Introduction
Methods
Cirsium arvense (Californian thistle) is an introduced weed of Eurasian
origin, and one of the worst pasture weeds in New Zealand. Currently there
is renewed effort to improve classical biological control of this weed which
has resuLted in recent reLeases of two biocontroL agents from Europe:
Surveys were carried out in Europe and NZ where the proportion of rust disease
was recorded. Also see Cripps et al. (2010) Plant Ecology 209:123-134.
Ceratapion onopordi, a stem-mining weeviL thought to vector the rust
pathogen, Puccinia punctiformis.
The impact of Cassida was assessed under different LeveLs of competition
with white clover + perenniaL ryegrass.
The influence of naturaL enemies on the popuLation dynamics of C. arvense
was tested in by using pesticide exclusion in Europe and NZ.
Cassida rubiginosa, a leaf-feeding beetle thought to reduce biomass
of C. arvense.
Results
EUROPE
Net change in population growth
5~------------------------------~
EUROPE
4
3
2007
2
2008
6
1
•
··· ··· ··0 ··· · ···
__ ___
4
o +----,-
QJ
VI
CH1
ro
D1
D2
F1
H1
H2
H3
H4
HS
H6
HR1
N
HR2
E
QJ
VI
."'tJ
.....
.
o
c::
5
::::e
o
4
20
40
60
~
~
-
~
--V
"O .. . .. . .. Q
80 100
o
20 40
60
80 100
-
~
NEW ZEALAND
.!!! 3
c
o
v-
~~- ----~-- ~~·: ~f -
o
VI
::J
~_ .. ,..... ...~._.:-
-2
NEW ZEALAND
+-'
,.,..0- -" - -""- -
2
C onl rol
Insec lic ide
Fungici de
Dua l
=
=
BP1
BP2
-
-
Lincoln
2
0
BP3
W1
W2
Green ark
o
=
AK1
AK2
01
SL 1
SL2
SL3
SL4
.. "".~-:::~ ---.-.--~.-­
.... "-
~:::-.. - " ,...- ~~
-2
SLS
No difference in rust disease between Europe (supposed vector, C. onopordi
present) and NZ (c. onopordi absent).
Cripps et al. (2009) Biocontrol Science & Technology 19:447-454.
:"-
......
-4
-6
-8
-10
-12
...>'D ..
v
....
'0
L-,.--~--~~--~---'.~--~--~~--~--'
o
20
40
60
80
o
20
40
60
80
Days after first census
*Significant main effect of insecticide (P<0.05).
III
'0
§
5
2.4
+ Significant main effect of fungicide (P<0.05).
1:
o 4
s:.
01
'Q,
III
2.0
J
~
]
...o
There were no significant treatment effects in NZ.
1.6
1.2
01
o
Conclusions
-I
SC
sc
Level Of
UC
cOin
petition
Level Of
co ...
UC
" IPetit'
10"
Plant competition caused a
significant reduction in
C. arvense growth
Cassida rubiginosa larvae failed
to have an impact on C. arvense
growth at tested densities
The incidence of the rust pathogen is similar in both ranges, regardless ofthe
presence of the supposed weevil vector, which is inconsistent with the weevil being
an important vector, casting doubt on it fulfiLLing this role in NZ.
Pasture-plant competition significantly reduces growth of C. arvense, however, high
density "outbreak" populations of C. rubiginosa will be necessary to cause an effect.
Insect herbivores can reduce population growth of C. arvense in its native range, but it is
uncertain which species are responsible. Application of fungicide decreased growth of C.
arvense suggesting it was either phytotoxic, or kiLLed beneficial mutualistic species.
Monitoring of C. onopordi and C. rubiginosa is necessary to determine their impacts in NZ.
Cripps et al. (2010) Biocontrol Science & Technology 20:641-656.