Milkweeds are as good for crop-pollinating Native Bees, as they are for Monarchs

October 13, 2014By

Field notes from a Western milkweed patch

 

Photo by: Gary Nabhan

Photo by: Gary Nabhan

 

Recently, my orchard and garden “decided” that I needed more time in the wild to see how plants and animals really worked together, so they evicted me from cultivated ground of my own making, somehow giving me a concussion and a fractured rib on my way out.

However slow I usually am to get the picture, this time, I got the message loud and clear: if I were truly interested in seeing how to design farmscapes to harbor beneficial insects such as monarch butterflies and native bees, I needed to “apprentice myself” to a wild habitat where such healthy relationships are the norm, not the exception. That is, I need to see what makes ecological relationships between plants and pollinators resilient and persistent even in the wake of climate change.

And so I opted for a vacation from the orchard, and have been going out every two or three days to identify floral visitors on three kinds of milkweeds that occur in the edges of a wet meadow tucked between the semi-arid hills of Southeastern Arizona.

Like many places in the semi-arid West, the larger working landscape of the Canelo Hills has ranches, farms, gardens, vineyards and orchards galore. The milkweeds and their pollinators are often surrounded by cattle, but the cows don’t eat or trample the milkweeds, nor have milkweeds poisoned any of the livestock there as far as I know. While not romantically “pristine,” the working landscape I chose to work in was exemplary of the food-producing landscapes of the West. And so, it was a good place to discern what insect visitors to milkweeds are also known to be good pollinators of neighboring field crops, orchard crops and pasture forages in the West.

What I found out was rather stunning—that one little acre-sized patch of milkweeds in a pasture attracted fifteen different species of native bees (in addition to honeybees) of the more than a hundred kinds of native bees of 32 genera found on milkweeds in the Western states. That count, by the way, was made possible by Terry Griswold, one of the few native bee specialists that the USDA employs to give full and meticulous attention to such issues.

And for which fruit, vegetable and forage crops do these native bees serve as effective pollinators? Included in the list of vegetables and oilseeds they visit are beans, cantaloupes, carrots, chile peppers, cucumbers, eggplants, lettuce, onions, radishes, safflower, sesame, sunflowers, tomatoes and watermelons. Among Western fruits, they visit apricots, apples, guavas, passion fruit, plums, peaches and prickly pears. And among forages, they visit alfalfa, red clover, sweet clover, most vetches and white clovers. The abundance of nectar offered by most milkweeds does a pretty good job of keeping pollinators present in an area where other plants need their pollination services.

My friends Bill and Athena Steen first introduced to the milkweed patches alongside their creek, but I soon learned that the monarch butterflies tagged near there by Gail Morris and others have been recaptured in the overwintering grounds both in Michoacan and California. This is a rare phenomenon—that monarchs tagged in the same landscape migrate in two very different directions and survive into winter to be recovered by those seeking tagged monarchs! But the greatest advantage of working at this site is that two old friends of mine, milkweed taxonomist and Sky Islands Alliance co-founder Mark Fishbein and ecologist Larry Venable—offered me a detailed record of what bees, butterflies and other insects visited the flowers of butterfly weed (Asclepias tuberosa) during two seasons in the same landscape more than two decades ago. Although I am apprenticing myself to a site where butterfly weed is less common, two other milkweeds also occur there (Asclepias subverticallata and A. englemanniana), so their different flowering times keep pollinators present and nourished over a rather long growing season.

Despite the fourteen year drought that occurred between when Mark began his field work and when I began mine, nearly every insect (and one hummingbird species) that Mark recorded on butterfly weed flowers remain in the area. To date, I have recorded over twenty-five of the same floral visitors as Mark and Larry documented. I am working hard to identify a good number of other beneficial insects I collected on milkweeds in the entomological references collections of the University of Arizona this fall. I have also seen one white-lined sphinx moth visit milkweed flowers in the wet meadows in the Canelo Hills that Mark may have missed.

But what strikes me the most is the great number of bees and wasps which Mark identified in the Nineties that I am seeing persisting in this wet meadow surrounded by a semi-arid landscape, despite the droughts, catastrophic freezes, wildfires and other stresses that have occurred over the intervening years.

In the Midwest this last fifteen years, roughly 100 million acres of farmscapes have lost perhaps as many as 700 million to a billion milkweed plants (or stems of perennials) due to untargeted use of herbicides, extreme weather events, agricultural land conversion to subdivisions, and poorly-managed timing of moving along highway and Railroad rights-of-way. Those are best scientific estimates mind you, but they are in an order of magnitude that has caused great remorse among monarch and native bee lovers throughout Canada, the U.S. and Mexico.

We can do better than that in our land stewardship practices, especially if we remind farmers that milkweeds are not only good for the monarch butterflies which their children and grandchildren love, but for the bees that they themselves need for the health of harvestable fruit and vegetable crops.

But here’s the kicker. Even for crops such as soybeans which most people assume to be purely self-pollinated and in “no insect pollinators,” recent studies in three countries point to 10 to 50% higher soybean yields in fields where bees are abundant. Iowa State researchers Matt O’Neil and Reed Palmer have found that some twenty different species of bees will pollinate bee flowers in a soybean field, and that many other beneficial insects will also improve yields if given habitat in or near the fields themselves.

Most milkweeds, by the way, are not very “weedy,” especially if you compare them to the twenty or more herbicide-tolerant superweeds now found in corn and soy fields across the Midwest and West. It seems that milkweeds offer far more benefits to farmers than their disparaging name implies.

Perhaps, as some of my farmer friends suggest, we should just rename each milkweed with a sexier name, like “butterfly bliss” or “bee joy.” In the meantime, I will forever be grateful to them for offering me one of my most joyful summers ever, watching the bees hover and butterflies waft through the air to take in the fragrance of some of most stunning plants in the North American farmscape. Let us do all we can to ensure that our grandchildren are offered the same experience of wonder among the milkweeds that every great American nature writer—from Henry David Thoreau and Rachel Carson to Robert Michael Pyle and Barbara Kingsolver—have lauded.

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Gary Paul Nabhan is based at the University of Arizona Southwest Center, where he facilitates pollinator recovery alliances. Learn more at makewayformonarchs.org. He is the co-author of Stitching the West Back Together (University of Chicago Press, 2014).

 

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