Das Duftorgan der Honigbiene und die physiologische Bedeutung ihres Lockstoffes

Summary

The scent organ of the honeybee was discovered by Nassonoff in 1883 (Nassonoff or Nasanov gland). Sladen (1901) was the first to recognize its true nature. He observed that bees had exposed the scent gland while they exhibited the so called “joyful hum”, that behaviour by which they produce a stream of air through rapid fanning of the wings, the head being bowed deeply forward and the tail raised sharply (Fig. 1). At the same time an pleasant smell can be perceived, which has been proven to be produced by the Nassonoff gland. The odour is quickly dispersed through the rapid fanning of the wings. That it is an odour with an alluring effect on other bees was demonstrated in 1923/24 by v. Frisch. Moreover, he found that the bees make use of their scent organs not only during fanning and scent dispersal (in German “sterzeln”) but also that they expose it at plentiful crops. In the latter case a rapid vibration of the wings does not take place (Fig. 3).

In 1926 v. Frisch and Rösch tried to find out whether the odour of the scent gland is specific for each colony and attracts only the hive-companions of that bee, which makes use of the scent gland, or wether it is of a general nature and has an alluring effect on all bees, regardless from what colony they come. Based on the results of this experiment, which pointed to a colony-specific effect, and on the grounds of a surmise which was made by v. Buttel-Reepen in 1915, many beekeepers and zoologists were up till now convinced that the colony odour of the bees receives its individual note through the odour of the scent organ. Also Kaltofen (1951) and Kalmus and Ribbands (1952) found the attractant to be colony-specific, while the experiments of Wojtusiak (1934) gave contrary results.

My observations and experiments brought the following results: an analysis of those situations in which the bees make use of their scent gland, makes it probable that the workers always fan and disperse scent — sterzeln —, after they have had lost for some time the customary (gewohnten) contact with their companions or with the queen. The ending of this situation, that is to say the renewal of contact, apparently causes the fanning and scent dispersal. A series of observations, which are reported, speak for the correctness of this hypothesis.

The scenting of the feeding place and the fanning (with scent dispersal) of bees at the hive-entrance and at the nesting place (of a swarm) serves in all cases to attract companions. In a few cases the purpose of the scent dispersal becomes only obvious, if one takes into consideration that the bees are insects, whose entire behaviour is directed to the society.

The colony odour of the bees is composed of at least 12 different components. That it receives its colony-individual note from the odour of the Nassonoff gland is unlikely, because the bees expose their scent organs only outside of the hive and never in it.

Twelve Zwei-Völker-Versuche according to the methods of v. Frisch and Rösch (1926) showed on the average a colony-specific behaviour of the newcomers, but the preference for the population's own feeding place was relatively insignificant. In 5 cases one of the two test colonies flew to the feeding place of the foreign colony.

This method (which also was used by Kalmus and Ribbands) has a disadvantage: since the recruits alight where the foragers with their functioning scent glands are collecting sugar water, it is not possible to separate the effect of the odour of the Nassonoff gland from the effect of the smell adhering to the bodies of the bees. On the other hand, unanimous results would be expected if the alluring odour could be obtained free of other components. This is relatively easy done in the following way: if one squeezes fairly firmly the abdomen of a bee held between the thumb and index finger, the scent gland becomes exposed. The odiferous substance can now easily be wiped away with a piece of filterpaper held with a pointed forceps (Fig. 6).

Both training and spontaneous choice experiments were carried out with odiferous substance obtained in this manner. In the case of the former, 20 to 30 forager bees were trained for several hours to the odour of the scent gland obtained from recruits from their own colony and thereafter they were tested in a choice-experiment, whether they were capable to distinguish the attractant on which they were trained from that which was obtained from bees of an other colony. Also reverse experiments — training to the scent gland odour obtained of bees of another colony — were carried out.

The spontaneous choice experiments are a type of Zwei-Völker-Versuche but by suitable provisions it was arranged, that the feeding places of the both groups of foragers (from A and B, which were alarming the newcomers) were seperated from those places where the newcomers sought for sugar-water. There 3 feeding dishes were set up in linear arrangement. One contained scent gland odour taken from recruits from colony A, the other the same from bees of colony B. The middle dish was free of alluring substance. Since in these experiments (as in most Zwei-Völker-Versuchen) colonies of different races were used, which differed distinctly from one another in their coloring, it could be recognized without further ado from which hive an arriving newcomer originated. Immediately after alighting they were caught and killed.

Both methods yielded unanimous results: again the strongly attractting effect of the scent gland substance was demonstrated. In the spontaneous experiments of the year 1954, for example, 1260 bees flew to the dishes with the odour and only 49 (less than 4%) to those dishes free of it. The odour of the scent gland definitely is differentiated by bees from the odour of stinger-poison and from other odours; it is, however, neither colony nor race specific. It attracts without distinction all races which I investigated (Apis mellifica ligustica, A. m. nigra and A. m. carnica). If one scent gland odour is given preference, this is an expression of the quantitative differences of both alluring substances used. The effect can be reversed by variation of the quantities.

Kalmus and Ribbands (1952) believed to have proven with their experiments that the type of crop influenced the quality of the odour of the scent gland or other surface-glands. The “kombinierten Versuche” which I made in 1954 (see p. 455) show, however, that a colony-specific behaviour of bees is to be attributed to the colony odour adhering to the surface of their bodies. With purebred Italian and Nigra colonies I carried out alternately Zwei-Völker-Versuche, in which the body odour of the forager bees could influence the decision of the newcomers as to where they would alight, and spontaneous choice experiments, in which these odiferous components were excluded. First of all I tested the untreated colonies, then the Nigra colony — and later both colonies — were scented in the hives with geranium oil; finally these odiferous substances were removed and a mixture of a half pound of honey and two tablespoons of black treacle was placed in the Italian colony in such a way that the bees could not feed on the sweet substance, nevertheless the smell of the treacle was able to exercise its effect. After additional experiments I removed the wire screen blocking the access to the mixture, so that Italian bees could now eat and store it. Then the behaviour of the bees was tested anew. Table 10 shows distinctly the different effects of body odour (in this case = colony odour) and the odour of the scent gland. If the colony odours are the same, the distribution of the newcomers to both feeding places in the Zwei-Völker-Versuche is approximately 1∶1; if they are differrent, the colony's own feeding place is preferred. In the spontaneous choice experiments the distribution of the newcomers in every case is nonspecific, for even then, when one of the odours was preferred, it always was preferred by the newcomers of both colonies, and this surprisingly universally.

The reported experiments show that if bees are able to distinguish the companions of their own colony from foreigners, this is to be attributed to the colony odour, which adheres to their bodies. The odour of the scent gland is nonspecific; it attracts without distinction all bees.