Monarch butterflies do not place all of their eggs in one basket: oviposition on nine Midwestern milkweed species

Authors: POCIUS, VICTORIA - Iowa State University; DEBINSKI, DIANE - Iowa State University; PLEASANTS, JOHN - Iowa State University; Bidne, Keith; Hellmich Ii, Richard

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2017
Publication Date: 1/8/2018
Citation: Pocius, V.M., Debinski, D.M., Pleasants, J.M., Bidne, K.G., Hellmich II, R.L. 2018. Monarch butterflies do not place all of their eggs in one basket: oviposition on nine Midwestern milkweed species. Ecosphere. 9(1):e02064. https://doi.org/10.1002/ecs2.2064.
DOI: https://doi.org/10.1002/ecs2.2064

Interpretive Summary: The population of monarch butterflies east of the Rocky Mountains has experienced a significant decline over the past two decades due to many factors including loss of habitat. Thus, habitat restoration within the summer breeding range is crucial to boost population numbers. Milkweeds are the only host plants for larval monarch butterflies, but female oviposition preference for different milkweed species, especially those with overlapping ranges, is not well documented. We examined the relative inclination to lay eggs on these nine milkweed species native to Iowa in no-choice and choice experiments. In the choice experiments oviposition preference among the four most commonly occurring Iowa species (swamp milkweed, common milkweed, butterfly milkweed and whorled milkweed). In both experiments, eggs were counted daily for four days. When females were given only a single species on which to lay eggs there were significant differences among milkweed species in the average number of eggs laid; swamp milkweed had the highest average egg count. When females were given a choice among swamp, common, butterfly and whorled milkweed plants, there were also differences among milkweed species in the number of eggs laid; again, swamp milkweed had the highest average number of eggs laid. Additionally, females laid more total eggs when four plants of different milkweed species were available than when there were four plants of a single milkweed species. Our results show that monarch butterflies will lay eggs on all nine milkweeds that were tested, but that there are clear preferences for some milkweed species over others, especially a preference for swamp milkweed. Thus, restoration efforts including a diversity of milkweed species could benefit monarchs in their summer range. This information is useful to all groups interested in restoring habitat for monarch butterflies.

Technical Abstract: Over the past two decades, the population of monarch butterflies east of the Rocky Mountains has experienced a significant decline in overwintering numbers. Habitat restoration that includes planting milkweeds is essential to boost monarch numbers within the breeding range. Milkweeds are the only host plants for larval monarch butterflies, but female oviposition preference for different milkweed species, especially those with overlapping ranges, is not well documented. We examined the relative inclination to lay eggs on nine milkweed species native to Iowa (no choice), and oviposition preference (choice) among the four most commonly occurring Iowa species (A. incarnata, A. syriaca, A. tuberosa, and A. verticillata). In both experiments, eggs were counted daily for four days. The milkweeds tested were Asclepias exaltata (poke milkweed), A. hirtella (tall green milkweed), A. incarnata (swamp milkweed), A. speciosa (showy milkweed), A. sullivantii (prairie milkweed), A. syriaca (common milkweed), A. tuberosa (butterfly milkweed), A. verticillata (whorled milkweed), and Cynanchum laeve (honeyvine milkweed). When females were given only a single species on which to lay eggs there were significant differences among milkweed species in the average number of eggs laid; A. incarnata had the highest average egg count. When females were given a choice among A. incarnata, A. syriaca, A. tuberosa, and A. verticillata, there were also differences among milkweed species in the number of eggs laid; again, A. incarnata had the highest average number of eggs laid. Additionally, females laid more total eggs when four plants of different milkweed species were available than when there were four plants of a single milkweed species. Our results show that monarch butterflies will lay eggs on all nine milkweeds, but that there are clear preferences for some milkweed species over others.