Practical applications of insects' sexual development for pest control.

Elucidation of the sex differentiation pathway in insects offers an opportunity to understand key aspects of evolutionary developmental biology. In addition, it provides the understanding necessary to manipulate insects in order to develop new synthetic genetics-based tools for the control of pest insects. Considerable progress has been made in this, especially in improvements to the sterile insect technique (SIT). Large scale sex separation is considered highly desirable or essential for most SIT targets. This separation can be provided by genetic methods based on sex-specific gene expression. Investigation of sex determination by many groups has provided molecular components and methods for this. Though the primary sex determination signal varies considerably, key regulatory genes and mechanisms remain surprisingly similar. In most cases studied so far, a primary signal is transmitted to a basal gene at the bottom of the hierarchy (dsx) through an alternative splicing cascade; dsx is itself differentially spliced in males and females. A sex-specific alternative splicing system therefore offers an attractive route to achieve female-specific expression. Experience has shown that alternative splicing modules can be developed with cross-species function; modularity and standardisation and re-use of parts are key principles of synthetic biology. Both female-killing and sex reversal (XX females to phenotypic males) can in principle also be used as efficient alternatives to sterilisation in SIT-like methods. Sexual maturity is yet another area where understanding of sexual development may be applied to insect control programmes. Further detailed understanding of this crucial aspect of insect biology will undoubtedly continue to underpin innovative practical applications.