ACTA BIOLOGICA SLOVENICA 
LJUBLJANA 2013 Vol. 56, [t. 1: 11–25 
ACTA BIOLOGICA SLOVENICA 
LJUBLJANA 2013 Vol. 56, [t. 1: 11–25 
The 
synergy 
of 
xenobiotics 
in 
honey 
bee 
Apis mellifera: 
mechanisms 
and effects 


Sinergizem ksenobiotikov v medonosni cebeli Apis mellifera: 
mehanizmi 
in 
ucinki. 


Gordana Glavan* and Janko Božic 


University of Ljubljana, Biotehnical faculty, Department of Biology, Vecna pot 111, Ljubljana 
SI-1000, Slovenia 
*correspondence: gordana.glavan@bf.uni-lj.si 


Abstract:Duringforagingactivitieshoneybeesarefrequentlyexposedtodifferent 
xenobiotics, most of them are agrochemical pesticides and beehive chemicals. Many 
pesticides are applied together and synergism is likely to occur in different organisms. 
The risk of synergisms is neglected and relatively few studies were performed 
concerning the effects and synergy mechanism of different xenobiotic combinations 
in 
honeybees. 
The 
understanding 
of 
synergy 
mechanisms 
between 
xenobiotics 
is 
very important for the control of defined mixtures use and also for the prediction of 
potential toxicity of newly developed substances in agriculture and apiculture. This 
review is focused on the effects, mechanisms and molecular targets of xenobiotics in 
honeybees and possible complex mechanisms of their synergisms. The main threat 
for 
honeybees 
are 
insecticides 
which 
primary 
molecular 
targets 
are 
few 
neuronal 
molecules therefore causing the impairment of neuronal system that have a profound 
effect on honeybee behavior, cognitive functions and physiology. However, the majority 
of synergistic effects observed in honeybees were ascribed to the inhibition of 
detoxifying midgut enzymes P450 involved in xenobiotic metabolism since most of 
studies were done with the mixtures xenobiotic/P450 inhibitor. The main inhibitors 
of P450 enzymes are specific compounds used to prolong the effects of pesticides as 
well as some fungicides. Some insecticides can also interact with these enzymes and 
influence the xenobiotis. Although the primary mechanisms of action of individual 
xenobiotics especially insecticides are well known and there are possible interactions 
in honeybees at their primary target sites, this issue is underestimated and it warrants 
further investigation. 


Keywords: 
synergism, xenobiotic, Apis mellifera, mechanism, pesticide, P450 


Izvlecek: 
Medonosne 
cebele 
so 
med 
iskanjem 
hrane 
pogosto 
izpostavljene 
razlicnim ksenobiotikom, vecinomaso to fitofarmacevtska sredstva in panjske kemikalije. 
Številna fitofarmacevtska sredstva se uporablja skupaj in znano je, da lahko 
pride do sinergisticnih interakcij v organizmih. Tveganje za nastanek sinergizmov 
je podcenjeno in narejenih je relativno malo študij na cebelah o ucinkih 
in mehanizmih 
sinergizmov 
razlicnih 
kombinacij 
ksenobiotikov. 
Razumevanje 
mehanizmov 
sinergizmov 
ksenobiotikov 
je 
zelo 
pomembno 
za 
nadzor 
nad 
uporabo 
definiranih 


Acta Biologica Slovenica, 56 (1), 2013 


mešanic in napovedovanje potencialne toksicnosti novih ksenobiotikov v kmetijstvu 
in cebelarstvu. Pregledni clanek se osredotoca na ucinke, mehanizme in molekulske 
tarce ksenobiotikov v medonosnih cebelah in osvetljuje morebitne primere ter mehanizmenastankasinergizmov.
Najboljnevarnizacebelesoinsekticidi,katerihprimarne 
tarce so nekatere molekule živcnih celic,zato le-ti motijo delovanje živcnega sistema. 
Insekticidi zato lahko mocno vplivajo na vedenje, kognitivne funkcije in fiziologijo 
cebel. 
Kljub 
temu 
raziskovalci 
vecino 
sinergijskih 
ucinkov 
v 
cebelah 
razlagajo 
z 
inhibicijo crevesnih detoksifikacijskih encimov P450, ki presnavljajo ksenobiotike, 
saj je bila 
vecina študij narejena z mešanicami ksenobiotik/zaviralec encimov P450. 
Glavni zaviralci encimov P450 so specificni inhibitorji za podaljšanje ucinka fitofarmacevtskih 
sredstev ter nekateri fungicidi. Tudi nekateri insekticidi lahko vplivajo na 
delovanje encimovP450 in tako vplivajo na interakcije med ksenobiotiki. Ceprav so 
primarni mehanizmi delovanja posameznih ksenobiotikov, še posebej insekticidov, 
precej znani in so sinergizmina ciljnih tarcah pri cebelah možni, je to podrocje pod-
cenjeno in neraziskano. 


Kljucne 
besede: 
sinergizem, ksenobiotik, Apis mellifera, mehanizem, pesticidi, 
P450 


Introduction 


In addition to gathering nectar to produce 
honey, 
honey 
bees 
carry 
out 
another 
crucial 
function: 
pollination 
of 
agricultural 
crops, 
home gardens, orchards and wildlife habitat. A 
substantial decline of honey bee populations so 
called colony collapse disorder was observed in 
the last 15 years in many countries in Europe and 
in North America 
(vanEngelsdorp and Meixner 
2010).Colony 
numbers 
in 
Europe 
for 
example 
decreased from over 21 million in 1970 to about 
15.5millionin2007(FAO,2009),aseveredecline 
occurredafter1990.Manyfactorssuchasdiseases, 
parasites, xenobiotics (pesticides and veterinary 
products), the environment, and socio-economic 
factorsprobablyinfluencemanagedbeepopulation, 
workingaloneorincombinations(vanEngelsdorp 
and Meixner 2010). 


Honey bees may frequently become exposed 
to 
xenobiotics, 
environmental 
chemicals 
as 
a 
consequence of their foraging activities. Most of 
them are agrochemical pesticides and beehive or 
veterinary products, many of them of insecticide 
action, used against parasitic honey bee mites: 
Acarapis sp., Varroa destructor 
and Aethina tumida 
(Thompson 2012). The use of pesticides to 
control weeds, fungi and arthropod pests seems 
inevitable in modern agriculture which seeks for 
thehighestyieldsoftheproduces.Nectarforaging 

bees are likely to experienced highest exposure 

to both sprayed and systemic seed and soil treatments 
compounds followed by nurse and brood-
attending bees. The residues of pesticides were 
found in pollen, wax and nectar within colonies, 
pollen and nectar residues from plants, in pollen 

loads on bees returning to the hives and in adult 

workers (Thompson 2012). Pesticide regulations 
sofarfocusedmainlyonprotectionofbeesagainst 
direct poisoning (Thompson and Wilkins 2003, 
Desneuxetal.,2007).Thedirectpoisoningisnow 
regulatedandpreventedbytheimplementationof 
EuropeanCouncilDirective91/414inEurope,and 
theFederalInsecticide,FungicideandRodenticide 
ActintheUS(Desneuxetal.2007,vanEngelsdorp 
and Meixner 2010). The standard approaches for 
determination of acute pesticide toxicity in bees 
are the calculation 
of the LD50 (median lethal 
dose) or LC50 (median lethal concentration) of 
a given substance with respect to adult bees or 
larvae.Inspiteofmoreorlesscontrolledprotection 
against direct poisoning, massive dying of honey 
bees is still present. For this reason many studies 
are focusing to the chronic sub-lethal exposure 
of 
xenobiotics 
causing 
a 
variety 
of 
sub-lethal 
effects 
on 
bees 
(reviewed 
by 
Desneux 
2007) 
which are physiological and behavioral, affecting 
the honeybee colony as a whole, resulting in 
the perturbations of learning and communication 
ability.Evenmore,asmanypesticidesareapplied 


Glavan et al.: The synergy of xenobiotics in honey bee Apis mellifera: mechanisms and effects 


together,scientistsarearguingforyearsthattoxic 
exposures to pesticides should be measured as 
they would normally occur, in combination with 
one another. The most intriguing or concerning 
aspectofpesticidemixturesistheopportunityfor 
complex interactions such as a synergy when the 
administration of one chemical increases the toxic-
ityofanother.Therearerelativelyfewexperimental 

data regarding synergistic effects of pesticides on 

honeybees, but in some cases pesticide mixtures, 
particularlywithinsecticides,havebeenshownto 
besynergistic,withreportedincreases intoxicity 
of up to100-fold (Thomson 1996). However, the 

effects of pesticide exposure on colony health is not 

systematicallymonitored,andtheEnvironmental 
Protection Agency (EPA) does not require data 
on sub-lethal or synergistic effects for pesticide 
registration (NAS, 2009) therefore this specific 
issue warrants special attention. 


This review focuses on the mechanisms and 
molecular 
targets 
of 
xenobiotics 
in 
honeybees 
which could be the basis of their synergism, especially 
insecticides which are the most potentially 
dangerousforhoneybees.Sinceofgreaterpotential 
to cause underestimation of the risk posed to the 
honeybeecoloniesdeclinethemodesofsynergisms 
of xenobiotics known so far are emphasized and 
summarizedinthissectionofourreview.Theaim 
istoexemplifythepossiblecomplexmechanisms 
of their interaction. 


Mechanisms 
and 
effectsof 
xenobiotics 


Agrochemical pesticides 

Theagrochemicalpesticidesaffectinghoneybee 
colonies arefungicides, herbicides and insecticides, 
applied to crops (Johnson et al. 2010). The large 
numberofcommercialpesticidesusedworldwide, 
whetherbasedonnaturalproductsorbeingentirely 
ofsyntheticorigin,actonrelativelyfew,perhaps 
95biochemicaltargetsinpestinsects,weeds,and 
destructive fungi (Casida 2009). Herbicides in 
general 
are 
blocking 
photosynthesis, 
carotenoid 
synthesis,oraromaticandbranchedchainamino 
acidsynthesisessentialinplants.Manyfungicides 
inhibit ergosterol (the fungal sterol) or tubulin 
biosynthesis or cytochrome c reductase. Others 
disturb basic cellular functions (Casida 2009). 


The pesticides that represent a main threat 
to the honeybees are insecticides. Many of the 
most 
effective 
insecticides 
in 
current 
use 
act 
on the insect nervous system (Narahashi 1992, 
Bloomquist 
1996).Others 
are 
insect 
growth 
regulators(Tasei2001,Thomsonetal.2005).The 
growth regulating insecticides are functioning as 
juvenile hormone analogues (fenoxycarb), chitin 
synthesis inhibitors (diflubenzuron), ecdysteroid 
synthesis inhibitors (azadirachtin) and ecdysteroid 
analogues (tebufenozide) (Tasei 2001, Thomson 
et 
al. 
2005).The 
main 
nerve 
targets 
of 
current 
insecticides are voltage-gated sodium channels, 
an enzyme acetylcholinesterase (AChE) and re-
ceptorsforneurotransmitters:L-glutamate-gated 
chloridechannelsworkingasglutamatereceptors 
(GluRs),ionotropic.-aminobutyricacid(GABA) 
receptors(GABARs) binding GABAand nicotinic 
cholinergic receptors (nAChRs) stimululated by 
acetylcholine (ACh) (Coats 1990, Fukuto 1990, 
Zlotkin1999,Bloomquist2003,Raymond-Delpech 
etal.2005,WolstenholmeandRogers2005,Davies 
etal.2007,JeschkeandNauen2008).Voltage-gated 
sodium channels are molecular targets for three 
big groups of insecticides, pyrethroid,DDT-type 
and organ chlorine insecticides 
(Coats 
1990). 
These 
channels 
mediate 
the 
transient 
wave 
of 
sodium 
entry 
spreading 
along 
the 
nerve 
axons 
and dendrites, carrying the action potential along 
thesestructuresandareubiquitousinthehoneybee 
nervous 
system 
(Sattelle 
and 
Yamamoto 
1988, 
Narahashi 1992). All three groups of insecticides 
cause death due to hyperexcitation of the nerves, 
butinslightlydifferentway.Pyrethroidpesticides 
by binding to voltage-gated sodium channels in-
ducehyperexcitationthatresultsfromprolongation 
of the open phase of sodium gate function results 
inneurotoxic effectssuch astremorsandconvulsions.
TheDDT-typeinsecticides,DDT(dichloro 
diphenyl trichloroethane) and DDT analogues 
(N-alkylamides,dihydropyrazoles),actprimarily 
on the peripheral nervous system (Coats 1990). 
The mechanism of DDTis the prevention of the 
deactivation or closing of that gate after activation 
and 
membrane 
depolarization. 
The 
result 
is a persistent leakage of Na+ ions through the 
nervemembrane,creatingadestabilizingnegative 
afterpotential.Thehyperexcitabilityofthenerveis 
theconsequenceoftrainsofrepetitivedischarges 
in the neuron after a single stimulus and/or occur 


Acta Biologica Slovenica, 56 (1), 2013 


spontaneously (Coats 1990).The acute toxic effectsinanimalsoforganchlorineinsecticidesare 
alsoduetohyperexcitationinthenervoussystem 
and death is frequently recognized as respiratory 
failure 
after 
the 
disruption 
of 
nervous 
system 
function (Coats 1990). 


Organophosphate 
and carbamate 
insecticides 
are inhibiting the action of AChE (Fukuto 
1990). AChEis an enzyme that terminates the syn-
apticactionsofACh,theimportantneurotransmitter 
of sensory neurons and interneurons of insect brain 
which is necessary for sensory-input processing 
and learning in honey bee (Massoulie et al. 1993, 
Homberg1994,Weinberger2006).AChEiswidely 
distributed in the insect brain, the thoracic and 
abdominal segments and the abdominal ganglia 
(Kreissl in Bicker 1989, Thany et al. 2010).The 
potential target sites for organophosphate and 
carbamate insecticides in the honeybee brain are 
the optic lobes, antennal afferents projecting into 
the dorsal lobe, fibers connecting the two brain 
hemispheres, and within the protocerebrum and 
the 
mushroom 
bodies 
where 
AChE 
is 
highly 
expressed (Kreissl in Bicker 1989). AChE was 
found also in the compound eye and ocelli (Kral 
1980, Kral and Schneider 1981).The inhibition 
of 
AChE 
by 
organophosphate 
and 
carbamate 
insecticides causes irreversible blockage leading 
to accumulation of the enzyme which results in 
overstimulation of cholinergic receptors (Fukuto 
1990).AsAChisamajorneurotransmitterofinsect 
nervoussystem(Homberg1994)theinhibitionof 
AChEcouldcauseasystemicfailureintheinsect 
body. Widely used organophosphate as hive var-
roacides is coumaphos. 


Insecticides that act selectively on insect 
nAChRs as potent agonists are neonicotinoids 
(Jeschke 
and 
Nauen 
2008). 
Among 
ionotropic 
receptors affected 
by insecticides, nAChRs are 
the most abundant excitatory postsynaptic receptors 
(Sattelle 1980).The central nervous system 
of insects is rich in nAChRs more so than any 
other organism (Jones and Sattelle 2010).They 
are located postysinaptically and directly activated 
by ACh, released from presynaptic 
cholinergic 
neurons facilitating fast excitatory synaptic 
transmission (Thany etal. 2010).In thehoneybee 
brain the highest binding site densities for nAChR 
arelocalizedinthesuboesophagealganglion,the 
optic tubercles, optic lobes medulla and lobula, 

antennal lobes, dorsal lobes and the a-lobes of 
the 
mushroom 
bodies 
(Scheidler 
et 
al. 
1990). 
Neonicotinoids cause excitation of the neurons 

and because of a high concentration of nACh 
receptors in honeybees the eventual paralysis could 

be very profound occurring at low concentration 
of neonicotinoids, leading to death. 


TheinsecticidesthatinterferewithGABARs 
are pyrethroidsandphenylpyrazoleinsecticides 
(Raymond-Delpech 
et 
al. 
2005, 
Davies 
et 
al. 
2007). In insects GABARs are associated with 
neurotransmitter 
GABA 
mediating 
inhibitory 
synaptic transmission in the nervous system and 
at 
nerve-muscle 
junctions 
(Homberg 
1994). 
In 
the 
central 
nervous 
system 
of 
honeybees 
the 
neurotransmitter GABA 
is generally present in 
neuropil, especially in structures that are associated 
with learning and memory, such as antennal 
lobe and the mushroom body and the optic lobe 
(SchaferandBicker1986,ElHassanietal.2009). 
The presence of the neurotransmitter GABA 
in 
the honeybee brain was shown mainly for local 
interneuronsandlessintheprojectionneurons.In 
thebrainandsubesophagealgangliononlyminority 
of neurons contained GABA(Bicker et al. 1985, 
Meyer et al. 1986, Schafer and Bicker 1986). By 
targeting the GABARs which are chloride channels 
pyrethroids and phenylpyrazole insecticides 
disrupt normal neuronal influx (e.g., passage of 
chloride ions) and, at sufficient doses, causing 
excessiveneuralexcitation,severeparalysis,and 
death (Cole et al. 1993, Gunasekara et al. 2007). 
Most 
known 
representative 
of 
phenylpyrazole 
insecticidesisfipronilandwidelyusedpyrethroid 
ashivevarroacidesistau-fluvalinate.Pyrethroids 
are very complex group regarding the molecular 
mechanisms of their functioning, because they 
don’tbindonlytoGABA-gatedchloridechannel, 
but they can also interfere with other molecules 
such as calcium regulation. They could inhibit 
bothCa-ATPaseandCa-MgATPase(Coats1990). 
In this respect direct effects on neurotransmitter 
releasehavebeenobserved,aswellastheinhibition 
of Ca2+ uptake. However, they have also various 
secondary targets such as signal transduction 
pathwaysbyalteringtheproteinphosphorylation 
cascade that may result, among other things, in 
programmed cell death (Ray and Fry 2006). In 
mammals a variety of different effects of pyre-
throidswerediscoveredlikemodulationofprotein 


Glavan et al.: The synergy of xenobiotics in honey bee Apis mellifera: mechanisms and effects 


phosphorylation,voltage-gatedsodiumchannels, 
voltage-gated 
chloride 
channels, 
noradrenaline 
release, membrane depolarization, GABA-gated 
chloride channels, nicotinic receptors, mitochondrial 
complex I, apopotosis induction, voltage-
gatedcalciumchannels,lymphocyteproliferation, 
volume-sensitiveanionchannels,calciumATP-ase, 
intercellular gap junctions and chromosomal damage, 
but many of these effects were not shown 
for insects (Ray and Fry 2006). 


The insecticides that activate GluRs which 
bind neurotransmitter L-glutamate are avermectin 
and milbemycin(Raymond-Delpech et al. 2005, 
WolstenholmeandRogers2005).Thedistribution 
of GluRs in the nervous system of honeybees is 
not known but they probably modulate excitability 
in the nervous system and muscle cells as 
neurotransmitterL-glutamateisenrichedinthese 
tissues 
(Cully 
et 
al. 
1996). 
Studies 
performed 
by 
Maleszka 
et 
al. 
(2000) 
and 
Locatelli 
et 
al. 
(2005) suggested that glutamatergic neurons in 
the honeybee brain, in particular those found in 
themushroombodies,maybepartofthecircuitry 
involvedinprocessingofolfactorymemory.Inthe 
honeybee, a high level of a glutamate transporter 
is present in the optic lobes and in restricted 
areas of the mushroom bodies corresponding to 
the Kenyon cells of the calyces (Kucharski et al. 
2000). GluRs are permeable to chloride ions and 
theactivationofthesereceptorswithinsecticides 
avermectin and milbemycin causes a very long-
lasting hyperpolarization or depolarization of 
the neuron or muscle cell and therefore blocking 
further function leading to paralysis and death 
(Wolstenholme and Rogers 2005). 


Insecticides have various neural effects 
in 
honeybees 
that 
were 
in 
details 
reviewed 
by 
Belzunces et al. (2012). They impair cognitive 
functions, including learning and memory, ha-
bituation,olfactionandgustation,navigationand 
orientation. They affect also behavior, including 
foraging and physiological functions, including 
thermoregulation and muscle activity. 


Acaricides 

Commonly used in hive varroacides are amitraz,
coumaphosandtau-fluvalinate(Johnsonetal. 
2010). Amitraz is a formamidine pesticide. The 
mode 
of 
action 
of 
formamidine 
pesticides 
such 

in insects is believed to be the toxic effects on a 

Gprotein-coupledreceptorforaneuromodulator 
octopamine, working as octopaminergic agonists 
(Evans 
and 
Gee 
1980, 
Dudai 
et 
al. 
1987). 
High 
levels 
of 
octopamine 
in 
the 
honey 
bee 
brain 
are 
associatedwithincreasedforagingbehavior(Schulz 
and Robinson 2001). Forager honey bees treated 
withoctopamineincreasedthereportedresource 
valuewhencommunicatingviathedancelanguage 
(Barronetal.2007).However,theeffectsofamitraz 
on foraging activity of honeybees were not investigated, 
but the acute toxicity of this compound was 
showninlarvaewhereitincreasesapoptoticcell 
death in the midgut (Gregorc and Bowen 2000). Another 
popular in hive varroacide is tau-fluvalinate 
which 
was 
initially 
very 
effective 
at 
controlling 
Varroa 
mites 
by 
blocking 
voltage-gated 
sodium 
channels 
(Davies 
et 
al. 
2007). 
Tau-fluvalinate 
was 
quite 
promising 
since 
it 
is 
tolerated 
by 
bees 
inhighconcentrationsduetorapiddetoxification 
bycytochromeP450monooxygenases,butmany 
Varroa populations are now resistant (Lodesaniet 
et al. 1995, Johnson et al. 2009). However, tau-
fluvalinateisnotcompletelyharmless,highdoses 
couldaffectqueenstogrowsmalleranddronesto 
dieuntil reaching sexual maturity (Rindereret et 
al. 
1999, 
Haarmann 
et 
al. 
2002).As 
the 
efficacy 
of tau-fluvalinate against Varroa was beginning 
to decrease, coumaphos, an organophosphate 
pesticide, 
was 
starting 
to 
be 
used 
(Elzen 
and 
Westervelt 2002). Although honey bees can tolerate 
similar to tau-fluvalinate therapeutic doses of 
coumaphos, 
probably 
as 
a 
result 
of 
detoxicative 
P450 
activity 
(Johnsonet 
et 
al. 
2009), 
negative 
effects from coumaphos exposure were observed. 
Queens exposed to coumaphos were smaller, sufferedhighermortalityandweremorelikelytobe 
rejected 
when 
brought 
into 
a 
colony 
(Haarmann 
etal.2002,Collinsetal.2004,Pettisetal.2004). 
Dronespermviabilitywaslowerinstoredsperm 
collected 
from 
drones treated with 
coumaphos 
(Burleyetal.2008).Coumaphosalsoaffectsfood 
transferbetweenworkersofhoneybee(Bevketal. 
2011).Fenpyroximateisapyrazoleacaricidethat 
presumably kills mites through the inhibition of 
electrontransportinthemitochondriaatcomplex 
I, thereby interfering with energy metabolism (Mo-
toba et al.1992). It wasfound that chronic exposure 
tofenpyroximate causesthe increasedgeneration 
of 
reactive 
oxygenspecies 
(Sherer 
et 
al. 
2007). 


Acta Biologica Slovenica, 56 (1), 2013 


Two monoterpenoid components of plant-
derived 
essential 
oils, 
thymoland 
menthol, 
are 
used 
for 
control 
of 
Varroa 
and 
tracheal 
mites. 
Theywerefoundtobeamongthemosttoxicofall 
terpenoidstestedwhenappliedtohoneybeesasa 
fumigant(EllisandBaxendale1997).Thethymol 
molecular targets include binding to octopamine 
receptors (Enan 2001) and AChE (Priestley et al. 
2003), but also insect tyramine and GABAreceptors(
Blenauetal.2011).Receptoractivationleads 
to changes in the concentration of intracellular 
second messengers such as cAMPor InsP3/Ca2+. 
Thymol could affect honeybees inducing brood 
removal (Marchetti and Barbattini 1984, Floris 
et al. 2004) and the increase of queen mortality 
(Whittington 
et 
al. 
2000). 
Exposure 
to 
thymol 
was shown to decrease phototactic behavior in 
the honeybee (Bergougnoux et al. 2013). 

Among 
organic 
acids, 
formic 
acid 
and 
oxalicacidareusedasvarroacides.Formicacidis 
inhibiting electrontransport in the mitochondria 
bindingofcytochromecoxidaseinmitesandmay 
produce a neuroexcitatory effect on arthropod 
neurons (Keyhani and Keyhani 1980, Song and 
Scharf 
2008). 
Formic 
acid 
can 
reduce 
worker 
longevity 
(Underwood 
and 
Currie 
2003) 
and 
harmingbroodsurvival(Fries1991).Themodeof 
action of oxalic acid against Varroa is unknown, 
but in mammals it interferes with mitochondrial 
electron transport leading to increased production 
of reactive oxygen species and to kidney toxicity 
(Caoetal.2004,Meimaridouetal.2005).Repeated 
treatment of colonies with oxalic acid can result 
in higher queen mortality and a reduction in the 
amount of sealed brood (Higes et al. 1999). The 
midguts of honey bees fed oxalic acid in sugar 
water exhibited an elevated level of cell death 
(Gregorc and Smodisskerl 2007).Recent studies 
arefocusingonmolecularmechanismsunderlying 
thesub-lethaleffectsofin-hiveacaricidesonhoney 
bees. Using a gene expression profiling Boncristiani 
et al. (2012) found that thymol,coumaphos 
and formic acid are able to alter detoxification 
gene 
expression 
pathways, 
components 
of 
the 
immune system responsible for cellular response 
anddevelopmentalgenes.Thisstudyindicatesthat 
these acaricides could significantly influence the 
health of individual honey bees and entire colonies 
(Boncristiani et al. 2012). 


Mechanisms 
and 
factors 
influencing 
the 
synergy 
of 
xenobiotics 
applied 
to honeybees 


Understanding the toxicity and synergy of 
chemicals in organisms requires considering the 
molecular mechanisms involved as well as the 
relationshipsbetweenexposureconcentrationand 
toxic effects with time (Tennekes and Sánchez-
Bayo 2013).In addition, the relevance of synergy 
of xenobiotics is a subject to understanding the 
routesofapplication,thewayoftransportationto 
targetmolecules in thetissueand themetabolism 
of pesticides in the target organism, all having a 
profound influence on the concentration and chemical 
structure of active substances at target sites. 
The analysis of the studies when monitoring the 
residuesinhoneybeesfollowingin-hivetreatments 
or pesticide applications revealed that the highest 
exposure routes were sprayed and systemic seed 
and soil compound treatmentsto which preferentially 
foraging bees are exposed during collecting 
contaminated nectar and the direct exposure to 
acaricidesusedinbeehives(Thomson2012).This 
is probably due to the availability of relatively 
high concentration of agricultural pesticides and 
in-hive 
compounds, 
but 
also 
the 
time 
between 
pesticide application to crops and bee exposure 
is very important as many pesticides degrade or 
dilute 
in 
the 
environment. 
The 
importance 
of 
other routes of exposure such as dusts produced 
during sowing of treated seeds, water from puddles 
or guttation droplets and beeswax might be 
relevantbutdataaboutthesearelimited.Thefinal 
actions of xenobiotics are greatly dependent on 
the 
mode 
of 
exposure, 
acute, 
sub-chronic 
and 
chronic, defining the nature and the intensity of 
their effects. Metabolism of xenobiotics elicited 
by 
intrinsic 
enzymes 
is 
remarkably 
important 
as it could result in the elevation or decrease of 
theirtoxicityoritcouldproducedifferenteffects. 
Chemicalinteractionsbetweenxenobioticsinthe 
mixture are also possible, causing the changes in 
chemicalstructuresofparticularsubstance.There 
are also other factors such as physiological states 
of the organisms including age, the season and 
the capacity of immune system that have impact 
on synergism (Thomson 2012). For example, the 
immunesystemofhoneybeescouldbeprofoundly 
affected by various pathogens, bacterial, fungal 


Glavan et al.: The synergy of xenobiotics in honey bee Apis mellifera: mechanisms and effects 


and viral pathogens as well as ecto- and endo-
parasites that in many cases elevate the toxicity 
of xenobiotics. Most of the studies in honeybees 
have focused on the synergisms at the level of 
midgut enzymes when certain xenobiotic inhibit 
the detoxifying ability of these enzymes and potentiate 
the toxicity of another substance, but the 
synergism at target site is poorly investigated. 

The synergism at the level of midgut detoxifying 

enzymes 

Probablythemostfrequentwayofthetransfer 
of xenobiotics into honeybee tissue is the consummation 
of 
contaminated 
nectar 
and 
absorption 
in the midgut thought the midgut wall into the 
hemolymph,butalsopassagethoughtcuticleand 
sometimes inhalation of vaporous compounds is 
possible. In the midgut of the honeybee xenobiotics 
are metabolized by enzymes glutathione-Stransferases 
(GSTs), cytochrome P450 monooxygenases 
(P450s) 
and 
carboxyl/cholinesterases 
(CCEs)(ScottandWen2001,Enayatietal.2005, 
Wheelocketal.2005).Theseenzymesmetabolize 
pesticidesbydifferentmechanisms,butP450sare 
probably 
the 
most 
important 
for 
honeybees 
as 
they play a significant role in the detoxification 
of phytochemicals 
present in the nectar, honey 
and pollen that bees consume (Mao et al. 2009). 
They catalyze a range of reactions including oxidation 
and demethylation which decrease pesticide 
activity or produce active metabolites (Scott and 
Wen 2001).For example, they convert the thion 
to 
oxon 
forms 
of 
organophosphorus 
pesticides 
or change neonicotinoid thiamethoxam to clothianidin. 
P450s can also oxidaze aromatic rings 
of tau-fluvalinate and flumethrin used in varroa 
control (Ortiz de Motellano and De Voss 2005). 
GSTs in insects can metabolize insecticides by 
facilitating their reductive dehydrochlorination or 
byconjugationreactionswithreducedglutathione, 
toproducewater-solublemetabolitesthataremore 
readily excreted. In addition, they contribute to 
the removal of toxic oxygen free radical species 
produced through the action of pesticides (Enayati 
et al. 2005).Carboxylesterases (CaEs) are hydrolazes 
and catalyze the hydrolysis of carboxyl 
estersofthreedifferentclassesofagrochemicals, 
pyrethroids, 
organophosphates 
and 
carbamates 
via the addition of water (Wheelocket al. 2005). 

The selective toxicity of xenobiotics is affected by 

the ratio and the levels of metabolizing enzymes 
which 
fluctuate 
in 
different 
insect 
species 
and 
alsoinindividualorganism.Thelevelofenzymes 
could be affected also by the season, the study on 
winterhoneybeesdemonstratedreducedlevelsof 
P450-mediateddetoxificationsincethesynergism 
between pyrethroid deltamethrin and the P450inhibitingfungicideprochlorazwasmuchreduced 
during winter periods (Meled et al. 1998). 


By far the majority of the studies of pesticide 
synergism 
in 
honeybees 
have 
focused 
to 
P450 
enzymes that are inhibited by specific pesticides 
mostly by monitoring the toxicity calculation of 
the LD50 or LC50 (Table 1.).The developers of 
insecticide synergists have often exploited inhibition 
of P450s activity to prolong the efficacy of 
pesticideswhichareotherwiserapidlydetoxified. 
ItwasshownthatP450-inhibitorselevatedtoxicity 
of pyrethroids (cyfluthrin, permethrinand tau-fluvalinate),
neonikotinoidinsecticides(imidacloprid, 
acetadimiprid, 
thiacloprid), 
and 
carbamate 
insecticide 
carbaryl 
(Georghiou 
and 
Atkins 
Jr. 
1964, Yu et al. 1984, Hagler et al. 1989, Iwasa et 
al. 2004, Johnson et al. 2006). It was also found 
that the classic P450 inhibitors PBO synergize 
with varroacides tau-fluvalinate and coumaphos 
at high levels but other inhibitors have minor effect 
(Johnson et al., 2009, Johnson et al., 2013). 
Many examples of synergy have been reported 
between EBI (ergosterol biosynthesis inhibitor) 
fungicides 
such 
as 
prochloraz, 
propiconazole, 
epoxiconazole, 
carbendazimand 
insecticides 
due to the fungicide inhibitory action on P450s. 
This was the case with neonicotinoids (acetamiprid, 
thiacloprid, 
imidacloprid) 
and 
pyrethroid 
insecticides 
(deltamethrin, 
lambda-cyhalothrin, 
alphacypermethrin) (Pilling 1992, Meled et al. 
1998, Vandame and Belzunces 1998a, Vandame 
and Belzunces 1998b, Papaefthimiou and Theo-
philidis 
2001, 
Thompson 
and 
Wilkins 
2003, 
Schmucketal.2003,Iwasaetal.2004,Thompson 
2013).TheeffectsofEBIfungicidesonthecontact 
toxicity of the active ingredients of the pyrethroid 
varroacides 
flumethrin 
and 
tau-fluvalinate 
are 
synergized by the fungicides with relatively high 
increases 
in 
toxicities 
(Thompson 
and 
Wilkins 
2003). Another EBI fungicide prochloraz which 
is also a P450s inhibitor elevated the toxicity of 
the 
acaricides 
coumaphos 
and 
fenpyroximate 


Acta Biologica Slovenica, 56 (1), 2013 


(Johnson et al. 2013). The studies on synergism 
between insecticidesin honeybees were rarely conducted, 
mostof thembetween in-hiveacaricides. 
Johnson et al. (2009) observed a large increase 
in the toxicity of tau-fluvalinate to bees that had 
been treated previously with coumaphos, and a 
moderate increase 
in the toxicity of coumpahos 
in 
bees 
treated 
previously 
with 
tau-fluvalinate. 
These compounds were chosen due to their low 
toxicity to honey bees which were attributed to 
rapid detoxification mediated by P450s. The synergisms 
occurred also between in-hive miticides 
coumaphos, thymol, amitraz, fenpyroximate and 
oxalic acid (Johnson et al. 2013). The observed 
synergism was explained as a result of competition 
between miticides for access to detoxicative 
P450s (Johnson et al. 2009).See the Table 1. for 
the 
list 
of 
synergisms 
of 
xenobiotics 
observed 
in honeybee. 


Thesynergismswerefoundalsoforcarbamate 
insecticides (carbaryl, carbofuran) and herbicide 
atrazine 
but 
the 
mechanism 
of 
this 
synergy 
is 
unknown (Sonnet et al. 1978). The synergy be-
tweenmonoterpenoidthymolandtau-fluvalinate 
orcoumaphoswasobservedandwasexplainedto 
betheconsequenceoftheP450sinhibitoryactivity 
of 
thymol, 
but 
thymol 
inhibitory 
property 
was 
shown only in human liver microsomes but not 
for honeybee midgut (Johnson et al. 2013). 


In 
other 
organisms, 
the 
synergisms 
were 
studied between insecticides and insecticide/ 
herbicideatthelevelofdetoxifyingenzymes.The 
interactionssuchasacompetitionwithmetabolic 
enzymes 
esterases 
are possible that are maybe 
not very significant for honeybees since it was 
shown that the role of these enzymes participating 
in the detoxification of xenobiotics is minor. 
It was also shown that certain organophosphate 
insecticides could bind to the active site associated 
with esterase enzymes responsible for detoxification 
of 
pyrethroid-based 
insecticides 
and 
so 
organophosphate insecticides may beconsidered 
usefulsynergistsforpyrethroids(Cloyd2011).The 
synergisms at the level of detoxifying enzymes 
was 
described 
also 
for 
organophosphates 
and 
pyretroids, P450 activated by organophosphates 
decrease the organism’s ability to detoxify pyretroids 
due to esterases inhibition, so greater than 
additive toxicity is often observed (Hernández et 
al. 2013). Recent studies have demonstrated the 

potentiatingeffectsoftriazineherbicides,suchas 
atrazinetothetoxicityoforganophosphateswhen 
these herbicides stimulate P450 activity by increas


ing the rate of bioactivation of organophosphates 
resulting in the potentiation of the cholinesterase 

inhibiting property of organophosphates (Hernández 
et al. 2013). 


It seems that the regulation of the P450s in 
honeybeesisunique.Contrarytootherinsects,in 
the honey bee these enzymes are rarely induced 
by a substrate itself. The honeybee genome has 
substantially fewer protein coding genesfor xenobioticdetoxifying 
enzymes than Drosophila melanogaster 
and Anopheles gambiae (Claudianosetal. 
2006)andmanyresearchersfailedtodemonstrate 
anincreaseofmidgutdetoxifyingenzymesinduced 
byxenobiotics(Yuetal.1984).Evenexposureto 
phenobarbitalwhichisaninducerofP450sshowed 
no alterations in the expression of many of P450 
genestestedinhoneybees(Maoetal.2011).Only 
twostudiesindicatedtheincreaseinP450activity 
in honeybees. Application of tau-fluvalinate and 
coumaphos 
elevated 
specific 
detoxifying 
P450 
enzymes CYP9Q1, CYP9Q2, and CYP9Q3 and 
benzo(a)pyrenemonooxidaseactivityinhoneybee 
guts was induced by exposure to benzo(a)pyrene 
itselfandbythein-hiveacaricidestau-fluvalinate 
and cymiazole hydrochloride (Kezic et al. 1992, 
Mao et al. 2011). As it has been at first suggested 
that reduced diversity of detoxification enzymes 
may contribute to the sensitivity of honey bees 
to certain pesticides (Claudianos et al. 2006) the 
importanceofmidgutdetoxifyingenzymesP450 
in honeybees was highlighted by the studies with 
specificP450-inhibitors.Twostudiesindicatethat 
GSTsandCaEsareactivedetoxifyingenzymesin 
honeybeesbuttheyplayarelativelyminorrolein 
detoxification as compared to P450s (Johnson et 
al. 2009, Iwasa et al. 2004). The CaEs inhibitor 
DEF(S,S,S-tributylphosphorotrithioate)andGSTs 
inhibitor DEM (diethyl maleate) were shown to 
increase the toxicity of certain pyrethroids and 
neonicotinoids but this effect was significantly 
smallerthatfortheP450inhibitorPBO(piperonyl 
butoxide) (Iwasa et al. 2004). Recently the interesting 
study performed by Johnson et al. (2012) 
suggested 
that 
regulation 
of 
honey 
bee 
P450s 
is affected by chemicals occurring naturally in 
the hive environment in the nectar, pollen and 
propolis since only quercetin, a common pollen 


Glavan et al.: The synergy of xenobiotics in honey bee Apis mellifera: mechanisms and effects 


Table 1: 
The list of synergisms of xenobiotics in honeybee Apis mellifera and proposed mechanisms. 
Tabela 1:Seznam sinergizmov med ksenobiotiki v medonosni cebeli Apis mellifera in predlagani mehanizmi. 


Xenobiotic 
Xenobiotic 
(P450 
inhibitor) 
Reference 
Mechanism 
of 
synergy: 
inhibition 
of 
P450 
detoxifying 
enzymes 
pyrethroid insecticides classical P450-inhibitor 
cyfluthrin 
piperonyl butoxide (Johnson et al. 2006) 
permethrin 
piperonyl butoxide (Hagler et al. 1989) 
lambda-cyhalothrin 
piperonyl butoxide (Johnson et al. 2006) 
tau-fluvalinate 
piperonyl butoxide 
neonicotinoid insecticides classical P450-inhibitor 
(Johnson et al. 2006; Johnson et al. 
2013) 
imidacloprid 
piperonyl butoxide (Iwasa et al., 2004, Johnson et al. 
2012) 
acetadimiprid 
piperonyl butoxide (Iwasa et al. 2004) 
thiacloprid 
carbamate insecticide 
piperonyl butoxide 
classical P450-inhibitor 
(Iwasa et al. 2004) 
carbaryl piperonyl butoxide (Georghiou and Atkins Jr. 
1964) 
hive varroacides classical P450-inhibitor 
tau-fluvalinate 
piperonyl butoxide (Johnson et al. 2009, Johnson et al. 
2013) 
coumaphos 
piperonyl butoxide (Johnson et al. 2009, Johnson et al. 
2013) 
fenpyroximate 
piperonyl butoxide (Johnson et al., 2013) 


neonicotinoid insecticides EBI (ergosterol biosynthesis inhibitor) 
fungicides 
acetamiprid 
epoxiconazole, propiconazole, 
triadimefon, triflumizole, uniconazole-P 
(Iwasa et al. 2004) 
thiacloprid prochloraz, propiconazole, 
tebuconazole, triflumizole 
(Schmuck et al. 2003, Iwasa et al. 
2004) 
imidacloprid 
propiconazole, triflumizole 
(Iwasa et al. 2004) 
pyrethroid insecticides EBI (ergosterol biosynthesis inhibitor) 
fungicides 
deltamethrin 
difenoconazole+carbendazim, 
prochloraz, prochloraz+ 
difenoconazole 850 
(Belzunces and Colin 1993, Colin 
and Belzunces 1992, Papaefthimiou 
and Theophilidis 2001, Vandame and 
Belzunces1998b, Vandame and 
Belzunces 1998a) 
lambda-cyhalothrin 
difenconazole, flusilazole, prochloraz, 
propiconazole, tebuconazole, 
thiophanate-methyl 
(Thompson and Wilkins 2003) 
alphacypermethrin 
difenconazole, flusilazole, prochloraz, 
propiconazole, tebuconazole 
(Thompson and Wilkins 2003) 


hive varroacides EBI (ergosterol biosynthesis inhibitor) 
fungicides 
coumaphos 
prochloraz (Johnson et al. 2013) 
flumethrin 
carbendazim, difenconazole, (Thompson and Wilkins 2003) 
flusilazole, prochloraz, propiconazole, 
tebuconazole, thiophanate-methyl 



20 
Acta Biologica Slovenica, 56 (1), 2013 
Xenobiotic 
tau-fluvalinate 
fenpyroximate 
Xenobiotic 
(P450 
inhibitor) 
carbendazim, difenconazole, 
flusilazole, prochloraz, propiconazole, 
tebuconazole, thiophanate-methyl, 
myclobutanil, metconazole, 
fenbuconazole, 
prochloraz 
Reference 
(Thompson and Wilkins 2003, Johnson 
et al. 2013 ) 
(Johnson et al. 2013) 


hive varroacides hive varroacides 
coumaphos 
tau-fluvalinate 
(Johnson et al. 2009, 2013) 
thymol 
tau-fluvalinate, coumaphos 
(Johnson et al. 2013) 
amitraz 
tau-fluvalinate, coumaphos, (Johnson et al. 2013) 
fenpyroximate 
fenpyroximate 
tau-fluvalinate, coumaphos 
(Johnson et al. 2013) 
Mechanism 
of 
synergy: 
increased 
oxidative 
stress 


hive varroacides Fungicides (mitochondrial inhibitors) 
tau-fluvalinate 
pyraclostrobin, boscalid 
(Johnson et al. 2013) 
fenpyroximate 
pyraclostrobin (Johnson et al. 2013) 


Unknown mechanism of synergy 
oxalic acid tau-fluvalinate, fenpyroximate, 
(Johnson et al. 2013) 
amitraz, thymol 
herbicide atrazine carbamate insecticides (carbaryl, (Sonnet et al. 1978) 
carbofuran) 
thio and coumaphos varroacide 
(Lienau 1990) 
dithiophosphoric ester 
pesticides – ethyl 
parathion, dimethoate, 
dialifos 
thiacloprid fungicides cyprodinil, tolyfluanid 
(Schmuck et al. 2003) 
(neonicotionoid) 
alphacypermethrin, 
fungicide chlorothalonil (Thompson and Wilkins 
lambda-cyhalothrin 
fungicide chlorothalonil 2003) 


and 
honey 
constituent, 
reduced 
tau-fluvalinate 
toxicity. Bees fed with extracts of honey, pollen 
andpropolisshowedelevatedexpressionofthree 
CYP6AS P450 genes. Non-naturally occurring 
inducers of cytochrome P450 enzymes did not 

alter the toxicity of certain xenobiotics and it 

seems that a wide range of synthetic pesticides 
do not induce in bees. It is now clearthat certain 
substancesfoundinbeeproductssuchasquercetin, 
p-coumaric acid, pinocembrin, and pinobanksin 
5-methyl ether naturally elevate the levels of bee 
detoxifying enzymes P450 and probably helping 

bees to resist the toxicity of certain xenobiotics 

(Johnson et al. 2012, Mao et al. 2013). 


The synergism of xenobiotics working at the 

same targets 

Although 
the 
basic 
molecular 
mechanisms 
of most xenobiotics are more or less known, the 
possible mechanisms of their synergy at primary 
target sites in honeybees are unexplored. One of 
plausible mechanism of this synergy is that effects 
at the site of toxic action include increased 
responseofthesite(suchasareceptor)following 
initial pesticide exposure and according to this 
direct synergistic effect could be predicted for sub-
stancesthathavesimilartargets(Thomson1996). 
In this respect only one study in honeybees was 
performed,onsemi-isolatedheart(Papaefthimiou 
and Theophilidis 2001).In this study the synergistic 
effect was observed between EBI fungicide 


Glavan et al.: The synergy of xenobiotics in honey bee Apis mellifera: mechanisms and effects 


prochlorazandpyrethroidinsecticidedeltamethrin 
which rapidly decreased the frequency and the 
force 
of 
the 
cardiac 
contractions 
with 
marked 
effects at 0.01 µM, equivalent to internal doses 
of 4–5 
µg kg-1 
body weight. Prochloraz showed 
to be more cardiotoxic than deltamethrin, what 
seemed surprising since deltamethrin is a neurotoxicsubstancewhereasprochlorazisaninhibitor 
andaninducerofdetoxifyingenzymesP450.So, 
authors concluded that there must be the neural 
basis 
of 
the 
deltamethrin 
prochloraz 
synergy. 
Belzunces et al. (2012) suggested that the basis 
of their synergy is the interaction of these two 
pesticides with shared molecular targets, such as 
ATPases, potassium and calcium channels. 

The existence of the synergy of insecticides 
at primary target sites was demonstrated also in 
the cockroach P. americana,inthecercal-afferent 
giant-interneuron synapses of the terminal abdominal 
ganglion (Corbel et al. 2006). Authors 
demonstrated 
that 
pyrethroid 
permethrin 
and 
carbamatepropoxurinsecticidesappliedtogether 
increaseddrasticallytheAChconcentrationwithin 
the 
synaptic 
cleft, 
which 
thereby 
stimulated 
a 
negative feedback 
of ACh release mediated by 
presynaptic muscarinic receptors causing the synergism.
Johnsonetal.(2013)demonstrated5-fold 
increaseinthetoxicityoftau-fluvalinatebyamitraz 
pretreatment in honeybees. Interactions between 
formamidinesandpyrethroidsareknowninother 
insects and may be due to synergism at the target 
site through cooperative binding (Liu and Plapp 
1992).It was shown that formamidine pesticides 
working as octopaminergic agonists change the 
binding properties of pyrethroid insecticides to 
nervemembranesodiumchannels.Thismechanism 
could be also the cause for the synergism of tau-
fluvalinate and amitraz in honeybees. Thomson 
(1996) reported another possible mechanism of 
pesticide interaction, when esterases can act as 
irreversible binding sites for organophosphate 
and carbamate insecticides, reducing the levels 
available to bind to AChE within the brain. Thus, 
prior exposure to an organophosphate may result 
in a reduction in the number of available binding 
sites and an increase in the blood levels of free 
pesticide.Allthesemechanismsmentionedabove 
are possible for honeybees, but they are not explored. 
The lack of similar studies suggests that 
the mechanisms of synergisms of xenobiotics at 

primary target sites in honeybees are very much 
ignored and underestimated and a need for additional 
studies is unavoidable. 

Conclusions 

Bees are very often exposed to mixtures of 
products applied to plants on which they forage 
suchasfungicides,herbicidesandinsecticidesand 
inadditionveryhighlevelsofvarroacidesmaybe 
present within colonies. The very potential risk 
from most mixtures of these substances is the developmentofsynergismsthatcanprofoundlyaffect 
honeybeecoloniesandmaysignificantlycontribute 
to honeybee colony loss observed in the last 15 
years. This risk is underestimated and relatively 
few relevant studies were performed concerning 
the effects and mechanisms of synergy of different 
xenobiotic combinations. The understanding 
the mechanisms of synergy betweenxenobiotics 
is very important for the restriction of the use of 
defined mixtures and also for the prediction of 
potential toxicity of newly developed substances 
in agriculture and apiculture. Many observable effects 
are induced by xenobiotics such as alternation 
of cognitive functions, behavior or integrity of 
physiological functions, many of them unambiguouslyexplainedbythemechanismsofxenobiotic 
actions at primary target sites. In spite of these 
physiologicalmechanismsofactionofindividual 
xenobioticsaremoreorlessidentified,especially 
forinsecticides,themajorityofsynergisticeffects 
observed in honeybees is ascribed to the inhibition 
of detoxifyingmidgutenzymes P450 involvedin 
xenobioticmetabolism.Evenmore,asmostofthe 
studies focused on synergistic effect of mixure xenobiotic/
P450inhibitor,onlyfewwereperformed 
oninsecticide/insecticideinteractions.Johnsonet 
al. (2013) proposed that the synergistic interactions 
occur when the compounds work through 
different modes of action, but few experiments 
in insects studying the synergism of insecticides 
at target sites suggest that the synergism is also 
possibleforsubstancesworkingthroughthesame 
mode of action, at least when they are working 
on the same system such as cholinergic synapse. 
Therefore,theaspectofmechanismsofsynergism 
at 
the 
similar 
targets 
is 
underestimated 
since 
only one study was performed in honeybee and 


Acta Biologica Slovenica, 56 (1), 2013 


therefore this issue demands extra investigation. 
The improved knowledge of the mechanisms of 
pesticide 
and 
bee-hive 
compound 
interactions 
would prevent the negative impact on beneficial 
organisms like honeybees. 


Povzetek 


Medonosne 
cebele 
so 
med 
iskanjem 
hrane 
pogosto izpostavljene razlicnim ksenobiotikom, 
vecinoma 
so 
to 
fitofarmacevtska 
sredstva 
in 
panjske 
kemikalije. 
Cebele 
v 
zadnjih 
15 
letih 
množicno umirajo, vzrok za to naj bi bila tudi 
uporabaksenobiotikov.Številnafitofarmacevtska 
sredstva se uporablja hkrati in znano je, da lahko 
pride do sinergisticnih interakcij v organizmih. 
Tveganjezanastaneksinergizmovjepodcenjeno 
in narejenih je relativno malo študij na cebelah 

o ucinkih in mehanizmih sinergizmov razlicnih 
kombinacij ksenobiotikov. Razumevanje mehanizmovsinergizmovksenobiotikovjezelopomembno 
za 
nadzor 
nad 
uporabo 
definiranih 
mešanic 
in 
napovedovanje potencialne toksicnosti novih ksenobiotikovvkmetijstvuincebelarstvu.
Pregledni 
clanek se osredotoca na ucinke, mehanizme in 
molekulske 
tarce 
ksenobiotikov 
v 
medonosnih 
cebelahinosvetljujeprimeremehanizmovnastanka 
sinergizmov. Opisani so tudi drugi dejavniki,ki 
vplivajonanjihovnastanek,okoljskiinfiziološki, 
poudarek je na detoksifikacijskih encimih me-
donosne 
cebele. 
Najbolj 
nevarni 
za 
cebele 
so 
insekticidi,kidelujejopredvsemnanekajrazlicnih 
živcnihmolekularnihtarcintakomotijodelovanje 
References 

živcnega sistema, kar vpliva na vedenje, kognitivne 
funkcije in fiziologijo cebel. Glavne živcne 
tarceinsekticidovsonapetostnoodvisninatrijevi 
kanalcki, 
encim 
acetilholinesteraza, 
glutamatni 
receptorji, 
receptorji 
za 
gama-aminomasleno 
kislino 
in 
nikotinski 
receptorji. 
Znane 
skupine 
insekticidov 
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piretroidi, 
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nekaterifungicidi.Študijnacebelah,skaterimibi 
raziskovalisinergizemmedinsekticidi,skorajni. 
Ceprav so sinergizmi ksenobiotikov, še posebej 
insekticidov,naprimarnihciljnihtarcahpricebelah 
možni,sajsobiliprikazanipridrugihorganizmih, 
je ta vidik podcenjen. Narejena je bila samo ena 
raziskava 
mehanizmov 
na 
tarcnem 
mestu 
pri 
medonosni cebeli, 
pa še to med insekticidom in 
fungicidom. 


Acknowledgements 


The 
work 
was 
financially 
supported 
by 
the 
Slovenian 
Research 
Agency 
(Grant 
No. 
V1-1129). 


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