Locust: the Plague

Why is locust a threat?

The locusts travel in group from one field to another and eating away the crops, from their leaves to branches and roots, in a short span. The length of a swarm is also said to be somewhere around 130 kilometers at a time. A specialty of this insect is that it can fly in the air for a long time and can travel the distance of 5,000 km in just 10 days. According to the Food and Agriculture Organization, this insect can eat up to two grams a day. A 130-km long locust swarm means about 40 to 80 million grasshoppers that can finish the supplies of 25,000 people in a day.

It will just take three to four days for the locust swarm to reach Nepal’s eastern part from the west, and in two to three days they can reach the northern part. This clearly shows the destructive nature of the insects. Recently, the locust has destroyed 500,000 hectares of crops including wheat, mustard, maize, and spices in areas of Punjab, Haryana, Rajasthan, Gujarat, and Uttar Pradesh of India. Food and Agriculture Organisation (FAO) has categorised it as a plague.

What are Locust ?

Locusts belong to the Acrididae family (in the order Orthoptera which includes grasshoppers and crickets) and when triggered by certain cues such as increased crowding with other locusts have the ability to change their morphology, behavior and physiology over several generations. This phase change occurs from a solitary to a gregarious phase, eventually causing the locusts to form dense hopper bands and swarms. One of the most serious locust pests is the Desert Locust.

A swarm consists of grasshoppers in millions and travels in such a way that it clouds the sunlight. The species scientific name is Schistocerca gregaria. It lays its eggs, about 60,000-80,000 in number, under sand, and does it three times in its lifetime. Its lifecycle takes up to 10 months, with eggs hatching in three months, turning adults in another three months, and completing the lifecycle in five months.

 

History of Locust in Nepal:

Prior to this, the insects were seen in Nepal way back in 1962. Back then, the swarm had attacked crops in Kathmandu, Nuwakot, Dhading and a few other districts damaging a large number of crops. This, in turn, invited a famine, according to agriculture history books but lack statistical data on how severe the damage was.

Recent route:

Couple of weeks before the pandemic, African nations including Kenya, Somalia, Tanzania, Uganda, South Sudan, and Ethiopia among others had started reporting a swarm of insects eating their crops away. The same locusts were reported to have started travelling eastward. So far, they have reached Iran, Pakistan, India and now Nepal.

The size of a locust today is said to be 20 times bigger than the one seen 70 years ago in Africa, the Middle East and Gulf countries of Asia.

Favorable Environment:

These insects like warm air and the strong winds from the seas can blow them away really far. The two to three weeks from the onset of monsoon is the most favorable environment for the locusts to reproduce, which increases the chances of spread in Nepal even more. The early outbreak of locusts in April, not in mid-May, hints that there is a change in their behavior and that it is getting the favorable environment to spread.

 

Management:

Chemical method includes use of pesticides like Malathion, Fenitrothion. As per FAO, organophosphate chemicals applied via vehicle-mounted and aerial sprayers have helped to control these insects.

Cultural Method include lighting a fire, bursting crackers, banging plates and tins, and playing the drums as these insects can't tolerate loud noises. (The advisory issued to farmer's read)

Biological Method: Use of duck to control locust is also very successful and has been employed by recently by Pakistan.

Biopesticides such as Metarhizium anisopliae have previously been applied successfully using ULV ( Ultra low volume) methods to control locust populations as part of locust integrated management programs. ULV spraying is one of the most preferred methods as it uses very low volumes of liquid in comparison to conventional spraying (0.5-3 liters/ha in comparison to 100s or 1000s of liters for other spraying methods) and uses oil based formulations which greatly reduce evaporation. The method is based on creating small, even sized droplets which are carried and impacted on the target by the wind.

Other techniques for managing locust swarms include digging, burning and baiting (scattering locust food impregnated with insecticides).

Strategies for control:

Ø Processing of survey data with geographical information systems (GIS),

Ø Survey and application techniques using global positioning systems (GPS) and precision spraying,

Ø Physiological and ecological studies focusing on phase change,

Ø Barrier applications with new persistent insecticides,

Ø Use of biopesticides, especially mycopesticides and insect growth regulators and

Ø Environmental monitoring.