Interaction patterns and combined toxic effects of acetamiprid in combination with seven pesticides on honey bee (Apis mellifera L.)

Influence of on-farm pesticide practices and processing methods on pesticide residue levels in potato tubers (Solanum tuberosum L.) in Nyandarua County, Kenya

In Kenya, the extensive use of agrochemicals in potato farming raises concerns about pesticide residues in potato tubers and products. This study aimed to document the pesticide application practices of potato farmers in Nyandarua County, Kenya and evaluate the effect of the practices on pesticide residues levels in raw potato tubers. Also, the study evaluated the effect of various heat processing methods on the pesticide residue levels in potatoes. A cross-sectional survey using semi-structured questionnaires was conducted on 275 randomly selected farmers. Alongside, raw Shangi potato variety samples (n=16) from respective farmers were analyzed for some of the most commonly used pesticide residues using LC-MS/MS and GC-MS/MS. The study found that 98.8% of farmers use synthetic pesticides, with 96.4% using fungicides, 68.2% insecticides, and 28.7% herbicides. Common fungicides contained mancozeb, metalaxyl, and cymoxanil as the main active ingredients. Insecticides contained α-cypermethrin and imidacloprid, while herbicides had glyphosate and 2,4-D as the main active ingredients. These chemicals were used either alone or in mixtures. Only 11.85% of farmers adhered to recommended manufacturer's application rates, with the majority relying on advice from agrochemical retailers (74.63%) or other farmers (13.32%). The frequent mixing of pesticides and weekly applications were also common practices. Residue analysis revealed that adherence to the manufacturer's instructions resulted in lower residue levels. Mixing pesticides and frequent applications led to higher residues, particularly for fungicides containing azoxystrobin. Longer preharvest intervals generally reduced residue levels. Most of the pesticide residues were below the EU and Codex Maximum Residue Limits (MRLs) limits in potatoes, however, the banned insecticides containing chlorpyrifos and fenitrothion were found at levels exceeding the EU and Codex MRLs of 0.01mg/kg. Processing methods such as frying, baking, boiling, and steaming significantly reduced pesticide residues,below the Codex MRLs. Frying and boiling were particularly effective for most pesticides. However, baking, roasting, and frying were not effective in reducing chlorpyrifos and fenitrothion below EU and Codex MRLs. The findings highlight the need for farmer education on proper pesticide use and adherence to recommended practices to minimize residue levels and ensure food safety.

Semi-field studies on biochemical markers of honey bee workers (Apis mellifera) after exposure to pesticides and their mixtures

Due to the fact that many different pesticides are used in crop production and their residues can accumulate in the environment, bees are in contact with various pesticides at the same time. Most studies on their influence on honey bees focus on single substances in concentrations higher than those found in the environment. Our study assessed the chronic effects of commonly used pesticides and their mixtures on selected biochemical markers in worker bee hemolymph. Workers developed in the hive and were provisioned with to pesticides in concentrations corresponding to residues detected in pollen, honey, and/or nectar. Colonies were exposed daily to 0.5L for 7 days by feeding a sugar syrup containing a formulation of acetamiprid (250 ppb) (insecticide), glyphosate (7200 ppb) (herbicide), and tebuconazole (147 ppb) (fungicide) administered alone, in a binary or ternary mixture. Administered alone, acetamiprid significantly decreased the level of urea in the hemolymph of worker honey bees. Glyphosate did not affect significantly the level/activity of any of the biochemical markers. Tebuconazole caused changes in the levels of most of the studied biochemical markers. We found that tebuconazole, which as a fungicide is generally considered safe for bees, may be harmful and more research is required. The impact of fungicides is a crucial element of the assessment of threats to honey bees.

Disease Management in Regenerative Cropping in the Context of Climate Change and Regulatory Restrictions

Regenerative agriculture as a term and concept has gained much traction over recent years. Many farmers are convinced that by adopting these principles they will be able to address the triple crisis of biodiversity loss, climate change, and food security. However, the impact of regenerative agriculture practices on crop pathogens and their management has received little attention from the scientific community. Significant changes to cropping systems may result in certain diseases presenting more or less of a threat. Shifts in major diseases may have significant implications regarding optimal integrated pest management (IPM) strategies that aim to improve profitability and productivity in an environmentally sensitive manner. In particular, many aspects of regenerative agriculture change risk levels and risk management in ways that are central to effective IPM. This review outlines some of the challenges, gaps, and opportunities in our understanding of appropriate approaches for managing crop diseases in regenerative cropping systems.

Short- and long-term effects of commercial formulations of imidacloprid, spirotetramat, and mixtures of these active ingredients on pupae of Diaeretiella rapae (Hymenoptera: Braconidae) and its progeny

BACKGROUND

Compatibility studies of insecticides and natural enemies usually focus on short-term lethal effects, without considering the long-term sublethal effects (including progeny). Even less-explored are the effects of commercial insecticides formulated with more than one active product. Short- and long-term lethal and sublethal effects were studied for the first time on the progeny of commercial formulations of spirotetramat, imidacloprid and a commercial mixture of these active ingredients on pupae of Diaeretiella rapae (M'ntosh) (Hymenoptera: Braconidae), an endoparasitoid of aphids considered to be a potential biological control agent. Insecticides were exposed topically on aphid mummies in which the parasitoid was in the pupal stage.

RESULTS

Imidacloprid reduced adult emergence by more than 30% and prolonged intra-host development time with respect to control from half the maximum recommended field dose (MFRD). Spirotetramat and commercial mixture only showed significant effects on these endpoints at doses above the MFRD. The tested formulations did not affect adult longevity, sex ratio, and percentage of parasitism in the exposed generation. At low concentrations the active ingredients in the commercial mixture behave synergistically, whereas at medium and high concentrations they behave antagonistically. Considering the 10% lethal dose (LD10), imidacloprid showed the highest hazard coefficient, whereas the commercial mixture was more hazardous when considering the LD50 and LD90. The commercial mixture and imidacloprid induced higher adult emergence and altered the sex ratio in the progeny.

CONCLUSIONS

The following order of toxicity on D. rapae can be established: imidacloprid > commercial mixture > spirotetramat. Joint use of this species with imidacloprid and commercial mixture should be avoided in integrated pest management programs. © 2024 Society of Chemical Industry.

Relative impacts of Varroa destructor (Mesostigmata:Varroidae) infestation and pesticide exposure on honey bee colony health and survival in a high-intensity corn and soybean producing region in northern Iowa

The negative effects of Varroa and pesticides on colony health and survival are among the most important concerns to beekeepers. To compare the relative contribution of Varroa, pesticides, and interactions between them on honey bee colony performance and survival, a 2-year longitudinal study was performed in corn and soybean growing areas of Iowa. Varroa infestation and pesticide content in stored pollen were measured from 3 apiaries across a gradient of corn and soybean production areas and compared to measurements of colony health and survival. Colonies were not treated for Varroa the first year, but were treated the second year, leading to reduced Varroa infestation that was associated with larger honey bee populations, increased honey production, and higher colony survival. Pesticide detections were highest in areas with high-intensity corn and soybean production treated with conventional methods. Pesticide detections were positively associated with honey bee population size in May 2015 in the intermediate conventional (IC) and intermediate organic (IO) apiaries. Varroa populations across all apiaries in October 2015 were negatively correlated with miticide and chlorpyrifos detections. Miticide detections across all apiaries and neonicotinoid detections in the IC apiary in May 2015 were higher in colonies that survived. In July 2015, colony survival was positively associated with total pesticide detections in all apiaries and chlorpyrifos exposure in the IC and high conventional (HC) apiaries. This research suggests that Varroa are a major cause of reduced colony performance and increased colony losses, and honey bees are resilient upon low to moderate pesticide detections.

Combined effect of a neonicotinoid insecticide and a fungicide on honeybee gut epithelium and microbiota, adult survival, colony strength and foraging preferences

Fungicides, insecticides and herbicides are widely used in agriculture to counteract pathogens and pests. Several of these molecules are toxic to non-target organisms such as pollinators and their lethal dose can be lowered if applied as a mixture. They can cause large and unpredictable problems, spanning from behavioural changes to alterations in the gut. The present work aimed at understanding the synergistic effects on honeybees of a combined in-hive exposure to sub-lethal doses of the insecticide thiacloprid and the fungicide penconazole. A multidisciplinary approach was used: honeybee mortality upon exposure was initially tested in cage, and the colonies development monitored. Morphological and ultrastructural analyses via light and transmission electron microscopy were carried out on the gut of larvae and forager honeybees. Moreover, the main pollen foraging sources and the fungal gut microbiota were studied using Next Generation Sequencing; the gut core bacterial taxa were quantified via qPCR. The mortality test showed a negative effect on honeybee survival when exposed to agrochemicals and their mixture in cage but not confirmed at colony level. Microscopy analyses on the gut epithelium indicated no appreciable morphological changes in larvae, newly emerged and forager honeybees exposed in field to the agrochemicals. Nevertheless, the gut microbial profile showed a reduction of Bombilactobacillus and an increase of Lactobacillus and total fungi upon mixture application. Finally, we highlighted for the first time a significant honeybee diet change after pesticide exposure: penconazole, alone or in mixture, significantly altered the pollen foraging preference, with honeybees preferring Hedera pollen. Overall, our in-hive results showed no severe effects upon administration of sublethal doses of thiacloprid and penconazole but indicate a change in honeybees foraging preference. A possible explanation can be that the different nutritional profile of the pollen may offer better recovery chances to honeybees.

Sublethal Effects of Four Insecticides Targeting Cholinergic Neurons on Partner and Host Finding in the Parasitic Wasp Nasonia vitripennis

Lethal and sublethal effects of pesticides on nontarget organisms are one of the causes of the current decline of many insect species. However, research in the past decades has focused primarily on pollinators, although other beneficial nontarget organisms such as parasitic wasps may also be affected. We studied the sublethal effects of the four insecticides acetamiprid, dimethoate, flupyradifurone, and sulfoxaflor on pheromone-mediated sexual communication and olfactory host finding of the parasitic wasp Nasonia vitripennis. All agents target cholinergic neurons, which are involved in the processing of chemical information by insects. We applied insecticide doses topically and tested the response of treated wasps to sex pheromones and host-associated chemical cues. In addition, we investigated the mating rate of insecticide-treated wasps. The pheromone response of females surviving insecticide treatment was disrupted by acetamiprid (≥0.63 ng), dimethoate (≥0.105 ng), and flupyradifurone (≥21 ng), whereas sulfoxaflor had no significant effects at the tested doses. Olfactory host finding was affected by all insecticides (acetamiprid ≥1.05 ng, dimethoate ≥0.105 ng, flupyradifurone ≥5.25 ng, sulfoxaflor ≥0.52 ng). Remarkably, females treated with ≥0.21 ng dimethoate even avoided host odor. The mating rate of treated N. vitripennis couples was decreased by acetamiprid (6.3 ng), flupyradifurone (≥2.63 ng), and sulfoxaflor (2.63 ng), whereas dimethoate showed only minor effects. Finally, we determined the amount of artificial nectar consumed by N. vitripennis females within 48 h. Considering this amount (∼2 µL) and the maximum concentrations of the insecticides reported in nectar, tested doses can be considered field-realistic. Our results suggest that exposure of parasitic wasps to field-realistic doses of insecticides targeting the cholinergic system reduces their effectiveness as natural enemies by impairing the olfactory sense. Environ Toxicol Chem 2023;42:2400-2411. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Sulfoxaflor effects depend on the interaction with other pesticides and Nosema ceranae infection in the honey bee (Apis mellifera)

Honey bees health is compromised by many factors such as the use of agrochemicals in agriculture and the various diseases that can affect them. Multiple studies have shown that these factors can interact, producing a synergistic effect that can compromise the viability of honey bees. This study analyses the interactions between different pesticides and the microsporidium Nosema ceranae and their effect on immune and detoxification gene expression, sugar consumption and mortality in the Iberian western honey bee (Apis mellifera iberiensis). For this purpose, workers were infected with N. ceranae and subjected to a sugar-water diet with field concentrations of the pesticides sulfoxaflor, azoxystrobin and glyphosate. Increased sugar intake and altered immune and cytochrome P450 gene expression were observed in workers exposed to sulfoxaflor and infected with N. ceranae. None of the pesticides affected Nosema spore production in honey bee gut. Of the three pesticides tested (alone or in combination) only sulfoxaflor increased mortality in honey bees. Taken together, our results suggest that the effects of sulfoxaflor were attenuated in contact with other pesticides, and that Nosema infection leads to increase sugar intake in sulfoxaflor-exposed bees. Overall, this underlines the importance of studying the interaction between different stressors to understand their overall impact not only on honey bee but also on wild bees health.

Pesticide residues in honey bee (Apis mellifera) pollen collected in two ornamental plant nurseries in Connecticut: Implications for bee health and risk assessment

Honey bees (Apis mellifera L.) are one of the most important managed pollinators of agricultural crops. While potential effects of agricultural pesticides on honey bee health have been investigated in some settings, risks to honey bees associated with exposures occurring in the plant nursery setting have received little attention. We sought to identify and quantify pesticide levels present in honey bee-collected pollen harvested in two ornamental plant nurseries (i.e., Nursery A and Nursery B) in Connecticut. From June to September 2018, pollen was collected weekly from 8 colonies using bottom-mounted pollen traps. Fifty-five unique pesticides (including related metabolites) were detected: 24 insecticides, 20 fungicides, and 11 herbicides. Some of the pesticide contaminants detected in the pollen had not been applied by the nurseries, indicating that the honey bee colonies did not exclusively forage on pollen at their respective nursery. The average number of pesticides per sample was similar at both nurseries (i.e., 12.9 at Nursery A and 14.2 at Nursery B). To estimate the potential risk posed to honey bees from these samples, we utilized the USEPA's BeeREX tool to calculate risk quotients (RQs) for each pesticide within each sample. The median aggregate RQ for nurse bees was 0.003 at both nurseries, well below the acute risk level of concern (LOC) of ≥0.4. We also calculated RQs for larvae due to their increased sensitivity to certain pesticides. In total, 6 samples had larval RQs above the LOC (0.45-2.51), resulting from the organophosphate insecticide diazinon. Since 2015, the frequency and amount of diazinon detected in pollen increased at one of our study locations, potentially due to pressure to reduce the use of neonicotinoid insecticides. Overall, these data highlight the importance of considering all life stages when estimating potential risk to honey bee colonies from pesticide exposure.

Acaricidal Toxicity of Four Essential Oils, Their Predominant Constituents, Their Mixtures against Varroa Mite, and Their Selectivity to Honey Bees (Apis cerana and A. mellifera)

The honey bee (Apis mellifera) faces a significant threat from Varroa destructor, causing the losses of millions of colonies worldwide. While synthetic acaricides are widely used to control Varroa infestations, excessive application has led to resistant strains and poses side effects on the host. Consequently, there is an urgent need for a new acaricide that is both effective and affordable, yet safe to use on bees. One potential source of these acaricides is essential oils (EOs) and their constituents. This study evaluated the acaricidal properties of four essential oils (Eucalyptus globulus, Rosemary officinalis, Trachyspermum ammi (Ethiopian and Indian varieties), their constituents and mixture of constituents against V. destructor through the complete exposure method. Our finding showed that a 1:1 mixture of thymol and carvacrol (4 h-LC50 = 42 μg/mL), thymol (4 h-LC50 = 71 μg/mL), and T. ammi oil (4 h-LC50 = 81-98 μg/mL) were the most toxic test samples against V. destructor. Honey bee behavior and selectivity were also assessed with one additional EO Thymus schimperi, indicating that T. schimperi, T. ammi, and their components were selective and did not affect the learning and memory of bees. In conclusion, the thymol and carvacrol (1:1) mixture was shown to be a promising replacement for synthetic acaricides, being three times more toxic than a commercial acaricide, fluvalinate (4 h-LC50 = 143 μg/mL).

Implementing IPM in crop management simultaneously improves the health of managed bees and enhances the diversity of wild pollinator communities

Impacts of insecticide use on the health of wild and managed pollinators have been difficult to accurately quantify in the field. Existing designs tend to focus on single crops, even though highly mobile bees routinely forage across crop boundaries. We created fields of pollinator-dependent watermelon surrounded by corn, regionally important crops in the Midwestern US. These fields were paired at multiple sites in 2017-2020 with the only difference being pest management regimes: a standard set of conventional management (CM) practices vs. an integrated pest management (IPM) system that uses scouting and pest thresholds to determine if/when insecticides are used. Between these two systems we compared the performance (e.g., growth, survival) of managed pollinators-honey bees (Apis mellifera), bumble bees (Bombus impatiens)-along with the abundance and diversity of wild pollinators. Compared to CM fields, IPM led to higher growth and lower mortality of managed bees, while also increasing the abundance (+ 147%) and richness (+ 128%) of wild pollinator species, and lower concentrations of neonicotinoids in the hive material of both managed bees. By replicating realistic changes to pest management, this experiment provides one of the first demonstrations whereby tangible improvements to pollinator health and crop visitation result from IPM implementation in agriculture.

Gut microbiota composition and gene expression changes induced in the Apis cerana exposed to acetamiprid and difenoconazole at environmentally realistic concentrations alone or combined

Apis cerana is an important pollinator of agricultural crops in China. In the agricultural environment, A. cerana may be exposed to acetamiprid (neonicotinoid insecticide) and difenoconazole (triazole fungicide), alone or in combination because they are commonly applied to various crops. At present, our understanding of the toxicological effects of acetamiprid and difenoconazole on honey bee gut microbiomes is limited. The primary objective of this study was to explore whether these two pesticides affect honey bees' gut microbiota and to analyze the transcriptional effects of these two pesticides on honey bees' head and gut. In this study, adults of A. cerana were exposed to acetamiprid and/or difenoconazole by contaminated syrup at field-realistic concentrations for 10 days. Results indicated that acetamiprid and/or difenoconazole chronic exposure did not affect honey bees' survival and food consumption, whereas difenoconazole decreased the weight of honey bees. 16S rRNA sequencing suggested that difenoconazole and the mixture of difenoconazole and acetamiprid decreased the diversity index and shaped the composition of gut bacteria microbiota, whereas acetamiprid did not impact the gut bacterial community. The ITS sequence data showed that neither of the two pesticides affected the fungal community structure. Meanwhile, we also observed that acetamiprid or difenoconazole significantly altered the expression of genes related to detoxification and immunity in honey bees' tissues. Furthermore, we observed that the adverse effect of the acetamiprid and difenoconazole mixture on honey bees' health was greater than that of a single mixture. Taken together, our study demonstrates that acetamiprid and/or difenoconazole exposure at field-realistic concentrations induced changes to the honey bee gut microbiome and gene expression.

Mixture toxic effects of thiacloprid and cyproconazole on honey bees (Apis mellifera L.)

Pesticide exposure remains one of the main factors in the population decline of insect pollinators. It is urgently necessary to assess the effects of mixtures on pollinator risk assessments because they are often exposed to numerous agrochemicals. In the present study, we explored the mixture toxic effects of thiacloprid (THI) and cyproconazole (CYP) on honey bees (Apis mellifera L.). Our findings revealed that THI possessed higher acute toxicity to A. mellifera (96-h LC₅₀ value of 216.3 mg a.i. L^-1) than CYP (96-h LC₅₀ value of 601.4 mg a.i. L^-1). It's worth noting that the mixture of THI and CYP exerted an acute synergistic effect on honey bees. At the same time, the activities of detoxification enzyme cytochrome P450s (CYP450s) and neuro target enzyme Acetylcholinesterase (AChE), as well as the expressions of seven genes (CRBXase, CYP306A1, CYP6AS14, apidaecin, defensing-2, vtg, and gp-93) associated with detoxification metabolism, immune response, development, and endoplasmic reticulum stress, were significantly altered in the combined treatment compared with the corresponding individual exposures of THI or CYP. These data indicated that a mixture of THI and CYP could disturb the physiological homeostasis of honey bees. Our study provides a theoretical basis for in-depth studies on the impacts of pesticide mixtures on the health of honey bees. Our study also provides important guidance for the rational application of pesticide mixtures to protect pollinators in agricultural production effectively.

Toxicity interactions of azole fungicide mixtures on Chlorella pyrenoidosa

It is acknowledged that azole fungicides may release into the environment and pose potential toxic risks. The combined toxicity interactions of azole fungicide mixtures, however, are still not fully understood. The combined toxicities and its toxic interactions of 225 binary mixtures and 126 multi-component mixtures on Chlorella pyrenoidosa were performed in this study. The results demonstrated that the negative logarithm 50% effect concentration (pEC₅₀ ) of 10 azole fungicides to Chlorella pyrenoidosa at 96 h ranged from 4.23 (triadimefon) to 7.22 (ketoconazole), while the pEC₅₀ values of the 351 mixtures ranged from 3.91 to 7.44. The high toxicities were found for the mixtures containing epoxiconazole. According to the results of the model deviation ratio (MDR) calculated from the concentration addition (MDR_CA ), 243 out of 351 (69.23%) mixtures presented additive effect at the 10% effect, while the 23.08% and 7.69% of mixtures presented synergistic and antagonistic effects, respectively. At the 30% effect, 47.29%, 29.34%, and 23.36% of mixtures presented additive effects, synergism, and antagonism, respectively. At the 50% effect, 44.16%, 34.76%, and 21.08% of mixtures presented additive effects, synergism, and antagonism, respectively. Thus, the toxicity interactions at low concentration (10% effect) were dominated by additive effect (69.23%), whereas 55.84% of mixtures induced synergism and antagonism at high concentration (50% effect). Climbazole and imazalil were the most frequency of components presented in the additive mixtures. Epoxiconazole was the key component induced the synergistic effects, while clotrimazole was the key component in the antagonistic mixtures.

Mixture effects of thiamethoxam and seven pesticides with different modes of action on honey bees (Aplis mellifera)

Even though honey bees in the field are routinely exposed to a complex mixture of many different agrochemicals, few studies have surveyed toxic effects of pesticide mixtures on bees. To elucidate the interactive actions of pesticides on crop pollinators, we determined the individual and joint toxicities of thiamethoxam (THI) and other seven pesticides [dimethoate (DIM), methomyl (MET), zeta-cypermethrin (ZCY), cyfluthrin (CYF), permethrin (PER), esfenvalerate (ESF) and tetraconazole (TET)] to honey bees (Aplis mellifera) with feeding toxicity test. Results from the 7-days toxicity test implied that THI elicited the highest toxicity with a LC₅₀ data of 0.25 (0.20-0.29) μg mL^-1, followed by MET and DIM with LC₅₀ data of 4.19 (3.58-4.88) and 5.30 (4.65-6.03) μg mL^-1, respectively. By comparison, pyrethroids and TET possessed relatively low toxicities with their LC₅₀ data from the range of 33.78 (29.12-38.39) to 1125 (922.4-1,442) μg mL^-1. Among 98 evaluated THI-containing binary to octonary mixtures, 29.59% of combinations exhibited synergistic effects. In contrast, 18.37% of combinations exhibited antagonistic effects on A. mellifera. Moreover, 54.8% pesticide combinations incorporating THI and TET displayed synergistic toxicities to the insects. Our findings emphasized that the coexistence of several pesticides might induce enhanced toxicity to honey bees. Overall, our results afforded worthful toxicological information on the combined actions of neonicotinoids and current-use pesticides on honey bees, which could accelerate farther comprehend on the possible detriments of other pesticide mixtures in agro-environment.

Biochemical responses, feeding and survival in the solitary bee Osmia bicornis following exposure to an insecticide and a fungicide alone and in combination

In agricultural ecosystems, bees are exposed to combinations of pesticides that may have been applied at different times. For example, bees visiting a flowering crop may be chronically exposed to low concentrations of systemic insecticides applied before bloom and then to a pulse of fungicide, considered safe for bees, applied during bloom. In this study, we simulate this scenario under laboratory conditions with females of the solitary bee, Osmia bicornis L. We studied the effects of chronic exposure to the neonicotinoid insecticide, Confidor® (imidacloprid) at a realistic concentration, and of a pulse (1 day) exposure of the fungicide Folicur® SE (tebuconazole) at field application rate. Syrup consumption, survival, and four biomarkers: acetylcholinesterase (AChE), carboxylesterase (CaE), glutathione S-transferase (GST), and alkaline phosphatase (ALP) were evaluated at two different time points. An integrated biological response (IBRv2) index was elaborated with the biomarker results. The fungicide pulse had no impact on survival but temporarily reduced syrup consumption and increased the IBRv2 index, indicating potential molecular alterations. The neonicotinoid significantly reduced syrup consumption, survival, and the neurological activity of the enzymes. The co-exposure neonicotinoid-fungicide did not increase toxicity at the tested concentrations. AChE proved to be an efficient biomarker for the detection of early effects for both the insecticide and the fungicide. Our results highlight the importance of assessing individual and sub-individual endpoints to better understand pesticide effects on bees.

Using the Honey Bee (Apis mellifera L.) Cell Line AmE-711 to Evaluate Insecticide Toxicity

One of the main contributors to poor productivity and elevated mortality of honey bee colonies globally is insecticide exposure. Whole-organism and colony-level studies have demonstrated the effects of insecticides on many aspects of honey bee biology and have also shown their interactions with pathogens. However, there is a need for in vitro studies using cell lines to provide greater illumination of the effects of insecticides on honey bee cellular and molecular processes. We used a continuous cell line established from honey bee embryonic tissues (AmE-711) in assays that enabled assessment of cell viability in response to insecticide exposure. We exposed AmE-711 cells to four formulations, each containing a different insecticide. Treatment of cells with the insecticides resulted in a concentration-dependent reduction in viability after a 24-h exposure, whereas long-term exposure (120 h) to sublethal concentrations had limited effects on viability. The 24-h exposure data allowed us to predict the half-maximal lethal concentration (LC50) for each insecticide using a four-parameter logistical model. We then exposed cells for 12 h to the predicted LC50 and observed changes in morphology that would indicate stress and death. Reverse transcription-quantitative polymerase chain reaction analysis corroborated changes in morphology: expression of a cellular stress response gene, 410087a, increased after an 18-h exposure to the predicted LC50. Demonstration of the effects of insecticides through use of AmE-711 provides a foundation for additional research addressing issues specific to honey bee toxicology and complements whole-organism and colony-level approaches. Moreover, advances in the use of AmE-711 in high-throughput screening and in-depth analysis of cell regulatory networks will promote the discovery of novel control agents with decreased negative impacts on honey bees. Environ Toxicol Chem 2023;42:88-99. Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Biochemical and histopathological responses in Nile tilapia exposed to a commercial insecticide mixture containing dinotefuran and lambda-cyhalothrin

The indiscriminate use of pesticides has led to an increased risk of environmental contamination and pest resistance worldwide, favoring the development of less hazardous formulations. The commercial insecticide ZEUS® (Ihara, Brazil) combining dinotefuran and lambda-cyhalothrin was recently formulated in order to meet the environmental sustainability and food security. However, little is known about the potential toxic effects of ZEUS® to aquatic species. Thus, we report, for the first time, the biochemical and histological responses in tilapia (Oreochromis niloticus) following 96 h exposure to 0.01 mg/L, 0.05 mg/L and 0.1 mg/L ZEUS®. Different biochemical endpoints, including acetylcholinesterase (AChE), gamma-glutamyltransferase (GGT) and alkaline phosphatase (ALP), were assessed as potential biomarkers of insecticide effects. Glutathione S-transferase (GST) was evaluated as a marker of phase II biotransformation, and histopathological changes were measured to indicate gill alterations following ZEUS® exposure. After 96 h exposure, ZEUS® treatment increased GST activity in the liver of fish exposed to the highest concentration, while the intermediate dose increased both renal GGT and hepatic ALP activities. These findings reflect the importance of the liver and kidneys in the detoxification of ZEUS® and highlight the need to understand further toxicity effects. Likewise, the histopathological analysis of gills provided evidence that ZEUS® caused moderate damages. Despite biomarkers alterations reported for O. niloticus following ZEUS® exposure, by comparing our findings with data on toxicity of individual compounds, the commercial ZEUS® mixture seems to present similar or even lower adverse effects on freshwater fish.

The acute toxicity of pesticide mixtures to honeybees

Honeybees (Apis mellifera) frequently live in complex environments where exposure to mixtures of pesticides is possible. Although several studies have expressed concern regarding the combined effects of pesticide mixtures, other studies did not find increased toxicity. Thus, the primary objective of this study was to identify peer-reviewed literature measuring the toxicity of pesticide mixtures to honeybees and determine how frequently synergistic interactions occur. Many experiments (258) were identified that met the criteria for inclusion. When considering all experiments, 34% of experiments had model deviation ratios (MDR; expected toxicity/observed toxicity) greater than 2, suggesting greater-than-additive toxicity. Twelve percent of experiments had MDR values greater than 5, with several studies exceeding 100. However, most experiments that had higher MDRs included azole fungicides or acaricides as a component of the mixture. After removal of these groups, only 8% of experiments exceeded an MDR of 2, and no experiments exceeded 5. Moreover, the influence of the azole fungicides was dose dependent. If only experiments that used azole exposure at environmentally relevant concentrations were considered, azole fungicides had limited impact on neonicotinoid insecticides. However, pyrethroid insecticides still had greater than expected toxicity with 80% of experiments having MDR values greater than 2. Acaricides also had greater than expected incidence of synergy with approximately 30% of studies reporting MDR values greater than 2. It should be noted that even the azole studies considered environmentally relevant frequently used maximum exposure rates and worst-case exposure scenarios. The primary finding is that synergy is uncommon except for a few cases where known synergists (azole fungicides) and pesticides with variable metabolism potential, such as some pyrethroids, are in combination. Future work is still needed to refine the relevance of azole fungicides at commonly occurring environmental concentrations. Integr Environ Assess Manag 2022;18:1694-1704. © 2022 SETAC.

Monitoring the effects of field exposure of acetamiprid to honey bee colonies in Eucalyptus monoculture plantations

Eucalyptus plantations occupy 26 % of Portuguese forested areas. Its flowers constitute important sources for bees and beekeepers take advantage of this and keep their honey bee colonies within or near the plantations for honey production. Nonetheless, these plantations are susceptible to pests, such as the eucalyptus weevil Gonipterus platensis. To control this weevil, some plantations must be treated with pesticides, which might harm non-target organisms. This study aimed to perform a multifactorial assessment of the health status and development of Apis mellifera iberiensis colonies in two similar landscape windows dominated by Eucalyptus globulus plantations - one used as control and the other with insecticide treatment. In each of the two selected areas, an apiary with five hives was installed and monitored before and after a single application of the insecticide acetamiprid (40 g a.i./ha). Colony health and development, resources use, and pesticide residues accumulation were measured. The results showed that the application of acetamiprid in this area did not alter the health status and development of the colonies. This can be explained by the low levels of residues of acetamiprid detected only in pollen and bee bread samples, ~52 fold lower than the sublethal effect threshold. This could be attributed to the low offer of resources during and after the application event and within the application area, with the consequent foraging outside the sprayed area during that period. Since exposure to pesticides in such complex landscapes seems to be dependent on the spatial and temporal distribution of resources, we highlight some key monitoring parameters and tools that are able to provide reliable information on colony development and use of resources. These tools can be easily applied and can provide a better decision-taking of pesticide application in intensive production systems to decrease the risk of exposure for honey bees.

Exposure and risk assessment of acetamiprid in honey bee colonies under a real exposure scenario in Eucalyptus sp. landscapes

Honey bee colonies have shown abnormal mortality rates over the last decades. Colonies are exposed to biotic and abiotic stressors including landscape changes caused by human pressure. Modern agriculture and even forestry, rely on pesticide inputs and these chemicals have been indicated as one of the major causes for colony losses. Neonicotinoids are a common class of pesticides used worldwide that are specific to kill insect pests, with acetamiprid being the only neonicotinoid allowed to be applied outdoors in the EU. To evaluate honeybees' exposure to acetamiprid under field conditions as well as to test the use of in-situ tools to monitor pesticide residues, two honeybee colonies were installed in five Eucalyptus sp. plantations having different area where Epik® (active substance: acetamiprid) was applied as in a common spraying event to control the eucalyptus weevil pest. Flowers, fresh nectar, honey bees and colony products samples were collected and analyzed for the presence of acetamiprid residues. Our main findings were that (1) acetamiprid residues were found in samples collected outside the spraying area, (2) the amount of residues transported into the colonies increased with the size of the sprayed area, (3) according to the calculated Exposure to Toxicity Ratio (ETR) values, spraying up to 22 % of honeybees foraging area does not harm the colonies, (4) colony products can be used as a valid tool to monitor colony accumulation of acetamiprid and (5) the use of Lateral Flow Devices (LFDs) can be a cheap, fast and easy tool to apply in the field, to evaluate the presence of acetamiprid residues in the landscape and colony products.

Pesticide usage practices and the exposure risk to pollinators: A case study in the North China Plain

Due to the frequent pesticide applications, bees are suffered from pesticide exposure risks via consumption and direct contact with sprayed drifts. However, if pesticides are misused and the potential exposure risk to bees based on realistic pesticide application data are still little reported. In this study, pesticide application patterns in wheat-maize rotation system, vegetable and apple producing areas, was studied by interviewing farmers in Quzhou County, the North China Plain. The pesticide use status was evaluated by the recommended and actual applied dose and risk quotient (RQ) based Bee-REX model was used to assess the exposure risks of pesticide to bees based on the collected pesticide application data. The results showed that over half (52 %) of farmers in selected sites misused pesticides and orchard owners were frequently misused pesticides. Positive correlations were found between pesticide usage performance and farmers' specialized training experience. Pesticides applied in orchards have caused higher exposure risks to bees with the mean of RQs exceed 120 and 1880 via acute contact and dietary routes, respectively. Pesticide misuse significantly elevates the exposure risk to bees that the mean RQ under misuse scenarios was 5.8 times than that of correct use. Abamectin, fipronil and neonicotinoids contributed most to the pesticide exposure risk to bees. The main findings of this study imply that more sustainable pest and pollinator management strategies, including the moratorium high-risk insecticides and providing diverse flower resources and habitats, are highly needed. Additionally, measures such as implementing farmer educating and training programs should also be put on the agenda.

The use of insecticide mixtures containing neonicotinoids as a strategy to limit insect pests: Efficiency and mode of action

Synthetic insecticides continue to be the main strategy for managing insect pests, which are a major concern for both crop protection and public health. As nicotinic acetylcholine receptors play a central role in insect neurotransmission, they are the molecular target of neurotoxic insecticides such as neonicotinoids. These insecticides are used worldwide and have shown high efficiency in culture protection. However, the emergence of insect resistance mechanisms, and negative side-effects on non-target species have highlighted the need for a new control strategy. In this context, the use of insecticide mixtures with synergistic effects have been used in order to decrease the insecticide dose, and thus delay the selection of resistance-strains, and limit their negative impact. In this review, we summarize the available data concerning the mode of action of neonicotinoid mixtures, as well as their toxicity to various insect pests and non-target species. We found that insecticide mixtures containing neonicotinoids may be an effective strategy for limiting insect pests, and in particular resistant strains, although they could also negatively impact non-target species such as pollinating insects.

Pesticide risk to managed bees during blueberry pollination is primarily driven by off-farm exposures

When managed bee colonies are brought to farms for crop pollination, they can be exposed to pesticide residues. Quantifying the risk posed by these exposures can indicate which pesticides are of the greatest concern and helps focus efforts to reduce the most harmful exposures. To estimate the risk from pesticides to bees while they are pollinating blueberry fields, we sampled blueberry flowers, foraging bees, pollen collected by returning honey bee and bumble bee foragers at colonies, and wax from honey bee hives in blooming blueberry farms in southwest Michigan. We screened the samples for 261 active ingredients using a modified QuEChERS method. The most abundant pesticides were those applied by blueberry growers during blueberry bloom (e.g., fenbuconazole and methoxyfenozide). However, we also detected highly toxic pesticides not used in this crop during bloom (or other times of the season) including the insecticides chlorpyrifos, clothianidin, avermectin, thiamethoxam, and imidacloprid. Using LD50 values for contact and oral exposure to honey bees and bumble bees, we calculated the Risk Quotient (RQ) for each individual pesticide and the average sample RQ for each farm. RQ values were considered in relation to the U.S. Environmental Protection Agency acute contact level of concern (LOC, 0.4), the European Food Safety Authority (EFSA) acute contact LOC (0.2) and the EFSA chronic oral LOC (0.03). Pollen samples were most likely to exceed LOC values, with the percent of samples above EFSA's chronic oral LOC being 0% for flowers, 3.4% for whole honey bees, 0% for whole bumble bees, 72.4% for honey bee pollen in 2018, 45.4% of honey bee pollen in 2019, 46.7% of bumble bee pollen in 2019, and 3.5% of honey bee wax samples. Average pollen sample RQ values were above the EFSA chronic LOC in 92.9% of farms in 2018 and 42.9% of farms in 2019 for honey bee collected pollen, and 46.7% of farms for bumble bee collected pollen in 2019. Landscape analyses indicated that sample RQ was positively correlated with the abundance of apple and cherry orchards located within the flight range of the bees, though this varied between bee species and landscape scale. There was no correlation with abundance of blueberry production. Our results highlight the need to mitigate pesticide risk to bees across agricultural landscapes, in addition to focusing on the impact of applications on the farms where they are applied.

Mild chronic exposure to pesticides alters physiological markers of honey bee health without perturbing the core gut microbiota

Recent studies highlighted that exposure to glyphosate can affect specific members of the core gut microbiota of honey bee workers. However, in this study, bees were exposed to relatively high glyphosate concentrations. Here, we chronically exposed newly emerged honey bees to imidacloprid, glyphosate and difenoconazole, individually and in a ternary mixture, at an environmental concentration of 0.1 µg/L. We studied the effects of these exposures on the establishment of the gut microbiota, the physiological status, the longevity, and food consumption of the host. The core bacterial species were not affected by the exposure to the three pesticides. Negative effects were observed but they were restricted to few transient non-core bacterial species. However, in the absence of the core microbiota, the pesticides induced physiological disruption by directly altering the detoxification system, the antioxidant defenses, and the metabolism of the host. Our study indicates that even mild exposure to pesticides can directly alter the physiological homeostasis of newly emerged honey bees and particularly if the individuals exhibit a dysbiosis (i.e. mostly lack the core microbiota). This highlights the importance of an early establishment of a healthy gut bacterial community to strengthen the natural defenses of the honey bee against xenobiotic stressors.

Acute exposure to sublethal doses of neonicotinoid insecticides increases heat tolerance in honey bees

The European honey bee, Apis mellifera L., is the single most valuable managed pollinator in the world. Poor colony health or unusually high colony losses of managed honey bees result from a myriad of stressors, which are more harmful in combination. Climate change is expected to accentuate the effects of these stressors, but the physiological and behavioral responses of honey bees to elevated temperatures while under simultaneous influence of one or more stressors remain largely unknown. Here we test the hypothesis that exposure to acute, sublethal doses of neonicotinoid insecticides reduce thermal tolerance in honey bees. We administered to bees oral doses of imidacloprid and acetamiprid at 1/5, 1/20, and 1/100 of LD₅₀ and measured their heat tolerance 4 h post-feeding, using both dynamic and static protocols. Contrary to our expectations, acute exposure to sublethal doses of both insecticides resulted in higher thermal tolerance and greater survival rates of bees. Bees that ingested the higher doses of insecticides displayed a critical thermal maximum from 2 ˚C to 5 ˚C greater than that of the control group, and 67%–87% reduction in mortality. Our study suggests a resilience of honey bees to high temperatures when other stressors are present, which is consistent with studies in other insects. We discuss the implications of these results and hypothesize that this compensatory effect is likely due to induction of heat shock proteins by the insecticides, which provides temporary protection from elevated temperatures.

Toxicity of the Pesticides Imidacloprid, Difenoconazole and Glyphosate Alone and in Binary and Ternary Mixtures to Winter Honey Bees: Effects on Survival and Antioxidative Defenses

To explain losses of bees that could occur after the winter season, we studied the effects of the insecticide imidacloprid, the herbicide glyphosate and the fungicide difenoconazole, alone and in binary and ternary mixtures, on winter honey bees orally exposed to food containing these pesticides at concentrations of 0, 0.01, 0.1, 1 and 10 µg/L. Attention was focused on bee survival, food consumption and oxidative stress. The effects on oxidative stress were assessed by determining the activity of enzymes involved in antioxidant defenses (superoxide dismutase, catalase, glutathione-S-transferase, glutathione reductase, glutathione peroxidase and glucose-6-phosphate dehydrogenase) in the head, abdomen and midgut; oxidative damage reflected by both lipid peroxidation and protein carbonylation was also evaluated. In general, no significant effect on food consumption was observed. Pesticide mixtures were more toxic than individual substances, and the highest mortalities were induced at intermediate doses of 0.1 and 1 µg/L. The toxicity was not always linked to the exposure level and the number of substances in the mixtures. Mixtures did not systematically induce synergistic effects, as antagonism, subadditivity and additivity were also observed. The tested pesticides, alone and in mixtures, triggered important, systemic oxidative stress that could largely explain pesticide toxicity to honey bees.

Binary and ternary toxicological interactions of clothianidin and eight commonly used pesticides on honey bees (Apis mellifera)

Although many toxicological evaluations have been conducted for honey bees (Apis mellifera), most of these studies have only focused on the effects of individual chemicals. However, honey bees are usually exposed to pesticide mixtures under field conditions. In this study, we examined the effects of individual pesticides and mixtures of clothianidin (CLO) with eight other pesticides [carbaryl (CAR), thiodicarb (THI), chlorpyrifos (CHL), beta-cyfluthrin (BCY), gamma-cyhalothrin (GCY), tetraconazole (TET), spinosad (SPI) and indoxacarb (IND)] on honey bees using a feeding method. Toxicity tests of a 4-day exposure to individual pesticides revealed that CLO had the highest toxicity to A. mellifera, with an LC₅₀ value of 0.24 μg a.i. mL^-1, followed by IND and CHL with LC₅₀ values of 3.40 and 3.56 μg a.i. mL^-1, respectively. SPI and CAR had relatively low toxicities, with LC₅₀ values of 7.19 and 8.42 μg a.i. mL^-1, respectively. In contrast, TET exhibited the least toxicity, with an LC₅₀ value of 258.7 μg a.i. mL^-1. Most binary mixtures of CLO with other pesticides exerted additive and antagonistic effects. However, all the ternary mixtures containing CLO and TET (except for CLO+TET+THD) elicited synergistic responses to bees. Either increased numbers of components in the mixture or/and a unique mode of action appeared to be responsible for the higher toxicity of mixtures. Our findings emphasized the need for risk assessment of pesticide mixtures rather than the individual chemicals. Our data also provided information that might help growers avoid increased toxicity and unnecessary injury to pollinators.

Pesticide residues in the pollen and nectar of oilseed rape (Brassica napus L.) and their potential risks to honey bees

Research evidence suggests that pesticide residues are one of the leading potential causes of the decline in pollinators, especially during vulnerable periods such as foraging in the early springtime. In China, no research quantifies pesticide residues in the nectar and pollen of honey bee colonies during this period or examines the potential risks and toxicity of pesticides to honey bees. Oilseed rape is one of the first and primary bee-attractive plants in most parts of China. Here, we investigated the pesticide residues in the oilseed rape of the years 2017 and 2018 in China. The hazard quotient (HQ) from pollen and nectar and the BeeREX risk assessment were used to evaluate the potential risks of the pesticide residues to honey bees. We detected 48 pesticides in pollen samples and 34 chemicals in nectar samples. The maximum pollen HQ (PHQ) values (contact or oral) ranged from 0.16 to 706,421, and the maximum nectar HQ (NHQ) values (contact or oral) ranged from 0.07 to 185,135. In particular, carbofuran, cyfluthrin, deltamethrin, and fenpropathrin have relatively high PHQ and NHQ values. Our results indicated that further investigation of nearly half of the tested compounds is needed because their PHQ or NHQ values are more than 50. Especially cyfluthrin and carbofuran need advanced tier assessment due to their maximum RQ (risk quotient) values exceeding the level of concern. These results provide valuable guidance for protecting bees and other pollinators in China.

Toxicological status changes the susceptibility of the honey bee Apis mellifera to a single fungicidal spray application

During all their life stages, bees are exposed to residual concentrations of pesticides, such as insecticides, herbicides, and fungicides, stored in beehive matrices. Fungicides are authorized for use during crop blooms because of their low acute toxicity to honey bees. Thus, a bee that might have been previously exposed to pesticides through contaminated food may be subjected to fungicide spraying when it initiates its first flight outside the hive. In this study, we assessed the effects of acute exposure to the fungicide in bees with different toxicological statuses. Three days after emergence, bees were subjected to chronic exposure to the insecticide imidacloprid and the herbicide glyphosate, either individually or in a binary mixture, at environmental concentrations of 0.01 and 0.1 μg/L in food (0.0083 and 0.083 μg/kg) for 30 days. Seven days after the beginning of chronic exposure to the pesticides (10 days after emergence), the bees were subjected to spraying with the fungicide difenoconazole at the registered field dosage. The results showed a delayed significant decrease in survival when honey bees were treated with the fungicide. Fungicide toxicity increased when honey bees were chronically exposed to glyphosate at the lowest concentration, decreased when they were exposed to imidacloprid, and did not significantly change when they were exposed to the binary mixture regardless of the concentration. Bees exposed to all of these pesticide combinations showed physiological disruptions, revealed by the modulation of several life history traits related mainly to metabolism, even when no effect of the other pesticides on fungicide toxicity was observed. These results show that the toxicity of active substances may be misestimated in the pesticide registration procedure, especially for fungicides.

Insights into the degradation and toxicity difference mechanism of neonicotinoid pesticides in honeybees by mass spectrometry imaging

Honeybees are essential for the pollination of a wide variety of crops and flowering plants, whereas they are confronting decline around the world due to the overuse of pesticides, especially neonicotinoids. The mechanism behind the negative impacts of neonicotinoids on honeybees has attracted considerable interest, yet it remains unknown due to the limited insights into the spatiotemporal distribution of pesticides in honeybees. Herein, we demonstrated the use of matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) for the spatiotemporal visualization of neonicotinoids, such as N-nitroguanidine (dinotefuran) and N-cyanoamidine (acetamiprid) compounds, administered by oral application or direct contact, in the whole-body section of honeybees. The MSI results revealed that both dinotefuran and acetamiprid can quickly penetrate various biological barriers and distribute within the whole-body section of honeybees, but acetamiprid can be degraded much faster than dinotefuran. The degradation rate of acetamiprid is significantly decreased when piperonyl butoxide (PBO) is applied, whereas that of dinotefuran remains almost unchanged. These two factors might contribute to the fact that dinotefuran affords a higher toxicity to honeybees than acetamiprid. Moreover, the toxicity and degradation rate of acetamiprid can be affected by co-application with tebuconazole. Taken together, the results presented here indicate that the discrepant toxicity between dinotefuran and acetamiprid does not lie in the difference in their penetration of various biological barriers of honeybees, but in the degradation rate of neonicotinoid pesticides within honeybee tissues. Moreover, new perspectives are given to better understand the causes of the current decline in honeybee populations posed by insecticides, providing guidelines for the precise use of conventional agrochemicals and the rational design of novel pesticide candidates.

Honey bee exposure scenarios to selected residues through contaminated beeswax

Twenty-two pesticides and veterinary drugs of which residues were detected in beeswax in Europe were selected according to different criteria. The risk to honey bee health posed by the presence of these residues in wax was assessed based on three exposure scenarios. The first one corresponds to the exposure of larvae following their close contact with wax constituting the cells in which they develop. The second one corresponds to the exposure of larvae following consumption of the larval food that was contaminated from contact with contaminated wax. The third one corresponds to the exposure of adult honey bees following wax chewing when building cells and based on a theoretical worst-case scenario (= intake of contaminants from wax). Following these three scenarios, maximum concentrations which should not be exceeded in beeswax in order to protect honey bee health were calculated for each selected substance. Based on these values, provisional action limits were proposed. Beeswax exceeding these limits should not be put on the market.

Occurrence of environmental contaminants (pesticides, herbicides, PAHs) in Australian/Queensland Apis mellifera honey

Honey is a popular agricultural product containing mostly sugars and water, but due to its nutritious components and natural production by honeybees (Apis mellifera) from floral nectar, it is marketed as a premium health food item. As environmental monitors, honeybees can potentially transfer environmental contaminants to honey. Whilst pesticides can have ubiquitous presence in agricultural and urban areas, polycyclic aromatic hydrocarbons (PAHs) can be more prevalent in higher density urban/industrial environments. Australian beehives are customarily located in rural areas/forests, but it is increasingly popular to keep hives in urban areas. This study assessed the levels of environmental contaminants in honeys (n = 212) from Queensland/Australian sources including rural, peri-urban and urban areas. Honey samples were analysed by LC-MS/MS and GC-MS/MS for 53 herbicides, 83 pesticides, 18 breakdown products (for certain pesticides/herbicides) and 33 PAHs and showed low/negligible pesticide, herbicide and PAHs contamination, consistent regardless of honey origins.

Pesticides residues and metabolites in honeybees: A Greek overview exploring Varroa and Nosema potential synergies

The aim of this study was to investigate reported cases of honeybee mortality incidents and the potential association to pesticide exposure and to their metabolites. The same honeybee samples were also assessed for Varroa mites, and Nosema microsporidia provoked infections to provide an integrated picture of all observable stressors that may impact bees' survival. Thus, honeybee samples from different areas of Greece (2014-2018) were analyzed for the presence of pesticide residues and metabolites. In this context, an existing LC-ESI-QqQ-MS multiresidue method of analytes of different chemical classes such as neonicotinoids, organophosphates, triazoles, carbamates, was enriched with additional active substances, developed and validated. A complementary GC-EI-QqQ-MS method was also exploited for the same scope covering pyrethroid compounds. Both methods monitored more than 150 active substances and metabolites and presented acceptable linearity over the ranges assayed. The calculated recoveries ranged from 65 to 120% for the three concentration levels, while the precision (RSD%) values ranged between 4 and 15%. Therefore, this approach proved sufficient to act as a monitoring tool for the determination of pesticide residues in cases of suspected honeybee poisoning incidents. From the analysis of 320 samples, the presence of 70 active substances and metabolites was confirmed with concentrations varying from 1.4 ng/g to 166 μg/g. Predominant detections were the acaricide coumaphos, several neonicotinoids exemplified by clothianidin, organophosporous compounds dimethoate and chlorpyrifos, and some pyrethroids. Metabolites of imidacloprid, chlorpyrifos, coumaphos, acetamiprid, fenthion and amitraz were also identified. Concerning Nosema and Varroa they were identified in 27 and 22% of samples examined, respectively, verifying their prevalence and coexistence with pesticides and their metabolites in honeybees.

Differences in larval pesticide tolerance and esterase activity across honey bee (Apis mellifera) stocks

Honey bee populations in North America are an amalgamation of diverse progenitor ecotypes experiencing varying levels of artificial selection. Genetic differences between populations can result in variable susceptibility towards environmental stressors, and here we compared pesticide tolerances across breeding stocks using a mixture of seven pesticides frequently found in colonies providing pollination services. We administered the pesticide mixture chronically to in vitro reared larvae at four concentrations of increasing Hazard Quotient (HQ, or cumulative toxicity) and measured mortality during larval development. We found that different stocks had significantly different tolerances to our pesticide mixture as indicated by their median lethal toxicity (HQ₅₀). The intensively selected Pol-Line stock exhibited the greatest pesticide sensitivity while Old World (progenitor) and putatively feral stocks were the most pesticide-tolerant. Furthermore, we found that activity of the detoxification enzyme esterase was positively correlated with pesticide tolerance when measured using two different substrate standards, and confirmed that larvae from the Pol-Line stock had generally lower esterase activity. Consistent with an increased pesticide tolerance, the Old World and putatively feral stocks had higher esterase activities. However, esterases and other detoxification enzymes (CYP450s and GSTs) were found in similar abundances across stocks, suggesting that the differences in enzyme activity we observed might arise from stock-specific single nucleotide polymorphisms or post-translational modifications causing qualitative variation in enzyme activity. These results suggest that selective breeding may inadvertently increase honey bees' sensitivity to pesticides, whereas unselected, putatively feral and Old World stocks have larvae that are more tolerant.

A syringe-aided apta-nanosensing method for colorimetric determination of acetamiprid

A syringe-aided apta-nanosensing method is reported for the colorimetric determination of acetamiprid. The method employs double-stranded (ds) DNA-conjugated gold nanoparticle@magnetic agarose beads, i.e., dsDNA-AuNP@MABs as peroxidase-mimicking composite probes, in which the aptamer is indirectly attached to the AuNP surface through its hybridization with complementary DNA (cDNA). Upon contact with the acetamiprid target, the probes can give perceptible color change due to the possible conformation switch from dsDNA's brush-like to cDNA's 'pancake' regime. An "air-spaced pumping" procedure using a syringe equipped with ring magnets as the operation platform was proposed to facilitate the magnetic separation of the sensing probes. Therefore, the analytical steps can be easily accomplished in a syringe, including probe loading, acetamiprid capture and magnetic separation from crude samples, chromogenic reagent loading and colorimetric visualization. Acetamiprid concentration down to 3.3 ppb can be easily identified by the naked eye. The final solution also can be transferred for quantitative measurement. Under spectrometer, the ratio of the absorbance at 652 nm in the presence and absence of acetamiprid (A/A₀) is linearly related to the acetamiprid concentration in the 0.4-4.5 ppb range. The limit of detection is calculated to be 0.24 ppb. Moreover, satisfactory recoveries ranging from 90.90 to 91.82% with relative standard deviations of ≤2.96% were obtained in analyzing real spiked samples.

Exposure to acetamiprid influences the development and survival ability of worker bees (Apis mellifera L.) from larvae to adults

In most cases, honey bees experience pesticide pollution in a long-term period through direct or indirect exposure, such as the development process from larvae to the pre-harvest stage. At present, little is known about how honey bees respond to pesticide stresses during the continuous development period. This study aims to examine effects of long-term acetamiprid exposure on the development and survival of honey bees, and further present the expression profile in larvae, 1-day-old, and 7-day-old adult worker bees that related to immune, detoxification, acetylcholinesterase (AChE) and memory. Honey bees from 2-day-old larvae to 14-day-old adults except the pupal stage were continuously fed with different acetamiprid solutions (0, 5, and 25 mg/L). We found that acetamiprid over 5 mg/L disturbed the development involving birth weight and emergence rate of newly emerged bees, and reduced the proportion of capped cells of larvae at 25 mg/L; gene expression related to immune and detoxification of worker bees exposed to acetamiprid was roughly activated, returned and then inhibited from larval to emerged and to the late adult stage, respectively. Moreover, lifespans of bees treated with acetamiprid at 25 mg/L were significantly reduced. The present study reflects the potential risk for honey bees continuously exposed to acetamiprid in the development stage.

Sublethal acetamiprid doses negatively affect the lifespans and foraging behaviors of honey bee (Apis mellifera L.) workers

The neonicotinoid insecticide acetamiprid is applied widely for pest control in agriculture production. However, little is known about the effects of acetamiprid on the foraging behavior of nontarget pollinators. This study aims to investigate effects of sublethal acetamiprid doses on lifespans and foraging behaviors of honey bees (Apis mellifera L.) under natural swarm conditions. Newly emerged worker bees of each treatment received a drop of 1.5 μL acetamiprid solution (containing 0, 0.5, 1, and 2 μg/bee acetamiprid, diluted by water) on the thorax respectively. Bees from 2-day-old to deadline were monitored on foraging behaviors involving the age of bee for first foraging flights, rotating day-off status and the number of foraging flights using the radio frequency identification (RFID) system. We found that acetamiprid at 2 μg/bee significantly reduced the lifespan, induced precocious foraging activity, influenced the rotating day-off status and decreased foraging flights of worker bees. The abnormal behaviors of worker bees may be associated with a decline in lifespan. This work may provide a new perspective into the neonicotinoids that accelerate the colony failure.

Toxicities of Neonicotinoid-Containing Pesticide Mixtures on Nontarget Organisms

Neonicotinoids are a widely used class of pesticides. Co-exposure to neonicotinoids and other classes of pesticides can exert potentiating or synergistic effects, and these mixtures have been detected in human bodily fluids. The present review summarizes studies into the effects of neonicotinoid-containing pesticide mixtures on humans and other nontarget organisms. Exposure to these mixtures has been reported to result in reproductive and hormonal toxicity, genotoxicity, neurotoxicity, hepatotoxicity, and immunotoxicity in vertebrates. Mortality of pollinators and toxicity in other organisms has also been reported. The underlying mechanism of pesticide mixture toxicity may be associated with impairment of cytochrome 450 enzymes, which are involved in metabolizing pesticides. However, a comprehensive explanation of the adverse effects of neonicotinoid-containing pesticide mixtures is still required so that effective prevention and control measures can be formulated. Environ Toxicol Chem 2020;39:1884-1893. © 2020 SETAC.

Science production of pesticide residues in honey research: A descriptive bibliometric study

This work aims to provide a comprehensive study of the available research information on pesticide residues in honey through literature analysis. The research advancements within this research field from 1948 to 2019 are addressed using the Web of Science database. The results from the 685 articles analyzed indicate that this research field is in the focus of interest nowadays (Price index: 47.5%). The yearly production increased steadily from 2001 on, and authors, journals, and institutions followed Lotka's law. On the other hand, Pico, Y (Spain) (2.5%), Journal of Chromatography A (5.8%), the USA (15.0%) and Agricultural Research Service (USA) (4.0%) were the most productive author, journal, country and institution, respectively. The research hotspots of this field, according to keyword analysis, are related to the chromatographic techniques for the determination of pesticides such as imidacloprid, neonicotinoids, or coumaphos in honey and derivate products such as propolis and wax.