Bee learning and communication

Honey bees learn and communicate in order to find food sources and for other means.

Learning
Learning is essential for efficient foraging. Honey bees are unlikely to make many repeat visits if a plant provides little in the way of reward. A single forager will visit different flowers in the morning and, if there is sufficient attraction and reward in a particular kind of flower, she will make visits to that type of flower for most of the day, unless the plants stop producing reward or weather conditions change. Honey bees are quite adept at associative learning, and many of the standard phenomena of conditioning take the same form in honey bees as they do in the vertebrates that are the more usual subjects of such experiments.

Honey bees can perform learning tasks that go beyond simple conditioning. Foragers were trained to enter a simple Y-shaped maze that had been marked at the entrance with a particular color. Inside the maze was a branching point where the bee was required to choose between two paths. One path, which led to the food reward, was marked with the same color that had been used at the entrance to the maze, while the other was marked with a different color. Foragers learned to choose the correct path, and continued to do so when a different kind of marker (black and white stripes oriented in various directions) was substituted for the colored markers. When the experimental conditions were reversed, rewarding bees for choosing the inner passage marked with a symbol that was different from the entrance symbol, the bees again learned to choose the correct path. Extending the length of the tunnel to increase the time between seeing the one marker indicating the correct path and a second marker identifying the correct path show that the bees can retain the information for about 5 seconds, equivalent to the short-term memory of birds.

Communication
Foragers communicate their floral findings in order to recruit other worker bees of the hive to forage in the same area. The factors that determine recruiting success are not completely known but probably include evaluations of the quality of nectar and/or pollen brought in.

There are two main hypotheses to explain how foragers recruit other workers &mdash; the "waggle dance" or "dance language" theory and the "odor plume" theory. The dance language theory is far more widely accepted, and has far more empirical support. The theories also differ in that the former allows for an important role of odor in recruitment (i.e., effective recruitment relies on dance plus odor), while the latter claims that the dance is essentially irrelevant (recruitment relies on odor alone).

Dance language
It has long been known that succesfully foraging Western honey bees perform dances on their return to the hive, known as round dance and waggle dance. The laden forager dances on the comb in a circular pattern, occasionally crossing the circle in a zig-zag or waggle pattern. Aristotle in 330 BC, described this behaviour in his Historia Animalium. It was thought to attract the attention of other bees.

In 1947, Karl von Frisch correlated the runs and turns of the dance to the distance and direction of the food source from the hive. The orientation of the dance correlates to the relative position of the sun, and the length of the waggle portion of the run is correlated to the distance from the hive. There is no evidence that this form of communication depends on individual learning.

Von Frisch performed a series of experiments to validate his theory. He was awarded the Nobel Prize in Physiology or Medicine in 1973 for his discoveries.

One of the most important lines of evidence on the origin and utility of the dance is that all of the known species and races of honey bees exhibit the behavior, but details of its execution vary among the different species. For example, in Apis florea and Apis andreniformis (the "dwarf honeybees") the dance is performed on the dorsal, horizontal portion of the nest, which is exposed. The runs and dances point directly toward the resource in these species. Each honey bee species has a characteristically different correlation of "waggling" to distance, as well.

Various experiments document that changes in the conditions under which the dance is performed lead to characteristic changes in recruitment to external resources, in a manner consistent with von Frisch's original conclusions.

Odor plume
While the majority of researchers believe that bee dances give enough information to locate resources, proponents of the odor plume theory argue that the dance gives no actual guidance to a nectar source. They argue that bees instead are primarily recruited by odor. The purpose of the dance is simply to attract attention to the returning worker bee so she can share the odor of the nectar with other workers who will then follow the odor trail to the source.

The primary lines of evidence used by the odor plume advocates are
 * 1) clinical experiments with odorless sugar sources which show that worker bees are unable to recruit to those sources and
 * 2) logical difficulties of a small-scale dance (a few centimeters across) giving directions precise enough to hold the other bees on course during a flight that could be several kilometers long. Misreading by even a few degrees would lead the bee off course by hundreds of meters at the far end.

Neither of these points invalidate the dance theory, but simply point out that odor must be involved, which is indeed conceded by all proponents of dance theory. Critics of the odor plume theory counter that most natural nectar sources are relatively large - orchards or entire fields. Precision may not be necessary or even desirable. They have also challenged the reproducibility of the odorless source experiment.

The academic debate between these two theories is extremely polarized and often hostile. Adrian Wenner, a modern bee researcher, is the chief proponent of the odor plume theory (anti-dance). One supporter of Wenner's theories, Julian O'Dea, has proposed an evolutionary explanation for the "waggle dance" that does not involve communication from one bee to another, by claiming it may be a simple idiothetic movement that conveys no information. Conversely, experiments with robotic dummies were indeed able to induce some recruitment, which should not have been possible if the dance contains no information.

The controversy persists, though it does so primarily due to an asymmetry between the two "camps"; those who study dance communication freely admit that odor is an essential component of the system, and even necessary at various stages of the recruitment process, including once a recruited forager reaches the vicinity of the resource (e.g. ), while odor-plume advocates do not acknowledge that the dance contains any information whatsoever. Various experimental results demonstrate that the dance does convey information, but the use of this information may be context-dependent (e.g. ), and this may explain why the results of earlier studies were inconsistent. In essence, both sides of the "controversy" agree that odor is used in recruitment to resources, but they differ strongly in opinion as to the information content of the dance.

Note: much of the research on the two competing hypotheses of communication has been restricted to Western honey bees (but see the work of F.C. Dyer . Other species of Apis use variants on the same theme, and other types of bees use other methods altogether.

Trophallaxis
The exchange of food, trophallaxis, is also used by means to communicate and includes information on the quality of and thus competition for a food source, temperature and water demand, and the condition of the queen (Sebeok, 1990).

Primer Pheromones

 * For more background on this topic, see Pheromone (honey bee).

Research that was published in November 2004, by scientists under the leadership of Dr. Zachary Huang, Michigan State University indicates that so called primer pheromones play an important part in how a honey bee colony adjusts its distribution of labor most beneficially. In order to survive as a bee colony of sometimes 50,000 -100,000 individual bees, the communal structure has to be adaptable to seasonal changes and the availability of food. The division of labor has to adjust itself to the resources available from foraging. While the division of labor in a bee colony is quite complex, the work can be roughly seen as work inside the hive and outside the hive. Younger bees play a role inside the hive while older bees play a role outside the hive mostly as foragers. Huang's team found that forager bees gather and carry a chemical called ethyl oleate in the stomach. The forager bees feed this primer pheromone to the worker bees, and the chemical keeps them in a nurse bee state. The pheromone prevents the nurse bees from maturing too early to become forager bees. As forager bees die off less of the ethyl oleate is available and nurse bees more quickly mature to become foragers. It appears that this control system is an example of decentralized decision making in the bee colony.

Cognition
Experiments by James Gould suggest that honey bees may have a cognitive map for information they have learned, and utilize it when communicating.

In one test reported in a 1983 issue of Science News, he moved a supply of sugar water 25% further away from a hive each day. The bees communicated to each other as usual on its location. Then he placed the sugar water on a boat anchored in the middle of a small lake. When scouts returned to the hive to communicate their find, other bees refused to go with them, not expecting to find food in the middle of a lake, even though they frequently flew over the lake to reach pollen sources on the opposite shore.

In another test related in the August 1986 issue of Discover ("A Honey of a Question: Are Bees Intelligent?"), Gould lured some bees to a dish of artificial nectar, then gradually moved it farther from the hive after they became accustomed to it. He marked the addicted bees, placed them in a darkened jar, and relocated them to a spot where the hive was still visible, but not the dish. When released one by one, the bees would appear disoriented for a few seconds, then fly directly for the covert dish. 73 of 75 bees reached it in about 28 seconds. They apparently accomplished this feat by devising a new flight path based on a cognitive map of visible landmarks.