Plant-Pollinator Synchrony

I wrote to the membership of the International Butterfly Breeders Association on May 26, 2026, to get us all thinking more about what we're observing all over the world during season changes. Butterfly breeders are asked all sorts of questions about butterflies, and we try our best to inform people and be butterfly advocates. The IBBA shares information, like what was written here, to the membership frequently, to ensure we're up to date with current studies and important concepts in pollinator conservation.

Good morning, IBBA!

We're almost through our first official week of Spring! Hard to believe for me since we're all still wondering if it might snow here every other day, but I'm sure it's nice and spring-like somewhere out there. Something I think at this time of year is, "When will I see the insects come out?" and "Did my perennials survive the winter?" But which should we see first: the plants or the insects? 

Most of us have probably noticed changes in the bloom times for plants, when we first see wild butterflies in the Spring, or the length of our growing season. These are phenological changes, or changes in timing for plant and animal life cycles. Anthropogenic climate change has led to these disturbances. Plant-pollinator interactions are the most at risk from changes to the timing of bloom times or insect flight times, but are they actually out of sync? As butterfly professionals, it's important for us to take a look at what's happening. 

Many studies have tried to answer this question, with several showing that plants and insect pollinators are actually evolving together to adjust to warmer climates. Most studies focus on generalist pollinator-plant mutualistic relationships, though. Another issue with the current data is how pollinator-plant interactions were recorded. There’s a misconception, even within the scientific community, that an insect visiting a flower is thereby contributing to pollinating the flower (Willmer, 2012). This isn’t always the case. In fact, some insects “rob” flowers of their nectar or pollen without providing any service to the plant. So when a scientist uses visitation counts as a metric for a study on pollination, the results will not be fully accurate. Other issues with current studies are that they focus only on bee species and rely too heavily on pollinator occurrence records that may not be representative of all ecosystems.

I went out last week to observe what pollinators and spring ephemerals I could find in my Cincinnati neighborhood forests. I was thrilled to see tons of fawn lilies and Virginia bluebells; however, there was way more Lesser Celandine, an invasive non-native, and I mostly saw insects on their bright yellow blooms over the white, blue, and purple blooms of the native species. I believe this is happening all across the US, as iNaturalist had a worldwide project for their birthday over the weekend, with Lesser Celandine being the sixth highest reported plant species in the US, but the highest reported for the entire project. 

Native Hymenoptera nectaring on invasive and native flowers in Cincinnati, OH, Photo credit - Jen Lichtefeld, 2026

What’s interesting with the majority of results is that historically, insects had emerged in the Spring sooner than their plants, but there has been a shift over time, with plants “catching up” to insects. So they had been more asynchronous previously and are now more in sync. The problem here is that if they continue with the rate of increase of their phenological events, they will eventually become asynchronous, but in the other direction: plants emerging way too early to be pollinated by insects (Freimuth et al., 2022). This has already been observed with hoverflies. Again, this is what has been documented for generalist pollinators, not specialists.

A study of specialist pollinators in Costa Rica found that not only was the rate of asynchrony higher with specialist plant-pollinator interactions vs generalists, but specialists tend to prefer plants with shorter bloom times (Maglianesi et al., 2020). This means specialist pollinators are most at risk from asynchronous phenology. What’s worse, specialist pollinators are already experiencing exacerbated extinction threats due to habitat loss.

Most models show that, in time, natural selection will weed out the plant-pollinator interactions that are most susceptible to phenological changes and asynchrony. Insects are already adapting faster than plants by expanding their ranges latitudinally in response to climate change, since insects can travel more easily than plants. This may actually be more of an issue than phenological asynchrony. The rate of increase for emergence in plants and insects is found to be heavily species-dependent and varies by location. So, while urban areas see blooming plants sooner due to their “heat island” effect, the corresponding insects in those areas are emerging sooner, too. In many observations, the overlap of insect flight time to bloom time is becoming shorter, but not totally asynchronous, except in the case of specialists (Willmer, 2012).

The best chance for the future is to increase biodiversity in all ecosystems and increase habitat for specialist pollinators (Bartomeus et al., 2013). We may not be able to prevent the extinction of certain species at this point, but having an abundance of pollinators will ensure pollination services are provided.

References

Bartomeus, I., Park, M. G., Gibbs, J., Danforth, B. N., Lakso, A. N., Winfree, R., & Eubanks, M. (2013). Biodiversity ensures plant–pollinator phenological synchrony against climate change. Ecology Letters, 16(11), 1331–1338. https://doi.org/10.1111/ele.12170

Freimuth, J., Bossdorf, O., Scheepens, J. F., & Willems, F. M. (2022). Climate warming changes synchrony of plants and pollinators. Proceedings of the Royal Society B, 289(1971), 1–9. https://doi.org/10.1098/rspb.2021.2142

Maglianesi, M. A., Hanson, P., Brenes, E., Benadi, G., Schleuning, M., & Dalsgaard, B. (2020). High levels of phenological asynchrony between specialized pollinators and plants with short flowering phases. Ecology (Durham), 101(11), 1–10. https://doi.org/10.1002/ecy.3162

Willmer, Pat. “Ecology: Pollinator–Plant Synchrony Tested by Climate Change.” Current Biology [England], vol. 22, no. 4, Feb. 2012, pp. R131–32, https://doi.org/10.1016/j.cub.2012.01.009.