Sex Sorting for Pest Control: It’s Raining Men!

Abstract

In the pursuit of better pest-and vector-control strategies, attention returns to an old proven technology, the sterile insect technique (SIT) and related insect population-suppression methods. A major obstacle for any of these approaches that involves the release of sterile males is the separation of males from females during the mass rearing stage, in order to improve the cost-efficiency of these methods and to prevent the release of biting and disease-vectoring females. This review describes recent sex-sorting developments in dipteran flies with an emphasis on assessing the suitability of these methods for large-scale rearing of male vectors for mass release. Sexing Is an Obstacle in Genetic Pest-control ProgramsHighlights Sexing Diptera represents a major obstacle to operationalizing vector-control methods based on the mass release of males, such as the sterile insect technique or the incompatible insect technique.

A novel drug-inducible sex-separation technique for insects

“…Traditionally the construction of genetic sexing lines was based on linking a selectable marker gene, such as insecticide resistance 12,18,19 , the temperature-sensitive lethal (TSL), and phenotypic loci 25 to a Yautosome or X-autosome via induced chromosomal translocations. Such engineered lines are not stable, and chromosomal rearrangements will break the genetic linkage between a selective marker and a sex chromosome 13,15,18,25,31,32 . It was found that when large numbers of insects were produced from an engineered GSS line, rare chromosomal rearrangements persisted or were selected for, and would contaminate the original line making it unusable for sex sorting 15,32 .…”

“…Such engineered lines are not stable, and chromosomal rearrangements will break the genetic linkage between a selective marker and a sex chromosome 13,15,18,25,31,32 . It was found that when large numbers of insects were produced from an engineered GSS line, rare chromosomal rearrangements persisted or were selected for, and would contaminate the original line making it unusable for sex sorting 15,32 . The novel approach does not require the genetic linkage to sex chromosomes, instead it relies on the sex-specific rescue of lethality and any mutations affecting the functionality of antibiotic resistance genes will be selected out during sex-sorting.…”

“…The methods based on mechanical separation of different sexes are entirely species specific and cannot be adopted to other species. In addition, they are not practical in most insects, since they require optimal rearing conditions, lead to a significant error rate, and are not suitable for high-throughput insect production 13,15,25,31,32 . Classic GSS approaches were achieved serendipitously in one species at a time, and thus are species specific.…”

“…Consequently, this constant exposure can generate unwanted fitness effects such as negative effects on mitochondrial functions [34][35][36] . Therefore, to improve the efficiency of current methods for insect population control, novel approaches for sex-sorting that are genetically stable, suitable for a large-scale insect production, and can be adopted to different insect species are required 13,15,32 .…”

Female-to-male sex conversion in Ceratitis capitata by CRISPR/Cas9 HDR-induced point mutations in the sex determination gene transformer-2

“…In addition, the release of sterile females could still result in crop damage due to oviposition or, in case of vector insects, in disease transmission. Sexing, classified as the removal of females from a mass-reared insect population, can be achieved by physical sorting, female-specific lethality, or by converting females into males 7 . Such solutions have been developed for multiple pest species using naturally occurring or classically induced mutations 8 – 11 or transgenesis 12 – 17 .…”