A neonicotinoid impairs olfactory learning in Asian honey bees (Apis cerana) exposed as larvae or as adults

Changes in the proteome of Apis mellifera acutely exposed to sublethal dosage of glyphosate and imidacloprid

Uncontrolled use of pesticides has caused a dramatic reduction in the number of pollinators, including bees. Studies on the effects of pesticides on bees have reported effects on both metabolic and neurological levels under chronic exposure. In this study, variations in the differential expression of head and thorax-abdomen proteins in Africanized A. mellifera bees treated acutely with sublethal doses of glyphosate and imidacloprid were studied using a proteomic approach. A total of 92 proteins were detected, 49 of which were differentially expressed compared to those in the control group (47 downregulated and 2 upregulated). Protein interaction networks with differential protein expression ratios suggested that acute exposure of A. mellifera to sublethal doses of glyphosate could cause head damage, which is mainly associated with behavior and metabolism. Simultaneously, imidacloprid can cause damage associated with metabolism as well as, neuronal damage, cellular stress, and impairment of the detoxification system. Regarding the thorax-abdomen fractions, glyphosate could lead to cytoskeleton reorganization and a reduction in defense mechanisms, whereas imidacloprid could affect the coordination and impairment of the oxidative stress response.

Insight into Olfactory Learning, Memory, and Mortality of Apis mellifera jemenitica after Exposure to Acetamiprid Insecticide

The honey bee, a significant crop pollinator, encounters pesticides through various routes of exposure during foraging and flower visitation. Considering the potential threat of pesticide poisoning, the indigenous Saudi bee Apis mellifera jemenitica is susceptible to the risks associated with acetamiprid, a neonicotinoid insecticide. This study investigates the acetamiprid-induced effects on the survival, olfactory learning, and memory formation of A. m. jemenitica through two exposure routes: topical application and oral ingestion. Field-realistic and serially diluted concentrations (100, 50, 25, and 10 ppm) of acetamiprid led to notable mortality at 4, 12, 24, and 48 h after treatment, with peak mortality observed at 24 h and 48 h for both exposure routes. Bee mortality was concentration-dependent, increasing with the rising concentration of acetamiprid at the tested time intervals. Food consumption following oral exposure exhibited a concentration-dependent pattern, steadily decreasing with increasing concentrations of acetamiprid. Oral exposure resulted in a substantially higher cumulative mortality (55%) compared to topical exposure (15%), indicating a significant disparity in bee mortality between the two exposure routes. The 24 h post-treatment LC50 values for acetamiprid were 160.33 and 12.76 ppm for topical application and oral ingestion, respectively. The sublethal concentrations (LC10, LC20, and LC30) of acetamiprid were 15.23, 34.18, and 61.20 ppm, respectively, following topical exposure, and 2.85, 4.77, and 6.91 ppm, respectively, following oral exposure. The sublethal concentrations of acetamiprid significantly decreased learning during the 2nd-3rd conditioning trials and impaired memory formation at 2, 12, and 24 h following both topical and oral exposure routes, compared to the control bees. Notably, the sublethal concentrations were equally effective in impairing bee learning and memory. Taken together, acetamiprid exposure adversely affected bee survival, hindered learning, and impaired the memory retention of learned tasks.

Toxicity evaluation of novel imidacloprid nanoribbons, using somatic mutation and fitness indexes in Drosophila melanogaster

Nanoribbons of imidacloprid, a systemic and chloronicotinyl insecticide, were successfully synthesized by laser-induced fragmentation/exfoliation of imidacloprid powders suspended in water, with widths ranging from 160 to 470 nm, lengths in the micron scale, and thickness of a few atoms layers. The aim of the present study was to examine the effects of acute and chronic exposure to imidacloprid (IMC) bulk and compare its effects with synthesized imidacloprid nanoribbons (IMCNR) on larval and adult viability, developmental time, olfactory capacity, longevity, productivity, and genotoxicity in Drosophila melanogaster. Larvae or adults were exposed at 0.01, 0.02, or 0.03 ppm to IMC or IMCNR. Results demonstrated that IMCNR produced a significant reduction in viability and olfactory ability. IMC did not significantly alter viability and olfactory ability. Similarly, marked differences on longevity were detected between treatment with IMC and IMCNR where the lifespan of males treated with IMC was significantly higher than control while IMCNR produced a reduction. As for productivity, developmental time, and genotoxicity, no marked differences were found between both forms of IMC.

Imidacloprid disrupts larval molting regulation and nutrient energy metabolism, causing developmental delay in honey bee Apis mellifera

Imidacloprid is a global health threat that severely poisons the economically and ecologically important honeybee pollinator, Apis mellifera. However, its effects on developing bee larvae remain largely unexplored. Our pilot study showed that imidacloprid causes developmental delay in bee larvae, but the underlying toxicological mechanisms remain incompletely understood. In this study, we exposed bee larvae to imidacloprid at environmentally relevant concentrations of 0.7, 1.2, 3.1, and 377 ppb. There was a marked dose-dependent delay in larval development, characterized by reductions in body mass, width, and growth index. However, imidacloprid did not affect on larval survival and food consumption. The primary toxicological effects induced by elevated concentrations of imidacloprid (377 ppb) included inhibition of neural transmission gene expression, induction of oxidative stress, gut structural damage, and apoptosis, inhibition of developmental regulatory hormones and genes, suppression of gene expression levels involved in proteolysis, amino acid transport, protein synthesis, carbohydrate catabolism, oxidative phosphorylation, and glycolysis energy production. In addition, we found that the larvae may use antioxidant defenses and P450 detoxification mechanisms to mitigate the effects of imidacloprid. Ultimately, this study provides the first evidence that environmentally exposed imidacloprid can affect the growth and development of bee larvae by disrupting molting regulation and limiting the metabolism and utilization of dietary nutrients and energy. These findings have broader implications for studies assessing pesticide hazards in other juvenile animals.

Effects of sublethal fipronil exposure on cross-generational functional responses and gene expression in Binodoxys communis

The effective systemic insecticide fipronil is widely used on a variety of crops and in public spaces to control insect pests. Binodoxys communis (Gahan) (Hymenoptera: Braconidae) is the dominant natural enemy of Aphis gossypii Glover (Homoptera: Aphididae), an important cotton pest, and has good efficiency in inhibiting aphid populations. The direct effects of environmental residues of sublethal fipronil doses on adult B. communis have not previously been reported. This study therefore aimed to evaluate the side effects and transcriptomic impacts of sublethal fipronil doses on B. communis. The results showed that exposure to the LC10 dose of fipronil significantly reduced the survival rate and parasitism rate of the F0 generation, but did not affect these indicators in the F1 generation. The LC25 dose did not affect the survival or parasitic rates of the F0 generation, but did significantly reduce the survival rate of F1 generation parasitoids. These results indicated that sublethal doses of fipronil affected B. communis population growth. Transcriptome analysis showed that differentially expressed genes (DEGs) in B. communis at 1 h after treatment were primarily enriched in pathways associated with fatty acid elongation, biosynthesis of fatty acids, and fatty acid metabolism. DEGs at 3 days after treatment were mainly enriched in ribosomal functions, glycolysis/gluconeogenesis, and tyrosine metabolism. Six DEGs (PY, ELOVL, VLCOAR, MRJP1, ELOVL AAEL008004-like, and RPL13) were selected for validation with real-time fluorescent quantitative PCR. This is the first report of sublethal, trans-generational, and transcriptomic side effects of fipronil on the dominant parasitoid of A. gossypii. The results of this study show that adaptation of parasitoids to high concentrations of pesticides may be at the expense of their offspring. These findings broaden our overall understanding of the intergenerational adjustments used by insects to respond to pesticide stress and call for risk assessments of the long-term impacts and intergenerational effects of other pesticides.

Field-realistic exposure to neonicotinoid and sulfoximine insecticides impairs visual and olfactory learning and memory in Polistes paper wasps

Exposure to insecticides may contribute to global insect declines due to sublethal insecticide effects on non-target species. Thus far, much research on non-target insecticide effects has focused on neonicotinoids in a few bee species. Much less is known about effects on other insect taxa or newer insecticides, such as sulfoxaflor. Here, we studied the effects of an acute insecticide exposure on both olfactory and visual learning in free-moving Polistes fuscatus paper wasps. Wasps were exposed to a single, field-realistic oral dose of low-dose imidacloprid, high-dose imidacloprid or sulfoxaflor. Then, visual and olfactory learning and short-term memory were assessed. We found that acute insecticide exposure influenced performance, as sulfoxaflor- and high-dose imidacloprid-exposed wasps made fewer correct choices than control wasps. Notably, both visual and olfactory performance were similarly impaired. Wasps treated with high-dose imidacloprid were also less likely to complete the learning assay than wasps from the other treatment groups. Instead, wasps remained stationary and unmoving in the testing area, consistent with imidacloprid interfering with motor control. Finally, wasps treated with sulfoxaflor were more likely to die in the week after treatment than wasps in the other treatment groups. Our findings demonstrate that sublethal, field-realistic dosages of both neonicotinoid- and sulfoximine-based insecticides impair wasp learning and short-term memory, which may have additional effects on survival and motor functioning. Insecticides have broadly detrimental effects on diverse non-target insects that may influence foraging effectiveness, pollination services and ecosystem function.

Neonicotinoid effects on tropical bees: Imidacloprid impairs innate appetitive responsiveness, learning and memory in the stingless bee Melipona quadrifasciata

Together with other anthropogenic factors, pesticides play a major role in pollinator decline worldwide. Most studies on their influence on pollinators have focused on honey bees given the suitability of this insect for controlled behavioral testing and raising. Yet, studies on pesticide impact should also contemplate tropical species, which contribute a major part of biodiversity and which have remained so far neglected. Here we focused on the stingless bee Melipona quadrifasciata and asked if the widely used neonicotinoid imidacloprid disrupts its learning and memory capabilities. We fed stingless bees with 0.1, 0.5 or 1 ng of imidacloprid, tested their innate appetitive responsiveness and trained them to associate odors and sucrose reward using the olfactory conditioning of the proboscis extension response. The same experiments were performed on Africanized honey bees. One hour after intoxication, both species decreased their innate responsiveness to sucrose but the effect was more accentuated in stingless bees. In both species, learning and memory were affected in a dose-dependent manner. These results indicate that pesticides have dramatic consequences on tropical bee species and claim for rational policies regulating their use in the tropics.

Exposure of chlorothalonil and acetamiprid reduce the survival and cause multiple internal disturbances in Apis mellifera larvae reared in vitro

Background: Chlorothalonil and acetamiprid are chemical pesticides commonly used in agricultural production and have been shown to have negative effects on bee's fitness. Despite many studies have revealed that honey bee (Apis mellifera L.) larvae are posting a high risk on exposure to pesticides, but the toxicology information of chlorothalonil and acetamiprid on bee larvae remain limited. Results: The no observed adverse effect concentration (NOAEC) of chlorothalonil and acetamiprid for honey bee larvae were 4 μg/mL and 2 μg/mL, respectively. Except for CarE, the enzymic activities of GST and P450 were not influenced by chlorothalonil at NOAEC, while chronic exposure to acetamiprid slightly increased the activities of the three tested enzymes at NOAEC. Further, the exposed larvae showed significantly higher expression of genes involved in a series of different toxicologically relevant process following, including caste development (Tor (GB44905), InR-2 (GB55425), Hr4 (GB47037), Ac3 (GB11637) and ILP-2 (GB10174)), immune system response (abaecin (GB18323), defensin-1 (GB19392), toll-X4 (GB50418)), and oxidative stress response (P450, GSH, GST, CarE). Conclusion: Our results suggest that the exposure to chlorothalonil and acetamiprid, even at concentrations below the NOAEC, showed potentially effects on bee larvae's fitness, and more important synergistic and behavioral effects that can affect larvae fitness should be explored in the further.

Chronic larval exposure to thiacloprid impairs honeybee antennal selectivity, learning and memory performances

The use of agricultural neonicotinoid insecticides has sub-lethal chronic effects on bees that are more prevalent than acute toxicity. Among these insecticides, thiacloprid, a commonly used compound with low toxicity, has attracted significant attention due to its potential impact on the olfactory and learning abilities of honeybees. The effect of sub-lethal larval exposure to thiacloprid on the antennal activity of adult honeybees (Apis mellifera L.) is not yet fully understood. To address this knowledge gap, laboratory-based experiments were conducted in which honeybee larvae were administered thiacloprid (0.5 mg/L and 1.0 mg/L). Using electroantennography (EAG), the impacts of thiacloprid exposure on the antennal selectivity to common floral volatiles were evaluated. Additionally, the effects of sub-lethal exposure on odor-related learning and memory were also assessed. The results of this study reveal, for the first time, that sub-lethal larval exposure to thiacloprid decreased honeybee antenna EAG responses to floral scents, leading to increased olfactory selectivity in the high-dose (1.0 mg/L) group compared to the control group (0 mg/L vs. 1.0 mg/L: p = 0.042). The results also suggest that thiacloprid negatively affected odor-associated paired learning acquisition, as well as medium-term (1 h) (0 mg/L vs. 1.0 mg/L: p = 0.019) and long-term memory (24 h) (0 mg/L vs. 1.0 mg/L: p = 0.037) in adult honeybees. EAG amplitudes were dramatically reduced following R-linalool paired olfactory training (0 mg/L vs. 1.0 mg/L: p = 0.001; 0 mg/L vs. 0.5 mg/L: p = 0.027), while antennal activities only differed significantly in the control between paired and unpaired groups. Our results indicated that exposure to sub-lethal concentrations of thiacloprid may affect olfactory perception and learning and memory behaviors in honeybees. These findings have important implications for the safe use of agrochemicals in the environment.

Facultative symbionts are potential agents of symbiont-mediated RNAi in aphids

Aphids are major crop pests, and they can be controlled through the application of the promising RNA interference (RNAi) techniques. However, chemical synthesis yield of dsRNA for RNAi is low and costly. Another sustainable aphid pest control strategy takes advantage of symbiont-mediated RNAi (SMR), which can generate dsRNA by engineered microbes. Aphid host the obligate endosymbiont Buchnera aphidicola and various facultative symbionts that not only have a wide host range but are also vertically and horizontally transmitted. Thus, we described the potential of facultative symbionts in aphid pest control by SMR. We summarized the community and host range of these facultative symbionts, and then reviewed their probable horizontal transmitted routes and ecological functions. Moreover, recent advances in the cultivation and genetic engineering of aphid facultative symbionts were discussed. In addition, current legislation of dsRNA-based pest control strategies and their safety assessments were reviewed.

Review on effects of some insecticides on honey bee health

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

Honey Bees (Hymenoptera: Apidae) Decrease Foraging But Not Recruitment After Neonicotinoid Exposure

Honey bees (Linnaeus, Hymenoptera: Apidae) are widely used as commercial pollinators and commonly forage in agricultural and urban landscapes containing neonicotinoid-treated plants. Previous research has demonstrated that honey bees display adverse behavioral and cognitive effects after treatment with sublethal doses of neonicotinoids. In laboratory studies, honey bees simultaneously increase their proportional intake of neonicotinoid-treated solutions and decrease their total solution consumption to some concentrations of certain neonicotinoids. These findings suggest that neonicotinoids might elicit a suboptimal response in honey bees, in which they forage preferentially on foods containing pesticides, effectively increasing their exposure, while also decreasing their total food intake; however, behavioral responses in semifield and field conditions are less understood. Here we conducted a feeder experiment with freely flying bees to determine the effects of a sublethal, field-realistic concentration of imidacloprid (IMD) on the foraging and recruitment behaviors of honey bees visiting either a control feeder containing a sucrose solution or a treatment feeder containing the same sucrose solution with IMD. We report that IMD-treated honey bees foraged less frequently (-28%) and persistently (-66%) than control foragers. Recruitment behaviors (dance frequency and dance propensity) also decreased with IMD, but nonsignificantly. Our results suggest that neonicotinoids inhibit honey bee foraging, which could potentially decrease food intake and adversely affect colony health.

First insights into the honey bee (Apis mellifera) brain lipidome and its neonicotinoid-induced alterations associated with reduced self-grooming behavior

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First bee brain characterization shows distinctive low plasmalogens and high alkyl-ether levels.

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PC 20:3e/15:0, PC 16:0/18:3, PA 18:0/24:1 increased by the highest dose of clothianidin.

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Levels of CL 18:3/18:1/14:0/22:6, TG 6:0/11:2/18:1 and eLPE 18:0e were linked to intense grooming.

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Membrane lipids, like PC 18:1e/20:3, ePC 8:1e/20:3, and pPE 16:1p/24:1 were up-regulated by clothianidin.

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Clothianidin exposure up-regulated genes linked to GPI-anchor biosynthesis pathway.

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Lipids can be used as biomarkers to assess the effect of neurotoxins on behaviors.

Introduction

Honey bees (Apis mellifera) play key roles in food production performing complex behaviors, like self-grooming to remove parasites. However, the lipids of their central nervous system have not been examined, even though they likely play a crucial role in the performance of cognitive process to perform intricate behaviors. Lipidomics has greatly advanced our understanding of neuropathologies in mammals and could provide the same for honey bees.

Objectives

The objectives of this study were to characterize the brain lipidome of adult honey bees and to assess the effect of clothianidin (a neurotoxic insecticide) on the brain lipid composition, gene expression, and performance of self-grooming behavior under controlled conditions (cage experiments).

Methods

After seven days of exposure to oral sublethal doses of clothianidin, the bees were assessed for self-grooming behavior; their brains were dissected to analyze the lipidome using an untargeted lipidomics approach and to perform a high throughput RNAseq analysis.

Results

Compared to all other organisms, healthy bee brain lipidomes contain unusually high levels of alkyl-ether linked (plasmanyl) phospholipids (51.42%) and low levels of plasmalogens (plasmenyl phospholipids; 3.46%). This could make it more susceptible to the effects of toxins in the environment. A positive correlation between CL 18:3/18:1/14:0/22:6, TG 6:0/11:2/18:1, LPE 18:0e and intense self-grooming was found. Sublethal doses of a neonicotinoid altered PC 20:3e/15:0, PC 16:0/18:3, PA 18:0/24:1, and TG 18:1/18:1/18/1 levels, and affected gene expression linked to GPI-anchor biosynthesis pathway and energy metabolism that may be partially responsible for the altered lipid composition.

Conclusion

This study showed that lipidomics can reveal honey bee neuropathologies associated with reduced grooming behavior due to sublethal neonicotinoid exposure. The ease of use, unusual brain lipidome as well as characterized behaviors that are affected by the environment make honey bees a promising model organism for studying the neurolipidome and associations with neurobehavioral disorders.

Long-term field-realistic exposure to a next-generation pesticide, flupyradifurone, impairs honey bee behaviour and survival

The assessment of pesticide risks to insect pollinators have typically focused on short-term, lethal impacts. The environmental ramifications of many of the world's most commonly employed pesticides, such as those exhibiting systemic properties that can result in long-lasting exposure to insects, may thus be severely underestimated. Here, seven laboratories from Europe and North America performed a standardised experiment (a ring-test) to study the long-term lethal and sublethal impacts of the relatively recently approved 'bee safe' butenolide pesticide flupyradifurone (FPF, active ingredient in Sivanto®) on honey bees. The emerging contaminant, FPF, impaired bee survival and behaviour at field-realistic doses (down to 11 ng/bee/day, corresponding to 400 µg/kg) that were up to 101-fold lower than those reported by risk assessments (1110 ng/bee/day), despite an absence of time-reinforced toxicity. Our findings raise concerns about the chronic impact of pesticides on pollinators at a global scale and support a novel methodology for a refined risk assessment.

Agroecological Strategies to Safeguard Insect Pollinators in Biodiversity Hotspots: Chile as a Case Study

Industrial agriculture (IA) has been recognized among the main drivers of biodiversity loss, climate change, and native pollinator decline. Here we summarize the known negative effects of IA on pollinator biodiversity and illustrate these problems by considering the case of Chile, a “world biodiversity hotspot” (WBH) where food exports account for a considerable share of the economy in this country. Most of Chile’s WBH area is currently being replaced by IA at a fast pace, threatening local biodiversity. We present an agroecological strategy for sustainable food production and pollinator conservation in food-producing WBHs. In this we recognize native pollinators as internal inputs that cannot be replaced by IA technological packages and support the development of agroecological and biodiversity restorative practices to protect biodiversity. We suggest four fundamental pillars for food production change based on: (1) sharing the land, restoring and protecting; (2) ecological intensification; (3) localized knowledge, research, and technological development; and (4) territorial planning and implementation of socio-agroecological policies. This approach does not need modification of native pollination services that sustain the world with food and basic subsistence goods, but a paradigm change where the interdependency of nature and human wellbeing must be recognized for ensuring the world’s food security and sovereignty.

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).

Organ-specific transcriptome analysis reveals differential gene expression in different castes under natural conditions in Apis cerana

Honeybees are one of the most environmentally important insects, as their pollination of various plant species contributes to the balance among different ecosystems. It has been studied extensively for their unique attribute of forming a caste society. Unlike other insects, honeybees communicate socially by secreting pheromones or by exhibiting specific patterns of motion. In the honeybee industry, the Asian honeybees (Apis cerana) and the Western honeybees (Apis mellifera) are dominant species. However, molecular research on the transcriptomes of A. cerana has not been studied as extensively as those of A. mellifera. Therefore, in this study, caste-specific transcriptional differences were analyzed, which provides a comprehensive analysis of A. cerana. In our dataset, we analyzed gene expression profiles using organs from worker, drone, and queen bees. This gene-expression profile helped us obtain more detailed information related to organ-specific genes, immune response, detoxification mechanisms, venom-specific genes, and ovary development. From our result, we found 4096 transcripts representing different gene-expression pattern in each organ. Our results suggest that caste-specific transcripts of each organ were expressed differently even under natural conditions. These transcriptome-wide analyses provide new insights into A. cerana and that promote honeybee research and conservation.

The Power of Drosophila melanogaster for Modeling Neonicotinoid Effects on Pollinators and Identifying Novel Mechanisms

Neonicotinoids are the most widely used insecticides in the world and are implicated in the widespread population declines of insects including pollinators. Neonicotinoids target nicotinic acetylcholine receptors which are expressed throughout the insect central nervous system, causing a wide range of sub-lethal effects on non-target insects. Here, we review the potential of the fruit fly Drosophila melanogaster to model the sub-lethal effects of neonicotinoids on pollinators, by utilizing its well-established assays that allow rapid identification and mechanistic characterization of these effects. We compare studies on the effects of neonicotinoids on lethality, reproduction, locomotion, immunity, learning, circadian rhythms and sleep in D. melanogaster and a range of pollinators. We also highlight how the genetic tools available in D. melanogaster, such as GAL4/UAS targeted transgene expression system combined with RNAi lines to any gene in the genome including the different nicotinic acetylcholine receptor subunit genes, are set to elucidate the mechanisms that underlie the sub-lethal effects of these common pesticides. We argue that studying pollinators and D. melanogaster in tandem allows rapid elucidation of mechanisms of action, which translate well from D. melanogaster to pollinators. We focus on the recent identification of novel and important sublethal effects of neonicotinoids on circadian rhythms and sleep. The comparison of effects between D. melanogaster and pollinators and the use of genetic tools to identify mechanisms make a powerful partnership for the future discovery and testing of more specific insecticides.

Insects Provide Unique Systems to Investigate How Early-Life Experience Alters the Brain and Behavior

Early-life experiences have strong and long-lasting consequences for behavior in a surprising diversity of animals. Determining which environmental inputs cause behavioral change, how this information becomes neurobiologically encoded, and the functional consequences of these changes remain fundamental puzzles relevant to diverse fields from evolutionary biology to the health sciences. Here we explore how insects provide unique opportunities for comparative study of developmental behavioral plasticity. Insects have sophisticated behavior and cognitive abilities, and they are frequently studied in their natural environments, which provides an ecological and adaptive perspective that is often more limited in lab-based vertebrate models. A range of cues, from relatively simple cues like temperature to complex social information, influence insect behavior. This variety provides experimentally tractable opportunities to study diverse neural plasticity mechanisms. Insects also have a wide range of neurodevelopmental trajectories while sharing many developmental plasticity mechanisms with vertebrates. In addition, some insects retain only subsets of their juvenile neuronal population in adulthood, narrowing the targets for detailed study of cellular plasticity mechanisms. Insects and vertebrates share many of the same knowledge gaps pertaining to developmental behavioral plasticity. Combined with the extensive study of insect behavior under natural conditions and their experimental tractability, insect systems may be uniquely qualified to address some of the biggest unanswered questions in this field.

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).

Floral tea polyphenols can improve honey bee memory retention and olfactory sensitivity

Animal-pollinated plants face a common problem, how their defensive anti-herbivore compounds may impair or alter pollinator behavior. Evolution has tailored multiple solutions, which largely involve pollinator tolerance or manipulation, to the benefit of the plant, not the removal of these compounds from pollen or nectar. The tea plant, Camilla sinensis, is famous for the caffeine and tea polyphenols (TP) that it produces in its leaves. However, these compounds are also found in its nectar, which honey bees readily collect. We examined the effects of these compounds on bee foraging choices, learning, memory, and olfactory sensitivity. Foragers preferred a sucrose feeder with 100 µg or 10 µg TP/ml over a control feeder. Caffeine, but not TP, weakly increased honey bee learning. Both caffeine and TP significantly increased memory retention, even when tested 7 d after the last learning trial. In addition, TP generally elevated EAG responsiveness to alarm pheromone odors. These results demonstrate that other secondary plant compounds, not only caffeine, can attract pollinators and influence their learning and memory.

Effects of Nosema ceranae (Dissociodihaplophasida: Nosematidae) and Flupyradifurone on Olfactory Learning in Honey Bees, Apis mellifera (Hymenoptera: Apidae)

The health of insect pollinators, particularly the honey bee, Apis mellifera (Linnaeus, 1758), is a major concern for agriculture and ecosystem health. In response to mounting evidence supporting the detrimental effects of neonicotinoid pesticides on pollinators, a novel 'bee safe' butenolide compound, flupyradifurone (FPF) has been registered for use in agricultural use. Although FPF is not a neonicotinoid, like neonicotinoids, it is an excitotoxic nicotinic acetylcholine receptor agonist. In addition, A. mellifera faces threats from pathogens, such as the microsporidian endoparasite, Nosema ceranae (Fries et al. 1996). We therefore sought 1) to increase our understanding of the potential effects of FPF on honey bees by focusing on a crucial behavior, the ability to learn and remember an odor associated with a food reward, and 2) to test for a potential synergistic effect on such learning by exposure to FPF and infection with N. ceranae. We found little evidence that FPF significantly alters learning and memory at short-term field-realistic doses. However, at high doses and at chronic, field-realistic exposure, FPF did reduce learning and memory in an olfactory conditioning task. Infection with N. ceranae also reduced learning, but there was no synergy (no significant interaction) between N. ceranae and exposure to FPF. These results suggest the importance of continued studies on the chronic effects of FPF.

No evidence for neonicotinoid preferences in the bumblebee Bombus impatiens

Neonicotinoid pesticides can have a multitude of negative sublethal effects on bees. Understanding their impact on wild populations requires accurately estimating the dosages bees encounter under natural conditions. This is complicated by the possibility that bees might influence their own exposure: two recent studies found that bumblebees (Bombus terrestris) preferentially consumed neonicotinoid-contaminated nectar, even though these chemicals are thought to be tasteless and odourless. Here, we used Bombus impatiens to explore two elements of these reported preferences, with the aim of understanding their ecological implication and underlying mechanism. First, we asked whether preferences persisted across a range of realistic nectar sugar concentrations, when measured at a series of time points up until 24 h. Second, we tested whether bees' neonicotinoid preferences were driven by an ability to associate their post-ingestive consequences with floral stimuli such as colour, location or scent. We found no evidence that foragers preferred to consume neonicotinoid-containing solutions, despite finding effects on feeding motivation and locomotor activity in line with previous work. Bees also did not preferentially visit floral stimuli previously paired with a neonicotinoid-containing solution. These results highlight the need for further research into the mechanisms underlying bees' responses to these pesticides, critical for determining how neonicotinoid-driven foraging preferences might operate in the real world for different bee species.

Lethal and sublethal effects of toxicants on bumble bee populations: a modelling approach

Pollinator decline worldwide is well-documented; globally, chemical pesticides (especially the class of pesticides known as neonicotinoids) have been implicated in hymenopteran decline, but the mechanics and drivers of population trends and dynamics of wild bees is poorly understood. Declines and shifts in community composition of bumble bees (Bombus spp.) have been documented in North America and Europe, with a suite of lethal and sub-lethal effects of pesticides on bumble bee populations documented. We employ a mathematical model parameterized with values taken from the literature that uses differential equations to track bumble bee populations through time in order to attain a better understanding of toxicant effects on a developing colony of bumble bees. We use a delay differential equation (DDE) model, which requires fewer parameter estimations than agent-based models while affording us the ability to explicitly describe the effect of larval incubation and colony history on population outcomes. We explore how both lethal and sublethal effects such as reduced foraging ability may combine to affect population outcomes, and discuss the implications for the protection and conservation of ecosystem services.

Insecticide exposure during brood or early-adult development reduces brain growth and impairs adult learning in bumblebees

For social bees, an understudied step in evaluating pesticide risk is how contaminated food entering colonies affects residing offspring development and maturation. For instance, neurotoxic insecticide compounds in food could affect central nervous system development predisposing individuals to become poorer task performers later-in-life. Studying bumblebee colonies provisioned with neonicotinoid spiked nectar substitute, we measured brain volume and learning behaviour of 3 or 12-day old adults that had experienced in-hive exposure during brood and/or early-stage adult development. Micro-computed tomography scanning and segmentation of multiple brain neuropils showed exposure during either of the developmental stages caused reduced mushroom body calycal growth relative to unexposed workers. Associated with this was a lower probability of responding to a sucrose reward and lower learning performance in an olfactory conditioning test. While calycal volume of control workers positively correlated with learning score, this relationship was absent for exposed workers indicating neuropil functional impairment. Comparison of 3- and 12-day adults exposed during brood development showed a similar degree of reduced calycal volume and impaired behaviour highlighting lasting and irrecoverable effects from exposure despite no adult exposure. Our findings help explain how the onset of pesticide exposure to whole colonies can lead to lag-effects on growth and resultant dysfunction.

Potential Impacts of Translocation of Neonicotinoid Insecticides to Cotton (Gossypium hirsutum (Malvales: Malvaceae)) Extrafloral Nectar on Parasitoids

Neonicotinoid seed treatments are frequently used in cotton (Gossypium hirsutum L. [Malvales: Malvaceae]) production to provide protection against early-season herbivory. However, there is little known about how these applications affect extrafloral nectar (EFN), an important food resource for arthropod natural enemies. Using enzyme-linked immunosorbent assays, we found that neonicotinoids were translocated to the EFN of clothianidin- and imidacloprid-treated, greenhouse-grown cotton plants at concentrations of 77.3 ± 17.3 and 122.6 ± 11.5 ppb, respectively. We did not find differences in the quantity of EFN produced by neonicotinoid-treated cotton plants compared to untreated controls, either constitutively or after mechanical damage. Metabolomic analysis of sugars and amino acids from treated and untreated plants did not detect differences in overall composition of EFN. In bioassays, female Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae) parasitoid wasps that fed on EFN from untreated, clothianidin-treated, or imidacloprid-treated plants demonstrated no difference in mortality or parasitization success. We also conducted acute toxicity assays for C. marginiventris fed on honey spiked with clothianidin and imidacloprid and established LC50 values for male and female wasps. Although LC50 values were substantially higher than neonicotinoid concentrations detected in EFN, caution should be used when translating these results to the field where other stressors could alter the effects of neonicotinoids. Moreover, there are a wide range of possible sublethal impacts of neonicotinoids, none of which were explored here. Our results suggest that EFN is a potential route of exposure of neonicotinoids to beneficial insects and that further field-based studies are warranted.

The novel butenolide pesticide flupyradifurone does not alter responsiveness to sucrose at either acute or chronic short-term field-realistic doses in the honey bee, Apis mellifera

BACKGROUND

Sublethal exposure to neonicotinoids, a popular class of agricultural pesticides, can lead to behavioral effects that impact the health of pollinators. Therefore, new compounds, such as flupyradifurone (FPF), have recently been developed as 'safer' alternatives. FPF is an excitotoxic nicotinic acetylcholine receptor agonist, similar to neonicotinoids. Given the novelty of FPF, what data exist are focused mostly on assessing the effect of FPF on pollinator mortality. One important avenue for investigation is the potential effect of FPF on the sensitivity of nectar foragers, such as Apis mellifera, to sucrose concentrations. Neonicotinoids can alter this sucrose responsiveness and disrupt foraging. Compounding this effect, neonicotinoid-containing solutions are preferred by A. mellifera over pure sucrose solutions. We therefore conducted four studies, administering FPF under both acute and chronic conditions, and at field-realistic and higher than field-realistic doses, to assess the influence of FPF exposure on sucrose responsiveness and sucrose solutions with FPF in A. mellifera nectar foragers.

RESULTS

We found no evidence that FPF exposure under acute or chronic field-realistic conditions significantly altered sucrose responsiveness, and we did not find that bees exposed to FPF consumed more of the solution. However, at the much higher median lethal dose (48 h), among bees that survived, FPF-exposed foragers responded to significantly lower concentrations of sucrose than controls and responded at significantly higher rates to all concentrations of sucrose than controls.

CONCLUSION

We found no evidence that FPF alters the sucrose responsiveness of nectar foragers at field-realistic doses during winter or early spring, but caution and further investigation are warranted, particularly on the effects of FPF in conjunction with other stressors. © 2019 Society of Chemical Industry.

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

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

Impact of acute oral exposure to thiamethoxam on the homing, flight, learning acquisition and short-term retention of Apis cerana

BACKGROUND

Thiamethoxam (TMX) represents the second generation of neonicotinoids that has been widely applied in agricultural activities, while how TMX alters the behavior of Apis cerana, an important native honey bee species in China, is not clear. We carried out three independent experiments to study the impact of acute oral treatment of 20 μL TMX at concentrations of 2.4 ppb (0.048 ng/bee) and 10 ppb (0.2 ng/bee) on the homing, flight, learning acquisition and short-term retention ability of A. cerana. The homing ability was assessed by the catch-and-release method, the flight ability was assessed by flight mills, and the learning acquisition and short-term retention were evaluated by the proboscis extension response method.

RESULTS

When treated with 10 ppb of TMX, bees had a significantly higher average homing time, mean flight velocity, flying distance, and flying duration than the control, whereas 2.4 ppb concentration did not cause any significant effect on homing or flight ability. Bees treated with either 2.4 ppb or 10 ppb TMX had significantly lower learning acquisition and short-term retention ability.

CONCLUSION

Results suggest that acute oral exposure to 10 ppb of TMX altered the short-distance homing time, flight ability, and learning acquisition and short-term retention ability. Our study also highlights the concern that acute oral exposure to a low concentration of 2.4 ppb could have consequences on the behavior of A. creana. Those multiple sublethal alterations on A. cerana's behavior indicate that TMX are likely having complex but negative consequences on bee health in the field. © 2019 Society of Chemical Industry.

Acute exposure to urban air pollution impairs olfactory learning and memory in honeybees

While the ecological effects of pesticides have been well studied in honeybees, it is unclear to what extent other anthropogenic contaminants such as air pollution may also negatively affect bee cognition and behaviour. To answer this question, we assessed the impacts of acute exposure to four ecologically relevant concentrations of a common urban air pollutant-diesel generated air pollution on honeybee odour learning and memory using a conditioned proboscis extension response assay. The proportion of bees that successfully learnt odours following direct air pollution exposure was significantly lower in bees exposed to low, medium and high air pollutant concentrations, than in bees exposed to current ambient levels. Furthermore, short- and long-term odour memory was significantly impaired in bees exposed to low medium and high air pollutant concentrations than in bees exposed to current ambient levels. These results demonstrate a clear and direct cognitive cost of air pollution. Given learning and memory play significant roles in foraging, we suggest air pollution will have increasing negative impacts on the ecosystem services bees provide and may add to the current threats such as pesticides, mites and disease affecting colony fitness.

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.

Modality-specific impairment of learning by a neonicotinoid pesticide

Neonicotinoid pesticides can impair bees' ability to learn and remember information about flowers, critical for effective foraging. Although these effects on cognition may contribute to broader effects on health and performance, to date they have largely been assayed in simplified protocols that consider learning in a single sensory modality, usually olfaction. Given that real flowers display a variety of potentially useful signals, we assessed the effects of acute neonicotinoid exposure on multimodal learning in free-flying bumblebees. We found that neonicotinoid consumption differentially impacted learning of floral stimuli, impairing scent, but not colour, learning. These findings raise questions about the mechanisms by which pesticides might differentially impair sensory systems, with implications for how neonicotinoids affect multiple aspects of bee ecology.

Effect of Sub-lethal Doses of Imidacloprid on Learning and Memory Formation of Indigenous Arabian Bee (Apis mellifera jemenitica Ruttner) Adult Foragers

The indigenous bee race Apis mellifera jemenitica Ruttner of Saudi Arabia can learn and retain memories established by the classical conditioning of proboscis extension response (PER). The insecticide imidacloprid has shown a drastic effect on the olfactory behavior of A. m. jemenitica in the harsh arid climatic conditions of central Saudi Arabia. The oral feeding of single imidacloprid sub-lethal doses (1.0 ng, 0.5 ng, or 0.1 ng) under laboratory conditions significantly impaired associative learning during the 2nd and 3rd conditioning trials compared to control bees (0 ng). The memory tests also revealed significant impairment in memory formation at 1 h, 2 h, and 24 h after conditioning compared to control bees. Even the lowest dose (0.1 ng/bee) can significantly impair the bees' ability to learn and memorize. This impairment effect was dose dependent and increased with increasing doses. The higher dose (1.0 ng) completely impaired the learning but still showed a little memory and reflected the potential recovery of bees from insecticide-induced impairment with the passage of time. To our knowledge, this is the first study in A. m. jemenitica that demonstrated the drastic effect of neonicotinoids on associative learning in indigenous bees. This study further expresses the possible severity of insecticidal exposure to bees in actual field conditions and its effect on the neural functions used in important behavior involved in the foraging of bees.

Lethal and sublethal synergistic effects of a new systemic pesticide, flupyradifurone (Sivanto®), on honeybees

The honeybee ( Apis mellifera L.) is an important pollinator and a model for pesticide effects on insect pollinators. The effects of agricultural pesticides on honeybee health have therefore raised concern. Bees can be exposed to multiple pesticides that may interact synergistically, amplifying their side effects. Attention has focused on neonicotinoid pesticides, but flupyradifurone (FPF) is a novel butenolide insecticide that is also systemic and a nicotinic acetylcholine receptor (nAChR) agonist. We therefore tested the lethal and sublethal toxic effects of FPF over different seasons and worker types, and the interaction of FPF with a common SBI fungicide, propiconazole. We provide the first demonstration of adverse synergistic effects on bee survival and behaviour (poor coordination, hyperactivity, apathy) even at FPF field-realistic doses (worst-case scenarios). Pesticide effects were significantly influenced by worker type and season. Foragers were consistently more susceptible to the pesticides (4-fold greater effect) than in-hive bees, and both worker types were more strongly affected by FPF in summer as compared with spring. Because risk assessment (RA) requires relatively limited tests that only marginally address bee behaviour and do not consider the influence of bee age and season, our results raise concerns about the safety of approved pesticides, including FPF. We suggest that pesticide RA also test for common chemical mixture synergies on behaviour and survival.

Learning of monochromatic stimuli in Apis cerana and Apis mellifera by means of PER conditioning

Honey bees are globally distributed and have received increased attention due to their high economic and ecological value for pollination, their exceptional eusocial lifestyle and complex behavioral repertoire. Interestingly, most research on learning and memory in honey bees has been performed in the Western honey bee, Apis mellifera L., and other honey bee species were largely neglected. In the current study, we thus compared visual learning performance of A. mellifera and the Eastern honey bee, A. cerana Fabr., using the proboscis extension response (PER) paradigm. Workers of A. mellifera and A. cerana were differentially conditioned to two monochromatic light stimuli, with peak maxima at 435 and 528 nm. Both honey bee species were able to form an association between the color stimulus and a sugar reward and significantly distinguished between the two color stimuli in a differential discrimination test. However, besides similar performance levels during visual learning, A. cerana showed a reduced mid-term memory (tested after 2 h) compared to A. mellifera. Finally, performance of the visual PER conditioning in our study reached similar levels as found in olfactory PER conditioning, and we thus recommend the visual PER conditioning approach in addition to olfactory conditioning as a useful tool for studying species-specific learning and memory capabilities in honey bees under controlled laboratory conditions.

A neonicotinoid pesticide impairs foraging, but not learning, in free-flying bumblebees

Neonicotinoids are widely-used pesticides implicated in the decline of bees, known to have sub-lethal effects on bees’ foraging and colony performance. One proposed mechanism for these negative effects is impairment to bees’ ability to learn floral associations. However, the effects of neonicotinoids on learning performance have largely been addressed using a single protocol, where immobilized bees learn an association based on a single sensory modality. We thus have an incomplete understanding of how these pesticides affect bee learning in more naturalistic foraging scenarios. We carried out the first free-foraging study into the effects of acute exposure of a neonicotinoid (imidacloprid) on bumblebees’ (Bombus impatiens) ability to learn associations with visual stimuli. We uncovered dose-dependent detrimental effects on motivation to initiate foraging, amount of nectar collected, and initiation of subsequent foraging bouts. However, we did not find any impairment to bees’ ability to learn visual associations. While not precluding the possibility that other forms of learning are impaired, our findings suggest that some of the major effects of acute neonicotinoid exposure on foraging performance may be due to motivational and/or sensory impairments. In light of these findings, we discuss more broadly how pesticide effects on pollinator cognition might be studied.

Chronic contact with realistic soil concentrations of imidacloprid affects the mass, immature development speed, and adult longevity of solitary bees

The non-target effects of pesticides are an area of growing concern, particularly for ecologically and economically important organisms such as bees. Much of the previous research on the effects of neonicotinoids, a class of insecticide that has gained attention for non-target effects, on bees focused on the consumption of contaminated food resources by a limited number of eusocial species. However, neonicotinoids are known to accumulate and persist in soils at concentrations 2 to 60 times greater than in food resources, and may represent an important route of exposure for diverse and ecologically important ground-nesting bees. This study aimed to assess the effect of chronic contact exposure to realistic soil concentrations of imidacloprid, the most widely used neonicotinoid pesticide, on bee longevity, development speed, and body mass. Cohorts of Osmia lignaria and Megachile rotundata were used as proxies for ground-nesting species. We observed species- and sex-specific changes to adult longevity, development speed, and mass in response to increasing concentrations of imidacloprid. These results suggest that chronic exposure to nesting substrates contaminated with neonicotinoids may represent an important route of exposure that could have considerable physiological and ecological consequences for bees and plant-pollinator interactions.

Degradation of sex pheromone and plant volatile components by an antennal glutathione S-transferase in the oriental fruit moth,Grapholita molesta Busck (Lepidoptera: Tortricidae)

Insect antennae have a primary function of perceiving and discerning odorant molecules including sex pheromones and host plant volatiles. The assumption that genes highly expressed in the antennae may have an olfactory-related role associated with signal transduction. Here, one delta subfamily glutathione S-transferase (GST) gene (GmolGSTD1) was obtained from an antennal transcriptome of Grapholita molesta. Quantitative real-time polymerase chain reaction results revealed that GmolGSTD1 was mainly expressed in antennae and the expression levels were significantly higher in female antennae than in male antennae. The recombinant GmolGSTD1 (rGmolGSTD1) showed glutathione-conjugating activity toward 1-chloro-2,4-dinitrobenzene (CDNB) as substrates. The pH range for optimal rGmolGSTD1 enzyme activity was 6.0-6.5, and rGmolGSTD1 enzyme activity had maximal peaks at 35-40°C. Spectrophotometric analysis indicated that insecticides had weak inhibitory effects on the activity of rGmolGSTD1 with the inhibitory rates of 28.82% for chlorpyrifos, 22.27% for lambda-cyhalothrin, 18.07% for bifenthrin, 20.42% for acetamiprid, 17.57% for thiamethoxam, 25.67% for metaflumizone, 27.43% for abamectin, and 7.24% for chlorbenzuron. rGmolGSTD1 exhibited high degradation activity to the sex pheromone component (Z)-8-dodecenyl alcohol and the host plant volatile butyl hexanoate with the degradation efficiency of 75.01% and 48.54%, respectively. We speculate that GmolGSTD1 works in inactivating odorant molecules and maintaining sensitivity to olfactory communication of G. molesta.

Neonicotinoid exposure disrupts bumblebee nest behavior, social networks, and thermoregulation

Neonicotinoid pesticides can negatively affect bee colonies, but the behavioral mechanisms by which these compounds impair colony growth remain unclear. Here, we investigate imidacloprid’s effects on bumblebee worker behavior within the nest, using an automated, robotic platform for continuous, multicolony monitoring of uniquely identified workers. We find that exposure to field-realistic levels of imidacloprid impairs nursing and alters social and spatial dynamics within nests, but that these effects vary substantially with time of day. In the field, imidacloprid impairs colony thermoregulation, including the construction of an insulating wax canopy. Our results show that neonicotinoids induce widespread disruption of within-nest worker behavior that may contribute to impaired growth, highlighting the potential of automated techniques for characterizing the multifaceted, dynamic impacts of stressors on behavior in bee colonies.

Functional characterization of CYP4G11-a highly conserved enzyme in the western honey bee Apis mellifera

Determining the functionality of CYP4G11, the only CYP4G in the genome of the western honey bee Apis mellifera, can provide insight into its reduced CYP4 inventory. Toward this objective, CYP4G11 transcripts were quantified, and CYP4G11 was expressed as a fusion protein with housefly CPR in Sf9 cells. Transcript levels varied with age, task, and tissue type in a manner consistent with the need for cuticular hydrocarbon production to prevent desiccation or with comb wax production. Young larvae, with minimal need for desiccation protection, expressed CYP4G11 at very low levels. Higher levels were observed in nurses, and even higher levels in wax producers and foragers, the latter of which risk desiccation upon leaving the hive. Recombinant CYP4G11 readily converted octadecanal to n-heptadecane in a time-dependent manner, demonstrating its functions as an oxidative decarbonylase. CYP4G11 expression levels are high in antennae; heterologously expressed CYP4G11 converted tetradecanal to n-tridecane, demonstrating that it metabolizes shorter-chain aldehydes. Together, these findings confirm the involvement of CYP4G11 in cuticular hydrocarbon production and suggest a possible role in clearing pheromonal and phytochemical compounds from antennae. This possible dual functionality of CYP4G11, i.e., cuticular hydrocarbon and comb wax production and antennal odorant clearance, may explain how honey bees function with a reduced CYP4G inventory.

The identification and expression analysis of candidate chemosensory genes in the bird cherry-oat aphid Rhopalosiphum padi (L.)

The bird cherry-oat aphid Rhopalosiphum padi (L.) is one of the most important wheat pests with polyphagia and autumn migrants. And, chemosensory genes were thought to play a key role in insect searching their hosts, food and mate. However, a systematic identification of the chemosensory genes in this pest has not been reported. Thus, in this study, we identified 14 odorant-binding proteins, nine chemosensory proteins, one sensory neuron membrane protein, 15 odorant receptors, 19 gustatory receptors and 16 ionotropic receptors from R. padi transcriptomes with a significantly similarity (E-value < 10-5) to known chemosensory genes in Acyrthosiphon pisum and Aphis gossypii. In addition, real-time quantitative polymerase chain reaction (RT-qPCR) was employed to determine the expression profiles of obtained genes. Among these obtained genes, we selected 23 chemosensory genes to analyze their expression patterns in different tissues, wing morphs and host plants. We found that except RpOBP1, RpOBP3, RpOBP4 and RpOBP5, the rest of the selected genes were highly expressed in the head with antennae compared with body without head and antennae. Besides that, the stimulation and depression of chemosensory genes by plant switch indicated that chemosensory genes might be involved in the plant suitability assessment. These results not only provide insights for the potential roles of chemosensory genes in plant search and perception of R. padi but also provide initial background information for the further research on the molecular mechanism of the polyphagia and autumn migrants of it. Furthermore, these chemosensory genes are also the candidate targets for pest management control in future.

Enhancement of chronic bee paralysis virus levels in honeybees acute exposed to imidacloprid: A Chinese case study

Though honeybee populations have not yet been reported to be largely lost in China, many stressors that affect the health of honeybees have been confirmed. Honeybees inevitably come into contact with environmental stressors that are not intended to target honeybees, such as pesticides. Although large-scale losses of honeybee colonies are thought to be associated with viruses, these viruses usually lead to covert infections and to not cause acute damage if the bees do not encounter outside stressors. To reveal the potential relationship between acute pesticides and viruses, we applied different doses of imidacloprid to adult bees that were primarily infected with low levels (4.3×10⁵ genome copies) of chronic bee paralysis virus (CBPV) to observe whether the acute oral toxicity of imidacloprid was able to elevate the level of CBPV. Here, we found that the titer of CBPV was significantly elevated in adult bees after 96h of acute treatment with imidacloprid at the highest dose 66.9ng/bee compared with other treatments and controls. Our study provides clear evidence that exposure to acute high doses of imidacloprid in honeybees persistently infected by CBPV can exert a remarkably negative effect on honeybee survival. These results imply that acute environmental stressors might be one of the major accelerators causing rapid viral replication, which may progress to cause mass proliferation and dissemination and lead to colony decline. The present study will be useful for better understanding the harm caused by this pesticide, especially regarding how honeybee tolerance to the viral infection might be altered by acute pesticide exposure.

Quantifying the impact of pesticides on learning and memory in bees

Most insecticides are insect neurotoxins. Evidence is emerging that sublethal doses of these neurotoxins are affecting the learning and memory of both wild and managed bee colonies, exacerbating the negative effects of pesticide exposure and reducing individual foraging efficiency.

Variation in methodologies and interpretation of results across studies has precluded the quantitative evaluation of these impacts that is needed to make recommendations for policy change. It is not clear whether robust effects occur under acute exposure regimes (often argued to be more field‐realistic than the chronic regimes upon which many studies are based), for field‐realistic dosages, and for pesticides other than neonicotinoids.

Here we use meta‐analysis to examine the impact of pesticides on bee performance in proboscis extension‐based learning assays, the paradigm most commonly used to assess learning and memory in bees. We draw together 104 (learning) and 167 (memory) estimated effect sizes across a diverse range of studies.

We detected significant negative effects of pesticides on learning and memory (i) at field realistic dosages, (ii) under both chronic and acute application, and (iii) for both neonicotinoid and non‐neonicotinoid pesticides groups.

We also expose key gaps in the literature that include a critical lack of studies on non‐Apis bees, on larval exposure (potentially one of the major exposure routes), and on performance in alternative learning paradigms.

Policy implications. Procedures for the registration of new pesticides within EU member states now typically require assessment of risks to pollinators if potential target crops are attractive to bees. However, our results provide robust quantitative evidence for subtle, sublethal effects, the consequences of which are unlikely to be detected within small‐scale prelicensing laboratory or field trials, but can be critical when pesticides are used at a landscape scale. Our findings highlight the need for long‐term postlicensing environmental safety monitoring as a requirement within licensing policy for plant protection products.

Interactions between immunotoxicants and parasite stress: Implications for host health

Many organisms face a wide variety of biotic and abiotic stressors which reduce individual survival, interacting to further reduce fitness. Here we studied the effects of two such interacting stressors: immunotoxicant exposure and parasite infection. We model the dynamics of a within-host infection and the associated immune response of an individual. We consider both the indirect sub-lethal effects on immunosuppression and the direct effects on health and mortality of individuals exposed to toxicants. We demonstrate that sub-lethal exposure to toxicants can promote infection through the suppression of the immune system. This happens through the depletion of the immune response which causes rapid proliferation in parasite load. We predict that the within-host parasite density is maximised by an intermediate toxicant exposure, rather than continuing to increase with toxicant exposure. In addition, high toxicant exposure can alter cellular regulation and cause the breakdown of normal healthy tissue, from which we infer higher mortality risk of the host. We classify this breakdown into three phases of increasing toxicant stress, and demonstrate the range of conditions under which toxicant exposure causes failure at the within-host level. These phases are determined by the relationship between the immunity status, overall cellular health and the level of toxicant exposure. We discuss the implications of our model in the context of individual bee health. Our model provides an assessment of how pesticide stress and infection interact to cause the breakdown of the within-host dynamics of individual bees.

Effects of chronic exposure to thiamethoxam on larvae of the hoverfly Eristalis tenax (Diptera, Syrphidae)

There is widespread concern over the use of neonicotinoid pesticides in the agro-ecosystem, due in part to their high water solubility which can lead to widespread contamination of non-target areas including standing surface water. Most studies investigating the negative fitness consequences of neonicotinoids have focused on bees, with little research on the impact on other non-target insects. Here we examined the effect of exposure on the aquatic larval stages of the hoverfly Eristalis tenax L. (Diptera: Syrphidae) to a range of concentrations (control, 5, 15, 50, 100 and 500 ppb) of the neonicotinoid thiamethoxam; no published studies have thus far examined the effects of neonicotinoids on hoverflies. Survival was significantly lower when exposed to 500 ppb thiamethoxam, but this concentration exceeds that likely to be found in the field. We observed no effect on survival, development or any latent effects on adult activity budgets resulting from exposure to lower concentrations (up to 100 ppb). Our results suggest that E. tenax exposed as larvae to thiamethoxam are unlikely to be negatively impacted by this neonicotinoid under field conditions.

The reluctant visitor: an alkaloid in toxic nectar can reduce olfactory learning and memory in Asian honey bees

The nectar of the thunder god vine, Tripterygium hypoglaucum, contains a terpenoid, triptolide (TRP), that may be toxic to the sympatric Asian honey bee, Apis cerana, because honey produced from this nectar is toxic to bees. However, these bees will forage on, recruit for, and pollinate this plant during a seasonal dearth of preferred food sources. Olfactory learning plays a key role in forager constancy and pollination, and we therefore tested the effects of acute and chronic TRP feeding on forager olfactory learning, using proboscis extension reflex conditioning. At concentrations of 0.5-10 µg TRP/ml, there were no learning effects of acute exposure. However, memory retention (1 h after the last learning trial) significantly decreased by 56% following acute consumption of 0.5 µg TRP/ml. Chronic exposure did not alter learning or memory, except at high concentrations (5 and 10 µg TRP/ml). TRP concentrations in nectar may therefore not significantly harm plant pollination. Surprisingly, TRP slightly increased bee survival, and thus other components in T. hypoglaucum honey may be toxic. Long term exposure to TRP could have colony effects, but these may be ameliorated by the bees’ aversion to T. hypoglaucum nectar when other food sources are available and, perhaps, by detoxification mechanisms. The co-evolution of this plant and its reluctant visitor may therefore likely illustrate a classic compromise between the interests of both actors.

First demonstration of olfactory learning and long term memory in honey bee queens

As the primary source of colony reproduction, social insect queens play a vital role. However, the cognitive abilities of queens are not well understood, although queen learning and memory are essential in multiple species such as honey bees, in which virgin queens must leave the nest and then successful learn to navigate back over repeated nuptial flights. Honey bee queen learning has never been previously demonstrated. We therefore tested olfactory learning in queens and workers and examined the role of DNA methylation, which plays a key role in long term memory formation. We provide the first evidence that honey bee queens have excellent learning and memory. The proportion of honey bee queens that exhibited learning was 5-fold higher than workers at every tested age and, for memory, 4-fold higher than workers at a very young age. DNA methylation may play a key role in this queen memory because queens exhibiting remote memory had a more consistent elevation in Dnmt3 gene expression as compared to workers. Both castes also showed excellent remote memory (7 day memory), which was reduced by 14-20% by the DNA methylation inhibitor, zebularine. Given that queens live about 10-fold longer than workers, these results suggest that queens can serve as an excellently long-term reservoir of colony memory.

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.