Assessment of Damage by the Tree Locust (Anacridium melanorhodon melanorhodon ) on Hashab Tree (Acacia senegal) using Ground Surveys and Remote Sensing Data

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Ahmed Ismail Ahmed Safi, Safi
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University of Khartoum
Abstract In the present study, a field survey, laboratory experiments and remote sensing were integrated and carried out for three successive seasons. The objectives were to access the role of tree locust infestation on quantity and quality of the produced gum arabic and to develop an alternative method for field survey of this pest. The field and remote sensing trials were conducted in an area of 28000 feddans (11331 hectares) of Acacia senegal plantation of the Acacia Project (Nawa and Elrahad locations), 37 km south east of El Obeid city, North Kordofan State. The results showed that adults were found throughout the year except in February, March and April and their number decreased with increase in rainfall and relative humidity. Hoppers appeared in July, August, September and October and their number increased with increase in rainfall and relative humidity. Experiments on quantitative effect on gum production due to natural and artificial defoliation of hashab (Acacia senegal) trees were carried out, where four blocks were chosen randomly, and the following treatments were arranged in a randomized complete block design: control (no defoliation), light natural defoliation, moderate natural defoliation, high natural defoliation, light artificial defoliation, moderate artificial defoliation and high artificial defoliation. The results revealed that tree locust infestation and the artificial defoliation of trees severely reduced gum production, and the reduction was highly significant (PX04;0.001) between means of all treatments except between high natural defoliation and high artificial defoliation. There was a negative correlation between gum production and levels of defoliation. Laboratory experiments showed that defoliation reduced gum viscosity, and the reduction was significant between all means except between light natural defoliation and light artificial defoliation. Defoliation also reduced gum optical rotation, but the reduction was not statistically significant. The developmental period of nymphs fed on young leaves was shorter than that of nymphs fed on old leaves. Both adults and hoppers daily consumed food equivalent to their body weight. Remotely sensed data, used in this study were collected from the American Landsat satellite (with sensors; ETM+) images dated August and October 2008, and the French Spot Satellite (with the sensors; XS) images dated August and November 2009. Visual interpretation of images showed that non-defoliated hashab trees appeared as red and defoliated ones appeared as grey. The Normalized Difference Vegetation Index (NDVI) differentiated between non-defoliated hashab trees and the three levels of natural defoliations. There was a positive relationship between NDVI value, tree greenness and gum production Supervised classification showed five major classes; non-defoliated, light, moderate and high defoliated hashab trees as well as areas of tree locust swarms. Supervised classes matched with NDVI classes
139 Pages
Assessment of Damage by the Tree Locust (Anacridium melanorhodon melanorhodon ) on Hashab Tree (Acacia senegal) using Ground Surveys and Remote Sensing Data