Twelfth Australian Weeds Conference
AN OVERVIEW OF THE ESTABLISHMENT, DISTRIBUTION AND
EFFICACY OF BIOLOGICAL CONTROL AGENTS FOR RAGWORT,
SENECIO JACOBAEA L., IN TASMANIA
J.E. Ireson1, R.J. Holloway1,
W.S. Chatterton1 and S.M. Leighton2
1 Tasmanian Institute of Agricultural Research, 13 St. John’s Avenue, New Town, Tas. 7008
2 PO Box Meander, Tas. 7304
Summary Ragwort, Senecio jacobaea, is a serious
pasture weed in Tasmania. Biological control is now
providing a solution to the problem. The ragwort flea
beetle, Longitarsus flavicornis, was first released in
Tasmania in 1979 and has reduced ragwort density by
up to 95% at many sites. The spread of L. flavicornis
has been accelerated by collecting nearly 2 million
adults from the field and transferring them to 879 new
sites. About 88% of these collections have been car-
ried out in summer since 1993. L. flavicornis is now
common throughout southern Tasmania and was esti-
mated to have spread over at least 90% of the major
infestations in the north by February 1999. L.
flavicornis has been an effective control agent in many
localities, however, its efficacy has been restricted in
some pastures. Mortality resulting from the use of her-
bicides and pugging of wet ground by cattle, particu-
larly in heavily stocked pastures, could be key factors.
Additional biological agents have also been released.
A second species of flea beetle, an Italian biotype of
Longitarsus jacobaeae, was released in 1988. Its cur-
rent distribution is unknown but it has been recovered
from only 5 sites and is not believed to be widespread.
Releases of the cinnabar moth, Tyria jacobaeae, have
been carried out annually in spring since the introduc-
tion of this species from New Zealand in 1993. How-
ever, there is still no evidence that it is permanently
established, possibly due to the effects of predation.
In localities where the impact of L. flavicornis has been
restricted, two other species, the introduced ragwort
stem and crown boring moth, Cochylis atricapitana,
and a native moth, the blue stem borer, Patagoniodes
farinaria, could be useful complementary agents. C.
atricapitana has now been permanently established at
sites in Tasmania from releases that commenced in
1995. P. farinaria is common on ragwort in parts of
northern Tasmania and its life cycle and feeding hab-
its are similar to those of C. atricapitana. We expect
that the integration of biological agents with traditional
control measures that enable agent survival will ulti-
mately provide cost effective control of ragwort
In Tasmania, ragwort is a serious weed of pastures in
high rainfall areas (>800 mm per year). Annual pro-
duction losses to the dairy and beef industries have
been estimated at ca. $3 million in some years. The
first attempt at biological control of ragwort in Tasma-
nia began in 1963 with the release of a consignment of
the ragwort seed fly Botanophila jacobaeae (Hardy)
(previously referred to as Pegohylemia seneciella
Meade) which failed to establish (Ireson and Terauds
1982). A French biotype of the ragwort flea beetle,
Longitarsus flavicornis (Stephens), was introduced to
Tasmania in 1979 (Cullen and Moore 1981). Multiple
releases of glasshouse reared adults and a redistribu-
tion programme has resulted in its widespread estab-
lishment (Ireson and Terauds 1982; Ireson et al. 1999).
Some of the Spanish biotypes of L. flavicornis that
were introduced to Australia between December 1984
and January 1986 (Field 1989) became established in
Tasmania from releases that commenced in 1986. A
second species of flea beetle, an Italian biotype of
Longitarsus jacobaeae (Waterhouse), which was im-
ported to Australia via Oregon (USA) and New Zea-
land (Julien and Griffiths 1998), was first released in
Tasmania in 1988 and also successfully established.
Two additional agents of European origin, the cinna-
bar moth, Tyria jacobaea (L.), and the ragwort stem
and crown boring moth, Cochylis atricapitana
(Stephens), are also now being investigated in Tasma-
nia as possible complementary agents to the
Longitarsus spp. Several previous attempts to estab-
lish T. jacobaeae in Victoria carried out between 1930
and 1982 were unsuccessful (Bornemissza 1966; Field
1989). Attempts to establish T. jacobaeae in Tasmania
commenced in 1993 with the introduction of rearing
stock from New Zealand where it has been established
since its release in 1929 (Miller 1929).
A Spanish biotype of C. atricapitana (Stephens) was
first released in Victoria in 1987 (McLaren 1992) and
introduced to Tasmania in 1994. Studies have also been
Twelfth Australian Weeds Conference
carried out on a native species of pyralid moth, the
blue stem borer, Patagoniodes farinaria (Turner),
whose larvae attack ragwort (Ireson and McQuillan
1984; McQuillan and Ireson 1987).
The aim of this paper is to summarise the outcomes
achieved in Tasmania from work carried out on the
biological control of ragwort since the introduction of
L. flavicornis in 1979.
STUDIES ON THE RAGWORT FLEA BEETLES,
L. flavicornis (French biotype) Studies on the biol-
ogy and efficacy of L. flavicornis were carried out at
two established sites (Lachlan in the south and
Mayberry in the north) from 1985-1989 (Ireson et al.
1991). L. flavicornis was released at both sites in 1979
and by May 1989 (ca. 9 years after its release) had
reduced ragwort densities by ca. 90%.
High densities of L. flavicornis, and corresponding
reductions in ragwort densities, have occurred over the
same time scale recorded by Ireson et al. (1991) in all
the major ragwort infested regions of the state (Ireson
1993; Ireson 1995). Population dispersal has been ac-
celerated by a successful redistribution programme
(Ireson et al. 1999). This has involved the field collec-
tion and transfer of around 2 million adults to 879 new
sites, 80% of which were carried out during a six year
period from 1993-1999. By February 1999, it was es-
timated that L. flavicornis had spread throughout all
the ragwort infestations in southern Tasmania and about
90% of the major infestations in the north (Fig. 1)
(Ireson et al. 1999).
On many dairy properties in northern Tasmania the
impact of L. flavicornis has been restricted, probably
by unfavourable site conditions and incompatible man-
agement practices. For instance it is suspected that the
pugging of wet ground by cattle is causing high larval
mortality at some sites (Ireson et al. 1999). The use of
boom sprayed herbicides could also be a major factor
restricting L. flavicornis population increases (Boersma
1996). Further studies are now being undertaken on
factors affecting L. flavicornis densities in these areas.
This should enable the production of a comprehensive
integrated management plan for farmers. Many farm-
ers are already being encouraged to improve their con-
trol programmes by utilising chemical and mechanical
control methods and grazing strategies that promote
the survival of L. flavicornis.
L. flavicornis (Spanish biotypes) Biotypes of L.
flavicornis collected from locations in Spain (Albares
de la Ribera, Sancti Spiritus and Sarria) (Field 1989)
were released at 8 sites in Tasmania between August
1986 and March 1989. Establishment was confirmed
at 6 sites (two in the north and four in the south) (Ireson
unpubl. data). The Spanish biotypes of L. flavicornis
released in Tasmania behave similarly to the French
biotype (Field 1989). It is therefore not possible to
distinguish the field populations of the Spanish bio-
type now that the release sites have since been over-
lapped by the spread of the French biotype.
Figure 1. Estimated distribution (by autumn 1999) of
the ragwort flea beetle, Longitarsus flavicornis, (dark
grey), in relation to the main ragwort infestations in
Tasmania. Ragwort infested areas where L. flavicornis
has not yet established are indicated in light grey.
L. jacobaeae (Italian biotype) Glasshouse reared
adults of the Italian biotype of L. jacobaeae were re-
leased at 26 sites between October 1988 and July 1990.
Surveys have indicated that it has survived at only 5
sites in northern Tasmania. Two of these sites are small,
isolated infestations of ca. 1-2 ha. and at the other 3
sites its distribution has overlapped with L. flavicornis,
which has spread from neighbouring release sites. A
detailed study is therefore required to confirm the
identity of L. jacobaeae at these 3 sites and accurately
Twelfth Australian Weeds Conference
determine its distribution and phenology. The species
is pre-adapted to survive hot dry summers (Frick and
Johnson 1973) and could be expected to perform bet-
ter than L. flavicornis at some locations in Tasmania
(Ireson et al. 1999). However, because L. flavicornis
has generally performed well in Tasmania, it is unlikely
that any further work with this species will be under-
taken, at least in the short term.
INVESTIGATIONS ON OTHER BIOLOGICAL
Release and monitoring of the cinnabar moth, T.
jacobaeae In January 1993, ca. 1600 larvae were im-
ported from North Canterbury, New Zealand into quar-
antine at New Town Research Laboratories near Ho-
bart. Progeny from this stock were used for the mass
rearing and annual field release of T. jacobaeae that
was carried out in Tasmania between November 1993
and December 1997. During this period over 250,000
larvae and over 2,000 adults were released at 36 sites.
Adult releases ranged from 300-500 per site. The
number of larvae released per site ranged from 1,000-
42,500 (mean 8,000).
Monitoring of the 36 release sites during summer has
indicated an annual decline in the size of field
populations and the number of sites at which the agent
has been recovered. By January 1999, surviving colo-
nies were found at only 4 (44%) of the 1 year old sites
and 1 (20%) of the 2 year old sites. No surviving colo-
nies were found at sites 3-5 years old.
In Canada, Harris et al. (1971) reported that field es-
tablishment of T. jacobaeae followed a pattern of high
mortality of laboratory reared stock during the first year
after release, approximate maintenance of the larval
population in the following 2 years and a 4 to 5 fold
increase in the fourth and later years. In Oregon (USA)
Isaccson (1973) found no significant increase in ei-
ther density or spread at any release site until 5 years
after release. A similarly lengthy build-up was also
reported by Syrett et al. (1991) in New Zealand where
establishment was recorded at 35% of the release sites.
In Tasmania, it is evident from the consistent annual
decline in the T. jacobaeae colonies that a similar pat-
tern of establishment is not being followed. Further-
more, the average size of the larval populations released
at the Tasmanian sites (8,000) was considerably higher
than those used for releases in Canada, the USA or
New Zealand where establishment has been achieved
through releases of 1,000 larvae or less (Harris et al.
1975; Brown 1989; Syrett et al. 1991).
Previously unsuccessful attempts at establishing the
species in Victoria between 1930 and 1982
(Bornemissza 1966; Schimidl 1972, 1981; Field 1989)
were attributed to disease in imported stocks, field pre-
dation mainly by the scorpion fly, Harpobittacus
nigriceps (Selys), and the importation of biotypes from
Europe and Canada that were ill adapted to the rag-
wort infested areas of Victoria.
For the Tasmanian programme, the introduction of a
New Zealand biotype has overcome the life cycle
asynchrony and disease problems associated with the
importation of northern hemisphere biotypes. However,
it is possible that predation could be having a signifi-
cant impact on establishing colonies of T. jacobaeae.
Dempster (1971) concluded that mortality of T.
jacobaeae due to arthropod predation was low during
the egg stage but was high amongst young larvae which
became more immune to predation as they matured. A
species of Harpobittacus was recorded in northern
Tasmania at only 1 of the 36 Tasmanian release sites
(Parkham: 41° 25´S, 146° 37´E). This species is there-
fore not considered to be the same threat to establish-
ing populations in this State as was the case in Victo-
ria, where Bornemissza (1966) noted H. nigriceps to
be common in all ragwort infested areas. The preda-
tory shield bug, Cematulus nasalis (Westwood), was
observed attacking T. jacobaeae larvae but is unlikely
to pose any significant threat as it too was only ob-
served in low numbers at one site in southern Tasma-
nia (Woodstock: 43° 05´S, 147° 02´E). However, other
polyphagous arthropod predators are common in Tas-
manian pastures (McQuillan and Ireson 1982) and were
collected at the Tasmanian release sites during sum-
mer when T. jacobaeae larvae were active or eggs
present (Ireson unpubl. data). Potential predators iden-
tified were species of carabid, staphylinid and cantharid
beetles, mites, spiders, isopods (slaters), ants and the
European earwig, Forficula auricularia L. These
groups or species have been recorded as attacking ei-
ther eggs, larvae and pupae of T. jacobaeae in over-
seas studies (Wilkinson 1965; Dempster 1971,1982;
Harris et al. 1975; Isaacson 1973; van der Meijden
1979). It is therefore possible that common arthropod
predators may be a key factor in preventing the estab-
lishment of T. jacobaeae in Tasmania.
Dempster (1971) observed that T. jacobaeae larvae
were distasteful to vertebrate predators, which had no
impact. Miller (1970) recorded 3 bird species attack-
ing larvae in New Zealand. However, Bornemissza
Twelfth Australian Weeds Conference
(1966) failed to observe any insectivorous birds or liz-
ards in Victoria and there was no evidence that any
significant avian predation has occurred at the Tasma-
nian release sites.
At this stage it appears unlikely that T. jacobaeae will
establish in Tasmania or may have a restricted distri-
bution if it does. The waterlogging which reduces the
survival of L. flavicornis larvae in some winter pas-
tures would also be detrimental to the survival of over-
wintering pupae of T. jacobaeae which cannot tolerate
wet soil (Dempster 1971).
Release, monitoring and establishment of C.
atricapitana This species was originally imported from
Salamanca, Spain and first released in Victoria in No-
vember 1987 (McLaren 1992). Adult C. atricapitana
derived from this stock were imported from Victoria
to Tasmania in October 1994 for mass rearing at New
Town Research Laboratories. The first field releases
from this culture commenced in September 1995 at
Woodstock and by September 1998 the agent had been
released at 27 sites.
Results of establishment assessments at these sites to
February 1999 (Table 1) show that C. atricapitana has
now successfully established at 4 (15%) of the sites, is
surviving at 18 (67%) of the sites and has failed to
establish at 9 sites. The maximum distance dispersed
(200 m in 3 years) compares favourably with sites in
Victoria where the maximum recorded dispersal in 3
years has been 100 m (McLaren 1992). These results
suggest that the agent has the potential to spread rap-
idly in Tasmania.
Status of the blue stem borer, Patagoniodes farinaria,
as a biological control agent for ragwort P. farinaria
is believed to be endemic to Australia and New Zea-
land (McQuillan and Ireson 1987). In Tasmania, fa-
voured native food plants are subspecies of Senecio
lautus which have biological similarities to ragwort
(McQuillan and Ireson 1987). Studies on the biology
and taxonomy of P. farinaria were conducted in Tas-
mania because of the ability of P. farinaria to exploit
ragwort as a larval food plant (Ireson and McQuillan
1984; McQuillan and Ireson 1987).
P. farinaria is common and widely distributed in the
larger ragwort infestations in the pastures of northern
Tasmania that are grazed mainly by dairy cattle (Ireson
and McQuillan 1984). Although the larvae often cause
severe damage to individual ragwort plants, the insect
by itself appears to have limited potential as a control
agent (Cottier 1931; Bornemissza 1966; Ireson and
McQuillan 1984). High levels of parasitism have been
recorded in field populations and this may be restrict-
ing its efficacy at some sites (Ireson and McQuillan
The larval feeding habits of this species are confined
mainly to aboveground tissues and are similar to those
of C. atricapitana. However, until C. atricapitana be-
comes more widely established and its densities start
to increase it will not be known how the two species
will interact. Preliminary surveys at C. atricapitana
release sites in Tasmania (Ireson unpubl. data) and
Victoria (McLaren pers. comm.), have found larvae of
the two species feeding on the same plant, suggesting
Table 1. Results of assessments on the establishment and dispersal of C. atricapitana at Tasmanian release sites.
Period after release 6 months 1 year 2 years 3 years Total
No. release sites assessed 4 13 6 4 27
Agent not recovered 0 7 2 0 9
Agent recovered from release site only 4 3 1 1 9
Agent at least 50m from release site 2 2 4
Agent at least 100m from release site 1 1 2
Agent at least 200m from release site 3 3
Sites where agent surviving* 4 6 4 4 18 (67%)
Sites where agent established** 0 0 1 3 4 (15%)
* Sites where C. atricapitana is surviving are those where it has been found within 100 m of the release site 6
months to 2 years after release. It also includes established sites.
** Established sites are those where C. atricapitana has survived for at least 2 years, is increasing its population
and has spread at least 100 m from the release site.
Twelfth Australian Weeds Conference
that the two species are compatible. If this is so, the
impact of these 2 species in combination with the root
and crown feeding activities of L. flavicornis could be
Successful biological control of ragwort has been
achieved in western Oregon (USA) using the Italian
biotype of L. jacobaeae in combination with T.
jacobaeae and the ragwort seed fly, Botanophila
seneciella (McEvoy et. al. 1991). Coombs et al. (1996)
report that this has resulted in annual savings of $5
million from reductions in livestock losses, increased
pasture production and reduced herbicide use. In Tas-
mania, control of ragwort with L. flavicornis has al-
ready been achieved at many sites. The number of con-
trolled infestations should increase now that the spe-
cies has become widespread and has been recorded in
high densities in all the main ragwort infested areas of
the state (Ireson et al. 1999). It is expected that the
impact of L. flavicornis will be augmented by C.
atricapitana or P. farinaria. These species will be par-
ticularly useful if they can survive well enough and
place sufficient additional stress on ragwort to facili-
tate its control in areas where the impact of L.
flavicornis is marginal. Other agents, such as the rag-
wort plume moth, Platyptilia isodactyla (Zeller), may
also be available for future release, pending the out-
come of host specificity tests (McLaren pers. comm.).
It is now possible that ragwort could cease to be a
weed of major economic importance in Tasmania, per-
haps during the next 10-15 years. This will, however,
depend on the widespread adoption of management
practices by Landholders that will complement the
impact of the biological control agents, particularly on
We thank Barry Rowe (Tasmanian Institute of Agri-
cultural Research) and Margaret Williams (Department
of Primary Industry, Water and Energy) for their com-
ments on the manuscript. We are also grateful to Wal
Ashby for technical assistance and the support. of the
Meander Valley Weed Strategy. Funding support for
the programme has been gratefully received from the
Dairy Research and Development Corporation and the
Natural Heritage Trust.
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