Lethal and sublethal effects, and incomplete clearance of ingested imidacloprid in honey bees (Apis mellifera)

Bumblebee (Bombus impatiens) queens prefer pesticide-contaminated soils when selecting underground hibernation sites

New evidence points to substantial impacts of exposure to pesticide residues in soil for a range of bee taxa that have close regular contact with this substrate. Among others, the risk of exposure is high for bumblebee (Bombus spp.) queens hibernating in agricultural soils. An important question is whether bumblebee queens can detect and avoid pesticide-contaminated soils, or whether they might be attracted to such agrochemical residues. To address this question, we performed a multiple-choice preference experiment in which newly emerged bumblebee (Bombus impatiens) queens were given access to arrays of 36 crates of soil treated with different pesticides in large mesh-covered enclosures. Five of the most commonly encountered pesticides in agricultural soils (boscalid, chlorantraniliprole, clothianidin, cyantraniliprole, difenoconazole) were selected for testing at two contamination levels (lower or higher), based on field-realistic exposure estimates. Bumblebee queens consistently avoided hibernating in pesticide-free soil at both contamination levels, while showing no avoidance for any pesticide-treated soil types. At the lower contamination level, queens selected the pesticide-free soil 1.3 to 2.4-fold less frequently on average than any of the spiked soils, while none of the queens from the higher contamination group selected pesticide-free soil. This apparent preference for pesticide-contaminated soils increases the likelihood of exposure to and potential hazard from pesticide residues in soil for bumblebee queens during hibernation, a critical and highly vulnerable period of their annual life cycle.

Influence of the pesticide flupyradifurone on mobility and physical condition of larval green lacewings

Global pesticide use in agriculture is one reason for the rapid insect decline in recent years. The relatively new pesticide flupyradifurone is neurotoxic to pest insects but considered harmless to bees according to previous risk assessments. With this study, we aim to investigate lethal and sublethal effects of flupyradifurone on larvae of the beneficial arthropod Chrysoperla carnea. We treated the animals orally with field-realistic concentrations of flupyradifurone and examined lethality as well as effects on condition, mobility and locomotion. For the lethal dose 50, we determined a value of > 120-200 ng/mg (corresponding to a mean amount of 219 ng/larva) after 168 h. Abnormal behaviors such as trembling and comatose larvae were observed even at the lowest concentration applied (> 0-20 ng/mg, 59 ng/larva). Mobility analysis showed impaired activity patterns, resulting in acute hypoactivity at all pesticide concentrations and time-delayed hyperactivity in larvae treated with > 40-60 ng/mg (100 ng/larva) and > 80-100 ng/mg (120 ng/larva), respectively. Even locomotion as a fundamental behavioral task was negatively influenced throughout larval development. In conclusion, our results demonstrate that flupyradifurone impacts life and survival of lacewing larvae and may pose-despite its status as bee-friendly-a major threat to insect fauna and environment.

Acute and chronic effects of sublethal neonicotinoid thiacloprid to Asian honey bee (Apis cerana cerana)

Pesticide pollution is one of the most important factors for global bee declines. Despite many studies have revealed that the most important Chinese indigenous species，Apis cerana, is presenting a high risk on exposure to neonicotinoids, the toxicology information on Apis cerana remain limited. This study was aimed to determine the acute and chronic toxic effects of thiacloprid (IUPAC name: {(2Z)-3-[(6-Chloro-3-pyridinyl)methyl]-1,3-thiazolidin-2-ylidene}cyanamide) on behavioral and physiological performance as well as genome-wide transcriptome in A. cerana. We found the 1/5 LC50 of thiacloprid significantly impaired learning and memory abilities after both acute and chronic exposure, nevertheless, has no effects on the sucrose responsiveness and phototaxis climbing ability of A. cerana. Moreover, activities of detoxification enzyme P450 monooxygenases and CarE were increased by short-term exposure to thiacloprid, while prolonged exposure caused suppression of CarE activity. Neither acute nor chronic exposure to thiacloprid altered honey bee AChE activities. To further study the potential defense molecular mechanisms in Asian honey bee under pesticide stress, we analyzed the transcriptomes of honeybees in response to thiacloprid stress. The transcriptomic profiles revealed consistent upregulation of immune- and stress-related genes by both acute or chronic treatments. Our results suggest that the chronic exposure to thiacloprid produced greater toxic effects than a single administration to A. cerana. Altogether, our study deepens the understanding of the toxicological characteristic of A. cerana against thiacloprid, and could be used to further investigate the complex molecular mechanisms in Asian honey bee under pesticide stress.

The Neonicotinoid Imidacloprid Impairs Learning, Locomotor Activity Levels, and Sucrose Solution Consumption in Bumblebees (Bombus terrestris)

Bumblebees carry out the complex task of foraging to provide for their colonies. They also conduct pollination, an ecosystem service of high importance to both wild plants and entomophilous crops. Insecticides can alter different aspects of bumblebee foraging behavior, including the motivation to leave the hive, finding the right flowers, handling flowers, and the ability to return to the colony. In the present study, we assessed how the neonicotinoid imidacloprid affects bumblebees' foraging behavior after exposure to four different treatment levels, including field-realistic concentrations (0 [control], 1, 10, and 100 μg/L), through sucrose solution over 9 days. We observed the behavior of several free-flying bumblebees simultaneously foraging on artificial flowers in a flight arena to register the bees' complex behavior postexposure. To conduct a detailed assessment of how insecticides affect bumblebee locomotor behavior, we used video cameras and analyzed the recordings using computer vision. We found that imidacloprid impaired learning and locomotor activity level when the bumblebees foraged on artificial flowers. We also found that imidacloprid exposure reduced sucrose solution intake and storage. By using automated analyses of video recordings of bumblebee behavior, we identified sublethal effects of imidacloprid exposure at field-realistic doses. Specifically, we observed negative impacts on consumption of sucrose solution as well as on learning and locomotor activity level. Our results highlight the need for more multimodal approaches when assessing the sublethal effects of insecticides and plant protection products in general. Environ Toxicol Chem 2023;42:1337-1345. © 2023 SETAC.

Sensitivity to imidacloprid insecticide varies among some social and solitary bee species of agricultural value

Pollinator health risks from long-lasting neonicotinoid insecticides like imidacloprid has primarily focused on commercially managed, cavity-nesting bees in the genera Apis, Bombus, and Osmia. We expand these assessments to include 12 species of native and non-native crop pollinators of differing levels of body size, sociality, and floral specialization. Bees were collected throughout 2016 and 2017 from flowering blueberry, squash, pumpkin, sunflower and okra in south Mississippi, USA. Within 30-60 minutes of capture, bees were installed in bioassay cages made from transparent plastic cups and dark amber jars. Bees were fed via dental wicks saturated with 27% (1.25 M) sugar syrup containing a realistic range of sublethal concentrations of imidacloprid (0, 5, 20, or 100 ppb) that are often found in nectar. Bees displayed no visible tremors or convulsions except for a small sweat bee, Halictus ligatus, and only at 100ppb syrup. Imidacloprid shortened the captive longevities of the solitary bees. Tolerant bee species lived ~10 to 12 days in the bioassays and included two social and one solitary species: Halictus ligatus, Apis mellifera and Ptilothrix bombiformis (rose mallow bees), respectively. No other bee species tolerated imidacloprid as well as honey bees did, which exhibited no appreciable mortality and only modest paralysis across concentration. In contrast, native bees either lived shorter lives, experienced longer paralysis, or endured both. Overall, longevity decreased with concentration linearly for social bees and non-linearly for solitary species. The percentage of a bee's captive lifespan spent paralyzed increased logarithmically with concentration for all species, although bumble bees suffered longest. Of greatest concern was comparable debilitation of agriculturally valuable solitary bees at both low and high sublethal rates of imidacloprid.

Method validation for simultaneous determination of four neonicotinoids in vegetables by liquid chromatography

Pesticides are widely employed to boost the production of vegetable crops, but their indiscriminate application leaves residue in the crops for long, even after harvesting. Among pesticides, neonicotinoids are the most commonly applied group of insecticides which are used on vegetables to defend against a variety of sucking pests. The purpose of this study was to validate an analytical approach focused on QuEChERS extraction for the validation and simultaneous determination of residues of four neonicotinoids (imidacloprid, clothianidin, acetamiprid and thiamethoxam) in six diverse crops such as cucumber, brinjal, tomato, beans, cabbage, and cauliflower. Insecticides were quantified using high-performance liquid chromatography (HPLC) fitted with a UV-Vis detector. Specificity, linearity, precision, accuracy, limit of detection, and the limit of quantification were all considered for validation. The fortification of the vegetables was done at three different levels (0.2, 0.3 and 0.5 µg mL^-1), for confirming the validity of the method adopted. The results demonstrated adequate recoveries ranging from 77.5 to 96.4% and good accuracy (RSDs between 0.3 and 8.9%). For all the insecticides, the approach had good linearity with R² ≥ 0.99. The limit of detection (LOD) and the limit quantification (LOQ) levels of all the four analytes were 0.05 µg mL^-1 and 0.2 µg mL^-1, respectively. The validation characteristics of the devised method are satisfactory in terms of specificity, linearity, precision, accuracy, limit of detection and limit of quantification and thus can be successfully employed for simultaneous determination of the neonicotinoids.

Water provisioning increases caged worker bee lifespan and caged worker bees are living half as long as observed 50 years ago

The high loss rates of honey bee colonies drive research for solutions aimed to mitigate these losses. While honey bee colonies are superorganisms, experiments that measure the response to stressors often use caged individuals to allow for inference in a controlled setting. In an initial experiment, we showed that caged honey bees provisioned with various types of water (deionized, 1%NaCl in deionized, or tap) have greater median lifespans than those that did not. While researching the history of water provisioning in cage studies, we observed that the median lifespan of caged honey bees has been declining in the US since the 1970's, from an average of 34.3 days to 17.7 days. In response to this, we again turned to historical record and found a relationship between this trend and a decline in the average amount of honey produced per colony per year in the US over the last 5 decades. To understand the relationship between individual bee lifespan and colony success we used an established honey bee population model (BEEHAVE) to simulate the predicted effects of decreased worker lifespans. Declines in downstream measures of colony population, overall honey production, and colony lifespan resulted from reduced worker bee lifespans. Modeled colony lifespans allowed us to estimate colony loss rates in a beekeeping operation where lost colonies are replaced annually. Resulting loss rates were reflective of what beekeepers' experience today, which suggests the average lifespan of individual bees plays an important role in colony success.

A Pilot Nationwide Survey on the Concentrations of Neonicotinoids and Their Metabolites in Indoor Dust from China: Application for Human Exposure

The present study assessed the residue levels of six parent neonicotinoids (p-NEOs) and four metabolites (m-NEOs) in indoor dust collected from 12 cities of China. Acetamiprid (ACE) and imidacloprid (IMI) were the predominated p-NEOs (detection rates: 98%) with the median values at 4.54 and 7.48 ng/g dry weight (dw), respectively. N-demethyl-acetamiprid (N-dm-ACE) was the most important m-NEO with the median value at 0.69 ng/g dw, while other m-NEOs were rarely detected (detection rates: < 15%). Significant correlation between ACE and thiacloprid (THD) was observed (p < 0.01), indicating their probably concurrent applications. ACE was significantly correlated to N-dm-ACE (p < 0.01), implicating the degradation of ACE in indoor environment. The estimated daily intake (EDI_ing) of NEOs via dust ingestion were far lower than the acceptable daily intake for NEOs. To our knowledge, this study provided a baseline nationwide investigation on the occurrence of NEOs in indoor dust of China.

An impact assessment of insecticides application on the non-targeted mosquito Aedes albopictus (Skuse) in Punjab rice fields, Pakistan

Insecticidal control of insect pests of rice crop may influence the environment and nontarget species in rice fields. Aedes albopictus, one of the most common nontarget species present in rice fields, received lethal and sublethal exposures to insecticides used in rice cultivated fields. The present work explores the effects of insecticides in six non-targeted Ae. albopictus strains collected from rice fields with a history of insecticidal usage in comparison with a laboratory susceptible reference strain (REF) and a strain (LHR) collected from a rice field with no, or minimal, history of insecticidal usage. Two types of effects, the resistance development and performance of biological traits, were studied by selecting seven commonly used insecticides in rice fields in Punjab, Pakistan. The results revealed that the strains collected from the rice fields with histories of insecticidal usage exhibited significant levels of resistance to flonicamid, chlorantraniliprole, gamma-cyhalothrin, fipronil, monomehypo, triazophos, and carbofuran, when compared with REF and LHR strains. In addition, Ae. albopictus strains revealed a significantly weaker performance of biological traits (rate of pupae formation, survival of male and female adults (except females of OKR and MTN strains), and ovipositing females) than those of the REF and LHR strains. However, the fecundity of all field strains was only significantly different with that of the REF strain. In conclusion, the results highlight the problem of the negative effects of insecticidal usage in rice fields on nontarget species present in the same environment, and emphasize the need to adopt pest management activities that are safe for the environment.

The impact of imidacloprid and thiacloprid on the mean species abundance in aquatic ecosystems

Neonicotinoids are currently the most widely used and sold insecticides in the world, providing effective pest control. Risk assessment of these and other pesticides by lab-based indicators is common. Yet, empirically and theoretically underpinning of extrapolation to indicators used in field surveys is severely limited. Consequently, the aim of our study was to quantify the toxicological and ecological impact of the neonicotinoids imidacloprid and thiacloprid to aquatic invertebrates. We derived Species Sensitivity Distributions (SSDs) based on chronic LC₅₀ data and Mean Species Abundance Relationships (MSARs), comparing these lab-based approaches to field data as well. MSARs are changes in mean species abundance (MSA) as a function of chemical exposure, providing insight into the overall decline of a community. The MSA expresses the mean abundance of species in disturbed conditions relative to their abundance in undisturbed habitat. The medians of the SSD of imidacloprid and thiacloprid for the different species were 16.45 μg/L and 26.40 μg/L, respectively. HC₅₀s of the MSAR of imidacloprid and thiacloprid were 4.25 μg/L and 5.12 μg/L, respectively. The three taxonomic groups tested (insects, crustaceans and mollusks) did not differ significantly in sensitivity for imidacloprid and thiacloprid, both according to the SSDs and MSARs derived. Quantile exposure-response curves (99%-tile) were plotted showing the relative abundance (RA) of aquatic invertebrate species at increasing imidacloprid levels. The 99%-tile of the Relative Abundances (RA₉₉) of species and corresponding imidacloprid concentrations monitored in field surveys in the Netherlands was significantly lower than the Potentially Affected Fraction (PAF) calculated from the SSD. Yet, the MSA was similar to the RA₉₉, suggesting that MSAR is an ecologically meaningful relationship for toxic stress estimated from lab data. Future efforts should be directed to additional empirical underpinning as well as determining the relationship of PAF to other metrics for ecosystem diversity and productivity.

Within-Body Distributions and Feeding Effects of the Neonicotinoid Insecticide Clothianidin in Bumblebees (Bombus terrestris)

Bumblebees can be exposed to neonicotinoid pesticides through nectar and pollen collected from treated crops, which can cause lethal and sublethal effects in these nontarget pollinators. However, the body distribution of the compound after exposure to neonicotinoids in bumblebees is not well studied. Bumblebee colonies (Bombus terrestris, n = 20) were exposed to field-realistic concentrations of clothianidin through artificial nectar (3.6-13 µg/L) for 9 d. Comparison of the nominal with the measured exposure in nectar indicated good compliance, confirming the applicability of the method. When quantified, clothianidin showed a concentration-dependent occurrence in the head and body of workers (head: <0.2-2.17 µg/kg; body: <0.2-3.17 µg/kg), and in the body of queens (<0.2-2.49 µg/kg), although concentrations were below those measured in the nectar (bioaccumulation factor = 0.2). Exposure to clothianidin did not affect mortality nor brood production, nor did it have a statistically significant effect on nectar consumption and size of food storage. However, visual inspection suggests higher nectar consumption of nectar with low clothianidin content compared with nectar with no or high clothianidin content. Our results show that dietary clothianidin is taken up in bumblebees, but does not bioaccumulate to elevated levels compared with exposure. Still, clothianidin may elicit responses that affect feeding behavior of the pollinator B. terrestris, although our endpoints were not significantly affected. Environ Toxicol Chem 2021;40:2781-2790. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Low Concentration of Quercetin Reduces the Lethal and Sublethal Effects of Imidacloprid on Apis cerana (Hymenoptera: Apidae)

Large-scale use of systemic pesticides has been considered a potential factor for pollinator population decline. Phytochemicals, e.g., quercetin, have been demonstrated to increase the pesticide tolerance of Apis mellifera Linnaeus (Hymenoptera: Apidae), which is helpful to develop strategies to reduce the pesticides hazards to pollinators. In this study, we hypothesized phytochemicals could reduce the detrimental effects of imidacloprid on Apis cerana Fabricius. The lethal and sublethal effects of imidacloprid on A. cerana workers were investigated. The results showed that A. cerana workers chronically exposed to 100 μg/liter imidacloprid had a significantly shorter longevity by 10.81 d compared with control. Acute exposure to imidacloprid at 100 μg/liter impaired the sucrose responsiveness and memory retention of the workers, and 20 μg/liter reduced the sucrose responsiveness. The treatment with 37.8 mg/liter quercetin for 24 h could increase the longevity of A. cerana workers when chronically exposed to 100 μg/liter imidacloprid, and 75.6 mg/liter quercetin feeding treatment alleviated the impairment of sucrose responsiveness. However, workers treated with 151.2 mg/liter and 75.6 mg/liter quercetin had a significantly shorter longevity compared to that of bees chronically exposed to 100 μg/liter imidacloprid without quercetin treatment. Our results suggested that quercetin treatment could produce a biphasic influence on the lethal effects of imidacloprid on A. cerana. Quercetin at 37.8 mg/liter and 75.6 mg/liter in the diet before pesticide exposure was able to reduce the lethal and sublethal effects of imidacloprid, respectively, providing potential strategies to reduce the pesticides hazards to native honey bees (A. cerana).

Ecotoxicity of imidacloprid to soil invertebrates in two tropical soils with contrasting texture

Imidacloprid is one of the most commercialized insecticides in agriculture in the world, with a broad spectrum of action. However, little is known about the effects of commercial formulations containing this active ingredient (a.i.) on non-target organisms in tropical soils. Our objective was to assess the toxicity based on the predicted environmental concentration (PEC) of imidacloprid, in the avoidance behaviour of earthworms and collembolans as well as in the reproduction of collembolans, in two representative soils of the Brazilian Cerrado with contrasting texture (clayey Oxisol and sandy Entisol). Ecotoxicity tests were carried out according to ISO protocols to assess the avoidance behaviour of earthworms (Eisenia andrei) and avoidance and reproduction of collembolans (Folsomia candida). In the earthworm's avoidance test, more than 80% of the individuals were found in the control, in all tested concentrations, indicating a possible habitat function loss in both soils. The avoidance behaviour of collembolans was observed in both soils, being more expressive (up to 75% of escape) in Oxisol. In Entisol, only the two highest concentrations were avoided (up to 63%). There was a negative effect on the reproduction of collembolans in both soils, with a higher EC₅₀ value (0.255 mg kg^-1) in Oxisol than in Entisol (0.177 mg kg^-1), demonstrating higher toxicity in the sandy soil. These differences were attributed to the contrasting texture of the studied soils, probably due to lower retention of the a.i. in the sandy soil, causing an increased bioavailability. This study demonstrated that imidacloprid can be highly toxic to soil invertebrates, even in soil concentrations lower than those expected from recommended dose, causing an impact on the edaphic organisms and, consequently, compromising its functions in the soil ecosystem.

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).

IPM-recommended insecticides harm beneficial insects through contaminated honeydew

The use of some systemic insecticides has been banned in Europe because they are toxic to beneficial insects when these feed on nectar. A recent study shows that systemic insecticides can also kill beneficial insects when they feed on honeydew. Honeydew is the sugar-rich excretion of hemipterans and is the most abundant carbohydrate source for beneficial insects such as pollinators and biological control agents in agroecosystems. Here, we investigated whether the toxicity of contaminated honeydew depends on i) the hemipteran species that excretes the honeydew; ii) the active ingredient, and iii) the beneficial insect that feeds on it. HPLC-MS/MS analyses demonstrated that the systemic insecticides pymetrozine and flonicamid, which are commonly used in Integrated Pest Management programs, were present in honeydew excreted by the mealybug Planococcus citri. However, only pymetrozine was detected in honeydew excreted by the whitefly Aleurothixus floccosus. Toxicological studies demonstrated that honeydew excreted by mealybugs feeding on trees treated either with flonicamid or pymetrozine increased the mortality of the hoverfly Sphaerophoria rueppellii, but did not affect the parasitic wasp Anagyrusvladimiri. Honeydew contaminated with flonicamid was more toxic for the hoverfly than that contaminated with pymetrozine. Collectively, our data demonstrate that systemic insecticides commonly used in IPM programs can contaminate honeydew and kill beneficial insects that feed on it, with their toxicity being dependent on the active ingredient and hemipteran species that excretes the honeydew.

Oral acute toxicity and impact of neonicotinoids on Apis mellifera L. and Scaptotrigona postica Latreille (Hymenoptera: Apidae)

Wild and managed bees are essential for crop pollination and food production. However, the widespread use of insecticides such as neonicotinoids may affect the survival, development, behavior, and maintenance of bee colonies. Therefore, in this study we evaluated the impacts of three neonicotinoid insecticides on the survival and walking abilities of the Africanized honeybee A. mellifera and stingless bee S. postica. A. mellifera was more susceptible than S. postica to all neonicotinoids tested. The median lethal concentrations LC₅₀ values estimated for acetamiprid, imidacloprid, and thiacloprid were 189.62, 22.78, and 142.31 ng µL^-1 of diet for A. mellifera, and 475.94, 89.11, and 218.21 ng µL^-1 of diet for S. postica, respectively. All tested neonicotinoids affected the speed, distance traveled, duration and frequency of resting, and continuous mobility of both bee species. The results showed that in spite of the different susceptibility to compounds with cyano and nitro radicals, the behavioral variables showed different levels of commitment according to the molecule insecticide and bee species. These results contribute not only to the understanding of the effects of neonicotinoid insecticides on A. mellifera and S. postica, but also to help in the development of protocols that aim to reduce the impact of these insecticides in Neotropical environments.

A review of the factors that influence pesticide residues in pollen and nectar: Future research requirements for optimising the estimation of pollinator exposure

In recent years, the impact of Plant Protection Products (PPPs) on insect pollinator decline has stimulated significant amounts of research, as well as political and public interest. PPP residues have been found in various bee-related matrices, resulting in governmental bodies worldwide releasing guidance documents on methods for the assessment of the overall risk of PPPs to different bee species. An essential part of these risk assessments are PPP residues found in pollen and nectar, as they represent a key route of exposure. However, PPP residue values in these matrices exhibit large variations and are not available for many PPPs and crop species combinations, which results in inaccurate estimations and uncertainties in risk evaluation. Additionally, residue studies on pollen and nectar are expensive and practically challenging. An extrapolation between different cropping scenarios and PPPs is not yet justified, as the behaviour of PPPs in pollen and nectar is poorly understood. Therefore, this review aims to contribute to a better knowledge and understanding of the fate of PPP residues in pollen and nectar and to outline knowledge gaps and future research needs. The literature suggests that four primary factors, the crop type, the application method, the physicochemical properties of a compound and the environmental conditions have the greatest influence on PPP residues in pollen and nectar. However, these factors consist of many sub-factors and initial effects may be disguised by different sampling methodologies, impeding their exact characterisation. Moreover, knowledge about these factors is ambiguous and restricted to a few compounds and plant species. We propose that future research should concentrate on identifying relationships and common features amongst various PPP applications and crops, as well as an overall quantification of the described parameters; in order to enable a reliable estimation of PPP residues in pollen, nectar and other bee matrices.

Dietary risk of neonicotinoid insecticides through fruit and vegetable consumption in school-age children

Although the systemic property of neonicotinoid (neonics) has become the most widely used insecticide worldwide since late 1990s, the current literature offers limited information about the human dietary intake and the potential risks of neonics. In this study, we aimed to assess the cumulative risk of total neonics intakes through fruit and vegetable consumption in 58 children ages 8-12 participated in the Hangzhou China (HZC) study over 5 consecutive weekends. Individual neonic residues in each food item were aggregated using the relative potency factor approach into a single metric (IMI_RPF), representing dietary intakes of imidacloprid-equivalent total neonics. We then estimated the average daily intake (ADI) of total neonics through fruit and vegetable consumption and evaluated the cumulative dietary risk of neonics. All of the 123 samples were detected with at least one neonic. Commonly consumed foods, such as carrots, green vegetables, baby cabbage, and apple were found with more than 6 neonics. The estimated ADIs of total neonics vegetable and fruit consumption using the mean IMI_RPF for apples and green vegetables, two most consumed food items, were 237.1*10^-6 and 106.8*10^-6 mg/kg/day, respectively. Although the estimated ADIs were below the current chronic reference dose (cRfD) of imidacloprid, we have stipulated the possible future downward revision of cRfD. The potential health risk of neonics to children via dietary exposure should raise more public concern considering the increase use of neonics and the ubiquitous presence in fruits and vegetables.

The novel pesticide flupyradifurone (Sivanto) affects honeybee motor abilities

Honeybees and other pollinators are threatened by changing landscapes and pesticides resulting from intensified agriculture. In 2018 the European Union prohibited the outdoor use of three neonicotinoid insecticides due to concerns about pollinators. A new pesticide by the name of "Sivanto" was recently released by Bayer AG. Its active ingredient flupyradifurone binds to the nicotinic acetylcholine receptor (AchR) in the honeybee brain, similar to neonicotinoids. Nevertheless, flupyradifurone is assumed to be harmless for honeybees and can even be applied on flowering crops. So far, only little has been known about sublethal effects of flupyradifurone on honeybees. Intact motor functions are decisive for numerous behaviors including foraging and dancing. We therefore selected a motor assay to investigate in how far sublethal doses of this pesticide affect behavior in young summer and long-lived winter honeybees. Our results demonstrate that flupyradifurone (830 µmol/l) can evoke motor disabilities and disturb normal motor behavior after a single oral administration (1.2 µg/bee). These effects are stronger in long-lived winter bees than in young summer bees. After offering an equal amount of pesticide (1.0-1.75 µg) continuously over 24 h with food the observed effects are slighter. For comparisons we repeated our experiments with the neonicotinoid imidacloprid. Intriguingly, the alterations in behavior induced by this pesticide (4 ng/bee) were different and longer-lasting compared to flupyradifurone, even though both substances bind to nicotinic acetylcholine receptors.

Late effect of larval co-exposure to the insecticide clothianidin and fungicide pyraclostrobin in Africanized Apis mellifera

Among the factors that contribute to the reduction of honeybee populations are the pesticides. These chemical compounds reach the hive through forager bees, and once there, they can be ingested by the larvae. We evaluated the effects of repeated larval exposure to neonicotinoid insecticide, both in isolation and in combination with strobilurin fungicide, at environmentally relevant doses. The total consumption of the contaminated diet was 23.63 ng fungicide/larvae (pyraclostrobin) and 0.2364 ng insecticide/larvae (clothianidin). The effects on post-embryonic development were evaluated over time. Additionally, we assessed the survival pattern of worker bees after emergence, and the pesticides’ effects on the behavior of newly emerged workers and young workers. Young bees that were exposed to the fungicide and those subjected to co-exposure to both pesticides during larval phase showed behavioral changes. The insecticide, both in isolation and in combination with fungicide reduced the bees’ longevity; this effect of larval exposure to pesticides was stronger in bees that were exposed only to the insecticide. Although the larvae did not have sensitivity to exposure to pesticides, they showed later effects after emergence, which may compromise the dynamics of the colony, contributing to the reduction of the populations of bees in agroecosystems.

Time-to-death approach to reveal chronic and cumulative toxicity of a fungicide for honeybees not revealed with the standard ten-day test

Synthetic fungicides are pesticides widely used in agriculture to control phytopathogenic fungi. The systemicity, persistency and intense application of some of these fungicides, such as boscalid, leads to long periods of exposure for honeybees via contaminated water, pollen and nectar. We exposed adult honeybees in the lab to food contaminated with boscalid for 33 days instead of the standard 10-day test. Most of the toxic effects were observed after 10 days. The median time to death (LT₅₀) ranged from 24.9 days (lowest concentration) to 7.1 days (highest concentration) and was significantly shorter in all cases than with the control (32.0 days). The concentration and dietary doses of boscalid inducing 50% mortality (LC₅₀ and LDD₅₀, respectively) decreased strongly with the time of exposure: LC₅₀ = 14,729 and 1,174 mg/l and LDD₅₀ = 0.318 and 0.0301 mg bee⁻¹ day⁻¹ at days 8 and 25, respectively. We found evidence of reinforced toxicity when exposure is prolonged, but with an unusual pattern: no cumulative toxicity is observed until 17–18 days, when a point of inflexion appears that suggests a reduced capacity of bees to deal with the toxicant. Our results show the importance of time-to-death experiments rather than fixed-duration studies for evaluating chronic toxicity.

Lethal and sub-lethal effects of select macrocyclic lactones insecticides on forager worker honey bees under laboratory experimental conditions

Selective insecticide application is one important strategy for more precisely targeting harmful insects while avoiding or mitigating collateral damage to beneficial insects like honey bees. Recently, macrocyclic lactone-class insecticides have been introduced into the market place as selective bio-insecticides for controlling many arthropod pests, but how to target this selectivity only to harmful insects has yet to be achieved. In this study, the authors investigated the acute toxicity of fourmacrocyclic lactone insecticides (commercialized as abamectin, emamectin benzoate, spinetoram, and spinosad) both topically and through feeding studies with adult forager honey bees. Results indicated emamectin benzoate as topically 133.3, 750.0, and 38.3-fold and orally 3.3, 7.6, and 31.7-fold more toxic, respectively than abamectin, spinetoram and spinosad. Using Hazard Quotients for estimates of field toxicity, abamectin was measured as the safest insecticide both topically and orally for honey bees. Moreover, a significant reduction of sugar solution consumption by treatment group honey bees for orally applied emamectin benzoate and spinetoram suggests that these insecticides may have repellent properties.

The pesticide flupyradifurone impairs olfactory learning in Asian honey bees (Apis cerana) exposed as larvae or as adults

Relatively little attention has focused on how pesticides may affect Asian honey bees, which provide vital crop pollination services and are key native pollinators. We therefore studied the effects of a relatively new pesticide, flupyradifurone (FLU), which has been developed, in part, because it appears safer for honey bees than neonicotinoids. We tested the effects of FLU on Apis cerana olfactory learning in larvae (lower dose of 0.033 µg/larvae/day over 6 days) and, in a separate experiment, adults (lower dose of 0.066 µg/adult bee/day) at sublethal, field-realistic doses given over 3 days. A worst-case field-realistic dose is 0.44 µg/bee/day. Learning was tested in adult bees. The lower larval dose did not increase mortality, but the lower adult dose resulted in 20% mortality. The lower FLU doses decreased average olfactory learning by 74% (larval treatment) and 48% (adult treatment) and reduced average memory by 48% (larval treatment) and 22% (adult treatment) as compared to controls. FLU at higher doses resulted in similar learning impairments. The effects of FLU, a pesticide that is reported to be safer than neonicotinoids for honey bees, thus deserve greater attention.