Lessons from Drosophila: Engineering Genetic Sexing Strains with Temperature-Sensitive Lethality for Sterile Insect Technique Applications

SIMPLE SUMMARY: The sterile insect technique is a pest control strategy used to suppress or eliminate regional populations of insects that pose significant threats to agriculture or human health. The process involves mass-rearing, sterilization and release of male insects who fail to produce viable offspring when they mate with wild females, which leads to a population decline. Females are essential for colony propagation in rearing facilities and their selective removal prior to sterile releases remains an ongoing challenge. Developing genetic sexing strains with conditional temperature sensitive lethal mutations offers one strategy to eliminate female embryos through heat treatment, while males carry a wild type allele translocated to the Y-chromosome (or sex determination locus) to maintain their fitness. Here we review point mutations in Drosophila melanogaster genes that cause temperature sensitive phenotypes with the potential or ability to cause embryonic lethality. Re-engineering these known temperature sensitive mutations in other insects using CRISPR/Cas9 technology presents new opportunities to engineer genetic sexing strains for the sterile insect technique. ABSTRACT: A major obstacle of sterile insect technique (SIT) programs is the availability of robust sex-separation systems for conditional removal of females. Sterilized male-only releases improve SIT efficiency and cost-effectiveness for agricultural pests, whereas it is critical to remove female disease-vector pests prior to release as they maintain the capacity to transmit disease. Some of the most successful Genetic Sexing Strains (GSS) reared and released for SIT control were developed for Mediterranean fruit fly (Medfly), Ceratitis capitata, and carry a temperature sensitive lethal (tsl) mutation that eliminates female but not male embryos when heat treated. The Medfly tsl mutation was generated by random mutagenesis and the genetic mechanism causing this valuable heat sensitive phenotype remains unknown. Conditional temperature sensitive lethal mutations have also been developed using random mutagenesis in the insect model, Drosophila melanogaster, and were used for some of the founding genetic research published in the fields of neuro- and developmental biology. Here we review mutations in select D. melanogaster genes shibire, Notch, RNA polymerase II 215kDa, pale, transformer-2, Dsor1 and CK2α that cause temperature sensitive phenotypes. Precise introduction of orthologous point mutations in pest insect species with CRISPR/Cas9 genome editing technology holds potential to establish GSSs with embryonic lethality to improve and advance SIT pest control.