Behavior In Honeybees

Some insects, such as certain species of bees, wasps, ants, and termites, live in complex colonies. In these colonies, some individuals gather food, others protect the colony, and others reproduce. Insects that live in such colonies are called social insects. The division of labor among social insects creates great interdependence and a heightened need for communication. This section will look at the behavioral adaptations of one well-studied species of social insect, the honeybee. As you read about the complex behaviors of honeybees, keep in mind that these behaviors are neither taught nor learned. Instead, they are genetically determined. Genetically determined behavior is called innate behavior.

A honeybee colony consists of three distinct types of individuals, which are illustrated in Figure 37-10: worker bees, the queen bee, and drones. Worker bees are nonreproductive females that make up the vast majority of the hive population, which may reach more than 80,000. The workers perform all the duties of the hive except reproduction. The queen bee is the only reproductive female in the hive, and her only function is to reproduce. Drones are males that develop from unfertilized eggs. Their only function is to deliver sperm to the queen. Their mouthparts are too short to obtain nectar from flowers, so the workers must feed them. The number of drones in the hive may reach a few hundred during the summer, but when the honey supply begins to run low, the workers kill the drones and clear them from the hive.

Worker Bees

Worker bees perform many functions during their lifetime, which lasts about six weeks. After making the transition from pupa to adult, workers feed honey and pollen to the queen, drones, and larvae. During this stage, the workers are called nurse bees. They secrete royal jelly, a high-protein substance that they feed to the queen and youngest larvae. After about a week, worker bees stop secreting royal jelly and begin to secrete wax, which they use to build and repair the honeycomb. During this stage, they may also clean and guard the hive and fan their wings to circulate air through the hive.

The workers spend the last weeks of their life gathering nectar and pollen. A number of structural adaptations aid them in this work. Their mouthparts are specialized for lapping up nectar, and their legs have structures that serve to collect and transport pollen from flowers.

The workers do not use their ovipositors for egg laying. Instead, their ovipositors are modified into barbed stingers that the workers use to protect the hive. When a worker bee stings an animal, the stinger and attached venom sac are left behind in the victim as the bee flies away. The worker, having lost part of its body and much of its hemolymph, dies a day or two later. Wasps also have stingers that are modified ovipositors. Unlike honeybees, they can sting many times because their stinger is not barbed.

The Queen Bee

The queen bee develops from an egg identical to the eggs that develop into the workers. Queen bees develop only when selected larvae are fed a continuous diet of royal jelly throughout their larval development. As a queen matures, she secretes a pheromone called the queen factor that prevents other female larvae from developing into queens.

The queen's role is to reproduce. Within a few days after she completes metamorphosis and emerges as an adult, she flies out of the hive and mates in the air with one or more drones. During mating, millions of sperm are deposited in the queen's seminal receptacle, where they will remain for the five or more years of her life. Although the queen mates only once, she may lay thousands of eggs each year.

When the hive becomes overcrowded, the queen leaves the hive. As she leaves, she secretes a swarming pheromone that induces about half of the workers in the hive to follow her and form a swarm. Eventually the swarm finds another location for a new hive. Meanwhile, in the old hive, the remaining workers begin feeding royal jelly to other larvae. When a new queen emerges, she produces the queen factor, and in response, the workers destroy the other developing queens. The new queen departs on a mating flight, and the cycle begins again.

The Dances of the Bees

When honeybees leave the hive and find a source of pollen and nectar, how do they communicate the location of this food source to other workers in the hive? An Austrian biologist, Karl von Frisch (1886-1982), spent 25 years answering this question. His careful experimentation earned him a Nobel Prize in 1973.

To study bees, von Frisch built a glass-walled hive and placed feeding stations stocked with sweetened water near the hive. He noted that "scout bees" returning from the feeding stations would perform a series of dancelike movements in the hive. The scout bee would circle first to the right and then to the left, a behavior that von Frisch called the round dance.

Interpreting Nonverbal Communication

Materials pencil, paper, wrapped candy pieces

Procedure

1. Choose one member of your group to play the part of the "scout" bee. The others in the group will be the "worker" bees.

2. Your teacher will secretly tell the scout bee where a "food source" (piece of candy) is located. The scout bee will develop a method of nonverbal communication to let the worker bees know where the food is hidden. The scout bee may not point to the food. Use Figure 3711 for ideas on how to develop your method of communication.

3. When the food has been located, the scout will hide another piece of food and select a new scout. The new scout will develop a different way to tell the group where the food is located. Repeat the procedure until everyone in your group has been a scout.

Analysis

1. How effective were each of your scout's methods for showing the location of the food?

2. Did the worker bees improve their ability to find the food after several trials?

3. List and describe some types of nonverbal communication that humans use.

(a) ROUND DANCE

(b) WAGGLE DANCE

figure 37-11

Honeybees use two types of dances to convey information about food sources. (a) The round dance indicates that a food source is nearby. (b) The waggle dance indicates the direction of food and the food's distance from the hive.

(b) WAGGLE DANCE

figure 37-11

Honeybees use two types of dances to convey information about food sources. (a) The round dance indicates that a food source is nearby. (b) The waggle dance indicates the direction of food and the food's distance from the hive.

A round dance pattern is shown in Figure 37-11a. After many observations, von Frisch concluded that the round dance told other worker bees that a food source was near the hive, but it did not inform them of the exact location of the food.

Von Frisch also observed that when the food source was far from the hive, the scout bees would perform another type of dance on a vertical surface inside the hive. He called this dance the waggle dance because the scout bees waggled their abdomens from side to side. As you can see in Figure 37-11b, the pattern of the waggle dance is like a figure eight. The scout bee makes a circle in one direction, then a straight run while waggling her abdomen, and then another circle in the opposite direction from the first. The direction of food is indicated by the angle of the straight run on the vertical surface. Straight up, for example, indicates a direction toward the sun. The distance to the food source is indicated by the duration of the dance and the number of waggles on each run.

Altruistic Behavior

When worker bees sting an intruder to defend the colony, they cause their own deaths. This behavior is an example of altruistic (AL-troo-IS-tik) behavior, which is the aiding of other individuals at one's own risk or expense. The stinging of honeybees is an innate behavior. You might think that the genes directing this behavior would eventually be eliminated from the population, since dead bees can't reproduce. However, this does not happen.

Genetics explains why evolution has selected for altruistic behavior in honeybees. Worker bees are nonreproductive. Therefore, they cannot pass on their own genes by reproducing. However, they can pass on some of their genes by helping a closely related individual reproduce. By defending the colony, a worker bee increases the chances that the queen bee will survive. If the queen survives, she will produce more workers who will share many of the same genes. Thus, by behaving altruistically, a worker can cause more of her genes to be propagated in the population. This mechanism of propagating one's own genes by helping a closely related individual reproduce is called kin selection.

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