Neonicotinoid-contaminated pollinator strips adjacent to cropland reduce honey bee nutritional status

Can Ahiflower® (Buglossoides arvensis) seed-oil supplementation help overcome the adverse effects of imidacloprid in honey bees?

In this study, we investigated the effects of nutritional supplementation as a strategy to mitigate the impacts of imidacloprid (neonicotinoid) on honey bees by using Ahiflower® (Buglossoides arvensis) seed-oil. This oil is rich in stearidonic-acid (SDA, 18:4n3), which is a precursor to eicosapentaenoic-acid (EPA) and docosahexaenoic-acid (DHA) that are known for their beneficial and protective effects. Specifically, we chronically fed newly emerged worker bees with sucrose syrup and pollen patties (control) that we supplemented with (i) imidacloprid (0.375 ng·μl-1), (ii) Ahiflower® oil (5 %) + imidacloprid (0.375 ng·μl-1), and (iii) Ahiflower® oil (5 %). Survival was recorded, and after 21 days, worker bees were sampled to measure mitochondrial respiration, ATP5A1 content, adenylate energy charge, lipid peroxidation in thorax as well as fatty acid composition and peroxidation index in whole bees. Our results indicate that (i) imidacloprid mostly hampers mitochondria, increases saturated fatty acids and decreases survival, (ii) oxidation of alternative substrates allows full recovery of mitochondrial respiration in the imidacloprid-treated group demonstrating mitochondrial flexibility, (iii) Ahiflower® oil in combination with imidacloprid partially restores mitochondrial respiration at the level of complexes I and II, restores fatty acid composition but fails to restore survival. These findings confirm the deleterious effects of imidacloprid on mitochondria while highlighting, for the first time, the potential benefits of Ahiflower® oil in mitochondrial function, though not on honey bee survival. In addition, this study highlights the importance of mitochondrial flexibility when organisms are exposed to toxicants at environmentally relevant levels.

Differential effects of clothianidin exposure on metabolic rates across life stages of Danaus plexippus (Lepidoptera: Nymphalidae)

The restoration of milkweed to agricultural landscapes is thought to be essential for bolstering declining monarch butterfly (Danaus plexippus) populations. However, the rise of neonicotinoid seed treatments in recent decades has severely increased the toxicity of these landscapes for insects. It is therefore crucial that we understand how monarchs utilize neonicotinoid-contaminated plants and their impacts on monarch health to better inform conservation efforts. We monitored monarch usage of milkweed (Asclepias syriaca) plantings adjacent to clothianidin-treated and untreated cornfields and found both were utilized with equal frequency. We then examined how plant-mediated larval clothianidin exposure affected monarch development, morphology, and energetics by tracking mortality rates, development times, body metrics, and metabolic rates across life stages. We found no difference in mortality rates or body metrics between the 2 treatment groups. Larvae feeding on clothianidin-treated plants required less time to reach pupation than those feeding on control plants, but there was no difference in the time between pupation and eclosion. Larval clothianidin exposure did not affect the resting metabolic rates of monarchs at any life stage; however, it lowered both the average and peak flight metabolic rates of adults, with the effects being stronger in males than females. These findings suggest that larval exposure to clothianidin-contaminated plants can have carry-over sublethal effects in adulthood, which may adversely affect flight capacity, particularly in males. Further studies are needed to elucidate the possible impacts on crucial aspects of monarch ecology, including their foraging, migratory, and reproductive potential.

Life stage dependent effects of neonicotinoid exposure on honey bee hypopharyngeal gland development

Functional Apis mellifera honey bee colonies rely on collaborative brood care typically performed by nurse bees with well-developed hypopharyngeal glands (HPGs). Neonicotinoids, widely used insecticides, have been shown to negatively affect HPG development when worker bees were exposed to field-realistic concentrations either as brood or adults. To date, it is unknown whether timing of neonicotinoid exposure influences the severity of these observed negative effects on HPGs. To address this, we conducted a fully-crossed field experiment assessing potential effects of a neonicotinoid blend (clothianidin and thiamethoxam combined) on worker HPGs when exposed during different life stages. We found that neonicotinoid exposure during the brood stage, but not the adult stage, significantly influenced subsequent HPG development. Since HPG morphogenesis begins during the brood stage, neonicotinoid-induced stress possibly impaired this process, resulting in smaller glands once these individuals became adult nurses. Because HPG productivity is correlated to their size, smaller glands as a result of neonicotinoid exposure could negatively affect colony functionality.

Bumble bees do not avoid field-realistic but innocuous concentrations of cadmium and copper

Bee populations are facing numerous stressors globally, including environmental pollution by trace metals and metalloids. Understanding whether bees can detect and avoid these pollutants in their food is pivotal, as avoidance abilities may mitigate their exposure to xenobiotics. While these pollutants are known to induce sublethal effects in bees, such as disrupting physiological mechanisms, their potential impacts on locomotive abilities, fat metabolism, and reproductive physiology remain poorly understood. In this study, utilising workers of the buff-tailed bumble bee and two prevalent trace metals, namely cadmium and copper, we aimed to address these knowledge gaps for field-realistic concentrations. Our findings reveal that workers did not reject field-realistic concentrations of cadmium and copper in sucrose solutions. Moreover, they did not reject lethal concentrations of cadmium, although they rejected lethal concentrations of copper. Additionally, we observed no significant effects of field-realistic concentrations of these metals on the walking and flying activities of workers, nor on their fat metabolism and reproductive physiology. Overall, our results suggest that bumble bees may not avoid cadmium and copper at environmental concentrations, but ingestion of these metals in natural settings may not adversely affect locomotive abilities, fat metabolism, or reproductive physiology. However, given the conservative nature of our study, we still recommend future research to employ higher concentrations over longer durations to mimic conditions in heavily polluted areas (i.e., mine surrounding). Furthermore, investigations should ascertain whether field-realistic concentrations of metals exert no impact on bee larvae.

Milkweed in agricultural field margins - A neonicotinoid exposure route for pollinators at multiple life stages

Neonicotinoid insecticides move from targeted crops to wildflowers located in adjacent field margins, acting as a potential exposure source for wild pollinators and insect species of conservation concern, including monarch butterflies. Monarchs rely on milkweed over multiple life stages, including as a host plant for eggs and a food source for both larvae (leaves) and adults (flowers). Milkweeds, which are closely associated with field margins, can contain neonicotinoid residues, but previous assessments are constrained to a single plant tissue type. In 2017 and 2018, we sampled milkweeds from 95 field margins adjacent to crop fields (corn, soybean, hay, wheat, and barley) in agricultural landscapes of eastern Ontario, Canada. Milkweeds were sampled during the flower blooming period and leaves and flower tissues were analysed. The neonicotinoids acetamiprid, clothianidin, thiamethoxam, and thiacloprid were detected. Maximum concentrations in leaf samples included 10.30 ng/g of clothianidin in 2017, and 24.4 ng/g of thiamethoxam in 2018. Clothianidin and thiamethoxam percent detections in flowers (72 % and 61 %, respectively) were significantly higher than detections in leaves (24 % and 31 %, respectively). Thiamethoxam concentrations were significantly higher in paired flower samples than leaf samples (median 0.33 ng/g vs <0.07 ng/g) while clothianidin concentrations also trended higher in flowers (median 0.18-0.55 ng/g vs <0.18 ng/g). Only thiamethoxam showed significant differences between years, and we found no effect of crop type, with hay, soybean and corn fields all yielding 50-56 % detections in leaves. We found significantly higher concentrations in older milkweed flowers than young flowers or leaves (medians 0.87 ng/g vs <0.18 ng/g and 0.45 ng/g vs <0.07 ng/g for clothianidin and thiamethoxam, respectively). Our results highlight the importance of considering variation in milkweed tissue type and age of flowers in neonicotinoid exposure risk assessments. Efforts to increase milkweed availability in agricultural landscapes should consider how exposure to neonicotinoids can be mitigated.

Nutrition, pesticide exposure, and virus infection interact to produce context-dependent effects in honey bees (Apis mellifera)

Declines in pollinator health are frequently hypothesized to be the combined result of multiple interacting biotic and abiotic stressors; namely, nutritional limitations, pesticide exposure, and infection with pathogens and parasites. Despite this hypothesis, most studies examining stressor interactions have been constrained to two concurrent factors, limiting our understanding of multi-stressor dynamics. Using honey bees as a model, we addressed this gap by studying how variable diet, field-realistic levels of multiple pesticides, and virus infection interact to affect survival, infection intensity, and immune and detoxification gene expression. Although we found evidence that agrochemical exposure (a field-derived mixture of chlorpyrifos and two fungicides) can exacerbate infection and increase virus-induced mortality, this result was nutritionally-dependent, only occurring when bees were provided artificial pollen. Provisioning with naturally-collected polyfloral pollen inverted the effect, reducing virus-induced mortality and suggesting a hormetic response. To test if the response was pesticide specific, we repeated our experiment with a pyrethroid (lambda-cyhalothrin) and a neonicotinoid (thiamethoxam), finding variable results. Finally, to understand the underpinnings of these effects, we measured viral load and expression of important immune and detoxification genes. Together, our results show that multi-stressor interactions are complex and highly context-dependent, but have great potential to affect bee health and physiology.

Transfer and bioaccumulation of pesticides in terrestrial arthropods and food webs: State of knowledge and perspectives for research

Arthropods represent an entry point for pesticide transfers in terrestrial food webs, and pesticide accumulation in upper chain organisms, such as predators can have cascading consequences on ecosystems. However, the mechanisms driving pesticide transfer and bioaccumulation in food webs remain poorly understood. Here we review the literature on pesticide transfers mediated by terrestrial arthropods in food webs. The transfer of pesticides and their potential for bioaccumulation and biomagnification are related to the chemical properties and toxicokinetic of the substances, the resistance and detoxification abilities of the contaminated organisms, as well as by their effects on organisms' life history traits. We further identify four critical areas in which knowledge gain would improve future predictions of pesticides impacts on terrestrial food webs. First, efforts should be made regarding the effects of co-formulants and pesticides mixtures that are currently understudied. Second, progress in the sensitivity of analytical methods would allow the detection of low concentrations of pesticides in small individual arthropods. Quantifying pesticides in arthropods preys, their predators, and arthropods or vertebrates at higher trophic level would bring crucial insights into the bioaccumulation and biomagnification potential of pesticides in real-world terrestrial food webs. Finally, quantifying the influence of the trophic structure and complexity of communities on the transfer of pesticides could address several important sources of variability in bioaccumulation and biomagnification across species and food webs. This narrative review will inspire future studies aiming to quantify pesticide transfers in terrestrial food webs to better capture their ecological consequences in natural and cultivated landscapes.

High pesticide exposure and risk to bees in pollinator plantings adjacent to conventionally managed blueberry fields

Wildflower plantings adjacent to agricultural fields provide diverse floral resources and nesting sites for wild bees. However, their proximity to pest control activities in the crop may result in pesticide exposure if pesticides drift into pollinator plantings. To quantify pesticide residues in pollinator plantings, we sampled flowers and soil from pollinator plantings and compared them to samples from unenhanced field margins and crop row middles. At conventionally managed farms, flowers from pollinator plantings had similar exposure profiles to those from unenhanced field margins or crop row middles, with multiple pesticides and high and similar risk quotient (RQ) values (with pollinator planting RQ: 3.9; without pollinator planting RQ: 4.0). Whereas samples from unsprayed sites had significantly lower risk (RQ: 0.005). Soil samples had overall low risk to bees. Additionally, we placed bumble bee colonies (Bombus impatiens) in field margins of crop fields with and without pollinator plantings and measured residues in bee-collected pollen. Pesticide exposure was similar in pollen from sites with or without pollinator plantings, and risk was generally high (with pollinator planting RQ: 0.5; without pollinator planting RQ: 1.1) and not significant between the two field types. Risk was lower at sites where there was no pesticide activity (RQ: 0.3), but again there was no significant difference between management types. The insecticide phosmet, which is used on blueberry farms for control of Drosophila suzukii, accounted for the majority of elevated risk. Additionally, analysis of pollen collected by bumble bees found no significant difference in floral species richness between sites with or without pollinator plantings. Our results suggest that pollinator plantings do not reduce pesticide risk and do not increase pollen diversity collected by B. impatiens, further highlighting the need to reduce exposure through enhanced IPM adoption, drift mitigation, and removal of attractive flowering weeds prior to insecticide applications.

Divergent impacts of the neonicotinoid insecticide, clothianidin, on flight performance metrics in two species of migratory butterflies

Long-distance flight is crucial for the survival of migratory insects, and disruptions to their flight capacity can have significant consequences for conservation. In this study, we examined how a widely used insecticide, clothianidin (class: neonicotinoid), impacted the flight performance of two species of migratory butterflies, monarchs (Danaus plexippus) and painted ladies (Vanessa cardui). To do this, we quantified the free-flight energetics and tethered-flight velocity and distance of the two species using flow-through respirometry and flight mill assays. Our findings show differential effects of the pesticide on the two species. For painted ladies, we found that clothianidin exposure reduced average free-flight metabolic rates, but did not affect either average velocity or total distance during tethered flight. Other studies have linked low flight metabolic rates with reduced dispersal capacity, indicating that clothianidin exposure may hinder painted lady flight performance in the wild. Conversely, for monarchs, we saw no significant effect of clothianidin exposure on average free-flight metabolic rates but did observe increases in the average velocity, and for large individuals, total distance achieved by clothianidin-exposed monarchs in tethered flight. This suggests a potential stimulatory response of monarchs to low-dose exposures to clothianidin. These findings indicate that clothianidin exposure has the potential to influence the flight performance of butterflies, but that not all species are impacted in the same way. This highlights the need to be thoughtful when selecting performance assays, as different assays can evaluate fundamentally distinct aspects of physiology, and as such may yield divergent results.

Negative but antagonistic effects of neonicotinoid insecticides and ectoparasitic mites Varroa destructor on Apis mellifera honey bee food glands

Collaborative brood care by workers is essential for the functionality of eusocial Apis mellifera honey bee colonies. The hypopharyngeal food glands of workers play a crucial role in this context. Even though there is consensus that ubiquitous ectoparasitic mites Varroa destructor and widespread insecticides, such as neonicotinoids, are major stressors for honey bee health, their impact alone and in combination on the feeding glands of workers is poorly understood. Here, we show that combined exposure to V. destructor and neonicotinoids antagonistically interacted on hypopharyngeal gland size, yet they did not interact on emergence body mass or survival. While the observed effects of the antagonistic interaction were less negative than expected based on the sum of the individual effects, hypopharyngeal gland size was still significantly reduced. Alone, V. destructor parasitism negatively affected emergence body mass, survival, and hypopharyngeal gland size, whereas neonicotinoid exposure reduced hypopharyngeal gland size only. Since size is associated with hypopharyngeal gland functionality, a reduction could result in inadequate brood care. As cooperative brood care is a cornerstone of eusociality, smaller glands could have adverse down-stream effects on inclusive fitness of honey bee colonies. Therefore, our findings highlight the need to further study how ubiquitous stressors like V. destructor and neonicotinoids interact to affect honey bees.

Review on effects of some insecticides on honey bee health

Insecticides, one of the main agrochemicals, are useful for controlling pests; however, the indiscriminate use of insecticides has led to negative effects on nontarget insects, especially honey bees, which are essential for pollination services. Different classes of insecticides, such as neonicotinoids, pyrethroids, chlorantraniliprole, spinosad, flupyradifurone and sulfoxaflor, not only negatively affect honey bee growth and development but also decrease their foraging activity and pollination services by influencing their olfactory sensation, memory, navigation back to the nest, flight ability, and dance circuits. Honey bees resist the harmful effects of insecticides by coordinating the expression of genes related to immunity, metabolism, and detoxification pathways. To our knowledge, more research has been conducted on the effects of neonicotinoids on honey bee health than those of other insecticides. In this review, we summarize the current knowledge regarding the effects of some insecticides, especially neonicotinoids, on honey bee health. Possible strategies to increase the positive impacts of insecticides on agriculture and reduce their negative effects on honey bees are also discussed.

Are native bees in Brazil at risk from the exposure to the neonicotinoid imidacloprid?

All across the world, different countries use Ecological risk assessments (ERA) of pesticides to pollinators as a regulatory tool to understand the safety of pesticide use in agriculture. However, pesticide application is still recognized as one of the main stress factors causing a decline in the global population of bees. In all ERA procedures, the effects of pesticides on the honey bee species Apis mellifera are used as a reference for the effects on all different bee species. To evaluate if tropical native bees are protected by the current risk assessment procedures and to propose improvements to the methods, we assessed the ecological risk of the neonicotinoid imidacloprid posed to native and exotic bee species. The risk was assessed through a low (TIER I) and an intermediate (TIER II) level of analysis. For TIER I the USEPA BeeREX model was used and for TIER II the Species Sensitivity Distribution (SSD) approach was adopted. For the imidacloprid exposure conditions, four different crops were taken into consideration; bean, passion fruit, sunflower and tomato. The imidacloprid risk on native species was assessed both by extrapolating the effects obtained to Apis species, and by using ecotoxicological data from tests performed with native species. In TIER I, the risks calculated through empirical data showed that more than 50% of the non-Apis species presented risk levels of 28-180% higher than those obtained with the extrapolation factor used in the Brazilian pesticide regulation. In TIER II, the SSDs showed that most of the native bees are more sensitive to imidacloprid than the Africanized A. mellifera. This is the first study in which an ERA of a pesticide was conducted on tropical bee species. Here we also present some gaps and perspectives for future studies aiming to improve the risk assessment of pesticides in terrestrial environments.

Butenolide Insecticide Flupyradifurone Affects Honey Bee Worker Antiviral Immunity and Survival

Honey bees face many environmental stressors, including exposure to pesticides and pathogens. A novel butenolide pesticide, flupyradifurone, was recently introduced to the US and shown to have a bee-friendly toxicity profile. Like the much-scrutinized neonicotinoids that preceded it, flupyradifurone targets the insect nervous system. Some neonicotinoids have been shown to interfere with antiviral immunity, which raised the concern that similar effects may be observed with flupyradifurone. In this study, we investigated how flupyradifurone and a neonicotinoid, clothianidin, affect the ability of honey bee workers to combat an infection of Israeli acute paralysis virus (IAPV). We exposed workers to field-realistic doses of the pesticides either with or without co-exposure with the virus, and then tracked survival and changes in viral titers. We repeated the experiment in the spring and fall to look for any seasonal effects. We found that flupyradifurone caused elevated mortality in the fall, but it did not lead to increased virus-induced mortality. Flupyradifurone also appeared to affect virus clearance, as bees co-exposed to the pesticide and virus tended to have higher viral titers after 48 hours than those exposed to the virus alone. Clothianidin had no effect on viral titers, and it actually appeared to increase resistance to viral infection in spring bees.

Neonicotinoid contamination in wildflowers collected from citrus orchards in a northwestern Mediterranean Region (Spain) after tree foliar treatments

Ground-cover vegetation attracts and harbors beneficial insects to the agrosystem, playing an important role in conservation biological control. Integrated pest management (IPM) program guidelines recommend the implantation of sowed or resident wild covers in perennial crops. Given the high-quality fruit requirements, even in IPM programs, insecticides can be required in citrus crops. This study presents, over a year, the levels of neonicotinoids (thiamethoxam and imidacloprid) in not-target ground-cover wildflowers growing spontaneously in citrus orchards after foliar treatment of citrus trees. The presence and persistence of these neonicotinoids in different wildflower species were studied. Concentrations of thiamethoxam and imidacloprid in whole wildflowers ranged from < method quantification limit (MQL) to 52.9 ng g-1 and from < MQL to 98.6 ng g-1, respectively. Thiamethoxam was more frequently detected than imidacloprid. Thiamethoxam and imidacloprid were detected up to 336 and 230 days after treatment, respectively. The highest detection frequencies (100%) and highest thiamethoxam and imidacloprid mean concentrations (26.0 ± 7.3 ng g-1 and 11.0 ± 10.6 ng g-1, respectively) occurred in wildflowers collected 9 days after the treatments. Since application, a clear decrease in the concentration of both compounds and differences in the accumulation depending on wildflower species were observed. Cross contamination was detected, indicating a transport from adjacent treated plots. Maintaining a cover crop in citrus orchards may lead to detrimental effects on non-target arthropods if these neonicotinoid compounds are used for pest control since they can entail a chronic exposure during at least 230 days for imidacloprid and 336 days for thiamethoxam.

Pollinator nutrition and its role in merging the dual objectives of pollinator health and optimal crop production

Bee and non-bee insect pollinators play an integral role in the quantity and quality of production for many food crops, yet there is growing evidence that nutritional challenges to pollinators in agricultural landscapes are an important factor in the reduction of pollinator populations worldwide. Schemes to enhance crop pollinator health have historically focused on floral resource plantings aimed at increasing pollinator abundance and diversity by providing more foraging opportunities for bees. These efforts have demonstrated that improvements in bee diversity and abundance are achievable; however, goals of increasing crop pollination outcomes via these interventions are not consistently met. To support pollinator health and crop pollination outcomes in tandem, habitat enhancements must be tailored to meet the life-history needs of specific crop pollinators, including non-bees. This will require greater understanding of the nutritional demands of these taxa together with the supply of floral and non-floral food resources and how these interact in cropping environments. Understanding the mechanisms underlying crop pollination and pollinator health in unison across a range of taxa is clearly a win–win for industry and conservation, yet achievement of these goals will require new knowledge and novel, targeted methods.

This article is part of the theme issue ‘Natural processes influencing pollinator health: from chemistry to landscapes’.

Agrochemical occurrence on colocated wildflowers and wild bees collected near beef cattle feed yards and row crops

It is well established that agrochemicals can pose significant threats to native pollinators; however, relatively little is known about pollinator risks associated with agrochemicals that are used on beef cattle feed yards. Recently, feed yard-derived agrochemicals and those from row crop agriculture were quantified on wildflowers growing on the High Plains, USA. To better characterize pollinator risks on the High Plains, we collected colocated wildflowers and foraging bees across three field seasons for analytical determination of residual agrochemicals. Agrochemicals were detected and quantified on the majority of wildflowers (85%) and nearly half of bees (49%). Permethrin was the most frequently detected analyte on wildflowers (32%) and bees (17%). Flower hazard quotients and flower hazard indices were calculated to deterministically evaluate risk to foraging pollinators. Mean flower hazard quotients exceeded one for 5/16 analytes (31%), and flower hazard quotients calculated for 30% of wildflowers were greater than 50. Flower hazard quotients for clothianidin exceeded 400 for 14% of wildflowers, which portends conditions conducive to frequent bee mortalities. Flower hazard indices were greater on wildflowers from mid-July to mid-September as compared with wildflowers collected earlier in the summer, which coincides with row crop planting and increased prevalence of feed yard flies. Hazard quotients and hazard index values calculated from agrochemical residue data suggest that pollinators frequenting wildflowers near beef cattle feed yards and row crops on the High Plains are at risk from both individual sources, and more so when considered in combination. Integr Environ Assess Manag 2022;18:163-173. © 2021 SETAC.

Inferring pesticide toxicity to honey bees from a field-based feeding study using a colony model and Bayesian inference

Honey bees are crucial pollinators for agricultural crops but are threatened by a multitude of stressors including exposure to pesticides. Linking our understanding of how pesticides affect individual bees to colony-level responses is challenging because colonies show emergent properties based on complex internal processes and interactions among individual bees. Agent-based models that simulate honey bee colony dynamics may be a tool for scaling between individual and colony effects of a pesticide. The U.S. Environmental Protection Agency (USEPA) and U.S. Department of Agriculture (USDA) are developing the VarroaPop + Pesticide model, which simulates the dynamics of honey bee colonies and how they respond to multiple stressors, including weather, Varroa mites, and pesticides. To evaluate this model, we used Approximate Bayesian Computation to fit field data from an empirical study where honey bee colonies were fed the insecticide clothianidin. This allowed us to reproduce colony feeding study data by simulating colony demography and mortality from ingestion of contaminated food. We found that VarroaPop + Pesticide was able to fit general trends in colony population size and structure and reproduce colony declines from increasing clothianidin exposure. The model underestimated adverse effects at low exposure (36 µg/kg), however, and overestimated recovery at the highest exposure level (140 µg/kg), for the adult and pupa endpoints, suggesting that mechanisms besides oral toxicity-induced mortality may have played a role in colony declines. The VarroaPop + Pesticide model estimates an adult oral LD50 of 18.9 ng/bee (95% CI 10.1-32.6) based on the simulated feeding study data, which falls just above the 95% confidence intervals of values observed in laboratory toxicology studies on individual bees. Overall, our results demonstrate a novel method for analyzing colony-level data on pesticide effects on bees and making inferences on pesticide toxicity to individual bees.

Synergistic and Antagonistic Interactions Between Varroa destructor Mites and Neonicotinoid Insecticides in Male Apis mellifera Honey Bees

Pressures from multiple, sometimes interacting, stressors can have negative consequences to important ecosystem-service providing species like the western honey bee (Apis mellifera). The introduced parasite Varroa destructor and the neonicotinoid class of insecticides each represent important, nearly ubiquitous biotic and abiotic stressors to honey bees, respectively. Previous research demonstrated that they can synergistically interact to negatively affect non-reproductive honey bee female workers, but no data exist on how concurrent exposure may affect reproductive honey bee males (drones). This is important, given that the health of reproductive females (queens), possibly because of poor mating, is frequently cited as a major driver of honey bee colony loss. To address this, known age cohorts of drones were obtained from 12 honey bee colonies—seven were exposed to field-relevant concentrations of two neonicotinoids (4.5 ppb thiamethoxam and 1.5 ppb clothianidin) during development via supplementary pollen patties; five colonies received patties not spiked with neonicotinoids. Artificially emerged drones were assessed for natural V. destructor infestation, weighed, and then allocated to the following treatment groups: 1. Control, 2. V. destructor only, 3. Neonicotinoid only, and 4. Combined (both mites and neonicotinoid). Adult drones were maintained in laboratory cages alongside attendant workers (1 drone: 2 worker ratio) until they have reached sexual maturity after 14 days so sperm concentration and viability could be assessed. The data suggest that V. destructor and neonicotinoids interacted synergistically to negatively affect adult drone survival, but that they interacted antagonistically on emergence mass. Although sample sizes were too low to assess the effects of V. destructor and combined exposure on sperm quality, we observed no influence of neonicotinoids on sperm concentration or viability. Our findings highlight the diverse effects of concurrent exposure to stressors on honey bees, and suggest that V. destructor and neonicotinoids can severely affect the number of sexually mature adult drones available for mating.

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.

Use of nest bundles to monitor agrochemical exposure and effects among cavity nesting pollinators

Cavity nesting bees are proficient and important pollinators that can augment or replace honey bee pollination services for some crops. Relatively little is known about specific pesticide concentrations present in cavity nesting insect reed matrices and associated potential risks to cavity nesting bees. Nesting substrates (Phragmites australis reeds in bundles) were deployed in an agriculturally intensive landscape to evaluate colonization and agrochemical exposure among cavity nesting pollinators over two consecutive field seasons. Composition of insect species colonizing reeds within nest bundles varied considerably; those placed near beef cattle feed yards were dominated by wasps (93% of the total number of individuals occupying reed nest bundles), whereas nest bundles deployed in cropland-dominated landscapes were colonized primarily by leaf cutter bees (71%). All nesting/brood matrices in reeds (mud, leaves, brood, pollen) contained agrochemicals. Mud used in brood chamber construction at feed yard sites contained 21 of 23 agrochemicals included in analysis and >70% of leaf substrate stored in reeds contained at least one agrochemical. Moxidectin was most frequently detected across all reed matrices from feed yard sites, and moxidectin concentrations in nonviable larvae were more than four times higher than those quantified in viable larvae. Agrochemical concentrations in leaf material and pollen were also quantified at levels that may have induced toxic effects among developing larvae. To our knowledge, this is the first study to characterize agrochemical concentrations in multiple reed matrices provisioned by cavity-nesting insects. Use of nest bundles revealed that cavity nesting pollinators in agriculturally intensive regions are exposed to agrochemicals during all life stages, at relatively high frequencies, and at potentially lethal concentrations. These results demonstrate the utility of nest bundles for characterizing risks to cavity nesting insects inhabiting agriculturally intensive regions.

Impacts of neonicotinoid seed treatments on the wild bee community in agricultural field margins

Wild bees support global agroecosystems via pollination of agricultural crops and maintaining diverse plant communities. However, with an increased reliance on pesticides to enhance crop production, wild bee communities may inadvertently be affected through exposure to chemical residues. Laboratory and semi-field studies have demonstrated lethal and sublethal effects of neonicotinoids on limited genera (e.g., Apis, Bombus, Megachile), yet full field studies evaluating impacts to wild bee communities remain limited. Here, we conducted a two-year field study to assess whether neonicotinoid seed treatment and presence in environmental media (e.g., soil, flowers) influenced bee nest and diet guild abundance and richness. In 2017 and 2018, we planted 23 Missouri agricultural fields to soybeans (Glycine max) using one of three seed treatments: untreated (no insecticide), treated (imidacloprid), or previously-treated (untreated, but neonicotinoid use prior to 2017). During both years, wild bees were collected in study field margins monthly (May to September) in tandem with soil and flowers from fields and field margins that were analyzed for neonicotinoid residues. Insecticide presence in soils and flowers varied over the study with neonicotinoids infrequently detected in both years within margin flowers (0%), soybean flowers (<1%), margin soils (<8%), and field soils (~39%). Wild bee abundance and species richness were not significantly different among field treatments. In contrast, neonicotinoid presence in field soils was associated with significantly lower richness (ground- and aboveground-nesting, diet generalists) of wild bee guilds. Our findings support that soil remains an underexplored route of exposure and long-term persistence of neonicotinoids in field soils may lead to reduced diversity in regional bee communities. Future reduction or elimination of neonicotinoid seed treatment use on areas managed for wildlife may facilitate conservation goals to sustain viable, diverse wild bee populations.

Can Solar Energy Fuel Pollinator Conservation?

As the expansion of solar power spreads through much of the United States, members of the solar industry are working to change how solar energy facilities are designed and presented to the public. This includes the addition of habitat to conserve pollinators. We highlight and discuss ongoing efforts to couple solar energy production with pollinator conservation, noting recent legal definitions of these practices. We summarize key studies from the field of ecology, bee conservation, and our experience working with members of the solar industry (e.g., contribution to legislation defining solar pollinator habitat). Several recently published studies that employed similar practices to those proposed for solar developments reveal features that should be replicated and encouraged by the industry. These results suggest the addition of native, perennial flowering vegetation will promote wild bee conservation and more sustainable honey beekeeping. Going forward, there is a need for oversight and future research to avoid the misapplication of this promising but as of yet untested practice of coupling solar energy production with pollinator-friendly habitat. We conclude with best practices for the implementation of these additions to realize conservation and agricultural benefits.

Newer characters, same story: neonicotinoid insecticides disrupt food webs through direct and indirect effects

During the Green Revolution, older classes of insecticides contributed to biodiversity loss by decreasing insect populations and bioaccumulating across food webs. Introduction of Integrated Pest Management (IPM) improved stewardship of insecticides and promised fewer non-target effects. IPM adoption has waned in recent decades, and popularity of newer classes of insecticides, like the neonicotinoids, has surged, posing new and unique threats to insect populations. In this review, we first address how older classes of insecticides can affect trophic interactions, and then consider the influence of neonicotinoids on food webs and the role they may be playing in insect declines. We conclude by discussing challenges posed by current use patterns of neonicotinoids and how their risk can be addressed.

Measuring foraging preferences in bumble bees: a comparison of popular laboratory methods and a test for sucrose preferences following neonicotinoid exposure

Animals develop food preferences based on taste, nutritional quality and to avoid environmental toxins. Yet, measuring preferences in an experimental setting can be challenging since ecologically realistic assays can be time consuming, while simplified assays may not capture natural sampling behavior. Field realism is a particular challenge when studying behavioral responses to environmental toxins in lab-based assays, given that toxins can themselves impact sampling behavior, masking our ability to detect preferences. We address these challenges by comparing different experimental methods for measuring sucrose concentration preference in bumble bees (Bombus impatiens), evaluating the utility of two preference chamber-based methods (ad libitum versus a novel restricted-sampling assay) in replicating bees' preferences when they fly freely between artificial flowers in a foraging arena. We find that the restricted-sampling method matched a free-flying scenario more closely than the ad libitum protocol, and we advocate for expanded use of this approach, given its ease of implementation. We then performed a second experiment using the new protocol to ask whether consuming the neonicotinoid pesticide imidacloprid, known to suppress feeding motivation, interfered with the expression of sucrose preferences. After consuming imidacloprid, bees were less likely to choose the higher-quality sucrose even as they gained experience with both options. Thus, we provide evidence that pesticides interfere with bees' ability to discriminate between floral rewards that differ in value. This work highlights a simple protocol for assessing realistic foraging preferences in bees and provides an efficient way for researchers to measure the impacts of anthropogenic factors on preference expression.

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.

Small-Grain Cover Crops Have Limited Effect on Neonicotinoid Contamination from Seed Coatings

Neonicotinoids from insecticidal seed coatings can contaminate soil in treated fields and adjacent areas, posing a potential risk to nontarget organisms and ecological function. To determine if cover crops can mitigate neonicotinoid contamination in treated and adjacent areas, we measured neonicotinoid concentrations for three years in no-till corn-soybean rotations, planted with or without neonicotinoid seed coatings, and with or without small grain cover crops. Although neonicotinoids were detected in cover crops, high early season dissipation provided little opportunity for winter-planted cover crops to absorb significant neonicotinoid residues; small grain cover crops failed to mitigated neonicotinoid contamination in either treated or untreated plots. As the majority of neonicotinoids from seed coatings dissipated shortly after planting, residues did not accumulate in soil, but persisted at concentrations below 5 ppb. Persistent residues could be attributed to historic neonicotinoid use and recent, nearby neonicotinoid use. Tracking neonicotinoid concentrations over time revealed a large amount of local interplot movement of neonicotinoids; in untreated plots, contamination was higher when plots were less isolated from treated plots.

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. ​.

Whole-Body Acute Contact Toxicity of Formulated Insecticide Mixtures to Blue Orchard Bees (Osmia lignaria)

Blue orchard bees, [Osmia lignaria (Say) (Hymenoptera: Megachilidae)], have been developed as an important pollinator for orchard crops in North America over the last 40 years. The toxicity of several pesticides to O. lignaria and other Osmia species has been previously reported. However, the field-realistic toxicity of formulated premix insecticides comprised of multiple active ingredients (each with a different mode of action) to O. lignaria has not been assessed. Here, we use a customized spray tower in a laboratory setting to assess adult male and female whole-body direct contact exposure to four formulated pesticide mixtures: thiamethoxam + lambda-cyhalothrin (TLC), imidacloprid + beta-cyfluthrin (IBC), chlorantraniliprole + lambda-cyhalothrin (CLC) and methoxyfenozide + spinetoram (MS) by directly spraying anesthetized bees in Petri dishes. Separately, adult male and female whole-body direct contact exposure to formulated imidacloprid (I), beta-cyfluthrin (BC) and their 1:1 binary combination (IBC) was assessed using the same experimental method. Resulting mortality in each study was screened up to 96 h post-treatment to determine acute whole-body contact toxicity. In the first study, TLC and IBC resulted in statistically higher mortality at 24 and 48 h than the two other insecticide combinations tested. The CLC and MS combinations were slower acting and the highest mortality for O. lignaria exposed to these mixtures was recorded at 96 h. We did observe significant differences in toxicity between CLC and MS. In the second study, exposure to the 1:1 binary combination of IBC caused overall significantly higher mortality than exposure to I or BC alone. Both active ingredients alone, however, demonstrated equivalent levels of mortality to the 1:1 binary combination treatment at the 96 h observation reading, indicating increased speed of kill, but not necessarily increased toxicity. Significant differences in the onset of mortality following acute contact whole-body exposure to the formulated insecticide mixtures and individual active ingredients tested were consistently observed across all experiments in both studies.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 1: new molecules, metabolism, fate, and transport

With the exponential number of published data on neonicotinoids and fipronil during the last decade, an updated review of literature has been conducted in three parts. The present part focuses on gaps of knowledge that have been addressed after publication of the Worldwide Integrated Assessment (WIA) on systemic insecticides in 2015. More specifically, new data on the mode of action and metabolism of neonicotinoids and fipronil, and their toxicity to invertebrates and vertebrates, were obtained. We included the newly detected synergistic effects and/or interactions of these systemic insecticides with other insecticides, fungicides, herbicides, adjuvants, honeybee viruses, and parasites of honeybees. New studies have also investigated the contamination of all environmental compartments (air and dust, soil, water, sediments, and plants) as well as bees and apicultural products, food and beverages, and the exposure of invertebrates and vertebrates to such contaminants. Finally, we review new publications on remediation of neonicotinoids and fipronil, especially in water systems. Conclusions of the previous WIA in 2015 are reinforced; neonicotinoids and fipronil represent a major threat worldwide for biodiversity, ecosystems, and all the services the latter provide.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 2: impacts on organisms and ecosystems

New information on the lethal and sublethal effects of neonicotinoids and fipronil on organisms is presented in this review, complementing the previous Worldwide Integrated Assessment (WIA) in 2015. The high toxicity of these systemic insecticides to invertebrates has been confirmed and expanded to include more species and compounds. Most of the recent research has focused on bees and the sublethal and ecological impacts these insecticides have on pollinators. Toxic effects on other invertebrate taxa also covered predatory and parasitoid natural enemies and aquatic arthropods. Little new information has been gathered on soil organisms. The impact on marine and coastal ecosystems is still largely uncharted. The chronic lethality of neonicotinoids to insects and crustaceans, and the strengthened evidence that these chemicals also impair the immune system and reproduction, highlights the dangers of this particular insecticidal class (neonicotinoids and fipronil), with the potential to greatly decrease populations of arthropods in both terrestrial and aquatic environments. Sublethal effects on fish, reptiles, frogs, birds, and mammals are also reported, showing a better understanding of the mechanisms of toxicity of these insecticides in vertebrates and their deleterious impacts on growth, reproduction, and neurobehaviour of most of the species tested. This review concludes with a summary of impacts on the ecosystem services and functioning, particularly on pollination, soil biota, and aquatic invertebrate communities, thus reinforcing the previous WIA conclusions (van der Sluijs et al. 2015).

Preparation and electrochemical treatment application of Ti/Sb-SnO2-Eu&rGO electrode in the degradation of clothianidin wastewater

This work investigated the preparation of Ti/Sb-SnO₂ electrode co-doped with graphene and europium and the electrochemical degradation of clothianidin in aqueous solution with Ti/Sb-SnO₂-Eu&rGO electrode. The physicochemical properties of different electrodes were characterized by using the scanning electron microscopy, X-ray diffraction, oxygen evolution potential and cyclic voltammetry tests. The results indicated that the Ti/Sb-SnO₂-Eu&rGO electrodes have a compact structure and fine grain size and have a higher oxygen evolution overpotential than Ti/Sb-SnO₂-None, Ti/Sb-SnO₂-Eu and Ti/Sb-SnO₂-rGO electrodes. Among the four electrodes, the Ti/Sb-SnO₂-Eu&rGO electrode showed the highest efficiency and was chosen as the experimental electrode. The main influence factors on the degradation of clothianidin, such as initial pH, electrolyte concentration, current density and initial concentration of clothianidin, were analyzed. The results showed that the removal rate of clothianidin can reach 96.44% under the optimal conditions for 120 min treatment. Moreover, a possible degradation pathway including the fracture of internal bonds of clothianidin such as the N-N bond, the C-N bond that connects nitroguanidine to the thiazole ring and mineralization was elucidated by intermediate products identified by HPLC-MS method and Fourier transform infrared spectroscopy (FTIR). This paper introduces the Ti/Sb-SnO₂-Eu&rGO electrode into an electrocatalytic degradation system and could provide basic data and technique support and guidance for the clothianidin wastewater pollution control.

Diverging landscape impacts on macronutrient status despite overlapping diets in managed (Apis mellifera) and native (Melissodes desponsa) bees

Declining pollinator populations worldwide are attributed to multiple stressors, including the loss of quality forage. Habitat management in agricultural areas often targets honey bees (Apis mellifera L.) specifically, with the assumption that native bees will benefit from an 'umbrella species' strategy. We tested this theory using a conservation physiology approach to compare the effects of landscape composition and floral dietary composition on the physiological status of honey bees and Melissodes desponsa in eastern South Dakota, USA. The total glycogen, lipid and protein concentrations were quantified from field collected bees. Next-generation sequencing of the trnL chloroplast gene from bee guts was used to evaluate dietary composition. The effects of landscape and dietary composition on macronutrient concentrations were compared between bee species. As the mean land-use patch area increased, honey bee glycogen levels increased, though M. desponsa experienced a decrease in glycogen. Protein levels decreased in honey bees as the largest patch index, a measure of single patch dominance, increased versus M. desponsa. Lipids in both species were unaffected by the measured landscape variables. Dietary analysis revealed that honey bees foraged preferentially on weedy non-native plant species, while M. desponsa sought out native and rarer species, in addition to utilizing non-native plants. Both species foraged on Asteraceae, Oleaceae and Fabaceae, specifically Melilotus sp. and Medicago sp. Dietary composition was not predictive of the macronutrients measured for either species. Together, these data highlight the management importance of including patch area in conservation recommendations, as bee species may have divergent physiological responses to landscape characteristics. While solitary bees may forage on weedy introduced plants in agricultural areas, robust strategies should also reincorporate native plant species, though they may not be preferred by honey bees, to maximize overall health and diversity of pollinator communities.

Determination of Neonicotinoids in Honey Samples Originated from Poland and Other World Countries

A method development for determination of neonicotinoid residues in honey samples was developed. The proposed methodology consisted in QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe). That was used for sample preparation and UHPLC/UV (ultra-performance liquid chromatography with ultraviolet detection) utilized for chromatographic analysis. The developed method proved to be sensitive, with LOD (Limit of detection) value in the range of 60.80 to 80.98 ng/g hence LOQ (Limit of quantification) value was in the range of 184.26 to 245.40 ng/g. The method has tested on Polish honey and applied to honey from various countries (Bulgaria, Czech Republic, France, Greece, Italy, Portugal, Romania, Australia, Brazil, Cameroon, Russia, USA and Turkey). Several honey types were tested, while physicochemical properties of all honeys and were investigated. The methodology for general characterization of pollen grains originated from selected plants, to confirm the type of honey was also presented. There was a total lack of the mentioned neonicotinoids in sunflower honey. Except of this, only two samples of rapeseed and two samples of acacia honey (from Poland and Romania) were neonicotinoids free. In 19 samples the targeted pesticides were detected above LOQ. In all other investigated samples, the neonicotinoids were found at least at the LOD or LOQ level.

Beyond the Headlines: The Influence of Insurance Pest Management on an Unseen, Silent Entomological Majority

For most of the last two decades, insect pest management in key grain and oilseed crops has relied heavily on an insurance-based approach. This approach mandates a suite of management tactics prior to planting and in the absence of pest data. Because there is little flexibility for using these tactics individually, most producers have adopted this full suite of practices despite mounting evidence that some components do not provide consistent benefits. In North America in particular, this preventive approach to insect pest management has led to steep increases in use of neonicotinoid insecticides and subsequent increases in neonicotinoids in soil and water within crop fields and beyond. These increases have been accompanied by a host of non-target effects that have been most clearly studied in pollinators and insect natural enemies. Less attention has been given to the effects of this practice upon the many thousands of aquatic insect species that are often cryptic and offer negligible, or undefined, clear benefits to humans and their commerce. A survey of the literature reveals that the non-target effects of neonicotinoids upon these aquatic species are often as serious as for terrestrial species, and more difficult to address. By focusing upon charismatic insect species that provide clearly defined services, we are likely dramatically under-estimating the effects of neonicotinoids upon the wider environment. Given the mounting evidence base demonstrating that the pest management and crop yield benefits of this approach are negligible, we advocate for a return to largely-abandoned IPM principles as a readily accessible alternative path.

Positive Correlation between Pesticide Consumption and Longevity in Solitary Bees: Are We Overlooking Fitness Trade-Offs?

The ubiquitous use of pesticides is one major driver for the current loss of biodiversity, and the common practice of simultaneously applying multiple agrochemicals may further contribute. Insect toxicology currently has a strong focus on survival to determine the potential hazards of a chemical routinely used in risk evaluations. However, studies revealing no effect on survival or even indicating enhanced survival are likely to be misleading, if potential trade-offs between survival and other physiological factors are overlooked. Here, we used standard laboratory experiments to investigate the sublethal (i.e., food consumption) and lethal (i.e., survival) effects of two common agricultural pesticides (Roundup® and clothianidin) on adult female solitary bees, Osmia bicornis. The data showed no significant effect of the treatment on cumulative survival; however, a significant positive correlation between herbicide and insecticide exposure and age was revealed, i.e., bees exposed to higher dosages lived longer. As no significant differences in daily food consumption were observed across treatment groups, increased food intake can be excluded as a factor leading to the prolonged survival. While this study does not provide data on fitness effects, two previous studies using solitary bees observed significant negative effects of neonicotinoid insecticides on fitness, yet not on survival. Thus, we conjecture that the observed non-significant effects on longevity may result from a trade-off between survival and reproduction. The data suggest that a focus on survival can lead to false-negative results and it appears inevitable to include fitness or at least tokens of fitness at the earliest stage in future risk assessments.

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.

Chronic within-hive video recordings detect altered nursing behaviour and retarded larval development of neonicotinoid treated honey bees

Risk evaluations for agricultural chemicals are necessary to preserve healthy populations of honey bee colonies. Field studies on whole colonies are limited in behavioural research, while results from lab studies allow only restricted conclusions on whole colony impacts. Methods for automated long-term investigations of behaviours within comb cells, such as brood care, were hitherto missing. In the present study, we demonstrate an innovative video method that enables within-cell analysis in honey bee (Apis mellifera) observation hives to detect chronic sublethal neonicotinoid effects of clothianidin (1 and 10 ppb) and thiacloprid (200 ppb) on worker behaviour and development. In May and June, colonies which were fed 10 ppb clothianidin and 200 ppb thiacloprid in syrup over three weeks showed reduced feeding visits and duration throughout various larval development days (LDDs). On LDD 6 (capping day) total feeding duration did not differ between treatments. Behavioural adaptation was exhibited by nurses in the treatment groups in response to retarded larval development by increasing the overall feeding timespan. Using our machine learning algorithm, we demonstrate a novel method for detecting behaviours in an intact hive that can be applied in a versatile manner to conduct impact analyses of chemicals, pests and other stressors.

Acetylcholine and Its Receptors in Honeybees: Involvement in Development and Impairments by Neonicotinoids

Acetylcholine (ACh) is the major excitatory neurotransmitter in the insect central nervous system (CNS). However, besides the neuronal expression of ACh receptors (AChR), the existence of non-neuronal AChR in honeybees is plausible. The cholinergic system is a popular target of insecticides because the pharmacology of insect nicotinic acetylcholine receptors (nAChRs) differs substantially from their vertebrate counterparts. Neonicotinoids are agonists of the nAChR and are largely used in crop protection. In contrast to their relatively high safety for humans and livestock, neonicotinoids pose a threat to pollinating insects such as bees. In addition to its effects on behavior, it becomes increasingly evident that neonicotinoids affect developmental processes in bees that appear to be independent of neuronal AChRs. Brood food (royal jelly, worker jelly, or drone jelly) produced in the hypopharyngeal glands of nurse bees contains millimolar concentrations of ACh, which is required for proper larval development. Neonicotinoids reduce the secreted ACh-content in brood food, reduce hypopharyngeal gland size, and lead to developmental impairments within the colony. We assume that potential hazards of neonicotinoids on pollinating bees occur neuronally causing behavioral impairments on adult individuals, and non-neuronally causing developmental disturbances as well as destroying gland functioning.

Nutritional status of honey bee (Apis mellifera L.) workers across an agricultural land-use gradient

Land use, habitat, and forage quality have emerged as critical factors influencing the health, productivity, and survival of honey bee colonies. However, characterization of the mechanistic relationship between differential land-use conditions and ultimate outcomes for honey bee colonies has been elusive. We assessed the physiological health of individual worker honey bees in colonies stationed across a gradient of agricultural land use to ask whether indicators of nutritional physiology including glycogen, total sugar, lipids, and protein were associated with land-use conditions over the growing season and colony population size the subsequent spring during almond pollination. Across the observed land-use gradient, we found that September lipid levels related to growing-season land use, with honey bees from apiaries surrounded by more favorable land covers such as grassland, pasture, conservation land, and fallow fields having greater lipid reserves. Further, we observed a significant relationship between total protein during September and population size of colonies during almond pollination the following February. We demonstrate and discuss the utility of quantifying nutritional biomarkers to infer land-use quality and predict colony population size.

The Impact of Pesticides on Flower-Visiting Insects: A Review with Regard to European Risk Assessment

Flower-visiting insects (FVIs) are an ecologically diverse group of mobile, flying species that should be protected from pesticide effects according to European policy. However, there is an ongoing decline of FVI species, partly caused by agricultural pesticide applications. Therefore, the risk assessment framework needs to be improved. We synthesized the peer-reviewed literature on FVI groups and their ecology, habitat, exposure to pesticides, and subsequent effects. The results show that FVIs are far more diverse than previously thought. Their habitat, the entire agricultural landscape, is potentially contaminated with pesticides through multiple pathways. Pesticide exposure of FVIs at environmentally realistic levels can cause population-relevant adverse effects. This knowledge was used to critically evaluate the European regulatory framework of exposure and effect assessment. The current risk assessment should be amended to incorporate specific ecological properties of FVIs, that is, traits. We present data-driven tools to improve future risk assessments by making use of trait information. There are major knowledge gaps concerning the general investigation of groups other than bees, the collection of comprehensive data on FVI groups and their ecology, linking habitat to FVI exposure, and study of previously neglected complex population effects. This is necessary to improve our understanding of FVIs and facilitate the development of a more protective FVI risk assessment. Environ Toxicol Chem 2019;38:2355-2370. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Why are monarch butterflies declining in the West? Understanding the importance of multiple correlated drivers

Understanding the factors associated with declines of at-risk species is an important first step in setting management and recovery targets. This step can be challenging when multiple aspects of climate and land use are changing simultaneously, and any or all could be contributing to population declines. We analyzed population trends of monarch butterflies in western North America in relation to likely environmental drivers. Unlike the larger eastern monarch population, past analyses of western monarchs have only evaluated the importance of climate (i.e., not land use) factors as drivers of abundance. We used partial least squares regression (PLSR) to evaluate the potential importance of changes in land use and climate variables. Trends in western monarch abundance were more strongly associated with land use variables than climate variables. Conclusions about importance of climate and land use variables were robust to changes in PLSR model structure. However, individual variables were too collinear to unambiguously separate their effects. We compared these conclusions to the more widely used technique of multiple regression, followed by multi-model inference (MRMI). Naïve interpretation of MRMI results could be misleading, if collinearity were not taken into account. MRMI was also highly sensitive to variation in model construction. Our results suggest a two-pronged approach to monarch conservation, specifically, starting efforts now to restore habitat, while also using experiments to more clearly delineate separate effects of climate and land use factors. They also demonstrate the utility of PLSR, a technique that is growing in use but is still relatively under-appreciated in conservation biology.

An assessment of acute insecticide toxicity loading (AITL) of chemical pesticides used on agricultural land in the United States

We present a method for calculating the Acute Insecticide Toxicity Loading (AITL) on US agricultural lands and surrounding areas and an assessment of the changes in AITL from 1992 through 2014. The AITL method accounts for the total mass of insecticides used in the US, acute toxicity to insects using honey bee contact and oral LD₅₀ as reference values for arthropod toxicity, and the environmental persistence of the pesticides. This screening analysis shows that the types of synthetic insecticides applied to agricultural lands have fundamentally shifted over the last two decades from predominantly organophosphorus and N-methyl carbamate pesticides to a mix dominated by neonicotinoids and pyrethroids. The neonicotinoids are generally applied to US agricultural land at lower application rates per acre; however, they are considerably more toxic to insects and generally persist longer in the environment. We found a 48- and 4-fold increase in AITL from 1992 to 2014 for oral and contact toxicity, respectively. Neonicotinoids are primarily responsible for this increase, representing between 61 to nearly 99 percent of the total toxicity loading in 2014. The crops most responsible for the increase in AITL are corn and soybeans, with particularly large increases in relative soybean contributions to AITL between 2010 and 2014. Oral exposures are of potentially greater concern because of the relatively higher toxicity (low LD₅₀s) and greater likelihood of exposure from residues in pollen, nectar, guttation water, and other environmental media. Using AITL to assess oral toxicity by class of pesticide, the neonicotinoids accounted for nearly 92 percent of total AITL from 1992 to 2014. Chlorpyrifos, the fifth most widely used insecticide during this time contributed just 1.4 percent of total AITL based on oral LD₅₀s. Although we use some simplifying assumptions, our screening analysis demonstrates an increase in pesticide toxicity loading over the past 26 years, which potentially threatens the health of honey bees and other pollinators and may contribute to declines in beneficial insect populations as well as insectivorous birds and other insect consumers.

Honeybee dietary neonicotinoid exposure is associated with pollen collection from agricultural weeds

Neonicotinoid insecticides have been linked to bee declines. However, tracking the primary exposure route for bees in the field has proven to be a major logistical challenge, impeding efforts to restore pollinator health in agricultural landscapes. We quantified neonicotinoid concentrations and botanical species composition in 357 pollen samples collected from 114 commercial honeybee colonies placed along a gradient of agricultural intensity between June and September. Neonicotinoid concentrations increased through the season, peaking at the end of August. As a result, concentrations in pollen were negatively associated with collection from woody and crop plants that flower early-mid season, and positively associated with collection from herbaceous plants that flower mid-late season. Higher clothianidin and thiamethoxam residues were correlated with samples containing a greater proportion of pollen collected from agricultural weeds. The percentage of agricultural land within 1500 m was positively correlated with thiamethoxam concentration; however, this spatial relationship was far weaker than the relationship with the proportion of pollen collected from herbaceous plants. These results indicate that both plant species identity and agricultural dominance are important in determining honeybee neonicotinoid exposure through the pollen diet, but that uncultivated plants associated with agriculture are the source of the greatest acute exposure.