Abstract

Experiments were conducted in order to determine the effects of carrying capacity (K) on populations of the house dust mite (HDM) Dermatophagoides pteronyssinus (Trouessart) within a mattress. Initial experiments were conducted using a set amount of food, thereby providing the mites with a finite environment, in terms of food and space (for the purposes of this experiment HDMs lived in the food). Mite growth was monitored over time and found to resemble a sigmoid curve. Once the population had peaked it remained constant for 6 weeks before gradually declining. At this stage it appeared likely that the population at its peak was being limited by space and its decline was being caused by a reduction in food quantity or quality. In order to clarify this point a) space in the form of ground up vermiculite and b) food, which also added space, were added to a population of mites whose numbers had stabilized. Both populations increased significantly in comparison with the control (the original culture), indicating that space was a constraining factor. However, the populations to which extra food was added grew to higher levels than those with vermiculite. This indicated that according to circumstances K can be affected by both food quantity/quality and space. Experiments were conducted that showed that both the number of mites added to food (2 mating pairs vs.1163 and 5810 mites) and the initial amount of food to which mites were added (0.5 to 1.5 g) could have a profound effect on the mite populations (mites per gram) within the tubes. The effects of population size on mite migration behaviour were also examined. It was found that mite migration increased significantly once the population had reached certain threshold levels.