Conspecific Pollen on Insects Visiting Female Flowers on the Oak Parasite Phoradendron coryae (Viscaceae)

Abstract

Phoradendron coryae (Viscaceae) is a dioecious, parasitic plant on oak trees and shrubs in Quercus (Fagaceae), and it occurs from Arizona to Texas and into northern Mexico. The species produces minute spherical flowers during summer. Dioecious flowering requires pollinating insects to carry pollen from male to female plants. I investigated the pollination of P. coryae parasitizing Quercus turbinella shrubs at 3 sites at different elevations in the Cerbat Mountains of northwestern Arizona during August–September 2015. I examined pollen from male flowers, aspirated insects landing on female flowers, and counted conspecific pollen grains carried by insects. The tricolpate pollen of P. coryae was semiangular to subangular in polar view and circular to depressed oval in equatorial view. Female flowers were visited by 2 species of Coleoptera in 2 families, 6 species of Diptera in 6 genera and 3 families, and 1 species of Hymenoptera. Insects on flowers were extremely small (most <3 mm in length), and nearly all (99%) of the pollen carried by insects was from P. coryae. Conspecific pollen was found on 67% of the insects identified. Pollen loads were low, with only 25% of the insects carrying ≥5 grains. The beetle Attalus futilis (Melyridae) was the most frequently aspirated species, comprising 71% of the insects collected and occurring at all 3 sites. Most A. futilis (64%) carried P. coryae pollen. The second most frequently collected insects were 2 species of Hippelates and Liohippelates flies (Chloropidae). The Liohippelates carried the most P. coryae pollen. Other insects with pollen included 2 additional species of Chloropidae, 2 species of flies in Tachinidae and Tephritidae, a species of beetle in Chrysomelidae, and a species of parasitic wasp in Figitidae. Phoradendron coryae appeared to be pollinated mostly by A. futilis beetles due to their apparent abundance and by Liohippelates flies due to their relatively high pollen loads.