Browsing by Author "Mullins, Donald E."

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    Assessing performance and compatibility of three Laricobius species as predators of hemlock woolly adelgid, Adelges tsugae
    Story, Heather Marie (Virginia Tech, 2010-05-19)
    Predation, egg production and survivorship of Laricobius nigrinus Fender, L. rubidus, LeConte, and L. osakensis Montgomery and Shiyaki (proposed), predators of hemlock woolly adelgid, Adelges tsugae, Annand, were investigated in the laboratory and in the field. In individual assays, L. rubidus oviposited fewer eggs than either L. nigrinus or L. osakensis. In assays containing congeneric or conspecific groups of adult Laricobius, L. osakensis preyed upon the greatest number of ovisacs. When all three species were together, the numbers of ovisacs preyed upon were similar to the mean of all three individual species. Adult predators fed on few eggs and did not exhibit any species preference. The numbers of A. tsugae ovisacs fed upon did not differ significantly by groups of congeneric or conspecific Laricobius larvae. Laricobius adults and larvae had high survival rates throughout all experiments. In the field, predators were enclosed in sleeve cages with both high (> 120 ovisacs) and low (< 90 ovisacs) A. tsugae densities for 1 wk. All branches with caged beetles had significantly greater numbers of ovisacs preyed upon than branches caged without beetles. No differences in predation or egg production were found among the conspecific and congeneric groupings. Predation was uniformly higher at the high prey-density than at the low prey-density. Survivorship among predators did not differ significantly at either prey density. Results from both laboratory and field experiments suggest that these species are able to co-exist and can be in the same location for biological control of A. tsugae.
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    Assessing the Economic Impacts of Tomato Integrated Pest Management in Mali and Senegal
    Nouhoheflin, Theodore (Virginia Tech, 2010-07-07)
    This study assesses the research benefits of IPM technologies and management practices aimed at reducing the virus problem in tomatoes in West Africa. Surveys are conducted with producers, extension agents, scientists, and other experts to obtain information and economic surplus analysis is used to project benefits over time. The determinants of adoption are assessed using a probit model. Results show that adoption of the host-free period reduced the amount of insecticide sprays by 71% and the production cost by $200/ha in Mali. The cost-benefit analysis indicated that the use of virus-tolerant seeds generated profits ranging from $1,188 to $2,116/ha in Mali and from $1,789 to $4,806/ha in Senegal. The likely factors influencing adoption of the technologies in both countries are the frequency of extension visits, farmer's field school training, gender, education, seed cost, tomato area, and experience in tomato losses. The benefits in the closed economy market vary from $3.4 million to $14.8 million for the host-free period, $0.5 million to $3 million for the virus-tolerant seeds, and $4.8 million to $21.6 million for the overall IPM program. In the same order, the benefits under the open economy market range from $3.5 million to $15.4 million, $0.5 million to $3million, and $5 million to $24 million. The distribution pattern indicates that producers gain one-third and consumers two-thirds of the benefits. Our results support policies aiming to increase the adoption rate or the expected change in yield.
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    An Assessment of Non-Apis Bees as Fruit and Vegetable Crop Pollinators in Southwest Virginia
    Adamson, Nancy Lee (Virginia Tech, 2011-02-03)
    Declines in pollinators around the globe, notably the loss of honey bees (Apis mellifera L.) to Colony Collapse Disorder, coupled with a dearth of quantitative data on non-Apis bee pollinators, led to this dissertation research, which documents the role of non-Apis bees in crop pollination in southwest Virginia. Major findings of this first study of its kind in the region were that non-Apis bees provided the majority of pollination—measured by visitation—for several economically important entomophilous crops (apple, blueberry, caneberry, and cucurbits); diverse bee populations may be helping to stabilize pollination service (105 species on crop flowers); landscape factors were better predictors of non-Apis crop pollination service than farm management factors or overall bee diversity; and non-Apis bees in the genera Andrena, Bombus, and Osmia were as constant as honey bees when foraging on apple. Non-Apis, primarily native, bees made up between 68% (in caneberries) and 83% (in cucurbits) of bees observed visiting crop flowers. While 37–59 species visited crop flowers, there was low correspondence between bee communities across or within crop systems ("within crop" Jaccard similarity indices for richness ranged from 0.12–0.28). Bee community diversity on crop flowers may help stabilize pollination service if one or more species declines temporally or spatially. A few species were especially important in each crop: Andrena barbara in apple; Andrena carlini and A. vicina in blueberry; Lasioglossum leucozonium in caneberry; and Peponapis pruinosa and Bombus impatiens in cucurbits. Eight species collected were Virginia state records. In models testing effects of farm management and landscape on non-Apis crop pollination service, percent deciduous forest was positively correlated in apple, blueberry, and squash, but at different scales. For apple and blueberry, pollination service declined with an increase in utilized alternative forage but was positively related to habitat heterogeneity. For squash, percent native plants also related positively, possibly due to increased presence of bumble bees in late summer. Species collected from both bowl traps and flowers was as low as 22% and overall site bee diversity had no effect on crop pollination service, highlighting the value in pollination research of monitoring bees on flowers.
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    Assessment of Soybean Leaf Area for Redefining Management Strategies for Leaf-Feeding Insects
    Malone, Sean M. (Virginia Tech, 2001-08-31)
    Commercially available leaf area index (LAI) meters are tools that can be used in making insect management decisions. However, proper technique must be determined for LAI estimation, and accuracy must be validated for the meters. Full-season soybean require LAI values of at least 3.5 to 4.0 by early to mid-reproductive developmental stages to achieve maximum yield potential, but the relationship between double-crop soybean LAI and yield is unknown. This research (1) evaluated minimum plot size requirements for mechanically defoliated soybean experiments using the LAI-2000 Plant Canopy Analyzer, (2) compared LAI estimates among LAI-2000 detector types which respond to different wavelengths of light, (3) compared LAI-2000 estimates with directly determined LAI values for 0, 33, 66, and 100% mechanical defoliation levels, (4) used linear and non-linear models to describe the response of full-season and double-crop soybean yields to reductions in LAI through mechanical defoliation, and (5) evaluated the response of double-crop soybean yields to reductions in LAI through insect defoliation. The minimum plot size for obtaining accurate LAI estimates of defoliated canopies in soybean with 91 cm row centers is four rows by 2 m, with an additional 1 m at the ends of the two middle rows also defoliated. The wide-blue detector, which is found in newer LAI-2000 units and responds to wavelengths of light from 360 to 460 nm, gave higher LAI estimates than the narrow-blue detector, which responds to light from 400 to 490 nm. The unit with the narrow-blue detector gave estimates equal to directly determined LAI in two of three years for 0, 33, and 66% defoliation levels, while the units with the wide-blue detectors gave estimates higher than directly determined LAI in the two years that they were studied, except for a few accurate 33% defoliation estimates. Therefore, the LAI-2000 usually provides reasonable estimates of LAI. Yield decreased linearly with LAI when LAI values were below 3.5 to 4.0 by developmental stages R4 to R5 in both full-season and double-crop soybean. Usually, there was no relationship between yield and LAI at LAI values greater than 4.0. There was an average yield reduction of 820 ± 262 kg ha⁻¹ for each unit decrease in LAI below the critical 3.5 to 4.0 level; maximum yields ranged from 1909 to 3797 kg ha⁻¹. Insect defoliators did not defoliate double-crop soybean plots to LAI levels less than 4.0, and there was no yield difference between insect-defoliated and control plots. Therefore, double-crop soybean that maintains LAI values above the 3.5 to 4.0 critical level during mid-reproductive developmental stages is capable of tolerating defoliating pest
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    Bed Bug Management in Low-Income, Multi-Unit Housing: An Evaluation of Resident Education and Cost-Effective, Minimally Toxic Suppression Methods
    Stedfast, Molly Logan (Virginia Tech, 2014-06-10)
    In the United States, we have been battling the bed bug (Cimex lectularius L.) resurgence for over ten years. Current treatment methods are labor intensive, time consuming, and very expensive. Many studies have evaluated the efficacy of treatment methods, but few have focused on bed bug suppression in multi-unit housing. Low income, multi-unit housing residents lack basic bed bug knowledge and are particulary vulnerable to bed bug infestations because they are unable to afford conventional treatment. In this study, diatomaceous earth (D.E.), an inexpensive desiccant dust labeled for bed bug control, was evaluated for its efficacy in killing bed bugs, and determined to be successful. A proactive bed bug suppression program that included D.E. was implemented in a low-income housing facility in Harrisonburg, VA. The program consisted of inexpensive, low toxicity, integrated bed bug management methods, including a novel strategy for applying a perimeter barrier of D.E. in apartment units (n = 121). Over the course of one year, both the number of initial infestations and the costs associated with bed bug treatments were reduced. Low-income, multi-unit housing residents (n = 479) from three cities (Harrisonburg and Richmond, VA; New Orleans, LA) were surveyed before and after an educational seminar to assess their bed bug. After attending the seminar, residents (n = 112) significantly improved (P < 0.0001) their bed bug knowledge, and were able to correctly answer more bed bug-related questions than they had before the educational seminar.
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    Behavior and daily activity patterns of specialist and generalist predators of the hemlock woolly adelgid, Adelges tsugae
    Flowers, Robbie Wayne; Salom, Scott M.; Kok, Loke T.; Mullins, Donald E. (University of Arizona, 2007-08-14)
    The behavior and daily activity patterns of two specialist predators, Laricobius nigrinus Fender (Coleoptera: Derodontidae) and Sasajiscymnus tsugae, Sasaji and McClure (Coleoptera: Coccinellidae), and a generalist predator, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), of hemlock wooly adelgid, Adelges tsugae (Hemiptera: Adelgidae), were examined using digital video recording in the laboratory...
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    Behavioral Model and Predistortion Algorithm to Mitigate Interpulse Instabilities Induced by Gallium Nitride Power Amplifiers in Multifunction Radars
    Tua-Martinez, Carlos Gustavo (Virginia Tech, 2017-01-27)
    The incorporation of Gallium Nitride (GaN) Power Amplifiers (PAs) into future high power aperture radar systems is certain; however, the introduction of this technology into multifunction radar systems will present new challenges to radar engineers. This dissertation describes a broad investigation into amplitude and phase transients produced by GaN PAs when they are excited with multifunction radar waveforms. These transients are the result of self-heating electrothermal memory effects and are manifested as interpulse instabilities that can negatively impact the coherent processing of multiple pulses. A behavioral model based on a Foster network topology has been developed to replicate the measured amplitude and phase transients accurately. This model has been used to develop a digital predistortion technique that successfully mitigates the impact of the transients. The Moving Target Indicator (MTI) Improvement Factor and the Root Mean Square (RMS) Pulse-to-Pulse Stability are used as metrics to assess the impact of the transients on radar system performance and to test the effectiveness of a novel digital predistortion concept.
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    Biology and Management of Brown marmorated Stink Bug, Halyomorpha halys (Stål), in Agricultural and Urban Environments
    Aigner, John D. (Virginia Tech, 2016-04-29)
    Brown marmorated stink bug, Halyomorpha halys (Stål), is a crossover pest impacting agriculture and invading urban environments. Studies were conducted to better understand the management of the bug through its physiology, behavior and susceptibility to insecticidal intervention. Halyomopha halys exhibit great variability in overwintering site selection with choices including manmade structures and tree bark. Because of these diverse sites, the bug must have the ability to withstand varying conditions throughout the overwintering cycle. We were able to determine that H. halys is chill intolerant and capable of adapting its tolerance to temperatures by season, sex, and location of acclimation. The mean supercooling point (± SEM) in the winter in Minnesota was -17.06°C ± 0.13° and in Virginia was -13.90°C ± 0.09°. Laboratory experiments conducted in Blacksburg, VA were able to determine baseline lethal high temperatures over time against H. halys adults. To achieve 100% mortality, temperatures fell between 45°C and 50°C, 40°C and 45°C, and 42°C and 45°C, over 15-min, 1-h, and 4-h, respectively. Moving forward, we were able to utilize this information to develop heat treatment guidelines for export shipping cargo infested with overwintering H. halys. In a controlled field experiment, we determined that exposing the coldest areas of an infested vehicle to temperatures greater than 50°C for a minimum of 15 minutes resulted in 100% mortality of overwintering BMSB adults. In 2012 and 2013, citizen scientists were recruited through Virginia Cooperative Extension to assist in evaluating several in home light traps designed to help eradicate overwintering H. halys adults in homes. Over the course of the two year study, fourteen houses participated in the study with 72% of those houses having stink bug activity. It was found that the most effective trap was an aluminum foil pan trap. In 2013, the trap was 19 times more effective at catching stink bug adults than any other trap tested. In September of 2014, a near-field experiment was conducted to determine the residual efficacy of several recommended and labeled insecticides for treatment of homes against invading H. halys adults. This study used constructed window screen bags that were dipped in insecticide solution. After the initial treatment, bugs were exposed to the bags for 24h weekly, up to 54 days after treatment (DAT). It was determined that 2 DAT all insecticides had activity except for indoxacarb. All insecticides lost efficacy after 29 DAT except for lambda-cyhalothrin, beta-cyfluthrin, beta-cyfluthrin + imidacloprid, lambda-cyhalothrin + thiamethoxam, and dinotefuran, which had some measureable activity even after 40 DAT. Each of these insecticides contained a pyrethroid alone or in combination with a neonicotinoid. Laboratory bioassays were conducted to determine the LC50 values of clothianidin, dinotefuran, imidacloprid, and thiamethoxam against H. halys nymphs using a systemic application method. Those LC50 values were found to be 0.077, 0.013, 0.068, and 0.018 ppm, respectively. Field experiments conducted in Virginia in 2012 and 2013 showed a significant reduction of stink bug damage using two soil applications of neonicotinoid insecticides in pepper and tomato. In North Carolina, a single drip irrigation application significantly reduced stink bug damage in 2012 and 2014 using dinotefuran or imidacloprid.
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    Cold Tolerance of Halyomorpha halys (Hemiptera: Pentatomidae) Across Geographic and Temporal Scales
    Cira, Theresa M.; Venette, Robert C.; Aigner, John D.; Kuhar, Thomas P.; Mullins, Donald E.; Gabbert, Sandra E.; Hutchison, W. D. (2016-04)
    The brown marmorated stink bug, Halyomorpha halys (Stål), is native to eastern Asia and is presently invading North America. Little is known about the exposure to and effects of winter temperatures in newly invaded regions on H. halys. The overwintering habitats that this species utilizes vary greatly in their thermal buffering capacity. They naturally overwinter in aggregations beneath loose bark on trees and in cliff outcroppings, but will also commonly aggregate in buildings. Effects of cold temperatures such as mortality and freezing have yet to be quantified in the invading population. We report that H. halys is chill intolerant (i.e., dies before reaching its freezing point), and that the degree of cold tolerance of populations in North America differs by season, sex, and acclimation location. The mean winter supercooling point (+/- SEM) of individuals acclimated in Minnesota was -17.06A degrees C A +/- 0.13 and in Virginia was -13.90A degrees C A +/- 0.09. By using laboratory assays of lower lethal temperatures and ambient air temperature records, we accurately forecasted mortality for field experiments in Minnesota and Virginia. Temperature refugia provided by human-built structures are likely crucial for overwintering survival during atypically cold winters and possibly contribute to the northern geographic range expansion of this economically damaging insect in the temperate climates of North America.
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    Cold-acclimation of the wood cockroach Crytocercus punctulatus (Scudder) (Dictyoptera: Cryptocercidae)
    Hamilton, Robert Lewis (Virginia Tech, 1985-07-05)
    The general overwintering strategy employed by the woodroach, Cryptocerclls punctulatus (Scudder) appears to be fairly typical among freeze-tolerant insects. In this species, as well as others, heat-labile hemolymph ice nucleating factors induce extracellular ice formation at a high subzero temperature (around -6°C), there is a seasonal accumulation of a cryoprotective substance (polyol) and internal ice is tolerated only during the winter. In addition, body water content does not fluctuate seasonally. Hemolymph Ice Nucleating Factors (INF's) have been previously described from members of the following orders of insects: Diptera, Coleoptera, and Hymenoptera. This study documents the occurrence of INF's in a fourth order: Dictyoptera. Cryptocercus punctulatus contains hemolymph ice nucleating factors through out the year. In this species, hemolymph serum freezes at -5.5°C all year long and appears to be initiated by a heat-labile proteinacious nucleating factor. These proteins may function primarily as nucleators in the winter, and perform other function (s) during the other seasons of the year. A sugar alcohol (ribitol), contained in the hemolymph of Cryptocercus punctulatus was found to fluctuate seasonally. Ribitol levels were highest in the winter months, and declined to undetectable levels in the summer. To date, five polyols have been reported as occurring in insect hemolymph. They are: glycerol, sorbitol, mannitol, erythritol, and threitol. There is one report of the occurrence of an unidentified 5-carbon polyol, possibly either arabitol or ribitol from whole body extracts of winter-acclimated collembolans. This thesis documents the occurrence of ribitol in insect hemolymph. It is assumed that ribitol, like other polyols acts as a cryoprotectant to stabilize protein structure, membrane integrity, and reduce osmotic fluctuations in freezing tissues.
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    Comparison of Subterranean Termite (Rhinotermitidae: Reticulitermes) Gut Bacterial Diversity Within and Between Colonies and to Other Termite Species Using Molecular Techniques (ARDRA and 16S rRNA Gene Sequencing)
    Fisher, Marc Lewis (Virginia Tech, 2006-04-25)
    Termites are known to harbor within their gut a diverse assemblage of symbiotic microorganisms. Little work has been done, however, to describe the diversity and function of the bacteria in the economically important eastern subterranean termite, Reticulitermes flavipes. The first object of this study was to characterize the bacterial diversity in the gut of R. flavipes using amplified rDNA restriction analysis (ARDRA) and 16S rRNA gene sequencing. It was determined that ARDRA was an effective technique for characterizing the diversity of the termite gut microbiota. Of the 512 clones analyzed in the ARDRA study, 261 different ARDRA profiles were found. Forty-two 16S rRNA gene sequences were also analyzed, resulting in 33 different ribotypes. Representatives from six major bacterial phyla, Proteobacteria, Spirochaetes, Bacteroidetes, Firmicutes, Actinobacteria, and the newly proposed "Endomicrobia," were discovered. Further analysis indicated that the gut of R. flavipes may harbor as many as 1,318 ribotypes per termite. The second objective was to determine if the gut bacterial diversity could be manipulated by changing the termite's food source. Using ARDRA analysis, I found no evidence that changing the food source affected the termite gut bacterial diversity. In addition, changing the food source did not induce aggression in nestmates fed on different food sources. The third objective was to search for patterns of coevolution between termites and their gut symbiotic bacteria. Using rRNA gene sequences from this study and sequences from public databases (1,450 sequences total), a neighbor-joining tree demonstrated strong evidence for coevolution of termites and their symbiotic bacteria, especially in the phyla Bacteroidetes, Actinobacteria, Spirochaetes, and "Endomicrobia." Many monophyletic clusters were entirely composed of phylotypes specific to Isoptera.
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    Competitive interactions among two specialist predators and a generalist predator of hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae)
    Flowers, Robbie Wayne (Virginia Tech, 2006-04-10)
    Competitive interactions among two specialist predators, Laricobius nigrinus Fender (Coleoptera: Derodontidae) and Sasajiscymnus tsugae Sasaji and McClure (Coleoptera: Coccinellidae), and a generalist predator, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), of hemlock woolly adelgid were evaluated using laboratory, field and video studies. The two specialist predators are part of a biological control program for A. tsugae, and the potential for competition among these species and previously established generalist predators is unknown. In laboratory studies of predator groups in Petri dish assays, the only significant negative effects from competition occurred among conspecifics, resulting in reduced net egg production by L. nigrinus and H. axyridis and reduced feeding by H. axyridis. In contrast, heterospecific combinations showed non-interference. In longer duration field studies of predator groups, held in branch enclosures, predator survival and feeding were not significantly affected by additional predators. Net reproduction was again significantly reduced by conspecifics, while heterospecifics showed non-interference for all predator responses. All predators reduced the number of A. tsugae nymphs of the next generation relative to no-predator controls; however, L. nigrinus had much greater impact overall due to the large number of progeny produced. Video studies revealed that predator behavior varied qualitatively and quantitatively by species, and did not appear to be coordinated temporally or spatially. All species exhibited continuous activity patterns that were punctuated by longer periods of rest. The specialist predators were more selective of feeding and oviposition sites, and rested at more concealed locations than H. axyridis. Conspecifics significantly altered the time allocated to specific behaviors for L. nigrinus and H. axyridis, resulting in reduced predator effectiveness due to increased searching and decreased feeding and oviposition. All predator groups maintained a high degree of spatial separation relative to assay size, suggesting that chemical or tactile cues may be used to regulate their distributions. Overall, these studies suggest that the three predator species will be compatible in this system. Management implications include using multiple-predator species combinations over single-species for biological control of A. tsugae and implementing low-density releases to reduce the potential negative effects of intraspecific competition.
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    A comprehensive modeling approach for BMP impact assessment considering surface and ground water interaction
    Cho, Jae-Pil (Virginia Tech, 2007-04-04)
    The overall goal of this study was to develop a comprehensive tool for assessing the effectiveness of selected BMPs on both hydrology and water quality and to demonstrate the applicability of the system by considering 1) temporally and spatially changing land use management practice in an agricultural watershed and 2) interaction between surface and ground water over the entire system. A user interface and Dynamic Agricultural Non-point Source Assessment Tool (DANSAT) were developed to achieve this goal. DANSAT is the only distributed-parameter, physically-base, continuous-simulation, and multi-soil layer model for simulating impacts of agricultural BMPs on hydrology and water qulality in small agricultural watersheds. DANSAT was applied to QNB plot (18m à 27m) and two agricultural watersheds in Virginia, including Owl Run watershed (1140 ha) and QN2 in the Nomini Creek watershed (216 ha), to evaluate the model components and its performance in predicting runoff, sediment yield, and pesticide load. DANSAT performed well in predicting total runoff and temporal variations in surface runoff for both field-scale and watershed-scale applications. Total percent errors between the measured and predicted results were less than 10% except for one case (39.8% within a subwatershed of Owl Run watershed), while the daily Nash-Sutcliffe model efficiencies were greater than 0.5 in all applications. Predicted total sediment yields were within ±35% of observed values in all applications. However, the performance of DANSAT in predicting temporal trend and spatial distribution of sediment loads was acceptable only within Owl Run watershed, where high correlations between flow rates and sediment loads exist. The predicted total pesticide loads were within ±100% of observed values. DANSAT failed to simulate the temporal occurrence of pesticide loads with a 0.42 daily Nash-Sutcliffe efficiency value. The Dual-Simulation (DS) was developed within the linked ground water approach to resolve problems encountered due to the existence of different temporal scales between DANSAT and the existing ground water models such as MODFLOW and MT3D. The linked approach performed better in predicting the seasonal trend of total runoff compared to the integrated approach by showing an increase in monthly Nash-Sutcliffe efficiency value from 0.53 to 0.60. Surface and subsurface output variables were sensitive to the changes in spatially distributed soil parameters such as total porosity and field capacity. A maximum grid size of 100 m was recommended to be appropriate for representing spatial distribution of topographic, land use, and soil characteristics based on accuracy analysis during the GIS manipulation processes. Larger time-step based on predefined acceptable maximum grid size, decreased the computational time dramatically. Overall sensitivity to different grid sizes and time-steps was smallest for hydrology components followed by sediment and pesticide components. Dynamic crop rotation was considered by DANSAT, and the model successfully simulated the impacts of temporal and spatial changes in crop rotations on hydrology and water quality for both surface and subsurface areas. DANSAT could prove to be a useful tool for non-point source pollution managers to assess the relative effectiveness of temporally and spatially changing BMPs on both surface and ground water quantity and quality.
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    Demography, cold hardiness, and nutrient reserves of overwintering nests of the carpenter ant Camponotus pennsylvanicus (De Geer) (Hymenoptera: Formicidae)
    Cannon, Colleen A. (Virginia Tech, 1990-10-09)
    Overwintering nests of C. pennsylvanicus were dissected and censused. All castes were assayed for glycerol and for changes in nutrient reserves. Spring queens were collected at swarming and allowed to initiate nests. Queens were analyzed for nutrient reserves during the early stages of nest founding. Overwintering nests contained large proportions of larvae and alates. Physical associations within the winter nest were evident between majors and alates, and between larvae and the queen; minors were associated with larvae to a lesser degree. Reproductives and larvae were negatively correlated, and worker caste ratios shifted according to whether an area was dominated by larvae or alates. Winter nest temperatures followed ambient temperatures, though fluctuations were less extreme. Glycerol was detectable in all castes and stages. Major and minor workers were similar in nutrient content. Lipid and protein contributed greater than 80% of dry weight, glycogen less than 20%, and free sugars less than 10%. Lipid was progressively depleted through winter. Majors lost most protein and dry weight between November and January, minors between February and April. Glycogen changes emulated mean ambient temperature patterns. Overwintering gynes possessed large reserves of lipid, up to approximately 62% in mid-winter. Glycogen levels rose and fell with mean ambient temperatures. Most nutrient reserves in founding queens were depleted from the head/thorax region between swarming and first larval emergence; between larval emergence and first worker eclosion, significant losses occurred only in the gaster. Protein alone increased significantly in the gaster prior to larval emergence, after which it was depleted.
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    Determination of Allosteric Solvent Effects Between Acetylcholinesterase and Mosquito Selective Carbamates: Implications for High Throughput Screening of Insecticides
    Swale, Daniel Robert (Virginia Tech, 2009-12-04)
    Malaria is vectored by the mosquito Anopheles gambiae (Ag) in Sub-Saharan Africa and infects approximately 500 million people annually. The increasing prevalence of pyrethroid-resistant mosquitoes has amplified the need for development of new, selective mosquitocides for use on insecticide-treated nets. We have developed several phenyl-substituted N-methylcarbamates producing a high degree of selectivity for Anopheles gambiae acetylcholinesterase (AgAChE) over human AChE. Molecular models suggest alternate conformations (flexibility) of W84 and W431 (Ag numbering) at the hydrophobic subpocket of the AgAChE active site and poor flexibility within human AChE, allowing for the high selectivity of our novel carbamates. Initial selectivity data was obtained through screening of these insecticides while using ethanol as a solvent. Re-screening of these carbamates in the presence of 0.1% DMSO (v/v) resulted in antagonism of inhibition for AgAChE, thus reducing the AgAChE-selectivity by at least 10-fold. However, the presence of 0.1% DMSO did not antagonize the inhibition of human, Drosophila melanogaster, or Musca domestica AChE. Non-selective carbamates also displayed no solvent-dependent antagonism of inhibition in any species studied, including AgAChE. Molecular models provide an explanation for antagonism of inhibition when DMSO is present. I, and collaborators, propose that W84 and W431 in AgAChE comprise an allosteric pocket that is stabilized by DMSO and is responsible for the solvent-dependent antagonism of inhibition observed with AgAChE.
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    Dissipation and Leachability of Formulated Chlorpyrifos and Atrazine in Organically-amended Soils
    Xiao, Yunxiang III (Virginia Tech, 1997-11-17)
    Bioremediation was studied in soils containing high concentrations of formulated chlorpyrifos (5 mg kg-1 Dursban® 4E) and atrazine (5 mg kg-1 AAtrex® 4L) using amendments including lignocellulosic sorbents, microbial nutrients (vegetable oil, corn meal and fertilizers), and microbial extracts from organic media previously exposed to these pesticides (chlorpyrifos and atrazine, respectively). Radiolabeled atrazine was used to examine the various dissipation routes in contaminated soil, also amended with lignocellulosic sorbents and microbial nutrients. Both chlorpyrifos and atrazine dissipation from contaminated soils was enhanced by organic-based material amendments. The half-lives of chlorpyrifos based on extractability for soils unamended and amended with vegetable oil and peat moss were 87 and 52 days, respectively. The half-lives of atrazine in unamended and amended soil (vegetable oil, peat moss and fertilizers) were 175 and 40 days, respectively. The leachability of chlorpyrifos from contaminated soil was dramatically reduced by 82% during the first 30 days of incubation in treatments amended with vegetable oil and peat moss while only a 28% of reduction in leachability occurred in the corresponding unamended controls. Only a slight reduction of atrazine leachability was detected in amended treatments after 120 days of incubation. Differences were found in the leachability of chlorpyrifos and atrazine when they were applied to soil either as technical grade or formulated material. The presence of surfactants and other adjuvants in formulated chlorpyrifos (Dursban® 4E) reduced chlorpyrifos leachability in contaminated soil. Chlorpyrifos leachability was reduced by 43% in the formulated chlorpyrifos treatments, whereas there was a negligible decrease in technical chlorpyrifos treated soil during the first 3 days after contamination. Atrazine extractability and leachability was not affected by its formulation (AAtrex® 4L). Amendments with lignocellulosic sorbents and nutrients decreased atrazine®s volatility from contaminated soils. After 16 weeks of incubation, less than 1% of 14C-atrazine was volatilized from incubated soils. Overall, after 16 weeks of incubation less than 4% of 14C-atrazine was mineralized and more radioactivity was recovered from amended treatments than unamended treatments as 14CO2. The major portion of radioactivity (62%) was associated with physisorbed atrazine represented by the ethylacetate extract I from unamended treatments while only 28% of initial applied radioactivity was recovered in the corresponding amended treatments. Based on the sum of radioactivity in humic and fulvic acids, approximately 14% of radioactivity was incorporated or chemisorbed atrazine and its metabolites in both unamended and amended treatments. Forty-five percent of the initially applied radioactivity was associated with alkali insoluble fraction in amended treatments but only 17% of the initially applied radioactivity was detected in the corresponding unamended treatments. Less than 2 % of initial activity associated with physisorbed portions of fulvic acids and alkaline insoluble fraction indicated as the radioactivity in methylene chloride and ethylacetate extract II . Over time, more radioactivity was associated with polar atrazine hydroxylated degradation products.
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    Distribution of Carrion Beetles (Coleoptera: Silphidae) in Different Geographic Regions of Virginia
    Beirne, Shana Margaret (Virginia Tech, 2013-01-24)
    The distribution of beetles in the Family Silphidae has not been well studied in Virginia.  The primary purpose of this study was to survey silphid beetles in a more systematic manner across different geographic regions of the state, with a special consideration for Nicrophorus species.  The seasonal abundance and diversity of silphid beetles in Montgomery County, Virginia, was also examined.  Baited pitfall traps were used to sample beetle distribution and abundance, and were placed in each of the five geographical regions of Virginia in the summers of 2007 and 2008.  Traps were placed approximately one kilometer apart and were checked daily over a five day period for each of three sampling periods.  A total of 4375 silphid beetles, consisting of 11 species in four genera, were collected in ten counties with beetles in the subfamily Silphinae being predominant.  Within the Nicrophorinae, Nicrophorus tomentosus and N. orbicollis were dominant in 2007; whereas in the summer of 2008, N. tomentosus and N. pustulatus were the most commonly collected.  Contingency analyses indicated that species abundance was associated with sampling period and geographic region.  Nicrophorus americanus was not collected during either summer of surveying and only three N. carolinus were trapped in Suffolk County in the summer of 2008.  For the Montgomery County survey, a total of 3276 beetles were found between the middle of April and the middle of October.  The prevalent species within Nicrophorinae was Nicrophorus tomentosus and within the Silphinae it was Necrophila americana.  Species abundance was associated with sampling period.
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    The Effects of Miticides on the Reproductive Physiology of Honey Bee (Apis mellifera L.) Queens and Drones
    Burley, Lisa Marie (Virginia Tech, 2007-08-02)
    The effects of miticides on the reproductive physiology of queens and drones were examined. The first study examined the effects of Apistan (fluvalinate), Check Mite+ (coumaphos), and Apilife VAR (74% thymol) on sperm production and viability in drones. Drones from colonies treated with each miticide were collected at sexual maturity. Sperm production was determined by counting the number of sperm in the seminal vesicles. Sperm for viability assays was analyzed by dual fluorescent staining. Apilife VAR and coumaphos significantly lowered (P<0.0001) sperm production and coumaphos treatments caused a significant decrease (P<0.0001) in the sperm viability. The effects of miticides on queens was examined by treating queen-rearing colonies and examining the number and viability of sperm in the spermathecae of newly mated queens. Queens from each treatment group were collected after mating and the spermathecae were removed and analyzed. Colonies treated with coumaphos failed to provide viable queens and were excluded. Apilife VAR was found to significantly decrease (P<0.0016) sperm viability. No significant differences in sperm numbers were found between treatments. The effect of miticides on sperm viability over time was also examined. Drones were reared as described, but the spermatozoa were collected as pooled samples from groups of drones. The pooled samples from each treatment were subdivided and analyzed periods of up to 6 weeks. Random samples were taken from each treatment (n = 6 pools) over a period of 6 weeks. The exposure of drones to coumaphos during development significantly reduced sperm viability for all 6 weeks, and caused a large decline in week 6. The potential impacts of these results on queen performance and failure are discussed.
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    Environmental Influences on Subterranean Termite Foraging Behavior and Bait Acceptance
    Swoboda, Lois Elizabeth (Virginia Tech, 2004-02-25)
    Reticulitermids were significantly more likely to discover subterranean baits connected by physical guidelines than freestanding baits under both laboratory and field conditions. In the laboratory, subterranean termites built significantly longer tunnels adjacent to cellulosic guidelines than plastic guidelines. In the field, all guideline materials were equally effective at directing tunneling activity. Reticulitermes spp. workers were tested to determine their preferred substrate temperature. The preferred range for Reticulitermes spp. workers was found to be 18 to 27 degrees C. A laboratory bioassay was performed to determine if Reticulitermes spp. aggregates within thermal shadows. Significantly more Reticulitermes spp. workers aggregated within cool thermal shadows than control areas. In a multiple choice bioassay, mean consumption was higher for paper baits treated with fructose, galactose, glucose, raffinose, sucrose, trehalose and uric acid than for control baits. In a multiple choice bioassay, mean consumption was significantly lower for baits treated with arbutin, and most amino acids than for control baits. In the no-choice bioassay, the amount of paper bait consumed did not differ significantly for any of the treated baits tested and control baits.
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    Environmental Study of Pesticide Residues in Soil and Water from Cotton Growing Areas in Mali
    Dem, Safiatou Berthe (Virginia Tech, 2004-05-26)
    A study was undertaken to obtain information on farmers' knowledge, attitudes and practices regarding pesticide usage and to determine the amount of pesticide in soil and water samples collected at four cotton producing areas of Mali. The results from a survey of 24 farmers identified various concerns regarding personal and environmental safety. Despite their training, sometimes growers did not use pesticides in an appropriate manner. Highly toxic pesticides are used by farmers with insufficient personal protective equipment. Sixty soil samples and eight water samples from four cotton growing areas in Mali were scanned for detectable levels of fifty pesticides in total. Pesticides were detected in 77% of the soil samples and the main pesticides were p,p-DDT and its breakdown products, endosulfan I endosulfan II, endosulfan sulfate and profenofos. Among the pesticides detected, p,p-DDT use in the study area had not been reported during the past ten years. The most common pesticide detected in the soil samples from cotton growing areas studied was endosulfan II constituting 65% of the detections with a maximum amount of 37 ng/g. Residues detected in soil samples were below the quantification limit for the newer cotton production region of Kita and for the intermediate region of San. Eight pesticides were detected in water samples: γ-BHC (lindane), endosulfan I, endosulfan II, endosulfan sulfate, dieldrin, p,p-DDD, p,p-DDE and atrazine. All detected pesticides in water had concentrations below the quantification limit except for atrazine. Even though pesticides were found at low concentrations in ground water samples, the fact that water from these wells is used for human and animal consumption is of concern. Also, soil pesticides may be taken up by plants and passed on to other organisms feeding on those plants. Further residues studies in the cotton growing areas of Mali are in order to monitor pesticides residues in Malian soils, water and living organisms.