Field season wrap up is underway in the butterfly bush plot, and there is so much to reflect on this year! The team has had a very productive summer, and as these bushes are better established and have reached their full spread and height, they have become more attractive to pollinators. As a reminder, the butterfly bush (Buddleja spp.) test plot consists of 34 butterfly bush cultivars of ranging fertility, habit, and breeding complexity. We have 6 -9 replicates of each individual cultivar, totaling 222 plants in the complete replicated block. The plot represents all the past and present (yes, we have some experimental cultivars) breeding that has been conducted to reduce fertility and hopefully invasiveness of Buddleja davidii. Much of that breeding centers around interspecific hybridization (breeding between 2 or more species in the same genus), so our plot represents hybridization of 7 different Buddleja species!
This summer we conducted pollinator observations the same as last year. This consisted of 5-minute timed counts at each location in full flower (we are calling full flower 50% or more of the buds or flowers on the individual plant are fully open) each week. During the timed count, we identify all visitors to morphology- which is simply differentiating between honeybees, bumblebees, butterflies, and other morphotypes. This presented new challenges this year because of the sheer mass some of our plants have reached! Though they were spaced 8 feet apart on all sides at planting, some have grown in together, making access an occasional issue. Many of the full-sized cultivars also reach well over my head, presenting more challenges in accurate counting. The team pushed through these difficulties, and by the end of the season we had counted 7,597 individual visitations on the plot. This is over 2,000 more than last year! You can view overall visitations by cultivar for both the 2020 and 2021 seasons below.
Though all the cultivars were most frequently visited by honeybee cultivars in 2020, three cultivars in 2021 were most frequently visited by bumblebees. Most notably the cultivar ‘Honeycomb’ attracted far and away more bumblebees than any other cultivar, and most of the visitors were male. Not only does ‘Honeycomb’ seem to be very attractive while sampling, it has an extremely long bloom season in comparison to the other cultivars in the study. It will bloom steadily from mid-June until the first deep frost of the season. Generally, there is an uptick in visitation across all the cultivars in 2021 as compared to 2020. Keep in mind the plants were substantially larger this season compared to last, meaning larger floral displays which are more attractive to pollinators.
In addition to pollinator observations, we collected nectar volume data for all 34 cultivars and attempted to collect pollen from a low and high fertility cultivar respectively. Tyler and Mallory were instrumental in getting nectar volume estimates collected, you can see them pictured below probing individual flowers with microcapillary tubes. Pollen collection turned out to be a very time-consuming process because there wasn’t a good alternative to good old hand collection. After about 80 hours of labor on the project, we were still a ways off of our mark, so we needed to reassess our methodology. More to report on that next year I’m sure.
Svea Bruslind and Jen Hayes also helped me take filtered photos of all my cultivars this season. You can read more about Svea’s excellent photography skills in her post ‘A Bee’s Eye View: UV photography and bee vision‘ but I’m sure the photographs she took of my cultivars in ‘Bee Vision’ will prove useful in understanding patterns of attraction out on the plot. Scroll through the pictures below to see examples of Svea’s work, in order of pollinator attraction in the 2021 field season.
This time of year, focus returns to the relative fertility portion of my study. This means time in the greenhouse monitoring controlled crosses I made over the summer, sowing seeds from the field and counting respective seedlings. This robust dataset will allow us to calculate relative fecundity of all our cultivars in both male and female roles, important information in assessing invasive species legislation.