LAUSR

Abstract. Nolina microcarpa (Asparagaceae) is a dioecious monocot shrub found in Arizona, New Mexico, and northern and central Mexico. Leaf rosettes of the species grow in colonies that produce tall inflorescences of small male or female flowers during spring. Dioecious flowering requires pollinating insects to carry pollen from flowers on male colonies to flowers on female colonies. I investigated pollination of female flowers at 12 colonies of N. microcarpa in the Cerbat Mountains in northwestern Arizona during May–June 2017. I examined pollen from male flowers, aspirated insects on female flowers, counted conspecific pollen grains carried by insects, and estimated floral constancies from proportions of conspecific pollen. Pollen on N. microcarpa was prolate and monosulcate with a deep furrow and reticulate sculpturing. The most abundant insect on female flowers was the native beetle Triarius trivittatus (Chrysomelidae), followed by the introduced honey bee Apis mellifera (Apidae). Activities of honey bees, but not beetles, were limited to flowers. Two species of native bees in Halictidae and Megachilidae were also found in low numbers on flowers. Nearly all insects carried N. microcarpa pollen, and conspecific pollen comprised most of the pollen load on most insects. Conspecific pollen loads were highest on A. mellifera, followed by the native bees and T. trivittatus. Amounts of conspecific pollen on A. mellifera and on T. trivittatus males, but not females, were dependent on the distance to the nearest male inflorescence and decreased exponentially as the distance increased. Nolina microcarpa appears to be pollinated primarily by bees and beetles. Pollination by these insects is consistent with pollination of other plants, such as palms (Arecaceae), that similarly produce open inflorescences and small, unisexual, diurnal flowers with nectar.