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Development of repressible sterility in Medfly for chemical-free pest control

Turkel, Ryan 2016. Development of repressible sterility in Medfly for chemical-free pest control. PhD Thesis, Cardiff University.
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Abstract

Medfly (Ceratitis capitata) is an invasive Tephritid fruit fly that severely disrupts global agricultural productivity. Pesticides are the primary control method despite genetic resistance, questionable efficacy, and negative effects upon the environment. The sterile insect technique (SIT) is an ecofriendly alternative, that suppresses the reproduction of wild Medfly by the mass release of sterilised males. Currently, males are sterilised by irradiation, which frequently reduces the ability of males to court females and thereby suppress reproduction. To address these undesirable effects, we developed a novel sterilisation strategy, based on the tetracycline-repressible expression of a nuclease effector in the male germline. Strains expressing these effectors were 99-100% sterile in the absence of tetracycline, but fertile in the presence of tetracycline. Male mating competitiveness was not detectably reduced in one strain expressing the effector, indicating that these expression systems are suitable for field use. Subsequently, a fluorescent marking system to label sperm was developed, which provided a useful tool to assess the mating competitiveness of sterile males: it was possible to accurately differentiate whether females had mated wild or transgenic males, under field-simulated conditions. These components may be merged with a tetracycline-repressible genetic switch to remove females from the rearing population, to improve the efficacy of the strategy by releasing sterile males alone. Thereafter, a full assessment of the life history traits of the strain and its mating competitiveness under field-like conditions will be performed, to confirm that the release of these sterile males is capable of suppressing wild populations of Medfly. Finally, an efficient expression system for CRISPR effectors in the germline was developed. This will facilitate the characterisation of novel transgenic systems for the reproductive control of Medfly, and expedite the development of commercial products, by the targeted integration of transgenic effectors.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Biosciences
Subjects: Q Science > QL Zoology
Uncontrolled Keywords: pest control; genetic engineering; engineered sterility; self-limiting; Oxitec Ltd; sterile insect; vector control; agriculture; Medfly; CRISPR; targeted modification; fluorescent sperm marking; spermatogenesis; eco-friendly;
Funders: BBSRC, Oxitec Ltd
Date of First Compliant Deposit: 21 March 2017
Last Modified: 05 Jun 2019 01:55
URI: http://orca.cf.ac.uk/id/eprint/99253

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