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Biology of the mountain pinhole borer, Platypus subgranosus Schedl, in Tasmania


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Candy, Steven Gregory 1990 , 'Biology of the mountain pinhole borer, Platypus subgranosus Schedl, in Tasmania', Unspecified thesis, University of Tasmania.

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Information on the life cycle and associations of the mountain pinhole borer,
Platypus subgranosus Schedl (Coleoptera : Curculionidae : Platypodinae) is reviewed.
Existing unpublished data combined with data collected in this study are used to
provide quantitative descriptions of aspects of P.subgranosus biology.
The within-tree spatial pattern of attack was found to be highly aggregated both
at high and low density of attack. Aggregation was very high around host tissue
infected with the pathogenic fungus Chalara australis Walker and Kile. A minimum
spacing between pinholes of approximately one centimetre was indicated but densities
were not sufficiently high for this to result in spatial regularity. Use of larval head capsule width and body length in a non-hierarchical
classification procedure confirmed the presence of five instars. Initial oviposition
occurred when the gallery ranged between 5 and 25cm in length. The natality rate at
initial oviposition was roughly one egg per centimetre beyond an initial length of 4cm.
Initial oviposition in galleries established in the late summer/autumn period occurred at
roughly the same date irrespective of establishment date. This was paralleled by a faster
rate of gallery development for autumn compared to late summer establishment.
Timing of emergence exhibited an analogous trend to that of initial oviposition. It is
postulated that these trends as well as a trend for emergence and subsequent gallery
establishment to occur less commonly in spring/early summer than late summer/autumn
are a response to high mortality of eggs and early instars in summer from desiccation.
For a sample of galleries established in the late summer/autumn period, initial
oviposition occurred in winter one to eight months after gallery establishment with eggs
usually laid in a batch with median size of seven. First to third instars appeared through the following spring and early summer with fourth and fmal instars appearing in
summer and subsequently the fmal instar predominating through winter until pupation
in the following spring. Emergence began in early summer.
A new model of insect phenology based on conditional probabilities is
developed and compared to existing ordinal regression and gamma entry time models.
The sex ratio of emergents over the population is very close to unity but
individual galleries can deviate markedly from this with an excess of either sex. The
mean number of emergents per gallery was 19.7 with a maximum of 92. The gallery
failure rate was 8% but negligible mortality of immature stages was observed. Development time ranged from ten months to two years depending on the
timing of gallery establishment as predicted by the linear day-degree model. Threshold
temperature for development and total day-degrees above this threshold from gallery
establishment to emergence, DD, were estimated from field data at 11°C and a mean of
DDii of 4047 respectively. A new estimation procedure based on maximum likelihood
is developed to estimate the parameters of the day-degree model under ambient
temperatures. Both gamma and inverse normal distributions were found to adequately
describe the empirical distribution of DD ii . Only for the gamma, though, was the
estimation algorithm successful.
The implications of P .subgranosus biology for rainforest ecology and
management are discussed.

Item Type: Thesis - Unspecified
Authors/Creators:Candy, Steven Gregory
Keywords: Platypus (Insect), Ambrosia beetles
Copyright Holders: The Author
Copyright Information:

Copyright 1990 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:

Includes bibliographical references (p. 176-183). Thesis (M.Agr.Sc.)--University of Tasmania, 1991

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