Browsing by Author "Brewster, Carlyle C."
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- Abundance and Species Diversity of Thrips (Thysanoptera: Thripidae) in Cotton, Soybean, and Peanut in Southeast Virginia, and Evaluation of Cyantraniliprole for Thrips ManagementSamler, Jessica Anne (Virginia Tech, 2012-04-24)Thrips are major agricultural pests throughout much of the United States. More information is needed about sampling methods, management practices, and insecticide susceptibility to help better control this pest. A two year survey was conducted to determine the species present in southeast Virginia and the population characteristics of those species. Thrips were monitored using yellow sticky traps. Tobacco thrips, Frankliniella fusca, were the most abundant species. In general thrips populations began to build up beginning in April, peaked in August, and then started to decline. Differences in this trend were observed between species. A study was conducted in seedling soybean to evaluate the within-plant location of thrips, whether a plant subsample could be used for thrips monitoring, and to determine the thrips species complex present. Soybean thrips, Neohydatothrips variabilis, were the most prominent species present. The greatest density of thrips larvae was located in the terminal bud of the seedling and suggests that immature thrips aggregate. Neither of the proposed subsamples of plant material explained the variability in immature thrips numbers and at this time we recommend whole-plant sampling for obtaining the most accurate estimate of thrips populations in seedling soybean. Tobacco thrips, F. fusca, as well as a complex of other thrips species attack cotton and peanut seedlings and can cause significant yield loss to these crops in the mid-Atlantic U.S. Experiments were conducted in these two crops to assess the efficacy of a novel diamide insecticide cyantraniliprole applied as a liquid in-furrow at planting and post-plant emergence broadcast spray treatment to control thrips. In both cropping systems cyantraniliprole significantly reduced the number of immature thrips and reduced thrips feeding injury to the plants. In several instances cyantraniliprole treatments resulted in increased yield as compared to the non-insecticide treated control and yields which were statistically similar to those obtained with standard thrips control insecticides. Laboratory bioassays were conducted to evaluate the toxicity (LC50 values) of cyantraniliprole and two conventional insecticides against F. fusca adults. Results of these assays were inconclusive. At times F. fusca adults were susceptible to the insecticides, but the results could not be replicated consistently.
- Biodiversity, conservation and mimicry rings of Appalachian millipedesMeans, Jackson C. (Virginia Tech, 2019-01-18)The Appalachian Mountains contain some of the highest millipede diversity on the planet, including many endemic and range-restricted species. Millipedes have extremely low dispersal capacity, strict environmental requirements for survival and, in the case of the family Xystodesmidae, are completely blind. Coupled with the complex topology of the Appalachians, xystodesmid millipedes have speciated in the eastern United States to a greater degree than in any other region. Many of the taxonomic relationships within the Xystodesmidae remain to be tested using modern molecular techniques, and numerous species await description. The subtribe Nannariina, for example, contains 3 genera and 19 species, yet evidence suggests the tribe may actually contain over 100 species. Traditional taxonomic work has been hindered by a paucity of researchers in the field, and a necessary reliance on morphological characters for species delimitation. The external male genitalia, known as gonopods, are the structures which have most often been used to define species boundaries. However, in many groups, including the Xystodesmidae, the gonopods are extremely simple, making it difficult to discern whether similarity between gonopods is a result of shared ancestry or morphological convergence. Further complicating matters, somatic characters are often uniform between species, and some obvious phenotypes, such as color pattern and hue, are shared between genera in aposematic mimicry rings. Leading to the formation of mimicry rings between distantly related genera, their bright coloration functions to advertise a cyanide-based defense. Some species have been recorded as having six color patterns, each a member of a different mimicry rings. The factors which drive some taxa to participate in mimicry rings, while others have a myriad of hues and patterns, unmatched by other species, are unknown. Here I investigate the phylogenetic relationships between the tribes and genera of the Xystodesmidae, with the aims of (1) understanding the role of homoplasy within the Xystodesmidae, (2) delineating tribal and generic boundaries within the family, (3) describing species in the genus Nannaria for the purposes of revising the subtribe Nannariina, and (4) investigating mimicry and color variability through a detailed color atlas for North American Xystodesmidae. I found that 95% of the morphological characters traditionally used in xystodesmid taxonomy are homoplasious (HI > 0.5), delineated the Apheloriini, Appalachioria and Sigmoria, described 34 new Nannaria species, and created a color and mimicry dataset of 956 Xystodesmidae for use in future studies of color variability.
- Biomarkers of oxidative stress in atrazine-treated honey bees: A laboratory and in-hive studyWilliams, Jennifer Rae (Virginia Tech, 2016-09-14)The decline of honey bee (Apis mellifera) colony numbers in recent years presents an economic and ecological threat to agriculture. One outstanding threat to honey bees is the unintended exposure to agricultural pesticides. Previous studies report that acute exposures to the common-use herbicide atrazine elicit oxidative stress in non-target insects; however, little information is currently available on the exposure risk of atrazine to honey bees. This project examined biochemical and molecular oxidative stress response markers of honey bees following laboratory and field treatments of atrazine. Laboratory experiments were conducted with honey bees exposed to increasing concentrations of atrazine for 24 h whereas hive experiments were conducted with bees exposed to one sub-lethal concentration of atrazine for 28 d. The overall antioxidant enzyme activities of atrazine-treated honey bees were decreased compared to the untreated honey bees in both the laboratory and hive experiments. After exposure to atrazine in the laboratory and field, semi-quantitative RT-PCR analysis of antioxidant-encoding genes reveals the differential expression of genes in atrazine-treated bees that are important for oxidative stress tolerance in the laboratory and field experiments. Here, we provide evidence that the laboratory and hive exposure of honey bees to the common-use herbicide atrazine results in oxidative stress responses that can compromise the health of bee colonies. The data will be discussed with regard to the protection of these pollinators against the untended exposure of agricultural pesticides.
- Bionomics of Ochlerotatus triseriatus Say (Diptera: Culicidae) and Aedes albopictus Skuse (Diptera: Culicidae) in emerging La Crosse virus foci in VirginiaBarker, Christopher M. (Virginia Tech, 2001-07-10)Recently, the number of human cases of La Crosse encephalitis (LACE), an illness caused by mosquito-borne La Crosse (LAC) virus, has increased in southwestern Virginia, resulting in a need for better understanding of the virus cycle and the biology of its vectors in the region. This project examined the spatial and temporal distributions of the primary vector of LAC virus, Ochlerotatus triseriatus, and a potential secondary vector, Aedes albopictus. Ovitrapping surveys were conducted in 1998 and 1999 to determine distributions and oviposition habitat preferences of the two species in southwestern Virginia. For virus assay, adult mosquitoes were collected at a tire dump and a human case site during 1998 and 1999, and ovitrap samples were taken from a human case site in 2000. In a separate study, a landcover map of Wise County was created by supervised classification of Landsat Enhanced Thematic Mapper imagery, and maps indicating posterior probabilities of high mosquito abundance were created by combining ovitrap survey-derived, landcover-based prior and conditional probabilities for high and low mosquito abundance using remote sensing techniques and Bayesian decision-making rules. Both Oc. triseriatus and Ae. albopictus were collected from all ovitrap sites surveyed in Wise, Scott, and Lee Counties during 1998. Numbers of Oc. triseriatus remained high from late June through late August, while Ae. albopictus numbers increased gradually through June and July, reaching a peak in late August and declining thereafter. Overall, Oc. triseriatus accounted for 90.1% of eggs collected during this period, and Ae. albopictus made up the remaining 9.9%. Abundance of the two species differed among the sites, and in Wise County, relative Ae. albopictus abundance was highest in sites with traps placed in open residential areas. Lowest numbers of both species were found in densely forested areas. Ovitrapping at a human LACE case site during 1998 and 1999 revealed that Aedes albopictus was well-established and overwintering in the area. An oviposition comparison between yard and adjacent forest at the Duncan Gap human LACE case site in 1999 showed that Ae. albopictus preferentially oviposited in the yard surrounding the home over adjacent forested areas, but Oc. triseriatus showed no preference. LAC virus was isolated from 1 larval and 1 adult collection of Oc. triseriatus females from the Duncan Gap human case site, indicating the occurrence of transovarial transmission at this site. The supervised landcover classification for Wise County yielded a landcover map with an overall accuracy of 98% based on comparison of output classification with user-defined ground truth data. Posterior probability maps for Oc. triseriatus and Ae. albopictus abundance reflected seasonal and spatial fluctuations in mosquito abundance with an accuracy of 55-79% for Oc. triseriatus (Kappa=0.00-0.53) and 70-94% for Ae. albopictus (Kappa=0.00-0.49) when model output was compared with results of an ovitrapping survey. Other accuracy measures were also considered, and suggestions were offered for improvement of the model.
- Brown Marmorated Stink Bug (Hemiptera: Pentatomidae) Infestations in Tree Borders and Subsequent Patterns of Abundance in Soybean FieldsAigner, Benjamin L.; Kuhar, Thomas P.; Herbert, D. Ames Jr.; Brewster, Carlyle C.; Hogue, J. W.; Aigner, John D. (Oxford University Press, 2017-04-01)The invasive brown marmorated stink bug, Halyomorpha halys (Sta° l) (Hemiptera: Pentatomidae), is an important pest of soybean (Glycine max L. Merr.) in the Mid-Atlantic United States. In order to assess the influence of nonmanaged wooded borders on H. halys infestation patterns in soybean, 12 soybean fields in Orange and Madison Counties, VA, were sampled each week from July to October in 2013 or 2014 for H. halys. At each location, five 2-min visual counts of H. halys life stages were made on tree of heaven (Ailanthus altissima Mill.) and other favorable host trees along a wooded border, on the adjacent soybean edge, 15 m into the soybean field, and 30 m into the field. Seasonal data showed a clear trend at all locations of H. halys densities building up on A. altissima-dominated wooded borders in July, then, gradually moving into adjacent soybean field edges later in the summer. Halyomorpha halys did not move far from the invading field edge, with approximately half as many bugs being present at 15 m into the field and very few being detected 30 m into the field. These results have implications for continued monitoring and management using field border sprays, particularly on edges adjacent to woods.
- Chagas Disease in the United States: the Emerging Threat and the Role Climate and Awareness Play in Its SpreadLambert, Rebecca Click (Virginia Tech, 2007-03-27)This study evaluates the roles of temperature variability and disease awareness in the emergence of Chagas disease (American trypanosomiasis). Chagas disease is endemic in Latin America and primarily spreads to humans directly via the triatomine vector. Hosts for most triatomine species are mainly rodents and occasionally dogs. The disease itself is caused by a parasitic protozoan, Trypanosoma cruzi (T. cruzi) which is found in the triatomine's feces and is often spread while the triatomine is consuming a blood meal. T. cruzi from feces enters the body via an abrasion on the skin, the mucous membranes, conjunctivae, or through consumption. To determine the risk of Chagas disease transmission one must define qualities that make the triatomine an effective disease vector as well as investigate the level of disease awareness among physicians and the population within the vector's range. This thesis maps triatomine species within the U.S. that harbor T. cruzi naturally and that exhibit qualities of domesticity. These qualities are defined by whether the species bites humans and dogs as well as reports that the species has been found in the domestic setting. Ranges illustrating temperature thresholds for increased triatomine activity for 2000 and 2030 are also depicted. Additionally, outcomes of a physician survey are presented to gauge the status of Chagas disease awareness in areas at higher risk for disease transmission. Results reveal limited consideration of Chagas disease in physician diagnosis despite the higher risk range which extends through the southern U.S. and is predicted to expand significantly by 2030.
- Chemical Manipulation of Honey Bee BehaviorLarson, Nicholas R. (Virginia Tech, 2017-06-09)The loss of managed honey bee colonies, resulting from their unintentional exposure to pesticides, is a topic of concern for the agricultural and apicultural industry. Current methods for reducing pesticide exposure to bees involve the application of pesticides before crop bloom or in the evening when foraging bees are less likely to be exposed to these applications. There is an urgent need for additional protection procedures to reduce the annual losses of managed bee colonies. Another method for protecting these pollinators is the use of chemical deterrents to reduce the interaction times of foraging bees with pesticide-treated crops. Historically, insect repellents (IRs) have been used to prevent the spread of deadly human diseases by arthropod vectors. However, it has been shown that bees can be repelled from pesticide-treated crops using DEET and bee pheromonal compounds. Here, I report the toxicological and deterrent effects of bee pheromonal compounds, as well as the deterrent effects of heterocyclic amines (HCAs) on bees. The results of this study indicate that the bee pheromonal compounds, at 8, 20, 60 and 100% concentrations, are toxic to bees and inhibit the feeding of bees within a confined space. Additionally, the pheromonal compounds and the HCAs are as efficacious as DEET in deterring bees from treated food sources. The HCA piperidine was observed to effectively deter bee foragers from a sugar feeder in a high-tunnel experiment as well as from melon flowers and knapweed in field experiments. Electroantennogram recordings were conducted to verify an olfactory response of the bees to the tested compounds. Pheromonal compounds were readily detected by bee antennae; whereas, the HCAs did not elicit significant responses in the bee antennae. These data suggest that bee pheromonal compounds, as well as HCAs, may serve as candidates for the further investigation as repellents to protect bees from unintentional pesticide exposures.
- Chlorothalonil Exposure Alters Virus Susceptibility and Markers of Immunity, Nutrition, and Development in Honey BeesO'Neal, Scott T.; Reeves, Alison M.; Fell, Richard D.; Brewster, Carlyle C.; Anderson, Troy D. (Entomological Society of America, 2019-05-23)Chlorothalonil is a broad spectrum chloronitrile fungicide that has been identified as one of the most common pesticide contaminants found in managed honey bees (Hymenoptera: Apidae: Apis mellifera L.), their food stores, and the hive environment. While not acutely toxic to honey bees, several studies have identified potential sublethal effects, especially in larvae, but comprehensive information regarding the impact of chlorothalonil on adults is lacking. The goal of this study was to investigate the effects of exposure to a field relevant level of chlorothalonil on honey bee antiviral immunity and biochemical markers of general and social immunity, as well as macronutrient markers of nutrition and morphological markers of growth and development. Chlorothalonil exposure was found to have an effect on 1) honey bee resistance and/ or tolerance to viral infection by decreasing the survival of bees following a viral challenge, 2) social immunity, by increasing the level of glucose oxidase activity, 3) nutrition, by decreasing levels of total carbohydrate and protein, and 4) development, by decreasing the total body weight, head width, and wing length of adult nurse and forager bees. Although more research is required to better understand how chlorothalonil interacts with bee physiology to increase mortality associated with viral infections, this study clearly illustrates the sublethal effects of chlorothalonil exposure on bee immunity, nutrition, and development.
- 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.
- Cross-reactivity among alphaviruses provides insight into viral emergence and novel defense strategiesWebb, Emily Morgan (Virginia Tech, 2022-04-13)Alphaviruses are a group of medically relevant arthropod-borne viruses (arboviruses) belonging to the Togaviridae family that are maintained by mosquito vectors. These zoonotic viruses are clustered into two groups: New World and Old World, depending on their geographical origin/distribution and clinical manifestations. Both of these groups cause disease symptoms of an acute febrile illness; however, each group has a distinct, hallmark disease symptom; New World alphaviruses, such as Eastern, Western, and Venezuelan equine encephalitis viruses (EEEV, WEEV, and VEEV, respectively), present with severe encephalitis while Old World alphaviruses, such as Sindbis, chikungunya, and Mayaro viruses (SINV, CHIKV, and MAYV, respectively) present with an incapacitating polyarthralgia that can persist for years following initial infection. To date, the most effective means of controlling these arboviral infections is through mosquito control programs. However, these programs have crucial limitations in their effectiveness; therefore, novel approaches are necessary to control the spread of these crippling pathogens and lessen their disease burden. Given the close phylogenetic and antigenic relationship between MAYV and CHIKV, we hypothesized that prior CHIKV immunity may affect the outcome of MAYV disease and/or limit its emergence in humans. Our work has shown that anti-CHIKV neutralizing antibodies can provide cross-protective immunity against MAYV disease. Alongside these studies, we have characterized the potency of a camelid-derived single-domain antibody (sdAb) that neutralizes a breadth of alphaviruses, including CHIKV and MAYV. With these data, we have designed and generated transgenic Aedes aegypti mosquitoes that express two anti-CHIKV sdAbs to target infection, dissemination, and transmission of MAYV and CHIKV within this deadly vector. These findings are particularly significant because they highlight the ability to co-target two emerging alphaviruses that are crippling public health and obliterating quality of life around the globe within a single defense strategy.
- Development of a Precision Mite Management Program for the Control of the Ectoparasite Varroa destructor in Hives of Apis mellifera L.Means, Jackson C. (Virginia Tech, 2014-06-03)The European honey bee, Apis mellifera, is an important pollinator of horticultural and agricultural field crops, providing ≈ 90% of all commercial pollination services (Genersch et al. 2010). The recent rise in colony loss due to Colony Collapse Disorder (CCD) has been a source of concern for both beekeepers and the apiculture industry. One of the factors implicated in CCD is infestation by the ectoparasitic mite, Varroa destructor. Initial efforts to control the mite relied heavily on regular application of miticides without regard to actual mite infestation levels. This approach has led to problems of resistance in the mite and contamination of the hive and hive-products. Because it is unlikely that miticides will be removed as an option for mite management, a precision mite management (PMM) approach using information on the spatiotemporal distribution of the mite to improve sampling and treatments is seen as a viable option, particularly with respect to treatment costs and impacts on the environment. The primary objective of this study was to develop an understanding of the spatiotemporal distribution of the Varroa mite and bee brood within hives for the purpose of developing a PMM approach for the mite. Varroa mite populations were sampled from May to June, 2012 and February to October, 2013. Sampling was conducted with three commonly used sampling methods: soapy water roll (SWR), brood uncapping, and a modified sticky board; brood uncapping, however, was discontinued during the study due to hive the labor cost and harmful effects of this method to the hives. Similar trends in mite population levels were observed using the soapy water roll and sticky board sampling methods. Spearman's nonparametric analysis showed that there was a significant correlation (ρ = 0.47, P<0.001) in mite population levels for the soapy water roll and sticky board methods for sampling conducted from February to September, 2013 (the SWR method was not used in October). This was despite the fact that there was no significant correlation (ρ= -0.03, P = 0.8548) between the two sampling methods during the spring sampling period from February to April, 2013. The observed lack of correlation between the two sampling methods in early spring was likely due to the low population of brood in the hive, which caused the majority of the mites to remain on adult bees. Mites per 100 adult bees, therefore, appear to reflect mite population levels within the hive more closely than mite fall on sticky borad during the February to April sampling period. This suggests that the soapy water roll method is a better method for estimating mite population levels within the hive in the early spring compared with the sticky board method. Geospatial analyses of the distributions of mite fall on the sticky boards were conducted using geostatistics and Spatial Analysis by Distance IndicEs (SADIE). Both analyses showed that mite fall on the sticky board was generally aggregated and the aggregation increased with mite population levels. The average range of the variogram from geostatistical analysis was estimated at 4 sticky board cells; this range value was increased to 5 cells and was used to develop a systematic outside-range sampling protocol for mites on a sticky board. The results showed that the accuracy of the systematic outside-range sampling compared well with that of the traditional sticky board counting method in estimating total mite fall, but required only 60% of the effort (i.e., counting 63 instead of 105 cells). SADIE analysis showed that there is an overall association between the distribution of mite fall on a sticky board and the distribution of brood within a hive. A greater degree of correspondence was also observed in the association of drone and mite distributions during May to June; greater correspondence in worker brood and mite associations was observed in August and September. These differences may be due to relative amounts of the two types of brood present within the hive. A test of the efficacy of precision application of Varroa mite treatment based on the association between drone brood and mite fall resulted in a significantly greater reduction in mite levels on the sticky board using a traditional miticide treatment method compared with the control and precision treatments (𝜒2 =362.571; df = 2; P <0.0001); mite population levels with the precision method, however, were significantly reduced compared with the control.
- Distribution and Management of the Red Imported Fire Ant, Solenopsis invicta Buren, in VirginiaAllen, Hamilton Ross (Virginia Tech, 2010-09-06)Red imported fire ant specimens were first collected in Virginia in 1989 from colonies located in Hampton, Va. Now colonies are established throughout the Hampton Roads area of Virginia. Because the fire ant is a new pest information regarding the distribution, biology, and management of the ant in Virgnia are absent. Therefore studies were conducted to compare the efficacies of four broadcast fire ant control products and an individual mound treatment to control fire ants and to determine the impact of Advion and Top Choice on non-target ant species. Additionally, twenty-six fire ant colonies in Virginia were sampled to determine colony social form and to detect biological control organisms. Lastly, the CLIMEX model was used to predict the potential spread of the fire ant in Virginia. Field trials showed that combination applications of Advion and Top Choice provided the fastest and greatest reduction in foraging three days after treatment and the longest residual control of fire ant colonies for one year. Field tests documenting the impacts of Advion and Top Choice on non-target ants indicate treatments do supress ant foraging but ant populations will rebound 10-12 months after treatment. Laboratory PCR assays revealed that colonies in Virginia are primarily polygyne. Also, Kneallhazia solenopsae, Pseudaction spp. parasitoid decapitating phorid flies, and Solenopsis invicta virues (SINV) genetic materials were detected in fire ant samples. CLIMEX model results indicate that fire ants will be able to spread as far east as the Greater Richmond area and as far north as Alexandria in Virginia.
- Dynamics of La Crosse virus: Surveillance, Control and Effect on Vector BehaviorYang, Fan (Virginia Tech, 2017-01-31)La Crosse virus (LACV) encephalitis is the most common and important endemic mosquito-borne disease of children in the U.S. with an estimated 300,000 annual infections. The disease is maintained in a zoonotic cycle involving the eastern treehole mosquito, Aedes triseriatus and small woodland mammals such as chipmunks and squirrels. The objectives of this study were 1) to conduct surveillance of LACV and other mosquito-borne viruses; 2) to evaluate the effect of virus infection on mosquito host-seeking and neurotransmitter levels, and 3) to determine the effectiveness of barrier sprays to control infected mosquito vectors. Our surveillance study demonstrated the involvement of an invasive species, Aedes japonicus, in the transmission cycle of Cache Valley virus (CVV). CVV is a mosquito-borne virus that is closely related to LACV. Thus, surveillance is a critical step in public health, providing pathogen distribution and frequency data as well as identifying and incriminating new vectors. LACV infection did not affect the host-seeking behavior of Ae. triseriatus females. Using high performance liquid chromatography with electrochemical detection (HPLC-ED), the levels of serotonin and dopamine were measured in infected and uninfected mosquitoes. Serotonin is known to affect blood-feeding and dopamine affects host-seeking. Serotonin levels were significantly lower in LACV-infected mosquitoes but dopamine levels were unaffected by virus. A previous study found that LACV infection caused an alteration in mosquito blood-feeding in a way that could enhance virus transmission. This work showed that LACV infection can reduce the level of serotonin in the mosquito, promoting virus transmission through altered blood-feeding without impairing the vector's ability to locate a host. Standard CDC bottle assays were used to evaluate the efficacy of two pyrethroids and two essential oil sprays on LACV infected and uninfected mosquitoes. LACV-infected Ae. triseriatus females were more susceptible to both pyrethroids than uninfected ones. Infection status did not affect the susceptibility of Ae. albopictus to either pyrethroid. The essential oils were inconsistent in their effects. These results demonstrate that barrier sprays may be a viable part of a mosquito control program, not just to reduce the biting rate but to potentially reduce the virus-infected portion of the vector population.
- Ecology of Root-Feeding Insect Assemblages in Fire-Manipulated Longleaf Pine-Wiregrass EcosystemsDittler, Matthew Jason (Virginia Tech, 2013-05-23)Root-feeding insects can have top-down influence on vegetative composition and ecosystem processes; however, they may respond to bottom-up factors such as soil resources, site productivity, and disturbance. My research addressed the following questions: (1) Do disturbance (fire), vegetative composition, soil resources, and fine root standing mass influence the structure of root-feeding insect assemblages? (2) What types of roots do root-feeding insects eat, and do they forage selectively? (3) Do root-feeding insects influence fine root productivity? To address these questions, I studied root-feeding insect assemblages in longleaf pine wiregrass (Pinus palustris-Aristida stricta) ecosystems of southwestern Georgia, U.S.A. On a random basis, study sites were burned at least every other year (B), or left unburned (UB) for about 9 years. Fine root productivity and root-feeding insect abundances were sampled repeatedly across 54 random plots in UB and B sites. In Chapter 2, I characterized spatial and temporal patterns of root-feeding insect abundance, understory plant composition, soil resource availability, and fine root standing mass within each plot. Insect population densities were low overall, but abundance, patchiness, and diversity were greater in UB sites. Abundance patterns were significantly related to vegetative composition. In Chapter 3, I quantified the diet of root-feeding insects by measuring the natural abundance of carbon (C) and nitrogen (N) stable isotopes in insects and fine roots. Using 13C abundance, I examined the contribution of warm season grass roots to insect diet, relative to the proportion of warm season grass roots within adjacent root standing crop samples; 15N abundance was used to detect omnivory. Overall, insects appeared to be non-selective herbivores and omnivores that may alter foraging behavior to maintain a mixed diet (i.e. reducing or increasing warm season grass consumption when its abundance was high or low, respectively). The extent of omnivory varied within and among taxa. In Chapter 4, I estimated the top-down influence of root-feeding insects on fine root productivity by comparison of ingrowth cores with or without an insecticide treatment. I detected a weak positive effect of herbivores on the productivity of non-grass fine roots (< 10% of fine root productivity).
- An economic evaluation of alternative soil management technologiesWyeth, P.; Traoré, Boureima; Badini, Oumar; Sidi, M.; Touré, M.; Brewster, Carlyle C. (Wallingford, Oxon; Cambridge, Mass.: CABI Publishing, 2005)In chapter 12, Wyeth et al. pursue the issue of sustainability of technologies for enhancing soil fertility from economic and financial perspectives. This analysis takes into account the results of three years of on-farm trials and combines those findings with the output of the computer modeling analyses of Badini et al. (chapter 11). Their results suggest that corralling livestock in the fields, spreading manure and micro-dosing with chemical fertilizer are adoptable within the range of farmers' risk preferences.
- Economic interdependence among socio-economic groups in Madiama Commune of the Niger Delta of MaliKaboré, D.; Brewster, Carlyle C.; Bertelsen, Michael; Wyeth, P. (2001)One aim of the SANREM West Africa Project is to identify the linkages among socio-economic groups in the Madiama commune of northern Mali. The results from compiling a Social Accounting Matrix (SAM) were reported earlier. These results clearly demonstrated that transhumants are the least favored of the occupational groups, so that any development interventions should address this group separately. In this paper, the SAM is disaggregated further and decomposed multipliers computed. Three groups of decomposed multipliers are computed - direct effect, open loop and closed loop multipliers. The process of decomposition separates the impact of interactions among production activities from that due to interactions among socio-economic groups. These latter interdependencies are important to understand in a commune where rivalry among groups for resources is strong. Analysis of the multipliers and the pattern of primary commodity sales and microenterprise activity reinforces earlier conclusions about the importance of the livestock sub-sectors and the fragile position of the transhumant pastoralists.
- Economic linkages among occupational groups in the commune of MadiamaBrewster, Carlyle C.; Kaboré, D.; Bertelsen, Michael; Wyeth, P. (Wallingford, Oxon; Cambridge, Mass.: CABI Publishing, 2005)In chapter 13, Brewster et al. model the economic linkages between different groups of natural resource users and analyze the effect of the potential growth strategies. Using data from the PLLA (chapter 6) and an extensive household and enterprise level data set, a Social Accounting Matrix (SAM) model for the Commune of Madiama was developed. Application of this model demonstrated that the largest impacts from exogenous changes in demand are associated with rice and livestock sectors. Furthermore, impacts are shared differentially among socioeconomic groups with agropastoralists benefiting most and the transhumant group benefiting least.
- Effects of antemortem ingestion of ethanol on insect successional patterns and development of Phormia regina (Diptera : Calliphoridae)Tabor, Kimberly L.; Fell, Richard D.; Brewster, Carlyle C.; Pelzer, Kevin D.; Behonick, George S. (Oxford University Press, 2005-05-01)The effects of antemortem ingestion of ethanol by domestic pigs, Sus scrofa L., on postmortem insect successional patterns and the development of Phormia regina (Meigen) were studied during summer 2003 in Blacksburg, VA. Insect samples were collected from the carcasses of ethanol-treated and untreated pigs for 10 d postmortem during two successional studies. In total, 32 insect taxa were collected during the two studies, with 29 and 27 taxa observed on the carcasses of ethanol-treated and untreated pigs, respectively. The earliest arrivers to both carcass types were dipterans. This group was represented by six families, with P. regina and Phaenicia coeruleiviridis (Macquart) being the most common calliphorids. Beetles in six families were collected on the carcasses of ethanol-treated pigs, but only three of the families were collected on carcasses of the untreated pigs. Permutation analyses to test the null hypothesis of no similarity between successional patterns of insect taxa from carcasses of ethanol-treated and untreated pigs showed that the successional patterns were similar between carcass types in the first (P = 0.003) and the second (P = 0.01) studies. The results of the development study of P. regina maggots in the field show that there was a significant difference between the distributions of length for maggots reared on loin tissue from ethanol-treated and untreated pigs. Maggots that fed on tissue from ethanol-treated pigs took approximate to 11.9 11 longer to reach the pupal stage than maggots that fed on tissue from untreated pigs. The longer developmental time for maggots on tissue from ethanol-treated pigs was due mainly to the longer postfeeding period of the third instar.
- The Effects of European corn borer on whole-plant yieldand root knot nematode fitness in cornTiwari, Siddharth (Virginia Tech, 2007-04-26)Field studies were conducted over two growing seasons to evaluate the effect of different levels of third instar European corn borer, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae), on whole-plant dry matter in corn grown for silage. Mean (± SEM) whole-plant dry matter was significantly greater by 18.8% in uninfested control plants than in plants with an infestation level of 6 larvae/plant in 2004. Whole-plant dry matter in 2005 was significantly greater by 10.5% in control plants than in plants with an infestation level of 5 larvae/plant. Economic injury levels were calculated for each year using regression equations between whole-plant dry matter and European corn borer infestation level. Plant growth stage and infestation level had no effect on percent acid detergent fiber, neutral detergent fiber, and crude protein values for either year. Greenhouse studies were conducted to examine the relationship between aboveground herbivory by European corn borer and belowground herbivory by root knot nematode, Meloidogyne incognita Chitwood (Tylenchida: Heteroderidae), in corn. Two experiments were conducted to measure belowground herbivory by M. incognita in juvenile penetrations and eggs/root system. In the first experiment, the main effects interaction was not significant for either M. incognita juvenile penetrations or eggs/root system. Overall mean juvenile penetrations/root system across all three growth stages, at infestation levels of 1 and 3 larvae/plant were significantly less than in the non-infested control. In addition, overall mean eggs/root system at an infestation level of 3 larvae/plant were significantly less than in the control. In the second experiment, the main effects interaction was significant for both juvenile penetrations and eggs/root system. At the 8 and 10 leaf growth stages, juvenile penetrations/root system at infestation levels of 1 and 3 larvae/plant were significantly less than in the control. In addition, eggs/root system at an infestation level of 3 larvae/plant were significantly less than in the control, at all growth stages. In the reciprocal study, which examined the effect of different M. incognita inoculation levels on European corn borer stalk tunneling, no significant effect of inoculation level on European corn borer stalk tunneling was found.
- Effects of La Crosse virus infection on the host-seeking behavior and levels of two neurotransmitters in Aedes triseriatusYang, Fan; Chan, Kevin K.; Brewster, Carlyle C.; Paulson, Sally L. (2019-08-09)Background La Crosse virus (LACV) infection has been shown to manipulate the blood-feeding behaviors of its main vector, Aedes triseriatus. Here, we investigated the effects of virus infection on serotonin and dopamine and their potential roles in host-seeking. In mosquitoes, serotonin depletion has been shown to interfere with blood-feeding but not host-seeking. Dopamine depletion does not affect either blood-feeding or host-seeking; elevations of dopamine, however, has been shown to inhibit host-seeking. The purpose of this study was to determine the effects of LACV infection on the host-seeking behavior of and neurotransmitter levels in Ae. triseriatus. Methods Host-seeking behavior was evaluated using a uni-port olfactometer and a membrane feeder assay. Levels of serotonin and dopamine in infected and control mosquito heads were measured using HPLC-ED. Results Infection with LACV significantly inhibited the activation and attraction of Ae. triseriatus females to a host. A higher proportion of uninfected Ae. triseriatus females were activated by the presence of a host compared to infected mosquitoes and more uninfected mosquitoes were full responders (95.7%) compared to infected ones (91.1%). However, infection with LACV did not significantly affect the landing, probing, or blood-feeding rates of female mosquitoes. LACV-infected mosquitoes had lower serotonin levels than controls (104.5 vs 138.3 pg/head) while the dopamine levels were not affected by infection status (282.3 vs 237 pg/head). Conclusions Our work suggests that virus-induced reduction of serotonin is related to previously reported blood-feeding alterations in LACV-infected mosquitoes and could lead to enhanced transmission and increased vectorial capacity. In addition, some aspects of host-seeking were inhibited by virus infection.