Colonization and usage of eight milkweed (Asclepias) species by monarch butterflies and bees in urban garden settings

Published source details Baker A.M. & Potter D.A. (2018) Colonization and usage of eight milkweed (Asclepias) species by monarch butterflies and bees in urban garden settings. Journal of Insect Conservation, 22, 405-418.
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This study is summarised as evidence for the following.

	Action	Category
	Plant parks, gardens and road verges with appropriate native species Action Link

Plant parks, gardens and road verges with appropriate native species

A replicated, randomized, controlled study in 2016–2017 in an arboretum in Kentucky, USA (Baker & Potter 2018) found that following planting of eight milkweed species Asclepias spp. the number of monarch butterfly Danaus plexippus eggs and caterpillars was higher on taller species than on shorter species, but that caterpillar growth and survival were similar across all species. Taller milkweed species (Asclepias syriaca, A. speciosa, A. incarnata, A. fascicularis) had a higher number of monarch butterfly eggs and caterpillars (3.0–16.8 individuals/plot) than shorter species (0.0–5.4 individuals/plot). However, caterpillar growth (final weight: 169–437 mg) and survival (56–100%) were similar on all milkweed species in two of three trials. In the third trial, survival (40–65%) was similar but caterpillars were larger on A. verticillata, A. tuberosa and A. speciosa (868–1,032 mg) than on the other species (300–706 mg). Eight species of milkweed native to Kentucky or the central or western USA (common A. syriaca, swamp A. incarnata, butterfly A. tuberosa, green antelopehorn A. viridis, whorled A. verticillata, showy A. speciosa, Mexican whorled A. fascicularis, broadleaf milkweed A. latifolia) were grown from seed in a greenhouse. In May 2016, seedlings were transplanted into five (1.22 × 9.75 m) garden plots, each with eight subplots (1.22 × 1.22 m). Four individuals of a single species were sown into each subplot. From May–October 2016 and April–September 2017, monarch eggs and caterpillars were counted on all plants once every two weeks. The following three experiments measured monarch caterpillar growth and survival. In August 2016, two first or second instar monarch caterpillars were caged in white fine mesh bags (25 × 40 cm) on each of two plants/plot for nine days. In September 2016, three caterpillars were caged on each of nine plants for seven days. In August 2017, a single 1-day-old caterpillar was caged on each of 10 plants of each species in a greenhouse for five days.

(Summarised by: Andrew Bladon)