Entomology Theses and Dissertations

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AGRICULTURAL DRAINAGE DITCHES AS SOURCES OF BENEFICIAL SPIDERS TO ENHANCE CONSERVATION BIOCONTROL IN ADJACENT CROPLANDS
(2020) Kutz, Dylan James; Lamp, William O.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Agricultural drainage ditches are uncropped areas on farms located above high-water tables to assist in the hydrologic control of croplands. Drainage ditches have increasingly become the subject of research as sources of beneficial arthropods for agroecosystems. Spiders, the most common generalist predator in most field crops, are an important component of conservation biocontrol, but little is known of spider assemblages in drainage ditches or the extent they colonize adjacent croplands from these ditches. To better understand the composition and population dynamics of spider assemblages in drainage ditches, my objectives were (1) to assess the structure of spider assemblages inhabiting drainage ditches in Maryland and (2) to determine how spider assemblages in drainage ditches and adjacent soybean fields change throughout the soybean growth cycle. Overall, my work contributes to understanding how valuable drainage ditches are as habitats for natural enemies like spiders and how ditches influence spider assemblages in adjacent croplands.
The alarm-defense system of Cimex lectularius and its implications for pest management
(2015) Ulrich, Kevin Richard; Thorne, Barbara L; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
In this dissertation, I focus on the alarm-defense system of the common bed bug, Cimex lectularius, its effectiveness against pathogen attacks, and its role as a mechanism of communication for conspecifics. This dual role of an alarm-defense system is efficient and effective considering that the two functions are typically required simultaneously in times of danger; the same substance should serve both purposes. First, I surveyed the most common types of commercial bed bug treatments to determine long-term efficacy. Regardless of the treatment, chemical or heat, retreatments for bed bug infestations were required. After 3 years, 20.8% of housing units receiving a chemical treatment required additional treatments; 9.5% of units receiving heat treatments required a retreatment during the same period. Multifamily units required retreatments significantly more than all other housing types. Given these findings that emphasize the necessity for a multifaceted IPM program, I investigated whether the entomopathogenic fungus, Metarhizium anisopliae, could be used to control bed bugs. Feeding experiments demonstrated that bed bugs were innately susceptible to this fungus. However, regardless of whether bed bugs were sprayed with a fungal solution or contacted a treated surface, only at 98% humidity was mortality high. In addition, the two major aldehydes (E)-2-hexenal and (E)-2-octenal emitted as defensive secretions by bed bugs inhibited the in vitro growth of an isolate of M. anisopliae. The ability to accurately and quickly detect new infestations is a critical element to an IPM-based strategy. This detection requires an understanding of attraction behavior and cues. I show through use of video-tracking software, (E)-2-hexenal and (E)-2-octenal attract adult bed bugs. Behavioral assays determined both males and females were attracted to 0.04 ug of an aldehyde blend for up to two hours after initial treatment of filter paper disks. Results suggest that these bed bug secretions may be candidates for lures and monitors. Taken together, this research describes the chemical ecology of bed bugs, providing insight into relevant signaling and defensive behavior, which has direct implications on pest management practices.
Alterations to headwater stream microbial communities and carbon cycling in response to environmental change.
(2015) Hosen, Jacob Daniel; Palmer, Margaret A; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Organic carbon, principally as dissolved organic matter (DOM), is a fundamental energy source that powers microbial metabolism and shapes food webs in stream ecosystems. The community structure and metabolic activity of stream microbes are significantly impacted by the quantity and quality (i.e. molecular structure) of organic matter resources. Much of the organic matter in headwater streams originates on landscapes. Thus, external inputs of terrestrial organic carbon shape microbial community structure and, subsequently, food webs of headwater streams. Despite the recognized importance of DOM, there is limited understanding of how stream organic matter resources and bacterial community structure respond to watershed urbanization. I studied DOM quantity and quality, microbial heterotrophic function, and bacterial community composition along a gradient of watershed urbanization in headwater streams of the Parkers Creek watershed (Coastal Plain, Maryland, USA). In Chapter 1, I found that watershed impervious cover was significantly related to stream water DOM composition: increasing impervious cover was associated with decreased amounts of natural humic-like DOM and enriched amounts of anthropogenic fulvic acid-like and protein-like DOM. The DOM found in urbanized streams was more bioavailable, but only during spring and summer experiments. I report in Chapter 2 that microbial heterotrophic enzyme production was not strongly related to urbanization. Instead, enzyme levels were most strongly related to temperature and natural groundwater chemical gradients. I show in Chapter 3 that bacterial community composition and co-occurrence patterns also changed significantly in response to increasing urbanization, becoming more dominated by primary producers common to eutrophic waters. I conclude from my research that watershed urbanization fundamentally alters microbial communities and carbon cycling in headwater streams. This urbanized material is more readily metabolized by microbial communities, but only during warmer months. Increased biodegradation of DOM in warm seasons was related to greater microbial enzyme activity, which generally responds positively to increasing temperature. Thus, rising temperatures with climate change and urbanization combined with altered organic matter content are predicted to result in greater CO2 evasion from urbanized streams.
Applying Insect Ecology and Behavior to Improve Sustainable Pest Management for Drosophila suzukii
(2021) Lewis, Margaret Theresa; Hamby, Kelly; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The introduction of the invasive vinegar fly Drosophila suzukii (spotted-wing drosophila) to the continental United States substantially disrupted integrated pest management (IPM) in fall-bearing caneberries (raspberries and blackberries). Prior to D. suzukii’s introduction, the caneberry pest complex was primarily composed of plant pathogenic fungi and fruit rot pathogens, with few interventions needed to control insect damage. However, tolerance for D. suzukii larvae in fruit is low, and a lack of management options has necessitated calendar-based insecticide applications, significantly increasing pesticide usage. As part of a larger effort to restore IPM in caneberries, my dissertation aims to advance our knowledge of D. suzukii’s ecology towards more sustainable pest management. Part of this work includes evaluating insecticide spray coverage on diversified fruit farms, with the overarching objective of improving spray coverage in the regions of the caneberry canopy that have the highest D. suzukii activity levels. Optimizing spray coverage may increase the impact and efficacy of each insecticide application, suppressing D. suzukii populations with fewer insecticide applications. Improved spray coverage can also benefit disease management in caneberries. I additionally investigated interactions between D. suzukii and fungal microbes; both yeasts and hyphal fungi interact with D. suzukii throughout its life history, representing weak points that may be exploited for pest management. I tested how different species of yeast impact fitness and feeding behavior in larval D. suzukii and evaluated potential vectoring associations between D. suzukii and fruit rot fungi. Although further work is needed to fully understand D. suzukii’s patterns of microbial resource use, these studies demonstrate that interactions between D. suzukii and fungal microbes have the potential to alter both insect and pathogen pressure. Advancing our understanding of these interactions may facilitate the development of new pest management tactics. For example, yeasts could be used to develop species-specific insecticidal baits or lures for monitoring. Likewise, an epidemiological link between D. suzukii and fruit rot fungi would indicate that improved control of D. suzukii also provides benefits for pathogen management.
ASSESSING THE SUSCEPTIBILITY TO RNA INTERFERENCE OF THE MILKWEED BUG, ONCOPELTUS FASCIATUS (HEMIPTERA)
(2023) Argaez, Ebony Michelle; Pick, Leslie; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
RNA interference (RNAi) is an effective method to knock down gene expression in insects and other organisms. It has been adopted for basic research, to elucidate gene function, and applied research, to control insect pests. Here, I examined parameters needed for effective RNAi in the milkweed bug, Oncopeltus fasciatus, an emerging insect model species. For two developmental genes, Sex combs reduced, and even-skipped, very small amounts of dsRNA trigger a robust parental RNAi response. The higher the dose of dsRNA applied, the longer the duration of embryos laid with defects. Testing length-dependence, effectiveness decreased with dsRNAs in the 150 bp to 75 bp range. These developmental genes resulted in subtle, gene-specific defects which provided a more sensitive assay than lethality. Finally, effects of RNAi were transmitted across generations through trophic interactions, the first such discovery to our knowledge. This suggests potential unanticipated environmental risk to non-target insects from RNAi-based insecticides.
An assessment of host preference, reproductive suitability and feeding injury of the brown marmorated stink bug, Halyomorpha halys, on selected vegetables
(2014) Zobel, Emily S.; Hooks, Cerruti R.R.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The brown marmorated stink bug, Halyomorpha halys (Heteroptera), is an invasive insect from Asia that has become a major agricultural pest of field and vegetable crops in the Mid-Atlantic States. A field study was conducted to asses the seasonal abundance, host plant preference, reproductive suitability, and injury potential of H. haly on green bean, sweet corn, eggplant, okra and bell pepper. H. halys abundance, life stage phenology, and resulting feeding injury were monitored biweekly throughout the growing season. Overall seasonal abundance consisted of both overwintered adults and their F1 progeny. Sweet corn, okra and bell pepper had significantly higher abundances of H. halys compared to green bean, eggplant, and tomato. Eggplant, okra and bell pepper were the most suitable host plants for H. halys reproduction and development. Sweet corn, okra, bell pepper and tomato were very susceptible to feeding injury and experienced the highest injury rate per stink bug day. The implications of these findings with respect to sampling and management of H. halys in vegetable production are discussed.
The Bee Louse, Braula coeca Nitzsch, its Distribution and Biology on Honey Bees
(1978) Smith, Irving Barton Jr.; Caron, Dewey M.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Bee lice were found in 28% of Maryland apiaries and 18% of the colonies examined. In apiaries with lice, 50% of the colonies contained lice. Laboratory tests demonstrated that bee lice had no preference between 1, 5, 15, and 30 day old honey bee (Apis mellifera L.) workers at 25° while there was a preference for 1 day old workers at 34° C. Lice preferred young drones over old drones and virgin and mated queens over young drones at 25 and 34° C. Lice preferred virgin queens over old drones at 25° C while no preference was observed at 24° C. Mated queens were preferred over old drones at 25 and 34° C. There was a preference of lice for foraging age workers over old drones at 25° C while there was no preference at 34° C. Lice preferred both virgin and mated queens over random age workers at 25 and 34° C. Louse larval tunnels were numerous in nucs (4 frame honey bee colonies) stocked with lice from May through August corresponding with periods of nectar flow when bees were capping honey. In field colonies, louse populations decreased in the late spring to a low in early June. During July and after, populations of lice rose with the emergence of new lice. Few immature and adult lice were observed in control nucs having similar populations of bees. In nucs, 1 or more lice were observed on 24% of the queens between August and December. Only 2% of the virgin queens contained lice during the same period. In field colonies, 62% of the queens examined from June through the rest of the season harbored lice; 58% of these lice were pale in color indicating they were less than 1 day old. One louse was observed on 98.6% of the workers with lice, while 1.2% harbored 2 lice and 0.2% had 3 lice; 4 .2% of the lice were on drones. A single bee louse was observed on 3,092 foraging honey bees sampled. One-hundred-seventeen lice were collected on 14,459 bees collected from the brood nest of the same hives. Control samples indicated a 14 to 15% loss of lice during sampling. Tests demonstrated that during visual observations of lice on bees only 49% of the lice present were observed. Fluctuation in louse population levels were similar to those found elsewhere in this study.
BIODIVERSITY AND CONSERVATION BIOLOGICAL CONTROL: DO BUFFER STRIPS WITH WILDFLOWERS ENHANCE NATURAL ENEMIES IN NEIGHBORING CROP HABITATS?
(2010) Moore, Laura; Dively, Galen P; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Grass buffer strips are commonly deployed along crop borders in North American agricultural landscapes. Such borders filter nutrient and pesticide runoff to neighboring habitats and foster biodiversity. The addition of wildflowers in these strips to provide nectar and pollen resources can positively impact natural enemies of crop pests, particularly hymenopteran parasitoids. I investigated the presence/absence of wildflowers on natural enemy abundance in buffer strips and in neighboring soybean fields in 2005 and 2006. I predicted that wildflowers would attract and act as a source of natural enemies which would then disperse into neighboring crop fields. In both years, sticky cards were used to measure the abundance of aerial arthropods in pure stands of wildflowers and in neighboring soybean plots. Pitfall traps were also used in 2006 to measure abundance of epigeal taxa. In the 2005 experiment, sticky card captures of hymenopteran and dipteran parasitoids were 72.7% higher in buffers containing partridge pea compared to the other buffer types. Similarly, communities of all beneficial arthropods captured by sticky card and pitfall traps in 2006 were significantly 79.8% to 72.3 % higher, respectively, in the partridge pea buffers compared to communities in the soybean crop. However, buffer effects on populations of parasitoids and predators in the neighboring crop were mixed in both experiments depending on the particular functional group and specific family of arthropods. Results suggest that partridge pea was a source for canopy-dwelling dipteran parasitoids and saprovores, but acted as a sink for canopy-dwelling mymarids, canopy-dwelling predators and ground-dwelling ants, and had a neutral effect on all others. However, these effects did not extend far into the soybean crop and were generally not discernible beyond 6m. This study provides evidence that a pure stand of an attractive source of floral resources in a bordering non-crop area may not be desirable for enhancing conservation biological control. The species of flower and desired natural enemy should be taken into consideration before determining the mix of plant species to include in a buffer strip.
Biosystematics and the evolution of gall formation in hackberry psyllids Pachypsylla (Insecta: Homoptera: Psylloidea: Psyllidae)
(1995) Yang, Man-Miao; Mitter, Charles; Miller, Douglass R.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
This dissertation is a study of the phylogeny and evolutionary biology of gall formation in psyllids of the subfamily Spondyliaspidinae, with particular focus on North American hackberry gallers in the genus Pachypsylla. Species in this genus produce a variety of gall types on the leaves, petioles, buds and twigs of their hosts, four species of Celtis subgen. Euceltis (Ulmaceae). The homogeneity of adult morphology in Pachypsylla, contrasted to the great variation in gall morphology and phenology, has led to much difficulty in delimiting species. Chapter I investigates species limits as related to gall type and host specificity in Pachypsylla. Strong differences in allozymes, morphology and life history confirm that leaf, petiole, bud and twig gallers belong to different species or species groups. Different leaf gall morphs probably also represent different species, as evidenced by significant allozyme frequency differences among sympatric pairs of gall morphs, consistent frequency difference between co-occurring morphs across localities, and discrete differences in gall type between progenies of individual females. Differences in allozymes, female phenology, adult and nymphal coloration, as well as laboratory rearings and field manipulations, show that side cell individuals within two nipple gall types represent an inquiline sibling species (Chapter II). Chapter III is an analysis of phylogenetic relationships within Pachypsylla, based on allozyme, morphological, life history and chromosome characters. Galler populations attacking the same plant tissue form monophyletic groups. The leaf galler morphs are little diverged, and phylogenetic relationships among them are unclear. Populations of inquilines from two different gall types appear closely related; the inquiline appears to be derived from a gall-forming ancestor. Phylogenetic relationships among gallers on different plant parts are consistent with an evolutionary sequence of gall position from leaf to petiole to bud to twig. Chapter IV is a morphological study of phylogenetic relationships within Spondyliaspidinae. The tribe Pachypsyllini, including Pachypsylla and two related Celtis feeders, is monophyletic. The tree favors the hypothesis of Burckhardt over that of White and Hodkinson. The distribution of lerp and gall formation is shown to be non-random within Spondyliaspidinae.
Biting Midges of the Genus Culicoides (Diptera: Ceratopogonidae) from Southwest Asia
(1977) Navai, Shahin; Messersmith, Donald H.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
A study was made of the Southwest Asian species of the genus Culicoides Latreille 1809 from six countries: Afghanistan, Iran, Israel, Pakistan, Saudi Arabia and Turkey. Thirty-eight species of Culicoides belonging to seven subgenera: Trithecoides, Pontoculicoides, Avaritia, Culicoides, Oecacta, Beltranmyia and Monoculicoides are described and illustrated. A key is provided to the subgenera and slide mounted species of both sexes. Seven new species are described.
Bottom up effects of nutrients and water on black vine weevil Otiorhynchus sulcatus (Coleoptera: Curculionidae) and Heuchera micrantha "Palace Purple" (Saxifragacea)
(2004-08-19) Bejleri, Kreshnik; Raupp, Michael J; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This thesis investigated: a) the effect of fertilization and water regimes on chemistry and growth of Heuchera micrantha and the effect of plant quality on black vine weevil performance b) the effect of black vine weevil larvae on Heuchera micrantha growth and c) the effect of fertilization on tolerance of Heuchera micrantha plants to different densities of black vine weevil. I found a positive effect of nitrogen fertilization and water on plant chemistry and growth. Leaf nitrogen, carbon: nitrogen ratio, and phenols were strongly affected by nitrogen fertilization. Fertilization had no effect on adult and larval survivorship, ovipositional period or feeding preference of black vine weevil adult. Larvae had a strong effect on top and root biomass and this effect increased with increasing levels of fertilizer when water was not limited. Fertilizer did not increase tolerance of Heuchera micrantha to adults or larvae of black vine weevil.
Can Cover Crop Residues Suppress Pests and Improve Yield in Eggplant?
(2018) Coffey, Peter Lawson; Hooks, Cerruti RR; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Field studies were conducted over three growing seasons to investigate the effects of planting eggplant following three winter cover crop treatments on the abundance, predation, and colonization of Colorado potato beetle (Leptinotarsa decemlineata) and flea beetle (Epitrix spp.) abundance. Colorado potato beetle densities were observed to be significantly higher in the early season, and lower in the mid- and late- season when eggplant was planted into a crimson clover residue, compared with a crimson clover – rye mixture or bare ground control. Flea beetle abundance was significantly higher in treatments planted with a winter cover crop. Seedbed preparation treatments for weed control did not significantly affect pest abundance. These results contrast with previous research, raising new questions about how cover crop mixtures interact with pests, and how suppression methods influence the effects cover crops have on arthropod populations.
Characterization of Female Specific Salivary Gland Glycoproteins of Anopheles Gambiae and their Interaction with Plasmodium Berghei Sporozoites
(1999) Bartels-Andrews, Lucy; Sina, Barbara; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
This study investigated the female specific salivary gland glycoproteins of Anopheles gambiae mosquitoes and their possible role in malaria sporozoite invasion of the salivary glands. Male and female Anopheles gambiae salivary gland proteins were analyzed by western blot with various lectins to identify glycoproteins that are specific to the female salivary glands. At least, 14 female glycoproteins were detected by specific lectins in the female glands but not in the male glands and were designated as female specific. The different morphological regions of the female salivary glands showed distinct lectin binding characteristics with the distal lateral and the median regions displaying the most glycoproteins. The lectins that identified the most female specific glycoproteins were tested in a transplantation assay to determine their effect on Plasmodium berghei sporozoite invasion of the salivary glands. The transplantation procedure was similar to that reported by Rosenberg (1985) with some improvements which resulted in 90-95% mosquito survival after the transplant procedure. Up to 3% of the total sporozoites that invaded the salivary glands were found in the transplanted glands. The results of our analyses showed that the lectins soybean agglutinin (SBA) and wheat germ agglutinin (WGA) significantly reduced sporozoite invasion while the lectins Concanavalin agglutinin (Con A) and Dolichos biflorus agglutinin (DBA) had no effect on sporozoite invasion. The pattern of distribution of glycoconjugates on the female salivary glands showed that Con A bound uniformly and moderately to the whole gland while SBA and WGA bound intensely to the distal ends of the median and lateral lobes of the salivary glands. The binding pattern of SBA and WGA corresponds to the regions of the female glands where sporozoites enter the glands. These results suggest that malaria sporozoites interact with specific carbohydrate molecules on the salivary glands for invasion. To characterize salivary gland surface glycoproteins that may be involved in sporozoite invasion, salivary gland surface proteins were labeled by the biotinylation reagent sulfosuccinimidyl 6-biotinamido hexanoate, followed by lectin affinity chromatography. 7 of the labeled surface glycoproteins detected by sporozoite blocking lectins (SBA and WGA) had molecular weights corresponding to female specific glycoproteins. These female specific salivary gland surface glycoproteins are of potential interest in studying sporozoite interaction with salivary gland glycoconjugates. To determine that malaria sporozoites capable of invading mosquito salivary glands interact with carbohydrate molecules, hemagglutination and carbohydrate binding assays were conducted using sporozoites isolated from infected mosquito midguts. The results obtained suggest that interaction of sporozoites with mosquito salivary gland glycoconjugates may be mediated by sporozoite proteins other than the circumsporozoite protein, the major protein covering the surface of sporozoites.
Characterizing effectiveness of and obstacles to best beekeeping management practices
(2020) Kulhanek, Kelly; vanEngelsdorp, Dennis; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Honey bees (Apis mellifera, L.) provide critical pollination services to many US crops, but decades of high colony loss rates have strained beekeepers’ ability to provide sufficient colonies for crop production. In a national survey of colony losses for the 2015-2016 season, beekeepers reported losses averaging at 37.4%, and that the parasitic mite Varroa destructor was a leading cause of mortality. Survey results were used to create empirical best management practices (BMPs) to reduce colony loss rates. Best practices were the top four practices which correlated to significant reductions in winter colony loss. This set of BMPs was tested on 140 colonies in 7 locations across the US, compared to average beekeeping practices. At the end of 3 years, apiaries managed according to BMPs exhibited reduced Varroa loads, which resulted in reduced fall viral loads and reduced winter mortality. However, colony loss rates still exceeded rates that beekeepers have deemed acceptable. A prominent factor affecting colony health and mortality in the BMP study was Varroa. After identifying Varroa treatment as a preventative measure, the effects of Varroa management were evaluated in non-experimental apiaries. Citizen scientist beekeepers participating in the Sentinel Apiary Program provided Varroa samples and Varroa management information. Out of 192 Varroa treatments applied to 155 apiaries over 2 years, only 45 treatments resulted in reduced Varroa loads. Common hypotheses of factors affecting Varroa population growth failed to explain the rapid increases in Varroa loads experienced by beekeepers in critical fall months. Finally, a more novel explanation for rapid increases in Varroa load was explored: horizontal transmission of mites between apiaries. Colonies that were visited by non-natal bees experienced larger increases in Varroa loads than unvisited colonies, but not as a result of visitation to or from high mite colonies. High mite colonies in the landscape represent a threat to nearby colonies, and cooperative Varroa management is likely to mediate colony losses resulting from Varroa. This dissertation supports the critical need for proactive, cooperative Varroa management to improve colony health and reduce mortality.
COMBINING THE DROSOPHILA AND METARHIZIUM MODEL SYSTEMS TO INVESTIGATE HOST-PATHOGEN INTERACTIONS
(2021) Wang, Jonathan; St. Leger, Raymond; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Even closely related individuals vary in their response to infection. In this dissertation, I combined the fruit fly model system with multiple pathogens, including 16 strains of the fungus Metarhizium, to dissect how pathogens with different virulence strategies interact with variable host resistance and tolerance mechanisms. I began by infecting 188 sequenced Drosophila melanogaster lines [the Genetic Reference Panel (DGRP)] with broad host range Metarhizium anisopliae (Ma549) or the bacterium Pseudomonas aeruginosa (Pa14, originally from a human host). Resistance to the two pathogens was correlated (suggestive of general multipurpose defense mechanisms) and associated with oxidative stress sensitivity, starvation resistance, and in particular sleep indices (flies that take a lot of naps are particularly resistant to disease). I followed up by showing that this nonspecific defense extends to the specialist co-evolved Drosophila pathogen, Entomophthora muscae. A genome wide association study implicated several metabolic pathways and physiological processes in individual variation to disease, but not the canonical antifungal Toll immune pathway.Indeed, Metarhizium strains that killed faster induced a stronger and earlier Toll immune response, indicating virulence does not depend on suppressing immunity. Disrupting the Toll pathway component Dif only increased susceptibility to the early diverged broad host range Metarhizium frigidum, whereas flies disrupted in Persephone (a sensor of pathogen proteases) succumbed quickly to all Metarhizium strains. Microarray analysis of mutants revealed a suppressed transcriptomic response to infection when either Persephone or Dif were disrupted, with overlap with GWAS-implicated pathways.
Community Ecology and Sirex noctilio: Interactions with Microbial Symbionts and Native Insects
(2013) Thompson, Brian Matthew; Gruner, Daniel S; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Sirex noctilio is an invasive woodwasp with a global distribution that feeds on the sapwood of pine trees. Wood-feeding in the basal Hymenoptera (sawflies) arose out of sequential adaptations to feeding on nutrient poor and digestively refractive internal plant organs (xylem). Symbiotic association with White-rot fungi are thought to aid overcoming nutritional and digestive barriers, including exceedingly low nitrogen (N) and refractory lignocellulosic polymers. In this dissertation I evaluate wood-feeding relative to nutrition, symbiosis and biotic resistance to invasion of exotic North American habitats in Sirex noctilio [Hymenoptera: Siricidae]. I evaluated nutrient relations within fungal mutualism using: 1) functional morphological analysis of insect feeding, 2) sterol molecules to determine diet sources and 3) metagenomic and isotopic analyses for discovery of novel microbial associates and their associated nutrient pathways. Nutritional constraints of wood feeding are potentially compounded by the presence of diverse fungal and insect communities as they divide the tree resource. I examined the role biotic resistance to Sirex and its fungal mutualist, Amylostereum, in North America using field and laboratory experiments. Morphological evidence supported a role for Amylostereum in external digestion of wood. Observational evidence confirmed Sirex larvae did not ingest wood biomass but preferentially extracted liquid substances via specialized structures of mandibles. Sterol analysis indicated plant compounds as the primary constituent of the diet, while metagenomic analysis of bacteria and their metabolic pathways showed a bacterial microbiome adapted to short chain plant polymers, starch and sugar metabolism. Stable isotopes suggested an additional symbiotic association with nitrogen fixing bacteria enriched the nitrogen deficient food substrate. These studies point toward herbivory with microbial supplementation of nutrients as a tri-partite relationship, pending conclusive identification of the bacterial symbiont for Sirex. Specific constraints of wood feeding by the Sirex-Amylostereum symbiotic complex were antagonized by intraguild predation and fungal competition in North America. Competition interfered with Amylostereum, while intraguild predation accounted for an additional 15% mortality of larval populations. This research describes the evolutionary role of microbial symbionts in wood-feeding in the Hymenoptera and the internal and external constraints to foraging this ubiquitous, yet nutrient poor food resource.
COMPARATIVE GENOMICS OF CHEMOSENSORY GENE FAMILIES AMONG MEMBERS OF THE HELIOTHINAE
(2023) Guo, Rong; Fritz, Megan L; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Insect chemosensory systems play crucial roles in the perception of chemical signals that regulate sexual behaviors and odors that mediate insect-host plant interactions. These processes, mate-finding and acceptance, as well as host plant identification and use, strongly contribute to diversification and speciation among plant-feeding insects, including the Lepidoptera. Chloridea virescens and Chloridea subflexa are an ideal pair species to study the evolution of insect chemosensory systems because they are closely related but show pheromone-based sexual isolation and divergent host plant preferences. My dissertation focuses on the development of genomic tools that enable investigation into genetic mechanisms of host plant and mate recognition, and applies these tools to examine inter- and intraspecific diversity of chemosensory genes among members of the Heliothinae.In chapter 2, I produced a novel Illumina short read C. subflexa genome assembly and an improved, highly contiguous C. virescens genome assembly. Due to quality limitations common to short read assemblies, I used our Heliothine genomes to examine the feasibility of reference-assisted assembly, an approach that leverages existing high quality genomic resources for genome improvement in closely related taxa. My work demonstrated that reference-assisted assembly has the potential to enhance contiguity and completeness of existing insect genomic resources with minimal additional laboratory costs. Both the potential and pitfalls of reference-assisted assembly are discussed in light of my results. In chapter 3, I manually curated two chemosensory gene families, the odorant receptors (ORs) and odorant binding proteins (OBPs), in C. virescens. In total, I identified 80 ORs, 1 Orco and 49 OBPs. Three types of OBPs were identified according to the number and positions of conserved cysteine residues: 34 classic OBPs, 8 Minus-C OBPs, and 7 Plus-C OBPs. In addition, I used phylogenetic analyses to study evolutionary divergence of OR and OBP gene families among Heliothine moths, which revealed both gene duplications and losses. In chapter 4, I studied the strength and nature of selection on the ORs of field-collected C. virescens and C. subflexa, with focus on the pheromone receptor genes. I characterized the host plant use of these species in central Maryland by comparing the larval densities and infestation rates in 2020 and 2021. Sequencing followed by analysis of selection on field-collected samples indicated that the pheromone receptor, OR6, was under very strong purifying selection in both C. virescens and C. subflexa. AMOVA tests suggested that in C. virescens, host plant-associated population differentiation existed in genes OR6, OR55, OR66 and OR78. Further analyses of genetic divergence analysis focused on OR6 showed that the most highly divergent sites were all in introns. The new genomic tools and analyses of chemosensory gene families described here will serve as a platform for future investigations into the genetic mechanisms underlying host plant specialization and sexual communication among lepidopteran insects.
Consequences of omnivory and alternative food resources on the strength of trophic cascades
(2007-07-10) Frank, Steven David; Shrewsbury, Paula M; Denno, Robert F; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Omnivorous predators that feed on prey and plant resources are recognized as an important component of food webs but their impact on herbivore populations and trophic dynamics is unpredictable. Feeding on food items from multiple trophic levels increases the reticulate nature of food webs and the labile role of omnivores in promoting trophic cascades. Using carabid beetles in a corn agroecosystem, this research explored the interactive effects of predator guild (omnivore or carnivore) and the trophic origin of alternative food resources (seeds or fly pupae) on the control of herbivores (black cutworms) and plant survival. I demonstrated that the trophic guild and feeding performance of carabids can be predicted from their mandibular morphology. Carnivorous carabids, using mandibles with sharp points and a long shearing edge, kill and consume caterpillars more efficiently than omnivores that have mandibles with wide molar areas adapted for consuming prey and seeds. Omnivore preference for seeds and pupae further reduced their consumption of cutworms, which resulted in increased plant damage, ultimately dampening trophic cascades. In open field plots the abundance of omnivorous carabids and ants increased in response to seed but not pupae whereas neither subsidy affected the abundance of carnivorous predators. Pupae subsidies reduced predation of cutworms by carnivores and omnivores, consequently reducing seedling survival. However, in seed subsidized plots omnivorous predators switched from seeds to higher quality cutworm prey. Thus, predation of cutworms increased with cascading positive effects for seedlings. This research demonstrated that omnivorous carabids interacted more strongly with alternative food resources, particularly seeds, than carnivores. In addition, this difference can be linked to morphological differences that reduced omnivore efficiency as predators suggesting omnivores may be less effective agents of biological control. However, increased tenure time and aggregation to plant resources by omnivores helped restore trophic cascades, and should enhance biological control. Understanding the predacious behavior of omnivores in resource diverse environments is essential to predicting their role in trophic dynamics. I provide evidence that the trophic origin of alternative food drives the strength of this interaction and the extent to which omnivores promote trophic cascades.
DEVELOPING A PERRENIAL LIVING MULCH SYSTEM FOR MANAGING PESTS AND AUGMENTING NATURAL BIOCONTROL IN MARYLAND CANTALOUPE SYSTEMS
(2022) Nunez, Demian Antonio; Hooks, Cerruti RR; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This study investigated how alsike clover (Trifolium hybridum) and Virginia wildrye (Elymus virginicus), when interplanted as a living mulch with cantaloupe, (Cucumis melo var. cantalupensis) would impact herbivorous and beneficial arthropod numbers. An additional objective was to determine how these living mulches would impact fruit yield and quality. It was hypothesized that there would be a reduction of cantaloupe pest herbivores and increase in natural enemy abundances in the interplanting compared to monoculture cantaloupe system. Some arthropods conformed to these expectations. However, most had a neutral or inconsistent response to the living mulches. Striped cucumber beetles (Acalymma vitattum), a major pest, were unaffected by the living mulches on most sampling dates. During several periods in both study years, leaf piercing herbivores including aphids were found in greater numbers on cantaloupe interplanted with clover than wildrye and/or monoculture. Spiders were found in greater abundance in cantaloupe interplanted with clover than wildrye or monoculture plantings during several sampling periods. Other natural enemy guilds such as parasitic wasps and piercing predators were inconsistently influenced by living mulch types. Yield was highest in the monoculture plots and living mulch was correlated with changes in fruit texture and color.
Development of gene expression-based biomarkers of exposure to metals and pesticides in the freshwater amphipod Hyalella azteca
(2016) Gott, Ryan Christopher; Lamp, William O; Hawthorne, David J; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Ecological risk assessment (ERA) is a framework for monitoring risks of exposure and adverse effects of environmental stressors to populations or communities of interest. One tool of ERA is the biomarker, which is a characteristic of an organism that reliably indicates exposure to or effects of a stressor like chemical pollution. Traditional biomarkers which rely on characteristics at the tissue level and higher often detect only acute exposures to stressors. Sensitive molecular biomarkers may detect lower stressor levels than traditional biomarkers, which helps inform risk mitigation and restoration efforts before populations and communities are irreversibly affected. In this study I developed gene expression-based molecular biomarkers of exposure to metals and insecticides in the model toxicological freshwater amphipod Hyalella azteca. My goals were to not only create sensitive molecular biomarkers for these chemicals, but also to show the utility and versatility of H. azteca in molecular studies for toxicology and risk assessment. I sequenced and assembled the H. azteca transcriptome to identify reference and stress-response gene transcripts suitable for expression monitoring. I exposed H. azteca to sub-lethal concentrations of metals (cadmium and copper) and insecticides (DDT, permethrin, and imidacloprid). Reference genes used to create normalization factors were determined for each exposure using the programs BestKeeper, GeNorm, and NormFinder. Both metals increased expression of a nuclear transcription factor (Cnc), an ABC transporter (Mrp4), and a heat shock protein (Hsp90), giving evidence of general metal exposure signature. Cadmium uniquely increased expression of a DNA repair protein (Rad51) and increased Mrp4 expression more than copper (7-fold increase compared to 2-fold increase). Together these may be unique biomarkers distinguishing cadmium and copper exposures. DDT increased expression of Hsp90, Mrp4, and the immune response gene Lgbp. Permethrin increased expression of a cytochrome P450 (Cyp2j2) and decreased expression of the immune response gene Lectin-1. Imidacloprid did not affect gene expression. Unique biomarkers were seen for DDT and permethrin, but the genes studied were not sensitive enough to detect imidacloprid at the levels used here. I demonstrated that gene expression in H. azteca detects specific chemical exposures at sub-lethal concentrations, making expression monitoring using this amphipod a useful and sensitive biomarker for risk assessment of chemical exposure.

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