The Desert Locust

    Today I am going to post some facts about the desert locust whch may be of use to all our farmer brethren and the community as a whole.

                                DESERT  LOCUST AND THEIR CONTROL

    1. INTRODUCTION:      
           Locusts are essentially grasshoppers which are capable of forming large migratory swarms (adults) or hopper bands (nymphs) and cause great devastation of natural and cultivated vegetation. When they are present in large numbers they become gregarious, wherein they tend to group together rather than remaining dispersed throughout the environment. Second major distinguishing feature is that locusts migrate during the day time in swarms containing many millions of individuals.When the locusts exist as solitary individuals then distinction between locust and grasshoppers breaks down almost completely.

 2. MAJOR LOCUST  SPECIES       

                     Important locust species are: 

 Desert Locust                    :     Schistocerca gregaria F.

African Migratory Locust    :     Locusta migratoria migratorioides

Oriental Migratory Locust   :     Locusta migratoria manilensis

Red Locust                         :    Nomadacris septemfasciata

Brown Locust                     :    Locustana pardalina

Tree Locust                        :    Anacridium species

Bombay Locust                  :     Nomadacris succincta ( Formerly Patanga succincta  )

Sudan Plague Locust          :     Aiolopus simulatrix

Senegalese grasshopper     :     Oedaleus senegalensis

 Rice grasshopper              :     Hieroglyphus daganensis

  3. DISTRIBUTION

       

                                                            The invasion area of desert locust covers about 30 million square kilometers which includes whole or parts of  nearly 60 countries. This includes countries like North West and East African countries, Arabian Peninsula, the Southern Republic of USSR, Iran, Afghanistan, the Indian sub-continent.

                                                 During recession periods when locust occurs in low densities, it inhabits a broad belt of arid and semi-arid land which stretches from the Atlantic Ocean to North West India covering over 16 millions square kilometers in 30 countries.

 

 4. LIFE CYCLE

     

The life cycle has three stages:

    (a)  Egg

    (b)  Hopper

    (c)  Adult

Egg :  The eggs are laid by females in pods in the moist sandy soil at a depth of about 10 cms. Egg pods are laid at intervals of 7-10 days. Gregarious females usually lay 2-3 egg pods, each with about 60-80 eggs. Solitarious females mostly lay 3-4 times. Each pod contains 100-160 eggs. The rate of egg development is dependent upon soil temperature and moisture. There is no development below 15 degree centigrade. The period of incubation decreases from about 70 days at 19 degrees centigrade to 10-12 days at 32-35 degrees centigrade. Rates of egg development have been found to be characteristics of particular seasonal breeding areas and can be used to forecast dates of hatching.

Hopper:   After completing the incubation period the eggs hatch and nymph (young ones) emerges. There are five instars in gregarious population and 5-6 instars in solitarious individuals. In each instar there is growth of nymph and have characteristic colouration.

Ist Instar	When newly hatched are white in colour but turn black in 1-2 hours.
IInd Instar	Pale colour pattern is more obvious and the head is much larger than the first instar.
IIIrd instar	Easily recognized by two pairs of wing buds which can be seen projecting on each side of thorax (neck).
IVth instar	Colour is conspicuously black and yellow.
Vth instar	Colour is bright yellow with black pattern.

 

 

                                                      The rate of development of nymph is mainly dependent on temperature, from about 22 days under hot conditions (mean air temperature approx. 37 degrees celcius) to over 70 days under cool conditions (mean air temperature approx. 22 degrees celcius).

                          Adults:Fifth instar hopper moults into the adult state. This change is called fledging and young adult is called a fledgling. After this there is no further moulting and the adult can not grow in size but gradually increase in weight. Fledglings gradually become hard and able to fly. Locusts in this conditions are called immature adults.The period of sexual maturity of adults is very variable. If conditions are suitable, the adults may mature in 3 weeks. More usually, however, theymigrate downwind until they encounter favourable breeding conditions, which may be thousands of kilometers away. Under cool and / or dry conditions they may remain immature for as long as 8 months. Young immature gregarious adults are pink but old ones may become  dark red, brown under cool condition. On maturation adults become bright yellow. Males mature before females but oviposition usually commences within  two days of copulation.

5. LOCUST PHASES 

                                             

Since the desert locust gregarises and dissociates very readily in response to population density and as crop damage is done by gregarious phase, it is essential to be aware of difference between phases and to watch the signs of phase transformation.

              Phase characters of the desert locust are given below:

 

Characteristics	Solitary	Gregarious
Behaviour	Do not form groups.	Form persistent and cohesive groups- Bands and Swarms
	Roost, bask, feed and move as individuals.	Roost, bask, feed and move together.
	Hoppers move little, adults fly as individuals at night.	Very mobile- fly as swarms by day. Concerted movement by hoppers in a band marching.
Colour	Hoppers uniformly green in early instars but may be brown in last two instars.	Hoppers heavy black pattern on yellow or orange background.
	Adults pale grayish brown, buffer peach coloured. Males change to pale yellow on sexual maturation. Females show no colour changes on maturation at very low densities.	Adults rosy pink on fledging, darken in with age to grayish or brownish red then to yellow on sexual maturation (brighter in males).
Morphometrics	F/C Male 3.75 and over Females 3.85 and over	3.15 and under 3.15 and under
	E/F Males 2.025 and under Females 2.075 and under	2.225 and over 2.272 and over
	C = Width of head,  E = length of forewing F = length of hind femur.

 

 

      

         6. METHODS  OF CONTROL          

     

Spraying is the most commonly used method for locust control . It      involves using a sprayer to atomize a liquid pesticide, i.e. to break it into droplets, which are then distributed over the target area. A technique using much smaller volumes of spray liquid, called ultra low volume ( ULV ) spraying, was initially developed in the 1950s for use against the Desert Locust , and is now the most efficient and commonly used method. It is defined as applying between 0.5 - 5 liters of spray liquid per hectare, although between 0.5 and 1.0 l. / ha is preferred for ULV locust control. This small quantity of concentrated insecticide is not mixed with water or any other liquid; the special formulation, known as a ULV ( UL ) formulation, is usually supplied ready to spray.

           In order to spread such small volumes over the target, the liquid must be broken up into small droplets light enough to be carried easily by the wind. To prevent these small droplets evaporating in the hot conditions that are typical during locust control operations, ULV formulation are based on oil rather than other solvents such as water or petrol fractions which may be too volatile, i.e. evaporate too quickly.

                                                     These small droplets do not deposit ( land on surfaces ) very easily. They fall very slowly, so tend to be carried sideways by the wind rather than sedimenting ( raining down) on to horizontal surfaces. In addition, if they are too small or the wind is too light, they tend to go around objects rather than hit them, somewhat like smoke. However, if the droplets are the right size and there is sufficient wind, they deposit by impaction on vertical surfaces such as vegetation or locusts.

       Special sprayers are required for ULV  spraying if the insecticide is to be used safely and efficiently . ULV sprayers can be carried by an operator( portable sprayer) , mounted on a four-wheel drive vehicle (  Vehicle-mounted sprayer ) or on an aeroplane or helicopter ( aircraft-mounted sprayer) , The principle of use is the same for  all of them, but the scale and speed of operation and certain practical limitations  are different.