Pollinators of Butterfly Bush (and Other Questions)

I’m pleased to present the work of my very first field season as a master’s student here at OSU.  My project centers around presumptive sterile cultivars of Buddleja, or butterfly bush.  Over the next few years, I will be studying how breeding for sterility affects pollinator attraction, pollinator nutrition, and if this breeding is truly effective in slowing the invasiveness of this particular plant.  The hope is that this research will be able to serve as a framework for assessing putative sterile varieties of other potentially economically lucrative, but invasive, ornamentals.

Buddleja davidii was designated as a B-list noxious weed in 2004, and was placed in quarantine in conjunction with this designation.  Since then, the ODA (Oregon Department of Agriculture) has begun to allow sale of B. davidii cultivars that display a 98% reduction in fertility in comparison to fully fertile ‘old school’ cultivars such as ‘Black Knight’ or ‘Nanho Blue’.  At the moment, 14 cultivars of Buddleja davidii are legal to sell, propagate, transport or import in Oregon though no science has been conducted to assess how a reduction in fertility actually translates to reduced weediness. 

The other questions I am researching are how pollinators behave around these new, ‘sterile’ cultivars in comparison to how they interact with fertile ones, and what kind of nutrition pollinators can obtain from sterile varieties.  These are ever more important questions as we continue to put pollinator health at the forefront of plant selection decisions.  To that end the team has been conducting timed pollinator counts through the summer in the test plot.

The test plot is located at Lewis-Brown Horticulture Farm, in the beautiful countryside surrounding Corvallis, Oregon.  There, we have randomly allocated six to nine replicant plantings of six fertile cultivars and 28 putative sterile cultivars.  Working in this gorgeously fragranced field (seriously-think notes of honey, spice, and fruit) has been a true delight all summer.  Cultivars of Buddleja run the gambit in terms of color, plant habit, and floriferousness.  There is everything from Buddleja ‘Purple Haze’, a prostrate variety with blue-violet flowers, to my personal favorite, Buddleja x weyeriana ‘Honeycomb’, an absolutely uprightly enormous variety with unique yellow blooms.

Once a week, I go to the field and determine which of the 204 plants are at maximum flower.  These plants are slated for our weekly pollinator counts.  To conduct a pollinator count, we simply set a timer for 5 minutes and watch the plant for visitors.  These visitors are identified to morpho-type in the field (i.e. Honeybee, Bumblebee, Syrphid fly, Butterfly…).  Here are the full counts for this season:

You may notice that there are less than 34 cultivars on this graphic!  That is because we are in possession of several cultivars that have yet to be released to the general public, so unfortunately, I cannot share them here with you today.  It does seem clear, for this season at least, that honeybees are the most prevalent visitor of butterfly bush. Though we can’t draw conclusions from this season’s data alone, we hope that with a few more seasons of data we will be able to identify patterns of attraction and biodiversity.   Until then I will be back in classes and working on other aspects of my research-looking forward, of course, to next field season.

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