Trans. of the Academy of Science of St. Louis 6(14): 441-442 (Apr 26, 1894)
Flowers and Insects: Rosaceae and Compositae
By Charles Robertson

ROSA HUMILIS Marsh.— The flowers expand several centimetres. The stamens are turned outwards so strongly that insects landing near the center of the flower are likely to touch the stigmas before becoming dusted with pollen from the same flower. Nectar is wanting. The principal visitors are bumblebees and other large bees, which collect the pollen, and a common beetle, Trichius piger, which feeds upon it. Small bees may collect the pollen without touching the stigmas.

The blooming time of Rosa humilis is from May 22 to July 8. Anthophora abrupta , whose time of flight is from May 13 to the last of June, seems to depend for pollen almost exclusively upon this rose.

On twelve days, between May 22 and June 20, I observed the following visitors:—

Hymenoptera — Apidae: (1) Bombus virginicus Oliv.☿; (2) B. americanorum F. , ab.; (3) B. separatus Cr ; (4) Anthophora abrupta Say , ab.; (5) Synhalonia speciosa Cr. ; (6) Ceratina dupia Say ; Andrenidae: (7) Halictus conifusus Sm. ; (8) Augochlora pura Say ; (9) Agapostemon viridula F. —all collecting pollen.

Coleoptera — Scarabaeidae: (10) Trichius piger F., ab.; Chrysomelidae: (11) Diabrotica 12-punctata Oliv.— both feeding on pollen.

ROSA SETIGERA Michx. — The flowers resemble those of Rosa humilis, but the styles cohere in a column, which enables the stigmas to touch a visiting bumblebee a little more readily. I have noted the flowers in bloom from June 16 to July 4. June 16 I saw them visited for pollen by (1) Bombus americanorum F ; (2) Anthophora abrupta Say ; and (3) Trichius piger F.

Heslop-Harrison (1921) also dealt with pollinators in section Pollination in the Rosae.