Publications by authors named "Tharaka Ranathunge"

8 Publications

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Voltage-Gated Sodium Channel () Mutation-Based Pyrethroid Resistance in Populations of Three Endemic Dengue Risk Areas of Sri Lanka.

Biomed Res Int 2021 22;2021:8874092. Epub 2021 May 22.

Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya, Sri Lanka.

Background: Pyrethroid insecticides are widely used in many countries for chemical-based control of . Regardless of their efficacy, the constant use of insecticides has induced insecticide resistance mechanisms, such as knockdown resistance () in mosquitoes. Sri Lankan Vector Controlling Entities (VCE) have been using a variety of pyrethroid insecticides as the primary approach for dengue control. However, development of any resistance among the mosquitoes has been limitedly studied in the country. Therefore, the current study was conducted to evaluate the prevalence of F1534C, V1016G, and S989P mutations among mosquito populations in three dengue endemic high-risk regions of Sri Lanka. . Immature (both pupae and larvae) stages of mosquitoes were collected from Colombo, Gampaha, and Kandy districts of Sri Lanka from February 2018 to December 2019. Polymerase Chain Reaction- (PCR-) based assay for molecular genotyping of mutations was performed to identify the prevalence of mutations in collected populations, separately. The frequencies of the resistant and susceptible kdr alleles were determined by using the Hardy-Weinberg equilibrium.

Results: The populations from Colombo, Gampaha, and Kandy districts showed 46%, 42%, and 22% of F1534C mutation allele frequencies, along with 15%, 12%, and 6% of V1016G mutation allele frequencies, respectively. The mutation allele frequencies of S989 in Colombo, Gampaha, and Kandy districts were 9.5%, 8.5%, and 4.5%, respectively. The wild-type (PP) genotype remained predominant within all the three districts, whereas the homogenous (QQ) mutation genotype occurred only in minority. The abundance of Q allele frequency in mosquitoes was relatively higher for all the three mutations in Colombo.

Conclusions: The findings clearly indicate that long-term insecticide applications and multiple use of pyrethroids have led to the acquisition of mutations, leading to the development of insecticide resistance among local populations, especially in the Colombo and Gampaha districts. Therefore, evaluation of the prevalence levels of these mutations highlights the necessity for shifting towards novel vector control strategies.
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http://dx.doi.org/10.1155/2021/8874092DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8166465PMC
May 2021

Development of an Alternative Low-Cost Larval Diet for Mass Rearing of Mosquitoes.

Biomed Res Int 2020 24;2020:1053818. Epub 2020 Nov 24.

Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya, Sri Lanka.

Background: 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 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 in Sri Lanka.

Method: Three batches of the first instar larva, each containing 250 larvae, were exposed to three different larval diets as standard dry fish powder (D), dry fish powder meal and brewer's yeast (D), and International Atomic Energy Agency- (IAEA-) recommended diet (D), separately. Morphometric and developmental parameters of the 4 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 ( > 4.811; < 0.05) of larvae. The highest pupation success and the larval size were observed from the larvae fed the D diet, while the lowest was reported from D. All adult morphometric parameters of adult male and female mosquitoes also denoted significant dietary variations, reporting the best-sized adults from the D diet ( > 3.54; < 0.05). Further, significantly higher fecundity and male longevity were also shown by the adult ( > 7.897; < 0.01) mosquitoes reared under diet D.

Conclusion: Based on all the growth and developmental parameters, the D diet tends to perform similar to the IAEA-recommended diet in mass rearing of mosquitoes, while being more inexpensive. Therefore, larval diet D could be suggested as the ideal diet for mass rearing of for IIT and SIT-based vector control in Sri Lanka.
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http://dx.doi.org/10.1155/2020/1053818DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7718045PMC
May 2021

Use of cyclopoid copepods for control of (Diptera: Culicidae) mosquito larvae to prevent re-emergence of malaria in Sri Lanka.

J Vector Borne Dis 2019 Jul-Sep;56(3):200-206

Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya, Ragama, Sri Lanka.

Background & Objectives: Although malaria is eliminated from Sri Lanka, there is a possible risk of spread from infected persons coming from malaria endemic countries. The presence of major and potential vectors in several parts of the country along with drug resistance, necessitates the identification of effective and novel control methods. The present study focused on identifying effective biological control agents for anopheline larvae using carnivorous copepods under laboratory and field conditions to prevent re-introduction of malaria in the country.

Methods: Three copepod species, namely Mesocyclops scrassus, Cyclops varicans and C. languides collected from different areas in the country were cultured by adding supplementary food, and their predatory efficacy was evaluated under laboratory and field conditions.

Results: Significant variation (p <0.05) was observed in predation rates of studied copepod species. The species M. scrassus showed the highest predacious efficiency, and consumed the highest number of anopheline larvae under laboratory and field conditions. Further, M. scrassus had higher survival rate than C. varicans and C. languides.

Interpretation & Conclusion: The results of the study suggest that the predatory copepod M. scrassus can be used as a bio-control agent for the control of Anopheles mosquitoes to prevent re-emergence of malaria in the country. Additional research is suggested to identify naturally available copepod species and their predatory efficacy.
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http://dx.doi.org/10.4103/0972-9062.289393DOI Listing
August 2020

Predatory efficacy of five locally available copepods on Aedes larvae under laboratory settings: An approach towards bio-control of dengue in Sri Lanka.

PLoS One 2019 28;14(5):e0216140. Epub 2019 May 28.

Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya, Sri Lanka.

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.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0216140PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6538144PMC
January 2020

Use of mechanical and behavioural methods to eliminate female Aedes aegypti and Aedes albopictus for sterile insect technique and incompatible insect technique applications.

Parasit Vectors 2019 Mar 28;12(1):148. Epub 2019 Mar 28.

Department of Paraclinical Sciences, Faculty of Medicine, Sir John Kotelawala Defence University, Ratmalana, Sri Lanka.

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.
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http://dx.doi.org/10.1186/s13071-019-3398-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6437921PMC
March 2019

Larvicidal Potential of Five Selected Dragonfly Nymphs in Sri Lanka over (Linnaeus) Larvae under Laboratory Settings.

Biomed Res Int 2018 3;2018:8759459. Epub 2018 Dec 3.

HELPO Eco Green Ltd., Talbot Town, Galle, Sri Lanka.

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 vectors, to manage dengue epidemics. The present study attempted to investigate the predation efficiency of locally available dragonfly nymphs over 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 . 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 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 (110±7.14 per day) indicated the highest, followed by (54.07±5.15) and (49.00±11.89), while (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 (p<0.05). Regardless of statistical significance, a relatively higher larvicidal activity was observed at dusk than in dawn. , which is characterized by the highest predation rate, and 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 larvae.
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http://dx.doi.org/10.1155/2018/8759459DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6304608PMC
April 2019

Efficacy of Blood Sources and Artificial Blood Feeding Methods in Rearing of (Diptera: Culicidae) for Sterile Insect Technique and Incompatible Insect Technique Approaches in Sri Lanka.

Biomed Res Int 2017 15;2017:3196924. Epub 2017 Aug 15.

Dengue Mega Project, Faculty of Medicine, University of Kelaniya, Ragama, Sri Lanka.

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 . 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 significantly differed among the membrane feeding techniques as suggested by one-way ANOVA ( < 0.05). The metal plate method was identified as the most efficient and cost-effective feeding technique. Blood feeding rate of 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 ( > 0.05).

Conclusions: Metal plate method could be recommended as the most effective membrane feeding technique for mass rearing of , due to its high feeding rate and cost effectiveness. Cattle blood could be recommended for mass rearing .
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http://dx.doi.org/10.1155/2017/3196924DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5574269PMC
May 2018
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