Biological Control

Abstract

The invention relates to a non-human multicellular organism carrying a dominant lethal genetic system, the lethal effect of which is conditional, wherein the lethal effect of the lethal system occurs in the natural environment of the organism.

Description

[0001] The present invention relates to a method for controlling the population of an organism. BACKGROUND OF THE INVENTION [0002] Methods of biological control are known for insects and plants. One method currently employed for the control of insect populations is termed the “sterile insect technique” (SIT), also known as the “sterile insect release method” (SIRM). In this method, sterile males are released into the environment, wherein they compete with the wild-type (fertile) males for mates. Females which male with sterile males produce no offspring, and fee release of large numbers of sterile males, therefore, leads to a decrease in the size of the next generation. In this way fee size of the wild population is controlled. [0003] SIT requires some mechanism for insect sterilisation. In addition, SIT commonly also employs separation of males from females, with the release of only one sex. This is desirable is the case of an agricultural pest, such as the medfly, where the female...

AI Technical Summary

Benefits of technology

[0085] In one aspect the invention relates to a son sex-specific system, in which both males and females are killed by the lethal genetic system. Such an approach is preferred in certain organisms. In such a case, one advantage of the invention lies in the avoidance of sterilisation by irradiation. By way of example, mixed sex releases are preferred in pink bollworm (a lepidopteran pest of cotton), but irradiated moths are estimated to suffer at least a 10 fold reduction is effectiveness as a consequence of the irradiation due to loss of vigour and reduced life spas. Similar advantages are predicted in other organisms. In medfly, irradiated males are about 50% less effective than the non-irradiated equivalent in competitive mating tests and they live 3-5 days instead of the non-irradiated 10-15. This gives a composite 4-10 fold potential performance improvement by avoiding irradiation.

[0086] The method of the invention alternatively uses a sex-specific lethal system to achieve sex separation before or after release of organisms into the environment. In a preferred embodiment, the multicellular organism is an insect containing a homozygous dominant lethal system, the lethal effect of which is lethal only to females. In this embodiment males released into the natural environment will not be killed. After mating with females, female offspring will contain at least one copy of fee dominant system and be killed. However, male offspring, 50% of which contain the dominant system, are viable and may mate with further females. In tins way, the dominant system may be transmitted to subsequent generations, although without further artificial introductions the system will eventually be lost from the gene pool

[0087] In the case in which a male contains a lethal generic system with a female specific lethal effect, then males released into the environment will not be Idled. However, the lethal effect of the lethal system is still manifested in the natural environment—even if this effect is limited to females.

[0088] Sex-specific lethality may be achieved in a number of different ways. For example, it is possible to use a sex-specific lethal gene as part of the lethal system, whose gene product is toxic only in one sex. This approach will allow killing of a single sex even if expression of the lethal gene of gene product is not sex specific. Candidates for female sex-specific lethal genes include genes from the sex determination pathway, for example normally active only in males and toxic in females, or genes derived from sexual differentiation or gametogenesis systems.

[0089] Alternatively, expression of the lethal gene or gene product may be controlled so that it is expressed or produced only in one sex (or in only one gamete or sexual organ of a hermaphrodite). For example, sex-specific promoters or enhancers may be used, either in combination with sex-specific lethal genes or non-specific lethal genes. Sex-specific splicing provides another mode for sex-specific gene expression. All possible combinations of non-specific lethal genes, sex-specific lethal genes, non-specific promoters and sex-specific promoters are envisaged by the present invention, hi addition, other sex-specific factors which control the lethal effect of the lethal gene are included in the present invention.

[0090] The present invention also includes a method of biological control in which the lethal effect may be sex-specific at one stage of the life cycle, but be lethal to both sexes at another stage. For example, the lethal system may be female specific in an adult organism, but be lethal to both males and females in the larval stage. In such a case, one sex may be killed by expression of the lethal system in the adult form. When the organism men breeds in the wild, passing on the genetic construct, then both males and females can be killed. Such an effect can be achieved by a promoter which is sex specific at one life cycle stage, but not at another, or by placing the lethal gene under control of two different promoters, for example. Multiple lethal systems might also be employed.

Problems solved by technology

Females which male with sterile males produce no offspring, and fee release of large numbers of sterile males, therefore, leads to a decrease in the size of the next generation.

In some eases it is possible to separate males and females by criteria such as pupal mass of time of eclosion, hut these methods are unlikely reliably to yield a truly single-sex population.

Separation of males and females often involves the use of mutant strains, which have been mutagenised to induce a visible or otherwise selectable difference between fee sexes, but such mutagenesis can reduce the fitness of the resultant stock with respect to the wild types which is undesirable.

As such, sterile organisms are frequently impaired in their ability to mats.

Furthermore, both chemical and irradiation methods utilise technologies which are not specific to the target organism, with consequent potential danger to workers.

Both methods produce as environmental hazard, as the irradiation source or chemicals will need to be disposed of.

In addition, there are inherent dangers and additional labour costs in the use of as irradiation source such as a strontium source.

However, this method can be ineffective due to varying field conditions, where the environments does not provide suitably cold conditions.

Moreover, organisms that live in a range of temperature habitats may not be controlled under all conditions.

However, this method suffers from the drawback referred to above, in that released flies have reduced fitness due to the sterilisation treatment.

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