Theses and Dissertations at Montana State University (MSU)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/732
Browse
5 results
Search Results
Item Homology of the spheroidin gene from entomopoxviruses isolated from Melanoplus sanguinipes and Amsacta moorei(Montana State University - Bozeman, College of Agriculture, 1994) Wilson, SuzanneItem Sainfoin trypsin inhibitor : preparation and characterization of the low molecular weight protein(Montana State University - Bozeman, College of Letters & Science, 1985) Baginsky, Walter FrankItem Synthetic studies toward natural products(Montana State University - Bozeman, College of Letters & Science, 1982) Schwartz, Timothy RyallItem 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.