Low-Level Dietary Clothianidin Exposure Preferentially Causes Prepupal Mortality of Monarch Butterflies (Danaus plexippus)

Data from prior research indicate the prepupal stage of the monarch butterfly life cycle is more sensitive to clothianidin exposure than the larval stage. A set of experiments was conducted to determine if the dietary clothianidin exposures that cause prepupal mortality are environmentally relevant. Monarch larvae were raised from egg to pupae on clothianidin-contaminated swamp milkweed plants (Asclepias incarnata). Larval growth as well as larval and prepupal survival were monitored throughout the experiments, in which the exposures ranged from 1.4 to 2793.1 ng/g leaf. Exposures of 5.4 to 46.9 ng/g leaf resulted primarily in prepupal mortality, whereas higher exposures of 1042.4 to 2793.1 ng/g leaf resulted exclusively in larval mortality, indicating the prepupal stage is more sensitive to clothianidin exposure than the larval stage. A median lethal concentration and a 10% lethal concentration of 37 and 6 ng/g leaf, respectively, were estimated for prepupal mortality. Both effect concentrations are within the range of clothianidin concentrations reported in leaves collected from wild milkweed plants, indicating prepupal mortality is an environmentally relevant effect. Environ Toxicol Chem 2024;00:1-6. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Current trends and mismatches on fungicide use and assessment of the ecological effects in freshwater ecosystems

Despite increasing evidence of off-site ecological impacts of pesticides and policy efforts worldwide, pesticide use is still far from being ecologically sustainable. Fungicides are among the most sold classes of pesticides and are crucial to ensure global food supply and security. This study aimed to identify potential gaps of knowledge and mismatches between research and usage data of fungicides by: (i) systematizing the current trends in global sales of fungicides, focusing on the European context in particular (where they are proportionally important); (ii) reviewing the scientific literature on the impacts of synthetic fungicides on non-target freshwater organisms. Sales data revealed important global and regional asymmetries in the relative importance of fungicides and the preferred active ingredients. The literature review on the ecological effects of fungicides disclosed a mismatch between the most studied and the most sold substances, as well as a bias towards the use of single species assays with standard test organisms. To ensure a proper evaluation, risk scenarios should focus on a regional scale, and research agendas must highlight sensitive aquatic ecorreceptors and improve the crosstalk between analytical and sales data.

Monarch Butterflies in Western North America: A Holistic Review of Population Trends, Ecology, Stressors, Resilience and Adaptation

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.

Pesticide contamination of beeswax from managed honey bee colonies in New York State

The New York State (NYS) beekeeping industry generated >$11M worth of honey in 2020 and >$300M in pollination services to agriculture annually. Bees are frequently exposed to pesticides through foraging and husbandry practices. Lipophilic pesticides can remain in beeswax for extended periods. We analyzed for pesticides in wax comb samples collected from NYS apiaries at the end of the growing season, comparing residue numbers and concentrations among beekeepers of different operation scales: commercial beekeepers (>300 colonies), sideliners (50-299 colonies), and hobbyists (<50 colonies). We analyzed samples collected from 72 managed honey bee colonies for 92 insecticides, herbicides, and fungicides by liquid chromatography-tandem mass spectrometry. Pesticides were detected in all samples and included 34 fungicides, 33 insecticides, and 22 herbicides. Each wax sample contained 7-35 different residues (x¯ = 17.8 residues). Wax from colonies managed by commercial beekeepers contained the most residues (x¯ = 21.9 residues), hobbyists were second (x¯ = 16.3 residues), and sideliners had the fewest (x¯ = 11.7 residues). Nearly all wax samples (98.6%) contained the pesticide synergist piperonyl butoxide, most samples (86%) contained common varroacides used to control honey bee parasites, including coumaphos and amitraz breakdown products, and 93.1% contained the fungicide difenoconazole. We detected 34 fungicides, 7 of which were found in 50% or more of the samples. We detected 22 herbicides. We found pesticide contamination of beeswax to be common, with commercial beekeepers experiencing the greatest contamination.

Complexity, humility, and action: a current perspective on monarchs in Western North America

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.

Transforming entomology to adapt to global concerns: 2021 student debates

The 2021 Student Debates of the Entomological Society of America (ESA) were held at the Annual Meeting in Denver, CO. The event was organized by the Student Debates Subcommittee (SDS) of the Student Affairs Committee (SAC). The theme of the 2021 Student Debates was "Transforming Entomology to Adapt to Global Concerns", with 3 topics. Each topic had an unbiased introduction and 2 teams. The debate topics were (i) Nonnative insect introduction is an ethical approach for counteracting proliferation and overpopulation of consumers, (ii) What is the best technology to control undesirable insect pests in urban and agricultural settings? and (iii) Compared to other solutions, like plant-based diets, insect farming is the best method to address rising human global food and nutrient supply demands. Unbiased introduction speakers and teams had approximately 6 months to prepare for their presentations.

A neonicotinoid pesticide alters Drosophila olfactory processing

Neonicotinoid pesticides are well-known for their sublethal effects on insect behavior and physiology. Recent work suggests neonicotinoids can impair insect olfactory processing, with potential downstream effects on behavior and possibly survival. However, it is unclear whether impairment occurs during peripheral olfactory detection, during information processing in central brain regions, or in both contexts. We used Drosophila melanogaster to explore the potential for neonicotinoids to disrupt olfaction by conducting electrophysiological analyses of single neurons and whole antennae of flies exposed to varying concentrations of the neonicotinoid imidacloprid (IMD) that were shown to cause relative differences in fly survival. Our results demonstrated that IMD exposure significantly reduced the activity of a single focal olfactory neuron and delayed the return to baseline activity of the whole antenna. To determine if IMD also impacts olfactory-guided behavior, we compared flies' relative preference for odor sources varying in ethanol content. Flies exposed to IMD had a greater relative preference for ethanol-laced pineapple juice than control flies, demonstrating that neuronal shifts induced by IMD that we observed are associated with changes in relative preference. Given the interest in the sensory impacts of agrochemical exposure on wild insect behavior and physiology, we highlight the potential of Drosophila as a tractable model for investigating the effects of pesticides at scales ranging from single-neuron physiology to olfactory-guided behavior.

Additive and interactive effects of anthropogenic stressors on an insect herbivore

The pressures of global change acting on wild plants and animals include exposure to environmental toxins, the introduction of non-native species, and climate change. Relatively few studies have been reported in which these three main classes of stressors have been examined simultaneously, allowing for the possibility of synergistic effects in an experimental context. In this study, we exposed caterpillars of the Melissa blue butterfly (Lycaeides melissa) to three concentrations of chlorantraniliprole, under three experimental climates, on a diet of a native or a non-native host plant throughout larval development in a fully factorial experiment. We find that high pesticide exposure and a non-native diet exhibit strong negative effects on caterpillars, resulting in 62% and 42% reduction in survival, respectively, while interactive effects tend to be weaker, ranging from 15% to 22% reduction in survival. Interactive effects have been shown to be strong in other contexts, but do not appear to be universal; however, our study shows that the cumulative effects of stressors acting in isolation (additively) are sufficiently strong to severely reduce survival and by extension population persistence in the wild.

Wild bees are exposed to low levels of pesticides in urban grasslands and community gardens

Globally documented wild bee declines threaten sustainable food production and natural ecosystem functioning. Urban environments are often florally abundant, and consequently can contain high levels of pollinator diversity compared with agricultural environments. This has led to the suggestion that urban environments are an increasingly important habitat for pollinators. However, pesticides, such as commercial bug sprays, have a range of lethal and sub-lethal impacts on bees and are widely available for public use, with past work indicating that managed bees (honeybees and bumblebees) are exposed to a range of pesticides in urban environments. Despite this, we still have a poor understanding of (i) whether wild bees foraging in urban environments are exposed to pesticides and (ii) if exposure differs between genera. Here we assessed pesticide exposure in 8 bee genera foraging across multiple urban landscapes. We detected 13 different pesticides, some at concentrations known to have sub-lethal impacts on pollinators. Both the likelihood of pesticides being detected, and the concentrations observed, were higher for larger bees, likely due to their greater foraging ranges. Our results suggest that restricting agrochemical use in urban environments, where the economic benefits are limited, is a simple way to reduce anthropogenic stress on wild bees.

Microbial Technologies Employed for Biodegradation of Neonicotinoids in the Agroecosystem

Neonicotinoids are synthetic pesticides widely used for the control of various pests in agriculture throughout the world. They mainly attack the nicotinic acetylcholine receptors, generate nervous stimulation, receptor clot, paralysis and finally cause death. They are low volatile, highly soluble and have a long half-life in soil and water. Due to their extensive use, the environmental residues have immensely increased in the last two decades and caused many hazardous effects on non-target organisms, including humans. Hence, for the protection of the environment and diversity of living organism's the degradation of neonicotinoids has received widespread attention. Compared to the other methods, biological methods are considered cost-effective, eco-friendly and most efficient. In particular, the use of microbial species makes the degradation of xenobiotics more accessible fast and active due to their smaller size. Since this degradation also converts xenobiotics into less toxic substances, the various metabolic pathways for the microbial degradation of neonicotinoids have been systematically discussed. Additionally, different enzymes, genes, plasmids and proteins are also investigated here. At last, this review highlights the implementation of innovative tools, databases, multi-omics strategies and immobilization techniques of microbial cells to detect and degrade neonicotinoids in the environment.

Host Plant Species Mediates Impact of Neonicotinoid Exposure to Monarch Butterflies

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.

The complexity of global change and its effects on insects

Global change includes multiple overlapping and interacting drivers: 1) climate change, 2) land use change, 3) novel chemicals, and 4) the increased global transport of organisms. Recent studies have documented the complex and counterintuitive effects of these drivers on the behavior, life histories, distributions, and abundances of insects. This complexity arises from the indeterminacy of indirect, non-additive and combined effects. While there is wide consensus that global change is reorganizing communities, the available data are limited. As the pace of anthropogenic changes outstrips our ability to document its impacts, ongoing change may lead to increasingly unpredictable outcomes. This complexity and uncertainty argue for renewed efforts to address the fundamental drivers of global change.

Neonicotinoids can cause arrested pupal ecdysis in Lepidoptera

Recently, we reported a novel mode of action in monarch butterfly (Danaus plexippus) larvae exposed to neonicotinoid insecticides: arrest in pupal ecdysis following successful larval ecdysis. In this paper, we explore arrested pupal ecdysis in greater detail and propose adverse outcome pathways to explain how neonicotinoids cause this effect. Using imidacloprid as a model compound, we determined that final-instar monarchs, corn earworms (Helicoverpa zea), and wax moths (Galleria mellonella) showed high susceptibility to arrested pupal ecdysis while painted ladies (Vanessa cardui) and red admirals (Vanessa atalanta) showed low susceptibility. Fall armyworms (Spodoptera frugiperda) and European corn borers (Ostrinia nubilalis) were recalcitrant. All larvae with arrested ecdysis developed pupal cuticle, but with incomplete shedding of larval cuticle and unexpanded pupal appendages; corn earworm larvae successfully developed into adults with unexpanded appendages. Delayed initiation of pupal ecdysis was also observed with treated larvae. Imidacloprid exposure was required at least 26 h prior to pupal ecdysis to disrupt the molt. These observations suggest neonicotinoids may disrupt the function of crustacean cardioactive peptide (CCAP) neurons, either by directly acting on their nicotinic acetylcholine receptors or by acting on receptors of inhibitory neurons that regulate CCAP activity.

Oviposition Response of Monarch Butterfly (Lepidoptera: Nymphalidae) to Imidacloprid-Treated Milkweed

Monarch butterfly (Danaus plexippus) populations have declined over the last two decades, attributable in part to declines in its larval host plant, milkweed (Asclepias spp.), across its breeding range. Conservation efforts in the United States call for restoration of 1.3 billion milkweed stems into the Midwestern landscape. Reaching this goal will require habitat establishment in marginal croplands, where there is a high potential for exposure to agrochemicals. Corn and soybean crops may be treated with neonicotinoid insecticides systemically or through foliar applications to provide protection against insect pests. Here, we investigate whether ovipositing monarchs discriminate against milkweed plants exposed to the neonicotinoid insecticide imidacloprid, either systemically or through foliar application. In our first experiment, we placed gravid females in enclosures containing a choice of two cut stems for oviposition: one in 15 ml of a 0.5 mg/ml aqueous solution of imidacloprid and one in 15 ml water. In a second experiment, females were given a choice of milkweed plants whose leaves were treated with 30 µl of a 0.825 mg/ml imidacloprid-surfactant solution or plants treated with surfactant alone. To evaluate oviposition preference, we counted and removed eggs from all plants daily for 3 d. We also collected video data on a subset of butterflies to evaluate landing behavior. Results indicate that neither systemic nor foliar treatment with imidacloprid influenced oviposition behavior in female monarchs. The implications of these findings for monarch conservation practices will be informed by the results of ongoing egg and larval toxicity studies.

Monarch Butterfly (Danaus plexippus) Life-Stage Risks from Foliar and Seed-Treatment Insecticides

Conservation of North America's eastern monarch butterfly (Danaus plexippus) population would require establishment of milkweed (Asclepias spp.) and nectar plants in the agricultural landscapes of the north central United States. A variety of seed-treatment and foliar insecticides are used to manage early- and late-season pests in these landscapes. Thus, there is a need to assess risks of these insecticides to monarch butterfly life stages to inform habitat conservation practices. Chronic and acute dietary toxicity studies were undertaken with larvae and adults, and acute topical bioassays were conducted with eggs, pupae, and adults using 6 representative insecticides: beta-cyfluthrin (pyrethroid), chlorantraniliprole (anthranilic diamide), chlorpyrifos (organophosphate), imidacloprid, clothianidin, and thiamethoxam (neonicotinoids). Chronic dietary median lethal concentration values for monarch larvae ranged from 1.6 × 10^-3 (chlorantraniliprole) to 5.3 (chlorpyrifos) μg/g milkweed leaf, with the neonicotinoids producing high rates of arrested pupal ecdysis. Chlorantraniliprole and beta-cyfluthrin were generally the most toxic insecticides to all life stages, and thiamethoxam and chlorpyrifos were generally the least toxic. The toxicity results were compared to insecticide exposure estimates derived from a spray drift model and/or milkweed residue data reported in the literature. Aerial applications of foliar insecticides are expected to cause high downwind mortality in larvae and eggs, with lower mortality predicted for adults and pupae. Neonicotinoid seed treatments are expected to cause little to no downslope mortality and/or sublethal effects in larvae and adults. Given the vagile behavior of nonmigratory monarchs, considering these results within a landscape-scale context suggests that adult recruitment will not be negatively impacted if new habitat is established in close proximity of maize and soybean fields in the agricultural landscapes of the north central United States. Environ Toxicol Chem 2021;40:1761-1777. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The decline of butterflies in Europe: Problems, significance, and possible solutions

We review changes in the status of butterflies in Europe, focusing on long-running population data available for the United Kingdom, the Netherlands, and Belgium, based on standardized monitoring transects. In the United Kingdom, 8% of resident species have become extinct, and since 1976 overall numbers declined by around 50%. In the Netherlands, 20% of species have become extinct, and since 1990 overall numbers in the country declined by 50%. Distribution trends showed that butterfly distributions began decreasing long ago, and between 1890 and 1940, distributions declined by 80%. In Flanders (Belgium), 20 butterflies have become extinct (29%), and between 1992 and 2007 overall numbers declined by around 30%. A European Grassland Butterfly Indicator from 16 European countries shows there has been a 39% decline of grassland butterflies since 1990. The 2010 Red List of European butterflies listed 38 of the 482 European species (8%) as threatened and 44 species (10%) as near threatened (note that 47 species were not assessed). A country level analysis indicates that the average Red List rating is highest in central and mid-Western Europe and lowest in the far north of Europe and around the Mediterranean. The causes of the decline of butterflies are thought to be similar in most countries, mainly habitat loss and degradation and chemical pollution. Climate change is allowing many species to spread northward while bringing new threats to susceptible species. We describe examples of possible conservation solutions and a summary of policy changes needed to conserve butterflies and other insects.

Experimental field evidence shows milkweed contaminated with a common neonicotinoid decreases larval survival of monarch butterflies

Neonicotinoid insecticides are the most widely used class of insecticides in the world and can have both lethal and sub-lethal effects on non-target organisms in agricultural areas. Monarch butterflies Danaus plexippus have experienced dramatic declines in recent decades and, given that a large proportion of milkweed on the landscape grows in agricultural areas, there is concern about the negative effects of neonicotinoids on this non-target insect. In the field, we exposed common milkweed Asclepias syriaca, an obligate host plant of monarch butterflies, to agriculturally realistic levels of clothianidin, a widely used neonicotinoid insecticide. We tested whether this treatment influenced the number of eggs laid and larval survival over 2 years. Milkweeds were transplanted into 60 experimental plots alongside a corn crop planted with a clothianidin seed coat and 60 control plots alongside an untreated corn crop. The number of eggs, larvae at each stage (first to fifth instar), and the presence of other arthropods were recorded weekly from June to the end of August and survival from egg to fifth instar was estimated using a Bayesian state-space statistical model. We counted more eggs in treated plots compared to control plots, suggesting a preference for treated milkweed. The number of plots with arthropods did not differ between treatments, but within treated plots, there was a greater decrease in the number of arthropods throughout the season. There was no evidence that monarchs selected plots with fewer arthropods for oviposition. Larval survival was lower in clothianidin-treated plots compared to control plots. Our results suggest milkweed near clothianidin-treated crops can reduce larval survival of monarch butterflies. While we provide some evidence that clothianidin could also act as an ecological trap for this species, further work is needed to identify additional components of fitness, including individual egg-laying rates and survival beyond the pupal stage. Our findings add to a growing body of evidence that neonicotinoids can negatively affect non-target organisms. ​.

Effects of early-life exposure to sublethal levels of a common neonicotinoid insecticide on the orientation and migration of monarch butterflies (Danaus plexippus)

Migratory insects use a variety of innate mechanisms to determine their orientation and maintain correct bearing. For long-distance migrants, such as the monarch butterfly (Danaus plexippus), these journeys could be affected by exposure to environmental contaminants. Neonicotinoids are synthetic insecticides that work by affecting the nervous system of insects, resulting in impairment of their mobility, cognitive performance, and other physiological and behavioural functions. To examine how neonicotinoids might affect the ability of monarch butterflies to maintain a proper directional orientation on their ∼4000 km migration, we grew swamp milkweed (Asclepias incarnata) in soil that was either untreated (0 ng g-1: control) or mixed with low (15 ng g-1 of soil) or high (25 ng g-1 of soil) levels of the neonicotinoid clothianidin. Monarch caterpillars were raised on control or clothianidin-treated milkweed and, after pupation, either tested for orientation in a static flight simulator or radio-tracked in the wild during the autumn migration period. Despite clothianidin being detectable in milkweed tissue consumed by caterpillars, there was no evidence that clothianidin influenced the orientation, vector strength (i.e. concentration of direction data around the mean) or rate of travel of adult butterflies, nor was there evidence that morphological traits (i.e. mass and forewing length), testing time, wind speed or temperature impacted directionality. Although sample sizes for both flight simulator and radio-tracking tests were limited, our preliminary results suggest that clothianidin exposure during early caterpillar development does not affect the directed flight of adult migratory monarch butterflies or influence their orientation at the beginning of migration.

Butterfly Conservation in China: From Science to Action

About 10% of the Earth's butterfly species inhabit the highly diverse ecosystems of China. Important for the ecological, economic, and cultural services they provide, many butterfly species experience threats from land use shifts and climate change. China has recently adopted policies to protect the nation's biodiversity resources. This essay examines the current management of butterflies in China and suggests various easily implementable actions that could improve these conservation efforts. Our recommendations are based on the observations of a transdisciplinary group of entomologists and environmental policy specialists. Our analysis draws on other successful examples around the world that China may wish to consider. China needs to modify its scientific methodologies behind butterfly conservation management: revising the criteria for listing protected species, focusing on umbrella species for broader protection, identifying high priority areas and refugia for conservation, among others. Rural and urban land uses that provide heterogeneous habitats, as well as butterfly host and nectar plants, must be promoted. Butterfly ranching and farming may also provide opportunities for sustainable community development. Many possibilities exist for incorporating observations of citizen scientists into butterfly data collection at broad spatial and temporal scales. Our recommendations further the ten Priority Areas of China's National Biodiversity Conservation Strategy and Action Plan (2011-2030).

Larval pesticide exposure impacts monarch butterfly performance

The long-term decline of monarch butterflies has been attributed to loss of their milkweed (Asclepias sp.) host-plants after the introduction of herbicide-tolerant crops. However, recent studies report pesticide residues on milkweed leaves that could act as a contributing factor when ingested as part of their larval diet. In this study, we exposed monarch larvae to six pesticides (insecticide: clothianidin; herbicides: atrazine, S-metolachlor; fungicides: azoxystrobin, pyraclostrobin, trifloxystrobin) on their primary host-plant, A. syriaca. Each was tested at mean and maximum levels reported from published analyses of milkweeds bordering cropland and thus represent field-relevant concentrations. Monarch lethal and sub-lethal responses were tracked over their complete development, from early instar larvae to adult death. Overall, we found no impact of any pesticide on immature development time and relatively weak effects on larval herbivory or survival to adulthood. Comparatively stronger effects were detected for adult performance; namely, a 12.5% reduction in wing length in response to the fungicides azoxystrobin and trifloxystrobin. These data collectively suggest that monarch responses to host-plant pesticides are largely sublethal and more pronounced in the adult stage, despite exposure only as larvae. This outcome has important implications for risk assessment and the migratory success of monarchs in North America.