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Oral toxicity of essential oils and organic acids fed to honey bees (Apis mellifera)


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Natural plant products have been studied for potential use as in-hive fumigants for suppression of parasitic mites and other pests. A more direct application through direct feeding of bees would avoid problems with fumigant volatility in cold climates and provide a more systemic route of exposure for the target pest. However, there must be a balance between toxicity to hive pests and toxicity (safety) to the bees. We focused on adult bee toxicity when testing ten products: cineole, clove oil, formic acid, marjoram oil, menthol, oregano oil, oxalic acid, sage oil, thymol, and wintergreen. Each product was tested at several concentrations in a sugar syrup fed to bees over several days, and dead bees were counted daily. Oxalic acid was the most toxic of the products tested. Menthol and cineole had mortality levels no different from controls fed plain syrup after 8 days of treatment. At 14 days of treatment, wintergreen was the least toxic, but neither menthol nor cineole were a part of the testing that went to 14 days. Our results indicate that the tested products could all be used safely for treating bees orally if dose is carefully managed in the hive.
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Oral toxicity of essential oils and organic
acids fed to honey bees (Apis mellifera).
Timothy A Ebert1*, Peter G Kevan2, Bert L Bishop3, Sherrene D Kevan2, and Roger A Downer1
1Laboratory for Pest Control Application Technology, Ohio Agricultural Research and Development Center, The Ohio State University,
1680 Madison Ave. Wooster, OH 44691, USA.
2Enviroquest Ltd., 352 River Road, Cambridge, ON N3C 2B7, Canada.
3Computing and Statistical Services, Ohio Agricultural Research and Development Center, The Ohio State University, 1680 Madison
Ave. Wooster, OH 44691, USA.
Received 27 March 2007, accepted subject to revision 8 June 2007, accepted for publication 17 June 2007.
*Corresponding author. Email:
Natural plant products have been studied for potential use as in-hive fumigants for suppression of parasitic mites and other pests.
A more direct application through direct feeding of bees would avoid problems with fumigant volatility in cold climates and provide
a more systemic route of exposure for the target pest.However, there must be a balance between toxicity to hive pests and toxicity
(safety) to the bees. We focused on adult bee toxicity when testing ten products: cineole, clove oil, formic acid,marjoram oil,
menthol, oregano oil, oxalic acid, sage oil, thymol, and wintergreen. Each product was tested at several concentrations in a sugar
syrup fed to bees over several days, and dead bees were counted daily. Oxalic acid was the most toxic of the products tested.
Menthol and cineole had mortality levels no different from controls fed plain syrup after 8 days of treatment. At 14 days of
treatment, wintergreen was the least toxic, but neither menthol nor cineole were a part of the testing that went to 14 days. Our
results indicate that the tested products could all be used safely for treating bees orally if dose is carefully managed in the hive.
Toxicidad oral de aceites esenciales y ácidos orgánicos en la
alimentación de la abeja de la miel (Apis mellifera)
Los productos naturales de plantas han sido estudiados para su uso potencial como agentes fumigantes de represión de ácaros
parásitos y otras plagas. Una aplicación más directa a través de la alimentación de las abejas evitaría problemas como la volatilidad de
los fumigantes en climas fríos y proporcionaría una vía más sistémica de exposición para las plagas. Sin embargo, debe haber un
equilibrio entre la toxicidad para las plagas y la toxicidad (seguridad) para las abejas. Nosotros nos hemos centrado en la toxicidad
sobre abejas adultas de diez productos: eucaliptol, aceite de clavo, ácido fórmico, aceite de mejorana, mentol, aceite de orégano,
ácido oxálico, aceite de salvia, timol y aceite esencial de wintergreen (salicilato de metilo).Cada producto fue probado con
diferentes concentraciones en un jarabe de glucosa que alimentó a las abejas durante varios días, las abejas muertas fueron contadas
diariamente. El ácido oxálico fue el producto más tóxico de todos los analizados. El mentol y el eucaliptol presentaron niveles de
mortalidad similares a los controles, que fueron alimentados únicamente con jarabe después de 8 días de tratamiento. Tras 14 días
de tratamiento, el aceite esencial wintergreen fue el menos tóxico, pero ni el mentol ni el eucaliptol se incluyeron en el análisis a los
14 días. Nuestros resultados indican que todos los productos testados pueden ser utilizados con seguridad por vía oral para el
tratamiento de las abejas si la dosis es administrada cuidadosamente en la colmena.
Keywords: Medicaments, oral toxicity, natural plant products, mortality, miticides, protectants
Journal of Apicultural Research and Bee World 46(4):220–224 (2007) © IBRA 2007
Oral toxicity of essential oils and organic acids fed to honey bees 221
Various essential oils and organic acids have been evaluated as
materials to manage mite populations afflicting honey bees. In
general, these products are proposed to be used as in-hive
fumigants (Imdorf et al. 1999) or as contact treatments (Amrine
et al. 1996). In-hive fumigants have the disadvantage of needing
warmth for sublimation or evaporation, and therefore they are
less effective in colder weather (Scott-Dupree & Otis 1992).
Nevertheless, organic acids like formic acid, and essential oils like
thymol, have been found to be effective in management against
mite pests in honey bee hives (Imdorf et al. 1999). Oral
application circumvents the problems of fumigation in cold
weather, but this application strategy has been mostly neglected.
Menthol can be administered orally to honey bees, in
microencapsulated formulation, with beneficial effects in
suppressing population growth of tracheal mites (Acarapis woodi)
(Kevan et al. 1997;2003). If essential oils and organic acids are to
be considered as potential medicaments, rather than fumigants,
one must be sure that the target animals (e.g. honey bees) are
not poisoned. As with the research on menthol, we investigated
oral toxicity of various essential oils and organic acids with the
aim of assessing the potential problem of poisoning the patients
with the active ingredient of the medicine (Kevan et al. 1999). As
a control, we also used a plant compound, amygdalin, known to
be poisonous to honey bees (Kevan & Ebert 2005), and
reassessed menthol as a compound known to be innocuous to
honey bees (Kevan et al. 1999). Menthol provides a positive
control that is useful in evaluating the toxicity of other
This research was on the toxicity of various natural plant
compounds to honey bees with the intent to use these
compounds to treat hives for various hive pest problems. It is
likely that such treatments will involve exposing the colony to the
compound for weeks or months. It is therefore necessary to
assess how both the dose and the length of exposure influence
Materials and Methods
Honey bees (Apis mellifera ligustica) were obtained from hives at
the Ohio Agricultural Research and Development Center
(OARDC) Honey bee Lab, and placed in cages similar to those
used by Kulencevic & Rothenbuhler (1973), and previously
described in Kevan & Ebert (2005). Each cage had an average of
48 bees (+/-15 S. D.; range 20–134). Fed bees were given sugar
syrup (69% sucrose), or a 69% sucrose syrup spiked with one of
10 possible natural plant products: cineole (CAS 470-82-6), clove
oil, formic acid (CAS 64-18-6), marjoram, L-menthol (CAS 2216-
51-5), DL-menthol (CAS 1490-04-6), oregano oil, oxalic acid
(CAS 144-62-7), sage oil, thymol (CAS 89-83-8), or natural
wintergreen oil (CAS 119-36-8). The clove oil was a commercial
extract from Eugenia caryophyllata Thunb. (Myrtaceae). The main
chemical components of clove oil are eugenol, eugenol acetate,
iso-eugenol and caryophyllene
( The
oregano oil was a commercial extract from Origanum vulgare L.
(Lamiaceae). The main chemical components are carvacrol,
p-cymene, y-terpinene, and b-caryophyllene (Chorianopoulos et
al. 2004). The marjoram oil was a commercial extract from
Origanum marjorana L. (Lamiaceae). The main chemical
constituents are sabinene, a-terpinene, y-terpinene, p-cymene,
terpinolene, linalool, cis-sabinene hydrate, linalyl acetate, terpinen-
4-ol and y-terpineol (
oils/marjoram.htm). The sage oil was a commercial extract from
Salvia sclarea L. (Lamiaceae). The main chemical components of
sage oil are linalool, a-terpenol, linalyl acetate, neryl acetate, and
sclareol (Pitarokill et al. 2002). All solutions, including the control,
had 5ml ethanol added to bring the total syrup volume to 100ml.
Insoluble potential medicaments were dissolved in the ethanol
first, then mixed with the syrup to bring the volume up to 100ml.
In addition to these treatments, we included an unfed control,
with no food or water. The starvation treatment was necessary
because it was rumored that some of these medicaments would
reduce feeding. We needed a starvation treatment to
differentiate between toxicity and death due to starvation or
Bees were fed ad libitum for the duration of the experiments.
No additional water was provided, except what they could get by
feeding on the syrup solution. We will call this days of treatment
(DOT), since the bees are continually exposed for the entire
duration. Each treatment was replicated four times. Mor tality was
checked daily, and dead bees were removed. Bees were
considered dead when they would no longer move in response
to poking with forceps. At the end of the experiment, the live
bees were frozen and then counted. Cages were kept in open
laboratory conditions that ranged from 17 to 25°C with a R.H.
(Relative Humidity) from 18 to 37%.
We present the results from two tests. The first test
evaluated the toxicity of all potential medicaments every day over
an 8 day period at concentrations of 100 and 1000 ppm. The
second test evaluated the toxicity of clove oil, formic acid, oxalic
acid, oregano oil, and sage oil along with a fed and a starved
control over a 14 day period. Potential medicament
concentrations in the second test were at 100, 500, 1000, 5000,
10000, and 100000 ppm. Note; the 100000 ppm solutions for all
potential medicaments tended to separate, or crystals developed
in the solution. It is likely that the bees never experienced a
potential medicament at 100000 ppm, even though we tried
mixing the potential medicament back into the sugar syrup by
shaking up the bottles once per day. Also note that we tested
both D and DL menthol because sometimes a particular isomer
is more toxic than others. However, we could not find any
evidence of such a difference in the toxicity of these products.
Therefore, our discussion of menthol will be the results from the
combined data of the L-menthol and DL-menthol treatments.
Data were analyzed in SAS using a time-dose-mortality
analyses and probit analyses. The time-dose-mortality model was
a complimentary log-log model using a SAS program that was
written as an implementation of the work by Priesler & Robinson
(1989). However, the Hosmer-Lemeshow goodness-of-fit test
(Nowierski et al. 1996) was highly significant for all models. We
suggest that this lack-of-fit was caused by long tails in the data.
When individual time intervals were of special interest, we used
222 Ebert, Kevan,Bishop, Kevan, Downer
Proc Probit to estimate the LD50 values for that day. Although the
Proc Probit corrected for control mortality, the results from the
time-dose-mortality analysis did not correct for control mortality.
For this reason, the time-dose-mortality analysis overestimates
the toxicity of these products.
We have included the results from the amygdalin (known to be
toxic to honey bees) trials for comparison (Kevan & Ebert 2003).
Relative to amygdalin, all of the materials we tested were
innocuous. Although oxalic acid is quite toxic relative to the other
materials (Table 1), Table 2 shows it to be somewhat less than
half as toxic as amygdalin on a molecule per molecule basis.
Starved bees do not live long, with 40% dying in the first 24
H, and all the bees dead within four days (Table 1). No other
treatment had higher first day mortality rates. High
concentrations of oxalic acid were the most toxic treatment, and
differed from the starvation treatment by having relatively low
first day mortality. Mortality was 100% at the highest oxalic acid
concentration, but bees at the lowest concentration only had
about 60% mortality after 14 days (there was 40% mortality in
the controls by this time). The second most toxic was formic acid,
for which the last survivors died eight days post treatment at the
highest concentration tested. However, mor tality was only 30%
after 14 days at the lowest concentration. A few other potential
medicaments also showed high mortality levels at the maximum
concentration tested. In contrast to these products, we conclude
that cineole, menthol, marjoram, and thymol are non-toxic to
bees because their mortality levels never exceeded background
mortality at any concentration tested (Table 2).
All products tested were much less toxic than amygdalin on a
molecular basis. Although the LT50 for oxalic acid and amygdalin
are similar, it takes over twice the number of molecules of oxalic
acid to achieve an equivalent level of toxicity (Table 2). However,
when comparing LD50s at 8 days of treatment (DOT), oxalic acid
appears more toxic (Table 3). The reason the model is non-
significant (α<_0.01) in this case is because mor tality in all
treatments was too high and too variable (average mortality in
lowest dose was 50% +/- 40% S. D.). The reason the model for
sage is also non-significant (α<_0.01) is because, even at the
highest dose, mortality was only 60% +/- 40% S. D.
The critical feature in the potential utility of all these products
is their long term effects on bee health. This was assessed by
keeping bees in the cages as long as possible. Treatment with sage
oil resulted in highly variable mortality, for which we have no
explanation. Oxalic acid, with the lowest LD50 value, was most
toxic and wintergreen was the least (Table 4).
All LD50 levels decline over time. However, most show a rapid
decline in LD50 values within the first few days, followed by a
leveling off. In part this trend reflects ever increasing levels of
background mortality. However, most cages of bees had a few
individuals that lived many days longer than their sisters. This
made the tails of the mortality distribution long, and probably
accounted for most of the significance in the lack-of-fit tests.
Day 1 Number
Potential Average Average % mortality of Bees
Medicament % mortality 1000 ppm 100,000 ppm*Tested
Amygdalin 0 79** 221
Cineole 2 11 214
Clove oil 3 28 96 927
Control – fed 1 10 40 1189
Control – unfed 46 100*** 100*** 495
Formic acid 1 33 100 1438
Marjoram oil 2 34 308
Menthol DL 1 25 256
Menthol L 1 21 239
Oregano oil 1 41 92 953
Oxalic acid 6 96 100 1217
Sage oil 3 21 87 1289
Thymol 8 43 201
Wintergreen 1 24 99 1308
Table 1. Twenty four hour mortality and average mortality at 8 days and 14 days exposure (DOT) for various essential oils and
organic acids fed to honey bees, together with the total number of bees tested (sum of all replicates and dosages).
*Cells with missing data are left blank. ** Dosage for amygdalin was 2250 ppm. *** All bees were dead in 4 days.
Oral toxicity of essential oils and organic acids fed to honey bees 223
Table 2. Estimated LT50 for potential medicaments at 1000 ppm. In this analysis, data from tests 1 and 2 were combined to estimate
the LT50. Except as noted, all terms in the models were significant (α<_0.01), and all lack-of-fit tests were also significant (α<_0.01).
Material Molarity*LT 50 Lower 95% Upper 95%
in days Fudicial Fudicial
Limit Limit
Amygdalin** 0.0049 4.6 3.0 6.3
Cineole 0.0065 NS
Clove Oil 11.2 10.2 12.8
Controls – Fed 17.0 15.9 18.7
Controls – unfed 1.9 1.7 2.1
Formic Acid 0.0217 11.8 8.1 30.3
Marjoram Oil 27.0 15.0 3935.0
Menthol 0.0064 NS
Oregano Oil 10.8 9.9 12.1
Oxalic Acid 0.0111 4.8 2.6 5.9
Sage Oil 11.5 10.6 12.7
Thymol 0.0067 NS
Wintergreen 0.0029 14.4 12.6 17.7
NS = no significant model. Mortality in these tests did not reach 50%, so accurate estimates cannot be made.
* These plant extracts are blends of several compounds so it is not possible to calculate the molarity of each component.
** Amygdalin concentration was 2,250 ppm, the lowest concentration tested by Kevan and Ebert (2005).
Table 3. Estimated LD50 for the tested essential oils and organic acids at 8 Days exposure (DOT).
Material LD50 Lower 95% Upper 95%
in ppm Fudicial Fudicial
Limit Limit
Amygdalin 1600 1300 1800
Clove Oil 7800 2300 18100
Formic Acid 5600 3500 8100
Oregano Oil 14900 0 43400
Oxalic Acid NS
Sage Oil NS
Wintergreen 13500 8500 21700
NS = model non-significant (α<_0.01). Oxalic acid was too toxic and mortality by Sage Oil was too variable.
Table 4. LD50 values 14 days exposure (DOT).
Material LD50 Standard Lower 95% Upper95%
in ppm Error of Fudicial Fudicial
Log10 (dose) Limit Limit
Clove Oil 240 0.1483 80 710
Formic Acid 450 0.0653 280 720
Oregano Oil 600 0.1327 230 1620
Oxalic Acid 80 0.0635 50 130
Sage Oil*NS
Wintergreen 800 0.0632 500 1270
*dose was not a significant variable in the time-dose-mortality model.
Looking at mortality in Table 1, we conclude that wintergreen,
menthol, sage oil, and cineole all are relatively innocuous, and that
marjoram oil is quite benign. At the other extreme, oxalic acid
and, as expected, amygdalin were the most toxic, and has the
potential to cause high levels of mortality if the dosage is high.
These results also demonstrate that development of hive
treatment protocols require balancing the exposure time and the
dose given to the hive. Our results are sufficient for dosing bees
for up to 14 days, but we expect that dosage would have to be
more limited if the exposure period is lengthened. If continuous
dosing is the best treatment option, then additional research
would be needed to assess toxicity during the over-wintering
period and the effects these products may have on egg laying
viability of the queen, and development of larvae. However, all of
these products have a low enough toxicity that they could be
used as ingested medicines (rather than fumigants) with minimal
effects on the hive. Clearly, the next phase is to determine if safe
doses of these products can be fed to bees to effectively manage
hive pests, and whether it is better to shock the hive with a short
term massive dose, or to try long term exposures at low dosages.
We would like to caution readers that these results are most
relevant to adult worker health. It is possible that the adult
workers could feed the medicaments to larvae, and that the
larvae may be more sensitive. It is also possible that the
medicaments fed to the queen or drones could affect their
reproductive capacity. However, exposure of these individuals is
buffered through the workers. Unless the only source of food for
the entire hive is the treated sugar water, there will be a dilution
effect where the treated sugar water is mixed in the hive with
nectar from outside sources. A queen that gets one drop of
treated syrup from one worker followed by a droplet of nectar
from outside the hive is effectively consuming a nectar at half the
dosage of the treated syrup. Consequently, workers will be
exposed to greater dosages of these medicaments than will other
members of the hive. Therefore, testing the toxicity of the
medicaments to the workers is a natural first step, and it may be
the only necessary step unless other problems occur as these
products are developed.
We thank SBIR (Small Business Innovation Research) of the
United States Department of Agriculture for support to Robert
A. Stevens and Betterbee Inc. (Greenwich, NY). Alison Skinner
and team of the Ontario Beekeepers’ Association assisted with
bee wrangling and technical instruction. Jim Tew and the Ohio
State University Honey bee Lab supplied the bees for the
research in Wooster. Rebecca Eber t provided additional
laboratory support in Wooster.
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224 Ebert, Kevan,Bishop, Kevan, Downer
... When determining concentrations for oregano oil, thymol, and carvacrol, oral toxicity in honey bees was also considered [54,55]. ...
... However, it may be less desirable as a treatment compared to purified thymol or carvacrol as the amount of active ingredients cannot be controlled in a plant extract. For example, carvacrol levels in oregano oil can vary between 50 and 70% [54]. Like carvacrol and thymol, oregano oil did not affect bee mortality in the primary screening, although oregano oil has been shown to have a slightly toxic effect on bees [54,55]. ...
... For example, carvacrol levels in oregano oil can vary between 50 and 70% [54]. Like carvacrol and thymol, oregano oil did not affect bee mortality in the primary screening, although oregano oil has been shown to have a slightly toxic effect on bees [54,55]. ...
Full-text available
Nosema ceranae is a microsporidian parasite that causes nosemosis in the honey bee (Apis mellifera). As alternatives to the antibiotic fumagillin, ten nutraceuticals (oregano oil, thymol, carvacrol, trans-cinnmaldehyde, tetrahydrocurcumin, sulforaphane, naringenin, embelin, allyl sulfide, hydroxytyrosol) and two immuno-stimulatory compounds (chitosan, poly I:C) were examined for controlling N. ceranae infections. Caged bees were inoculated with N. ceranae spores, and treatments were administered in sugar syrup. Only two compounds did not significantly reduce N. ceranae spore counts compared to the infected positive control, but the most effective were sulforaphane from cruciferous vegetables, carvacrol from oregano oil, and naringenin from citrus fruit. When tested at several concentrations, the highest sulforaphane concentration reduced spore counts by 100%, but also caused 100% bee mortality. For carvacrol, the maximum reduction in spore counts was 57% with an intermediate concentration and the maximum bee mortality was 23% with the highest concentration. For naringenin, the maximum reduction in spore counts was 64% with the highest concentration, and the maximum bee mortality was only 15% with an intermediate concentration. In the longevity experiment, naringenin-fed bees lived as long as Nosema-free control bees, both of which lived significantly longer than infected positive control bees. While its antimicrobial properties may be promising, reducing sulforaphane toxicity to bees is necessary before it can be considered as a candidate for controlling N. ceranae. Although further work on formulation is needed with naringenin, its effect on extending longevity in infected bees may give it an additional value as a potential additive for bee feed in honey bee colonies.
... However, there is still scarce information about the effect of prolonged systemic administration of EOs containing carvacrol on honeybees (Ebert et al., 2007;Porrini et al., 2017). Therefore, the aim of this study was to evaluate and compare the sublethal effects of long term consumption of carvacrol and thymol on Carnolian honeybee workers (Apis mellifera carnica). ...
... The sublethal effects of thymol and carvacrol on honeybees, from existing literature data, are difficult to compare as in many studies the EOs tested contained a mixture of different terpenoids. In addition to the limited number of studies on the prolonged administration of EOs or their main compounds, the data is also methodologically diverse (Albo et al., 2003;Ebert et al., 2007;Sammataro et al., 2009). Furthermore, the toxicity of the main EO compounds in honeybees has mainly been evaluated with acute exposure experiments. ...
... Similar to carvacrol, there is also a lack of studies investigating prolonged honeybee exposure to thymol in laboratory conditions. Ebert et al. (2007) orally exposed honeybees to 0.1% thymol for 8 days that resulted in an average 43% mortality, however, our data shows the same mortality at a concentration 10-times higher (e.g. 1%; 7 days exposure). ...
The parasitic mite Varroa destructor is a threat to beekeeping colonies. Among naturally derived acaricides, the monoterpenoid essential oil compound thymol is used in beekeeping for varroa mite control, but adverse impacts on honeybees has been already documented. Carvacrol, another monoterpenoid, also has a high acaricidal potential and could thus be promising for regular use in beekeeping, but information is scarce regarding the effects of prolonged systemic administration of carvacrol on honeybees. In this study, we evaluate and compared the sublethal effects of long term consumption of carvacrol and thymol on Carnolian honeybee workers (Apis mellifera carnica). Survival and feeding rate were determined preliminary to assess sublethal concentrations. The sublethal effects were analysed by the activity of the acetylcholinesterase (AChE), enzyme involved in the control of neurotransmission, and the activity of detoxifying enzyme glutathione S-transferase (GST) in heads and thoraces. We found that, thymol and carvacrol, caused mortality only at the highest concentrations tested, 1% and 5% respectively. As demonstrated by others, both substances could be effective against varroa at concentrations ten times lower than those causing significant honeybee mortality. However, we demonstrated sublethal effects at the 0.05% carvacrol and thymol exposure concentrations evidenced as increased activity of AChE and GST in the honeybee heads. In conclusion, prolonged treatment with thymol and carvacrol affects bee nervous system and induce detoxification processes possibly resulting in a limited use for acaricidal purposes. We postulate that under the same chronic exposure conditions carvacrol and thymol will have similar sublethal effects on honeybees.
... The long-term sublethal effects of xenobiotics on honeybees [10,14], and specifically of acaricides used in beehives, have been somewhat studied [13]. Yet, information is scarce in particular for essential oils or their individual components [27,[50][51][52]. Sub-lethal effects on adult honeybees include changes in their appetitive behavior [18,20], motor function, grooming and wing fanning behaviors [53], olfactory memory and learning performance [20][21][22][23]51], and reduction of phototaxis [27]. ...
... EOEb was applied in the diet to ensure that the putative sub-lethal effects could be observed, since the toxicity of xenobiotics in honeybees is usually greater by oral intake [54]. Moreover, direct feeding with sanitary products provides a more direct and systemic approach for the exposure of the etiological agents of various honeybee pathologies, and circumvents issues related to variable fumigant volatility [52]. Neither survival nor the amount of diet consumed by honeybees was affected by the consumption of EOEb (up to 6000 ppm in the diet). ...
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When developing new products to be used in honeybee colonies, further than acute toxicity, it is imperative to perform an assessment of risks, including various sublethal effects. The long-term sublethal effects of xenobiotics on honeybees, more specifically of acaricides used in honeybee hives, have been scarcely studied, particularly so in the case of essential oils and their components. In this work, chronic effects of the ingestion of Eupatorium buniifolium (Asteraceae) essential oil were studied on nurse honeybees using laboratory assays. Survival, food consumption, and the effect on the composition of cuticular hydrocarbons (CHC) were assessed. CHC were chosen due to their key role as pheromones involved in honeybee social recognition. While food consumption and survival were not affected by the consumption of the essential oil, CHC amounts and profiles showed dose-dependent changes. All groups of CHC (linear and branched alkanes, alkenes and alkadienes) were altered when honeybees were fed with the highest essential oil dose tested (6000 ppm). The compounds that significantly varied include n-docosane, n-tricosane, n-tetracosane, n-triacontane, n-tritriacontane, 9-tricosene, 7-pentacosene, 9-pentacosene, 9-heptacosene, tritriacontene, pentacosadiene, hentriacontadiene, tritriacontadiene and all methyl alkanes. All of them but pentacosadiene were up-regulated. On the other hand, CHC profiles were similar in healthy and Nosema-infected honeybees when diets included the essential oil at 300 and 3000 ppm. Our results show that the ingestion of an essential oil can impact CHC and that the effect is dose-dependent. Changes in CHC could affect the signaling process mediated by these pheromonal compounds. To our knowledge this is the first report of changes in honeybee cuticular hydrocarbons as a result of essential oil ingestion.
... For instance, savoury or spearmint oils were investigated and showed acaricidal properties with low rate of honeybee mortality while dillsun induced higher death rates [157]. Menthol in sugar syrup displayed encouraging short-term results [150,158] whereas neem oil killed mites [159], but also increased brood mortality and reduced the worker's walking activity [160]. Finally, another plant extract, relying on hop leaves, was shown to contain polyphenols with high miticide effect and low acute toxicity for bees [161,162]. ...
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Varroadestructor is a real challenger for beekeepers and scientists: fragile out of the hive, tenacious inside a bee colony. From all the research done on the topic, we have learned that a better understanding of this organism in its relationship with the bee but also for itself is necessary. Its biology relies mostly on semiochemicals for reproduction, nutrition, or orientation. Many treatments have been developed over the years based on hard or soft acaricides or even on biocontrol techniques. To date, no real sustainable solution exists to reduce the pressure of the mite without creating resistances or harming honeybees. Consequently, the development of alternative disruptive tools against the parasitic life cycle remains open. It requires the combination of both laboratory and field results through a holistic approach based on health biomarkers. Here, we advocate for a more integrative vision of V. destructor research, where in vitro and field studies are more systematically compared and compiled. Therefore, after a brief state-of-the-art about the mite’s life cycle, we discuss what has been done and what can be done from the laboratory to the field against V. destructor through an integrative approach.
... In apiculture, it is known to suppress the parasitic mite Varroa destructor (Chiesa, 1991). Recent research has shown that thymol fed orally to adult bees is not toxic (Ebert et al., 2007). ...
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This book chapter covers how honey bee reproduces, variation in castes and development among Thai species, and how sex determines the vision of labor in this population. The discovery of the oldest bee species and the evolution of honey bees also have been discussed. In addition to behavior related to the nesting and colony defense. Honey bee pheromones also have been discussed how honey bee produce their pheromones, and how they detect pheromone and other odorants.
... High values of cis-sabinene hydrate were found for all honey samples. According to Ebert, Kevan, Bishop, Kevan, & Downer (2007), cissabinene hydrate is one of the main components of clove oil which is used to protect bees from diseases. ...
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The aim of this study was to determine the physicochemical parameter changes, aroma, melissopalynological properties, and heavy metal content of honey produced from different types of flora (chestnut and highland) in the Senoz Valley. For this purpose, the distribution of beehives at different elevation levels in the research area was determined by a layered random sampling method. Some characteristics of the honey samples were analyzed by standard laboratory methods. The highest average color (L and b) and the glucose, sucrose, Brix, Cd, Pb, Ni, Zn, and Cr values were found in the highland honeys; the highest color (a) and fructose, F/G ratio, proline, pH, conductivity, Fe, Cu, Al, and Mn values were found in the chestnut honeys. The difference between highland and chestnut honeys was statistically significant in terms of color (L and a), F/G ratio, proline, pH, electrical conductivity, Pb, Cu, and Mn. A total of 146 aromatic components were isolated in the chestnut and highland honeys.
... This notion applies to naturally occurring chemicals. A laboratory analysis evaluating the toxicity of various essential oils and organic acids by Ebert et al. (2007) revealed that compounds such as wintergreen, menthol, sage oil and cineole were found to be fairly benign. However, Carayon et al. (2013) found that there were negative effects resulting from honey bee exposure to thymol at approved concentrations. ...
Pedigo and Rice (2009) described a concept that some ecologists subscribe to called the “balance of nature” phenomenon. This idea holds that spe-cies in communities achieve certain status in their ecosystem and that this status becomes fixed and resistant to change. On average, individuals are only able to replace themselves. Fluctuations may occur, but ultimately the various species in the community will retain their position and relative population size in the ecosystem. According to these ecologists, when humans alter and reduce the diversity of an ecosystem they are acting counter to this balance. In an attempt to re-turn the altered system to its ordinary state, ex-traordinarily strong forces of nature will act in op-position to these activities. It could be argued that among these forces are biotic maladies which im-pair or destroy European honey bee (Apis mellifera) colonies. Oftentimes when honey bee diseases and pests explode and devastate apiaries, these activi-ties are merely a reaction to the “overpopulation” of the single species which humans have selected. Thus many of the problems with honey bees should come as no surprise; they function just as they would in any other scenario where a single species becomes too numerous. The only distinction is these insects are of value to humans. This is not to suggest that honey bees should be kept at “natural” rates. Honey bees provide ap-proximately $15 billion dollars in annual pollination services in the United States (U.S.) (Morse and Cal-derone, 2000). If the environment is left on its own to determine how many honey bee colonies are to exist, it could have severe humanitarian and eco-nomic consequences. Such a proposal is just as ab-surd as keeping apples, melons or tomatoes at the rate which nature sees fit. Honey bee diseases and pests are considered in ecology to be perfectly density-dependent, meaning that an increase in the density of the honey bees will result in more intense pressure from hon-ey bee pests. To attribute all of the problems in beekeeping to this single notion is a gross oversim-plification. Indeed many European honey bee pests came from other hosts such as the Asiatic honey bee (Apis cerena); therefore their deleterious effects are much more severe than would be if they had coevolved with their host. Furthermore, some of the problems with honey bee health have been attributed to abiotic factors such as inadequate nu-trition and pesticide exposure. Yet the point re-garding density-dependence is made because popu-lar sentiment often suggests that the solution to problems with honey bees is simply that more hon-ey bees are needed. The human population on Earth is expected to reach 10 billion in the 21st cen-tury (Bongaarts, 2009). As a result, there will likely need to be more honey bees added to our global agroecosystems in order to meet future food de-mands and keep food affordable. However, as new colonies are added it is imperative that disease and pest issues are kept under control, colonies are managed to maximize pollination capabilities and alternative pollinators are incorporated. Merely adding honey bee colonies without any considera-tion for the pest and disease “reaction” will only exacerbate problems in beekeeping . This guidebook is meant to assist in the promotion of honey bee health and prepare for the likely inevi-table need for an increased number of managed colonies. However it is not intended to be a diag-nostic tool or a prescription for solutions. Rather it is a summary of scientific knowledge about honey bee immunity, disease etiology, pest problems and abiotic stressors. The goal of this guide is for the reader to: 1) develop a deeper familiarity with hon-ey bee biology and the conditions that harm these insects; and 2) better understand the relative im-portance of the various problems that negatively affect colonies.
... Chemical and biological control of pests require selective products for integrated pest management programs and insecticides should not impact pollinator insects, which are indispensable for the propagation of many cultivated and native plants 2,10,11 . The botanical product toxicity to insects such as natural enemies and pollinators should be evaluated due to the demand for organic food 29,30 . Insecticide stress in arthropods is not restricted to lethal effects, and sublethal ones are as important because the insects remain exposed to sublethal concentrations. ...
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The toxicity of essential oils that can be used in insect pest management to pollinators needs further studies. Apis mellifera Linnaeus and Trigona hyalinata (Lepeletier) (Hymenoptera: Apidae) foragers were exposed by three pathways to ginger, mint, oregano and thyme essential oils to provide their LC50, LD50 and LC90, LD90. Oregano and thyme were more toxic through contact and topically for A. mellifera while the toxicity of mint and ginger was lower. Trigona hyalinata was more tolerant to the essential oils than A. mellifera. In the walking test, the area was treated (totally or partially) with sub-doses (LC50) obtained via contact. The area fully treated with oregano reduced the distance traveled and the movement speed increased the number of stops by A. mellifera. Similar results were observed for T. hyalinata with oregano and thyme oils. Apis mellifera showed irritability remaining shorter time in the area partially treated with ginger, mint and thyme essential oils while T. hyalinata had similar behavior with ginger and thyme. Essential oils did not repel A. mellifera or T. hyalinata, but those of ginger, mint and thyme reduced the time spent by A. mellifera in areas treated with sublethal doses. Oregano and thyme essential oils reduced the survival, mainly, of A. mellifera, while ginger and mint were selective for both pollinators.
... In addition, the essential oil of O. majorana demonstrateda toxic effect on A. mellifera bees, as verified by Gashout and Guzm an-Novoa (2009). However, Ebert, Kevan, Bishop, Kevan, and Downer (2007) and Sabahi, Gashout, Kelly, and Guzman-Novoa (2017) did not verify the effect of oils from this same species on A. mellifera. ...
This work attempted to determine the effects of the aqueous extracts of Echinodorus grandiflorus, Origanum majorana, Punica granatum and Matricaria chamomilla on Africanized Apis mellifera workers, as well as their effects on the digestive tracts of these insects and chromatographic analysis of its compounds. For this, the methods of direct spraying, contaminating diets and treatment of contact surfaces (soybean leaves) were used. Five treatments were established: sterilized distilled water (control), aqueous extract of “leather hat” (E. grandiflorus), marjoram (O. majorana), pomegranate (P. granatum) and chamomile (M. chamomilla) at concentrations of 5%. Each treatment consisted of five replicates with 20 bees per replicate; each bee was an experimental unit. The workers of A. mellifera submitted to the treatments were conditioned in gearbox boxes, and these were kept in a climatic chamber (27 ± 2 °C, 60 ± 10% U.R.). The mortality of the workers was evaluated at different hours. The workers killed by the ingestion of contaminated paste were separated for midgut histological analysis. Plant extracts were submitted to chromatography. It was verified that all vegetal extracts reduced the survival of the workers of A. mellifera in all the bioassays. Plant extracts O. majorana and P. granatum caused morphometric changes, reducing the length of A. mellifera mesenteric cells. The extract of O. majorana showed a negative effect on A. mellifera; it reduced the survival of the workers in all the bioassays in which it was evaluated. It also caused morphometric alterations in the cells of the midgut.
... In apiculture, it is known to suppress the parasitic mite Varroa destructor (Chiesa and D'Agaro, 1991). Recent research has shown that thymol fed orally to adult bees is not toxic (Ebert et al., 2007). Therefore, protofil is a natural product obtained from plants through hydro-alcoholic extraction. ...
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A new book for those who are interested in honeybees that play a pivotal role in natural and rural ecosystems by increasing food production through pollination services. This book provides an introduction to why Thai honeybees are so important, focusing on the role of honeybees in pollination ecology and on potential threats to Thai honeybee health. The nesting, reproduction, variation in caste development, division of labor, foraging, communication, and colony defense behaviors are discussed. The discussion of forage marking pheromones in Thai honeybee, the role of parasites, predators and pathogens on Thai honeybees and Thai apiculture and agriculture. There are seven chapters in this book: 1) introduction: why are honeybees so important 2) diversity of Thai honeybees; 3) honeybee castes and development; 4) honeybee anatomy, including the structure of the pheromone glands and exocrine glands 5) honeybee pollination in Thailand 6) honeybee pathogens, parasites and diseases 7) beekeeping in Thailand.
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A number of plants produce nectar or pollen that contains toxins which can adversely affect honey bees. Almond (Amygdalus communis L. (Rosaceae)) produces amygdalin, a toxic cyanoglycoside, in its nectar and pollen. Although beekeepers regard almond as a valuable nectar and pollen plant, and honey bees are deployed extensively for almond pollination, prolonged reliance on almond may be detrimental to honey bees' health. Our results suggest that almond nectar is not sufficiently rich in amygdalin to pose a hazard, but that almond pollen could be toxic if exclusively consumed by honey bees for much more than a week. Further tests are needed to determine if honey bees in almond orchards are at risk, or if they somehow cope with the toxin.
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Tracheal mites, Acarapis woodi (Rennie) (Acari: Tarsonemidae), are important parasites of honeybees, Apis mellifera L. (Morse and Flottum 1997). They enter the prothoracic tracheae and feed through the walls on haemolymph. Currently, these mites are controlled by applying 50 g of menthol crystals in a perforated bag per hive when ambient temperatures are 15°C or more. Even then, it takes 2 weeks for the menthol to perfuse the hive (Herbert et al. 1988; Wilson et al. 1990). In cold climates, sublimation of menthol is too slow to be effective in controlling mites, especially in spring and fall when control is most needed (Scott-Dupree and Otis 1992). Because menthol fumes enter the bees' trachea and kill the mites therein, it may be possible to kill the mites with menthol that is delivered to them via the haemolymph. Therefore, finding if menthol could become systemic when ingested by bees and it could kill tracheal mites by that route, an ingestible menthol medicament for the bees would hold potential for mite control (Kevan and Kevan 1997).
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Mortality of last instar western spruce bud worm, Choristoneura occidentalis Freeman, exposed to a series of increasing doses (topical application) or concentrations (diet incorporation) of 10 insecticides was analyzed over 7 d by time-dose-mortality regression. Regression based on the complementary log-log model was useful for analyzing time trends for all dose levels simultaneously. Each of the 10 insecticides acted more quickly when applied topically. In both kinds of experiments, speed of lethal action of the insecticides depended on dose or concentration. The statistical methods developed to estimate lethal doses as functions of time and median times of death as functions of dose are more efficient than methods published previously.
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Essential oils and essential oil components offer an attractive alternative to synthetic acaricides for the control of Varroa jacobsoni. They are generally inexpensive and most pose few health risks. Terpenes (mainly monoterpenes) are the main components of essential oils, comprising about 90 % of the total. More than 150 essential oils and components of essential oils have been evaluated in laboratory screening tests. Very few of them, however, have proven successful when tested in field trials. Thymol and thymol blended with essential oils or essential oil components offer a promising exception. Mite mortality obtained with these formulations typically exceeds 90 % and often approaches 100 %. In addition, residues in honey are low, even after long-term treatments. The exact conditions under which these formulations will yield reliable and effective control, however, have only been determined for certain European regions. Based on the available studies, relying solely on a single treatment with an essential oil or essential oil component is generally not sufficient to maintain mite populations below the economic injury level. Therefore, efforts are necessary to optimize the use of these substances and to incorporate them, along with other measures for limiting mite populations, into an integrated pest management strategy for control of Varroa jacobsoni. © Inra/DIB/AGIB/ Elsevier, Paris
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Four miticides in various formulations and concentrations were applied in a fall treatment program to honey bee colonies infested with Acarapis woodi. The miticides tested were menthol, Amitraz, fluvalinate (Apistan®), and cymiazole (Apitol®). None of the miticides significantly reduced mite prevalence in treated colonies relative to the control treatment. Additional studies should be undertaken in temperate climates to determine whether the efficacy of the miticides tested in this study can be improved by administering them at other time during the year or by adjusting dosages rates to improve their efficacy when applied to infested colonies during a fall management program.
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A complementary log-log (CLL) model was used to model time-dose-mortality relationships from bioassay tests of 26 fungal isolates mostly from Madagascar, Africa, against three acridid species, all referred to here as "grasshoppers." The fungal pathogens included 15 isolates of Beauveria bassiana, 9 isolates of Metarhizium flavoviridae, and 2 isolates of Paecilomyces spp. Grasshopper species tested included Melanoplus sanguinipes, Locusta migratoria migratorioides, and Schistocerca gregaria. The scaled deviance, mean deviance, Pearson X2 statistic, Hosmer-Lemeshow (H-L) C statistic, and three-dimensional time-dose-mortality graphs were used to assess extra-binomial variation, data points that were potential outliers, conformance of the scaled deviance statistic and Pearson's X2 statistic to a chi2 distribution, and the fit of the CLL model. The H-L C statistic also was found to be useful in showing the goodness of fit of the CLL model for the fungal isolates prior to modeling the extra-binomial variation. After the extra-binomial variation was modeled using Williams' method, the slope from maximum likelihood estimation, modified log(LD50) estimates (which were corrected for background mortality using the CLL model), a dynamic ranking of the log(LD50) values over time, and a three-dimensional plot of time, dose, and mortality of the three grasshopper species were used to evaluate the effectiveness of the fungal isolates. In general, the CLL model provided a rather poor fit of the fungal isolates which had a large number of replicate trials in the bioassay tests (i.e., a large sample size) due to extra-binomial variation. The CLL model provided an excellent fit of the time-dose-mortality relationships of such isolates after the extra-binomial variation was modeled and included in the CLL model. Metarhizium isolates MFV and SP5 were found to be the most virulent isolates tested against M. sanguinipes, followed by Metarhizium isolates: SP8, SP7, SP9, SP6, and SP1, and Beauveria isolate S33B. Metarhizium isolates SP3, SP5, SP6, and SP9, and Beauveria isolates SP11, SP12, SP13, and SP16 showed higher levels of virulence against L. migratoria migratorioides over more of the time periods tested than the other pathogen isolates examined. Metarhizium isolates SP9 and SP5 were the most effective isolates tested against S. gregaria. In general, the Metarhizium isolates were more virulent against the grasshoppers than the Beauveria isolates, which were more virulent than the Paecilomyces isolates. The CLL model was found to be very useful in describing grasshopper mortality as a function of time and dose. This approach combined with model and fungal isolate assessment statistics will be helpful for determining which pathogen isolates have the greatest potential for controlling grasshoppers and other pests in the future.
Hoarding behaviour was measured in the laboratory by putting 50 newly emerged bees into a small box-like cage and noting the time the bees required to remove 20 ml of sugar syrup from their feeder, some of which was consumed and some stored in their comb. Bees from brood of the same colony usually required similar times; bees from brood of different colonies varied widely. The time required by bees from 21 colonies in these laboratory tests was negatively correlated with the weight gained by the colonies in the field (r = −0.33). It is suggested that the laboratory test may therefore provide an indication of colony hoarding behaviour, which directly affects the weight gained and consequently the honey production by the colony.