Minggu, 22 Mei 2011

LEBAH 3 - Anatomi Lebah 1

LEBAH 3 - Anatomi Lebah 1

Bee Anatomy

David M. Stone, Teaching Associate, University Laboratory High School, Urbana, IL, U.S.A.

Like all insects, the body of a bee consists of three regions, the head, the thorax, and the abdomen.
The head houses two compound eyes, which are used for distance vision outside of the hive, as well as orienting the bee's flight relative to the sun. Each eye consists of 3000 to 5000 visual processing units called ommatidia. The eyes do not perceive shapes clearly but identify color well. A bee's compound eyes are receptive to ultraviolet light, but less receptive to reds. Bees recognize blue, yellow, white and black.

 Worker head showing distinct compound eyes, antennae, and chewing-lapping mouthparts. Photo by Zach Huang.

You can experience the visual world of the bee, seeing the world as they do, at B-EYE: The world through the eyes of a bee (http://pandora.nla.gov.au/nph-arch/1999/O1999-Sep-6/http://cvs.anu.edu.au/andy/beye/beyehome.html).
Simple eyes, called ocelli, are found near the front and top of the head. Ocelli register intensity, wavelength, and duration of light. At dusk the ocelli estimate extent of approaching darkness, causing the bees to return to their hives.

Top of the head, showing the three ocelli. Photo by Zach Huang.

Antennae receive and analyze highly volatile substances that are responsible for odor and taste. Antennae also perceive vibrations and movement of air, sounds, temperature (the five terminal segments of the flagellum) and humidity (the eight terminal segments of the flagellum) .

Worker antenna showing its three regions.Photo by Zach Huang.

The thorax includes the legs and the wings. At the end of each leg are structures called tarsi, which taste what they touch (more specifically, they detect quality and concentration of different chemicals). Claws and arolia (soft pads between the paired claws of each leg) combine to provide an effortless hold on both smooth and rough surfaces (Apiculture: Know the Bee, Manage the Apiary).

Paired claws and suction pad-like arolium at the end of a bee's leg. Photo by Zach Huang.

The first (frontmost) pair of legs has a notch in its first terminal segment for cleaning antennae. The middle pair has spines on one side specialized for removal of masses of pollen brought to the hive. The third (hindmost) pair of legs each possess a pollen basket (corbicula) in which the pollen mass is kept during transportation from the flowers to the hive. The lower side of this pair of legs also possesses a row of stiff hairs, collectively called the pollen comb.

Front leg showing antenna cleaning notch.

Hind leg showing pollen basket and comb.

Wings of each bee species vary in their venation (vein) pattern. The slight differences in Apis mellifera wing venation can be useful in differentiating between races. The forewing is always larger than the hind wing. The front and hind wings are held together (coupled) by approximately 20 small hooks located along the front margin of the hind wing. Bee wings can beat 400 to 450 beats per minute.

Coupled fore- and hindwings. Photo by Zach Huang.

The abdomen consists of seven visible segments. The first is very narrowed and makes up the petiole (waist) of the bee, while the seventh segment of workers (sterile females) and queens includes the sting (Apiculture: Know the Bee, Manage the Apiary). Wax glands on the underside of worker abdomens secrete the wax that makes up the honeycomb.

Wax scales secreted by the four pairs of glands on the underside of a worker's abdomen. Photo by Zach Huang.

The sting is a modified ovipositor, so it is found only in females. When pushed from the end of the abdomen, it locks into position at a right angle to the base. Muscular abdominal plates then push the stinger into the flesh. The sting has a scalpel-sharp point, with two serrated retractable rods (lancets) on the sides. The venom bulb is positioned at the top of the sting. It continues to pump venom 30 to 60 seconds after breaking off from the abdomen of the worker bee.

Sting with attached venom sack. Photo by Zach Huang.

Closeup of sting showing barbs that prevent easy removal. Photo by Zach Huang.

Up to half of the venom stored in the bulb consists of melittin, a chemical substance that causes pain, impacts blood vessels, and damages tissues. In response, the body of the stung organism produces histamines, which cause localized itching, redness and swelling. Photolipase A2 and hyaluronidase contribute to the swelling and spread of the toxin. Additionally alarm pheromone is released at the time of the sting, stimulating further defensive response in the workers. Each worker dies shortly after stinging her victim because the sting and part of the digestive tract are left are left at the site of the stinging incident (Bishop, 2005).

Tearing away of sting and part of digestive tract. Photo by Zach Huang.


Bee Anatomy

Scientists suspect that bees and flowering plants both evolved around 100 million years ago, in the middle of the Cretaceous period. Before this period, many plants reproduced the way today's conifers do. They released seeds and pollen using cones. The wind carried the cones, and eventually the pollen came into contact with the seeds and fertilized them. During the Cretaceous period, some plants began to reproduce using flowers. Unlike conifers, these plants, called angiosperms, needed the help of insects and other animals to reproduce. Insects had to physically move pollen grains from plants' anthers, or their male structures, to their stigmas, or female structures.

At about the same time, bees differentiated themselves from their wasp-like ancestors. Prehistoric wasps were carnivores that lay their eggs in the bodies of their prey. Bees became herbivores, eating pollen and nectar from the newly-evolved plants and pollinating flowers as they went. Fossil evidence supports this theory -- the oldest known bee fossil is 100 million years old, and the preserved bee has several wasp-like features. This doesn't necessarily mean that bees evolved from wasps. It's more likely that bees and wasps both evolved from a mutual, wasp-like ancestor.

Today, bees still have several physical features in common with their wasp cousins. They also share some traits with ants. Together, bees, wasps and ants make up the insect order Hymenoptera, which means "membranous wings."
A bee's body has a lot in common with the bodies of other insects. Much of it is covered in an exoskeleton made from small, movable plates of chitin. A bee's body is also covered in lots of fuzzy, branched hair, which collects pollen and helps regulate body temperature. The body also has three sections -- the head, the thorax and the abdomen.

The head houses the brain, a collection of about 950,000 neurons. These neurons are specialized, and they communicate with specific neighboring neurons. This division of tasks is part of why a bee's brain, which is a fraction of the size of the bee's head, can perform complex tasks that might ordinarily require a bigger brain. A system of nerves allows the brain to communicate with the rest of the body.
On its head, a bee has two sensory antennae. It also has five eyes -- three simple eyes, or ocelli, and two compound eyes. The compound eyes are made of lots of small, repeating eye parts called ommatidia. In each compound eye, about 150 ommatidia specialize in seeing patterns. This allows bees to detect polarized light -- something human beings cannot do. 

Like most insects, a bee has complex mouth parts that it uses to eat and drink. The sizes and shapes of these parts can vary from species to species, but in general, most have:
  • Paired mandibles, or jaws
  • A glossa, or tongue
  • A labrum and two maxillae
The labrum and maxillae are like lips. They support a proboscis, or tube for collecting nectar.

A bee's two pairs of wings and three pairs of legs connect to its thorax. The wings are extremely thin pieces of the bee's skeleton. In many species, the front wings are larger than the back wings. A row of hooks called hamuli connect the front and rear wings so they beat together when the bee is flying.


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