Emerging threat to Agriculturist- Desert Locust

Introduction

Locust are devastating agricultural pest which lead to famine and starvation and are more harmful than armyworm. Locust came from a Latin word ‘Locusta’ which means grasshopper. However there is a difference between locust and grasshopper. A major difference is that locust can form swarm while grasshopper can’t and locust change their behavior and habits and can migrate over large distances. Locust belongs to the family Acrididae. Desert locust, Schistocerca gregaria (Forskal) is dangerous among all other species and have been found at Nepal in recent times. The lifespan of locust is about 3 to 5 months. Due to its destructive nature and insatiable appetite, FAO recognized this pest as plague.

Lifecycle of locust

Lifecycle of desert locust comprises of 3 stages i.e. egg, nymph also known as hopper and winged adult.

Egg

Locust lay eggs in batch called pods. Female locust can lay egg 1-4 egg pods in its whole lifetime. The egg looks like rice grain and is yellow in color. Egg pods are laid after 7-30 hours of copulation which consists of 80-158 eggs. However locust lay less eggs in its gregarious phase. Initially egg is yellow in color which later turns into brown on soil. Females can lay egg at least 3-4 times in their lifespan usually at an interval of about 6-11 days. To lay eggs it needs moist soil up to 5-10 cm depth from surface which they check by probing soil with their tip of abdomen in soil. Egg hatch at 15-35ºC in 2 weeks. Locust lay eggs at night after 1.5-6 hours of sunset. It requires less time to hatch eggs in summer but more in winter.

Nymph

This stage starts after hatching of eggs, and are also called hopper. Schistocerca gregaria hopper develops in about 30-40 days and undergoes 5-6 stages. In these stages, solitarious hopper shed their skin for 5-6 times and gregarious locust shed their skin for 5 times which is called as moulting. The phase between moulting are known as instar. The first instar after hatching are white in color and gets converted into black within 1-2 hours. With the change in instar color, body structure, size and appetite changes. In fifth instar it is bright yellow with black color pattern. After 5th moulting, wingless hopper gets developed into a winged adult. Winged adult is also called fledging. After development of fledging, moulting stops. The total period from egg to fledging is 40-50 days. In nymph stage large number of locust mortality takes place especially in first instar than other stages due to predation by ants, cannibalism and lack of water resources.

Adult
Fledging develops into an immature adult which later develops in to a mature adult. Under optimal condition it develops into an adult in 10 days. The mature adult is yellow in color. The distinguishing feature between male and female adult is male are brighter yellow in color than female.
The male and female locust mate, the female locust lay eggs and the entire cycle begins.

Locust show polyphonic trait in which they can induce multiple discrete phenotypes from a single genotype. A plague species has two phase –one solitary phase where locust are solitary in nature, active at night and with diet restricted habit. They usually walk slowly with creeping sound. The coloration of locust are green. Individuals are repelled from each other in this phase. Solitarious locust have ability to change themselves into a gregarious form.

And the other one is gregarious phase where the locust are attracted to join specific group resulting to the formation of swarm. They are usually active at day time and are highly motile with the habit of broad diet. They are greyish or brownish in color leading to yellow with black patches.

Triggering factors for swarm of locust

Normally the locust are not destructive, their numbers are low and they do not pose a threat to agriculture. However under suitable conditions i.e. draught followed up by a rapid vegetation growth, serotonin in their brain triggers them to change their behavior from solitary to gregarious. These behavior include abundant breeding, creating swarm and becoming nomadic. The stimulation of the hind legs as they crawl over and jostle each other or by combined sight and sight and smell of other locust also play a key role in changing their phase.

Climate change also plays a key factor. As due to deforestation, urbanization CO2 content is increasing, increasing temperature and creating a rainfall in draught areas inducing the triggering factor i.e. serotonin.

Locust attack

Because of its polyphagus feeding habit it causes a lot of damage to different types of crops. The largest swarm reported was about 2400 sq. km. Even the smallest swarm can consume a food equivalent for 3500 people. The swarm destroys all the agriculture products from leaves to the bark and can even eat poisonous plant to protect itself from being predated. An adult swarm eats its entire weight everyday.

Locust attack in Nepal

Nepal faced the first locust attack in 1962 and in 1996 Nepal experienced worst locust invasion where 80% of crops were destroyed in Chitwan. On 27th June, 2020 locust swarm was reported from Bara, Parsa, Sindhuli, Sarlahi and Rupandehi. On 28th and 29th June, 2 swarms continuously entered Nepal which expanded to 53 districts within 10 days. Damage of crops was noticed from 12 districts by infestation where damage was remarkably high in 5 districts. Plant Quarentine and Pesticides Management Centre (PQPMC) under the ministry of agriculture and livestock development reported crop damage of 1118 hectare. Crops damage in Dang, Pyuthan, Makwanpur, Arghakanchi and Palpa was observed in a land area of 580, 283, 105, 100 and 50 hectare respectively.

Preventive Measures

Locust as a human food and animal feed

Locust are highly edible by humans and animals. It has high energy content of 179 kcal/ 100g (fresh weight basis) and protein content of 14-18 g/ 100 g, fat content is about 11.5g/100 gin which 53% is unsaturated fat and also are enriched with minerals like Na, K , Ca. P, Zn, Mg and Fe. Locust is also religiously accepted in Muslim culture as Halal and Jewish culture as Kosher. Eating locust cam prevent heart cancer. In feed industry, locust are grinded and given as a protein supplement.

Trapping of Locust

Gregarious locust are nocturnal in habitat and do not fly at night. So it is easy to capture locust by using nets. Trapped locust can be used for food and feed industry. It is also a good source of income for farmers.

Use of Biological remedies

Biological control for locust is a fungus called Metarhizum which acts as a natural pesticide and kills locust within 14-20 days with no measurable impact on other organism. Also the natural predator for locust are ants, ducks, spider and lizards. Use of neem, linseeds, garlic extracts on plant can depress the locust attack. However this remedy works late and and are suitable for small plot of land.
Surveillance of the places where locust breed and lay eggs can reduce the harmful impacts later on. Burning of locust egg in a deep soil can reduce their populations.

Loud noise

Locusts can be scared away by producing noise by beating of drums and utensils, using loud speakers.

Chemical insecticide

Insecticides like organophosphates like fenitrothion, malathion, chloropyrites, lambdacythalothrin and deltamethsin can be used in small concentrated doses by vehicles mounted and aerial sprays.

Conclusion
Locust is a dangerous pest and a threat to agriculture. It arises due to our action of global warming. Practices such as surveillance and biological pest management should be used to prevent this havoc.

Writer: Jenisha Pun (Student, Bsc. Ag IAAS Paklihawa Campus)