Northwest Montana (United States) also known as the last best place, is one of the most pristine habitats for bumble bees, as well as other keystone pollinators. Though, due to anthropogenic influences, wildflower populations in recent years have been fragmented and captivated by exotic invasive plants, which will likely alter and reduce the fecundity of these pollinator species. In Montana, Centaurea stoebe (Spotted Knapweed) has been a very prolific non-native plant due to its ability to displace entire native plant populations. Pollen, due to its nutritional properties, is the most important resource to bumble bees. While some invasive forbs may serve as a refuge for nectar resources in an altered ecosystem, they may not be ideal sources of pollen for bees. By looking at the pollen sacks of bumble bees and identifying individual grains of pollen, an estimate of preference can be calculated when compared to the resources available to them. It is assumed that the amount of Spotted Knapweed pollen found within the pollen sacks of bumble bees would be proportionally similar to the amount of Spotted Knapweed available within the environment. However, alternatively, bumble bees may prefer to collect pollen from native flowers due to a symbiotic relationship with these known forbs. Pollen collection and identification from bumble bees using light microscopy were compared to floral abundance stem count surveys throughout the temporal dynamics of the 2020 and 2021 seasons. The mean proportion of Spotted Knapweed pollen seen in the pollen sacks was estimated to be 18%, while the mean proportion of Spotted Knapweed present at the study site was 32%. At an alpha level of 0.05, it is statistically significant that the bumble bees are selecting less pollen than there are floral resources of spotted knapweed available. This provokes further research mapping the relationship between bumble bees and their host flowers to better understand the loss of pollinators in a changing environment.

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