Submitted to: Medical and Veterinary Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2008
Publication Date: 6/1/2009
Citation: Handler, A.M., Allen, M.L., Skoda, S.R. 2009. Development and utilization of transgenic New World screwworm, Cochliomyia hominivorax. Medical and Veterinary Entomology. 23(s1):98-105. Interpretive Summary: The creation of transgenic strains of economically important insects for the development of more effective biological control programs is a major goal of our laboratory at CMAVE. The primary type of biocontrol is the sterile insect technique (SIT) which has been highly effective in controlling tephritid fruit fly pests, and animal pests such as the New World screwworm (NWS), Cochliomyia hominivorax. This paper describes research performed under the auspices of the FAO/IAEA Coordinated Research Project on “Enabling technologies for the expansion of SIT for old and new world screwworm” that involved the use of insect transgenesis technology, originally developed for tephritid flies, in NWS to improve SIT. The first transformation experiments were highly successful, resulting in eight transgenic NWS strains marked with an enhanced green fluorescent protein that can be used for the field detection of released males. Several of these transgenic strains had viability, life fitness and mating competitiveness characteristics comparable to non-transgenic strains currently used for SIT, making them potential candidates for use in SIT. Now it is possible to consider further improvement of SIT in NWS by development of new transgenic strains that allow genetic sexing by female lethality or male-specific fluorescent sorting, and male sterility by testis-specific lethality. Further improvement of SIT may result from new strategies that cause embryonic lethality in the offspring of released insects. New transgene vector systems are also being developed that enhance the creation of new highly fit transgenic strains and their ecological safety when released into the environment, which will be essential to fostering the development and application of this technology.
Technical Abstract: The New World Screwworm (NWS), Cochliomyia hominivorax, was the first insect to be effectively controlled using the sterile insect technique (SIT). Recent efforts to improve NWS SIT biological control have centered on the development of genetically transformed strains using the piggyBac transposon vector system. Eight transgenic strains were produced incorporating an enhanced green fluorescent protein (EGFP) marker gene under polyubiquitin regulation, that has the potential for use as a genetic marking system for released males. The transgenic strains were genetically and phenotypically characterized, including life fitness parameters and mating competitiveness. These characteristics were unique for each strain, and some were deemed suitable for incorporation into the SIT eradication program, with the CLAY strain having the best attributes. Four of the strains, including CLAY, have been successfully cryopreserved so that their original characteristics should be unchanged when further evaluation is required. With demonstration of efficient germline transformation in NWS, allowing production of fit and competitive transformants, it is now possible to consider further transgenic strain development to improve SIT that are currently being tested in other dipteran species. This includes strains that allow genetic marking with fluorescent proteins, genetic sexing by female lethality or male-specific fluorescent sorting, and male sterility by testis-specific lethality. SIT may also be improved upon by new strategies resulting in lethality of offspring of released insects using conditional lethal systems based upon temperature-dependent or dietary tetracycline regulation of lethal gene expression. Both the creation of new NWS transgenic strains and the ecological safety for their release will be enhanced by new vector systems that allow specific genomic targeting of vector constructs, and their subsequent immobilization ensuring transgene and strain stability.