some work at rothamsted on the social behaviour of honeybees

Some Work at Rothamsted on the Social Behaviour of HoneybeesAuthor(s): C. G. ButlerSource: Proceedings of the Royal Society of London. Series B, Biological Sciences, Vol. 147, No.928 (Dec. 3, 1957), pp. 275-288Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/83180 .

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Some work at Rothamsted on the social behaviour of honeybees

BY C. G. BUTLER

(Lecture delivered 6 June 1957-Received 18 June 1957)

I am very grateful for this opportunity to discuss some of the work that has been carried out in the Bee Research Department at Rothamsted in recent years.

The department is a small one, with a scientific staff of eight, and we are concerned with three main lines of research. First, with work on insect pollination of crops, which involves investigation of such problems as: bee/flower relationships; the foraging behaviour of individual bees, including solitary bees and bumblebees as well as honeybees; the influence of physical and biological factors of the environ- ment on bee activity; and communication between honeybees and their recruit- ment to particular crops. Secondly, with problems of practical beekeeping other than disease, problems such as: colony management; bee breeding; queen rearing and introduction; swarming, etc. And, thirdly, with the control of diseases both of the larval and adult honeybee: diseases which are caused by bacteria, protozoa, mites, fungi, and, in one case at least, by a virus. This latter part of the department's work is, of course, rather different from the rest and is carried out by Dr L. Bailey and his assistants, who are obtaining some very interesting and useful results.

It has become increasingly clear in recent years that little real progress is likely to be made in solving the practical problems of pollination and of beekeeping until far more is known about the fundamentals of bee physiology and behaviour, and of colony organization. The research of the department has, therefore, apart from work on bee diseases and on the poisoning of bees by agricultural sprays, been largely concerned with investigation of the way in which the social life of a honeybee community is organized, and of the behaviour, both in the hive and in the field, of the individuals of which it is composed.

Since the work covers a wide field I propose only to discuss that part of it which is concerned with the organization of the honeybee colony and the social behaviour of its members.

Unlike the great majority of insects the honeybee, in common with other social animals, is attracted by other members of its species. This is true both of worker and of queen honeybees (I know of few data concerning drones) and it has no sexual significance.

Although a worker honeybee can survive for 2 or 3 weeks in isolation, provided that conditions are favourable-for instance, in a properly equipped cage in the laboratory-no individual bee will do so from choice, and should a bee fail to find her own colony on returning from the field she will attempt to join any group, any cluster, of bees she comes across, whether or not a queen is associated with them.

This attraction of a group of worker bees, without a queen, for an individual

Vol. 147. B. (3 December I957) [ 275 ] I8



worker bee was first studied in France by Lecomte (I950), who found that a number of lightly anaesthetized worker bees scattered in a small box in the dark

would, on recovering consciousness, eventually form a single group or cluster. This occurred at any temperature between 15 to 30? C, provided that sufficient bees were present. He found that clustering took place when he used 100 or more bees, but only occurred in about half the experiments in which he used about 50 bees, and that when he used smaller numbers still the bees remained dispersed or only formed small, temporary groups, each of which contained no more than three or four individuals.

Very similar results were obtained at Rothamsted by Free & Butler (1955) when

they repeated these experiments, and they were led to agree with Lecomte's conclusion that until a certain number, probably about fifty, of the scattered worker bees had come together on some convenient support which had attracted

them-such, for example, as an empty wire-gauze cage-the cluster formed failed to produce sufficiently powerful stimuli either to keep the bees of which it was

composed at any given moment together, or to attract other bees to join it. Lecomte also concluded that part of the attractive stimulus exerted by an established cluster of bees is olfactory and comes from the abdomens of its

members, and that another part is vibratory and caused by the movements of the bees themselves. He did not, however, mention the abdominal scent-producing organ, the Nassanoff gland, of the worker bee in connexion with this olfactory stimulus, and failed to demonstrate that either an olfactory or a vibratory stimulus is, by itself, sufficient to attract individual bees to join a cluster, and he concluded that these stimuli have to be presented simultaneously to produce any measurable effect.

Free & Butler (i955) re-investigated this problem and obtained further information concerning the factors that stimulate worker honeybees to cluster together, and which enable individual bees to locate in darkness a cluster which has already formed nearby.

First, they tried to find out whether the scent of the bodies of bees forming a cluster is by itself sufficient to attract stray bees.

In seventeen trials, using different bees in each, they found that scattered bees did not exhibit any tendency to cluster on a cage containing bodies of dead workers any more frequently than on another empty cage. In a further experiment, however, which was repeated six times, very many more bees went to a cage containing recently excised scent glands of worker bees than to one containing recently excised dorsal tergites of the second abdominal segments of other bees, and it was concluded that they had been attracted by a scent given off by these

glands. As the scent gland of a dead bee usually remains unexposed this could

explain why the scattered bees were not attracted towards the bodies of the dead bees in the first experiment. It was likely that any scent present on the body surfaces of the fifty dead bees was insufficient to provide an adequate stimulus, and it seems probable that the scent glands of at least some of the bees forming such a small group would have to be exposed if sufficient scent is to be given off to attract other bees to the group.

276 C. G. Butler



Social behaviour of honeybees

In an attempt to obtain further evidence in support of this conclusion a series of

experiments were carried out with an olfactometer in which individual worker bees had to choose between two routes, down each of which an airstream was

flowing towards them. One of these streams of air was passed over the bodies of dead bees or, in some experiments, over a number of excised scent glands. Some of the results obtained are shown in table 1.

TABLE 1. RESULTS OF OLFACTOMETER EXPERIMENTS

response: no. of bees following route

along which experi- along which control mental (scent-bearing) (unscented) stream

stimulus stream of air passed of air passed dead worker bees, killed by severe cold 11 19 excised scent glands from bees from the 68 16

same colonies as those being tested excised scent glands from bees from 25 5

different colonies from those being tested

It is clear that the individual bees were attracted by the scent from the excised scent glands, and, as some of this scent is likely to be given off by clustering bees, it probably helps individual bees to find a cluster.

It was also found that scattered worker honeybees were attracted towards a metal container in which live bees were imprisoned in such a way that their odour could not reach the scattered bees, and that the attractiveness of such occupied containers was due to two distinct factors. First, to a slight increase in the

temperature of the container above that of the surrounding atmosphere and, secondly, to vibration of its walls caused by movements of the bees inside. Indeed, an empty tin whose walls were maintained at a slightly higher temperature- about 2? C-than that of another tin, was definitely preferred to the latter until a temperature between 37 and 38? C was reached. Similarly, a tin whose walls were caused to vibrate by means of a mechanical vibrator was far more attractive than a similar tin whose walls were not vibrating, even when the latter was maintained at a slightly higher temperature than the former.

All these experiments were carried out in darkness, so that the sight of a cluster could not have played any part in attracting bees to join it. However, in another

experiment it was demonstrated that sight probably does play a small part in

helping a bee to find a cluster. It was concluded, therefore, that scattered worker bees are attracted to a cluster

of bees by a variety of stimuli including scent, vibration, temperature and sight, each of which, provided that it is of sufficient magnitude, can serve as an attraction

by itself. Such attraction of the group for the individual is clearly an important adaptation to social life.

All the experiments mentioned so far were carried out with worker bees only. No queen bees were present. When queens were introduced into experiments it

very soon became clear that they play an important role in keeping the worker 18-2

277



bees of a colony together. For instance, Butler (I954a) arranged two small hives in such a way that their entrances communicated with a common vestibule or arena, and found that if queenless worker bees (i.e. worker bees unaccompanied by a queen) from any source were placed on combs containing food and larvae in one of these hives they would, overnight, move across the arena and join a group of bees in the other hive, which had similar combs of larvae and food, if this latter

group of bees was accompanied by a queen of any kind, either a virgin queen or a mated one. Queenless worker bees were found even to desert young larvae in order to join a group of bees with a queen and it is clear, therefore, that a queen honeybee serves as a very powerful attraction to such worker bees.

Unfortunately, it has not yet been possible to determine whether the attraction of these various stimuli to honeybees is innate or acquired, as it is technically very difficult to rear a worker honeybee, from egg to adult, in complete isolation. How-

ever, Free (I956) has shown that other social responses of the adult worker bee are

probably innate. He caught adult worker bees whilst they were emerging from their cells and kept each in isolation. When, later, he placed them with other bees he found that they both offered food to, and begged food from, these bees, and

that, although the precision of offering and begging behaviour improves with age, these processes do not have to be learned in the first instance.

These observations on the clustering behaviour of honeybees suggest some of the

ways in which worker bees are attracted to each other, but they give little information on the way in which a colony is welded together to form a social unit-on the

way in which colony cohesion, which is a most interesting feature of honeybee behaviour, is maintained.

Some years ago, in the course of some work on the possible danger to honeybees of certain herbicides and other substances, Glynne-Jones (I947) released about 200 worker honeybees, taken at random from a large colony, in a small, well- ventilated glasshouse at Rothamsted. Within 3 h these bees had formed a tiny, queenless cluster in one corner of the roof. The next day he observed that although these bees possessed neither brood, combs, nor queen, a few individuals were

regularly leaving the cluster to visit dishes of sugar syrup and other substances which were exposed on a bench inside the glasshouse. Whilst these bees were

feeding at the dishes each of them was given a distinguishing paint mark so that she could be recognized again. It was then found that only about a dozen individuals were visiting the dishes and that they did so over and over again. They were in fact acting as foragers for the other members of their group who remained con-

tinuously in a cluster throughout the several days that this experiment was continued. Similar observations have since been made when working with other small clusters of bees, with and without queens, in arenas in the laboratory. It

appears that even under such very abnormal conditions only certain bees act as

foragers for their clusters, and that such clusters can indeed be regarded as incipient colonies, amongst the members of which the beginning of a division of labour is

apparent, a few bees only, foraging for the whole group. One of the factors which helps to keep the members of a cluster, or colony,

together, is the collective odour of the bees themselves (Lecomte I950; Free &

C. G. Butler 278




Butler I955). In 1926 von Frisch & R6sch, working with two colonies, produced some evidence which showed that the foraging honeybees belonging to these colonies were preferentially attracted by members of their own colonies to dishes of sugar syrup, and they were also led to conclude that the odour produced by the bees of either of these colonies was not attractive to the bees of the other. Unfortu-

nately, as they only worked with bees from two colonies, which although unrelated were not conspicuously different, it is not possible to draw any general conclusions from their results, which could have been due to a simple genetical difference between the members of these two colonies. However, Kalmus & Ribbands ( 952), working at Rothamsted, have repeated and greatly extended this work, and have shown that every colony of honeybees possesses its own particular odour which

appears to be shared, at any rate to a considerable degree, by all the members of the colony and which, as a general rule, differs from those of all other colonies. In their experiments they used a technique in which they trained a certain number of individual foragers from two different colonies to visit separate dishes of sugar syrup (one for each colony) placed near one another but separated by a wooden screen to minimize the intermingling of any scents around the dishes. The foragers from each hive were distinctively marked, and when they had been successfully trained to their dishes the concentration of the sugar syrup in each was increased, with the result that the foragers, on returning to their hives, recruited other members of their colonies to visit the dishes. These bees also were marked for

recognition. At the end of each experimental day both colonies were examined and all marked bees recorded and killed.

In their first experiments, using this technique, Kalmus & Ribbands were able to demonstrate, both with colonies of Yellow Italian and Swiss nigra stock, and also with colonies of Italian and Buckfast stock, that the number of recruits who went to the dish frequented by the trained members of their own colony was

significantly greater than could be explained by random distribution (P < 0-001). In other experiments they were able to show that bees are attracted by a dish at which other bees have fed and on which they have left some scent. Furthermore, they were able to show that such an attractive bee scent can persist on a dish for at least 2 hours.

In still other experiments they succeeded in demonstrating that a change in a

colony's odour can be induced by changing the food supply of the colony concerned. This they did by dividing a large colony, from which they had removed the

queen, into three equal parts, D, E and F. The next day a mixture of black treacle and heather honey, which has a strong aroma and which bees cannot obtain for themselves anywhere near Rothamsted, was fed to the bees in part F, but not to the bees in parts D and E. Eight days later the bees from parts D and F were

compared for similarity or otherwise of colony odour, by the method outlined, and it was found that a highly significant difference had developed between the fed part F and the unfed part D. A similar result was obtained when the bees in the other unfed part E were compared with the bees in the fed part F a week later. On the other hand, when the bees in the two unfed parts D and E were compared, it was found that no significant difference had developed between them even after

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C. G. Butler

a fortnight. Presumably little or no natural forage was available to the bees during this experiment.

Kalmus & Ribbands (I952) have argued, therefore, that since it has been demonstrated by Nixon & Ribbands (i952) that rapid and widespread food transmission takes place between adult worker honeybees of the same colony, and especially between its foragers, it may be inferred that the food of the foragers of any colony is fairly uniform, and likely to produce volatile waste products in similar proportions. They have argued that differences in the food supplies of different colonies will lead to the production of dissimilar odours by the foragers of these colonies. In other words, to quote these authors, 'uniform and distinguishable colony odours are a consequence of widespread food transmission among the foragers of each

colony'. Now, Synge (I947), working at Rothamsted, has shown that the foragers of the

different colonies in an apiary normally collect different proportions of the food for their colonies from each of the kinds of flowers available to them at any given time; so, if this hypothesis of Kalmus & Ribbands (I952) is correct, one would

expect that the foragers of each colony would share a common odour which would differ from those of the foragers of the other colonies in the apiary, and, indeed, this appears to be the case. On the other hand, if their hypothesis is correct, one would expect that if all the colonies in an apiary were deprived of their stores of food and were transported to a site where only one kind of flower-one source of food-were available to the foragers of their colonies, then all the foragers would

develop a common odour and would become unable to distinguish between members of their own colonies and bees from other colonies. The truth of this

corollary has been demonstrated by Ribbands (1953) who took a number of colonies, whose stores of food he had removed, to a Welsh heather moor where Calluna vulgaris was the only source of forage available to them, and left them there for about 8 weeks. When tests were subsequently made he found that the

foragers of these colonies were no longer able to distinguish members of their own colonies from bees from the other colonies taken to the heather, in the way that

they had been able to do before being taken to the moor. We can conclude, therefore, that the distinctive odour of a colony, which appears

to be common to its adult members, has its origin, at any rate to a considerable extent, in the food which its members are sharing between themselves.

Distinctive colony odours, apart from helping to attract the foragers of a colony to sources of food that other members of their colonies have found, as demonstrated

by Kalmus & Ribbands (I952) as well as by von Frisch & R6sch (I926), also help to guide returning foragers to the entrances of their hives as Ribbands & Speirs (1953) have shown. All observers are agreed that distinctive colony odours also

play a very important role in enabling the members of a colony to distinguish between returning members of their own colonies and potential marauders, and thus to be able to guard their nests against the latter (Butler & Free I952; Free

1954; Ribbands 1954). It is of interest to note that whereas most of the behaviour of a foraging honeybee, whilst she is in the field, differs little, if at all, from that of a non-social bee who is foraging, the foraging honeybee does exhibit one adaptation

280




to social life, as she will expose her scent gland when she finds a rich source of food and so assist other members of her colony to find it.

Worker honeybees who have been without a queen for several hours will try to

join any group of honeybees of whose whereabouts they become aware, even a

group from another colony, if it contains a queen of any kind. Since a group of bees which has recently become queenless will desert combs, containing both food and brood in all stages, to join another group which differs from their own group only in possessing a queen, it can reasonably be concluded that it does so in search of a queen. Presumably the bees of such a group are either seeking to obtain

something from a queen or to give something to her, or both. If a group or colony of worker honeybees which possesses combs of food and young female, worker

larvae, loses its queen and does not find another one within a few hours two things happen. First, the worker bees' ovaries, which normally remain almost, if not

quite, undeveloped so long as a queen is present, begin to develop and, secondly, the adult worker bees modify one or more of the ordinary worker cells, containing young female larvae, to form emergency queen cells. The larva in one of these

queen cells is destined, all being well, to become the new queen of the colony. In other words the queenless worker bees begin to rear a new queen to replace the one they have lost. Normally the presence of a queen in a colony is sufficient, therefore, to inhibit both development of the workers' ovaries and also the production of further queens; two very important features in the social organization of a honeybee community.

So quickly do the workers of a colony become aware of the absence of their

queen, after she has been removed, that it is very difficult indeed to believe that each of them is normally kept aware of her presence by making frequent and regular contact with her. One is, therefore, led to conclude that the bees are either kept aware of her presence because some queenly odour from her permeates the atmo-

sphere of their hive, or else because those bees who have recently been in contact with their queen somehow inform the other members of their colony of this fact, which information is quickly passed from bee to bee.

During 1952 and 1953 Butler (1954a) examined both these hypotheses, and in a first series of experiments attempted to find out what degree of separation is

necessary between the queen of a normal colony and her workers before the latter will construct emergency queen cells and rear a new queen for themselves. It was found, amongst other things, that if a queen was placed, with or without a few workers and some food, in a small wire-gauze cage and suspended amongst her workers for 48 h, emergency queen cells were not always produced provided that the colony was a small one, consisting of less than 3000 bees. The bees contacted their queen, fed her and licked her, through the meshes of the walls of her cage. If, on the other hand, the workers were prevented from feeding and touching her

by using a cage whose walls were made of two sheets of wire-gauze separated from one another by about ? in. then emergency queen cells always appeared within 48 h. As it was clear that any odours emitted by the queens used in such experiments could pass freely through the walls of cages of both types and permeate the hive atmosphere, it was concluded that the odour of a queen is insufficient, at all events

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C. G. Butler

by itself, to inhibit the workers of her colony from constructing emergency queen cells.

The results of these and other, similar, experiments indicated that the worker bees of a colony must be able to touch the body of their queen if they are to remain inhibited from building emergency queen cells. This suggested that the workers of a colony either obtain from their queen regular supplies of some substance which leads to such inhibition, and that it is necessary for them to make physical contact with her in order to obtain this 'queen substance', or else that the relatively few bees who do contact their queen are somehow able to inform the other members of their colony that they have done so by means of a signal of some kind, and that this signal is sufficient to cause inhibition of all the bees. Of these two hypotheses, the former was considered to be the more probable, and it was thought likely that the reason that the workers of larger colonies-colonies of more than about 3000 individuals-were not always inhibited from building queen cells when their

queens were placed in single-walled cages so that they could make some contact with them, was that they could not reach their queens readily enough to obtain sufficient queen substance through the meshes of the walls to inhibit so many individuals.

From 1952 onwards Butler (I954a, 1956) collected a considerable amount of circumstantial evidence, much of it being of a quantitative nature, in favour of this queen substance theory. For example, he found that if several groups con-

taining similar numbers of worker honeybees were taken from a colony and each was allowed to have its queen for a predetermined period each hour, the bees of the groups which had their queen with them for the shortest periods were much more liable to build queen cells than those of the group who had her longest (Butler I954a). However, although further strong circumstantial evidence was

collected, all of which pointed to the existence of some definite queen substance, it was not until a few weeks ago that sufficient queens were obtained and a technique devised by means of which it has been possible to demonstrate that an alcoholic extract of a substance from the bodies of queen honeybees when fed to queenless worker bees effectively inhibits them from building emergency queen cells under conditions in which they would otherwise do so (Butler & Gibbons I957a). Similar alcoholic extracts prepared from the bodies of worker bees from normal

colonies, headed by actively laying queens, have not been found to be capable of

doing so. It is improbable, especially in the case of a large colony of 40000 to 50 000 bees,

that every worker bee obtains a share of queen substance directly from her queen. It seems much more likely that only a few bees obtain this substance directly from the queen and that they rapidly share it with the other members of their colony.

The queen of a colony is usually surrounded by a circle of workers some of whom examine her body with their antennae, which bear organs of taste as well as smell, etc., whilst others lick it. It seems possible, therefore, that it is by licking their

queen's body that worker bees obtain queen substance, and that those who do so then share it with the other members of their colony. In an attempt to determine whether in fact this does happen, observations were made of the individual

282




behaviour of forty worker bees throughout a 5 min period immediately after each had left her queen. Twenty of these bees had licked her body, and twenty of them had examined it thoroughly with their antennae, but had definitely not touched it with their mouthparts. None of the bees in this latter group, the ones who examined their queen but did not lick her, was seen to offer food to any other member of her colony during this 5 min period; on the other hand, every one of the bees who had licked their queen's body offered food to several other bees in

quick succession and fed at least one of them, usually three or four, within 5 min of leaving her queen (Butler I954a). These observations suggest that those bees who had licked their queen obtained something from her and passed some of it on to other members of their colony, probably in regurgitated food. Subsequently, it was shown that a substance which inhibits ovary development when fed to worker honeybees, and which may well be identical with queen substance, is obtained by worker bees when they lick the body of a queen, and can be recovered from their honeystomachs and still prove effective as an ovary inhibitor when fed to other worker bees (Butler 1956).

Nixon & Ribbands (I952) have shown that food obtained by worker honeybees can become quickly and widely distributed amongst the members of a colony. They allowed six marked worker bees, belonging to a colony of over 24000 individuals, to collect 20 ml. (379 bee loads) of sugar syrup containing a small quantity of radioactive phosphorus. Samples of bees were then taken from various parts of the hive and tested for radioactivity, 5 h after all the syrup had been collected and

again 24 h later. It was found that over 25 % of the bees in the samples taken 5 h after feeding contained some of the radioactive syrup, and that well over 50 % of those in the samples taken 29 h after feeding did so.

In a later experiment in which he made use of radioactive carbon, instead of radioactive phosphorus, Ribbands (see Butler I954b) showed that a load of syrup which was collected by a single worker honeybee was ultimately shared amongst nearly all the 20000 members of her colony.

It is clear, therefore, that a mechanism suitable for the distribution of queen substance amongst the members of a colony exists, and it seems likely that the

relatively small proportion of the members of a colony of honeybees who obtain this substance directly from their queen quickly distribute it amongst the other bees in regurgitated food.

Once the existence of queen substance had been established, and the probable way in which it is collected from the queen and distributed amongst the workers of a colony determined, one of the next problems was to find out from what part of a queen's body the workers obtain it. In order to do this a number of hives con-

taining small colonies of bees were each divided into two equal parts by means of vertical wooden partitions. Each partition had an aperture, covered with thin sheet rubber, in the centre of it. There was a small hole in each of these rubber

diaphragms and the queen of each colony was held in it in such a way that her head, or head and thorax, and their appendages, were exposed to the bees on one side of the partition, and her thorax and abdomen, or abdomen alone, to the bees on the other side of it. The bees in that part of the hive with the head of the queen

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continued to feed her and the bees in both parts paid a great deal of attention to those parts of her body that they could reach.

Forty-eight hours after a colony had been arranged in this way both parts were examined for emergency queen cells. If none was found the experiment was continued for a further 48 h when both parts were again examined. In other experiments the areas of those parts of their queen which the bees could reach were still further reduced by covering them with wire-gauze or Polythene sheeting.

The data obtained in these experiments show that it is unnecessary for the workers of a colony to feed their queen, collect her faeces, or come into contact with any particular part of her body in order that they shall remain inhibited from

building emergency queen cells; they strongly suggest that queen substance is obtained by licking any part of a queen's body (Butler 1954a). However, de Groot & Voogd (1954) have obtained data which suggest that although it is present both on a queen's head and on her abdomen, it is most concentrated on her head. One of my colleagues, Simpson (I957 a), has suggested that it may perhaps be produced in a queen's mandibular glands. If this is so it could very easily become distributed over her body when she is cleaning it. Unfortunately, however, we have not yet identified its source. It seems possible that its production is in some way related to activity of a queen's ovaries. It is certainly present on a virgin queen but, apparently, not so abundantly as on a mated queen, as it has been possible to demonstrate that whereas the presence of an actively laying queen is usually sufficient to inhibit the members of her colony from constructing emergency queen cells, the presence of a virgin queen, although it causes some inhibition, is by no means always sufficient to cause complete inhibition. There is evidence that this cannot be explained by the fact that a virgin queen normally lays no eggs, as mated

queens have been found who, although they had stopped laying any eggs at all, nevertheless, were shown to maintain full inhibition of queen cell production in a number of normal, large, colonies in which they temporarily replaced the resident

queens (Butler I957a). If one removes the queen of a colony its workers soon modify a number of worker

cells containing young female larvae to form emergency queen cells. They do not, however, build an unlimited number of queen cells, and it has been shown that the number built depends upon the number of bees present and also on the strain to which they belong (Butler 1954a). The greater the number of bees of a given strain that are present, the greater the number of emergency queen cells they will build. Such emergency queen cells are usually constructed within 48 h of the queen's removal, and all are built about the same time. Thereafter, although they usually have ample opportunity to do so, the bees do not generally construct another

queen cell until one or more of the cells of this first batch have been sealed. It seems probable, therefore, that the number of queen cells constructed by a given number of bees gives an approximate measure of the deficit of queen substance which they are experiencing, and that the bees obtain sufficient queen substance, or some similar inhibitory material, from the open queen cells to satisfy their immediate requirements and to inhibit them from building further cells until the first have been sealed. Recently Butler & Gibbons (i957b) have been able to

284 C. G. Butler




demonstrate experimentally that the presence of open queen cells is sufficient to inhibit queenless bees from building emergency queen cells under conditions in which they would otherwise do so. It seems probable that the inhibitory material is produced by the royal larva in such a cell, and is obtained by the bees licking her, but this has not yet been demonstrated.

A worker bee whose ovaries have developed in the absence of a queen and who

lays unfertilized eggs-a so-called 'laying worker'-also appears to be a source of a small quantity of this inhibitory material.

It has not yet been shown whether the substance that worker bees obtain from their queen, which inhibits development of their ovaries, is identical with the

substance, also produced by the queen, which inhibits them from rearing further

queens. Some evidence in support of the view that a single substance is involved was obtained by Perepelova (I929) who found developing ovaries in some workers of colonies in which laying queens were present but in which queens were also

being reared preparatory to swarming. Voogd (I956) has suggested that in addition to an inhibitory substance, which

is soluble in acetone and ethyl alcohol, a psychological factor is also involved in the

suppression of ovary development in worker bees in the presence of a queen. She has claimed that the worker bees must obtain the inhibitory substance from some-,

thing which they regard as a queen if it is to prove effective. In her experiments, with small numbers of queenless, caged bees, this was either the body of a dead

queen or that of a dead worker. However, we have been able to show that this is

unnecessary and that effective inhibition is obtained when an extract of the substance from a queen is supplied in the workers' food in the absence of any corpse to act as a psychological stimulus (Butler I956, 1957b; Butler & Gibbons

957 a). Unfortunately, we do not yet know the chemical nature of the inhibitory substance (or possibly substances) which worker bees obtain from their queens, nor whether it influences the recipient bee directly or serves to release within her

body another substance which is the actual inhibitor. Under natural conditions a colony of honeybees only exceptionally loses its

queen suddenly, and produces a new one by means of an emergency queen cell. As a rule queens are replaced by the processes of supersedure and swarming, the former differing from the latter in that the queen is replaced without the occurrence of colony reproduction.

Many suggestions have been made to explain the initiation of the process of

supersedure, in which the bees of a colony rear a new queen whilst the old one is still present; the new queen eventually replacing-superseding-the old one. Two of the suggestions that have been put forward have been that the queen is diseased

(Farrar I947), or that she is producing insufficient eggs on account of old age or because of injury (Root I945; Wedmore I942). However, it has now been shown that several queens, who had actually been superseded by their workers, were

each, nevertheless, capable of inhibiting the production of queens by small, but not by large, groups of bees; and that their failure to inhibit large groups of bees from rearing replacement queens was almost certainly due to the production of insufficient queen substance by them (Butler I957 a). It was concluded that shortage

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of queen substance is the only direct cause of queen supersedure, and that any other factors that tend to initiate this process do so by reducing a queen's output of this substance. Data were also obtained which suggest that a reduction in queen substance output may sometimes be related to loss of mobility on the part of the

queen concerned. It also seems probable that the immediate cause of queen production in colonies

preparing to swarm is insufficiency, or ineffectiveness, of queen substance but, as

Simpson (I957b) has pointed out, it is still uncertain whether this is a cause or a consequence of the swarm preparations.

In favour of the hypothesis that queen substance deficiency can initiate swarm

preparations there is evidence that the quality of its queen influences the tendency of any particular colony to swarm. For instance, as Simpson (I957c) has shown, swarm preparations occur much less frequently in colonies whose queens are less than 2 months old than they do in colonies with queens that are more than a year old. Again, it is also generally believed that colonies of certain strains of honeybees are much more prone to swarm than those of others. Furthermore, since Becker

(I925) and Zander (I925) have both shown that bees intermediate in form between a queen and a worker can readily be produced experimentally, it seems probable that even under natural conditions queens are sometimes reared which lack certain normal characteristics and, in particular perhaps, tend to have a low output of

queen substance. These facts suggest that the capacity of a queen to produce this substance varies with her age, genetical constitution, and the conditions under which she was reared, and may determine the tendency of her colony to swarm.

It has not yet been shown that this is the correct explanation but, as Simpson (1957d) has pointed out, if it is, then some other factor must determine whether a colony will supersede its queen or will swarm when its workers experience a

deficiency of queen substance. He has suggested that queen supersedure may take

place when a lack of queen substance occurs under conditions that are unsuitable for swarming. If this is true, it is reasonable to suppose that small colonies are more likely to supersede their queens than to swarm, as swarming by a small

colony would be hazardous both for the swarm itself and for the remnants of the

parent colony. Furthermore, since only a very unsatisfactory queen would be unable to prevent a small colony from rearing further queens it would seem desirable for her colony's survival that such a queen should be eliminated by supersedure. Simpson (I957d) has suggested that the condition which determines that supersedure rather than swarming will occur, is always that the colony's queen substance requirement is small, either because it is itself a small colony or because the queen substance requirement of its individual worker bees is low. To test this

hypothesis he is attempting to discover whether the normal variation in the incidence of swarming throughout the year is reflected in a corresponding variation in the queen substance requirement of the individual worker bees.

If we consider other insect communities, we find that evidence is rapidly accumulating in support of the view that inhibitory substances, or 'ecto-hormones' as they have sometimes been called, also play an important part in their organization. For example, Light (I944), Liischer (I953, 1956), and others, have obtained

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data which strongly suggest that certain queen termites produce a substance which inhibits the development of supplementary reproductives, and Bier (I954) has obtained evidence which indicates that queen ants of several species produce a substance which tends to inhibit development of the ovaries of the workers of their colonies. Butler (I957c) also obtained data from a number of experiments which suggest that the substances produced by queen honeybees and by queen ants, which tend to inhibit ovary development in workers of their colonies are similar and, indeed, are probably interchangeable. Again Carlisle & Butler (1956) have obtained results which suggest that the substance produced by a queen honeybee which inhibits development of a worker bee's ovaries, and an ovary inhibiting substance extractable from the sinus-glands in the eye-stalks of prawns (Leander serratus), are also interchangeable.

In collaboration with Dr Callow and Miss Johnston, of the National Institute for Medical Research, we are now trying to isolate and identify queen substance, and we are also testing various steroids to see whether they produce similar effects on worker honeybees.

Having established that colony cohesion is due partly to the attraction that

groups of bees have for the individual, and that the presence in the hive of a source of sufficient queen substance for all the members of the colony is of paramount importance in this connexion, we are, of course, still working on the control of

colony behaviour by this substance and possibly others. It does seem possible that other aspects of social behaviour in insect communities--such as, for example, the division of labour amongst the workers of a honeybee colony-may also be found to be controlled by substances passed, perhaps in regurgitated food, between the various individuals concerned. We hope to be able to investigate some of these

problems in the future.

REFERENCES

Becker, F. I925 Erlanger Jb. Bienenk. 3, 163-223. Bier, K. 1954 Insectes Sociaux, 1, 7-19. Butler, C. G. 1954a Trans. R. Ent. Soc. Lond. 105, 11-29. Butler, C. G. 1954b Annu. Rep. Bee Dept. Rothamsted Exp. Sta., p. 132. Butler, C. G. 1956 Proc. R. Ent. Soc. Lond. (A) 31, 12-16. Butler, C. G. I957a Insectes Sociaux, 4, 211-223. Butler, C. G. I957b Experientia, 13, 256. Butler, C. G. I957c (In preparation.) Butler, C. G. & Free, J. B. 1952 Behaviour, 4, 262-292. Butler, C. G. & Gibbons, Doreen A. I957a, I957b (In preparation.) Carlisle, D. B. & Butler, C. G. 1956 Nature, Lond. 177, 276-277. Farrar, C. L. I947 J. Econ. Ent. 40, 333-338. Free, J. B. I954 Behaviour, 7, 233-240. Free, J. B. 1956 Brit. J. Anim. Behaviour, 4, 94-101. Free, J. B. & Butler, C. G. I955 Behaviour, 7, 304-316. Frisch, K. von & Rosch, G. A. I926 Z. vergl. Physiol. 4, 1-21.

Glynne-Jones, G. D. 1947 (Personal communication.) Groot, A. P. de & Voogd, Stien I954 Experientia, 10, 384-385. Kalmus, H. & Ribbands, C. R. I952 Proc. Roy. Soc. B, 140, 50-59. Lecomte, J. 1950 Z. vergl. Physiol. 32, 499-506.

Light, S. F. I944 Univ. Calif. Publ. Zool. 43, 413-454. Liischer, M. I953 Rev. suisse Zool. 60, 524-528. Liischer, M. I956 Insectes Sociaux, 3, 119-128.

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288 C. G. Butler

Nixon, H. L. & Ribbands, C. R. 1952 Proc. Roy. Soc. B, 140, 43-50.

Perepelova, L. 1929 Bee World, 10, 69-71. (Translation from Opitnaia Paseka, May-June, 1928.)

Ribbands, C. R. 1953 The behaviour and social life of honeybees. London: Bee Research Association.

Ribbands, C. R. 1954 Proc. Roy. Soc. B, 142, 514-524. Ribbands, C. R. & Speirs, Nancy 1953 Brit. J. Anim. Behaviour, 1, 59-66. Root, E. R. 1945 The ABC and XYZ of bee culture. Ohio: A. I. Root, Co.

Simpson, J. I957 (Personal communication.) Simpson, J. i957b Proc. R. Ent. Soc. Lond. A. (In the Press.) Simpson, J. I957 J. Agric. Sci. (In the Press.) Simpson, J. 1957d Insectes Sociaux, 4. (In the Press.) Synge, Anthea D. 1947 J. Anim. Ecol. 16, 122-138.

Voogd, Stien 1956 Experientia, 12, 199-201. Wedmore, E. B. 1942 A manual of beekeeping. London: Arnold. Zander, E. 1925 Erlanger Jb. Bienenk. 3, 224-246.



some work at rothamsted on the social behaviour of honeybees

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