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

Abstract

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.