Browsing by Author "Rajapaksha, R. D. T."

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    Assessment of the relationship between rainfall patterns and human-elephant conflict in Nochchiyagama and Vanathavilluwa, Sri Lanka
    (Faculty of Science, University of Kelaniya Sri Lanka, 2024) Kalanika, G. I.; Rajapaksha, R. D. T.; Dahanayaka, D. D. G. L.; Padmalal, U. K. G. K.; Wijeyaratne, W. M. D. N.
    Wilpattu National Park (WNP), the largest and oldest national park in Sri Lanka, spans across eight Divisional Secretariats (DS), where Human-Elephant Conflict (HEC) remains a significant concern. This research investigates the HEC in areas surrounding WNP and examines its correlation with rainfall patterns. A questionnaire survey was conducted in Nochchiyagama, the most densely populated of the eight DS divisions, to capture farmers’ perspectives on HEC. The HEC data were collected from the Department of Wildlife Conservation from 2015 to 2022 across the eight DS divisions and the highrisk and low-risk areas were identified. Additionally, rainfall data of Nochchiyagama and Vanathavilluwa DS divisions from 2015 to 2022 were examined to explore any potential relationship between rainfall and HEC incidents. Findings indicated that Cheddikulam and Karuwalagaswewa are high-risk divisions for HEC, while Rajanganaya is the lowest risk division. According to the survey, 71.3% of respondents believe that elephants invade villages searching for food where 45.5% of total responses indicate that coconut is the most attractive crop to elephants. Mangoes were the second most preferred crop (36.4%), followed by Kurakkan and paddy (26.4% each), and pumpkin, corn, and sugarcane (22.3%, 19.8%, and 16.5%, respectively). All respondents were familiar with elephant repellent methods, with "ali Vedi" being the most prominent. Additionally, 47.2% of respondents suggested establishing an electric fence to minimize conflict, while constructing ditches and using shotguns were recommended by 30.4% and 22.4% of respondents, respectively. Rainfall patterns in Nochchiyagama and Vanathavilluwa showed minor variations, with January-March and JuneSeptember being relatively dry periods, and March-June and September-December being rainy months. Despite 56% of survey respondents indicating that elephant incursions predominantly occur during the dry season, statistical analysis (Spearman test, p = 0.260, p = 0.347) found no significant correlation between HEC and rainfall in either division over the study period. In summary, while the study highlights areas and crops most affected by HEC and identifies community-preferred mitigation strategies, no significant correlation was found between rainfall patterns and HEC incidents. Although there is no direct relationship between rainfall and HEC, the HEC is influenced by the other proximate factors related with food availability which are in turn affected by the rainfall. Therefore, there might be an indirect relationship between rainfall and HEC in Nochchiyagama and Vanathavilluwa. Further research is recommended to confirm this idea and investigate seasonal variations in elephant movements and behaviors in other areas surrounding WNP to develop more effective mitigation strategies.
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    Effect of aqueous extracts of Annona glabra plant and extracellular metabolites of two Trichoderma species on the survival of larval Culex quinquefasciatus and eggs of Aedes aegypti
    (Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Aberathna, A. A. A. U.; Ranasinghe, H. A. K.; Rajapaksha, R. D. T.; Amarasinghe, L. D.
    Phytochemicals constitute a rich source of bioactive chemicals and some microbial products carry selective toxicity to many insect species, hence those are considered as alternatives to chemical insecticides. This study aimed to determine the potential of concentration gradient of Annona glabra aqueous leaf and fruit extracts for the mortality of third instar larvae of Culex quinquefasciatus; and to determine the ovicidal activity of extracellular metabolites of Trichoderma harzianum and Trichoderma viride at concentration gradient of 100, 200, 300, 400, 500 g/L on field collected eggs of Aedes aegypti with four replicates including controls for all bioassays. For the bioassays, aqueous crude extraction of plant materials was done by overnight shaking and extraction of extracellular metabolites of T . harzianum and T . viride was done using Richard ’ s broth . Study revealed that LC50 for A . glabra aqueous leaf extract for third instar larvae of Cu . quinquefasciatus was 16.26 g/L and 8.29 g/L in 24 hr and 48 hr exposure respectively (Minitab 14, Probit analysis). LC50 for A . glabra aqueous fruit extract, for third instar larvae of Cu . quinquefasciatus were higher than the LC50 for A . glabra leaf extract; 422.54 g/L and 114.01 g/L in 24 hr and 48 hr exposure respectively. 100% mortality was observed in mosquito larvae under 69.86 g/L of leaf and 1000g/L of fruit extract treatments after 24 hours of exposure. Mosquito larvae mortality compared to those in the control group reveals that the mortality of mosquito larvae may be due to the toxic compounds found in the plant. Although literature has shown that most Trichoderma strains produce volatiles and non-volatile toxic metabolites, significant ovicidal activity of extracellular metabolites of T . harzianum and T . viride on field collected eggs of Ae . aegypti was not observed (One-Way ANOVA; P>0.05) after 24 hr of exposure. The results of the study revealed that, both A . glabra fruit and leaf extracts are potential mosquito larvicides for Cu . quinquefasciatus. This may contribute to the formulation of an environmentally friendly measure to control Cu . quinquefasciatus vector mosquito species, which is a vital need to overcome the use of synthetic insecticides.