Entomology
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Item Ground-dwelling beetles as bioindicators in transgenic corn(2009) Lepping, Miles; Shrewsbury, Paula M; Dively, Galen P; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ecological risk assessment for transgenic crops requires identification of appropriate biological indicator organisms for use in laboratory and field biomonitoring studies. Ground-dwelling predatory beetles in the families Carabidae and Staphylinidae comprise a diverse and abundant group of nontarget organisms in field corn systems where rootworm-resistant transgenic varieties are deployed. First, the utility of two sampling methods (pitfall trapping and suction-based litter extraction) was assessed for estimating ground beetle (Coleoptera: Carabidae) population parameters in Maryland cornfields. Sampling bias was established for pitfall trapping, confirming the limitations of this semi-quantitative method for capturing a representative portion of the epigeal community. Litter extraction data conformed to predictions for abundance in relation to trophic identity, body size and biomass. Litter extraction identified smaller bodied carabid omnivores and carnivores as numerically dominant over larger bodied species that have received focus in risk assessment studies. A small-bodied carabid, Elaphropus xanthopus (Dejean), was identified as the dominant carnivore, and therefore selected for nontarget exposure and toxicity studies. Second, in choice and no-choice experiments, corn pollen was identified as a realistic, direct exposure pathway to transgenic proteins for E. xanthopus. Third, organism-level exposure to Cry34Ab1 rootworm-resistant protein was demonstrated for E. xanthopus in the laboratory and field during corn pollen shed. Field studies also revealed contamination across transgenic and non-transgenic test plots, indicating experimental design must account for the movement of study organisms and/or transgenic plant tissues. Finally, a toxicity study examined the effects of dietary exposure to rootworm-resistant Cry34/35Ab1 corn pollen for two beetle species, a carabid, E. xanthopus, and a staphylinid, Strigota ambigua (Erichson). Transgenic pollen exposure did not affect longevity or sub-lethal behaviors for either species. Small-bodied, predatory ground beetles are recommended as candidate bioindicator organisms in risk assessment studies designed to optimize field monitoring, exposure detection, and bioassay for transgenic pesticides.Item GENETIC DIVERSIFICATION, SAPROPHYTIC COMPETENCE AND GENETIC ENHANCEMENT OF THE ENTOMOPATHOGENIC FUNGUS METARHIZIUM(2009) Pava-Ripoll, Monica Patricia; St. Leger, Raymond J; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Entomopathogenic fungi are being investigated as alternatives to chemical insecticides. This study explored the versatility of the entomopathogenic fungus Metarhizium anisopliae by examining its diversification, saprophytic competence and potential for genetic enhancement. M. anisopliae is a radiating species containing both generalist and specialized lineages with broad and narrow host ranges and as such provides an excellent model system to study the evolution of pathogenesis. Using 18S RNA and protease sequences, I demonstrated that strains can be selected representing evolutionary distances ranging from <1 to 8 MY and their natural molecular variation allows analysis of processes of adaptive change. M. anisopliae is particularly abundant in the rhizosphere. Germination of M. anisopliae strain 2575 was >96% in 1 mg/ml root exudate (RE) and growth in RE resulted in 29 (58%) genes being up-regulated and 21 (42%) down-regulated. The identity of these genes is helping to define the physiological requirements for rhizosphere competence. Hypothetical and orphans proteins (41.4%) were also actively expressed indicating that many previously uncharacterized genes may have functions related to survival at the soil-root interphase. Using the fungus as a delivery vehicle for foreign toxins presents a powerful approach for increasing virulence. M. anisopliae was modified to express a scorpion toxin (AaIT) in insect haemolymph and bioassayed against the coffee berry borer Hypothenemus hampei. AaIT increased mortality up to 56.6%, and reduced the medial lethal concentration (LC 50 ) by 15.7-fold and the average survival time (AST) by 20.1%. The AaIT gene and the M. anisopliae esterase gene (Mest1) were inserted into three strains of Beauveria bassiana (ARSEF 252, 8998 and 9184) with high, medium and low mortality, respectively, against the Colorado potato beetle (CPB) Leptinotarsa decemlineata. Mortality rates were strain- and dose- dependant and increased from 16.1 to 36.7% in single transformants (AaIT or Mest1) and from 7.1 to 33.5% in double transformants (AaIT-Mest1). The AST was reduced up to 33% and the LC50 up to 5.9-fold. Although singly both AaIT and Mest1 increased the killing power of B. bassiana against second instar CPB, combining AaIT and Mest1 together did not produce synergistic effects.Item KINEMATICS OF THE MAYFLY NYMPH GILL ARRAY: AN INTERMEDIATE REYNOLDS NUMBER VENTILATION PUMP(2009) Sensenig, Andrew T.; Shultz, Jeffrey W.; Kiger, Ken T.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Comparative studies encompassing a wide range of aquatic animals have shown that rowing is exclusively used at low Reynolds numbers (Re <1) while flapping is predominantly used at Re > 100, but few studies have been undertaken to document the transition in individual species that traverse the intermediate Re regime using a single set of appendages. Thus, it is not generally known whether a gradual increase in Re within a system results in a gradual or sudden shift between rowing and flapping. Here I document both the kinematics of the appendages and the surrounding fluid of a nymphal mayfly Centroptilum triangulifer that uses a serial array of seven pairs of abdominal gill plates and operates at Reynolds numbers ranging from 2-22 during ontogeny. I found that some kinematic variables (stroke frequency and metachronal phase lag) did not change during ontogeny but that others changed substantially. Specifically, gills in small instars used strokes with large pitch and stroke-plane deviations, while larger instars used strokes with minimal pitch and minimal stroke-plane deviation. Gills in larger instars also acquired an intrinsic hinge that allowed passive asymmetric movement between half strokes. Net flow in small animals was directed ventrally and essentially parallel to the stroke plane (i.e. rowing), but net flow in large animals was directed dorsally and essentially transverse to the stroke plane (i.e. flapping). The metachronal phasing of the gills produced a time-dependent array of vortices associated with a net ventilatory current, a fluid kinematic pattern here termed a "phased vortex pump". Significantly, absolute vortex size did not change with increasing animal size or Re, indicating that the vortex diameter (Lv) decreased relative to intergill spacing (Lis) during mayfly growth. Given that effective flapping requires organized flow between adjacent appendages, I proposed the hypothesis that rowing should be favored when Lis / Lv < 1 and flapping should be favored when Lis / Lv > 1. Significantly, the rowing-to-flapping transition in Centroptilum triangulifer occurs at Re ~5, when maximum dynamic intergill distance equals vortex diameter. This result suggests that the Re-based rowing-flapping demarcation observed in a wide array of aquatic organisms is determined by the relative size of the propulsive mechanism and its self-generated vortices.Item Nutrient regulation by an omnivore and the effects on performance and distribution(2009) Pearson, Rachel Estelle Goeriz; Gruner, Daniel S; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Omnivores have a unique interaction with their nutritional environment because they have adapted to consume food from different trophic levels. To successfully navigate their variable resources, omnivores must maintain some level of nutrient regulation. To explore the effects of nutrient regulation by an omnivore, I used a salt marsh katydid, Conocephalus spartinae. To first address the ability of Conocephalus to perform on a wide range of diets and to regulate their nutritional intake, I used artificial diets that differed in relative amounts of protein and carbohydrate (Chapter 1). I found that Conocephalus survival decreased on a high protein diet due in part to a decrease in lipid stores but growth was not affected by diet. In a second experiment Conocephalus showed a degree of nutrient regulation as evidenced by the difference in what they actually ate and the predicted consumption if they had been feeding equally on the diets presented in each treatment. However, I did not find evidence for tight macronutrient regulation. Next I explored capacity of Conocephalus to regulate their nutrient intake (nitrogen and lipid) when fed naturally co-occurring prey (Chapter 2). I first established that the prey differed in their protein and lipid content and that these differences were related to the size of the prey species. When Conocephalus were fed different prey species individuals showed no differences in either growth or survival. In the final experiment, I found that Conocephalus did show evidence of a degree of nitrogen and lipid regulation because they did not feed equally on all of the prey species offered. Lastly, I documented the relationship between the ability of Conocephalus to locate plant and prey resources and the effect that these resources have on omnivore performance (Chapter 3). I found that Conocephalus aggregates in areas of high plant quality but that their numbers do not correspond to areas of high prey density. However, I found that katydid growth and survival was enhanced by prey availability but not plant quality. Overall, I documented how an organism like an omnivore relates to its nutritional environment and how nutrient regulation might affect performance and distribution. Last, I documented the relationship between the ability of katydids to locate plant and prey resources and the effect that these resources have on omnivore performance (Chapter 3). I found that katydids aggregate in areas of high plant quality but that their numbers do not correspond to areas of high prey density.Item Soldier neotenics of Zootermopsis nevadensis (Hagen) and Archotermopsis sp. (Isoptera: Termopsidae): Morphology, Development, Behavior, and Evolution(2009) Johnson, Susan Elaine; Thorne, Barbara L; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)I: The relictual reproductive soldier neotenics of primitive Termopsid termites may offer insights into the evolution of eusociality and sterile castes in termites. II: Soldiers and helpers in a new Thai species of Archotermopsis do not display unusually complete gonad development. The first neotenic pair ever reported for this genus is described. III: Morphological differences between soldiers and soldier neotenics in the head and gonads are quantified in Z. nevadensis. There is not necessarily a clear delineation in morphology between soldiers and soldier neotenics. IV: Colony age and size do not significantly influence the differentiation or survival of male replacement reproductives in colonies of Z. nevadensis. Soldier neotenics' development is not significantly influenced by the presence of normal soldiers. V: Soldier neotenics and related female neotenics tend to have greater initial survival after interactions with colonies with only normal neotenics. Mostly helpers are aggressors, never soldier neotenics or neotenics.Item Indirect Effects of Imidacloprid on Natural Enemies of Spider Mites in Two Systems(2009) Creary, Scott; Raupp, Michael J; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With a growing number of reports showing secondary outbreaks of spider mites following systemic applications of imidacloprid, a study was designed to test the indirect effects of this insecticide on natural enemies of spider mites. We exposed two predators, Chrysoperla rufilabris and Stethorus punctillum, to mites that were reared on boxwoods and elms treated with imidacloprid and examined prey consumption, predator mobility and mortality. Mites reared on treated foliage were extremely toxic to predators, eliciting sharp reductions in feeding, locomotion, and longevity. These findings document that non-target pests feeding on plants treated with imidacloprid cause lethal and sublethal responses in natural enemies. We discuss implications on the compatibility of imidacloprid with IPM practices and infer impacts on generalist and specialist natural enemies.Item Mechanisms underlying outbreaks of spider mites following applications of imidacloprid(2009) Szczepaniec, Adrianna; Raupp, Michael J.; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Imidacloprid is a widely used neonicotinoid insecticide with high efficacy and long residual activity, and it is frequently applied to manage insect pests in urban landscapes. Recent reports of secondary outbreaks of spider mites after imidacloprid applications have prompted research endeavors to explain the driving force of the abrupt increases in abundance of mites. In this research, I documented outbreaks of spider mites in field and greenhouse experiments, and explored the three main mechanisms that have been proposed to explain the outbreaks: elimination of natural enemies, direct stimulation of spider mite fecundity and changes in plant quality, specifically, changes in defense pathways. To this end, I examined if the outbreaks occur in field and greenhouse experiments, and tested if imidacloprid applications disrupted communities of beneficial insects and caused increased reproductive performance of spider mites in two woody ornamental systems, elm trees and boxwood shrubs. Additionally, I used a model organism, tomato plants, to address the hypothesis of altered plant defenses in plants treated with imidacloprid. I found overwhelming evidence that outbreaks of spider mites occur consistently following applications of imidacloprid in landscape and greenhouse experiments. Moreover, surveys of arthropods on elms and boxwoods showed no evidence of disruption of a key predator of spider mites that could explain the outbreaks. Importantly, I found a plant-mediated effect of imidacloprid on fecundity of spider mites, while there was no evidence that the insecticide applied directly to the mites exerted the same effect on their reproductive performance. Lastly, two genes involved in jasmonic and salicylic acid showed a differential expression in tomatoes treated with imidacloprid, indicating that it affected plants' defense pathways in ways that could render plants more suitable for spider mites. This research demonstrated that changes in quality of plants brought about by imidacloprid seem to be the driving mechanism of secondary outbreaks of spider mites.Item EFFECTS OF ABIOTIC STRESS AND PREDATOR REFUGE ON TERRESTRIAL PREDATOR-PREY INTERACTIONS(2009) Lewis, Danny; Denno, Robert F.; Gruner, Daniel; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A major goal of ecology has been to understand how abiotic stress modifies species interactions, including predation. In marine habitats, a well-supported hypothesis holds that stress reduces the importance of predation because predators are more vulnerable to stress than prey, but this hypothesis has not been well-tested in terrestrial systems. The effect of refuge from stress on predation level has been studied even less, particularly in terrestrial systems. My research examines the effects of two types of stress, and refuge from them, on predation in a terrestrial salt-marsh food web. I investigated the stress of winter weather and asked first, whether the top predator used a particular marsh habitat as a winter refuge, second, how inter-year variation in winter severity affected refuge use, and third, how refuge use affected the predator's spatial distribution later in the year (Chapter 1). I found that spring predator density was higher within the refuge than outside, a difference that increased following colder winters. Consequently, predators were forced to re-colonize the rest of the marsh from the winter refuge, creating a long-lasting density gradient with lower densities farther from the refuge. In contrast, prey densities were not affected by winter temperatures, and were higher outside the refuge. This prey distribution may have facilitated predator colonization of non-refuge habitats. I investigated the stress of tidal inundation on marsh predators and prey, and their use of vegetation above water as a refuge from submersion. I found that densities of two key predators were more highly correlated with refuge availability than with tidal intensity. Notably, this correlation with refuge increased during the highest tides of the month. In contrast, distribution of the most abundant herbivore was not correlated with refuge availability (Chapter 2). These results suggested that tides impacted predators more than herbivores, but that refuge negated tidal effects on predators. To test these hypotheses, I eliminated tidal inundation from experimental field mesocosms while allowing control mesocosms to experience normal tides (Chapter 3). I found that tides caused substantial mortality at all trophic levels, but affected predators significantly more than herbivores and decreased predation levels.Item Metarhizium anisopliae's persistence as a saprophyte, genetic basis of adaptation and role as a plant symbiont(2008-11-17) O'Brien, Tammatha Rose; St Leger, Raymond; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Metarhizium anisopliae is a model for elucidating the basis of entomopathogenicity. However, many aspects of the saprophytic life of M. anisopliae remain unclear, including: 1) how the rhizosphere maintains populations of M. anisopliae; 2) the potential for microevolution; 3) the genetic factors that allow M. anisopliae to adapt to a saprophytic life and 4) the extent to which plant ecology is impacted by the rhizospheric competence of M. anisopliae. To extend our knowledge of plant-insect-fungal interactions, a field trial was conducted with M. anisopliae applied to turf. The specific objectives were to: 1) investigate the genetic basis of adaptation and strain stability of M. anisopliae; 2) monitor long-term survival of M. anisopliae, 3) compare the winter survival of M. anisopliae ΔMcl1 (disrupted in an immune evasion gene and nonpathogenic) with M. anisopliae ΔMad2 (adhesin-deficient and unable to adhere to plant epidermis) and 4) investigate root colonization and its impact on plant growth of Triticum aestivum seeds coated with conidia. Results showed that M. anisopliae ΔMad2 had a linear decrease in population and did not colonize roots, while M. anisopliae and M. anisopliae ΔMcl1 cycled with seasons in the soil and colonized roots. Microarray analyses were used to assay for any mutations affecting gene expression during survival in the field. After 3.5 years, field recovered Metarhizium isolates differed in gene expression by an average of 0.26 % for the 1,749 expressed sequence tags. Mutations disproportionately affected cell wall and stress responses, while genes coding for pathogenicity determinants such as adhesins and toxins were highly conserved. Triticum seeds inoculated with M. anisopliae ΔMcl1 and M. anisopliae ΔMad2 prior to planting in the field produced a 14.92%, 4% and 0% increase in seed weight respectively. M. anisopliae increased growth rates of winter wheat in microcosms and may act as a biofertilizer by making insoluble phosphate available to plants. This study showed Metarhizium benefits plants by protecting them from insect pests and by potentially solubilizing otherwise unavailable nutrients. Metarhizium, therefore, may be implemented in an integrated pest management (IPM) approach to reduce the use of chemical insecticides and fertilizers.Item Ecological dynamics of macrolepidoptera feeding on box elder (Acer negundo L.)(2008-08-29) Lind, Eric; Barbosa, Pedro; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding species abundances and distributions is a major goal of ecology. Although manipulative experiments can reveal mechanistic properties of interactions among a small number of species, and macroecological studies can draw fundamental insights from patterns at a large scale, inference about local communities as a whole requires a combination of these approaches. I used a suite of techniques to better understand the ecological dynamics of a group of insect herbivores, the assemblage of moth caterpillars feeding on box elder, a common riparian tree. I examined the landscape ecology of the assemblage to determine the degree of turnover at multiple scales, and how diversity of the assemblage depended on host plant context. I found apparent homogeneity of caterpillar diversity masked important differences in co-occurrence even at small scales, though the expected influence of host plant diversity was not observed. Examining the species through time, I investigated how species abundance was related to body size, intrinsic population growth rate, and diet breadth. Whereas body size did not scale significantly with abundance in this group of species, and diet breadth had a complex relationship with abundance, the population growth rate developed in association with the host plant explained the differential abundance of species on the plant quite well. Finally, I quantified elemental content of species in the group, to determine how stoichiometric constraints related to size and growth rates of caterpillars in the assemblage. I found some support for a theory connecting elemental composition to ecological interactions, though the results were species-dependent. Throughout these investigations I explicitly considered the evolutionary relatedness of co-occurring species using phylogenetic methods. By merging ecological and phylogenetic data, a more unified picture of the important mechanisms underlying species properties can be obtained. Through tests of theory at the landscape, community, and individual level, I have presented a clearer picture of the forces structuring this assemblage of caterpillars, and provided a template for investigations of community dynamics at a similar scale.