Theses and Dissertations at Montana State University (MSU)
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Item Can conservation biocontrol of wheat stem sawfly be improved? Contributions of supplemental nutrition to longevity, egg load, and egg volume of Bracon cephi and B. lissogaster(Montana State University - Bozeman, College of Agriculture, 2022) Cavallini, Laissa; Chairperson, Graduate Committee: David K. Weaver; This is a manuscript style paper that includes co-authored chapters.Wheat stem sawfly (WSS), Cephus cinctus, is a major pest of wheat, causing losses that exceed $350 million annually across the Northern Great Plains. Two native parasitoids, Bracon cephi and B. lissogaster, suppress C. cinctus populations in wheat fields, where the immatures feed on and kill C. cinctus larvae. The success of natural enemies is linked to access to supplemental food in the field, which increases their life span and benefits their reproductive parameters. To assess the benefits that supplemental nutrition might have on B. cephi and B. lissogaster, we reared adult females on carbohydrate-rich diets combined with and without amino acids, with water and water plus amino acids as controls. We also conducted greenhouse experiments with the non-native, warm-season cover crop cowpea, Vigna unguiculata, as an extrafloral nectar source for parasitoids. Cages containing individual females were placed on living plants enclosing either cowpea inflorescence stalk extrafloral nectar (IS-EFN) or the leaf stipel extrafloral nectar (LS-EFN), with a supply of water as the negative control and buckwheat nectar as the positive control. In both lab and greenhouse experiments, females were observed daily to assess longevity, while egg load and volume were assessed 2, 5, and 10 days after placement. Results show that both species increased longevity when provided carbohydrate-rich food. B. cephi enhanced egg load and volume with carbohydrate-rich diets, and the addition of amino acids tending to benefit these parameters. Results show that IS-EFN increases longevity in both parasitoids. B. lissogaster kept constant egg load and volume, while B. cephi increased reproductive parameters with IS-EFN. These native braconid parasitoids are unfamiliar with non- native cowpea plants. Hence, we tested their attraction to cowpea volatiles, where positive responses were observed. Our results show that supplemental nutrition greatly benefits B. cephi and B. lissogaster females, with cowpea IS-EFN improving their longevity and reproductive parameters. Therefore, we suggest that cowpea has potential to be considered as a food supplement crop in conservation biocontrol programs to reduce WSS populations.Item Population dynamics of wheat stem sawfly, Cephus cinctus Norton, in barley in Montana(Montana State University - Bozeman, College of Agriculture, 2020) Achhami, Buddhi Bahadur; Chairperson, Graduate Committee: David K. Weaver; Gadi V. P. Reddy, Jamie D. Sherman, Robert K. D. Peterson and David K. Weaver were co-authors of the article, 'Antixenosis, antibiosis, and potential yield compensatory responses in barley cultivars exposed to wheat stem sawfly under field conditions' which is contained within this dissertation.; Gadi V. P. Reddy, Jamie D. Sherman, Robert K. D. Peterson and David K. Weaver were co-authors of the article, 'Effect of precipitation and temperature on larval survival of Cephus cinctus (Hymenoptera: Cephidae) in barley cultivars' which is contained within this dissertation.; Robert K. D. Peterson, Jamie D. Sherman, Gadi V. P. Reddy and David K. Weaver were co-authors of the article, 'Multiple decrement life tables of Cephus cinctus Norton (Hymenoptera: Cephidae) across a set of barley cultivars: the importance of plant defense versus cannibalism' which is contained within this dissertation.; Gadi V. P. Reddy, Megan L. Hofland, Robert K. D. Peterson, Jamie D. Sherman and David K. Weaver were co-authors of the article, 'Host selection and oviposition behaviors of Cephus cinctus (Hymenoptera: Cephidae) in barley' which is contained within this dissertation.Wheat stem sawfly (WSS) is an economically devastating pest of cereals grown in North America. The larva is the only feeding stage and remains confined within a host stem until it emerges as an adult the following year. This limited mobility increases larval vulnerability to mortality factors when host plant traits are hostile to survival. For instance, larval mortality is greater in barley than in solid stemmed wheat cultivars known to be resistant. Both solid stemmed wheat and barley kill neonates via host plant resistance traits. Traditionally, barley was recommended as an alternative rotational crop to prevent WSS outbreaks in wheat crops. There is limited data available regarding barley host plant resistance and questions persist. Has barley resistance changed over time? What is the impact of larval feeding injury on grain yield of barley? Do females display similar oviposition behaviors across barley cultivars that vary in susceptibility? To answer these questions. I conducted field experiments to assess resistance and possible tolerance to WSS in eight barley cultivars. Based on the number of eggs, 'Hockett' was the most attractive cultivar to WSS female (less antixenosis), while 'Craft' and 'Celebration' killed the greatest number of neonates due to antibiosis. Multiple decrement life table studies revealed that plant defense and cannibalism were two major causes of larval mortality. We measured greater yield in infested stems with dead larvae (potential tolerance) than for cut stems and both were greater than uninfested stems in all cultivars except 'Celebration'. A greenhouse study revealed that females preferred 'Hockett' over 'Craft' in frequencies of oviposition behaviors and numbers of eggs deposited. Additionally, a greater amount of the WSS attractant (Z)-3-hexenyl acetate was found in aerations from 'Hockett' plants than from 'Craft.' The amount of defensive compound linalool was greater in aerations from 'Craft' than from 'Hockett.' These results suggest that barley cultivars are equipped with varying levels of antibiosis, antixenosis, and tolerance traits against WSS. Thus, we can exploit these traits in the development of cultivars which can reduce WSS populations and decrease economic loss caused by this species.Item Assessment of host selection behaviors and oviposition preferences of Cephus cinctus Norton (Hymenoptera: Cephidae) using wheat and smooth brome(Montana State University - Bozeman, College of Agriculture, 2020) Bhandari, Rekha; Chairperson, Graduate Committee: David K. Weaver and Tracy M. Sterling (co-chair)Wheat stem sawfly, Cephus cinctus Norton (WSS), is an important pest of cereal crops in Northern Great Plains. Smooth brome has historically been suggested as a potential trap crop around wheat fields in Montana. The objective of this study was to compare oviposition preference and selection behaviors of female WSS and measure subsequent larval survival in wheat and smooth brome stems. We compared infestation, parasitism and larval development of WSS using field transects in smooth brome and adjacent wheat fields. We found no clear difference in infestation between the two host plants. There was greater larval mortality and less tunneling in smooth brome stems compared to wheat at a site near Big Sandy, Montana. At a second site near Big Sandy, there was greater infestation in smooth brome compared to wheat, but there were more dead larvae and greater parasitism in smooth brome. In Y-tube olfactometer studies, WSS females were more attracted to volatiles emitted by smooth brome than wheat. In greenhouse trials, the observation of specific behaviors leading to oviposition indicated differences in duration of ovipositor insertion and in number of ovipositor insertions that favored greater oviposition in smooth brome, but only by emergence of the first awn of the inflorescence (Zadoks 49 growth stage). There were different numbers of eggs in smooth brome stems relative to wheat, with no difference in the proportion of infested stems in choice tests conducted for two days at Zadoks 49. In no-choice tests, there were differences in both infested stems and in the number of eggs in stems at Zadoks 49. We found significantly greater amounts of key behaviorally active compounds used by female WSS, like (Z)-3-hexenyl acetate and beta-ocimene, that were among the few differences in the amounts of volatile compounds collected from two plant species. The greater amount of these compounds leads to more eggs that subsequently experience greater larval mortality in young plants, resulting in fewer cut stems in mature plants. Our findings support the consideration of smooth brome for use in trap crops to improve integrated pest management strategies for WSS.Item The effects of increasing crop diversity on populations of wheat stem sawfly (Cephus cinctus) and associated braconid parasitoids(Montana State University - Bozeman, College of Agriculture, 2019) Fischer, Benjamin Vernon; Chairperson, Graduate Committee: David K. WeaverWheat stem sawfly, Cephus cinctus (Norton) (WSS) is the most damaging pest of wheat in the Northern Great Plains. Insecticides are not widely used to control this insect, and cultural control methods provide inconsistent management of this pest. However, biological control by the parasitoids Bracon cephi (Gahan) and Bracon lissogaster Muesebeck has been shown to reduce damage caused by WSS. In addition, increased agroecosystem diversity has benefitted biological control agents in many other systems. Therefore, this study assessed the effect on populations of WSS and associated parasitoids by the inclusion of pulse and cover crops near wheat fields. Field trapping, dissection of postharvest crop residue, and rearing of insects out of crop residue were used to survey WSS and parasitoid populations in pairs of wheat fields throughout the major wheat producing regions of Montana. One wheat field in each pair was seeded next to a fallow field, and the other was seeded next to a field of either pulse or cover crop. Postharvest stem dissection samples show that wheat fields next to pulse or cover crops had a mean increase of 51 parasitoids per m 2 than wheat fields next to fallow. A corresponding 3% reduction in stem cutting was also observed in postharvest samples from wheat fields adjacent to flowering pulse or cover crops. Land-use data from CropScape TM were used as well to evaluate other land-use impacts around each wheat field such as wheat, fallow, grassland/pasture, flowering crops, and developed space. The regression equation Y = 18.96X + 6.08, where X = proportion of fallow land within 2 km of the wheat field and Y = square root of WSS abundance in a 7.5 m sample of crop residue from rows of wheat, can be used to predict WSS abundance in wheat fields. Replacing fallow fields with flowering pulse or cover crops in the Northern Great Plains may be an important integrated pest management tactic to reduce WSS damage. Cultural practices such as crop diversification are key to developing consistent biological control for WSS.Item Impacts of dryland farming systems on biodiversity, plant-insect interactions, and ecosystem services(Montana State University - Bozeman, College of Agriculture, 2018) Adhikari, Subodh; Chairperson, Graduate Committee: Fabian D. Menalled; Laura Burkle (co-chair)Farming system impacts the structure and functioning of associated biodiversity and plant-insect interactions. However, the extent of these impacts is largely unknown in drylands of the Northern Great Plains, an important region for cereal, pulse, oilseed, and forage production. Using three complementary studies, I compared the impacts of conventional and organic systems on associated biodiversity (weeds, bees, insect pests, and parasitoids), bee-flower networks, and bumblebee colony success. First, I assessed stem cuts by and parasitism on Cephus cinctus (wheat stem sawfly) in spring and winter wheat cultivars grown in conventional and organic fields. I found that organic fields had less C. cinctus infestation and more braconid parasitoids of C. cinctus, indicating an increased pest regulation in organic system. I compared C. cinctus preference and survival on Kamut with Gunnison and Reeder wheat cultivars and found the lowest C. cinctus oviposition and survival in Kamut, suggesting that Kamut is a potential genetic source for this pest. Second, I assessed the impacts of conventional and organic systems on forb and bee communities. I found greater forb diversity and more connected bee-flower networks in organic fields, but bee communities did not differ between systems. Comprising only 12% of the landscape, natural habitat did not affect small-bodied bees in either system but had a positive effect on large-bodied bees at the scale of 2000 m radius. These results indicate that an increased forb diversity and bee-flower interaction in organic fields is not enough to offset the negative effects of landscape homogeneity on bees. Third, I compared Bombus impatiens colony success, worker condition, and colony-collected pollen between farming systems. I found greater growth rate, brood cells, and pollen species richness in B. impatiens colonies as well as lower wing wear and greater body lipid mass in workers from organic fields, than in conventional fields. The greater colony success and better worker conditions could be a proxy for better ecosystem services provided by organic fields. Overall, my studies show that organic farming supports greater associated biodiversity, more complex bee-flower networks, and better biodiversity-based ecosystem services in the Northern Great Plains.Item The potential of sugar resources in the reproductive biology of wheat stem sawfly parasitoids(Montana State University - Bozeman, College of Agriculture, 2018) dos Reis, Dayane Andrade; Chairperson, Graduate Committee: David K. Weaver; Robert K. D. Peterson, Megan L. Hofland and David K. Weaver were co-authors of the article, 'Differences in longevity, egg load, and egg volume due to sucrose feeding in two sympatric congeneric braconids that are specialist parasitoids of the wheat stem sawfly ' which is contained within this thesis.; Robert K. D. Peterson, Megan L. Hofland and David K. Weaver were co-authors of the article, 'The effect of cultivated and native floral species as resources in the reproductive biology of wheat stem sawfly parasitoids' which is contained within this thesis.The wheat stem sawfly, Cephus cinctus, is the most destructive insect pest of wheat, Triticum aestivum, in the Northern Great Plains of North America. Biological control by Bracon cephi and Bracon lissogaster is an important tool for integrated pest management of this pest, but parasitism rates are difficult to predict. Therefore, the main objective of this research was to characterize aspects of the reproductive biology of both parasitoid species to provide information that could enhance their effectiveness in biological control of C. cinctus. First, we investigated the role of diapause and the effects of sucrose feeding on reproduction of females. For that, we provided sucrose solution to overwintering and summer generation adult females, and we quantified and compared their longevity, egg load and egg volume. Our results showed no differences between overwintering and summer individuals of B. cephi and B. lissogaster. In contrast, sucrose feeding, increased longevity and egg load of both species and generations. The egg load of B. cephi was surprisingly low compared to B. lissogaster. However, only B. cephi increased egg volume when sucrose was provided. Our findings highlighted the contrasting life histories of both species, and showed the potential of sugar resources in enhancing their reproductive capacity. Subsequently, we investigated the effect of flower nectar on the same, above mentioned, reproductive traits of parasitoids. We chose buckwheat (Fagopyrum esculentum), lacy phacelia (Phacelia tanacetifolia), deerhorn clarkia (Clarkia pulchella), canola (Brassica napus), and safflower (Carthamus tinctorius) based on their occurrence as native plants, use in pollinator enhancement, and occurrence in rotational or cover crop plantings in Montana. We found that only B. cephi females benefitted from these flowering plants. The longevity and egg volume of females increased with buckwheat, and egg volume increased with both buckwheat and the native species, deerhorn clarkia. The strong effect of buckwheat on reproduction of B. cephi females suggests that flowers with similar nectar quality might have similar impacts. This information will be of great importance for selection of suitable flower species to enhance reproductive capacity of parasitoids through habitat management. Collectively, this research showed that there is potential to enhance effectiveness of parasitoids with sugar supplementation.Item Crop damage by wheat stem sawfly as related to soil water holding properties(Montana State University - Bozeman, College of Agriculture, 1995) Heilig, Jeanne Ann KirchnerItem Spatial and biotic interactions of the wheat stem sawfly with wild oat and Montana dryland spring wheat(Montana State University - Bozeman, College of Agriculture, 2002) Sing, Sharlene ElizabethItem 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 Integrated management of the Wheat Stem Sawfly by exploiting semiochemicals to enhance trap crops(Montana State University - Bozeman, College of Agriculture, 2008) Buteler, Micaela; Chairperson, Graduate Committee: David K. Weaver; Perry R. Miller (co-chair)The wheat stem sawfly, Cephus cinctus Norton (WSS) causes significant damage in cereal crops in the northern Great Plains of North America. Recently, the use of winter wheat as a trap crop to protect spring wheat from this insect pest in a wheat-fallow cropping system was evaluated, yielding promising results. Subsequently, the overall objective of this dissertation research was to improve the efficacy of winter wheat trap crops to manage the WSS. Oviposition behavior studies in the presence of hosts infested by conspecifics showed that WSS did not avoid infested hosts. These results confirmed the potential of a trap to provide a sink for multiple eggs, resulting in increased WSS mortality due to cannibalism. I identified suitable winter wheat cultivars based on agronomic characteristics that influence WSS behavior in conjunction with the emission of behaviorally active plant volatiles, as well as the performance of the cultivars in the area where the pest occurs. Results from this study identified five cultivars, Norstar, Morgan, BigSky, Neeley, and Rampart, with good potential as trap crops. Norstar emitted greater amounts of attractive volatile compound ⁷-ocimene, and was the preferred host in greenhouse choice tests. Based on these results, a perimeter trap cropping trial comparing three winter cultivars as traps (Norstar, Neeley and Rampart) to protect spring wheat was conducted for two consecutive years. Two spring wheat cultivars differing in suitability for infestation by sawflies were chosen as the main crop.