Bee Mortality Research Articles

The impact of smoke and fogged/vaporized thyme oil on honey bee (Apis mellifera) survival and behavior in vitro

Essential oils, such as thyme oil, are natural chemicals used to treat Varroa destructor infestations in western honey bee (Apis mellifera L.) colonies. We compared the effects of thyme oil/mineral oil mixtures delivered with an insect fogger or vaporizer to those of smoke from a smoker on the mortality and behavior of adult honey bees (Apis mellifera). Thyme oil delivered by fogging significantly increased caged bee mortality over that of the controls. The behaviors of thyme oil-treated bees in the observation hives were somewhat similar to those of the control bees exposed to smoke.

Identification of the Toxic Compounds in Camellia oleifera Honey and Pollen to Honey Bees (Apis mellifera).

Identifying the components of Camellia oleifera honey and pollen and conducting corresponding toxicological tests are essential to revealing the mechanism of Camellia oleifera toxicity to honey bees. In this research, we investigated the saccharides and alkaloids in honey, nectar, and pollen from Camellia oleifera, which were compared with honey, nectar, and pollen from Brassica napus, a widely planted flowering plant. The result showed that melibiose, manninotriose, raffinose, stachyose, and lower amounts of santonin and caffeine were found in Camellia oleifera nectar, pollen, and honey but not in B. napus nectar, pollen, and honey. Toxicological experiments indicated that manninotriose, raffinose, and stachyose in Camellia oleifera honey are toxic to bees, while alkaloids in Camellia oleifera pollen are not toxic to honey bees. The toxicity mechanism of oligosaccharides revealed by temporal metabolic profiling is that oligosaccharides cannot be further digested by honey bees and thus get accumulated in honey bees, disturbing the synthesis and metabolism of trehalose, ultimately causing honey bee mortality.

Longevity-enhancing Effects of Rosmarinic Acid Feeding on Honey bees (Apis mellifera L.) after Exposure to Some Pesticides Used in Strawberry Greenhouse

Bee pollination plays important roles in increasing the yield, weight, and quality of strawberries grown in greenhouses. Use of pesticides is often included in the pest management strategy to control insects, fungi and weeds. However, these pesticides can negatively affect bees, compromising greenhouse pollination programs. In this study, we investigate the effect of rosmarinic acid (RA) feeding on the longevity of honey bees after oral and contact exposure of bees to some selected 14 different pesticides and G-3KM (commercial product) was used as a positive control. Among the 14 pesticides tested, six were found to be highly toxic to honey bee workers as indicated by their 48h-LD50 (㎍/bee) values obtained from oral and spray bioassays; thiamethoxam (0.0002/0.0011), dinotefuran (0.005/0.018), emamectin benzoate (0.002/0.0002), spinetoram (0.018/0.001), sulfoxaflor (0.04/0.01), and cyantraniliprole (0.1/0.03), respectively. It was interesting to note that RA and G-3KM-supplemented feeding reduced honey bees mortality by 20-30% after they were exposed to high concentrations of the 6 highly toxic pesticides. The results indicate that RA could be used effectively in reducing honey bee mortality caused by pesticides.

In pursuit of the ultimate pollen substitute (insect larvae) for honey bee (Apis mellifera) feed

Finding a pollen substitute for honey bees that is nutritionally adequate and affordable is a scientific and practical challenge. We attempted a new rational approach and tried to exploit honey bees’ natural cannibalistic behavior. We tested processed insect larvae as a food source that is nutritionally similar to bee brood, and which can easily be produced on a large scale. In cage experiments, monitoring bee mortality, food consumption and changes in bee body parts’ weights showed that flour obtained by grinding dried yellow mealworm larvae has the potential to become an excellent component for pollen substitution. Bees from the cage group fed Tenebrio molitor patties (TG) demonstrated overall best results in comparison to sugar patties fed bee group (CG), yeast patties fed bee group (YG) and pollen patties fed bee group (PG). They did not lose weight as rapidly as the CG, did not defecate inside cages as the YG, nor show increased mortality as the PG. At the same time, TG consumed less food (mean 13.7 g/cage) than CG (16.8 g/cage), YG (20.4 g/cage) and PG (23.9 g/cage) within the period of 28 days. Bees’ gut increase in weight was lowest in the CG, followed by TG and PG and was the highest in the YG which resulted in diarrhea after 14 days. Bees from TG did not lag behind other bees in head, thorax and abdomen weight after 28 days. We demonstrated that processed yellow mealworm larvae (T. molitor) can be used as an ingredient for honey bee feed.

Acute and chronic ingestion of polyethylene (PE) microplastics has mild effects on honey bee health and cognition

The massive use of plastic has contributed to huge quantities of hazardous refuse at a global scale and represents one of the most prominent issues of the Anthropocene. Microplastics (MPs) have been detected in almost all environments and pose a potential threat to a variety of plant and animal species. Many studies have reported a variety of effects, from negligible to detrimental, of MPs to aquatic organisms. Conversely, much less is known about their effect on terrestrial biota, and particularly on animal behavior and cognition. We assessed the oral toxicity of polyethylene (PE) MPs at three different concentrations (0.5, 5, and 50 mg L−1), and at different timescales (1 day and 7 days of exposure) and tested for their effects on survival, food intake, sucrose responsiveness, habituation to sucrose and appetitive olfactory learning and memory in the honey bee Apis mellifera. We found that workers were not completely unaffected by acute and prolonged ingestion of this polymer. A significant effect of PE on bee mortality was found for the highest concentration but not for lower ones. PE affected feeding behavior in a concentration-dependent manner, with bees consuming more food than controls when exposed to low concentration PE. Regarding our behavioral and cognitive experiments, the high concentration PE was found to affect only bees’ ability to respond consistently to sucrose but not sucrose sensitivity, habituation to sucrose or learning and memory abilities, even for prolonged exposure to PE. While these last results may look somewhat encouraging, we discussed why caution is warranted before ruling out the possibility that PE particles at environmental concentrations are harmful to honey bees.

A Detoxification Enzyme for Apis mellifera Newly Characterized by Recombinant Expression: 10-Formyl Tetrahydrofolate Dehydrogenase.

Honeybees are important managed pollinators that perform important ecological and economic functions. In recent decades, the obligate ectoparasite Varroa destructor severely affected survival of honeybees as it either feeds on hemolymph and fat bodies or acts as a vector for viruses. A common treatment against the varroa mite is formic acid, which has been used for many years by beekeepers. This treatment is known to be effective, but the therapeutic index is very narrow. Many beekeepers report negative effects of formic acid on bees, which include damage to brood, worker bee mortality, and queen loss. Little is yet known about the molecular mechanisms of formic acid detoxification in honeybees. Our previous study shows the upregulation of predicted 10-formyl tetrahydrofolate dehydrogenase (10-FTHFDH) transcripts in honeybees exposed to formic acid. Here, the predicted honeybee-specific 10-FTHFDH is recombinantly expressed, and its hydrolase and dehydrogenase activities are investigated. As a result, the enzyme shows similar dehydrogenase activity in comparison to known 10-FTHFDHs. This study provides further knowledge to better understand the detoxification mechanisms of formic acid in Apis mellifera.

Green Veterinary Pharmacology for Honey Bee Welfare and Health: Origanum heracleoticum L. (Lamiaceae) Essential Oil for the Control of the Apis mellifera Varroatosis.

Varroatosis, caused by the Varroa destructor mite, is currently the most dangerous parasitic disease threatening the survival of honey bees worldwide. Its adverse effect on the welfare and health of honey bees requires the regular use of specific acaricides. This condition has led to a growing development of resistance phenomena towards the most frequently used drugs. In addition, another important aspect that should not be understated, is the toxicity and persistence of chemicals in the environment. Therefore, the identification of viable and environmentally friendly alternatives is urgently needed. In this scenario, essential oils are promising candidates. The aim of this study was to assess the contact toxicity, the fumigation efficacy and the repellent effect of Origanum heracleoticum L. essential oil (EO) against V. destructor mite. In the contact tests, each experimental replicate consisted of 15 viable adult female mites divided as follows: 5 treated with EO diluted in HPLC grade acetone, 5 treated with acetone alone (as negative control) and 5 treated with Amitraz diluted in acetone (as positive control). The EO was tested at concentrations of 0.125, 0.25, 0.5, 1 and 2 mg/mL. For each experimental replicate, mortality was manually assessed after one hour. The efficacy of EO fumigation was evaluated through prolonged exposure at different time intervals. After each exposure, the 5 mites constituting an experimental replicate were transferred to a Petri dish containing a honey bee larva and mortality was assessed after 48 h. The repellent action was investigated by implementing a directional choice test in a mandatory route. During the repellency tests the behavior of the mite (90 min after its introduction in the mandatory route) was not influenced by the EO. In contact tests, EO showed the best efficacy at 2 and 1 mg/mL concentrations, neutralizing (dead + inactivated) 90.9% and 80% of the mites, respectively. In fumigation tests, the mean mortality rate of V. destructor at maximum exposure time (90 min) was 60% and 84% at 24 and 48 h, respectively. Overall, these results demonstrate a significant efficacy of O. heracleoticum EO against V. destructor, suggesting a possible alternative use in the control of varroatosis in honey bee farms in order to improve Apis mellifera welfare and health and, consequently, the hive productions.

SAD but True: Species Awareness Disparity in Bees Is a Result of Bee-Less Biology Lessons in Germany

Bee and insect mortality has recently moved to the forefront of current nature conservation debates and experiences intensive media coverage worldwide. In order to understand the complexity, it is necessary to raise awareness of the diversity of bees. This study investigated whether students are aware of the species diversity of bees. We are guided by the concept of ‘plant blindness’ and show that it cannot be assumed that people are only ’plant-blind’. Therefore, we introduce the concept of Species Awareness Disparity (SAD) in bees to describe a phenomenon which can be defined as the failure to appreciate the significance of wild bee species and the inability to distinguish between individual species of the Apidae family. A total of 421 German students in grades 5–7 participated. The majority of students did not associate a diversity of species with the term ‘wild bee’ but rather consider the honeybee as the bee. Only 2.7% (N = 421) of the students were able to correctly identify pictures of wild bees and the honeybee. This highlights the importance of educating students about the identity and nature of bees in their environment so that they become aware of their meaning from both a personal and an ecological perspective.

Impact of Neem Oil on Developmental Stages of Honey Bee Apis mellifera L.

Toxicity of neem oil on developmental stages of Apis mellifera L. was evaluated by applying three concentrations within the marked comb cells with micropipette as single (applied only once) and multiple exposures (at one day interval up to capping of cells) on different age groups of larvae (1-2, 3-4 and 5-6 days). Results revealed that maximum survival was observed in controls (both negative and positive) and at par with 0.05% (T1) and 0.1 % (T2) concentrations. Minimum survival of larval stage was found in 1% (T3). Same trend was also observed in emerged pupae (CD=17.9) and in mortality of adult bees (CD=15.3). Significant difference in the survival of larval (p<0.05), emerged pupae (p<0.05) and mortality of adult (p<0.05) honey bees was found within stages originating from treated larvae. Both in single or multiple doses, it was found that larvae treated at 1-2 days age group was significantly affected as compared to other stages.

Miticidal activity of fenazaquin and fenpyroximate against Varroa destructor, an ectoparasite of Apis mellifera.

BACKGROUNDThe Varroa mite (Varroa destructor) is an ectoparasite that can affect the health of honey bees (Apis mellifera) and contributes to the loss of colony productivity. The limited availability of Varroacides with different modes of action in Canada has resulted in the development of chemical resistance in mite populations. Therefore, an urgent need to evaluate new potential miticides that are safe for bees and exhibit high efficacy against Varroa exists. In this study, the acute contact toxicity of 26 active ingredients (19 chemical classes), already available on the market, was evaluated on V. destructor and A. mellifera under laboratory conditions using an apiarium bioassay. In this assay, groups of Varroa‐infested worker bees were exposed to different dilutions of candidate compounds. In semi‐field trials, Varroa‐infested honey bees were randomly treated with four vetted candidate compounds from the apiarium assay in mini‐colonies.RESULTSAmong tested compounds, fenazaquin (quinazoline class) and fenpyroximate (pyrazole class) had higher mite mortality and lower bee mortality over a 24 h exposure period in apiariums. These two compounds, plus spirotetramat and spirodiclofen, were selected for semi‐field evaluation based on the findings of the apiarium bioassay trials and previous laboratory studies. Consistent with the apiarium bioassay, semi‐field results showed fenazaquin and fenpyroximate had high efficacy (>80%), reducing Varroa abundance by 80% and 68%, respectively.CONCLUSIONThese findings suggest that fenazaquin would be an effective Varroacide, along with fenpyroximate, which was previously registered for in‐hive use as Hivastan. Both compounds have the potential to provide beekeepers with an alternative option for managing Varroa mites in honey bee colonies. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Gut Microbiota Provides a New Mechanism for Explaining Agrochemical-Induced Synergistic Effects on Bee Mortality.

ADVERTISEMENT RETURN TO ISSUEPREVViewpointNEXTGut Microbiota Provides a New Mechanism for Explaining Agrochemical-Induced Synergistic Effects on Bee MortalityYueyue LiuYueyue LiuState Key laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, ChinaCollege of Water Science, Beijing Normal University, Beijing, 100875, ChinaMore by Yueyue Liu, Chen Wang*Chen WangState Key laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China*(C.W.) Phone/Fax: +86-15201423767; email: [email protected]More by Chen WangView Biographyhttps://orcid.org/0000-0003-2765-6109, Suzhen QiSuzhen QiInstitute of Apicultural Research, Chinese Academy of Agricultural Sciences, Beijing, 100093, ChinaMore by Suzhen Qi, and Fengchang Wu*Fengchang WuState Key laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China*(F.W.) Phone/Fax:+86-010-84931804; email: [email protected]More by Fengchang WuView Biographyhttps://orcid.org/0000-0001-8595-2243Cite this: Environ. Sci. Technol. 2022, 56, 3, 1489–1491Publication Date (Web):January 12, 2022Publication History Received8 December 2021Published online12 January 2022Published inissue 1 February 2022https://doi.org/10.1021/acs.est.1c08406Copyright © 2022 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1146Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Nutritional efficacy of different diets supplemented with microalga Arthrospira platensis (spirulina) in honey bees (Apis mellifera)

In honey bees, food, gut microorganisms, and their nestmates may contribute to the health status of newly emerged worker bees. However, relatively little data are available regarding the extent to which supplemental protein feeding impacts bee colony health and mortality. The present research compared the efficacy of different diets supplements, i.e., bee pollen, ajeena (commercially available pollen substitute), and date paste either alone or admixed with varying percentages of microalga Arthrospira platensis (spirulina) for caged honey bees (Apis mellifera jemenitica). In addition, to investigate diet preference and mortality percentage in honey bees, the physicochemical analysis of these diets were also performed. Our results indicated that the honey bees consumed bee pollen (11.51 ± 2.22 mg/bee) and ajeena diet (10.68 ± 1.29 mg/bee) significantly higher than other diets.In contrast, the maximum consumption was 4.68 ± 2.82 mg/bee for date paste admixed with 2.5% spirulina than date paste diet only (2.41 ± 0.91 mg/bee). In addition, the mortality percentage was significantly lower when bees fed pollen (56.67% ± 3.88%) and ajeena diet (39.33% ± 2.08%) in comparison to combination with spirulina supplement. Overall, the mean maximum diet consumption for ajeena was 15.72 ± 3.65 mg/bee followed by bee pollen diet (11.97 ± 2.41 mg/bee) and date paste (2.08 ± 0.94 mg/bee), respectively, resulting mean percentage of mortality of 13.37% ± 3.77%. Physicochemical analysis revealed that glucose and fructose were higher in the date paste diet. In contrast, total sugar content, sucrose, and protein content were higher in the ajeena diet. Future research is needed to determine the impact of diet supplementation with spirulina on colony health and bee physiology.

Attractiveness and toxicity of two insecticides to Tetragonula laeviceps (Apidae: Meliponinae)

Stingless bee, Tetragonula laeviceps, plays a primary role in ecosystem services as a pollinator for coffee, cocoa, and pepper. Attacks of insect pests cause low production of several plantation plants. Farmers commonly use synthetic insecticides to control insect pests. However, improper use of insecticides often adversely affects the ecosystem and human health, including pollinators. In Indonesia, research on the side effects of insecticides on non-target insects such as flower visitor insects (pollinators) is minimal. This study aimed to evaluate the attractiveness and toxicity of two insecticides to T. laeviceps. Stingless bees were obtained from beekeepers at Banten. Y-tube olfactometer test was used to determine the attractiveness of bees to insecticides, and a topical test was used to determine the mortality effect of insecticide on bees. The insecticides used were insecticide A (a.i. alpha-cypermethrin) and insecticide B (a.i. spinetoram) at 100 ppm and 60 ppm, respectively. The results showed that bees were more attracted to insecticide B by 73.3% than insecticide A (26.7%). Insecticide B caused 100% bee mortality after 48 hours after treatment (HAT), while Insecticide A caused 0% bee mortality after 48 HAT. The results indicate that insecticide B attracted stingless bees and has a high mortality level.

Comparison of Feature Extraction Methods for Sound-Based Classification of Honey Bee Activity

Honey bees are one of the most important insects on the planet since they play a key role in the pollination services of both cultivated and spontaneous flora. Recent years have seen an increase in bee mortality which points out the necessity of intensive beehive monitoring in order to better understand this phenomenon and try to help these important insects. In this scenario, this work presents an algorithm for sound-based classification of honey bee activity reporting a preliminary comparison between various extracted features used separately as input to a convolutional neural network classifier. In particular, the orphaned colony situation has been considered using a dataset acquired in a real situation. Different experiments with different setups have been carried out in order to test the performance of the proposed system, and the results have confirmed its potentiality.

EFFECT OF GRAPE SEED EXTRACT («NI NU NA» SUPPLEMENT) ON THE NATURAL BEES EXTINCTION

Introduction. Grape seeds contain vitamins B, C, PP, A, E, organic acids, minerals, proteins, folic acid, essential oils, sucrose, fructose, fiber, pectin, etc. Therefore, supplement «Ni Nu Na» on the basis of grape seed extract can be an effective mean for increasing the strength of bee colonies. The goal of the work. Investigate the effect of grape seed extract feeding, namely «Ni Nu Na» supplement, on the lifespan of bees isolated in cages, under laboratory conditions, depending on the concentration. Materials and methods of research. The experiment was conducted on flying bees of summer generation. Bees were kept in cages at a temperature of 34–35 °C until the end of their natural extinction. 150 bees per variant (three repetitions, 50 bees in each). Supplement was fed twice with an interval of 7 days with sugar syrup in concentrations of 10; 1; 0.1; 0.01%. The experiment included control: syrup feeding without supplement. Experiments with «Ni Nu Na» supplement were carried out under the contract between NSC «Institute of Beekeeping named after P.I. Prokopovich» and «Sanaturi UA» LLC. Results of research and discussion. It was found that double bees feeding of syrup with grape seed extract in concentrations of 10%; 1%; 0.1%; 0.01% slowed down their natural extinction compared to the control, where bees were fed syrup without supplement, at different stages of the life cycle from 1.93% (14.25±8.54 in the experiment and 12.32±1.17 in the control) up to 53.17% (18.65±1.43 in the experiment and 71.82±13.49 in the control). Bees died slower compared to the control at feeding the supplement in concentrations of 0.1 and 1%. Bee mortality decreased compared to the control at concentrations 0.1% by 5.27–52.5% (75.54±11.93 in the experiment and 80.81±10.90 in the control) – (23.06±6,9 in the experiment and 75.56±12.81 in the control), respectively, and for 1% by 8.75–53.17% (3.57±2.06 in the experiment and 12.32±1.17 in the control) – (18.65±1.43 in the experiment and 71.82±13.49 in the control), respectively. Conclusions and prospects for further research. «Ni Nu Na» bee supplement based on grape seed extract in 0.01–1% concentrations slows down the natural bee extinction compared to control at different stages of the life cycle on 1.93–53.17%, and therefore can be used to accelerate the development of bee colonies.

Translocation of clothianidin to guttation fluid and its potential impact on honey bee, Apis mellifera anatoliaca Maa, 1953 (Hymenoptera: Apidae)

Honey bees, Apis mellifera anatoliaca Maa, 1953 (Hymenoptera: Apidae) forage water from guttation fluid so transported neonicotinoid insecticides in guttation fluid poses a risk to the bees. The first aim of this study was to determine the toxicity and risk of clothianidin to honey bees. In addition, the changes of clothianidin residue in the guttation fluid of maize plants in Turkey were determined in 2018 and 2019. Also, the toxicity of guttation fluid collected from the maize plants to bees was determined in ecotoxicological tests. The acute oral LD50 of clothianidin to honey bees in the first 24 h was 1.80 ng bee-1 and residue analysis demonstrated that honey bees were exposed to clothianidin concentration in guttation fluid ranging from 0.02 to 6.0 mg L-1 with mortality ranging between 80 and 100%. As the measured concentration of clothianidin in guttation fluid can lead to the mortality of honey bees, present study indicates that clothianidin, and possibly related pesticides in treated maize seed poses a risk to honey bees. Future studies are needed to determine the scale and distribution of this risk in Turkey.

Edge-Based Detection of Varroosis in Beehives with IoT Devices with Embedded and TPU-Accelerated Machine Learning

One of the causes of mortality in bees is varroosis, a bee disease caused by the Varroa destructor mite. Varroa destructor mites may occur suddenly in beehives, spread across them, and impair bee colonies, which finally die. Edge IoT (Internet of Things) devices capable of processing video streams in real-time, such as the one we propose, may allow for the monitoring of beehives for the presence of Varroa destructor. Additionally, centralization of monitoring in the Cloud data center enables the prevention of the spread of this disease and reduces bee mortality through monitoring entire apiaries. Although there are various IoT or non-IoT systems for bee-related issues, such comprehensive and technically advanced solutions for beekeeping and Varroa detection barely exist or perform mite detection after sending the data to the data center. The latter, in turn, increases communication and storage needs, which we try to limit in our approach. In the paper, we show an innovative Edge-based IoT solution for Varroa destructor detection. The solution relies on Tensor Processing Unit (TPU) acceleration for machine learning-based models pre-trained in the hybrid Cloud environment for bee identification and Varroa destructor infection detection. Our experiments were performed in order to investigate the effectiveness and the time performance of both steps, and the study of the impact of the image resolution on the quality of detection and classification processes prove that we can effectively detect the presence of varroosis in beehives in real-time with the use of Edge artificial intelligence invoked for the analysis of video streams.

Evaluating the Efficacy of 30 Different Essential Oils against Varroa destructor and Honey Bee Workers (Apis mellifera).

Simple SummaryWorldwide, mass losses of honey bee colonies are being observed more frequently due to Varroa mite infestation. Therefore, varroosis is considered a major problem in beekeeping participating to a large extent in colony collapse disorder. Except for direct damage of bees and suppressing their immune system caused by parasitism, Varroa mites transfer viral particles straight to bee hemolymph which can have a fatal impact. To control the mite population, several acaricidal treatments are used. Commonly used treatments are synthetic acaricides with a high risk of developing Varroa resistance population and contamination of bee products by acaricidal residues. Other commonly used treatments are organic acids, which are increasingly associated with damage of brood, adult bees, and premature deaths of queens. Therefore, in this study, we evaluated the varroacidal effect of 30 individual essential oils. The toxicity of the most effective oils selected by screening was subsequently tested on Varroa mites and adult honey bee workers simultaneously. In addition, the main components of these essential oils were specified. Several essential oils were proven to be effective against the adult female of Varroa mites and at the same dose safe for adult honey bee workers under laboratory conditions, especially manuka, peppermint, oregano, litsea, and cinnamon.Essential oils and their components are generally known for their acaricidal effects and are used as an alternative to control the population of the Varroa destructor instead of synthetic acaricides. However, for many essential oils, the exact acaricidal effect against Varroa mites, as well as the effect against honey bees, is not known. In this study, 30 different essential oils were screened by using a glass-vial residual bioassay. Essential oils showing varroacidal efficacy > 70% were tested by the complete exposure assay. A total of five bees and five mites were placed in the Petri dishes in five replications for each concentration of essential oil. Mite and bee mortality rates were assessed after 4, 24, 48, and 72 h. The LC50 values and selectivity ratio (SR) were calculated. For essential oils with the best selectivity ratio, their main components were detected and quantified by GC-MS/MS. The results suggest that the most suitable oils are peppermint and manuka (SR > 9), followed by oregano, litsea (SR > 5), carrot, and cinnamon (SR > 4). Additionally, these oils showed a trend of the increased value of selective ratio over time. All these oils seem to be better than thymol (SR < 3.2), which is commonly used in beekeeping practice. However, the possible use of these essential oils has yet to be verified in beekeeping practice.

Glucosinolate Bioactivation by Apis mellifera Workers and Its Impact on Nosema ceranae Infection at the Colony Level.

The microsporidian fungus Nosema ceranae represents one of the primary bee infection threats worldwide and the antibiotic fumagillin is the only registered product for nosemosis disease control, while few alternatives are, at present, available. Natural bioactive compounds deriving from the glucosinolate–myrosinase system (GSL–MYR) in Brassicaceae plants, mainly isothiocyanates (ITCs), are known for their antimicrobial activity against numerous pathogens and for their health-protective effects in humans. This work explored the use of Brassica nigra and Eruca sativa defatted seed meal (DSM) GSL-containing diets against natural Nosema infection in Apis mellifera colonies. DSM patties from each plant species were obtained by adding DSMs to sugar candy at the concentration of 4% (w/w). The feeding was administered in May to mildly N. ceranae-infected honey bee colonies for four weeks at the dose of 250 g/week. In the treated groups, no significant effects on colony development and bee mortality were observed compared to the negative controls. The N. ceranae abundance showed a slight but significant decrease. Furthermore, the GSL metabolism in bees was investigated, and MYR hydrolytic activity was qualitatively searched in isolated bee midgut and hindgut. Interestingly, MYR activity was detected both in the bees fed DSMs and in the control group where the bees did not receive DSMs. In parallel, ITCs were found in gut tissues from the bees treated with DSMs, corroborating the presence of a MYR-like enzyme capable of hydrolyzing ingested GSLs. On the other hand, GSLs and other GSL hydrolysis products other than ITCs, such as nitriles, were found in honey produced by the treated bees, potentially increasing the health value of the final product for human consumption. The results are indicative of a specific effect on the N. ceranae infection in managed honey bee colonies depending on the GSL activation within the target organ.

Natural extracts as potential control agents for Nosema ceranae infection in honeybees, Apis mellifera

Nosema disease is one factor that can cause colony decline in honeybees (Apis mellifera L.) worldwide. Nosema ceranae has outcompeted Nosema apis in the Western honeybee (A. mellifera) which is its original host. Fumagilin is an effective antibiotic treatment to control Nosema infection but currently it is forbidden in many countries. In this study, 12 plant extracts were evaluated for their toxicity to adult bees and antimicrosporidian activity under laboratory and field conditions. N. ceranae-infected adult bees were fed ad libitum with 50% sucrose solution containing 1% and 5% (w/v) of each plant extract. Bee mortality in N. ceranae-infected groups fed with plant extracts was higher than that in the control group treated with fumagilin. The results demonstrated that 9 of 12 extracts had high antimicrosporidian activity against N. ceranae and their efficacies were comparable to fumagilin. Spore reduction in infected bees was 4–6 fold less after extract treatment. Following laboratory screening, Annona squamosa, Ocimum basilicum, Psidium guajava and Syzygium jambos were tested in honeybee colonies. Plant extracts of 2% concentration (w/v) inhibited the development of Nosema spores after 30 days of treatment. At the end of experiment (90 days), spores in the plant extract treated groups were lower than in group treated with fumagilin but there was no significant difference. Although, extracts tested in this study showed high toxicity to bee in laboratory cages, they did not show negative affects on bees under whole colony conditions. Therefore, the effectiveness of plant extracts tested in this study was notable and warrants further study as potential Nosema control agents in honey bees. Plant extracts would offer a non-antibiotic alternative for Nosema control and help reduce the overuse of antibiotics in livestock.