LESSON M

The WOWBu,Closer Look

;: Getting a

A compound light microscope

estimated to be 40-50 years old

INTRODUCTIONMany of the organisms pictured on the organ-ism photo cards in Lesson 1 cannot be seenvery well, or at all, with the naked eye. Thosephotos were made with the aid of magnifica-tion. To view the organisms yourself, you woulduse a microscope. In this lesson, you will learnhow to prepare a dry-mount slide and how touse a compound light microscope to observeorganisms. You will also learn how to preparescientific drawings according to a specific set ofguidelines, which you will use throughout themodule. You will learn these skills while observ-ing and learning about an interesting organismcalled the "WOWBug," a tiny wasp that isharmless to humans.

OBJECTIVES FOR THIS LESSON

Learn the parts of a microscope, andpractice manipulating them to obtain thebest image of slide-mounted specimens.

Measure the diameter of the field of

view under different magnifications ofthe compound microscope.

Learn how to handle, manipulate, andrecapture WOWBugs.

Prepare dry-mount slides of liveWOWBugs.

Observe WOWBug grooming behavior.

Draw, label, and measure a WOWBug,following specific guidelines forscientific drawings.

Update your organism photo card forWOWBugs.

12 ST(VMH I M O R G A N I S M S — F R O M M A C R O TO M I C R O

THROUGH THE COMPOUND EYEFor thousands of years, humanbeings have used tools. For abiologist, one of the most impor-tant tools is the microscope.Since its invention in the early1600s, the microscope has beentransformed into a relativelyinexpensive, yet efficient, wayfor scientists such as yourself toview a world invisible to thenaked eye.

You probably will use a com-pound light microscope duringthis module. In this type ofmicroscope, light is providedeither by a mirror or a small,built-in lightbulb. The word"compound" refers to the twolenses—one in the eyepieceand one in an objective—thattogether magnify the image.You can calculate the totalmagnification by multiplying themagnification of the lens of theeyepiece by that of the lens inthe objective.

The drawing on page 14shows the parts of a compoundmicroscope and explains thefunction of each part.

As you use your microscopeduring this module, you will gaina working knowledge of its partsand their functions and becomemuch more proficient at usingthis important tool of science.

(continued)

Since the eyepiece is lOx and the objective is 4x, the total magnification of these

two lenses used together is 40x.

13

LESSON 2 THE WOWBuG: G E T T I N G A CLOS ER LOOK

(continued from pg. 13)

The compound light microscope

Eyepiece—Usually contains a lOx lens

Nosepiece—Holds theobjective lenses;rotates to enablechanging magnification

Objective Lenses—Usedin combination with theeyepiece; provide a rangeof magnifications, usuallyfrom 40x to 400x

Arm—Supports the upper part ofthe microscope; serves as a handle

Stage Clip—Usually one oneach side of hole in stage;helps to hold slides in place

Stage—Supports the slides

Diaphragm—Wheel or lever thatadjusts amount of light thatpasses through hole in stage;provides proper contrast

Coarse Adjustment Knob—Raises and lowers thestage or objective lenses

Light—Sends light through thehole in the stage to illuminatespecimen on slide

Base—Supports the microscope;serves as a handle

Fine Adjustment Knob—Raises and lowers the stageor objective lenses a tinydistance for exact focusing

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LESSON2 Tiii< WO\VBu(.i: GKTTINC A C L O R K K LOOK

When you thinkabout insects, whichcome to mind first?Butterflies? Ants?Bees? In fact, beetlesare the most com-mon insect. If youlined up every kind ofplant mid animal in arow, every fourthorganism would likelybe a beetle. And bee-tles are only one kindof insect!

There are hun-dreds of types ofinsects on Earth,ranging from thecommon to the exot-ic. You're probablyquite familiar withwasps, flies, mosqui-toes, moths, crick-ets, fireflies, anddragonflies. Haveyou ever heard of acicada known as the"buffalo head"because its headresembles a buffalo's,complete with a setof horns? Or thewhirligig beetle,which uses its twosets of eyes in aclever way when it goes swimming? One setlooks above the water's surface, while theother checks out the action below. Anddon't forget the fruit fly, Drosophila. Thescientific study of the brief life cycle of thistiny fly laid the groundwork for moderngenetics.

What do all of these insects have in com-mon? They all have three distinct body

These are just a few of the thousands of varieties of beetles found all over the world.

parts—a head, a thorax, and an abdomen.They also have six legs, four wings, and anouter covering called mi "exoskeleton."

When you think about it, insects are justabout everywhere. They live in our houses, inour gardens, on our pets, and sometimes evenon us. You find them in lakes, ponds, andstreams. They survive on the coldest mountainsand in the hottest deserts.

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LESSON 2 T H E WOWBtIG: G E T T I N G A C L O S E R LOOK

Good Guys andBad GuysSome people don'tlike insects at all.However, each kindof insect has a role toplay in the world, andeach affects our livesin a different way.

Some insects seemto cause more thantheir share of trouble.According to Dr.Robert Matthews, aprofessor at theUniversity of Georgia,insects have causedan enormous amountof human suffering. Some mosquitoes transmitdiseases, like malaria and yellow fever, whichare major threats to human health in much ofthe world. Flying grasshoppers called migratorylocusts destroy entire fields of crops.

We consider other insects to be good guys.Honeybees pollinate the flowers of many of ourfavorite food crops. Anyone who has enjoyed abiscuit with honey also appreciates their efforts.

Less familiar insects, such as parasitic wasps,lay their eggs in or on other insects. A parasiteis an organism that obtains its nutrients fromanother organism, generally damaging the otherorganism in the process.

A World Without WaspsParasites may sound destructive, but they alsoplay an important role. For example, a worldwithout parasitic wasps would be a very differ-ent place. These insects help lower Earth's pestpopulation. In fact, scientists have calculatedthat a single pair of houseflies, if left alone,could potentially produce enough descendantsin a year to cover the surface of the earth sev-eral centimeters deep. Fortunately, this doesn'thappen, thanks to natural enemies such as par-asitic wasps, which kill large numbers of flieseverv vear. D

Few crops can stand up to a swarm of insects such as this.

As you can see, grasshoppers can do considerable

damage to a field of com.

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LESSON 2 THE WOWBUG: GETTING A Cl.USEK LOOK

Dr. Matthews and the WOWBug

Dr. Matthews, second from left, sharing a butterfly collection with

members of the WOWBugs team.

These WOWBugs are only 1.5 millimeters long, but they play a very

large role in helping to control bee and fly populations. Female (left);

male (right). Note the male's unusual antennae.

Dr. Robert Matthews is an ento-mologist, a scientist who studiesinsects. He has studied insectsfor many years and in manyparts of the world.

One of Dr. Matthews's favoriteinsects is a small parasitic waspcalled Melittobict digitata. That'squite a mouthful, which is whyDr. Matthews nicknamed it the"WOWBug." He and his studentshave learned much about thestrange habits of this intriguinginsect. Through their efforts, theWOWBug has become one ofthe newest organisms studied inthe science classroom.

What's so special aboutWOWBugsV And how did theymake their way into the class-room? It was an unlikely begin-ning. Dr. Matthews did not findthe bugs—they found him!While he was a graduate student,Dr. Matthews decided to exam-ine the nests of some little wildbees he found outdoors. lie tookthe nests inside and put them ona shelf in his laboratory. Later,he got the nests clown to studythem. To his surprise, he foundnot little bees, but WOWBugs!Unnoticed, they had sneakedinto the nests, fed, and multi-plied. They had destroyed nearlyall of his bees, and Dr. Matthewswas pretty angry.

Many years later, while think-ing about new ways to teach biol-ogy, Dr. Matthews rememberedthe WOWBug. He realized thatthe same WOWBug behaviors

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LESSON 2 T H E W O W B l I G : ( J E T T I N G A C L O S E R L O O K

Wings

Eye

Hindle§

Female, lateral view

Female, dorsal view

that nearly ruined his early research would makethese little parasites wonderful in the seienceclassroom. WOWBugs breed easily in large num-bers, they have a very short life cycle, and theydon't take up much spaee. Best of all, they can'thurt humans with their stingers.

As he worked with WOWBugs, Dr. Matthewscontinued to learn new and fascinating thingsabout their biology and behavior. He wanted toshare what he was learning. With the help ofother scientists and teachers, Dr. Matthews

developed a set of teaching activities to helpstudents learn science concepts and skills byworking with WOWBugs.

Scientists on the WOWBugs team at theUniversity of Georgia continue to make newdiscoveries every day. They write a newsletter,give workshops for teachers, and develop newlab investigations. If you'd like to learn aboutthe latest developments on WOWBugs, visit theNSRC Web site (http://www.si.edu/nsrc) to finda link to the WOWBugs Web site. D

25

LESSON2 T H E WOWBuc: GETTING A CLOSER LOOK

MICROSCOPE PIONEERSYou can't study organisms thoroughly without agood microscope. This tool, which today's sci-entists take for granted, has played a major rolein helping scientists understand more about Hy-ing things.

Robert Hooke and Antony van Leeuwenhoek(Lay-ven-IiOKE) were important pioneers inthe development of this important scientificinstrument. Hooke was born in England in1635. A member of the Royal Society ofEngland, he was one of the most famous scien-tists of his time. Leeuwenhoek was born in theDutch town of Delft in 1632.

Cork cells as seen by Robert Hooke

Hooke: Discovering the Mysteries of CorkToday, Robert Hooke is remembered more as amathematician than as a biologist. But like allscientists of his day, he had broad interests. Hemade many contributions to biology. In hisbook, Micrographici, Hooke described and illus-trated the discoveries he had made using acompound microscope that he'd built. Hookeused the microscope to observe familiar objectssuch as insects, sponges, and feathers. "When heput a thin slice of cork under the lens of hismicroscope, Hooke made a very important dis-cover)'. He saw the cell walls in the cork tissue.Hooke had discovered plant cells.

Even though his discoveries were amazing inhis day, Hooke's microscope was quite crude. Itdidn't look that different from today's micro-scopes, but it had poorly ground lenses, whichcaused Hooke's view of the objects to be blurredor distorted. YiTiat's more, early microscopescould not magnify objects more than 20 or 30times their actual size. By contrast, most micro-scopes found in middle schools today can mag-nify objects up to 430 times.

Leeuwenhoek Perfects the LensLeeuwenhoek's major contribution to the devel-opment of the microscope was to make lensesthat were much more finely ground than thoseused by Hooke and others. He never went tocollege, and he earned a living by selling fabricin a small shop. For him, making microscopeswas a hobby that became a lifelong obsession.

Leeuwenhoek learned to grind lenses byobserving the craftsmen who made eyeglassesin Delft. Leeuwenhoek's lenses, often no morethan 0.3 centimeters across, were so even andperfect they provided clear images that werefree of distortion. They could magnify objects tobetween 50 and 300 times their actual size. Hemounted the tiny lenses in frames of gold andsilver that he also crafted himself.

26 STC/MS™ O K G A N M S M S — F R O M MACRO TO MICRO

LESSON2 Tin-: \YOWBiu; : G E T T I N G A C I . O S K R LOOK

i a

I I

Hooka's microscope was called a "compound micro-

scope " because it had two lenses.

Unlike Hooka's compound microscope,Leeuwenhoek's device had only one lens. It wasmounted in a tiny hole in a brass plate.Leeuwenhoek placed the object lie wanted toexamine on a sharp point in front of the lens.He adjusted the position with the screws. Theentire device was less than 10 centimeters long.

For a scientist, good tools are just the start.Scientists also need the ability to observe care-fully and to record theirfindings accurately. Theyneed patience.Leeuwenhoek had all thesequalities; in addition, hewas very curious. He wroteabout everything he saw,from algae on pond waterto mineral crystals andfossils. He discoveredmicroscopic organisms inrainwater. He discoveredblood cells and was thefirst to see living sperm inan insect. He is creditedwith publishing the firstdrawing of bacteria.

Leeuwenhoek stuck justabout everything under hislens—including plaque from

Leeuwenhoek's microscope

his own teeth! What did he see? Something thatwouldn't surprise your dentist at all. "I saw . . .many very little living animalcules," he wrote."Very prettily a-moving. The biggest . . . had avery strong and swift motion . . . and shotthrough the water. The second . . . spun aroundlike a top."

Hooke passed away in 1703, and Leeuwenhoekdied in 1723, at the age of 91. Both had become

world famous.Leeuwenhoek was sofamous that Peter theGreat, czar of Russia,once came to Delft tovisit him at his home.

The science ofmicroscopy has madegreat progress since thetime of Ilooke andLeeuwenhoek. To get anidea of how muchprogress, take a look atthe image of a mite. Itwas taken through a

This mite, which measures 150-200 microns

in length (Yiooo mm), is magnified 850 times

its actual size.

scanning electronmicroscope that has amagnification range offrom 15 to 200,000times! D

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