Submitted to: Uludag Bee Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2009
Publication Date: 9/12/2009
Citation: Barthell, J.F., Clement, M.L., Song, D.S., Savitski, A.N., Hranitz, J.M., Petanidou, T., Thorp, R.W., Wenner, A.M., Griswold, T.L., Wells, H. 2009. Nectar Secretion and Bee Guild Characteristics of Yellow Star-Thistle on Santa Cruz Island and Lesvos: Where Have the Honey Bees Gone. Uludag Bee Journal. (9)3:109-121. Interpretive Summary: Yellow star thistle is an invasive weed in the western United States that is native to the Mediterranean region. A comparison of the attractiveness of yellow star thistle for bees was made on Santa Cruz Island where it is a weed compared to Lesvos, a Greek island where the plant is natural. Less nectar was produced and available for bees on the island in yellow star thistle's native range. There was a greater diversity of kinds of bees in the plants native range compared to Santa Cruz Island. Interestingly, honeybees, which are native to the Mediterranean, rarely visited yellow star thistle on Lesvos but are common on this weedy plant in California, where honey bees are not native.
Technical Abstract: We compared nectar secretion rates and bee guilds of yellow star-thistle, Centaurea solstitialis on Santa Cruz Island (USA) and the Northeast Aegean Island of Lesvos (Greece). This plant species is non-native and highly invasive in the western USA but native to Eurasia (including Lesvos). "Nectar flow" was assessed by measuring nectar volumes in florets of flower heads covered with mesh bags (preventing visitation by bees); "nectar standing crop" data were taken from open (unbagged) flower heads to which all bees could gain access. We censused bees at C. solstitialis during comparable periods on both islands and determined the bee guild composition of the plant on Lesvos. Significant differences in nectar levels occurred between bagged and unbagged florets at each locale, especially during the period that pollinators were most common. Nectar flow and nectar standing crop volumes were lower on Lesvos than on Santa Cruz Island. The bee guild diversity at Lesvos was higher relative to Santa Cruz Island. Surprisingly, however, honey bees were not recorded during our monitoring periods on Lesvos.