A new concern: early locusts

On April 11-12, scientists at the Locust Warning Organisation (LWO) observed groups of grasshoppers at Sri Ganganagar and Jaisalmer districts of Rajasthan. But far from ordinary hoppers, these were desert locusts — the same destructive migratory pests currently devouring acres of maize, sorghum and wheat crops in East Africa.

 

While locusts are seen in India as well, that is normally only during July-October and mostly as solitary insects or in small isolated groups. Their being spotted along the India-Pakistan border before mid-April this time — and coming after the damage they caused to the growing rabi crops along western Rajasthan and parts of northern Gujarat during December-January — has raised the alarm bells, and comes at a time when the country is battling the more high-profile novel coronavirus pandemic.

 

The desert locust (Schistocerca gregaria) is a short-horned grasshopper that is innocuous while it is in a “solitary phase” and moving about independently. These winged insects differ from normal hoppers, and become dangerous only when their populations build up rapidly and the close physical contact in crowded conditions triggers behavioural changes. They, then, enter the “gregarious phase”, by grouping into bands and forming swarms that can travel great distances (up to 150 km daily), while eating up every bit of vegetation on the way. If not controlled at the right time, these insect swarms can threaten the food security of countries. Kenya is already reporting its worst locust outbreak in 70 years, while Ethiopia and Somalia haven’t seen one this bad in quarter of a century.

 

How seriously should the first sightings of the locusts by the LWO be viewed?
 

There’s nothing much to worry right now, as the rabi crop has already been harvested and farmers are yet to commence plantings for the new kharif season. The LWO (part of the Union Agriculture Ministry’s directorate of plant protection, quarantine & storage and with its field headquarters at Jodhpur in Rajasthan) has since the second fortnight of April detected “gregarious” hopper groups, including at Fazilka in Punjab adjoining the Pakistan border. But these have been low-density nymphs in “2nd to 4th instar” stages or immature winged adults. No breeding or swarm movement has also been seen so far.

 

The timing, though, is cause for concern. The normal breeding season for locusts in India is July-October. But this time, they have been sighted by mid-April. Last year, too, they were seen towards end-May as isolated grasshoppers. They could, nevertheless, breed to high enough populations for forming swarming and wreaking havoc during the rabi season in Rajasthan (especially Ganganagar, Hanumangarh, Bikaner, Jaisalmer, Jodhpur, Nagaur, Jalore and Sirohi) and Gujarat (Banaskantha). The longer time to breed is more conducive for build-up of gregarious insect swarms, as opposed to solitary, innocuous hoppers.

 

Locusts are polyphagous, i.e. they can feed on a wide variety of crops. Secondly, they have an ability to multiply rapidly. A single female desert locust lays 60-80 eggs thrice during its roughly 90-day life cycle. K L Gurjar, deputy director of LWO, estimates that a 1-square-km area can accommodate 40-80 million of these insects, making the growth of their swarms exponential quite like the Covid-19 virus. The damage potential of locusts has been limited in India only because of the country hosting a single breeding season — unlike Pakistan, Iran and East Africa, where they also multiply during January-June.

 

What is the genesis of the present locust upsurge, particularly in East Africa?
 

It lies in the Mekunu and Luban cyclonic storms of May and October 2018 that struck Oman and Yemen, respectively. These turned large desert areas in remote parts of the southern Arabian Peninsula into lakes, which allowed the insects to breed undetected across multiple generations. The swarms attacking crops in East Africa reached peak populations from November onwards, while building up since the start of this year in southern Iran and Pakistan (Balochistan and parts of the Indus Valley and Punjab). Widespread rains in East Africa in late March and April have enabled further breeding.

 

According to Keith Cressman, senior locust forecaster at the Food and Agricultural Organization of the UN, a part of the new generation of swarms forming there in late-June/July may migrate from the Horn of Africa across the Indian Ocean to the desert areas along both sides of the India-Pakistan border. Prior to that, the locusts from spring breeding areas of southwest Pakistan and southern Iran would arrive in Rajasthan and Gujarat during May-June. They would, then, breed with the onset of the southwest monsoon rains and continue doing so through the kharif cropping season.