Ontogenesis of the mite Varroa jacobsoni Oud. in drone brood of the honeybee Apis mellifera L. under natural conditions

Experimental & Applied Acarology, 19 (1995) 199-210 199 Ontogenesis of the mite Varroa jacobsoni Oud. in drone brood of the honeybee Apis mellifera L. under natural conditions ABSTRACT S.J. Martin National Bee Unit, Central Science Laboratory, Luddington, Stra~ord-upon-Avon, Warwickshire, CV37 9SJ UK A study carded out during the summer of 1994, in southern England, investigated the developmental times and mortality of Varroa jacobsoni in Apis mellifera drone cells. The position and time of capping of 2671 naturally infested drone cells were recorded. Six hours after the cell was capped, 90% of the mites were free from the brood food~o start feeding on the developing drone. The developmental time of the mite's first three female offspring (133+_3 h) and the male offspring (150 h) and the intervals between egg laying (20-32 h) were similar to those found in worker cells. However, the mortality of the offspring was much lower in drone cells than worker cells. The mode numbers of eggs laid were six and five in drone and worker cells, respectively. All offspring had ample time to develop fully in drone cells with the sixth offspring reaching maturity approximately 1 day before the drone bee emerged. Normal mites (those which lay five or six viable eggs) produced on average four female adult offspring but since only around approximately 55% of the mite population produced viable offspring the mean number of viable adult female offspring per total number of mother mites was 2 to 2.2 in drone cells. Key words: Varroajacobsoni, Apis meuifera, ontogenesis, reproduction. INTRODUCTION Varroajacobsoni Oud. is a parasitic mesostigmatid mite that lives exclusively on honeybees (Apis spp.). In Apis cerana E, the mite's natural host, it is present in some of the sealed drone cells of almost all colonies (Rath, 1989; Rath and Drescher, 1990) but damage to the colony is not serious since the host-parasite relationship is balanced. This is due to the mites' reproduction being restricted almost exclusively to a drone (male) sealed brood (Koeniger et al., 1983; De Jong, 1988; Tewarson et al., 1992; Rosenkranz et al., 1993) and the ability of the adult bees to remove mites effectively from sealed worker cells (Peng et al., 1987; Rath and Drescher, 1990) and from themselves by self- or communally grooming (Peng et al., 1987; Btichler et al., 1992). The absconding behaviour ofa. cerana may also reduce the mite load but this factor has not yet been investigated. Such behaviour does not allow the mite population to build up to levels that cause significant 0168-8162 1995 Chapman & Hall

200 s.j. MARrtn damage to the colony. In the mites' new host Apis mellifera L., this balance is not present due to the reduced extent which the adult bees groom and the mite's ability to reproduce undetected successfully in both worker and drone sealed brood. The mites in A. mellifera colonies infest drone cells more than worker cells (7.2 times, Sulimanovic et al., 1982; 8.6 times, Schulz, 1984; 7.2 times, Takeuchi and Sakai, 1986; 5.1 times, Woyke, 1987; 8.3 times, Fuchs, 1990). Drone cells remain attractive to the mites for a longer period of time prior to sealing (45 h, Ifantidis, 1988; 40-50 h, Boot et al., 1992) than the worker cells (15 h, Ifantidis, 1988; 15-20 h, Boot et al., 1992). In addition, the area of the drone cell opening is 1.7 times larger than that of worker cells (Boot et al, 1992) and drones may receive more visits by the bees, due to their larger body size. However, taking all these factors into account the mites still show a strong preference towards the drone brood. Despite this preference and the fact that mites can only reproduce successfully in A. cerana drone cells, most previous studies on the reproduction of the mite in A. mellifera have concentrated on studies using worker brood. Seven previous studies (Ifantidis, 1983, 1984; Schulz, 1984; Fuchs and Langebach, 1989; Accorti and Nannelli, 1990; Muszynska et al., 1992; Donz6 and Guerin, 1994) have looked specifically at mite reproduction in drone brood. Although the reproductive potential of the mite is higher in drone cells than in worker cells, it may be of little importance since when drone cells are being produced they represent only a small (5-10%, Allen, 1965; 13-i7%, Seeley and Morse, 1976) fraction of the total number of cells available in which the mites can reproduce. Therefore, mites reproducing in drone cells may have little influence on the overall population dynamics of the mite (Fries et al., 1994). However, due to the low productivity of mites in worker cells caused by the mortality of the offspring (Martin, 1994), the role of mites breeding in drone cells could be important in enhancing the reproduction rate of the mite at low infestation rates (Fuchs, 1986) during the initial build up of the population or in colonies with artificially maintained low levels of mites, e.g. colonies undergoing control measures. The aim of this study was to investigate the development times and mortality of the mite offspring in drone cells and compare the data with previous findings. MATERIALS AND METHODS The study was carried out in mid-devon in southern England during May-July 1994 using 14 chemically untreated A. mellifera colonies in which 6-51% of the sealed drone brood were naturally infested with V. jacobsoni. In order to obtain sufficient data to cover the development of all stages of the mite, the experiment had to be repeated three times. The drone population in the study colonies was artificially depressed by destroying all natural drone ceils and brood prior to the start of each experiment. At the same time a frame (Standard Smith, 37.8 23.0 cm) containing drone cells was placed directly above the brood nest and queen

ONTOGENESIS OF VARROA JACOBSONI 201 excluder, allowing the bees to clean and become accustomed to the comb. At the start of the experiment the drone frame was placed in the centre of the brood box (nest). Initially the queen was confined to the drone frame using a queen cage, but it was later found that the queen's preference for laying eggs in the drone cells was so great that the cages were unnecessary. Frames were checked several days later to determine which had suitable (similar-aged) drone brood. During the period of mite entry (starting 40-50 h prior to cell sealing; Boot et al., 1992) some of the frames were placed into more heavily infested hives in order to boost the infestation rate. This was achieved by monitoring the natural mite drop (mites which fell from the colony) of all colonies throughout the study. As soon as sealing commenced in drone cells, the position and time that each cell was sealed during each 2 h period during the day, starting at 06:00 or 08:00 and an 8-12 h period during the night, starting at 20:00 or 22:00 were recorded on transparent sheets temporarily held over the frames. The frames were removed from the colonies at predetermined times and the cell contents recorded. Recording was either done immediately or, more often, the frames were placed in a freezer and analysed later. The developmental stages of the bee and mites were recorded as previously stated (Martin, 1994). Steiner et al. have shown that the laid egg contains a pharate protonymph and not a hexapod larva, as was incorrectly reported by Martin. Therefore in keeping with other workers, this stage will be referred to as an egg. To estimate the developmental times of individual offspring using the composition of the population, it was assumed that the mother mites start reproduction at a similar time and the developmental time for all examples of a particular offspring (first, second, etc.) is similar. Donz6 and Guerin have shown that the individual variation in the development time of the offspring is small and since over 90% of the mites are free from the brood food within 6 h after the cell is sealed (Ifantidis, 1988; Martin, 1994), the assumptions are valid. Only cells that contained one reproductive mother mite were analysed in this study, with the exception of cells which had been sealed for less than 20 h. Drone cells containing more than one reproductive mite will be considered elsewhere (S.J. Martin, in preparation). RESULTS The position and time of capping of 16 252 drone cells were recorded during 26-28 May, 17-19 June and 10-12 July. Of these, 5142 (32%) had been uncapped and their contents removed by the worker bees. The percentage of the sealed drone brood removed from the study combs were similar irrespective of the time of the study (May 33%, June 28% and July 34%) or whether the combs had being moved between colonies (29%) or remained in the original colony (32%). In this study drones emerged from 340 h (14 days 4 h) to 360 h (15 days) after the cells were sealed, which is normal fora. mellifera (15 days, Jay, 1963; 14 days, Dade, 1977). There was no correlation between the level of comb infestation and the number of

202 s.j. M~a~Tn~ sealed drone cells removed (r = 0.03, n = 27 combs). Of the remaining 10 783 cells, 2671 (25%) were infested with a total of 3455 mother mites. A total of 151 2 h and 39 8-12 h interval observations were made. Emergence from the brood food A total of 227 cells within 12 h of sealing and 297 recently sealed cells (0-16 hours post-capping [hpc], all infested with three or fewer mites were recorded. Table 1 shows that 16% of the mites in pre-sealed cells were free, hidden beneath the larvae but not in the brood food; after 8 h over 90% of the mites were free in drone cells. Reproductivity of the mother mite The reproductive status of the mother mites is given in Table 2 and indicates that a total of 67.8% of the mites produced potentially viable offspring (one or more mated female offspring). However, this value (67.8%) is an over-estimate since it does not consider the distribution of the data with respect to the development time of the bee brood. A more accurate result is obtained from Fig. 1 which takes this into account, giving a figure of approximately 55% for mites producing potentially viable offspring by the time the bee emerges. The normal category is defined as a family of mites whose development fits that expected for the age of the cell, as shown in Fig. 2. The percentage of non-reproducing mites, those laying non-viable eggs (Fig. 1) and dead mites all remained fairly constant throughout the development of the drone pupa. For the first time some of the mother mites were found to produce two viable (live) male offspring (n = 7). In two of these cases female offspring were also produced but died during the final moult. Development and mortality of the offspring The sequence of mite ontogenesis and development of each offspring (Fig. 2) is similar to that found in sealed worker brood (Martin, 1994) and the study of Donz6 and Guerin (see Table 3). A major difference was the most common (mode) TABLE 1 Timing of the Varroa emergence from the brood food in drone cells Time (h) after sealing of drone cell L*(--0) 0-2 2-4 4-6 6-8 8-10 10-12 12-14 14-16 Number of mites in the brood food 256 32 10 7 7 2 2 2 0 Number of mites out of the brood food 49 49 41 72 59 45 28 19 22 Percentage of mites out of the brood food 16 60 80 91 89 96 93 91 100 L*, cells containing larvae up to 12 h before sealing Cells with more than three mites were excluded.

ONTOGENESIS OF VARROA JACOBSONi 203 100._= 8O,..~ 60.,L g 4o e- 2O A. gls,a- -zk,~, ~- A,~ ~- -A- -~ ~NO VIABLE OFFSPRING 0,r 10 ~-... ~.".. ~ / ' ~ ; '. ~ N O N VIABLE EGGx, S - ~ " v -r "r NON REPRODUCING 50 90 130 170 210 250 290 330 370 Time after cell sealed (hours) Fig. 1. Changes in the frequency of reproduction type (Table 2) and viability of offspring produced by V. jacobsoni mother mites in relation to the development of the A. mellifera sealed drone brood. Mites were grouped into consecutive 20 h periods. TABLE 2 Reproductivity of I:. jacobsoni mother mites Time from cell sealing Reproduction of mites when measured 0ape) Number of mites % of mites Normal 0 1295 64 Abnormal With viable offspring 60 76 3.8 With no viable offspring 60 231 11.4 a Only single male offspring 120 199 9.8 Non-reproducing 50 67 3.3 Mite dead Trapped in cell wall 40 50 2.5 In cell 0 105 5.2 Seven per cent due to death of immature male

204 P l~,, o_ 2.,2 :2.~o E 2~ p s4 n.ae ~.tls E se,- i. 4o u.o~..m --'~ o-* t 2o P 2 o ;'4.~l r.17s n.188 ~:'. ~19 e ~e c) 7~ ^-me.-2e2 3oe *.'.L~ --'-,,, A... D., CO.OIIION OF MOTHIX MITE OEVELOPMENTI OAONE lee w* y,.........,~o ~io,;o ~io =~o =+o =i* =i. =io 3o0 310 3~o.0 T/MEIHOUR$) Fig. 2. Timing and duration of development of V. jacobsoni offspring in relation to the development of the sealed drone brood and condition of the mother mite. Mite condition (ventral side): A = concave (dead), B = flat, C = convex, D --- highly convex; a dotted line indicates the mites which laid five eggs. Mite: E = egg, P = protonymph, D = deutonymph, A = adult, (est.) = duration estimated not measured; the development time is given above the line with the sample size (n) given below, and the dotted line indicates the range. Bee: cs = cocoon spinning, sl = stretched larva, pw = pupa with white eyes, l x) = eyes pale, pp = eyes pink, pr = eyes purple, yt = thorax yellow, gp = wing pads grey, gt -- thorax grey, r = resting adult, e = bee emerges. number of offspring the mites produced in drone cells (six eggs) compared to worker ceils (five eggs) (Table 4). The mortality in the offspring of normally producing mother mites (those which lay five or six eggs) (Fig. 3) is considerably lower than that found in the sealed worker brood (Martin, 1994). Using the mortality data it is possible to calculate that a normal mother mite would produce, on average 3.9-4.1 adult female offspring (98% second offspring plus 93.5% third offspring plus 84% fourth offspring plus 76% fifth offspring plus 63-38% sixth offspring (the percentage varies for the last offspring depending on what percentage of the mothers lay six eggs, e.g. 38% = 0.63 0.61 since only 61% of mites produce six eggs; Table 4)). In order to determine the number of offspring produced by a mite in a drone cell accurately, a total of 429 singly infested ceils were sampled between 322 hpc and bee emergence. Normal mother mites produced a mean of 4.08 offspring which is similar to the figure gained from the mortality data. Sixty-two (14%) mother mites produced five healthy female adult offspring and another 35 (8%) mothers produced five female offspring but one or more died during the final moult (necrotic phenomena; Ifantidis, 1994). Ifanfidis (1984) found that only 3% of mites produced five female adult offspring. When the entire population is taken into account the mean number of viable female offspring per mother mite drops to 1.9 using

ONTOGENESIS OF VARROA JACOBSONI 205 TABLE 3 Developmental lime of the different stases of V. jacobsoni Development time (!1) Sex Egg number of egg Cell type Egg Protonymph Deutonymph Total Study 1 Male Drone 28 68 54 150 Worker 30 52 72 154 Both 29.9 62.5 63.2 155.6 2 Female Drone 28 40 68 136 Worker 22 32 76 130 Both 27.4 40 75.3 142.7 3 Female Drone 26 34 68 128 Worker 24 34 80 138 Both 26.8 40 74.8 141.6 4 Female Drone 22 36 76 134 Worker 22 26 86 134 Both 25.4 35.9 74.7 136 5 Female Drone 20 26 74 120 Worker 22 28 - - Both 24 36.5 - - 6 Female Drone 20 28 68 116 Worker.... Both.... This study Martin Donz~ and Guerin This study Martin Donz~ and Guerin This study Martin Donz~ and Guenn This study Martin Donz~ and Guerin This study Martin Donz~ and Guerin This study Martin Donz~ and Guenn our data set. Using the mortality data and percentage of mites producing normal offspring the entire population will produce 2.2 viable female offspring (four offspring 55%). DISCUSSION The mite starts to feed (start of reproductive cycle) immediately after it leaves the brood food (Donzd and Guerin, 1994) and not when the cell is sealed. Therefore it is important to determine when the mite is free from the brood food accurately, since this will be a source of variation if mites emerge from the brood food at greatly differing times. The time of 'release' of mites from the brood food in drone cells is similar to that found in worker cells (Ifantidis, 1988; Martin, 1994) which fits well with the observation that the bee larva feeds on the brood food for a period of 5 h after sealing before starting to spin its cocoon (Donz~ and Guerin, 1994).

206 Sj. ]vlm~3"]n 100 ~ 80 o 60 I.U O Z w 0 ~ 2o (1374) 1 (1191)]~ (1009) I (808) (508) lo ~ 29 39 49 59 6g ORDER OF OFFSPRING Fig. 3. Percentage of mortality incurred by each offspring during its development from normally reproducing V. jacobsoni mother mites. The sample size (dead and alive offspring) is given in brackets. Any mites which fail to emerge from the brood food may then become trapped in the cell between the cell wall and the cocoon and die. In this study this mortality accounts for 2.5% (Table 2) of all mother mites and was a major cause (32%) of death within the drone cell. Rath (1993) showed that contact with the brood food triggers an akinesis reaction in the mite within 30 s. It is possible that mites which do not recover from this reaction become entombed in the cell. Ifantidis' (1988) data showed that mite emergence was very prolonged (up to 20 h) in drone cells but no observations between 6 and 20 h were reported and it is unknown whether the remaining three trapped mites, in the 20 h group were already dead and so would become entombed in the cell. When the results of this and other recent studies (Donz6 and Guerin, 1994; Marlin, 1994) are compared (Table 3) a fairly consistent picture of mite development time emerges, regardless of whether the mite is reproducing in a worker or drone brood or whether the study has been carded out in the field or the laboratory. The' central position within the study hives of the experimental worker and drone cells were similar in both field studies so conditions (i.e. temperature and humidity) are assumed to be similar. This is slightly artificial in the case of drone cells, which are normally found on the edge of the combs where the temperature may be lower or fluctuating. The reason for the variation in the male offspring development times was caused by the difficulty of distinguishing accurately the end of the protonymph stases and the beginning of the deutonymph stases in the frozen material. The present developmental times are at the lowest end of the scale when compared with studies carried out over the past 25 years. This is primarily due to the improve-

ONTOGF_ffq~IS OF VARROA JACOBSONI 207 TABLE 4 Number and percentage of Varroa mites eggs laid in single infested A. mellifera sealed drone or worker cells Number of eggs laid 3 4 5 6 7 Source Drone ceils n 22 52 214 % 2.7 6.6 27.0 Worker cells n 4 12 104 % 3 9 79 Drone cells (%) 22.5 35.0 28.8 Worker cells (%) 28.9 36.2 33.7 482 23 This study 60.8 2.9 11 0 Calculted from Martin 8 0.0 11.2 2.5 Ifantidis (1984)* 1.2 0.0 * Data recalculated excluding mites producing one or two offspring. Only cells which had being sealed for more than 204 h and contained three or more eggs were used. The degree of swollenness of the mother mite was also as an indicator to when it had stopped egg laying. Data from Ifantidis's (1984) study has being included for comparison. TABLE 5 Time (minimum/mean/maximum) in hours, after the A. mellifera cell is sealed, when each V. jacobsoni egg is laid Egg number 1 2 3 4 5 6 7 Author 60/-/64 94/-/96 120/-/124 148/-/154 190/-/192 Ifantidis (33) (27) (29) (40) (1983) -Fill- -/88/-- -/118/- -/144/- -11781- Donz6 and (30) (28) (30) (26) (34) Guerin 50160164 90192/94 -/1181120-11441152 -/172/- Martin (32) (26) (26) (28) 52/60/64 84/88/96 114/118/122 144/146/152 170/178/180 194/202/206 -/222/- This study (28) (30) (28) (32) (24) (20) The interval between eggs is given in parentheses. ment of study techniques and reductions in the observation interval, culminating in the studies of Donz6 and Guerin, in which the development of individuals was observed. The developmental times recorded by Donz6 and Guerin are consistently slightly longer than the times found in this and the previous study (Martin, 1994). This may be due to the different experimental techniques.

208 s.j.u.~rn~ Table 5 compares the time when each egg was laid and reveals that the times of Donz6 and Guerin were delayed approximately 10 h in each case, since the intervals between ovipositions are similar in all studies (Table 5). However, the times when the drone bee undergoes its final larval moult are 104-106 hpc (this study) and 110 hpc (Ifantidis, 1984), which are considerably shorter than the time reported in the Donz6 and Guerin study (121 hpc) and could account for the 10 h delay shown in Table 5. Unlike mite offspring in worker cells, in drone cells they all have enough time to develop fully, in fact in many cells there was enough time for a seventh offspring to develop (Fig. 2). Although some mites (2.9%, Table 4) lay a seventh egg all these failed to develop into adults (Fig. 2). InA. cerana the developmental time for drones in sealed cells lies between 13.5 and 14.5 days (Tan et al., 1993; EA. Shah, personal communication) so it should be possible for the mite to produce up to five adult female offspring (see Fig. 2). Sasaki (1989) found that four to five adult female offspring were produced from singly infested A. cerana drone cells. Sometimes an extra egg is laid (Ifantidis, 1984) making the maximum number of eggs oviposited six in worker and seven in drone cells (Table 4) although the extra egg always fails to mature. Successful reproduction in the worker cells may be a quite recent occurrence for the mite since prior to the 1950s V.jacobsoni was only reported to be a parasite ofa. cerana (indica) (Smirnov, 1978), so it may be that the mite's reproductive behaviour is changing (reduction of egg numbers in worker cells and increase in egg numbers in drone cells) to cope with its new environment. Whether the different reproductive behaviour shown by the mites in worker and drone cells is due to genetic (mite) or environmental (bee) factors has yet to be determined. A comparison between worker and drone sealed brood shows that the levels of mite infertility (13.7% drone, 21.4% worker, Sulimanovic et al., 1982; 5% drone, 27% worker, Schulz, 1984; 3.5% drone, 18.7% worker, Ifantidis, 1984) and offspring mortality are consistently lower in drone cells (Fig. 3) than in worker cells (Martin, 1994). The pattern of offspring mortality is similar in both cell types with the second offspring showing the lowest level of mortality. However, in this study the number of dead mother mites in drone cells (Table 1) was higher (7.7%) than in worker cells (2%, Martin, 1994); the reasons for this are unclear. The number of adult female mite offspring produced in drone cells is fairly constant in several other studies (2.77, Ifantidis, 1984; 2.69, Schulz, 1984; 2.76, Fuchs and Langebach, 1989; 2-2.2, this study) despite these being carried out in several countries and with different races of A. mellifera. Furthermore, Rath (1993) showed that, on average, a mite in ana. cerana drone cell could produce 2.3 adult female offspring. This may be due to the fact that the biology of the mite is fairly consistent across the mite's range regardless of the host race or species.

ONTOGENESIS OF VARROA JACOBSONI 209 ACKNOWLEDGEMENTS I am grateful to J. van Breda for help with the field work and useful comments during the study, I. Fries of the Swedish University of Agricultural Sciences, Sweden and N. Milani of Udine University, Italy for reviewing the manuscript. This work was funded by the Horticulture and Potatoes Division of the Ministry of Agriculture, Fisheries and Food. REFERENCES Accorti, M. and Nannelli, R. 1990. [Oviposition sequence and developmental time of the progeny of Varroajacobsoni Oud. on drone brood ofapis meuifera ligustica Spin.] Apicoltura (Roma), 6:153-168 (in Italian). Allen, M.D. 1965. The effect of a plentiful supply of drone comb on colonies of honeybees. J. Apicult Res.,: 109-119. Boot, W.J., Calls, J.N.M. and Beetsma, J. 1992. Differential periods of Varroa mite invasion into worker and drone cells of honey bees. Exp. Appl. Acardol., 16: 295-301. Biichler, R., Drescher, W. and Tornier, I. 1992. Grooming behaviour ofapis cerana, Apis mellifera andapis dorsata and its effect on the parasitic mites Varroajacobsoni and Tropliaelaps clareae. Exp. Appl. Acarol., 16: 313-319. Dade, H.A. 1977. Anatomy and Dissection of the Honeybee. International Bee Research Association, London. De Jong, D. 1988. Varroajacobsoni does reproduce in worker cells ofapis cerana in South Korea. Apidologie, 19: 241-244. Donzt, G. and Guerin, M. 1994. Behavioural attributes and parental care of Varroa mites parasitizing honeybee brood. Behav. Ecol. Sociobiol., 34:305-319. Fries, I., Camazine, S. and Sneyd, J. 1994. Population dynamics of Varroajacobsoni: a model and a review. Bee World 75: 4-28. Fuchs, S. 1986. [Conditions when reproduction of Varroa in worker cells is advantageous. The relationship between mite reproduction, mite population size, numbers of worker cells and numbers of drone cells.] Apidologie, 17:368-371 (in German). Fuchs, S. 1990. Drone brood cell preference of Varroajacobsoni Oud. in colonies ofapil meuifera carnica. Apidologie, 21: 193-199. Fuchs, S. and Langebach, K. 1989. Multiple infestation of Apis mellifera L. brood cells and reproduction in Varroajacobsoni Oud. Apidologie, 20: 257-266. Ifantidis, M.D. 1983. Ontogenesis of the mite Varroa jacobsoni in worker and drone brood cells. J. Apicult. Res., 22: 200-206. Ifantidis, M.D. 1984. Parameters of the population dynamics of the Varroa mite on honeybees. J. Apicult. Res., 23: 227-233. Ifantidis, M.D. 1988. Some aspects of the process of Varroa jacobsoni mite entrance into honeybee (Apis meuifera) brood cells. Apidologie, 19: 387-396. Ifantidis, M.D. 1994. Factors influencing the population growth rate of the parasitic mite Varroa jacobsoni. In New perspectives on Varroa, A. Matheson (ed.). International Bee Research Association, Cardiff, UK. Jay, S.C. 1963. Colour changes in honeybee pupae. Bee World, 43:119-122. Koeniger, N., Koeniger, G. and Delfmado-Baker, M. 1983. Observations on mites of Asian honeybee species. Apidologie, 14: 197-204. Martin, S.J. 1994. Ontogenesis of the mite Varroajacobsoni Oud. in worker brood of the honeybee Apis meuifera L. under natural conditions. Exp. Appl. Acarol., 18: 87-100.

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