We identified adult insects aspirated from tamarisk, Tamarix ramosissima Ledebour (Tamaricaceae), flowers during May–August 2005 next to the Colorado River at Topock Marsh, Arizona. We compared tamarisk pollen loads and flower constancies, estimated as percentages of T. ramosissima pollen, of genera with >3 specimens. Insects from tamarisk flowers represented four orders, 16 families, and 37 genera. Detritus-feeding flies in Syrphidae were the predominant insects collected and comprised mostly of introduced Syritta pipiens (L.). Bees were second most-frequently aspirated and predominated by introduced Apis mellifera L. Wasps comprised the highest diversity of genera and included parasitic Tiphiidae and predaceous Vespidae and Sphecidae. Tamarisk pollen loads were greatest on A. mellifera and least on S. pipiens. All adult insects collected exhibited high flower constancies with tamarisk pollen averaging >91% of the pollen load in each genus. Introduced honey bees appear to be the most important pollinators of T. ramosissima at Topock Marsh based on their abundance, pollen loads, and flower constancies. Insects visiting T. ramosissima flowers require a variety of resources to reproduce such as cavities for nesting or soil for excavating burrows and insect prey or decomposed plants for feeding larvae.