Effects of acute sublethal exposure to coumaphos or diazinon on acquisition and discrimination of odor stimuli in the honey bee (Hymenoptera: Apidae)

Current Insights into Sublethal Effects of Pesticides on Insects

The effect of pesticides on insects is often discussed in terms of acute and chronic toxicity, but an important and often overlooked aspect is the impact of sublethal doses on insect physiology and behavior. Pesticides can influence various physiological parameters of insects, including the innate immune system, development, and reproduction, through a combination of direct effects on specific exposed tissues and the modification of behaviors that contribute to health and reproductive success. Such behaviors include mobility, feeding, oviposition, navigation, and the ability to detect pheromones. Pesticides also have a profound effect on insect learning and memory. The precise effects depend on many different factors, including the insect species, age, sex, caste, physiological condition, as well as the type and concentration of the active ingredients and the exposure route. More studies are needed to assess the effects of different active ingredients (and combinations thereof) on a wider range of species to understand how sublethal doses of pesticides can contribute to insect decline. This review reflects our current knowledge about sublethal effects of pesticides on insects and advancements in the development of innovative methods to detect them.

Acute ozone exposure impairs detection of floral odor, learning, and memory of honey bees, through olfactory generalization

Air pollution stemming from human activities affects the environment in which plant and animal species live and interact. Similar to primary air pollutants which are emitted, secondary air pollutants, such as tropospheric ozone (O₃) formed from nitrogen oxides, are also harmful to human health and plant physiology. Yet, few reports studied the effects of O₃ on pollinators' physiology, despite that this pollutant, with its high oxidative potential, likely affects pollinators behaviors, especially the perception of signals they rely on to navigate their environment. Volatile Organic Compounds (VOCs) released by plants are used as signals by different animals. For pollination services, VOCs attract different insects to the flowers and strengthen these interactions. Here, we used the honey bee Apis mellifera as a model to characterize the effects of acute exposure to different realistic mixing ratios of O₃ (80-, 120-, and 200-ppb) on two crucial aspects: first, how exposed honey bees detect VOCs; and second, how O₃ affects these pollinators' learning and memory processes. With electroantennogram (EAG) recordings, we showed that increasing O₃ mixing ratios had a biphasic effect: an initial 25% decrease of the antennal activity when bees were tested directly after exposure (O₃ direct effect), followed by a 25% increase in activity and response when bees were allowed a two-hour rest after exposure (O₃ delayed effect). In parallel, during olfactory conditioning, increasing O₃ mixing ratios in both exposure protocols scarcely affected olfactory learning, followed by a decrease in recall of learned odors and an increase of response to new odors, leading to a higher generalization rate (i.e., discrimination impairment). These results suggest a link between O₃-related oxidative stress and olfactory coding disturbance in the honey bee brain. If ozone affects the pollinators' olfaction, foraging behaviors may be modified, in addition with a possible long-term harmful effect on pollination services.

Effects of Insecticides and Microbiological Contaminants on Apis mellifera Health

Over the past two decades, there has been an alarming decline in the number of honey bee colonies. This phenomenon is called Colony Collapse Disorder (CCD). Bee products play a significant role in human life and have a huge impact on agriculture, therefore bees are an economically important species. Honey has found its healing application in various sectors of human life, as well as other bee products such as royal jelly, propolis, and bee pollen. There are many putative factors of CCD, such as air pollution, GMO, viruses, or predators (such as wasps and hornets). It is, however, believed that pesticides and microorganisms play a huge role in the mass extinction of bee colonies. Insecticides are chemicals that are dangerous to both humans and the environment. They can cause enormous damage to bees' nervous system and permanently weaken their immune system, making them vulnerable to other factors. Some of the insecticides that negatively affect bees are, for example, neonicotinoids, coumaphos, and chlorpyrifos. Microorganisms can cause various diseases in bees, weakening the health of the colony and often resulting in its extinction. Infection with microorganisms may result in the need to dispose of the entire hive to prevent the spread of pathogens to other hives. Many aspects of the impact of pesticides and microorganisms on bees are still unclear. The need to deepen knowledge in this matter is crucial, bearing in mind how important these animals are for human life.

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.

Review on Sublethal Effects of Environmental Contaminants in Honey Bees (Apis mellifera), Knowledge Gaps and Future Perspectives

Honey bees and the pollination services they provide are fundamental for agriculture and biodiversity. Agrochemical products and other classes of contaminants, such as trace elements and polycyclic aromatic hydrocarbons, contribute to the general decline of bees' populations. For this reason, effects, and particularly sublethal effects of contaminants need to be investigated. We conducted a review of the existing literature regarding the type of effects evaluated in Apis mellifera, collecting information about regions, methodological approaches, the type of contaminants, and honey bees' life stages. Europe and North America are the regions in which A. mellifera biological responses were mostly studied and the most investigated compounds are insecticides. A. mellifera was studied more in the laboratory than in field conditions. Through the observation of the different responses examined, we found that there were several knowledge gaps that should be addressed, particularly within enzymatic and molecular responses, such as those regarding the immune system and genotoxicity. The importance of developing an integrated approach that combines responses at different levels, from molecular to organism and population, needs to be highlighted in order to evaluate the impact of anthropogenic contamination on this pollinator species.

Impact of sublethal exposure to synthetic and natural acaricides on honey bee (Apis mellifera) memory and expression of genes related to memory

Acaricides are used by beekeepers in honey bee (Apis mellifera L.) colonies to control parasitic mites, but may also have adverse effects to honey bees. In this study, five commonly used acaricides were tested for their sublethal effects on memory and expression of neural-related genes in honey bees. Memory measured with the proboscis extension reflex (PER) assay was significantly reduced by topical treatment of bees with a single LD₀₅ dose of formic acid at 2 and 24 h post treatment (hpt). However, tau-fluvalinate, amitraz, coumaphos, and formic acid, but not thymol, resulted in memory loss at 48 hpt. The LD₀₅ doses of the acraricides did not affect expression of neuroligin-1, related to memory, or expression of major royal jelly protein-1, related to both memory and development, although expression of both genes was affected at LD₅₀ doses. The LD₀₅ doses of thymol, formic acid, amitraz and coumaphos increased defensin-1 expression, which is related to both memory and immunity. The effect of thymol, however, may have been due to its impact on the immune response rather than memory. This study demonstrates that acaricides vary in their effects on bee's memory, and that the widely used acaricide, formic acid, is particularly damaging.

Real-Time Measurement of Herbicides in the Atmosphere: A Case Study of MCPA and 2,4-D during Field Application

Atmospheric sources of herbicides enable short- and long-range transport of these compounds to off-target areas but the concentrations and mechanisms are poorly understood due, in part, to the challenge of detecting these compounds in the atmosphere. We present chemical ionization time-of-flight mass spectrometry as a sensitive, real-time technique to detect chlorinated phenoxy acid herbicides in the atmosphere, using measurements during and after application over a field at Colorado State University as a case study. Gas-phase 2,4-dichlorophenoxyacetic acid (2,4-D) mixing ratios were greatest during application (up to 20 ppt_v), consistent with rapid volatilization from spray droplets. In contrast, atmospheric concentrations of 2-methyl-4-chlorophenoxyacetic acid (MCPA) increased for several hours after the initial application, indicative of a slower source than 2,4-D. The maximum observed gas-phase MCPA was 60 ppt_v, consistent with a post-application volatilization source to the atmosphere. Exposure to applied pesticides in the gas-phase can thus occur both during and at least several hours after application. Spray droplet volatilization and direct volatilization from surfaces may both contribute pesticides to the atmosphere, enabling pesticide transport to off-target and remote regions.

Lethality of synthetic and natural acaricides to worker honey bees (Apis mellifera) and their impact on the expression of health and detoxification-related genes

In this study, honey bees (Apis mellifera L.) were exposed to LD₀₅ and LD₅₀ doses of five commonly used acaricides for controlling the parasitic mite, Varroa destructor. LD₅₀ values at 48 h post-treatment showed that tau-fluvalinate was the most toxic, followed by amitraz, coumaphos, thymol, and formic acid. However, the hazard ratios, which estimate the hive risk level based on a ratio of a standard dose of acaricide per hive to the LD₅₀ of the acaricide, revealed that tau-fluvalinate was the most hazardous followed by formic acid, coumaphos, amitraz, and thymol. The expression of the honey bee acetylcholinesterase gene increased after treatment with the LD₀₅ and LD₅₀ acaricide doses and could distinguish three patterns in the timing and level of increased expression between acaricides: one for amitraz, one for tau-fluvalinate and formic acid, and one for coumaphos and thymol. Conversely, changes in cytochrome P450 gene expression could also be detected in response to all five acaricides, but there were no significant differences between them. Changes in vitellogenin gene expression could only detect the effects of tau-fluvalinate, amitraz, or coumaphos treatment, which were not significantly different from each other. Among the acaricides tested, coumaphos, amitraz, and thymol appear to be the safest acaricides based on their hazard ratios, and a good marker to detect differences between the effects of sub-lethal doses of acaricides is monitoring changes in acetylcholinesterase gene expression.

Transfer of the Active Ingredients of Some Plant Protection Products from Raspberry Plants to Beehives

Plant protection products (PPPs) have been found increasingly in the environment. They pose a huge threat to bees, contributing to honeybee colony losses and consequently to enormous economic losses. Therefore, this field investigation was designed to determine whether their active ingredients (AIs) were transferred from raspberry plants to beehives located in the immediate neighbourhood of the crop and to what extent they were transferred. Every week for 2 months, samples of soil, raspberry leaves, flowers and fruits, worker bees, honeybee brood, and honey were collected and analysed for the presence of propyzamide, chlorpyrifos, iprodione, pyraclostrobin, boscalid, cypermethrin, difenoconazole, azoxystrobin, and pyrimethanil residues. Five of these substances were found in the worker bee bodies. Chlorpyrifos, applied to only the soil through the irrigation system, also was detected in the brood. A small amount of boscalid was noted in the honey, but its residues did not exceed the maximum residue level. For chlorpyrifos, boscalid, and pyrimethanil, a positive correlation between the occurrence of PPPs in the crops and the beehives was found. Statistical methods confirmed that the application of PPPs on a raspberry plantation, as an example of nectar-secreting plants, was linked to the transfer of their AIs to beehives.

Different response of acetylcholinesterases in salt- and detergent-soluble fractions of honeybee haemolymph, head and thorax after exposure to diazinon

Organophosphate pesticide diazinon is a specific inhibitor of acetylcholinesterase (AChE), which is a common neurotoxicity biomarker in environmental studies. In honeybees, AChE exists in two forms having different physiological roles, one existing as a soluble form and the other as membrane-bound. In most studies AChE activity has been analysed without paying considerable attention to different forms of AChE. In this study, we exposed honeybees Apis mellifera carnica for 10days to diazinon via oral exposure and analysed the total AChE activities in salt soluble (SS) and detergent soluble (DS) fractions. We assumed that SS fraction would preferentially contain the soluble AChE, but the DS fraction would contain only membrane AChE. On the contrary, our results showed that SS and DS fractions both contain soluble and membrane AChE and the latter has considerably higher activity. Despite this we obtained a differential response of AChE activity in SS and DS fractions when exposed to diazinon. The head/thorax AChE activity in DS fraction decreased, while the head/thorax AChE activity in SS fraction increased at sublethal concentrations. The AChE activity in honeybee hemolymph shown here for the first time is a salt soluble enzyme. Its activity remained unaltered after diazinon treatment. In conclusion, we provide evidence that varying results regarding AChE activity alterations upon stressor exposure are obtained when extracted through different procedures. In further environmental studies with honeybees this differential response of AChE activity should be given considerable attention because this affects the outcome of ecotoxicity study.

Transfer and Metabolism of Triadimefon Residues from Rape Flowers to Apicultural Products

This paper presents a study on the transfer and metabolism of triadimefon residues from rape flowers to apicultural products. In the field trials, honeybee colonies were placed in four rape greenhouses treated with triadimefon on standard dosage. Apicultural products (pollen, honey, and royal jelly) were collected on a regular basis. Sample preparation and extraction procedure were established. HPLC/ESI-MS/MS method was validated. The respective residues of triadimefon and metabolite triadimenol were 0.03 ± 0.002 mg/kg and 0.13 ± 0.02 mg/kg in pollen on the 18th day, and both had reached the limits of detection in honey on the 24th day, while they were 0.004 ± 0.0005 mg/kg and 0.010 ± 0.0002 mg/kg in royal jelly on the 22nd day. Mathematical curve fitting studies were further investigated. On the basis of recommended dosage, the degradation half-lives of triadimefon in pollen, honey, and royal jelly were about 0.7, 12.5, and 19.5 days, respectively. Transfer of triadimefon residues from rape flowers to apicultural products diminished over spraying time. The residues of triadimefon and metabolite triadimenol in pollen were about 10 times higher than those in honey and jelly. Time to attain the maximum permissible limit of pollen in the European Union was 14.9 days, predicted from the index function.

Effects of Bacillus thuringiensis strains virulent to Varroa destructor on larvae and adults of Apis mellifera

The sublethal effects of two strains of Bacillus thuringiensis, which were virulent in vitro to Varroa destructor, were measured on Apis mellifera. The effects of five concentrations of total protein (1, 5, 25, 50 and 100μg/mL) from the EA3 and EA26.1 strains on larval and adult honey bees were evaluated for two and seven days under laboratory conditions. Based on the concentrations evaluated, total protein from the two strains did not affect the development of larvae, the syrup consumption, locomotor activity or proboscis extension response of adults. These same parameters were also tested for the effects of three concentrations (1, 10 and 15μg/kg) of cypermethrin as a positive control. Although no significant differences were observed after two days of treatment with cypermethrin, a dose-response relationship in syrup consumption and locomotor activity was observed. A significant reduction in the proboscis extension response of the bees treated with cypermethrin was also observed. Therefore, in contrast to cypermethrin, our results indicate that the EA3 and EA26.1 strains of B. thuringiensis can be used in beehives to control V. destructor and reduce the negative effects of this mite on colonies without adverse effects on the larvae and adults of A. mellifera. Additionally, the overuse of synthetic miticides, which produce both lethal and sublethal effects on bees, can be reduced.

Acute Exposure to Worst-Case Concentrations of Amitraz Does Not Affect Honey Bee Learning, Short-Term Memory, or Hemolymph Octopamine Levels

Amitraz, an acaricide used to treat Varroa destructor Anderson & Trueman, is one of the most commonly detected pesticides in honey bee (Apis mellifera L.) hives. Acaricides sometimes negatively impact honey bee cognition, but potential effects of amitraz on honey bee learning have been rarely studied. We topically exposed foragers to 95th percentile field-relevant levels of amitraz and, 24 h later, tested the ability of bees to associate a sucrose reward with a conditioned odor (learning response) using the proboscis extension response (PER). We then tested the ability of the bees to retain this memory 1 h and 2 h post-conditioning. Because amitraz is thought to affect octopamine metabolism in honey bees, and because octopamine is directly related to honey bee learning and memory, we also examined effects of exposure to amitraz on octopamine levels in honey bee hemolymph. We found that acute exposure to 95th percentile doses of amitraz had no impact on honey bee learning or short-term memory as measured by PER. Concentrations of octopamine in hemolymph from our low amitraz treatment were 1.4-fold higher than control levels, but other treatments had no effect. Our results from worst-case acute exposure experiments with worker bees in the laboratory suggest that typical field-relevant (within hive) exposures to amitraz probably have little effect on honey bee learning and memory.

Transfer Assessment of Carbendazim Residues from Rape Flowers to Apicultural Products

Carbendazim is usually used to control the Sclerotinia sclerotiorum of rapes during the flowering period. This paper presents a study on transfer assessment of carbendazim residues from rape flowers to apicultural products. In the field trials, the rapes were sprayed with carbendazim on standard dosage. Bees produced apicultural products (bee pollen, honey, and royal jelly) from sprayed rapes. Apicultural products were collected on a regular basis. Carbendazim residues were extracted from bee pollen, honey, and royal jelly, respectively. HPLC/ESI-MS/MS method was developed and partially validated to identify and quantify carbendazim residues. The limits of quantification in pollen, honey, and royal jelly were 0.01 mg/kg. Mathematical curve fitting was carried out on the basis of transfer assessment of carbendazim residues from rape flowers to apicultural products. The respective carbendazim residues were 1.10 ± 0.03 mg/kg in pollen on 18th day, 0.032 ± 0.001 mg/kg in honey on 24th day, and 0.077 ± 0.002 mg/kg in royal jelly on 22nd day. Transfer assessment and mathematical curve fitting of carbendazim residues from rape flowers to apicultural products show carbendazim diminished over spraying time. The gap of carbendazim residues between pollen and honey is decreased with time. The carbendazim residues in pollen are 10 times higher than that of honey and jelly.

Measurements of Chlorpyrifos Levels in Forager Bees and Comparison with Levels that Disrupt Honey Bee Odor-Mediated Learning Under Laboratory Conditions

Chlorpyrifos is an organophosphate pesticide used around the world to protect food crops against insects and mites. Despite guidelines for chlorpyrifos usage, including precautions to protect beneficial insects, such as honeybees from spray drift, this pesticide has been detected in bees in various countries, indicating that exposure still occurs. Here, we examined chlorpyrifos levels in bees collected from 17 locations in Otago, New Zealand, and compared doses of this pesticide that cause sub-lethal effects on learning performance under laboratory conditions with amounts of chlorpyrifos detected in the bees in the field. The pesticide was detected at 17 % of the sites sampled and in 12 % of the colonies examined. Amounts detected ranged from 35 to 286 pg.bee(-1), far below the LD50 of ~100 ng.bee(-1). We detected no adverse effect of chlorpyrifos on aversive learning, but the formation and retrieval of appetitive olfactory memories was severely affected. Chlorpyrifos fed to bees in amounts several orders of magnitude lower than the LD50, and also lower than levels detected in bees, was found to slow appetitive learning and reduce the specificity of memory recall. As learning and memory play a central role in the behavioral ecology and communication of foraging bees, chlorpyrifos, even in sublethal doses, may threaten the success and survival of this important insect pollinator.

Effects of environmentally-relevant mixtures of four common organophosphorus insecticides on the honey bee (Apis mellifera L.)

We assessed whether exposure to environmentally-relevant mixtures of four organophosphorus insecticides (OPs) exerted adverse effects on honey bees. Adult and worker bees were orally exposed for five days under laboratory conditions to mixtures of four insecticides, diazinon, malathion, profenofos and chlorpyrifos at two concentrations. Concentration in the mixtures tested were equivalent to the median and 95th centile concentrations of the OPs in honey, as reported in the literature. Effects on survival, behavior, activity of acetylcholinesterase (AChE), and expression of genes important in detoxification of xenobiotics and immune response were examined. Survival of worker bees was not affected by exposure to median or 95th centile concentrations of the OPs. Activity of AChE was significantly greater in worker bees exposed to the 95th centile concentration mixture of OPs compared to the median concentration mixture. Expression of genes involved in detoxification of xenobiotics was not affected by treatment, but the abundance of transcripts of the antimicrobial peptide hymenoptaecin was significantly greater in worker honey bees exposed to the median concentration mixture. Results suggest that short-term exposure to environmentally relevant concentrations of a mixture of OPs do not adversely affect worker honey bees.

Quick and label-free detection for Coumaphos by using surface plasmon resonance biochip

Coumaphos is a common organophosphorus pesticide used in agricultural products. It is harmful to human health and has a strictly stipulated maximum residue limit (MRL) on fruits and vegetables. Currently existing methods for detection are complex in execution, require expensive tools and are time consuming and labor intensive. The surface plasmon resonance method has been widely used in biomedicine and many other fields. This study discusses a detection method based on surface plasmon resonance in organophosphorus pesticide residues. As an alternative solution, this study proposes a method to detect Coumaphos. The method, which is based on surface plasmon resonance (SPR) and immune reaction, belongs to the suppression method. A group of samples of Coumaphos was detected by this method. The concentrations of Coumaphos in the samples were 0 µg/L, 50 µg/L, 100 µg/L, 300 µg/L, 500 µg/L, 1000 µg/L, 3000 µg/L and 5000 µg/L, respectively. Through detecting a group of samples, the process of kinetic reactions was analyzed and the corresponding standard curve was obtained. The sensibility is less than 25 µg/L, conforming to the standard of the MRL of Coumaphos stipulated by China. This method is label-free, using an unpurified single antibody only and can continuously test at least 80 groups of samples continuously. It has high sensitivity and specificity. The required equipments are simple, environmental friendly and easy to control. So this method is promised for a large number of samples quick detection on spot and for application prospects.

The First Order Transfer Function in the Analysis of Agrochemical Data in Honey Bees (Apis Mellifera L.): Proboscis Extension Reflex (PER) Studies

This paper describes a mathematical model of the learning process suitable for studies of conditioning using the proboscis extension reflex (PER) in honey bees when bees are exposed to agrochemicals. Although procedural variations exist in the way laboratories use the PER paradigm, proboscis conditioning is widely used to investigate the influence of pesticides and repellents on honey bee learning. Despite the availability of several mathematical models of the learning process, no attempts have been made to apply a mathematical model to the learning curve in honey bees exposed to agrochemicals. Our model is based on the standard transfer function in the form Y = B3e^{−B2 (X−1)} + B4 (1−e^{−B2 (X−1)}) where X is the trial number, Y is the proportion of correct responses, B2 is the learning rate, B3 is readiness to learn, and B4 is ability to learn. We reanalyze previously published data on the effect of several classes of agrochemicals including: (1) those that are considered harmless to bees (e.g., pymetrozine, essential oils, dicofol); (2) sublethal exposure to pesticides known to harm honey bees (e.g., coumaphos, cyfluthrin, fluvalinate, permethrin); and (3) putative repellents of honey bees (e.g., butyric acid, citronella). The model revealed additional effects not detected with standard statistical tests of significance.

Effects of fluvalinate on honey bee learning, memory, responsiveness to sucrose, and survival

Contaminants can affect organisms' behaviour and, as a consequence, survival. Tau-fluvalinate (hereafter fluvalinate) is the active ingredient in a pesticide commonly used in North America to control Varroa destructor mites in honey bee (Apis mellifera) colonies. Fluvalinate's effects on honey bees are not well known. Honey bee cognitive and neural function can be assessed using the proboscis extension reflex (PER), which applies Pavlovian conditioning techniques. This study used PER to evaluate effects of fluvalinate on honey bee acquisition learning, (long-term) memory recall, responsiveness to sucrose, and mortality. We also evaluated how exclusion criteria for honey bees that did not exhibit PER during training and memory trials affected interpretation of results. Fluvalinate was administered both orally and dermally at high and low doses to mimic routes by which honey bees are exposed. We found negative effects of fluvalinate on honey bee learning, memory, responsiveness to sucrose, and survival, especially in high oral doses. We also found significant consequences to interpretation of results using different exclusion criteria. For example, almost 50% of individuals that failed to show evidence of learning subsequently showed evidence of memory. The latter results have important implications regarding traditional assessment of PER-based learning and memory; the former results suggest that evaluation of honey bee exposure to fluvalinate and attendant consequences warrants further investigation.

Exposure to multiple cholinergic pesticides impairs olfactory learning and memory in honeybees

Pesticides are important agricultural tools often used in combination to avoid resistance in target pest species, but there is growing concern that their widespread use contributes to the decline of pollinator populations. Pollinators perform sophisticated behaviours while foraging that require them to learn and remember floral traits associated with food, but we know relatively little about the way that combined exposure to multiple pesticides affects neural function and behaviour. The experiments reported here show that prolonged exposure to field-realistic concentrations of the neonicotinoid imidacloprid and the organophosphate acetylcholinesterase inhibitor coumaphos and their combination impairs olfactory learning and memory formation in the honeybee. Using a method for classical conditioning of proboscis extension, honeybees were trained in either a massed or spaced conditioning protocol to examine how these pesticides affected performance during learning and short- and long-term memory tasks. We found that bees exposed to imidacloprid, coumaphos, or a combination of these compounds, were less likely to express conditioned proboscis extension towards an odor associated with reward. Bees exposed to imidacloprid were less likely to form a long-term memory, whereas bees exposed to coumaphos were only less likely to respond during the short-term memory test after massed conditioning. Imidacloprid, coumaphos and a combination of the two compounds impaired the bees' ability to differentiate the conditioned odour from a novel odour during the memory test. Our results demonstrate that exposure to sublethal doses of combined cholinergic pesticides significantly impairs important behaviours involved in foraging, implying that pollinator population decline could be the result of a failure of neural function of bees exposed to pesticides in agricultural landscapes.

Serial dilutions: a new area of research for animal behavior

This paper attempts to stimulate the psychological investigation of homeopathy and serially agitated dilutions. The history of homeopathy and serial dilutions is provided in a literature review of selected research areas. Two original illustrative experiments are also presented and discussed. The first examined the effect of serially agitated dilutions of Sevin on the mortality rate of honey bees (Apis mellifera). In a second experiment, the effect of serially agitated dilutions of sucrose on proboscis extension in honey bees was assessed. No differences were found between serially agitated dilutions of pesticides and sucrose compared with dilutions alone. Implications, limitations, and proposed further work are discussed.

Acute exposure to a sublethal dose of imidacloprid and coumaphos enhances olfactory learning and memory in the honeybee Apis mellifera

The decline of honeybees and other pollinating insects is a current cause for concern. A major factor implicated in their decline is exposure to agricultural chemicals, in particular the neonicotinoid insecticides such as imidacloprid. Honeybees are also subjected to additional chemical exposure when beekeepers treat hives with acaricides to combat the mite Varroa destructor. Here, we assess the effects of acute sublethal doses of the neonicotinoid imidacloprid, and the organophosphate acaricide coumaphos, on honey bee learning and memory. Imidacloprid had little effect on performance in a six-trial olfactory conditioning assay, while coumaphos caused a modest impairment. We report a surprising lack of additive adverse effects when both compounds were administered simultaneously, which instead produced a modest improvement in learning and memory.

The proboscis extension reflex to evaluate learning and memory in honeybees (Apis mellifera): some caveats

The proboscis extension reflex (PER) is widely used in a classical conditioning (Pavlovian) context to evaluate learning and memory of a variety of insect species. The literature is particularly prodigious for honeybees (Apis mellifera) with more than a thousand publications. Imagination appears to be the only limit to the types of challenges to which researchers subject honeybees, including all the sensory modalities and a broad diversity of environmental treatments. Accordingly, some remarkable insights have been achieved using PER. However, there are several challenges to evaluating the PER literature that warrant a careful and thorough review. We assess here variation in methods that makes interpretation of studies, even those researching the same question, tenuous. We suggest that the numerous variables that might influence experimental outcomes from PER be thoroughly detailed by researchers. Moreover, the influence of individual variables on results needs to carefully evaluated, as well as among two or more variables. Our intent is to encourage investigation of the influence of numerous variables on PER results.

Gene expression in honey bee (Apis mellifera) larvae exposed to pesticides and Varroa mites (Varroa destructor)

Honey bee (Apis mellifera) larvae reared in vitro were exposed to one of nine pesticides and/or were challenged with the parasitic mite, Varroa destructor. Total RNA was extracted from individual larvae and first strand cDNAs were generated. Gene-expression changes in larvae were measured using quantitative PCR (qPCR) targeting transcripts for pathogens and genes involved in physiological processes, bee health, immunity, and/or xenobiotic detoxification. Transcript levels for Peptidoglycan Recognition Protein (PGRPSC), a pathogen recognition gene, increased in larvae exposed to Varroa mites (P<0.001) and were not changed in pesticide treated larvae. As expected, Varroa-parasitized brood had higher transcripts of Deformed Wing Virus than did control larvae (P<0.001). Varroa parasitism, arguably coupled with virus infection, resulted in significantly higher transcript abundances for the antimicrobial peptides abaecin, hymenoptaecin, and defensin1. Transcript levels for Prophenoloxidase-activating enzyme (PPOact), an immune end product, were elevated in larvae treated with myclobutanil and chlorothalonil (both are fungicides) (P<0.001). Transcript levels for Hexameric storage protein (Hsp70) were significantly upregulated in imidacloprid, fluvalinate, coumaphos, myclobutanil, and amitraz treated larvae. Definitive impacts of pesticides and Varroa parasitism on honey bee larval gene expression were demonstrated. Interactions between larval treatments and gene expression for the targeted genes are discussed.

The effect of pymetrozine (Plenum WG-50) on proboscis extension conditioning in honey bees (Apis mellifera: Hybrid var. Buckfast)

Experiments are designed to examine the effects of pymetrozine (Plenum WG-50), a recent systemic pesticide of the pyridine-azomethin family, on Pavlovian conditioning of harnessed foragers. In one set of experiments bees learned a task in which they associated a conditioned stimulus with feeding. A second set of experiments required the bees to learn a discrimination task. Within each experiment, bees received 5 μl of sucrose only, the recommended field dose of Plenum (5 μL of .3 gL(-1), .16 gL(-1) of pymetrozine measured), or 100 times the field dose of Plenum WG 50 thirty minutes prior to training (5 μL of 30 gL(-1), 14 gL(-1) of pymetrozine measured). The Plenum WG 50 was diluted with .88 M sucrose to facilitate the drinking of the pesticide. In addition to varying the concentration, we also investigated the effect of Plenum WG 50 on bees confined to an observation hive and a hive located outside. The results indicated that prior exposure to Plenum WG 50 affected Pavlovian conditioning only when bees were exposed to 100 times the recommended dosage.

Pollen nutrition affects honey bee stress resistance

The honey bee,Apis, is perhaps the most beneficial insect to humans because most of our fruits and vegetables depend on them for pollination. Yet these iconic insects have been plagued by many types of stresses. This paper reviews many lines of evidence pointing to the importance of pollen nutrition in honey bee health. In laboratory studies that used caged honey bees, poor pollen nutrition led to a reduction of worker bees’ resistance to the microsporidian,Nosema apis, an increase of bee’s sensitivity to pesticides, and an increased titer of bee virus. On the other hand, polyfloral pollen made bees more resistant to stresses by enhancing their immune related enzyme activities. At the colony level, good pollen nutrition increased honey bee’s resistance toNosema ceranaeor the ectoparasitic mite,Varroa destructor. The effects of both transportation and habitat changes on honey bees seem most likely mediated via decreased diversity, or amount, of pollen to the colonies. Pollen nutrition, therefore, might work together with other factors in reducing the bees’ resistance and exacerbate the effects of viruses, pesticides, or parasites, eventually resulting in Colony Collapse Disorder. Besides paying attention to all of these other factors, pollen nutrition should be an important focus in the future for maintaining healthy bee colonies.

Effects of cold immobilization and recovery period on honeybee learning, memory, and responsiveness to sucrose

In addition to human error and variation in laboratory conditions, there are numerous factors that can complicate comparisons among studies. Furthermore, differences in how experimental methods are executed can make it difficult to distinguish between effects of focal versus extraneous variables. Insect neural function is commonly evaluated using Pavlovian conditioning techniques; learning and memory in many species can be assessed using the proboscis extension reflex (PER). However, there are significant inconsistencies in methods used to immobilize insects prior to PER tests. We compared responses of honeybees immobilized in a refrigerator, on ice, and in a freezer, and evaluated influence of recovery interval before testing. Ice-chilling weakly decreased learning (response to an originally neutral odor) more so than refrigeration or freezing, but not 24-h recall of odor. We found no significant differences in responsiveness to sucrose relative to cooling method, but responsiveness was significantly lower among honeybees left to recover for only 0.75h versus 1.5 or 3h. Finally, we observed increased responsiveness to sucrose and geraniol between June and August. Our results suggest that inconsistencies in cold immobilization methods could confound interpretation and comparison of results from a large body of work on honeybee learning and memory.

Synthesis and antioxidant evaluation of some new 3-substituted coumarins

3-Acetylcoumarin (1) was utilized as a key intermediate for the synthesis of 2-aminothiazole derivative 3 via bromination of 1 to afford acetylbromide 2 followed by treatment with thiourea or via Biginelli reaction of 1. Treatment of 3 with 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde, 2-methyl-4H-benzo[d][1,3]oxazin-4-one, furo[3,4-b]pyrazine-5,7-dione or 2-methyl-5,6,7,8-tetrahydro-4H-benzothieno[2,3-d][1,3]oxazin-4-one afforded diazine derivatives 4-7. Also, pyridopyrimidine 8 was obtained via a one pot reaction of 6-aminothiouracil, p-chlorobenzaldehyde and 3-acetylcoumarin. Moreover, refluxing of 6-aminothiouracil with one equivalent amount of 2 afforded the thiazolopyrimidine 9, while the pyrrolothiazolopyrimidine 10 was revealed when two equivalent amounts of 2 was used. Furthermore, treatment of enamine 11 with 2-aminobenzothiazole or 6-aminothiouracil afforded the pyrimidine derivatives 12 and 13, respectively. Transamination of enamine 11 with m-anisidine followed by cyclization of the resulting enaminone 14 gave the desired quinoline 15. Also, treatment of 11 with thiophenol in dioxane gave the mercapto derivative 16. Moreover, coupling of 11 with 4,6-dimethyl-1H-pyrazolo[3,4-b]pyridin-3-yl-diazonium chloride, followed by complete cyclization of the resulting product afforded the pyridopyrazolothiazine 19 via the intermediate 18. Furthermore, the pyrazolopyrimidine 20 was revealed via a one pot condensation of 11, 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one and ammonium acetate. The thiadiazine derivatives 21-23 were obtained via treatment of 2 with the corresponding o-aminothiols. Desulphonation of 23 afforded the pyrazolotriazine 24. Finally, reaction of 2 with 2-hydroxybenzaldehyde gave benzofuran derivative 25. Representative compounds of the synthesized products were evaluated as antioxidant agents.

Toxic effect and biochemical study of chlorfluazuron, oxymatrine, and spinosad on honey bees (Apis mellifera)

Under laboratory conditions, the comparative effects of two insect growth regulators, chlorfluazuron and oxymatrine, and spinosad as a biopesticide were examined on honey bee workers (Apis mellifera L.). Separate groups of bees were left for 24 h to feed on 50% sucrose solution containing different concentrations of the tested insecticides, and the lethal concentration that caused 50% mortality (LC(50)) was estimated. The inhibitory effects on acetylcholinesterase (AChE) and adenosine triphosphatase (ATPase) activities as biochemical indicators were determined in vivo after 24 h in head, thorax, and abdomen of surviving bees obtained after treatments with a view to explore the possible mode of action of these compounds. Results indicated that exposure to spinosad showed toxicity to honey bees with LC(50) value of 7.34 mg L(-1), followed by oxymatrine (LC(50) = 10.68 mg L(-1)), while chlorfluazuron was the least acutely toxic of the tested compounds (LC(50) = 2,526 mg L(-1)). Oxymatrine and spinosad at the same tested concentrations (2.5, 5, 10, and 20 mg L(-1)) significantly inhibited AChE activity in different organs of honey bee workers, and high inhibition percentage was obtained with the enzyme isolated from the thorax. However, chlorfluazuron at 400, 1,000, 2,000, and 4,000 mg L(-1) caused high inhibition of AChE activity isolated from the head (39.65% and 44.22% at 2,000 and 4,000 mg L(-1), respectively). In addition, the toxic effects of the tested compounds on activity of ATPase indicated that spinosad caused the highest inhibitory effect in different organs compared with oxymatrine at the same concentrations, and high inhibition was found with ATPase isolated from the head. The results also indicated that oxymatrine was the least active compound for inhibition of AChE and ATPase.

Residues of Pesticides in honeybee (Apis mellifera carnica) bee bread and in pollen loads from treated apple orchards

Honey bee (Apis mellifera carnica) colonies were placed in two apple orchards treated with the insecticides diazinon and thiacloprid and the fungicide difenoconazole in accordance with a Protection Treatment Plan in the spring of 2007. Pollen and bee bread were collected from combs inside the hives. The residue of diazinon in pollen loads 10 days after orchard treatment was 0.09 mg/kg, and the same amount of residue was found in bee bread 16 days after treatment. In pollen loads 6 days after application 0.03 mg/kg of thiacloprid residues and 0.01 mg/kg of difenoconazole were found on the first day after application. Possible sub-lethal effects on individual honey bees and brood are discussed.

Does Cry1Ab protein affect learning performances of the honey bee Apis mellifera L. (Hymenoptera, Apidae)?

Genetically modified Bt crops are increasingly used worldwide but side effects and especially sublethal effects on beneficial insects remain poorly studied. Honey bees are beneficial insects for natural and cultivated ecosystems through pollination. The goal of the present study was to assess potential effects of two concentrations of Cry1Ab protein (3 and 5000 ppb) on young adult honey bees. Following a complementary bioassay, our experiments evaluated effects of the Cry1Ab on three major life traits of young adult honey bees: (a) survival of honey bees during sub-chronic exposure to Cry1Ab, (b) feeding behaviour, and (c) learning performance at the time that honey bees become foragers. The latter effect was tested using the proboscis extension reflex (PER) procedure. The same effects were also tested using a chemical pesticide, imidacloprid, as positive reference. The tested concentrations of Cry1Ab protein did not cause lethal effects on honey bees. However, honey bee feeding behaviour was affected when exposed to the highest concentration of Cry1Ab protein, with honey bees taking longer to imbibe the contaminated syrup. Moreover, honey bees exposed to 5000 ppb of Cry1Ab had disturbed learning performances. Honey bees continued to respond to a conditioned odour even in the absence of a food reward. Our results show that transgenic crops expressing Cry1Ab protein at 5000 ppb may affect food consumption or learning processes and thereby may impact honey bee foraging efficiency. The implications of these results are discussed in terms of risks of transgenic Bt crops for honey bees.

The sublethal effects of pesticides on beneficial arthropods

Traditionally, measurement of the acute toxicity of pesticides to beneficial arthropods has relied largely on the determination of an acute median lethal dose or concentration. However, the estimated lethal dose during acute toxicity tests may only be a partial measure of the deleterious effects. In addition to direct mortality induced by pesticides, their sublethal effects on arthropod physiology and behavior must be considered for a complete analysis of their impact. An increasing number of studies and methods related to the identification and characterization of these effects have been published in the past 15 years. Review of sublethal effects reported in published literature, taking into account recent data, has revealed new insights into the sublethal effects of pesticides including effects on learning performance, behavior, and neurophysiology. We characterize the different types of sublethal effects on beneficial arthropods, focusing mainly on honey bees and natural enemies, and we describe the methods used in these studies. Finally, we discuss the potential for developing experimental approaches that take into account these sublethal effects in integrated pest management and the possibility of integrating their evaluation in pesticide registration procedures.

Comparative sublethal toxicity of nine pesticides on olfactory learning performances of the honeybee Apis mellifera

Using a conditioned proboscis extension response (PER) assay, honeybees (Apis mellifera L.) can be trained to associate an odor stimulus with a sucrose reward. Previous studies have shown that observations of conditioned PER were of interest for assessing the behavioral effects of pesticides on the honeybee. In the present study, the effects of sublethal concentrations of nine pesticides on learning performances of worker bees subjected to the PER assay were estimated and compared. Pesticides were tested at three concentrations. The highest concentration of each pesticide corresponded to the median lethal dose value (48-h oral LD50), received per bee and per day, divided by 20. Reduced learning performances were observed for bees surviving treatment with fipronil, deltamethrin, endosulfan, and prochloraz. A lack of behavioral effects after treatment with lambda-cyalothrin, cypermethrin, tau-fluvalinate, triazamate, and dimethoate was recorded. No-observed-effect concentrations (NOECs) for the conditioned PER were derived for the studied pesticides. Our study shows that the PER assay can be used for estimating sublethal effects of pesticides on bees. Furthermore, comparisons of sensitivity as well as the estimation of NOECs, useful for regulatory purposes, are possible.