Buzzing bees (Hymenoptera : Apidae, Halictidae) on Solanum (Solanaceae): Floral choice and handling time track pollen availability

Flower selection and pollen-collecting effort were monitored for 3 species of bees that sonicate flowers of Solanum wendlandii Hook. for pollen in sou thern Costa Rica. Between 0700-0900 hours, Bombus pullatus (Fkln.), Eugloss a erythrochlora Moure, and Pseudaugochloropsis graminea (Fabricius) foraged more frequently at new flowers (that had opened the day of observation) th an old ones (that had opened at least 1 day before observation). Between 09 00-1100 hours, however, this preference was no longer evident, and all 3 sp ecies visited new and old flowers with similar frequency. E. erythrochlora and P. graminea spent more time harvesting pollen during 1) initial (first or second) visits to new flowers than initial visits to old flowers and 2) initial visits to new flowers than final (seventh or later) visits to new f lowers. Similar, although not statistically significant, trends were eviden t for B. pullatus as well. An experiment using pollinator exclusion bags re vealed that the reduced foraging effort at individual flowers was resource- dependent and was not simply a time-dependent phenomenon.