"October 2004" / Includes bibliographical references (leaves 223-243) / xvi, 243 leaves : ill. (col.), maps, plates ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, School of Agriculture and Wine, Discipline of Plant and Pest Science, 2004

Bibliography: leaves 162-198. This thesis investigates the mechanism(s) involved in the protection of Capsicum seedlings by two isolates of BNR against the damping-off fungus, P.u. sporangiiferum. Emphasis is placed on ecological attributes of the antagonists in relation to the pathogen, in conditions resembling those of the nursery environment for which biological control is intended. It is proposed that competition for resources, such as the host tissues with exudate-rich infection sites and the organic residue in the potting mix, is the principal factor influencing the interactions between P.u. sporangiiferum and BNR. It is also suggested that BNR isolates employ at least three strategies to exert competitive advantage over P.U. sporangiiferum. It is postulated that the ability of BNR to capture and utilise resources, in the presence of a potential competitor, is the principal attribute of these biocontrol agents that brings about a sucessful control of P.u. sporangiiferum in nursery potting mix.

Bibliography: leaves 213-233. This thesis studies the influence of the two common syrphid species on populations of rose aphids in rose gardens in Adelaide. The study determines whether the provision of attractive flowers increases the suppressive effect of syrphids on rose aphids and analyses some ecological and biological aspects of two syrphid species -- Melangyana viridiceps (Macquart) and Simosyrphus grandicornis (Macquart) -- in a Mediteranean climate to obtain a better understanding of their biological control potential.

We identified and evaluated a phytoseiid predator as a biological control agent of multiple spider mites pests that occur in ornamental nurseries. When comparing species, Neoseiulus fallacis (Garman) had a wider prey range than Galendromus occidentalis (Nesbitt), a higher probability of overwintering than Neoseiulus califomicus McGregor and was equally or more effective at suppressing spider mites than either of the other 2 phytoseiids in 4 field tests. To further evaluate N. fallacis we 1) measured prey range when held with 29 ornamental pests or alternative foods under laboratory conditions, 2) tested biological control of spider mites on representative plant species at both small and large spatial scales, 3) developed release and conservation strategies of the predator, and 4) examined the efficacy of the predator in controlling recently introduced pests. Neoseiulus fallacis had greatest survival and reproduction when feeding on spider mites but eriophyid mites, other mites and pollen enhanced survivorship and, in some cases, reproduction. When inoculated into ornamental plants, spider mite suppression was "acceptable" in 81% of small scale tests and-in all large scale tests. Limitations in control occurred in tall, vertical growing plants with little foliar canopy. Inoculation of N. fallacis at low prey densities into apple rootstocks was successful at suppressing Tetranychus urticae Koch and similar to control achieved at moderate prey densities. In small scale banker plant studies, high densities of adult and immature mites of N. fallacis were produced and moved downwind to receiver plants. In field tests with receiver plants placed at greater distances, only N. fallacis adult females readily dispersed to 30 m or more. When comparing overwintering survival of adult females among plant types, N. fallacis survived most on conifers, intermediate on evergreen shrubs and least on herbaceous perennials, deciduous shrubs and shade trees. Covering plants with protective plastic reduced overwintering survival of the predator. Neoseiulus fallacis successfully suppressed the newly introduced pests Panonychus citri (McGregor) and Schizotetranychus celarius (Banks) on Skimmia japonica Thunberg and Sasaella hidaensis (Makino and Uchida), respectively. Initial studies suggest that N. fallacis can be an effective biological control agent of multiple spider mites in low-growing and selected higher-growing ornamental plants. / Graduation date: 2000

I conducted field studies to determine the effect of insect herbivory and intraspecific plant competition on ragwort Senecio jacobaea. The objectives were to determine the patterns and causes in the distribution of the ragwort flea beetle Longitarsus jacobaeae foraging among varying densities of ragwort, to measure the behavioral and numerical responses of the beetle to changes in ragwort density, and to estimate the impact of insect herbivory and intraspecific competition on ragwort performance. Host density was manipulated by planting 1, 4, 8, or 16 plants per 0.5 x 0.5 m patch. Beetles were counted in each patch to assess the effect of host density on the beetle population. I measured four components of reproductive success represented by growth rate, development rate, reproduction, and annual survivorship to assess the effect of herbivory and intraspecific plant competition on ragwort performance In the first experiment, beetle populations were manipulated by establishing equal numbers of beetles in patches with unequal number of hosts (1, 4, 8, 16 plants per patch), which were then subsequently allowed to move freely about. Beetles rapidly re-distributed themselves, such that the number of beetles was strongly and positively correlated with the number of hosts. This indicates that ragwort flea beetles are highly sensitive to local distribution of their food plants. In the second experiment, host density was manipulated by planting ragwort in densities of 1, 4, 8, 16 plants per patch, and beetles were then allowed to colonize the experimental patches. Beetle behavioral response to a change in host density was dependent on host population size: the numbers of colonizing beetles increased asymptotically with increasing plant density. The number of beetle-days ranged from 261 for 1-plant patches to 1822 for 16-plant patches. In contrast, the numerical response (represented as observed multiplication rate per capita per generation per year) appears to be inexplicably low in the single plant population and levels off in the 4, 8, and 16 plant patches (grand mean for multiplication rate 1 was 5 and for multiplication rate 2 was 10.4 progeny per individual per generation). Combining these results, the beetles apparently respond to spatial variation in the density of hosts primarily by changes in their movement behavior rather than by changes in their per capita reproductive rates. These results highlight the importance of a natural enemy's colonizing behavior for controlling a sudden upsurge in pest abundance. Both insect herbivory and intraspecific competition had an effect on ragwort performance. For example, over approximately one year, ragwort's rate of biomass accumulation was 48% lower, and seed-head production was 18% lower in exposed compared to protected plots, while intraspecific competition reduced ragwort's rate of biomass accumulation and seed-head production, such that a 16-fold increase in host density (in protected patches) led to a 12-fold decrease in biomass per plant and a 11-fold decrease in the number of seed-heads per plant. Herbivore effects were independent of host density: variation in plant density from 1 to 16 plants led to no detectable change in magnitude of the herbivore effect. This suggests there is no density-dependent refuge for host plants operating at these local scales of observation. Keywords: Host density effects, behavioral response, reproductive response, biological control agent, Longitarsus jacobaeae, Senecio jacobaea. / Graduation date: 1995

Lygus hesperus is an important pest on different crops including cotton and alfalfa in the western U.S. Anaphes iole is a common parasitoid of Lygus spp. eggs in the U.S. and has potential as a biological control agent against L. hesperus in different crops. Its foraging behavior has been studied to a limited extent, but it is unknown whether A. iole females rely on plant volatiles to locate host habitats. L. hesperus feeding and oviposition are known to induce emission of plant volatiles in cotton and maize, but no studies have addressed the role of plant volatiles in the host searching behavior of A. iole. The objectives of this study were to evaluate the attraction of A. iole females toward volatiles derived from L. hesperus habitats and flight response of A. iole females toward cotton plants harboring L. hesperus eggs or treated with methyl jasmonate. Results from olfactometry bioassays showed that female wasps were attracted to odors emanating from different plant-L. hesperus complexes and from adult L. hesperus, while plants damaged by non-hosts or mechanically-damaged were not attractive. These findings suggested that A. iole females use specific plant volatiles released following L. hesperus feeding and oviposition to locate host habitats. In addition, in flight chamber tests A. iole females discriminated between cotton plants with moderate (41 eggs) and high (98 eggs) levels of L. hesperus infestations relative to uninfested plants, but not between plants with low (7 eggs) infestations compared to uninfested plants. In larger scale experiments conducted in the greenhouse, female wasps responded to L. hesperus-infested plants but not to methyl jasmonate-treated plants under similar conditions. Overall, results from this study revealed that A. iole females employ volatile signals to locate its host’s habitat and that they are attracted to plants damaged by L. hesperus feeding and oviposition. However, further research should seek to identify the chemical elicitors involved in the release of plant volatiles attractive to A. iole females.

Inclusion/exclusion field experiments demonstrated that the red imported fire ant, Solenopsis invicta Buren, did not affect the abundance of 49 groups of insects and spiders collected in pitfall traps. However, arthropod diversity was significantly greater (H' = 2.829) in exclusion plots relative to inclusion plots (H' = 2.763). Moreover, this study demonstrated that S. invicta can have an important impact upon cotton arthropod communities, including key predator species. Densities of ground beetles (Carabidae), spiders, lacewings (Chrysoperla spp.), and minute pirate bugs (Orius spp.) were significantly lower in the presence of S. invicta. However, populations of aphidophagous insects such as Hippodamia spp. and Scymnus spp. increased with cotton aphid (Aphis gossypii Glover) density early in the season. Abundance of cotton aphids was ca. 5x greater in inclusion plots, likely due to protection and tending by S. invicta. This increase was observed early in the season, though aphid populations did not reach economic levels. Predation of sentinel bollworm [Helicoverpa zea (Boddie)] and beet armyworm (Spodoptera exigua Hubner) eggs increased 20-30%, when S. invicta was present. Most predation of sentinel beet armyworm egg masses, measured via direct nocturnal observations, was due to S. invicta (68%) and cotton fleahopper [Pseudatomoscelis seriatus (Reuter)] (21%) in plots with S. invicta, and by the mite Abrolophus sp. (52%), spiders (13%) and minute pirate bug (13%) in plots without S. invicta. The frequencies of minute pirate bug, cotton fleahopper, S. invicta and native ants in beat bucket samples did not accurately reflect the frequency with which they were observed feeding on sentinel noctuid eggs. Overall, the results of these studies demonstrated that S. invicta was associated with declines in the abundances of minute pirate bug, spiders, and lacewing and with an increment in cotton aphid populations, though they did not reach the economic threshold. Moreover, S. invicta significantly increased predation of bollworm and beet armyworm eggs. All together, the results suggested that S. invicta has a net positive impact on cotton pest management.

Four separate but complimentary studies investigated the role of grain sorghum as a predator source for Southern Rolling Plains cotton in 2001 and 2002. Objectives were to: (1) determine the timing and magnitude of predator movement between crops, (2) test putative causes of movement by manipulating prey levels at different stages of crop phenology, (3) explore the feeding and reproductive behavior of a common predator colonizing cotton, and (4) examine the effects of grain sorghum and uncultivated areas on cotton predator abundance at an area-wide scale. Rubidium mark-recapture experiments indicated grain sorghum fields produced a net predator gain for adjacent cotton. Analysis suggested two coccinellids, Hippodamia convergens Guérin-Méneville and Scymnus loewii Mulsant, were responsible for the overall pattern of predator movement. Predator movement into cotton did not appear to be concentrated at specific stages of sorghum phenology. Manipulations of aphid levels in field cages were used to determine if prey abundance or phenology influenced the movement of H. convergens into cotton. In both years, more lady beetle adults were collected on cotton during the latest stages of sorghum phenology. In the second year, relatively low aphid densities (15 per plant) appeared to influence the movement of beetles onto caged cotton. Carbon isotope ratios of H. convergens were used to assess adult feeding behavior after colonizing cotton and to determine if prey consumed in sorghum contributed to egg production in cotton. Though aphids were absent 2001, H. convergens adults stayed in cotton, did not produce eggs and apparently consumed few prey. Cotton aphids were present in 2002 and H. convergens isotope ratios changed from prey consumed in cotton. The isotope ratios of egg masses collected in 2002 indicated prey consumed in grain sorghum contributed very little to egg production in cotton. An area-wide pattern analysis suggested the abundance of grain sorghum and uncultivated areas both positively influenced cotton predator levels. While these landscape effects were less important overall than prey levels and cotton planting dates, in some sampling periods landscape composition appeared to be the most important factor in determining cotton predator levels.

Environmental hazards and health problems due to the application of chemical pesticides in agricultural sectors incite huge public concerns. Therefore, one of the better solutions is through introduction of biological control means to manage the outbreaks of plant diseases. To date, only small numbers of beneficial microorganisms - belonging to the category of hyperparasitic or mycoparasitic fungi have proven to keep plants or protect crops from plant pathogen infection. The objective of this study was to characterize a group of <i>Fusarium</i>-associated melanosporaceous biotrophic mycoparasitic fungal isolates, which were identified and pre-selected by Dr. Vladimir Vujanovic and deposited in the Saskatchewan Microbial Collection and Database (SMCD). Particular objectives were to examine spore germination of a biotrophic mycoparasite, to test effects of this fungus on seed germinations, to study interactions between the mycoparasite and Fusarium hosts, and to investigate relationships between the mycoparasite-the <i>Fusarium</i> host-wheat root under controlled conditions in the university Phytotron facilities.<p> Information related to this group of fungi is relatively limited. In order to characterize potential biotrophic mycoparasitic fungal isolate(s), molecular and microscopy methods were performed to accomplish taxonomical, phylogenetical and morphological studies. Since, spore germination is a very crucial stage in fungal life cycle and growth, ascospores (sexual spores) of the biotrophic mycoparasite were isolated from a fungal colony. These spores were inoculated on media supplemented with different <i>Fusarium</i>-filtrates or suspended in different <i>Fusarium</i>-filtrates to examine spore germination rates and growth patterns. Together with other mycoparasitic fungi, this biotrophic mycoparasite was inoculated on spring wheat seeds, to test effects of these fungal inoculants on seedlings growth using <i>in vitro</i> assays. Dual-culture, slide culture, and microscopy approaches were carried out to elucidate intimate and special relationship between the biotrophic mycoparasite and <i>Fusarium</i>-hosts. In order to study tritrophic interactions (biotrophic mycoparasite-<i>Fusarium</i> host-wheat root), spring wheat was grown in the phytotron with different treatments of fungal inoculations. Wheat roots were then subjected to genus-specific quantitative real-time PCR analyses.<p> One melanosporaceous biotrophic mycoparasitic strain was identified as a new species in the genus <i>Sphaerodes</i>. This biotrophic mycoparasite was isolated from <i>Fusarium</i>-infected fields in Saskatchewan and Quebec, and named <i>Sphaerodes mycoparasitica</i>. Germination of <i>S. mycoparasitica</i> sexual spores was improved when treated with filtrates or extracellular extracts from the <i>Fusarium</i>-host as compared to <i>Fusarium</i>-non-host filtrates. No pathogenic effects on wheat seeds were observed when inoculated with <i>S. mycoparasitica</i>. Furthermore, seedlings growth was enhanced with this biotrophic mycoparasite compared to other mycoparasitic fungi. Later, this biotrophic mycoparasitic strain was found to establish biotrophic fusion and haustorial contact relations with <i>F. avenaceum, F. oxysporum</i>, and two F. graminearum chemotypes. Since, 3-Acetyldeoxynivalenol-producing <i>F. graminearum</i> is one of the most highly toxigenic and aggressive wheat pathogens in Saskatchewan and North America, therefore, this pathogen strain was chosen for tritrophic interaction study. Under controlled conditions in the phytotron, <i>S. mycoparasitica</i> improved seedlings growth when these were challenged with <i>F. graminearum</i> as compared to seedlings only inoculated with the <i>Fusarium</i> pathogen. In conclusion, S. mycoparasitica could be a potential candidate for biological control of <i>Fusarium</i> diseases in wheat.

Antagonistic effects of Epicoccum purpurascens, Aureobasidium pullulans, Trichoderma spp., and Botrytis cinerea on establishment of Monilinia fructicola infections in cherry and peach blossoms were assessed in field and mist chamber studies. Conidia of each fungus were applied to blossoms that were subsequently inoculated with conidia of M fructicola. Mist chamber experiments on forced cherry blossoms demonstrated that recovery of M. fructicola was significantly reduced (P=.05) when spores of E. purpurascens and B.cinerea had been applied 24 hr prior to inoculation with M. fructicola. Reduction in recovery of M. fructicola was comparable to that obtained with the fungicide benomyl. In field trials done in 1990 and 1991, applications of E. purpurascens and A. pullulans reduced cherry blossom blight relative to nontreated blossoms by 47 to 65 and 54 to 58%, respectively, compared to reductions of 80 to 96 and 84 to 97% with the fungicides benomyl and iprodione, respectively. Twig blight in peach, an indicator of blossom blight infection, was reduced by 37% relative to nontreated blossoms with applications of E. purpurascens, compared to 54 and 51% reductions with benomyl and iprodione, respectively. Analysis of the influence of antagonistic fungi sprayed onto blossoms on fruit set indicated that B.cinerea was a weak pathogen of stone fruit blossoms. Significant reductions (P=.05 and P=.10) were obtained in fruit set compared with the nontreated control when conidia of B. cinerea were applied to both cherry and peach blossoms in 1991. Latent Monilinia infections were evaluated by dipping green cherries in the herbicide paraquat. Applications of E. purpurascens and A. pullulans to blossoms caused reductions in the number of latent Monilinia infections in green cherries by 18 and 49%, respectively in 1990, and 61 and 66% respectively in 1991. This compares with reductions of 98 and 92% in 1990 and 1991, respectively, with the fungicide iprodione. It was observed that the antagonists E. purpurascens and B. cinerea also became established as latent infections. These fungi were recovered at a significantly (P=.05) higher percentage on green cherries where they had been applied as antagonists to blossoms. No meaningful differences were detected in the amount of brown rot that developed on fruit due to the influence of fungal treatments on blossoms. / Graduation date: 1992