Entomology Dissertations Collection

Biological Control of the Ambermarked Birch Leafminer (Profenusa thomsoni) in Alaska

Soper, Anna L. — Thu, 13 Dec 2012 06:40:21 PST

The ambermarked birch leafminer (AMBLM) (Profenusa thomsoni) is an invasive leafminer native to the Palearctic from the United Kingdom to Turkey to Japan. It was introduced to the eastern United States in 1921 and has since spread to the mid-western U.S. states and Canadian provinces. This leafminer was introduced to Alaska in 1996, where it has since spread over 140,000 acres, from Haines to Fairbanks. The most severe damage is found throughout the Anchorage bowl, which extends south to Girdwood and North to Wasilla. The damage caused by P. thomsoni can be severe, defoliating entire trees. In 2006, it was noted that urban areas in Alaska experienced higher densities of AMBLM leafminer than adjacent forested areas. To examine the effects of habitat on leafminer densities, twenty permanent plots were established in Anchorage, Alaska in 2006 and were classified as urban and forest (ten each). Temperature records for the twenty permanent sites showed that average daily temperatures and average accumulated degree-days differed significantly between urban and forest sites. In 2007 and 2008, leafminer abundance in each habitat was examined weekly at six plots (three urban and three forest) within the city of Anchorage. Asynchronous emergence, flight, and oviposition times were observed between leafminers in forests versus urban areas, with peaks of these parameters in forests being about three weeks later than in urban areas. To control the spread and effects of P. thomsoni, a cooperative biological control project was launched in 2003 and the parasitoid wasp Lathrolestes thomsoni (Hymenoptera: Tenthredinidae) was selected for release. Parasitized leafminer larvae were collected from the provinces of Northwest Territories and Alberta, in Canada and transferred in soil tubs as pre-pupae to Alaska. From 2004-2008, 3636 adult L. thomsoni adults were released in birch tree stands in Anchorage, Soldotna, and Fairbanks, Alaska. Parasitoids have been recovered at all release sites in Alaska and have established populations at most release sites. Currently, AMBLM densities have declined by over 40% in the Anchorage area and the spread of the leafminer throughout the state appears to have slowed. Throughout the course of the biological control program two additional parasitoids were discovered attacking P. thomsoni in Alaska. The first, Lathrolestes soperi, an endoparasitoid with similar biology to the released parasitoid L. thomsoni, was found to attack early instar larvae within the leaf. The second species, Aptesis segnis, is an ecotoparasitoid that attacks pupae and prepupae in their earthen cells in soil. Lathrolestes soperi was found to contribute a significant proportion of mortality against the leafminer. The presence of A. segnis in the parasitoid guild raised mortality of P. thomsoni to 40.3%, showing that the percent parasitism by A. segnis was 26%, double that provided by L. soperi. This suggests that A. segnis is the dominant parasitoid in the guild. It is unknown what effect that the introduced wasp L. thomsoni will have on the presumably native L. soperi and if one species will outcompete the other over time, or both will coexist. Future work on this system is recommended in five to ten years to see if L. thomsoni and L. soperi populations remain stable or to see if one parasitoid outcompetes the other and if A. segnis maintains its dominant place in the system.

First-principle electronic structure calculations within real-space mesh framework: Applications to atoms, molecules and nanostructures

Zhang, Deyin — Wed, 18 Jan 2012 12:11:06 PST

This dissertation is organized as follows. Beginning with physical background discussions of many-body problems, Chapter 1 introduces the central Kohn-Sham equations of Density Functional Theory for electronic structure calculations. In order to discretize the system, the real-space mesh techniques are selected to apply to the Kohn-Sham equations because of their advantages over other discretization techniques. In addition, the high-order basis functions employed by real-space mesh technique are used to reduce the size of the system matrices and improve the simulation convergence. In the self-consistent simulations, the current challenge posed by the first-principle calculations is the high cost for computing the electron density, and this becomes a limiting factor for large-scale device simulations. Consequently, Chapter 2 investigates the relevance of mode decomposition techniques (i.e. mode approach) for solving the Schrödinger-type equation within a real-space mesh framework. It is shown how the full mode approach or its asymptotic counterpart can be of benefit to two distinct highly efficient numerical procedures for computing the electron density: (i) the CMB strategy and (ii) the FEAST algorithm. The numerical simulation examples of CNTs (carbon nanotubes) using empirical pseudopotential are also presented in this chapter to show the efficiency of the proposed techniques. In addition to the applications to empirical pseudopotential, Chapter 3 shows that these techniques are also successfully applied to all-electron calculations for systems of a single atom, molecules and polysparaphenylene, in which bare local core potential is taken. These simulations achieve high-accuracy using the 3^rd order finite element method and non-uniform mesh. For large-scale simulation, it becomes necessary to implement parallelism on different levels of modeling process. Therefore, Chapter 4 proposes a domain decomposition technique to divide a large problem into small ones and then carry out calculations for subproblems simultaneously. In this dissertation, the linear system solver in FEAST is further customized to solve the solution on the coarse mesh level, while solution of fine mesh inside each independent subdomain can be retrieved simultaneously accounting for the information at the interfaces of fine/coarse mesh. In such way, the size of system can be reduced significantly, and the scalability of the all-electron calculations can be improved.^

Modeling of surface morphological response to the simultaneous action of multiple external fields

Vivek, Vivek — Wed, 28 Jul 2010 17:57:41 PDT

Surface morphological instability underlies various reliability problems of technologically important materials, which have a broad range of applications from aerospace engineering to microelectronics and nanotechnology. Applied mechanical stress has been known to induce surface morphological instabilities in crystalline solid materials. Specifically, linear stability analyses and numerical simulations have demonstrated that the competition between elastic strain energy and surface energy can cause the growth of perturbations from a planar surface morphology evolving into deep crack-like grooves by surface diffusion. These theoretical predictions are consistent with experimental findings over a broad class of materials. However, the effects of the simultaneous action of another external field on the surface morphological response of a stressed solid have not been explored systematically. The findings of this thesis contribute to our fundamental understanding of the morphological response of crystalline solid conductors to the simultaneous action of mechanical stresses and electric fields.^ A significant part of this thesis is focused on the surface morphological stability analysis of stressed conducting crystalline materials under the simultaneous action of an electric field. Combining the results of linear stability analysis with self-consistent dynamical simulations based on a fully non-linear model of driven surface morphological evolution, it is demonstrated that a sufficiently strong and properly applied electric field can inhibit the stress-induced surface instability and stabilize surfaces of crystalline solids that are otherwise vulnerable to surface cracking. Furthermore, the effects of surface crystallographic orientation and strength of surface diffusional anisotropy on the morphological stability of planar surfaces of stressed elastic solids under surface electromigration conditions are investigated systematically. The numerical simulations also have revealed a new long-wavelength surface instability that leads to the formation of patterns of ripples on the conducting solid surfaces; the rippled surface morphologies have been characterized in detail.^ Additionally, the thesis investigates complex oscillatory asymptotic states reached in the electromigration-driven morphological evolution of void surfaces in thin films of face-centered cubic metals under the simultaneous action of mechanical stress. Based on self-consistent dynamical simulations according to a realistic, well-validated, fully nonlinear model, the intriguing dynamics of electromechanically driven void surfaces has been analyzed. The corresponding complex asymptotic states range from time-periodic to fully chaotic. Specifically, in such thin films with <110>-oriented film planes, it is demonstrated that a sequence of period-doubling bifurcations sets the doubly driven nonlinear system on a route to chaos. Such a chaotic void morphological response is not observed in <100>-oriented thin films.^