| Bee Research
Digest ABJ - October, 1992 - Pages 641-644 |
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EDWARD E. SOUTHWICK Department of Biological Sciences State University of New York College at Brockport, New York 14420 BITNET: SOUTHWIK@Brock1P FAX:716-395-2416 Research Digest - a down-to-earth look at what's going on in apicultural research. The purpose of this column is to keep you, the beekeeper, informed of on-going and recent developments in bee research. Further details may be obtained from the referenced articles available through interlibrary loan through your local or state library. Foraging, Recruitment, and Search Behavior of Honey Bees Considerable field data has been gathered during the past few decades on honey bee foraging, recruitment, and searching behavior. The dance language observed and described so well by Karl von Frisch (for which he was awarded the Nobel Prize in 1973) fits nicely with much of the data. In essence, this theory of recruitment involves individual foragers indicating their floral resource in the hive by body movements which can be "read" by other workers which then go out in the proper direction and the proper distance to locate the same floral patch. Though this dance language seems unlikely, it can be observed by anyone in a glass sided observation hive, and can, in fact, be quantified by setting out feeding stations of sugar water at defined locations and seeing the resulting dances. Human observers can readily read the dance of foragers and determine the foraging area being worked. There has been for some time, however, an undercurrent of question about the bee's actual use of this mode of recruitment. No other insects or even any other groups of animals show such a complex method of communication. Most social insects utilize chemical odors, especially in indicating routes to food sources. The best known of these are the ants which leave an odor trail followed by other ants to food sources. The chemical odor communication is common among both social and non-social insects. So are we certain that such signals are not also used by honey bee foragers? Actually, even von Frisch recognized the use of odors to some degree, but his evidence seemed to show an overriding dependence on the dance language, and he became convinced that the bees were using this language to communicate food locations. The best treatment of the possible use of odor in honey bee recruitment to food resources was recently published in the American Zoologist and is referenced below (Wenner, et al 1992). This paper records the early work (as far back as Aristotle around 330 B.C.) up to the present, that newly recruited honey bee workers rely principly on odor cues as they search for food sources exploited by hivemates.The early work of many observers (as far back as Wildman in 1768 and up to date) in the use of dance language for information transfer to new recruits is also referenced. There is no disagreement among scientists that returning foragers dance in the hive. Everyone also agrees that once a forager locates a good food source, she will be able to fly directly to and from that flower patch. That is, she flies a straight line (a bee-line) to the food patch from the hive using local landmarks and the sun for orientation. The disagreement comes in answering the question of just how the recruits find the flower patch being exploited by the successful forager. By noting the times it takes for foragers to fly directly, it is easily seen that recruits seem to take too long a time for a straight-line flight. If they read the direction and distance from the forager's dance, then why cannot they too fly directly, or nearly so, to the flower patch? Of course, they might be a little off in their direction, but then when they get close to the patch they should recognize the fragrance of the flowers which were present on the forager bee whose dance they followed back in the hive, and be able to quickly zero-in on the patch. If, on the other hand, the recruits are merely excited by the forager dance and then go out in search of the patch, they would be expected to take a much longer time to find the patch, but again when they perceive the same flower fragrance carried by the dancing forager back in the hive, they should be able to locate the patch and from then on fly directly to and from it. Wenner and his colleagues at the University of California at Santa Barbara, use their own collected data along with considerable data collected by other investigators, including von Frisch and others promoting the dance langnage hypothesis, to show that recruits do indeed take too long to find the flower source for a direct flight. In fact, often recruits end up at test feeding stations in the opposite direction of the station from which the succesful forager was feeding. By looking at the numbers of recruits that actually come to the feeding station from which the foragers came and the numbers of bees that were in contact with the dancer that ended up at other feeding stations, one wonders why more recruits do not go to the "correct" food patch. In one study discussed in the referenced paper, when a feeding station with which bees were familiar was moved to a new site some distance away, some foragers eventually found this new site and when they returned to the hive they danced. But only 14 of the 70 bees attending the dances of the foragers actually came to the correct location. Twenty other bees attending the dances left the hive but did not arrive at the feeder. The other 36 former foragers that were watched did not contact the dancers. Of the 14 recruits that found the feeding station, 10 required repeated contacts with the dancers between as many as nine exploratory flights before they finally located the station. The four recruits that located the patch on the first flight had search times two to six times longer than the 30 second bee-line required of the experienced foragers. |
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| In other experiments examined, search times for recruited bees were even more at variance with the recruits having any knowledge of direction or distance from dancing foragers. In one case (Figure 1), outgoing flight times between the colony and the food patch for experienced foragers was under 20 seconds, yet recruited bees searched a median time of 8 minutes (and as long as 75 minutes) before they found the station indicated by the dance. Also, other data show that search times downwind are less than those upwind. | |
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| These interpretations
lend credance to the authors' suggestion that honey bees are
likely to utilize odors more in finding flower patches than they
do the dance language (which may only serve as a stimulus to
go out and search). Their odor-search hypothesis involves recruited
bees leaving the colony and flying in ever-expanding spirals
until they perceive odor molecules similar to those present on
the body of the returned forager back in the hive (Figure 2).
When they encounter the odor, they begin a zig-zag pattern of
flight moving toward the increasing concentration of odor molecules
(kind of similar to a person moving toward a neighbor's barbecue
at dinner time). Should the bees stray from the odor plume, they
immediately reverse their direction to get back into the plume
(casting area in the figure). In this way they can zero-in
on the food source. Once they find the food source, if it is
within the range of the hive with which they are familiar, the
recruits can find their way more directly back to the hive using
known landmarks (experienced forager flight in the figure). One of the attractive features of the odor hypothesis in honey bees is the very wide use of odors by so many other social insects. The description for bees sounds remarkably similar to the chemical odor trail marking used in the foraging pattern of many insects and especially well described for leafcutter ants by Edward 0. Wilson in his book entitled Biophilia (see description in Books & Media in this issue). Wilson's description is so well done it takes you down to the level of the ant, a few millimeters above the ground surface, scurrying along a scent trail to and from a food source and the nest. The ant, too, follows a zig-zag pattern along the trail as it moves into and out of the center of the odor cloud. More research effort is needed in the area of honey bee foraging, recruit flight and orientation of bees in the field. Reference: Wenner, A.M., D.E. Meade, L.J. Friesen. 1992. Recruitment, search behavior, and flight ranges of honey bees. Am. Zoologist 31:768-782. |