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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.
1

Stress physiology and biological weed control : a case study with Canada thistle (Cirsium arvense (L.) Scop.)

Forsyth, Sheila Florence. January 1983 (has links)
The success of biological weed control programs has been limited by a lack of understanding of the stress physiology of insect damage and pathogen development. This case study with the perennial weed, Cirsium arvense, (L.) Scop. evaluated the stress of five natural enemies. Attack by a seed head predator, Orellia ruficauda (F.) caused about 21.5% predation and may reduce seed dispersal. The stress of stem gall formation (Urophora cardui (L.)) is greatest when the gall occurs on young plants and on the mainshoot and defoliation simulation (Cassida rubiginosa Muller) is most effective at high levels on young plants. In nature, however, the latter two natural enemies are not synchronized with these susceptible stages, thereby reducing their effectiveness. Although Cleonus piger Scop., a root crown inhabitant, can result in plant death, regeneration of damaged vascular tissue can occur. Plants which emerge systemically infected with Puccinia punctiformis (Str.) Rohl. (rust) rarely survive the season. A matrix model simulating the effects on Canada thistle population dynamics by the natural enemies was applied.
2

Development of a Colletotrichum dematium as a bioherbicide for the control of fireweed

Léger, Christian. January 1997 (has links)
An anthracnose-inducing pathogen, Colletotrichum dematium, was studied as a bioherbicide for Epilobium angustifolium. A comparative study involving other C. dematium isolates suggests that the isolate from E. angustifolium is a forma specialis and should be designated as Colletotrichum dematium f.sp. epilobii. The most severe damage was achieved on seedlings using a conidial density of $1 times 10 sp9$ conidia m$ sp{-2}$. Virulence decreased with plant maturity. Satisfactory levels of control were limited to long dew duration ($>$18 h) and high temperature treatments. Of various adjuvants tested, significantly higher levels of control were achieved when inoculum was sprayed in a vegetable oil emulsion (25% v/v). An inoculum buffered to acidic pH levels (pH 3.0) similarly increased level of control compared with an unbuffered conidial suspension and the adjustment to more alkaline pH levels using the citrate-phosphate buffer (pH $>$ 4.0), inhibited disease expression. In host range studies, C. dematium f.sp. epilobii was restricted to the Onagraceae family. Both Camissonia bistorta and Clarkia pulchella were susceptible whereas the fungus was highly virulent on all but one E. angustifolium ecotype. Among nine commercial tree species tested for susceptibility yellow birch (Betula alleghaniensis) was susceptible to the fungus when conidia were applied in an oil emulsion. The application of inoculum in a tank mix combination with the oil emulsion and a low rate of glyphosate provided significant growth control of E. angustifolium seedlings (7-wk-old), whereas the effectiveness of this suspension significantly decreased with plant maturity. Under controlled conditions, post-emergence application of an oil-based formulation including the ground colonized substrate of another bioherbicide candidate of E. angustifolium, Alternaria sp., significantly reduced above-ground biomass when provided a 12-h dew and applied at a rate as low as $5 times 10 sp6$ conidia m$ sp{-2}$.
3

An evaluation of two strains of Cyrtobagous salviniae Calder and Sands as natural enemies of the aquatic weeds salvinia molesta Mitchell and Salvinia minima Baker

Dye, Jeremiah M. 12 April 2006 (has links)
The floating aquatic weeds common salvinia (Salvinia minima Baker) and giant salvinia (Salvinia molesta Mitchell) degrade aquatic systems through fast, mat forming growth. The Salvinia specialist weevil Cyrtobagous salviniae Calder and Sands has been used to reduce the severity of giant salvinia infestations and associated with reduced severity of common salvinia infestations. Genetically, morphologically and biologically distinct strains of C. salviniae exist, but their relative potential for success as biological control agents of Salvinia species has not been evaluated. This thesis (1) describes a recirculating water system designed for conducting such studies and (2) reports the results of C. salviniae strain comparisons. A recirculating water system with a high degree of replication and minimal variation in water flow, temperature and light intensity was used for laboratory experiments using sixty-day temperature profiles averaging 31.4, 26.5 and 8.0ºC derived from surface water temperatures measured at lakes in expected range of Salvinia species in the North America. Larval and adult population numbers of two C. salviniae strains (Australia and Florida) were determined for each temperature profile along with feeding induced plant necrosis on both Salvinia species. Australia C. salviniae had lower survivorship rates to adulthood on common salvinia than did Florida C. salviniae at the 31.4 and 26.5ºC temperature profiles. Neither strain reproduced, and no significant between-strain differences in plant necrosis were detected at the 8.0ºC temperature profile. At 31.4ºC there were no significant differences in adult counts, larval counts or plant damage between the two strains on giant salvinia. At 26.5ºC, however, significantly fewer larvae were collected from initially released adults and significantly less plant necrosis was associated with weevil feeding by Florida strain compared to Australia strain weevils. These results may have arisen from comparing Australia weevils from a growing colony to Florida weevils from a declining colony. Overall, the results indicate that only Florida C. salviniae should be released against common salvinia. Florida C. salviniae may be equally suitable to Australia C. salviniae for releases against giant salvinia, but further study is needed to fully assess the potential for using Florida C. salviniae against giant salvinia.
4

Impact of interspecific interactions among parasitoids on inoculative biological control of leafminers attacking chrysanthemum

Bader, Amy Elaine 17 September 2007 (has links)
Indigenous natural enemies occur within field grown crops at varying densities dependent upon a variety of other biotic and abiotic parameters. This natural control often does not provide adequate suppression, which results in the application of other remedial pest management solutions including augmentative biological control. When releasing mass-reared natural enemies into a backdrop of indigenous natural enemy populations, competitive interactions are likely to occur. To assess the influence of these interspecific interactions on the outcome of such biological control practices, studies were conducted both in a laboratory and in a simulated, field grown, cut chrysanthemum (Asteraceae: Dendranthema grandiflorum) production system. Competitive interactions of two commercially available parasitoids were studied both in terms of parasitoid-host population dynamics and the impact of interspecific interactions on crop quality at harvest in this type of system. The parasitoids Diglyphus isaea and Dacnusa sibirica attacking the leafminer Liriomyza langei were used as the model insect system. Both parasitoids are cosmopolitan and are known to occur in many ornamental production areas. Conclusions drawn from laboratory experiments were that D. sibirica produces more offspring that D. isaea over approximately the same number of days. Treatment comparisons in the field included single species releases with complimentary releases of both species either simultaneously or with two-week time lags, as well as a no release control to measure the background effects of natural mortality. Conclusions drawn from results of population-level studies replicated within and among years were that levels of interspecific competition among parasitoid species were undetectable at leafminer densities typical of field-grown ornamental crops; thus, the efficacy of one species released into a backdrop of potentially competing parasitoids did not negatively affect the outcome of the augmentative biological control. The two species were able to coexist inside field cages for the duration of the crop. Most of the release treatments suppressed host densities lower than the control cages where no parasitoids were released, and there were no treatment effects on host suppression. Even though parasitoid release combination did affect the amount of damage visible at harvest, there was no influence on the number of flowers produced (yield).
5

Initial frequencies of alleles for resistance to Bacillus thuringiensis toxins in field populations of Plutella xylostella and Helicoverpa armigera

Ahmad, Mahmood. January 1999 (has links) (PDF)
Leaves 101-104 are misnumbered. Bibliography: leaves 155-215. In this study thirteen populations of P. xylostella from crucifer growing areas of Queensland, Victoria, Tasmania, South Australia and Western Australia were surveyed for resistance to Bt (Bacillus thuringiensis) toxins using a leaf-dip bioassay method.
6

Investigation of Aleochara bipustulata (Coleoptera: Staphylinidae) adult diet and community interactions

Andreassen, Lars David 25 October 2013 (has links)
The exotic cabbage maggot (CM) infests canola on the prairies, feeding on roots in its larval stage, which disrupts the uptake of nutrients and water and provides an entry point for fungal plant pathogens. The European staphylinid, Aleochara bipustulata L., may be introduced for control of CM, but only if the risk to other species is low and if A. bipustulata has demonstrable potential to increase mortality already caused by natural enemies in Canada. Aleochara bipustulata could contribute to pest management as a predator of CM eggs and larvae, and as a parasitoid of CM puparia; however, it could affect non-pest species in the same two ways. A variety of invertebrates that share the soil of Brassica fields with immature CM were screened in laboratory no-choice assays to determine what adult A. bipustulata eat. In these assays, immobile or barely mobile invertebrates were accepted regularly and could be at risk. The majority of groups were seldom or never consumed. Also, a molecular assay developed to test for CM DNA in the guts of field-collected A. bipustulata revealed its high potential as a predator, and a similar assay developed for two carabid beetle species showed these to be seldom if ever consumed. Laboratory and field cage assays with other CM egg predators showed A. bipustulata has potential to disrupt other species, particularly the closely related A. bilineata Gyllenhal, as they seem to forage in similar microhabitats. Measurements of field-collected beetles indicate CM is unlikely to be the primary host in Europe, so introducing A. bipustulata to Canada may bring risks to non-target Diptera species. This was observed even though a series of laboratory experiments demonstrated CM is a superior and preferred host relative to the smaller, acalyptrate cheese skipper.
7

Studies on selected fungi and their ability to control nematode populations.

Davies, John Stephen. January 1970 (has links)
No description available.
8

The reproductive biology and behaviour of #Leptomastidea abnormis', a hymenopterous parasitoid of the citrus mealybug #Planococcus citri'

Jackson, Alison January 1995 (has links)
No description available.
9

Studies on the physiology and biochemistry of infective juveniles of entomopathogenic steinernematid nematodes

Patel, Mavji Nanji January 1997 (has links)
No description available.
10

Pasteuria pentrans as a biocontrol agent of Meloidogyne species and its field evaluation in Malawi

Daudi, Andrew Timothy January 1991 (has links)
No description available.

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