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Ecology, behaviour and integrated control of cabbage insect pests in Tasmania

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Alishah, A (1987) Ecology, behaviour and integrated control of cabbage insect pests in Tasmania. PhD thesis, University of Tasmania.

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Abstract

The cabbage white butterfly (CWB), diamondback moth
(DM) and cabbage aphid (CA) are the most important pests
of brassica crops in Tasmania.
The basic biology and ecology of these pests were studied
in laboratory and field experiments and commercial cabbage
crops. Key biotic and abiotic factors influencing the
seasonality and abundance were identified by regular
sampling. Populations of CWB and DM were markedly seasonal
with maximum densities recorded in December-January. In
contrast, CA persisted in cabbage fields throughout the
year and was the most abundant in spring and autumn.
Number of generations of each species was related to the
amount of heat they experienced as measured by degree-days
and were 5, 5 and 13 for CWB, DM and CA respectively.
Direct counts of insects per plant were the most reliable
measure of abundance as conventional trapping techniques
sampled insects in general flight rather than the
population on the crops. Natural enemies were
insignificant factors in population regulation.
In the examination of the insect-plant interaction,
the cabbage plant was classified into 6 readily
identifiable growth stages, the development of which
required a specific number of degree-days. The cabbage
plant was able to compensate for insect damage however,
attack by CWB at cupping, DM at early cupping, and pre
heading and CA at post seedling, cupping and pre heading resulted in irreversible losses in vegetative growth and final marketable product. Plant sensitivity to defoliation
is discussed in relation to the growth and development
pattern of cabbage plant.
Regular insecticide sprays promoted pest resurgence
while lack of sanitation e.g. non-removal of crop wastes
and residues, inappropriate insecticides and time of
applications were found to be common features in
commercial fields that aggravated pest status. A
beneficial consequence of this study was that regular
monitoring of crop and destruction of stubbles and crop
residues became part of the commercial grower's programme.
Criteria for spraying decisions were developed based on
the kind and frequency of chemicals employed, the plant
growth stage and the density and stage of the respective
pests.
Integrated control schedules including chemical
insecticides and bacterial, fungal and nematode pathogen
formulations were compared to recommended spray schedules.
Although less damaging to natural enemies these
alternative treatments were unreliable being dependent on
appropriate plant growth stage and environmental
conditions for effectiveness. Resource partitioning in
multipest infestations was observed and the unilateral
impact of infestation on plant economy was quantified.
Spray application decisions based on plant stage and
minimum damaging pest levels provided economic control for
a lower cost.
Oviposition and larval damage of lepidopterans were directly related to the degree of waxiness of cabbage
cultivars. In contrast, CA was not affected by waxes but
utilizes an alternative strategy involving direct testing
(probing) and plant water status. Non-preference was the
dominant mode of cabbage plant resistance to pest
infestation.
Experimental disruption of the leaf wax bloom by
solvent sprays or systemic wax inhibitors was found to
suppress oviposition and larval feeding in CWB and DM and
alate colonization and larviposition by CA. The
physiological and chemical basis of this phenomenon was
investigated and it is hypothesized that CWB and DM
behaviour is modified by changes in levels of wax
components notably alkanes, ketones, alcohols, aldehydes
and the triterpenoids a and (3 amyrin while CA is directly
influenced by water status of plant as determined by
probing.
In summary, this dissertation provides :
(i) a practical appraisal of cabbage pest control
in terms of materials employed and cultural
practices and makes recommendations for
decision making related to pest infestation
levels and plant growth stage and ;
(ii) an alternative explanation to the mechanism
of host plant selection by insect pests.

Item Type: Thesis (PhD)
Keywords: Cabbage
Copyright Holders: The Author
Copyright Information:

Copyright 1987 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:

Thesis (Ph.D)--University of Tasmania, 1988. Bibliography: p. 391-435

Date Deposited: 25 Nov 2014 00:44
Last Modified: 23 Aug 2017 05:20
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