Biological control

1. A recombinant insect whose genome comprises a dominant lethal genetic system with a conditional lethal effect, the system comprising:

(i) a lethal gene under the control of a promoter, wherein the lethal gene is present in the system regardless of sex of the insect,

(ii) a transactivator gene, which expresses a repressible transactivator protein and is under the control of sex-specific promoter; and

(iii) a binding sequence for the repressible transactivator protein, wherein the lethal effect of the system is sex-specific, and expression of the lethal gene is activatable by the repressible transactivator protein which is repressible by a tetracycline, tetracycline analogue, or tetracycline derivative,

wherein the lethal effect of the genetic system is repressible by the tetracycline, analogue, or derivative, and

wherein the insect is a mosquito, medfly or pink bollworm.

2. The recombinant insect of claim 1 , wherein the lethal gene is a sex-specific lethal gene.

3. The recombinant insect of claim 1 , wherein a product of the lethal gene is lethal to only one sex of the recombinant insect.

4. The recombinant insect of claim 1 , wherein the lethal gene is expressed in only one sex of the recombinant insect or a product of the lethal gene is produced in only one sex of the insect.

5. The recombinant insect of claim 1 , wherein the lethal effect is controlled by a sex-specific promoter or enhancer or by sex-specific splicing.

6. The recombinant insect of claim 1 , wherein the sex-specificity of the genetic system is mediated by sex-specific splicing.

7. The recombinant insect of claim 1 , wherein the lethal system is homozygous at more than one locus.

8. The recombinant insect of claim 1 , wherein the lethal system is located on the X chromosome.

9. The recombinant insect of claim 1 , wherein the conditional lethal effect of the genetic system is specific for an embryonic or larval life cycle stage.

10. The recombinant insect of claim 1 , wherein the conditional lethal effect is specific to females or female tissue for at least one life cycle stage.

11. The recombinant insect of claim 1 , wherein the lethal gene comprises an inhibitor sequence selected from the group consisting of: antisense RNA, sense RNA, and double stranded RNA.

12. A method for breeding a stock of recombinant insects, comprising the steps of:

(i) obtaining a stock of recombinant insects of the same species of claim 1 ; and

(ii) breeding the stock of recombinant insects from step (i) under permissive conditions.

13. The method of claim 12 , wherein both males and females are distributed in step (iii).

14. The method of claim 12 , wherein a single sex is distributed in step (iii).

15. The method of claim 12 , wherein the method further comprises sex-separation prior to step (iii).

16. The method of claim 12 , wherein the method results in killing of greater than 90% of the target class of the progeny resulting from the breeding of stock insects with wild-type insects.

17. The method of claim 12 , further comprising distributing the stock of recombinant insects from step (ii) into an environment lacking tetracycline, tetracycline analog or tetracycline derivative, whereby individual recombinant stock insects breed with the same species in the wild-type population to produce offspring expressing the lethal gene.