General Meeting Report:
March 15 Judy King
gave an
excellent talk on the introduced Sirex wasp, Sirex noctilio,
supported by computer-driven illustrations and annotations. Females don't sting, but have a huge saw-like ovipositor, orange legs, and are quite
large, up to 6 cm long (including antennae). Males are orange on the back and abdomen, with black legs and
wings. The larvae feed on a fungus growing
through
timber, Amyleostereum areolatum.
Females introduce the food fungus into the
tree when they lay there. They drill
holes into the bark, firstly to inject the fungal spores and a
phytotoxic
mucus. Stressed, damaged, or otherwise
unhealthy trees are targeted and if the female is satisfied the tree is
sufficiently unhealthy, she will then drill another hole and deposit up
to 400
eggs. The holes can be seen as pin
holes; beads of resin show where they are.
The mucus dries off the tree, the fungus causes a brown tea
staining as it grows and slowly kills it, from the bottom up. The needles go brown, the whole tree goes a
coppery brown colour.
The larvae tunnel through the
fungal-infested wood, pupate just under the bark. Tunnels
go in all directions and ruin the wood. The larva is
white and has a spine on its end.
Adults cut an oval emergence hole, 3-6mm in diameter. The life cycle is usually 1 year but can
take up to 3 years. Adults are present
from October to early May. They live a
few weeks and can fly up to 50 km.
The wasp is native to the Mediterranean
region of southern Europe from Spain to Turkey. It
now occurs in South America, New Zealand, the tip of South
Africa and southern Australia. Within
28-30 years of its appearance in New Zealand
it had devastated NZ softwood plantations.
In its native area it is not a problem, but
it has found its new host, Pinus radiata, to be very much to
its
liking. The pine plantations of
Australia had few pests until the advent of this wasp.
It was found in Tasmania in 1950-51 near
Hobart, and in the years 1952-59 killed 40% of the trees in an 1100 ha
plantation. It arrived on the mainland,
at Melbourne, in 1961 and an eradication program was started, to be
carried on
until 1972 when it was abandoned and a biological control program was
begun. This aimed at minimising damage,
as eradication was not possible. The
controls used are nematodes and parasitic wasps, as well as the removal
of
stressed or unhealthy trees. Then in
the 1980s there was a huge outbreak in South Australia.
Robin Bedding, of CSIRO, studied the life
cycle of the nematode and worked out how to manipulate it to control
the
wasp. The nematode has two parts to its
life cycle: a free-living cycle when it feeds on the Amylosterium
fungus, and a parasitic cycle where the female feeds on the wasp larva.
In a somewhat complicated process, the
nematodes sterilise the female wasps so that they lay sacs of nematodes
instead
of fertile wasp eggs, thus increasing the nematode population. The process is further assisted by the
injection of nematode larvae into trees affected by the fungus when
they under
5 days old as it is then that they become infective.
To do this, personnel use a special hammer with a small sharp
point to make a hole in suspect trees and inject (with a sauce bottle)
liquid
contained the nematodes.
Of the parasitic wasps introduced, only two
have been successful, Ibalia leucospides, which targets eggs
and very
small larvae; and Megarhyssa nortoni, which parasitises older
larvae; thus
covering a wide scope.
Sirex has reached Tenterfield and is
expected to arrive in Queensland soon.
It is likely that it will adapt to the warmer climate here, as
it has
done so in South America. The question
remains as to whether it will affect the other Pinus species that are
mainly
grown here.
Excursion
Report: Enoggera Army Reserve, March 21.
Thirty-four members and
friends arrived at the gates of the Gallipoli Barracks. A list of
people and
cars was presented to the gatehouse and we drove in convoy to the
barracks
reservoir.
The
weather was very pleasant. It was warm, overcast and with a
breeze. Our walk took us across the reservoir embankment, then uphill
along 4wd
tracks towards Enoggera Hill. The bush
thinned out and the canopy was higher as we moved away from the
reservoir.
The
breeze did not help birding. Twenty-four species were
sighted, the highlight being three Wedge-tailed Eagles, two large and
one
smaller, which patrolled low over us for some minutes. The three birds
were
quite dark and may have been old.
Weeds
were more obvious on foot than on the 4wd reconnaissance.
Molasses grass was widespread and flowering. In all 20 grasses were
identified,
with 10 introduced species. The
poisonous Rosary Bean, Abrus precatorius,
with its ricin load was common and caused some discussion.
Copies of
the keys for the eucalypts of Brisbane had been
distributed and many used them to good effect. Recent winds had brought
down
branches and uprooted some trees. The fallen branches with attached gum
nuts assisted
in identifying the species in our area. Some excellent examples of
Tallowood, E. microcorys, and E. major were
close to our path. Brush box, Lophostemon confertus
was common throughout; Forest Oak, Allocasuarina torulosa,common
on the
slopes.
Members
worked hard compiling lists of
plant species (including ferns and grasses), birds and butterflies. There were 118 species of plants, with 28
weed species and 5 spreading native plants.
One of interest was a small vine, Aristolochia
sp. ‘D’Aguilar’, not only for itself but also because there was a
final
instar larva of the Big Greasy butterfly, Cressida
cressida, feeding on it, having almost exhausted its supply of this
hostplant and with no others in sight.
Another interesting plant was Pultenaea
spinosa, more often found further north.
Several
larvae and pupae of the Common
Imperial Hairstreak butterfly were found on a Black Wattle, Acacia
leiocalyx, with many ants of the
genus Iridomyrmex in attendance. Only
three common species of skippers
(Hesperiidae) were seen, in spite of good conditions for grass, matrush
and
sedge growth, their main hostplants.
However, 37 species of butterflies were identified on the day.
Our
thanks to the Enoggera Army Unit for
permission to visit their reserve.
David Shaw
No.
789
Mystery frog
In
the handy guide, Wildlife of Greater
Brisbane, Greg Czechura, the author of the frog section, mentions
that Litoria
brevipalmata, the Green-thighed Frog is a >mysterious=
frog that
suddenly erupts in large numbers only to disappear quickly again. I personally had only seen one specimen on
two separate occasions over the last 15 years.
Recently, however, while with a group surveying the fauna of a
new
National Park near Ravensbourne, I had the good fortune to observe at
least 5
pairs mating in a small ephemeral pond in a gully in the forest and the
following night five patches of spawn were seen. Small
black eggs were suspended in a clear jelly-like substance,
which floated just under the surface.
Each oval patch of eggs was 130-150mm by 80-100mm in size.