Tunez. Tratamientos químicos contra Varroa Jacobsoni. Eficiencia y efectos secundarios

martes 26 de febrero de 2013
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Tunez. Chemotherapy against Varroa jacobsoni: 

Efficiency and side effects 

T. BEN 

INSTITUT DE LA RECHERCHE VETERINAIRE 

DE TUNISIE (IRVT) 

20 RUE JEBEL LAKHDHAR, LA RABTA 

1006 TUNIS 

TUNISIA 

Resumen

Los tratamientos químicos han permitido un control muy eficaz de varroosis previniendo grandes pérdidas de colonias y permitiendo la restauración de las explotaciones apícolas altamente dañados a su estado anterior. Muchos acaricidas  de varios grupos químicos diferentes han sido probados en varios países por su eficacia contra Varroa jacobsoni. Una gama de sustancias han demostrado su eficacia y han sido aprobados para el control en los países infestados con los procedimientos apropiados para la aplicación. Una reducción en la eficacia de un producto ampliamente utilizado, piretroide sintético, se informó por primera vez en Italia se ha demostrado que es una consecuencia de la propagación de cepas de varroa resistentes a los fármacos. Esto pone de relieve el riesgo de basar las estrategias de control de un solo producto y por lo general, en el tratamiento de un solo químico. Además del efecto de control requerido, algunos de los fármacos tienen también efectos negativos. Los efectos secundarios más importantes, incluyen los efectos no deseados en las abejas adultas y la cría y especialmente la contaminación de los productos de la colmena. Entre los productos de la colmena, la cera de abejas, como una sitio de almacenamiento eficaz de residuos, tiene el papel central en el proceso de acumulación residual.

SUMMARY - Chemical treatments have enabled a highly effective control of varroosis preventing great losses of colonies and allowing restoration of highly damaged apiaries to their former condition. Many acaricides of various chemical groups have been tested in several countries for their efficacy against Varroa jacobsoni. A range of substances have proved successful and have been approved for control in the infested countries with the appropriate modes of application. A reduction in the effectiveness of a widely used synthetic pyrethroid product, reported for the first time in Italy has been shown to be a 

consequence of the spread of Varroa drug resistant strains. This highlights the risk of basing control strategies on a single product and more generally on chemical treatment alone. Besides the required control effect, some of the drugs have also negative effects. The most important secondary effects include undesired effects on adult bees and brood and especially contamination of the beehive products. Among the hive products, the beeswax, as an effective residue store, has the central role in the residue accumulation process. 

words: Chemotherapy, Varroa jacobsoni, acaricides, resistance, side effects, residues. 

RESUME - "La chimiothérapie contre Varroa jacobsoni: efficacité et effets secondaires", La 

chimiothérapie appliquée dans la lutte contre la varroose a permis d'éviter d'énormes pertes en colonies 

et de restaurer l'état sanitaire des ruchers endommagés. Plusieurs molécules acaricides de différents 

groupes chimiques ont été testées pour leur efficacité sur Varroa jacobsoni. Certaines de ces 

substances dont l'efficacité varroacide a été prouvée ont été enregistrées dans les pays infestés pour 

une mise en oeuvre dans le contrôle de l'acarien varroa selon les modes d'application les plus adaptés. 

L'apparition et la propagation de souches de varroa résistantes auxpyréthrinoïdes de synthèse, montre 

le risque qu'il y a à baser une stratégie de contrôle sur í'emploi continu d'une seule et même substance 

et plus généralement sur une lutte chimique exclusive. A côté des propriétés acaricides requises, 

certains produits peuvent avoir des effets secondaires néfastes les plus importants étant une toxicité 

pour l'abeille et l'accumulation de résidus dans les produits de la ruche. Parmi ces produits, le rôle de 

la cire, en tant que réserve de résidus est à considérer en premier. 

Mots-clés : Lutte chimique, Varroa jacobsoni, acaricides, résistance, effets secondaires, résidus. 

Efficiency of the chemical control of Varroa jacobsoni infestation 

Following the invasion of western Europe by the disastrous mite pest Varroa 

jacobsoni, there has been an urgent need to develop and put into practice control 

measures. This caused a boost to research on varroosis control resulting in a 

tremendous amount of work and great efforts have been done in this field to find 

effective control methods. Now, since the apicultura1 practice showed that non 

chemical control methods in general are very labour intensive and often achieve a low 

efficacy, an organized fight against varroosis is almost possible with the help of 

77 

CIHEAM - Options Mediterraneenneschemotherapeutic measures (Ritter, 1981). The same situation will probably continue 

as chemical treatment will presumably keep on being more effective and less time 

consuming than biotechnical methods which must be at present combined with 

chemotherapy, including the use of natural substances. 

Chemical treatments have enabled a highly effective control of varroosis preventing 

great losses of colonies and allowing restoration of highly damaged apiaries to their 

former condition. However, none of the methods used can eradicate the mites or stop 

them from spreading (Cavalloro et al., 1988), because treatments with most acaricides 

are effective only when very little or no capped brood is present, a condition that 

occurs in colder regions during autumn and winter, but may never been satisfied in 

warmer regions. In addition, many products may be applied only over a given 

temperature, and this additional constraint is difficult to combine with the absence of 

brood (Milani and Barbattini, 1989). 

Many chemicals (acaricides) have been tested all over the world for their efficacy 

against Varroa jacobsoni. A useful synopsis of products and active ingredients (a.¡.) 

used for varroatosis control has been published by Wienands, (1988). Among these, 

a number of substances have proved successful. 

Beside an optimal efficiency against Varroa, products administered into hives should 

also achieve the following important characteristics; they have to be: (i) well tolerated 

by the bee; and (¡i) non toxic for man, consumer of the hive products and manipulator 

of varroacide agents. The efficiency of a given acaricide is varying depending on many 

factors such as bee colonies, climates, bee races, the time of treatment, modes of 

application, etc. The highest efficiency is reached when the active ingredient is evenly 

distributed into the hive so that each Varroa mite is exposed to a lethal dose. It is than 

possible to eliminate 90% or more of the mites born by adult bees, which result is 

remarkable in the apicultura1 practice (Colin and Gonzalez-Lopez, 1986). Most 

medications, whatever is the way of administration, do only hit mites parasitizing adult 

bees, while those reproducing inside the sealed brood are not reached. 

Modes of application of chemotherapeutic agents 

The early methods of chemotherapy of varroosis were mainly traditional pest control 

methods. Spraying, dusting, fumigation.and aerosol were typical modes of application 

used in the "first generation" of covitrol methods for Varroa jacobsoni. 

on 

Currently used in Greece and Rumania, this mode is applied to treat colonies in 

activity before and after the collecting period. Active ingredients (Malathion, 

naphthalene, thymol, chlorobenzylate, etc.) are mixed with a vehicle which can be 

glucose, marble dust, kaolin or cellulose. About 50 gr are necessary for one 

application. The main disadvantage of this method is the contamination of the hive 

products either by the a.i. and the excipient. 

78 

CIHEAM - Options MediterraneennesEvaporation 

Evaporating agents which are volatile compounds have been widely used for the 

control of the tracheal mite, Acarapis woodi. Treatment with these agents can be 

carried out without disturbing too much the bee colonies; it necessitates doses ranging 

between 0.5 to 50 gr of a.¡. and a period of application spreading from one to several 

weeks. It is difficult to control the daily evaporated quantity of the product since this 

quantity depends on the external temperature. In addition, beeswax absorbs, reversibly 

or not, a non-negligible amount of the volatile compounds leading to accumulation 

problems. The main substances used are menthol, thymol, formic acid, naphthalene, 

etc. 

spray 

Spray products were very common. Spray treatment however is very time 

consuming as combs have to be taken out and treated individually, constraining 

therefore the manipulator to spray during daytime only (Ritter, 1983). The main 

products which have been used by spray application were Kelthane and Tactik (a.¡. 

= amitraz). 

Fumigation 

Treatments using fumigation have replaced evaporation in the control of the 

tracheal mite Acarapis woodi. Active substances incorporated to the fumigant strip 

must have a good stability since the molecule has to sublimate into the hive near a 

source of heat (heat emitted by nitrate combustion in some cases). In order to reduce 

the important irritation caused to the bee colony when treated by fumigation, artificial 

means like enlargement of the beehive are used. Main substances used in such a way 

are, dicofol, phenothiazine, bromopropylate (Folbex V.A.@), etc. Bromopropylate was 

shown to have an adequately good effect against Varroa mites (Klepsh et a/., 1983) 

while in the same time it is well tolerated by the bees and the brood.Treatments 

applied by fumigation led to residue accumulation problems. 

The further development of chemical varroa control methods brought a change in 

the application method. Modern methods include: 

Systemic treatments 

The first systemic acaricide used for Varroa control was chlordimeform (Ruttner et 

al. 1980) which was abandoned because of residue problems. Later, Perizin@ (Ritter 

1985) was developed and commercialized as a precursor of the "second generation" 

of varroosis treatments. Fed to bees and biologically distributed by trophallaxis in the 

colony, the acaricide passes into the haemolymph of the bees and kills the mites 

feeding on them. The treatment of colonies is easy and fast: the medicinal syrup is 

sprinkled into the bee ways. A specific problem with systemic acaricides is that the 

bees which take up the administered syrup absorb a so high amounts of acaricides 

up to the level of toxicity that some initial bee mortality has. to be accepted (Koeniger 

and Chmielewzky, 1986). 

79 

CIHEAM - Options MediterraneennesHeated aerosol treatments 

Aerosol is constituted by a suspension of microdroplets in an air volume heated at 

35-4OQCC. These fine particles, evenly distributed through the hive, settle on all the 

surfaces including bees and mites (Colin and Faucon, 1983). 

The warmth of the aerosol breaks up the cluster of bees when the brood is absent 

allowing treatment when ambient temperature is low; in addition the efficacy of the 

acaricide is improved by the heat. The production of a heated aerosol necessitates 

special devices not always at beekeeper's disposal. 

Slow releasing methods 

Another way of distributing the active ingredient with the help of the bees 

themselves is by using the mechanism by which the bees distribute the queen 

substance throughout the colony continuously (de Ruijter and Van ,Den Eijnde, 1988). 

In this type of drug the active ingredient is released slowly from a plastic strip and is 

actively dispersed by the bees themselves by contact. This new approach to 

chemotherapy has brought considerable improvement in controlling varroatosis. The 

use of impregnated inserts with a prolonged effectiveness has evident advantages 

compared to the previously practised treatments; once applied these products are 

effective for a long period of time, mites being killed as they gradually leave brood 

cells and reinfestation is avoided as the product remains active. Inserts are 

prefabricated plastic strips which are ready to be hung directly between the frames in 

a honeybee colony. Among these products, polyvinylchloride strips containing 

fluvalinate (Borneck and Merle, 1987) quickly became one of the most widely used 

products over the world. Similar strips made with polyethylene and containing 

flumethrin, another Pyrethroid, (Koeniger and Chmielewsky, 1986; Koeniger and 

Fuchs, 1988) are commercialized in some European countries. Recently, amitraz, an 

a.¡. belonging to the formamidines group and known for his high efficiency against 

Varroa has been incorporated to plastic strips and commercialized in France under the 

name of Apivar@. 

Acaricides used for control 

The choice of acaricides and their mode of administration changes from one country 

to another; the making of rules dealing with beekeeping chemotherapeutic products 

is not the same everywhere depending on wether beekeeping is considered as an 

animal or a vegetal production. Post-therapeutic residue levels of many substances 

have not been fixed by specific norms. All these factors led to a great diversity in the 

treatments being practised in different areas. However, if efficiency and safety for 

human consumer are taken into account, the number of proposed treatments will 

decrease appreciably. 

Table 1 (modified after Ritter, 1988) shows the main products being used in Europe 

and some Mediterranean countries, their a.¡., form of application, way of 

administration, dosage, etc. 

80 

CIHEAM - Options Mediterraneennesb . 

.g 

81 

CIHEAM - Options MediterraneennesChemical control, resistance of V. jacobsoni to acaricides 

Selection of resistant mites to pesticides is a well known phenomenon. The first 

cases of resistance to organophosphates have been reported since 1947. According 

to Delorme and Dacol (1 989), all crops enemies may develop resistance to pesticides 

used in control strategies. This possibility is especially greater as mites have in 

general short life cycles particularly Varroa which perform twelve generations per year. 

It also becomes more probable to see Varroa mites developing resistance as a result 

of a prolonged contact with an acaricide. That is one of the reasons why 

manufacturers of products for controlling Varroa, advise users to limit the frequency 

and period of use. In spite of all, it is now proved that varroacides such as fluvalinate 

(Lodesani et al., 1992) accumulate in wax creating conditions for a prolonged contact 

with Varroa especially inside the cells alveoles where it reproduces (Vandame et al. 

submitted). It is likely for Varroa to develop resistance more especially as many other 

mesostigmatid mites have already been reported to be resistant in particular to 

synthetic pyrethroids including fluvalinate. 

Ineffectiveness of fluvalinate in Italy 

This active ingredient for varroatosis control has become widespread over the last few 

years because it is easy to use and relatively cheap. A specific product for varroatosis 

control consists in polyvinylchloride (PVC) strips impregnated with the a.¡. at a concentration 

of 10% under the commercial name Apistan@. This product have been proved to be highly 

effective against Varroa (Borneck and Merle, 1990: 99.38-99.72%; Llorente Martinez et al., 

1989: 99.33%; Llorente Martinez et al, 1989: 99.33%). Nevertheless, Apista# strips have 

often been replaced by operators on their own initiative with another product containing the 

same active ingredient. Klartan@ and Mavrik@ are a not authorized products for use in 

beekeeping but they are widely administered using especially wooden inserts where the 

fluvalinate content cannot be controlled. leading to problems of effectiveness. 

Studies conducted in Italy (Lombardy) to investigate if, in fact, there was some 

resistance of Varroa to fluvalinate, showed individual colony variation and differences 

in the average effectiveness obtained in the apiaries. These observations provide 

evidence for the presence of strains of Varroa jacobsoni resistant to fluvalinate in the 

apiaries where treatments were unsatisfactory. 

To assess the susceptibility of Varroa mites to fluvalinate and other pyrethroids, 

Milani, (1995) has developed a bioassay which was tested on strains of Varroa 

believed to be susceptible and strains of mites surviving Apistana treatment and thus 

supposed to be resistant. The median lethal concentration (Lso) of mites originating 

from areas where treatments with fluvalinate are no longer effective was about 25-50 

times higher than that of susceptible mites. The (Lso) of flumethrin and acrinathrin on 

mites surviving Apistan treatments increased 10-60 times. In a similar study, Colin et 

al. using another laboratory test found great differences in the resistance level values 

calculated for Varroa populations originating from geographically distinct regions of 

France. These values range between 1.92 and 182.7. 

Resistance have also been reported to other acaricides belonging to different chemical 

groups. Resistance to bromopropylate and to chlordimeform was shown to be favoured 

by underdoses and this has been verified with laboratory tests (Ritter and Roth, 1988) 

82 

CIHEAM - Options MediterraneennesThe presence in different countries of Varroa strains simultaneously resistant to 

different pyrethroids, points out the risk of basing the control strategies on chemical 

treatments only, particularly when the substances used belong to the same chemical 

family. 

Chemical control of Varroa, adverse side effects 

Effects on bees 

Many papers on the chemical control of varroatosis make observations on bee 

tolerance of varroacide products. Some papers compare the toxicity to bees and to 

mites, which is more interesting than the absolute DL,, for bees (Milani, 1992). All 

acaricide substances have weak feeble insecticide characteristics, thus, the clinical 

signs of an eventual toxicity for bees will not express themselves under an acute form 

but rather under a chronic form essentially for the queen which has the greatest 

longevity in the colony. Some varroacide products have been shown to cause some 

bee mortality immediately after the treatment (Kilani et al., 1981), others have an 

influence on viability (queen loss) and fertility of the queen or an appreciable toxicity 

for the brood which is more susceptible to acaricides than adult bees (Marin, 1977). 

Residue problems 

The risk that residues can be detected in bee products such as honey, wax and 

propolis is as high as lipophilic pesticides are more frequently introduced into hives. 

Since most insecticides and acaricides are more or less lipophilic, they are 

accumulated in wax and then may be slowly released into honey. The presence of 

residues is detrimental to the image of the beekeeping which products are well-known 

to be natural and unpolluted. Contamination of the hive products has become a 

serious problem entailing checking for residues of the acaricides employed. Though 

studying interactions between varroacides and each hive product is necessary, the 

beeswax, as an effective store, has the central role. Higher levels of some insecticides 

used for agricultural purposes are usually found in old beeswax indicating that 

residues accumulate in combs over the years (Gayger and Dustmann, 1985). Tests 

with more than five hundred wax samples showed that in all countries where 

varroacides are used, uncontaminated beeswax can hardly be found. Often various 

pesticides can be detected in one sample (Wallner, 1995). The residues accumulation 

of acaricide products in wax has negative implications especially the consumption of 

contaminated honey and the use of this wax in the cosmetic and pharmaceutical 

industries. Another important consideration is the induction of drug resistant Varroa 

strains as a consequence of the presence of the active ingredient in wax at sublethal 

levels and for long periods of time. 

For certain varroacides which are weakly bound to wax, like coumaphos (Perizin@), 

bromopropylate (Folbex VA Neu@), fluvalinate (Apistan@ - 10% a.¡. Klartan@ and 

Mavrik@-24% a.¡) the higher the concentration in the wax is, the more residues can be 

detected in the honey. With these products, concentration in wax of only 1mg/kg is 

sufficient to detect them in honey. In contrast, active ingredients (flumethrin) known 

as having an extremely high affinity for wax and consequently a feeble tendency to 

migrate are not detected in the honey even with a wax concentration of 400 mg/kg 

(Wallner, 1995). When treatments are carried out properly according to the directions 

83 

CIHEAM - Options Mediterraneennesfor use, the levels of residues of a.¡. of products legally registered are rather low. 

These residue levels overstep the limits allowed by current regulations when 

beekeepers do not conform to the directions for use either applying a greater number 

of treatments than required or using doses higher than necessary. The use of 

agricultural products, not suitable for use in the beehive leads to the same problems. 

Cohabitation with varroosis has been achieved owing to chemotherapy, but 

problems either of residue accumulation in the beehive products or varroa drug 

resistant strains highlight the risk of carrying control strategies based only on chemical 

treatments. 

References 

Borneck, R. and Merle, B. (1989). New tests for Varroa control with Apistan 

(Fluvalinate). Present status of varroatosis in Europe and progress in varroa mite 

control. Proc. Meet. €C-Experts' Group, Udine, 1988, R. Cavalloro (ed.), C.E.C., 

Luxembourg, pp. 31 5-330. 

Cavalloro, R. et al. , (1 988). Current situation of varroatosis infestation and control. 

Proc. Meet. €C-Experts' Group, Udine, 1988, R. Cavalloro (ed.). C.E.C., 

Luxembourg, pp. 13-54. 

Colin, M.E. and Faucon, J.P. (1983). Utilisation of aerosol to treat bee-colonies against 

varroatosis In Proceeding of a Meeting of the EC Experts' Group, Wageningen, 

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CIHEAM - Options MediterraneennesLlorente Martinez, J., Robles Portela, E. and Salvachua Gallego, J.C. (1989). Ensayo 

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85 

CIHEAM - Options Mediterraneennesof Apistan on varroa mites in bee colonies and the effect on spring development of 

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Chemotherapy against Varroa jacobsoni: Efficiency and side effects

Ben Hamida T.

The varroosis in the Mediterranean region

Zaragoza : CIHEAM

Cahiers Options Méditerranéennes; n. 21

1997

pages 77-86

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Ben Hamida T. Chemotherapy against Varroa jacobsoni: Efficiency and side effects. The

varroosis in the Mediterranean region. Zaragoza : CIHEAM, 1997. p. 77-86 (Cahiers Options

Méditerranéennes; n. 21)