Theses and Dissertations at Montana State University (MSU)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/732
Browse
9 results
Search Results
Item Wheat stem sawfly parasitism in varying field sizes and tillage systems in dryland wheat in Montana(Montana State University - Bozeman, College of Agriculture, 2001) Runyon, Justin BlakeItem The venom of the mud-dauber wasp Sceliphron caementarium(Montana State University - Bozeman, College of Letters & Science, 1964) Rosenbrook, WilliamItem Revision of the species of Psenini in America north of Mexico (Hymenoptera: Schecidae)(Montana State University - Bozeman, College of Agriculture, 1963) Gittins, Arthur RichardItem Aphelinus sp. nr. varipes (Hymenoptera: Aphelinidae) as a potential biological control agent of Russian wheat aphid Diuraphis noxia (Mordvilko) (Homoptera: Aphididae)(Montana State University - Bozeman, College of Agriculture, 1991) Lajeunesse, Sherry E.Item Structural characterization of a polydnaviral protein involved in wasp parasitism(Montana State University - Bozeman, College of Letters & Science, 2001) Einerwold, Jerrod GrantItem Mechanisms for reproductive isolation in two congeneric parasitoids of the wheat stem sawfly(Montana State University - Bozeman, College of Agriculture, 2013) Davis, Rex Addison; Chairperson, Graduate Committee: David K. WeaverCephus cinctus Norton, the wheat stem sawfly, is Montana's most damaging wheat pest. The species is responsible for large yield reductions across the northern Great Plains, costing hundreds of millions of dollars every year. Two congeneric braconid parasitoid species, Bracon cephi Gahan and Bracon lissogaster Muesebeck (Hymenoptera: Braconidae), are found simultaneously in Montana wheat fields, are active at the same time of year and both use C. cinctusas a host. Their role as biological control agents of C. cinctusis currently being explored. It is unknown how these morphologically similar parasitoid species maintain reproductive isolation. This study explored several mechanisms allowing B. cephiand B. lissogaster to remain reproductively isolated and exposed new areas of study and questions of interest regarding the reproductive isolation of these species. No differences in reproductive timing were observed using field-based population abundance surveys, suggesting that alternative isolation mechanisms are being used. A group of candidate sex pheromones analyzed for presence, absence, and relative concentration in each of the parasitoid species' Dufour's glands indicated substantial differences between the two species. These differences suggest a possible role for the Dufour's gland in maintaining reproductive isolation. However, these candidate sex pheromones did not produce significantly different electrophysiological responses in B. cephiand B. lissogaster. Although this suggests that these candidate sex pheromones may not play a role, mating trials and behavioral assays conducted to assess the interactions between sex and species indicated that the species maintain reproductive isolation in laboratory settings.Item Behavioral and sensory responses of endemic braconid parasitoids to changes in volatile emissions induced by wheat stem sawfly, Cephus cinctus herbivory(Montana State University - Bozeman, College of Agriculture, 2009) Perez, Oscar Gerardo; Chairperson, Graduate Committee: David K. Weaver.Bracon cephi (Gahan) and Bracon lissogaster Muesebeck are considered the most effective biological control agents of the wheat stem sawfly, Cephus cinctus Norton, probably the most serious wheat insect pest in the northern Great Plains of North America. The great difficulty in controlling this pest suggests an urgent need to improve our understanding of the chemical ecology of these parasitoids to enhance effective control of this pest. Chemical ecology has been demonstrated to be an effective tool in the control of important pests. Plants produce volatile compounds as defenses against herbivory. These compounds play an important role in host selection by herbivores and their natural enemies. Studies revealed that wheat plants infested by C. cinctus produce different amounts of specific compounds compared to uninfested plants. Synthetic compounds matching those produced by sawfly infested wheat plants were tested in three different concentrations against males and females B. cephi and B. lissogaster parasitoids using an electroantennogram system. Six compounds generated positive electrophysiological responses from the parasitoid antennae. Behavioral bioassays using the previous responsive compounds determined that three compounds were attractive to parasitoids of both sexes. To better understand parasitoid host seeking, it was important to quantify and determine the spatial distribution of these behaviorally active compounds as they were emitted from wheat plants. Volatile compounds were collected from infested and uninfested wheat plants at three different heights and two distances in the greenhouse. Greater amounts were collected from the infested plants immediately adjacent to the base of the plants. Field studies were performed to compare concentrations of volatile compounds between areas of heavy and light sawfly infestation. Greater amounts of behaviorally active volatile compounds were collected from areas of heavier sawfly infestation. In conclusion, results show that chemical ecology is a valuable tool in better understanding host seeking in this tritrophic system. This new information on volatile production and dispersal by sawfly infested plants and host seeking behavior of these parasitoids establishes the basis for future exploration of optimal blends of behaviorally active compounds used by parasitoids in host seeking, which may allow for more effective control of the wheat stem sawfly.Item Mass rearing of Bracon cephi (Gahan) and B. lissogaster Muesebeck parasitoids of wheat stem sawfly, Cephus cinctus Norton, and temperature-induced mortality in host immatures(Montana State University - Bozeman, College of Agriculture, 2006) Robert, Godshen Robert Pallipparambil; Chairperson, Graduate Committee: David K. Weaver.Bracon cephi (Gahan) and B. lissogaster Muesebeck are host specific larval parasitoids of the wheat stem sawfly, Cephus cinctus Norton. A reliable source of these parasitoids is needed for inoculative releases into sawfly infested wheat fields in Montana. Large walk-in field screen cages were used to confine sawflies and parasitoids on wheat. Factors affecting the successful establishment of sawflies in wheat and subsequent attack by parasitoids were tested. Treatments consisted of cage modifications such as windows for enhancing the amount of light, food sources for parasitoids, increased light plus food sources, and a control. Methods for delivering adult sawflies into the cages were also investigated. The mass rearing cages with the windows had significantly greater sawfly infestation and parasitism when compared to the cages without windows. The sawfly infestation was low the first year, while the percent parasitism was quite high, indicating that the major impediment to mass rearing was obtaining greater sawfly infestation. We obtained higher amounts of infestation and parasitism for the second year when the method of introduction of C. cinctus adults into the rearing cage was changed, and this difference was more obvious than any treatment effects.Item Impact of harvest operations on parasitism of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae)(Montana State University - Bozeman, College of Agriculture, 2005) Meers, Scott Byron; Chairperson, Graduate Committee: Wendell L. Morrill.Wheat stem sawfly, Cephus cinctus, has been a long term pest management challenge for wheat producers in Alberta, Saskatchewan, North Dakota and Montana. Many studies have laid the groundwork for biological control of this pest. Two species of parasitoids, Bracon cephi and B. lissogaster, have been shown to effectively attack C. cinctus in wheat Triticum aestivum L. Their effectiveness as part of an integrated pest management plan, however, has been highly variable. A survey was conducted to assess the distribution of the two Bracon parasitoids. A two pronged approach was used to better understand parasitoid spatial dynamics and parasitoid promotion. First, intensive field sampling was performed to determine the overwintering location of parasitoid cocoons in wheat fields. Second, wheat stems were cut at varying lengths to stimulate harvest management techniques that producers could employ. B. cephi occurred at most locations where sawflies were an agricultural concern, although the level is sometimes very low. B. lissogaster was only found in wheat in Montana. The vast majority of overwintering cocoons (>80%) were consistently found in the bottom third of standing wheat stems when measured prior to harvest.