Browsing by Author "Vidanage, S. P."

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Assessment of the potential distribution areas for two endemic plant species of Sri Lanka under climate change by species distribution modelling
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Kodikara, K. N.; Vidanage, S. P.; Kadupitiya, H. K.
Climate Change is arising as a major threat on biodiversity. Long term climatic conditions have direct links with the occurrence or prevalence of a species in a particular locality. Early predictions facilitate making necessary management options to reduce the negative impacts of this phenomenon. Calophyllum walkeri is a severely affected species from the dieback. It has a conservation status as vulnerable. Syzygium rotundifolium is a range restricted species. Both are endemic to Sri Lanka and dominant species in montane forests. The objective of this study was to predict the best suitable areas for both species currently and by 2070. Maximum Entropy (MaxEnt) modelling method was used, due to its accuracy and well performance even with small sample sizes as the number of records for Calophyllum walkeri was very low. Secondarily obtained data from the National Herbarium for the whole country were used for Calophyllum walkeri (n=29) and primarily obtained presence only data by field surveys covering the whole study area namely Horton Plains National park along with secondary data for less accessible places for Syzygium rotundifolium were used as species occurrence data (n=55). Climate data were obtained through the databases of WorldClim website which contains climate data as spatial data with high resolution, specifically have been developed for spatial modelling activities. Average monthly weather data for 2010-2018 with 2.5 minutes spatial resolution were used as current climate data and future climate data for 2070 for MIROC6, Global Circulation Model climate projection with 30s spatial resolution were used as future climate data. All the cllimate data were converted into ascii format by using ArcMap 10.2.2 and occurrence data were converted into csv format and introduced into the model while selecting random test percentage as 25%. Nuwara Eliya district along with some parts of Kandy and Matale districts were resulted as the best areas for Calophyllum walkeri currently, while Ratnapura and Kegalle districts show moderate suitability. There is a possibility in reduction of suitability in Kandy and Matale districts in 2070 while Nuwara Eliya district will remain as the best area. There is a possibility of wet zone of the country to become suitable for Calophyllum walkeri including Batayaya, Denuwakanda, Dolekanda. For Syzygium rotundifolium, Nuwara Eliya district was the best suitable area and Ratnapura district indicated slight suitability under both current and future climate conditions. The resulting value for the Area Under Curve test which is a main statistical test of this modelling method for Calophyllum walkeri was 0.947 and it was 0.968 for Syzygium rotundifolium. Since these values are greater than 0.5, the models have performed accurately. This study recommends further studies to check the possibility of the wet zone of the country including Western and Southern regions which was resulted as a suitable region with the changing climate, to introduce Calophyllum walkeri in a requirement to take more conservation efforts. Conservation efforts for Syzygium rotundifolium can be increased within the montane region, since it is the most suitable area for it, according to the results of this study.
Infestation and emergence of Bactrocera dorsalis (Diptera: Tephritidae) on two varieties of Mangifera indica from selected locations in the wet and dry zones of Sri Lanka
(Faculty of Science, University of Kelaniya, Sri Lanka., 2021) Wijekoon, W. M. C. D.; Ganehiarachchi, G. A. S. M.; Wegiriya, H. C. E.; Vidanage, S. P.
Bactrocera dorsalis Hendel, (Diptera: Tephritidae) is one of the most serious fruit pests in Sri Lanka. There has been a dearth of documented records of infestation and damages of fruit flies on commercially important fruit varieties in the country. Hence, the present study aims to estimate the percentages of infestations and emergence of B. dorsalis on two commercially important mango varieties grown in the wet zone and dry zone in Sri Lanka. The study was conducted from September 2020 to February 2021 in Ratnapura and Embilipitiya. Ratnapura was selected as the study site in the wet zone and Embilipitiya was selected as the study site in the dry zone. In each site, two sub sampling sites were selected. Twenty ripened fruits (per variety) of Willard (Wld) and Karutha kolomban (Kc) were collected randomly from selected trees. Sampling was done once a month and fruits which have already fallen to the ground were collected. Collected fruits were observed for signs of fruit fly infestations by examining fresh oviposition marks visually using a hand lens. Fruits with confirmed infestations were placed in plastic containers with pre- sterilized sand and muslin cloth cover (storing four fruits; same variety, ≈ weight, temperature: 250 C, RH: 75-85 %) until the emergence of adults. After fifteen days, the average number of adults that emerged per fruit per location was calculated. Two indices; percentage infestations and adult fly emergence were calculated. Mean weight (g) (mean ± SE) of mango fruits used for the study were (127.47 ± 9.05) g and (203.65 ± 9.5) g for Wld and Kc respectively. The percentages of average infestation were 35% for Wld in dry zone and 30% in wet zone, and for Kc, 24% in dry zone and 20% in wet zone. For both varieties, comparatively high percentage infestations recorded from the dry zone site than that of the wet zone site (p> 0.05). The slightly high infestations for both Wld and Kc observed from dry zone site were in October 2020 and February in 2021 (during the season). The average number of adults that emerged per variety was (3.33 ±0.73) for Wld and (3.83 ±0.93) for Kc. The average adult emergence significantly varied between dry zone (4.25± 1.0) and wet zone (2.92±0.57) sites (p< 0.05). This study provides baseline information of infestation and emergence of B. dorsalis adults on two commercially important mango varieties in Sri Lanka.
Seasonal forecasting of Bactrocera dorsalis Hendel, 1912 (Diptera: Tephritidae) in bioclimatic zones of Sri Lanka using the SARIMA model
(CABI Agriculture and Bioscience, 2024) Wijekoon, W. M. C. D.; Ganehiarachchi, G. A. S. M.; Wegiriya, H. C. E.; Vidanage, S. P.
Bactrocera dorsalis Hendel is a severe fruit pest that causes significant economic losses globally. Despite B. dorsalis having been distributed mostly across Asia, studies on its current and future density variation in Sri Lanka are sparse to date. The present study was thus carried out to assess the contemporary density variation (2020–2022) and future density fluctuation (2023–2025) of B. dorsalis in bioclimatic zones of Sri Lanka. The density was assessed using the monthly-based fruit fly trap collection method from randomly selected 40 locations in all bioclimatic zones (wet, intermediate, dry, and arid). The SARIMA modelling technique was applied for delineating the best-fit model and for density forecasting in each bioclimatic zone. The density variations were depicted for the year and for the bioclimatic zone (2020–2025) by colour intensity maps using QGIS. According to the findings, B. dorsalis shows a seasonal component to its year-round density variation and an ascending trend in its density from 2020 to 2025. Density forecasting records a 20%, 30%, 26%, and 37% density increase in the wet, intermediate, dry, and arid zones, respectively, in 2025. In 2025, the highest predicted B. dorsalis density from the arid zone and the lowest predicted density from the wet zone were recorded. This study contains the first forecasting attempt for B. dorsalis density using the SARIMA approach as well as the application of colour-intensity depiction for its density variation in Sri Lanka, which leads decision makers and stakeholders in economic agriculture to plan the scientific management of B. dorsalis to avoid its current and potential future threat to the country’s fruit industry.