Do Native Pollinators Prefer Exotic Plants?

Certainly this is not a new question but a recent comment by someone about pollinators seeming to like - even prefer - the flowers of naturalized exotic plants made me go looking for information, specifically about native pollinators.

Tiger swallowtail on Tithonia

I do think that we have to establish first that native insects are dealing with an altered landscape; non-native flowers have only been here about 400-500 years, a blip in evolutionary time as far as insects are concerned. Second, as a result of some naturalized plants (like Queen Anne’s lace, an exotic species that is related to a native but less common species called wild carrot), the abundance of exotic weeds may have now almost replaced whichever native plants would have been present, leaving native insects little choice but to use exotics. Third, we should recognize that pollinator preferences for certain flower types (short vs. long floral tubes, for example), will affect what plants they can use and if they can adapt.

We know from publications like this one from The Xerces Society that eco-regionally appropriate native plants give us the best diversity of native pollinators. That is, a diversity of native plants brings us a bigger mix of native bees, butterflies, flies, beetles, wasps - including specialists. We should use native plants from our same ecoregion (e.g., Piedmont, Coastal Plain, etc.) to ensure we support pollinators of the same area. 

Specialist bee: Southeastern blueberry bee

What can we expect when native pollinators live in areas of more exotic than native plants vs. when they have appropriate native plants in more abundance: do they prefer the newer plants (exotic) or do they prefer the indigenous plants?

Research published in 2020 by folks in the Department of Entomology at Cornell University found that native pollinators do prefer native plants when available: “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.” That is, when native pollinators have access to more native flowering plants, they prefer the native ones.  

Another study published in 2020 based on research in 2016 and 2017 in Maryland, found similar results. The authors feel that exotic plants in pollinator mixes may help pollinators in early spring for generalist insects, but "non-native plants also alter the composition of plant communities, may not support as many specialist bees, and appear to affect individual and network specialization of bee communities with unknown consequences for plants and bees." More study is needed, they conclude.  

Certainly pollinators are using what plants are available and, increasingly, those plants are exotic ones. But don't be fooled that this helps native pollinators overall. Some pollinators - the specialists - may be quietly disappearing if the native plants they need are no longer available.

While exotic and naturalized flowers may provide floral benefits to some native pollinators, the better human strategy is to continue to add regionally appropriate native plants back to degraded and residential areas to support native pollinators, particularly specialist ones.

Mountain mint is powerhouse native for pollinators