Honey bees are ineffective pollinators of C. quamash
Although honey bees visit C. quamash frequently, they are ineffective pollinators compared to native bees and extract pollen and nectar without pollinating C. quamash flowers. Both visit frequency and visit quality (i.e., pollination effectiveness) determine the relative importance of different floral visitors as pollinators (King et al. 2013). In some other systems, frequent honey bee visits increase pollination, even when honey bees are less effective than other visitors on a per-visit basis (Sun et al. 2013). However, in our system, increased visit quantity by honey bees does not compensate for poor visit quality. As such, the direct contribution of honey bees to pollination in this system is negligible, and, if anything, negative.
We suspect that honey bees are ineffective pollinators because of their behavior at flowers. Native bees contacted stigmas nearly six times more often than honey bees, who frequently removed nectar from behind petals without contacting reproductive structures. Such “robbing” is common for honey bees and results in low stigma contact compared to other pollinators (Goodell & Thomson 1997; Rammell et al . 2019; Vicens & Bosch 2000; Westerkamp 1991). We expect indirect negative effects of honey bee visits to be severe when this behavior is frequent.