Locust and their control

Species

Locust are those species of grasshoppers (Acarididae) which under certain favourable conditions, multiply, congregate, more together in their nymphal stages as bands and the resultant swarms fly to distant areas in dense. Their epidemics occur in all continents.

There are nine well-recognized species. The following species occur in India.

The Bombay locust : - Patanga succincta

The migratory locust : - Locusta migratorin

The desert locust : - Schistocerca gregaria

Very common and most destructive

Bombay locust

Area of distribution: - India, Ceylon and Malaya, in India area extending from Gujarat to Madras and in certain year’s upto Bangal.

Breeding grounds: - Open areas of Western Ghats.

No. of breeds : - 1 in a year (diapause in adult)

Period of plague: - 1935-45, 1864-66 and 1901-1908 resulting in heavy damage to crops.

These hoppers do not congregated to form bands but remain scattered among crops of grasses.

Migratory locust

Distribution: - Europe, Africa, E.Asia and Australia.

Swarms

In India they were observed in 1898 in Madras, and in Bangalore in 1954.

Breeding ground

Breeds in spring in Pakistan (Baluchistan) and resultant adults migrate into the desert area of India as individuals and breed during summer in (Rajasthan – Gujarat) areas of India. Scattered locusts may gather together in ecologically favourable pockets and lay eggs innumerably i.e. there are several broods in a year.

Desert locust

The desert locust is a pest of worldwide importance as it is known to migrate in swarms from one country to another leaving behind famine.

Distribution

It is international pest affecting about 60 countries, mainly India, Pakistan, Afghanistan, Arebia, Persia, Iraq and Africa.

Breeding regions

The pest breeds during the soring season in the costal and other areas of West African countries like Parsia where the winter rains bring about the required degree of soil moisture and vegetation. The adults emerging from this breeding stage migrate eastward to Pakistan and India by about the beginning of the monsoon.

The phase theory of locust

The phase theory was first put forth by Uvarov on the basis of his studies on Locusta in Russia. Previously Locusta migratoria and L. danica were recognised as two district species as they exhibited market differences in colour, morphology, physiology and behaviour. Investigations by Uvarov, however, revealed that the L.migratoria and danica were the same species, which existed in two phases. The two forms gregarious and solitary are connected by intermediate form transiens.

Gregarious phase

Exhibit black colour pattern and the same is absent in solitary. Solitary has uniform colour, which resembles that of the vegetation on which they live. Under laboratory condition the colour of the solitary phase hoppers can be changed into that of gregarious by breeding them under crowded condition and vice-versa.

Reasons of outbreak

In breeding regions there are regular showers of rainfall in both the rainfall belts, which brings about the required degree of soil moisture and vegetation. However, the strong winds do not scatter the swarms.

Nature of damage

Locusts are voracious feeders, each adult, consuming its own weight of vegetation daily. It is estimated that 1 sq. mile settled swarm contains about 300 tons of locusts.

Biggest 300 Sq.miles swarm is on record. Similarly hoppers eat 6-8 times more than they’re own weight. It has been assessed that in India during 1926-31 plague, the damage caused to crops, fodder etc., was about 10 crores of rupees and consequential loss due to premature death of cattle and other livestock was incalculable.

Methods of locust control

The chief aim of locust control is to destroy the locust in all its’ stages.

Destruction of eggs

Locating the egg laid areas is always important, then trench them round, so as to entrap the young hoppers as they move out after hatching. Even actual destruction of eggs on organised scale may be carried out by ploughing, harrowing and hand digging.

Hopper Control

The mechanical methods included entrapping making hopper bands in 2’ x 2’ trenches and burrying. The chemical method includes use of poison baits and dusting of insecticides.

Poison baits

5% BHC or pairs green or sodium fluosilicate & 2 Dusting 5 to 10% BHC against hoppers 25 to 30kg/ha has seen found to bring a complete control of the pests. Aldrin 4% dust can also be effectively use.

Control of adults or winged locust swarms

During 5% or 10% BHC or 4% aldrin may be carried out to achieve better control when swarms are resting on the bare ground at night or in early morning can be beaten or swept up and destroyed. If they are resting on bushes or hedges, they can be easily burnt with help of flame throwers. When flying locusts are about to descend in large swarms in cultivated areas, the best way to tackle them is to prevent then alighting by all possible methods, such as waving a white cloth, or creating a cloud of smoke, by burning refuse, etc., spraying with neem kernel suspension as a deterrent to the crop, has also been tried with success. Recently with the introduction of aerial application of insecticide like aldrin, the control of locust swarms has become easier. The advantages associated with aerial spraying are:

1. Vast areas can be treated in relatively short time.
2. The swarm in fight can also be treated.
3. When swarms settle down in a particular area that area can be quickly covered by aerial application.
4. The movements of swarms can be watched with ease.

Locust control organisations in the world and in India

In India: Locust warning organisation of the Govt. of India was established from April 1939. In 1942, a coordination Antilocust Scheme was put into operation.

In the world

United Nations Special Fund Desert Locust Project, which was sponsored by the F.A.O. in 1960. This is being subscribed by several countries including India. It’s purpose is to develop more effective and less expensive control of the desert locust.