Browsing by Author "Ode, Paul, advisor"
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Item Open Access Improving integrated pest management of wheat stem sawfly (Hymenoptera: Cephidae)(Colorado State University. Libraries, 2021) Peirce, Erika S., author; Ode, Paul, advisor; Peairs, Frank, advisor; Rand, Tatyana, committee member; Haley, Scott, committee memberThe wheat stem sawfly (Cephus cinctus Norton) has been a major pest of cultivated wheat (Triticum aestivum L.) for over 100 years. It is difficult to estimate the damage of this insect. Still, conservative calculations estimate the grain-yield loss to exceed 30%, and the economic losses exceed $350 million annually in affected regions in the United States of America. This estimate does not include Colorado, so we expect the current figure to be much higher. Most economic loss is caused when the larva reaches the final instar when it creates a hibernaculum (stub) by cutting the stem above ground level just before harvest, which causes the wheat stem to fall. Fallen stems are difficult to harvest and are easily blown away. The life cycle of this pest makes it difficult to control, and current management strategies are not always effective. My dissertation aims to improve current integrated pest management strategies to control the wheat stem sawfly better. Chapter 1 briefly introduces the three aspects of integrated pest management that I studied: plant resistance, biological control, and cultural control using trap crops. Breeding for host-plant resistance is of particular importance for the management of wheat stem sawfly and is often considered the most effective. In Chapter 2, I review the current literature on plant resistance to the wheat stem sawfly. First, I examine host plant resistance using solid pith expression. Solid pith expression is the most common mechanism of resistance to the wheat stem sawfly. However, expression and control are inconsistent and often impacted by environmental variables. Another drawback to solid stemmed varieties is how biological control can be affected by solid stem expression. Next, moving away from the solid stem, I explore the literature on resistance due to host-preference and new resistance mechanisms derived from wheat landraces. I conclude this chapter by suggesting improvements to breeding for wheat stem sawfly resistance, such as screening for resistance and a deeper analysis of host plant metabolism. Given the variability of current resistant genotypes, I developed a new screening method for resistance described in Chapter 3. I report a novel screening method where plants are grown in the greenhouse in conetainers under optimal conditions and then subjected to a natural infestation in the field. Using this method, I was able to examine host preference as well as host suitability. For this experiment, I chose seven winter wheat genotypes with different levels of pith expression to measure host preference and suitability and compared results to field trials. Results of the conetainer study showed similar sawfly infestation amounts as those observed in the field study, which confirms the robustness of the conetainer assay. In addition, the smallest larvae and lowest infestation amounts were found in a solid-stemmed variety in 2019 and a semi-solid stemmed variety in 2020. This screening method will allow wheat breeders and entomologists to evaluate host plants for various resistance traits gather information on host preference and suitability. The wheat stem sawfly can be successfully controlled by biological control. However, in Colorado, we have not observed high populations of the common biological control agents of the wheat stem sawfly. Chapter 4 examined the prevalence of two Bracon parasitoids, Bracon cephi Gahan and B. lissogaster Muesebeck, and their host the wheat stem sawfly. I assessed the degree of non-crop and crop host plant use and responses to landscape composition. I also found no parasitism by either Bracon species in our three-year statewide winter wheat survey. Still, I found small populations of Bracon in non-crop landscapes throughout eastern and western Colorado. I used model selection to examine how local (500 m scale) and landscape (5 km scale) cover of suitable non-crop and crop habitats potentially affect Bracon and wheat stem sawfly abundances. My best fit model for wheat stem sawfly suggests that a decrease in non-crop cover at the landscape scale increases wheat stem sawfly infestation in non-cultivated grasses. My best fit model for Bracon parasitism suggests an increase in wheat cover at the local level results in the greatest increase in the odds of parasitism by either species of Bracon. Herbaceous cover at local and landscape scales were also significant predictors of Bracon parasitism. This study suggests that pests and natural enemies respond differently to landscape composition, and these responses should be evaluated before management decisions are made.Item Open Access Indirect interactions between galling insects as mediated by a non-native plant(Colorado State University. Libraries, 2021) Lucci-Rimer, Hayley, author; Ode, Paul, advisor; Balgopal, Meena, advisor; Bean, Dan, committee member; Ocheltree, Troy, committee memberRussian knapweed (Rhaponticum (=Acroptilon) repens) is a non-native plant species that has spread throughout the western United States, out-competing native and crop species. Two host-specific gall forming insects - the stem-gall wasp Aulacidea acroptilonica (Hymenoptera: Cynipidae) and the tip-gall midge Jaapiella ivannikovi (Diptera: Cecidomyiidae) - have been employed as biological control agents to manage its spread. However, the nature of the intra- and interspecific interactions between these two insect species is not fully understood even though this information is vital to successfully controlling Russian knapweed. Examining these interactions also contributes to a growing body of knowledge on plant-mediated indirect interactions, which are prevalent among herbivorous insects. To determine the nature of these interactions (e.g., positive, negative, or neutral) and the effects that the insects, together and separately, have on Russian knapweed, I performed studies in the greenhouse and at field sites throughout Colorado. I found evidence for a negative or neutral interspecific relationship, a negative or neutral intraspecific relationship among midges, and a positive or neutral relationship among wasps. The nature of these interactions is likely density and resource dependent. The associations between each insect species and measures of plant growth and reproductive capacity were mixed across the two studies, at times showing positive, negative, or neutral relationships. More studies that consider insect density, water availability, and resource allocation within Russian knapweed should be performed to better determine how the insects interact with one another and what their effects on Russian knapweed may be under varying conditions.Item Open Access Plant-mediated interactions among gall forming insects(Colorado State University. Libraries, 2020) Barosh, Theresa, author; Ode, Paul, advisor; Bean, Dan, committee member; Smith, Melinda, committee member; Kondratieff, Boris, committee memberRussian knapweed (Rhaponticum (=Acroptilon) repens (L.) Hidalgo) is one of the most troubling exotic weeds throughout the western United States invading many public and private lands. A classical biological control agents, the gall midge (Jaapiella ivannikovi Fedotova), is a parasite on Russian knapweed, forming galls on the plant, inside which J. ivannikovi broods feed and develop. This system provides an opportunity to consider plant-mediated interactions between midge individuals and considered the merits of integrating other weed management techniques (grazing, mowing, and chemical control before insect release) with biological control. To accomplish this, I conducted releases of gall midge agents at replicated sites throughout Colorado, field cage experiments with simulated grazing, and greenhouse studies. We found that J. ivannikovi initially established across Colorado, however, failed to maintain populations in subsequent years. Interestingly, grazing increases J. ivannikovi establishment. Of further note, J. ivannikovi broods compete with one another even when feeding on different parts of the plant. The results of these experiments indicate that integrating management techniques can increase biocontrol agent establishment. I also question how effective this midge is at reducing Russian knapweed flowering and vegetative growth in the field. This research resulted in recommendations regarding the most judicious use of J. ivannikovi biocontrol agents in terms of where and when agents are most effective for management, and practitioners at the Colorado Department of Agriculture Palisade Insectary have adjusted their strategies accordingly.Item Open Access Plant-mediated interactions between herbivory and soil microbial communities in biocontrol programs of Russian knapweed(Colorado State University. Libraries, 2024) Matos Franco, Giovana, author; Ode, Paul, advisor; Pearse, Ian, committee member; Smith, Melinda, committee member; Trivedi, Pankaj, committee memberRussian knapweed (Rhaponticum repens) is an invasive noxious weed present in the United States and two insect biocontrol agents have been released to assist with its management: the gall midge (Jaapiella ivannikovi) and the gall wasp (Aulacidea acroptilonica). Since their establishment, no concrete impacts of biocontrol agents onto Russian knapweed have been measured, neither their impacts on interactions between Russian knapweed and local microbiomes. To address this knowledge gap, observational and manipulative studies were conducted to investigate the effects of biocontrol agents on Russian knapweed fitness as well as its associated microbiomes. We found that Russian knapweed associates with a core microbiome that can assist with invasion in the introduced range as well as, in root samples collected from sites where gall wasp were present, lower microbiome diversity was observed, indicating potential negative effects on overall plant health. In garden conditions, water availability positively correlated with plant growth, negatively correlated with insect establishment, and shaped microbiomes in root associated tissues. Results of this dissertation highlights how introduction of biocontrol agents shifts pre-established relationships between invasive plants and microbiomes as well as how such relationships could be impacting the success of biocontrol programs.Item Open Access What's the story? The effects of narratives in science classrooms(Colorado State University. Libraries, 2018) Leipzig, Peter, author; Balgopal, Meena, advisor; Ode, Paul, advisor; Doe, Sue, committee member; Knapp, Alan, committee memberWhile effective science communication is crucial, it also presents multiple obstacles for natural science researchers and specialized communicators. This includes a language divide between scientists and the general public, making science less approachable to novices. The use of narratives within science represents a powerful strategy for overcoming these issues. We examined the reported effects of narratives as a communication strategy and reviewed the varying definitions of narratives in the literature. We propose a set of essential elements that differentiate narrative communication from other forms, all of which are useful for researchers seeking to understand the impacts of stories. These elements include events, characters, causality/agency, and conflict/resolution. We also studied the effects of training graduate teaching assistants (GTAs) using narrative communication. We examined i) what narrative elements GTAs incorporated into their own lessons, ii) why they chose to include stories in their classes, and iii) how training affected content knowledge and self-perceptions for GTAs and their undergraduate students. We found that GTAs who were trained using stories were more likely to integrate the narrative elements into their lessons. Additionally, when employing narratives, GTAs focused on the process of science rather than the results. However, the GTAs did not demonstrate or perceive any concrete knowledge gains. Finally, we argue that narratives can and should be incorporated into more introductory courses across multiple disciplines.Item Open Access Wheat stem sawfly oviposition preference and survivorship on winter wheat and downy brome(Colorado State University. Libraries, 2016) Altilmisani, Nuha Mustafa, author; Peairs, Frank, advisor; Ode, Paul, advisor; Bjostad, Louis, committee member; Byrne, Patrick, committee memberThe wheat stem sawfly Cephus cinctus Norton (Hymenoptera: Cephidae) is a major economic pest of wheat in the United States can decrease the yield and grain quality. Wheat stem sawfly infests both cultivated and uncultivated host plants. It is important to understand the oviposition behavior and host selection of the female wheat stem sawfly. Wheat stem sawfly selects the most suitable host for oviposition. The host selection behavior and oviposition preference of wheat stem sawfly for downy brome (Bromus tectorum L.) grass and winter wheat (Triticum aestivum L.) in Colorado was studied to assess whether downy brome is affecting the presence and infestation levels of wheat stem sawfly in winter wheat in northeastern Colorado. Infestation rates and larval development of the wheat stem sawfly were studied for two years (2013 and 2014) at seven commercial winter wheat fields and eight nearby downy brome sites in northeastern Colorado. Stem samples of each plant species were randomly collected per site weekly and sweep samples of sawfly adults were taken after adult emergence. Infestation rate in winter wheat was 12 to nearly 14 times higher than in downy brome throughout the two year survey. Larval mortality was twice as high in downy brome than in winter wheat over the two year survey. More adults were collected in May from winter wheat than from downy brome in the two year survey. Wheat stem sawfly females preferred to oviposit in wheat plants over downy brome. Female oviposition behavior influences by different host quality cues such stem height and diameter, volatile production, and growth stage. Host selection and oviposition preference by wheat stem sawfly females were studied with a combination of greenhouse choice and no-choice tests using a susceptible (hollow stem) winter wheat variety 'Byrd', a resistant (solid stem) winter wheat variety 'Bearpaw', and downy brome. Female sawflies in the no-choice tests laid similar numbers of eggs in Byrd and Bearpaw plants irrespective of growth stage, which were approximately 2.5 times the number of eggs laid on downy brome. Similarly, when given a choice, females laid similar numbers of eggs on Byrd and Bearpaw, but nearly twice as many eggs on either of these two cultivars than on downy brome. Females preferred to oviposit in larger diameter plant stems. However, stem height did not affect female preference for plants at growth stage Zadoks 49, but females prefered taller stems at growth stages Zadoks 32 and 60. Larval survivorship was lowest in the solid stem Bearpaw and was highest in downy brome and the hollow-stem Byrd. Hollow stem wheat had the highest larval survivorship. Female wheat stem sawflies use chemical cues from plants to identify a suitable host for oviposition. A Y-tube bioassay was developed to evaluate female wheat stem sawfly behavior in response to an airflow that passed over winter wheat cultivars and downy brome. Choice and no-choice tests were conducted with three host plants: wheat cultivars Byrd and Bearpaw and downy brome at three different growth stages: Zadoks 32, 49, and 60. Adult females were attracted to wheat cultivars Byrd and Bearpaw over downy brome at all growth stages. Downy brome was least preferred (31.82%) by female wheat stem sawfly in choice test of Bearpaw vs. downy brome at Zadoks 32 while it was equally preferred (49.21%) in the choice test of ‘Byrd vs. downy brome' at growth stage of Zadoks 60. The female's response speed did not differ when given a choice between the two wheat cultivars Byrd and Bearpaw. However, females were faster in making a choice (100% ≈ 86% females made fast choice) toward each of wheat cultivars over downy brome in the choice tests of Bearpaw vs. downy brome and Byrd vs. downy brome at all growth stages.Item Open Access Winners and losers in toxic relationships affecting parasitoid wasps(Colorado State University. Libraries, 2020) Paul, Ryan Lee, author; Ode, Paul, advisor; Bjostad, Louis, committee member; Blumenthal, Dana, committee member; Naug, Dhruba, committee memberParasitoids are insects that develop on or inside another insect host, ultimately killing the host to complete their own development. Nearly every terrestrial plant-herbivore system has a suite of associated parasitoids. Success of parasitoids and their ability to regulate herbivore populations depends on interactions between multiple trophic levels. Of particular interest is the role of toxic chemicals that mediate interactions among species of plant-herbivore-parasitoid (tri-trophic) systems. My dissertation explores interactions involving toxins that affect parasitoids via multiple trophic levels. Plants produce a number of toxins to defend against herbivores that can also have consequences for parasitoids. In Chapter 2, I review the current published research on plant defense toxins and parasitoid interactions. The effects on parasitoids vary based on mechanism of interactions, study system, and life history of parasitoids. I first discuss the evidence of plant defense impacts on host immunity and the direct impacts of plant chemistry on parasitoid fitness. Then I explore the well-studied glucosinolate defenses found in the plant families Brassicaceae and Capparaceae as a case study on plant toxin and parasitoid interactions. I also review the current evidence for the commonly presented hypothesis that plant defense effects are reduced at higher trophic levels. Finally, I examine the recent advances in research on reciprocal influence of parasitoids on plant toxin expression. Despite the growing number of studies exploring the effects of plant toxins on parasitoids, the effects of variability in the expression of plant toxins on parasitoids has received little attention. Variability in plant toxins negatively affects herbivores but the influence of toxin variability on the ability of parasitoids to suppress herbivore populations is unclear. In Chapter 3, I studied the effects of variability in the plant defensive toxin, xanthotoxin, on development of a polyembryonic parasitoid of a generalist caterpillar. Parasitized caterpillars were fed artificial diets containing either different constant concentrations of xanthotoxin or multiple diets containing varying levels of xanthotoxin but with the same mean as the constant concentration treatment. Parasitoids performed worse on diets containing constant high levels of xanthotoxin. However, parasitoids were unaffected when herbivores fed on diets varying between high and low levels of xanthotoxin, compared to constant diets with the same mean. Herbivore suppression is therefore greatest when experiencing varying plant defense diets which strengthens bottom-up impacts and maintains equal top-down pressures. Parasitoids may also influence expression of plant defense toxins. Many solitary parasitoids reduce herbivore feeding by killing the host before it completes development. However, gregarious parasitoids often cause the host to feed more, removing the plant's advantage of attracting these parasitoids. Since toxins are costly to produce, plants whose herbivores are consistently attacked by gregarious parasitoids which increase herbivore damage are expected to increase toxin production. In Chapter 4, I compared the induction response of glucosinolate defenses in Brassica rapa plants to feeding by caterpillars parasitized by either solitary or gregarious parasitoids. Plants produced increased concentrations of defensive toxins when fed upon by caterpillars parasitized by gregarious parasitoids than when unparasitized or parasitized by solitary parasitoids. By using caterpillars at the same earlier developmental stages, which feed the similar amounts, I show that plants respond to parasitoid identity rather than feeding amount. This research demonstrates the unique response plants can have to herbivores attacked by parasitoids with different life histories. Toxins in tri-trophic systems are not only used by plants to defend against colonizing insects, but also by parasitoids in competition. A single herbivore species is often attacked by more than one parasitoid species (multiparasitism). When multiparasitism occurs, the larval parasitoids of the different species must compete for control of the host, usually to the death. In one such system, the solitary parasitoid Cotesia rubecula generally outcompetes the gregarious C. glomerata when they share a host. In the final chapter (Chapter 5), I explore the role of oviposition fluids as a source of toxins in larval competition between C. rubecula and C. glomerata. Oviposition fluids are injected along with eggs into a host by adult C. rubecula. These fluids are responsible for many physiological changes in the host, but their role in competition has received little attention. I injected caterpillars parasitized by C. glomerata with individual oviposition fluids from C. rubecula without a C. rubecula egg or larva. Many C. glomerata individuals were deformed in caterpillars injected by C. rubecula oviposition fluids. I demonstrate a physiological suppression mechanism that a C. rubecula larva uses to outcompete heterospecific larvae inside the host. Furthermore, I provide evidence for C. rubecula larvae using multiple mechanisms to suppress competitor development at several life stages. This study demonstrates a secondary competitive function beyond the physiological host changes for C. rubecula oviposition fluids and highlights the importance of competition in driving characteristics of parasitoids.