Conditional lethality strains for the biological control of tephritid pest species

Two approaches towards the release of transgenic insects carrying dominant conditional lethal genes to improve SIT include use of a dominant temperature-sensitive (DTS) mutation, and a tetracycline (tet)-suppressible embryonic lethality system. For DTS lethality, we tested a heat-sensitive mutation in the proteasome subunit gene, Prosâ2, that acts as “poison subunit” to disrupt proteasome function, resulting in late larval or pupal death in insects reared at 29°C. The native AsProsâ2 gene cognate was isolated from the caribfly, Anastrepha suspensa, and mutated to the AsProsâ2-1 allele by in vitro mutagenesis and transformed into a host wild type caribfly strain. Transgenic lines homozygous for the mutant transgene developed into pupae at similar frequencies at both 25°C and 29°C, but exhibited pupal lethality at rates of 96-100% at 29°C. For tet-suppressible lethality we have isolated and tested genetic elements for the promoter-driver and lethal gene effector cassettes from A. suspensa and the mexfly, A. ludens. Embryonic genes whose promoters may be used to drive lethality, or from which dsRNA may act as lethal effectors have been isolated, including serendipity (sry) and slow as molasses (slam). Putative lethal effector genes include cognates to the Drosophila cell death genes hid, reaper and sickle that have been isolated and successfully tested in in vitro cell death assays. For transgenic release, use of dual, yet independent lethal systems may be preferable to ensure that reversion or modification of either one does not allow transgenics to survive that, potentially, might result in re-population of the targeted species.