Original article

Performance of hygienic honey bee coloniesin a commercial apiary

Marla Spivak Gary S. Reuter

Department of Entomology, 219 Hodson Hall, University of Minnesota,St. Paul, MN 55108, USA

(Received 12 March 1997; accepted 10 August 1997)

Abstract - Colonies with naturally mated queens from a hygienic line of Italian honey bees(Apis mellifera ligustica) were compared to colonies from a commercial line of Italian bees notselected for hygienic behavior. The following characteristics were compared: rate of removal offreeze-killed brood; amount of chalkbrood; incidence of American foulbrood; honey produc-tion; and the number of mites, Varroa jacobsoni, on adult bees. The hygienic colonies removedsignificantly more freeze-killed brood than the commercial colonies, had significantly less chalk-brood, had no American foulbrood, and produced significantly more honey than the commercialcolonies. Estimates of the number of Varroa mites on adult bees indicated that the hygieniccolonies had fewer mites than the commercial colonies in three of four apiaries. In previous stu-dies on the relation between hygienic behavior and resistance to diseases and mites, the testcolonies contained instrumentally inseminated queens. This is the first study to evaluate hygienicstock in large field colonies with naturally mated queens. © Inra/DIB/AGIB/Elsevier, Paris

Apis mellifera / hygienic behavior / Varroa / chalkbrood / American foulbrood

1. INTRODUCTION

For over 50 years, honey bee hygienicbehavior has been recognized as an impor-tant mode of resistance to American foul-brood disease (AFB) [12]. Woodrow andHolst [24] stated, "... resistance to Ame-rican foulbrood consists of the colony’s ability to detect and remove diseased

brood before the causative organism,Bacillus larvae White, reaches the infec-tious spore stage". Over 14 years ago, itwas determined that hygienic behavioralso is a mechanism of resistance to chalk-

brood, caused by the fungus Ascosphaeraapis (Maassen ex Claussen) Olive andSpiltoir [5]. Recently it has been demons-trated that hygienic bees detect and remove

* Correspondence and reprintsE-mail: spiva001 @maroon.tc.umn.edu

pupae infested with the parasitic mite, Var-roa jacobsoni Oudemans [1, 2, 13, 18].The removal of infested pupae interruptsthe reproductive cycle of the mite [4, 14].However, the extent to which the beha-vior actually reduces the mite-load ininfested colonies remains to be determi-ned.

Hygienic behavior occurs in approxi-mately 10 % of most commercial honeybee populations thus far surveyed in theUS (Spivak, unpublished observations).Despite the potential advantages of main-taining hygienic honey bee lines, fewqueen producers select for hygienic behav-ior.

Rothenbuhler [16] postulated that thebehavior is controlled by two indepen-dently assorting, recessive genes: one foruncapping the diseased brood (u) and onefor removing diseased brood from the nest(r) (but see Moritz [10]). When colonieswere composed of mixtures of hygienicand non-hygienic bees (progeny of ins-trumentally inseminated queens frominbred lines), Trump et al. [23] concludedthat "for removal of all dead brood from asmall colony, the proportion of the beesthat must be of the hygienic type is higherthan 13 % but less than 50 %". These earlyexperiments suggested that a small per-centage of bees, possibly within particularpatrilines, may actually perform the beha-vior.

The genetics of the trait may be control-led by raising queens from hygienic colo-nies and instrumentally inseminating themwith semen from drones of other hygieniccolonies [5]. However, instrumentallyinseminated queens are used only as bree-der stock in the beekeeping industry; com-mercial beekeepers use naturally matedqueens in their production colonies. Gene-tic control may be obtained by saturatingthe mating area with hygienic dronemother colonies [8]. If lines of bees selec-ted for hygienic behavior are to be utilizedby the beekeeping industry, it is first

necessary to examine colonies with queensreared from hygienic stock and matednaturally with unselected drones. Do colo-nies with naturally mated queens rearedfrom a hygienic line remove freeze-killedbrood more rapidly than commercial colo-nies? Do they have lower incidences ofchalkbrood and AFB? Do they have fewerVarroa mites? And importantly, do theyproduce as much honey? The present studyis the first to address these questions in acommercial apiary.

2. MATERIALS AND METHODS

2.1. Hygienic breeding stock

The hygienic queens used in the experimentwere bred from ’Starline’ stock, derived fromItalian Apis mellifera ligustica Spinola, andwere maintained at the University of Minne-sota. The degree of hygienic behavior wasdetermined by a freeze-killed brood assay inwhich the time was recorded for colonies to

detect, uncap and remove brood from a 5 cm x6 cm comb section (containing approximately100 capped larvae and pupae per side of thecomb) that had been cut from a frame withinthe brood nest of the same or different colony,frozen at -20 °C for 24 h, and placed in thenest of the test colony [19, 21]. Colonies thatremoved the freeze-killed brood from the combsection within 48 h on two consecutive trialswere considered hygienic [20, 21]. To esta-blish and maintain a hygienic line of bees,beginning in 1993, queen bees were raisedfrom colonies that consistently removed at least95 % of the freeze-killed brood within 48 h.Each daughter queen was instrumentally inse-minated (II) with 4-6 μL semen from dronescollected from other colonies with similarremoval rates. The colonies containing the IIqueens were wintered and tested again usingthe freeze-killed brood assay in the followingspring. Only the colonies that removed 100 %of the freeze-killed brood within 48 h and alsohad good wintering ability, strong populationsin spring, and no visible signs of chalkbrood orother brood diseases were considered breedercolonies. Daughter queens were propagated inthe next generation from these breeder colo-nies.

2.2. Experiment 1

Hygienic queens were reared from onebreeder colony containing a second generationII queen at the University of Minnesota in lateMay 1995. This colony consistently removed100 % of freeze-killed brood within 48 h. Thesister queens emerged in an incubator (34 °Cand 70 % RH) and were marked with a dot ofenamel paint on the thorax. They were thenintroduced into mating nuclei distributed inthree apiaries owned by a commercial bee-keeper near Hammond, Wisconsin. The apia-ries were located over 80 km from the Uni-

versity of Minnesota. The queens matednaturally, and when they had begun layingeggs, were introduced into colonies in the samethree apiaries in Wisconsin. Each apiary contain-ed at least 24 colonies on pallets, with fourcolonies per pallet. Each colony occupied twostandard Langstroth deep hive bodies. For com-parison, half of the colonies in each apiary (twoper pallet) contained laying queens reared fromcommercial Italian stock that had mated natu-

rally in eastern Texas in March 1995. The com-mercial queens were reared from two differentbreeder queens, and therefore, were not sisters.

Beginning in late August 1995, when allthe bees in the hygienic colonies were progenyof the introduced queens, three consecutivefreeze-killed brood assays were conducted onall colonies in the three apiaries. The brood forthe first assay was obtained by cutting sectionsof comb containing capped brood from colo-nies located at the University of Minnesota.These sections were frozen for 24 h and thenintroduced into the test colonies in Wisconsin.As an individual section of frozen brood wasinserted into each test colony, a comb sectionof similar size that contained sealed brood wascut out from the colony. These new sectionswere frozen and used in the second assay.Freeze-killed brood for the third assay wasobtained in the same way as that for the second

assay. Previous experiments demonstrated thatthe source of the freeze-killed brood (from thesame or different colony) had no effect on itsremoval rate by hygienic colonies [19]. In alltrials, the number of intact capped cells wascounted before the sections were inserted, andthe number of emptied cells was counted after48 h. Cells were not counted as empty if theywere only uncapped or if any part of the deadbrood remained. In this way, the most conser-vative measure of removal was recorded. Theresults of the three successive tests were ana-

lyzed using a repeated measures 2-wayANOVA [17].

The weather during the first assay (24-26August 1995) was rainy and relatively cool(daytime highs: 20-25 °C). By the time of thesecond assay (29-31 August), the weather clea-red and mean daytime temperatures remainedabove 26 °C. In addition, a goldenrod (Soli-dago spp.) bloom provided a strong source ofincoming nectar during both this second assayand third assay (8-10 September).

2.3. Experiment 2

Hygienic breeder colonies containing thirdgeneration II queens from the University ofMinnesota were wintered in eastern Texas in1995 in an apiary owned by the same com-mercial beekeeper whose apiaries located inWisconsin were used in experiment 1. In

February 1996, the colonies in Texas were eva-luated for population size and brood area, andwere tested for hygienic behavior using thefreeze-killed brood assay. Daughter queenswere reared from the most populous colonythat consistently removed freeze-killed broodwithin 48 h. The breeder colony also removed65 % of pupae experimentally infested withVarroa mites in subsequent tests conducted inJuly 1996 at the University of Minnesota (afterthe breeder colony was transported back toMinnesota from Texas in May) using tech-niques described in Spivak [18].

Additional queens were reared from one

colony of commercial stock of Italian descentalso wintered in Texas. The commercial colonywas chosen on the basis of the size of both the

population of adult bees and the brood area. Afreeze-killed brood assay indicated that thecommercial colony removed less than 50 % ofthe frozen brood within 48 h. This colony wasnot tested for its ability to remove pupae expe-rimentally infested with Varroa.

Daughter queens from both hygienic andcommercial lines emerged within mating nucleiand mated naturally with the drones from thesurrounding area in Texas. Two weeks afterthe queens emerged, they were marked withenamel paint on the thorax. In May 1996, allcolonies with naturally mated queens weretransported to Wisconsin. The hygienic andcommercial colonies were equally distributedamong four apiaries. The colonies were situa-ted on pallets, and each pallet contained twohygienic and two commercial colonies.

Each colony that was transported to Texaswas treated for Varroa mites using one Apis-tan® strip per colony in the fall of 1995. Nosubsequent Apistan treatment was given to anycolony (mating nucleus or full-size colony)until after the experiment was terminated inSeptember 1996. All colonies transported fromTexas to Wisconsin were treated with 50 gmenthol crystals for the tracheal mite, Acara-pis woodi (Rennie), and were given six pre-ventative dustings of oxytetracycline (a totalof 1 000 mg TM-25® in powdered sugar) forEuropean foulbrood and AFB in May and June1996.

In June, the hygienic and commercialqueens in every colony in the four apiaries inWisconsin were located to determine if theywere marked. If they were, the colony was eval-uated on colony strength and degree of chalk-brood infection and incidence of AFB. Ini-

tially, four colonies were evaluated togetherby all recorders to standardize the scoring pro-cedure. After that, two people evaluated eachremaining colony, and both scores were aver-aged for each criterion.

Colony strength was estimated from thenumber of frames covered by bees [11] andnumbers of frames containing brood (cellscontained egg, larvae, and/or pupae) were esti-mated.

The degree of chalkbrood infection wasmeasured by counting the number of chalk-brood mummies found in cells on both sidesof two frames containing capped brood percolony. Only mummies in uncapped cells werecounted. The colony was given a score from0 to 3 (uninfected to highly infected), where 0= no mummies, 1 = 1-5 mummies, 2 = 5-20mummies, and 3 = over 20 mummies. Colo-nies were scored 0 or 1 for incidence of AFB:0 = not infected; 1 = at least one infected pupain an uncapped cell was noticed. If AFB wasfound, the colony was treated with oxytetra-cycline dust, as before.

After the June evaluations, the colonieswere provided with honey supers ad libitum. Inearly September, the honey was harvested, andthe colonies (in two deep hive bodies) wereevaluated again for degree of chalkbrood infec-tion and incidence of AFB. In addition, eachcolony was evaluated for honey production,removal of freeze-killed brood, and levels ofVarroa. The amount of honey produced wasmeasured by marking each super of honey as itwas removed to indicate its colony of origin

and then weighing the super on a floor scalein a honey extraction facility. The tare weightof the supers and frames was calculated byweighing the extracted supers.

To assay for hygienic behavior, each colonywas assayed once with freeze-killed brood, andthe amount of brood removed from each combsection was recorded after 48 h. At the time ofthe assay, goldenrod was in bloom, and meandaytime temperatures were over 26 °C.

The number of Varroa mites on adult beeswas calculated by collecting samples ofapproximately 300-400 bees from each colonyinto enough 70 % ethanol to cover the bees,and hand-shaking each sample to dislodge themites. The number of mites per sample wascounted and from the weight of bees in eachsample and a known weight of 100 wet bees,the number of mites per 100 bees was calcu-lated.

All measures, except incidences of AFB,were analyzed using a 2-way ANOVA to sepa-rate the effects of bee type (hygienic versuscommercial) and apiary site [17].

3. RESULTS

3.1. Experiment 1

Forty-three marked, laying queens fromthe hygienic stock were successfully intro-duced into the full-size colonies in June. Atthe time of the freeze-killed brood assaysin August, seven of the marked queenshad been superseded. Colonies headed bythese queens comprised the hygienic-supersedure group.

The results of the three successivefreeze-killed brood assays are shown in

figure 1. In all tests, the 36 hygienic colo-nies (with marked, sister queens) remo-ved significantly more brood than the 56commercial colonies (F = 16.1, d.f. = 2, 96;P < 0.001). The mean percent (± s.d.)brood removed over the three tests by thehygienic, hygienic-supersedure, and com-mercial colonies was 82.9 % ± 10.49,58.9 % ± 28.79, and 58.9 % ± 21.52, res-pectively. In the second and third tests,the hygienic colonies removed signifi-

cantly more brood than the seven colo-nies containing supersedure queens(Tukey’s HSD test) [17]. In addition,there was a significant effect of test date(F = 61.9; d.f. = 2, 192; P < 0.001). Allcolonies removed less freeze-killed broodin the first test compared to the two suc-cessive tests.

Seven (19.4 %) hygienic and two (3.6 %)commercial colonies removed 95 % of thefreeze-killed brood within 48 h on all threetests. Eleven (30.6 %) hygienic and three(5.4 %) commercial colonies removed90 % or more of the brood in all tests.

3.2. Experiment 2

In June 1996, 49 marked queens werefound in the hygienic colonies and 46 mar-ked queens in the commercial colonies.The evaluations of colony strength indi-cated that the mean numbers of frames ofbees and brood in the two colony typeswere not significantly different. The hygie-nic colonies had 17.4 ± 1.43 frames ofbees and 10.1 ± 1.85 frames of brood. Thecommercial colonies had 17.3 ± 1.74frames of bees and 10.0 ± 1.52 frames ofbrood.

The evaluations of chalkbrood mum-mies on two frames containing cappedbrood in June and September are shownin figure 2. In all apiaries, the hygieniccolonies had significantly less chalkbroodthan the commercial colonies in both June

(F = 32.24; d.f. = 1, 87; P < 0.001) andSeptember (F=17.74; d.f.=1, 87; P<0.001).There was no significant apiary effect andno significant interaction between bee typeand apiary.

At least one AFB-infected pupa wasnoted in six (13 %) of the commercialcolonies in June and in five (10.9 %) ofthe colonies in September. No AFB wasnoted in any hygienic colonies duringeither inspection.

An average of 40.5 ± 16.45 kg (90.0 ±36.56 1b; mean ± s.d.) of honey was har-vested from the 49 hygienic colonies inlate August 1996 (figure 3). In compari-son, 30.1 ± 14.49 kg (66.8 ± 32.20 1b)honey was harvested from the 46 com-mercial colonies. The difference was

highly significant (F = 9.81; d.f. = 1, 87;P = 0.002). There was no significantapiary effect and no significant interac-tion between bee type and apiary.

The results of the single hygienic assayin September 1996 indicated that thehygienic colonies removed significantlymore freeze-killed brood (94.2 % ± 12.16;mean ± s.d.) than the commercial colo-nies (82.31 %±22.91) (F=10.71;d.f.=1,87;P = 0.002). Thirty-eight (77.6 %) of thehygienic colonies and 20 (43.5 %) of thecommercial colonies removed 95 % ormore of the freeze-killed brood within 48 h.

The hygienic colonies had 0.6 ± 0.86(mean ± s.d.) Varroa mites per 100 adultbees, and the commercial colonies had 1.0± 1.0 (figure 4). Overall, the hygienic colo-nies had significantly fewer mites than thecommercial colonies (F = 5.78; d.f. = 1, 87;P = 0.013). However, there was a signi-ficant interaction between bee type andapiary (F = 4.06; d.f. = 3, 87; P = 0.009)because on average, more mites werefound in the second apiary within thehygienic colonies than in the commercialcolonies.

4. DISCUSSION

The results of these experimentsdemonstrated that colonies with naturallymated queens from stock bred for hygienic

behavior were significantly more hygie-nic (based on rate of removal of freeze-killed brood) and had lower incidences ofchalkbrood and AFB than commercialcolonies not selected for hygienic behav-ior. The hygienic colonies in this studyalso produced more honey than the com-mercial colonies. These results indicatethat it is possible to select for hygienicbehavior without compromising honeyproduction; it does not imply that hygienicbehavior and honey production are genet-ically linked traits. It is very important forqueen breeders to simultaneously selectfor hygienic behavior and other commer-cially desirable traits (honey production,wintering ability). Finally, estimates ofthe number of Varroa mites on adult beesindicated that most of the hygienic colo-nies had fewer mites than unselected com-mercial colonies.

The hygienic colonies removed a higherpercentage of freeze-killed brood than thecommercial colonies in all three tests in1995 and in the single test in September1996. Rothenbuhler [16] found that F1progeny of hygienic queens from theBrown line, each instrumentally insemi-nated with semen of a single drone fromthe non-hygienic Van Scoy line, removed

diseased brood at the same rate as the non-

hygienic line. The hygienic queens in thepresent study were mated with multipledrones of unknown genotype, but stillremoved significantly more freeze-killedbrood within 48 h than the commercialcolonies. These results suggest the inher-itance of hygienic behavior may becontrolled by more than two recessive loci(also see Moritz [10]).

The increased rate of removal by allcolonies in the second and third assays in1995 coincided with a goldenrod bloom.The expression of hygienic behavior isknown to be strongly influenced by envi-ronmental factors, particularly the amountof nectar available to the colonies. A

strong nectar flow increases the expres-sion of hygienic behavior [9, 22]. In 1996,both the hygienic and commercial colo-nies had relatively rapid rates of removal,although the hygienic colonies had signi-ficantly higher removal rates. There was astrong nectar flow from goldenrod duringthe assay; however, it is unclear why somany of the commercial colonies remo-ved high percentages of the freeze-killedbrood. It is possible that a second assay,conducted before or after the goldenrodbloom, would have resulted in lower ratesof removal by the commercial colonies.

The difference in the degree of chalk-brood infection between the hygienic andcommercial colonies was very apparentduring the field inspections. It also wasnotable that no hygienic colonies becameinfected with AFB, despite the fact thatinfected commercial colonies were locatedon the same pallets. In previous experi-ments on the relation between hygienicbehavior and resistance to chalkbrood and

AFB, the test colonies contained instru-mentally inseminated queens [5, 6, 16,20]. The present study is the first to com-pare levels of chalkbrood and AFB in largefield colonies with naturally mated queensraised from hygienic stock.

Colonies infected with chalkbrood mayexperience a reduction in foraging force

and a subsequent reduction in honey pro-duction [7]. In the present study, the com-mercial colonies produced, on average,26 % less honey than the hygienic colo-nies; however there was no significantnegative correlation between amount ofchalkbrood in June and honey yield inSeptember (Pearson correlation = -0.181,P = 0.079). The lower yields by the com-mercial colonies could have been due tothe source of Italian stock from which the

queens were reared and not to their degreeof chalkbrood infection.

Hygienic behaviour may limit the popu-lation growth of Varroa mites in threeways: 1) the immature mites may be killedwhen the infested pupae are removed,which would decrease the average numberof offspring per reproducing mite; 2) thephoretic period of adult female mites thatsurvive removal of the pupae may be

extended; and 3) the mortality of the adultmites may increase if they are damagedby grooming adult bees when the mitesescape through the opened cell [4]. Thehygienic queens in the present study werereared from colonies that removed signi-ficantly more pupae infested with Varroamites than non-hygienic colonies in a pre-vious study [18]; thus, it was hypothesizedthat the hygienic colonies would havelower levels of Varroa mites. In fact, mostof the hygienic colonies in the 1996 exper-iment had fewer Varroa mites than thecommercial colonies. However, the Var-roa mite counts estimated the number ofmites found on adult bees only; miteswithin brood cells were not assessed. Ove-

rall, the mean numbers of Varroa mitesfound on the adult bees in all the colonieswere relatively low and may have beenunderestimated because the mites wereshaken off the bees by hand rather thanby a mechanical shaker [3]. Studies are inprogress to compare the levels of Varroamites in hygienic and commercial colo-nies left untreated for a longer time andto obtain more detailed estimates of the

number of mites by examination of bothadult bees and cells containing worker anddrone brood.

Despite the obvious advantages ofselecting bee colonies for hygienic beha-vior, few commercial queen producersselect for the trait in their breeding pro-grams. One reason may be due to the com-mon misconception that hygienic coloniesare highly defensive. This assumptionstems from the reputation of the Brownline of hygienic bees, maintained byRothenbuhler, which was notoriouslydefensive. However, in backcrossed colo-nies between the inbred Brown line andthe inbred Van Scoy (non-hygienic) line,Rothenbuhler [16] demonstrated clearlythat stinging and hygienic behaviors wereinherited separately. The colonies used inthe present study were gentle and therecorders, none of whom wore gloves,received few if any stings throughout theevaluations.

A second reason why apiculturists havenot selected for the trait may be due toinconsistencies inherent in the assay for

hygienic behavior. The rate of removal ofthe freeze-killed brood within a particu-lar colony even under the same environ-mental conditions is not always consistentbetween assays [ 15]. In addition Rodrigueset al. [ 15] found that colonies more quicklyremoved freeze-killed brood that had been

recently capped than brood that had beencapped for 5 days. However, in similarexperiments, Spivak and Downey [19]found that the developmental stage of thebrood did not influence the removal rate

by colonies that consistently removedfreeze-killed brood within 48 h.

In conclusion, the results of this studydemonstrate that hygienic behavior is ahighly desirable trait. The hygienic colo-nies in the present study were derived froman Italian line of bees; however, the beha-vior can be found in other races of bees

(e.g. Carniolan bees, pers. obs.). Theamount of chalkbrood and AFB in colo-

nies can be reduced by requeening colo-nies with naturally mated queens from ahygienic line of bees. Continuing studieswill determine the extent to which the Var-roa mite load is reduced in hygienic colo-nies.

ACKNOWLEDGMENTS

We thank Gary Lamb and his son MikeLamb for providing us with the commercialbee colonies and apiary sites, raising and mar-king the queens, keeping track of the coloniesas they were transported between Wisconsinand Texas, and helping with the colony eva-luations. We also thank Ed Barry, John Brey-fogle, Laura Heuser and Rebecca Mastermanfor their assistance with different phases of thisstudy. Martha Gilliam, Roger Moon, and SteveTaber III provided valuable editorial adviceon the manuscript. The research was fundedby grants from the Minnesota Agricultural Uti-lization Research Institute (AURI- PRO 130)and the Almond Board of California with mat-

ching funds from beekeeping associations inMinnesota, Wisconsin, North Dakota, SouthDakota, and California. Special thanks to theMinnesota Honey Producers Association fortheir generous support of this research. This ispublication no. 971170103 from the Agricul-tural Experiment Station of the University ofMinnesota.

Résumé - Les performances dans unrucher commercial de colonies d’abeilles

présentant un comportement hygié-nique. Le comportement hygiénique desabeilles est un mécanisme de résistance àla loque européenne et aux maladies cryp-togamiques et l’un des modes de défensecontre Varroa jacobsoni. Malgré les avan-tages évidents que procurent des coloniesd’abeilles sélectionnées pour leur com-

portement hygiénique, peu d’éleveurs dereines sélectionnent ce caractère. Le butde cette étude était de comparer des colo-

nies, avec des reines fécondées naturelle-ment, issues d’une lignée hygiéniqued’abeilles italiennes (Apis mellifera ligus-tica Spinola) avec des colonies issues

d’une lignée commerciale d’abeilles ita-liennes non sélectionnées pour ce carac-tère. Dans les études précédentes sur larelation entre le comportement hygiéniqueet la résistance aux maladies et aux aca-

riens, les colonies testées possédaient desreines inséminées artificiellement. Ceciest la première étude qui évalue les per-formances d’une lignée hygiénique dansde fortes colonies avec des reines fécon-dées naturellement. On a évalué les para-mètres suivants : taux d’élimination ducouvain tué par le froid, quantité de cou-vain plâtré, présence de loque américaine,production de miel et nombre de varroassur les abeilles adultes. Au cours de deuxétudes indépendantes (1995 et 1996) lescolonies hygiéniques (respectivement 36et 49 colonies) ont éliminé significative-ment plus de couvain tué par le froid queles colonies commerciales témoins (res-pectivement 56 et 46 colonies) (figure 1).Les comparaisons en 1996 montrent queles colonies hygiéniques avaient signifi-cativement moins de couvain plâtré queles colonies commerciales et n’avaient pasde loque américaine, malgré le fait que lescolonies commerciales aient été placéessur les mêmes palettes (figure 2). Les colo-nies de la lignée hygiénique ont aussi pro-duit plus de miel (40,5 ± 16,45 kg) quecelles de la lignée commerciale (30,1 ±14,49 kg) (figure 3), ce qui montre qu’il estpossible de sélectionner le caractère hygié-nique sans pour autant compromettre laproduction de miel. Les estimations dunombre de varroas sur les abeilles adultes

indiquent que les colonies de la lignéehygiénique ont eu, dans trois cas surquatre, des niveaux d’acariens inférieurs àcelles de la lignée commerciale (figure 4).Dans l’ensemble les colonies de la lignéehygiénique avaient 0,6 ± 0,86 varroas pour100 abeilles adultes tandis que celles de la

lignée commerciale en avaient 1,0 ± 1,0.Pourtant, des estimations plus précises duparasitisme, qui devraient inclure lescomptages d’acariens dans les cellules decouvain, sont nécessaires avant de tirer

des conclusions définitives concernant lerôle du comportement hygiénique sur laprévalence de Varroa dans les coloniesd’abeilles. &copy; Inra/DIB/AGIB/Elsevier,Paris

Apis mellifera / comportement hygié-nique / Varroa / couvain plâtré / loqueaméricaine

Zusammenfassung - Eigenschaftenhygienischer Bienenvölker in einerkommerziellen Bienenhaltung. Dashygienische Verhalten von Honigbienen(das Ausräumen erkrankter Brut) ist einResistenzmechanismus gegenüber derAmerikanischen Faulbrut sowie der Kalk-brut und ist einer der Abwehrmechanis-men gegen Varroa jacobsoni. Trotz deroffensichtlichen Vorteile einer Selektionauf hohes hygienisches Verhalten wirddiese nur von sehr wenigen professionel-len Königinnenzüchtern durchgeführt. Inunserer Untersuchung sollten Völker mitnatürlich gepaarten Königinnen einerhygienischen Zuchtlinie von Italienerbie-nen (Apis mellifera ligustica) mit einerkommerziellen Linie von Italienerbienen

verglichen werden, welche nicht auf diesesVerhalten hin selektiert war. Die in frü-heren Untersuchungen über die Beziehungzwischen dem hygienischen Verhalten undder Resistenz gegenüber Krankheiten undMilbenbefall verwendeten Völker hattenkünstlich besamte Königinnen. Dies istdaher die erste Studie, in der die Eigen-schaften einer hygienischen Linie ingro&szlig;en Völkern mit natürlich gepaartenKöniginnen bewertet werden. In den Völ-kern wurde das Entfernen von durch Käl-

teeinwirkung abgetöteter Brut, der Kalk-brutbefall, das Vorkommen AmerikanischerFaulbrut, die Honigproduktion und dieAnzahl von Varroamilben auf den Bienen-arbeiterinnen erfa&szlig;t. In zwei getrenntenUntersuchungen (1995 und 1996) ent-fernten die Völker der hygienischen Linie

(36 bzw. 49 Völker) signifikant mehr derabgetöteten Brut als die kommerzielleLinie (56 bzw. 46 Völker, Abb. 1). DieUntersuchung 1996 zeigte, da&szlig; in der

hygienischen Linie der Befall durch Kalk-brut signifikant geringer war, und in die-sen keine Amerikanische Faulbrut ange-troffen wurde, obwohl befallene Völkerder kommerziellen Linie auf den gleichenPaletten standen (Abb. 2). Die Völker derhygienischen Linie produzierten mehrHonig (40.5 ± 16.45 kg) als die kommer-ziellen Völker (30.1 ± 14.49 kg, Abb. 3).Dies belegt, da&szlig; eine Selektion auf hygie-nisches Verhalten ohne negative Auswir-kungen auf die Honigproduktion durch-geführt werden kann. Die Schätzungender Anzahl von Varroa auf Arbeiterinnendeuten darauf hin, da&szlig; die Völker der

hygienischen Linie auf vier der Bie-nenstände einen geringeren Milbenbefallaufwiesen als die kommerzielle Linie

(Abb. 4). Insgesamt hatten die hygieni-schen Völker 0.6 ± 0.86 Varroamilben

pro 100 Arbeiterinnen, während es in denkommerziellen Völkern 1.0 ± 1.0 waren.Bevor sichere Schlu&szlig;folgerungen bezü-glich einer Auswirkung des hygienischenVerhaltens auf den Milbenbefall gezogenwerden können, sind jedoch genauereMessungen des Milbenbefalls nötig, in dieauch Zählungen der Milben in der Bruteinbezogen werden. &copy; Inra/DIB/AGIB/

Elsevier, Paris

Apis mellifera / hygienisches Verhalten /Varroa / Kalkbrut / AmerikanischeFaulbrut

REFERENCES

[1] Boecking O., Drescher W., Response of Apismellifera L. colonies infested with Varroajacobsoni Oud, Apidologie 22 (1991) 237-241.

[2] Boecking O., Drescher W., The removal res-ponses of Apis mellifera L. colonies to brood inwax and plastic cells after artificial and naturalinfestation with Varroa jacobsoni Oud. and tofreeze-killed brood, Exp. Appl. Acarology 16(1992) 321-329.

[3] De Jong D., De Andrea Roma D., GoncalvesL.S., A comparative analysis of shaking solu-tions for the detection of Varroa jacobsoni onadult honeybees, Apidologie 13 (1982)297-306.

[4] Fries I., Camazine S., Sneyd J., Populationdynamics of Varroa jacobsoni: a model and areview, Bee World 75 (1994) 5-28.

[5] Gilliam M., Taber S. III, Richardson G.V.,Hygienic behavior of honey bees in relation tochalkbrood disease, Apidologie 14 (1983)29-39.

[6] Gilliam M., Taber S. III, Lorenz BJ, Prest D.B.,Factors affecting development of chalkbrooddisease in colonies of honey bees, Apis melli-fera, fed pollen contaminated with Ascosphaeraapis, J. Invertebr. Pathol. 52 (1988) 314-325.

[7] Heath L.A., Development of chalk brood in ahoneybee colony: A review, Bee World 63(1982) 119-130.

[8] Hellmich R.L., Waller G., Preparing for Afri-canized honey bees: Evaluating control inmating apiaries, Am. Bee J. 130 (1990)537-542.

[9] Momot J.P., Rothenbuhler W.C., Behaviourgenetics of nest cleaning in honeybees. VI.Interactions of age and genotype of bees, andnectar flow, J. Apic. Res. 10 (1971) 11-21.

[10] Moritz R.F.A., A reevaluation of the two-locusmodel for hygienic behavior in honeybees (Apismellifera L.), J. Hered. 79 (1988) 257-262.

[11] Nasr M.E., Thorp R.W., Tyler T.L., BriggsD.L., Estimating honey bee (Hymenoptera:Apidae) colony strength by a simple method:Measuring cluster size, J. Econ. Entomol. 83(1990) 748-754.

[12] Park O.W., Testing for resistance to Americanfoulbrood in honeybees, J. Econ. Entomol. 30(1937) 504-512.

[13] Peng Y.S., Fang Y., Xu S., Ge L., Nasr M.E.,Response of foster Asian honey bee (Apis ceranaFabr.) colonies to the brood of European honeybee (Apis mellifera L.) infested with parasiticmite Varroa jacobsoni Oudemans, J. Invertebr.Pathol. 49 (1987) 259-264.

[14] Rath W., Drescher, W., Response of Apiscerana Fabr. towards brood infested with Var-roa jacobsoni Oud. and infestation rate of colo-nies in Thailand, Apidologie 21 (1990) 311-321.

[15] Rodrigues I., Beetsma J., Boot W.J., Calis J.,Testing hygienic behavior in four differenthoneybee strains, in: Sommeijer M.J., FrankeP.J. (Eds.), Proc. Sec. Exp. Appl. Entomol.Netherlands Entomol. Soc. 7, Netherlands Ento-mological Society, Amsterdam, the Nether-lands, 1996, pp. 83-88.

[16] Rothenbuhler W.C., Behavior genetics of nestcleaning in honey bees. IV. Responses of F1and backcross generations to disease-killedbrood, Am. Zool. 4 (1964) 111-123.

[17] SAS Institute Inc., Release 6.10, Cary N.C.,SAS Institute, Inc., 1995.

[18] Spivak M., Hygienic behavior and defenseagainst Varroa jacobsoni, Apidologie 27 (1996)245-260.

[19] Spivak M., Downey D., Field assays for hygie-nic behavior in honey bees (Hymenoptera: Api-dae), J. Econ. Entomol. 91 (1998) 64-70.

[20] Spivak M., Gilliam M., Facultative expressionof hygienic behaviour of honey bees in rela-tion to disease resistance, J. Apic. Res. 32(1993) 147-157.

[21] Taber S., Gilliam M., Breeding honey bees forresistance to diseases, Korean J. Apic. 2 (1987)15-20.

[22] Thompson V.C., Behaviour genetics of nestcleaning in honeybees. III. Effect of age ofbees of a resistant line on their response todisease-killed brood, J. Apic. Res. 3 (1964)25-30.

[23] Trump R.F., Thompson V.C., RothenbuhlerW.C., Behaviour genetics of nest cleaning inhoneybees V. Effect of previous experienceand composition of mixed colonies on responseto disease-killed brood, J. Apic. Res. 6 (1967)127-131.

[24] Woodrow A.W., Holst E.C., The mechanismof colony resistance to American foulbrood,J. Econ. Entomol. 35 (1942) 327-330.