Breeding Bumble Bees

Journal of A picultural Research 5(3): 155 – 165 (1966)

REARING BUMBLE BEE COLONIES IN CAPTIVITY

R. C. Plowright AND S. C. Jay

Department of Entomology, University of Manitoba, Winnipeg, Canada

Manuscript received for publication 16th June 1966

SUMMARY

Three methods were used to induce the following Bombus species to start colonies in captivity: B. nevadensis, B. rufocinctus, B. borealis, B. fervidus, B. terricola, B. perplexus, B. ternarius, B. vagans. The first method, in which waxed-paper containers were used, was tried only on queens which had not hibernated; although it was unsuitable for rearing colonies, queens of B. rufocinctus, B. terricola, B. perplexus and B. ternarius laid eggs. The other two methods were used only on queens captured in the spring. Successful results were obtained for B. terricola and B. perplexus, and moderately successful results for B. rufocinctus, using upholsterer's cotton as nest material at room temperature. A method using no nest material, but maintaining the temperature at 29ºC., was successful for B. terricola and B. ternarius. No queens of B. fervidus laid eggs in any test but, of the small numbers of B. nevadensis, B. borealis and B. vagans queens tested, most reared colonies.

Practical details of rearing the colonies are discussed; the presentation of fresh pollen seems particularly important.

INTRODUCTION

There is much interest in conserving and augmenting wild populations of bumble bees (Bombus) for pollinatin,g (see review by Holm, 1966). Some workers (Sladen, 1912; Frison, 1927; Plath, 1923; Hasselrot, 1952; Valle, 1955; Holm, 1960; Zapletal, 1961) have attempted to culture colonies in the laboratory; others (e.g. Sladen, 1912; Frison, 1926; Fye & Medler, 1954; Hobbs, 1960, 1962) set out domiciles for use by overwintered queens in the field. If it can be performed on an economic scale, year-round laboratory culture appears to be the best long-term method for mass rearing. Not only can optimum conditions far colony growth be provided and attack by parasites and predators eliminated in the laboratory; the reproductive rate might be much increased by rearing several generations of colonies in the course of the year. Horber (1961) maintained a laboratory culture of B. hypnorum for five generations and showed that diapause is not obligatory for queens of ~this species. However, a number of biological problems (e.g. control of mating, ovary development, colony initiation, rate of oviposition) remain to be solved before large-scale production of all economically important Bombus species can successfully be undertaken. We have tried to induce the following North American bumble bees to found colonies in captivity in autumn 1964 and summer 1965: B. nevadensis Cresson, B. rufocinctus Cresson, B. borealis Kirby, B. fervidus (Fabrieius), B. terricola Kirby, B. perplexus Cressy, B. ternarius Say, B. vagans F. Smith. Because this was dane to provide colonies for experiment, rather than to study colony-founding as such, numerous modifications in technique were made as the work progressed, and controls were not always provided.

MATERIALS AND METHODS

Series I

Queens and males of B. fervidus, B. terricola, B. perplexus and B. ternarius were reared from colonies collected in the field in southern Manitoba during Augur 1964. Some were mated in cages in the laboratory and others in a greenhouse. Some queens of B. terricola, B. perplexus and B. ternarius became 'broody' after mating in the greenhouse, and built honey pots near pollen lumps, but none of the eggs they laid survived more than a few days. B. terricola queens also secreted wax in a laboratory mating cage. Most of the queens that did not become 'broody' were found torpid in piles of Sphagnum on their cage floor. Unfortunately, we did not distinguish torpid and 'broody' queens when colony-founding trials were started in mid-September.

B. rufocinctus queens and males were reared from colonies collected in the field,. but because the males were killed by workers unless removed from their colonies within a few days of emergence it was necessary to capture about 100 males in late August and early September in order to provide at least one male for each queen. Unlike B. terricola and B. ternarius, B. rufocinctus mated in small containers, and even in nest boxes exposed to light. So a much smaller mating cage (2 4 X 1 2 X 1 2 m.) was used for B. rufocinctus than for any other species. When the cage was dismantled in late September, all the surviving queens were torpid in piles of moss. They were stored at 5ºC. for four weeks before being placed in colony-founding containers. All the trials with B. rufo-cinctus were thus started two months later than for other species used in Series I, and it was possible to remedy some of the earlier defects; pollen was changed more frequently, and the rearing temperature was gradually increased to 29º.

Queens were put singly or in pairs in a container consisting of two waxed-paper cartons ($ pint, 0-3 1.), connected by a short tube and left at room temperature (ca 21º). A lump of pollen (about 0 75 g.), moistened with honey solution (equal volumes of honey and water) was put in one carton, which was covered to exclude light. The other carton contained a plastic vial-cap, filled with honey solution which was renewed daily.

Series lI

Queens of B. nevadensis, B. rufocinctus, B. borealis, B. fervidus, B. terricola, B. perplexus, B. ternarius and B. vagans were captured in the field in May and early June 1965, and were either (a) placed in nest boxes, or (b) stored over damp vermiculite at 1º until needed, or (c) confined at room temperature with access to food in a plas:tic cage (1-2 X 0 6 X 0 6 m.) if it was necessary to store them for periods not exceeding 24 hours.

Queens were installed singly or in pairs in a wooden container consisting of two boxes (7 5 X 7 5 X 5 am. internal dimensions) with glass roofs and corrugated-paper floors (Fig. 1) at 29º and 50% R.H. All boxes were kept in total darkness with minimal disturbance.

Honey solution was provided in glass gravity feeding tubes inserted through the wall of the outer box. By sterilizing the filled tubes in a pressure cooker it was found unnecessary to replace them more often than every third day.

pic

Fro. 1. Box used for Series II queens

P = pollen lump G = g!lass cover (cut away)

In early trials the pollen lump was placed in the inner box, but several queens built their egg cells directly on the cardboard floor of the outer box; in later experiments the pollen was put in the outer box, next to the feeding tube, so that the inner chamber was used only for defaecation.

The pollen lumps were renewed at least every three days, end more often if queens persistently fragmented their lumps.

In eight trials with single or paired queens of B. terricola and 11 trials with B. ternarius, the inner box contained cellulose wadding in which a central cavity confined the pollen lump.

From about three days after a queen had laid eggs, small pieces of pollen dough were introduced iso the nest box on alternate days; these were put as far away from the brood as possible so &at eggs cells were not built on them.

During the development of the first brood, some queens neglected larvae and/or tore down the wax envelope surrounding them. Although many of these rejected larvae were underweight for their instar, they appeared healthy; on seven occasions we either replaced such larvae in the original envelope or in a new one made of beeswax and pollen; they were always accepted by their mother, but were often neglected again later. We also transferred egg cells to pollen lumps in instances where they had been constructed elsewhere, but they were always destroyed or ignored alter introduction.

Following Frison (1927), an attempt was made to induce broodiness in ten queens of B. ternarius by confining them together in a cage with plenty of pollen and honey. After one week the eight survivors were installed singly in nest boxes, at the same time as a control series of eight queens brought in from the field immediately after capture.

Series 111

The queens were obtained and handled in the same way as in Series IL

Two wooden boxes (at ca 21º) were used for each bee; the larger (17 5 X 12 5 X 10 cm. iMernal dimensions) contained the feeding tube and was lined with corrugated cardboard and had a glass roof. The smaller chamber (7-5 x 7 5 X 5 cm. internal dimensions) was lined with upholsterer's cotton (Fig. 2). The sides and roof of the cavity thus formed were smeared with honey solution, to simulate

pic

the natural situation in which the nest material appears to act as a temporary food store. A pollen lump (about 0-75 g.) was placed in &e centre of the cavity.

Each queen was left undisturbed for the first three days after installation; the progress of her nesting activity could be assessed by the appearance and amount of faeces in the antechamber, since oviposition is always preceded by the production of large amounts of pollen-containing faeces. If no eggs had been laid by the third day, a new pollen lump was supplied, and the nest material changed. This process was repeated every third day until the queen had laid her first eggs. After this, pollen was supplied on alternate days in increasing quantities until the first workers emerged, when it became necessary to supply pollen every day. When giving pollen to brooding queens, care was taken not to obstruct her 'brooding-groove'. In ithe earlier trials of this series, pollen replenishment was undertaken only when the queen had left her nes~t to feed or defaecate, but it was found that this precaution was unnecessary. None of the 45 queens which laid eggs deserted her brood, although four died before the emergence of their first pupae; three of these broods were reared by foster-queens.

After the first or second group of workers had emerged, some boxes containing B. terricola and B. perplexus colonies were put out-of-doors, with the nest box placed inside the antechamber and the excess space filled with nest material. A wooden lid covered with polythene sheet was stapled on to provide a waterproof cover.

The remaining coilonies were kept within the laboratory to provide material for experiment. As these colonies became larger, the nest material was removed and the colonies were kept in darkness at 30º, to facilitate inspection and the addition of pollen.

Two colonies, one of B. perplexus and one of B. terricola, were connected to separate plastic cages (1-2 x 0-6 x 0 6 m.) in which petri dishes containing honey solution and wood-wool were placed. Apart from the slight saving in time gained when feeding honey solution, no advantage could be found in this method of housing the colonies, since by keeping the colonies in darkness much smaller containers can be used.

RESULTS AND DISCUSSION

The results are summarized in Table 1 (for detailed records see Plowright, 1966); the two B. terricola queens which were parasitized by nematodes are not included in this Table.

No queen of B. terricola, B. perplexus or B. ternarius which laid eggs in Series I succeeded in rearing her brood. However, two B. terricola and one B. ternarius eventually reared adults after being transferred to nest boxes containing cellulose wadding. Two of these queens produced only males, suggesting that they had not mated, or were no longer able to pass viable sperm.

Greater success was achieved with B. rufocinctus, but since the temperature was gradually raised during the experiment, the trials with this species are not comparable with those using B. terricola, B. perplexus and B. ternarius.

TABLE

Although no B. fervidus queen in Series I laid eggs, one became broody and constnxted an egg cell on the day before she died.

The data for B. ternarius in Series IIA„B, C, D were examined by analysis of variance, each queen (or pair of queens) being scored 1 or 0 aocording to whether or not she laid eggs within 21 days after installation:

Source of variance Number of queens per box Presence or absence of nest material Residual D.F. 1 1 24

*P(005

Estimated variance

1-0549*

0 2727

0 1947

161

Paired queens thus gave significantly hetter results than so.litary queens. Nest material had no significant effeat; but since four of the five pairs which oviposited in boxes containing nest material (Series IID) laid their eggs on the floor of the outcr compartment rather than within the nest material, ithe provision of nest material at 29º seems to have served no useful purpose.

The greater success obtained by confining B. ternarius queens in pairs does not necessarily imply that oviposition was stimulated by social interaction; the improved results may have arisen from the fact that in boxes containing pairs of queens, only the queens ithat oviposited first contributed data for statistical analysis. Thus when the 13 single bees in Series IIA> and IIB are arranged in 60 sets of six pairs obtained by drawing random combinations of the numbers 1 – 13, and the mean incidence of success for each set of six pairs is calculated (by scoring 1 for any pair including a queen that laid eggs during the 21-day period, and 0 for any pair in which neither queen oviposited), the mean of all 60 sets (0 759) is not significantly different from the mean (0 857) of the 14 pairs in Series IIC and IID, but it significantly exceeds (P ( 0 05) the mean (0 462) for the 13 single bees (Series IIA, IIB) from which the 60 pair combinations were taken.

The mean time intervals between installation and oviposition of the B. ternarius queens that laid eggs in series IEA, and IIA, were 7-0 and 32 5 days respectively (P ( 0 01), indicating that queens confined together in a cage for a week before installation in nest boxes were less ready to start colonies than queens put in nest boxes after capture in the field at the end of the one week period.

Of the queens in Series II which did not lay eggs within 21 days, three B. ternarius and six B. terricola were dissected; all except two B. terricola parasitized by nematodes had well developed ovaries, and in some it appeared that egg resorption bad occurred (see Medler, 1962). Four randomly selected unsuccessful B. terricola queens from the same series were transferred after 21 days to Series III boxes, where they laid eggs within five days; four controls which were left in their Series II boxes failed to start colonies during the Eve-day period and eventually died without ovipositing.

In each of 7 pairs of B. terricola and 12 pairs of B. ternarius which oviposiited in Series IIC and IID, one queen died within the 21-day test period. The mean time of death was 0 64 days after the first eggs were laid (S.E. = 0-88 days with 17 d.f.).

Comments on experimental methods

Though the use of waxed paper cartons at 21º was unfavourable for brood rearing, many queens of B. terricola, B. ternarius and B. rufocinctus in Series I laid eggs, suggesting that it will be feasible to obtain colonies of these species from queens that have not overwintered, by using improved techniques.

The wooden containers used in Series II were convenient for handling, and tihe corrugated-paper floor covering absorbed faeces well and was easy to renew. Since most of the queens used only the inner chamber for defaecation, in all but the earliest trials the pollen lump was placed near the feeding tube in the outer chamber.

However, some modification of the Series II design is required to prevent queens building their erst egg cells upon the floor. Those that did so usually built an excessive number of cells, with the result that the larvae in the earliest celh were neglected, or more larvae were produced than the queen could rear unaided. This led to the ejection of some or all of the larvae, unless the excess were removed by hand or one or two workers added fram another colony.

.On,the other hand, queens which had constructed their first egg cells upon the pollen lump rarely built more cells upon the fioor, though the addition of fur.ther pollen often stimulated renewed oviposition, unless the new pollen was placed at a distance from the original lump. So it seems that the covering of the pollen lump wiA egg cells, at least in B. terricola and B. ternarius, inhibits further egg laying. Some type of nest maMrial may thus be necessary, even at high temperatures, if only to ensure that queens build their first egg cells upon their pollen lumps rather than on the floors of their boxes; but cellulose wadding seems unsuitable for this purpose.

Attempts to save moribund first broods in Series II by adding workers. repairing tom larval clumps, transferring larvae and adding wax, were mostly very successful. We do not, however, consider that such delicate manipulations would be possible when dealing with large numbers of colonies, since a great deal of time is required to carry them out successfully.

The design of the Series III boxes is quite similar to that of Hasselrot (1952). However, Hasselrot (personal communication) states that with his method great care is required when adding fresh pollen or inspecting the progress of the brood, because the queen may otherwise desert her progeny. Though queens in Series III were frequently inspected while brooding eggs or young larvae, none deserted her brood; this may have been associated with the fact that the Series III nest chambers were much smaller than those Hasselrot used, though until more work has been done it is not possible to rule out interspecific differences. Smearing the nest material with honey appears to have a beneficial effect in inhibiting the tunnelling activi,ties of the queen, and in retarding the drying out of the pollen dough.

Other considerations

Failure of queen bumble bees to start vigorous colonies in oaptivity may

resuilt from:

(a) their failure to oviposit within the duration of the experiment

(b) long delay between confinemen:t and oviposition

(c) failure to rear the first brood

(d) abnormally early production of sexual forms.

It is only possible by dissection to ascertain whether failure resulted from lack of development of the queen's ovaries, or from lack of suitable stimuli for egg laying. Since dissection of the unparasitized queens that had failed to oviposit in Series II showed their ovaries to be well developed, and since the unsuccessful Series II queens quickly started colonies when transferred to Series III boxes, it seems that unsuitability of nest box design was the oause here. However, undeveloped ovaries were found in many queens of these two species which had not overwintered and which had failed to oviposit in Series II boxes (Plowright, 1966), even after long periods of confinement, and Medler (1962) recorded that 15 out af 32 queens of various species that were confined in laboratory boxes for more than 40 days contained only smal.l (0 – 1-5 mm.) eggs, i.e. their ovaries were comparatively undeveloped. It thus appears thai inadequate ovary development may be the major obstacle to colony founding in captivity in some circumstances, though there was no evidence for this in the overwintered queens tested in Series II and III.

Sladen (1912) and Free and Butler (1959) reported that oviposition occurred more often when several queens, or one queen and one (or more) workers, were confined together than when queens were in solitary confinement. However, Frison (1927) obtained a greater (though non-significant) incidence of colony founding in boxes containing single queens &an in boxes housing pairs of queens. Our results from B. ternarius suppart the observations of Sladen and Free, but there is no evidence that the greater incidence of oviposition in the Series II boxes containing pairs of queens resuks from anything other than a bias of data caused by including only the result from rthe first queen to oviposit within each pair. Further experiments are necessary to determine whether oviposition is stimulated or inhibited when B. ternarius queens are confined in pairs, but oviposi0on was delayed when ten B. ternarius queens were confined together in a cage for a week before being placed in nest boxes, at least in comparison with queens brought in from &e field at the end of the seven days. Possibly the latter bees were physio-logically more ready to start colonies than the caged group because of nutritional differences; alternatively, social effects amo.ng the caged queens, such as the establishment af 'dominance' (see Free, 1955) by one queen over her companions, may have inhibited ovary development in Ae non-dominant queens.

Sladen (1912) found that when pairs of queens were confined together, oae killed the other at about the time the first eggs were laid. Sl@den's resuilts are confirmed for B. terricola and B. ternarius, since the mean time of death for these queens in the pairs in Series II did not differ significantly from the time art which the first eggs were laid. However, in contrast to Sladen's finding, 14 out of the surviving 19 members of these pairs successfully reared aduits; other authors (e.g. Frison., 1927; Plath, 1923, 1934; Free & Butler, 1959) have found that the death of one queen does not always occur when two are confined together; in Series I, some of the pairs of B. rufocinctus queens coexisted until after the first workers emerged.

Free and Butler (1959) suggested that Hasselrot's (1952) success in getting colonies started in captivity might be due in part to the amount of insulation provided, since it had been shown that ovary development in worker bumble bees was accelerated by high temperatures. Although no attempt seems to have been made to compare the incidence of colony founding at high and low temperatures, Horber (1961) reported Cat though most of 24 queens of B. hypnorum (from which he attempted to get colonies) started building nests when they were exposed in an unheated greenhouse, real progress was observed only after the nests had been moved to a rearing cabinet where the temperature could be kept above 25º and later between 33º and 35º. However, Horber's results may not have been associated with ovary development.

The laying of eggs by queens in Series I was always preceded by a period of 'broodiness', during which the queen flattened herself over her pollen lump, or on the floor of the container, at the same time making rhythmic abdominal movements. Similar behaviour was observed in most of the Series II queens – and in all those of Series III that were inspected shortly before oviposition. Presumably this br~diness is amociated width heat production; it is not known whether it has any connection with the degree of ovary development.

In addition to lack of adequate fresh pollen, it is probable that chilling of eggs and young larvae contributed towards the failure of Series I queens to rear their brood. The use of a high temperature for starting Bombus colonies without nest material (whether or not it encourages oviposition) seems justified because it allows survival of eggs and 4rvae even when the queens fail to incubate them.

Most of the B. rufocinctus queens in Series I, which started colonies after long periods of confinement in nest boxes, produced small colonies which started to rear queens and males earlier than usual; similar results were obtained with other species in mme recent trials (Plowright, 1966; see also Sladen, 1912; Holm A Haas, 1961), so it appears that for the culture of vigorous colonies, from which it is intended to obtain a large worker population, iit is necessary that queens should be induced to oviposit as early as possible. However, promptness of egg laying cannot be the only factor involved, for in trials with artificially overwintered B. terricola queens (Plowright, 1966), all of which oviposited within ten days of confinement in nest boxes, all colonies produced males and/or queens in the first or second broods.

Provided that the success obtained in the Series III trials on overwintered B. terricola queens can be upheld in future years, and that the method proves suitable for the large-scale culture of B. borealis and other economically important species, there seems to be no reason why the culture of colonies in captivity from niaturally overwintered queens should not play an important part in providing stocks of bumble bees for pollination services. However, further research will probably be needed to develop effective methods for rearing vigorous colonies from queens that have been overwintered in captivity, or from queens that have not overwintered at all.

ACKNOWLEDGEMENTS

The authors thank Dr. J. B. Free (Rothamsted Experimental Station, England) for his helpful criticisms of the manuscript and Mr. L. P. Lefkovitch (Agricultural Research Council, Slough, England) for his assistance in analysing the data.

REFERENCES

Fame, J. B. (1955) The behaviour of egg-laying workers of bumblebee colonies. Br.I. Anlm

Behav. 3(4): 147-153

FREe, J. B. & BurLaR, C. G. (1959) Bumblebees. London: Collins

Frison, T. H. (1926) Experiments in attracting queen bumblebees to artificial domiciles.

l. econ. Ent. 19: 149 – 155

(1927) Experiments in rearing colonies of bumblebees (Bremidse) in artificial nests.

Biol. Bull. mar. biol. Lab., Woods Hole 52: 51 – 67

Fva, R. E. & Medler, J. T. (1954) Field domiciles for bumblebees. J. econ. Ent. 47(4):

672 – 676

Hasselrot, T. B. (1952) A new method for starting bumblebee colonies. Agron.l. 44(4):

218 – 219

– (1960) Studies on Swedish bumblebees (genus Bombus Latr.): their domestication and

biology. Opusc. end. Suppl. 17: 1-192

Hobbs, G. A., Virostek, J. F. & NUMMr, W. O. (1960) Establishment of Bombus spy.

(Hymenoptera: Apidae) in artificial domiciles in southern Alberta. Can. Ent. 92(11):

868 – 872

HoBBS, G. A., Nvw»r, W. O. & ViROSTEK, J. F. (1962) Managing colonies of bumble bees

(Hymenoptera: Apidae) for pollination purposes. Can. Ent. 94(11): 1121 – 1132

Holm, S. N. (1960) Experiments on the domestication of bumblebees (Bombus Latr.) in

particular B. lapidarius L. and B. terrestris L. Arsskr. K. Vet.-LandbohØjsk.: 1-19

– (1966) The utilization and management of bumble bees for red clover and alfalfa seed

production. A. Rev. Ent. 11: 155 – 182

Holm, S. N. & HAzs, H. (1961) Erfahrungen und Resultate dreijahriger Domestikations-

versuche mit Hummeln (Bombus Latr.). Albrecht-Thaer-rfrch. 5(4): 282 – 304

HoaseR, E. (1961) Beitrag zur Domestikation der Humrmeln. Vjschr. naturf. Ges. Ziirich

106: 424-447

Medler, J. T. (1962) Development and absorption of eggs in bumblebees (Hymenoptera:

Apidae). Can. Ent. 94(8): 825 – 833

Plath, O. E. (1923) Breeding experimen,ts width confined Bremus (Bombus) queens. Biol.

Bull. mar. biol. Lab., Woods Hole 45: 325 – 341

(1934) Bumblebees and their ways. New York: MacMillan.

Plowright, R. C. (1966) Domestication and caste differen,tiati6n in bumblebees. University

of Manitoba: Ph.D. Thesis

Sladen, F. W. L. (1912) The bumblebee, ih life history and how to damesticaM it. London;

MacMillan

VAr.r.a, O. (1955) Untersuchungen zur Sich@rung der Bestaubung van Rotkilee. Suom.

maatal. Seur Julk. 83: 205 – 220

Zur.arAr., F. (1961) Ueber die Domestikation der Hummeln. Arch. Gefliigelz. Zleintierk.

1(K4): 256 – 262