Introgression of the Aedes aegypti Red-Eye Genetic Sexing Strains Into Different Genomic Backgrounds for Sterile Insect Technique Applications

Abstract

Aedes aegypti is an invasive mosquito species and major vector of human arboviruses. A wide variety of control methods have been employed to combat mosquito populations. One of them is the sterile insect technique (SIT) that has recently attracted considerable research efforts due to its proven record of success and the absence of harmful environmental footprints. The efficiency and cost-effectiveness of SIT is significantly enhanced by male-only releases. For mosquito SIT, male-only releases are ideally needed since females bite, blood-feed and transmit the pathogens. Ae. aegypti genetic sexing strains (GSS) have recently become available and are based on eye colour mutations that were chosen as selectable markers. These genetic sexing strains were developed through classical genetics and it was shown to be subjected to genetic recombination, a phenomenon that is not suppressed in males as is the case in many Diptera. The genetic stability of these GSS was strengthened by the induction and isolation of radiation-induced inversions. In this study, we used the red eye mutation and the inversion Inv35 line of the Ae. aegypti red-eye GSS s and introgressed them in six different genomic backgrounds to develop GSS with the respective local genomic backgrounds. Our goal was to assess whether the recombination frequencies in the strains with and without the inversion are affected by the different genomic backgrounds. In all cases the recombination events were suppressed in all Inv35 GSS strains, thus indicating that the genomic background does not negatively affect the inversion result. Absence of any effect that could be ascribed to genetic differences, enables the introgression of the key elements of the GSS into the local genomic background prior to release to the target areas. Maintaining the local background increases the chances for successful matings between released males and wild females and addresses potential regulatory concerns regarding biosafety and biosecurity.

Genetic Stability and Fitness of Aedes aegypti Red-Eye Genetic Sexing Strains With Pakistani Genomic Background for Sterile Insect Technique Applications

“…Indeed, releasing GSS males carrying the local genomic background will enhance the efficiency of SIT since their mating competitiveness is likely to be higher than that of males of different origin. In addition, the SIT application with local males is not expected to raise biosafety and biosecurity concerns compared to a trial which would be based on mosquitoes originated from a different geographical region ( Bouyer et al, 2020 ; WHO and IAEA, 2020 ; Augustinos et al, 2022 ). In the present study, the red eyes mutation and the inversion Inv35, which were used in the initial construction of the Ae.…”

“…In our recently published studies, we reported the construction of the red-eye GSS ( Koskinioti et al, 2021 ) and the introduction of Inv35 to suppress recombination ( Augustinos et al, 2020 ). However, the recombination rate as well as the overall performance of a strain depends on several factors, including genomic background ( Ouda and Wood, 1985 ; Augustinos et al, 2020 , 2022 ; Carvalho et al, 2020 ). Therefore, in the present study, we introgressed the red eye mutation and the chromosomal inversion Inv35 in a wild population from Pakistan to assess the impact of the local genomic background on the genetic stability and the biological quality of newly constructed strains under laboratory rearing conditions.…”

“…The Rexville red eye mutant strain used in the present study is a long-domesticated laboratory strain (kindly provided by Dr. Margareth Capurro at the Department of Parasitology, University of Sao Paulo, Brazil) and had previously been used in other studies including the construction of the Ae. aegypti red-eye GSS ( Costa-da-Silva et al, 2017 ; Augustinos et al, 2020 , 2022 ). The color of both compound and simple eye of this strain remains red throughout development.…”

“…PAK is a recently domesticated strain from mosquitoes collected from Northern areas of Pakistan’s KP Province and was used as a source of the local genomic background. The introgression of the red eye mutation and Inv35 was performed as described previously ( Augustinos et al, 2022 ), consisted of a series of backcrosses and was expected to result into two new GSS, Red-eye GSS-PAK and the Red-eye GSS/Inv35-PAK with ∼98.8 and ∼98% PAK genetic background, respectively. The two new GSS were evaluated for their genetic stability until the seventh generation while their biological quality was assessed at the third generation in the present study.…”

“…aegypti SIT programs ( Koskinioti et al, 2021 ). In a subsequent study it was shown that the recombination frequency in the GSS strains, with and without the inversion, is not affected if the red-eye mutation and the Inv35 are introduced to six different genomic backgrounds, Brazil, Indonesia, Mexico, Sri Lanka, Singapore, and Thailand ( Augustinos et al, 2022 ).…”