PS 31-109
Daylily flower slitting by carpenter bees during the California dry season and 3-year extreme drought

Tuesday, August 11, 2015
Exhibit Hall, Baltimore Convention Center
Edward M. Barrows, Biology, Georgetown University, Washington, DC

The main aim of this study is to describe flower slitting of Hemerocallis ‘Stella De Oro' (Stella De Oro Daylily, SDO) by female Xylocopa varipuncta (Valley Carpenter Bees) in Sacramento, California during the dry season and 3-year extreme drought. This widely-planted, daylily cultivar is derived from crosses of Eurasian daylily species and their hybrids. Its flowers each open for only 1 day. Hemerocallis species and thousands of Hemerocallis cultivars occur in urban and other gardens worldwide and many are nectar and pollen sources of pollinators and other animals. I observed SDO floral visitors in August 2014, in the Cesar E. Chavez Memorial Plaza which had four automatically watered, heavily mulched, monoculture SDO beds. To determine how bee-generated floral-slitting frequency changed during a day, I sampled 193 new flowers in the morning and afternoon. To determine whether the flowers contained nectar, I dissected 20 SDO flowers and examined them at 10x magnification.


Xylocopa varipuncta made longitudinal slits in SDO corolla bases with their proboscides. During a sampling day, floral-slit frequency increased from 0–25% in 193 flowers. These bees frequently made new slits and inserted their proboscides into previously made slits, suggesting that they obtained cell fluid, nectar, or both via the slits. I did not see nectar in SDO flowers, which suggests that the bees were imbibing cell fluid. I have observed SDO and thousands of other daylily cultivars throughout the U.S. over decades, but so far have seen such slitting only in the California SDO. The long California drought and dearth of nectar in Sacramento may have favored daylily floral-slitting by X. varipuncta. Worker Apis mellifera collected SDO pollen and probed slits with their proboscides, acting like possible secondary cell-fluid robbers. Ants were inside corollas, but were not seen to enter corollas through slits. A Colias butterfly entered SDO flowers through their natural corolla openings and did not extend its proboscis through slits. The common, Eastern U.S. Xylocopa virginica virginica slits non-daylily flowers, nectar robs several plant species, and collects daylily pollen; however, I have not seen this bee slit daylily flowers.