NEBRASKAland Magazine is dedicated to outstanding photography and informative writing with an engaging mix of articles and photos highlighting Nebraska’s outdoor activities, parklands, wildlife, history and people.
Issue link: http://mag.outdoornebraska.gov/i/695082
the seeds of milkweed plants are wonderfully suited to wind dispersal. All of Nebraska's milkweeds have the characteristic floss (pappus) that allows the seed to float away even under a light breeze. In addition to its primary purpose of transporting seeds, that floss has been used commercially for stuffing everything from pillows to life preservers. In addition, of course, fluffy milkweed seeds against a golden background of prairie grasses is one of the most recognized images of autumn in Nebraska's prairies. Milkweed is named for the white latex that seeps out when leaves or stems are injured. That latex is different from the sap used by plants to carry nutrients from roots to leaves and back. Latex production happens in a separate network of cells that can transport the substance to the site of a wound. Other plants create latex as well, including spurges, dandelions, and (most famously) rubber trees. While humans have found productive uses for latex, the toxic, sticky substance is most valuable to plants as a defense mechanism against herbivory. All Nebraska milkweed species except the orange-flowered butterfly milkweed produce latex. Latex helps with defense against insects, but milkweeds have additional weapons in their arsenal, including cardenolides (a kind of steroid and heart arresting toxin). Cardenolides are produced throughout a milkweed plant and are toxic to most creatures, including humans. The concentration of cardenolides varies by milkweed species, with the lowest concentrations found in butterfly milkweed, swamp milkweed and whorled milkweed. One would think with latex, cardenolides, and other defense structures such as dense hairs (on many milkweeds), milkweed plants would be pretty well immune to herbivorous insects. Monarch caterpillars, though, are not the only creatures that have figured out how to deal with the array of challenges presented by milkweeds. Other insects, including long-horned milkweed beetles, milkweed bugs, dogbane beetles and others have adaptations that let them feed on milkweed plants. Interestingly, studies of the evolutionary development of those adaptations show that, for the most part, each insect species evolved its defense independently of the others. In most cases, including that of the monarch, not only can the insects consume the toxin safely, the toxin in their body then helps prevent the insects from being eaten by predators. Monarch butterflies are an iconic insect in North America and their dramatic population declines have been linked to two main factors: the loss of habitat – particularly prairies with good plant diversity – and declines in milkweed populations. The majority of monarchs that reach Mexico each winter fed on common milkweed as caterpillars, making that species very important. However, other species are also eaten by caterpillars, including some that help monarch generations traveling north during the spring when/where common milkweed is not available. At least 12 of Nebraska's milkweed plants have been known to host monarch caterpillars, and continuing research may increase that number. However, the vast majority of monarch use Large milkweed bug on butterfly milkweed in Lincoln Creek Prairie, Aurora, Nebraska. Red milkweed beetle on whorled milkweed. This beetle and the milkweed bug shown above are two species that have adaptations to allow them to safely feed on milkweed leaves and stems. 56 NEBRASKAland • JULY 2016