Appendix C3
Appendix C Biosecurity risk assessment – Cottony Urbicola Scale (Pulvinaria
urbicola) and Yellow Crazy Ant (Anoplolepis gracilipes)
Status
Cottony Urbicola Scale (Pulvinaria urbicola, CUS) is native to the West Indies and was first
described in Jamaica (Smith, Papacek et al. 2004). CUS has established throughout the
Indian and Pacific Oceans, northern continental Australia, Central and North America and
Israel (Smith, Papacek et al. 2004). CUS is established on Christmas Island and was first
detected in June 2011 (Neumann, Green et al. 2011). In Australia, it’s naturalised on
mainland Queensland and its islands, including in the Capricornia Cays, where is has had
catastrophic impacts (Greenslade 2008, Queensland State Government 2010, Biosecurity
Queensland 2012). CUS are not present on North Keeling Island (Pulu Keeling National
Park, PKNP).
Originating from West Africa (Slip and Comport 2008) or the West Indies (Neumann, Green
et al. 2011), yellow crazy ants (Anoplolepis gracilipes, YCA) are one of the most abundant
and damaging ant species in the world and have invaded most continents with tropical and
subtropical climates (Figure 1). YCAs have naturalised on the continents of Africa and Asia,
the Caribbean islands, and the islands of the Indian and Pacific Oceans (O’Dowd, Green et
al. 2003, Slip and Comport 2008). They are widespread in pan-tropical areas, where they
are considered environmental pests (Slip and Comport 2008).
Figure 1 Global distribution of Yellow Crazy Ants (Global Biodiversity Information
Facility n.d.)
The YCA is a national conservation priority and has been identified as a species that is likely
to threaten the biodiversity of Australia and its territories (Commonwealth of Australia 2006).
It is also listed as a ‘key threatening process’ on Christmas Island and in New South Wales
(Biosecurity Queensland 2012).
On Christmas Island, various species of scale insect and YCA benefit from a mutualistic
relationship (Abbott 2006). YCA were accidentally introduced to Christmas Island sometime
between 1915 and 1934 (Donisthorpe 1935). They were first detected at high densities in
1989 and reached widespread supercolony densities in the 1990’s (O’Dowd, Green et al.
2003, Abbott 2006). By 2001, YCAs had covered a quarter of the islands forests (O’Dowd,
Green et al. 2003). The interactions between scale insects and YCAs have disrupted the
islands trophic web causing an “invasional meltdown” (O’Dowd, Green et al. 2003, Abbott
2005, Abbott 2006).
YCAs occupy every island in CKIs (Slip and Comport 2008) and were first recorded on North
Keeling Island in 1941 (Gibson-Hill 1948, Gibson-Hill 1950). They are widespread although
sparse in the southern atoll (Slip and Comport 2008) and have not reached supercolony
densities on PKNP (Detto 2012). It’s likely that ongoing monitoring will be required to ensure
that CUS are not introduced to the park so that YCAs do not reach densities that will cause
environmental damage of the parks values.
Biology & ecology
The following knowledge of CUS was collected in their naturalised distribution where they
have caused environmental damage. It is particularly relevant in terms of assessing risk of
introduction to PKNP and its potential impact on island biodiversity. The biology and ecology
of CUS follows:

hatchlings (crawlers) have 3 pairs of legs, paired eye spots and antennae. Crawlers are
mobile and travel towards the light on shoots and tree tops

once in the air currents they can disperse by wind hundreds of metres to fresh hosts.
Long distance dispersal may occur between islands by birds (up to a few days survival
time)

males are winged and are short-lived mating before death

adult females produce ~8000 eggs held in a white ovisack ~8 millimetres (mm) length

live in terrestrial habitats and are host species generalists attacking dicots, monocots
and fern species

host species include: Pisonia grandis (pisonia), maiden hair fern, capsicum, tomato,
dahlia, dianthus, lantana and blackberry nightshade, guava, frangipani, taro, pineapple,
milk thistle, cobblers peg and cape gooseberry

feed by inserting a tube into the host plants sap and high densities on host leaves are up
to 100/leaf

lifecycle is two months producing 2-4 generations per annually (observed between 6–7
weeks in Christmas Island)

CUS excretes honeydew that is tended by ants

in most places where it occurs, CUS are attacked by natural enemies (both predators
and parasitoids) and is not generally regarded as a pest (Smith and Papacek 2001,
Smith, Papacek et al. 2004, United States Government 2005, Neumann, Green et al.
2011).
NB: Successful biological control of CUS has been undertaken on North East Herald Islet on
the Great Barrier Reef by several natural enemies (Smith, Papacek et al. 2004). Combined
predation from wasp parasitoids (Coccophagus ceroplastae, Euryischomyia flavithorax) and
a predatory ladybird (Cryptolaemus montrouzieri) provided the best control (Smith and
Papacek 2001, Smith, Papacek et al. 2004).
The mutualism between CUS and YCAs plays an important role in the success of both
invasive species (O’Dowd, Green et al. 2003). Their interactions cause a cascade of
detrimental ecological impacts. YCA biology and ecology is outlined below:

workers have uniform morphology: a long slender body, legs and neck, antennae in
segments to 1.5 times the head length, gaster has an acidopore, erect hairs and is
darker than head and thorax, head is oval with convex eyes and hairs

workers live for 76–84 days and the queen can live up to several years

interbreed whilst maintaining high heterozygosity. Offspring can be produced throughout
the year but generally 2–3 months prior to the monsoon season

when ‘budding’ can disperse up to 1100 m but rely on human dispersal to establish
distant colonies, winged dispersal is rare

predominant nesting habit is on the ground (fallen vegetation, ground cracks, tree bases)
and potentially transient

require “a carbohydrate source (fruit, plant exudates, honeydew) for energy and a
protein based source (insects, small vertebrates, dead vertebrates or invertebrates) for
reproduction” (Slip and Comport 2008)

opportunistic and scavenge, often overcoming prey >100 times their own biomass using
their formic acid defence. This blinds prey leading to death by starvation often within 24–
48 hours

display unicoloniality (many queens in a small area) in their introduced ranges forming
supercolonies that can have up to 300 queens and cover large spatial scales. This
facilitates a rapid increase in population numbers, increasing their invasive impact
(Abbott 2005, Slip and Comport 2008, Biosecurity Queensland 2012).
Establishment risk
There are a range of factors relevant to the assessment of the risk of introduction and
establishment of CUS on PKNP which are considered below.
Departure points
The following table outlines the major pathways that CUS may use to invade PKNP (Table
1). It shows areas where the CUS is currently established, origins with potential for
naturalised distribution, the potential pathways and the risk of introduction. It also shows
areas where YCA are currently established. The range of CUS does not currently extend to
PKNP; however it is foreseeable the island could form part of the future range of this species
as conditions are high suitable. The following information has been used to identify where
threat prevention work is needed.
Table 1 Cottony Urbicola Scale invasive pathways and likelihood of introduction
Origin
Perth (Australian Mainland)
Broome (Australian Mainland)
Darwin (Australian Mainland)
Fremantle (Australian Mainland)
Christmas Island2
Cocos Home Island
Cocos Horsburgh Island
Cocos West Island
Remaining islands within the
southern atoll
Indonesia3
Sri Lanka3
Pathway
CUS
Est.? Air
Sea
N
Y
N
1
N
Y
N
N1
Y
N
N
N
Y
Y
Y
Y
1
N
N
Y
N1
N
Y
1
N
N
Y
Likelihood of
introduction
Very unlikely
Very unlikely
Very unlikely
Very unlikely
Possible
Unlikely
Unlikely
Unlikely
YCA
Est.?
N
Y
Y
N
Y
Y
Y
Y
N1
N
Y
Unlikely
Y
N1
Y
N
N
Y
Y
Unlikely
Unlikely
Y
Y
1
Potential for naturalised distribution.
Detected on Christmas Island in 2011.
3 Suspected Illegal Entry Vessels (SIEVs). Recorded in Sri Lanka in 2011 (Sirisena, Watson et al.
2013), data for Indonesia lacking.
2
Currently, there are no direct local conveyance pathways, either air or sea, between the CKI
and PKNP as CUS is not naturalised at any of the local origins points. The current risk via
local pathway has been identified as low but if introduced1 to the southern atoll from
Christmas Island it would be high.
As CUS is established on Christmas Island the risk of introduction via the domestic pathway
is possible. There are two potential pathways for transport:

pelagic seabirds travel great distances between breeding colonies and it is possible that
they would travel the ~970 km distance between the two islands in less than 60 hours
(Neumann, Green et al. 2011). The likelihood of controlling this natural dispersal
pathway is impossible as threat prevention strategies will not reduce the introduction
risk.

Neumann and Green et. al.(2011) reported that there is no direct human traffic between
Christmas Island and PKNP. However, Parks staff do travel periodically between the two
islands to assist with on-island conservation. CUS could be transported in live or moist
vegetative material and fruit/vegetable grown or sold on Christmas Island. There is also
a chance that CUS could travel to PKNP in equipment or clothing if they had not been
adequately disinfected.
1
PKNP is one of the largest seabird rookeries in the Indian Ocean. Parks Australia run a conservation
program rehabilitating seabirds in the communities on the southern atoll. If CUS established on the
southern atoll of the CKIs it is foreseeable that a seabird could introduce scale insect to the park once
rehabilitated.
For these reasons the risk via domestic pathways has been identified as high.
The risk of introduction by SIEVs via the international sea pathways is less certain due to the
lack of ability to control its arrival using threat prevention strategies. However, CUS could be
transported in moist vegetative material or fruit/vegetables, thus the risk has been identified
as medium.
Transportability
The population of CUS on Christmas Island is the most likely origin for its introduction to the
CKIs and PKNP (Neumann, Green et al. 2011). The insect must be transported between 24
hours and 3 days of its detachment from a host species. If the ~3 day survival time is
exceeded the insect could desiccate and perish. For this reason, human transport by visitors
or Parks staff from Christmas Island appears possible. Care must be taken by visitors not to
accidentally infest PKNP via soil, wood and vegetative material including vegetable scraps
and fruit rinds (Smith and Papacek 2001).
Natural dispersal methods are the most likely transport vector. Christmas Island is the
closest land mass to PKNP where CUS is present. Both islands contain large populations of
seabirds and transport between the islands is the most probable future source of introduction
(Smith and Papacek 2001, Neumann, Green et al. 2011). Red-footed Booby’s (Sula sula),
Greater Frigatebird’s (Fregata minor) are common on both islands are the most likely
seabirds to migrate between the islands. Therefore, CUS transport to PKNP is possible.
Climatic & habitat suitability
CUS are habitat generalists and PKNP habitat is considered highly suitable. The tropical,
high-humidity climate and distinct wet season on PKNP closely match that of CUS in its
naturalised range and is also highly suitable. If introduced, it’s likely that CUS and YCA
numbers would increase and populations would spread island-wide. One predicts that the
interactions between YCAs and CUS on PKNP would mimic those of the populations on
Christmas Island where climate and habitat are similar.
Impact on biodiversity
The principal biodiversity impacts of scale insects2 stem from their establishment on host
trees and the resulting interaction between them, their host and species and the supporting
ant species. There is a high likelihood of the following adverse biodiversity impacts occurring
if CUS was introduced and YCAs reached supercolony densities on PKNP:

2
CUS numbers are amplified by a facultative mutualistic association with YCA species:
scale provide carbohydrate food source (honeydew) to ants  ants protect scale insect
from predators  populations of both insects elevated
Scale insects Parasaissetia nigra and Dysmicoccus finitimus are present on PKNP. Currently, the
interactions between these insects and the YCAs have been minimal. However, if there is an
explosion in population numbers, CUS was introduced or YCA behavior changed, impacts could
become significant. The interactions between scale insects and YCAs continue to be monitored in
annual Island Wide Surveys (IWS) (Detto 2012).

high numbers of YCAs in multi-queen supercolonies (1000s ants/m2) cause rapid,
catastrophic shifts in the forest ecosystems, affecting multiple trophic levels

YCA extirpate land crabs (the dominant forest floor consumer) which causes enhanced
seedling recruitment, species richness, and litter breakdown. Thereby changing the
structure of forest vegetation

YCA have also been determined as the cause for seabird nesting failures and chick
deaths and directly disrupt bird frugivory influencing bird abundances and behaviours

CUS infestation correlates with reductions in pisonia forest canopy cover. Scale density
correlates with tree health. High densities = sooty mould growth, poor health, canopy
dieback and tree death

CUS outbreaks have been implicated in island-wide pisonia mortality. Pisonia are the
dominant canopy species and are structurally and functionally important. They provide
vital nesting habitat for a wide range of seabird species, including EPBC listed migratory
birds and the largest population of red-footed booby birds in the Indian Ocean. Pisonia
are protected in their own right under the EPBC Act and worldwide (O’Dowd, Green et
al. 2003, United States Government 2005, Abbott 2006, Neville, O’Dowd et al. 2008,
Davis, O'Dowd et al. 2009, Queensland State Government 2010, Neumann, Green et al.
2011)

YCA in supercolony numbers could impact upon the endemic subspecies Gallirallus
philippensis andrewsi (Cocos Buff-banded rail) that nest on PKNP.
The extent of future impacts/consequences on PKNP is uncertain but could be
majorcatastrophic. It is integral that biosecurity threat prevention protocols be introduced
addressing the threat of CUS introduction to PKNP (Slip and Comport 2008). The presence
of this honeydew producing insect would allow YCA numbers to increase. Although there is
no current threat, if YCAs reached supercolony densities, the impacts to the natural values
of the park would be catastrophic.
In the event that CUS established on PKNP, it is likely the benefits provided by YCA
chemical eradication would be greater than the off-target impacts of the control program.
However, it is important that the control methods do not compromise the islands ecosystems
and impacts on the islands natural values are minimised (Slip and Comport 2008).
YCA or CUS biocontrol is another option. Substantial risks typically accompany the release
of a biological control agent. Unlike chemical control, biocontrol, if successful, involves a
permanent change to the ecosystem. Therefore, non-target risks must be assessed
carefully.
On Christmas Island, biocontrol research into the indirect control of YCA through the control
of the scale insect mutualist Tachardina aurantiaca (T. aurantiaca) is underway.
T. aurantiaca is the principle scale mutualist for YCA on Christmas Island and as such the
project aims to reduce YCA densities by limiting, through parasitism, the prevalence of this
particular scale insect. The biocontrol project will require the importation to Christmas Island
of a wasp/s to parasitise the scale insect. As CUS was accidentally introduced to Christmas
Island along with the parasitoid wasp Coccophagus ceroplastae current work designed to
minimise impacts to P. grandis and P. umbelifera forest is geared around the production of
Coccophagus ceroplastae (C. ceroplastae) parasitoids using host plants that are then used
to inoculate infected Pisonia forest. This work is a precursor for when a biocontrol agent/s for
T. aurantiaca is available as a multiple species approach will provide the greatest chance of
a successful reduction in YCA densities.
If CUS does travel to PKNP from Christmas Island the importation of the parasitoid
C. ceroplastae during the same event would be fortuitous as a biocontrol mechanism would
then be in place. Failing this, the importation of C. ceroplastae to PKNP should be prioritised
and undertaken immediately to reduce detrimental impacts to pisonia forest and the islands
flora and fauna.
Conclusions
It is possible that CUS could be introduced to PKNP via the domestic pathway. Both by
human transport with Parks staff visiting from Christmas Island and natural dispersal by the
islands seabird population.
CUS have naturalised across many continents and in varying tropical to sub-tropical climates
and is considered highly suitable for establishment on PKNP. If CUS were introduced, the
likelihood of establishment is almost certain.
The consequences of CUS introduction and establishment on PKNP have been assessed as
catastrophic respectively. This is based on the number of biodiversity impacts that would
occur if CUS and YCAs formed a mutualistic relationship that resulted in an explosion of
population numbers. If YCAs reached supercolony densities, one could expect the same
type and magnitude of impacts experience on Christmas Island and mainland Australia.
Based on the above assessments, introduction of CUS via the domestic pathway represents
a HIGHEXTREME biosecurity risk to PKNP.
The outcomes of this assessment are summarised in matrix below.
COTTONY URBICOLA SCALE INTRODUCTION AND
ESTABLISHMENT RISK MATRIX
Consequences
Likelihood of Introduction
Almost certain
Will probably occur once in 1
month
Insignificant
Minor
Moderate
Major
Catastrophic
Low
Medium
High
Very
High
Extreme
Low
Medium
High
Very
High
Very High
Low
Low
Medium
High
High
Minimal
Minimal
Low
Medium
High
Minimal
Minimal
Low
Low
Medium
Likely
Will probably occur once in 6
months
Possible
Will probably occur once in 2
years
Unlikely
Will probably occur once in 10
years
Very Unlikely
May occur only once in 50
years or more
Likelihood of
Establishment
Almost certain
Will probably occur once in 1
month
Consequences
Insignificant
Minor
Moderate
Major
Catastrophic
Low
Medium
High
Very
High
Extreme
Low
Medium
High
Very
High
Very High
Low
Low
Medium
High
High
Minimal
Minimal
Low
Medium
High
Minimal
Minimal
Low
Low
Medium
Likely
Will probably occur once in 6
months
Possible
Will probably occur once in 2
years
Unlikely
Will probably occur once in 10
years
Very Unlikely
May occur only once in 50
years or more
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