Browsing by Author "Harishchandra, J."

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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.
Dynamics of aedes population in western province of Sri Lanka and a study on the feasibility of sterile insect technique (SIT) for controlling aedes albopictus
(University of Kelaniya, Sri Lanka, 2022) Harishchandra, J.
INTRODUCTION - Dengue is the most important vector-borne disease in Sri Lanka. Controlling dengue vectors is a challenge which needs multiple approaches. Sterile Insect Technique (SIT), which has been successfully applied in other countries, is a potential candidate for integrated control of dengue vectors in Sri Lanka. This study aimed to determine the dynamics of Aedes populations and to study the feasibility of SIT for controlling Aedes albopictus (Skuse) under laboratory and semi-field settings. METHODOLOGY - Dynamics of dengue vector populations were studied in two study areas in dengue high burdened districts, Colombo and Gampaha, in relation to climatic factors. Study area in the District of Gampaha where only a single dominant Aedes species reported was selected for the further studies. Size of the wild male population, survival and dispersal of Ae. albopictus were studied in Gampaha using Mark-Release-Recapture (MRR) method. A protocol for application of SIT for Ae. albopictus was developed including rearing, blood feeding, separation of male pupae, optimum radiation dose for sterilization and optimum release ratios of sterile males. RESULTS - The study revealed the presence of both Ae. aegypti and Ae. albopictus in Colombo and Ae. albopictus in Gampaha with a seasonal pattern. Significant correlations of entomological indices were found with rainfall, rainy days and relative humidity. Released males survived and dispersed up to 15 days and 200m respectively. Optimal radiation dose giving 99% induced sterility was 50Gy. Mating competitiveness quantified using Fried Competitiveness Index (FCI) of irradiated males against non-irradiated wild males resulted 0.5 which has met the international standards for competitiveness of Sri Lankan mosquitoes for application of SIT. Further, approximately 1245 male mosquitoes per hectare (ha) need to be released based on the density of the wild population. CONCLUSION - Densities of dengue vectors correlate with key climatic factors. Study area in the District of Gampaha where the presence of a single dominant Aedes species was selected for future SIT field trials. Developed protocols and study on behaviour of the selected mosquito species in the field will be useful for future application of SIT in integrated management of Ae. albopictus in Sri Lanka.
Effect of γ-radiation on fertility and survival of Aedes albopictus (skuse) males in the laboratory for Sterile Insect Technique
(Moleclar Medicine Unit, Faculty of Medicine, University of Kelaniya, Sri Lanka, 2015) Harishchandra, J.; Abeyewickreme, W.; Hapugoda, M.; Premaratne, R.G.; Gilles, J.R.S.
BACKGROUND: It is believed that Aedes albopictus, one of the dengue vectors in Sri Lanka can be controlled using Sterile Insect Technique (SIT) when integrated with other conventional control methods. The objective of this study was to determine the effective dose of gamma radiation for producing sterile males of Ae. albopictus mosquitoes. METHODS: A batch of male pupae (n=32) aged 24-48 hours in F1 was irradiated using a gamma-ray irradiator (Gamma 220, Atomic Energy of Canada Ltd., Co60) with 25 Gy in duplicates. Following the same procedure, different doses (30 Gy, 40 Gy, 50 Gy, 60 Gy and 70 Gy) were given to each pupal batch in duplicates. Then they were transferred to laboratory cages (30 cm X 30 cm X 30 cm) for emergence and supplied with 10% sucrose solution. Adult emergence rate and male longevity were recorded. Virgin females from the same cohort (F1) were introduced into each cage for mating and fed blood starting 5 days after emergence. Females were then isolated in to individual tubes and hatching rate of individual egg batches was determined after two weeks of egg maturation in hatching solution containing 0.25 g BNB, 0.05g BY in 700 ml distilled water. Spermachecae of female mosquitoes were dissected and insemination rates were calculated after egg laying. RESULTS: Male mosquito pupae in F1 showed low mortality (0-3.12%) immediately after exposing to radiation (0-48 hours). After 21 days of the irradiation, probability of survival of male mosquitoes in F1 were 0.578, 0.494, 0.453, 0.313, 0.328, 0.381 and 0.219 at 0Gy, 25 Gy, 30 Gy, 40 Gy, 50 Gy, 60 Gy and 70 Gy respectively (Kaplan Meier survival analysis). Log Rank test indicated significant differences of survival of control males with males irradiated at 40Gy, 50 Gy, 60 Gy and 70 Gy. The survival of males irradiated at 25 Gy and 30 Gy did not differ from each other and from the control. The survival of males irradiated at 40 Gy, 50 Gy, 60 Gy were not significantly different among each other. The mean hatching rate (Mean+SE) of the F2 progeny of Ae. albopictus males (F1 progeny) were 10.89+2.76%, 7.36+1.75%, 3.09+0.71%, 0.79+0.27%, 0.66+0.23% and 0% when irradiated at 25 Gy, 30 Gy, 40 Gy, 50 Gy, 60 Gy and 70 Gy respectively. The control group showed a hatching rate of 64.26 + 7.12%. It was found that insemination rate of the irradiated males among different doses and controls were above 90% in F1 based on spermatheca dissection of blood-fed females (F1). CONCLUSION: 50 Gy is recommended as the most suitable γ radiation dose to produce 99% sterility in Ae. albopictus males which has 0.328 survival probability after 21 days of irradiation. This dose can be used to produce sterile males of Ae. albopictus for population suppression.
Food niche overlap among some common fish species contributing to the fishery of the Batalagoda reservoir in the North Western Province of Sri Lanka
(2008) Harishchandra, J.
IGamma- ray irradiation as a method for sterilization of males of Aedes albopictus (skuse) for its control through Sterile Insect Technique (SIT)
(Faculty of Graduate Studies, University of Kelaniya, 2015) Harishchandra, J.; Abeyewickreme, W.; Hapugoda, M.D.; Premaratne, R.G.; Gilles, J.R.L.
Sterile Insect Technique (SIT) can be integrated with other conventional control methods to suppress population of Aedes albopictus, a vector of dengue in Sri Lanka. A study was conducted to determine the effective dose of gamma radiation for producing sterile males of Ae. albopictus mosquitoes. A batch of male pupae (n=32) aged 24-48 hours in F1 was irradiated using Gamma 220, (Co60) irradiator with 25, 30, 40, 50, 60 and 70Gy in duplicates. Adult emergence rate and male longevity were recorded. Virgin females from the same cohort (F1) were introduced into each cage for mating and fed blood starting 5 days after emergence. Then, females were isolated in individual tubes and hatching rate of individual egg batches was calculated after two weeks of egg maturation in hatching solution. Spermacheca of female mosquitoes were dissected and insemination rates were calculated after egg laying. Male mosquito pupae in F1 showed low mortality (0-3.12%) immediately after exposing to radiation (0-48 hours). After 14 days of the irradiation, survival rate of male mosquitoes in F1 were 82.7%, 79.7%, 56.3%, 73.4%, 76.6%, 76.1% and 56.3% when irradiated at 0Gy, 25Gy, 30Gy, 40Gy, 50Gy, 60Gy and 70Gy respectively. No significant difference was observed among survival of males in different doses except in 30 Gy and 70 Gy (Kaplan-Meier survival analysis, Log Rank test). Low survival rate at 30 Gy could be due to mosquito handling errors and need to be retested. Based on the hatching rate of the F2 progeny, males (F1) showed 89%, 93%, 97%, 99%, 99% and 100% sterility when irradiated at 25Gy, 30Gy, 40Gy, 50Gy, 60Gy and 70Gy respectively. Insemination rate of the irradiated males among different doses and controls were above 90% in F1 based on spermatheca dissection of bloodfed females (F1). 50 Gy is recommended as the most suitable radiation dose to produce 99% sterility in Ae. albopictus males which has 76% survival after 14 days of irradiation. This dose can be used to produce sterile males of Ae. albopictus for a SIT programme.
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.
Sterile Insect Technique for Controlling Aedes albopictus (Skuse); Sex Separation and Mating Competitiveness
(19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Harishchandra, J.; Hapugoda, M.; Premaratne, R.G.; Abeyewickreme, W.
Sterile Insect Technique (SIT) introduced by Edward F. Knipling in 1950s has been shown as an effective and sustainable genetic approach to control populations of selected pest insects in area wide integrated pest management programmes. Successfulness of this approach depends on the availability of an efficient sexing method and production of sterile males competitive enough to compete with wild males. In the context of developing SIT for the control of dengue vector Aedes albopictus (Skuse) in Sri Lanka, a method for separation of male pupae was tested and mating competitiveness of irradiated males against wild males was evaluated under laboratory conditions. Male pupae of the F42 generation of Ae. albopictus (Gampaha strain) were separated from female pupae using mechanical sieving method. A set of three stainless steel sieves of mesh sizes 1.4, 1.25 and 1.12mm were placed one on the other in descending order of size towards the bottom, forming a column immersed in a water jar. All pupae were poured on to the top sieve and shaken gently for seven minutes. Pupae were collected from each sieve and the male and female counts were taken after emergence of adults. Male and female pupae used for the competitiveness assessment were separated by the above sieving method. Male pupae (F42, age 28-40hours) were exposed to Gamma radiation (Gamma 220, Atomic Energy of Canada Ltd., Co60) at a dose of 50Gy by placing 300 male pupae in each plastic vial with 10ml of water. Dosimetry was performed using Frickey method. Wild fertile males and females reared from field-collected eggs from Gampaha (F1) were used to compete and cross with irradiated males respectively in different ratios. Two days after the emergence, the adult mosquitoes were caged (Bug Dorm 30X30X30cm) with ratios of irradiated males: wild males: wild virgin females 1:1:1, 3:1:1 and 5:1:1 (females, n = 100). Fertile control was set with wild males and wild virgin females 1:1. and an irradiated control was set with irradiated males with wild virgin females 1:1. Mosquitoes were allowed to mate for 3 days with access to 10% sugar solution. Then the mosquitoes were fed with cattle blood and engorged females were isolated in oviposition tubes. After 4 days, females were returned into cages and the filter papers containing eggs were allowed to dry. Eggs were hatched after one week and the hatching rates were compared. From the pupae retained in the sieve of mesh size 1.12mm, 98.3% were males. The mean hatch rates of fertile and irradiated controls and with ratios of irradiated males: wild fertile males: wild virgin females 1:1:1, 3:1:1, 5:1:1 were 80.24%±1.63SEM, 2.42%±0.57SEM, 56.74%±5.79SEM, 37.33%±4.76SEM and 34.23%±4.73SEM respectively. Fried Competitive Index (C) of irradiated males compared to controls was 0.43. Results show sieving method can be used for separating male pupae for irradiation with 98% accuracy. Irradiated males were less than 50% competitive as wild males under laboratory conditions