Honey bees and wild pollinators differ in their preference for and use of introduced floral resources

Abstract

Introduced plants may be important foraging resources for honey bees and wild pollinators, but how often and why pollinators visit introduced plants across an entire plant community is not well understood. Understanding the importance of introduced plants for pollinators could help guide management of these plants and conservation of pollinator habitat. We assessed how floral abundance and pollinator preference influence pollinator visitation rate and diversity on 30 introduced versus 24 native plants in central New York. Honey bees visited introduced and native plants at similar rates regardless of floral abundance. In contrast, as floral abundance increased, wild pollinator visitation rate decreased more strongly for introduced plants than native plants. Introduced plants as a group and native plants as a group did not differ in bee diversity or preference, but honey bees and wild pollinators preferred different plant species. As a case study, we then focused on knapweed (Centaurea spp.), an introduced plant that was the most preferred plant by honey bees, and that beekeepers value as a late‐summer foraging resource. We compared the extent to which honey bees versus wild pollinators visited knapweed relative to coflowering plants, and we quantified knapweed pollen and nectar collection by honey bees across 22 New York apiaries. Honey bees visited knapweed more frequently than coflowering plants and at a similar rate as all wild pollinators combined. All apiaries contained knapweed pollen in nectar, 86% of apiaries contained knapweed pollen in bee bread, and knapweed was sometimes a main pollen or nectar source for honey bees in late summer. Our results suggest that because of diverging responses to floral abundance and preferences for different plants, honey bees and wild pollinators differ in their use of introduced plants. Depending on the plant and its abundance, removing an introduced plant may impact honey bees more than wild pollinators.

Are native and non‐native pollinator friendly plants equally valuable for native wild bee communities?

“…For example, honeybees ( A. mellifera ) or the sweat bee L. tegulare were more abundant on non‐native plants than on native plants, while other polylectic bees, such as X. virginica or L. trigeminum , were more abundant on native than on non‐native plants. This result supports previous findings showing bee species‐specific responses to non‐native plants (Pardee & Philpott, 2014; Schweiger et al., 2010; Urbanowicz et al., 2020), which may be due to species‐specific nutritional requirements (Leonhardt & Blüthgen, 2012; Nicolson, 2011; Vaudo et al., 2016), previous experiences (Harmon‐Threatt & Kremen, 2015; Vaudo et al., 2015), or competition (Somme et al., 2015; Wilms et al., 1996).…”

“…Similarly, studies found bee species richness either higher (Bartomeus et al, 2008;Lopezaraiza-Mikel et al, 2007;Vilà et al, 2009), lower Morandin & Kremen, 2013), or the same (Pardee & Philpott, 2014) on non-native plants versus native plants. The majority of this research has been conducted in Europe and the United States, while studies from the southern hemisphere are still scarce (but see Morales and Aizen (2006) and Gibson et al (2013) for examples from Argentina and South Africa) despite the often negative effects of non-native (invasive) plant species on native flora and fauna (Bellard et al, 2017;Van Kleunen et al, 2015). Most of these studies focused on invasive non-native plants instead of directed pollinator friendly plantings and were observational, rather than the result of hypothesis-driven field trials.…”

Dominant bee species and floral abundance drive parasite temporal dynamics in plant-pollinator communities

“…Per species, we estimated the number of floral units per stem and averaged this across the sites and weeks the species was in bloom (minimum five measurements per species). We define a floral unit as being the typical unit (single flower or inflorescence) that a bee typically foraged from 53 . This definition of a floral unit was also consistent with the amount of plant material we used for each sample during parasite screening.…”

Beyond the Decline of Wild Bees: Optimizing Conservation Measures and Bringing Together the Actors

“…In environments with very few bee-friendly native plants, some exotic invasive species can help populations to recover. Again, these choices should be taken based on strong empirical evidence since a recent study in New-York suggested that many exotic plants could mainly help honeybees more than wild bees [220]. In these anthropogenic environments, the way to manage bee-friendly areas have also to be re-think, notably by finding alternatives to pesticides.…”