Applying new CRISPR-based technology to a broad agricultural need, researchers at the University of California, San Diego set their sights on a global pest known to decimate valuable food crops.
Nikolay Kandul, Omar Akbari and their colleagues demonstrated for the first time the system of precision-guided sterile insects, or pgSIT, in Drosophila melanogaster, the common fruit fly, in 2019. The technology, later adapted to mosquitoes, uses programmable CRISPR procedures to alter key genes that control sex determination and fertility. Under the new system, insect eggs developed by pgSIT are deployed in a targeted population and only sterile males hatch, resulting in a fertility dead end for that species.
Kandul, Akbari and colleagues have now adapted the technology for use in Drosophila suzukii, an invasive fruit fly (also known as spotted-wing drosophila) responsible for millions of dollars of crop damage. The advancement is described in the journal GEN Biotechnology.
“It is a safe and steadily scalable system,” said Akbari, a professor in the Department of Cellular and Developmental Biology at the ‘School of Biological Sciences. “Furthermore, the system does not lead to uncontrolled spread and does not persist in the environment – two important safety features that will help it gain approvals for use.”
D. suzukii flies have invaded many parts of the world and caused widespread agricultural and economic damage to several crops including apples, cherries, raspberries, blueberries, strawberries, peaches, grapes, olives and tomatoes.
Flies are known to breed by laying their eggs inside growing fruit. They are notoriously difficult to control because their larvae consume the pulp of ripening fruits, which limits the effectiveness of insecticide sprays. Some flies are known to become resistant to insecticides and many chemicals used in pesticides are now banned due to threats to human health. 1930, when farmers found ways to release sterile males into their crops to reduce pest damage. In the middle of the century, American farmers began to use radiation to sterilize pests such as the New World screw fly.
With CRISPR, scientists at UC San Diego avoided the need for harmful radiation and instead used CRISPR editing to specifically target genes essential for female D viability. suzukii and male fertility. As expected, pgSIT eggs could be produced in a factory and released at sites invaded by pests such as D. suzukii. Eggs could be deployed directly to areas where flies are causing damage and only sterile males would hatch after about two weeks. Since only two genes are knocked out, the males emerge fit enough to compete with their wild counterparts and quickly seek out females to mate with, resulting in inviable offspring.
“This technology would replace the need for insecticides and only suppress the population of the target species,” Akbari said. “Over the past four years we have developed pgSIT for several different species. In the future, we hope to use it as a platform technology that can be ported to a range of pests to safely solve real-world problems.”
Agragene Inc., a private biotechnology company co-founded by Akbari, has licensed the pgSIT core technology from UC Riverside (where Akbari initially led technology development) and is implementing trials on the field administered by the US Department of Agriculture of pgSIT in D. suzukii. The company hopes the trials will demonstrate the safety and efficacy of pgSIT and lead to regulatory approval of the technology for widespread agricultural use.
The GEN Biotechnology article was co-written by: Nikolay Kandul, Junru Liu, Anna Buchman, Isaiah Shriner, Rodrigo Corder, Natalie Warsinger-Pepe, Ting Yang, Amarish Yadav, Maxwell Scott, John Marshall and Omar Akbari.