Tangled Ecosystem: Soybean and buckthorn

Tangled Ecosystem: Soybean and buckthorn


I’m Dr. Marcella Windmuller-Campioni,
the project lead for research working across landscapes and disciplines
investigating how forest management and buckthorn removal may impact agriculture
and soybean yields. I’m here with entomologist Dr. Bob Koch,
looking at an ecosystem as normally hidden from view. The central player is
soybean aphid, the No. 1 pest of soybean crops. During the growing season, the
soybean aphid occurs in our soybean fields. They feed on the sap of the
plants and they overcome the plants by sucking out the the nutrients from the
plants. When the soybean aphids are on soybean, it’s only the females that occur
there and those females, they don’t have to waste time mating because there are
no males. They give live birth, so they don’t waste their time laying eggs and
those babies that they’re laying–the live babies–are actually born pregnant.
We call that telescoping generations. And this combination of features allows them
to have very rapid population growth. Where the soybean goes, beneficial
insects that feed on the soybean aphid will often follow. One of these insects
is the multicolored Asian lady beetle. It’s a predatory insect, a great predator
to the aphids, and it’ll help to prevent aphid populations from reaching
outbreaks, and if they do start to increase, they can suppress the size of
those outbreaks. The downside of this predatory insect is that it likes to
invade people’s homes in the fall, where it can be a nuisance throughout the
winter. An additional insect is a tiny parasitic wasp, and this wasp lays its
eggs inside the aphids the larvae of the wasp feeds inside the aphid eventually
killing the aphid leaving dried crusty remains that we call a mummy. And the
adult wasp will eventually chew its way out of that mummy and start its life
cycle over again. A benefit to scouting for soybean aphids–actually getting into
the fields estimating aphid populations and using that threshold of 250 aphids
per plant to decide when to apply the insecticides–is that it gives these
beneficial insects a chance to suppress the aphid populations before we need to
apply the insecticides because many of the
insecticides we use for soybean aphid management are very toxic to these
beneficial insects. Now at this time of the year, the soybean fields are
beginning to siness. Day lengths are getting shorter. The soybean aphids are
actually leaving the soybean fields by developing a winged form that will fly
to neighboring wood lines like we have here with buckthorn. On the buckthorn the
soybean aphids will mate because you have males and females produced at that
time and they’ll lay eggs and it’s that egg stage that will survive the winter.
So Bob, do we know which buckthorn the aphids are queuing in to for that
overwintering? We know a lot about soybean aphids when they’re on the
soybean but when they’re on the buckthorn we know relatively little
there. We don’t know which buckthorn plants they’re queuing in on, how far
they’ll fly, and we also don’t know if if we manage the buckthorn or the
aphids on the buckthorn what impact that will necessarily have to the populations
in the soybean fields the next year. Thank you, Bob. Let’s take a look at who else finds a
home on buckthorn. Oat crown rust is a fungi, a pathogen that thrives in oats
and barley, reducing crop yields by as much as 40%. When it’s not on oats or
barley, this pathogen lives on buckthorn, causing small brown leaf spots that
aren’t problematic to buckthorn. Buckthorn grows abundantly in the Upper Midwest.
It’s everywhere. How did this tree that offers safe harbor for the soybean aphid
and oak crown rust become so prominent? It had a little help from other species
new to North America. These other new species came with the first European
settlers way back in the 1600s on plants and in the soil. In the soil from Europe,
there are earthworms. Earthworms are not native to most of Minnesota. They are not
good for native forest, as they gobble up the leaves on the forest floor,
disrupting an ecosystem that coexists with the native plants, disrupting things
like microbes, fungi, insects, plants and wildlife. The European earthworm and its
predator, the Asian flatworm, digest the plant matter and turn it into soil. This
worm-digested soil is inviting for new species of plants to move in. Buckthorn
seeds like bare mineral soil, compounding the problem. People first brought
buckthorn to North America in the mid-1800s and sold it as an ornamental
landscaping plant. Buckthorn was planted in yards, in towns and on farms. People
planted it because it made a great hedgerow. If we only knew then what we
know now. But there’s one more non-native player
in this story. In honor of the birds from Shakespeare’s writing, a group of
Shakespeare fans brought over European starlings from across the Atlantic, had a
ceremony and let them loose in Central Park. That was 1890. These birds took to
their new landscape and, along with other species, help spread buckthorn seeds.
Seeds of Buckthorn may look inviting to wildlife, but are not nutritious. The
birds dropped seeds on the soil that was made friendly for invasives by the
advanced team of earthworms living and multiplying below our feet. Buckthorn
gained a foothold, invading the landscape, and the soybean aphid moved in, causing
problems in the field starting around 2000. We use a number of techniques to
manage soybean aphid populations. From aphid- resistant soybean seeds, to
insecticides and predator insects, these treatments focus on where the soybean
aphid lives in the summer soybean fields. But what can we learn if we investigate
their winter home–buckthorn? That’s what we’re researching right now. The people
that manage the lands where these ecosystems live, private landowners, state
and federal land managers, may have different overarching goals, but one
thing they have in common: they all are negatively impacted by buckthorn. Looking
at this web of organisms and how they are connected to buckthorns helps us
understand how to approach managing pests that span across multiple
ecosystems. We may not know the exact relationship between soybean aphid and
buckthorn, but we do know that managing buckthorn has a host of other ecosystem
benefits.