Scientists have become extremely concerned with the decline in pollinator abundance and diversity, because of the potential negative impacts such declines may have on agriculture, plant reproduction, and ecosystem function. Despite this interest, large gaps remain in our knowledge about fundamental features of pollinator biology such as their foraging behavior and nesting requirements. Because native bees are important for maintaining community structure, it is essential that we try to understand how habitat fragmentation may affect their reproduction in order to implement an effective conservation plan. We investigated the effects of urban fragmentation on the reproduction of native solitary bee species that inhabit Sonoran Desert fragments created by the growth and development of the city of Tucson, Arizona.  Specifically, we compared nesting success and parasitism rates of specialist and generalist cavity nesting bees that forage on creosote bush (Larrea tridentata, Zygophyllaceae), between large (>2 ha) and small fragments (<1 ha).   Preliminary results suggest that nest occupation by native bees is linked to the availability of creosote flowers, and that although larger fragments may contain a greater number of flowers, smaller fragments have more flowers on a per area basis, which may allow bees to complete their nests at a faster rate.