Milkweeds (and monarchs) across the middle of America

On July 24^th 2017, I set out with my family from Ithaca, NY, for year-long sabbatical leave from Cornell University.  Our destination for the fall semester is Missoula, Montana, but our first major stop was a family visit in Urbana, IL.  Given my travel companions, especially the kids Jasper (12) and Anna (8), we decided to take our time driving across the country, and to stop and smell the milkweeds.  I was particularly interested in roadside populations of milkweed and what insects might be found on them.  To give away the lessons learned from this trip:

• There is lots of milkweed along roadsides, even in the highly agriculturalized midwest, and the milkweed fauna seems to be intact.  It has been a very good year for monarch butterflies!
• We need a LOT LESS mowing along roadsides. In addition to the cost in terms of fuel and person hours, reduced mowing (every two years?) will allow for the proliferation of natural plant communities, including milkweeds.
• Stop and smell the milkweeds, look for all the brilliant milkweed insects, not just monarchs, and enjoy the “turn-over” among the plants and bugs as you travel across habitats in America.

After 130 miles from Ithaca, we took a pit stop in Cuba, NY, where just next to the parking lot of a Dollar Store was this little milkweed.  We saw a lot of common milkweed (Asclepias syriaca) along the way.  The large monarch caterpillar dwarfed the little Lygeaus seed bug (who ran away when I approached) and the four-eyed milkweed beetle (out of focus on the ground next to the big monarch poops [entomologically known as “frass”]. Note the carefully cut notch in the petiole that the monarch made to drain the leaf of latex… once that the leaf was hanging down, the monarch voraciously ate the leaf.

We spent Monday night in Little Italy, on the east side of Cleveland, OH.  Although we didn’t have much time for downtown milkweed hunting, I did see this tall shaded individual in our hotel parking lot.  No monarchs, but it did have several splotches of the milkweed leaf mining fly (Liriomyza asclepiadis).

The southwest ride from Ohio was spectacular… agriculture turned from smaller to more industrial.  I started noticing a very short, cream-colored plant that I thought was another milkweed (Asclepias verticillata, whorled milkweed), but I wasn’t sure for another 100 miles (see below).  We stopped to gas up outside of New Haven, IN, with abundant milkweed in an open lot next to the fast food and petrol.  There weren’t signs of monarchs in this neighborhood, but the rest of the fauna was in full bloom, with abundant Oncopeltus seed bugs (the large milkweed bug, a relative of the smaller Lygaeus) and another sucker – the bright yellow Aphis nerii.  Perhaps most common at all sites, and the most common form of leaf damage, was that of four-eyed Tetraopes adults (their larvae feed on milkweed roots).   A pleasant surprise at this site was a visitor, Chrysochus auratus, the Dogbane leaf beetle (another beetle whose larvae eat roots)… which spilled over from nearby dogbane (which is in the same family as milkweed).  It did not appear to be feeding, but was apparently a tourist on milkweed.

On day two, we had pushed passed 650 miles from Ithaca, and just past Crawfordsville, IN, I pulled off the on-ramp to I-74 for the final stretch to Urbana.  I again saw the short creamy white milkweed in abundance, and it turned out to be Asclepias verticillata, the whorled milkweed.  At this point, in the depths of the corn and soy belt, there was less milkweed than in Ohio or New York.  Very patchy, seemingly tens of miles of sterility, without much milkweed. But then patchily, dense clumps of these two milkweeds… both common and whorled milkweed are highly clonal and form dense patches when healthy. Both species were at this very active site, with flitting monarchs among other milkweed insects.  In addition, this was my first sighting of a pompilid wasp (predaceous spider wasps), which are highly attracted to milkweed flowers and good pollinators in the midwest and west.

Urbana-Champaign, IL is a classic Midwestern college town.  The Univ. Illinois is a Big 10 school, with a long history in plant-herbivore interactions.  I stopped in to see May Berenbaum, one of the best known scientists studying coevolution and plant-insect interactions.  Below she is pictured with her cabinet of monarch butterfly memorabilia that she curates in the Entomology Department at UIUC. It contains everything from cartoons to costumes to paper towels embossed with monarchs. On campus I also found a milkweed vine, Cynanchum laeve (aka honey vine), which is said to be a host plant for monarchs.  Although I didn’t find monarchs on them, I did see Aphis nerii, dancing as they perceived my breath and a bumbling swamp milkweed beetle (Labidomera clivicolis). I didn’t see eggs or larvae of Labidomera, so I can only assume it was attracted by chemical compounds which are shared by plants in this botanical family (Apocynaceae). I also found a spectacular tourist, the Ailanthus Webworm Atteva aurea, a moth that has expanded its range north from Florida.  It, however, appears to just be resting on the honey vine, perhaps seeking some nectar. In a family garden nearby was some swamp milkweed (A. incarnata) with two monarch eggs!

Onward west. We stopped at the Krisdala Baka rest area in Western Illinois, just before the Quad Cities. There was abundant corn and soy all along the way, with little land left for fields and trees.  Illinois and Iowa are the top two producers of Corn and soy, and I consider these two states to be the toughest for monarchs and milkweed. At the rest stop, there was some common milkweed as well as dogbane, but still no sight of Sullivant’s milkweed. In Illinois a couple of years ago, I had found abundant Asclepias sullivantii, but none so far on this trip. At the rest stop, I found a monarch egg and some of the lovely clear (sometimes pink) milkweed aphids, Myzocallis asclepiadis.  Common milkweed is apparently the *only* host plant for Myzocallis. Much to my surprise, Illinois is a state that celebrates entomologists, as can be seen from this placard at the rest stop.

Next, on Friday July 28^th, we drove across Iowa on highway 80. It was surprisingly beautiful with rolling hills (somehow I was expecting to only see the laser-level flats), but still it was a sea of corn and soybean crop fields always in site. We stopped at a rest stop, about 25 miles from the border with Nebraska. There was a decent population of common milkweed, and also some whorled milkweed. I was glad to see my first Tetraopes femoratus, the midwestern and Western red milkweed Beetle, that is a close relative of our eastern T. tetrophthalmus… Nice to see the two species coexisting at one site. A big monarch caterpillar and some other insects too.

At our campsite slightly west of Omaha, there was abundant dogbane and some common milkweed, A. syriaca, again with dogbane’s Chrysochus visiting on a milkweed stem.

One goal of the drive through the Midwest was to stop at praire, something reminiscent of the tall grass written about in the Little House books. At the Prairie Plains Research Institute’s Gjerloff Prairie near Marquette, NE we found a spectacular walk along the hills and valleys next to the Platte River, which is wide but shallow.  One of the amazing things about visiting such places is seeing some of the natural ecology of milkweed that I have never seen before. Here there was a parasitic plant “dodder” (Cuscuta sp.) vining around and “eating” milkweed.  Dodder has no chlorophyll, and gets all of its nutrients and water (and often defense chemicals) by putting root-like suckers (called haustoria) into the stems of other plants. I have seen several other species of Cuscuta across the US, but have never seen it on milkweed.  In the east I have tried to entangle dodder onto milkweed twice before, but have never been successful.  In the picture below, the thick bands of twine around milkweed are the parasitic plant’s flowers.  Also at this site were many milkweed weevils in the genus Rhyssomatus.  The precise species in unclear, in part because of the unusual feeding behavior I saw at this site.  Rhyssomatus typically trenches or pokes the stems of milkweed and then lays eggs inside, which feed on the pith tissue (see Lina Arcilia-Hernandez’s research on these weevils).  Here the weevils were exclusively feeding on seed pods, something I have occasionally seen on common milkweed (and more commonly on swamp milkweed), but never in this abundance.  The prairie also gave us the surprise of an additional species of milkweed, Asclepias pumila, the plains milkweed.

On the next day, we passed into the northeast corner of Colorado, and stopped for lunch near the town of Sterling.  In the parking lot were two new milkweeds.  We were now 1800 miles from Ithaca, NY.  No more common milkweed A. syriaca!  Almost all areas within the USA have several species of milkweed that are native, but as one moves from region to region, there is “turn-over” in which species are found. Common milkweed does no grow well in the west (presumably because of the aridity), and so here was the first sign of its western close relative, Asclepias speciosa (the “showy” milkweed).  Next to it was another species (perhaps A. viridiflora, but difficult to know).  As we progressed to Pawnee National Grassland, it was drier and drier and with fewer milkweeds.  Ever since it started to get drier (in Nebraska) the crop fields saw more irrigation and the milkweeds seemed less common and also less clonal (patches of plants were smaller). Nonetheless, even in the highly spaced milkweeds, some of the insects found them.  Driving along the dusty roads to the Pawnee Buttes, we some regrowing milkweeds with Tetraopes and an adult monarch fluttering by.  On the way out of Pawnee, on the last day of July, we found a few beautiful specimens of Asclepias latifolia the Broadleaf Milkweed, another close (western) relative of common milkweed.

From Pawnee in northeastern Colorado, we went north to the Wind River Range in Wyoming, and west through Idaho… we traveled several hundred miles with very little milkweed.  The few that I saw (mostly showy milkweed) came at times when stopping wasn’t a good option, and so we traveled on. Especially in the higher elevations there was no milkweed to be found.  On August 4^th, our 12^th day on the road and travelling across Idaho, our trip’s odometer read 2530 and we ran into some small patches of showy milkweed.  At this patch, already in full fruit, was Chrysochus cobaltinus, the metallic blue sister species to our dogbane beetle (C. auratus) … the cobalt beetle mostly eats dogbane, but it is known to spill over and feed on some milkweeds (I have mostly heard of it feeding on Asclepias eriocarpa in California)… here several adults were clearly feeding on showy A. speciosa, although it is unclear if the larvae can complete development on milkweed roots.  Here also was Tetraopes femoratus, which has the unusual behavior of laying eggs in grass stems (see picture below).  When the larvae hatch, they do not eat the grass, but rather fall to the soil and search for milkweed roots to feed on!

Now that we have come 3500 miles, we’ll loop back towards Idaho and Montana.  See you next time!  -Anurag

Lessons learned from this trip:

• There is lots of milkweed along roadsides, even in the highly agriculturalized midwest, and the milkweed fauna seems to be intact.  It has been a very good year for monarch butterflies!
• We need a LOT LESS mowing along roadsides. In addition to the cost in terms of fuel and person hours, reduced mowing (every two years?) will allow for the proliferation of natural plant communities, including milkweeds.
• Stop and smell the milkweeds, look for all the brilliant milkweed insects, not just monarchs, and enjoy the “turn-over” among the plants and bugs as you travel across habitats in America.