In this article we will discuss about:- 1. Distribution of Desert Locust 2. Breeding Season and Migration of Desert Locust 3. Origin 4. Life-Cycle 5. Damage 6. Management 7. Anti-Locust Organization.
Distribution of Desert Locust:
The desert locust is an inhabitant of the dry grasslands of desert areas and is found in many countries of the world. Its distribution extends from Rajasthan to Afghanistan, Iran, Iraq, Arabia and northern Africa. In India, the breeding grounds are located in Rajasthan, part of Gujarat, and the Hisar and Mohindergarh districts of Haryana.
These places are not the permanent home but are merely the outbreak areas where the locusts undergo change in their phase from gregarious to solitary. These parts of India as well as Sind and Bahawalpur of Pakistan are the summer breeding areas. The winter breeding areas are located in Baluchistan and in the Middle East.
Most of the swarms that invade India originate from these winter breeding grounds but in certain years, supplementary swarms are also formed in the summer breeding areas. The swarming locusts are always in the gregarious phase and from the winter breeding grounds they spread in all directions and invade southern Europe, Spain, major parts of African Continent, Israel, southern and western parts of Russia, Afghanistan, Iran and other adjoining areas.
Such swarms have been seen 1930 km at sea and, in one instance, a swarm was recorded 6440 km away from the place of the origin. It is on record that some swarms flew straight from the Arabian coast to Gujarat. The swarms fly quite high and they are known to have crossed mountains as high as 4,600 metres.
In India, the locusts invade the north-western region, penetrating the hilly tracts of the north. Sometimes, they reach as far east as Assam and as far south as Tamil Nadu. However, their breeding- grounds do not extend beyond the western districts of Uttar Pradesh and northern Madhya Pradesh. In 2006, the locusts from China invaded there Zansker valley of Ladakh and destroyed crops over an area of 240 km2.
Breeding Season and Migration of Swarms:
The breeding of locust depends upon the rainfall and the subsequent vegetation. The eggs are laid in the sandy soil and adequate moisture is required before they can hatch.
In India, there are two breeding seasons during the year, viz.:
(i) The summer breeding-season, and
(ii) The monsoon breeding-season.
In countries where the rainfall is in winter and early spring, as for example, south-eastern Arabia, the Red Sea coast, southern Iran, Baluchistan, etc., and wherever vegetation is available, the locust breeds late in winter or in the spring.
There may be one or two broods during that season. In Baluchistan, for example, breeding starts in January and then again in April. Thus, the swarms that originate in Africa or Arabia breed in Baluchistan and the surrounding countries during the spring and they migrate to Pakistan and India in the summer.
In countries such as India and the Sudan where the rainfall occurs in summer, the locusts breed during that season. However, even in these countries, at places where there is some rainfall in winter along with plentiful supply of wild grasses, the locust can breed in the spring. Punjab is such an area.
Ordinarily, in western India there is vegetation after the monsoon and locust swarms breed up to the end of September, October or even November, provided the temperature is fairly high, as it was in 1949. That year the locusts completed two broods during the summer.
Some of the swarms produced in the monsoon season may fly westwards to Baluchistan, erstwhile Russia and Eastern Arabia. A great many of the swarms formed in Rajasthan and Sind fly north, east and south, thus invading all parts of India. They damage the kharif crops.
Some swarms may over winter in north western India, and when the temperature conditions are suitable early next spring, they may damage the rabi crops. Thus, the locust cycle continues from season to season, sometimes for a number of years at a stretch.
Eventually, in a given year, if the rainfall is low and vegetation poor or the conditions are otherwise unsuitable, the locust population dwindles and is transformed into the solitary phase, scattered throughout the area of its invasion. Even in this solitary phase, the locust continues to breed for some time and damage some of the crops.
Origin of a New Locust Cycle:
The following sequence of events generally marks the beginning of the locust cycle:
i. Extensive breeding on coastal areas of Arabian countries as a result of heavy winter and spring rainfall, and the formation of gregarious swarms.
ii. Migration of locusts from the Arabian coast into the interior (Baluchistan, Afghanistan) in spring.
iii. Migration of these swarms, in summer, to Sind and Rajasthan.
iv. Extensive breeding of these swarms in Rajasthan in July-August and September.
v. Migration of the subsidiary gregarious swarms from Rajasthan to Punjab in late summer.
Life-Cycle of Desert Locust:
The locust has three stages in its life cycle, viz. the egg stage, the hopper stage and the adult stage. When sexually mature, the adults are yellowish, sluggish, reluctant to fly and cluster on the ground. While mating, the male clings to the back of the female who takes him around. Copulation lasts 8-24 hours and egg-laying starts soon after mating, sometimes even when the male is clinging to the back of the female.
Egg-laying continues for many weeks. A single female may lay up to 11 egg-pods, each pod containing up to 120 eggs. A female normally lays 500 eggs in about 5 pods. Before egg-laying, the female, with the help of her ovipositor, bores a hole into the loose sandy soil, 5-10 cm deep. It takes 1-4 hours to dig a hole.
Having laid a pod, she secretes a frothy material over the eggs, which hardens on drying and makes the pod water-proof. While laying eggs, the females may be sitting very close to one another and as many as 5,000 eggs may be laid in one square metre. The ground used for laying eggs is easily recognized by numerous holes, which are of the diameter of an ordinary lead-pencil.
The egg, resembling grain of rice, is lightly curved and 7-9 mm long. The duration of the egg stage depends upon the soil conditions, temperature and moisture. The eggs laid in February and March hatch in 3-4 weeks and those laid in May- September hatch in 12-15 days. In very dry soils, the eggs may remain unhatched for a long time until there is a shower of rain.
The nymphs, at the time of emerging, break the egg-shell and creep out of the holes. These freshly hatched hoppers are light yellow but soon turn black (in the gregarious brood). They exhibit the gregarious instinct and March in swarms, feeding on all kinds of vegetation as they move. The duration of the nymphal (hopper) stage lasts 6-8 weeks in spring and 3-4 weeks in summer.
The young adults are bright pink and when sexually mature, they turn bright yellow. The pink locust adults are very active and are likely to cause much damage to crops, whereas the yellow swarms, though not so destructive, are equally dangerous as they lay eggs which give rise to destructive nymphs.
The locust swarms and the hopper bands generally rest during the night on bushes, crops, trees, etc. In the morning, they hop around at first and fly to form a swarm only when the temperature rises to an appropriate degree. The flight temperature varies from day-to-day and is determined by the maximum temperature on the previous day. During summer, if the day temperature is too high, the locusts rest again.
There are two broods in a year and their life-cycle is completed in various months, viz., summer brood (February-April- Pairing and egg laying; March-May- Hoppers; May-June- Adults) and monsoon brood (July-September- Pairing and egg laying; July-October: Hoppers; September-October: Adults). Adults of the monsoon brood either overwinter in India when the locust cycle is manifested or they migrate to other north-western countries.
Damage Caused by Desert Locust:
The locust is harmful in both the adult and the hopper stages. These gregarious and voracious feeders eat almost any vegetation, except a few plant species such as ak (Calotropis procera), dharek (Melia azedarch), neem (Azadirachta indica), dhatura (Datura stramonium), etc. When in swarms, they can consume all the green vegetation and cause a famine. In spite of some expensive control measures, the damage to crops caused by locusts during the 1926-31 cycles was estimated at 100 million rupees.
In addition to the damage to crops, orchards, forests, etc., the locust can be nuisance in houses, as these creatures climb over the walls, invade kitchens, store-rooms and even enter into the beds. They fall into wells by the million and thus make water unfit for drinking. If an army of hoppers or adults marches on to the railway lines, all traffic is suspended because the crushed hoppers cause slippery rails.
Management of Desert Locust:
Management operation can be carried out against all stages of the locust, the most practicable and effective measures are against the nymphs. Operations are directed towards the destruction of all the locust population rather than towards protecting a certain area or a given crop field.
(i) The adults can be beaten to death with thorny sticks, brooms or can be swept together and buried underground in heaps. These things are easy to do when the females are laying eggs. When resting on trees or bushes in the waste-lands, they should be scorched to death with fire torches or with flame-throwers.
Burning is particularly effective at night or early morning when adults are sluggish because of the cold. During the cold weather, the adults rest at night on top of trees from where they can be easily shaken off, swept together and burnt or buried. During the day, the swarms can be prevented from settling on crops by waving white pieces of cloth or by the beating of drums.
(ii) Diazinon 2 per cent, if dusted on crops, trees and the ground, is very effective.
(iii) Diazinon (2%), in an oil medium, is also effective when sprayed with an aeroplane on top of a flying swarm. Diazinon 25EC in water suspension can also be sprayed on locusts, on the ground.
(iv) If eggs are laid in a well-defined area, a trench may be dug around it, so that the young nymphs on emerging drop into it and can be buried alive, filling the ditch with soil. If these trenches are heavily dusted with lindane, it may not be necessary to bury the nymphs. The eggs can also be collected by sifting the soil ‘with sieves but this method is not very practicable.
Destruction of Nymphs:
The hopper stage is the most vulnerable and control measures are most effective before the second moult.
The nymphs may be destroyed either with chemicals or by using mechanical methods:
(i) The principal mechanical method of control lies in digging trenches in front of the moving army of nymphs and driving them into these trenches, with brooms or with twigs of trees and then, buried alive. The nymphs can also be guided to the trenches along metal or canvas barriers, 45 cm high. Two barriers, one on each side of the army of the marching hoppers are so fixed that they converge on a narrow gap that leads to a trench in which they drop.
The trench should be deep enough to accommodate a large number of hoppers most of which would then die under the weight of their own fellow-creatures. Later, the trench can be filled with earth. In the early stages, a trench, 30-45 cm wide and 60 cm deep, is sufficient but when the hoppers are older, the width should be 75 cm and the depth more than 60 cm.
(ii) At night when the hoppers rest on bushes, they can be burnt with flame-throwers.
(iii) Poison baits such as the poisoned bran mash or sawdust, if scattered in the early morning or in the evening, are effective. During day, the bait dries quickly so the hoppers do not eat it.
(iv) Diazinon dust and diazinon spray (0.2%) are very effective.
(v) Diazinon as a spray can also be applied shortly before the emergence of the hoppers, so that as soon as they come out, they come into contact with the insecticide and die.
(vi) Spraying the crop with neem seed kernel powder suspension (1%) has been found to be very promising.
(vii) A number of birds attack locusts and of these, the common myna and the tiliar (starling) are the most important. During the locust cycle, if practicable, these birds should be protected.
Anti-Locust Organization:
The Anti-Locust Organisation in India consists of:
(a) The Central Anti-Locust Organization.
(b) The State Anti-Locust Organizations.
(a) Central Anti-Locust Organization:
This organization is called the Locust Warning Organization and was established in 1939. It is handled by the Plant Protection Adviser to the Government of India, who is also the Director of Locust Control, having his headquarters at Faridabad (Haryana).
The Directorate is required to:
i. Record the weekly density of locusts per unit area in the breeding areas located in India and to carry out control operations there.
ii. Interpret the records and pass on the information on locust movements to the various State Locust Control and Warning Officers and to the revenue authorities of the concerned districts before the locust reaches there so that arrangements for control can be made in advance.
iii. Keep watch on the coming swarms of extra-Indian origin, their direction and size.
iv. Give technical and material assistance to the various States.
v. Coordinate the anti-locust work in India by issuing a fortnightly bulletin on the locust situation both in India and in foreign countries.
In India, the work of this organization extends both to the scheduled desert areas where locusts breed and to the cultivated areas where they do the damage. In the scheduled desert areas, the Central Anti-Locust Organization operates over an area of 2,05,785 square kilometers in the States of Rajasthan, Haryana, Maharashtra and Gujarat. This area is divided into 23 locust outposts who are grouped into 5 circles with headquarters at Bikaner, Jodhpur, Barmer, Jaisalmer and Palanpur (Gujarat).
The responsibility of the control work is entrusted to the Locust Entomologist incharge of the circle. During the 10th Five Year Plan, it has been proposed to restructure the organisation with 10 circles each at Bikaner, Jaisalmer, Barmer, Palanpur, Churu, Jalore, Nagaur, Sikar, Phalodi and Bhuj besides one field headquarter at Jodhpur and a Central Headquarter at Faridabad by merging existing 5 circles and 23 locust outposts for-
(i) Monitoring of locust activity.
(ii) Issuance of fortnightly locust situation bulletins.
(iii) Organizing Indo-Pak border meetings on locust situation.
(iv) Conducting trainings to the farmers, state functionaries and locust staff on locust control.
(v) Conducting research on locusts and grasshoppers.
(b) State Anti-Locust Organizations:
In the scheduled area of the desert as well as in the adjoining States where locusts cause damage, there are State Anti-Locust Organizations to take suitable measures against the swarms. The State organization is headed by the Locust Control and Warning Officer who is well connected with the local revenue authorities, from the Deputy Commissioner to the Tehsildar and Patwari.
When the latter official receives information from district headquarters warning him of a locust invasion, he alterts the villagers to be ready with machines and insecticides, kerosene, flame-throwers, spades etc. When the swarm actually arrives, the farmers try to kill it as well as they can and then the Patwari intimates the Locust Control Officer and his own Deputy Commissioner of the extent of success achieved. In case the swarm settles down to lay eggs, the Locust Control Officer or his staff visits the place to devise suitable control measures.
During the locust invasion of 1949-53 and subsequently in 1960-64, the organization proved to be very efficient and effective. They have been admired as one of the best in the world.