Browsing by Author "Amarasinghe, L. D."

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Abundance and distribution pattern of Aedes aegypti and Aedes albopictus in selected urban, sub-urban and rural areas of Gampaha District, Sri Lanka
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Dalpadado, C. P. R. D.; Amarasinghe, L. D.
The abundance and distribution of Aedes aegypti and Aedes albopictus, vectors of dengue fever, were determined at six localities in Gampaha District, which is the district with the occurrence of second highest number of dengue cases during last five years. Negombo and Wattala areas were selected to represent urbanized communities, Gampaha and Attanagalla to represent sub-urban communities and Dompe and Divulapitiya were selected for the rural communities based on population density. Percentage of premises infected with Aedes larvae (Premise Index) and the number of positive containers for 100 premises inspected (Breteau Index) were used as a proxy to determine the abundance of vectors. Larval collections were done monthly during April 2016 to June 2018 using random sampling technique for minimum 100 houses within a radius of 300 m. Potential breeding places in each site were identified and categorized accordingly. Out of 7916 premises examined, 1011 (12.8%) premises were found to be positive for Aedes mosquitoes. Among them 10.1% and 89.9% were found to be positive for Ae . aegypti and Ae . albopictus, respectively . Ae . aegypti was mostly prevalent in highly urbanized MOH areas (73%) while it showed low abundance in sub urban (21%) and rural (6%) areas. On contrary, abundance of Ae . albopictus was highest in sub-urban areas (47%) and lowest in urban areas (18%). Premise index (PI) for Ae . aegypti in urbanized areas were significantly higher than that of sub-urban (F=9.13, p<0.05) and rural areas (F=15.49, p<0.05) in Gampaha District and there was no significant difference (F=4.04, p>0.05) between PI of Ae . aegypti in sub urban and rural areas. The PI of Ae . albopictus in sub-urban areas was significantly higher than that of urban areas (F=15.43, p<0.05). There was no significant difference (F=1.44, p>0.05) between PI of Ae . albopictus in sub-urban and rural areas. Similarly, there was no significant difference between mix indices for Ae . aegypti and Ae . albopictus in Gampaha district (p>0.05). There was a strong correlation between the Breteau Index and the number of dengue patients reported in urbanized areas (r<0.5). Higher correlation was recorded with Ae . aegypti than Ae . albopictus. Therefore, occurrence of dengue epidemics are strongly correlated with Ae .aegypti indices in city areas of Gampaha District and present study suggests that Stegomyia indices can be used as a proxy to determine dengue transmission risk.
Assessingthe Filariasis Causing Parasites in Adult Mosquitoes and the Vector Mosquito Larval Breeding in Selected Medical Officer of Health Areas in Gampaha District, Sri Lanka
(Journal of Tropical Medicine, 2021) Pilagolla, S. A. S.; Amarasinghe, L. D.
The present study was conducted to determine the prevalence of filariasis causing parasites in adult mosquitoes and vector mosquito larval breeding in four Medical Officer of Health (MOH) areas in Gampaha district, Sri Lanka. Adult female mosquitoes at their resting places were collected using a prokopack aspirator operated twice a day from 7.00 am to 8.00 am and 8.00 pm to 9 pm in predetermined dates. Microfilarial worms in dissected mosquitoes were morphologically identified. Nine species of mosquitoes, namely, Culex quinquefasciatus, Cx. pipiens, Cx. fuscocephala, Cx. gelidus, Armigeres subalbatus, Mansonia uniformis, Ma. annulifera, Aedes aegypti, and Ae. Albopictus, were captured. A total of 1194 mosquito larvae were collected that belonged into three genera, namely, Culex (62.73%), Armigeres (25.62%), and Mansonia (11.64%), from blocked drains, polluted drains, blocked canals, large polluted water bodies, stagnant water bodies, marsh lands, rice field mudflats, and concrete pits. Large polluted water bodies (Shannon-Wiener diversity index/H’ = 1.5591) were the most diversed habitat type. In breeding water, average pH mainly lied in between 6 and 8 and average dissolved oxygen ranged from 3 to 7 mg/L. Cx. quinquefasciatus and Armigeres subalbatus adult female mosquitoes captured from Kelaniya MOH area were positive for microfilariae and were identified as Wuchereria bancrofti and Dirofilaria repens, respectively. This study concludes possible lymphatic filariasis situation is in extremely very low level persistent (0.06%) where transmission cannot be sustained and is restricted only to isolated pockets in the study area. The zoonotic strains of filariasis causing subcutaneous dirofilariasis in humans by Dirofilaria repens is continuing to survive due to the presence of stray dogs that serve as reservoir hosts.
Comparative Effect of Nanoparticles of Sliver, Europium Doped ZnO and CaF2 on Aedes aegypti and Daphnia magna
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Kumarasinghe, G. D. S. S.; Amarasinghe, L. D.; De Silva, C. R.
Aedes aegypti mosquitoes are responsible for transmitting dengue fever. Using nanoparticles is a better suggestion to combat vector mosquito spread. Daphnia magna is the keystone species in freshwater food webs. The sensitivity of Daphnia magna to low metal concentrations underscores its importance in evaluating the impact of nanoparticles on the ecosystem. This study examined the impact of Silver, ZnO, CaF2, Europium-doped ZnO, and CaF2 nanoparticles on Aedes aegypti larvae and adult Daphnia magna. The batch of 25 third instar larvae of Aedes aegypti and the batch of 25 adult Daphnia magna were exposed to each nanoparticle in a concentration series for 24 and 48 hours. For Aedes aegypti, nanoparticles of ZnO and CaF2 at 20 mg/L, 40 mg/L, 60 mg/L, 80 mg/L, and 100 mg/L; nanoparticles of Europium-doped ZnO and CaF2 at 50 mg/L; and Silver nanoparticles at 1 mg/L, 2 mg/L, 3 mg/L, 4 mg/L, and 5 mg/L. For the Daphnia magna, ZnO nanoparticles at 0.2 mg/L, 0.4 mg/L, 0.6 mg/L, 0.8 mg/L, and 1 mg/L; Europium-doped ZnO nanoparticles at 0.5 mg/L; CaF2 nanoparticles at 1 mg/L, 2 mg/L, 3 mg/L, 4 mg/L, and 5 mg/L; Europium-doped CaF2 nanoparticles at 4 mg/L; and Silver nanoparticles at 2.36 mg/L. The percentage mortality of Aedes aegypti larvae and Daphnia magna was calculated for each nanoparticle. The study revealed that nanoparticles of ZnO and CaF2 did not affect Aedes aegypti larvae but caused significant mortality in Daphnia magna. LC50 value at 24 hours for ZnO nanoparticles was 0.51 mg/L, while for CaF2 nanoparticles, it was 4.44 mg/L. The study also revealed that increasing europium doping in ZnO and CaF2 nanoparticles led to higher Daphnia magna mortality. The study revealed that exposure to silver nanoparticles for 24 hours significantly increased Aedes aegypti larvae mortality rates. LC50 value was 2.36 mg/L. All Daphnia magna were dead within 24 hours of exposure to silver nanoparticles. The study concludes that ZnO and CaF2 nanoparticles did not affect Aedes aegypti larvae. Silver nanoparticles showed lethal effects but cannot be recommended for Aedes aegypti control due to being toxic to Daphnia magna, a keystone species in aquatic ecosystems.
Diversity of microbiota associated with dengue vector mosquito breeding habitats in Udapalatha MOH Division, Sri Lanka
(Kumari J. Y.; Amarasinghe L. D.; Ranasinghe H. A. K.; (2021), Diversity of microbiota associated with dengue vector mosquito breeding habitats in Udapalatha MOH Division, Sri Lanka, Proceedings of the International Conference on Applied and Pure Sciences (ICAPS 2021-Kelaniya) Volume 2, Faculty of Science, University of Kelaniya Sri Lanka. Page 3., 2022) Kumari, J. Y.; Amarasinghe, L. D.; Ranasinghe, H. A. K.
Microbiota associated with mosquito breeding habitats are among biotic factors and serve as parasites, pathogens, predators, competitors, non-competitors, and food items for developing larvae. Therefore, there are naturally occurring microbiota species that serve as potential controlling agents against mosquito larvae, causing lethal effects on them. This information can be used in developing novel mosquito vector control strategies. Besides, the degree of parasitic, pathogenic, or predatory effects may also vary with the geographical location, influencing environmental conditions, including abiotic factors and other biotic factors within the habitat. Therefore, the current study was carried out to determine the diversity of microbiota associated with different breeding habitats of dengue vector mosquitoes; Aedes aegypti and Ae. albopictus. Sampling was performed from a variety of breeding habitats at Udapalatha MOH division in Gampola urban area from November 2021 to January 2022. Microbiota in water samples were preserved using Rose Bengal solution and Lugol’s iodine and were identified under microscope, using standard identification keys. During the survey, twelve different breeding habitats, namely plastic containers, metal containers, concrete slabs, glassware, tires, leaf axils, tree holes, coconut shells, bamboo trees, ornamental ponds, discarded roof tiles and clay pots, were identified as key breeding sites of Aedes mosquitoes. From the collected samples 54.54% of habitats were positive for Ae. albopictus and 45.46% were positive for Ae. aegypti. Eleven microbiota species; Canthocamptus staphylinus, Canthocamptus sp., Parastenocaris sp., Lepadella ovalis, L. patella, Rotatoria rotatoria, Rotatoria sp., Asplanchna brightwelli, Trichocerca rattus, Euglena sp., and Flagilaria sp. were encountered from breeding habitats associated with Ae. aegypti. Meanwhile, Canthocamptus staphylinus, Parastenocaris sp., L. ovalis, L. patella, R. rotatoria, Rotatoria sp., Euglena sp. and Flagilaria sp. recorded from breeding habitats associated with Ae. albopictus. The highest Shannon Weiner diversity index and gamma diversity relating to the Ae. aegypti were recorded from leaf axils, while for Ae. albopictus, it was from metal containers. For Ae. aegypti, the highest heterogeneity in microbiota diversity was recorded from tire habitats and it was from plastic containers for Ae. albopictus. Out of the microbiota species recorded, no species was identified as parasitic or pathogenic to Aedes mosquito larvae. Updated information from the present investigation would facilitate implementing appropriate vector control interventions.
Diversity of midgut symbiotic bacteria in Aedes mosquito genera: A meta-analysis
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Kumari, J. Y.; Amarasinghe, L. D.; Udayanga, N. W. B. A. L.; Ranasinghe, H. A. K.
The gut bacterial composition of mosquitos has the capability of altering mosquito pathogen transmission through numerous mechanisms, which is useful in novel transmission control strategies. Therefore, understanding the diversity of gut bacteria in different mosquito genera is highly important. The present analysis was carried out to evaluate the variations in gut-bacteria in field-caught Aedes adult mosquitos from different geographical locations. A literature survey was conducted to identify quantitative data related to the midgut bacterial abundance in Aedes, using standard search terms and keywords. The collected data were arranged at the bacterial class level and were subjected to a square-root transformation. A resemblance matrix was constructed based on the Bray-Curtis resemblance. Cluster analysis followed by the Analysis of Similarities (ANOSIM) and Distance based Redundancy Analysis (dbRDA) were used for data analysis. Gut bacterial abundance from six different countries; Netherlands, USA, Sri Lanka, India, Brazil, and Panama, were used in the study. A total of 12 bacterial classes, were recorded and bacterial classes of Alphaproteobacteria and Gammaproteobacteria accounted for the highest abundance in Aedes mosquitoes from most of the countries. Interestingly, Aedes mosquitoes from Brazil, India and Sri Lanka, did not report the abundance of Alphaproteobacteria in their gut contents. Based on the Bray-Curtis similarity-based cluster analysis, four major clusters were identified at a similarity level of 48.9%, based on the overall abundance of bacterial classes. Aedes mosquitoes of Sri Lanka and India formed one cluster, sharing a similarity of 81.6%, while Brazil and Panama formed another cluster. Meanwhile, Aedes mosquitoes from Netherland and USA formed two separate clusters. The statistical significance of aforementioned clustering status was further verified by the Analysis of Similarities (ANOSIM), which reported a Global R value of 0.96. The clustering status suggested by the cluster analysis was further verified by the findings of the dbRDA. As indicated by the loadings of the dbRDA axes, the abundance of Gammaproteobacteria and Bacilli bacterial classes were found to be responsible for the similarity between gut bacterial diversity in Aedes mosquitoes from India and Sri Lanka. Further studies on the gut-microbial diversity of Aedes mosquitoes are recommended to support the implementation of novel vector control strategies in Sri Lanka.
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.
The effect of egg desiccation period on the hatching success, morphometrics of emerged larvae and F1 generation adults of Aedes aegypti and Aedes albopictus (Diptera: Culicidae)
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Kumari, A. G. Y. G.; Dalpadado, R.; Amarasinghe, L. D.
Dengue is a seasonal vector-borne disease that is transmitted by female Aedes aegypti and Aedes albopictus mosquitoes. One of the most significant challenges in controlling these mosquitoes is the ability of Aedes eggs to withstand prolonged desiccation. This study aimed to investigate the effect of egg desiccation on the hatchability, larval and adult morphometrics, and duration of adult emergence of Ae. aegypti and Ae. albopictus. The Aedes eggs were collected from the field using oviposition traps and soaked in larval-rearing trays. Hatched larvae were reared with fish feed. They were differentiated into Ae. aegypti and Ae. albopictus and transferred to separate pupalrearing containers. The resulting adult mosquitoes were provided with a sugar solution and a cattle blood meal using a membrane feeding system. They were allowed to lay eggs on cloth strips. Initially, the hatchability of fresh eggs was calculated for two species. The head length and total length of the fourth instar larvae and head, thorax, abdomen, total length, wing length, and wing width of adults of both species that emerged from fresh eggs were measured. The days needed for adult emergence from fresh eggs were counted. Subsequently, other egg sheets were air dried and stored within the insectary (at 27±2°C and 75±5 % humidity), and monthly measurements of the aforementioned parameters were collected for eggs subjected to desiccation over six months. According to the results, the hatchability of both Ae. aegypti and Ae. albopictus decreased with increasing egg desiccation periods. The hatchability of Ae. aegypti and Ae. albopictus eggs was highest (75.0±0.6% and 58.3±0.3% respectively) when the eggs were fresh, and lowest (22.0±1.2% and 13.3±0.9% respectively) when they were desiccated for six months. There was a strong negative correlation between hatchability and the desiccation period of both Ae. Aegypti and Ae. albopictus (Pearson's correlation, p<0.05, R2 = 0.840 and R2 = 0.957 respectively). Pearson's correlation also indicated a strong negative correlation between egg desiccation period and head length (p<0.05, R2 = 0.875 for Ae. aegypti and R2 = 0.846 for Ae. albopictus), as well as total length (p<0.05, R2 = 0.812 for Ae. aegypti and R2 = 0.888 for Ae. albopictus) of the fourth instar larvae. The adult emergence was delayed with increasing egg desiccation periods, with the longest duration (Ae. aegypti; 15.0 ± 0.2 days and Ae. albopictus; 26.0 ± 0.2 days) observed when eggs were desiccated for six months. However, no significant differences were found in the morphometrics of adult mosquitoes of both species that emerged from desiccated eggs (one-way ANOVA, p > 0.05). In conclusion, the study showed that prolonged egg desiccation reduced hatchability, delayed adult emergence, and negatively affected the morphometrics of fourth instar larvae of Ae. aegypti and Ae. albopictus. However, the morphometrics of the F1 generation adult mosquitoes were not significantly different from those of fresh eggs, suggesting that the egg desiccation period does not negatively affect the overall morphometrics of adult Aedes mosquitoes.
Indoor resting preference of Aedes (Stegomia; Culicidae) mosquitoes in urban human dwellings of Gampaha District, Sri Lanka
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Dalpadado, C. P. R. D.; Amarasinghe, L. D.
The current study was designed to identify the preferred resting height, place and surface of Dengue vectors, Aedes aegypti and Aedes albopictus, near human dwellings located in urban cites in Gampaha District, Sri Lanka during August 2017 to February 2018. Adult mosquitoes were collected systematically using manual aspiration technique, during 6:00 a.m. and 9.00 a.m. and 4:00 p.m. and 7:00 p.m. from all the resting localities from 280 premises. At each station, resting place, nature of the resting surface and resting height were recorded and mosquitoes were identified down to species level. In total, 378 Aedes mosquitoes (Aedes aegypti 82.3%, Aedes albopictus 17.7%) were collected and of the collected Aedes mosquitoes, 1:8 male to female ratio was observed. 68.3% of Aedes mosquitoes preferred to rest closer to the ground level and 24.9% mosquitoes rested between 1 m to 2 m above the ground level. 4.8% Aedes mosquitoes were found resting between 2 m to 3 m of height and only 1.5% Ae . aegypti mosquitoes were found resting 3 m above the ground level and none of the Ae . albopictus was recorded above 3 m from the ground level. There was no significant difference (p=0.001<0.05) between males and females in resting height for both vectors. Bedrooms were more frequently visited by resting Ae. aegypti mosquitoes (51.8%), followed by living rooms (28.5%) and kitchen (12.4%) while 52.4% female Ae . albopictus were found resting on living rooms and 28.6% in bed rooms. Identified indoor resting places were significantly different for Ae . aegypti and Ae . albopictus in Gampaha district (χ2= 20.895, P< 0.05). Majority of Aedes female mosquitoes were found resting on cloth hangings and curtains (49.3% Ae . aegypti, 77.8% Ae . albopictus) followed by under furniture (24.3% Ae . aegypti, 22.2% Ae . albopictus) . The mean number of mosquitoes per positive premise was 1.35 and maximum total number of Aedes mosquitoes collected at a premise was 7. The maximum number of females collected was 6 and maximum for males were 2 per premise. Higher abundance of Ae . aegypti in the region increases the transmission risk greatly, since Ae . aegypti bites more than one host to complete one blood meal. Since females were found resting closer to floor level especially in hidden locations such as cloth hangings, curtains and under furniture, indoor space spraying should be strengthened targeting these locations to control dengue in future.
Larvicidal and pupicidal activity of Trichoderma longibrachiatum (Tl-AgNPs) and Trichoderma viride (Tv-AgNPs) mediated silver nanoparticles against dengue vector Aedes aegypti
(Faculty of Graduate Studies, University of Kelaniya Sri Lanka, 2022) Perera, D. S.; Amarasinghe, L. D.; Wickramarachchi, S.
Dengue and dengue hemorrhagic fever play major public health problems in Sri Lanka, being endemic within the country since 1960s. Aedes aegypti vectors transmit dreadful diseases like Dengue, Chikungunya, Yellow fever and Zika causing millions of deaths every year throughout the world. An efficient biosynthesis process for the rapid production of nanoparticles would enable the development of a “microbial nanotechnology” for mass-scale production. In the present study, biological silver nanoparticle synthesis using the endo-lichenic fungus, Trichoderma longibrachiatum and Trichoderma viride, where the cell filtrate of the fungus will be used as a reducing and stabilizing agent in the process of nanoparticle synthesis and the filtrate is mixed with silver nitrate solutions to obtain nanoparticles. Fungi are attractive agents for biogenic synthesis of silver nanoparticles because they offer high tolerance to metals and are easy to handle. They also secrete large quantities of extracellular proteins that contribute to the stability of the nanoparticles. They also provide good biomass production and do not require additional steps to extract the filtrate. The mycelial mass of fungi is more resistant to agitation and pressure, so it is more suitable for large-scale syntheses. In the present study, larvicidal and pupicidal effects of T. longibrachiatum and T. viride mediated silver nanoparticles (Tl-AgNPs and Tv-AgNPs) against third instar stage Ae. aegypti larvae and pupae were investigated. The fungi were grown in Richards’ broth containing glucose, agar, potassium nitrate, potassium dihydrogen phosphate, magnesium sulphate and ferric chloride. Fungal biomass filtrates obtained after keeping 48 hours with deionized water and the desired weight(10mg) of fungal mass, were mixed with AgNO3 solution. Synthesized Tl-AgNPs and Tv-AgNPs were characterized by UV-Vis spectroscopy with maximum absorption at 445nm for T. viride and 448nm for T. longibrachiatum. Transmission Electron Microscopy (TEM) showing the formation of monodispersed spherical shaped particles with a mean diameter ranging from 15 to 25 nm. The color changes from pale yellow to dark brown in the solutions with time indicated the formation of nanoparticles initially. Larval and pupal toxicity tests were assessed according to WHO standard protocol. Data were analyzed using IBM SPSS version 20 software. Probit analysis was carried out to determine the LC50 and LC90 of larvicida and pupicidal effect of Tl-AgNPs and Tv-AgNPs for Ae. aegypti after 24 hours and 48 hours of exposure. Study revealed that LC50 for Tl-AgNPs for 24 hours(2.607mg/L) and 48 hours (2.174 mg/L) were higher than LC50 for Tv-AgNPS 24 hours (2.153 mg/L) and 48 hours (1.842 mg/L) exposure time for Ae. aegypti larvae. In addition, LC50 value obtained in pupal toxicity tests revealed Tl-AgNps (4.92 mg/L) is higher than that of Tv-AgNPs(4.79 mg/L) for 24 hour exposure time. It concludes that both Tl-AgNPs and Tv-AgNPs could be used as potential larvicidal and pupicidal agents and Tv-AgNPs are more efficient in controlling Ae. aegypti larvae and pupae.
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.
Mosquito larvicidal effect of Annona glabra fruit extract on dengue vector, Aedes aegypti
(Faculty of Science, University of Kelaniya, Sri Lanka., 2021) Wijebandara, N. R. Y.; Ranasinghe, H. A. K.; Amarasinghe, L. D.; Wickramarachchi, S. R.
Annona glabra is a plant of Family Annonaceae and many plant species belong to this family have been intensively studied since they were discovered to contain compounds with important biological properties. These properties include cytotoxic, antitumor, antiparasitic, antifungal, antispasmodic, repellent, and insecticidal activities. Insecticidal effects of plant extracts vary depending on the plant parts (leaf, seed, fruit, bark) used for the extraction. Larvicidal effect of A. glabra aqueous extract from leaves and seeds have been evaluated against Aedes aegypti mosquitoes in Sri Lanka, and larvicidal effect of fruit is not determined yet. Therefore, the present study was conducted to evaluate the effect of A. glabra fruit extract for its larvicidal efficacy on third instar larvae of Ae. aegypti. Fresh ripen fruits of A. glabra plant were collected from Hunupitiya, (N 06º 58.904/, E 079° 54.281/) in Gampaha district, Sri Lanka. The aqueous crude extract was prepared from powdered A. glabra fruits. Seven concentrations were prepared between the range of 3 g/L – 300 g/L. Batches of 25 third instar larvae of Ae. aegypti were used for larval bioassays. Ae. aegypti mosquito larvae were evaluated in accordance with guidelines of World Health Organization. The experimental setup was repeated four times per each concentration. Probit analysis was used to evaluate the relationship of mortality with the concentration of aqueous crude extract. The A. glabra fruit extract showed a dose-dependent effect against Ae. aegypti larvae after the 48-hour exposure period. The percentage mortality rates have shown a significant variance among different concentrations (P = 0.000). The recorded LC50 and LC90 values for aqueous crude extract were 87.71 ± 5.41 gL-1 and 510.79 ± 12.56 gL-1 respectively, after 48 hours of exposure period. Larvicidal activity of A. glabra plant is supported by previous literature, where the presence of phytochemicals such as saponins, flavonoids, steroids and tannins have shown combined effects in terms of larvicidal action against mosquitoes. Hence, there is a potential of A. glabra aqueous fruit extract as a potential source for the development of an environment-friendly plant-based larvicide against Aedes aegypti.
Naturally Occurring Microbiota in Dengue Vector Mosquito Breeding Habitats and Their Use as Diet Organisms by Developing Larvae in the Kandy District, Sri Lanka
(BioMed Research International, 2020) Ranasinghe, H. A. K.; Amarasinghe, L. D.
Naturally occurring microbiota in mosquito larval habitats are among biotic factors which affect the population dynamics of developing larvae. Many microbiota species serve as food items for vector mosquito larvae, and food limitations within habitats adversely affect larval survival, developmental rate, adult fitness, and thereby vector competence. Therefore, identification of microbiota as associates with larvae reveals their relationship between each other as parasites, pathogens, epibionts, or diet organisms. Analysis of associated microbiota species in the dengue vector larval breeding habitats (n = 40) and the mosquito larval gut content were conducted in Kandy District in Sri Lanka. Study revealed that a total of 22 microbiota species belong to nine phyla (Amoebozoa, Bacillariophyta, Ciliophora, Chlorophyta, Sarcodina, Cyanobacteria/Cyanophyta, Euglenozoa, Ochrophyta/Heterokontophyta, and Rotifera) were encountered from different Ae. aegypti mosquito breeding habitats while 26 microbiota species that belonged to ten phyla were recorded from Ae. albopictus mosquito breeding habitats with one additional phylum Arthropoda. Considering Ae. aegypti breeding habitats, only Philodina citrina in low roof gutters existed as constant species. Considering Aedes albopictus breeding habitats, Volvox aureus in plastic containers, Lecane luna in coconut shells, Phacus pleuronectes in concrete slabs, and Pinnularia sp. in tree holes existed as constant species. The rest of the microbiota existed as common or accidental/rare species in a variety of habitat types. The Shannon-Weiner diversity (21.01 and 19.36) and gamma diversity (eight and eight) of the microbiota associated with Ae. aegypti and Ae. albopictus larvae, respectively, in ponds were found to be higher than other types of breeding habitats recorded during the study. Twelve microbiota species were recorded from larval gut analysis as food organisms of both species of mosquito larvae. However, the distribution of gut microbiota species differed between Ae. aegypti and Ae. albopictus (Chi − square = 21:294, P = 0:002). Identification of microbiota as food items of vector mosquito larvae led to a focus on larval food limitation by introducing food competitors, which could be a potential additional tool for integrated vector control approaches within the country.
Nematicidal activity of Annona glabra aqueous plant extract and extracellular metabolites of two Trichoderma species on root knot nematode Meloidogyne incognita
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Lakmini, W. V.; Amarasinghe, L. D.
The root knot nematode, Meloidogyne incognita, is the most widespread and serious nematode pest damaging root systems of a variety of agricultural and ornamental crops in tropical and subtropical countries throughout the world. Management of this nematode species by integrated application of synthetic insecticides and variety of non-chemical methods are suggested but many are not very effective. Even though, mature leaf extraction of Annona glabra (pond apple or alligator apple; Family Annonaceae), contains some insecticidal properties, there is no clear evidence of its nematicidal effect. This study was conducted to find the efficacy of aqueous leaf extracts of A . glabra, on root knot nematode species, M . incognita attacking spinach plants in comparison to the extracellular metabolites of two species of antagonistic fungi, Trichoderma harzianum and T . viride. Polythene bags were filled with nematode free soil. Single spinach plants having 6 leaves were transplanted into each pots. 10-12 mature adult female nematodes were added to spinach plant pots. These pots were kept outdoor for 2 weeks prior to inoculating the treatments. Above ground growth parameters such as number of total leaves, length of stem, below ground growth parameters such as number of root galls, root length were used to determine nematicidal effect on the nematode infested plants. One-way ANOVA was performed to test whether there is significant difference (95% confidence interval) between each concentrations of treatments. Results revealed that spinach plants treated with A . glabra plant aqueous leaf extract showed highest stem length and higher number of leaves compared to the control treatment. Nematicidal effect of A . glabra aqueous extract is more effective than T . viride but lower than T . harzianum when considering above ground plant growth parameters. 125 g/L of A . glabra plant aqueous leaf extract and 140 mg/L of fungal mycelium T . viride extract and 100 mg/L of T . harzianum concentrations showed the highest effect for controlling root knot nematodes. This study concludes that there is a nematicidal activity of A . glabra aqueous plant leaf extract even at lowest concentration (100 mg/L) and extracellular metabolites of T . harzianum and T . viride on M . incognita.
Photocatalytic Activity of Biosynthesized of Silver Nanoparticles Using Leaf Extract of Annona glabra
(International Postgraduate Research Conference 2019, Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2019) Paragodaarachchi, Y.L.; Wickramarachchi, P.A.S.R.; De Silva, C.; Amarasinghe, L. D.
Recently metallic nanoparticles were found to possess photocatalytic activity on organic molecules under visible radiation a phenomenon which will be useful in degrading and removing hazardous organic dyes. During this study the photocatalytic activity of Annona glabra - AgNPs (bare NPs) and Tween 80-stabilized Annona glabra – AgNPs (stabilized NPs) was studied by monitoring the degradation of methylene blue as a model dye. AgNPs were synthesized by incubating the leaf extract of A. glabra (2 mL) with silver nitrate (1 mM, 20.00 mL) for 3 hours. The solution was kept under dark conditions with continuous slow agitation. The solution was centrifuged at 6000 rpm for 20 minutes to separate the AgNPs and NPs were washed with water. The synthesized AgNPs were characterized using UV – Visible spectrometer, particle size analyzer, scanning electron microscope. In order to synthesize stabilized AgNPs, biofabricated AgNPs as above were ultrasonicated for 15 mins and added to a solution of Tween 80 (1% w/v, 20.0 mL) and kept stirring for 3 hours. To determine the photocatalytic activity, above prepared AgNPs (25mg/mL, 2.0 mL) were added to a Methylene blue solution (1 x 10-5 M, 50.0 mL). The suspension was stirred under dark conditions for 30 mins. It was exposed to sunlight under slow agitation. Photodegradation was monitored at 30-minute intervals by withdrawing 5 mL aliquots of AgNP added methylene blue solution. The aliquots were centrifuged, and the absorbance was measured using the UV-Visible spectrophotometer at 665for a period of 3 hours. The AgNPs are spherical in shape and show a characteristic absorbance peak at 417 nm. This peak is due to the surface plasmon resonance of the AgNPs. The average size range of the nanoparticles is 10 – 190 nm. Methylene blue solution with added AgNPs became opaque overtime. Initially, the methylene blue solution with bare AgNPs showed subtle reduction of absorbance of the solution. Then the reduction of absorbance was leveled off near the end of the experiment. The absorbance decreased from 0.985 to 0.796 within a period of 3 hours which is a 19.19% reduction of the initial absorbance of the solution. The opacity of the methylene blue solution with stabilized AgNPs increased only by the end of the experiment. Stabilized AgNPs showed methylene blue degradation with higher efficiency than bare AgNPs. The absorbance of the solution reduced from 1.361 to 0.145 within a period of 3 hours which is an 89.34% reduction of the initial absorbance of the solution. Both bare and Tween 80-stabilised AgNPs showed photocatalytic activity on the degradation of methylene blue. The Photocatalytic activity was enhanced by the stabilization of biogenic A. glabra AgNPs with Tween 80.
A Preliminary Study on the Relationship between Arthropod Diversity and Vegetation Diversity in Four Contrasting Ecosystems in Hanthana Mountain Range of Sri Lanka, during the Post-Monsoon Dry Season
(2023) Weerathunga, W. A. Manasee; Athapaththu, A. M. Gihan; Amarasinghe, L. D.
This study assesses the relationship between arthropod and vegetation diversity in four ecosystems with different types of vegetation, during a post-monsoonal season. We determined the arthropod diversity in vegetation surrounding an aquatic environment (AQ), a broad-leaved wet, evergreen forest ecosystem (BL), a Pinus caribaea monoculture plantation (PN), and a Pinus plantation artificially enriched with indigenous broad-leaved tree species (PNEN) located in the Hanthana mountain range, Sri Lanka. Arthropods randomly sampled from three randomly selected sites (5 m × 5 m) of each ecosystem were identified up to the highest possible taxa using standard identification keys. Woody and herbal vegetation was identified via a plant census. Arthropod and vegetation diversities were computed separately for each site using the Shannon–Wiener Index (H). Arthropods of 68 species and 43 families were found. AQ had the greatest arthropod diversity (H 2.642), dominated by Olios spp., followed by BL (H 2.444), dominated by a tettigonid species, Oxytate spp. and Psechrus spp. PN was third (H 1.411), dominated by Dicaldispa spp. PNEN had the lowest (H 1.3500), dominated by an ant species. Contrastingly, PNEN had the highest plant diversity (H 2.614) and PN, the lowest (H 0.879). In AQ, BL, and PN, the arthropod diversity was linearly dependent on plant diversity (R2 0.423, p≤ 0.001), whereas it was not so when PNEN was also included (R2 0.008, p≤ 0.001). This shows that higher plant diversity contributes to greater arthropod diversity in ecosystems where human intervention is minimal. But this pattern was not visible in PNEN, which is an artificially created ecosystem.
Prevalence of micro-fauna associated in rice field habitats in Kurunegala district in Sri Lanka and potential mosquito larvicidal effect of Vorticella microstoma
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Ranasinghe, H. A. K.; Amarasinghe, L. D.
Micro-fauna are associated with most of the mosquito larval breeding habitats in tropical climate. There may be parasitic, pathogenic or even predatory species among these biota to mosquito larvae and their potential use against mosquitoes is a new avenue of study in vector control. Rice fields are common breeding sites for certain vector mosquito species in Sri Lanka. The objective of the present study was to find the prevalence of micro-fauna in order to search for potential parasitic or pathogenic taxa/ species associated with mosquito larvae inhabiting rice field breeding habitats and to carry out bioassays for potential taxa. Sampling was done from paddy fields (n=12) in Kurunegala district using a metal larval scooper and the samples were preserved using Rose Bengal solution. Twelve micro-fauna species were recorded; the highest abundance was recorded from Vorticella microstoma (62.68%). Other micro-fauna species recorded were Zoothamnium sp., Diurella stylata, Keratella valga, Lecane luna, Monostyla bulla, Philodina citrina, Acanthocystis aculeata, Canthocamptus staphylinus, Daphnia longis, Notholca acuminata, Arcella arenaria . Also, 98 . 60 % of mosquito larvae which were collected from rice fields belonged to the genus Culex . Culex gelidus and Culex tritaeniorynchus represented the majority of samples (76.26%) and the highest abundance was recorded from Cu . gelidus . Study revealed that Vorticella microstoma trophont stage was lethal to Cu . tritaeniorynchus and Cu . quinquefasciatus larvae. Bioassay resulted that, 32.14% of Cu . quinquefasciatus died 05 days after infection with lab maintained V . microstoma cultures . Pupation was also delayed compared to the duration of normal life-cycle and only 10.71% of population emerged as adults. 100% mortality was recorded from Cu . quinquefasciatus in 2 days of infection with V . microstoma. The mean mortality percentage of two mosquito species studied were significantly different from each other (IBM SPSS Software, One-Way ANOVA: P<0.05). Trophonts of V . microstoma were infected to thorax, abdominal segments and anal papillae regions of larvae. The results of study revealed that Vorticella microstoma could be used as killing agent of mosquito larvae in future studies and would be a new avenue to work on environmentally agreeable manner in reducing the Culex spp . mosquito populations .
Volatiles from host plant brinjal attract the brinjal Fruit and Shoot Borer -Leucinodes orbonalis Guenee
(Journal of Asia-Pacific Entomology, 2021) Nusra, M. S. F.; Udukala, D. N.; Amarasinghe, L. D.; Paranagama, P. A.
Brinjal Fruit and Shoot Borer- Leucinodes orbonalis Guenee is a major insect pest on brinjal- Solanum melongena worldwide. An effective strategy used in developing pest controlling agents is the synergism between insect pheromones and host plant volatiles, which can increase the attraction of insect pest. The present study was aimed at investigating the chemical constituents and attractant effects of the volatiles extracted from different parts of the host plant brinjal on the behavior of adult L. orbonalis. Bioassay using Y-shaped olfactometer revealed that the one-day old virgin female, gravid female and male insects respond positively to the host plant volatiles extracted from fruits, leaves and shoots but not to that of flowers. It was shown that the gravid females were significantly attracted to all three volatiles (p < 0.05). Bioassay using X-shaped olfactometer identified that all three types of insects highly preferred the volatiles from fruits (p < 0.05). Gas chromatography-mass spectrometry analysis of volatiles indicated that brinjal plant produces volatile secondary metabolites, which include 2,2′ -(Ethane-1,2-diylbis(oxy))bis(ethane-2,1-diyl) dibenzoate (12.11%), 3,7-dimethylocta-1,6-dien-3-ol (22.38%), Benzyl alcohol (22.9%) and Benzyl alcohol (27.06%) as major constituents from fruits, shoots, leaves and flowers respectively. Responses of insects to the volatiles from host plant in the absence of visual cues direct us to focus on the importance of host plant volatiles to locate the plant. Results of this study emphasize the major role that host plant volatiles play in the attraction of insect pests towards the plant.
Volatiles from host plant brinjal attract the brinjal Fruit and Shoot Borer -Leucinodes orbonalis Guenee
(Journal of Asia-Pacific Entomology, 2021) Nusra, M. S. F.; Udukala, D. N.; Amarasinghe, L. D.; Paranagama, P. A.
Brinjal Fruit and Shoot Borer- Leucinodes orbonalis Guenee is a major insect pest on brinjal- Solanum melongena worldwide. An effective strategy used in developing pest controlling agents is the synergism between insect pheromones and host plant volatiles, which can increase the attraction of insect pest. The present study was aimed at investigating the chemical constituents and attractant effects of the volatiles extracted from different parts of the host plant brinjal on the behavior of adult L. orbonalis. Bioassay using Y-shaped olfactometer revealed that the one-day old virgin female, gravid female and male insects respond positively to the host plant volatiles extracted from fruits, leaves and shoots but not to that of flowers. It was shown that the gravid females were significantly attracted to all three volatiles (p < 0.05). Bioassay using X-shaped olfactometer identified that all three types of insects highly preferred the volatiles from fruits (p < 0.05). Gas chromatography-mass spectrometry analysis of volatiles indicated that brinjal plant produces volatile secondary metabolites, which include 2,2′ -(Ethane-1,2-diylbis(oxy))bis(ethane-2,1-diyl) dibenzoate (12.11%), 3,7-dimethylocta-1,6-dien-3-ol (22.38%), Benzyl alcohol (22.9%) and Benzyl alcohol (27.06%) as major constituents from fruits, shoots, leaves and flowers respectively. Responses of insects to the volatiles from host plant in the absence of visual cues direct us to focus on the importance of host plant volatiles to locate the plant. Results of this study emphasize the major role that host plant volatiles play in the attraction of insect pests towards the plant.
Volatiles from host plant brinjal attract the brinjal Fruit and Shoot Borer -Leucinodes orbonalis Guenee
(2021) Nusra, M. S. F.; Udukala, D. N.; Amarasinghe, L. D.; Paranagama, P. A.
Blinjal Fruit and Shoot Borer- Leucinodes orbo11alis Guenee is a major insect pest on brinjal- Sola11u111 111elo11ge11a worldwide. An effective strategy used in developing pest controlling agents is the synergism between insect pheromones and host plant volatiles, which can increase the attraction of insect pest. The present study was aimed at investigating the chemical consti tuents and attractant effects of the volatiles extracted from different parts of the host plant brinjal on the behavior of ad ult L. orbo11alis. Bioassay using Y-shaped olfactometer revealed that the one-day old virgin female, gravid female and male insects respond positively to the host plant volatiles exU'acted from fruits, leaves and shoots but not to that of flowers. It was shown that the gravid females were significantly attracted to all three volatiles (p < 0.05). Bioassay using X-shaped olfactometer identified that all three types of insects highly preferred the volatiles from fruits (p < 0.05). Gas chromatography-mass specuomeuy analysis of volatiles indicated that brinjal plant produces volatile seconda1y metabolites, which include 2,2' -(Ethane-l ,2-diylbis(oxy))bis(ethane-2,1-diyl) di benzoate (12.11 %), 3,7-dimethylocta-1,6-dien-3-ol (22.38%), Benzyl alcohol (22.9%) and Benzyl alcohol (27.06%) as major constituents from fruits, shoots, leaves and flowers respectively. Responses of insects to the volatiles from host plant in the absence of visual cues direct us to focus on the importance of host plant volatiles to locate the plant. Results of this study emphasize the major role that host plant volatiles play in the attraction of insect pests towards the plant.