Entomology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2767

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Subject: search.filters.subject.Biology, Animal Physiology

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    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.
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    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.
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    THE INFLUENCE OF THERMAL ENVIRONMENT ON DEVELOPMENT AND VULNERABILITY TO PREDATION OF THE AZALEA LACE BUG, STEPHANITIS PYRIOIDES (HETEROPTERA: TINGIDAE)
    (2004-01-09) Lepping, Miles; Shrewsbury, Paula M; Raupp, Mike J; Denno, Robert F; Entomology
    Differential thermal environments were examined for their influence on performance traits of a key ornamental pest, the azalea lace bug, Stephanitis pyrioides, in the presence and absence of a generalist predator, the green lacewing, Chrysoperla carnea. In laboratory studies, duration of development increased for nymphal instars of S. pyrioides as temperature decreased, producing significant developmental lags in cooler environments. Predation trials identified early nymphal stages as more susceptible to predation than older, dispersal-capable stages, specifically in warmer environments. Additionally, morphological characteristics attained at adulthood combined with behavioral defenses may mediate the reduction in consumption of later S. pyrioides stages by piercing-sucking arthropods such as C. carnea. Field studies confirmed development and life-stage vulnerability findings from the laboratory, however, differential thermal environments created by shading did not generally influence predation. In urban landscapes, S. pyrioides may attain a degree of enemy-free space by occupying a thermal refuge in sunny, exposed habitats.