Sex separation strategies: past experience and new approaches

Abstract

The success of the sterile insect technique (SIT) and other genetic strategies designed to eliminate large populations of insects relies on the efficient inundative releases of competitive, sterile males into the natural habitat of the target species. As released sterile females do not contribute to the sterility in the field population, systems for the efficient mass production and separation of males from females are needed. For vector species like mosquitoes, in which only females bite and transmit diseases, the thorough removal of females before release while leaving males competent to mate is a stringent prerequisite. Biological, genetic and transgenic approaches have been developed that permit efficient male-female separation for some species considered for SIT. However, most sex separation methods have drawbacks and many of these methods are not directly transferable to mosquitoes. Unlike genetic and transgenic systems, biological methods that rely on sexually dimorphic characters, such as size or development rate, are subject to natural variation, requiring regular adjustment and re-calibration of the sorting systems used. The yield can be improved with the optimization of rearing, but the scale of mass production places practical limits on what is achievable, resulting in a poor rearing to output ratio. High throughput separation is best achieved with scalable genetic or transgenic approaches.

Genetic control ofAedesmosquitoes

“…Several have been developed. [60][61][62][63][64][65] In principle, any selectable induced sexual dimorphism could be used, but in practice two approaches have been followed, either sex-specific expression of a fluorescent marker allowing automated sorting, 61,66 or sex-specific conditional lethality allowing facile elimination of one sex from a cohort during rearing.…”

A draft genome sequence of an invasive mosquito: an ItalianAedes albopictus

“…[78][79][80] Their usage in approaches such as SIT and similar techniques in which sex separation is involved obviously jumps to mind. 81 …”

Genetic elimination of dengue vector mosquitoes

“…SITapproaches for mosquito control have been tried (17)(18)(19) and continue to be proposed (20,21). Factors that may have limited the success of these initial mosquito SIT programs and that are of continued concern in proposed SIT applications include reduced mating competitiveness and residual fertility of irradiated males (22,23), the need to release exclusively males (male mosquitoes do not take blood meals) (20,24), and reduction of density-dependent larval mortality due to early acting lethality (22,25,26). These limitations may be overcome using recombinant DNA technology to engineer repressible dominant-lethal transgenes for an RIDL strategy (4-7).…”