Findings on spatial foraging patterns of bumblebees (Bombus ignitus) from a bee-tracking experiment in a net cage

To obtain basic information on spatial foraging patterns of the bumblebee Bombus ignitus, we conducted a tracking experiment of marked bumblebees foraging among systematically arranged potted plants, Cosmos sulphureus, in an enclosed system, i.e., a net cage, for 21 days. A sequence of 100 plant visits by a bumblebee typically comprised visits to about 30 individual plants on average, not all the plants. The bees showed gradual changes in their spatial foraging patterns, and we found that the size of the foraging area varied across days in the same bees and among bees foraging on the same days. Air temperature and bee body size were unlikely to affect their spatial foraging patterns. The observed bees visited the same plants at significantly different rates on 11 of the 17 days for which sufficient data could be collected, perhaps resulting from displacement of foraging areas among the bees. From this result, we suggest that the presence of simultaneously foraging bees may affect their spatial foraging patterns. The preferences for large display plants were significant on 15 of the 21 days if data were pooled for all bees foraging on the same day, but the preference of individuals was not significant in most cases, suggesting the possibility that spatial foraging patterns of individual bees may not simply depend on such preference. These results are important for future studies to examine factors affecting spatial foraging patterns of bumblebees.