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- ItemActivation of Ftz-F1-Responsive Genes through Ftz/Ftz-F1 Dependent Enhancers(PLoS (Public Library of Science), 2016-10-10) Field, Amanda; Xiang, Jie; Anderson, W. Ray; Graham, Patricia; Pick, LeslieThe orphan nuclear receptor Ftz-F1 is expressed in all somatic nuclei in Drosophila embryos, but mutations result in a pair-rule phenotype. This was explained by the interaction of Ftz-F1 with the homeodomain protein Ftz that is expressed in stripes in the primordia of segments missing in either ftz-f1 or ftz mutants. Ftz-F1 and Ftz were shown to physically interact and coordinately activate the expression of ftz itself and engrailed by synergistic binding to composite Ftz-F1/Ftz binding sites. However, attempts to identify additional target genes on the basis of Ftz-F1/ Ftz binding alone has met with only limited success. To discern rules for Ftz-F1 target site selection in vivo and to identify additional target genes, a microarray analysis was performed comparing wildtype and ftz-f1 mutant embryos. Ftz-F1-responsive genes most highly regulated included engrailed and nine additional genes expressed in patterns dependent on both ftz and ftz-f1. Candidate enhancers for these genes were identified by combining BDTNP Ftz ChIP-chip data with a computational search for Ftz-F1 binding sites. Of eight enhancer reporter genes tested in transgenic embryos, six generated expression patterns similar to the corresponding endogenous gene and expression was lost in ftz mutants. These studies identified a new set of Ftz-F1 targets, all of which are co-regulated by Ftz. Comparative analysis of enhancers containing Ftz/Ftz-F1 binding sites that were or were not bona fide targets in vivo suggested that GAF negatively regulates enhancers that contain Ftz/Ftz-F1 binding sites but are not actually utilized. These targets include other regulatory factors as well as genes involved directly in morphogenesis, providing insight into how pair-rule genes establish the body pattern.
- ItemAdjacent Habitat Influence on Stink Bug (Hemiptera: Pentatomidae) Densities and the Associated Damage at Field Corn and Soybean Edges(PLOS (Public Library of Science), 2014-10-08) Venugopal, P. Dilip; Coffey, Peter L.; Dively, Galen P.; Lamp, William O.The local dispersal of polyphagous, mobile insects within agricultural systems impacts pest management. In the mid- Atlantic region of the United States, stink bugs, especially the invasive Halyomorpha halys (Stal 1855), contribute to economic losses across a range of cropping systems. Here, we characterized the density of stink bugs along the field edges of field corn and soybean at different study sites. Specifically, we examined the influence of adjacent managed and natural habitats on the density of stink bugs in corn and soybean fields at different distances along transects from the field edge. We also quantified damage to corn grain, and to soybean pods and seeds, and measured yield in relation to the observed stink bug densities at different distances from field edge. Highest density of stink bugs was limited to the edge of both corn and soybean fields. Fields adjacent to wooded, crop and building habitats harbored higher densities of stink bugs than those adjacent to open habitats. Damage to corn kernels and to soybean pods and seeds increased with stink bug density in plots and was highest at the field edges. Stink bug density was also negatively associated with yield per plant in soybean. The spatial pattern of stink bugs in both corn and soybeans, with significant edge effects, suggests the use of pest management strategies for crop placement in the landscape, as well as spatially targeted pest suppression within fields.
- ItemAGRICULTURAL 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.
- ItemThe 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.
- ItemAll wet or dried up? Real differences between aquatic and terrestrial food webs(Proceedings of the Royal Society B: Biological Sciences, 2006) Shurin, Jonathan; Gruner, Daniel; Hillebrand, HelmutEcologists have greatly advanced our understanding of the processes that regulate trophic structure and dynamics in ecosystems. However, the causes of systematic variation among ecosystems remain controversial and poorly elucidated. Contrasts between aquatic and terrestrial ecosystems in particular have inspired much speculation, but only recent empirical quantification. Here, we review evidence for systematic differences in energy flow and biomass partitioning between producers and herbivores, detritus and decomposers, and higher trophic levels. The magnitudes of different trophic pathways vary considerably, with less herbivory, more decomposers and more detrital accumulation on land. Aquatic– terrestrial differences are consistent across the global range of primary productivity, indicating that structural contrasts between the two systems are preserved despite large variation in energy input. We argue that variable selective forces drive differences in plant allocation patterns in aquatic and terrestrial environments that propagate upward to shape food webs. The small size and lack of structural tissues in phytoplankton mean that aquatic primary producers achieve faster growth rates and are more nutritious to heterotrophs than their terrestrial counterparts. Plankton food webs are also strongly size-structured, while size and trophic position are less strongly correlated in most terrestrial (and many benthic) habitats. The available data indicate that contrasts between aquatic and terrestrial food webs are driven primarily by the growth rate, size and nutritional quality of autotrophs. Differences in food web architecture (food chain length, the prevalence of omnivory, specialization or anti-predator defences) may arise as a consequence of systematic variation in the character of the producer community.
- ItemAlterations 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.
- ItemApplying 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.
- ItemArthropod surveys on Palmyra Atoll, Line Islands, and insights into the decline of the native tree Pisonia grandis (Nyctaginaceae)(Pacific Science, 2007) Handler, Alex; Gruner, Daniel; Haines, William; Lange, Matthew; Kaneshiro, KenPalmyra Atoll, in the Line Islands of the equatorial Pacific, supports one of the largest remaining native stands of Pisonia grandis forest in the tropical Pacific Ocean. In 2003, we surveyed terrestrial arthropods in order to document extant native and introduced species richness, compare these lists to historical records, and assess potential threats to native species and ecosystem integrity. In total, 115 arthropod taxa were collected, bringing the total number of taxa recorded since 1913 to 162. Few native species were collected; most taxa were accidental introductions also recorded from the Hawaiian Islands, the presumed main source of introductions to Palmyra. The overlap with previous historical surveys in 1913 and 1948 was low (<40%) and new species continue to establish, with one species of whitefly reaching pest status between 2003 and 2005. We observed numerous dead or dying large Pisonia grandis, and the green scale Pulvinaria urbicola (Coccidae) was particularly abundant on trees of poor health. Abundant introduced ants, particularly Pheidole megacephala, tended this and other hemipterans feeding on both native and introduced plants. We hypothesize that the Pheidole--Pulvinaria facultative mutualism is causing the decline of Pisonia grandis. Because of the unique properties of Pisonia grandis forest on oceanic atolls, its importance for nesting seabirds, and its alarming global decline, immediate conservation efforts should be directed at controlling introduced Hemiptera and disrupting their mutualisms with non-native ants on Palmyra Atoll.
- ItemArthropods from ‘ōhi‘a lehua (Myrtaceae: Metrosideros polymorpha), with new records for the Hawaiian Islands(Bishop Museum Occasional Papers, 2004) Gruner, DanielThis paper presents new records, range extensions, and a checklist of arthropod species found associated with the most common and widespread native tree in the Hawaiian Islands, ‘öhi‘a lehua (Myrtaceae: Metrosideros polymorpha Gaudichaud-Beaupré). Metrosideros polymorpha is found on all the main islands, naturally occurs from sea level to tree line (>2000 m), in dry, mesic, and wet forests, and is the canopy dominant in old growth and the first woody colonist on recent basaltic lava flows (Dawson & Stemmerman, 1990). Numerous insect species use ‘öhi‘a lehua as a resource for either food or habitat space, and it may have the largest fauna of any native plant (Southwood, 1960; Stein, 1983). Metrosideros is an important, year-round nectar resource for native bees, moths, thrips and other insects, and for native nectarivorous birds, such as the ‘apapane (Himatione sanguinea), ‘i‘iwi (Vestiara coccinea), and ‘akohekohe (Palmeria dolei). Metrosideros also provides important habitat for birds that forage for arthropod prey in the foliage (e.g., ‘akepa [Loxops coccineus]) and bark (e.g., Hawai‘i creeper [Oreomystis mana]). It can be argued that M. polymorpha is the backbone of Hawaiian forests and one of the most important resources for the long-term stability of ecosystems and watersheds in the islands.
- ItemAssessment of Chronic Sublethal Effects of Imidacloprid on Honey Bee Colony Health(PLoS (Public Library of Science), 2015-03-18) Dively, Galen P.; Embrey, Michael S.; Kamel, Alaa; Hawthorne, David J.; Pettis, Jeffery S.Here we present results of a three-year study to determine the fate of imidacloprid residues in hive matrices and to assess chronic sublethal effects on whole honey bee colonies fed supplemental pollen diet containing imidacloprid at 5, 20 and 100 μg/kg over multiple brood cycles. Various endpoints of colony performance and foraging behavior were measured during and after exposure, including winter survival. Imidacloprid residues became diluted or non-detectable within colonies due to the processing of beebread and honey and the rapid metabolism of the chemical. Imidacloprid exposure doses up to 100 μg/kg had no significant effects on foraging activity or other colony performance indicators during and shortly after exposure. Diseases and pest species did not affect colony health but infestations of Varroa mites were significantly higher in exposed colonies. Honey stores indicated that exposed colonies may have avoided the contaminated food. Imidacloprid dose effects was delayed later in the summer, when colonies exposed to 20 and 100 μg/kg experienced higher rates of queen failure and broodless periods, which led to weaker colonies going into the winter. Pooled over two years, winter survival of colonies averaged 85.7, 72.4, 61.2 and 59.2% in the control, 5, 20 and 100 μg/kg treatment groups, respectively. Analysis of colony survival data showed a significant dose effect, and all contrast tests comparing survival between control and treatment groups were significant, except for colonies exposed to 5 μg/kg. Given the weight of evidence, chronic exposure to imidacloprid at the higher range of field doses (20 to 100 μg/kg) in pollen of certain treated crops could cause negative impacts on honey bee colony health and reduced overwintering success, but the most likely encountered high range of field doses relevant for seed-treated crops (5 μg/kg) had negligible effects on colony health and are unlikely a sole cause of colony declines.
- ItemAn 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.
- ItemAttenuation of top-down and bottom-up forces in a complex terrestrial community(Ecology, 2004) Gruner, DanielCarnivore (top-down) and resource (bottom-up) influences in food webs are strong and pervasive, but few studies have investigated their interactive effects in species-rich terrestrial ecosystems. This study focused on arthropods associated with the dominant tree species, Metrosideros polymorpha (Myrtaceae), in Hawaiian forests. Severe soil nutrient limitation on a 120-yr-old lava flow was removed by fertilization and combined with bird predator exclusion cages in a randomized block design. Arthropod densities were measured from clipped foliage at the outset and conclusion of a 33-mo experiment, and their biomass was estimated using regression equations. Metrosideros foliar nitrogen, tree growth, and biomass increased directly in response to fertilization but did not change with bird exclusion. Fertilization increased detritivore densities but not biomass, and both density and biomass of herbivores, while bird exclusion increased both density and biomass of carnivores. Fertilization also increased spider density and biomass, but bird exclusion increased spider numbers (15 species) only in high resource plots. Overall, trophic level biomass responses were less pronounced than density because smaller bodied individuals responded more to enrichment. Bottom-up factors controlled basal trophic levels, and detritivores comprised the largest fraction of arthropod density and biomass. Conversely, top-down impacts were apparent but variable, limited to higher order consumers, and did not cascade to the level of primary producers. These experimental results were consistent with the view that complex forest ecosystems are structured on a bottom-up template.
- ItemThe 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.
- ItemBIODIVERSITY 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.
- ItemBiosystematics 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.
- ItemBiotic resistance to an invasive spider conferred by generalist insectivorous birds on the island of Hawai‘i(Biological Invasions, 2005) Gruner, DanielA central problem for ecology is to understand why some biological invasions succeed while others fail. Species interactions frequently are cited anecdotally for establishment failure, but biotic resistance is not well supported by quantitative experimental studies in animal communities. In a 33-month experiment on Hawaii Island, exclusion of native and alien forest birds resulted in a 25- to 80-fold increase in the density of a single non-indigenous spider species (Theridiidae: Achaearanea cf. riparia). Caged plots held large aggregations of juveniles and more large-bodied individuals, suggesting potential reproductive individuals are more susceptible to bird predation. Most examples of biotic resistance involve competition for limiting resources among sessile marine animals or terrestrial plants. The present results show that generalist predators can limit the success of introductions, even on oceanic islands, generally assumed less resistant to invasion.
- ItemBirds as predators in tropical agroforestry systems(2008-04) Van Bael, Sunshine; Philpott, Stacy; Greenberg, Russell; Bichier, Peter; Barber, Nicholas; Mooney, Kailen; Gruner, DanielInsectivorous birds reduce arthropod abundances and their damage to plants in some, but not all, studies where predation by birds has been assessed. The variation in bird effects may be due to characteristics such as plant productivity or quality, habitat complexity, and/or species diversity of predator and prey assemblages. Since agroforestry systems vary in such characteristics, these systems provide a good starting point for understanding when and where we can expect predation by birds to be important. We analyze data from bird exclosure studies in forests and agroforestry systems to ask whether birds consistently reduce their arthropod prey base and whether bird predation differs between forests and agroforestry systems. Further, we focus on agroforestry systems to ask whether the magnitude of bird predation (1) differs between canopy trees and understory plants, (2) differs when migratory birds are present or absent, and (3) correlates with bird abundance and diversity. We found that, across all studies, birds reduce all arthropods, herbivores, carnivores, and plant damage. We observed no difference in the magnitude of bird effects between agroforestry systems and forests despite simplified habitat structure and plant diversity in agroforests. Within agroforestry systems, bird reduction of arthropods was greater in the canopy than the crop layer. Top-down effects of bird predation were especially strong during censuses when migratory birds were present in agroforestry systems. Importantly, the diversity of the predator assemblage correlated with the magnitude of predator effects; where the diversity of birds, especially migratory birds, was greater, birds reduced arthropod densities to a greater extent. We outline potential mechanisms for relationships between bird predator, insect prey, and habitat characteristics, and we suggest future studies using tropical agroforests as a model system to further test these areas of ecological theory.
- ItemBiting 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.
- ItemBottom 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.
- ItemCan 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.