Browsing by Author "Ranathunge, T."

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Biocontrol potential of six locally available fish species as predators of Aedes aegypti in Sri Lanka
(Elsevier Ltd, 2021) Ranathunge, T.; Kusumawathie, P.H.D.; Abeyewickreme, W.; Udayanga, L.; Fernando, T.; Hapugoda, M.
ABSTRACT: This study was conducted to evaluate the potential of six locally abundant fish species to control Aedes mosquito larvae and thereby manage dengue epidemics in a sustainable, cost-effective and environmentally friendly manner. The biocontrol efficacy of six larvivorous fish species, namely, Poecilia reticulata, Rasbora daniconius, Aplocheilus dayi, Oriochromis mossambicus, O. niloticus and Puntius bimaculatus, was evaluated under laboratory and field conditions. Five size-matched fish (of the same species) were introduced into separate tanks (replicates) containing 2 L of dechlorinated water and 200 third instar larvae of Aedes aegypti (L.). The number of larvae consumed by each fish species was recorded at three-hour intervals for 24 h. Acclimatized fish were introduced into a total of eighteen artificial breeding habitats located in the Gampola Medical Officer of Health (MOH) area at the species level with three replications. In addition, three breeding sites without fish were monitored as controls. Aedes larvae were monitored by dipping and siphoning methods in each breeding habitat at weekly intervals for three months and the number of fish surviving in each habitat was tallied. Over 24 h under laboratory conditions, O. mossambicus showed the highest predation rate, consuming 320.2 ± 14.5 larvae per day, with a predatory efficiency of 87.5 ± 3.5%. In comparison, O. niloticus consumed 264.6 ± 12.2 larvae per day with consumption efficiciency of 78.1 ± 3.7%, whereas R. daniconius had the lowest larval consumption (33.2 ± 2.7 larvae per day) and predatory efficiency (33.2 ± 3.2%). Over 12 weeks of observation under field conditions, breeding sites with Ap. dayi had the lowest Aedes larval counts, followed by Po. reticulata. Considering predation efficiency and survival under field conditions, Ap. dayi and Po. reticulata were considered to be the best potential candidates for biological control of Ae. aegypti. Further studies under field settings are warranted to evaluate the survival and predatory potential of the selected candidates under more varied environmental conditions.
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.
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.
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.
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.
Evaluation of the Pyrethroid Resistance based on Voltage-Gated Sodium Channel (VGSC) Mutations in Aedes aegypti populations of Colombo, Gampaha and Kandy Districts in Sri Lanka
(International Postgraduate Research Conference 2019, Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2019) Ranathunge, T.; Udayanga, L.; Sarasija, S.; Karunathilaka, S.; Nawarathne, S.; Rathnarajah, H.; Dulficar, F.F.; Shafi, F.N.; Dassanayake, R.S.; Gunawardene, Y.I.N.S.
Many countries focus on chemical based vector control strategies to restrict the disease transmissions, where pyrethroid insecticides are widely used as the first line of defense against Ae. aegypti. However, the constant use of insecticides have proven to induce insecticide resistance in mosquitoes. The knockdown resistance (kdr) occurs due to mutations in the Voltage Sensitive Sodium Channel (VSSC) or mutations in the Voltage-Gated Sodium Channel (VGSC), coded by the VSSC gene. Only three kdr mutations namely, the V1016G, S989P, and F1534C have been confirmed as commonly occurring amino acid substitutions among mosquito populations in Southeast Asia. Therefore, to extend this observation, current study was conducted to evaluate the prevalence of V1016G and F1534C mutations among Ae. aegypti mosquito populations in three different geographical regions of Sri Lanka. Immature (both pupae and larvae) stages of Ae. aegypti mosquitoes were collected from Colombo, Gampaha and Kandy districts from March to December 2018 and samples were transported to the Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya. A total of 855 Ae. aegypti larvae were collected from all districts and polymerase chain reaction (PCR) assay for molecular genotyping of mutations was performed for collected all Ae. aegypti larvae (III instar), to identify the prevalence of kdr mutations in the three Ae. aegypti populations. The frequencies of the resistant and susceptible kdr alleles were determined by using the Hardy–Weinberg Equilibrium for each of the point mutation. The Ae. aegypti populations from Colombo, Gampha and Kandy districts showed 40.07% (123/307), 39.58% (114/288) and 19.58% (47/240) of V1016G and F1534C mutations, respectively. The wild type (RR) genotype remained predominant within all the three districts, whereas the homogenous (SS) mutation genotype occurred only in minority. Further, the F1534C was predominant in Ae. aegypti populations of all districts. Among the kdr mutation population, heterogeneous genotyping (RS) for both V1016G and F1534C was prominent, while SS genotyping for V1016G mutation was not observed in the Kandy district. The findings clearly denote that long-term insecticide applications and multiple use of pyrethroids has led to the progression of insecticide resistance among local Ae. aegypti populations. Therefore, evaluation of the prevalence levels of these kdr mutations highlights the necessity for shifting towards novel vector control strategies
Hemocup blood feeder: An affordable and simplified blood-feeding device for maintenance of aedes aegypti mosquito colonies in Sri Lanka
(Academic Press, 2023) Dilani, P.V.D.; Wickramasinghe, P.D.S.U.; Lakshman, G.V.C.P.; Ranathunge, T.; Dassanayake, R.S.; Silva, G.Y.I.N.
Dengue is a mosquito-borne viral disease mainly transmitted by Aedes aegypti and disease control is primarily reliant on mosquito vector control strategies. In the failure of conventional vector control strategies, new strategies are being developed which specifically require the maintenance of mosquito colonies in the laboratories. Blood-feeding is an essential part of the routine colony maintenance of Ae. aegypti. Therefore, the current study was focused on developing a simplified artificial membrane-feeding device, "Hemocup" feeder out of affordable material. viz., plastic cups, styrofoam insulation system, parafilm-M, and preheated water to facilitate the Ae. aegypti artificial blood feeding. The performance of the device was compared to that of a commercially available blood-feeding device, "Hemotek", by assessing the blood-feeding rate, fecundity, and egg hatchability. Similar blood feeding rates were observed for Hemocup and Hemotek methods (91.8 ± 1.6 and 94.3 ± 1.6 respectively>0.05) as well as comparable fecundity between the two methods (20.8 ± 0.7 and 22.0 ± 1.5 respectively; p > 0.05). Furthermore, there was no statistically significant difference in egg hatchability between the two methods (91.9 ± 1.4 and 93.8 ± 1.4, respectively; p > 0.05). The results indicate that this simple Hemocup blood-feeding system can be used for routine colonization of laboratory strains of Ae. aegypti and for mass-rearing purposes.
Isolation of a Potential Microbial Agent for Controlling Dengue Vector Mosquitoes in Sri Lanka
(19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Induwara, R.; Fernando, M.; Ranathunge, T.; Parakrama, G.; Hapugoda, M.
Controlling dengue vector mosquito is the most appropriate controlling method for dengue in the absence of an effective drug or a vaccine for dengue viruses. Vector control can be performed using variety of approaches such as environmental management, chemical and biological control etc.; which have been used in recent vector control activities. Due to the development of resistant varieties against chemical insecticides, the present study attempted to identify larvicidal activity of bacteria collected from the natural environment, as an ideal environmental friendly and effective strategy for controlling Aedesaegypti (Linnaeus), a dengue vector mosquito species. Zero dengue infection was reported in Pudumurippu area in the District of Kilinochchi, Northern Province of Sri Lanka in a preliminary survey. Spore forming microbes were isolated through spread plate technique using water and sediment samples collected from a reservoir in Pudumurippu. Larvicidal activity of each isolate was tested by Ae. aegypti third instar Larvae (L3) in vitro. The highest larvicidal activity was observed in an isolated bacterium from a reservoir water sample under laboratory and field conditions. This bacterium was presumptively identified and subjected to 16s-rRNA sequence analysis. Larvicidal activity of this bacterium was compared with a currently used Bacillus thuringiensisisraelensis (Bti). As well as optimum physiological characteristic features of isolated strain was determined by growing the bacteria strain on nutrient agar supplemented with different NaCl concentrations and different pH values. Isolated bacterium was confirmed as a new strain of Bacillus cereus (SL001; MG827268). This bacterial strain showed the highest larvicidal activity at 5% (1×105 CFU/ml), with mean cumulative mortality rate 92±4.1% and 84.2 ±5.3% at 48 hours’ post challenged under laboratory and field conditions respectively. When compared with Bti, this novel strain showed significantly higher (p < 0.05) larvicidal activity. B. cereus (SL001) displayed high growth rate while tolerating wide range of salinity (0-30gL-1) and pH (6-10). Based on the findings, B. cereus (SL001) with the highest larvicide efficiencies could be an ideal candidate for biological controlling of Ae. aegypti dengue vector mosquitoes in Sri Lanka. Further analysis of this bacterium is on going at present.
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.
Optimization of Irradiation Dose for Sterilization of Aedes aegypti (Linnaeus) Mosquitoes for Application of Sterile Insect Technique (SIT) Program in Sri Lanka
(International Postgraduate Research Conference 2019, Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2019) Ranathunge, T.; Adikari, D.; Harishchandra, J.; Gunawardene, N.S.; Hapugoda, M.
There is an increasing demand for exploration of the potential of applying sterile insect techniques (SIT) in area-wide integrated vector management (AW-IVM) in many countries. Sterility of male insects can be accomplished with ionizing irradiation and SIT focus on release of sufficient sterile male mosquitoes to induce sterility in the wild females which over time causes decline of the target mosquito population. Therefore, current study was focused on determining the effects of different doses of radiation on survival, flight ability and reproductive capacity of local strains of Aedes aegypti (Linnaeus) for SIT application in Sri Lanka. Adults Ae. aegypti were maintained under standard laboratory conditions at the Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya, Sri Lanka. Male pupae and female pupae were separated using a Fay and Morlan glass plate technique. A total of 100 male Ae. aegypti pupae were exposed to each different irradiation doses (40, 50, 60, 70 and 80 Gy) using Co60 source of gamma rays. Effects of irradiation on pupal mortality, flight ability, fertility and adult male survival were monitored under laboratory conditions. One-way analysis of variance (ANOVA) was used to investigate the significance in the variations among observed factors. Kaplan-Meier survival analysis was conducted to estimate the survival functions of irradiated males. The survival in relation to different radiation doses were compared using ANOVA followed by Tukey’s pairwise comparison. The survival of irradiated pupae was invariably greater than 90% in control- and in test groups and they did not differ significantly (P > 0.05). Irradiation had no significant adverse effects on the flight ability (capacity to fly out of a test device) of male mosquitoes, which consistently exceeded 90%. The fertility of female mated with irradiated male was significantly reduced in Ae. aegypti at all doses and zero fertility was observed at 70 and 80 Gy. Ae. aegypti, fertility in irradiated males mated with female was less than 1% at 50 and 60 Gy. The male mean survival time was reduced by irradiation in a dose-dependent manner. However, the mean survival time in control and sterilizing doses of 40, 50, 60 and 70 did not differ significantly (P > 0.05). Therefore, 50 Gy dose will be used as the optimal radiation dose Ae. aegypti population for future evaluations of SIT-based control. The results of the present study will be applied to studies of male sexual competitiveness and for stepwise evaluations of the SIT for suppression of Ae. aegypti population in Sri Lanka.
Oviposition preferences of dengue vectors; Aedes aegypti and Aedes albopictus in Sri Lanka under laboratory settings.
(CABI Publishing, 2018) Gunathilaka, N.; Ranathunge, T.; Udayanga, L.; Wijegunawardana, A.; Abeyewickreme, W.
Investigations on oviposition behaviour of dengue vectors are critical for effective controlling of vector breeding. Therefore, the aim of the present study was to determine the oviposition behaviour of dengue vectors, Aedes aegypti and Aedes albopictus in Sri Lanka. Batches of 1000 adult mosquitoes (1 : 1, male: female ratio) housed in rearing cages were used for each experimental setup from Ae. aegypti and Ae. albopictus. Oviposition responses with respect to the size of the ovitrap, colours of the ovitrap, water source, sodium chloride (NaCl) concentration and presence/absence of larvae were evaluated by enumerating the number of eggs laid in the ovitraps. The analysis of variance and cluster analysis were used to investigate the significance in the variations among oviposition. The number of eggs laid by both species were improved with the increasing size of ovitraps. Ae. albopictus indicated the highest mean number of eggs in 0.2% of NaCl than in the ovitraps filled with distilled water. However, the egg laying preference was reduced with increasing salinity in both species. Drain water with low dissolved oxygen (DO) level (0.43 ± 0.12 mg l-1) was the preferred water source for both species, while a significantly high oviposition rate was observed in ovitraps with larvae. Black colour ovitraps attracted the majority of gravid females, while white was least preferred. There were no significant variations among oviposition behaviours of Ae. albopictus and Ae. aegypti. The ability of these vectors to breed in waste water with low DO levels may lead them to attain wide dissemination in the natural environment, enhancing their potential threat to human life.
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.
Study on the resting preferences of Aedes aegypti (Linnaeus) and Ae. albopictus (Skuse) adult mosquitoes in the district of Colombo
(Faculty of Graduate Studies, University of Kelaniya Sri Lanka, 2022) Perera, E. H. L.; Gunawardene, Y. I. N. S.; Hapugoda, M. D.; Ranathunge, T.; Udayanga, N. W. B. A. L.
Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) are the world’s most widely distributed mosquito species and, act as major contributors to many mosquito-borne diseases. Remarkable behavioral and ecological attributes make these mosquitoes as efficient vectors. Due to the behavioral and ecological plasticity of Ae. aegypti and Ae. Albopictus, it has become a major limitation in vector control and disease management measures in Sri Lanka. The objective of this study was to determine key bionomics aspects, namely resting preferences of Ae. aegypti and Ae. albopictus in the District of Colombo. Three Medical Officer of Health (MOH) areas were selected for the current study based on previous dengue cases. The two high risk areas (Maharagama and Kolonnawa) and a low-risk area (Padukka) were selected as study sites. Adult mosquito surveillance was conducted in outdoor and indoor settings using a mouth aspirator for one year (November, 2019-October, 2020). Adult mosquito collection included the aspiration from all rooms within the home including furniture, behind hanging clothes and curtains, behind and around cooking utensils and from dark and humid places, where mosquitoes were found resting. A total of 658 Aedes adult mosquitoes were collected from both indoor and outdoor resting locations (total number of resting sites= 432). The most abundant vector species was Ae. aegypti (65.0%; n=428), followed by Ae. albopictus (35.0%; n= 230) in Maharagama and Kolonnawa MOH areas. The most and least abundant Aedes mosquito collection MOH areas were Maharagama 44.5% (n=293) and Padukka 23.2% (n=153), respectively. Ae. Aegypti adult mosquitoes denoted an endophilic behaviors (97.1%; n=416), while Ae. albopictus denoted an exophilic resting behavior (81.30% n= 187). In terms of resting places, Ae. aegypti was mostly found in resting places such as bedroom (36.0%; n=154), kitchen (26.2%; n=112) living room (21.3%; n=91), and outdoor vegetation (1.4%; n=06). Meanwhile, Ae. albopictus was conducive to rest on the vegetation (50.4%; n=116), front of the house-external (23.8%; n=109). The highest percentage of Aedes mosquitoes were found resting on wooden surfaces in both indoor and outdoor sites (52.3%; n=344), followed by clothes/curtains (24.2%; n=159) and cement surfaces (17.0%). Resting behavior of vectors is an important fact since they are prerequisites to determine their role in disease transmission in endemic settings. This study revealed that the resting behavior varied between the two Aedes vector species, were Ae. aegypti adult mosquitoes denoted highly endophilic nature, while Ae. albopictus demonstrated exophilic behavior. In this study Ae. aegypti was mainly found resting in bedrooms, living rooms and kitchens and Ae. albopictus was found resting mainly among outdoor vegetation. The outcome of this study facilitates the relevant health authorities who engage with dengue control programs, to successfully eradicate the vector from resting sites.
Use of cyclopoid copepods for control of Anopheles (Diptera: Culicidae) mosquito larvae to prevent re-emergence of malaria in Sri Lanka
(Malaria Research Centre, Indian Council of Medical Research, 2019) Ranathunge, T.; Abeyewickreme, W.; Iqbal, M. C. M.; Hapugoda, M.
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. KEYWORDS: Anopheles; Sri Lanka; biological control; copepods; malaria vectors; predatory efficacy.
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.
Voltage-Gated Sodium Channel ( Vgsc) mutation-based pyrethroid resistance in Aedes aegypti populations of three endemic dengue risk areas of Sri Lanka
(Hindawi Pub. Co., 2021) Ranathunge, T.; Udayanga, L.; Sarasija, S.; Karunathilaka, S.; Nawarathne, S.; Rathnarajah, H.; Dulficar, F.F.; Shafi, F.N.; Dassanayake, R.S.; Gunawardene, Y.I.N.S.
BACKGROUND: Pyrethroid insecticides are widely used in many countries for chemical-based control of Ae. aegypti. Regardless of their efficacy, the constant use of insecticides has induced insecticide resistance mechanisms, such as knockdown resistance (kdr) 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 Aedes 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 Ae. aegypti mosquito populations in three dengue endemic high-risk regions of Sri Lanka. Methodology. Immature (both pupae and larvae) stages of Ae. aegypti 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 kdr mutations in collected Ae. aegypti populations, separately. The frequencies of the resistant and susceptible kdr alleles were determined by using the Hardy-Weinberg equilibrium. RESULTS: The Ae. aegypti 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 Ae. aegypti 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 kdr mutations, leading to the development of insecticide resistance among local Ae. aegypti populations, especially in the Colombo and Gampaha districts. Therefore, evaluation of the prevalence levels of these kdr mutations highlights the necessity for shifting towards novel vector control strategies.