Bibliography: leaves 233-263. / xxix, 263, 14 leaves. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1999

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This thesis was designed to address three seldom studied aspects of the relationship between herbivores and vegetational diversity. 1. Interactions between vegetational diversity and herbivore mortality due to predation were assessed by experimentally manipulating both the species diversity of plants and the densities of a common generalist predator, the spider Enoplagnatha ovata. 2. The importance of plant size to herbivore densities was examined by quantifying plant size (measured as plant height, width, leaf area and growth rates) and adjusting for it through covariate analysis. 3. Differences in population responses of several species of herbivores to both vegetational diversity and a predator, were compared by concurrently studying four lepidopterans. The main experiment used a two factor design, with two planting treatments and two predator treatments. The planting treatments consisted of plots planted with monocultures of brussels sprouts (Brassica oleraceae) and dicultures of brussels sprouts intercropped with peppermint (Mentha piperita). The natural enemy treatments involved augmentations of E ovata in some plots and untreated controls. Two of the herbivores studied, Plutella xylostella and Pieris rapae are monophagous lepidopterans, specializing on crucifers, while the others, Autographa californica and Mamestra configurata are polyphagous. For two species, P. xylostella and M. configurata responses to augmentations of the spider, E. ovata. were different in monocultures and dicultures. Reduced densities of these two species were found in monoculture plots with added spiders; in dicultures increased densities were found in plots with added spiders. This interaction effect points out that generalist predators can be effective in monocultures. I suggest that the importance of natural enemies in monocultures is often overlooked because only the initial colonization phase is being studied. By augmenting predator populations I was able to simulate densities equivalent to those in more established cropping systems. The increased herbivore densities in dicultures with added spiders might be explained by possible predation by E. ovata on other natural enemies of P. xylostella and M. configurata in dicultures but not in monocultures. Supporting evidence for this interpretation lies in the fact that percent parasitism of P. xylostella by the ichneumonid, Diadegma insulare was lower in plots with added spiders than in control plots. Furthermore, parasitism of P. xylostella by D. insulare increased with host density in diculture plots, but not in monoculture plots. Mamestra configurata was not subject to parasitism in this study, precluding assessment of a similar relationship. No A. californica larvae were found in plots with additional spiders. In contrast, P. rapae larvae were not affected by the experimental treatments. Plant size was a crucial determinant of both herbivore populations and percent parasitism of those herbivores. Most importantly, had plant size not been accounted for, the importance of vegetational diversity to both herbivore densities and percent parasitism would have been overestimated. For example, the incorrect conclusion, that vegetational diversity alone was important in determining the abundance of both of the generalist feeders would have been reached. The greater densities of A. californica in monocultures and M. configurata in dicultures were accounted for by plant size. Without plant size adjustments, percent parasitism of P. xylostella by D. insulare would have been misinterpeted as being greater in monocultures than dicultures. With plant size adjustments, the importance of E. ovata augmentations on lowering percent parasitismwas unmasked. All important interaction effects were discovered only after adjustments for plant size had been made. Despite the low densities of all herbivore species, significant responses to experimental treatments were found in three of the four species studied. Only P.l rapae was unaffected by any of the treatments. However, conclusions based on the feeding ng habits of the herbivores could not be made. The polyphagous feeders were affected by generalist predation as much as the crucifer specialist. Parasitism was found in only two of the species, P. xylostella and A. californica. Of these two species parasitism of the specialist, P. xylostella was affected by both vegetational diversity and generalist predation, whereas parasitism of A. californica was not. My study emphasizes multifaceted interactions between the size and diversity of a primary resource and several trophic levels of consumers. Multifactor models, involving several aspects of a cropping system, are required to uncover the important mechanisms behind variable herbivore responses to vegetational diversity. / Land and Food Systems, Faculty of / Graduate

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Competitive exclusion has been the mechanism hypothesized to account for the biological control of fire blight disease of pear and apple by the bacterium Pseudomonas fluorescens A506 (A506). Recent laboratory assays demonstrated, however, that A506 produces an antibiotic that is toxic to the fire blight pathogen, Erwinia amylovora, when cultured on media amended with iron (Fe����� or Fe�����). This study investigated this iron-dependent antibiosis by A506 by: 1) examining bioavailability of iron to A506 on blossom surfaces, 2) mutagenizing A506 to disrupt genes involved in antibiotic production, and 3) evaluating suppression of fire blight by A506 when co-treated with an iron chelate (FeEDDHA). Bioavailability of iron on blossoms was investigated with an iron biosensor [iron-regulated promoter (pvd) fused to an ice nucleation reporter gene (inaZ)] in A506. A506 (pvd-inaZ) expressed high ice nucleation activity (INA) on blossoms indicating a low-iron environment unlikely to induce antibiosis by A506. Spraying blossoms with FeEDDHA at concentrations ���0.1 mM significantly suppressed INA by A506 (pvd-inaZ). Transposon mutagenesis was used to generate and select mutants of A506 exhibiting altered antibiotic production profiles. One antibiotic-deficient mutant, A506 Ant���, was recovered; this mutant showed reduced epiphytic fitness on blossoms of apple and pear trees compared to the parent stain, A506. Another mutant, A506 Ant���, lost the characteristic fluorescent phenotype and exhibited iron-independent antibiotic production in defined culture media. A506 Ant��� established high populations on blossoms of apple and pear trees, similar to populations attained by A506, and reduced incidence of fire blight between 20 to 40%, levels comparable to A506 in orchard trials. In orchard trials, A506 was co-treated with FeEDDHA and fire blight suppression was evaluated. Bacterial strains established high populations on blossoms when co-treated with 0.1 mM FeEDDHA or in water. Significantly enhanced suppression of fire blight incidence by antibiotic producing strains of A506 amended with 0.1 mM FeEDDHA was observed in 2 of 5 trials, providing some evidence that iron-induced antibiosis can be a contributing mechanism in disease control. Lack of disease control by the antibiotic deficient strain, A506 GacS, and by 0.1 mM FeEDDHA alone added support to this hypothesis. / Graduation date: 2004

There is a need for effective and environmentally sensitive methods of controlling vertebrate pest problems in agriculture and urban environment. Nonlethal natural repellents may meet this need where more traditional methods of control, such as scaring, shooting, and trapping, are either ineffectual or unacceptable. Neem (Azadirachta indica A Juss) extracts: oil, seed and leaf powder and chemicals from cockroach (Blaberus giganteus L.) were tested for their repellent properties. In addition defensive volatiles from B. giganteus were tested in an arena based on choice by smell (cheese or insect volatiles). This arena test used laboratory rats (Rattus norvegicus Berk.); females were more active than males. Both sexes visited the holes with cheese more than holes containing insect's volatiles. However in a feeding test with one choice of food the control did not differ from the treatment. Neem products seem to act as antifeedant on rats: neem seed oil, neem seed powder and neem leaf powder reduced rats feeding respectively at concentration of 15 ml of oil/kg, 15--50 g of seed powder/kg, and 25--50 g of leaf powder/kg of rat chow. Overall neem leaf powder was less effective than seed powder and oil. Neem and insect products may have potential in controlling rats particularly in storage situation, which could lead to an important reduction of post-harvest loss of grains in Sahelian and Asian countries.