Ecology of Bract Milkweed: A plant for roadside and right-of-way management

By Shaun M. McCoshum, Wildlife Biologist at Westwood, and Anurag A. Agrawal, James A. Perkins, Professor of Environmental Studies 

In an effort to protect the monarch butterfly and other pollinators, the Candidate Conservation Agreement with Assurance (CCAA) and U.S. Fish and Wildlife Services have approved an “enhancement of survival” permit application.  

For solar developers interested in land that is declared to support the monarch system, Westwood’s Wildlife Studies team can educate you on the permitting process with our knowledgeable staff of botanists and landscapers by providing the best management practices for botanical services. 

Recently, Westwood’s very own Shaun M. McCoshum, Wildlife Biologist, co-wrote a research article on the ecology of bract milkweed, which is an important host plant for monarchs in the arid southwest. Bract milkweed will be important when applying for the permit as it supports conservation for the monarch butterfly and other pollinators. Read the article to learn more about this plant species and reach out to our Wildlife Studies team with any questions you may have on the “enhancement of survival” permit application. 

Read the full article originally published in Native Plants Journal: 
Ecology of Asclepias brachystephana (bract milkweed): a plant for roadside and right-of-way management 

EXTENDED ABSTRACT  
McCoshum SM, Agrawal AA. 2021. Ecology of Asclepias brachystephana: a plant for roadside and right-of-way management. Native Plants Journal 22(3):256–267. 

KEY WORDS  
roadside, bract milkweed, cardenolides, milkweed, Apocynaceae 

Declining insect abundance is occurring around the world (Kluser and Peduzzi 2007; Colla and Packer 2008; Potts and others 2010; Cameron and others 2011; Hallmann and others 2017; McArt and others 2017). Habitat loss is one of the leading causes of these declines, and such losses can include habitat conversion (Kremen and Ricketts 2000; Kremen and others 2002; Buchmann and Ascher 2005; Potts and others 2010) and vegetation community conversion for roads, urbanization, and right-of-way (Winfree and others 2007; Potts and others 2010; Jantz and others 2015; McCoshum and Geber 2020). Monarch butterfly (Danaus plexippus Linnaeus [Nymphalidae]) population declines have brought attention to habitat loss because larval host plant habitat and abundance have been reduced (Hartzler 2010; Pleasants and Oberhauser 2013; Pleasants 2017; Zaya and others 2017), although data are available that question the causality of this relationship (Inamine and others 2016; Agrawal and Inamine 2018). Landowners and conservation groups have started reintroducing larval host plants, specifically in the genus Asclepias (Apocynaceae), or the milkweeds, to areas including gardens as a conservation strategy (Thogmartin and others 2017; Geest and others 2019), while further research elucidates the ecology of monarch host plants (Hartzler and Buhler 2000; Hartzler 2010; Baker and Potter 2018) and restoration (Kasten and others 2016; Pleasants 2017; Thogmartin and others 2017; Pitman and others 2018), which is primarily focused on a handful of common milkweed species. 

Milkweeds produce cardenolides as chemical defense (Züst and others 2019), which most organisms cannot ingest, and plant toxicity can vary depending on growing conditions (Agrawal and others 2012a, 2012b). Some insects have evolved resistance to these chemicals and even sequester these compounds for their own defenses (Birnbaum and others 2017; Birnbaum and Abbot 2018). Furthermore, many insects, including beneficial insects and pollinators, utilize milkweed flowers (Jennersten and Morse 1991; Ivey and others 2003; Nabhan and others 2015; James and others 2016). Approximately 130 species of Asclepias occur in North America (Woodson 1954; Weitemier and others 2015; Fishbein and oth ers 2018), with a wide range of preferred habitats (Wilbur 1976; Borkin 1982; Fishbein and others 2011). For example, there are desert species such as desert milkweed (A. erosa Torr.), soil specialists such as serpentine milkweed (A. solanoana Woodson) (Lynch 1977), prairie species such as showy milkweed and green antelopehorns (A. speciosa Torr. and A. viridis Walter), and wetland-obligate species that include swamp milkweed and aquatic milkweed (A. incarnata L. and A. perennis Walter). 

In the arid Southwest, climatic variables include hot, dry months as well as monsoon seasons that vary in rainfall totals across the region (Hochstrasser and others 2002; Weiss and others 2004). The region is governed by both the US and Mexico and contains the Warm Deserts, Southern Semi-arid Highlands, Temperate Sierras, and the Tropical Dry Forests (USDA Ecoregions of North America Level II). Numerous cities, roads, right-of-way, and other disturbed habitats occur throughout the area, which makes it important to study the plants that can live in these disturbed habitats in order to create robust local conservation plantings. Approximately 50 species of Asclepias are known to occur in the arid Southwest (Nabhan and others 2015; GBIF 2021). Within the area, the Chihuahuan Desert is the largest ecoregion with the northeastern portion having populations of bract milkweed (A. brachystephana Engelm. ex Torr.), broadleaf milkweed (A. latifolia (Torr.) Raf.), zizotes milkweed (A. oenotheroides Cham. & Schitdl.), and horsetail milkweed (A. subverticillata (A. Gray) Vail) (GBIF 2021). 

Our project focuses on A. brachystephana, which is commonly known as “Inmortal pequeño,” “Kacosi,” and “Lechosillo” in Spanish or Indigenous names and as “short-crowned milkweed” and “bract milkweed” in English (Nabhan and others 2015). Bract milkweed is poorly studied, but the few known details of the species include: It is toxic to mammals (Rowe and others 1970; Mellado and others 2003); it is closely related to A. fournieri Woodson (Fishbein and others 2011, 2018), which occurs in the southern and western range of bract milkweed; and various insects can forage on it (Agrawal and others 2015; Navarro and others 2015). By determining the concentration of defense chemicals in this species, we can determine the suitability of this species for insect development, including monarch and queen butterflies (Danaus gillipus Kramer [Nymphalidae]).  

In this article, we investigate the ecology of bract milkweed:  
1) Modeling the potential range using MaxEnt 
2) Documenting where populations occur in west Texas and southeastern New Mexico, focusing on populations growing near roadsides and right-of-way 
3) Exploring reproductive biology including candidate pollinators and how many seeds a plant can produce 
4) Determining which insect herbivores utilize the plant and the concentration of defensive cardenolides in wild plants compared to laboratory-grown offspring. 

READ THE FULL ARTICLE 
Ecology of Asclepias brachystephana (bract milkweed): a plant for roadside and right-of-way management 

MORE BY THIS AUTHOR 
Milkweeds, Monarchs, seed cleaning and germination with Dr. Shaun McCoshum: LETMN Sept 2021 Texas - YouTube 

Dr. McCoshum presents on how to identify local milkweed species found in west Texas (Ector and Midland Counties). Discuss the milkweed ecology and the importance of using local seed for restoration projects.