Abstract
Genetically modified conditional lethal strains have been created to improve the control of insect pest populations damaging to human health and agriculture. However, understanding the potential for the genetic breakdown of lethality systems by rare spontaneous mutations, or selection for inherent suppressors, is critical since field release studies are in progress. This knowledge gap was addressed in a Drosophila tetracycline-suppressible embryonic lethality system by analyzing the frequency and structure of primary-site spontaneous mutations and second-site suppressors resulting in heritable survivors from 1.2 million zygotes. Here we report that F1 survivors due to primary-site deletions and indels occur at a 5.8 × 10−6 frequency, while survival due to second-site maternal-effect suppressors occur at a ~10−5 frequency. Survivors due to inherent lethal effector suppressors could result in a resistant field population, and we suggest that this risk may be mitigated by the use of dual redundant, albeit functionally unrelated, lethality systems.
Highlights
Modified conditional lethal strains have been created to improve the control of insect pest populations damaging to human health and agriculture
If mass-reared Genetically modified (GM) conditional lethal strains are released in the field at current levels of 106–108 insects/week for SIT14,15, there is a high likelihood that rare primary- or second-site mutations will occur resulting in lethal revertant survivors
The applied use of Tet-off embryonic lethality system (TELS) in the field would require the mass release of double-homozygous P1 males reared on Tet-diet, with the expectation that their double-heterozygous F1 progeny would be inviable by the first larval instar in the absence of Tet
Summary
Modified conditional lethal strains have been created to improve the control of insect pest populations damaging to human health and agriculture. Understanding the potential for the genetic breakdown of lethality systems by rare spontaneous mutations, or selection for inherent suppressors, is critical since field release studies are in progress This knowledge gap was addressed in a Drosophila tetracycline-suppressible embryonic lethality system by analyzing the frequency and structure of primary-site spontaneous mutations and second-site suppressors resulting in heritable survivors from 1.2 million zygotes. In laboratory control studies for RIDL, survival in the medfly, Ceratitis capitata, and the yellow fever mosquito, A. aegypti, were reported at frequencies of 0.5% and 3.5%, respectively[7,9], while survival for the Drosophila melanogaster TELS strain was approximately 0.01%6 These levels of initial F1 survival are likely due, primarily, to inherent “leakiness” in the respective systems due to variable transgenic lethal effector expression or function, though heritable survival due to mutations in genetic components of the system have yet to be reported. This would result in the persistence of GM insects in the field, and for some mutations (especially at second sites), revertants may be resistant to further control by the same or similar lethality system
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