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The Tasmanian Naturalist 141 (2019)
120
A new larval host plant for Tragocerus spencii Hope,
1834 (Coleoptera: Cerambycidae) in Tasmania
Karen Richards & Chris P. Spencer
141 Valley Road, Collinsvale, Tasmania 7012
spenric@gmail.com
Whilst investigating the use of Banksia
marginata saplings by the jewel beetle
Cyrioides imperialis Fabricius, 1801 near
Cleveland in June 2018 (Richards &
Spencer 2018), the authors observed
sizeable stem galls on a number of the
juvenile trees; these occurred between
30 cm – 2 m above the ground (Plate 1).
Many galls displayed emergence holes
similar in size, but differing in shape, to
those formed by C. imperialis (Plate 2).
Multiple emergence holes, varying in age,
were observed on some galls, suggesting
successional larval occupation; those
considered older showed dead wood
encircling the inner section of the hole
whereas the occupied ones displayed
fresh grazing scars. For the most part,
the saplings above the galls showed
no negative effects resulting from the
stem incursion (i.e. no dead trees were
recorded as a result of larval activity),
Plate 1. Banksia marginata stem gall with
emergence hole of Tragocerus spencii.
Button diameter: 10 mm.
Plate 2. Emergence hole of Cyrioides
imperialis in Banksia marginata stem.
Button diameter: 10 mm.
The Tasmanian Naturalist 141 (2019)
121
although some trees did exhibit small
dead patches on the stem immediately
beneath the swelling.
The unaffected stem diameter at the
base of the galls ranged from 40 x 32
mm and 53 x 45 mm. Gall dimensions
signicantly increased the stem girth
of the aforementioned, to 70 x 52 x 42
mm and 150 x 78 x 62 mm respectively;
indicating that the larval presence
induced abnormal stem growth,
approximately doubling the girth over the
gall length. Emergence hole dimensions
varied between 10 x 7 mm and 14 x 7
mm; the shape was consistently oval,
and the maximum dimension randomly
oriented. The location of emergence
appeared arbitrary, with exit holes
occurring both near the top and base of
galls; nor was there any evidence of an
orientational preference.
Several galls, with and without
emergence holes, were collected in an
effort to rear out the occupants. These
were housed inside a plastic crate with
a substrate of moistened paper towel
and stored at constant temperature
(12°C). Upon close examination, some
emergence holes displayed evidence of
fresh phloem grazing around the inside
of the hole, suggesting the occupant was
still in residence. A gall possessing one
such emergence hole was split (Plate 3)
to reveal a coleopteran larva of 38 x 11
mm (Plate 4). The larva conformed to
the general description of Cerambycidae,
(elongate sub-cylindrical body, lacking
sclerotised thoracic plates, three
pairs of short legs, dorsal and ventral
locomotory ampullae on abdominal
segments); but in this instance lacking
a process on the abdominal tergum 10,
as evidenced in some other cerambycid
larvae e.g. Uracanthus pallens Hope, 1841
(Duffy 1963; Richards & Spencer 2017).
After carefully reinstating the larva in
its chamber, the gall was repaired using
cable ties and wood frass paste to seal
the saw cut. Conrmation of identity
was established a few months later,
when a male Tragocerus spencii Hope, 1834
emerged. An additional two males and
a female emerged from other galls over
the subsequent week, including one from
a hole displaying fresh grazing scars, as
described above. Adult female T. spencii
are generally larger than males, but given
the variability in hole dimensions from
which the specimens emerged, it was
not possible to differentiate between
those formed by male or female beetles.
Following eclosion, one gall possessing
two emergence holes was dissected to
establish patterns of larval activity. The
two larval galleries within were spatially
separated with no connection, each
having a central bore linking the pupal
chamber to grazing areas in the sap-
wood; the older of the two exhibited
areas of dead wood with no fresh
grazing scars.
Plate 3. Opened Banksia marginata gall
showing larval tunnelling.
The Tasmanian Naturalist 141 (2019)
122
Tragocerus Latreille, 1829 is an Australasian
cerambycid genus containing eight
described species, one from New
Guinea, the others from the Australian
east coast (with one species also recorded
from Western Australia) (Ślipiński &
Escalona 2016). Adult Tragocerus are
reported to be diurnal blossom feeders,
recorded from Angophora, Eucalyptus,
Hakea, Leptospermum, Xanthorrhoea and
Melaleuca species (Ślipiński & Escalona
2016). Tragocerus spencii (Plate 5) is the
only member of the genus recorded
in Tasmania (Semmens et al. 1992),
it also occurs in coastal SA, Vic and
NSW (Atlas of Living Australia 2019).
This species has previously been reared
from Eucalyptus amygdalina (Bashford
1990) and an unidentied species of
Banksia (Williams 1985). The authors
have recorded adult T. spencii feeding
on Hakea sp., Leptospermum laevigatum,
L. scoparium, Eucalyptus obliqua and on
Coriandrum sativum (coriander) blossom.
Only one other author mentions the
feeding behaviour of the larvae. Williams
(1985), writing on larval host plants for
a number of buprestid and cerambycid
species, noted that “dead and dying
stems of young Banksia sp. were
girdled by adults and the larvae bored
downwards in these dying sections”;
however, neither Williams nor Bashford
made any reference to gall formation.
The larval activity we observed differs
substantially from that described by
Williams, and no stem girdling by
adults was recorded. The current paper
provides the rst conrmed record of T.
spencii larvae using B. marginata as a food
plant in Tasmania, as well as the resulting
formation of stem galls, which may host
successive generations of the species.
Plate 4. Tragocerus spencii larva.
The Tasmanian Naturalist 141 (2019)
123
References
ALA (2019). Tragocerus spencii. Accessed
online August 2019.
Bashford, R. (1990). Tasmanian forest
insects and their host plants. Forestry
Commission, Tasmania.
Duffy, E.A.J. (1963). A monograph of the
immature stages of Australasian timber
beetles (Cerambycidae). Trustees of the
British Museum, London.
Richards, K. & Spencer, C.P. (2017).
New distribution and food plant
observations for several coleopteran
species in the Tasmanian Central
Highlands, summer 2017. The
Tasmanian Naturalist 139: 99–106.
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.
Semmens, T.D., McQuillan, P.B. &
Hayhurst, G. (1992). Catalogue of the
Insects of Tasmania. Department of
Primary Industry, Hobart, Tasmania.
Ślipiński, A. & Escalona, H.E. (2016).
Australian longhorn beetles (Coleoptera:
Cerambycidae) Volume 2 Subfamily
Cerambycinae. CSIRO Publishing,
Canberra.
Williams, G. (1985). New larval
food plants for some Australian
Buprestidae and Cerambycidae
(Coleoptera). Australian Entomological
Magazine 12: 41–46.
Plate 5. Tragocerus spencii adult. Overall length: 32 mm.
The Tasmanian Naturalist 141 (2019)
124
