June 19,
Researchers Develop Genetic Control Mechanism for Major Livestock Pest
Researchers from North Carolina State University have developed a technique to control populations of the Australian
sheep blowfly – a major livestock pest in Australia and New Zealand – by making female flies dependent upon a common
antibiotic to survive.
Dr. Max Scott, professor of entomology at NC State, and his research team genetically modified lines of female
Australian sheep blowflies (Lucilia cuprina) so that they required doses of tetracycline in order to live. Female
blowflies that did not receive the antibiotic died in the late larval or pupal stages, before reaching adulthood.
Several genetically modified lines lacking tetracycline showed 100 percent female deaths.
Scott says that the gene construct responsible for lethality in antibiotic-free diets is female-specific. Interestingly
and unexpectedly, the genetically modified female larvae containing the tetracycline lethality genes also took on a
crimson color due to overexpression of the linked red fluorescent protein “marker gene.” This allows scientists to tell
which larvae will be females and which will be males.
“Overexpression of the gene responsible for the reliance on tetracycline also seems to overexpress this marker gene,”
Scott says.
Since the females will die when not provided tetracycline in their diets, the males can be separated out in the larval
stage. This is essential for a “male-only” genetic control program to reduce blowfly populations, Scott says, as fertile
males would pass the lethality construct on to female offspring, which would die in the absence of tetracycline. Male
larval offspring, however, would still be dangerous to livestock.
In the study, the researchers showed that the tetracycline gene construct also works in Drosophila, the fruit fly “lab
rat” of the insect world that is a distant cousin of the sheep blowfly. This holds promise that the genetic system will
function in the New World and Old World screwworm, two major livestock pests that are close relatives of the sheep
blowfly. Scott is working with the U.S. Department of Agriculture to make “male-only” strains of the New World screwworm
(Cochliomyia hominivorax).
“The New World screwworm is a devastating pest of livestock that was eradicated from North and Central America by
releasing sterilized male and female flies,” Scott says. However, a male-only strain offers several advantages,
including potentially more efficient population suppression for the ongoing program. “Efficient genetic control systems
have the potential to help eradicate some of the biggest problem pests across the globe,” he said.
The research is funded by the U.S. Department of Agriculture, National Institute of Food and Agriculture and NC State.
- kulikowski –
“Transgenic sexing system for genetic control of the Australian sheep blow fly Lucilia cuprina”
Authors: Fang Li, Holly Wantuch, Rebecca Linger, Esther Belikoff and Max Scott, North Carolina State University
Published: June 2014 online in Insect Biochemistry and Molecular Biology
DOI: 10.1016/j.ibmb.2014.06.001
Abstract: The New World screwworm and the Australian sheep blow fly Lucilia cuprina are devastating pests of livestock. The
larvae of these species feed on the tissue of the living animal and can cause death if untreated. The sterile insect
technique or SIT was used to eradicate screwworm from North and Central America. This inspired efforts to develop
strains containing complex chromosomal rearrangements for genetic control of L. cuprina in Australia. Although one field
trial was promising, the approach was abandoned due to costs and difficulties in mass rearing the strain. As the
efficiency of SIT can be significantly increased if only sterile males are released, we have developed transgenic
strains of L. cuprina that carry a dominant tetracycline repressible female lethal genetic system. Lethality is due to
overexpression of an auto-regulated tetracycline repressible transactivator (tTA) gene and occurs mostly at the pupal
stage. Dominant female lethality was achieved by replacing the Drosophila hsp70 core promoter with a Lucilia hsp70 core
promoter-5/UTR for tTA overexpression. The strains carry a dominant strongly expressed marker that will facilitate
identification in the field. Interestingly, the sexes could be reliably sorted by fluorescence or color from the early
first instar larval stage as females that overexpress tTA also overexpress the linked marker gene. Male-only strains of
L. cuprina developed in this study could form the basis for a future genetic control program. Moreover, the system
developed for L. cuprina should be readily transferrable to other major calliphorid livestock pests including the New
and Old World screwworm.
ENDS