The eastern population of monarch butterflies has declined significantly over the past 20 years. As the figure here illustrates, Iowa is in the heart of the summer breeding range for this iconic insect. Habitat restoration that includes planting native milkweed species is critical for monarch conservation. There are 18 native milkweed species in Iowa, but much of the existing research is based on data that includes only common milkweed, A. syriaca.
Recent research by Iowa State University graduate Victoria Pocius, Ph.D. took a closer look at oviposition on nine different milkweed species, all of which are native to Iowa. The study included the following native species of milkweed:
- Common milkweed (Asclepias syriaca)
- Swamp milkweed (A. incarnata)
- Butterfly milkweed (A. tuberosa)
- Whorled milkweed (A. verticillata)
- Showy milkweed (A. speciosa)
- Poke milkweed (A. exaltata)
- Prairie milkweed (A. sullivantii)
- Tall green milkweed (A. hirtella)
- Honeyvine milkweed (Cynanchum laeve)
Milkweeds in the genera Asclepias and Cynanchum are the only host plants for larval monarch butterflies in North America, but data regarding females’ preference for egg laying, especially on milkweeds that have overlapping geographic ranges, is limited. Results from this field study, conducted for three seasons from 2015 - 2017, indicate that monarch butterflies will lay eggs on all nine milkweed species used in the study. However, A. incarnata and A. syriaca had the highest egg totals in all years. This study is one of many that will be featured in the North American Monarch Butterfly Ecology and Conservation special issue.
Findings from this study highlights the importance of including a diversity of milkweed species in monarch habitat restorations. The results also suggest that A. tuberosa and A. verticillata are not the best plants for oviposition, although they are valuable food sources for monarch larvae.
This work was partially funded by the USDA National Institute of Food and Agriculture, Hatch project number 1009926 (IOW05478) and by the USDA, Natural Resources Conservation Service’s Conservation Innovation Grant program under Agreement Number 69-3A75-16-006. Additional support was provided by Prairie Biotics Inc. and the Iowa Monarch Conservation Consortium.