RIDL insects contain a genetic modification that causes their offspring to die, but the RIDL insects can live and reproduce normally when they are fed a diet containing a supplement.
RIDL males are released to mate with wild female pest insects; their progeny inherit the RIDL gene and do not survive to adulthood. Releases of RIDL males in large enough numbers over a sufficient time will suppress, or even eliminate, the target pest population.
Bisex RIDL strains have no progeny unless supplied with the supplement; both male and female progeny die. Strains can be designed to die at different life stages. Released bisex RIDL insects and all of their progeny die within a few weeks so releases must be sustained to maintain the control. Where a male-only release is required, the sexes must be separated mechanically, which is possible in only a few insect species. Bisex RIDL is included in Oxitec’s products Aedes aegypti OX513A and pink bollworm OX3402.
Female-specific RIDL (fsRIDL) strains have no female progeny unless supplied with the supplement, but male progeny survive. Strains can be designed to die at different life stages. The sexes can be separated easily by excluding the supplement from the diet of the final, pre-release generation so that only males are produced for release. This eliminates potential damage caused by handling in mechanical sex separation. fsRIDL males are released to mate with wild type females. Their female progeny do not survive and the population is thereby suppressed. Their male progeny carry one copy of the RIDL gene, so half their female progeny will also die. There is therefore some carry-through of the birth control activity but releases must be continued for total control. fsRIDL is included in Oxitec’s products Aedes aegypti OX3604C and Mediterranean fruit fly OX3647.