Locust swarms: How can they be warded off?

In May 2019, when the Union and state governments were caught off-guard by the locust attack, their response was to pass the buck. Union Minister of State for Agriculture Kailash Choudhary during his visit to the affected areas blamed Pakistan, while the Rajasthan government complained that the Centre had not provided any help to control the menace.

But the fact was that since the last major locust upsurge in 1993, both the state and the Union governments had become complacent.

“Locust Warning Organization (LWO) was on the verge of getting disbanded because no locust attack had happened in over two decades,” said a district agriculture official, who does not wish to be named.

As on June 2018, as many as 117 of the 250 positions were lying vacant across its 12 circle offices. “This time we were prepared,” said KL Gurjar, deputy director, LWO.

“Now we have more than 200 staff personnel. Last year, we had just 45 vehicles. Now, we have placed an order for 55 control vehicles and 60 ultra-low-volume spray vehicles,” he added.

LWO has also improved its monitoring system and uses the eLocust2 device developed by the Food and Agriculture Organization (FAO) to monitor the movement of swarms on a real-time basis.

Locust officers on the field enter all survey and control-related data into the handheld device which then transmits the information via satellite. This is complimented by the village level data provided by agriculture supervisors, farmers and revenue officials.

However, there do not appear to be many changes in the insecticides being used. In 1993, during the last locust upsurge, LWO used benzene hexachloride (BHC), dieldrin, fenitrothion and malathion.

While the use of BHC and dieldrin stopped after the government banned them, malathion is now the preferred insecticide by LWO. Agriculture officials who accompany them during control operations mostly use chlorpyrifos and lambda cyhalothrin.

Surprisingly, on May 14, 2020, the Union Ministry of Agriculture and Farmers’ Welfare issued a draft proposal on the ban of 27 insecticides likely to “involve risk to human beings and animals”. The list includes malathion and chlorpyrifos.

Though the ministry said the insecticides can be used on locusts, it does highlight the toxic effects of the chemicals on human health and the environment. During the five weeks till June 7, LWO used 70,700 litres of malathion during operations over 71,000 hectares across 43 districts. Between May last year and February this year, LWO used 302,686 litres of malathion.

The use of insecticides in such huge quantities has raised an alarm among many. MS Swaminathan, the father of the Green Revolution, on June 3 took to Twitter and said: “The #locust menace is causing serious damage to agriculture. Farmers are worried. The best way to control locust invasion is to spray neem seed decoction over plants. Neem is a strong repellent and fertiliser. I hope our farmers will manage the serious threat to crop security.”

Biswajeet Paul, principal scientist at the Indian Agricultural Research Institute, said the volume of insecticides currently used is atrocious. Fire engines spray bigger droplets that hold large amount of pesticides.

This will cause severe pollution. “Unfortunately, spraying chemical insecticides is the only effective method when desert locusts are in such large numbers,” said Keith Cressman of the FAO at a webinar by Down To Earth. However, experiments over last three decades show promise.

Bio-control methods

At present, there are three major contenders. One is the spores of fungus Metarhizium acridum. When it falls on the locust, it germinates and penetrates the body of the insect. It then kills the insect both by expanding its filaments and releasing toxins on the insect.

Some 70 to 90 per cent of locusts treated with it die within 14 to 20 days. In 2009, FAO recommended the use of Green Muscle, a Metarhizium biopesticide by the International Institute for Tropical Agriculture.

This year, the FAO ordered four tonnes of it to treat 80,000 ha in Somalia. The fungus has also been used in Australia, Brazil, China, and African countries like Tanzania.

Locust pheromone and phenylacetonitrile can also be used to control the swarms. It governs swarming behaviour in adult males who use it to warn other males to leave them in peace while they mate.

When a minute dose is used on juvenile hoppers, it instructs them to resume solitary behaviour. It is, however, still being experimented with. It has been found that exposure to this chemical confuses the insects who often show cannibalistic behaviour.

Then we have chemicals that work as insect growth regulators (IGRs) that hinder the ability of hoppers to moult and grow properly. Ingredients of the neem tree come in this category. Its chemicals are similar to the shape and structure of a locust’s own hormones.

When a locust’s body absorbs neem compounds, they block its endocrine system and affect its behaviour and physiology. They fail to reproduce and their populations plummets. Lab experiments show neem oil can also induce “solitarisation” among them. As neem trees grow well in locust-affected areas, the oil required to control the swarm can be locally produced.

There are very few takers for these methods despite proven effectiveness and low cost. Locusts attacks are only going to increase with changing climate. It’s time we got our ammunition right.

Toxic tale Four to five times more insecticides are needed to kill locusts than for other pests CHLORPYRIFOS It belongs to the class of organophosphates, which are essentially nerve agents, attacking chemical pathways and causing a breakdown in the ability of nerves to communicate. One can be exposed to it by inhaling, eating or getting it on the skin. Being moderately persistent in soil, it can take weeks to years to break down, can reach rivers, lakes and streams where it accumulates in the fatty tissue of fish. In surface water in urban areas and in agricultural areas, it has been found at levels potentially harmful to aquatic life. Its use is not approved in the European Union. LAMBDA CYHALOTHRIN It belongs to the class of pyrethroid insecticides, which are known for moderate acute toxicity to humans and can cause irritation to the skin, throat, nose and other body parts. Some temporary symptoms of exposure includes skin tingling, burning and prickling feelings, particularly around the face. In severe poisoning cases, seizures and coma may occur. Its residue in agricultural or urban runoff sediment have been found to be toxic to aquatic organisms including fish and amphipods. MALATHION 96 Being an organophosphate pesticide, it can be absorbed by all routes. It can cause numbness, tingling sensation, headache, dizziness, difficulty breathing, weakness, irritation of skin, abdominal cramps and death, depending on the exposure level. EU recognises it as an endocrine disrupter. It is however highly toxic to honeybee, earthworms and leads to soil contamination.

This was first published in Down To Earth’s print edition (dated 16-30 June, 2020)

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