International Postgraduate Research Conference (IPRC)
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Item 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.Item 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.Item 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 strategiesItem 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.