Genetic control of screwworm using transgenic male-only strains

Authors: SCOTT, MAX - North Carolina State University; CONCHA, CAROLINA - Smithsonian Tropical Research; YAN, YING - North Carolina State University; Skoda, Steven; Phillips, Pamela; SAGEL, AGUSTIN - Us Embassy, Panama

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/16/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The New World screwworm is a blue blow fly that is a devastating pest of livestock in South America and some Caribbean islands. Female screwworm flies lay their eggs on an open wound and after hatching, the larvae eat the animal. The common name derives from the habit of the larvae to burrow into the animal. Over a 50-year period this pest was eradicated from North and Central America through area-wide releases of radiation sterilized male and female flies, a control program known as the Sterile Insect Technique or SIT. Currently the USDA-COPEG biosecurity facility in Panama, mass rears and releases millions of sterilized screwworm adult flies in the barrier zone between Panama and Colombia, preventing the re-introduction of the pest from southern countries. As SIT is significantly more efficient if only males are released, we have developed transgenic male-only strains of this insect that carry tetracycline repressible female-lethal genetic systems. In the first generation system, lethality is due to overexpression of an auto-regulated tetracycline repressible transactivator (tTA) gene and occurs mostly at the pupal stage. Only females die as the tTA gene carries the sex-specifically spliced intron from transformer, a gene that determines sex in flies. Females survive if fed tetracycline, which inhibits tTA. The transgenic lines have been tested for fitness parameters that are relevant for mass rearing and performance in the field, appearing similar to the wild type strain currently used in the program. One transgenic line is currently being tested under mass rearing conditions and an application to perform field trials with sterilized transgenic males in Panama has been approved. Lastly, second generation systems designed to be lethal to females at the embryo stage have been developed and are currently being evaluated. These male-only strains could provide an economical advantage as larval diet is a major cost for the mass rearing facility. The genetic systems developed for screwworm also function in the Australian sheep blowfly Lucilia cuprina and should be readily transferrable to other flies that are livestock pests such as the Old World screwworm.