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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 Effect of agronomic practices on disease incidence, severity, and impacts in Montana cropping systems(Montana State University - Bozeman, College of Agriculture, 2017) Ranabhat, Nar Bahadur; Chairperson, Graduate Committee: Fabian D. Menalled; Mary Burrows (co-chair)Integrated pest management is at the foundation of sustainable cropping systems. This thesis investigated 1) the influence of alternative host plants and agronomic practices on Wheat streak mosaic virus (WSMV) risk, and 2) how cover crop termination methods influence diseases in grazed organic, tilled organic, and chemical no-till systems. To assess the influence of alternative hosts including volunteer wheat, Bromus tectorum, Setaria viridis, and Zea mays on WSMV incidence and its vector, the wheat curl mite (Aceria tosichella, WCM) movement during the fall, a 'trap plant' capture system was used. In 2013, alternative hosts had similar WCM infestation levels compared to the control in most weeks. In 2014, spring planted B. tectorum and volunteer wheat increased the incidence of WSMV and abundance of WCM compared to control. In a study assessing the impact of planting date and winter wheat variety on WSMV incidence, there was almost no infection of WSMV across resistant wheat varieties. However, Pronghorn, a susceptible wheat variety, had a higher WSMV incidence at the early planting date than recommended and late planting dates. In a companion study of the impact of wheat variety and timing of N application on WSMV incidence, results did not differ across N application timing across resistant varieties. However, early spring N application in 2014 had a higher WSMV incidence compared to fall and late spring N application in Pronghorn and Yellowstone. A study assessing the impact of cropping systems on diseases indicated that disease incidence during the transition to organic period in 2013 and 2014 as well as an established organic year, 2016, was similar at tillering and flowering stages of winter wheat between the grazed organic, tilled organic, and chemical no till system. However, disease incidence was variable between systems at the matured growth stage in 2014 and 2016. In 2015, disease incidence varied between systems at all growth stages. Overall, disease severity was similar in winter wheat between grazed organic, tilled organic, and chemical no till systems, indicating disease is not a major constraint to organic methods of crop production during the transition period.Item Exposure and risk to non-target receptors for agricultural spray drift of formulation types and adjuvants(Montana State University - Bozeman, College of Agriculture, 2017) Preftakes, Collin James; Chairperson, Graduate Committee: Robert K. D. Peterson; Jerome J. Schleier III, David K. Weaver, Greg Kruger, Ryan Henry and Robert K. D. Peterson were co-authors of the article, 'Effect of insecticide formulation and adjuvant combination on agricultural spray drift' which is contained within this thesis.; Jerome J. Schleier III, David K. Weaver and Robert K. D. Peterson were co-authors of the article, 'Non-target insect risk assessment of drift reduction insecticide formulations and spray adjuvants' which is contained within this thesis.Agricultural applications of crop protection products can have negative economic and ecological consequences when spray drift occurs. Among the ways to reduce spray drift is to manipulate the physical properties of the spray solution with formulated products and tank additives, but further research is required to better understand their effects. By measuring spray drift under field conditions and using the results to estimate ecological risk, we characterize the effect on drift for two formulation types and two adjuvants. A field study was conducted where off-target ground deposition and droplet size were measured to indicate spray drift for different combinations of the formulations and adjuvants, accounting for environmental conditions. Each treatment combination was also sprayed in a wind tunnel set up to precisely measure droplet spectra so that these could be related to deposition in the field. Finally, an efficacy experiment was conducted to test for tradeoffs between drift reduction and pest control. Results from the field study suggest that as much as 32% drift reduction was achieved by selecting between the tested formulation types, and as much as 62% by incorporating certain spray adjuvants, but this effect depended on the formulation/adjuvant combination. Treatments with smaller droplet sizes had greater drift, and there was no tradeoff between drift reduction and pest control. We assessed ecological risk for terrestrial insects in non-target habitats using a novel approach to estimate insecticide residue on plant surfaces based on ground deposition data from the field study. Exposure concentrations were combined with a cumulative distribution of species sensitivities to statistically represent the risk of toxicity for the active ingredient that was used and the levels of drift that were observed. We found that substantial reductions in the percentage of insect species affected in an off-target area could be achieved by certain formulation types and adjuvants. This work could be useful for developing a classification scheme for formulated products and tank additives based on their potential for reducing spray drift and ecological risk to non-target receptors.Item Toxicity, exposure, and risk of insecticides used for mosquito management on the alfalfa leafcutting bee, Megachile rotundata(Montana State University - Bozeman, College of Agriculture, 2017) Piccolomini, Alyssa Margaret; Chairperson, Graduate Committee: Robert K. D. Peterson; Shavonn R. Whiten, Michelle L. Flenniken, Kevin M. O'Neill and Robert K. D. Peterson were co-authors of the article, 'Acute toxicity of permethrin, deltamethrin, and etofenprox to the alfalfa leafcutting bee, Megachile rotundata (Hymenoptera: Megachilidae)' which is contained within this thesis.; Michelle L. Flenniken, Kevin M. O'Neill and Robert K. D. Peterson were co-authors of the article, 'Leaf residue toxicity and risk of mosquito insecticides to the bees, Megachile rotundata and Apis mellifera' which is contained within this thesis.; Michelle L. Flenniken, Kevin M. O'Neill, Ruth P. O'Neill, Casey M. Delphia and Robert K. D. Peterson were co-authors of the article, 'The effects of an ultra-low-volume application of etofenprox for mosquito management on Megachile rotundata (Hymenoptera: Megachilidae) larvae and adults in an agricultural setting' which is contained within this thesis.The alfalfa leafcutting bee, Megachile rotundata F. (Hymenoptera: Megachilidae), is one of the most managed solitary bees and is an important pollinator of many crops, especially alfalfa, Medicago sativa L. However, little is known about its response to insecticides, specifically pyrethroids, which are frequently used to manage populations of adult mosquitoes that inhabit the same areas. Current regulatory requirements for insecticide toxicity to non-target insects focus on one pollinator, the honey bee, Apis mellifera L., but this species does not represent all insect pollinator species in terms of response to insecticides. Therefore, we characterized the toxicity and risk of three pyrethroid insecticides (permethrin, deltamethrin, and etofenprox) on adult M. rotundata in both laboratory and field settings. The median lethal dose, LD 50, was estimated for adult M. rotundata females when exposed to each pyrethroid to serve as a baseline toxicity test to determine the susceptibility of M. rotundata to these insecticides. The range of concentrations for permethrin and etofenprox ranged from 0.0075-0.076 microgram/bee and the range for deltamethrin was 0.0014-0.0075 microgram/bee. The estimated LD 50 results for permethrin, etofenprox, and deltamethrin were 0.057, 0.051, and 0.0016 microgram/bee, respectively. After obtaining the LD 50 values, we compared female respiration rates after dosing of each LD 50 endpoint. In a field study, we applied a formulated version of each active ingredient at the maximum labeled rate of 0.017 kg/ha over an alfalfa field via ultra-low-volume (ULV) applicator and observed mortality of both adult A. mellifera and M. rotundata for 48-hr after exposure. In both species, there was no significant difference in mortality between control and treated groups for any of the formulations. In another field study, a formulated version of etofenprox was applied in an alfalfa field at the half-maximum labeled rate of 0.003 kg/ha and directly targeted to M. rotundata nests. There was no significant difference in mortality between control and treated groups. We also did not observe a significant difference in the number of adults reared between treated vs. control shelters. Results from the field studies suggest that the risk of mortality from these insecticides applied via ULV applicators may be relatively low.Item Development of an environmental fate model for risk assessment of ultra-low-volume insecticides(Montana State University - Bozeman, College of Agriculture, 2012) Schleier, Jerome Joseph, III; Chairperson, Graduate Committee: Robert K. D. Peterson.One of the most effective ways of managing adult mosquitoes that vector human and animal pathogens is the use of ultra-low-volume (ULV) insecticides. The U.S. Environmental Protection Agency uses models that are not validated for ULV insecticide applications and exposure assumptions to perform their human and ecological risk assessments. Currently, there is no validated model that can accurately predict deposition of insecticides applied using ULV technology for adult mosquito management. In addition, little is known about the deposition and drift of small droplets like those used under conditions encountered during ULV applications. The objectives of my dissertation were to perform field studies to measure environmental concentrations of insecticides and to develop a validated model to predict the deposition of ULV insecticides, and use the data generated from the field study to perform refined human and aquatic ecological risk assessments. To model the field data collected during the summers of 2009-2011 a regression model selected by the Bayesian Information Criterion and k-fold cross validation was used to validate the selected model. k-fold cross validation demonstrated that the mean square error and mean square prediction error were similar indicating good predictive ability. The human-health risk assessment demonstrated that previous risk assessments used conservative exposure scenarios that overestimated risks, thus being conservative in protecting human health. Our results demonstrated a 10-fold reduction in the RQ estimates when comparing risk assessments using estimated environmental concentrations and actual environmental concentrations from the environmental fate model. Because I used a large data set to model concentrations deposited on surfaces, this variance in exposure is due to the inherent variability in deposition concentrations after ULV applications and, therefore, would not warrant further refinement to improve risk assessments. The aquatic risk assessment using actual environmental concentrations showed that the 95th percentile estimated concentration would result in less than 0.0001% of the potentially affected fraction of species reaching their respective LC50. Our results are supported by the weight of evidence that pyrethroids applied by ground-based ULV applications will not result in deleterious effects on aquatic organisms.