Browsing by Author "Perera, S. A. D. S."

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Larvicidal activity of chemically synthesized and Trichoderma longibrachiatum mediated silver nanoparticles against Aedes aegypti
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Gunawardana, W. G. T. N.; Perera, S. A. D. S.; Amarasighe, L. D.; Wickramarachchi, S. R.
The mosquito Aedes aegypti is a critical vector of infectious diseases, including dengue, chikungunya and yellow fever. Prevention of these diseases is mainly achieved through mosquito population control due to the non-availability of a commercial vaccine except for yellow fever. The use of biogenic nanoparticles to control insect vectors has been studied in several research. Byproducts of the metabolism of organisms, including bacteria, fungus, and plants, which act as reducing and stabilizing agents, can be used in the green synthesis of nanoparticles. This study aims to determine the mosquito larvicidal potential of green synthesized silver nanoparticles using Trichoderma longibrachiatum biomass (Tl-AgNPs) and chemically synthesized silver nanoparticles (C-AgNPs). Synthesized AgNPs were characterized by ultraviolet-visible spectroscopy (UV-VIS), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). The colour change from pale yellow to dark brown of the solution indicated the formation of AgNPs initially. The surface Plasmon Resonance (SPR) band in the range 415 - 400 nm in the UV-VIS confirmed the formation of Tl-AgNPs and C-AgNPs. TEM and SEM images confirmed that Tl-AgNPs and C-AgNPs were spherical in shape. Third instar larvae of dengue vector mosquito Ae. aegypti were subjected to larvicidal bioassay in a range of concentrations of Tl-AgNPs and C-AgNPs (10-50 mg/L). Both types of AgNPs were larvicidal against Ae. aegypti larvae. The percentage mortality of the Ae. aegypti was found to increase with the increase in tested concentrations of AgNPs. LC50 value of Tl-AgNPs was 16.82 ± 0.17 mg/L whereas C-AgNPs was 22.10 ± 0.71 mg/L for Ae. aegypti at 48 h exposure. Hence, Tl-AgNPs exhibit higher larvicidal activity than C-AgNPs. Tl-AgNPs have the potential to be developed as a green larvicidal treatment for Ae. aegypti.
Larvicidal effect of extracellular extracts of Trichoderma longibrachiatum and Trichoderma viride against Aedes aegypti
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Tharaka, W. G. H.; Perera, S. A. D. S.; Amarasinghe, L. D.; Wickramarachchi, S.
Aedes aegypti is a potential vector for transmitting dreadful diseases such as yellow fever, ZIKA, dengue and chikungunya, leading to global health problems. However, there is no warranted controlling method for these diseases other than controlling the vector. Apart from destroying breeding sites, use of larvicides is also important in larval control of the vector. Synthetic chemical insecticides, which dominate mosquito control programmes, are hazardous and exert unwarranted toxicity on non-targeted organisms, and lead to develop physiological resistance in target insects. Therefore, environmentally friendly, fungal mediated insecticides have been a priority at present. In current study, larvicidal effect of extra cellular fungal extracts of Trichoderma longibrachiatum and Trichoderma viride against 3rd instar larvae of Ae. aegypti was investigated. The fungi were grown in Richard’s broth medium containing glucose, agar, potassium nitrate, potassium dihydrogen phosphate, magnesium sulphate and ferric chloride. Eighteen different test concentrations of extracellular fungal filtrates, in a range from 0.625gL-1to 175gL-1, were prepared and batches of 25 number of laboratory reared 3rd instar larvae of Ae. aegypti were exposed to each test concentration separately with three replicates. Control bioassays were conducted with distilled water and larval mortality was recorded after 24 and 48 hour exposure periods. Results revealed that extracellular extracts of T. viride exhibited high larvicidal activity against Ae. aegypti larvae compared to the larvicidal activity of T. longibrachiatum. LC50 values for 3rd instar larvae of Ae. aegypti at 24 hours to the extracellular extracts of T. viride and T. longibrachiatum were 99.92 gL-1 and 114.98 gL-1respectively whereas LC50 values at 48 hours of exposure to the extracellular extracts of T. viride and T. longibrachiatum were 92.46 gL-1 and 108.71 gL-1 respectively. This study concludes that extracellular fungal extracts of T. longibrachiatum and T. viride can act as potential larvicides against Ae. aegypti and they can be used as alternatives for hazardous synthetic insecticides.