Locust Control Management: Moving from Traditional to New Technologies – An Empirical Analysis

The desert locust (schistocerca gregaria forskal)
The life cycle of the desert locust consists of three stages: egg, hopper
and adult and duration of the life is 2-6 months on an average. 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. 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 the colour of the solitarious
hopper is green throughout all instars but the gregarious hoppers have
characteristic colouration of black and yellow. The rate of development
of nymph is mainly dependent on temperature, from about 22 days
under hot conditions (mean air temperature approx. 37 degrees
Celsius) to over 70 days under cool conditions (mean air temperature
approx. 22 degrees Celsius). 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 cannot grow in
size but gradually increase in weight. Fledglings gradually become hard
and able to fly. Locusts in this condition 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,
they migrate 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 or brown under cool condition. On maturation adults
become bright yellow. Males mature before females but oviposition
usually commences within two days of copulation.
   0px; "> The desert locust exhibit two distinct behavioral phases – the
solitary phase – when individual actively avoid one another and – the
gregarious phase – when they form marching hopper bands (mass
aggregations of flightless nymphs) and swarms (adult aggregations with
high mobility). Both these stages of gregarious phase, hopper bands
and swarms are capable of devastating crops and pastures [1-3]. A
series of complex interaction between high rainfall, high survival rates,
the lush green vegetation and the behavior wherein there is an increase
in the rate at which hairs on the back legs are touched by other locusts
in a group is responsible for change from the solitary to gregarious
phase [4]. The desert locust only migrate to invasion areas in the form
of swarms once they begun to gregarise [5]. Dense groups that have
strong cohesion among individuals migrate long distance together are
swarms and their size may range from less than one to 300 sq miles.
The biggest swarm recorded in India being 1200 sq miles. One sq mile
of locust swarm may weigh about 150-200 tonnes and consumes 200
tonnes food daily. The swarms have been known to travel over 250 km
in a day and as much as 4500 km in a month and may fly 2000 km at a
stretch and at height of 7000 ft. and fly generally at the speed of 12-15
km per hour and on an average 9-12 hours per day, generally move into
areas of low level convergence of winds (Inter Tropical Convergence
Zone) and move down wind, fly during day time and settle by nightfall.
En route mature ones settle on ground for breeding while those not yet
mature fly on. A copulating and laying swarm usually stays in the same
area for 3-4 days.
 Solitarious adult occur at low density or individually, starts flying
after dusk on warm evening and can migrate long distances during
 dth: 0px; "> night. During day time they fly or flush only when disturbed and fly
low, settle quickly, eats it own weight of food per day (about 2.5 gm)
and are generally bigger than its gregarious counterparts. The desert
locust has no fixed or static outbreak area where a swarming population
can be observed and controlled, as in the case of the Red Locust and the
African Migratory locust. On the contrary, the Desert locust is able to
breed, when suitable conditions prevail, in any part of its distribution
area. The desert locust is one of the most difficult insects to control on
a national basis due to the vastness of its distribution area, pronounced
adaptability to utilize wide range of environmental conditions,
migratory nature and the potential ability of swarms to fly thousands
of kilometers, and the speed at which they can move from one part to
another. Thus the presence of swarms in any country is a threat to other
countries, even though these countries may be thousands of kilometers
away from the source of invasion. This fact calls for the importance of
international cooperation in desert locust control.
As the desert locust belt is so vast and includes many countries and
places that vary in many ecological, geographical and climatological
aspects and in view to control this pest the International Conferences
have divided the Desert Locust belt into following five regions and each
region consist several countries having special desert locust cycles and
movements. The activities between all these five regions are coordinated
by the FAO. Its breeding seasons have also been demarcated. For
example there is a particular cycle for the eastern region where
movements of swarms occur in India, Pakistan, Iran and Afghanistan.
There is also a cycle of this pest in East Africa, in North and West Africa
and in the Arabian peninsula and the North East countries.
1. South West Asia Region—India, Pakistan, Iran and
Afghanistan.
2. Near East Region—Iraq, Jordan, Kuwait, Lebanon, Saudi
Arabia, Syria, turkey, Egypt, United Arab Republic, Bahrain,
Yemen Arab Republic and the People’s Republic of Southern
Yemen.
3. East African Region—Ethiopia, Djibouti, Somali Republic,
Sudan,Kenya, Tanzania and Uganda.
4. Northwestern African region—Algeria, Libya, Morocco and
Tunisia.
5. West African Region—Chad, Dahomey, Cameroun, Gambia,
Ivory Coast, Mali, Mauritania, Niger, Senegal and Upper Volta.