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

Abstract

The mosquito species Aedes aegypti is the primary transmitter of viruses that cause endemic diseases like dengue in Pakistan. It is also a cause of other vector-borne diseases like yellow fever, Zika fever, and chikungunya, which significantly impact human health worldwide. In the absence of efficient vaccines (except for yellow fever) or drugs, vector control methods, such as the sterile insect technique (SIT), have been proposed as additional tools for the management of these diseases. Mosquito SIT programs are based on the release of sterile males and it is important female releases to be ideally zero or to be kept at a minimum, since females are the ones that bite, blood-feed and transmit pathogens. Recently, an Ae. aegypti genetic sexing strain (GSS), with and without a recombination-suppressing inversion (Inv35), was developed using the eye color as a selectable marker, with males having black eyes and females red eyes. In the present study, we introgressed the sexing features and the Inv35 of the Ae. aegypti red-eye GSS into the Pakistani genomic background aiming to their future use for SIT applications in the country. Both introgressed strains, the Red-eye GSS-PAK and the Red-eye GSS/Inv35-PAK, were evaluated in respect to their genetic stability and biological quality by assessing parameters like recombination rate, fecundity, fertility, pupal and adult recovery, time of development, pupal weight, survival, and flight ability in comparison with a wild Pakistani population (PAK). The results suggest that the sexing features and the recombination suppression properties of Inv35 were not affected after their introgression into the local genomic background; however, some biological traits of the two newly constructed strains were affected, positively or negatively, suggesting that a thorough quality control analysis should be performed after the introgression of a GSS into a new genomic background prior to its use in SIT field trials or applications. The importance of using GSS with local genomic background for SIT applications against Aedes aegypti is also discussed.

The Effect of an Irradiation-Induced Recombination Suppressing Inversion on the Genetic Stability and Biological Quality of a White Eye-Based Aedes aegypti Genetic Sexing Strain

“…As genetic recombination can affect the stability of a GSS, we isolated an irradiation-induced chromosomal inversion, Inv35, which was subsequently incorporated in the GSS, thus significantly suppressing their recombination rates [ 23 , 30 ]. Moreover, RGSS and RGSS/Inv35 were introgressed into different genomic backgrounds, and it was shown that the sexing properties of the GSS remained fully functional, as well as the recombination-suppressing activity of Inv35, for many generations [ 32 , 33 ]. The results of these studies indicated that the recombination frequency between the white-eye and M loci can be reduced by Inv35, as monitored for a period of 16 generations, thus significantly improving the stability of the genetic sexing strain, particularly under filtering conditions.…”

“…The initially constructed RGSS and WGSS were comparatively assessed, and it was shown that the RGSS was a better performing strain in several quality control parameters and was selected for further evaluation including the incorporation of Inv35 [ 23 , 32 ]. It was recently shown that the introgression of the red-eye selectable marker and Inv35 in Pakistani genetic background did not affect the sexing properties and genetic stability, but it did have an impact, positive or negative, on several quality control parameters [ 33 ]. It is also known that chromosomal inversion may also affect fitness, positively or negatively [ 39 , 40 , 41 ].…”

“…Recovery rates during development : All counted L1 larvae from three replicates of the fertility test were shifted to white plastic trays and provided with 15 mL of larval diet as described previously [ 33 ]. The L1 larvae that survived up to pupal and adult stage were counted to estimate the respective recovery rates during development (from egg to adult).…”

“…In addition, the red-eye mutation and Inv35 were introgressed into seven different genomic backgrounds for the development of the respective GSS. In all cases, the sexing character of the strains was maintained and all novel GSSs presented significantly reduced genetic recombination rates in the presence of Inv35 [ 32 , 33 ]. In the present study, the long-term genetic stability and biological quality of White-eye GSS, with and without the Inv35, was assessed, as well as their suitability for SIT applications against Ae.…”