Theses and Dissertations at Montana State University (MSU)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/732
Browse
2 results
Search Results
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 Potential semiochemicals of wheat (Triticum aestivum L.) induced by oviposition and feeding of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae)(Montana State University - Bozeman, College of Agriculture, 2004) Peck, Gavin Earl; Chairperson, Graduate Committee: David K. Weaver.Cephus cinctus Norton (Hymenoptera: Cephidae), the wheat stem sawfly, is currently the most devastating insect pest of wheat production in Montana. Currently, no effective controls are in place to check its damage and spread throughout wheat fields in the northern Great Plains. Natural biological control of sawflies occurs primarily in the form of larval parasitoids which attack the sawfly larva in the stem; however, these parasitoids are not reliably effective in controlling sawfly populations. Insect damage induces chemical changes in plants, and often these changes are part of a defensive response to the insect injury. Some of these chemical changes are apparent in the volatile chemicals produced by the plants and may include semiochemicals used by sawflies and parasitoids. Identifying the changes in volatile production could enhance the understanding of sawfly-wheat plant-parasitoid interactions and lead to more effective control measures for the wheat stem sawfly. I investigated the differences in the volatile chemicals produced by sawfly-infested and uninfested wheat plants and endeavored to determine if those differences were qualitative or quantitative. Additionally, I wanted to determine if changes in volatile production induced by the wheat stem sawfly could be mimicked by wounding coupled with the application of sawfly cuticular wax to wheat stems or by the injection of frass-treated water into the internodes of wheat stems. Volatiles of infested and uninfested wheat plants were collected and compared, with the results indicating that sawfly damage induces quantitative changes in some volatile chemicals produced by wheat. These results are discussed regarding their context within sawfly-wheat plant-parasitoid interactions and implications for better sawfly control. Volatiles from sawfly-infested, uninfested, frass-water-injected, and pin-pricked/waxtreated plants were also collected, and differences in 11 compounds selected from the results of the 1st experiment were compared. The results of this experiment found that pin-pricked/wax-treated plants came closer to mimicking the volatile production changes induced by sawfly infestation, but neither frass-water injection nor pin-pricked/cuticular wax application reliably induced the same changes in wheat volatiles that sawfly infestation did. There was, however, a definite response of the wheat to the application of the sawfly cuticular wax, and its significance is discussed.