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Leaves and fruit of nine apple (Malus x domestica Borkh.) genotypes were evaluated for insect injury in 1998 and 1999. Foliar and fruit injury from 12 insect species was inconsistently affected by genotype. Spraying trees with oil affected neither fruit insect injury nor fruit phytotoxicity. In choice feeding assays, incidence of Japanese beetle (JB) feeding and leaf area consumed was greater for 'Liberty' than for 'York.' Genotypes did not differ in no-choice feeding assays. Choice and no-choice feeding assays between apple and oak indicated that JB could distinguish host plants in an artificial environment. Trichome density appeared different among three genotypes. 'York', the non-preferred genotype, had highest specific leaf weight and concentration of phloridzin, a feeding repellent. 'Liberty' the preferred genotype, had the lowest specific leaf weight, and had the highest concentration of quercitrin, a feeding stimulant. Olfactory stimuli of JB was evaluated with a Y-tube olfactometer. Beetles preferred the side of the Y-tube containing leaf tissue of apple or Virginia creeper over the side with no leaf. Beetles did not choose one plant species over the other. Bias test of beetle orientation in the Y-tube olfactometer indicated that in the morning, but not the afternoon, beetles preferentially moved into the left side of the Y-tube. Humidity did not affect beetle orientation. In darkness JB preferred a leaf disc over a paper disc and beetles tended to remain on the leaf. / Ph. D.

The small hive beetle (Aethina tumida) is an invasive pest from sub-Saharan Africa that has posed increasing threats to European honey bee (Apis mellifera) colonies in the United States over the past two decades. While control has been attempted, consistently effective management strategies still not been developed. This study sought to explore novel experimental methods to better understand and use A. tumida biology to target this pest. One aspect of A. tumida biology that has emerged as potential basis for improved control is olfactory manipulation, which could be used to disrupt beetles as they seek out A. mellifera colonies. Through olfactometry and electroantennography, key volatiles in A. tumida attraction and repulsion were tested and sensitivity of A. tumida to several attractants and repellents was quantified on behavioral and physiological levels. An additional source of attractive volatiles is the A. tumida fungal symbiont Kodamaea ohmeri, which ferments larval waste and is present throughout the A. tumida lifecycle, both externally and in the GI tract. This study explored the development of feeding and soil bioassays to test the effects of several insecticides on A. tumida larvae. Feeding and injection bioassays were also used to deliver a fungicide with the goal of repressing K. ohmeri, which was expected to detrimentally impact A. tumida health. The results of this work enhance our current knowledge or A. tumida biology and provide a useful basis for development of safe and selective management A. tumida management options for the future. / Doctor of Philosophy / The small hive beetle is an invasive European honey bee pest that poses a significant threat to apiaries in the United States. These beetles feed on hive products and brood, pollute the hive with fermenting waste, and, in severe infestations, cause colonies to abandon their hives. This project investigated previously unexplored control options that take small hive beetle biology into account. Small hive beetles have an exceptional sense of smell compared to other beetles, and this ability helps them to locate honey bee hives. Therefore, behavioral responses to attractants and repellants were tested through olfactometry, in which beetles were given a choice to travel toward or away from specific odors or odor blends. Responses to these odors on a physiological level were also quantified through electrical recordings of beetle antennae. Small hive beetles are also known to have a yeast-like symbiont, which is present throughout the small hive beetle lifecycle, both externally and internally. Feeding bioassasy for small hive beetle larvae, along with soil bioassays for the delivery of insecticides were also developed and used to test several compounds against small hive beetle larvae. Feeding bioassays were also used to deliver a fungicide to larval and adult beetles with the goal of repressing internal fungal activity The results of these studies help expand the knowledge of small hive beetle olfaction and provide a background for the development of novel control options to effectively manage this destructive pest.

The anther culture response of diploid Solanum chacoense (chc) - S. phureja (phu) hybrids and the regeneration potential of anther-derived monoploids was evaluated. In vivo evaluation of interspecific hybrids was also performed. Three hybrids were anther cultured to observe the effects of reduced nitrogen source on androgenesis. Anthers were distributed to five reduced nitrogen sources. The N concentration was 30 mM. No tested reduced nitrogen source proved superior to the control. Genotype significantly affected embryo production. Eleven monoploid genotypes were included in a leaf disc regeneration procedure utilizing three separate transfers to fresh medium differing by growth regulator composition; six genotypes responded. Silver thiosulfate (STS) at either of two steps in the process proved detrimental to diploid recovery. Hybrids between phu and chc involving six phu clones and eight chc clones or accessions, all resistant to Colorado potato beetle (CPB), were used. No inter-family differences for germination, fruit/pollination, or seed/fruit were observed. Substantial mortality, ascribed to the phenomenon of “hybrid breakdown”, occurred in three families by month four of the study. Field plantings revealed adequate CPB resistance, while Ambush (147 g/ha) application increased total tuber weight per plant and average tuber weight. Hybrids produced less total tuber weight than S. tuberosum (tbr), while chc genotypes produced the smallest average tuber size. Interspecific hybrids produced tuber sizes intermediate between chc and phu. Tbr tubers were the largest. Chc families, regardless of selection for leptine glycolakaloids, suffered the least CPB damage and phu parental clones and hybrid families suffered the most. / Master of Science

Abdominal pumping is a widespread behavior in insects. However, there remains ambiguity surrounding the abdominal pumping behavior, both in terms of describing what exactly abdominal pumping is (i.e., if various modes of operation exist) and also what function(s) abdominal pumping serves (and if function is conserved across groups of insects). In some insects respiratory patterns have been correlated with abdominal movements, although the specific mechanical effects of these movements on the animal\'s respiratory system are generally unknown. Conversely, some insects (such as beetles, ants, and crickets) create convection in the respiratory system by compressing their tracheal tubes, yet the underlying physiological mechanisms of tracheal collapse are also unknown. This study aimed to investigate the relationship between abdominal pumping and the compression of tracheal tubes in the darkling beetle, Zophobas morio. I observed the movements of the abdomen and tracheal tubes using synchrotron x-ray imaging and video cameras, while concurrently monitoring CO2 expiration. I identified and characterized two distinct abdominal movements differentiated by the synchrony (the pinch movement) or lack of synchrony (the wave movement) of abdominal tergite movement. Tracheal tube compressions (and corresponding CO2 pulses) occurred concurrently with every pinch movement. This study provides evidence of a mechanistic linkage between abdominal movements and tracheal tube compressions in the ground beetle, Zophobas morio. / Master of Science

Within-field variation in mortality of Colorado potato beetle, Leptinotarsa decemlineata (Say), in a filter-paper insecticide bioassay was determined in three Virginia potato fields in 1989 and five fields in 1990. Bioassays were performed for each of three different insecticides on Colorado potato beetle larvae collected from 12-16 different locations (equal sized blocks) per field. Comparisons of 95% mortality confidence intervals between all block combinations per field indicated that field size had no influence on variation in Colorado potato beetle mortality in the bioassay. No apparent relationship existed between the level of Colorado potato beetle insecticide susceptibility (LC₉₀ value) and percentage of mortality confidence interval overlap among field blocks. Bioassay data from the sample fields indicated that a single bioassay (of potato beetles from one location per field) will yield at least a 0.50 probability (> 0.90 in six of the eight fields) of estimating the mean mortality response (± 5%) of Colorado potato beetle in the entire field. The probability of sampling potato beetles from one location which differed in mean mortality (P ≤ 0.05) from individuals collected in another location within the same field decreased as the number of locations sampled increased (i.e., the probability is 0.12 if three locations are sampled). Filter paper insecticide bioassays were performed on Colorado potato beetles collected from three commercial potato fields to determine the most cost-effective number of bioassay sample units (filter paper disks, 10 larvae per disk). Relative net precision values from three different insecticide bioassays were used as an indication of sample size efficiency, and were based on variation in larval mortality and sample cost. Greatest sample size efficiency in all insecticide bioassays was achieved from a sample of two to five filter paper disk sample units (20-50 total larvae). Additional insecticide bioassays were performed on Colorado potato beetle larvae collected at different times during the potato growing season (from a commercial potato field and from experiment station plots) to determine whether the larval generation sampled or previous insecticide application affected results of the bioassay. Although trends in mortality were not always consistent among first generation larvae sampled on different dates (from insecticide-treated and untreated plots), first generation larvae exhibited significantly (P ≤0.05) greater mortality in the bioassay compared with second generation larvae. Based on these results, we recommend that bioassays to estimate the effectiveness of a particular insecticide against Colorado potato beetle be performed on the target generation immediately before the planned insecticide treatment. PIES (potato insect expert system) is a knowledge-based system for Colorado potato beetle insecticide management in commercial potato fields on the Eastern Shore of Virginia. PIES was written using VP-Expert, a rule-based expert system shell, and uses Colorado potato beetle lifestage, potato growth stage, percent defoliation, and other factors to decide if an insecticide application is necessary to prevent tuber yield loss due to Colorado potato beetle pressure. Field tests at the Eastern Shore Agricultural Experiment Station compared PIES with conventional spray thresholds based on the number of Colorado potato beetles per stem. Tuber yields were not significantly different (P ≤ 0.05) between the two methods, while PIES recommended, on average, 3.7 insecticide applications and conventional thresholds required six insecticide applications. An additional benefit of PIES is that scouting requirements are simpler and quicker than the conventional stem counts. Supercooling points determined for Colorado potato beetle populations from Maine, Washington, and Prince Edward Island, Canada, suggest these populations are freeze-tolerant, that is, they can sustain ice formation within their body fluids. Colorado potato beetles collected from Virginia supercooled at a significantly (P ≤ 0.05) lower temperature than the other Colorado potato beetle populations. The temperature at which Virginia Colorado potato beetle supercooled is indicative of freeze-sensitive species and may indicate divergence in the mechanisms Colorado potato beetle are using for cold tolerance. Two polyhydric alcohols (polyols) were isolated in the hemolymph of Colorado potato beetle using high performance thin layer chromatography. The polyols were tentatively identified as inositol and xylitol. / Ph. D.

Mountain pine beetles (Dendroctonus ponderosae) are native insects that have decimated millions of hectares of mature pine (Pinaceae) forests in western North America. The purpose of this study is to investigate biophysical and climatic correlates of Mountain Pine Beetle (MPB) insect outbreaks in the Crown of the Continent Ecosystem (CCE) from 1962 to 2014 using Aerial Detection Survey (ADS) and climate data. Specific objectives were: 1) to develop statistical models to determine how selected biophysical correlates (slope, aspect, elevation, and latitude) and 2) to understand how local and global climate variables relate to the extent of the MPB infestations in the CCE, and 3) to contextualize the results of the models with historical climate data. Overall, the major findings of this study are: 1) despite its limitations, the ADS data seems suitable for analysis of beetle damage with respect to climate and topographic factors, on a regional scale, 2) there appears to be a link between local biophysical factors and winter precipitation and TPA within the CCE, and 3) a combination of a negative-phase PDO and La Niña is important in forecasting a decline in MPB spread, during a given year. This study is the first, to our knowledge, to explore spatio-temporal patterns of MPB outbreaks using biophysical factors, and both local and global climate variables, over a fifty-year timespan in the CCE. In the future, additional geospatial analyses may enable a landscape assessment of factors contributing to variability of MPB infestation and damage as this insect continues to spread. / Master of Science / Mountain pine beetles (Dendroctonus ponderosae) are a native insect that has decimated millions of hectares of mature pine forests in western North America. The purpose of this study was to investigate, using GIS-derived variables, biophysical and climatic factors that have influenced past mountain pine beetle insect outbreaks, as evident by beetle-induced tree mortality in the Crown of the Continent Ecosystem (CCE) from 1962 to 2014. Specific objectives of this study were to determine how selected biophysical variables (slope, aspect, elevation, and latitude), regional climate variables (temperature, precipitation, and drought) and global climate oscillations (ENSO, PDO, NAO, AO, and PNA) relate to bark beetle infestations in the Crown of the Continent Ecosystem from 1962 through 2014, as measured by aerial surveyrecorded tree mortality. We sought to contextualize the results of the statistical models with historical data to further understand the relationship between increases and decreases of tree mortality by comparing these trends to geopotential height and sea-surface temperatures that may influence CCE climate. Our work revealed first, that while the aerial survey data has important limitations, overall it is a useful dataset for analyzing historical spatio-temporal patterns of insect infestations. Second, there appears to be a link between local biophysical factors, such as latitude, elevation, and winter precipitation (as opposed to global climate factors) and tree mortality within the CCE. Local climate analysis revealed the importance of winter precipitation to be the biggest influence of MPB decrease or increase along with lower geopotential heights during a decline in MPB spread over the CCE. Finally, a combination of a negative PDO and El Niño was important in forecasting a decline in MPB spread, as shown by damage, during a given year. This is the first study to use aerial survey data in a geospatial analysis incorporating biophysical variables for the US portion of the Crown of the Continent Ecosystem. Additionally, this study is unique to explore the potential relationship between global teleconnections and regional climate in the CCE area, and the spatio-temporal extent of mountain pine beetle infestations.

<div>Native and invasive bark and ambrosia beetles threaten the health and productivity of natural and planted forests worldwide. Management of these pests relies on semiochemical-based tactics, but these are often ineffective at monitoring for incipient populations or decreasing pest populations. The role of fungal and non-host volatiles in colonization behavior remains unknown for many important bark and ambrosia beetle species, thereby hindering their control. In this dissertation, I tested the hypothesis that fungal and tree-associated volatiles influence the host colonization behavior of bark and ambrosia beetles that affect hardwood trees. This work describes the identification of novel fungal and host-associated semiochemicals that may aid in future management of these important pests.</div><div><br></div><div>In Chapter 1, I review the current literature describing the volatile chemical ecology of bark and ambrosia beetles that inhabit hardwood trees. A review of groups with numerous identified semiochemicals, as well as considerations for future research is included.</div><div><br></div><div>In Chapter 2, I test the hypothesis that host colonization by the peach bark beetle (Phloeotribus liminaris) is chemically mediated by compounds associated with infested hosts. I found that benzaldehyde mediates colonization by the peach bark beetle, and that that benzaldehyde lures are effective attractants in field-trapping studies.</div><div><br></div><div>In Chapter 3, I test the hypothesis that ambrosia beetle attraction to host stress compounds can be modified by symbiotic fungal volatiles. I found that for three species of invasive ambrosia beetles individual fungal volatiles act as repellents, with species-specific differences in response to different compounds.</div><div><br></div><div>In Chapter 4, I test the hypothesis that attraction of the walnut twig beetle (Pityophthorus juglandis) to its pheromone lure can be enhanced by symbiotic fungal volatiles. I found that symbiotic fungal volatiles consistently enhance attraction of the beetles to their fungus, while one symbiotic fungal volatile of ambrosia beetle species repelled the walnut twig beetle.</div><div><br></div><div>In Chapter 5, I summarize results from each of the chapters and discuss patterns observed in the response to fungal and host-associated volatiles among the focal bark and ambrosia beetle species. I also discuss future research needs and directions to continue development of the knowledge surrounding scolytine chemical ecology and management of these pest beetle species.</div>