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| Rural Industries |
Objective
Background
The Banksia moth, Arotrophora arcuatalis, is a pest of
banksias grown under plantation conditions for the cut flower
market. Eggs are laid on the surface of the flower spike early
in its development and the larvae bore into the fruit. Although
the biological damage is minor, the distortion caused in a flower
by a single larva renders it cosmetically unacceptable. The larvae
can be killed by insecticide sprays whilst on the surface but
once they tunnel inside they are effectively immune to contact
insecticides. It is therefore important to synchronise spray schedules
with egg-laying by the adults and emergence of the larvae from
the eggs. A monitoring system based on sex-pheromones would provide
a non-labour intensive method of doing this.
Research
Banksia flowers with identified larval entries were collected
in South Australia and sent to the Division of Entomology in Canberra
where the adult moths were allowed to emerge in a temperature
and light-controlled environment. Pheromone glands were excised
from the females, extracted with solvents and analysed using gas
chromatography (GC). The electroantennogram (EAG) technique was
used to study responses from male moth antennae to compounds with
chemical configurations similar to the sex pheromones of most
moths.
Outcomes
The amounts of material present in the sex pheromone glands was
very small (<100pg per moth). So it was necessary to pool the
glands from at least 20 individuals to provide enough material
for GC analysis. The GC traces showed large variations between
extracts in the amounts of material present and the pattern of
peaks. A peak for (Z)-11-tetradecenyl acetate was found consistently
with the corresponding alcohol appearing less frequently. Indications
of a 12-C acetate or 14-C aldehyde were also sometimes present.
Other peaks appeared in only single records. The overall assessment
of the contents of the pheromone glands is confusing except for
(Z)-11-tetradecenyl acetate.
EAG investigations on the male antennae confirmed a 14-C acetate
with the double bond at the 11th position as the most likely compound
for the main component of the pheromone in agreement with the
GC data. Single cell recordings confirmed responses from most
sensilla to the same compound but none to any 14-C alcohol. A
survey of aldehyde compounds found very strong single cell responses
to (Z)-9-tetradecenyl aldehyde.
With no clear indication of the composition of the sex pheromone
from the data available, baits were prepared using (Z)-11-tetradecenyl
acetate and other compounds which at times appeared on the GC
graces. When these were sent to South Australia they did not trap
any insects. Neither did male moths respond to the various combinations
in a wind tunnel. One would have to conclude that we did not manage
to identify some essential components of the pheromone. These
were either absent or in too low a concentration to be detectable
by the GC. Whether the aldehyde detected by electrophysiology
is a component of the pheromone or an inhibitor could not be determined.
Attempts at mating the insects in the laboratory failed and this
suggests that the environmental conditions necessary for the mating
behaviour of the insect to be properly expressed were not reproduced.
One reason may be that the females were not producing and releasing
their pheromone for mating which may explain why the amounts of
compounds found in the glands were so small.
Implications
Although some progress was achieved and the major component of
the pheromone was probably identified, it is clear that the full
range of compounds was not detected probably due to incompatibilities
in the environment conditions required by the insect. If another
attempt at pheromone identification were to be made one would
have to consider how and where to collect the pheromone glands
from the females. Sending further batches of infected fruit from
South Australia to Canberra is unlikely to succeed.
The best course of action would be to collect pheromone from the
females in their natural environment. Unfortunately pheromone
collection requires expertise and would require someone from South
Australia to be trained at the Division of Entomology. It would
be up to the industry to consider whether they would meet the
expense involved together with the costs of analysing any collected
material.
RIRDC Project No: CSE-64A
RESEARCHERS: Dr T E Bellas, Dr E R Rumbo
ORGANISATION: CSIRO Division of Entomology
Black Mountain Laboratories
Clunies Ross Street
ACTON ACT 2601
PHONE: 06 246 4093 (Bellas)
PHONE: 06 3214 2524 (Rumbo)
Last updated: 22 November 1996
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