Pollinator adaptation to oil-secreting flowers: Rediviva and Diascia

Rediviva Friese (Melittidae) comprises the largest group of oil-collecting bees in southern Africa. Several Rediviva species collect oil from the paired floral spurs of Diascia species. Within these spurs, near the tips, are numerous oil-secreting trichomes. Female Rediviva bees insert their forelegs into these spurs and, with the aid of modified setae, extract the oil, transfer it to the hind legs, and carry it to the nest. Initial study indicated that Diascia species in the summer rainfall region of southern Africa vary in spur length. Subsequently we noticed substantial variation in foreleg and body size among populations of R. neliana Cockerell, the primary pollinator of the 12 different Diascia species and a relatively wide ranging bee. The purpose of this investigation was to quantify this variation and to determine whether variation in foreleg length could be explained as a simple evolutionary response to Diascia floral spur lengths. We also wished to determine whether corresponding variation in spur length could be found among populations of the Diascia host plants.