Medicine
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This repository contains the published and unpublished research of the Faculty of Medicine by the staff members of the faculty
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Item Development of the sterile Insect technique to control the dengue vector Aedes aegypti (Linnaeus) in Sri Lanka(Public Library of Science,San Francisco, 2022) Ranathunge, T.; Harishchandra, J.; Maiga, H.; Bouyer, J.; Gunawardene, Y.I.N.S.; Hapugoda, M.Background: The Sterile Insect Technique (SIT) is presently being tested to control dengue in several countries. SIT aims to cause the decline of the target insect population through the release of a sufficient number of sterilized male insects. This induces sterility in the female population, as females that mate with sterilized males produce no offspring. Male insects are sterilized through the use of ionizing irradiation. This study aimed to evaluate variable parameters that may affect irradiation in mosquito pupae. Methods: An Ae. aegypti colony was maintained under standard laboratory conditions. Male and female Ae. aegypti pupae were separated using a Fay and Morlan glass sorter and exposed to different doses of gamma radiation (40, 50, 60, 70 and 80 Gy) using a Co60 source. The effects of radiation on survival, flight ability and the reproductive capacity of Ae. aegypti were evaluated under laboratory conditions. In addition, mating competitiveness was evaluated for irradiated male Ae. aegypti mosquitoes to be used for future SIT programmes in Sri Lanka. Results: Survival of irradiated pupae was reduced by irradiation in a dose-dependent manner but it was invariably greater than 90% in control, 40, 50, 60, 70 Gy in both male and female Ae. aegypti. Irradiation didn't show any significant adverse effects on flight ability of male and female mosquitoes, which consistently exceeded 90%. A similar number of eggs per female was observed between the non-irradiated groups and the irradiated groups for both irradiated males and females. Egg hatch rates were significantly lower when an irradiation dose above 50 Gy was used as compared to 40 Gy in both males and females. Irradiation at higher doses significantly reduced male and female survival when compared to the non-irradiated Ae. aegypti mosquitoes. Competitiveness index (C) scores of sterile and non-sterile males compared with non-irradiated male mosquitoes under laboratory and semi-field conditions were 0.56 and 0.51 respectively at 50 Gy. Signification: Based on the results obtained from the current study, a 50 Gy dose was selected as the optimal radiation dose for the production of sterile Ae. aegypti males for future SIT-based dengue control programmes aiming at the suppression of Ae. aegypti populations in Sri Lanka.Item Development of an alternative low-cost larval diet for mass rearing of Aedes aegypti mosquitoes(Hindawi Publishing, 2020) Senevirathna, U.; Udayanga, L.; Ganehiarachchi, G.A.S.M.; Hapugoda, M.; Ranathunge, T.; Gunawardene, N.S.BACKGROUND: Aedes aegypti is a major vector of arboviruses that may be controlled on an area-wide basis, using novel approaches such as Sterile Insect Technique (SIT) and Incompatible Insect Technique (IIT). Larval diet is a critical factor to be considered in mass rearing of Aedes mosquitoes for SIT and IIT programs. Therefore, the current study is aimed at evaluating the effects of two novel diets developed from dry fish powder on the growth and development of immature stages and adult fitness-related characteristics of Ae. aegypti in Sri Lanka. METHOD: Three batches of the first instar Ae. aegypti larva, each containing 250 larvae, were exposed to three different larval diets as standard dry fish powder (D1), dry fish powder meal and brewer’s yeast (D2), and International Atomic Energy Agency- (IAEA-) recommended diet (D3), separately. Morphometric and developmental parameters of the 4th instar larvae, pupae, and adult mosquitoes reared under different dietary treatments were measured. The entire experimental setup was replicated thrice. A General Linear Model (GLM) in the form of two-way ANOVA was used for the statistical analysis. RESULTS: Significant diet-based variations were observed in the head length, head width, thoracic length, thoracic width, abdominal length, abdominal width, and total length (; ) of Ae. aegypti larvae. The highest pupation success and the larval size were observed from the larvae fed the D2 diet, while the lowest was reported from D1. All adult morphometric parameters of adult male and female Ae. aegypti mosquitoes also denoted significant dietary variations, reporting the best-sized adults from the D2 diet (; ). Further, significantly higher fecundity and male longevity were also shown by the adult Ae. aegypti (; ) mosquitoes reared under diet D2. CONCLUSION: Based on all the growth and developmental parameters, the D2 diet tends to perform similar to the IAEA-recommended diet in mass rearing of Ae. aegypti mosquitoes, while being more inexpensive. Therefore, larval diet D2 could be suggested as the ideal diet for mass rearing of Ae. aegypti for IIT and SIT-based vector control in Sri Lanka.Item Larvicidal potential of five selected Dragonfly Nymphs in Sri Lanka over aedes aegypti (Linnaeus) larvae under laboratory settings.(Hindawi Pub. Co., 2018) Samanmali, C.; Udayanga, L.; Ranathunge, T.; Perera, S.J.; Hapugoda, M.; Weliwitiya, C.INTRODUCTION: Limitations in breeding source reduction practices, development of insecticide resistance in mosquitoes, and ill effects of chemical controlling methods on human and ecosystem health have motivated Sri Lankan authorities working for dengue control to seek for alternative, ecofriendly, and sustainable approaches for controlling of Aedes vectors, to manage dengue epidemics. The present study attempted to investigate the predation efficiency of locally available dragonfly nymphs over Aedes aegypti under laboratory conditions, aiming to evaluate the potential of using dragonflies as biocontrol agents against dengue. METHODS: Nymphal stages of five locally abundant dragonfly species were collected from different stagnated water bodies in Belihuloya area. After morphological identification, a well grown individual of each species was starved for 12 hours and introduced into a glass tank containing 1L of pond water with 200 larvae (4th instar) of Aedes aegypti. Number of larvae survived in the tank was enumerated hourly up to 48 hours. In case where >75% of larvae are consumed by dragonfly nymphs, additional Ae. aegypti larvae were introduced into such tanks. Experiment was repeated for five times. Same procedure was followed with different stages of growth of the dragonfly nymphs characterized by the highest predation rate. General Linear Model followed by Tukey's pairwise comparison was used for statistical analysis. RESULTS: The predation rates of different dragonfly species varied significantly (p<0.05), whereby Anax indicus (110±7.14 per day) indicated the highest, followed by Pantala flavescens (54.07±5.15) and Gynacantha dravida (49.00±11.89), while Tholymis tillarga (23.47±2.48) had the lowest. Further, significant variations in the larval predation were found among different maturity stages (10-20; 25-35; and 35-45 mm in body length) of Ana. indicus (p<0.05). Regardless of statistical significance, a relatively higher larvicidal activity was observed at dusk than in dawn. Conclusion. Ana. indicus, which is characterized by the highest predation rate, and P. flavescens that has the widest geographical distribution within Sri Lanka along with a notable predation efficacy could be recommended as potential candidates for field trials in biological control of dengue outbreaks via suppression of Ae. aegypti larvae.Item Predatory efficacy of five locally available copepods on Aedes larvae under laboratory settings: An approach towards bio-control of dengue in Sri Lanka.(San Francisco, CA : Public Library of Science, 2019) Udayanga, L.; Ranathunge, T.; Iqbal, M. C. M.; Abeyewickreme, W.; Hapugoda, M.Many countries are in search of more effective and sustainable methods for controlling dengue vectors, due to undeniable inefficiencies in chemical and mechanical vector control methods. Bio-control of vectors by copepods is an ideal method of using interactions in the natural ecosystem for vector management, with minimum consequences on the environment. Current study determined the predatory efficacy of five locally abundant copepod species on, Aedes larvae under laboratory conditions. Copepods were collected from the pre-identified locations within the districts of Gampaha and Kandy, and identified morphologically. Individual species of copepods were maintained as separate colonies with Paramecium culture and wheat grain as supplementary food. Five adult copepods of each species was introduced into separate containers with 200 larvae (1st instar) of Aedes aegypti. Number of larvae survived in containers were enumerated at 3 hour intervals within a duration of 24 hours. Each experiment was repeated five times. The same procedure was followed for Ae. albopictus. Significance in the variations among predation rates was evaluated with General Linear Modelling (GLM) followed by Tukey's pair-wise comparison in SPSS (version 23). Significant variations in predation rates of studied copepod species were reported (p<0.05), whereby M. leuckarti indicated the highest followed by M. scrassus, while C. languides indicated the lowest predatory efficacy. The effect of different Aedes larval species on the predation rates of copepods remained significant (p<0.05), even though the effect on predatory efficiency was not significant. Based on the findings, both M. leuckarti and M. scrassus, with the highest predatory efficiencies, could be recommended as potential candidates for biological controlling of Aedes vectors in Sri Lanka.Item Use of mechanical and behavioural methods to eliminate female Aedes aegypti and Aedes albopictus for sterile insect technique and incompatible insect technique applications.(BioMed Central, 2019) Gunathilaka, N.; Ranathunge, T.; Udayanga, L.; Wijegunawardana, A.; Gilles, J. R. L.; Abeyewickreme, W.BACKGROUND:Sex separation of mosquitoes at different stages is currently being attempted to ensure the successful release of male mosquitoes in novel vector control approaches. Mechanical and behavioral techniques have been tried most frequently. METHODS: Batches of (n = 300) Aedes aegypti and Ae. albopictus pupae were used for standard sieving (using sieves with 1.12, 1.25, 1.40 and 1.60 mm mesh sizes) and the Fay-Morlan glass plate separation methods. Male and female separation by each method was calculated. For behavioral separation, a spiked blood meal with different concentrations (0, 2, 4, 6, 8 and 10 ppm) of ivermectin and spinosad (spinosyn, 12% w/v), were provided to a batch (n = 300) of adult Ae. aegypti and Ae. albopictus (1:1 sex ratio) followed by observation of mortality. An additional "double feeding method" involved provision of a further blood meal after 24 h, with the same concentrations of ivermectin and spinosad as the initial feeding, followed by a 48-h observation of mortality. All experiments were repeated five times. RESULTS: In the standard sieving method, the percentage of males and females separated at different pore sizes differed significantly (P < 0.05). The majority of the male pupae were collected in the 1.12 mm pore sized sieve for both Ae. aegypti (73%) and Ae. albopictus (69%) while females were retained mainly in the sieve with the pore size of 1.25 mm. In the Fay-Morlan glass plate separation, 99.0% of the Ae. aegypti and 99.2% of the Ae. albopictus introduced male pupae could be separated, but with female contaminations of 16 and 12%, respectively. Provision of a blood meal spiked with 8 ppm of ivermectin under the "double feeding" was identified as the most effective way of achieving 100% female elimination for both Aedes species. CONCLUSIONS: With 100% separation, use of a spiked blood meal is a more effective method of sex separation than the mechanical methods. Application of the spiked blood meal approach as a second separation level for sexes, after applying the Fay-Morlan glass plate method, could achieve 100% sex separation of sexes whilst allowing a reduction in the amount of toxicants required.Item Corrigendum to "Larvicidal Potential of Five Selected Dragonfly Nymphs in Sri Lanka over Aedes aegypti (Linnaeus) Larvae under Laboratory Settings"(Hindawi Publishing Corporation, 2019) Samanmali, C.; Udayanga, L.; Ranathunge, T.; Perera, S.J.; Hapugoda, M.; Weliwitiya, C.ABSTRACT: [This corrects the article DOI: 10.1155/2018/8759459.]. Erratum for, Larvicidal Potential of Five Selected Dragonfly Nymphs in Sri Lanka over Aedes aegypti (Linnaeus) Larvae under Laboratory Settings. BioMed Research International. 2018; 2018:8759459.Item Efficacy of blood sources and artificial blood feeding methods in rearing of aedes aegypti (Diptera: Culicidae) for sterile insect technique and incompatible insect technique approaches in Sri Lanka(Hindawi, 2017) Gunathilaka, P.A.D.H.N.; Ranathunge, T.; Udayanga, L.; Abeyewickreme, W.INTRODUCTION: Selection of the artificial membrane feeding technique and blood meal source has been recognized as key considerations in mass rearing of vectors. METHODOLOGY: Artificial membrane feeding techniques, namely, glass plate, metal plate, and Hemotek membrane feeding method, and three blood sources (human, cattle, and chicken) were evaluated based on feeding rates, fecundity, and hatching rates of Aedes aegypti. Significance in the variations among blood feeding was investigated by one-way ANOVA, cluster analysis of variance (ANOSIM), and principal coordinates (PCO) analysis. Results. Feeding rates of Ae. aegyptisignificantly differed among the membrane feeding techniques as suggested by one-way ANOVA (p<0.05). The metal plate method was identified as the most efficient and cost-effective feeding technique. Blood feeding rate of Ae. aegypti was higher with human blood followed by cattle and chicken blood, respectively. However, no significant difference was observed from the mosquitoes fed with cattle and human blood, in terms of fecundity, oviposition rate, and fertility as suggested by one-way ANOVA (p>0.05). CONCLUSIONS: Metal plate method could be recommended as the most effective membrane feeding technique for mass rearing of Ae. aegypti, due to its high feeding rate and cost effectiveness. Cattle blood could be recommended for mass rearingAe. aegypti.