The brushtail possum (Trichosurus vulpecula) is regarded as New Zealand's number one vertebrate pest in both economic and ecological terms.

At present, approximately $111 million is spent annually on the control of possums for conservation purposes and for the control of bovine Tb. Given that the benefits of this level of control have been clearly demonstrated, this expenditure will likely continue for at least the next seven years. Whilst conventional control methods (poisons and traps) are effective, the risks posed by the dependence on poisons (environmental, trade, public acceptance and cost) may pose difficulties for their continued long-term use. Thus, new tools are needed that can be used in conjunction with current control methods. Biological management offers the only foreseeable technologies that will cost-effectively reduce dependence on conventional control methods and this was identified as a priority research area by the National Science Strategy Committee for Possum and Bovine Tuberculosis Control (NSSC). There are several subtly different, but important understandings of the term biocontrol. Listed below are some of these:

Different meanings of the term biocontrol

  1. Biological control or biocontrol can mean natural control, in other words, the control of one population by another in the absence of human intervention - a native organism, occurring at normal densities, controls a native or introduced pest (Lockwood 1996).
  2. Most commonly, biocontrol is the control of a pest, or destructive organism, by the introduction of a natural predator, rather than by using chemical means. This definition of biocontrol can be either classical (the introduction of an exotic agent) or augmentative (actions to conserve or maintain and enhance the actions 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.
  3. The concept of a natural predator is extended to include other natural enemies & biological agents, usually microorganisms such as parasites and pathogens (viruses or bacteria). In New Zealand, one such organism is the virus resulting in wobbly possum disease. However, the nature of this virus precludes its use as a biocontrol.
  4. The biological agents themselves may be manipulated. Compared with natural control (i.e. "control that occurs without man's intervention") biocontrol is defined as the "manipulation of natural enemies by man to control pests"(van den Bosch, The objective of this action is to enable the agents to control, enhance their control of, or become more specific in their effects on, or deliver agents which will control pest species.
  5. The fifth definition is, in some ways a subset of the previous definition, in using biological organisms (e.g. parasites, viruses) as vectors to distribute technologies such as immunocontraceptive agents and toxins while the organisms themselves cannot be regarded as biological controls (Barlow, 1997).
  6. The active ingredient for a biocontrol is extracted or manufactured from a bacterium or fungus. Rather than using a living organism to directly regulate a pest population (as in the previous definition), this technique uses the products of living organisms, although both may involve biotechnology and genetic modification.
  7. Finally, there is the more limited claim that any reagent used to control fertility is a biocontrol.

In New Zealand there are no natural predators or known pathogens (virus or parasite) that can be used to control possums. The types of biocontrols being investigated and developed by the NRCPB are in line with definitions 5-7 above.

The management of wildlife species is becoming increasingly necessary throughout the world. The research being done in New Zealand on the development and application of new technologies for the control of possums is world leading and may lead to applications in other wildlife or pest species in NZ and other countries.


The NRCPB is a national possum biocontrol research platform formed through partnership between the major science providers (AgResearch and Landcare Research) and key end-user organisations (Animal Health Board, Department of Conservation, Ministry for Agriculture and Forestry, Regional Councils). It is funded by the Foundation for Research, Science and Technology (FRST) as an outcome based investment (OBI) and is also supported by co-funding from various research organisations (e.g. University of Otago, AHB).
The objectives of the NRCPB partnership are to:

Science Programme

Current research has reached a point from which model systems for the biological management of possums will emerge in the next 4-5 years. Achievement of the National Research Centre for Possum Biocontrol (NRCPB) objectives will aid in reducing possum numbers, reduce the welfare cost of possum management and use of non-specific poisons, and increase the scale of the management effort.
A multi-stranded approach to biological control is being undertaken. As is the case with conventional toxins, multiple approaches are likely to be required to deal with the range of situations in which control must be applied. Research will address the identification of potential targets, delivery mechanisms (non-transmissible and transmissible), and the testing and refinement of developed methods for the biological control of possums.

Scope of Research in NRCPB

The first four years of research is focused on the highly technical aspects needed for developing biological controls; the application of biotechnology to the development of working models combining physiological targets and delivery systems.

These model systems are:

Key research collaborations have been established to achieve the objectives of the programme and include:

AgResearch, Invermay
  • expertise in oral possum gut ion transporter system toxins
  • functional studies on gut epithelial transporters
  • expertise in formulation science
  • oral formulations to protect and deliver protein bioactives
  • expertise on genomics/bioimformatics
  • possum EST database
AgResearch, Wallaceville
  • expertise in oral possum hormone- toxin conjugates
  • immunisation against GnRH and oocyte specific growth factors
  • toxin/GnRH conjugation and conjugate testing
  • expertise in transgenic possum-specific nematode (or virus) expressing proteins inhibitory to possum fertility
  • possum enterovirus epidemiology, biology and genetic manipulation
  • nematode parasite transgenesis
  • persistence and transmission of nematode parasites
  • nematode modelling
  • possum EST database
Landcare Research, Lincoln
  • expertise in oral possum zona pellucida protein-based vaccines
  • ZP antigens and mechanisms of infertility
  • optimisation of bacterial ghost expression
  • testing and formulation of bacterial ghosts
  • target specificity; plant-derived vaccines
  • expertise in ethical and social risks
  • communication and risk management strategies
Landcare Research Palmerston North
  • expertise in modelling impacts of non- transmissible and transmissible possum fertility control
  • optimal strategies for use of non-transmissible and vectored biocontrols
Kotare Bioethics
  • expertise in ethical and social risks
  • communication and risk management strategies
Physiology Dept., Otago University
  • expertise in epithelial cell physiology
University of Vienna
  • expertise in bacterial ghost vaccine production
Colorado State University
  • design and provision of GnRH-toxin conjugates and other reagents including immortal cell lines
School of Pharmacy, Otago University
  • expertise in pharmaceutical science
Melbourne University
  • identification and characterisation of proteins involved in early embryonic development
Newcastle University
  • marsupial reproduction and plant-derived vaccines

There are currently 5 post-doctoral fellows, 5 PhD students and 3 other students involved in this or closely related research.

Related Links

Possum EST Browser and data downloads
Landcare Research (Information sheets)
Landcare Research (Biocontrol)
Animal Health Board
Department of Conservation
Ministry of Agriculture and Forestry
National Possum Control Agencies (Web site addresses for the regional councils can be found here)
Caught in the headlights: New Zealanders reflections on possums, control options and genetic engineering. Parliamentary Commissioner for the Environment
Biotechnology Learning Hub Focus Stories : Biological control of possums
Possum Biocontrol Wiki 



Duckworth J, Wilson K, Cui X, Molinia F, Cowan P (2007). Immunogenicity and contraceptive potential of three infertility relevant possum ZP2 epitopes in the Brushtail Possum (Trichosurus vulpecula). Reproduction 133, 177-186.

Eymann J, Herbert CA, Thomson BP, Trigg TE, Cooper DW, Eckery DC (2007) Effects of deslorelin implants on reproduction in the common brushtail possum (Trichosurus vulpecula). Reproduction, Fertility and Development (In Press).

Duckworth J, Byrom A, Fisher P, Horn C (2006) Pest control: does the answer lie in new biotechnologies?    Chapter 27 In: Biological Invasions in New Zealand Ecological Studies Series Vol 186, R.B.Allen and W.G. Lees (Eds)   Springer-Verlag, Heidelberg. pp. 421-434

Crawford JL, Thomson BP, Beaumont MF, Eckery DC (2006) Plasma concentrations of prolactin in brushtail possums (Trichosurus vulpecula) in different physiological states. J Endocrinology 190, 295-305

Crawford JL, Lun S, Demmer J, Eckery DC (2005) Prolactin in the brushtail possum (Trichosurus vulpecula): Development of homologous radioimmunoassay using recombinant possum prolactin.  General and Comparative Endocrinology 142, 297-307.

Fink JW, McLeod BJ, Assinder SJ, Parry LJ, Nicholson HD. (2005) Seasonal changes in mesotocin and localization of its receptor in the prostate of the brushtail possum (Trichosurus vulpecula).   Biology of Reproduction 72, 143-151.

Wilson JD, Shaw G, Renfree MB, Auchus RJ, Leihy MW, Eckery DC. (2005) Ontogeny and pathway of formation of 5a-androstane-3a,17b-diol in the testes of the immature brushtail possum Trichosurus vulpeculaReproduction Fertility and Development 17, 1-7.

Cui X, Duckworth J. (2005) Mapping of B cell epitopes on the zona pellucida 2 protein of a marsupial, the brushtail possum (Trichosurus vulpecula). Molecular Reproduction and Development 70, 485-93

Polkinghorne I, Hamerli D, Cowan P, Duckworth,J (2005) Plant-based immunocontraceptive control of wildlife - potentials, limitations, and possums
Vaccine 23, 1847-1850

Eckery DC (2004) Impacts of pests and their management in New Zealand: possums and fertility control.  Lifting the veil: finding common ground.  Proceedings of the ANZCCART Conference, Christchurch, New Zealand, 18-19 August 2003.

Sizemore RJ, Hurst PR, McLeod BJ. (2004) Effect of steroid hormones on tissue remodelling and progesterone receptors in the uterus of seasonally anoestrous Brushtail possums (Trichosurus vulpecula) Reproduction 127, 255-264.

Mahoney PM, Hurst PR, McLeod BJ, McConnell MA, Thompson EG. (2003) The effect of oestradiol treatment on mast cell populations and microflora in the vaginal cul-de-sac of seasonally anoestrous Brushtail possums (Trichosurus vulpecula) Reproduction 125, 733-741.

Western AH, Eckery DC, Demmer J, Juengel JL, McNatty KP, Fidler AE (2003) Expression of the FcRn receptor (a and b) gene homologues in the intestine of suckling brushtail possum (Trichosurus vulpecula) pouch young.  Molecular Immunology 39, 707-717.

Whale LJ, Eckery DC, Juengel JL (2003) Determination of steroidogenic potential of ovarian cells of the brushtail possum (Trichosurus vulpecula).  Biology of Reproduction 69, 947-958.

Eckery DC, Whale LJ, Lawrence SB, Wylde KA, McNatty KP, Juengel JL (2002) Expression of mRNA encoding growth differentiation factor 9 and bone morphogenetic protein 15 during follicular formation and growth in a marsupial, the brushtail possum (Trichosurus vulpecula). Molecular and Cellular Endocrinology 192, 115-126.

Eckery DC, Juengel JL, Whale LJ, Thomson BP, Lun S, McNatty KP (2002) The corpus luteum and interstitial tissue in a marsupial, the brushtail possum (Trichosurus vulpecula).  Molecular and Cellular Endocrinology 191, 81-87.

Eckery DC, Lun S, Thomson BP, Ng Chie W, Moore LG, Juengel JL (2002) Ovarian expression of mRNA encoding the receptors for LH and FSH in a marsupial, the brushtail possum (Trichosurus vulpecula).  Biology of Reproduction 66, 1310-1317.

Eckery DC, Lawrence SB, Juengel JL, Greenwood P, McNatty KP, Fidler AE (2002) Gene expression of the tyrosine kinase receptor c-kit during ovarian development in the brushtail possum (Trichosurus vulpecula).  Biology of Reproduction 66, 346-353.

Juengel JL, Whale LJ, Wylde KA, Greenwood P, McNatty KP, Eckery DC (2002) Expression of anti-mullerian hormone mRNA during gonadal and follicular development in the brushtail possum (Trichosurus vulpecula).  Reproduction Fertility and Development 14, 345-353.

Mahoney PM, Hurst PR, McLeod BJ, McConnell MA. (2002) Quantification of mast cells and microflora in the cul-de-sac of the brushtail possum (Trichosurus vulpeculaReproduction 124, 399-408

Mate KE, Buist JM, Duckworth JA (2002) Expression in Escherichia coli and immunological characterisation of three zona pellucida proteins (ZP1, ZP2 and ZP3 from a marsupial, the brushtail possum (Trichosurus vulpecula). MolecularReproduction and Development 64,136-143.

Khalil AM, McFarlane, RG, Duckworth JA (2001) Humoral immunity to cholera toxin and ovalbumin in the brushtail possum (Trichosurus vulpecula). New Zealand Veterinary Journal 49, 54–59.

Cowan PE 2000 Biological control of possums: prospects for the future.  In: The brushtail possum: biology impact and management of an introduced marsupial T Montague (Ed) Manaaki Whenua Press Lincoln, New Zealand, pp 56: 262-270.

Crawford JL, McLeod BJ, Thompson EG, Hurst PR, Colbourne LE, Lun S, Eckery DC. (1999) Plasma gonadotrophin concentrations in the cyclic female brushtail possum (Trichosurus vulpecula) General and Comparative Endocrinology 116, 73-80.

Crawford JL, McLeod B J, Hurst PR. (1999) Cyclical changes in epithelial cells of the vaginal cul-de-sac of brushtail possums (Trichosurus vulpecula) The Anatomical Record 254, 307-321.

Eckery DC, Colbourne LE, Heath DA, Lawrence SB, Lun S, Ng Chie W, Whale L, Juengel JL, Fidler AE, Moore LG, McNatty KP (1999) Fertility control of possums:  The search for regulators of gonadal development and pituitary function.  Proceedings of the New Zealand Society of Animal Production 59, 239-244.

McLeod BJ, Thompson EG, Crawford JL, Mahoney PM, Eckery DC (1999) Monitoring oestrus and ovulation in brushtail possums. Proceedings New Zealand Society of Animal Production 59, 236-238.

McLeod BJ, Hunter MG, Crawford JL, Thompson EG. (1999) Follicle development in cyclic, anoestrous and FSH-treated brushtail possums (Trichosurus vulpecula) Animal Reproduction Science 57, 217-227.

McLeod BJ, Thompson EG, Crawford JL. (1999) Synchrony of onset and cessation of breeding activity in brushtail possums (Trichosurus vulpecula) in coastal Otago, New Zealand. Proceedings New Zealand Society of Animal Production 59, 229-232.

Duckworth JA, Scobie S, Jones DE, Selwood L (1998): Determination of oestrus and mating in captive female brushtail possums (Trichosurus vulpecula) from urine samples. Australian Journal of Zoology 46, 547–555. 

Crawford JL, Thompson EG, McLeod BJ, Hurst PR. (1998) Presence of males affects the incidence of ovulation following pouch young removal in brushtail possums (Trichosurus vulpecula) Animal Reproduction Science 51, 45-55

Duckworth JA, Buddle BM, Scobie S (1998) Fertility of brushtail possums (Trichosurus vulpecula) immunised against sperm. Journal of Reproductive Immunology 37, 125–138. 

Crawford JL, Shackell GH, Thompson EG, McLeod BJ, Hurst PR. (1997) Preovulatory follicle development and ovulation in brushtail possums (Trichosurus vulpecula) monitored by repeated laparoscopy. Journal of Reproduction and Fertility 110, 361-370.

Legge M, Hill BL, Shackell GH, McLeod BJ. (1996) Uterine and vaginal cul-de-sac tissue glycosaminoglycans in the Brushtail possum (Trichosurus vulpecula) Reproduction, Fertility and Development 8, 819-823.

Shackell GH, Norman NG, McLeod BJ, Hurst PR. (1996) A morphometric study of early ovarian development in pouch young of the Brushtail possum (Trichosurus vulpecula) The Anatomical Record 246, 224-230.


Wen J-Y, McLeod BJ, Davies NM, Ledger R, Tucker IG, Butt AG (2007) Enhancing absorption of fluorescein and LHRH across the hindgut epithelia in a marsupial, the common brushtail possum Trichosurus vulpecula. Journal of Pharmaceutical Sciences 96, (in press)

McDowell A, McLeod BJ, Rades, T, Tucker IG (2006) Application of pharmaceutical drug delivery systems for biological control of the common brushtail possum in New Zealand – a review Wildlife Research 33, 679-689.

McDowell A, Nicoll JJ, McLeod BJ, Tucker IG and Davies NM (2005) Gastrointestinal transit in the common brushtail possum (Trichosurus vulpecula) measured by gamma scintigraphy.  International Journal of Pharmaceutics 302, 125-132.

McDowell A, McLeod BJ, Thompson EG, Tucker IG. (2005) A morphometric study of the gastrointestinal tract of the common brushtail possum in southern New Zealand.  Australian Mammalogy 27, 61-67.

McLeod BJ, Huang L, Zhang H, Thompson EG, Butt AG, Tucker IG (2005) An in situ single-pass perfusion model for assessing absorption across the intestinal mucosa of the brushtail possum. New Zealand Veterinary Journal 53, (4) 234-241.

Wen JY, Ledger R, McLeod BJ, Davies NM, Butt AG, Tucker IG. (2002)  Enzymatic degradation of luteinizing hormone releasing hormone (LHRH) by mucosal homogenates from the intestine of common brushtail possum (Trichosurus vulpecula) Life Sciences 71, (25) 3019-3030

Wen JY, Ledger R, Butt AG, McLeod BJ, Davies NM, Tucker IG. (2002) Inhibition of proteolysis in luminal extracts from the intestine of the brushtail possum. Journal of Pharmacy and Pharmacology 54, 1365-1372

Wen JY, Ledger R, McLeod BJ, Davies NM, Butt AG, Tucker IG. (2002) Protein and peptide degradation in the intestine of the brushtail possum (Trichosurus vulpeculaJournal of Comparative Physiology B 172, 553-559

Wen JY, Davies NM, Ledger R, Butt AG, McLeod BJ, Tucker IG. (2002) Isocratic liquid chromatographic assay for monitoring the degradation of Luteinizing Hormone Releasing Hormone by extracts from the gastrointestinal tract of possums Journal of Chromatography B: Analytical Technologies in the Biomedical and Life Sciences 779, 221-227


Sorensen JS, Forbey KC, Tanquay R, McLeod BJ (2007) Tissue distribution of cytochrome P450 3A (CYP3A) in brushtail possums (Trichosurus vulpecula) exposed to Eucalyptus terpenes Journal of Comparative Physiology & Biochemistry C 145, 194-201

Butt AG, Mathieson SE, McLeod BJ. (2002) Aldosterone does not regulate amiloride-sensitive Na+ transport in the colon of the common Australian brushtail possum Trichosurus vulpecula. Journal of Comparative Physiology B 172, 519-527

Butt AG, Mathieson SE, McLeod BJ. (2002) Electrogenic ion transport in the intestine of the common Australian brushtail possum, Trichosurus vulpecula: Indications of novel transport patterns in a marsupial. Journal of Comparative Physiology B 172, 495-502


Ramsey D, Coleman J, Coleman M, Horton P (2006).  The effect of fertility control on the transmission of bovine tuberculosis in wild brushtail possums.  New Zealand Veterinary Journal 54(5), 218-223. 

Ramsey D (2007) Effects of fertility control on behavior and disease transmission in brushtail possums.  Journal of Wildlife Research 71,109-116.

Tompkins D.M. (2007). Minimum specifications for transmissible transgenic biocontrol agents for brushtail possum (Trichosurus vulpecula) population eradication. New Zealand Journal of Zoology 34, 125-140.

Tompkins DM, Ramsey D (2007). Optimising bait-station delivery of fertility control agents to brushtail possum (Trichosurus vulpecula) populations. Wildlife Research 34, 67-76.

Cowan PE, Ralston MJ, Heath DD, Grant WN (2006) Infection of naive, free-living brushtail possums (Trichosurus vulpecula) with the nematode parasite

Parastrongyloides trichosuri and its subsequent spread.  International Journal for Parasitology 36, 287-293.

Ramsey D, Efford M, Cowan P, Coleman, J (2002). Factors influencing annual variation in breeding by common brushtail possums (Trichosurus vulpecula) in New Zealand Wildlife Research 29, 39-50.

Ramsey D, Spencer N, Caley P, Efford M, Hansen K, Lam M, Cooper D (2002)  The effects of reducing population density on contact rates between brushtail possums: implications for transmission of bovine tuberculosis  Journal of Applied Ecology 39, 806-818.

Caley P, Ramsey D (2001). Estimating disease transmission in wildlife, with emphasis on leptospirosis and bovine tuberculosis in possums, and effects of fertility control  Journal of Applied Ecology 38, 1362-1370.


McLeod BJ, Thompson EG. (2002) Predation on house sparrows (Passer domesticus) and hedge sparrows (Prunella modularis) by brushtail possums (Trichosurus vulpecula) in captivity. Notornis 49, 95-99

McLeod BJ, Thompson EG, Crawford JL, Shackell GH. (1997) Successful group housing of wild-caught brushtail possums (Trichosurus vulpecula) Animal Welfare 6, 67-76.


Thompson EG, McLeod BJ, Gill JM. (1999) The prevalence of Wobbly Possum disease in a bush/farmland environment. Proceedings New Zealand Society of Animal Production 59, 233-235.

Mackintosh, CG, Crawford JL, Thompson EG, McLeod BJ, Gill JM, O'Keefe JS. (1995) A newly discovered disease of the brushtail possum: Wobbly possum syndrome. New Zealand Veterinary Journal 43, 126.

For further information, contact Bernie McLeod, AgResearch Limited. Phone (03) 489 9187 or email