Browsing by Author "Weerakoon, S. N."

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    Effects of hydrological regimes and limnological parameters on plankton community properties in tropical irrigation reservoirs: A Sri Lankan case study
    (Lakes & Reservoirs, 2021) Weerakoon, S. N.; Chandrasekara, W. U.; Amarasinghe, U. S.
    Water-level fluctuations are reported to be key processes influencing ecosystem structure and functions in lentic aquatic ecosystems such as reservoirs. The plankton community structure in reservoirs, being useful mon1toring tools as reservoir trophic status indicators, are influenced by water quality parameters and water-level fluctuations. The present study tested the hypothesis that plankton community properties in irrigation reservoirs are influenced by hydrological regimes and physical and chemical parameters. Accordingly, the effects of physical, chemical and hydrological parameters on plankton density and taxa richness were Investigated for 10 selected irrigation reservoirs of Sri Lanka. The relative reservoir level fluctuation (RRLF), an index of the magnitude of water-level fluctuation In relation to mean depth, had a positive influence on phytoplankton density. Because the RRLF positively influenced phytoplankton density, this index appeared to favour eutrophy in reservoirs. Canonical correspondence analysis (CCA) indicated both the phytoplankton and zooplankton community structure in the study reservoirs was influenced by physical and chemical characteristics. CCA also indicated the plankton taxa abundance and water quality parameters could be used for the trophic classification of irrigation reservoirs. The results of the present study highlight the need for examining attributes based on hydrological regimes in the context of reservoir water quality management.
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    Oviposition attraction and larval performances of Aedes aegypti and Aedes albopictus under different leaf concentrations of invasive flora
    (Faculty of Science, University of Kelaniya Sri Lanka, 2022) Chathurangi, N. E.; Weerakoon, S. N.; Ganehiarachchi, G. A. S. M.
    Aedes aegypti and Aedes albopictus (Diptera: Culicidae) are the vectors of dengue and dengue hemorrhagic fever. The survival and population density of Aedes mosquitoes depend on the characteristics of the oviposition media. Thus, the objective of the present study was to evaluate the attraction and larval development of Ae. aegypti and Ae. albopictus to different oviposition media prepared using alien invasive flora in rubber plantations. Three oviposition media, each having 25%, 50%, 75% and 100% concentrations, were prepared by the selected invasive flora namely, Guinea grass (Megathyrsus maximus), Alligator weed (Alternanthera philoxeroides) and Austroeupatorium (Austroeupatorium inulifolium) to evaluate the attraction of mosquito populations in a rubber plantation at Palmadulla (6°36'50.5"N 80°33'03.3"E). Forty-five ovitraps (four concentrations from each infusion with three blanks were placed on the identified sites for vector breeding in a completely randomized manner for four days. The experimental setup was replicated three times. The number of eggs at each concentration of leaf extracts was enumerated and reared under laboratory conditions until adults. The emerged mosquitoes were identified using morphological taxonomic keys. The highest number of Aedes eggs (n=32) were found in ovitraps with 25% concentration of M. maximus. At 25% concentration, the highest hatch rate (65%) was obtained from A. philoxeroides and at 50% of concentration, the highest hatch rate (75%) was obtained from M. maximus infusion. At 75% of concentration, the highest hatch rate (75%) was obtained from M. maximus infusion during the second day of rearing. But at 100% of concentration, the highest hatch rate (50%) was obtained by M. maximus within the first day of rearing. The highest ovitrap positivity index (number of positive ovitraps/number of ovitraps placed X 100) value of 100, was obtained by A. philoxeroides at concentrations of 25%, 50%, and 75%, by M. maximus at concentrations of 25, 50, and 100%, and by A. inulifolium at concentrations of 25% and 75%. A. philoxeroides achieved the lowest value 33.3 at 100% concentration. The maximum Egg Density Index (Total number of eggs/Total number of positive traps) value 22.0 was obtained by M. maximus at 25% concentration and the minimum value 2.5 was obtained by A. inulifolium at 100% concentration. The larval density shows a significant difference with the different plant infusions. (F=12.90, df =2, P<0.05) and also in different concentration (F=13.81, df=3, P<0.05). The interaction of plant infusion type and their concentrations showed a significant effect on the larval densities (Two-Way ANOVA, F=6.57, df =6, P<0.05). The leaf infusions attracted gravid females of both Ae. aegypti and Ae. albopictus. The mosquitoes exhibit a vastly different response to each plant species. The present study demonstrates the potential of plant infusions in stimulating oviposition by Aedes mosquitoes using ovitraps in mosquito surveillance. These findings confirm the critical importance of the plant species that are used to make leaf concentrations.