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This thesis is concerned with developing a theory of model-theoretic tree properties. These properties are combinatorial properties of a formula or family or formulas that place strong constraints on the behavior of forking and dividing yet are compatible with certain forms of model-theoretic randomness. The most significant and intensively studied is \emph{the tree property}, whose negation characterizes the simple theories, and a successful theory for simple theories was developed by Hrushovski, Kim, Pillay, and others, in the late 90s and early 2000s. Motivated by parallels with simplicity theory, we introduce a theory of independence called \emph{Kim-independence} and present a structure theory for NSOP$_{1}$ theories in terms of it. This unifies and explains simplicity-like phenomena observed in several non-simple examples, such as existentially closed vector spaces with a bilinear form and $\omega$-free PAC fields. This machinery also gives a streamlined method for establishing that a given theory is NSOP$_{1}$ and for showing that certain generic constructions preserve NSOP$_{1}$. We also develop techniques for the manipulation of tree indiscernibles to address several questions concerning the syntax of the related model-theoretic tree properties TP$_{1}$, weak $k$-TP$_{1}$, and the associated cardinal invariants.

The parasitic mite Varroa destructor is the most significant single driver of the global honey bee health decline. Better understanding of the association of this parasite and its host is critical to developing sustainable management practices. This work shows that Varroa is not consuming hemolymph as has been the accepted view, but damages host bees by consuming fat body. Feeding wounds in adult bees were imaged for the first time showing that Varroa feed on the underside of the abdomen where fat body is the immediate underlying tissue. Fat body at the wound site showed evidence of external digestion. Hemolymph and fat body in honey bees were then marked with fluorescent biostains. Fluorescence associated with the fat body was consistently detected in the gut of mites fed on these bees while comparatively little fluorescence was detected from the hemolymph biostain. Mites were then fed a diet composed of one or both tissues. Mites fed fat body tissue survived longer and produced more eggs than those fed hemolymph. Mites fed hemolymph showed fitness metrics no different from the starved control group. Collectively, these findings show that Varroa are exploiting the fat body as their primary source of sustenance; a tissue integral to proper immune function, pesticide detoxification, overwinter survival and several other essential processes in healthy adult and immature bees. Additional study was undertaken to better understand how the Varroa accelerates its reproductive rate. Via gel electrophoresis and immunodetection, undigested honey bee vitellogenin was found in Varroa eggs. The presence and identity of these host proteins was confirmed via HPLC MS/MS. This particular cleavage of vitellogenin is found only in the fat body. These findings fundamentally alter our understanding of the etiology of varroosis and underscore a need to revisit our understanding of this parasite and its impacts, both direct and indirect, on honey bee health. Further study of Varroa adaptations focused on expanding knowledge of Varroa morphology with the aim of determining features that can distinguish between Varroa species. Using low temperature scanning electron microscopy, we were able to provide better resolution of key morphological features, detail variability within traits, and provide novel descriptions of certain characters.

Bal arıları ölüyor. Avrupa, Kuzey ve Güney Amerika, Asya ve Afrika’da olmak üzere arıların bulunduğu her yerde yüksek oranlarda kayıplar kayıt edilmiştir. Bu kayıpların altında yatan neden veya nedenler ile ilgili pek çok teori bulunmaktadır; yetersiz beslenme, pestisitler, hastalık ve parazitler bunlar arasında en sık bahsedilenlerdir. Tek başlarına veya birlikte hepsinin büyük ihtimalle rolü bulunsa da, parazitik varroa akarının tüm dünyada görülen koloni ölümlerinde büyük rol oynadığı konusunda fikir birliği bulunmaktadır., Honey bees are dying. High rates of losses have been reported in Europe, North and South America, Asia, and Africa – virtually everywhere bees are kept. There are many theories about what the underlying cause or causes of these losses are; poor nutrition, pesticides, diseases and parasites are a few of the most commonly mentioned. While all probably play some role, either on their own or in combination, there is growing consensus that one - the parasitic varroa mite, plays a large, if not the largest, role in the high rates of colony mortality experienced in many places around the world.