Researchers have developed a CRISPR/Cas9-based "homing gene drive system" that can be used to suppress populations of the spotted-winged fruit fly Drosophila suzukii, according to a new study from North Carolina State University. The fruit fly, a so-called "spotted-wing Drosophila," destroys soft-skinned fruit in parts of North America, Europe and South America.


Researchers at NC State University have developed a double CRISPR gene drive system targeting a specific spotted wing Drosophila gene called doublesex that is important for the fly's sexual development. CRISPR stands for "ordered short palindromic repeats," and Cas9 is an enzyme that cuts DNA like molecular scissors. Derived from the bacterial immune system, which recognizes and destroys viruses and other invaders, the CRISPR system is being developed as a solution to human, plant and animal health problems, among other uses.


North Carolina State entomologist Max Scott is the corresponding author of the study in the Proceedings of the National Academy of Sciences. In many experiments, targeting doublesex resulted in female infertility because the females were unable to lay eggs, he said.


"This is the first time a so-called homing gene drive has been performed in an agricultural pest, potentially for pest suppression," Scott said.


Gene drives can preferentially select, alter, or delete specific traits and "drive" those edits to future generations, sometimes resulting in a far greater than 50 percent chance of passing those changes on to future generations.


"Gene drives imply biased inheritance," Scott said.


The researchers used a fluorescent red protein to mark the presence of CRISPR/Cas9 genetic changes in the Drosophila genetic blueprint, or genome. The gene drive system delivered the fluorescent protein to 94-99 percent of its offspring, the paper said.


The researchers also used mathematical models to predict how efficiently the gene drive system would suppress specific fruit fly populations in laboratory terrariums. The model showed that releasing one transgenic fly for every four "wild" flies (non-transgenic) could reduce the fruit fly population in about eight to 10 generations.


"Because doublesex is such a conserved gene and is required for female development in so many Drosophila species, I think the homing gene drive strategy could be used in other pests," Scott said.


Scott and his collaborators had previously successfully suppressed spotted wing Drosophila populations with a male-only strain and used a similar approach to reduce laboratory populations of the New World screwworm fly.


Next steps include a trial in North Carolina.


"We're doing population cage suppression experiments. We want to see if releasing flies repeatedly at a 1:4 ratio will suppress the population of flies in the cage as the model suggests," Scott said.