Insects As Helpers

Insects as Helpers

Some other helpful insects we call predators and parasites. Insect Friends The predators are the lions and tigers of the insect world. Some devour of Man a large part or all of their prey. Others, such as the ant-lions, merely suck the body fluids. F. C. Bishopp The predatory insects of greatest economic importance are the dragonflies, damselflies, aphis-lions, ground We must spend some time in our beetles, lady beetles, and syrphid flies. gardens watching insects at work to ap- Among the many other predators are preciate how they cooperate in giving the ant-lions or doodle-bugs, robber us food, flowers, and comfort and to flies, snipe flies, tiger beetles, and wasps know that insects arc not all bad. and ants. Some insects improve soil. Air penetrates the soil through the burrows of DRAGONFLIES AND DAMSELFLIES are ants, grubs, beetles, and wild bees. interesting and familiar. There are These burrowing hordes also bring about 2,000 known species, 300 of earth to the surface from the deeper which occur in the United States. The soil layers and thus aid in improving gauzy-winged, brilliantly colored crea- its physical condition and in burying tures called dragonflies, devil's-darn- decaying vegetable matter. The grubs, ing-needles, or mosquito hawks live or larvae, of many wood-inhabiting around ponds, lakes, and swamps. beetles, ants, termites, and minute in- Their enormous eyes, made up of as sects (like the springtails) are con- many as 20,000 sight units, or facets, stantly at work, tearing to pieces leaves, occupy a large part of the head and twigs, and trunks of fallen trees so that are so curved as to permit the insect to they may be returned to the soil to pro- see in all directions at once. A network vide nutrients for other plant growth. of veins covers the two pairs of large, Insects hasten the decay of animal rigidly extended wings. bodies and their return to the soil. Thus Its highly developed eyes and speedy they figure in the endless cycle that in- flight enable the dragonfly to catch in volves all life. Not that the insects en- flight the mosquitoes and other small gaged in soil-forming activities are insects that are its only food. In flight wholly beneficial. Some, like white the legs form a sort of basket into grubs and cicadas, in their young stages which the small insects are scooped. may damage plants by feeding on the The dragonfly, while still on the wing, roots and (as adults) by attacking the promptly devours the insects with its stems, twigs, leaves, or fruit. Others, stout jaws, which work sidewise. such as blow fly maggots, after they Among our dragonflies is the big green have done their work of carrion dis- darner, Anax junius. posal and soil penetration may become The dragonflies are fast fliers and disease-bearing flies. may travel far. Some of the larger spe- 79 8o Yearbook of Agriculture 1952 cics commonly hunt several miles from plant. The many species have similar their breeding grounds. They migrate habits and general appearance. Some long distances when swamps dry up. are pale green. Others are brownish. Migrations from Australia to Tasma- The adult lacewing usually lives 4 to 6 nia, 200 miles away, have been weeks. In that time the female may lay recorded. several hundred eggs. The damselfiies are smaller and To keep the ravenous little aphis- more delicate than the dragonflies, flit about more leisurely, and fold the wings on the back when at rest. They prey on small, soft-bodied insects. The young of dragonflies and damselfiies, known as nymphs or naiads, destroy mosquitoes and other insects in the water. These strange-looking creatures live among the debris of stones on the bottom of streams and ponds. They have an odd, jointed extension of the imder lip, or labium, which folds over the mouth parts but can be suddenly extended to grasp prey with its two ]Jovverful hooks. The tiny naiads usually grow to full size, I to 2 inches long, in several Enallagma exsulans, a damselfly. months, but some species may spend 3 or 4 years in this stage. When it is lion that first hatches from devouring grown, the naiad crawls out of the its brothers and sisters before they water on a stick or stone. When it has hatch ( and perhaps to give protection dried ofl^, the skin splits down the back, from, other enemies ), the mother lace- and the head, thorax, netted wings, wing lays each oval egg on the top of legs, and finally the long abdomen are a delicate stalk projecting from the sur- drawn out. Soon the beautiful wings face of a leaf or twig. The incubation are spread, the metallic colors appear, period is 6 to 14 days. The larvae are and the new predatory life begins. odd, grayish-brownish creatures. They have a rather broad abdomen and con- THE APHIS-LIONS are among the spicuovis curved jaws, which extend most helpful insects of prey. There are forward from the head. With its pin- 15 families in this group of nerve- cerlike jaws the larv'â seizes its prey and winged insects. All arc predaccous. sucks out its body juices. Among them are the dobsonflies; the W-hen the larvae attain full growth, ant-lions, or doodle-bugs; and the in 2 or 3 weeks, they spin oval, yellow- aphis-lions, or golden-eyed lacewings. ish-white pea-sized cocoons on a leaf. The aphis-lions are in gardens every- The larva in its spinning operations where. They destroy many kinds of de- tops off each cocoon with a circular structive insects, the eggs of many cap, which the pupa pushes off when câterpillars, all stages of plant-feeding it is ready to become an adult. The mites, scale insects, aphids, and mealy- change to the adult stage takes i to 3 bugs. weeks in warm weather. Aphis-lions are the young, or larvae, of delicate, gauzy-winged insects with PRAYING MANTIDS are odd-looking rather long antennae and beautiful relatives of the grasshoppers. The name, golden eyes. These lacewings often are comes from the attitude they assume seen crawling about on the leaves or as they rest on twigs or stalk their prey. flying rather clumsily from plant to The Chinese mantis is 4 inches long Insect Friends of Man 81 and can capture, hold, and devour fourth inch long. It then attaches it- large insects. Since it came into the self to a leaf or stem by the tip of its United States about 1896, it has spread abdomen, draws itself up, and pupates. through much of the East. Like all The cast skin often remains more or less members of its family, it lives on insects over the pupa. The adult splits the in its nymphal and adult stages. The pupal skin and crawls forth to make mantid is cannibalistic. The female de- further inroads on the fast-multiplying vours the male with which she mates aphids. Some species congregate in and often eats her own young. great masses in the fall and spend the The eggs, laid in rather large masses, winter in that way in some protected are firmly attached to twigs of trees. place. Each mass contains 50 to 400 eggs. A The vedalia, the small, reddish- female often deposits 3 to 6 masses. brown Australian lady beetle, has done Winter is passed in the egg stage. There yeoman service against the cottony- is usually only one generation a year. cushion scale on fruit trees in the The young resemble the adults except United States, Hawaii, New Zealand, that they have no wings. and other countries into which it was imported to do just that. We tell more LADY BEETLES have habits that are about the vedalia on page 380. anything but ladylike. Both the young Syrphid flies help in the pollination and adult beetles kill and greedily eat of crops. The sluglike larvae of many various soft-bodied insects. Most famil- species are effective killers of various iar are the bright reddish-yellow spe- plant pests, especially aphids. The flies cies, which has black spots on the wing usually are brightly colored. Some have covers, or elytra, and the black species, banded bodies and buzz loudly in fly- which has red spots. Less well known ing, so they are often mistaken for bees. are the numerous minute black species. The eggs are laid on the leaves near Not many persons associate the rather aphid colonies. Even the newly hatched clumsy-looking dark-colored larvae larvae capture and destroy aphids. with the bright-colored adults. Neither Adults and larvae of many other do gardeners, familiar with the Mexi- groups of the true flies prey upon other can bean beetle and the squash beetle insects and are of value in reducing and their depredations, recognize them pest damage. as lady beetles gone astray. Many of the lady beetles are native to the THE PARASITIC INSECTS are less spec- United States. Their combined action tacular in their work than the preda- in destroying the eggs and young of de- tory ones but are more interesting and structive aphids, scales, and other soft- helpful to man. Several groups of in- bodied plant-feeding insects is of great sects contain species that are parasitic value to those who raise crops and on other insects. The most abundant flowers. and important of these are two-winged Sometimes they are called lady birds, flies and the wasps. as in the old rhyme : "Lady bird, lady Parasites attack insects of all types in bird! Fly away home! Your house is all stages of development. The host is on fire, your children do roam." not killed at once. Usually the larva of The eggs of lady beetles are oval and the parasite enters the body of its host yellow or orange. They are laid in small and feeds on its tissues until it is nearly masses, usually on the under side of grown ; then the host dies. The parasite leaves, and hatch in a few days. The may then pupate within the dead body young larva, with its six long legs and or emerge and pupate on or nearby the tubercle-covered body, starts in search remains of the host insect. for soft insects. It devours one aphid Tachinid flies resemble large, bristly after another. In about 20 days it be- house flies. The many species prey on a comes full-grown and is about one- wide variety of insects, especially cater- 82 Yearbook of Agriculture 1952 pillars. The flies arc seen frequently feed to their young. Both yellow-jack- about flowers, feeding on the nectar. ets and the larger wasps, reddish to Most of the species lay eggs, but some mahogany in color and known as deposit maggots. The eggs are usually Polisies, kill such destructive caterpil- attached to. the skin of the host. On lars as the corn earworm and army- hatching, the maggot penetrates the worm. The yellow-jackets build large^ skin. A caterpillar may be killed by a globular, enclosed paper nests on build- single fly larva, or it may serve as host ings, in trees or shrubs, or in under- for a dozen or more. ground cavities. The Polist es build flat, Some species lay their eggs on the open nests in similar situations. They soil, and newly hatched maggots seek a can be a nuisance about houses because host, penetrate its body, and develop they sting viciously when they are mo- within it. The troublesome European lested. The benefits derived from the earwig is heavily parasitized by a fly predacious habits of the Polist es out- of this type. Other species oviposit on weigh their objectionable traits. the leaves of plants. When a caterpillar These wâsps are social. Their fam- eats the leaf, the small eggs are swal- ilies are made up of males, females, lowed, the maggots hatch, bore and sterile workers. Usually the ferti- through the wall of the digestive tract, lized females of Polist es pass the win- and develop in the body cavity. ter in protected places like attics while Compsilura concinnata, a fly im- the yellow-jackets overwinter in pro- ported from Europe to combat the tected places out of doors. In the spring gypsy moth and brown-tail moth, in- they start a small paper nest, lay eggs serts its young into the caterpillar. The in its cells, and rear a small number of fly has been found to develop in the workers, which continue to build more larvae of about i oo different species of cells and largely take over the care of destructive caterpillars, which it checks the young. During a season a Polist es effectively. nest may become 6 to 8 inches in di- The flesh flies are a large family. ameter and house several hundred Some are small and some are rather wasps; the yellow-jacket family may large and gray. They have varied reach several thousand. habits. Some are parasites of warm- The mud daubers, thread-waisted blooded animals. Others are scaven- wasps, and digger wasps are not social. gers. Many are parasitic on many kinds The mud daubers construct nests of of insects, some of which are serious mud in buildings or other protected crop pests. All flesh flies deposit living places and store them with soft-bodied young. insects or spiders, upon which the The grasshopper maggot, a parasite young feed. The other two groups of of grasshoppers, is a member of this wasps I mentioned make individual family. The adult fly emerges in spring nests in the soil or in logs and store from the soil where it has spent the them with insects or spiders. In this winter as a pupa, soon mates, and be- group are the so-called tarantula killers gins depositing its maggots on grass- and horse guards. Horse guards do hoppers, usually while the grasshopper much good by catching horse flies, horn is in flight. The fly darts at a hopper in flies, and stable flies on livestock. the air and attaches one of its minute The parasitic wasps help man by sticky maggots to its host. The larva combatting destructive insects of prac- bores in; when it is fully developed/the tically all kinds. Like other parasitic host dies. The large maggot then and predatory insects, however, they crawls out and enters the soil to pupate. do not confine themselves to injurious Wasps feed mostly on other insects. insects. Some direct their attack against The yellow-jackets eat vegetable mat- other parasitic insects and are called ter, such as overripe fruit, and soft- secondary parasites. bodied insects, the juice of which they The appearance, host relations, and Insect Friends of Man 83 other habits of the parasitic wasps are Lysiphlebus testaceipes, a useful and varied beyond the possibiHty of gen- readily observed parasite, is a slender eralizing about them. Typically^ the but industrious little insect that de- adults have four wings, usually clear, stroys millions of aphids. It becomes with various types of veins. The body very active on sunny days. Then it color is mostly brown or black. The scurries about among the aphids on a leaf and stops here and there to tap an aphid with its antennae. Afterwards, it thrusts its ovipositor into the aphid with a quick motion and deposits an egg within. The aphid shows no ill effects for about 3 days, when it stops reproducing. Soon the rapidly devel- oping parasite larva devours the vital organs of the aphid. The minute egg parasites are ex- Lysiphlebus testaceipes ovipositing in an tremely numerous and of great eco- aphid. nomic importance. One of these, Tri- chogramma minutum, which destroys wasps difiPer greatly in size. Some are the eggs of many of our most injurious so small that several may develop with- pests, such as the cotton leafworm, boll- in an insect egg no larger than a pin- worm, codling moth, and sugarcane head. Others have a body length of 2 borer, has been propagated and re- inches or more. leased by the millions in infested fields Among the parasitic wasps are di- and groves. There is doubt, however, as verse types of reproduction and host to the degree of control these parasites relations. Females of some species in can achieve. several families reproduce generation after generation without males. Others INSECTS are indispensable as polli- have both sexes in certain generations. nizers of plants. Many insects serve us In general, virgin females produce in this way—thrips, butterflies, ants, female offspring. Among the wasplike beetles, flies, wasps, and bees. parasites two to a dozen or more in- The chapters that follow give details dividuals may develop from a single of this vital subject, but it is hardly egg—a phenomenon known as polyem- bryony. It occurs in several families of '7f''''"%>. this group. Their reproductive capacity often is enormous. A number of species deposit several hundred eggs a day and lay a total of 1,000 to 1,500. In some species the developmental cycle may be completed in 5 to 10 days. If suitable hosts are present, therefore, the number of offspring of a single female might reach millions in one season. Certain species of parasitic wasps attack only one species of insect or are restricted to closely related species as hosts. Many, though, will attack a great variety of hosts. Some species of parasites lay their eggs in the (^gg of the host, and the larvae do not complete Trichogramma minutum female stinging a development until the host has reached moth e^g and placing its own egg larval maturity or has pupated. within it. 84 Yearbook of Agriculture 1952 amiss to give some of the main points pupate. In this quiet stage the larva here, too. transforms to the winged insect in Some 50 seed and fruit crops depend about 12 days. Thus the development on honey bees or yield more satisfac- from egg to adult takes 21 days. Drones torily because of their presence. Some, require 24 days and queens only 16. such as red and white clover, onions, The worker bee, on reaching maturity, most varieties of apples, sweet cherries, cuts out the cell cap and crawls out. and plums, would be barren without For a time it is relatively inactive. insect pollinators. Then it becomes a nurse or house bee A strong colony of honey bees may and helps care for its sisters. Later it contain 60,000 or more workers. An takes up the work as a field bee. Some estimated 37,000 loads of nectar are field bees gather nectar. Others collect required to make a pound of honey; pollen, which is tucked into the pollen the bees in a colony, each making 10 baskets formed of hairs on the outside field trips a day, would visit 300,000 of the tibia of the hind legs. flowers a day. Thus honey bees are The place of bees in agriculture is more important in fertilizing crops coming to be recognized, and more at- than in producing honey—even though tention is being given to the use of 200 million pounds of honey and 4 mil- honey bees in the replacement of wild lion pounds of wax are produced each bees as crop pollinizers. Intensive cul- year in the United States. tivation of land and the general use Beeswax, extensively used in indus- of insecticides are rapidly eliminating try and the arts, is secreted as thin native pollinating insects. Increasing scales or flakes by glands on the under the number of hives of honey bees and side of the abdomen of the worker bee. the numerical strength of those colo- The bee uses wax to make the comb, nies is a means of overcoming this defi- in which honey is stored and the young ciency in our agriculture. reared. The artistry and engineering ability of the bee can be appreciated AN EXAMPLE of the unusual rela- by noting the perfection of the hexag- tions of insects to plants—the delicate onal cells and the evenness of their balance between plants and their pol- delicate walls in a section of comb linators—is that of the minute fig wasp honey. and the Smyrna fig. The fig is a fleshy, In every colony there are three hollow, pear-shaped growth, which forms, the queen or female, drones or contains hundreds of minute flowers males, and workers. The workers, im- lining the interior surfaces of a cavity. perfectly developed females, arc most The cavity has a tiny opening at the numerous and do all the work. The apex, the free end. The Smyrna fig drones are somewhat larger than the produces only female flowers and no workers, devoid of stings, and few in pollen. Before 1900 the Smyrna figs number. They appear most plentifully produced in the United States were in the early summer at swarming time, inferior to those grown in Asia Minor. after which the workers drive them out An investigation revealed that this was of the hives. due to the absence in California of the The queen is much larger than the minute, wasplike insects that serve as worker bees and her sole duty is to lay pollinators of the Asiatic figs, their sole eggs. During the 2 or 3 years of her agent of pollination. The insects de- existence she may lay as many as a velop in wild inedible figs known as million eggs. These are placed in the caprifigs, which produce only male bottom of newly cleaned and polished flowers with an abundance of pollen cells and hatch into minute w^hite, leg- and which are the parent stock of our less grubs, or larvae, in 3 days. edible figs. The male insects are wing- The cells are capped by the workers, less and never leave the fruit in which and the larvae spin their cocoons and they develop. They find a female still Insect Friends of Man 85 in a gall-like formation within the fig, The largest yields of lac and dye are puncture this cell; and fertilize the fe- obtained by harvesting the infested male. She then gnaws her way out and twigs while the females are still living. in escaping from the fig becomes cov- That is done twice a year, about June ered with pollen. She is winged and and November. The encrusted twigs flies about seeking a place to lay her are known as stick lac. About 40 mil- eggs. She enters Smyrna figs as well as lion pounds of the material are har- caprifigs if they grow near each other. vested each year. The stick lac is The Smyrna figs are not suitable for ground, largely in crude mortars. The the development of the fig wasp, but resulting granular lac is called seed pollen from her body accomplishes fer- lac; the ffne particles are molded into tilization of the fig flowers and the toys and ornaments, and the wood is development of a delicious fruit. used for fuel. The seed lac is then Repeated efforts to introduce the fig washed, melted, spread out in a thin wasps from Asia Minor into California layer, and dried, thus forming the shel- were finally successful. Recently these lac of commerce. Many people of In- wasps began causing trouble by carry- dia depend upon the lac industry for ing a disease, brown rot, from the wild a living. figs to the Smyrnas. This was met by The red dye from the lac insects is rearing the ñg wasps by millions in in- little used today. It is made by evapo- cubators free from the disease and rating the water in which the seed lac liberating them in the fig orchards. is washed. A dye formerly widely used in in- MOST SCALE INSECTS are injurious dustry, known as cochineal, is made because they suck the juices from many from the dried, pulverized bodies of an of our cultivated plants. Some, how- insect related to the lac insect. It lives ever, have been turned to our benefit. on a cactus or pricklypcar. Cochineal The lac insect, Laccifer lacea, is one. is used mainly in cosmetics, as a color- It lives on trees of the fig family, coming for beverages, and in decorating monly in the East Indies, Malay, and cakes and pastries. It used to be prized India. The minute young lac insect, or as a dye for textiles because of its per- crawler, finds a suitable place on a manence. twig, or branch, inserts its beak into the Cochineal is produced mainly in plant tissue, grows, and secretes a resin- Honduras, the Canary Islands, and ous material, which ultimately covers Mexico. The insects are kept over win- it. The thousands of crawlers settle ter on cactus plants in houses. In spring side by side, and the resinous secretion the females are transferred to cacti out- builds up around them and completely doors and can be harvested in 3 encases the twig. Most of the crawlers months. About 70,000 insects are re- develop in about 3 months into fe- quired to make a pound of dye. males, which occupy small cavities in the resinous mass and from which they GALLS are peculiar growths pro- never escape. The males emerge and duced by a number of insects. They fertilize the females through the small usually damage somewhat the plants openings which extend to the surface they attack, but some kinds are used of the encrustation. As the eggs de- as a source of dyes and tanning mate- velop in the body of the female, she rials and for medicines. assumes a saclike, bright-red appear- The Aleppo gall, or gallnut, pro- ance. The red pigment is the source of duced by a wasplikc insect on several the lac dye of commerce. The female species of oaks in western Asia and east- dies, the eggs hatch, the crawlers ern Europe, has been used for centuries escape and move to a nearby unin- as a tonic, astringent, and antidote for f estcd part of the twig, and the process certain poisons. The early Greeks used is repeated. it for dyeing wool, mohair, and skins. 86 Yearbook of Agriculture 1952 Other galls have been used for dyeing hatch in 10 days. The larval stage re- fabrics and as a tattoo dye. The Aleppo quires 30 to 40 days, during which gall is used for preparing a permanent four molts occur. The baby worms are type of ink. It has been specified in one-eighth inch long, and the full- formulas for ink by the United States grown caterpillar is fully 3 inches long. Treasury and the Bank of England. It is grayish or creamy in color and hairless. It has a hump behind the head SILK originates in the spittle of an and a spinelike horn at the tail. When insect. In China and Japan, thousands full-grown, the larvae become restless of families care for silkworms as a part and, if they are given a suitable place, of their daily activities.during the sum- such as dried brushy plants, they soon mer months. begin to spin their cocoons. The opera- The silk industry began in China, tion takes about 3 days of constant where the source of silk was kept a motions of the head from side to side secret for more than 2,000 years. At- at the rate of about 65 a minute. The tempts to take silkworm eggs out of cocoon is formed from a secretion •the country were punishable by death. from two large glands that extend A few eggs were smuggled out of China along the inside of the body and open about A. D. 555 and taken to Constan- through a common duct on the lower tinople. Since that time commercial lip. As the clear viscous fluid is exposed production has sprung up in some of to the air it hardens into the fine silk the warmer countries^ but the industry fiber. The filament forming a cocoon has been confined largely to China, Ja- is continuous and ranges in length from pan, India, and the Mediterranean 800 to 1,200 yards. The cocoons are region* oval and vary in color, according to Sericulture has been attempted in strain or race, from white to a beautiful the United States and interest in it is golden yellow. considerable. Silkworms can be raised The larva pupates within the co- and mulberry trees grown successfully coon. In about 2 weeks the moth es- here, but a tremendous amount of capes through an opening in the end hand labor is involved and Americans of the cocoon. The cocoons from which must compete with the low labor costs the moths ^ emerge are called pierced in China, Japan, and India. Silk also cocoons. They are of low value because must now compete in price with syn- they cannot be reeled, but they are thetic fibers, which can be produced at carded and made into thread. relatively low cost. Men in the Depart- For rearing moths, the cocoons are ment of Agriculture conducted experi- usually strung on a thread and hung ments with silk culture in 1884-91 and in a cool, dark place until the moths 1902-8. That work and many commer- emerge. The males and females are cial undertakings in different parts of then put on cheesecloth, where they the country proved the impracticabil- mate and where the eggs are deposited ity of silk culture in the United States. ..and adhere lightly to the cloth. The silkworm is the larva, or cater- The race of silkworms most com- pillar, of the moth Bombyx mon. Man monly used produces only one genera- has taken care of it so long that it has tion of worms a year, but other races become thoroughly domesticated. The produce two and still others produce ashy-white moth has a fat body and a several. The eggs are held in cold stor- wing expanse of about 2 inches. It age until they are to be hatched. An takes no food and seldom attempts to ounce of eggs will produce 30,000 to fly. After mating, the female deposits 35,000 worms, which will yield 100 to 300 to 400 round, yellow eggs, which 120 pounds of fresh cocoons. The co- soon become gray or lilac and paler as coons produce i o to 12 pounds of raw hatching time approaches. silk. At summer temperatures, the eggs Mulberry leaves arc used almost en- Insect Friends of Man 87 tirely as food for silkworms. The white low cost. About 1787 cactus plants mulberry. Morns alha, is the preferred were taken to Australia by Capt. species. Foliage of Osage-orange has Arthur Phillip for culturing cochineal been used as a substitute. Lettuce insects for dye. Various species of cacti leaves are sometimes used when the escaped later from gardens so that by larvae arc small. 1925 some 20 difiPerent kinds were The rearing of silkworms is labori- found growing wild. In the absence ous. The larvae are kept in a rearing of natural enemies the prickly pears house on trays in constant shade at a spread rapidly. By 1925 about 60 mil- temperature between 65° and 78° F. lion acres were affected, half of it so They are first fed on chopped mulberry densely covered as to make the land leaves supplied about eight times a day. useless. After 4 or 5 days, fresh leaves are put Australia established a Common- in a tray with bobbinet bottom. On it is wealth Prickly Pear Board in 1920 and placed the tray that contains the sent entomologists to America, the larvae. They soon crawl up onto the original home of these cacti, to study fresh food. As they grow, the larvae the insect enemies and methods of are transferred frequently to fresh rearing and shipping them to Aus- leaves on clean trays. They consume a tralia. This work was continued in surprising quantity of leaves, which North and South America in coopera- must always be dry. Wet leaves or other tion with American entomologists adverse conditions favor the develop- from 1920 to 1937, during which time ment of certain diseases which often more than a half million insects of 50 take a heavy toll of the silkworms. different species were dispatched to For reeling silk, the cocoons are Australia. Several were successfully es- gathered about 8 days after spinning tablished, including cochineal insects, begins, and the pupae are killed, a large plant bug, a moth borer, and a usually with heat, and thoroughly spider mite. The insects checked the dried. They are assorted and are ready new growth of cactus and reduced the for reeling. Reeling also involves much density of the plants so that some grass hand work, although recently devel- was returning. It was not until 1930, oped reels work largely automatically. however, when 3 billion eggs of a The cement holding the fibers together moth, Cactohlastis cactorum, from Ar- is loosened by putting the cocoons into gentina had been released throughout boiling water. After the loose strands the territory, that the hope of control- have been removed by a revolving ling the pest began to be realized. brush the cocoons are put in warm Seven years after the first introduction water and the filament from four or of this moth the last dense growth of fiwe of them is caught up and twisted pricklypear was destroyed and the into a thread which is wound on a reel. land reclaimed and opened to settle- This raw silk is removed from the reel ment and livestock production. in 2-oun(ê hanks, which are weighed The total cost was about £168,600, and baled. or a fraction of a penny an acre—a modest figure as compared with £10 INSECTS do not feed entirely on per acre for the much less satisfactory plants we are interested in growing. chemical and mechanical procedure Many kinds feed on weeds. Certain previously used. species of this sort have been intro- duced with beneficial results into re- F. C. BiSHOPP, a native of Colorado^ gions where some plant has become a has been conducting or directing re- serious nuisance. search in the Bureau of Entomology The control of pricklypear by in- and Plant Quarantine on insects since sects in Australia is an example of what igo^. Since 1941 he has been assistant can be accomplished in this way at chief of the Bureau.