Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart
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Benefits of Rabbit
Biocontrol in Australia
Tarnya Cox, Tanja Strive, Greg Mutze,
Peter West and Glen Saunders
Benefits of Rabbit Biocontrol in Australia
Benefits of Rabbit
Biocontrol in Australia
Tarnya Cox1
Tanja Strive2
Greg Mutze3
Peter West1
Glen Saunders1
1
Vertebrate Pest Research Unit, Department of Primary Industries
Locked Bag 6006, Orange NSW 2800
2
Division of Ecosystem Sciences, CSIRO
GPO Box 1700, Canberra ACT 2600
3
Natural Resources Management Biosecurity, Biosecurity South Australia
GPO Box 1671, Adelaide SA 5001
2013
An Invasive Animals CRC Project
Benefits of Rabbit Biocontrol in Australia Disclaimer: The views and opinions expressed in this report reflect those of the author and do not necessarily reflect those of the Australian Government, Invasive Animals Ltd, or the Invasive Animals Cooperative Research Centre. The material presented in this report is based on sources that are believed to be reliable. Whilst every care has been taken in the preparation of the report, it is “as is”, without warranty of any kind, to the extent permitted by law. Published by: Invasive Animals Cooperative Research Centre. Telephone: (02) 6201 2887 Facsimile: (02) 6201 2532 Email: contact@invasiveanimals.com Internet: http://www.invasiveanimals.com ISBN: 978-1-921777-63-9 Web ISBN: 978-1-921777-64-6 © Invasive Animals Cooperative Ltd 2013 This work is copyright. The Copyright Act 1968 permits fair dealing for study, research, information or educational purposes. Selected passages, tables or diagrams may be reproduced for such purposes provided attribution to the owner is acknowledged. Major extracts of the entire document may not be reproduced by any process. The IA CRC gratefully acknowledges funding support from the Australian Government through its Caring for our Country program for the IA CRC rabbit research and the publication of this document. This document should be cited as: Cox TE, Strive T, Mutze G, West P and Saunders G (2013). Benefits of Rabbit Biocontrol in Australia. PestSmart Toolkit publication, Invasive Animals Cooperative Research Centre, Canberra, Australia. Front cover photo: G. Chapman, CSIRO. Available online at: www.feral.org.au/PestSmart ii Invasive Animals CRC
Contents
Executive Summary ..........................................1
Introduction....................................................8
Project terms of reference ................................... 8
Overview of rabbit distribution, abundance and impacts
..................................................................... 8
Benefits of current rabbit biocontrol technology ... 14
Environmental benefits ......................................15
Social benefits .................................................15
Economic benefits .............................................15
General benefits of future rabbit biocontrol
technology ................................................... 16
Current rabbit biocontrol initiatives ................... 18
Image: Rabbit plague on Wardang Island in 1963
RHD-Boost .......................................................18
(Source: National Archives of Australia)
Strain selection ............................................18
Overcoming immunity to existing RHDV strains .....19
Interfering endemic non-pathogenic caliciviruses
RCV-A1 .......................................................20
Overcoming genetic resistance in wild rabbits ......21
RHD-Boost Release and Performance Measurement 21 Reducing risks associated with future RHDV strain
Measuring Impact ..........................................21 releases ....................................................... 27
Integrating conventional control .......................21 RHD-Boost Release and Performance Measurement . 27
Impact of RHD-Boost ......................................22 Maximising RHD Boost impact by optimising release of
new RHDV strains when RCV-A1 prevalence is low .. 27
Benefits of RHD-Boost ....................................22
Building and maintaining diagnostic capability to track
RHD Resistance Model ........................................22 biocontrol performance .................................. 27
RHD Accelerator ...............................................23 Conclusions and recommendations ..................... 28
Objective and rationale ..................................23 References ................................................... 29
Replicating natural selection ...........................23 Appendix 1: Background information on rabbit
Impact of RHD Accelerator ...............................24 biocontrol agents ........................................... 32
Benefits of RHD Accelerator .............................24 Myxomatosis ................................................ 32
Bioprospecting .................................................24 Rabbit fleas ................................................. 32
Objective and rationale ..................................24 Rabbit haemorrhagic disease ............................ 32
Impact of Bioprospecting ................................25 Virally-vectored immunocontraception ............... 33
Benefits of Bioprospecting ...............................25 Appendix 2: Diagrammatic representation of benefits
Technology opportunity ......................................25
from RHD Boost, RHD Accelerator, Bioprospecting
and DSS/Rabbit Facilitator ................................ 34
Environmental and economic benefits of new biocontrol
technologies ....................................................26
Benefits of Rabbit Biocontrol in Australia iii
iv Invasive Animals CRC
Executive Summary Myxomatosis – MV, a highly infectious poxvirus disease
which causes severe generalised disease in European
rabbits. It was introduced in to Australia in 1950 as a
EUROPEAN RABBITS (Oryctolagus cuniculus) are a biocontrol agent for rabbits.
severe continental-scale threat to Australia’s globally
important biodiversity and agriculture. The extreme Rabbit Haemorrhagic Disease – RHD, a highly
sensitivity of many native plant species to rabbit infectious disease specific to European rabbits caused
damage – as few as one rabbit per hectare can impede by the calicivirus Rabbit Haemorrhagic Disease Virus
natural regeneration - has resulted in 75 nationally (RHDV). It escaped quarantine in Australia in 1995
threatened plant species and five threatened and was subsequently released as a biocontrol agent
ecological communities being at risk from rabbit from 1996 to the present day.
impacts. Rabbits are also Australian agriculture’s most
costly vertebrate pest animal causing more than $200 continued persistence of many native threatened
million in production losses each year. species, large scale carbon biosequestration, and
improved landscape and ecosystem resilience. The
Without rabbit biocontrol agents, however, these cumulative economic benefits for agriculture alone
impacts would be much worse: the combination of from MV and RHDV over 60 years are estimated at $70
myxoma virus (MV) and rabbit haemorrhagic disease Billion, or an average of $1.17 billion per year.
virus (RHDV) still limits rabbit numbers to about 15% of
their potential numbers, and without them the cost for To maintain these benefits and keep rabbit abundance
agriculture alone would be in excess of $2 billion a below or near the rabbit impact threshold, strategic
year. The cumulative environmental benefits of the rabbit biocontrol research is critical to strengthen the
release of MV in 1950 and RHDV in 1995 includes effectiveness of existing rabbit biocontrol agents, and
landscape scale native vegetation regeneration, identify and evaluate new potential biocontrol agents.
increased abundance of native plants and animals, This is being partially progressed through three key
Benefits of Rabbit Biocontrol in Australia 1
Rabbit Calicivirus Australia-1 – RCV-A1, a pre-existing
initiatives in the Invasive Animals CRC rabbit research benign calicivirus which causes no disease and offers
program (2012-17): rabbit’s partial protection to infection by the
introduced pathogenic calicivirus RHDV. RCV-A1 is
1. RHD Boost – selection and evaluation of naturally mainly found in the cool-wet regions of Australia with
occurring overseas RHDV strains shown to have > 400mm annual rainfall.
improved effectiveness over the one endemic
RHDV strain introduced in 1995,
2. RHD Accelerator – proof of concept for a platform In the medium term, there is an urgent need to
technology to continuously develop new RHDV develop a coordinated program of rabbit disease
strains through accelerated natural selection, and
monitoring and surveillance across the various climatic
3. Bioprospecting - identify and assess feasibility of
new potential biocontrol agents. regions of the Australian continent to understand
prevalence, seasonal fluctuations and interactions of
This research program has been designed to deliver rabbit pathogens such as RHDV, MV and the interfering
strengthened RHDV strains from about 2015 to 2030, benign calicivirus RCV-A1. Understanding these
augmented by any new evaluated biocontrol agents mechanisms is critical to identifying the factors that
from about 2030. The benefits of these three define the success of potential biocontrol/biocide
technologies are summarised below. The predicted releases. An integral component of this is to ensure
impact of these technologies on rabbit abundance is availability of state-of-the-art differential diagnostic
outlined in four scenarios in the graph above: tools and epidemiological modelling. Capabilities in
Scenario 1: Business as usual shows an on-going these areas need to be increased and maintained.
increase in rabbit abundance that erodes all the gains In the longer term it is essential to ensure that applied
from RHDV and leads to major increases in economic
biocontrol research can continue. If successful in their
and environmental impacts over time.
proof of concept stages, the RHD-Accelerator and the
Scenario 2: Release of new RHD-Boost RHDV strains
regains most of the benefits of the original RHDV Bioprospecting projects will need ongoing support to
release, followed by a progressive increase in rabbit be further developed to the product stage. In addition,
abundance scientific research needs to continue to increase our
Scenario 3: Release of new RHD-Boost RHDV strains understanding of the long term effects of evolution and
followed by new RHD-Accelerator RHDV strains which genetic resistance development, as well as cumulative
regain the benefits of the RHD-Boost release. or neutralising effects that may arise from co-occurring
Subsequent releases of RHD-Accelerator strains every pathogens. The latter is of particular importance as
5-10 years see a repeated relative knockdown in rabbit more and more pathogens and viral variants are added
numbers.
to the environment. This need is reinforced by the
Scenario 4: Releases of new RHD-Boost RHDV strains
National Biosecurity Research and Development
followed by new RHD-Accelerator RHDV strains and a
Capability Audit commissioned by the National
new biocontrol agent have the greatest impact on
Biosecurity Committee, which suggested that Australia
rabbit numbers.
should invest more heavily in the long term funding of
While this balanced research portfolio aims to deliver a biological control programs, including monitoring of
rabbit biocontrol technology pipeline in the short to field effectiveness.
medium term, there remain important gaps that create
The imperative for strategic rabbit biocontrol research
significant risk to the effectiveness of these research
is based on four facts: rabbits are becoming
outputs and the seamless continuation of effective
increasingly resistant to existing rabbit biocontrol
rabbit biocontrol. In the short term, knowledge gaps of
agents, in good seasons rabbit populations can increase
the seasonal patterns of the endemic benign rabbit
7–10 fold, rural populations and labour continues to
calicivirus (RCV-A1) remain, which is critical to ensure
decrease, and the cost of rural labour continues to
impacts from the release of RHD-Boost strains are
increase. Proactive investment in strategic rabbit
maximised by knowing when the impeding RCV-A1 virus
biocontrol research will ensure rabbit abundance can
is least prevalent in a landscape. Additional resources
be kept near the rabbit impact threshold which is less
also need to be secured to enable the performance and
than one rabbit per hectare.
benefits of RHD Boost strains to be quantitatively
measured in various landscapes.
2 Invasive Animals CRC
Improved RHDV Objective Benefits
effectiveness
RHD Boost Identify, seek approval, Net Present Value: $1.4 Billion over 15 years made up of $840
rollout release and selectively million of agricultural benefits and $560 million in carbon
measure the performance sequestration benefits.
of new naturally
Benefit Cost Ratio: 563 to 1
occurring overseas RHDV
strains found to be Internal Rate of Return: 217%
superior to the one
Biodiversity benefits: increased regeneration of native vegetation,
existing RHDV strain in
and in longer term increase in abundance of many threatened
Australia
species
Carbon benefits: increase in standing biomass via regeneration
Soil benefits: reduced soil erosion and land degradation
Assumes selection and release about 2015
RHD Develop a platform Net Present Value: $79 million over 15 yrs and $300 million over 30
Accelerator technology for on-going years (60% are agricultural benefits, 40% carbon sequestration
platform laboratory based benefits)
technology selection of superior
Benefit cost Ratio: 48 to 1 over 15 yrs
RHDV strains
Internal Rate of Return: 38%
Biodiversity benefits: increased regeneration of native vegetation,
and in longer term increase in abundance of many threatened
species
Carbon benefits: increase in standing biomass via regeneration
Soil benefits: reduced soil erosion and land degradation
Assumes new RHDV strains able to sustain the benefits delivered
by RHD Boost
Comprehensive Understanding the nature Improves effectiveness of RHD Boost and RHD Accelerator
RHD resistance and geographical technologies
model distribution of rabbit
genetic resistance, to
develop a framework for
the optimisation of
additional virus releases
New biocontrol
agents assessed
Assessment and Assess the feasibility of Net Present Value: $28 million over 30 years
prospecting for new potential rabbit
Benefit Cost Ratio: 115 to 1
potential new biocontrol agents and
biocontrol establish an international Internal Rate of Return: 21.5%
agents alert network
Assumes additional research of new biocontrol agent to enable
release from 2030.
Benefits of Rabbit Biocontrol in Australia 3
2000
2012
Native grass regeneration post RHDV arrival and rabbit control on Thackaringa Station,
Broken Hill. The regeneration occurred during a period of drought (Images: David Lord).
4 Invasive Animals CRCExclusion fencing showing the change in vegetation structure due to rabbits on Macquarie
Island (top) and in Coorong, SA (bottom) (Images: Brian Cooke).
Benefits of Rabbit Biocontrol in Australia 5Native plants wich are especially susceptible to browsing by rabbits, even at low rabbit
densities. Top left: Myporum insulare, Boobiala, Coorong SA; Top right: Acacia ligulata,
Sandhill wattle, Hattah-Kulkyne National Park, VIC; Bottom left: rabbit damage to tree
guard and sheoak; Bottom right and left: rabbit damage to Allocasuarina and Callitris sp.,
Hattah-Kulkyne National Park, VIC. (Images: Brian Cooke).
6 Invasive Animals CRCThis Melaleuca lancelota grew during a period of rabbit relief after the spread of MV. Note
the lack of understory and the browsing at rabbit height. Increases in rabbit numbers are
winding back any gains made by the releases of MV and RHDV (Image: Brian Cooke).
Benefits of Rabbit Biocontrol in Australia 7Introduction
The 2009-10 Caring for our Country business plan
included a priority outcome to reduce rabbit impacts
with the following key target:
to suppress rabbit populations over the
next three years to densities that are low
enough to allow regeneration and recovery
of critically endangered and endangered
species and communities in identified
priority areas.
To achieve this outcome, the investment portfolio
included $1.5 million of the $2.7 million required for
the RHD-Boost project. The RHD-Boost project aimed
to identify and evaluate new naturally occurring
overseas strains of rabbit haemorrhagic disease virus
(RHDV) - the causative agent of rabbit haemorrhagic benign and lethal varieties of RHD and myxomatosis
disease (RHD) - which were suitable for release into (MV).
Australian rabbit populations and which sought to
overcome the developing acquired immunity and
Overview of rabbit distribution, abundance
genetic resistance to the current Czech 351 RHDV and impacts
strain, and the impact of the benign calicivirus Rabbit Wild rabbits were successfully introduced into Australia
Calicivirus Australia 1 (RCV-A1) which offers partial in 1859 and within 70 years had spread to inhabit 70%
protection to infection by pathogenic RHDV. of Australia’s landmass (5.3 million km 2) (Figures 1 and
This report reviews previous biological control efforts 2). They are widespread throughout most locations
for rabbits in Australia, the likely economic and where they are found (NLWRA and IACRC 2008).
environmental benefits of the release of a new strain/s Rabbits feeding habits include removing vegetation to
of RHDV (RHD-Boost), and the benefits of investing in ground level and digging for roots which can result in
future areas of rabbit biocontrol research such as the significant soil destabilisation and erosion, leading to
development of a performance management the desertification of heavily impacted areas. Such
framework (RHD-Boost Release and Performance damage is added to through the excavation of warren
Measurement), the ongoing selection of improved RHDV systems – often extensive and in ecologically sensitive
strains (RHD-Accelerator), the continued search for areas. Rabbits are also prolific breeders. In good
new biocontrol agents (Bioprospecting) and It also seasons populations can increase 7–10 fold. Rabbits
describes current knowledge about the distribution of impact 75 Commonwealth Environment Protection and
rabbits, and benign rabbit calicivirus (RCV-A1). Biodiversity Conservation Act 1999 listed threatened
plant species and five threatened ecological
Project terms of reference communities (Figure 3) and are the most costly pest
This project’s statement of work required Invasive animal to agricultural production: the annual cost
Animals Ltd to undertake a desk top evaluation of a exceeding $200 million (Gong et al. 2009).
successful release of an additional effective rabbit
biocontrol agent. The evaluation was to include the
likely benefits to production and the environment
based on a literature review, historical information
about the 1990’s release of RHD, and current
knowledge about the distribution of rabbits and the
8 Invasive Animals CRCFigure 1: Reported abundance of European rabbits (Oryctolagus cuniculus) across Australia (Source data: Invasive Animals CRC, RabbitScan, and NLWRA and IACRC 2008). Benefits of Rabbit Biocontrol in Australia 9
Figure 2: Rate of spread of wild rabbits since their introduction to Geelong, Victoria in 1859 to their current
known distribution (Source data: Invasive Animals CRC, Stoddard and Parer 1988).
10 Invasive Animals CRCFigure 3: Locations of critically endangered and endangered communities and species that may be
adversely affected by rabbits (Commonwealth of Australia 2008).
Benefits of Rabbit Biocontrol in Australia 11Brief history of rabbit invasion and rabbit Recent research conducted by the Invasive Animals
biocontrol pipeline Cooperative Research Centre (IA CRC) has shown that
(adapted from Department of Environment and Australian native vegetation is very sensitive to rabbit
Primary Industries 2011) damage. A specific example is Mulga (Acacia aneura)
which occurs across vast areas of central Australia.
Recruitment of seedlings for this species is greatly
1859 24 wild rabbits released at Barwon Park near
Geelong, Vic, for hunting become impacted upon by rabbit densities as low as 1
established. Invasion across Australia at about rabbit/km2 (Mutze et al. 2008). This greatly impedes
130 km per year. Some farms abandoned as natural regeneration. Similar stories can be told for a
early as 1881 variety of palatable trees and shrubs across much of
the distribution of the rabbit (Sandell 2002, Murdoch
1926 Estimated 10 billion rabbits in Australia with
70% of continent invaded 2005, DEWHA 2008, Bird et al. 2012, Cooke 2012).
1950 World’s first vertebrate pest biocontrol - While the direct impact of rabbits on vegetation is
myxoma virus (MV) - released and kills 99.8% obvious, their impact on native animals via competition
of infected rabbits is less so. For example, both kangaroo (Macropus
rufus, M. fuliginosus & M. robustus) and wombat
1969 Rabbit flea species (Spilopsyllus cuniculi)
approved for release to act as an improved (Vombatus ursinus) numbers increased following native
vector to spread MV in areas low in vegetation regeneration after the release of RHDV,
mosquitoes suggesting that high populations of rabbits may restrict
these species (Mutze et al. 2008; Bird et al. 2012).
1990 Rabbit population about 600 million
Rabbit impact on native pastures affects a variety of
1993 Spanish rabbit flea (Xenophsylla cunicularis)
other species, including endangered or critically
adapted for arid conditions approved for
release and improves transmission of MV endangered species such as the plains-wanderer
(Pedionomus torquatus) (Baker-Gabb 2002) and the
1995 Rabbit haemorrhagic disease virus (RHDV) golden sun moth (Synemon plana) (Clarke and O'Dwyer
introduced and kills up to 98% of rabbits in
2000). Competition and land degradation by rabbits is
arid areas
listed as a Key Threatening Process under the
2000s Rabbits begin to develop resistance to RHDV Commonwealth Environmental Protection and
infection. Increasing resistance and Biodiversity Conservation Act 1999.
increasing food availability as drought breaks
results in observed increasing rabbit numbers The general trend in rabbit abundance across Australia
is upward. Figure 4 summarises information available
2009 Benign endemic rabbit calicivirus (RCV-A1)
on changes in rabbit numbers in the arid pastoral area
that confers partial protection to rabbits
discovered and characterised of north-eastern South Australia associated with the
introduction of MV, then RHDV in an area where other
2009+ New naturally occurring overseas RHDV control measures, such as poisoning and warren ripping
strains that have observed increased lethality were not often applied. In that region, where
to rabbits are imported from Europe and Asia
mosquitoes were scarce, the release of European
and evaluated as part RHD Boost project co-
funded through Caring for our Country rabbit fleas (Spilipsyllus cuniculus) in 1969 enhanced
Program the spread of MV. Importantly, it shows a marked
increase in rabbit abundance since the early 2000s.
2012 Successful Invasive Animals CRC extension
includes strategic rabbit biocontrol research
program to boost effectiveness of RHDV,
assess feasibility of new potential rabbit
biocontrol candidates, and increased
capabilities to promote regional integrated
rabbit control
12 Invasive Animals CRCFigure 4: Diagram showing how rabbit abundance in semi-arid South Australia has varied through time in response to the release of biological control agents and the estimated Australia-wide economic losses to rabbits (black triangles). Scale for losses shown on right-hand side of figure (Cooke et al. 2013). Benefits of Rabbit Biocontrol in Australia 13
Benefits of current rabbit biocontrol technology
By far the most successful method of reducing rabbit The benefits of rabbit biocontrol are not uniform across
impacts in Australia has been the use of biological Australia. This is particularly the case for RHDV, which
control agents. At times these have reduced rabbit was generally more effective in drier, lower rainfall
numbers in some areas by as much as 99 per cent. areas (Figure 5). Monitoring of rabbit abundance
Their impact has allowed land managers to apply showed an average decrease by two-thirds (67.3%) in
complementary conventional control techniques (e.g. low rainfall areas, and only a quarter (27.5%) in high
warren ripping, baiting and fumigation) in a more cost rainfall areas.
efficient and effective manner. The continued
The application of biocontrol agents has a number of
suppression of recovering and/or reinvading
benefits, particularly when applied to large-scale pest
populations with biocontrol agents post conventional
problems such as that presented by the European
control has also been of benefit, greatly improving the
rabbit in Australia. The benefits of using biocontrol
value of applied conventional control. Australia has
can be counted in environmental, social and economic
introduced four biocontrol agents for rabbits over the
terms and, in the case of biocontrol for rabbits, is the
last 60 years: two viral diseases and two insect vectors
most cost effective way of managing a pest species.
to aid their transmission, and undertaken extensive
research into another: virally-vectored immuno-
contraception (Hardy et al 2006, Saunders et al 2010).
Background information is provided in Appendix 1.
Figure 5: The decline in rabbit populations by rainfall zone after the arrival of RHDV.
14 Invasive Animals CRCEnvironmental benefits
The environmental benefits of RHDV were high, One negative social impact of effective rabbit
especially in semi-arid areas where significant biocontrol is that rabbits have lost some of their public
regeneration of native vegetation occurred, despite profile as a major pest species. An increasing
below average rainfall (Sandell 2002, Murdoch 2005, percentage of both the urban and rural population do
Mutze et al. 2008, Bird et al. 2012, Figure 5). After not remember pre-RHDV or pre-MV rabbit numbers and
the introduction of RHDV, studies have shown that damage. This has reduced the general awareness of
populations of native animals also increased. rabbits as a problem, which in turn often results in
diminished public support for ongoing rabbit research
Populations of Spinifex hopping mice (Notomys alexis) and control.
and plains mice (Pseudomys australis) (Read 2003),
common wombats (Vombatus ursinus), red kangaroos Economic benefits
(Macropus rufus) and western grey kangaroos (M.
fuliginosus) (Mutze et al. 2008) all showed signs of Recent estimates value the cumulative benefit of MV
recovery post RHDV introduction. Fox and feral cat and RHDV to Australia’s pastoral industries at
numbers decreased in the Flinders Ranges National approximately AU$70 billion over the last 60 years
Park after the rabbit population was reduced by 85% (Cooke et al. 2013). In the period immediately after
(Holden and Mutze 2002). The most notable impact was its release, MV resulted in AU$68 million in increased
on feral cats with their body condition falling by 17%. production (AU$48 million in increased wool clips and
AU$20 million in increased sheep and lamb meat)
Social benefits (Sobey 1981). The economic savings generated by
RHDV are estimated to be in excess of AU$350 million
There has been very little systematic research into the annually, indicating that in the 17 years since its
social impacts of rabbits or any other vertebrate pests release RHDV has generated benefits of almost AU$6
in Australia (Fitzgerald and Wilkinson 2009). It is likely billion to the rural industries alone (Cooke et al. 2013).
that the effects of pest animals, for the most part, are Considering that government and industry investment
economic and environmental, but there are flow-on for the introduction of RHDV was in the order of AU$12
social impacts. A collection of personal stories (Quealy million (Cooke et al. 2013) this return on investment is
2011) recounts that prior to the introduction of MV unmatched by any other investments in rabbit control
many farmers and their families were forced to walk research, or perhaps any other area of government
away from their properties because of the rabbit. investment, in the last 50 years.
Many talk of the psychological distress at having to
make a new life away from the farm. Similarly, When MV was first released it provided an estimated
competing interests lead to conflict between those $1.4 billion p.a. benefit (2011 A$) (Cooke et al. 2013).
prospering from high rabbit numbers e.g. commercial MV and RHDV combined reduce rabbit numbers by 85%
harvesters, and those suffering because of the rabbit. compared to their potential numbers, a benefit that
would be lost if there was no biocontrol. If the initial
A case study of the social impacts of rabbits in the myxo knockdown is used as a baseline, the current
Hunter Valley region of NSW in 2009 highlighted that benefit of biocontrol is 85% of $1.4 billion or some
residents in this area were more concerned with the $1.19 billion p.a. This equates with the average
impact of rabbits on mine rehabilitation sites, damage estimated annual benefit of $1.17 billion derived from
to grape vines and the risk of injury to horses due the the calculated $70 Billion benefit over 60 years from
presence of warrens (Fitzgerald and Wilkinson 2009). MV and RHDV (Cooke et al. 2013). In comparison,
While this region is not necessarily representative of without rabbit biocontrol, the estimated national
the attitudes of the whole of the area of Australia impact of some 10 billion rabbits caused livestock
where rabbits occur, it does highlight the shift in production losses of $2 billion/yr (Department of
attitude, by some, from a concern about the impacts of Environment and Primary Industries 2011, Cooke et al.
rabbits on making a living, to a concern about the 2013).
impacts of rabbits on their living amenity.
Benefits of Rabbit Biocontrol in Australia 15General benefits of future rabbit biocontrol
technology
Rabbit control is costly, especially in pastoral areas, of rabbit control as one of its objectives. The conduct
and many pastoralists believe that investment in of research to maximise the effectiveness of existing
conventional controls such as rabbit warren ripping is biocontrols, and the investigation of new biocontrols, is
not feasible (e.g. in sand hill country) and gains in a high priority, long term action under the TAP.
production are unlikely to meet costs. There is
While investment risk in the Bioprospecting model
therefore a continuing demand for the persistent use of
depends on the chance of finding another pathogen or
biological control agents as the only plausible solution
agent, Australia is well placed in that rabbits are an
to current residual rabbit problems in arid areas.
introduced species, unrelated to any other domestic or
Furthermore, biological control agents are usually the
native species, and in that context the risk of harming
only means of limiting rabbit damage in conservation
non-target species by a rabbit pathogen are reduced.
areas because of the high cost and the potential
In terms of RHD-Accelerator, the development of a
damaging impact of conventional control.
platform technology to sustainably address the rabbit
Biological control research is high risk in that potential problem can be expected to greatly enhance
new pathogens would need to be discovered first and profitability and ecological sustainability in the long
then imported into Australia under strict regulatory term. The current RHD-boost project if successful will
requirements. However the benefits can be extremely provide a net present value of over $1.4 billion over a
high as demonstrated by the economic returns. The 15 year period (Agtrans Research 2009). This value is
principal benefits of continuous investment into likely to be an underestimation as the benefits to
biocontrol research are (Agtrans Research 2009): biodiversity were not valued.
Increased pasture biomass for animal production; The impact of biocontrol on rabbit populations in
Decreased effort and cost associated with Australia has been significant. Continued investment in
traditional rabbit control measures; biocontrol and the roll-out of variations of existing
Increased ground cover leading to decreased soil agents or the release of new agents is expected to
erosion; capitalise on previous gains made by MV and RHDV
Improved native vegetation and associated (Figure 6). If no further investment in biocontrol is
habitats; made, then rabbit numbers will continue to increase
Increased carbon sequestration, and and all gains from RHDV will be eroded. The release of
Improved biodiversity.
additional strain of RHDV are expected to reduce rabbit
The introduction of new and/or additional biocontrol numbers close to where they were following the
agents to control vertebrate pests is the most cost original RHDV release; however rabbit numbers will
effective way of conserving biodiversity when analysed eventually begin to increase again. Investment in the
against all other mechanisms (Morton et al. 2002, RHD-Accelerator project will see the release of strains
Possingham et al. 2002). New or additional agents that will regain the benefits seen by the release of
would supplement existing agents (MV, rabbit fleas and RHD-Boost. The impact of the release of a new
RHDV) and avoid serious resurgence of rabbits in a biocontrol agent in conjunction with these other
timely way. The Threat Abatement Plan for efforts will ensure maximum impact on rabbit numbers.
Competition and Land Degradation by Rabbits (TAP)
Continued investment in biocontrol agents will have
(Department of the Environment, Water, Heritage and
benefits to the environment through increased standing
the Arts (DEWHA) 2008) lists the improvement of
biomass and therefore an increase in carbon
efficacy, target specificity, integration and humanness
sequestration (Fitzgerald and Wilkinson 2009). While
16 Invasive Animals CRCthere is currently no specific published research on increase in biomass would have on the wildlife ecology
assessing the carbon sequestration benefits of rabbit in these areas is not quantified.
control, estimations are available. A 70% reduction in
Without continued investment in rabbit biocontrol, it is
rabbit numbers could see a benefit of up to $34 million
expected that the subsequent increase in rabbit
in carbon sequestration based on the government
numbers will result in an increase in the biodiversity
carbon price of $20 per tonne (Table 1). This could
impacts of rabbits, along with a reduction in carbon
increase to $45 million if an 85% reduction was
sequestration as the regeneration of woody perennials
achieved (Agtrans Research 2009). The impact this
declines (Fitzgerald and Wilkinson 2009).
Figure 6: General trends in rabbit numbers since the release of myxomatosis in (1950) and projected
benefits of future releases of biocontrol agents into the Australian rabbit population. The abundance
baseline was arbitrarily set at an index level of 100 prior to myxomatosis. Pre-RHD figures are based on
spotlight counts and established relationships between rainfall and rabbit abundance, and an average 90%
reduction due to the initial impact of myxomatosis.
Table 1: Assumed impacts of a reduction in rabbit numbers on carbon sequestration (Agtrans Research 2009).
Assumption of tonne/ha saved Area of Valued CO2 equivalent
% Rabbit removal
with rabbit reduction sequestration at $20 per tonne
85 0.14 1.5 million km2 $42 million
70 0.115 1.5 million km2 $34.5 million
Benefits of Rabbit Biocontrol in Australia 17Current rabbit biocontrol initiatives
Rabbits are a key species of interest of the new
RHD-Boost
Invasive Animals CRC (2012–17). The IA CRC strategic
rabbit biocontrol technology pipeline is focussed on The RHD-Boost project was developed to address
two objectives: 1. Increasing the effectiveness of increasing evidence that rabbit numbers are building
RHDV, and 2. Identifying feasible new biocontrol agents up again after the 15 year long respite provided by the
that warrant further investment. initial release of RHDV. The follow on RHD-Boost
Release and Performance Measurement project builds
The three rabbit biocontrol technology projects
on the work undertaken in the RHD-Boost project and
specifically aimed at improving the biological control
is designed to undertake a performance management
of rabbits in Australia are:
evaluation of how differing strains of RHDV interact in
RHD Boost and RHD Boost Release and the environment.
Performance Measurement
Strain selection
RHD Accelerator
RHD Boost aims to identify new RHDV strains with high
Bioprospecting for a new potential rabbit
lethality to rabbits immune due to the endemic RCV-
biocontrol agent.
A1 and rabbits that are genetically resistant to
The impact of the IA CRCs rabbit portfolio will increase infection with Czech 351 derived RHDV strains.
over time and vary across climatic regions (Table 2).
The objective, prospective benefits and technology To select the most appropriate strain for release in
opportunities for the three biocontrol technologies is Australia, a number of overseas strains of RHDV were
discussed below and a diagrammatic representation of evaluated. The overseas strains had to show evidence
the benefits of each of the projects can be found in of high mortality in the field and the ability to
Appendix 2. outcompete existing field strains and the benign RCV-
A1. More than 10 of these candidate strains, including
antigenic varieties (RHDVa), were imported into
Australia for evaluation under quarantine conditions.
Table 2: Estimates of changing impacts in future by climatic zones with the IA CRC investment (Agtrans Research
2011).
High rainfall Wheat Sheep Zone Pastoral Zone
Reduction in Rabbit Impact 50% in 2014/15 compared 50% in 2014/15 70% in 2014/15 compared
to impacts assumed for compared to impacts to impacts assumed for
2013/14 in the assumed for 2013/14 in 2013/14 in the
counterfactual scenario the counterfactual counterfactual scenario
scenario
Impact level at which 50% of 2013/14 impact 50% of 2013/14 impact 70% of 2013/14 impact
reduction stabilises level held for eight years level held for eight level held for eight years
and then impacts years and then impacts and then impacts increase
increase again at 5% per increase again at 5% per again at 10% per annum
annum thereafter to a annum thereafter to a thereafter to a maximum of
maximum of 150% of maximum of 150% of 150% of 2008/09 impact
2008/09 impact levels 2008/09 impact levels levels
18 Invasive Animals CRCThese strains were genetically compared to the Czech inclusion of two new promising strains that were
351 strain to ensure that the most successful and most identified late 2012) and it is expected that
genetically distinct strain/s would be selected for recommendations for the release of additional strains
further testing. Five strains were selected for further will be made based on the results of this study. As
testing, including a prototype strain, several antigenic different properties of a putative new strain may be
variants and a highly virulent recent Australian field required to overcome each of the three problems listed
isolate. above, it is feasible that different strains may be
recommended to combat the different issues
The project is premised on the following facts:
underlying RHDV-mediated biocontrol.
Australia has only one RHDV strain (Czech 351 or
CZ351), Overcoming immunity to existing RHDV strains
In some areas Australian rabbits are beginning to A rabbit that survives infection with RHDV will be
develop genetic resistance to the original Czech immune to lethal RHD for the rest of its life. Re-
strain infection can occur, but will only result in a boost in
Australia’s one RHD strain has limited immunity. Virtually every rabbit population on the
effectiveness in cooler, wetter environments, that Australian continent has been exposed to RHDV at some
coincide with prime agricultural regions and many stage since its release, and in most populations natural
threatened ecological communities and species, outbreaks occur regularly, albeit with varying
due to presence of RCV-A1 frequency. Rabbit kittens generally do not die from
RHDV until they are 3–4 weeks old; thereafter they
In Europe, a greater variety of RHDV strains is
circulating. European wild rabbit numbers have become gradually more susceptible to infection and
been suppressed for much longer than in Australia less likely to survive viral challenge until 12 weeks of
despite attempts to aid their recovery, and similar age, and if first infected beyond that age most rabbits
influences on RHD impact such as genetic will die (Cooke 2002; Robinson et al. 2002). Young
resistance to infection and the presence of non- rabbits that become infected but do not die will
pathogenic viruses. develop antibodies to RHDV that will make them
The European experience, in particular, shows that immune for the rest of their life, and these rabbits are
additional variants of RHDV and new sub-strains like likely to be recruited into the immune breeding
RHDVa are likely to compete better against the pre- population. Maternal antibodies from immune female
existing RCV-A1 recently isolated in Australia. RCV-A1 rabbits are passed on to their offspring and may
is almost certainly the cause of limited effectiveness of prevent infection. These younger rabbits in turn can
Czech 351 in cooler wetter parts of Australia. In receive their first RHDV infection at a later age, closer
contrast, in Europe new variants of RHDV are to when they become susceptible to lethal infection
continuing to suppress wild rabbit populations in (Robinson et al. 2002). In some situations, maternal
wetter, cooler regions, despite the presence of benign antibodies my not prevent infection but may slow the
viruses similar to RCV-A1. In addition, the resistance to course of disease in the infected individuals and reduce
infection due to altered carbohydrate structures on the mortality rates (Cooke 2002).
mucosal surfaces of some European rabbit populations Depending on regional rainfall patterns, most rabbit
can be overcome by different virus variants that bind kittens are born in late winter/spring. Consequently,
slightly different carbohydrate receptor structures RHD epizootics are most effective in the autumn/early
(Nystrom et al. 2011) winter period when susceptible sub-adult rabbits are
The selected strains are currently being evaluated for challenged, before the breeding season, when young
their competitive advantage, their ability to overcome rabbits are present (Cooke 2003, Kerr and Strive 2012).
both genetic resistance and acquired immunity and However, spring is the usual time of RHD outbreaks in
their effectiveness against animals previously infected many populations across the country, as this is the time
with the benign virus RCV-A1. The results of these when young rabbits reach the susceptible age and
trials should be reported by December 2013 (after the enough individuals are present to carry an epidemic. At
Benefits of Rabbit Biocontrol in Australia 19the same time there are still enough young rabbits that rainfall areas than it did the arid, semi-arid areas of
will survive the outbreak with resulting immunity. In Australia (Mutze et al. 1998, Saunders et al. 1999,
addition, areas with more homogenous rainfall patterns Henzell et al. 2002). This patchy efficacy of RHD has
allow low level rabbit breeding throughout the year been attributed to the partial cross-protection of RCV-
and thus constant availability of unsusceptible rabbits, A1, a benign calicivirus which prevents infection with
further diminishing the impact of RHD outbreaks in the pathogenic RHDV (Nagesha et al. 2000, Cooke et
these areas. al. 2002, Robinson et al. 2002). This virus was recently
identified and confirmed to provide partial and
The RHD-Boost project is addressing this problem by
transient protection to lethal RHDV infection (Strive et
investigating naturally occurring antigenic variants of
al. 2009, Strive et al. 2010, Strive et al. 2013). This
RHDV, also referred to as RHDVa. There is evidence
virus is most prevalent in the cool/temperate-wet
that RHDVa can partially overcome vaccination with
regions of Australia and probably arrived in Australia
the prototype virus (Schirrmeier et al. 1999), and there
with the first wild rabbits in 1859 (Jahnke et al. 2010.
is also evidence that RHDVa strains are replacing the
Recent work (Liu et al., in preparation) has shown that
prototype strain in wild rabbit populations in Europe.
the distribution of RCV-A1 is closely linked to those
Furthermore, a recent report from China describes a
cool/temperate-wet areas where RHDV has
further variant (‘RHDVb’) that can partially overcome
traditionally had limited or patchy impact, and that
immunity to RHDVa (Wang et al. 2012), indicating that
encompass both Australia’s high production areas and
antigenic differences can be advantageous in the field.
the areas where rabbits cause serious ecological
Interfering endemic non-pathogenic caliciviruses – damage (Figure 7).
RCV-A1
When RHDV was first released in Australia it noticeably
caused lower rabbit mortality in the temperate, high
Figure 7: Distribution of the
benign endemic calicivirus RCV-
A1 in Australia. Red dots
indicate current and historical
sites that have tested positive
for RCV-A1. (Commonwealth of
Australia 2008, RCV-A1 data
from Liu et al., in preparation).
20 Invasive Animals CRCOvercoming genetic resistance in wild rabbits MV may be of considerable benefit to rabbit
conservation efforts in Europe. Australia is in the
A recently published study links the initiation of RHD
fortunate position of having only one variant of RHDV,
resistance in Australia’s wild rabbits to low dose
unlike Europe, and as such, can evaluate the impact of
infection with the originally released strain. These
additional strains on rabbit populations.
genetically resistant populations were mainly located
in the more arid areas of Australia (Elsworth et al. Measuring impact
2012). The exact mechanisms for this resistance are
unknown at this stage. However, one of the genetically The release of any new strains will not have the same
resistant populations identified in the Hattah region of impact as the initial release of RHDV had on completely
Victoria (Nystrom et al. 2011) has been shown to have naïve populations in the 1990s, and the effects will be
a higher proportion of rabbits that lack the more subtle and difficult to measure. As such, the RHD-
carbohydrate structures on the mucosal surfaces that Boost Release and Performance Measurement project
are likely to facilitate the uptake of RHDV. Notably, will require a number of sites to be intensively
despite this reported genetic resistance to infection, monitored, both before and after the release of any
serological studies at this site reveal a very high new RHDV strain, to accurately assess its impact. Both
prevalence of RHDV antibodies in the population treatment and control sites will need to be established
(Tarnya Cox, unpublished). across a range of climate and habitat types. Specific
diagnostic tests will need to be implemented to
RHD-Boost Release and Performance Measurement determine which strain is present during an outbreak,
and multiple samples will need to be collected from
The RHD-Boost Release and Performance Measurement
multiple sites before the true impact of any new
project will address fundamental questions about the
strains can be known.
release of a new strain of RHDV into the Australian
rabbit population. What impacts do these new strains While the effects can be expected to be more subtle
have on rabbits? What do those impacts mean for the than the initial release of RHDV into a naïve
Australian environment? How will native wildlife population, the aim of the project is to slow down the
recover? Can these new strains provide a respite for recovery of rabbit populations by maintaining the
the recovery of threatened or endangered species? significant benefits that RHDV has provided over the
Will the new strain/s reduce rabbit numbers to a level last 15 years. In addition, introducing a new strain of
to allow native vegetation regeneration? What impact RHDV may also increase the genetic diversity of the
will this have on carbon sequestration? Answers to virus and therefore provide opportunity for the virus to
these questions are of vital importance if we are to more quickly adapt to any acquired immunity or
continue to use strains of RHDV as biocontrol agents genetic resistance developed by the rabbit. This
into the future. project will also provide a framework for investigation
and performance management of releases of any new
This research also has far reaching consequences.
biocontrol agents for rabbits and/or other vertebrate
Populations of rabbits declined greatly following the
pest species in Australia.
spread of RHDV across their original home range on the
Iberian Peninsula. The rabbit is listed as near Integrating conventional control
threatened in its natural range by the World
Conservation Union (IUCN) and vulnerable in Spain. The Improving our understanding of virus interactions in the
decline in populations of rabbits on the Iberian field will better inform current conventional control
Peninsula have impacted on populations of their highly practices. Improved understanding of the impact of
dependent predators the Iberian lynx (Lynx pardinus, additional virus strains on rabbit populations under a
critically endangered) (Ward 2004) and the Spanish variety of landscape and climatic conditions will lead
Imperial eagle (Aquila adalberti, vulnerable) to the improved application of conventional control
(Margalida et al. 2007). Research into the interaction techniques to maximise the impact of biocontrol
and impact of additional strains of RHDV on rabbits, as agents. The National Rabbit Facilitator position
well as the interaction of multiple RHDV variants and (established through the IA CRC and due to start in
Benefits of Rabbit Biocontrol in Australia 21mid-2013) will draw on the information obtained from previously released strain of RHDV, it is assumed that it
the RHD-Boost Release and Performance Measurement will then spread naturally throughout the rabbits
project to ensure best practice management is applied range, augmented by further intentional releases at
across the landscape. Conventional control needs to strategic sites. As such, usage of this output is assumed
be applied in conjunction with the use of biocontrol to be 100% provided it will occur over the rabbit's
agents for maximum impact. The National Rabbit entire range. Usage, however, should not be confused
Facilitator will encourage this combination of with effectiveness as this will vary between climatic
conventional control and biocontrol techniques, as well regions (Agtrans Research 2009). The release of new
as advice on the appropriate variant of RHDV for RHDV strains has the potential to suppress rabbit
release, based on information gathered during the populations over 5.33 million square kilometres (entire
RHD-Boost Roll-out. rabbit range) (West 2008).
Impact of RHD-Boost Risk factors for not achieving some of the outputs and
outcomes have been included in the estimates made of
The probability of impact of the RHD-Boost project the expected benefits. Results show that, for a
given usage is 80%. The expected impacts of the discount rate of 5%, the present value of the
usages of the outputs produced by the investment are: anticipated R&D investment of $2.6 million (2008/09
Observed spread of the released strains so that terms) will provide a large return on investment.
they are endemic throughout Australia within Investment criteria are a net present value of over $1.4
three years. billion over a fifteen year period and a net present
The virus is effective in killing rabbits in the field value of over $1.8 billion if a 30 year planning period is
and rabbit numbers decrease in most regions of assumed. For the fifteen year period, the industry
Australia over the first three year period. This benefits dominate at 60% of the total benefits, with
likely impact is supported by recent experience in the carbon sequestration benefits contributing 40%
France (Le Gall-Recule et al. 2011) based on the government carbon price of $20 per
Costs of rabbit control using traditional methods tonne. The benefit cost ratios are 563 to 1 and 708 to 1
fall. for each of the 15 and 30 year periods. The internal
rate of return is 217% for the 15 year period and similar
The new strains are effective in those areas where
for the 30 year period (Agtrans Research 2009).
the strain introduced in 1995 was ineffective and
antibodies produced from RCV-A1 are no longer The biodiversity benefits include the regeneration of
effective in protecting rabbits from RHDV. five endangered ecological communities and the
Individual commercial grazing animal productivity regeneration of the 75 listed critically endangered and
is observed to increase as a result of the release endangered plant species (excluding off-shore islands)
of the new strains. listed in the rabbit Threat Abatement Plan.
Greater shrub and tree natural establishment
(including some threatened ecological
RHD Resistance Model
communities) is observed due to the decline in Collection and genetic sequencing of RHDV recovered
rabbit numbers and there is an observed from rabbits around Australia has shown that since the
secondary biodiversity impact via reduced rabbit initial introduction and spread of the Czech351 strain
predators such as foxes and/or wild cats.
into Australia, the virus has undergone a process of
The increase in standing vegetation from improved gradual genetic changes. Three distinct genetic groups,
regeneration acts as a carbon sink. each containing a range of genetically distinct variants,
have evolved in separate but overlapping regions of the
Benefits of RHD-Boost country (Kovaliski et al. 2011). Three RHDV variants,
The RHD Boost output will initially be released in collected from outbreaks in different years at
strategic sites throughout the rabbits range using the IA Turretfield in South Australia, have been shown to
CRC’s freeze-dried RHDV bait technology. Like the cause different mortality rates in wild-type rabbits,
22 Invasive Animals CRCwith associated different times to death (Elsworth et strains that will hopefully extend RHDV-derived
al. in prep.). Of these, the most recent viruses were benefits for several more years, co-evolution of host
the most lethal and all were more lethal than the and virus is likely to again lead to genetic resistance
original Czech strain. Taken together with the evidence development. Similarly, widespread immunity will
of emerging genetic resistance to infection in develop once the new strains have become endemic in
Australian rabbit populations (Elsworth et al. 2012), rabbit populations. In contrast, the RHD Accelerator
this indicates that both gentic resistance in rabbits and project aims at developing a platform technology that
RHDV virulence are co-evolving in a complex, ongoing will allow the ongoing selection of tailored RHDV
manner. We need to understand how these processes strains able to better overcome immunity to existing
are interacting to aid selection of appropriate RHD field strains of RHDV and RCV-A1, by exploiting the
Boost variants for release. The RHD resistance project principles of natural selection.
will use results from laboratory challenge studies and
field epidemiology to develop a statistical model of Replicating natural selection
RHD resistance that can be used to project the likely RNA viruses such as RHDV have naturally very high
benefit of RHD Boost candidates with different mutation rates. During replication, virus genes are not
epidemiological characteristics. replicated exactly, producing a mixture of progeny
viruses that are all slightly different (Domingo et al.
RHD Accelerator 2001). Some of these viruses will have altered surface
structures that may not be neutralised by antibodies
Objective and rationale
specific to the original strain. These variants are
The RHDV accelerator strategy takes the RHDV Boost slowly selected for in natural infections, as RHDV often
project to the next level. While RHD-Boost can be kills the animals too quickly for these selection
expected to deliver one or several additional virus processes to occur. The Accelerator project aims at
Table 3: Summary of the economic, environmental and social benefits from the RHD Accelerator Investment
(Agtrans Research 2011).
Economic Environmental Social
Higher level of grazing Increased regeneration of native Continuance of a more humane
productivity translated into vegetation and habitats, and in method for limiting rabbit
additional farm profits in each the long term improved numbers and reduced
of the three rainfall zones biodiversity of fauna and flora externalities from poisoning
Reduced costs of rabbit Increase in standing biomass via control methods
control costs by governments regeneration leading to Stronger rural communities from
and landholders absorption of carbon dioxide. ‘drought proofing’ and enhancing
Reduced damage to crops Greater ability to capitalise on the continuing viability of some
summer rains as native grasses pastoral properties.
re-establish Improved landscape amenities
Improved biodiversity from
reduced numbers of feral cats
and foxes
A possible cost in the potential
increase in greenhouse gas
emissions if ruminant livestock
numbers increase
Reduced soil erosion and land
degradation
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