Hypsipyla Shoot Borers of Meliaceae in Sri Lanka - Australian ...

Table 8. Summary of current and past research effort on
various aspects of Hypsipyla robusta biology and control.
o – none; * minor; ** major.
Area of study Current
research
Biology
Past
research
Biology
Taxonomy * o
Life history ** *
Ecology in natural stands * *
Ecology in plantations * *
Population dynamics * *
Natural enemies * *
Other o o
Control
Biological control o o
Chemical control o *
Silvicultural control * **
Host resistance * o
Pheromones * o
Genetic engineering o o
Other o o
There have been few attempts to investigate directly
the biology, ecology or taxonomy of H. robusta in
Australia. This is despite the recognition of the
critical role of the species in limiting the commercial
planting of T. ciliata. Early biological observations
were made by Froggatt (1923, 1927) and staff of the
Queensland and New South Wales forestry services,
much of which is contained in unpublished reports.
More recent work has been undertaken by Griffiths
(1997) and Mo (1996). These studies confirmed that
the shoots, fruits and the flowers of T. ciliata and the
fruit of the closely related Xylocarpus mangrove
species are fed upon by H. robusta in Australia.
Infestation of young T. ciliata trees was positively
correlated with rainfall and, to a lesser extent, temperature.
Infestations were concentrated on opengrown
trees, trees greater than 1.5 m high, and shoots
in the upper canopy. The percentage of shoots
attacked per tree decreased as tree size increased.
More than 75% of eggs were laid on leaves. When
ovipositing on young trees, H. robusta preferred the
upper leaf surface to the lower leaf surface, and was
least inclined to choose the stem and petiole. When
laid on fruits, eggs were often deposited among or
close to the frass and borings of previous damage.
Losses of both eggs and early instar larvae were high
on young T. ciliata trees. Initial feeding was concentrated
in the terminal foliage with larvae wandering
extensively before and in the few days following
their first feeding. Feeding bioassays confirmed the
existence of feeding stimulants in the ethanol
extracts of young shoots.
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The number of larval instars ranged from five to
seven under laboratory conditions. This developmental
polymorphism is also likely to be a characteristic
of natural populations. Success of matings was
increased by exposure to light and wind. Observations
on the patterns of female calling, mating and
flight activity indicated that mated females are
responsible for host finding.
There are considerable differences in the biology
and behaviour of the species in Australia when compared
with other regions. For example, Australia and
northern India share a similar climate and have the
same species of host trees, however, Australian
populations lack a distinct sequence of larval generations
feeding on different plant parts, have a very
low incidence of flower feeding, and have other
behavioural and physiological differences in larvae
feeding on fruit. These differences call into question
the assumption that H. robusta is one species.
Biological control
Although there has been some reference to the possibility
of obtaining control of H. robusta in Australia
through utilising natural enemies (Jolly 1914;
Queensland Forest Service 1921; K.G. Campbell,
formerly of the Forestry Commission of New South
Wales, pers. comm.) this possibility has never been
addressed. A number of reports have identified insect
parasitoids and insect, bird and mammal predators
associated with H. robusta in Australia (Queensland
Forest Service 1921; Girault 1938; Campbell pers.
comm.). However, most of these are generalist
species and offer little potential as biological control
agents (Sands and Murphy these Proceedings).
Chemical control
Chemical control of H. robusta has been investigated
in Australia since the early 1920s with the initiation
of at least 13 insecticide trials utilising 12 different
compounds. Most trials failed or were terminated
after only one season. The insect has proved difficult
to control due to its concealed feeding habit, long
period of activity, the tropical climate in which it
occurs, low damage threshold of the host, and long
protection period required. Many trials have been
hampered by logistical problems including a lack of
moth attack, severe damage from other insects,
equipment failure, and loss of trees to frost, cyclones
and hormone spray. In addition, the scheduled spray
regimes were frequently disrupted by rain and
flooding.
Contact poisons such as DDT and endrin provided
reasonable to good control in some trials. However,
the required frequency of application, particularly in
the tropical north where the period of heaviest