Motility of unicellular algal cells, especially its ability to respond to environmental cues, is crucial in industrial and ecological contexts and has been studied extensively with the model organism Chlamydomonas. However, little is known about the relationship between motility and the cell-cycle, despite the apparent link of mitosis dependent morphological changes which involve the flagella and the dependency on light/dark conditions of the cellular reactions. In this study, the cell swimming speed, the rotational diffusivity and its swimming bias against gravity were measured with high-speed video microscopy with Chlamydomonas reinhardtii cultures highly synchronised to a diurnal cycle. A simulation of gravitactic cell trajectories was developed to assist the statistical analysis of the cell trajectories from the images, which subject to a projection effect and has not been addressed previously. Its morphological changes, including cell size, shape, mass density, and presence of flagella were also evaluated. Un unforeseen change of cell motility at a critical mitosis time point was discovered, and our analysis suggests a connection to the alternating cell energetic regimes rather than the cell morphology. As indicated by results obtained from imaging based experimental measurements and by computational methods, the motility variation has direct consequences on the collective motion of algal cells in a Hagen-Poiseuille flow, a relevant component flow for air-lift photobioreactors. The cell number density profiles were calculated by an individual-based simulation and a continuum system inclusive of the buoyancy effect imposed by the aggregated cells on their surrounding fluid. Qualitative experimental-theoretical agreement suggests that the models can be employed for optimisation problems of photobioreactor flow designs inclusive of the non-negligible cell-cycle effects, which has been commonly overlooked in previous studies.

Building design, maintenance, and management can have significant impacts on accessibility and suitability for pest species. The brown marmorated stink bug, Halyomorpha halys (Stål), causes household nuisance pest problems because of its habit of using human homes as winter refuges. Studies were conducted to understand behaviors and characteristics relevant to this problem, including response to gravity, ability to pass through openings, responses to heat, and mortality estimations in wall assemblies. In the lab, winter shelter seeking bugs were shown to exhibit upward movement, and field observations of bugs on building exteriors gave similar results. In experiments testing the size limits on openings through which bugs could pass, height limited tests excluded most females at 4 mm, and all bugs at 3 mm. Pronotum width limited tests excluded most females at 8 mm and nearly all bugs at 7 mm. Accompanying measurements of over 900 bugs found an average female pronotum width of 8.33 mm and height of 4.03 mm, and male pronotum width of 7.47 mm and height of 3.50 mm, with minimum sizes indicating that only a small percentage of bugs will pass the smallest openings tested. Heat response experiments of shelter seeking bugs were first piloted outdoors, and then modified to be a forced choice indoor test. In outdoor tests on a flat plane wall section with alternating heated sections, bugs did not respond to thermal contrast but rather immediately walked off of the wall. In the indoor forced choice test, a box of four cavity walls was used. Bugs did not respond to the heated sections in either the adjacent or opposite configuration. Thermal simulation modeling was used to evaluate the possible effects of varying wall assembly materials and configurations on cold-related mortality of bugs overwintering in the cavity space behind cladding. Simulation results indicated that bugs electing to overwinter in the space between cladding and sheathing were at risk of freezing deaths, with mortality expectations increasing in better insulated buildings. The results of these studies will inform future control measures and impact studies in buildings. / Ph. D.