The Varroa destructor mite has been associated with the recent decline in honey bee populations. While experimental data are crucial in understanding declines, insights can be gained from models of honey bee populations. We add the influence of the V. destructor mite to our existing honey bee model in order to better understand the impact of mites on honey bee colonies. Our model is based on differential equations which track the number of bees in each day in the life of the bee and accounts for differences in the survival rates of different bee castes. The model shows that colony survival is sensitive to the hive grooming rate and reproductive rate of mites, which is enhanced in drone capped cells.

Seagrasses play an important role in coastal ecosystems and serve as important marine carbon stores. Acoustic monitoring techniques exploit the sensitivity of underwater sound to bubbles, which are produced as a byproduct of photosynthesis and present within the seagrass tissue. To make accurate assessments of seagrass biomass and productivity, a model is needed to describe acoustic propagation through the seagrass meadow that includes the effects of gas contained within the seagrass leaves. For this purpose, a new seagrass leaf model is described for Thalassia testudinum that consists of a comparatively rigid epidermis that composes the outer shell of the leaf and comparatively compliant aerenchyma that surrounds the gas channels on the interior of the leaf. With the bulk modulus and density of the seagrass tissue determined by previous work, this study focused on characterizing the shear moduli of the epidermis and aerenchyma. These properties were determined through a combination of dynamic mechanical analysis and acoustic resonator measurements coupled with microscopic imagery and finite element modeling. The shear moduli varied as a function of length along the leaves with values of 100 and 1.8 MPa at the basal end and 900 and 3.7 MPa at the apical end for the epidermis and aerenchyma, respectively.

No abstract

Previous investigations related to acoustic propagation through seagrass have shown that sound waves are sensitive to the gas contained within seagrass tissue as well as free bubbles produced by photosynthesis. The acoustical effects include reduced low-frequency sound speed and increased sound attenuation. The effects are more pronounced when the density of vegetation is higher as well as during daylight hours when sunlight-driven photosynthesis occurs. However, the application of mathematical models to describe these phenomena have been limited to effective medium models for water containing spherical gas bubbles. These approaches neglect both the effects of elastic properties of seagrass tissue as well as the shape of the aspherical gas bodies constrained within the plant. In this work, a finite element model of an acoustic resonator containing seawater and seagrass blades was developed to explain previously published measurements. Themodel utilizes independently measured values of the elastic propertiesof seagrass tissue and microscopic cross-section imagery of the gas volumes contained within the seagrass tissue. These results represent a step towards defining an appropriate effective medium model for acoustic propagation through seagrass tissue. [Work supported by ARL:UT IR&D and ONR.]