What is killing the mosquitoes?

We’ve introduced a gene into the mosquitoes which stops their cells from functioning normally, and this only affects the mosquito. The self-limiting gene is able to tie up the normal processes in an insect cell and as a result, the modified mosquitoes can’t develop properly and die before they become adults which can reproduce and spread disease. Oxitec mosquitoes do not produce offspring with other species so the control is species-specific and the genes don’t spread. The mosquitoes and their offspring die and so the genes also do not persist in the environment. The colour marker and self-limiting pest control genes are non-toxic and non-allergenic, so if animals were bitten by Oxitec mosquitoes or predators ate Oxitec mosquitoes it would be the same as getting bitten by or eating wild ones.

We need to be able to rear millions of males per week so we have engineered the mosquito to make production cost effective. If the mosquito larvae in the production unit are given tetracycline, this acts as an antidote inactivating the self-limiting gene. The antidote is not present in sufficient quantities in the environment to allow inactivation of the self-limiting gene, so offspring of OX513A will not reach adulthood.

Further reading:

Gossen, M. and Bujard, H. (1992) Tight control of gene expression in mammalian cells by tetracycline-responsive promoters. PNAS 89(12): 5547-5551

Lin, H., McGrath, J., Wang, P. and Lee, T. (2007) Cellular Toxicity Induced by SRF-Mediated Transcriptional Squelching. Toxicological Sciences 96 (1) 83-91.