MITE VARROA JACOBSON/IN WORKER AND DRONE BROOD CELLS OYER DlFFERENT YEARS AND PRODUCTION SEASON

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1 PSZCZELNICZE ZESZYTY NAUKOWE Rok XXXVI 1992 MITE VARROA JACOBSON/IN WORKER AND DRONE BROOD CELLS OYER DlFFERENT YEARS AND PRODUCTION SEASON J a n i n a M u s z y ń s k a, Z o C i a K o n o p a c k a, Małgorzata Bieńkowska Institute or Pomology and Floriculture Division of Apiculture, Pulawy, Poland Summary The rollowing was found after surveying worker cells and drone cells in different development stages in the years 1985and 1986: l) Drone brood is preferred by V. jacobsoni to worker brood. However, the percentage or non reproducing females in the total number of females parasitizing drone brood may be higher. Conversely, the number of light-pigmented Icmales and deutonymphs per l progeny-beańng female as well as the number of eggs per l cocoon spinning drone larva may be lower. 2) The above indices relevant to the reproduction rate or the V. jacobsoni mite population may vat)' with years and over the production season. Keywords: bee diseases, varroatosis, mites, INTRODUcrlON The objective of this study was to contributc lo the current knowlcdgc on the factors rełevant to the reproduction of Varroa jacobsoni Oud. populations infesting the honey bee under the temperale climate conditions. The investigations were aimed al ascerlaining the timing of the V. jacobsoni females entering the open brood cells and starring egg-laying, An attempt was made to compare the degree of preference by the mite of the two types of brood - thc worker brood and the drone brood. Another aim was to compare the parameters essential to the reproduction rate of V. jacobsoni on workcr brood and dronc brood and to measure the reproduction rate on the worker brood over differenl dates of the production season. MATERIALAND METHODS The investigation were conducted in thc apiary of the Division of Apiculture in the years 1985 and Three groups of bee colonies were studied, each group be ing composed of 6 colonies ofthe cariolan hybrid bee placed in the Dadant type hives. Ali the brood-containing combs of group 1 colonies were laken out of thc hive every 6 wk. from mid-april lo early October for inspection, The brood of thc 3

2 colonies of the remaining groups was inspected from earły June to September on seven daten. Those were the trap combs containing worker brood (group 2) and drone brood (group 3) removed in accordance with the recommendations to eontrel the mite mechanically. The ceu inspection was carried out according to the method by I f a n t i d i s (1984). A method development by the authors was used to pick out the cells to be inspected. Care was taken to select cells representative of those present in a givcn comb and a given colony as combs and even the brood of different age the same sealed comb may vary considerably for the degree of mite infestation F u c h s (1986 a,b). Two screening procedures were adopted. One involved all cells along the four diameters dividing the brood area into eigh~ parts, and in the other au cells were screened that lay within four equidistant circles placed parallei to the extreme edge of the brood area. Either procedure was used on different combs but for the same c.olonies and dates. Atotal of worker brood cells and drone.brood cells were screened. The investigated cells comparised all worker bee and drone stages from the uncapped larva to the adult bee emerging from the celi. The percentage of infestation was calculated for cells containing a defined developmental stage of either a worker or a dr one. The reproduction rate of the v. jacobsoni population was based on the screening of cells containing white-bodied, dark-eyed and older pupae I f a n t i d i s (1984). Distinctly dark-coloured females found in the cells were assumed to be the parental females. Light-coloured females were assumed to be the offspring of the females as were au the other devełopmental stages of V. jacobsoni females and the males. Obviously, such an assumption is a simplification and involves a certain error. However, it was used throughout the study due to technical considerations. The foliowing parameters were taken into account to study the reproduction rate of v. jacobsoni in the investigated colonies: 1. Percentage of femalcs without offspring in the total number of dark-bodied females. As having no offspring were assumed dark-bodied females found alone in cells containing no other stage of the mite. 2. Total number of offspring per 1 progeny-producing female. It was determined by rełating all mite growth stages found in the cells as well as lightcoloured females to the totalnumber of dark females present in the cells. 3. Number of deutonymphs and light-coloured. females per progeny-producing female. 4. Percentage of males in the offspring expressed as the average number of males per 1 progeny-producing female. The relationship between the inspection date on one hand and the infestation rat e and v. jacobsoni reproduction rate on the other wcre dcterrnined oniy for worker brood since it is only that type of brood that is present in the colony throughout the whole active season. Drone and worker bee growth stages in unsealed cells were classified based on its size estimates and positioning within the celi as well as by observing the degree of celi capping. As being hrs. of age were considered łarvae that łay at the bottom of the celi and did not fili it up compłeteły whereas larvae ołder than 120 hrs. did occupied the entire celi. Where appropriate the results were subjected lo the anałysis of variance and tested for significiant differences by means of Duncan test. 4

3 RESULTS Open brood and lis altraction for V. jacobsoni females. The investigations revealed that under the experiment conditions V. [acobsoni females do not get on worker larvae that are 95 hrs. old or younger. There was a single case of V. jacobsoni females invading hrs. old drone brood. However, they were frequently found in open brood cclls with both workcrs and droncs that werc more than 120 hrs. of age (Table l).. Table l InCestation diccerent stage of honeybee brood cetls by Varroa jacobsoni in relation to the age of the larvae (years 1985 and 1986, ) Porażenie różnych stadiów rozwojowych czerwiu przez samice Varroa jacobsoni (lata 1985 i 1986, ) Type ocbrood Typ czerwiu worker pszczeli Ageofbrood Numberof Infested cells cells Komórek porażonych with brood Stadium rozwojowe Liczba number percent czerwiu komórek liczba procent z czerwiem h larvae 384 O godz. larwy > 120 h larvae ,96 larwy > 120 godzinne stretched larvae ll ,ll larwy przędzące cappęd brood ,72 czerw kryty drone trutowy h la rvae 153 0, godz. larwy > 120 h larvae ,89 larwy> 120 godzinne stretched larvae ,96 larwy przedzące cappcd brood ,36 czerw kryty' -light-bodied and dark - eyed pupae and older one poczwarki z ciemnymi oczami i starsze A newly capped drone brood was found to be 1.3times more infested than newly capped worker brood (Table 1). The differences were more pronounced for both lypes being present on the same comb (Table 2). 5

4 Table 2 Relation between type oc romb and Varroa tnfestation rate ocworker and drone brood Poraienie rotnych stadiów rozwojowych pszczoły robotnicy i trutnia przez samice Varroa jacobsoni w związku z typem plastra Type oc broodffyp czerwiu Type worker/pszczeli ofcomb Ageofbrood drene/trutowy number infesta- number infesta- Typ Stadium rozwo- of eells tion(%) of cells tion(%) plastra jowe czerwiu with brood with brood liczba ko- poraże- liczba ko- porażemórekz nie(%) mórekz nie(%) czerwiem czerwiem drone h larvae O O trutowy godz. larwa > 120 h larvae 4 O 641 5,30 larwy > 120 godz. stretched larvae 280 5, ,47 larwy przędzące cappęd brood 832 4, ,00 czeiw kryty worker h larvae 20 O O O pszczeli godz.larwa > 120 h larvae 852 0, ,56 larwy > 120 godz. stretched larvae 9S45 2, ,29 larwy przędzące cappęd brood , ,89 czeiw kryty - light bodies and dark-eyed pupae and older one poczwarki z ciemnymi oczami i starsze In the sealed cells containing stretched larvae living mite eggs were found alongside the v. jacoosoni females (Table 3). There was an average of 0,12 eggs per 1 dark-coloured female in the worker larva-containing cells and 0,07 eggs in the drone brood cells i.e. nearly half that amount, 6

5 Table3 Number of Varroa jacobsoni Iemales and eggs on different steges of worker and drone brood (years 1985 and 1986, ) Liczba jaj i samic Varroa jacobsoni na różnych stadiach rozwojowych czerwiu pszczelego i trutowego (lata 1985 i 1986, ) Type Numberof Numberof Number ofbrood Age ofbrood Infested females pigmented ofeggs cells dark light Typ Stadium Liczba ko- Liczba samic Liczba czerwiu rozwojowe mórekpo- ciem- jas- jaj rażonych nych nych worker h larvae O pszczeli larwy godz. > 120 h larvae O larwy > 120 godz. stretched larvae larwy p~dzące drone h larvae O O trutowy larwy godz. > 120 h larvae O O larwy > 120 godz. stretched larvae larwy przędzące Relatłonship between observation date and the occurrence of V. jacobsoni females on the early and late stages of the worker bee. There was a relationship between the observation date and the degree of infestation of the worker brood by V. jacobsoni. In both years the highest brood infestation was found on the last (Sept. 30) and the first (April 16) date. The differences between the last dat e and the remaining ones were statistically valid. On each date larvae of more than 120 hrs. of age were distinctly less infested than the stretched (Table 4). On each date V. jacobsoni females were found in the brood cells from 0,5 to 23 hrs. prior to capping. Interestingly, light-coloured females were occasionally found there alongside the dark-coloured ones. On Cheother hand, the presence of light-coloured females in the cells containing stretched larvae were more frequent. The females infesting the open brood were found to be able to lay eggs even before the cells were capped. An egg was found in l worker larva-containing celi aged more than 120 hrs. out of 21 infested cells (Tab le 5). In stretched larvae containing cells the eggs were not infrequent and were found on any date. Most of them were found on the last as well as on the first date (Table 5). 7

6 Table 4 Relation between date of examination and infestation rate of younger and oldest worker bee brood Zależność mi~dzy terminem badań a porażeniem przez Varroa jacobsoni wczesnych i ostatnich stadiów rozwojowych pszczoły robotnicy Ageofbrood Stadium rozwojowe pszczoły > 120 h larvae stretched larvae cappęd brood larwa > 120 godz. larwa przędząca czerw kiyty Date Year Termin Rok number infesta- number infesta- number infestaofcells tion(%) of cells tion(%) ofcells tion(%) with with with brood brood brood liczba komórek liczba komórek liczba komórek komórek porażo- komórek porażo- komórek porażez czer- nych(%) z czer- nych(%) z ezer- nych(%) wiem wiem wiem , , , , , , O , , , , , , , , , , , , , , , , , , , , , , ,38 -Iight-bodies and dark-eyed pupae and older one poczwarki z ciemnymi oczami i starsze 8

7 Table5 Relation between date or examination and mean number females and eggs or V. jacobsoni per one infested worker bee brood (I group or colonies) Zależoośt mi~dzy terminem badań a obecnością samic i jaj V. jacobsoni w przeliczeniu na jedną komórk~ porażoną (czerw pszczeli, 1grupa rodzin) Ageof brood Stadium Date Termin Per one infested brood celi number of: Na jedną porażoną komórkę, liczba: darkbodied light bodied eggs females females samic ciemnych samic jasnych jaj >120h larvae > 120godz larwa ,09 1,0 1,0 O O O O 1,0 1,3 O O O O 1,0 1,0 O O O O 1,2 1,0 0,1 O O O 1,4 1,0 O O 0,2 O Stretched larvae Larwa 4.07 prz.~dząca ,11 1,36 0,08 0,22 0,07 0,19 0,92 1,02 0,22 0,15 0,11 0,16 0,98 1,05 0,29 0,78 0,Q1 0,01 1,03 1,23 0,94 0,13 0,03 0,03 1,85 1,80 0,24 0,37 0,60 0,17 The rates ocreproduction of V. jacobsoni on worker and dronebrood. The rates of reproduction were compared in the period of the intensive rearing of drone brood by bee colonies. Worker and drone brood were found to show similar values for most studied characters (Tabłe 6). It is onły the percentage of progeny-łess femałes in the popułation of parentał femałes that was higher in drone brood cells. 9

8 Table6 Reproduction rate ocv. jacobsoni on worker and drone brood (II and III group of colonies) Dynamika rozrodczości V. jacobsoni na czerwiu pszczelim i trutowym (rodziny II i III grupy) Feature Year Brood Average Range Cecha Rok Czerw Średnie Przedzial Non-reproducing 1985 wórker-pszczeli 13,43 6,65-16,29 females in parental drone-trutowy 37,51 11,26-82,83 generation (%) Samice bez potomstwa 1986 worker-pszczeli 18,43 6,93-29,53 (%) w ogólnej licz- d rone-trutowy 21,29 0,00-71,00 bie samic ciemnych Total number oc 19&5 worker-pszczeli 2,46 2,40-2,50 progeny per one drone-trutowy 2,30 2,20-2,40 reproducing Cemale Ogólna liczba potomstwa/jedną sarnicę wydającą potomstwo 1986 wórker-pszczeli 2,60 1,90-3,30 drone-trutowy 2,00 1,80-2,50 Number of light worker-pszczeli 1,50 1,40-1,50 -bodied Iemales and drone-trutowy 1,30 1,10-1,70 deutonymphs per one reproducing fernale 1986 worker-pszczeli 1,96 1,20-2,40 Liczba samic jasnych drone-trutowy 1,25 0,30-2,20 i deulonimc/l sarnicę wydającą potomstwo Number oc males in 1985 werker-pszczeli 0,70 0,60-0,80 progeny per one drene-trutowy 0,50 0,40-0,60 reproducing Cemale Liczba samców/l sa worker-pszczeli 0,40 0,20-0,60 micę wydającą drone-trutowy 0,50 0,20-0,60 potomstwo Year and date of study versus population dynamics of V. jacobsoni on worker brood. The study showed that any of the indices relevant to the reproduction rate of V.jacobsoni may vary considerably with date and year of the study (Table 7)_ 10

9 Table7 Relation between date of examination and reproductive rate of Varroa jacobsoni on wórker brood (I group of colonies) Zależność między rozrodczością roztocza Varroa jacobsoni na czerwiu pszczelim a okresem sezonu produkcyjnego (I grupa rodzin) Fcature Year Dale, Termin Cecha Rok Non-reproducing fe ,1 ab 6,5 ab 0,3 a 6,5 ab 13,4b males(%) in parental generation ,4 a 4,4 a 3,4 a 5,9 a 6,2 a Samice bez potomstwa (%) w ogólnej liczbie samic ciemnych Total number of progeny ,3 a 2,8 a 2,3 a 2,3a 2,6 a per one reproducing female ,3 a 3,1 c 2,6 abc 2,9bc 2,5 ab Ogólna liczba potomstwa /jedną samicę wydającą potomstwo Number of light-bodied ,9 a 1,4 a 1,2 a 1,2 a 1,6 a females and deutonymphs per one reproducing ,2a 2,1 b 1,8 b 2,1 b 1,7 b remale Liczba samic jasnych i deutonimf/i samicę wydającą potomstwo Number of males in ,7 a 0,9 a O,7a O,7a 0,7 a progeny per one reproducing female ,8 b O,7ab 0,5 a O,7ab O,7ab Liczba samców/l samicę wydającą potomstwo DISCUSSION In this study the number of screened cclls was much higher than that reported by other investigators D e J o n g (1981), R o s e n kra n z (1985), F u c h s (1986 a), R o m a n i u k et al. (1988). Presumably, this was the reason for finding a V. jacobsoni female infesting a less than 120 hrs. old larva under apiary conditions and for the frequent finds of the mite parasitizing larvae (Tabies 1, 2, 3). To dale V. jacobsoni females have not been thought to be able to parasitize such early devclopment stages of the bee. However, the dale by F u c h s et M u e II e r (1986) do point to such a possibility, The investigators report than even in -heavily infested colonies cells containing al least four days old larvae are mite-iree. According lo data by I f a n t i d i s (1988) and B o o t et C a I i s (1990) V. jacobsoni females start to enter worker brood cells twenty hours and drone brood cells forty hours before capping. However, most V. jacobsoni females invade the cells a few hours before capping. While trying to account for the fact that the mites enter cells containing relatively young hrs. old larvae one should consider a unique 11

10 attraction to the mite of either the larvae or the cells they are in. /D e J o n g (1981), D e R u i j t e r et C a li s (1988), Kra u s (1990)/. A widely accepted notion by l f a n t i d i s (1984) is that V. jacobsoni females lay their first egg only 60 to 64 hrs. after cell sealing Le. after the developing larva has turned into a white-eyed pupa. However, M o o s b e c k h o f e r et al. (1988) found eggs in 30% of infested larvae and prepupae evaluated jointly. Our results are in agreement with those data. lt is not quite elear why some of the females occasionally speed up egg laying. lt may spring from physiological variation witbing the parental females or a similar variation within the worker brood. This is suggested by the results of H a e n e l (1983) and M il a n i et C h i e s a (1990). If females start laying eggs as soon as the stretched larva stage but terminate oviposition at the same time as the remaining ones the oviposition on the Iight-eyed pupa should lead to an increase in mite reproduction rate. The validity of this view seems to be borne out by the data obtained by M o o s b e c k h o f e r et al. (1988). The data from this study substantiate earlier elaims of drone brood being more appealing to V. jacobsoni mites than worker brood T e war s o n (1983) after C a m a z i n e (1986), F u c h s (1986), W o y k e (1987), R o m a n i u k et al. (1988), I f a n t i d i s (1988). The results from this study are in agreemenl with those by I f a n t i d i s (1988) who found several females in a drone brood cell more frequently than in a worker brood celi. Even thought drone brood is preferred by Varroa females this study has shown the number of non-reprodueing females in drone eells to be higher than in the worker cells. Likewise, the number of older development stages (deutonymphs and light-eolored females) per one fertile femalr "\;IS in this study slightly lower on drone brood than on worker brood (Tab le 6). In addition, mile eggs were found less frequently on stretched drone larvae (Tab le 3) cases of accelerated oviposition by the mite being less frequent there. There is a remarkable variation of that trait within the studied colonies (Tab le 6). There being no differences for the remaining traits (Tab le 6) it is reasonable to suppose that the reproduction rate of V. jacobsoni on drone brood may, under ceralin circumstances, be lower than that on worker brood. In this study the faet ean be explaincd by the more frequent presenec of parenlal females per l drone brood eeu.as wasiound by M o o s b e c k h o f e r et al. (1988) number of progeny per l female decreases with an inerease in the number of mites per cell. The results from this study give evidenee than in V. jacobsolli-heavily infested colonies drone brood may not onły protect worker brood against the mites but it can also have a restrictive effect on their reproduction ratc in the cołony. Those results eonfirm the view by F u c h s (1986 a) that at low infestation drone brood enhances the reproduction rate of the V. jacobsoni population whereas at high infestation it brings it down. The data from this study show thata number of parameters essential to V. jacobsoni reproduction rate may vary with scason. It conforms with the data by other investigators K u I i n c e v i c et al. (1988). Those changes do not occur in all years (Tabłe 7). The variation of the traits over dates and years accounts for the considerable discrepancies in the results obtained by different rescarchers in different years and season. It also partly expłains why in cołonies with similar initial infestation rates the infestation differs widely towards the end of the season. 12

11 The results point lo the contribution of worker brood at the end of the active season to the development rate by the mite. It should be emphasized that this is the period of the heaviest infestalion (Table 4) which necessarily affecls the quality of bees from that brood D e J o n g, G o n c a Iv e s (1982), G l i ń s k i, Jar o s z (1984). REFERENCES B o o t W., C a I i s J. (1990) - Invasion of Varroa mites in honeybee brood cells. Observating of Varroa mite behaviour. Programme and Abstraets Symposium Bee. Pathology, Gent., Belgiurn A.24. C a m a z i n e S. (1986) - Differential reproductions of the mite Varroa jacobsoni (Mesostigmata, Varroaidae) on Arrieanized and European Boney Bces (1Iymenoptera: Apidae). Ann.Ent.Soc.Am. 79: F u c h s S. (1986 a) - Conditions when reproduction of Varroa in worker eells is advantageous. The relationship between mite reproduetion, mite population size, numbers of worker cells and numbers or drone eells. Apidologie 17(4): F u c h s S. (1986 b) - The distribution of Varroa jacobsoni on honeybee brood eombs and within brood eells as a eonsequence of fluetuation infestation rates. Proceedings of Meeting of the EC Expert's Group/Bad Homburg, October. F u c h s S., M u e II e r K. (1986) - Invasion of honeybee brood cells by Varroa jacobsoni in relation to the age ot the larvae. Proceedings of Meeting of the EC Expert's-Groap/Bad Homburg, October. G I i Ił s k i z., Jar o s z J. (1984) - Alterations in haemolymph proteins or drone honey bee larvae parasitized by Varroa jacobsoni. Apidologie 15(3): H a e n e I H. (1983) - Effect of HJ III on the reproduction of Varroa jacobsoni. Apidologie 14(2): I r a n t i d i s M. (1984) - Parameters of the populatlon dynamics of the t Varroa mile on honeybees. J.Apic.Res.23(4): I r a n t i d i s M. (1988) - Some aspects of the process Varroa jacobsoni mile entrance into honey bee (Apis metlifera) brood cells. Apidologie 19(4): D e J o n g D. (1981) - Effect of queen celi construction on the rate of invasion of honeybee brood cells by Varroa jacobsoni. J.Apic.Res. 20(4): D e J o n g P., G o n c a I v e s L. (1982) - Weight loos and other damage to developing worker honey bees Crom infestation with Varroa jacobsoni. J.Apic.Res. 21(3): Kra u s B. (1990) - Etheral oils interfere with orientation of Varroa jacobsoni. Programme and Abstracts, Symposium Bee Pat hol. Gent., Belgiurn A3I. K u I i n c e v i c J., R i n d e re r T., U r o s e v i c D. (1988) - Sesonality and colony variatlen of reproducing and non-reproducing Varroa jacobsoni females in western honey bee (Api s mellifera). Worker brood. Apidologie 20(2): M i I a n i N., C h i e s a F. (1990) - Some srimuli including oviposition in Varroa jacobsoni Oud. Bee Pathol, Gent., Belgiurn AIS. M o o s b e c k h o C e r M., F a b s i c z M., K o h I i c h A. (1988) - Untersuchungen uber die Abhangigkeil der Nachkommensrale von Varroa jacobsoni Oud, vom Befallsgrad der Bienenvoelker. Apidologie 19(2): R o m a n i u k K., B o b r z e c k i J., N o w a k Z. (1988) - Rozwój warrozy na czerwiu pszczelim i trutowym. Acta Acad. Agricult. Techn. Olst. Veterinaria 17: R o s e n kra n z P. (1985) - Temperaturpraferenz von Varroa jacobsoni und Verteilung des Parasiten im Brutnest von Apis metlifera. Apidologie 16(3): D e R u i j t e r A, C a I i s J. (1988) - Distribulion of Varroa jacobsoni female mites in honey bee worker brood cells of normal and manipulated depth (Acarina: Varroidae). Entomol.Gener, 14(2): W o y k e J. (1987) - Comparative population dynamies of Tropilaelaps clareae and Varroa jacobsoni mites on honeybees. J.Apic.Res. 26(3):

12 ROZTOCZ VARROA JACODSONI Oud. NA CZERWIU PSZCZELIM I TRUTOWYM W RÓŻNYCH LATACH I PORACH SEZONU PRODUKCYJNEGO J a n i n a M u s z y ri ska. Z o r i a K o n o p a c k a, Małgorzata Bierikowska Streszczenie Badania prowadzono w latach 1985 i 1986 w pasiece Oddziału Pszczelnictwa w Puławach w trzech grupach rodzin pszczełich (po sześć w każdej grupie) osadzonych w ulach typu dadanta, z pszczołą mieszańcem rasy krairiskiej. W okresie od polowy kwietnia do połowy października, z rodzin grupy pierwszej co około sześć tygodni, wyjmowano na kiłka godzin wszystkie plastry dla dokonania lustracji komórek. W rodzinach grupy II i III lustrację plastrów pułapek prowadzono w okresie od początku czerwca do początku sierpnia", Był to czerw pszczeli (grupa II) i C7.erw trutowy (grupa III). W czasie lustracji postępowano w sposób opisany przez I r a n t i d i s a (1984), a wyboru komórek dokonywano metodą własną, dążąc do tego, by były one reprezentatywne dla wszystkich znajdujących się na danym plastrze a także wszystkich obecnych w gnieździe. Łącznie wobu latach zbadano około 140 tysięcy kommorek z czerwiem pszczelim i około 50 tysięcy komórek z czerwiem trutowym, w których obecne były wszystkie stadia rozwojowe pszczoły robotnicy i trutnia. Ocenę czynników istotnych dla rozrodczości populacji V. jacobsoni oparto za I r a n t i d i s e m (1984) na wynikach lustracji komórek z" poczwarkami o ciemnych oczach i starszych, Przyjęto, że znajdowane w komórkach samice V. jacobsoni o wyraźnie ciemnym ubarwieniu są samicami założycielkami. Jasne uznano za potomstwo samic ciemnych podobnie jak i samce oraz stadia rozwojowe pasożyta. Oceniano następujące wskaźniki istotne dla rozrodczości: l. Udział samic bez potomstwa (z komórek bez żadnych stadiów rozwojowych) w ogólnej liczbie samic ciemnych 2. Ogólną liczbę potomstwa przypadającą na jedną sarnicę wydającą potomstwo 3. Liczb~ samic jasnych i deutonimf przypadającą na jedną sarnicę wydającą potomstwo 4, Liczb~ samców przypadających na jedną sarnicę z potomstwem. Liczba komórek lustrowanych w niniejszych badaniach znacznie przewyższała liczbę sprawdzanych przez innych autorów. Należy przyjąć, że właśnie to stało się przyczyną stwierdzenia w warunkach pasiecznych samicy V. jacobsoni na trutowej larwie godzinnej, a także częstej obecności jaj tego pasożyta na larwach przędzących (rab. 1,2,3) już w kilkanaściegodzin po zakryciu komórki, a nie jak zwykło się przyjmować dopiero po 60 godzinach. Wyniki niniejszej pracy potwierdzają wypowiadaną wcześniej opinię na temat większej niż czerwiu pszczelego atrakcyjności czerwiu trutowego dla roztocza. Stwierdzono to zarówno wtedy, gdy czerw obu typów znajdował się na odrębnych plastrach jak i wtedy, gdy był na tym samym plastrze (Tab. 1 i 2). Równocześnie jednak chociaż czerw trutowy byl dla pasożyta bardziej atrakcyjny, to właśnie na tym czerwiu stwierdzono więcej samic bezpotomnych, a liczba starszych stadiów rozwojowych przypadających na Jedną samicę z potomstwem była niższa (Tab, 6) podobnie jak liczba jaj na trutowych larwach przędząeych. Przy braku różnic między pozostałymi cechami (Tab. 6) istnieją podstawy by przypuszczać, że rozrodczość V. jacobsoni na czerwiu trutowym" może w pewnych okolicznościach być niższa niż na czerwiu pszczelim. Należy przyjąć za F u c h s e m (1986), że czerw trutowy w warunkach silnego porażenia rodzin obniża rozrodczość populacji V. jacobsoni. Dane przedstawione w niniejszej pracy świadczą o tym, że szereg parametrów istotnych dla dynamiki rozrodczości może, choć nie we wszystkich latach, ulegać w czasie sezonu produkcyjnego zmianom (rab. 7), Stwierdzone zróżnicowanie terminów i lat pod względem omawianych parametrów wyjaśnia występujące niekiedy znaczne rozbieżności między wynikami uzyskanymi przez poszczególnych autorów. Wyjaśnia także w pewnym stopniu obserwowane niejednokrotnie pod koniec sezonu znaczne zróżnicowanie nasilenia warrozyw rodzinach o podobnym porażeniu początkowym. 14