A Stem Gall on Muehlenbeckia australis (Forst. f.) Caused by the 
Moth Morova subfasciata Walk. 
B. C. Arnold 1 
The rampant, much-branched liane Muehlen- 
beckia australis is a familiar sight in many New 
Zealand forests, reaching into the tops of trees 
30 feet high with woody ropelike stems, or 
heaped in a tangled mass where no support is 
provided by other plants. 
Among the branches of Muehlenbeckia aus- 
tralis are sometimes found persistent woody 
hypertrophies which arise as spindle-shaped or 
nut-shaped galls on one-year-old stems. The 
diameter of the young galls may be about five 
times that of the stems on which they arise 
(Fig. 1). 
During the first year of growth, galls of M. 
australis are found to contain either the dark 
pupa of a moth, or the pale larva (Fig. 2) 
which actively feeds on the tissues of the pith. 
An exit passage for the later escape of the 
adult moth runs from the centre of the gall 
towards the surface, but stops short, separated 
from the outside wall by a thin membrane. 
Galls from which the small tawny moths 
(Fig. 3) have emerged can be recognized by the 
open escape hole. 
In a discussion on gall insects, Brues (1946) 
made a comparison of plant galls with animal 
tumours, stating that "the gall continues to 
develop only under the sustained action of the 
stimulating agent, while the growth of the ani- 
mal neoplasm is not thus limited.’’ Brues did not 
refer to the well known exception of crown gall 
(Mani, 1964), probably because of its relation 
to bacteria and not to insects. Brues’ claim may 
be valid in a general way since few cases of the 
continued growth of galls in the absence of the 
causal agent have been reported. Undoubtedly 
the moth-induced gall of M. australis is one of 
the few known exceptions. 
One aim of this study was to examine the 
histological make-up of the galls for any evi- 
1 Department of Botany, University of Canterbury, 
Christchurch, N.Z. Manuscript received August 31, 
1965. 
dence of cellular transformation which might 
be associated with differences in growth be- 
tween the gall and the normal stem. A second 
objective was to test extracts of the moth 
larvae for growth-stimulating capacity on stems 
of seedlings of M. australis. Finally, it was hoped 
to induce galls under laboratory conditions with 
young living larvae, preferably newly hatched 
from eggs. 
This work was supported by a research grant 
awarded by the University of Canterbury Grants 
Committee. 
METHODS AND MATERIALS 
Four dozen seedlings about 6 inches in 
length were dug up in the forest and grown 
separately in 4-inch plastic pots in a glasshouse 
in a mixture of gravel, sand, and garden loam. 
Growth over 18 months was active and healthy. 
Five active larvae were removed from their 
galls and immersed entirely in 1 ml pure 100% 
acetone. The larvae were crushed thoroughly in 
the acetone in a glass vial with a glass rod and 
were left in the stoppered vial for a week. The 
acetone was evaporated with the temperature at 
25 °C. To the dry residue of the ground-up 
larvae in the original vial was added 2 ml an- 
hydrous lanolin, which was mixed thoroughly 
with the larval material (using a glass rod) to 
give even dispersal. 
To each of 12 Muehlenbeckia seedlings a 
small globule of the paste mixture was added in 
the axil of a young leaf near the stem tip. 
With 12 other Muehlenbeckia seedlings, the 
tip of a shoot was removed in front of a node 
and a small blob of the paste mixture was 
placed on the cut surface on each plant. 
On 12 other seedlings small blobs of paste 
mixture were applied to the abaxial surface in 
the centre of young leaves. 
The remaining 12 seedlings were treated on 
cut shoot surfaces with plain lanolin lacking 
larval extract. 
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