© CILSS 2004 THEME : Weather, Climate and Migratory Locusts in West Africa Presented by : Brahima Sidibe AGRHYMET Regional Centre

© CILSS 2004 Outline of the Presentation 1. PRESENTATION OF CILSS 2. INTRODUCTION Distinctive Biological Characteristics Main Breeding Areas 3. Relations between Climatic Factors and Migratory Locusts Gregarization Sexual Maturation of Immature Adults Egg Laying Embryonic Development The Hopper and Nymphal Development Migration 4. Meteorological Data Required for Surveillance Recession Period Plague Period 5. Conclusions

© CILSS PRESENTATION OF CILSS CILSS Member Countries Burkina, Cape Verde, Chad, The Gambia, Guinea-Bissau, Mali, Mauritania, Niger and Senegal. Mandate: «To seek to assure food security and to combat the effects of drought and desertification for a new ecological balance»

© CILSS 2004 CILSS Food Security Strategic Framework Objective : « To ensure access to adequate food for all Sahelians at all times so that they can live a healthy and active life by the year 2015»

© CILSS 2004 CILSS Food Security Strategic Framework 1.To develop a sustainable, productive, diversified and integrated agriculture at regional level; 2.To develop, facilitate commodity trade and integrate national markets in the sub-region; 3.To sustainably improve the access of vulnerable groups and zones to food and basic social services; 4. To improve mechanisms for preventing and managing situational/temporary crises in line with the achievement of structural food security; 5. To build stakeholders’ capacities and promote good governance in food security. Specific Objectives

© CILSS 2004 THE THREE SITES OF CILSS The Executive Secretariat Based in Ouagadougou, Burkina Faso The Sahel Institute Headquartered in Bamako, Mali The AGRHYMET Regional Centre Based in Niamey, Niger

© CILSS 2004 Weather, Climate and Migratory Locusts in West Africa

© CILSS 2004 CHARACTERISTICS OF THE SAHEL Significant variations in climatic conditions with irregular rainfall in the range mm. Over the past thirty years, there has been a km southward shift of isohyets within the Sahelian region. Agriculture and animal husbandry are the mainstay of the economy: they employ more than half of the working population and account for about 40% of the GDP. Significant population growth (about 3.1 %) and very rapid urbanisation at an estimated increase rate of 7%

© CILSS 2004 INTRODUCTION Desert locust invasions like the one currently experienced in the Western Region in general and the Sahel in particular, originate from desert and semi- desert areas and correspond to particular insect behaviours. After the desert locust invasion experienced in , the 1997 African migratory locust upsurge around Lake Chad Basin, today the Sahel faced with a tragic situation, which has been forecasted, though. It was as if there were no echoes of the warnings issued by various institutions/services (FAO, AGRHYMET Regional Centre, National Crop Protection Services, etc.) in the countries concerned and the International Community.

© CILSS 2004 Distinctive Biological Characteristics The main characteristics of migratory locusts are as follows:  Phase polymorphism: existence of two extreme but reversible phases. The passage from one phase to the other occurs under the effect of density.  This phase change takes place in very small desert or semi-desert areas where the insect lives.  Capability to cover long distances (migration) with regard to the gregarious phase.

© CILSS 2004 Distinctive Biological Characteristics (Continued) The species of economic importance are:  Desert Locusts (Schistocerca gregaria), which are the cause of the current locust invasion across the Sahel.  African Migratory Locusts (Locusta migratoria migratorioides) which were involved in previous invasions and the cause of a new upsurge in 1997 around Lake Chad Basin.

© CILSS 2004 Main Breeding Areas Desert locusts Breeding is associated with seasonal rains received in two main areas in the Western Region. - The winter-spring breeding area. - - The summer breeding area. The second one crosses the Sahel. Outbreak areas can thus be found in Mauritania, Mali, Niger and Chad in areas with below 200 mm of rainfall. Breeding occurs there between June and September. This area, as in the case of other summer breeding areas was often the most active in the initiation of invasions. It also presented serious situations consisting of swarm formation from small locust populations.

© CILSS 2004 MAIN BIOTOPES OF DESERT LOCUSTS

© CILSS 2004 African Migratory Locusts The main breeding area is located in the Niger River Inland Delta, Mali, made up of flood plains. It is composed of semi-desert lands, marshes and transition zones. Non-flooded upland parts called Toguérés are beside flood plains. Grasses are predominant in the vegetation of the plains and Toguérés. The Lake Chad Basin also provides a habitat for this locust. Main Breeding Areas (Continued)

© CILSS 2004 Climatic effects on the development of pests in general and insects in particular have been known for a long time. But it is mainly with the acquisition of knowledge on the biology and behaviour of pests that the influence of climate was better clarified and increasingly expressed in the form of quantitative relations. In West Africa and particularly in the Sahel, characterized by a short rainy season and a long dry season, the influence of climate is undeniable. As a matter of fact, the rainy season constitutes the cropping season and also the period of heavy infestation of all kinds of pests including locusts. During the wet season, temperature, air moisture, soil moisture, day length and the vegetation have a direct effect on the biotic potential of insects including:  breeding potential  development rate  number of generations per year  biological rhythm and capability to spread  adaptation to climatic variations (estivation, hibernation, diapause) Relations between Climatic Factors and Migratory Locusts

© CILSS 2004 Gregarization The following situations result in the gregarization of desert locusts: - increased numbers as a result of breeding favoured by successive rains over large areas; - aggregation: regrouping on small surface areas with favourable conditions for development due to convergent winds or shrinkage in the surface areas of locusts’ habitat.

© CILSS 2004 Gregarization (Continued) The breeding cycle of the African migratory locust is associated with the Niger River’s flood pattern. Main outbreak area: the plains of the Niger River Inland Delta between Macina in the south and Timbuktu in the North. The flooding of the plains depends on flood conditions in the Niger River and its main tributary, that is, the Bani.

© CILSS 2004 JUNE-JULY: beginning Of food First egg laying in the flood plains AUGUST-SEPT: Northward movement of ITCZ Egg laying at the edge of the plains Maximum flood in the South OCTOBER: Beginnig of withdrawal of flood Egg laying by scattered adults in the south on lands of recent flooding, blown by harmattan NOVEMBER: Northward movement of adults Egg laying progress from southern lands to northern ones DECEMBER Appearance of first hoppers in the south along Bani River Maximum flood in the North APRIL: Appearance of first hoppers in the north in the area of Lake Debo

© CILSS 2004 Sexual Maturation of Immature Adults The sexual maturation of desert locusts depends on rainfall regime, which has an indirect effect through bushes on which locusts feed. The low percentage of some aromatic substances in the bushes during the dry season is believed to have an inhibiting effect on sexual maturation. The rains that fall enable the vegetation to regenerate, which increases the percentage of these substances in plants. The immature locusts, which arrive in an area that has received less than 20 mm of rainfall and where the daily average temperature is above 17°c become mature. Maturation is stimulated by the presence of sexually mature males in the population and significant density. In the absence of favourable conditions, adults can remain immature for quite a long time (6 months)

© CILSS 2004 Egg Laying After a variable period of time spent in search of an egg laying site following copulation, female desert locusts preferably lay their egg pods in the open, hot and moist soils with coarse sandy and dry surface. The egg laying occurs in a wet layer with a depth of 5-15 cm, 1 to 2 days after a 15 to 20 mm of rainfall Desert locusts preferably lay eggs on soils with granular texture or coarse sand. African migratory locusts normally lay eggs in soils moistened either by rains or flood waters that withdrew. Dry soil conditions bring egg laying to a halt. It occurs preferably on compact sand. In both cases, egg laying occurs in the daytime or night-time.

© CILSS 2004 Embryonic Development After egg laying, the eggs absorb the equivalent of their own weight of water for hatching to occur. Embryonic development rate depends on soil temperature. It has been shown that the incubation period of desert locusts decreases from 65 to 10 days when air temperature increases from 12°c to 34°c. In general, within the favourable thermal range, the two species’ embryonic development accelerates steadily as a result of temperature. Hopper and Nymphal Development It depends on temperature, hygroscopic conditions and availability of the vegetation which itself is dependent on rains. The duration of nymphal development of desert locusts ranges from 50 days at an air temperature of 24°c to about 25 days at 32°c. In their habitat of origin, hoppers feed on perennial and annual plants, which germinate during the rainy season after 25 mm of rainfall or more.

© CILSS 2004 Migration Desert locust swarms fly preferably in the daytime. Long migrations are facilitated by convective flow and strong winds in the daytime. The spontaneous take-off occurs when the temperature of thoracic muscles reaches or exceeds 24 – 25°c. Under cloudy conditions, immature and mature locusts take flight when the ambient temperature is 24°c or above and 26°c respectively. The flight can also take place at lower ambient temperatures when adults are exposed to the effects of the sun’s rays. Under cloudy conditions, the flight can persist only if the temperature is 23°c or above in the daytime and 25°c in the nighttime. Under sunny conditions, it can persist at air temperatures exceeding 9°c. Flights are brought to a halt by rains. Sometimes locusts land as soon as clouds hide the sun. Migration is orientated by the wind and leads locusts into convergence zones, which are rainfall areas. These rainfall areas are associated with the seasonal oscillations of the Intertropical Convergence Zone over West Africa. Solitary flights of desert locusts and migratory locusts occur at sunset. But, the distances covered are less significant.

© CILSS 2004 Meteorological Data Required for Surveillance In the light of what precedes, the meteorological data to be taken into account for surveillance will differ depending on whether we experience a recession period or plague period. Recession Period Solitary locusts are present in initial breeding areas. During the rainy season, temperature does not constitute a limiting factor of utmost importance. The proliferation of insects is influenced by rainfall, which creates favourable conditions for breeding: sexual maturation, moistening of the soil for egg laying, embryonic and post embryonic development. In other words, key factors are: rainfall, soil moisture and the rate of withdrawal of flood waters (for the African migratory locust). The rain fields derived from METEOSAT images make it possible to have indications on precipitations over initial breeding areas and soil moisture data through water balance models. The rate of withdrawal of flood waters can be estimated using hydrological models and remote sensing imagery. Plague Period Once locusts leave the breeding areas, their movement is mainly influenced by wind speed in the atmospheric boundary layer. They regroup in convergence zones, which are rainfall areas. Therefore, determining factors are: rainfall, wind direction and speed, the movements of the ITCZ which determine rainfall areas.

© CILSS 2004 Conclusion Migratory locusts are adapted to their environment because of their distinctive biological characteristics. Solitary desert locusts are confined to hot desert environments, where they take advantage of wetlands. Immature gregarious desert locusts can stand cold conditions and drought to some extent and are capable of covering long distances in order to find favourable environments for their breeding. Rainfall is the factor determining proliferation and the wind enables these insects to move. African migratory locusts live in an area that is not very large and composed of semi- desert areas, marshes and transition zone. This diversity of ecological conditions enables this insect to find a suitable habitat for its needs at any time. Rainfall and the rate of withdrawal of flood waters are the factors determining proliferation.

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