POLLEN TRANSPORT BY INSECTS VISITING BACCHARIS SERGILOIDES (ASTERACEAE) FEMALE FLORETS IN SOUTHERN NEVADA

Baccharis sergiloides A.Gray (Asteraceae) is a desert shrub found along rivers and in dry washes in and near the Mojave Desert in the southwestern United States. Plants in the species are dioecious, requiring pollen to be transported from male to female florets on different shrubs. I examined the pollination of B. sergiloides in southern Nevada during September 2023 by describing female and male florets and pollen, determining the insects that visit heads of female florets, comparing the relative amounts of conspecific pollen carried by insects, and describing where insects carry pollen on their bodies. The pistil of female florets extends above the tubular corolla and supports two stylar branches. The modified style of male florets is similar and pushes pollen from the anther tube. Nectar was not apparent in florets of either sex. Pollen is 3-zonocolporate with broad, elongated colpi, central apertures, and a microechinate exine. The shape of pollen is suboblate with a mean polar axis of 15 µm and a mean equatorial diameter of 17 µm. Female heads were visited by 13 species of insects in different genera and 9 families in Hymenoptera, Diptera, and Hemiptera. The sphecid wasps Clypeadon evansi Bohart, 1966 and Philanthus gibbosus Fabricius, 1775 (Sphecidae), and the flies Tripanurga aldrichi Parker, 1921 (Sarcophagidae) and Omomyia regularis Curran, 1935 (Richardiidae), were most frequently aspirated. All of the species carried conspecific pollen, and relative amounts of pollen sampled from insects did not significantly differ among species. Insects carried pollen dispersed mostly onto the sides and ventrum of their body. Baccharis sergiloides appears to be pollinated by a variety of unspecialized insects with mostly predaceous or saprophagous larval diets.