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Accueil du site → Doctorat → Pays-Bas → 2003 → Habitats and spatial pattern of solitarious desert locusts (Schistocerca gregaria Forsk.) on the coastal plain of Sudan

Wageningen Universiteit (2003)

Habitats and spatial pattern of solitarious desert locusts (Schistocerca gregaria Forsk.) on the coastal plain of Sudan

Woldewahid, G.

Titre : Habitats and spatial pattern of solitarious desert locusts (Schistocerca gregaria Forsk.) on the coastal plain of Sudan

Auteur : Woldewahid, G.

Université de soutenance : Wageningen Universiteit

Grade : Doctor Thesis 2003

Résumé partiel
TheRed Seacoastal plains ofAfricaand theArabian Peninsulaare an important breeding area for desert locust,Schistocercagregaria . This area has been implicated as a source or transit area for locust swarms that threaten agriculture. The spatial distribution of the desert locust on the southern part of theRed Seacoastal plain of Sudan, betweenPort SudanandTokar, was investigated to determine habitat associations of the desert locust and collect information that might help in planning survey and control operations. Observations were made during three subsequent rainy seasons, from November till March, in 1999/2000, 2000/2001 and 2001/2002. First of all, the main plant communities in the study area, a 120 km stretch of coastal plain, were classified and mapped. Sample sites were laid out in an approximately square 5 × 5 km grid of sample sites to collect vegetation data. Multivariate data analysis resulted in the delineation of four main plant communities, which were named after characteristic plant species : theSuaedamonoica scrubland near the coast, the Acaciatortilis scrubland near the Red Sea Hills, thePanicumturgidum grassland at intermediate location and altitude, andHeliotropium/millet, small pockets of cropland (mostly planted with millet) at the transition between thePanicumgrassland and theSuaedascrub. The croplands were characterized by relatively good moisture provision due to run-on water from spreadingwadis, and high abundance and vegetation cover of the locust host plantHeliotropiumarbainense . Rainfall was markedly different between the three seasons : 158 mm in 1999/2000, 138 mm in 2000/2001 and 30 mm in 2001/2002. This resulted in substantial differences in observed locust densities. During the first and wettest season,solitariousadult locusts were observed in substantial numbers, up to 100 per ha, in theHeliotropium/ millet plant community, but hardly in the plant communities characterized by S.monoica , P.turgidum , or A.tortilis . Egg laying and hopper development were found in theHeliotropium/millet plant community but not in the other communities.Gregarizinghoppers were found in one of the croplands. In the second year of the study,solitariousadult desert locusts were observed at low densities in theHeliotropium/millet plant community, and none were found in the other three communities. No egg laying or hopper development was observed in any community in the second season. In the third and driest season of the study, no adult locusts or hoppers were observed in the main study area. However, during the third season, it became possible to take samples in the delta of thewadiBaraka, nearTokar, to the south of the study area. This area receives more water than the main study area and adult solitary locusts were present here. They were associated with millet agriculture, as in the main study area.

Mots clés : SCHISTOCERCA GREGARIA / INSECT PESTS / HABITATS / SPATIAL DISTRIBUTION / PLANT COMMUNITIES / PATTERNS / MULTIVARIATE ANALYSIS / SUDAN

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