University the most potent stimulus is touch. Locusts have touch receptors all over their body but the receptor in their hind leg is especially important.
Swarming can be attributed as a part of polymorphic changes that occur in the life cycle of a locust. Swarming is usually triggered by overcrowding. The touch receptor, especially in the hind legs, gets stimulated and causes an increased serotonin production. This in turn causes the locust to change colour, eat more and breed more.
The meeting of desert locusts causes the release of serotonin by their nervous systems. The enhanced production of serotonin is crucial for swarming as it causes mutual attraction between them. Scientifically speaking, the solitary locust transforms into gregarious phase due to the several contacts per minute over a period of four hours. The sheer number of locusts in a large swarm can be in the billions as there might be a population of up to 80 million per square kilometer. Usually a large swarm is spread out over an area of thousands of square kilometers.
Controlling such a huge upsurge of locusts is not easy. Over the years different control techniques have been used by the farmers from ploughing the field with locust eggs to the use of pesticides and ultramodern technologies such as GPS and GIS tools.
One such method of controlling the locusts that is efficient is the use of a biological pesticide, Metarhizium acridum. The dried fungal spores when sprayed in the breeding areas cause the death of the locust by piercing the exoskeleton and entering the body cavity. This fungal effect is transmitted from insect to insect and hence, provides a continuous benefit to the farms. There is no need for repeated applications. This method was used across Africa to stop locust swarms.
Although locusts cause no harm to humans physically, their control becomes necessary in farming lands. The main aim of locust control is to make agricultural production easier and more secure in the many regions where growing crops is of vital importance to the survival of the local people.
Food and Agricultural Organisation of The United Nations has predicted that the locust invasion may continue in consecutive events until July across Rajasthan, and Northern India as far as Bihar and Orissa. But after July, there could be westward movement of swarm returning to Rajasthan in association with the changing winds of southwest monsoon.