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Mach BM, Glynn SE, Daniels JC, Dale AG. Target and non-target effects of insecticide use during ornamental milkweed production. ENVIRONMENTAL ENTOMOLOGY 2024; 53:648-658. [PMID: 38856688 DOI: 10.1093/ee/nvae056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2024] [Revised: 05/07/2024] [Accepted: 05/31/2024] [Indexed: 06/11/2024]
Abstract
There are widespread public efforts to conserve wildlife in urbanized landscapes via the installation of nursery-grown plants that support Lepidoptera taxa. Insecticides are commonly used during nursery production to suppress key plant pests, and many products have extended periods of toxicity and affect a wide range of herbivore taxa. While there are plentiful toxicological data on bee species, predominantly the Western honey bee (Apis mellifera L.), little is known about how insecticides affect nonpest lepidopterans. Lepidoptera has different modes of exposure (e.g., leaf-feeding) and differences in susceptibility to insecticide target sites compared to bees. Consequently, many products compatible with bee conservation pose an uncertain risk to nonpest lepidopterans and thus may represent an under-recognized conflict with conservation efforts. Using the monarch butterfly (Danaus plexippus, L.), tropical milkweed (Asclepias curassavica, L.), and oleander aphid (Aphis nerii, Fonscolombe, 1841) system, we conducted leaf and whole-plant feeding assays to evaluate effects of acute and chronic monarch exposure to industry standard and alternative reduced-risk insecticides used during nursery production. We also evaluated the efficacy of these insecticides against their target pest, the oleander aphid. Our results indicate that insecticides used to control pests on ornamental milkweed can cause monarch larval mortality up to 4 wk after treatment application. Furthermore, the duration of aphid suppression is often shorter than the duration of adverse effects on monarchs. This study demonstrates a conflict between insect pest management and Lepidoptera conservation during ornamental plant production and has implications for the conservation value of ornamentals after retail sale.
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Affiliation(s)
- Bernadette M Mach
- Entomology and Nematology Department, University of Florida, Gainesville, FL, USA
| | - Sacha E Glynn
- Entomology and Nematology Department, University of Florida, Gainesville, FL, USA
| | - Jaret C Daniels
- Entomology and Nematology Department, University of Florida, Gainesville, FL, USA
- Florida Museum of Natural History, Gainesville, FL, USA
| | - Adam G Dale
- Entomology and Nematology Department, University of Florida, Gainesville, FL, USA
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2
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Diffendorfer JE, Botello F, Drummond MA, Ancona ZH, Corro LM, Thogmartin WE, Ibsen PC, Moreno-Sanchez R, Lukens L, Sánchez-Cordero V. Changes in landscape and climate in Mexico and Texas reveal small effects on migratory habitat of monarch butterflies (Danaus plexippus). Sci Rep 2024; 14:6703. [PMID: 38509089 PMCID: PMC10954652 DOI: 10.1038/s41598-024-56693-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Accepted: 03/09/2024] [Indexed: 03/22/2024] Open
Abstract
The decline of the iconic monarch butterfly (Danaus plexippus) in North America has motivated research on the impacts of land use and land cover (LULC) change and climate variability on monarch habitat and population dynamics. We investigated spring and fall trends in LULC, milkweed and nectar resources over a 20-year period, and ~ 30 years of climate variables in Mexico and Texas, U.S. This region supports spring breeding, and spring and fall migration during the annual life cycle of the monarch. We estimated a - 2.9% decline in milkweed in Texas, but little to no change in Mexico. Fall and spring nectar resources declined < 1% in both study extents. Vegetation greenness increased in the fall and spring in Mexico while the other climate variables did not change in both Mexico and Texas. Monarch habitat in Mexico and Texas appears relatively more intact than in the midwestern, agricultural landscapes of the U.S. Given the relatively modest observed changes in nectar and milkweed, the relatively stable climate conditions, and increased vegetation greenness in Mexico, it seems unlikely that habitat loss (quantity or quality) in Mexico and Texas has caused large declines in population size or survival during migration.
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Affiliation(s)
- Jay E Diffendorfer
- U.S. Geological Survey, Geosciences and Environmental Change Science Center, Lakewood, CO, USA.
| | - Francisco Botello
- Departamento de Zoología, Instituto de Biología, Universidad Nacional Autónoma de México, Mexico City, Mexico
- Departamento de Monitoreo Biológico y Planeación de Conservación, Conservación Biológica y Desarrollo Social, Mexico City, Mexico
| | - Mark A Drummond
- U.S. Geological Survey, Geosciences and Environmental Change Science Center, Lakewood, CO, USA
| | - Zach H Ancona
- U.S. Geological Survey, Geosciences and Environmental Change Science Center, Lakewood, CO, USA
| | - Lucila M Corro
- U.S. Geological Survey, Geosciences and Environmental Change Science Center, Lakewood, CO, USA
| | - Wayne E Thogmartin
- U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, WI, USA
| | - Peter C Ibsen
- U.S. Geological Survey, Geosciences and Environmental Change Science Center, Lakewood, CO, USA
| | - Rafael Moreno-Sanchez
- Department of Geography and Environmental Sciences, University of Colorado Denver, 1200 Larimer St, NC 3016-C, Denver, CO, 80204, USA
| | - Laura Lukens
- Monarch Joint Venture, 2233 University Ave W., Suite 426, St. Paul, MN, USA
- Department of Forestry & Rangeland Science, Colorado State University, 1472 Campus Delivery, Fort Collins, CO, USA
| | - Victor Sánchez-Cordero
- Departamento de Zoología, Instituto de Biología, Universidad Nacional Autónoma de México, Mexico City, Mexico
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3
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James DG. Monarch Butterflies in Western North America: A Holistic Review of Population Trends, Ecology, Stressors, Resilience and Adaptation. INSECTS 2024; 15:40. [PMID: 38249046 PMCID: PMC10817040 DOI: 10.3390/insects15010040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 01/04/2024] [Accepted: 01/05/2024] [Indexed: 01/23/2024]
Abstract
Monarch butterfly populations in western North America suffered a substantial decline, from millions of butterflies overwintering in California in the 1980s to less than 400,000 at the beginning of the 21st century. The introduction of neonicotinoid insecticides in the mid-1990s and their subsequent widespread use appears to be the most likely major factor behind this sudden decline. Habitat loss and unfavorable climates (high temperatures, aridity, and winter storms) have also played important and ongoing roles. These factors kept overwintering populations stable but below 300,000 during 2001-2017. Late winter storm mortality and consequent poor spring reproduction drove winter populations to less than 30,000 butterflies during 2018-2019. Record high temperatures in California during the fall of 2020 appeared to prematurely terminate monarch migration, resulting in the lowest overwintering population (1899) ever recorded. Many migrants formed winter-breeding populations in urban areas. Normal seasonal temperatures in the autumns of 2021 and 2022 enabled overwintering populations to return to around the 300,000 level, characteristic of the previous two decades. Natural enemies (predators, parasitoids, parasites, and pathogens) may be important regional or local drivers at times but they are a consistent and fundamental part of monarch ecology. Human interference (capture, rearing) likely has the least impact on monarch populations. The rearing of monarch caterpillars, particularly by children, is an important human link to nature that has positive ramifications for insect conservation beyond monarch butterflies and should be encouraged.
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Affiliation(s)
- David G James
- Department of Entomology, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser, WA 99350, USA
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4
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Kendzel MJ, Altizer SM, de Roode JC. Interactions between parasitism and migration in monarch butterflies. CURRENT OPINION IN INSECT SCIENCE 2023; 59:101089. [PMID: 37506879 DOI: 10.1016/j.cois.2023.101089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 07/12/2023] [Accepted: 07/23/2023] [Indexed: 07/30/2023]
Abstract
In many species, migration can increase parasite burdens or diversity as hosts move between diverse habitats with different parasite assemblages. On the other hand, migration can reduce parasite prevalence by letting animals escape infested habitats, or by exacerbating the costs of parasitism, leading to culling or dropout. How the balance between these negative and positive interactions is maintained or how they will change under anthropogenic pressure remains poorly understood. Here, we summarize the relationship between migration and infectious disease in monarch butterflies, finding that migration can reduce parasite prevalence through a combination of migratory culling and dropout. Because parasite prevalence has risen in recent decades, these processes are now resulting in the loss of tens of millions of monarchs. We highlight the remaining questions, asking how migration influences population genetics and virulence, how the establishment of resident populations interferes with migration, and whether infection can interfere with migratory cognition.
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Affiliation(s)
| | - Sonia M Altizer
- Odum School of Ecology, University of Georgia, Athens, GA 30602, USA
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5
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Tenger-Trolander A. Environmental and genetic effects of captivity - are there lessons for monarch butterfly conservation? CURRENT OPINION IN INSECT SCIENCE 2023; 59:101088. [PMID: 37500011 DOI: 10.1016/j.cois.2023.101088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Revised: 07/17/2023] [Accepted: 07/17/2023] [Indexed: 07/29/2023]
Abstract
Rearing monarch butterflies in captivity for later release is a popular but contentious activity due to concerns about its potential negative effects on the wild population. In this review, I discuss how captive rearing and breeding could impact monarch fitness in the wild, the current evidence for such impacts in monarchs and other captive-reared/released organisms, and how this should inform our efforts to conserve monarchs and other species.
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6
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Steele C, Ragonese IG, Majewska AA. Extent and impacts of winter breeding in the North American monarch butterfly. CURRENT OPINION IN INSECT SCIENCE 2023; 59:101077. [PMID: 37336490 DOI: 10.1016/j.cois.2023.101077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Revised: 06/09/2023] [Accepted: 06/13/2023] [Indexed: 06/21/2023]
Abstract
Since the 1960s, scientists have observed the North American monarch butterfly (Danaus plexippus) continuing reproductive activities past the fall migration and into the winter months when the climate is mild. Recent work suggests that small populations of winter breeding monarchs are present in western and southeastern USA, as well as northwestern Mexico, with new winter breeding populations forming in areas where non-native milkweeds are planted. The year-round presence of milkweed plants and temperatures suitable for immature monarch development are vital factors allowing for winter breeding. Non-native milkweeds, in conjunction with novel barriers to migration, are likely contributing to the rise in winter breeding behavior. Warmer climates are already impacting milkweed phenology and range, possibly favoring winter breeding behavior. Similar pressures but different implications are expected for eastern and western winter breeding monarchs given the differences in the migration ecology, milkweed species, and climate changes in the two regions.
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Affiliation(s)
- Christen Steele
- Department of Ecology and Evolutionary Biology, Tulane University, 1430 Annunciation St, New Orleans, LA 70130, USA
| | - Isabella G Ragonese
- Odum School of Ecology, University of Georgia, 140 E Green Street, Athens, GA 30602, USA
| | - Ania A Majewska
- Department of Physiology and Pharmacology College of Veterinary Medicine, University of Georgia, 501 D.W. Brooks Drive, Athens, GA 30602, USA.
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7
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Yang LH. Complexity, humility, and action: a current perspective on monarchs in Western North America. CURRENT OPINION IN INSECT SCIENCE 2023; 59:101078. [PMID: 37380104 DOI: 10.1016/j.cois.2023.101078] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Revised: 06/16/2023] [Accepted: 06/19/2023] [Indexed: 06/30/2023]
Abstract
Recent studies have continued to shed light on the ecology of monarch butterflies (Danaus plexippus) in western North America. These studies have documented a declining overwintering population over several decades, punctuated by unexpected variability in recent years. Understanding this variability will require grappling with the spatial and temporal heterogeneity of resources and risks presented to western monarchs throughout their annual life cycle. Recent changes in the western monarch population further illustrate how interacting global change drivers can create complex causes and consequences in this system. The complexity of this system should inspire humility. However, even recognizing the limits of our current understanding, there is enough scientific common ground to take some conservation actions now.
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Affiliation(s)
- Louie H Yang
- Department of Entomology and Nematology, University of California, Davis, CA 95616, USA.
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8
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Mach BM, Long W, Daniels JC, Dale AG. Aphid infestations reduce monarch butterfly colonization, herbivory, and growth on ornamental milkweed. PLoS One 2023; 18:e0288407. [PMID: 37494406 PMCID: PMC10370756 DOI: 10.1371/journal.pone.0288407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Accepted: 06/26/2023] [Indexed: 07/28/2023] Open
Abstract
Anthropogenic disturbance is driving global biodiversity loss, including the monarch butterfly (Danaus plexippus), a dietary specialist of milkweed. In response, ornamental milkweed plantings are increasingly common in urbanized landscapes, and recent evidence indicates they have conservation value for monarch butterflies. Unfortunately, sap-feeding insect herbivores, including the oleander aphid (Aphis nerii), frequently reach high densities on plants in nursery settings and urbanized landscapes. Aphid-infested milkweed may inhibit monarch conservation efforts by reducing host plant quality and inducing plant defenses. To test this, we evaluated the effects of oleander aphid infestation on monarch oviposition, larval performance, and plant traits using tropical milkweed (Asclepias curassavica), the most common commercially available milkweed species in the southern U.S. We quantified monarch oviposition preference, larval herbivory, larval weight, and plant characteristics on aphid-free and aphid-infested milkweed. Monarch butterflies deposited three times more eggs on aphid-free versus aphid-infested milkweed. Similarly, larvae fed aphid-free milkweed consumed and weighed twice as much as larvae fed aphid-infested milkweed. Aphid-free milkweed had higher total dry leaf biomass and nitrogen content than aphid-infested milkweed. Our results indicate that oleander aphid infestations can have indirect negative impacts on urban monarch conservation efforts and highlight the need for effective Lepidoptera-friendly integrated pest management tactics for ornamental plants.
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Affiliation(s)
- Bernadette M. Mach
- Entomology and Nematology Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, United States of America
| | - William Long
- Entomology and Nematology Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, United States of America
| | - Jaret C. Daniels
- Entomology and Nematology Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, United States of America
- Florida Museum of Natural History, Gainesville, FL, United States of America
| | - Adam G. Dale
- Entomology and Nematology Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, United States of America
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9
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Kendrick MR, McCord JW. Overwintering and breeding patterns of monarch butterflies (Danaus plexippus) in coastal plain habitats of the southeastern USA. Sci Rep 2023; 13:10438. [PMID: 37369690 DOI: 10.1038/s41598-023-37225-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Accepted: 06/18/2023] [Indexed: 06/29/2023] Open
Abstract
Understanding variability in species' traits can inform our understanding of their ecology and aid in the development of management and conservation strategies. Monarch butterflies (Danaus plexippus) are native to the western hemisphere and are well-known for their long-distance migrations but have experienced significant population declines in recent decades. Here we use a 5-year capture-mark-recapture dataset to compare monarch distributions, mating activity, and larval host plant use between two coastal plain habitats in South Carolina, USA. We observed seasonally specific habitat use, with maritime habitats serving as overwintering areas while nearby inland swamps support significant breeding in spring, summer, and fall seasons due to an abundance of aquatic milkweed (Asclepias perennis). We also observed mating activity by fall migrating monarchs and their use of swallow-wort (Pattalias palustre) in the spring as an important larval host plant in maritime habitats. This phenology and habitat use of monarchs diverges from established paradigms and suggest that a distinct population segment of monarchs may exist, with significance for understanding the conservation status of monarch butterflies and associated habitats in eastern North America. Further research should explore how monarchs along the Atlantic coast of North America relate to other eastern monarch populations.
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Affiliation(s)
- Michael R Kendrick
- South Carolina Department of Natural Resources, Marine Resources Research Institute, 217 Fort Johnson Road, Charleston, SC, 29422, USA.
| | - John W McCord
- South Carolina Department of Natural Resources, Marine Resources Research Institute, 217 Fort Johnson Road, Charleston, SC, 29422, USA
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10
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Pocius VM, Cibotti S, Ray S, Ankoma-Darko O, McCartney NB, Schilder RJ, Ali JG. Impacts of larval host plant species on dispersal traits and free-flight energetics of adult butterflies. Commun Biol 2022; 5:469. [PMID: 35577926 PMCID: PMC9110344 DOI: 10.1038/s42003-022-03396-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Accepted: 04/22/2022] [Indexed: 12/03/2022] Open
Abstract
Animals derive resources from their diet and allocate them to organismal functions such as growth, maintenance, reproduction, and dispersal. How variation in diet quality can affect resource allocation to life-history traits, in particular those important to locomotion and dispersal, is poorly understood. We hypothesize that, particularly for specialist herbivore insects that are in co-evolutionary arms races with host plants, changes in host plant will impact performance. From their coevolutionary arms-race with plants, to a complex migratory life history, Monarch butterflies are among the most iconic insect species worldwide. Population declines initiated international conservation efforts involving the replanting of a variety of milkweed species. However, this practice was implemented with little regard for how diverse defensive chemistry of milkweeds experienced by monarch larvae may affect adult fitness traits. We report that adult flight muscle investment, flight energetics, and maintenance costs depend on the host plant species of larvae, and correlate with concentration of milkweed-derived cardenolides sequestered by adults. Our findings indicate host plant species can impact monarchs by affecting fuel requirements for flight. The growth of muscle and flight performance in monarch butterflies is influenced by the plant species the larvae grow on.
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Affiliation(s)
- Victoria M Pocius
- Department of Biological Sciences, The University of Alabama, Tuscaloosa, AL, USA
| | - Staci Cibotti
- Department of Entomology, The Pennsylvania State University, University Park, PA, USA
| | - Swayamjit Ray
- Department of Plant Pathology, Cornell University, Ithaca, NY, USA
| | - Obenewa Ankoma-Darko
- Department of Entomology, The Pennsylvania State University, University Park, PA, USA
| | - Nathaniel B McCartney
- Department of Entomology, The Pennsylvania State University, University Park, PA, USA
| | - Rudolf J Schilder
- Department of Entomology, The Pennsylvania State University, University Park, PA, USA.
| | - Jared G Ali
- Department of Entomology, The Pennsylvania State University, University Park, PA, USA.
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11
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Majewska AA, Davis AK, Altizer S, de Roode JC. Parasite dynamics in North American monarchs predicted by host density and seasonal migratory culling. J Anim Ecol 2022; 91:780-793. [PMID: 35174493 DOI: 10.1111/1365-2656.13678] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Accepted: 01/31/2022] [Indexed: 11/30/2022]
Abstract
Insect-pathogen dynamics can show seasonal and inter-annual variation that covaries with fluctuations in insect abundance and climate. Long-term analyses are especially needed to track parasite dynamics in migratory insects, in part because their vast habitat ranges and high mobility might dampen local effects of density and climate on infection prevalence. Monarch butterflies (Danaus plexippus) are commonly infected with the protozoan Ophryocystis elektroscirrha (OE). Because this parasite lowers monarch survival and flight performance, and because migratory monarchs have experienced declines in recent decades, it is important to understand patterns and drivers of infection. 3. Here we compiled data on OE infection spanning 50 years, from wild monarchs sampled in the USA, Canada, and Mexico during summer breeding, fall migrating, and overwintering periods. We examined eastern versus western North American monarchs separately, to ask how abundance estimates, resource availability, climate, and breeding season length impact infection trends. We further assessed the intensity of migratory culling, which occurs when infected individuals are removed from the population during migration. 4. Average infection prevalence was four times higher in western compared to eastern subpopulations. In eastern North America, the proportion of infected monarchs increased three-fold since the mid-2000s. In the western region, the proportion of infected monarchs declined sharply from 2000-2015, and increased thereafter. For both eastern and western subpopulations, years with greater summer adult abundance predicted greater infection prevalence, indicating that transmission increases with host breeding density. Environmental variables (temperature and NDVI) were not associated with changes in infected adults. We found evidence for migratory culling of infected butterflies, based on declines in parasitism during fall migration. We estimated that tens of millions fewer monarchs reach overwintering sites in Mexico as a result of OE, highlighting the need to consider the parasite as a potential threat to the monarch population. 5. Increases in infection among eastern North American monarchs post-2002 suggest that changes to the host's ecology or environment have intensified parasite transmission. Further work is needed to examine the degree to which human practices, such as mass caterpillar rearing and the widespread planting of exotic milkweed, have contributed to this trend.
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Affiliation(s)
| | - Andrew K Davis
- Odum School of Ecology, University of Georgia, Athens, GA, USA
| | - Sonia Altizer
- Odum School of Ecology, University of Georgia, Athens, GA, USA
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Monarchs Reared in Winter in California Are Not Large Enough to Be Migrants. Comment on James et al. First Population Study on Winter Breeding Monarch Butterflies, Danaus plexippus (Lepidoptera: Nymphalidae) in the Urban South Bay of San Francisco, California. Insects 2021, 12, 946. INSECTS 2022; 13:insects13010063. [PMID: 35055906 PMCID: PMC8778705 DOI: 10.3390/insects13010063] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 12/01/2021] [Accepted: 01/01/2022] [Indexed: 01/19/2023]
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13
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Pocius VM, Majewska AA, Freedman MG. The Role of Experiments in Monarch Butterfly Conservation: A Review of Recent Studies and Approaches. ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA 2022; 115:10-24. [PMID: 35069967 PMCID: PMC8764570 DOI: 10.1093/aesa/saab036] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Indexed: 06/14/2023]
Abstract
Monarch butterflies (Danaus plexippus) (Lepidoptera Danaidae Danaus plexippus (Linnaeus)) are an iconic species of conservation concern due to declines in the overwintering colonies over the past twenty years. Because of this downward trend in overwintering numbers in both California and Mexico, monarchs are currently considered 'warranted-but-precluded' for listing under the Endangered Species Act. Monarchs have a fascinating life history and have become a model system in chemical ecology, migration biology, and host-parasite interactions, but many aspects of monarch biology important for informing conservation practices remain unresolved. In this review, we focus on recent advances using experimental and genetic approaches that inform monarch conservation. In particular, we emphasize three areas of broad importance, which could have an immediate impact on monarch conservation efforts: 1) breeding habitat and host plant use, 2) natural enemies and exotic caterpillar food plants, and 3) the utility of genetic and genomic approaches for understanding monarch biology and informing ongoing conservation efforts. We also suggest future studies in these areas that could improve our understanding of monarch behavior and conservation.
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Affiliation(s)
- Victoria M Pocius
- Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, USA
| | | | - Micah G Freedman
- Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA
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14
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Brym MZ, van Gestel N, Henry C, Henry BJ, Lukashow-Moore SP, Kendall RJ. Evaluation of milkweed (Asclepias spp.) restoration in the Rolling Plains ecoregion of West Texas for the enhancement of monarch butterfly (Danaus plexippus) habitat. J Nat Conserv 2021. [DOI: 10.1016/j.jnc.2021.126076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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15
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Prouty C, Barriga P, Davis AK, Krischik V, Altizer S. Host Plant Species Mediates Impact of Neonicotinoid Exposure to Monarch Butterflies. INSECTS 2021; 12:insects12110999. [PMID: 34821799 PMCID: PMC8623494 DOI: 10.3390/insects12110999] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Revised: 10/27/2021] [Accepted: 11/02/2021] [Indexed: 11/16/2022]
Abstract
Simple Summary Neonicotinoids are the most widely used insecticides in North America and many studies document the negative effects of neonicotinoids on bees. Monarch butterflies are famous for their long-distance migrations, and for their ability to sequester toxins from their milkweed host plants. The neonicotinoids imidacloprid and clothianidin were suggested to correlate with declines in North American monarchs. We examined how monarch development, survival, and flight were affected by exposure to neonicotinoids, and how these effects depend on milkweed host plant species that differ in their cardenolide toxins. Monarch survival and flight were unaffected by low and intermediate neonicotinoid doses. At the highest dose, neonicotinoids negatively affected monarch pupation and survival, for caterpillars that fed on the least toxic milkweed. Monarchs fed milkweed of intermediate toxicity experienced moderate negative effects of high insecticide doses. Monarchs fed the most toxic milkweed species had no negative consequences associated with neonicotinoid treatment. Our work shows that monarchs tolerate low neonicotinoid doses, but experience detrimental effects at higher doses, depending on milkweed species. To our knowledge, this is the first study to show that host plant species potentially reduce the residue of neonicotinoid insecticides on the leaf surface, and this phenomenon warrants further investigation. Abstract Neonicotinoids are the most widely used insecticides in North America. Numerous studies document the negative effects of neonicotinoids on bees, and it remains crucial to demonstrate if neonicotinoids affect other non-target insects, such as butterflies. Here we examine how two neonicotinoids (imidacloprid and clothianidin) affect the development, survival, and flight of monarch butterflies, and how these chemicals interact with the monarch’s milkweed host plant. We first fed caterpillars field-relevant low doses (0.075 and 0.225 ng/g) of neonicotinoids applied to milkweed leaves (Asclepias incarnata), and found no significant reductions in larval development rate, pre-adult survival, or adult flight performance. We next fed larvae higher neonicotinoid doses (4–70 ng/g) and reared them on milkweed species known to produce low, moderate, or high levels of secondary toxins (cardenolides). Monarchs exposed to the highest dose of clothianidin (51–70 ng/g) experienced pupal deformity, low survival to eclosion, smaller body size, and weaker adult grip strength. This effect was most evident for monarchs reared on the lowest cardenolide milkweed (A. incarnata), whereas monarchs reared on the high-cardenolide A. curassavica showed no significant reductions in any variable measured. Our results indicate that monarchs are tolerant to low doses of neonicotinoid, and that negative impacts of neonicotinoids depend on host plant type. Plant toxins may confer protective effects or leaf physical properties may affect chemical retention. Although neonicotinoid residues are ubiquitous on milkweeds in agricultural and ornamental settings, commonly encountered doses below 50 ng/g are unlikely to cause substantial declines in monarch survival or migratory performance.
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Affiliation(s)
- Cody Prouty
- Odum School of Ecology, University of Georgia, Athens, GA 30602, USA; (P.B.); (A.K.D.); (S.A.)
- Correspondence:
| | - Paola Barriga
- Odum School of Ecology, University of Georgia, Athens, GA 30602, USA; (P.B.); (A.K.D.); (S.A.)
| | - Andrew K. Davis
- Odum School of Ecology, University of Georgia, Athens, GA 30602, USA; (P.B.); (A.K.D.); (S.A.)
| | - Vera Krischik
- Department of Entomology, University of Minnesota, St. Paul, MN 55108, USA;
| | - Sonia Altizer
- Odum School of Ecology, University of Georgia, Athens, GA 30602, USA; (P.B.); (A.K.D.); (S.A.)
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First Population Study on Winter Breeding Monarch Butterflies, Danaus plexippus (Lepidoptera: Nymphalidae) in the Urban South Bay of San Francisco, California. INSECTS 2021; 12:insects12100946. [PMID: 34680715 PMCID: PMC8537757 DOI: 10.3390/insects12100946] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Revised: 10/14/2021] [Accepted: 10/15/2021] [Indexed: 12/02/2022]
Abstract
Simple Summary Populations of western monarch butterflies, which formerly populated coastal overwintering sites in California in numbers exceeding one million, dwindled to less than 2000 in 2020/21. In the same winter, breeding populations of monarchs occurred commonly in the San Francisco Bay urban area for the first time. The urgent conservation need to understand this possible shift in overwintering strategy prompted this first study of the viability and ecology of monarch breeding populations in the South Bay urban area of San Francisco during January–June 2021. Adult monarchs along with eggs and larvae were common during winter and most of spring, utilizing non-native ornamental milkweed and multiple nectar sources from native and ornamental plants. Evidence from weekly counts and tagged butterflies indicated increased dispersal to the north and east during late April-mid-May, possibly representing spring migration to the Pacific Northwest and eastern California. Infection of reared adult monarchs with a protozoan parasite was high. Winter breeding of monarchs in the San Francisco urban area as an alternative and sustainable overwintering strategy for the western US population will likely depend on the continued presence of ornamental milkweeds, sustainable co-existence of monarchs and protozoan parasites, and successful migration to the greater western US during spring. Abstract The western North American monarch butterfly population assessed by counts of non-reproductive overwintering butterflies at coastal sites in California declined to less than 2000 in 2020/21. Simultaneously, reports of reproductive monarchs increased in San Francisco urban areas, perhaps representing a shift in overwintering strategy. To better understand monarch winter breeding in the Bay area, we studied adult and immature populations in Santa Clara County during January–June 2021. Adult monarchs were common with numbers ranging from 0.23–1.54/min during ~30 min weekly surveys at one site, with lowest numbers late April to mid-May. Eggs and larvae, primarily on ornamental milkweeds, were found on nearly all survey dates with lowest numbers mid-late April to mid-May. Levels of infection of adults by the parasite Ophryocystis elektroscirrha were consistently high during the study (69.3–77.5%). From 499 monarchs tagged post-eclosion, recovery rates of 19.2–23.6% occurred from releases in January-February and May-June but only 11.9–13.0% from March-April releases. Although distances were small, butterflies tagged in April were recovered from greater distances than other months. Tagged monarchs flew primarily north or east. There were reduced numbers of adult monarchs during late April-mid-May with some evidence of northerly and easterly emigration at the same time from tagged butterflies, suggesting some movement out of the South Bay area, perhaps representing spring migration. We conclude that monarchs can successfully breed and maintain populations on ornamental milkweeds during winter at urban sites in the South Bay of San Francisco and may still migrate during spring to remain part of the wider western population.
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James DG. Western North American Monarchs: Spiraling into Oblivion or Adapting to a Changing Environment? ANIMAL MIGRATION 2021. [DOI: 10.1515/ami-2021-0002] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Abstract
Monarch butterflies in western North America typically migrate each fall from the Pacific Northwest to overwintering sites in California. Winter 2020/21 saw the lowest number of overwintering western monarch butterflies ever recorded, but was also marked by a winter-breeding population in the San Francisco bay area that appeared to be the largest ever seen. Recoveries of monarchs with wing tags from the Pacific Northwest suggested that many non-reproductive migrants in fall 2020 became reproductive in the San Francisco bay area and did not reach coastal overwintering sites. Mean daily maximum temperatures for San Francisco during fall and winter increased by ~1 °C during the past decade and were 2.5 °C above the 30 year mean during September-October 2020. Warm fall and winter temperatures along with the availability of non-native milkweeds likely caused the increase in winter breeding in winter 2020/21. The outcome of continued winter-breeding in the San Francisco bay area is uncertain. Whether it becomes a sink or source will be dependent on whether winter-breeding monarchs can re-enter their migratory state during spring. However, endemic levels of infection by the protozoan parasite, Ophryocystis elektroscirrha (OE), are often high in winter-breeding monarchs which can limit migration success. The eventual co-existence of winter-breeding and non-breeding monarch populations in northern and central California is probable, with an optimistic view suggesting that the adaptability of the monarch butterfly will allow it to persist in a changed environment.
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Affiliation(s)
- David G James
- Department of Entomology, Irrigated Agriculture Research and Extension Center , Washington State University , 24106 North Bunn Road, Prosser, WA, 99350, USA
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