Investigation on the decline of Acacia nilotica, Acacia senegal and Balanites aegyptiaca trees associated with two cerambycid beetles in the Blue Nile area

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Date
2015-06-17
Authors
Ahmed, Elsiddeeg Mohammed Ali
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UOFK
Abstract
The periodic occurrence of loss of tree vigour, branch decline, tree mortality and wood general properties deterioration, for any reason, is a phenomenon wich has frustrated resouce managers and intrigued scienctists for many years. This study was ultimately devoted in the highlight and assessment of the impact, of two longhorn beetles ( Cerambycids), on three of the important tree species in the Sudan. The research was specifically concentrated in the investigation of the phenomenon of the decline, affecting Acacia nilotica tree by Crossotus robustus beetle besides Balanites aegyptiaca and Acacia senegal trees by Macrotoma palmata. A total of 42 plots were randomly selected from the three wood forests. The plots Comprised 14 plots in each of Gulgani, Khour Abuseif, and Tosi forest regenerated by A.nilotica, B.aegyptiaca and A.senegal wood tree species respectively. Each selected plot had a square shape, with an area of ¼ hectare (50x50 meter).In each selected plot, trees were counted and grouped into 2 different categories: sound trees and infested ones. Identification of the infested trees was based on the outer symptoms and dissection of the suspicious looking branches, to insure the presence of the cerambycid beetle, in one of its stages. Mean frequency of infestation was determined in each selected plot, of the 3 tree species, by counting the infested trees in each chosen plot. The overall mean frequency of infestation was approximately 18% from the whole computed trees, with higher percentage in B.aegyptiaca followed by A.nilotica and then A.senegal with significant differences between B.aegyptiaca and the other two species. In each selected plot, the measured different growth parameters in sound trees were compared with those of infested ones. Significant reductions, in the parameters of the infested trees, were recorded. The mean reductions happened in diameter at breast heigh, tree height, volume and mean annual increment of the infested trees, pooled in the 3 selected species, in reference to sound ones was approximately 11%, 14%, 32% and 31% respectively. The study was extended to include comparsion, of physical and strength properties, between sound and infested wood of A.nilotica and B.aegyptiaca. High significant differences, between the two status of wood of the two species, were found in all measured properties. The properties were also compared between A.nilotica and B.aegyptiaca wood, and the figured computed were found to be higher in the former, in reference to the latter, with significant differences between them. Regarding the physical attributes, the mean densities of sound A.nilotica and B.aegyptiaca wood were found to be 0.81389 and 0.65047 G/cm3 respectively, where in the infested wood, for the same parameter, were 0.75461 and 0.63509 G/cm3. In the mechanical properties, which include modulus of rupture; modulus of elasticity; compression and hardness, the absolute figures of sound A.nilotica wood were approximately 1014, 30234, 592 and 6133 respectively. In the infested wood these figures were reduced, by 31, 17, 15 and 32 per cent respectively. In the infested B.aegyptiaca wood the measured strength properties were reduced by 27.66, 8.76, 28.04 and 19.64 percent in M.O.R, M.O.E, compression and hardness respectively, in reference to sound wood. In this study, the systematic investigation was extended to include the life cycle of the 2 pest beetles, through rearing them in a 2 nutritional media which were planner splits and sawdust of the wood of their selected host tree species, A.nilotica, A. senegal and B.aegyptiaca.The total period of the life cycle, in days, with the length of time of each of the stages and instars, for the 2 pest beetles was determined
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167page
Keywords
Investigation,decline, Acacia nilotica, Acacia senegal,Balanites aegyptiaca trees associated,cerambycid beetles
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