Mortality of Immature Lepidop Tera: A Case Study with Heliothis Species (Lepidoptera: Noctuidae) In Agricultural Crops on the Darling Downs

Titmarsh , I.J. (1992) Mortality of Immature Lepidop Tera: A Case Study with Heliothis Species (Lepidoptera: Noctuidae) In Agricultural Crops on the Darling Downs. PhD thesis, University of Queensland.

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Heliothis annigera (Hiibner) and Heliothis punctigera Wallengren are "arguably the most important pests, insect or otherwise, of field crops in Australia". Their pest status broadly derives from a suite of characteristics - polyphagy, high mobility, high fecundity, and a facultative diapause - that enables them to survive in unstable habitats. These also make the species ideally suited to exploit the conditions of continuous change within agroecosystems. Over the last forty years in Australia, agricultural development has increased vastly the expanse and favourability of the temporary habitats available for Heliothis development. In effect, the probability that migrants will survive movements among habitat patches has increased. From a Heliothis management perspective, where immigration is important to local population dynamics control strategies arc limited to either discouraging prospective immigrants or increasing local mortality rates. Significant migration events in early spring, especially by Hgunctigera, apparently initiate Heliothis infestation of many agricultural areas, including the Darling Downs. This influx from "unknown" sources (possibly central Australia) is less common in H.armigera, but the later emergence of local individuals from diapausing pupae assures this species is well represented each season. As there is little practical way in which field workers can distinguish between the eggs of immigrant and local moths of either species, a pragmatic fvst step towards reducing the local Heliothis problem is to study local mortality factors to determine if, and how, increases in mortality rates might be achieved. A three-year study was undertaken to provide both qualitative and quantitative information on the natural mortality of Heliothis individuals infesting fields of agriculturally important plant species during the summer growing season on the Darling Downs of south-east Queensland. In-field variation in mortality was more important than variation in natality (the number of eggs laid) in determining the numbers entering subsequent Heliothis developmental stages; except on sunflower, where natality was the more important influence. On all plant hosts, agespecific life tables showed mortality affected the Heliathis eggs and fust instar larvae most severely, the latter being the critical stage influencing total intra-generational mortality and hence the subsequent larval infestation levels of particular fields. The causes of this mortality generally were not identified during direct observation.....

Item Type: Thesis (PhD)
Additional Information: Dr Myron Zalucki, as my supervisor, has caused many hours of mental gymnastics. Not only because of his clear and intuitive interpretations and understanding, but also through his manner of "guide and prompt" rather than "lead and tell".
Author Affiliation: University of Queensland
Subjects: Plant Protection
Statistics and Experimentation
Divisions: General
Depositing User: Mr Arbind Seth
Date Deposited: 28 Jul 2013 10:06
Last Modified: 28 Jul 2013 10:06

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