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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Susceptibility towards selected herbicides of two insect biocontrol agents for water hyacinth

Ueckermann, Claudia 23 November 2005 (has links)
Please read the abstract in the section 00front of this document / Dissertation (MSc (Botany))--University of Pretoria, 2005. / Plant Science / unrestricted
22

Tick control in Tswana, Simmental and Brahman cattle by means of Neem seed extracts (Azadirachta indica)

Davidi, Matayo 17 February 2006 (has links)
Please read the abstract in the section 00front of this document / Dissertation (MSc Agric (Animal Science))--University of Pretoria, 2006. / Animal and Wildlife Sciences / unrestricted
23

Predation behavior of spiders (Arachnida: Araneae) in Massachusetts cranberry bog ecosystems.

Bardwell, Carolyn J. 01 January 1995 (has links) (PDF)
No description available.
24

Factors affecting the establishment of a classical biological control agent, the horehound plume moth (Wheeleria spilodactylus) in South Australia

Baker, Jeanine. January 2002 (has links) (PDF)
Includes bibliographical references (leaves 168-198) The horehound plume moth (Wheeleria spilodactylus Curits), an agent introduced to control the invasive weed horehound (Murrubium vulgare L.), was used as a model system to investigate factors believed to influence the successful establishment of an introduced natural enemy. Retrospectively tests the use of generic population viability analysis and decision making tools for determining optimal release strategies for the horehound plume moth in South Australia and to compare outcomes with the emprical data collected during the course of this project
25

Factors affecting the establishment of a classical biological control agent, the horehound plume moth (Wheeleria spilodactylus) in South Australia / by Jeanine Baker.

Baker, Jeanine January 2002 (has links)
Includes bibliographical references (leaves 168-198) / xiv, 204 leaves ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The horehound plume moth (Wheeleria spilodactylus Curits), an agent introduced to control the invasive weed horehound (Murrubium vulgare L.), was used as a model system to investigate factors believed to influence the successful establishment of an introduced natural enemy. Retrospectively tests the use of generic population viability analysis and decision making tools for determining optimal release strategies for the horehound plume moth in South Australia and to compare outcomes with the emprical data collected during the course of this project / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2002
26

Influence of mite predation on the efficacy of the gall midge Dasineura sp. as a biocontrol agent of Australian myrtle Leptospermum laevigatum (Myrtaceae) in South Africa

Mdlangu, Thabisa Lynette Honey January 2010 (has links)
Dasineura sp. is a gall forming midge that was introduced into South Africa for the biocontrol of the Australian myrtle, Leptospermum laevigatum. It causes galls on both the vegetative and reproductive buds of the plant. Although Dasineura sp. was initially regarded as a potentially successful agent, galling up to 99 percent of the buds of the host plant, it has been preyed on by native opportunistic mites, which caused a decline in the performance of the midge as a biocontrol agent of L. laevigatum. This raised a concern about whether this fly will be able to perform effectively in the presence of its new natural enemies. Therefore, the objectives of this study were to: 1) ascertain whether mite abundance has seasonal variations; 2) determine if plant density and plant size have an effect on midge predation by the mites; and 3) determine if midge predation varies in different locations. The study was conducted at three sites in the Hermanus area, Western Cape Province. Every three weeks for thirteen months, galls were collected and dissected so as to count and record the numbers of midge larvae, pupae, adults and mites that were found. Data collected showed that predation varied with season, and the mites were scarce during the flowering season. Predation also varied among the study sites and plant density had an effect on midge predation. Midges in smaller plants (saplings) were more vulnerable to predation than those in the bigger plants (plants from isolates and thickets). It was concluded that although mites have an effect on midge populations, they do not prevent their establishment on the plant. Therefore, a survey should be done in two to three years time to check if the midges are still persisting on the plant, vi and recommendations are that a new agent should be released to supplement the midges.
27

Plant-insect interactions between yellow toadflax, Linaria vulgaris, and a potential biocontrol agent, the gall-forming weevil, Rhinusa pilosa

Barnewall, Emily C, University of Lethbridge. Faculty of Arts and Science January 2011 (has links)
Yellow toadflax, Linaria vulgaris (L.) Mill. (Plantaginaceae), is a non-native invasive plant. Rhinusa pilosa Germar (Coleoptera: Curculionidae) is a proposed biocontrol agent. Gall development by R. pilosa was described using histological methods and compared between plant populations from native and introduced ranges. Key stages of oviposition were isolated histologically to determine their importance in gall induction. Rhinusa pilosa galled and developed on four geographically distinct Canadian populations in a pre-release quarantine study. Low agent densities only negatively affected one population. High densities of R. pilosa reduced potential reproductive output and plant biomass. Conducting detailed investigations into the biology, impact, and development of R. pilosa on populations from invasive and native ranges may help predict the efficacy of R. pilosa in the field if approved for release and.goes beyond current pre-release testing requirements. / ix, 168 leaves : ill. (chiefly col.) ; 29 cm
28

Ecology and biological control of an apomictic invasive plant, Chondrilla juncea (Asteraceae) /

Campanella, Donald Michael. January 1900 (has links)
Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 112-121). Also available on the World Wide Web.
29

Assessing the safety of weed biological control : a case study of the cinnabar moth Tyria jacobaeae

Fuller, Jason L. 22 August 2002 (has links)
The cinnabar moth, Tyria jacobaeae (L.) (Lepidoptera:Arctiidae), was released in 1959 to control the grassland weed tansy ragwort, Senecio jacobaea L. (Asteraceae), despite evidence that caterpillars of this species can feed on native plants within the genera Senecio and Packera. Previous studies confirmed the moth's ability to develop on the native Senecio triangularis Hook., although no systematic study has been conducted to determine the extent of non-target impact on all potential host species. To address the lack of systematic studies we conducted a regional survey to determine the consequences of exposure of non-target plants to cinnabar moth caterpillars. We also conducted a local field experiment to determine the influence of habitat on the patterns of association of the moth and non-target plants. In the regional survey, we mapped the potential distribution of the cinnabar moth in Oregon to determine the extent of exposure of native Senecio and Packera species, and systematically sampled exposed species to assess the frequency and severity of feeding on these plants. We found that nine of the 20 native non-target species in Oregon were exposed to the cinnabar moth, three of the 10 native Senecio and six of the 10 native Packera. Ten of the native species escaped exposure because they occur east of the Cascade Mountain Range where the cinnabar moth does not occur. We found feeding damage on three of the nine exposed species: Packera cymbalarioides, P. pseudaurea, and S. triangularis were attacked at one of three (33%), two of six (33%), and seven of 15 (47%) sites that supported populations of each species, respectively. Within sites, attack frequency of stems was 33% (of six total stems sampled) for P. cymbalarioides, and ranged from 53% to 56% (of 20 to 108 total stems sampled) for P. pseudaurea and 7% to 64.5% (of 32 to 458 total stems sampled) for S. triangularis. Conditional median damage per site (median of attacked stems only) was 10% in P. cymbalarioides, 5% to 17.5% in P. pseudaurea, and 5% to 37.5% in S. triangularis. The attack rate on non-target plants (7.1 to 64.5 percent of stems attacked at a singe site) was equal to or greater than on the target weed (8.3 to 50.0 percent of stems attacked at a single site). At three sites, caterpillars attacked non-target plants but the target weed was absent, and at one site, the target was present but caterpillars fed on non-target plants only. We conclude that attack frequency and severity on the three species is not high, but equaled or exceeded the level of attack on the target weed. We also conducted a mark-release-recapture experiment to relate habitat preference to patterns of non-target host use in the field. We compared adult moth dispersal patterns and larval development between a meadow habitat and a forest habitat. We found that long-term dispersal distance (spanning days) was similar in both habitats but we recaptured a higher percentage of moths from the meadow (47%) compared to the forest (10%). Short-term displacements, based on direct observations of flights immediately after release, differed between habitats: moths in the meadow flew short distances (8.5m ± 1.5, n=13) at or below the herbaceous canopy (0.8 m ± 0.2, n=13) while moths in the forest flew longer horizontal (22.8 m ± 2.8, n=15) and vertical distances (5.9 m ± 0.9, n=15). We recovered seven fifth instar larvae (of 278 eggs) from the meadow habitat but no larvae beyond the second instar (of 119 eggs) were recovered from the forest habitat. We conclude that the cinnabar moth is limited to meadow habitats because adult moths display movement patterns that remove them from forest habitats (possibly due to disorientation) and larvae are unable to survive on plants growing in the forest. Taken together, the regional survey and the local field-experiment indicate that the cinnabar moth uses only a small proportion of available non-target host plant species. Other species are likely unused because of geographic isolation from the moth, habitat selection by the moth, or phenological differences between the moth and non-target plants. / Graduation date: 2003
30

Entomopathogenic nematodes for biological control of the Colorado potato beetle, Leptinotarsa decemlineata (Say)

Armer, Christine Andrea 28 August 2002 (has links)
The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is the most devastating foliage-feeding pest of potatoes in the United States. Potential biological control agents include the nematodes Heterorhabditis marelatus Liu & Berry and Steinernema riobrave Cabanillas, Poinar & Raulston, which provided nearly 100% CPB control in previous laboratory trials. In the present study, laboratory assays tested survival and infection by the two species under the soil temperatures CPB are exposed to, from 4-37°C. H. marelatus survived from 4-31°C, and S. riobrave from 4-37°C. Both species infected and developed in waxworm hosts from 13-31°C, but H. marelatus rarely infected hosts above 25°C, and S. riobrave rarely infected hosts below 19°C. H. marelatus infected an average of 5.8% of hosts from 13- 31°C, whereas S. riobrave infected 1.4%. Although H. marelatus could not survive at temperatures as high as S. riobrave. H. marelatus infected more hosts so is preferable for use in CPB control. Heterorhabditis marelatus rarely reproduced in CPB. Preliminary laboratory trials suggested the addition of nitrogen to CPB host plants improved nematode reproduction. Field studies testing nitrogen fertilizer effects on nematode reproduction in CPB indicated that increasing nitrogen from 226 kg/ha to 678 kg/ha produced 25% higher foliar levels of the alkaloids solanine and chaconine. However, the increased alkaloids did not affect nematode infection of, nor reproduction in, CPB prepupae. Nematodes applied to field plot soil at 50 infective juveniles/cm² reduced adult CPB by 50%, and increased numbers of dead prepupae in soil samples up to five times more than in non-nematode plots. Laboratory studies of H. marelatus and its symbiotic bacteria in CPB hemolymph indicated that immune responses did not limit nematode reproduction. A 58kD CPB hemolymph protein apparently caused the symbiotic bacteria to switch to the secondary form, which does not produce antibiotics and enzymes necessary for nematode growth and reproduction. Despite heat denaturation of the protein, the nematodes did not reproduce unless lipids were added to the hemolymph. Therefore, while H. marelatus may provide high levels of CPB control, nutritional constraints on the nematode and its bacteria inhibit reproduction in CPB and limit long-term multi-generation control. / Graduation date: 2003

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