Theses and Dissertations at Montana State University (MSU)
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Item Microbial ecology of mosquitos and ticks(Montana State University - Bozeman, College of Letters & Science, 2017) Pinkham, Nicholas Vernon; Chairperson, Graduate Committee: Seth WalkHost evolutionary history has been shown to select for distinct host associated microbial communities over large evolutionary time scales. The microbiomes of disease vector have been shown to alter the capacity of their host to vector pathogens. Much remains to be understood about how the microbiome of mosquitos and ticks assemble in situ. We conducted a large-scale investigation of microbiome composition between mosquito species as well as a second investigation of microbiomes of brown dog ticks collected in Iquitos, Peru. Intraspecific and interspecific bacterial community diversity was compared across 26 species of mosquitoes collected in Montana. Previous studies of lab reared mosquitoes report greater variation in microbial communities between species than within. Using 16S rRNA sequencing we observed a large amount of intraspecific variation in microbiomes, as well as different species hosting very similar microbiomes. The tick microbiome was found to be dominated by a few select community members that were seen at an extremely high abundance and resembled intracellular tick-borne pathogens. It is common for ticks to host endosymbionts that closely to human pathogens but are not pathogenic themselves. Negative interactions were seen between the most abundant organism observed in the ticks.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 Bionomic investigations of Aedes nigromaculis (Ludlow) (Diptera: Culicidae) with special reference to oviposition(Montana State University - Bozeman, College of Agriculture, 1958) Warren, Jack W.Item The influence of ambient temperature on the susceptibility of Aedes aegypti to the pyrethroid insecticide Permethrin(Montana State University - Bozeman, College of Agriculture, 2014) Whiten, Shavonn Reezale; Chairperson, Graduate Committee: Robert K. D. PetersonInsecticides are the most common management strategy used for the control of mosquitoes. Changes in ambient temperature can alter the toxicity of insecticides to ectothermic organisms. Studies show organophosphate insecticides exhibit a positive correlation between ambient temperature and mortality for many insect species, and carbamate insecticides exhibit a slightly negative to positive correlation between ambient temperature and mortality. Pyrethroid insecticides exhibit a distinctly negative correlation between increasing ambient temperature and mortality for insects. However, this relationship has not been systematically studied for adult mosquitoes. Therefore, we examined the influence of temperature on the susceptibility of adult Aedes aegypti (Diptera: Culicidae) when exposed to permethrin. Dose-response probit regression lines and the median lethal concentration, LC50, were estimated for adult Ae. aegypti when exposed to eight concentrations of permethrin (ranging from 0.06 - 0.58 ng/cm 2) at each of the following temperatures, 16, 23, 26, 30, 32, and 34 °C for 24 hours in bottle assays. The estimated LC50 for each temperature was 0.25, 0.34, 0.36, 0.48, 0.26, 0.31 ng/cm 2, respectively. Results indicated a negative correlation between temperature and mortality from 16 °C to 30 °C, a positive correlation between temperature and mortality from 30 °C to 32 °C, and a negative correlation between temperature and mortality from 32 °C to 34 °C. Most important, the largest negative temperature coefficient (-1.92) was observed at 30 °C. If mosquito populations are expanding in space and time because of increased temperatures due to global warming and cannot be managed as effectively with pyrethroids, the spread of mosquito-borne diseases may pose considerable risk to public health.Item An ecological risk assessment for mosquito insecticides(Montana State University - Bozeman, College of Agriculture, 2007) Davis, Ryan Scott; Chairperson, Graduate Committee: Robert K. D. Peterson.West Nile Virus (WNV) has been a concern for people across the North America since the disease was observed in the summer of 1999. WNV has caused the largest arboviral encephalitis epidemic in U.S. history. In response, vector management programs have been implemented. Concerns have been raised about these programs My ecological risk assessments focused on six common mosquito adulticides used in vector management, including 3 pyrethroids, pyrethrins, 2 organophosphates, a synergist, and 4 larvicides. Both aquatic and terrestrial non-target organisms were considered for acute and chronic exposures to the adulticides and larvicides. Tier I exposure estimates for adulticides were derived using modeling software. A probabilistic assessment was conducted for the adulticides to account for variability within the exposure models. The larvicide risk assessment included an even settling model into a standard farm pond. Risk quotients (RQ) were obtained by comparing exposure to toxic endpoints. Organophosphates breached a risk quotient (RQ) level of concern (LOC) for amphipods.Item Environmental concentrations, fate, and risk assessment of insecticides used for adult mosquito management(Montana State University - Bozeman, College of Agriculture, 2008) 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. Due to a lack of studies examining the environmental fate of ULV insecticides and because previous risk assessments have shown that environmental concentrations of insecticides contributed the largest amount of variance to the estimated total exposure, I measured deposition onto surfaces and air concentrations of permethrin and naled. I also conducted risk assessments for human and other non-target organisms using the values I measured. Deposition concentrations of permethrin and naled generally decreased as distance from the spray source increased. Overall, approximately 3.2% of the permethrin and 15% of the naled applied deposited on the ground within 75 m from the spray source 1 h after application. Concentrations of permethrin and naled 12 h after application were not significantly different than concentrations 1 h after application. The results of my probabilistic human-health risk assessment using actual environmental concentrations showed that previous risk assessments overestimated risks. Thus they were conservative in protecting human health. The non-target risk assessment and field bioassay using the house cricket, Acheta domesticus (L.), as a surrogate for medium- to large-bodied ground dwelling insects showed that ULV applications most likely would not result in impacts on populations. I also measured actual environmental concentrations of pyrethrins and piperonyl butoxide (PBO) after aerial ULV applications. Pyrethrins were not detected in the water or on deposition pads. However PBO was detected in the water and on deposition samples, but concentrations rapidly decreased to background levels by 36 h after application. The estimated risks of pyrethrins and PBO to aquatic surrogates were lower than those estimated by previous ecological risk assessments. My study is the first to relate actual environmental concentrations of ULV insecticides to estimates of human-health risks. Results of my environmental fate studies, human-health and non-target risk assessments, and the current weight of scientific evidence, demonstrate that the risks to humans and the environment after ULV applications of insecticides most likely are below regulatory levels of concern.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.Item Mosquito populations in the Powder River basin, Wyoming : a comparison of natural, agricultural and effluent coal bed natural gas aquatic habitats(Montana State University - Bozeman, College of Agriculture, 2007) Doherty, Melissa Kuckler; Chairperson, Graduate Committee: Greg Johnson.Coal bed natural gas development in northeastern Wyoming has increased surface water in ranching and agricultural areas over undeveloped land. This increase of water increases larval habitat for mosquitoes, potentially increasing adult populations of West Nile virus vector mosquitoes. I compared adult and larval mosquito populations in four different habitat types in the Powder River basin including agricultural, natural, CBNG and upland sagebrush steppe. Adult mosquitoes were sampled weekly (2004) or bi-weekly (2005) using CDC miniature black-light traps baited with dry ice. A fixed-effect mixed model indicated that in a normal rainfall year (2005) mature CBNG ponds had the highest adult mosquito populations of all sites sampled, and the highest population of the WNV vector Culex tarsalis. In a drought year (2004) where total rainfall from May - August was 59% of the seasonal average, agricultural areas had the highest mosquito abundance, likely due to increased irrigation. Adult Culex tarsalis tested positive for WNV across the PRB in 2004 and 2005, with highest minimum infection rates in those areas with large Culex tarsalis populations.