Browsing by Author "Jayasooriya, G. A. J. S. K."

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Insights into the effects of interspecific larval competition on Aedes aegypti (L.) and Aedes albopictus (Skuse) mosquitoes and dengue transmission
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Shalinda, K. A. N.; Jayasooriya, G. A. J. S. K.; Gunathilaka, R. A. K. M.; Samaraweera, S. A. P. T.; Ganehiarachchi, G. A. S. M.
In Sri Lanka, both Aedes aegypti and Aedes albopictus mosquitoes are prevalent and contribute to the transmission of dengue, a significant public health concern with high morbidity and mortality rates. Ae. aegypti predominates in urban environments and is a primary driver of dengue outbreaks, whereas Ae. albopictus, adaptable and found in both urban and rural areas, poses a persistent threat. While the effects on their life history and morphometrics when reared in isolation have been well investigated, the effects of their coexistence, which more closely reflect real-life scenarios in many parts of Sri Lanka, have not been thoroughly explored. Thus, this study addresses this gap by investigating the effects of interspecific larval competition on key biological parameters of both Ae. aegypti and Ae. albopictus, specifically focusing on larval duration, survival rates, and body size, particularly wing length. The study was conducted in the School of Entomology at the Medical Research Institute (MRI) in Colombo 08, Sri Lanka. The experimental design involved controlled laboratory settings where Ae. aegypti and Ae. albopictus larvae were reared either in isolation or in mixed-species groups. Eggs of both species, obtained from laboratory cultures, were hatched using the vacuum method to synchronize hatching times. Larvae were reared in 100 mL transparent plastic containers, with fifty larvae of each species reared separately and twenty-five larvae of each species reared together in mixed-species containers, each filled with 50 mL of distilled water. Larvae were fed with finely ground commercial fish food (Apex©), and feeding amounts were increased daily according to larval instar needs. Wing length was determined by mounting the separated wings on slides and measuring the radius vein length using a scale-mounted light microscope. Statistical analyses, including two-sample t-tests, were conducted using MINITAB 14 (Minitab Inc., 2004) to assess the effects of interspecific competition. Results indicate that both Ae. aegypti and Ae. albopictus exhibited longer larval durations when reared in mixedspecies conditions. Survival rates were not statistically significant for Ae. aegypti (p > 0.05) but increased in mixed-species environments, whereas survival of Ae. albopictus was significantly reduced in mixed-species conditions (p < 0.05). Morphometric analyses revealed significant differences in wing length between males and females of both species (p < 0.05). In males, wing length differences were not statistically significant (p > 0.05), but Ae. aegypti tended to have longer wings compared to Ae. albopictus in mixed-species environments. However, in females, wing length was significantly higher in Ae. aegypti and lower in Ae. albopictus (p < 0.05) when reared in mixed-species environments. In conclusion, interspecific competition between Ae. aegypti and Ae. albopictus influences larval development, survival rates, and body size differently for each species. Mixed-species conditions result in prolonged larval stages, altered survival rates, and distinct morphometric changes (i.e. wing length), with Ae. aegypti demonstrating characteristics suggestive of relative strength or competitive advantage compared to Ae. albopictus. The findings highlight the intricate dynamics of interspecific competition among Aedes mosquito species, emphasizing the need to consider these ecological interactions in strategies for controlling mosquito populations and mitigating dengue transmission, leading to more effective disease prevention efforts.
Preparation and laboratory evaluation of herbal stick formulations using mosquito repellent plant materials against Aedes aegypti and Aedes albopictus
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Fernando, M. U. D.; Jayasooriya, G. A. J. S. K.; Samaraweera, S. A. P. T.; Ganehiarachchi, G. A. S. M.
Dengue, caused by Aedes mosquitoes, remains a significant public health issue. Current vector control methods have been unable to effectively reduce the Aedes populations, thereby failing to control dengue transmission rates. This study has attempted to develop an effective and practical tool for the control of dengue transmission by dengue vectors, Aedes aegypti and Aedes albopictus by reducing vector population and human-vector contact using mosquito repellent plant materials. In the current study, to prepare the incense herbal sticks Ocimum Basilicum, Tagetes erecta, Mentha piperita, Syzygium aromaticum, Cinnamomum verum, Salvia rosmarinus, Laurus nobilis and Cymbopogon nardus were used as herbal materials while saw dust, charcoal powder and “Patta” powders were used as inactive ingredients. The final weight of the herbal stick was 1.5 g and three different herbal formulas were prepared. Adult mosquitoes were reared in the laboratory from eggs collected via ovitraps deployed in various locations. F1 generation of mosquitoes were used and, their age of exposure was 2 weeks. Ytube experiments (n = 21) were conducted to assess the repellent activity of incense sticks impregnated with different herbal extracts. Additionally, smoke toxicity tests were performed on adult female mosquitoes. Statistical analyses were conducted using JMP 5.01 (SAS Institute Inc., 2002). Data were initially tested for homogeneity of variances using O’Brien’s test (p < 0.05). For homogenous variances, ANOVA was applied; if variances were heteroscedastic, data transformation was attempted to rectify the issue. Persistent heteroscedasticity led to the use of Welch ANOVA. Significant treatment effects were further analyzed using the Tukey-Kramer HSD test (p < 0.05) to compare the mean values. Test results clearly indicated that all three treatments resulted in significant reductions in attraction of both A. aegypti (F2,6 = 10.23, p < 0.05); and A. albopictus (F2,6 = 13.07, p < 0.05). Among the three formulations, incense stick that contains 45 % of active ingredients acted as the best repellent to Aedes species. The smoke toxicity test results depicted that both Aedes species showed significant toxicity to three treatments i.e. 5%, 25% and 45%, p < 0.01). The highest mortality was obtained with 45% of active ingredients, followed by moderate toxicity at 25%, and the lowest mortality at 15%, demonstrating a dose-response relationship. Therefore, incense sticks that contain 45 % herbal ingredients could be recommended as supplementary method to reduce human-vector contact to both A. aegypti and A. albopictus mosquito species. For further improvement, long-term monitoring procedures should be established to evaluate the long-term effectiveness and user acceptability of these mosquito repellent formulations.