Browsing by Author "Amarasinghe, L.D."

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Acute Toxicity and Sub-lethal Effects of Chlorpyrifos to Three Larvivorous Fish, Poecilia eticulate Aplocheilus dayi, and Rasbora daniconius
(University of Kelaniya, 2012) Ganehiarachchi, G.A.S.M.; Amarasinghe, L.D.; Weerasinghe, T.
The insecticide belonging to the organophosphate group, chlorpyrifos 40 % EC, is reported to be highly toxic on fish and it is under restricted usage globally. This chemical is used by Dry Zone chena cultivators and hence, there is a possibility of contaminating the bordering water sources rich with larvivorous fish by tracer amounts of this chemical. Two naturally occurring fish species, Aplocheilus dayi (nalahandaya) and Rasbora daniconius (dandiya) and introduced fish species, Poecilia reticulata (wild guppy) are among the potential larvivorous fish in Sri Lanka. The present study was carried out to find out; acute toxicity of chlorpyrifos 40% EC (commando™), to Aplocheilus dayi, Rasbora daniconius and Poecilia reticulata, effects of sub-lethal concentrations of chlorpyrifos on offspring production and on histological alterations in the gill structure. The exposure media contained a series of concentrations (50, 5, 0.5 and 0 μg/l) of chlorpyrifos 40 EC in glass aquaria. Based on the mortality data, LC50 (24 hr) value of chlorpyrifos 40 EC for Aplocheilus dayi, Rasbora daniconius and Poeceilia reticulata was estimated as 0.514μg/l, 0.472 μg/l and 0.882μg/l respectively. It was also revealed that chlorpyrifos 0.5 μg/l of sub-lethal level to P. reticulata has induced production of hatchlings (mean number of 15 hatchings per female per day) whereas no production of hatchings was observed in other treatments during the exposure period. Histopathological study of the gills exposed to 5 and 50 μg/l of chlopyrifos for 48 hr showed hypertrophy of gill arches, lifting and degeneration of lamella epithelium, degeneration of gill filaments and vasodialation in the lamella axis of both Rasbora daniconius and Poecilia reticulata. This study concludes that LC50 values vary for three fish species tested and Poecilia reticulata is more resistant than the other two species. The sub-lethal levels of contaminants of chlorpyrifos 40EC cause histological and physiological aberration in freshwater fish.
An integrated approach to the management of rice root knot nematode, Meloidogyne graminicolain Sri Lanka
(Journal of Science of the University of Kelaniya, Sri Lanka, 2011) Amarasinghe, L.D.
This study was carried out to design tools for integrated management of root knot nematode, Meloidogyne graminicola, in rice in Sri Lanka. Rice varieties namely, At5, At353, Bg304, Bg305, Bg359, Bg450, Bg94-1, Bg379-2, Ld355 and Ld356 were tested for their reactions against M. graminicola. Effect of poultry manure, cow-dung and paddy husk with or without cinnamon-leaf oil in reducing M. graminicola was studied. It was revealed that rice varieties At5, At353, Bg304, Bg305, Bg450, Bg379-2, and Ld356 were tolerant to M. graminicola as compared to Bg94-1 which is highly susceptible with high rate of reproduction. Plants treated with poultry manure had significantly low nematode population. Plants grown in poultry manure enriched soil had lower yellow and dead leaves as compared to other plants. Addition of cinnamon-leaf oil improved the nematode control. This study concludes that rice varieties namely At353, Ld356, Bg304, At5, Bg305, Bg450 and Bg379-2 can be used for fields that are prone to M. graminicola infestation while poultry manure can be utilized at least occasionally as a nematicide cum fertilizer to reduce nematode infestation level in rice plants and to improve soil fertility.
Antagonist Potential of Vorticella microstoma on the larval development of Culex gelidus and Aedes aegypti
(19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Ranasinghe, H.A.K.; Amarasinghe, L.D.
Selection of effective biological agents which can suppress the growth of immature stages of mosquito vectors has drawn a wide attention in disease control programmes. Vorticella microstoma is a parasitic ciliate which has an ability to parsitize on larval stages of mosquitoes and inhibit their growth. However, the potential antagonist activity has not been evaluated in detail in Sri Lanka. Fifteen each of first, second, and third instar larvae of Cx. gelidus and Ae. aegypti were placed in separate V. microstoma culture bottles at room temperature (27± 2 ºC) and mortality rate of mosquito larvae was observed after 48 h. Bioassay was done in completely randomized design with controls. The first, second, and third instar larvae of Cx. gelidus were allowed to be infested with the trophont stage of V. microstoma. Heavily infested larvae with V. microstoma were identified by the presence of parasites attached all over the body surface. V. microstoma trophonts did not usually attach to siphon region of mosquito larvae when they are alive. None of the instar levels of Ae. aegypti showed susceptible to infection with V. microstoma. In the first instar larvae of Cx. gelidus, thorax and the abdominal segments had the attachment of 30–35 trophonts of V. microstoma, whereas 2–4 trophonts had attached to the anal papillae. Higher densities of V. microstoma were found in abdominal segments of second instar larvae of Cx. gelidus, whereas total of 45–50 trophonts had attached to thoracic region and abdominal segments. Fifty to fifty-five trophonts of V. microstoma had attached to third instar larvae of Cx. gelidus, with higher densities in the anal papillae followed by abdominal segments; in the anal papillae, 20–25 trophonts were found to be attached. V. microstoma infection was positively correlated with the body size of mosquito larvae. The percentage mortality of the first, second, and third instar larvae of Cx. gelidus did not significantly differ from each other (One-Way ANOVA: IBM SPSS Statistic Software, P<0.05). Therefore, the study results would be a new avenue to work on environmentally agreeable manner in reducing the Cx. gelidus vector mosquito populations.
Arthropod diversity in four different ecosystems in the Mid Country Wet Zone of Sri Lanka
(Department of Zoology and Environmental Management, University of Kelaniya, Sri Lanka, 2017) Weerathunga, W.A.M.T.; Athapaththu, A.M.G.K.; Amarasinghe, L.D.
Arthropods contribute significantly to biodiversity of natural environments. The present study was done to determine the diversity of arthropods in four ecosystems with different vegetation. 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 close to each other in Peradeniya were selected. In each environment, arthropods were sampled in three randomly-selected sites (5m x 5m) using four sampling methods, namely, pit-fall traps, sticky traps, sweep net and beating tray. Collected arthropods were identified upto the highest possible taxa using standard identification keys, based on morphological characteristics. Simultaneously, a plant census was conducted. Arthropod- and vegetation diversities were computed separately for each site using Shannon-Wiener Index (H). A total of 324 arthropod individuals were collected from all four sites. (AQ–71, BL–44, PN–20, and PNEN–189).They belonged to 68 species and 43 families. A total of 4416 plants were observed, from 84 species and 42 families. AQ had the greatest arthropod diversity (H=2.642), dominated by Olios spp. (Family Sparassidae) followed by BL (H=2.444), dominated by three arthropods, namely, a tettigonid species, Oxytate spp. (Family Thomisidae), and Psechrus spp. (Family Psechridae). PN had the next highest arthropod diversity (H=1.411), dominated by Dicaldispa spp. (Family Chrysomelidae). The lowest arthropod diversity was found at PNEN (H=1.3500), dominated by a formicid species. In contrast when considering plant diversity, PNEN had the highest diversity (H=2.614) and PN the lowest (H=0.879). AQ (H=1.810) and BL (H=1.871) had intermediate values. The arthropod diversity of AQ and BL was not significant from each other, while AQ was significant from the other two (F=5.50, P=0.024). PN and PNEN were not significant from each other. It was observed that in AQ, BL and PN the arthropod diversity was linearly dependent on plant diversity (R2=0.423) whereas it was not so when PNEN was also included (R2=0.008). This shows that higher plant diversity contributes to greater arthropod diversity in ecosystems where human intervention is minimum. But this pattern was not visible in PNEN, which is an artificially-created ecosystem.
Bacterial Diversity in the Midgut of Field Caught Culex tritaeniorhynchus
(International Postgraduate Research Conference 2019, Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2019) Ranasinghe, H.A.K.; Gunathilaka, P.A.D.H.N.; Amarasinghe, L.D.; Rodrigo, W.W.P.
Ingestion of blood meal by female mosquitoes triggers a series of physiological processes in midgut where symbiotic microbes also exist. These symbiotic microbes can be engineered to produce molecules that inhibit pathogens; through paratransgenic approach. Little is known about the midgut microbes of Culex mosquitoes and no attempt has been made so far in Sri Lanka. Cx. tritaeniorhynchus mosquitoes were separated from the entomological surveys conducted at Kelaniya Medical officer of Health (MOH) area from June – August 2019. Unfed adult female mosquitoes were sacrificed using a cold shock and were surface sterilized using 70% ethanol followed by rinsing with phosphate buffer saline (PBS). Midgut of mosquitoes were dissected and midgut of ten mosquitoes were pooled in sterile PBS (250 μL) to make a homogenized lysate. A dilution series (100- 10-7) was made from lysate. 100 μL from each dilution was plated on Plate Count Agar (PCA) and were incubated for 48 hours at 37 0C. Pure cultures for each microbe were obtained from the primary plates using streak plate method, sub culturing in Nutrient Agar. The experiment set up was repeated 25 times with ten mosquito pools at each effort. Colony separation was done based on phenotypical differences and basic biochemical tests. Stab cultures of isolates were sequenced for 16S ribosomal RNA partial gene. To identify the closest related sequence, obtained sequences were analyzed by Bioedit software package and completely aligned sequences were compared with the BLAST database. The evolutionary history was inferred using the neighbor-Joining method and the evolutionary analyses were conducted in MEGA X. A total of eight bacterial strains namely; Staphylococcus pasteuri, Bacillus megaterium, Staphylococcus cohnii, Pantoea dispersa, Staphylococcus chromogenes, Bacillus aquimaris, Staphylococcus arlettae, Staphylococcus scuiri was isolated from Cx. tritaeniorhynchus (n=250). All of these species were belonged to two phyla; Firmicutes and Proteobacteria. Phylum Firmicutes was the dominant phyla which include seven species. The evolutionary distances which were computed using Tajima-Nei method were used to infer the phylogenetic tree. It represented a close relationship between the species of two genera; Staphylococcus and Bacillus while the relationship was distant for genus Pantoea. The present data strongly encourage further investigations to explore the potential usage of these microbes through the paratransgenic approach which is a novel eco-friendly vector control strategy
Clonal susceptibility and population dynamics of Tea red spider mite, Oligonychus coffeae Nietner, (Acarina:Tetranichidae)
(Proceedings of the 45th Annual sessions of the Sri Lanka Association for the Advancement of Science, 1989) Thirugnanasuntharan, K.; Amarasinghe, L.D.
Clonal susceptibility and population dynamics of tea red spider mite, Oligonychus coffeae, Nietner (Acarina: Tetranychidae) under laboratory conditions
(Sri Lanka Journal of Tea Science, 1990) Thirugnanasuntharan, K.; Amarasinghe, L.D.
Comparative Effect of Parasitism of Ciliated Protists Associated with Selected Vector Mosquito Larvae in Selected Rice Field Habitats in Ganewatte, Kurunegala District, Sri Lanka
(Institute of Biology Sri Lanka, 2021-09) Wijesinghe, S.; Amarasinghe, L.D.
Mosquito breeding sites provide habitats for diversifying naturally occurring microbiota and favour different types of interactions including parasitism. This study was carried out to determine the natural occurrence of ciliated protist parasites associated with selected vector mosquito species inhabiting rice fields in Ganewattha area in Kurunegala district in Sri Lanka and to compare their parasitic effects on the selected vector mosquito larvae. Mosquito samples were collected from five rice field sites during the period from June to December 2020. The samples were observed for epibionts/parasitic infections under the microscope. Moribund or dead mosquito larvae in each sample collection were observed for internal parasitic infections. A comparative study was carried out to determine the lethal effect of ciliated organisms on Culex tritaeniorhynchus (n=50) and Culex gelidus larvae (n=50) in replicated trials (R=3). The minimum number of V. microstoma that cause a lethal effect on Cx. tritaeniorhynchus third instar larvae (n=100) was determined by a bioassay with ten replicates and two controls per each replicate. A total of 1650 third instar mosquito larvae of Culex tritaeniorhynchus (62.8%) and Culex gelidus (37.2%) were collected in this study. Ciliated protists namely Vorticella microstoma, Zoothamnium spp. and Chilodonella spp. associated with both species of mosquito larvae were identified. Results revealed that V. microstoma has the potential of infection to cause 71.33 (±5.23) mean percentage mortality of Cx. tritaeniorhynchus larvae. A minimum of 1000 V. microstoma is required to kill a third instar larva of Cx. tritaeniorhynchus at 69.60 (±2.40) hours of exposure. Culex gelidus larvae showed only 41.33 (±3.43) mean percentage mortality. This study concludes that V. microstoma is the most successful ciliated parasite as a killing agent of Culex tritaeniorhynchus vector mosquito larvae. Their abundance and effectiveness may contribute to develop them as an effective biocontrolling agent in the future.
Comparative study on larvicidal activity of green synthesized silver nanoparticles and Annona glabra (Annonaceae) aqueous extract to control Aedes aegypti and Aedes albopictus (Diptera: Culicidae)
(Heliyon 6, 2020) Amarasinghe, L.D.; Wickramarachchi, P.A.S.R.; Aberathna, A.A.A.U.; Sithara, W.S.; De Silva, C.R.
The present study reports mosquito larvicidal potential of green synthesized silver nanoparticles by using Annona glabra leaves (An-AgNPs). Synthesized An-AgNPs were characterized by Ultraviolet-Visible spectroscopy (UVVIS), Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS) technique and Fourier transform infrared spectroscopy (FTIR). Colur change from pale yellow to brick red of the plant extract and AgNO3 solution indicated the formation of An-AgNPs initially. Surface Plasmon Resonance (SPR) band at 435 nm in the UV-Vis confirmed the formation of An-AgNPs. SEM images showed that An-AgNPs were spherical in shape. FTIR proved that An-AgNPs were functionalized with biomolecules in A. glabra leaves. Based on DLS analysis the average size range of synthesized An-AgNPs was determine to be 10–100 nm and 100–1000 nm. Third instar larvae of dengue vector mosquitoes, Aedes aegypti and Aedes albopictus were subjected to larvicidal bioassays in a range of concentrations of An-AgNPs and A. glabra crude aqueous leaf extract (2–10 mg/L). AnAgNPs exhibited very high larvicidal activity against dengue vector mosquito larvae; LC50 value for Ae. aegypti at 24 h exposure to An-AgNPs (Plant extract: AgNO3 1 : 10) 5.29 mg/L; An-AgNPs (Plant extract: AgNO3 2 : 10) 2.43 mg/L while LC50 value for Ae. albopictus at 24 h exposure to An-AgNPs (Plant extract: AgNO31:10) 3.02 mg/ L; An-AgNPs (Plant extract: AgNO3 2:10) 2.51 mg/L. LC50 values obtained for A. glabra leaf extract tested against Ae. aegypti and Ae. albopictus are 5.94 mg/L and 5.00 mg/L respectively at 24-hour exposure. This study further revealed that Ae. albopictus is more susceptible than to Ae. aegypti to a given concentration of An-AgNPs and to crude aqueous leaf extract of A. glabra. Larvicidal effect of An-AgNPs is superior to the crude aqueous leaf extract of A. glabra. An-AgNPs is a potent larvicide for dengue vector control.
Contarinia maculipennis as an emerging threat to Dendrobium in Sri Lanka - A case study.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Dias, M.A.; Amarasinghe, L.D.; Jayalath, W.G.H.; Attanayake, R.N.
Blossom midge, Contarinia maculipennis which belongs to Order Diptera: Family Cecidomyiidae is considered as one of the major threat to ornamental and several crop plant species due to its wide host range. For the first time C. maculipennis was recorded from Dendrobium sp. in 1992 from Florida, but the origin of this species is considered as Southeast Asian region. In Korea, it is officially nominated as a quarantine pest since 2007 due to it’s sever economic impact on vegetable crops and ornamental plants. For the first time in Sri Lanka, completely damaged Dendrobium cultivation was found in an ornamental plant nursery at Gampaha district in 2017. It was noted that the symptoms were similar to that of blossom midge damage. Maggots were found to be feeding inside unopened flower buds, causing deformed, discolored buds and blossoms causing premature bud or blossom drop. Floral buds were often found to be rotted. Samples from immature bud stage to fully opened flowers were randomly collected from infected fields into polythene bags. To identify causative agent, floral buds with larval stages were kept in glass containers to allow them to complete their life cycle and thereby morphological characters were studied to confirm the pest species. In addition, yellow color grease sheets were kept inside the greenhouses to trap any adult stages of the pest species. Samples were collected and preserved using 70% ethanol for identification. Since all the damaged flower buds displayed symptoms of bacterial rots, to determine if any bacterial infection is also associated with the symptoms, bacterial isolation procedure was carried out. Different stages of floral samples were separately surface sterilized for two minutes using 70% ethanol and three serial washings with sterilized distilled water. Tissue macerate was prepared and kept for 3 hours before culturing on Nutrient Agar (NA) plates, Potato Dextrose Agar (PDA) and Luria-Bertani (LB) plates. Each sample had three replicates and ten samples were cultured. Growth from the tissues were observed and pure cultures were obtained. Relative length of the first and second flagellomeres, wing length and pattern, larval sternal spatula and its associated papillae and larval eighth abdominal segments were compared with identification keys which were used to identify the genera, Contarinia. The adult stages of trapped insects and adult stages of insect immerged from the larval stages were useful in confirming the species as C. maculipennis. Basic biochemical tests and Gram’s staining assisted in identifying the bacterium as belonging to the genera, Erwinia sp. and it appears that the bacterial infection occurs as a secondary infection after larval stages of C. maculipennis damage the floral tissues. This is the first record of C. maculipennis infecting orchid nurseries in Sri Lanka and if proper care is not taken it will invade other crop species as the pest has a broad host range. It is not clear whether the pest was a recent introduction through the imports of plant material or whether it is a result of host jump and therefore, it warrants further research.
Dengue risk based on sociocultural/socioeconomic geographic factors in Kelaniya MOH area
(Research Symposium 2009 - Faculty of Graduate Studies, University of Kelaniya, 2009) Nadeeka, P.V.J.; Amarasinghe, L.D.; Gunathilaka, P.A.D.H.N.; Madushani, I.L.D.
THIS STUDY INVOLVES GEOGRAPHIC, SOCIOCULTURAL AND SOCIOECONOMIC ANALYSIS CONDUCTED FOR THE YEAR 2008 DENGUE FEVER OUTBREAKS IN KELANIYA MEDICAL OFFICER OF HEALTH (MOH) AREA. LOCATIONS OF THE RESIDENCE OF THE 120 DENGUE CASES REPORTED AT KELANIYA MOH OFFICE WERE OBTAINED USING GPS. A STRUCTURED QUESTIONNAIRE THAT INCLUDED 16 OF PRIMARY DATA WAS GIVEN TO EACH PATIENT HOUSEHOLD AFTER VISITING INDIVIDUAL OF THEM AT RESIDENCE. GEOGRAPHIC ATTRIBUTES RELATED TO DENGUE INCIDENCE WERE RECORDED CONCURRENTLY. PRIMARY DATA INCLUDED FAMILY DETAILS, AGE AND GENDER OF THE FAMILY MEMBERS, LIVING CONDITIONS, AWARENESS AND KNOWLEDGE ABOUT DENGUE, HEALTH CARE, HUMAN DWELLINGS, OCCUPATIONAL STATUS, MOSQUITO PROTECTION PRACTICES, ACCESSIBILITY BY ROAD, SANITATION PRACTICES, WASTE DISPOSAL MANAGEMENT AND FREQUENCY, CULTURAL PRACTICES REGARDING STORAGE OF WATER CONTAINERS, VEGETATION COVER AROUND THE HOUSES, AND INDOOR /OUTDOOR AEDES MOSQUITO BREEDING PLACES. MOSQUITO LARVAE COLLECTED FROM BOTH INDOOR AND OUTDOOR POOLS WERE REARED UNTIL ADULTS ARE EMERGED IN THE LABORATORY. RESULTS REVEALED THAT 86% HOUSEHOLDS HAVE PERMANENT RESIDENCE. PERCENTAGE INFECTED MALE: FEMALE RATIO WAS 48%: 52% WHICH IS NOT SIGNIFICANTLY DIFFERENT. THE VULNERABILITY OF THE AGE GROUPS FOR DENGUE FEVER WERE FOUND AS 1-5 YRS (24%), 6-18 YRS (44%), 19-55 YRS (24%) AND MORE THAN 55 YRS (3%). THE ADULT MOSQUITO POPULATION CONTAINED 77.6% OF AEDES ALBOPICTUS ATTAINING INDOOR (20.7%) AND OUTDOOR (79.3%) BREEDING SITES WHILE 22.4% OF AE. AEGYPTI ATTAINING INDOOR (38.6 %) AND OUTDOOR (61.4%) BREEDING SITES. ONLY 32% OF HOUSE PREMISES WERE DENSELY COVERED WITH VEGETATION. RECORDED DENGUE CASES AND GEOGRAPHIC FACTORS WERE LINKED TO A GIS DATABASE AND PRESENTED IN DIGITIZED MAPS TO SHOW DENGUE RISK FACTORS IN KELANIYA MOH AREA.
Dengue vector mosquito surveillance and dengue risks based on environmental factors in Kelaniya MOH area
(Research Symposium 2010 - Faculty of Graduate Studies, University of Kelaniya, 2010) Nadeeka, P.V.J.; Amarasinghe, L.D.
Potential dengue vector mosquito surveillance was conducted at 25 sites in Kelaniya Medical Office of Health area that contains 37 Divisional secretariat areas and 6 PHI divisions, from April 2008 to Feb 2010 at monthly intervals. Sites were selected based on census using GPS. The abundance of Aedes albopictus and Ae. aegypti was determined using ovitraps installed in out door and indoor at each site and by adult emergence rate from eggs and field caught mosquitoes. Adult mosquito species were identified morphologically. Recorded dengue cases within the Kelaniya MOH area were obtained after a written approval from Regional Director of Health Services of Gampaha. Based on the ovitrap study it was revealed that oviposition prevalence of Aedes mosquitoes in outdoor was higher than that of indoor in all the study sites. It was highest in Hunupitiya PHI division followed by Dalugama, Kiribathgoda, Peliyagoda, Kelaniya and Wedamulla divisions. The study also reveald that indoor and outdoor adult mosquito populations based on the emergence rate are dominatwed by Ae.albopictus (75%) in the study sites. The highest abundance of Ae.albopictus was recorded in Hunupitiya PHI division in the outdoor site.There were positive correlations between the number of suspected dengue patients and the abundance of Ae.aegypti (P=0.027) and Ae.albopictus(P=0.049) in indoor sites of each PHI divisions.the least number of patients and mosquito populations were recorded at Wedamulla PHI division. Within the each year of study period, there were two peaks of the outdoor mean number of eggs per ovitrap each in April and December. Indoor mean number of eggs per ovitrap was significantly correlated with number of wet days (P=0.033). However, outdoor mean number of eggs per ovitrap was significantly correlated with humidity (P=0.049).Recorded dengue cases and environmental factors were linked to GIS database and presented in digitized maps. Financial assistance from NSF RG/2007/HS/14 is highly acknowledged.
Dengue vector mosquito surveillance in Kelaniya University premises
(Proceedings of the 1st Annual Research Symposium of the Rajarata University of Sri Lanka, 2010) Wadduwage; Amarasinghe, L.D.
Dengue vector surveillance in Kelaniya MOH area
(Research Symposium 2009 - Faculty of Graduate Studies, University of Kelaniya, 2009) Nadeeka, P.V.J.; Amarasinghe, L.D.
Potential dengue vector mosquito surveillance was conducted at 24 sites in Kelaniya Medical Office of Health area that contains 37 Divisional secretariat areas and 6 PHI divisions, from April 2008 to March 2009 in monthly interval. Sites were selected based on census using GPS. The abundance of Aedes albopictus and Ae. aegypti was determined using ovitrap method and by field caught mosquitoes. Ovitraps were installed at the rate of three out door and three indoor at each site. The minimum distance between two sites was not less than two km. Traps were collected after two overnights. Total number of mosquito eggs in each wooden paddle collected from indoor and outdoor of each site was counted separately. The wooden paddles with eggs were left in containers half filled with hay infusion and covered using a mosquito net until adults were emerged in the laboratory. Adult mosquito species were identified morphologically. Study revealed that adult mosquito population based on the emergence rate in the study site is dominated by Ae.albopictus (77%). Peak of the abundance of Ae.albopictus in outdoor was found in period of April to July 2008. The abundance of Ae.aegypti in outdoor did not show significant difference over the study period. There was a positive correlation of monthly mean temperature with the abundance of Ae.aegypti in outdoor (P=0.03, r=0.603). Within the first six months of study period the highest outdoor mean number of eggs per ovitrap was recorded in Hunupitiya PHI division (74). However during the latter six months it was reported in Kelaniya PHI division (28). When outdoor mean number of eggs per ovitrap is considered, numbers were significantly correlated with rainfall (P=0.008, r=0.724) and humidity (P=0.02, r=0.65). Peak Ovitrap Index values were shown in period followed by heavy rains (435.9mm), from April to July in both indoor 47.6-68.2% and outdoor 80.9- 90.9%. Lower Ovitrap index values were resulted in January where low level of rain fall is experienced (140.9mm).
Density and diversity of mosquito larvae associated with rice field and marshland habitats in two climatically different areas in Sri Lanka
(International Journal of Entomological Research, 2014) Amarasinghe, L.D.; Weerakkodi, W.G.I.S.
Rice field and marshland habitats have significant influence on production of mosquito larval populations including vector mosquitoes and hence the disease transmission. Study revealed that mosquito larval density in rice fields of two climatic regions were significantly different and that of rice fields in semi dry zone are more diverse than those of wet zone (H’ semi dry zone = 1.48; H’ wet zone = 1.35). Marshland habitats in wet zone were represented mainly by Culex gelidus. Both Culex gelidus and Culex tritaeniorhynchus larvae were highly available in rice fields of two climatic regions. They were mainly associated with high Total Dissolved Solids, (TDS) ≥10.00 mg/L, pH level of 6-8, low Dissolved Oxygen, (DO) 5.0 – 6.0 mg/L, low nitrate level, ≤ 5.0 mg/L and low phosphate level, ≤ 1.0 mg/L. However, they could tolerate a range of Biological Oxygen Demand (BOD) level in water. Mosquito larval density in two habitat types in wet zone was not significantly different. Temporal variation of C. gelidus and C. tritaeniorhynchus was positively or negatively correlated with cultivation cycle of rice in semi dry zone area. The main goal of this study was to determine the variation of mosquito larval diversity in the rice field and marshy land habitats in two climatically different areas, wet zone and semi-dry zone in Sri Lanka. Sampling of mosquito larvae was done using standard dipping method.
Determination of the efficiency of diets for larval development in mass rearing Aedes aegypti (Diptera: Culicidae)
(CABI Publishing, 2018) Gunathilaka, P.A.D.H.N.; Uduwawala, U.M.H.U.; Udayanga, N.W.B.A.L.; Ranathunge, R.M.T.B.; Amarasinghe, L.D.; Abeyewickreme, W.
Larval diet quality and rearing conditions have a direct and irreversible effect on adult traits. Therefore, the current study was carried out to optimize the larval diet for mass rearing of Aedes aegypti, for Sterile Insect Technique (SIT)-based applications in Sri Lanka. Five batches of 750 first instar larvae (L 1) of Ae. aegypti were exposed to five different concentrations (2-10%) of International Atomic Energy Agency (IAEA) recommended the larval diet. Morphological development parameters of larva, pupa, and adult were detected at 24 h intervals along with selected growth parameters. Each experiment was replicated five times. General Linear Modeling along with Pearson's correlation analysis were used for statistical treatments. Significant differences (P < 0.05) among the larvae treated with different concentrations were found using General Linear Modeling in all the stages namely: total body length and the thoracic length of larvae; cephalothoracic length and width of pupae; thoracic length, thoracic width, abdominal length and the wing length of adults; along with pupation rate and success, sex ratio, adult success, fecundity and hatching rate of Ae. aegypti. The best quality adults can be produced at larval diet concentration of 10%. However, the 8% larval diet concentration was most suitable for adult male survival.
Diversity and abundance of vector mosquitoes in Wanawasala area of Kelaniya in Sri Lanka and some factors affecting their abundance and distribution
(Institute of Biology, Sri Lanka, 2012) Dalpadado, C.P.R.D.; Amarasinghe, L.D.
Diversity of midgut bacteria in larvae and females of Aedes aegypti and Aedes albopictus from Gampaha District, Sri Lanka
(Parasites & Vectors volume 14, 2021) Ranasinghe, K.; Gunathilaka, N.; Amarasinghe, L.D.; Rodrigo, W.; Udayanga, L.
Abstract Background: The midgut microbiota of mosquitoes maintain basal immune activity and immune priming. In recent years, scientists have focused on the use of microbial communities for vector control interventions. In the present study, the midgut bacteria of larvae and adults of Aedes aegypti and Ae. albopictus were assessed using both fieldcollected and laboratory-reared mosquitoes from Sri Lanka. Methods: Adults and larvae of Ae. aegypti and Ae. albopictus were collected from three selected areas in Gampaha Medical Officer of Health area, Gampaha District, Western Province, Sri Lanka. Bacterial colonies isolated from mosquito midgut dissections were identified by PCR amplification and sequencing of partial 16S rRNA gene fragments. Results: Adults and larvae of Ae. aegypti and Ae. albopictus harbored 25 bacterial species. Bacillus endophyticus and Pantoea dispersa were found more frequently in field-collected Ae. aegypti and Ae. albopictus adults, respectively. The midgut bacteria of Ae. aegypti and Ae. albopictus adults (X2 = 556.167, df = 72, P < 0.001) and larvae (X2 = 633.11, df = 66, P < 0.001) were significantly different. There was a significant difference among the bacterial communities between field-collected adults (X2 = 48.974, df = 10, P < 0.001) and larvae (X2 = 84.981, df = 10, P < 0.001). Lysinibacillus sphaericus was a common species in adults and larvae of laboratory-reared Ae. aegypti. Only P. dispersa occurred in the field-collected adults of Ae. aegypti and Ae. albopictus. Species belonging to genera Terribacillus, Lysinibacillus, Agromyces and Kocuria were recorded from Aedes mosquitoes, in accordance with previously reported results. Conclusions: This study generated a comprehensive database on the culturable bacterial community found in the midgut of field-collected (Ae. aegypti and Ae. albopictus) and laboratory-reared (Ae. aegypti) mosquito larvae and adults from Sri Lanka. Data confirm that the midgut bacterial
The ecology of a montane grassland in Sri Lanka. VII. Biomass production
(Ceylon Journal of Science, Biological Sciences, 1983) Amarasinghe, L.D.; Pemadasa, M.A.
Biomass accumulation was studied monthly on 2 montane grasslands in Sri Lanka at 900 m and 560 m alt. from June 1976 to May 1977. The upper site was a dense sward dominated by Cymbopogon nardus (65.4%), Themeda tremula (25.4%) andEulalia trispicata (10.1% of standing crop) and the lower site was a sparse sward dominated by C. nardus (68.6%) and Panicum maximum (13.9%) with somePennisetum polystachyon (7.7%). Total standing crop biomass was higher at the upper site than at the lower site and increased 4-fold at both sites over the years. Productivity estimates were 911.2 g/m² for the upper sites and 679.5 g for the lower site. There was no significant difference in the amount of C. nardus between sites, but the upper site supported a much denser sward of T. tremula accounting for the higher productivity of this site.
Effect of cinnamon oils on the root-knot nematode Meloidogyne graminicola in rice seedlings and young rice plants
(Institute of Biology, Sri Lanka, 2011) Amarasinghe, L.D.; Wijesinghe, W.K.A.G.A.