Improving the Ecological Safety of Transgenic Insects for Field Release: New Vectors for Stability and Genomic Targeting

Genetically transformed insect pests provide significant opportunities to create strains to improve the sterile insect technique (SIT) and new strategies based on conditional lethality. A major concern for programmes that rely on the release of transgenic insects is the stability of the transgene, and maintenance of consistent expression of genes of interest within the transgene. Transgene instability could influence the integrity of the transformant strain upon which the effectiveness of the biological control programme depends. Loss or intragenomic transgene movement could result in strain attributes important to the programme being lost or diminished, and the mass-release of such insects could significantly exacerbate the insect pest problem. Instability resulting in intragenomic movement may also be a prelude to intergenomic transgene movement between species resulting in ecological risks. This is a minor concern for short-term releases where transgenic insects should not survive in the environment beyond one or two generations, but transgene movement may occur into infectious agents during mass-rearing, and the potential for movement after release is a possibility for programmes using many millions of insects. Random genomic insertion is also problematic for transgenic strain development due to genomic position effects that influence transgene expression, and insertional mutations that negatively affect host fitness and viability. New types of vectors are described that allow post-integration immobilization by deleting terminal vector sequences required for transposition, and genomic targeting by a recombinase-mediated cassette exchange strategy.

KEYWORDS biological control, transposable elements, transgenic strains, sterile insect technique, conditional lethality, insect transformation, vector stabilization, vector targeting, recombinase-mediated cassette exchange