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

Abstract

Aedes aegypti is the primary vector of diseases such as dengue, chikungunya, Zika fever, and yellow fever. The sterile insect technique (SIT) has been proposed as a species-specific and environment-friendly tool for the suppression of mosquito vector populations as a major component of integrated vector management strategies. As female mosquitoes are blood-feeders and may transmit pathogenic microorganisms, mosquito SIT depends on the release of sterile males. Genetic sexing strains (GSS) can be used for the efficient and robust separation of males from females. Two Ae. aegypti GSS were recently developed by exploiting eye colour mutations, resulting in the Red-eye GSS (RGSS) and the White-eye GSS (WGSS). In this study, we compared two WGSS, with and without the chromosomal inversion 35 (Inv35), and evaluated their biological quality, including genetic stability. Our results suggest that the WGSS/Inv35 presents a low recombination rate and long-term genetic stability when recombinants are removed from the colony (filtering) and a slow accumulation of recombinants when they are not removed from the colony (non-filtering). The two strains were similar with respect to fecundity, pupal and adult recovery rates, pupation curve, and pupal weight. However, differences were detected in fertility, survival rate of females, and flight ability of males. The WGSS/Inv35 presented lower fertility, higher survival rate of females, and better flight ability of males compared to the WGSS.

Keywords: Zika; chromosomal inversion; dengue; sterile insect technique; vector control.

Figure 1

Recombination rate of the WGSS/Inv35 strain over 16 generations under filtering and non-filtering conditions. Statistical analysis was carried out using a GLM with binomial distribution and indicated significant differences between filtered and non-filtered conditions. The lighter lines indicate the means of the experimental data, whereas the darker lines indicate the generalized linear model fitted curve for the binomial distribution.

Figure 2

Total fecundity assay (number of eggs per female) of WGSS and the White-eye WGSS/Inv35. Three replicates were performed per gonotrophic cycle per strain. Statistical analysis was carried out using a GLM with Poisson distribution. The whiskers indicate the variability outside the upper and lower quartiles (represented as the upper and lower boxes, respectively). The thick horizontal line represents the median and the triangles indicate a possible outlier. Significance symbol: ‘ns’ for ‘not significant’.

Figure 3

Fertility (100% × no. L1 larvae/total no. eggs) of WGSS and WGSS/Inv35. Three replicates were performed per gonotrophic cycle per strain. Statistical analysis was carried out using a GLM with binomial distribution and showed significant difference between the strains. The whiskers indicate the variability outside the upper and lower quartiles (represented as the upper and lower boxes, respectively). The thick horizontal line represents the median and the triangles indicate a possible outlier. Significance symbol: ‘***’ p value lower than 0.001.

Figure 4

Recovery rates during different developmental stages for WGSS and the WGSS/Inv35. Three replicates were performed per strain. Statistical analysis was carried out using a GLM with binomial distribution. The whiskers indicate the variability outside the upper and lower quartiles (represented as the upper and lower boxes, respectively). The thick horizontal line represents the median.

Figure 5

Pupation curves of females and males of WGSS and WGSS/Inv35. Three replicates were performed per strain. Statistical analysis was carried out using a GLM with binomial distribution.

Figure 6

Weight per 10 male and female pupae of WGSS and WGSS/Inv35 strains. Three replicates were performed per sex per strain. Statistical analysis was carried out using a GLM with Poisson distribution. The whiskers indicate the variability outside the upper and lower quartiles (represented as the upper and lower boxes, respectively). The thick horizontal line represents the median, and the dot indicates a possible outlier. Significance symbol: ‘ns’ for ‘not significant’.

Figure 7

Representative Kaplan–Meier survival curves are shown for WGSS and WGSS/Inv35 males (A) and females (B). Three replicates were performed per strain. Statistical analysis was carried out using a log-rank test and showed significant difference between the strains.

Figure 8

Flight ability of WGSS and WGSS/Inv35 males. Three replicates were performed per strain. Statistical analysis was carried out using a GLM with binomial distribution and showed significant difference between the strains. The whiskers indicate the variability outside the upper and lower quartiles (represented as the upper and lower boxes, respectively). The thick horizontal line represents the median. Significance symbol: ‘**’ for p value less than 0.01.