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.
