Key terms and definitions in possum biocontrol
A list of terms used in our content on the biological control of possums.
Antibodies
Fertilisation
Diagram showing the steps in fertilisation. The sperm attaches (1), binds (2) and penetrates (3) the zona pellucida. When the sperm fuses with the egg's membrane genetic material is released inside the egg. Fertilisation (4) occurs when the sperm's genetic material eventually combines with the egg's genetic material.
Proteins, also known as immunoglobulins, produced in the body as part of its immune response. Antibodies bind foreign particles and protect the body from infection.
Antigen
Any substance that is foreign to the body, causing the body to mount an immune response to destroy the antigens, and protect the body from harm.
Bacterial ghosts
Bacterial cell membranes with their organelles removed. Bacteria are engineered so that they expel their contents when heated leaving only the surrounding cell membrane. Proteins such as the GnRH hormone or zona pellucida protein can be incorporated into the membranes and used as antigens.
Biological control or biocontrol
There are several subtly different, but important understandings of the term biocontrol.
Most commonly, biocontrol is the control of a pest, or destructive organism, by the introduction of a natural predator. The natural predators of possums in Australia are the native species of carnivores including the carpet python, powerful owl, wedge-tailed eagle and dingoes, and the introduced feral cat, wild dog, and fox. The use of any of these natural predators is not suitable in NZ.
The concept of a natural predator can be extended to include other natural enemies – usually microorganisms such as parasites and pathogens (viruses or bacteria). This can include the manipulation of these microorganisms to enhance their effectiveness. As with predators, there are no known natural enemies that are suitable for possum control.
Biocontrol can also involve the use of microorganisms (e.g. parasites, viruses) as vectors to distribute a biocontrol agent such as a fertility control vaccine.
Rather than using a living organism to directly regulate a pest population, an active ingredient may be extracted or manufactured from a living organism and used for the biocontrol. This may involve the genetic modification of the living organism, but in containment.
Finally, there is the more general claim, when referring to possum biocontrol in New Zealand, that any reagent used to control fertility is a biocontrol.
The types of biocontrols being investigated and developed by the NRCPB are in line with definitions 3-5 above.
Contraceptive vaccine
A vaccine that acts as a contraceptive by inducing an immune response against proteins involved in reproduction. The reproductive cycle is broken, and the animal becomes infertile.
Corpus luteum
Tissue that develops from a collapsed follicle in the ovary, after an egg has been released from the follicle. The corpus luteum produces the hormone progesterone.
FSH or follicle-stimulating hormone
A reproductive hormone produced in the pituitary gland. In females, FSH stimulates the growth of follicles eggs are matured in the ovary. In males, FSH stimulates sperm production.
Glycoprotein
A protein that has carbohydrate molecules attached to it.
GnRH or gonadotrophin-releasing hormone
A hormone produced in the hypothalamus area of the brain, which stimulates the reproductive cycle in mammals.
Immunocontraception
The use of a contraceptive vaccine. A method of birth control that uses the body’s immune system to produce antibodies against its own proteins needed for reproduction.
LH or luteinising hormone
A reproductive hormone produced in the pituitary gland. In females, LH triggers ovulation (the release of an egg from the ovary). In males, LH stimulates the production of testosterone in the testes.
Lipid matrix (plural: matrices)
A cage of lipid molecules. Other molecules, such as the GnRH hormone, may be enclosed inside a lipid matrix and used as antigens.
Non-transmissible
A delivery system that cannot pass an agent from one organism to another.
Transmissible
A delivery system that passes an agent from one organism to another.
Vaccine
Material that stimulates an immune response to recognise a particular organism or molecule. Vaccines are used to protect the body against disease, because they prime the immune system to recognise infections.
Vector
A carrier used to deliver biological control agents such as vaccines or toxins.
Biocontrol and vectors: What is a vector?
In the case of biological control, it is an organism that carries, or transfers, the control agent to the target organism. For example, in the research into possum biocontrol being carried out at AgResearch, a vector is needed to spread the hormone toxin amongst possums in order to make them infertile.
Virus-like particles
Virus-like particles are made from the structural proteins that make a virus, so they resemble the virus from which they were derived, but they don’t contain any nucleic acids (DNA, RNA), so they are not infectious. The GnRH or ZP proteins are attached to the particle or engineered to have the proteins incorporated into the particle.
Zona pelluc ida
A glycoprotein membrane surrounding a mammalian egg (oocyte), that is required for fertilisation.
