Bumble Bee sightings in Iowa:
Bombus (Bombias) auricomus (Robertson, 1903)
Bombus (Psithyrus) citrinus (Smith, 1854)
Bombus (Psithyrus) variabilis (Cresson, 1872)
Bombus (Thoracobombus) fervidus (Fabricius, 1798)
Bombus (Thoracobombus) pensylvanicus (DeGeer, 1773)
Bombus (Cullumanobombus) fraternus (Smith, 1854)
Bombus (Cullumanobombus) griseocollis (DeGeer, 1773)
Bombus (Bombus) affinis Cresson, 1863
Bombus (Pyrobombus) bimaculatus Cresson, 1863
Bombus (Pyrobombus) impatiens Cresson, 1863
Bombus (Pyrobombus) vagans Smith, 1854

Above info from message on the Iowa Insect Mailing List-University of Iowa/Jan. 2014
Honey Bees are non-native to the prairie region.  Honey Bees
have a significant, unfavorable impact on the food supply
available for Bumble Bees.  Therefore, with Bumble Bees being
so ravaged by limited habitat; the introduction of Honey Bees
to a prairie wildflower garden is not a preferable practice.  
Please, put the priority of saving native pollinators above that
of installing a Honey Bee hive.