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The Tasmanian Naturalist 144 (2022)
79
Investigating the continued impact of a
Cyrioides imperialis (Fabricius, 1801) (Coleoptera:
Buprestidae) infestation on Banksia marginata
regeneration at ‘Templestowe’, Seymour, Tasmania
Karen Richards
1
, Chris Spencer
1*
, David Quon
2
& Cheryl Quon
2
1
65 Sinclair Avenue, Moonah, Tasmania 7009
spenric@gmail.com
*
deceased
2
‘Templestowe’, 48 Macquarie Street, Seymour, Tasmania 7215
Abstract
Stem-boring beetle attack can be devastating, both to the host plant, and to
conservation-minded landowners. Here we provide the results of our research
into the impact of the jewel beetle Cyrioides imperialis (Fabricius, 1801) on
Banksia marginata specimens in a mixed tree planting, established on a property
at Seymour, Tasmania, between 2007 and 2009. In nding 54% of the banskias
were attacked by the beetle, tree location, position in the planting and rainfall
were each likely to inuence the degree of attack on the trees.
Introduction
In 2020 we reported on an infestation
of the banksia borer Cyrioides imperialis
(Fabricius, 1801) occurring in Banskia
marginata saplings in mixed native tree
plantings at ‘Templestowe’, Seymour
(Richards et al. 2020) (Plate 1). The
plantings, then aged 10–13 years,
became the target of a monitoring
project investigating the impact of the
borer on the young host plants, which
has now been conducted annually for
three years.
Being a former sheep grazing property
cleared of native vegetation, and situated
in an undulating coastal location on the
drier east coast of Tasmania, the property
is subject to continual salt deposition
by sea spray, while its soils suffer from
a combination of historic compaction,
reduced organic matter, and poor quality.
These conditions combine to reduce the
capacity of the soil to retain moisture
at the site, increasing the likelihood
of water stress, pathogens and insect
attack in many shallow-rooted trees and
shrubs, including those in establishing
tree plantings. Such symptoms often
manifest during extended periods of
The Tasmanian Naturalist 144 (2022)
80
low rainfall, as occurred in 2019–20,
and were most apparent in the young
banksias in the plantings established
on the elevated section of the property.
While many trees in the mixed planting
appeared more stunted overall, evidence
of stress in the banksias was in the form
of considerable yellowing of leaves, leaf
drop, and increased presence and attacks
by insects on the foliage, compared
with those in the plantings downslope.
However, similar symptoms have
been observed in juvenile B. marginata
exploited by C. imperialis in the midlands,
under a different suite of climatic and
soil conditions (Richards & Spencer
Plate 1. Recently emerged adult Cyrioides imperialis on Banksia
marginata
Figure 1. Monitoring site locality; location of trees surveyed at ‘Templestowe’ (maps Google
Earth 2022)
The Tasmanian Naturalist 144 (2022)
81
2018), so the inuence of slope and soil
depth on banksia health may not be the
only controlling factor.
Following a year of higher rainfall along
the east coast, in 2022 the health of
the trees showed improvement, despite
the presence of several insect borers
and the usual assortment of native and
exotic invertebrates found in degraded
landscapes. The banksias in the top
planting showed ushes of new healthy,
green growth and fewer yellowing leaves.
Here we present the results of the three-
year study into the impact C. imperialis is
having on the B. marginata saplings on
this property.
Methods
A monitoring program incorporating 74
B. marginata trees selected from within
three neighbouring plantings 10–13
years old, was established in June 2020
(Richards et al. 2020). Each banksia was
given a unique identication number and
tagged with an aluminium label attached
to a lower branch. The location of
individual trees is presented in Figure 1.
Monitoring was performed annually in
autumn–winter, outside of the beetle
activity period, and was conducted for
three years. Healthy, dying, and dead
B. marginata specimens in each planting
were included in the study.
On each occasion individual banksias
were inspected for presence of
emergence holes of the buprestid
C. imperialis in the trunk, branches and
exposed roots (Plate 2), while stem
galls of the cerambycid beetle Tragocerus
spencii Hope, 1834 were also recorded.
Additional emergence holes, obvious
insect infestations and vertebrate
browsing/damage in the banksias were
also noted. During each monitoring
event every C. imperialis emergence hole
observed was marked with an ‘X’ placed
across the hole, using a permanent black
pen, to conrm accuracy of the count
Plate 2. Cyrioides imperialis emergence holes in stem and root of
Banksia marginata
The Tasmanian Naturalist 144 (2022)
82
and to allow for easy recognition of new
holes in subsequent surveys (Plate 3).
Data collected included geographic
location, tree number, number of
emergence holes, orientation/direction
of emergence holes on stems, and
their height above ground. Health of
each Banksia marginata was assessed as:
healthy, sick or dead, % dead, and leaf
colour. Notes on dying and/or dead
banksias with no evidence of emergence
holes were taken, and the cause
identied, where possible. Dead trees
were included in subsequent monitoring
events to investigate any continued use
by the beetle.
Monthly rainfall data from ve stations
in the mid-east coast region were
obtained to determine annual rainfall
uctuation. While none of the datasets
were complete for the period 2018
to 2022, used together they provided
evidence of a lower-rainfall year (2019–
20) occurring within the study period.
Results
Of the B. marginata included in the study,
six saplings (8.1%) were determined to
be dead at the outset. A further three
were classied as dead in the second
year (2021) (12.2% of total), with the
total climbing to 16 banksias (21.6%) in
2022. Details of dead trees, the number
of emergence holes originally recorded,
and number at nal count per plant are
presented in Table 1.
The majority of the 16 dead banksias
possessed C. imperialis emergence holes,
with only three showing no outward sign
of C. imperialis attack. Of the latter, one
had two Tragocerus galls, while another
had evidence of other borer damage
at its base, i.e. ne frass accumulating
on the soil around the trunk (hence
not Tragocerus or C. imperialis), as did
the adjacent Acacia bushes, which were
also dead. The cause of death of the
third banksia could not be determined;
however, it is possible that evidence of
Plate 3. Cyrioides imperialis emergence holes marked with ‘X’ in a
previous season
The Tasmanian Naturalist 144 (2022)
83
C. imperialis emergence will present in
the coming season.
Thirty-three (44.6%) of the banksias
surveyed possessed at least one
C. imperialis emergence hole at the
beginning of this research. By the
conclusion, 40 (54.1%) had hosted
C. imperialis at some point during the
study. There was no increase in the
total number of banksias infested
between 2021 and 2022, although more
emergence holes were located. The
cumulative total of emergence holes
recorded each season is presented in
Figure 2, but note that the 2020 tally
was already the accumulation of several
prior seasons of infestation. In 2020–
21 and 2021–22, the number of new
emergences recorded per monitoring
event was 34 and 46 respectively.
Beetle attack was not consistent between
banksia trees; 34 of the 74 banksias failed
to show sign of Cyrioides damage by the
end of the study. The largest number
of emergence holes (22) occurred in
a single dead banksia in 2022, a tree
that had only seven emergences the
previous season, at which point the
plant was alive and appeared healthy.
Of the 74 banksias, 11 (14.8%) had 7
Tree
no.
Year of death and total
emergence holes
Comments
2020 2021 2022
4 10 Recently fallen over, removed by owners prior to next
visit
31 2 (4) 2 at death, plus addional 2 post-death
36 3 All in roots
37 0 No cause of death evident
44 2 No further emergence. Tragocerus present
30 5 10 5 sick, plus 5 in year of death
33 4 7 7 sick, plus 2 Tragocerus galls in year of death
42 13 15 13 sick, plus 2 in year of death
22 0 0 0 borer damage at base, Acacia spp. adjacent also dead
32 0 7 9 7 sick, plus 2 in year of death
39 5 5 22 5 healthy, plus 17 in year of death
45 4 6 11 3 in stem, 3 in roots (sick), plus 5 in year of death
46 5 5 5 4 in stem, 1 in root (sick), no addional in year of death
52 6 6 8 6 healthy, plus 2 in year of death
60 5 5 5 5, plus one Tragocerus in year of death
61 0 0 0 0, plus Tragocerus at original survey
Table 1. Trees deaths recorded at ‘Templestowe’
The Tasmanian Naturalist 144 (2022)
84
Figure 2. Cumulative total of emergence holes recorded during the study
Figure 3. Emergence holes per Banksia marginata in 2022
The Tasmanian Naturalist 144 (2022)
85
or more holes; however, 1–3 holes per
banksia was most commonly observed,
occurring in 21 of the 74 trees (28.4%)
(Figure 3).
Banksias along the periphery of the
plantings had the most emergence
holes, while those in the interior rarely
showed evidence of beetle use, those
that did almost always presenting as
willowy specimens of poor form, very
thin and with minimal canopy. Dying or
visibly stressed B. marginata supported
the greatest number of emergence
holes. In some instances, such trees also
had increased insect damage to their
foliage and possessed above-average
numbers of emergence holes (7 or more
emergence holes). Dead trees, however,
seldom showed evidence of ongoing
C. imperialis use, and never for more than
a single season.
Visible signs of declining tree health
varied between seasons, with banksias
in April 2020 displaying the poorest
symptoms, such as distinct yellowing of
leaves, leaf drop and stunted, minimal
new growth, perhaps accounted for by
the lower annual rainfall. By April 2022,
many of the banksias were evidently
recovering, the leaves transitioning from
denite yellow to some green tinge,
and containing a ush of new, healthy
green (albeit light green) leaves on many
branches.
A few additional tree borers were
recorded on the banksias, including
the longhorn beetles: Tragocercus spencii,
Cnemoplites australis (Erichson, 1842)
and Toxeutes arcuatus (Fabricius, 1797),
weevil species (to be determined), and
lepidopteran larvae such as Psalidostetha
banksiae Lewin, 1805, also known as
the banksia moth. The main vertebrate
foliage browser, detected by presence
of scats and signs, was the common
brushtail possum Trichosurus vulpecula
(Kerr, 1792). Black cockatoo Zanda
funerea (Shaw, 1794) activity in the
plantings occurred in the form of stem
attack at the Tragocerus gall sites on two
of the banksias, the birds using their
powerful beaks to extract the larvae,
further damaging the plant in the
process. Clearly each of these species
contributes to the decline of some
banksia trees, but even where usage was
evident, all the trees remained alive, and
so no one species is likely to cause tree
death.
Discussion
Continual use of the banksia resource
by C. imperialis at ‘Templestowe’ was
conrmed by the increasing number
of emergence holes detected across the
period of study. By April 2022, over 54%
of the B. marginata specimens showed
sign of C. imperialis use. This level of
infestation, combined with damage
caused by other insects and vertebrates,
has resulted in the high mortality (over
20%) of the banksias within the rst
15 years of planting, suggesting that the
long-term viability of the banksias at
this site may be in doubt.
Despite the close proximity of the
plantings, the C. imperialis exploitation
appears highly localised, with the
inuence of plant position, i.e. ‘edge
effect’, notable. Easy access to larval
food plants appears to be important
to the selection of egg-laying sites by
The Tasmanian Naturalist 144 (2022)
86
the beetles; most favoured were the
banksias planted along tracks and other
open areas. The beetle’s ight pattern,
being slow and cumbersome and
therefore better suited to open areas,
may directly inuence the selection of
banksias in open positions. Frequency
of tree deaths, combined with increased
numbers of emergence holes in trees
adjacent to tracks appears to conrm
this, and it is supported by evidence from
the internally planted banksias, which
showed fewer signs of beetle attack,
albeit exhibiting reduced growth rates,
possibly as a result of light deciency
and competition with faster-growing
eucalypts.
However, other factors may contribute
to the localised beetle selection of
banksias. One potential explanation may
be the direct inuence of soil moisture
on banksia health, since the plants located
in more depauperate soils (shallower,
less nutrients) may have limited ability
to take up water and therefore suffer
reduced health. This could perhaps
signal to beetles a reduced capacity for
defence, thus attracting greater beetle
attention, beetles more likely to attack
trees in poor condition (Elliot & deLittle
1985). Alternatively, the proximity of
faster-growing eucalypts species with a
greater capacity for water uptake may
inuence banksia health, weakening
the banksia understorey, again making
them more prone to attack. While these
are possible explanations, it might also
be that a chemical signal emitted by
banksias following initial C. imperialis
usage attracts further beetle interest,
thus increasing the potential for further
infestations.
While it is clear C. imperialis inicts
signicant damage to many of the host
plants, a few banksias did reveal an
ability to heal emergence wounds. While,
in general, emergence holes expand
with tree growth and age, increasing
in diameter with the surrounding
bark cracking, occasionally a marked
emergence site would appear smaller
and misshapen, to the extent that it
would have been difcult to conrm its
origin without the marking of an ‘X’ to
signify a previous exit hole. Where this
was observed, the banksia tended to be a
faster-growing, healthier specimen.
The decline of banksias at
‘Templestowe’ is likely to have been
due to a combination of factors,
including dry summers, the locations
of trees planted on the higher ground
with poor soil structure and limited
water retention, as well as proximity
of natural populations of the beetle in
the landscape. Clearly there must be a
natural population of C. imperialis in the
stands of coastal banksia at Seymour.
What then does this mean for the future
of the ‘Templestowe’ banksias?
From the results, it appears likely that
C. imperialis will continue to target
specic trees in the conservation
planting, therefore the prospect of
additional banksia deaths remains high.
The survivorship of the banksias and
nal composition of the tree plantings
remains to be seen. The age at which
C. imperialis rst use trees is uncertain,
but previous research indicates that
the beetle prefers young banksia trees
(Richards & Spencer 2018). The nal
outcomes may hinge upon a combination
The Tasmanian Naturalist 144 (2022)
87
of factors including climate change,
which will impact rainfall levels, along
with the maturity of the banksias and
their resilience to beetle attack. It may
yet be that a proportion of the banksias
will survive the period of beetle attack,
since mature specimens are expected
to be less favourable to beetles. As the
trees mature, fatalities will likely decline,
the banksias becoming more able to
tolerate some level of infestation, while
the beetles continue targeting trees of
poorer condition.
Thus, while not all banksias will succumb
to C. imperialis use, consideration needs
to be given to replacing dead or dying
banksias. It is likely that replanting
banksias at this site will only prolong
the Cyrioides presence, so perhaps a
different suite of native trees or shrubs
less attractive to the beetle might be
introduced to the site into the future.
References
Elliot, H.J. & deLittle, D.W. (1985). Insect
Pests of Trees and Timber in Tasmania.
Forestry Commission, Tasmania,
Hobart.
Richards, K. & Spencer, C.P. (2018).
Exploitation of sapling Banksia
marginata by Cyrioides imperialis
(Fabricius, 1801) (Coleoptera:
Buprestidae) in Tasmania. The
Tasmanian Naturalist 140: 27–32.
Richards, K., Spencer, C.P., Quon, D. &
Quon, C. (2020). Impact of the jewel
beetle Cyrioides imperialis (Fabricius,
1801) (Coleoptera: Buprestidae) on
Banksia marginata revegetation at
Seymour, Tasmania. The Tasmanian
Naturalist 142: 61–65.
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