• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 70
  • 12
  • 12
  • 12
  • 1
  • Tagged with
  • 113
  • 113
  • 113
  • 113
  • 68
  • 42
  • 34
  • 34
  • 33
  • 31
  • 26
  • 21
  • 19
  • 18
  • 18
  • 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.

Biological control of spider mites (Acari: Tetranychidae) on grape emphasizing regional aspects

Prischmann, Deirdre A. 06 July 2000 (has links)
During summer of 1998 and 1999, 34 and 10 vineyard sites, respectively, were sampled to assess spider mite pests and associated biological control by phytoseiid mites. Vineyards studied spanned five major valleys in western Oregon where grape production occurs. Leaf samples were taken from site perimeters and centers. One leaf was taken every ten meters of border length, five meters inward from the border to prevent wind-biased or extreme edge effects, while 20 leaves were taken at regular intervals from centers. Variables recorded at each site were: plant age, grape variety, chemical spray information and local vegetation occurring in proximity to vineyards. Sites were categorized as either agricultural or riparian based on what surrounding vegetation type was in the majority. Several parametric and non-parametric tests were used to analyze data, including multiple linear regressions using a computer-based genetic algorithm in conjunction with the AIC criterion to pre-select a subset of explanatory variables. Typhlodromus pyri was the predominant phytoseiid mite and Tetranychus urticae was the most abundant tetranychid mite sampled. High levels of T. urticae were found when predator densities were very low, and low levels of T. urticae occurred when predator densities were moderate or high. Phytoseiid densities were highest in June and July, while T. urticae densities were highest from August to September. The latter's densities were significantly higher in vineyards surrounded primarily by agriculture, while phytoseiid densities were not significantly different between the two categories. Predatory phytoseiids had significantly higher densities on vineyard edges, while T. urticae densities were higher in vineyard centers. Caneberry, cherry and grape habitats appeared to be sources of predator immigration, while no vegetation type consistently served as a short-range or nearby immigration source for spider mites. Due to insufficient data, pesticide information was not included in multiple linear regression models, although certain chemicals used in vineyards can potentially impact mite populations. Impacts of surrounding vegetation type, grape variety, regional location, plant age, and presence of other mites on phytoseiid and T. urticae densities are discussed. / Graduation date: 2001

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

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

Genetic diversity in the biological control process : Acacia nilotica as a test case /

Wardill, Trevor James. January 2006 (has links) (PDF)
Thesis (Ph.D.) - University of Queensland, 2006. / Includes bibliography.

The evaluation of Phenrica sp. 2 (Coleoptera: Chrysomelidae: Alticinae), as a possible biological control agent for Madeira vine, Anredera cordifolia (Ten.) Steenis in South Africa /

Van der Westhuizen, Liamé. January 2006 (has links)
Thesis (M. Sc. (Zoology and Entomology))--Rhodes University, 2006.

Toadflax, fire, Mecinus janthinus, and compensatory growth

Anthony, Antoinette. January 2005 (has links)
Professional paper (M.S.)--Montana State University--Bozeman, 2005. / Title from PDF t.p. (viewed on July 4, 2006). Chairperson, Graduate Committee: Theodore Weaver. Includes bibliographical references (leaves 54-57).

Is everything connected? following the predators, pests, and plants within a no-till, western Montana agroecosystem /

Smith, Ethan A. January 2006 (has links)
Thesis (M.S.)--University of Montana, 2006. / Mode of access: Internet. Title from title screen. Description based on contents viewed Feb. 8, 2007. Includes bibliographical references (p. 63-72).

Biotic barriers to colonizing new hosts by the cinnabar moth Tyria jacobaeae (L.) (Lepidoptera: Arctiidae) /

Karac̦etin, Evrim. January 1900 (has links)
Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Control of the grape berry moth, Paralobesia viteana, using reduced-risk insecticides, cultural controls, and conservation of natural enemies

Jenkins, Paul E. January 2006 (has links)
Thesis (M.S.)--Michigan State University. Dept. of Entomology, 2006. / Title from PDF t.p. (viewed on June 19, 2009) Includes bibliographical references (p. 106-117). Also issued in print.

Evaluation of a plant-herbivore system in determining potential efficacy of a candidate biological control agent, cornops aquaticum for water hyacinth, eichhornia crassipes /

Bownes, Angela. January 2008 (has links)
Thesis (Ph.D. (Zoology & Entomology)) - Rhodes University, 2009.

Page generated in 0.1249 seconds