Journal of the Royal Society of Western Australia, 87:81-83, 2004 
Notes 
on .... 
Powdery bark in 
Eucalyptus accedens 
deters arthropods? An 
evaluation using ants 
J D Majer 1 , R D Cocquyt 1 and H F Recher 2 
1 Department of Environmental Biology, Curtin University of 
Technology, Perth, Western Australia 6845 
3 J.Majer@curtin.edu.au 
2 School of Natural Sciences, Edith Cowan University, 
Joondalup, Western Australia 6027 
3 hjrecher@pacific.net.au 
(Manuscript received January 2004 ; accepted June 2004) 
Abstract. Powderbark wandoo (Eucalyptus accedens) has a 
powdery triterpenoid-containing substance on the 
surface of its smooth bark, which is formed from 
sloughing peridermal cells. When compared with the 
similar-appearing wandoo (E. wandoo), which occurs in 
the same area and which does not accumulate powder, 
fewer bark-associated arthropods are found. Exposure to 
this powder accelerated mortality of the ant, lridomyrmex 
chasei, a species that tends scale and other sap-sucking 
insects on the foliage of eucalypts. Ants of this and two 
other species were unable to reach baits on the top of 
vertical wooden dowels that had been coated with 
powder taken from the bark of E. accedens. The powder 
may deter arthropods from living or moving on the bark 
by chemical or physical means. It is postulated that the 
function of the powder is to reduce the threat from 
herbivorous or scale-tending arthropods that may live 
on, or traverse, the bark of this species. 
species. They found that powderbark wandoo, when 
compared with wandoo, yielded generally lower 
numbers of arthropods (6301 vs 7754 individuals in bark 
traps on 20 trees) and fewer species (422 species from 140 
families vs 497 species from 159 families in bark plus 
intercept traps on 20 trees). These differences were 
significant for many of the invertebrate orders. 
Measurements of nutrient content of live and dead 
bark of the two tree species indicated some significant 
differences (Majer el al. 2003), but these differences were 
not consistent across elements, suggesting that nutrient 
levels are not a major determinant of the trends in 
arthropod levels on the two tree species. Our 
observations also indicate that there are no large 
differences in the bark roughness, presence of fissures, or 
general heterogeneity of bark microhabitats between the 
two species (see photos in Majer el al. 2002, 2003). It 
therefore appears that nutrient levels or gross bark 
texture is not related to the differences in arthropod 
assemblages between the two tree species. 
There are examples in the literature of leaves, fruits or 
stems of plants being covered with microscopic crystals 
of epicuticular wax, which may protect the plant against 
herbivorous invertebrates (Stork 1980; Edwards 1982; 
Eigenbrode 1996; Juniper 1995) or Hemiptera-tending 
ants (Haberlandt 1909). In view of the similarity in 
appearance of the trunks of the two eucalypt species in 
our study, and also the fact that they grow at the same 
sites, we postulated that the powder on the bark of 
powderbark wandoo contributed to the observed 
differences in arthropod abundance and richness. In this 
note, we report on the origin and nature of the powder 
of powderbark wandoo and the possible role of the 
powder in limiting arthropod use of the trunk of the tree. 
Methods 
Keywords: Tree trunk, invertebrate. Eucalyptus forest, 
powder. Eucalyptus accedens. 
Introduction 
Bark provides a wide range of refugia for 
invertebrates and represents an important source of 
nutrition to such animals, either directly, or through the 
fungi, lichens, algae and microorganisms that live on and 
within it. It also acts as a resting place for invertebrates 
that move within or across the area in which the trees 
occur. As part of a larger study of the fauna associated 
with trunks of Australian eucalypts, we recently 
examined the arthropod fauna associated with wandoo 
(Eucalyptus wandoo) and powderbark wandoo (E. 
accedens) in the Western Australian wheatbelt (Majer et al. 
2002, 2003). 
Both species possess exfoliating bark and have 
smooth, light-coloured trunks that are similar in 
appearance. Powderbark wandoo differs from wandoo 
in having a bark that is covered in a powdery substance, 
from which it receives its name. Majer et al. (2002, 2003) 
quantified the species richness and general abundance of 
various arthropod orders on the bark of these two tree 
© Royal Society of Western Australia 2004 
The study was undertaken in wandoo/powderbark 
woodland at Dryandra (32° 56'S, 117° ll'E), southwest 
Australia, approximately 160 km south-east of Perth. 
Trees were distributed throughout a 20 ha section of the 
administrative compartment known as Peters Block; 
powderbark wandoo trees tended to be on the upper 
half, while wandoo trees tended to be on the lower half 
of the landscape. Except where indicated, all 
measurements and samples were taken at 1.5 m above 
the ground. It was not possible to measure live bark 
because it merged in with other living tissue of the trunk. 
However, both species decorticate bark, so the thickness 
of 10 samples of freshly-fallen bark beneath each tree was 
measured with a micrometer. 
Powder was collected from powderbark wandoo trees 
using a clean paint brush by brushing the trunk in a 
downwards motion into a plastic food container. This 
material was stored in a refrigerator at 4°C. Sub-samples 
were plated on malt agar to see if there were any 
associated microorganisms. These were identified by a 
local specialist. A Liebermann-Burchard test (Brieskorn 
and Herrig 1959) was performed on the powder to test 
for the presence of triterpenoids. Slivers of phelloderm of 
both species were also collected for sectioning and 
microscopic examination. 
To examine the impact of powder on arthropods, five 
filter paper discs were dipped in bark powder, and the 
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