Enhancing the stability and ecological safety of mass‐reared transgenic strains for field release by redundant conditional lethality systems

Abstract

The genetic manipulation of agriculturally important insects now allows the development of genetic sexing and male sterility systems for more highly efficient biologically-based population control programs, most notably the Sterile Insect Technique (SIT), for both plant and animal insect pests. Tetracycline-suppressible (Tet-off) conditional lethal systems may function together so that transgenic strains will be viable and fertile on a tetracycline-containing diet, but female-lethal and male sterile in tetracycline-free conditions. This would allow their most efficacious use in a unified system for sterile male-only production for SIT. A critical consideration for the field release of such transgenic insect strains, however, is a determination of the frequency and genetic basis of lethality revertant survival. This will provide knowledge essential to evaluating the genetic stability of the lethality system, its environmental safety, and provide the basis for modifications ensuring optimal efficacy. For Tet-off lethal survival determinations, development of large-scale screening protocols should also allow the testing of these modifications, and test the ability of other conditional lethal systems to fully suppress propagation of rare Tet-off survivors. If a dominant temperature sensitive (DTS) pupal lethality system proves efficient for secondary lethality in Drosophila, it may provide the safeguard needed to support the release of sexing/sterility strains, and potentially, the release of unisex lethality strains as a form of genetic male sterility. Should the DTS Prosβ2(1) mutation prove effective for redundant lethality, its high level of structural and functional conservation should allow host-specific cognates to be created for a wide range of insect species.

The whole genome sequence of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), reveals insights into the biology and adaptive evolution of a highly invasive pest species

“…The RHG pro-apoptotic cell death gene family was identified in medfly and found to have a genomic organization analogous to Drosophila . Functional conservation of these genes is also expected, raising the possibility of using the reaper and grim genes, along with hid , for redundant secondary lethality [ 194 ]. SFPs present a large repertoire of potential targets for controlling reproduction, including peptides that might be modified for improved suppression of female multiple matings to enhance SIT.…”

Wolbachia pipientis Associated With Tephritid Fruit Fly Pests: From Basic Research to Applications

“…To prevent or minimize the harmful effects of tephritid pests, growers must comply with health and safety standards required by the market, applying an area-wide management approach involving chemical, biological, cultural, and autocidal control practices (Reyes et al, 2000;Enkerlin, 2005). Autocidal refers to methods that use the insect to control itself, by releasing insects that are sterile or induce sterility upon mating with wild insects in the next or subsequent generations (Black et al, 2011;Leftwich et al, 2014;Handler, 2016). Autocidal strategies include the sterile insect technique (SIT) (Knipling, 1955;Hendrichs and Robinson, 2009); one of the most widespread control methods used against fruit flies (reviewed in Dias et al, 2018).…”

Genetic breakdown of a Tet-off conditional lethality system for insect population control

“…Considering the possibility that resistance to current insect conditional lethality systems might occur, strategies to prevent or mitigate the survival of lethality-resistant individuals have been considered. Two strategies are based on the potential for redundant, yet independent, dual lethality (or reproductive sterility) systems mitigating the survival of revertant individuals in a mass release program 39,40 . Thus, based on the multiplicative law of probability [P(AB) = P(A)P(B)], an approximate 10 −6 lethal revertant frequency estimate for each system (A and B), as demonstrated here for a Drosophila TELS strain, could result in a frequency as low as~10 −12 for both to fail concurrently in the same genome, presuming that the lethality systems are functionally independent and do not differentially affect host physiology and fitness.…”