Potential use of a combined sterile insect technique(SIT) and Wolbachia- based approach for the control of the dengue vector Aedes albopictus in Sri Lanka.

Abstract

The overall work involved in this thesis was an assessment of the density and species abundance of wild mosquito populations, genotyping of Wolbachia strains naturally present in insect hosts, Microinjection of Wolbachia for artificial infection, introgression and characterization of Wolbachia triply infected Ae. albopictus line in a Sri Lankan genetic background and determination of minimum sterility dose for the males and females of the introgressed line. Results revealed that Ae. albopictus mosquito was the dominant vector species in the Narangodapaluwa Public Health Inspector area with an average ovitrap index of 75.25% (range; 56.9% - 94.7%) over the study year. The frequency of Wolbachia infection among the mosquito population was 17% (13/78) and among other insect species (five different orders) was 25% (18/72). The most prominent Wolbachia supergroup infecting the wild insect species was the B group 58% (18/31). Ae. albopictus was naturally infected with both strains A and B (double infected) while Ae. aegypti was infected with strain A with sample infection frequency of 2.5%. This is the second report of such an infection in Ae. aegypti mosqu ito in the world. Forty-three new alleles and 15 complete allelic profiles were submitted to the Wolbachia Multilocus sequence typing (MLST) data base and all sequencing data were deposited in the Gene bank. The application of direct maternal micro-injection techniques of Wolbachia (purified from infected mosquitoes) to Ae. albopictus mosquitoes resulted in the development of a common protocol for bio­ manipulation of mosquito vectors with enhanced survivability. Successful transfer of Wolbachia triple infection into Ae. albopictus with Sri Lankan genetic background was achieved through an introgression experiment. Characterization of the introgressed Wolbachia triply infected Ae. albopictus Sri Lankan line expressed partial Cytoplasmic incompatibility and revealed competitive fitness cost for fecundity, fertility and longevity compared with wild type while there was no cost for pupation rate, adult emergence and sex ratio. Therefore, integration of an irradiation (dose; 30Gy) is recommended to achieve complete male and female sterility prior to mosquito release. This minimum sterility dose is lower than the irradiation dose applied for SIT and had not resulted in a significant effect for male competitiveness.

Key words: SIT, IIT, Wolbachia, population suppression, Ae. albopictus