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Phenology of autumn gum moth, Mnesampela privata (Guenee) (Lepidoptera: Geometridae)


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Lukacs, Zoltan (Stanley) 1999 , 'Phenology of autumn gum moth, Mnesampela privata (Guenee) (Lepidoptera: Geometridae)', PhD thesis, University of Tasmania.

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The autumn gum moth, Mnesampela privata (Guenee) (Lepidoptera: Geometridae),
is an economically important pest of young eucalypt plantations, particularly those of
Tasmanian blue gum, Eucalyptus globulus Labill., and shining gum, E. nitens (Deane
& Maiden) Maiden, which are grown in commercial pulpwood plantations in
southern Australia. M privata is also a pest of flooded gum, E. grandis W. Hill
ex Maiden, plantations grown under irrigation in southern Australia outside that
tree's natural range. A major difficulty associated with M. privata management is
detecting large populations before host trees are severely damaged. Early detection
of populations is difficult because outbreaks are sporadic and may be localised, and
also because the seasonal occurrence of pest activity varies in some parts of its
geographic range. Damaging larval populations on the Australian mainland are
largely restricted to the autumn period, April to June, by which time most larvae have
pupated. In contrast, pest incidence usually extends from autumn to spring in
lowland areas of Tasmania, whereas at altitudes above 500 m ASL in Tasmania, pest
incidence usually extends from summer to autumn.
The primary objectives of this study were to identify the underlying
mechanisms influencing the phenology of M privata and to identify possible causes
of geographic variation in the phenology of the species, thereby increasing our ability
to predict the seasonal occurrence of pest activity throughout the distribution of the
Laboratory studies found that the phenology of adult M privata was
influenced by alternative developmental pathways initiated at specific points in the
pupal stage. A diapause or non-diapause pathway was possible early in the pupal
stage before adult differentiation began. Pupal diapause was induced by short
daylengths and low temperatures experienced during larval development and averted
by long daylengths and high temperatures, suggesting that M privata is a long-day
species (Type I of Beck's classification). Also possible before adult differentiation
began (in non-diapause pupae) was an aestival or non-aestival pathway. Low
temperatures led to continued development, high temperatures to aestivation. Unlike
diapause, which could only occur before adult differentiation began, aestivation
could also occur late in the pupal stage, enabling pharate adults to delay eclosion. The generation time of M. privata was approximately 1268 degree-days (DD)
above a developmental threshold of 5°C, consisting of 784 DD for egg-larval
development and 484 DD for pupal development. However, the period between
oviposition and the fourth instar, or `time-to-L4' (requiring 390 DD > 5°C) is
especially important as it represents the lead time between peak oviposition and the
onset of severe damage. At mean daily temperatures of around 12°C, typical of field
temperatures experienced by M privata during egg-larval development, time-to-L4 is
around 56 days. Hence, large populations of M. privata must be detected and
controlled within about two months of peak oviposition in order to minimise damage
to host trees.
Mnesampela privata females selectively oviposited on expanding terminal
shoots, but did not appear to discriminate on the basis of whether or not conspecific
eggs were present. It is considered that such oviposition behaviour may lead to
overexploitation of resources, but does not fully explain the eruptive population
dynamics of the species. Sedentary adult behaviour was observed on two evenings in
elevated plantations in Tasmania during summer, suggesting that low temperatures in
autumn in those areas might preclude nocturnal reproductive activity.
The incidence of larval feeding activity in Victorian blue gum plantations
surveyed at the end of summer was extremely low, suggesting that extensive damage
by M privata during summer is highly unlikely outside of Tasmania. Larval feeding
damage in the surveyed areas is thus likely to be restricted to the autumn-winter
It was concluded that pupal diapause and pupal aestivation are the primary
mechanisms regulating the phenology of M privata and that the interaction between
these mechanisms and local environmental conditions causes geographic variation in
the phenology of the species. The findings of this study will provide a basis upon
which reliable predictions may be made in relation to M. privata phenology.

Item Type: Thesis - PhD
Authors/Creators:Lukacs, Zoltan (Stanley)
Keywords: Moths, Eucalyptus
Copyright Holders: The Author
Copyright Information:

Copyright 1999 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Library has additional copy on microfiche. Thesis (Ph.D.)--University of Tasmania, 1999. Includes bibliographical references

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