Introduction: As per media reports, dated May 9, 2020, scientists at the ‘Locust Warning Organisation’ (LWO) observed groups of grasshoppers at Sri Ganganagar and Jaisalmer districts of Rajasthan though in India, locusts normally arrive during July-October. These locusts were very different from ordinary hoppers, and belonged to desert locusts—the same destructive migratory pests, which devoured acres of maize, sorghum, and wheat crops in East Africa. At a time when India is battling Covid-19, they caused a new worry with their potential for exponential growth and crop destruction. Locust attack is also a challenge for India’s food security.
Where the Swarms Arrived From: As per a senior locust forecaster of the UN Food and Agriculture Organization, spring-bred swarms from Pakistan started arriving in Rajasthan earlier this month. As this is before the monsoon rains, they found dry conditions so they continued to move east in Rajasthan looking for green vegetation for food and shelter.
Normally locusts are seen in India mostly as solitary insects or in small isolated groups. But their presence along the India-Pakistan border before mid-April and the damage they caused to thegrowing rabi crops along western Rajasthan and parts of northern Gujarat, Madhya Pradesh and Vidharbha region of Maharashtra has been a matter of concern. The situation really raised alarm bells.
Reasons for Their Early Arrival: As for their early arrival in India, it can be traced back to the cyclonic storms Mekunu and Luban that had struck Oman and Yemen respectively in 2018. These turned large deserts tracts into lakes, facilitating locust breeding that continued through 2019. In East Africa, swarms attacked crops and reached peak populations from November. They built up in southern Iran and Pakistan in the beginning of 2020. And heavy rains in East Africa in March-April enabled their further breeding.
Breeding of Swarms: An important aspect of the problem is the breeding of swarms. An adult female locust lays 80-90 eggs thrice in her three-month life cycle. As an estimate, a swarm can grow exponentially to 40-80 million locusts per square kilometre if left uncontrolled. If the locusts start laying eggs and continue breeding for two more months, newer generations come into existence. Breeding is fast in their natural habitat, desert or semi-arid regions.
However, for laying eggs, they require bare ground, which is rarely found in areas with dense vegetation. Therefore, they can breed in Rajasthan but not in the Indo-Gangetic plains or Godavari and Cauvery delta. But green vegetation is required for hopper development, which is the stage between the nymph (hatched from the eggs) and the winged adult moth. Such cover isn’t widespread enough in the deserts to allow growth of large populations of locusts.
Understanding Locusts: The Schistocerca gregaria or the desert locust is a short-horned grasshopper that is harmless while it is in a ‘solitary phase’ and moves about independently. They differ from normal hoppers and become dangerous only when their populations build up rapidly. Close physical contact in crowded conditions triggers behavioural changes. They, then, enter the ‘gregarious phase’, i.e., group into bands and form swarms that can travel great distances up to 150 km daily, while eating up every bit of vegetation on the way. If not controlled, the insect swarms can threaten the food security of countries.
Damage Potential of Locusts: In India, the damage potential of locusts has been limited only because of a single breeding season. On the contrary, they also multiply during January-June in Pakistan, Iran and East Africa. The locusts’ bands are less populated, but their timing is a cause for concern. Normally, breeding season for locusts is July-October. But this time, they have been sighted by mid-April. They were seen towards end-May as isolated grasshoppers last years also. The longer breeding time is more conducive for a build-up of gregarious insect swarms, as opposed to solitary, innocuous hoppers.
Locust Warming Organisation (LWO): India has a Locust Control and Research scheme, implemented through the Locust Warning Organisation (LWO), which was set up by the British colonial government in 1939. It was merged with the Directorate of Plant Protection Quarantine and Storage (PPQS) of the Ministry of Agriculture in 1946. Monitoring and controlling the locust situation in Scheduled Desert Areas, especially in Rajasthan and Gujarat, and partly in Punjab and Haryana is the responsibility of LWO. In this regard, the LWO publishes a fortnightly bulletin on the locust situation.
Locusts can feed on a wide variety of crops, i.e., they are polyphagous. They have the ability to multiply rapidly, and lay 60-80 eggs thrice, during its roughly 90-day lifecycle. About 40-80 million of these insects can be accommodated in a 1-square-km area, growing at an exponential rate.
How to control Locusts?: To control the menace, the Agriculture Ministry uses a website, which provides considerable details of the problem of locust control and plant protection through current methods of handling them. The Directorate of Plant Protection, Quarantine and Storage has a website at the ministry, which details the contingency plan for desert locust invasions, outbreaks, and upsurges.
Control also involves spraying insecticide on locusts’ night resting places like trees. The LWO carried out spraying over 21,675 hectares in Rajasthan. India has put an order of 60 more specialised insecticide sprayers with the UK, whereas, the country already has 50 such machines. Moreover, drones will be used to spray the resting places.
Traditionally, locust control involves spraying of organo-phosphate pesticides on the night resting places of the locusts. The Indian Institute of Sugarcane Research, Lucknow, advised farmers to spray chemicals like fipronil, lambdacyhalothirn, chlorpyriphos, deltamethrin, or malathion to control the swarms. However, the Centre had on May 14 banned the use of chlorpyriphos and deltamethrin. Malathion is also included in the list of banned chemicals but has been subsequently allowed for locust control. Special mounted guns were used to spray the chemicals on the resting places.
International Scenario: Most of Africa, West Asia, Iran and even parts of Australia also face this problem. The Food and Agricultural Organization (FAO) is a part of the United Nations, and is based in Rome, Italy, which co-ordinates and helps these nations with advises and funds in combating this plague. The Locust Environmental Booklet is an informative document of FAO, which gives an update on the situation and methods of handling locust swarms. An excellent update (available online) on ‘locust swarm and its management’ has been published on May 29 by the International Crops Research Institute for the Semi-Arid Tropics’ (ICRISAT) Development Centre (IDC), based in Hyderabad.
The general method is ‘detect the swarm and kill it as it moves’, and is being used across the world. However, better and more innovative methods to fight this plaque should be emphasised to win over it.
Formation of Swarms: According to researcher, Stephen Rogers of Cambridge University, U.K. and University of Sydney, Australia, when solitary locusts happen to come near each other (looking for food) and happen to touch each other, this tactile stimulation, even just in a little area of the back limbs, causes their behaviour to change. This mechanical stimulation affects a couple of nerves in the animal’s body, their behaviour changes, leading to their coming together. And if more locusts come nearby, the crowding starts, and what was once a simple looking insect becomes larger in size and shape, and its colour and morphology also changes.
In another paper, his group showed substantial changes in some molecules that modulate the central nervous system of the locust, the most important among them being serotonin. This part regulates mood and social behaviour.
Thus, spraying serotonin inhibitor molecules may be effective in stopping swarms from being formed. These findings were published in the journal Science in 2009.
How to Solve the Problem?: In the absence of control operations, the magnitude of attack could be worse than in the 2019-20 rabi season, which was first and most significant since 1993. Local authorities in Rajasthan and Gujarat had to treat over 4.30 lakh hectares of infested areas with sprayers mounted on tractors and other vehicles. The old generation organophosphate insecticide, such as Malathion (96 per cent ultra-low volume aerial application) is effective against locusts. About one litre of the pesticide is necessary to treat a hectare of their breeding areas, including trees where they halt for the night. Apart from that, there is ample stock of pesticides to solve this problem. The techniques of aerial spray of insecticides (using drones these days), as well as spraying by land-based workers in the field are being used now and they show good results.