Asclepias Speciosa Research Articles

Cattle Graze Central US Milkweeds at Least as Much as Grasses, Even Under Patch-Burn-Grazing Management

Most researchers assume cattle avoid milkweeds due to toxic compounds. However, observations suggest cattle graze common milkweed (Asclepias syriaca L.), an important summer host plant for monarch butterflies (Danaus plexippus L.) east of the Rocky Mountains, as well as showy milkweed (Asclepias speciosa Torr.). This directly relates to efforts to add over 1 billion stems of milkweed for monarch butterfly conservation. We sampled whether cattle regularly graze common/showy milkweed in a central Nebraska restored prairie patch-burn-grazing system with patches burned in the year of the main study (2018) or previous years (2017–2016). We also sampled burned control grasslands without livestock. This sampling therefore compared three different types of burn-graze management. Cow-calf pairs were put onto the grasslands in April, and we sampled every 2 wk through September. We found that wild grazers (e.g., deer) were not grazing common/showy milkweed stems in control grasslands, whereas by August > 73% of stems had been grazed in the patch-burn-grazed grasslands—with no noticeable negative effects on cattle. Also, cattle grazing of common/showy milkweed did not differ significantly in different patches, even though big bluestem grass (Andropogon gerardii Vitman) was grazed significantly more in patches burned in 2018. Finally, milkweed abundance in control grasslands ranged from 34- to 185-fold higher than the average milkweed abundance in patch-burn-grazed grasslands. These results suggest that cattle regularly graze common/showy milkweed and that patch-burn-grazing does not increase milkweed abundance when cattle begin grazing in April. The good news of these results is that cattle safely grazed low amounts of common/showy milkweed, suggesting control efforts for these milkweeds are often unnecessary. Future work should examine how to increase milkweed abundance without affecting cattle weight gain, possibly by deferring grazing in some areas during critical milkweed growth periods.

Climatic history, constraints, and the plasticity of phytochemical traits under water stress

AbstractEnvironmental stress can induce changes in organismal traits and in resulting intraspecific variation. The nature of such effects will depend on the plasticity of trait expression and on any ecological constraints to such expression. Plants can mitigate abiotic stress, like drought, by changing their chemistry, but the ability to induce costly metabolites may be under strong local selection and ecologically constrained. Here, we asked whether climate at the seed source predicts plant chemical plasticity in response to water stress and what the consequences are for intraspecific variation in phytochemical traits. To this end, we used common gardens of two widespread species of western milkweed (Asclepias fascicularis and Asclepias speciosa) that had been collected from sites across an aridity gradient. Both species produce high concentrations of leaf flavonols, which are hypothesized to mitigate water stress by functioning as antioxidants. These compounds were found in higher constitutive concentrations in plants sourced from drier sites, and both species responded to water stress in the common garden by increasing leaf flavonol concentrations. Interestingly, flavonol plasticity was higher in plants sourced from wetter sites in A. fascicularis, with similar, but weaker, patterns in A. speciosa. These opposing patterns in constitutive and induced flavonol expression reduced the variation between populations in leaf flavonol concentrations under water stress. These results suggest that local adaptation in plants can shape phytochemical strategies for water limitation but that the cost of metabolite production may ultimately limit the range of phytochemical variation.

Disentangling the direct, indirect, and combined effects of experimental warming on a plant–insect herbivore interaction

AbstractThere is increasing evidence that climate warming will have both direct and indirect effects on species. Whereas the direct effects of climate warming represent the proximate physiological consequences of changing abiotic conditions, the indirect effects of climate change reflect changes mediated by at least one other interacting species. The relative importance of these two kinds of effects has been unclear, limiting our ability to generalize the response of different species to climate change. Here, we used a series of experiments to disentangle some of the key direct and indirect effects of warming on the growth of monarch butterfly caterpillars (Danaus plexippus) and showy milkweed plants (Asclepias speciosa) during a window of rapid growth for both species. The effects of warming differed between direct, indirect, and combined effect experiments. Warming from 26°C to 30°C directly increased the growth of both monarch larvae and milkweeds, with monarch and milkweed growth rates showing similar sensitivity to warming. However, in a subsequent experiment, we did not observe significantly increased growth when comparing caterpillars and plants reared at 27°C and 31°C, suggesting that small differences can change the direct effects of warming. When caterpillars that were maintained at laboratory temperatures were fed leaves from host plants that were exposed to warmer temperatures, warming had a negative indirect effect on larval growth rates likely mediated by decreases in milkweed leaf quality. In experiments combining direct and indirect effects, we observed a net positive effect of warming on larval growth rates. Warming had no combined effects on milkweed growth, potentially due to opposing positive direct and negative indirect effects on growth mediated via increased monarch herbivory. These results show how variability among the direct, indirect, and combined effects of even relatively simple, short‐term climatic perturbations can present challenges for predicting the broader effects of climatic warming in multispecies communities.

Development and Verification of an Interspecific Hybridization Protocol for Asclepias

Milkweed (Asclepias sp.) is an important pollinator genus across North America and is a host plant for many butterfly species, notably the monarch butterfly (Danaus plexippus). Commercial production of Asclepias is limited to a few species, because most species lack commercial traits, with minimal branching habit, excessive height, and minimal color variation. This study used a commercially viable Asclepias species, butterfly weed (Asclepias tuberosa L.), as a maternal parent and trialed three different pollination methods in an attempt to create interspecific hybrids. Pollination methods included a traditional method, a pollen–solution-based method, and a novel inverted pollinia method. The inverted pollinia method increased pollination success rates 4-fold among intraspecific crosses of A. tuberosa. When pollination methods were optimized, A. tuberosa was used as the maternal parent, and one-way crosses were made to seven other Asclepias species using the inverted pollinia method. Of the seven species used as pollen donors, four developed hybrid seed successfully: green milkweed (Asclepias hirtella Woodson), purple milkweed (Asclepias purpurascens L.), showy milkweed (Asclepias speciosa Torr.), and common milkweed (Asclepias syriaca L.). As germination methods vary significantly among Asclepias species, three methods of germination were trialed on seed developed via interspecific hybridizations: direct seeded, cold–moist stratification, and embryo rescue. Of the three methods, cold–moist stratification was superior to direct seeding and embryo rescue. This research is the first documented case of a controlled interspecific hybridization event among these species.

Insufficient sampling constrains our characterization of plant microbiomes

Plants host diverse microbial communities, but there is little consensus on how we sample these communities, and this has unknown consequences. Using root and leaf tissue from showy milkweed (Asclepias speciosa), we compared two common sampling strategies: (1) homogenizing after subsampling (30 mg), and (2) homogenizing bulk tissue before subsampling (30 mg). We targeted bacteria, arbuscular mycorrhizal (AM) fungi and non-AM fungi in roots, and foliar fungal endophytes (FFE) in leaves. We further extracted DNA from all of the leaf tissue collected to determine the extent of undersampling of FFE, and sampled FFE twice across the season using strategy one to assess temporal dynamics. All microbial groups except AM fungi differed in composition between the two sampling strategies. Community overlap increased when rare taxa were removed, but FFE and bacterial communities still differed between strategies, with largely non-overlapping communities within individual plants. Increasing the extraction mass 10 × increased FFE richness ~ 10 ×, confirming the severe undersampling indicated in the sampling comparisons. Still, seasonal patterns in FFEs were apparent, suggesting that strong drivers are identified despite severe undersampling. Our findings highlight that current sampling practices poorly characterize many microbial groups, and increased sampling intensity is necessary for increase reproducibility and to identify subtler patterns in microbial distributions.

Phytochemistry-mediated disruption of ant-aphid interactions by root-feeding nematodes.

Plants link interactions between aboveground and belowground organisms. Herbivore-induced changes in plant chemistry are hypothesized to impact entire food webs by changing the strength of trophic cascades. Yet, few studies have explored how belowground herbivores affect the behaviors of generalist predators, nor how such changes may act through diverse changes to the plant metabolome. Using a factorial experiment, we tested whether herbivory by root-knot nematodes (Meloidogyne incognita) affected the aboveground interaction among milkweed plants (Asclepias fascicularis or Asclepias speciosa), oleander aphids (Aphis nerii), and aphid-tending ants (Linepithema humile). We quantified the behaviors of aphid-tending ants, and we measured the effects of herbivore treatments on aphid densities and on phytochemistry. Unexpectedly, ants tended aphids primarily on the leaves of uninfected plants, whereas ants tended aphids primarily at the base of the stem of nematode-infected plants. In nematode-infected plants, aphids excreted more sugar per capita in their ant-attracting honeydew. Additionally, although plant chemistry was species-specific, nematode infection generally decreased the richness of plant secondary metabolites while acting as a protein sink in the roots. Path analysis indicated that the ants' behavioral change was driven in part by indirect effects of nematodes acting through changes in plant chemistry. We conclude that belowground herbivores can affect the behaviors of aboveground generalist ant predators by multiple paths, including changes in phytochemistry, which may affect the attractiveness of aphid honeydew rewards.

Species-specific, age-varying plant traits affect herbivore growth and survival.

Seasonal windows of opportunity represent intervals of time within a year during which organisms have improved prospects of achieving life history aims such as growth or reproduction, and may be commonly structured by temporal variation in abiotic factors, bottom-up factors, and top-down factors. Although seasonal windows of opportunity are likely to be common, few studies have examined the factors that structure seasonal windows of opportunity in time. Here, we experimentally manipulated host-plant age in two milkweed species (Asclepias fascicularis and Asclepias speciosa) in order to investigate the role of plant-species-specific and plant-age-varying traits on the survival and growth of monarch caterpillars (Danaus plexippus). We show that the two plant species showed diverging trajectories of defense traits with increasing age. These species-specific and age-varying host-plant traits significantly affected the growth and survival of monarch caterpillars through both resource quality- and quantity-based constraints. The effects of plant age on monarch developmental success were comparable to and sometimes larger than those of plant-species identity. We conclude that species-specific and age-varying plant traits are likely to be important factors with the potential to structure seasonal windows of opportunity for monarch development, and examine the implications of these findings for both broader patterns in the ontogeny of plant defense traits and the specific ecology of milkweed-monarch interactions in a changing world.

FALL AVAILABLE TROPICAL MILKWEED (ASCLEPIAS CURASSAVICA L.) MAY BE A POPULATION SINK FOR THE MONARCH BUTTERFLY

Native plants provide the best habitat for pollinators, but non-native plants can supply resources to native pollinators. The non-native tropical milkweed (bloodflower or scarlet milkweed), Asclepias curassavica L., is a larval food source for the native monarch butterfly (Danaus plexippus). Asclepias curassavica has been widely planted in the southern U.S. where it blooms until late fall, retains healthy vegetation until frost, and does not die back until a hard freeze. In contrast, native Asclepias species senesce and are usually not suitable for monarch larvae consumption in the fall. The late availability of the non-native milkweed may trigger monarchs, normally migrating to Mexico, to break reproductive diapause and lay eggs on their host plant. To determine if non-native A. curassavica was more likely than native Asclepias species to attract egg-laying monarchs, we grew native Asclepias viridis Walter and Asclepias speciosa Torr. along with A. curassavica in Oklahoma and recorded the number of monarch eggs and caterpillars on each plant. From August 2019 until the first freeze, we observed 145 eggs and 39 caterpillars on 40 of 48 A. curassavica plants and one egg on one of 19 native Asclepias plants. First freeze occurred on 12 October. A majority of eggs were laid after 12 September resulting in most eggs having insufficient time to mature. This freeze date was nearly 3 weeks earlier than the average for this area. Our evidence suggests that the monarchs are differentially reacting to the availability of non-native and native Asclepias during late summer and fall.

Monarch Butterfly Distribution and Breeding Ecology in Idaho and Washington

Studies of monarch butterflies (Danaus plexippus) and their milkweed (Asclepias spp.) host plants in North America have focused primarily on monarch populations ranging east of the Rocky Mountains. We report the first systematic assessment of monarch butterfly and milkweed populations in the western states of Idaho and Washington, states at the northern tier of western monarch breeding range. Results of our 2-year study (2016–2017) offer new insights into monarch breeding habitat distribution, characteristics, and threat factors in our 2 states. We documented milkweeds and breeding monarchs in all 16 climate divisions in our study area. Milkweed and breeding monarch phenologies were examined with evidence supporting 2, and possibly 3 monarch generations produced in Idaho and Washington. Key monarch breeding habitats were moist-soil sites within matrices of grasslands, wetlands, deciduous forest, and shrub-steppe supporting large, contiguous, and high-density milkweed stands. Co-occurrence of showy milkweed (A. speciosa) and swamp milkweed (A. incarnata) was an important indicator of productive monarch breeding habitat in Idaho. Nectar plants were generally limited in quantity and richness across the study area, particularly in late summer, and included frequently-used non-native, invasive species. Primary threats at milkweed sites were invasive plant species, herbicide application, and mowing, followed by secondary threats of recreational disturbance, livestock grazing, insecticide application, loss of floodplain function, and wildfire. We provide management recommendations and research needs to address ongoing stressors and knowledge gaps in Idaho and Washington with the goal of conserving monarchs and their habitats in the West.

Modeling Current and Future Potential Distributions of Milkweeds and the Monarch Butterfly in Idaho

Monarch butterflies (Danaus plexippus) are widespread in North America but have experienced large rangewide declines. Causes of recent declines likely involve multiple biotic and abiotic stressors including climate change and loss and degradation of native milkweed (Asclepias spp.), monarchs’ obligate larval host plant. Recent broad-scale modeling efforts suggest milkweed and monarch distributions in the eastern United States will expand northward during summer months while fine-scale modeling of western population overwintering sites in California indicate shifts inland and upward in elevation. However, species’ response to climate measures varies at sub-regional scales across its range and both the impacts of climate change and potential adaptation measures may be sensitive to the spatial scale of climate data used, particularly in areas of complex topography. Here, we develop fine-scale models of monarch breeding habitat and milkweed distributions in Idaho, an area at the northern extent of the monarch breeding range in North America and important in western overwintering population recruitment. Our models accurately predict current distributions for showy milkweed (A. speciosa), swamp milkweed (A. incarnata), and monarch with AUC (area under the receiver operating characteristic curve) = 0.899, 0.981, and 0.929, respectively. Topographic, geographic, edaphic, and climatic factors all play important roles in determining milkweed and, thus, monarch distributions. In particular, our results suggest that at sub-regional and fine-scales, non-climatic factors such as soil depth, distance to water, and elevation contribute significantly. We further assess changes in potential habitat across Idaho under mid-21st century climate change scenarios and potential management implications of these changing distributions. Models project slight decreases (-1318km2) in potential suitable habitat for showy milkweed and significant increases (+5830km2) for swamp milkweed. Projected amounts of suitable habitat for monarch are likely to remain roughly stable with expansion nearly equal to contraction under a moderate scenario and slightly greater when under the more severe scenario. Protected areas encompass 8% of current suitable habitat for showy milkweed, 11% for swamp milkweed, and 9% for monarch. Our study shows that suitable habitat for monarchs and/or milkweeds will likely continue to be found in managed areas traditionally seen as priority habitats in Idaho through mid-century.

High-frequency somatic embryogenesis, nuclear DNA estimation of milkweed species (Asclepias latifolia, A. speciosa, and A. subverticillata), and genome size stability of regenerants

A high-frequency somatic embryogenesis was developed for three Asclepias species, A. latifolia (broadleaf milkweed), A. speciosa (showy milkweed), and A. subverticillata (horsetail milkweed) using gibberellic (GA3) and the amino acid l-proline. A somatic embryo initiation medium consisting of MS salts (Murashige and Skoog, in Physiol Plant 15:473–497, 1962) with Gamborg’s (1968) vitamins, 1.5 µM 2,4-D, 2.3 µM kinetin, and 2% (w/v) sucrose supplemented with various concentrations of l-proline (0, 8.7, or 17.4 mM) combined with various of concentrations of GA3 (0, 2.9, or 5.8 µM), resulting in nine different media (MWM0–MWM8). All media produced callus, but no embryos were obtained on the control medium which contained no l-proline or GA3. Once calli produced somatic embryos, they were transferred to a medium referred to as somatic embryo conversion medium or SECM, which contained MS salts with Gamborg’s vitamins (Gamborg et al., Exp Cell Res 50:151–158, 1968), 2.3 µM kinetin, 2.9 mM GA3, 1.5% (w/v) sucrose, 8 g/L. The conversion percentage of somatic embryos into plants was high for all media, in particular for MWM2 (17.4 mM l-proline + 0 µM GA3) with conversion rates of 90.2, 93.4, and 97% for A. latifolia, A. speciosa, and A. subverticillata, respectively. Flow cytometry was used to estimate the nuclear DNA content of both seed-derived and in vitro grown plants. The 2C-DNA values of all three species were 0.92 pg, which did not differ from the values of in vitro grown plants, thus verifying that the regeneration system produces genetically stable plants.

Effects of Short- and Long-Term Variation in Resource Conditions on Soil Fungal Communities and Plant Responses to Soil Biota.

Soil biota can strongly influence plant performance with effects ranging from negative to positive. However, shifts in resource availability can influence plant responses, with soil pathogens having stronger negative effects in high-resource environments and soil mutualists, such as arbuscular mycorrhizal fungi (AMF), having stronger positive effects in low-resource environments. Yet the relative importance of long-term vs. short-term variation in resources on soil biota and plant responses is not well-known. To assess this, we grew the perennial herb Asclepias speciosa in a greenhouse experiment that crossed a watering treatment (wet vs. dry treatment) with a manipulation of soil biota (live vs. sterilized soil) collected from two geographic regions (Washington and Minnesota) that vary greatly in annual precipitation. Because soil biota can influence many plant functional traits, we measured biomass as well as resource acquisition (e.g., root:shoot, specific leaf area) and defense (e.g., trichome and latex production) traits. Due to their important role as mutualists and pathogens, we also characterized soil fungal communities in the field and greenhouse and used curated databases to assess fungal composition and potential function. We found that the experimental watering treatment had a greater effect than soil biota origin on plant responses; most plant traits were negatively affected by live soils under wet conditions, whereas responses were neutral or positive in live dry soil. These consistent differences in plant responses occurred despite clear differences in soil fungal community composition between inoculate origin and watering treatments, which indicates high functional redundancy among soil fungi. All plants grown in live soil were highly colonized by AMF and root colonization was higher in wet than dry soil; root colonization by other fungi was low in all treatments. The most parsimonious explanation for negative plant responses in wet soil is that AMF became parasitic under conditions that alleviated resource limitation. Thus, plant responses appeared driven by shifts within rather than between fungal guilds, which highlights the importance of coupling growth responses with characterizations of soil biota to fully understand underlying mechanisms. Collectively these results highlight how short-term changes in environmental conditions can mediate complex interactions between plants and soil biota.

Monarch Butterflies Show Differential Utilization of Nine Midwestern Milkweed Species

Monarch butterfly overwintering numbers have declined over the past 20 years. Restoring habitat that includes milkweeds, the only host plants for larval monarch butterflies, is necessary to increase monarch numbers within the breeding range. The value of different milkweed species for restoration will depend, in part, on the extent to which they are utilized by ovipositing females. The number of eggs laid on different species over a season will be a function of plant size and phenology as well as female preference. We examined seasonal egg deposition and females’ oviposition choices by comparing the number of eggs laid by free-flying wild monarchs on each of nine native milkweed species occurring in Iowa (Asclepias syriaca, Asclepias tuberosa, Asclepias incarnata, Asclepias verticillata, Asclepias exaltata, Asclepias hirtella, Asclepias speciosa, Asclepias sullivantii, and Cynanchum laeve). One plot, consisting of clusters of each of the nine species, was established at each of 14 sites across the state of Iowa. Eggs were counted weekly in June, July and August 2015-2017. The highest egg totals were recorded on A. incarnata and A. syriaca in all years. Fewer eggs were counted on A. exaltata, A. hirtella, A. tuberosa, A. verticillata, and C. laeve. Our results show that monarchs prefer some milkweed species over others, but that they can use all nine native milkweed species for oviposition.

Sensitivity of Eleven Milkweed (Asclepias) Species to Ozone

Abstract We exposed 11 milkweed species to ozone within continuous stirred-tank reactor (CSTR) chambers in a greenhouse to determine species sensitivity and potential use as bioindicators to detect phytotoxic levels of ambient ozone. Asclepias syriaca (Common Milkweed), A. ovalifolia (Oval-leaf Milkweed), A. sullivantii (Prairie Milkweed), A. speciosa (Showy Milkweed), A. asperula (Spider Milkweed), A. incarnata (Swamp Milkweed), A exaltata (Tall Milkweed), and A. curassavica (Tropical Milkweed) developed typical ozone-induced dark stipple on the adaxial surface of older leaves. Tropical Milkweed also exhibited significant premature defoliation (accelerated leaf senescence). Asclepias tuberosa (Butterfly Milkweed), A. hirtella (Green Milkweed), and A. verticillata (Whorled Milkweed) were tolerant to ozone. Foliar stipple on Common Milkweed increased with ozone concentration and time. In addition to Common Milkweed, a bioindicator commonly used to detect phytotoxic levels of ozone, the other 7 ozone-sensit...

Genomics of physiological adaptations of two milkweed species (Asclepias) in their hybrid zone

Speciation is the source of diversity on the planet, but the genomic mechanisms that lead to the reproductive isolating barriers between populations that cause speciation are not well understood. Here we are studying the genomic differentiation between two species of milkweed that grow in the Western (Asclepias speciosa) and Eastern United States (A. syrica). In addition to different geographic locations, these species have diverged in a number of important phenotypes, including: production of secondary metabolites, flower morphology, and drought resistance. In the central US, these species have come into secondary contact and sometimes form hybrids in the wild. We are interested in quantifying the amount of gene flow between these species and identifying genomic locations that may be indicative of local adaptation within populations and reproductive isolation between species.To compare these species of milkweed, we isolated DNA from A. speciousa, A. syrica, and individuals that displays intermediate phenotypes from the hybridization zone. We extracted and isolated genomic DNA and sequenced their genomes with Oxford Nanopore technology. With the aligned genomes, we will be able to compare polymorphisms in these species and begin to quantify the amount of gene flow between them. We will also identify polymorphisms in candidate genes and pathways that may have led to ecological specialization between these species.Support or Funding InformationSouth Dakota EPSCoR IIA‐1355423South Dakota BRIN P20GM 103443This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Trait differences in responses to arbuscular mycorrhizal fungi are stronger and more consistent than fixed differences among populations of Asclepias speciosa.

Arbuscular mycorrhizal (AM) fungi can promote plant growth and reproduction, but other plant physiological traits or traits that provide defense against herbivores can also be affected by AM fungi. However, whether responses of different traits to AM fungi are correlated and whether these relationships vary among plants from different populations are unresolved. In a common garden experiment, we grew Asclepias speciosa plants from seed collected from populations found along an environmental gradient with and without AM fungi to assess whether the responses of six growth and defense traits to AM fungi are correlated. Although there was strong genetic differentiation in mean trait values among populations, AM fungi consistently increased expression of most growth and defense traits across all populations. Responses of biomass and root to shoot ratio to AM fungi were positively correlated, suggesting that plants that are more responsive to AM fungi allocated more biomass belowground. Responses of biomass and trichome density to AM fungi were negatively correlated, indicating a trade-off in responsiveness between a growth and defensive trait. Our results suggest that while there is substantial population differentiation in many traits of A. speciosa, populations respond similarly to AM fungi, and both positive and negative correlations among trait responses occur.

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

AbstractOver 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 (Asclepias incarnata, Asclepias syriaca, Asclepias tuberosa, and Asclepias verticillata). In both experiments, eggs were counted daily for four days. The milkweeds tested were Asclepias exaltata (poke milkweed), Asclepias hirtella (tall green milkweed), A. incarnata (swamp milkweed), Asclepias speciosa (showy milkweed), Asclepias 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.

Performance of Early Instar Monarch Butterflies (Danaus plexippusL.) on Nine Milkweed Species Native to Iowa

Over the past two decades, the population of monarch butterflies east of the Rocky Mountains has experienced a significant decline. Habitat restoration that includes milkweed plants is crucial to boost population numbers in the breeding range. Monarch butterfly larvae use milkweeds as their only host plant, but larval performance on different milkweed species is not well documented. We examined early instar survival and growth on nine milkweed species native to Iowa. These included 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 (honey vine milkweed). In laboratory and greenhouse experiments, larval survival on all nine milkweed species did not differ. Larvae that fed on C. laeve plants were an instar behind larvae that fed on any other species, while larvae that fed on A. verticillata weighed more than larvae that fed on any other species. Our results show that early instar larvae can survive on all nine milkweed species.

Growth and Survival of Two Western Milkweed Species: Effects of Container Volume and Fertilizer Rate

Diminishing milkweed (Asclepias sp.) populations are contributing to the conspicuous decline of the iconic monarch butterfly (Danaus plexippus). This research sought to improve milkweed propagation success, a core component of summer habitat restoration projects. Specifically, this research assessed the effects of container volume and fertilizer application rate on growth and first year field survival of two species of milkweed common to western North America, namely showy milkweed (A. speciosa) and narrowleaf milkweed (A. fascicularis). Generally, larger roots and shoots developed when plants were given the high rate of fertilizer (6.5 g·L−1) and when reared in the largest containers (2600 mL). For narrowleaf milkweed, nearly all plants developed a firm plug (i.e., one in which the root system remained intact when removed from the container) after 22 weeks. Most narrowleaf milkweed plants flowered 15 weeks after sowing when grown in the largest container with either the low (2.7 g·L−1) or high fertilizer rate or the midsized container (444 mL) with a high rate of fertilizer. For showy milkweed, a firm plug developed for nearly all individuals by the end of the growing season only when given the high fertilizer rate. None of the showy milkweed plants developed an inflorescence by 15 weeks. Results of this research improve our understanding of milkweed propagation and will aid in the efforts to restore the monarch butterfly’s summer breeding habitat by providing propagation protocols across a range of stocktypes.

Population Biology of Monarch Butterflies,Danaus plexippus(L.) (Lepidoptera: Nymphalidae), at a Milkweed-Rich Summer Breeding Site in Central Washington

ABSTRACT. The population biology of adult Monarch butterflies (Danaus plexippus) was studied during regular visits over three years (June–September 2013–15) at a milkweed (Asclepias speciosa)-rich site in central Washington. Small numbers of spring migrants colonized the site during June 5–17 each year and produced two adult generations one in early July and the other in late July–August, increasing the population at the site until mid–late August in 2013 and 2014. Greatest numbers of adults occurred in late July and August (20–24 per hour). In 2015 the population fell substantially in early August apparently as a consequence of heat wave conditions in late June–early July adversely affecting survival of second generation immature stages. Mark, release and recapture provided maximum population estimates at the site of 160–190 males, a recapture rate of 25–32% and intervals between tagging and recapture of 5–39 days. Sex ratio was imbalanced in favor of males on all dates ranging from 57–100%. Males patrol...