Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. Washington, D. C. July 10, 1924 THE EUROPEAN ELM SCALE IN THE WEST.’ By Frank B. HeErsert, Scientific Assistant, Forest Insect Investigations, Bureau of Entomology. CONTENTS Page. | Page. RMAEMAT HE 1 Life history and habits__________ 9 OLD UU ME G2 Se el 1 Seasonal history —_ Ps - ae P 11 eus¢pry-=- - 3s ee eee 2 | Natural enemies__________ Vee 12 Synony my es Fe Control expermments 2 a SE 13 Distribution and spread at ee _ 5 | Recommendations for control ______ 15 i a pitoios ppetan FT oy nary 8 = eon ae 17 Food plants_______ 2G Falher ee ie). akteree Cited 3 oe ae Fee er 18 _ ISSR aa 6 | INTRODUCTION. The European elm scale, Gossyparia spuria (Modeer), has long been known in Europe and the Eastern United States as a serious enemy of the elm. It was first discovered in the West in 1893, when E. M. Ehrhorn found it infesting elms on the Stanford University campus, Palo Alto, Calif. Prompt measures of eradication were attempted, but were not entirely successful. Since that time it has spread from this or other sources until it is now quite widely dis- tributed throughout the West. It is becoming of considerable impor- tance as a shade-tree pest owing to its distribution and to its par- ticularly aggressive habits in newly infested localities. IMPORTANCE. The elm is probably the most popular shade tree in America. It attains good size, produces a luxurious amount of green foliage, and is planted throughout the United States and elsew here in dooryards, along streets, and in parks for shade and ornament. In the East t Acknowledgments are due to Dr. A. D. Hopkins, Ferest Entomologist: H. FE. Burke, Specialist in Forest Entomology : Harold Morrison, Coccidologist; and others, for helpful suggestions and observations; to W. S. Fisher, Specialist in Forest Coleoptera, for identi- fication of the coccinellid predators : to S. B. Doten, Director and Entomologist of the Nevada Agricultural Experiment Station, and to Frank N. Wallace, State Entomolcgist of Indiana. for the use of a number of illustrations used in this publication, ? Resigned June 30, 1920. 69577°—24——__1 2 BULLETIN 1223, U. 8. DEPARTMENT OF AGRICULTURE. the native elm also produces wood which is particularly valuable it the making of vehicles, baskets, crating, ete. | The European elm scale infests all species of elm, having become such a very disagreeable and harmful pest that in many eastern localities these trees are no longer recommended for planting. In the West the scale insect is not so widely distributed, nor are many of its eastern associates present, so that in spite of the elm scale the tree 1s still recognized as one of the best for shade. Fortunately, the scale in America infests only elms and is not ¢ pest on fruit or other shade trees, as are many of the aggressiv scale insects. HISTORY. This insect was first noted in the United States in 1884, when Charles Fremd found it infesting elm trees in his nursery at Rye, Westchester County, N. Y. It had undoubtedly been imported from Europe, where it has been known for nearly 200 years. It was next reported by Professor Comstock from New York City, where he had found it rather abundant in the winter of 1886-7. A few months later John G. Jack sent specimens to the United States” Bureau of Entomology from slippery elm growing at Cambridge, Mass. In 1888 it was found at Washington, iD: ee infesting elms | on the grounds of the Department of Agriculture and also in two localities on the streets of the city. Up to this time it had not been positively identified, but the next year Dr. L. O. Howard made a thorough study of the insect and _ identified it as the European elm scale (10). A few years later this scale insect was found to have invaded the- western part of the United States. In 1894, Alexander Craw (2), of the California State Board of Horticulture, reported that during the previous season E. M. Ehrhorn had noted the European elm scale upon elms at Stanford University, California. The next year. Mr. Hillman, entomologist of Nevada, reported it from Reno, Nev., and in 1906 A. lL. Melander (6), entomologist of Washington, — stated that it had been in Spokane, Wash., for several years. From time to time it has been reported from one State or another until it is now known to occur in 27 States besides the District cf Columbia. SYNONYMY. As abel as 1788 this scale was known in n Europe, at which time — Reaumur (8) figured the female in all its stages and gave its natural history, but failed to give it a name except that of “pro- egallinsecte ” of the elm. The first name given to it was Coccus ulmi by Linnaeus (74, p. 265) in 1761. In 1875, Signoret (19, p. 27) removed this insect from the genus Coccus and erected a new genus, Gossyparia, with w/mi as the type. The specific name wlme was retained until recently, when it was discovered that it rightfully belonged to another insect named Coccus ulmi Linnaeus (1 3, p. 455) in 1758, since removed to the genus Lepidosaphes. Consequently the next ‘specific name used for the Huo pena elm seale, spwr?us, anvlied to it in 1778 by Modeer q 3 iNumbers in a ee (italic) refer to Literature cited, p. 18. THE EUROPEAN ELM SCALE IN THE WEST. 3 (17), was adopted, so that now the proper name is considered by most entomologists to be Gossyparia spuria (Modeer). The latest change has been by the European coccidologist Lind- inger (12, p. 331). who put this species into Eriococcus, where the writer feeada we that it rightfully belongs. No move has been made toward accepting this name in the United States so far, however, so that the writer does not feel inclined to use it in this paper. The two genera, Gossyparia and Eriococcus, are separable only from the fact that the adult female of the former secrets a semi- cocoon, while the latter entirely covers itself with a cottony cocoon. This means that Gossyparia spuria lacks wax- -secreting glands on the dorsum, which can har dly be considered a generic character. If the name Lricoccus spurius is accepted, then the genus Gossyparia will become a synonym of Eriococcus, as spuria is the type of that genus. From time to time this insect has been referred to under the fol- lowing names: Coccus ulmi, C. spurius, C. laniger, C. gramuntii, Chermes ulmi, Nidularia lanigera, N. qramuntii, Gossyparia ulmi, G. gramuntii, G. spuria, and finally Eriococcus spurius. DISTRIBUTION AND SPREAD. DISTRIBUTION. This common pest is widely distributed, not only in North America but also in Europe, where it reaches from Spain to Tur- key and as far north as Norway. Kuwana (//) has also reported it from the province of Shinano, Japan. The writer has seen speci- mens from there collected by Mr. Kuwana, however, which undoubt- edly are not Gossyparia spuria, but are some rather closely related species. The writer is informed that Mr. Kuwana is now of the same opinion. Instead of being encircled with fringe of wax, the body of the mature female is entirely covered with it—a character which should place this species in the genus Eriococcus. In America the scale is found both in C anada, where it has been reported from the provinces of Ontario and Quebec, and in the United States, where it occurs in 27 States and the District of Columbia. It is still spreading, for occasionally a new State is added to the list. The scale is known to occur in the following East- ern, Central, and Southern States: Maine, New Hamshire, Vermont, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Pennsylvania, Maryland, District of Columbia, Virginia, West Vir- ginia, Ohio, Michigan, Wisconsin, Indiana, ‘Tllinois, Iowa, Mis- sourl, Alabama and Louisiana. In the west the scale occurs in the following States: Colorado, Utah, Nevada, Idaho, Washington, and California. (Fig. 1.) Its distribution in these States is more or less limited) In Colorado, C. P. Gillette, State entomologist, reports that it has been doing damage for some time in the city of Denver. George M. List (/5), his chief deputy, has since reported it from Golden and from near Fruita, Mesa County. W. W. Henderson, entomologist of the Utah | Agricultural Exper iment Station, states that to his personal knowl- edge it exists in isolated places about 100 miles north and south ‘¢ 2 4 BULLETIN 1223, U. S. DEPARTMENT OF AGRICULTURE. of Salt Lake City and in the region between these two extremes, where it occasionally does severe damage. In Nevada it is confined to a limited area in the west-central part of the State, extending from Carson City to Reno, according to S. B. Doten (3, 5), director of the Nevada Agricultural Experiment Station, and from the writer’s personal observations. A. L. Melander (/6), entomologist of the Washington Agricultural Experiment Station, reports that he has not found it anywhere in the State of Washington, except at Spokane, where it has been for 15 years or more. The files of the Bureau of Entomology also contain records of this insect oc- curring at Coeur d’ Alene and Boise, Idaho. In California, the insect is somewhat more widespread, occuring in a number of localities in the northern and central portions of the State. It has been found in or near the following towns: Ukiah, San Rafael, Colusa, Woodland, Davis, Sacramento, Stock- ton, Modesto, Oak- dale, Woodside, Redwood City, Palo Alto, Stanford Uni- versity, Mayfield, Mountain View, Los Altos, Santa Clara, College Park, San Jose, Milpitas, Eden- vale, Los Gatos, and Saratoga. Additional locali- ties in the United States and Canada have been recorded by Albert Hart- zell (8). SPREAD. The elm scale was Ite. 1.—Known distribution of European elm scale in the West. in all probability brought to America from Europe on young elm trees. The shipment of elm stock from infested nurseries to various parts of the United States has also been the cause of its being scattered over such a wide territory. In these infested localities the scale has spread from tree to tree by several agencies. Birds, such as English sparrows, which are to be found in large numbers in the shade trees of almost any town, probably carry the young crawling scales for considerable distances on their feet. During the fall infested leaves drop to the ground and are blown for some distance by the wind. A certain percentage of these larve happen to find themselves at the base of an elm tree and crawl up to start a new infestation. The European elm scale has been seen spreading in this manner by both Professor Doten and the writer, The Argentine (/ridomyrmex humilis Mayr) and THE EUROPEAN ELM SCALE IN THE WEST. Bs) other ants are known to transport scale insects from one tree to another in order to increase their food supply, and this method of transportation probably applies to this species as well as to others, since it is usually attended by a great many ants. Elms are nearly always planted so close that some of their branches interlace, en- abling the larve to crawl at will from one tree to another. Thus it is not long before the European elm scale has thoroughly — estab- lished itself upon most of the elms in a locality. INJURY. Thousands of these scale insects sucking the plant juices from the leaves, twigs, and branches (figs. 2, 3) cause considerable in- jury toelm trees. Their effect upon the elm is shown by yellowing and premature dropping of the leaves, stunting of growth, and dying twigs, branches, and entire trees. Their injury is most apparent on young trees, which occasionally they kill. Mature trees are seldom killed. A less serious trouble is the production of a considerable amount of honeydew. which covers the leaves, twigs, and branches, making them black and sticky. It also drops on the street and sidewalk, making the pavement slippery and ; : 7 dangerous to passing ve- "%* 2—Adwlt females of European elm scale on elm hicles, besides having an 3 unpleasant appearance and odor. Many disagreeable insects are attracted by the honeydew. In some sections the American elm is reported as the favorite host of the European elm scale, while in other localities the English, Camperdown, or slippery elm is reported to be the favorite. The American and Camperdown elms seem to be preferred by it in Cali- fornia. Probably the degree of infestation depends upon the con- dition of the tree more than upon any other factor. 6 BULLETIN 1223, U. S. DEPARTMENT OF AGRICULTURE, Trees which have been attacked for a number of years by this insect, 1f they do not die, finally seem to develop a certain amount of resistance to its injury. The history of this scale insect through- out North America has been much the same. It causes much con-— cern to the owners of shade trees for a number of years after mak- ing its first appearance, and then seems slowly to lose its grip upon the trees until 1t causes a much smaller amount of damage. This— is especially true in sections of the Eastern States and Canada, where less attention than formerly is now paid to this once dreaded insect. FOOD PLANTS. The recorded food plants of the European elm scale in the United. States are English elm (Ulmus campestris), Scotch or Wych elm — (U. scabra), European species, and white or American elm (U. americana), cork elm (U. racemosa), and slippery elm (U. fulva), American species, and their varieties. Probably all species of elms are subject to attack by this insect, although some have not — yet been recorded as host to it.* } Tn 1895 Lintner, then State entomologist of New York, collected immature specimens of a scale insect on willow at Loudonville, N. Y., which were determined at that time as the Kuropean elm scale. This determination has since been corrected and those speci- mens have now been identified as a species of Eriococcus. Signoret (79, p. 21), a French entomologist, has stated that he collected Gossyparia spuria on alder in France. Lindinger (72, p. 54, G4, 122, 159, 338), also a European entomologist, gives the fol- lowing hosts in addition to elm: Acer sp., Alnus sp. (very prob- bly Signoret’s record), Corylus avellana, Frarinus excelsior, and Viscum album, all European records. From the fact that the Kuro- pean elm scale has not been found on any of these hosts in America, the writer is inclined to believe that some related species has been confused with it. At any rate there are no records of the European elm scale occurring on anything except elms in America. The writer has seen both alders and willows growing with their branches interlaced with those of infested elms, yet not a scale could be found on either of them. One specimen of Zelkova acuminata, which belongs to the elm family (Ulmaceae), has been seen growing near a large number of infested elms, but no infestation was apparent upon it. DESCRIPTIONS. EGG “(PI I, “A); Oval in outline, twice as long as wide, 0.36 by 0.19 millimeter. Color bright yellow; surface smooth and shiny. Eyes of larva visible as two black spots through the egg membrane. 4 Aside from the European elm scale the principal insect pests of the elm in the West are the carpenter worm, Prionorystus robiniae Peck, which bores into the trunks and main limbs, often killing large branches and occasionally whole trees; an aphid, Myzo- callis ulmifolii Monell, and a leafhopper, Empoa ulmi L., both of which suck the plant juice from the elm leaves and produce an abundance of honeydew. They are sometimes worse than the elm scale in this respect. ; The elm leaf-beetle, Galerucella luteola Miill., is probably the worst enemy of the elm in the East. where it defoliates a great number of trees every year. It has also been introduced into the West, having been reported several years ago from Portland, Oreg. This has not yet become a serious pest in the West, but may in the near future. THE EUROPEAN ELM SCALE IN THE WEST. - LARV. Figst Srace (Pu. I, B). Color bright yellow soon after hatching. Length 0.45 millimeter; width 0.19 millimeter. Of an elongate oval form, rounded anteriorly and tapering posteriorly to a pair of pointed processes, each bearing one long and several short sete. Anal ring, occurring between these processes or lobes, with six setz or hairs. Legs rather stout, with short tibize. Usual two pairs of thoracic spiracles present. A single row of blunt spines on the lateral margin of larva and a double row extending down the back, some reduced to rudiments. Also winter on corky elm (Doten. ) Fic. 3.—Females of the European elm scale: 1, Dead females in (natural size) ; 2, living females in summer (enlarged about 4 diameters). six extra spines on head and a number of very small spines on dorsum. An- tenn (Pl. III, A) rather stout and 6-segmented, sixth segment longest, fourth and fifth subequal and shortest, each segment bearing several hairs. SEconD Stace (Pt. I, C). Full-grown second-stage larva reddish brown in color. (In life of a gray appearance, due to the protruding wax.) 3ody oval in outline, rounded ante- riorly and rather pointed posteriorly, about 1.1 millimeters long and 0.6 milli meter wide. Eyes situated near margin of body behind antennz. Legs rather long and slender. Two pairs of thoracic spiracles present. Anal ring com- pound, bearing six sete and situated between two prominent pointed anal lobes, each bearing a long slender spine on its tip, also several shorter spines on lobes. Entire dorsum covered with stout blunt spines and arranged more or less in two rows on each abdominal segment. Few small spines on venter. 8 BULLETIN 1223, U. 8S. DEPARTMENT OF AGRICULTURE. In this stage one is able to distinguish the difference in sexes by th number of antennal segments. Antenne of male larva 7-segmented, first seg- ment broadest and seventh longest (Pl. III, B). Female larva with 6-segmen antenne, quite similar to those of male, except that third and fourth segments have been replaced by one long segment, practically equalling the other two CesT, C). Both sexes have pores of the quinquelocular type (Pl. III, #) on the venter, but only the male larva has large circular pores on the dorsum and margin of the venter. These circular pores communicate with internal cylindrical ducts, which bear cup-shaped depressions on their inner ends (Pi. III, @), and are presumably the ones used in secreting the wax to form the pupal cocoon. ADULT OR THIRD-STAGE FEMALE (PL. I, D, FE). Female dull red-brown or green-brown after molting, elliptical in outline, later becoming oval and at the same time forming a waxy fringe about the margin of the body. Upon becoming engorged with eggs the adult female attains a length of 2.1 millimeters and a width of 1.8 millimeters. Antenne (Pl. III, D) distinctly 7-segmented, third and fourth segments longest, fifth and sixth shortest. Previous writers have not always agreed upon the number of antennal segmen.s possessed by the adult female. In some species the number is not constant; however, all western specimens examined possessed ~ 7-segmented antenne. Usual coccid mouth parts and two pairs of thoracic spiracles present. Legs (Pl. III, J) rather long and slender. Anal ring compound, bearing eight sete, and situated between two prominent lobes (Pl. III, H), each bearing three dorsal spines and one termina! and two ventral sete, also a number of nodules which are particularly prominent and abundant on the inner surface. Entire dorsum covered with stout blunt spines, arranged as in preceding stage. Small slender spines and pores of quinquelocular type (PI. III, #) on venter. Large circular pores (Pl. III, G) occur on dorsum and margin of body, being more plentiful on latter. These communicate with internal -cylin- Grical ducts which bear cup-shaped depressions on their inner ends. There are also a few very smail circular pores on the margin of the body communi- eating with small, slender, internal tubular ducts. MALE PREPUPA (PL. II, A). The second-stage male larva after forming a cocoon molts to a prepupa, which is the first dormant stage of the male. Color brownish red. Length 1 millimeter, and width about 0.5 millimeter. Oval in outline with head somewhat pointed. Apex of abdomen 3-lobed, a slender seta occurring on each outer lobe. Antennze and-legs not now long and slender, but short, thick, and immovable. Antenns# indistinctly 10-segmented. Very short wing pads present. No eyes visible and mouthparts lacking. Segmentation of body indistinct. MALE PUPA (PL. II, B). The second dormant stage of the male.is also passed in the cocoon. ‘This is a separate stage from the prepupa, a -molt- having taken place in between. Brownish red in color, oval in outline, slightly longer (1.1 millimeter), and more slender than prepupa. Top of head -more rounded and tip of abdo- men more distinctly three-lobed, central lobe larger and more pointed. Antenne large and heavy, distinctly 10-segmented, reaching to base of wing pads. Wing pads larger, reaching to middle femora or beyond. Legs more distinctly segmented, longer and more slender, anterior pair folded over “ face.’ Body more distinctly segmented; mouth parts lacking, ADULT MALE. Reddish brown in color and longer and more slender than pupa; 1.3 milli- meters long and 0.4 millimeter wide. Head rounded, truncate between an- tennze. Eyes black, with usual dorsal pair present and one ventral pair replacing mouth parts. Antenne rather long and hairy, 10-segmented. Legs long and slender, tibia longer than femur. Caudal end 3-lobed, middle lobe large and pointed, bearing the genital organs; all -three lobes bearing a number of set#. Two large setz# on each outer lobe surrounded with a number Bul. 1223, U. S. Dept. of Agriculture. ZEPPLBIYNN Wat ZCOAAMPAANRIS EUROPEAN ELM SCALE. iA gees B; Dorsal view of first-sta arva. (Second-stage male larva is i D, Dorsal view of newly molted or virgin female. e larva. C, V entical except f E 0 entral view of second r antenne, which -stage female are 7-segmented.) , Ventral view of mature female. PLATE II. Bul. 1223, U. S. Dept. of Agriculture, TG is Ree COTS Et EUROPEAN ELM SCALE. A, Male prepupa. B, Male pupa. C, Wingless male adult. D, Winged male adult. oa PE Bul. 1223, U. S. Dept. of Agriculture. PLATE III. | | / | ' | | | A E )) f) & EUROPEAN ELM SCALE. A, Antenna of first-stage larva. B, Antenna of second-stage male larva. C, Antenna of second-stage female larva. D, Antenna of adult female. £, Quinquelocular type of pore. F, Trilocular type of pore. G, Circular pore and cross-section of internal communicating duct. H, Ventral view of tip of abdomen of adult female. J, Leg ol adult female. PLATE IV. 3, U. S. Dept. of Agriculture. 22 1 Bul. EUROPEAN ELM SCALE in elm (X 10). (Doten.) k B, Larve and male cocoons in early spring (X 16). aled in crac y conce artl p in winter Larvee A, PLATE V. ure. ve L Bul. 1223, U. S. Dept. of Agricul CALE. EUROPEAN ELM S 1 under midrib or cocoons on ) alons A, Larve in late summer Male 16). en.) surface of elm leaf ( elm bark (xX 10). (Dot PLATE VI. SUTyS ySvO ‘MOOD0_ ‘¢ ‘oreur pesurmM “7 On i (‘uej0q) ‘wdnd pure evAiez jo ‘SOTBUT SSOTSUTAA ‘¢ pues “SJUSUTeTY [vue pue SssuUIM Sutpnayoid YAM W00d0| ‘7 “AIVOS W14y NVadOdYeNS THE EUROPEAN ELM SCALE IN THE WEST. 9 of trilocular pores (Pl. III, /'). These are presumably what produce the wax - filaments on some males. There are two forms of the male, winged and wingless. The winged form (Pl. Il, D) has full-sized wings folded over the dorsum when not in use, while the wingless form (PI. II, C) has only short wing pads. The body of the wing- less form is occasionally broader than that of the winged. There are, moreover, ~ all grades between these two extremes, having all sizes of malformed wings. Two wax filaments, borne on the anal lobes, extend posteriorly and equal the length of the body in perfect males. These also vary in length, however, and _ may be present or entirely lacking on either the winged or wingless forms. LIFE HISTORY AND HABITS. In the spring after mating the female scales are found to con- tain a few eggs. By the time “they have completed their semicocoons, _ however, they are well filled with eggs and have increased consid- erably in size. OVIPOSITION. The eggs remain in the body of the adult female until the embryos are about to hatch. As each embryo becomes fully developed the egg is expelled ventrally from near the tip of the abdomen. They are thus laid in a sort of pocket, being protected by the body of the mother and the surrounding fringe of wax. Each female is capable of laying a large number of eggs. Adults ex- — amined on July 5, 1919, after having laid for some time, contained from _ 97 to 138 eggs. Professor Doten, of Nevada, reports having counted _ 60 to nearly 300 dead larvee, which had been unable to escape from under different females. A drawing of the ovaries of an adult female by R. E. Snodgrass (20, fig. 19), would indicate a still larger number. He figures over 200 on one branch of the oviduct making a total of approximately 425 eggs from one female. This would indicate that the rate of increase is quite large, yet not as great as that of many other scale insects. The eggs are laid slowly, covering a considerable period of time, and only during the warm part of the day. One female observed laid 16 eggs in 54 hours, or 1 about every 20 minutes. The larve hatch from these eggs ¢ honk 40 minutes later and are ready to crawl away in another half hour. It has several times been reported that the adult females give birth to living young. These misstatements are probably due to the - fact that the eggs hatched very soon after deposition and were not seen by these observers. LARV. Newly hatched larve are active and soon seek a place for attach- ment. Some attach themselves to twigs and branches, while a large majority of them migrate to the leave es, where they settle on both the upper and lower surfaces along the midribs, the aa ence of the leaf-veins affording them some protection. (Pl. V, 4.) They remain in these positions until fall. By this time ine are second- stage larve, having undergone their first molt about six weeks after hatching. 7 10 BULLETIN 1223, U. S. DEPARTMENT OF AGRICULTURE. In the autumn, when the leaves begin to fade and fall, these larv move to more permanent places, locating in the crevices of the bark on the twigs and branches (Pl. [V, A) and clustering about the win- | ter buds, where they spend the winter. Some of the larve fail to | move from the leaves before these fall from the trees, and are carried considerable distances by the wind. Some of these die from starva- tion, while others crawl up the trunks of near-by trees to new feeding grounds. The first-stage larve excrete very httle wax, but the second-stage larvee are weil covered with sugary-appearing particles of it. This protects them in the winter from frost and rain and incidentally makes them immune to any mild form of spray material. The larvee remain in the second stage for from six to seven months, or from late summer to late winter or early spring. The male larve are the first to leave their winter quarters. In fact, some of them do not wait for winter to end, for on the first mild days in late January they begin to form their cocoons in which to pupate. They seem to be particularly fond of making their cocoons (Pl. IV, 2) on dead twigs or branches, in the bark crevices, or near the crotches of living limbs. Their cocoons may even be found massed together in large white patches (Pl. V, 4) on smooth exposed parts of the trunk or branches. ACTIVITIES OF THE MALE. The cocoon is made of waxy threads, secreted from the pores on the body of the larva. These are woven and twisted about until a definite covering has been formed. After completing the cocoon, which requires several days, the larva changes to a prepupa, which is the first dormant stage in the transformation from larva to adult. A definite molt takes place at this time, the cast skin being pushed out through a shit in the rear end of the cocoon. A week or so later another molt occurs, this time to a true pupa, the second cast skin being pushed back out of the cocoon. (PI. VI, 5.) This stage occupies from one to two weeks, whereupon the pupa changes either to a winged (Pl. VI, 4) or a wingless (PI. VI, 2, 2) adult male. All the first pupe to transform become wingless males, while all the last become winged males. During part of the inter- vening time both winged and wingless adults can be found, together with different forms between these two extremes. For instance, - some males will have partly formed to nearly fully formed wings, while the wax anal filaments may vary from partly formed to full length or even be entirely lacking on either extreme. ‘Temperature and humidity probably cause these variations. E. P. Felt (7), of New York, reports a definite period occurring between the appear- ance of the two forms of the adult male in the State. There is no such period in the West. The wax filaments may be seen protruding from the cocoons for a day or so before the males emerge (Pl. VI, 7). which they accom- plish by backing out. They live only a few days, dying soon after they mate, THE EUROPEAN ELM SCALE IN THE WEST. igt ACTIVITIES OF THE FEMALE. The hibernating female larve begin their activities a little later | than the male larve. In fact, most of them show no sions of activity until March, when they begin molting for the last time m(Pl. IV, 2B). The white cast skins appear quite conspicuous on the bark. The newly molted or virgin females are smooth and of a -dull brown or greenish-brown color. After mating they move about and settle cea for the last time, most of ‘hen selecting the lower side of the larger limbs and branches. They soon take on a 3 grayer appearance and begin to form waxy fringes of cotton or _ semicocoons about the margins of their bodies. By the middle of © May they have about completed their semicocoons and are full. grown, ready to begin oviposition. Egg laying lasts for several ~ months, or until about the middle of ‘August. During this time _ the females have ‘slowly shriveled and die upon completing ovi- position. Soon after molting to the third stage thé females begin excret- _ ing honeydew, and do not stop until egg laying is completed. This _ drops onto the foliage and the ground beneath, making the trees and ground very sticky. A black smut fungus grows in this sticky material, giving the foliage a black appearance which can be seen for erat distances. SEASONAL HISTORY. There is orly one generation a year of the European elm scale. The second- stage male and female larve are the forms hibernating. Late in January in the milder climates a few of the male larve start forming cocoons in which to pupate. These become more abundant during February and March. Adult males begin emerging from their cocoons in February, becoming more abundant in March and April. A few of the last to transform emerge in May. The hibernating female larve molt for the last time in March and April, whereupon they move to a proper place for the summer and mate. They soon begin to increase considerably in size, at the same time forming waxy semicocoons about their bodies. Egg laying starts the last of May or the first of June and continues through June, July, and part of August. Having completed ovi- position the females shrivel and die. The eggs hatch in less than an hour after being deposited and the tiny yellow larve crawl about, some setthng on the twigs and branches, but most of them settling along the midribs of the leaves. About the middle of July the first of these larve molt for the first time, becoming reddish brown and later gray from the sugary particles of wax which are secreted over the back. The last of the yellow larve> molt early in September. ‘These second-stage brown or gray larve are the overwintering forms, and are found mostly clustered about the winter buds and in the rough areas of the twigs and branches. A definite relationship has been observed between the activity of - the European elm scale and its host. As the events in the life cycle ata Peed ee ra ~ whi eo Werte ont ee ee eee ee eo clas Pee Pe OL a SE 12 BULLETIN 1223, U. S. DEPARTMENT OF AGRICULTURE. of the elm are more evident than those of the scale insect, it is well to indicate this relationship, especially since the time of application of control measures often depends upon both. The tree and the insect awaken from hibernation at the same time. The females undergo their last molt while the fruit is forming on the tree. Most of them have attained a large size and are secreting their semi- cocoons when the fruit begins to fall from the tree. The semi- cocoons are completed by the time most of the leaves are full grown, and egg laying starts two or three weeks later. The second- -stage — larve migrate from the leaves back to the twigs and branches when — the tree sap becomes sluggish and the leaves begin to yellow and fall. NATURAL ENEMIES. The insect enemies of the European elm scale are very scarce and play but a small part in its control. The first and only record of the rearing of a parasite from this scale in the United States was in 1898 by Rh. A. Cooley (7), who reared half a dozen specimens at _ Concord, Mass. These have never been described, but remain under the manuscript name of Coccophagus gossypariae Howard. The writer endeavored a number of times to obtain parasites from west- ern material, but was unsuccessful. Either there are none in the West or they are so scarce that they do not figure in the control of this scale insect. The predatory enemies of the European elm scale are somewhat more numerous, but even they can not be considered as important agencies in its control. The twice-stabbed lady-beetle, CAclocorus bivulnerus Mulsant, is the most common enemy of the European elm scale. Essig (6, p. 119-120) mentions that Dr. A. J. Cook reported this beetle as preying upon the scale insect at San Rafael, Calif. The writer also has observed beetles of this species feeding upon the body contents of adult females. Both larve and beetles of the black lady-beetle, Rhizobius ven- tralis Erichson, ted upon this scale insect when in captivity. and in all probability feed upon it when free, as it is usually found abundant upon scale-infested trees. The common black-spotted red lady- beetle, Hippodamia convergens Guérin, and its variety, ambigua LeConte, have been found rather plentiful upon infested trees and probably prey upon this scale insect, yet none have been observed actually feeding upon it. The green lacewing Chrysopa californica Coquillett has also been reared upon the European elm scale and is found to some extent upon infested elms. No other insect enemies of this pest have been observed. : THE EUROPEAN ELM SCALE IN THE WEST. ~-- -13 CONTROL EXPERIMENTS. . TABLE 1.—Haperiments performed upon the European elm seale. Date. Spray material. Dilution. Trees. ae Remarks. Per cent. pre 19USc) Watebon ci. 225 an. we os 100 to 160 pounds 191 85 | Used fire engine® and pressure. hose, large trees. Apr. 191918 |}. - GOS). -se ee hea: 50 pounds pressure. 2 95 | Used garden hose and nozzle, small trees. Wepie 20,1918.) 2... - DOP eat oe ae hs se GOesssscise5.: 1 80 | Used garden hose, ex- tension rod, and 12- foot platform, medi- um-sized tree. May 14,1919 |.-... Ot ete ae Dad ee eee dOSis5-5 os... 2 97 | Used garden hose, small tree. Dec. 3,1918 | Distillate emulsion....} 1 to5............- 3 60 | Hibernating larve. Mar. 5,1919 | Crude-oilemulsion..__|_.... GOs eee Mees 3 60 Do. ae a dose |sDistillateemulsions. -|1to4...) 2 S23 8 60 Do. TIE do-=--~-+| Kerosene emulsion. -.-|1t04.5...-...:.2.- 3 25 Do. pe at Gone el Distillateemulsion= =.) lto4— 22)... .: 1 65 Do. pret 1919 |=. : GO Gakic bea Stee ees es UC a eee 3 60 | Trees in leaf, slight burning. Jan. 19,1920 | Crude-oilemulsion....| 1 to5......-...... 4 60 | Hibernating larve. fhe does sees Distillate enrulsion. | 1 to 4 2.2. 3.22... 3 20 Do. NST SGis 5 ye SE SENG Ks se es eee cere I rok pe ce 3 20 Do. Apr. 12,1919 | Fish-oilsoap.......... 1 pound to 7 gal- 3 5 | Trees in leaf, no burn- lons. ing, young females. yess dope es Etinie-sulp huts a 1 GOO seo a 3 20 Do. Dec. 3,1918 | Miscible oil, 33°...__.. etoulo see ee 5 10 | Hibernating larve. Mar. 5,1919 Miscible oil, Aare ieee GOT see te 3 99 Do. Jan. 19,1920 |..... iis, 2. a eee fea Meee dosceperien 4 98 Do. eee Beene elo, ge wm | AGG... ee 2 100 Do. Mar. 4, 1920 ove 5 ee Se eee dsc 522 ate 4 30 Do. Suse ene ere O Ste en IEG 1D a 3 20 Do. ae: pose” MMiscibie oil, DB gat SARE OO. eae oe. = b= 3 97 Do. Dense ae |e aes OL os oe ek A OMe see eee 4 99 Do. Apr. 18, 1920) |. 222 COPE ets Paes WE Osh Re ee a= ee 2 40 | Young females. = oe 60 Oa ee od ees CG ae pe es ore Ocean sero: 2 95 Do. Sn Ee aes te “a 1A SIO gpa rae rire (BS US 0 al yee a a 1 8 Do. In experiment No. | the trees were large, in No. 3 the tree was medium-sized, and in all the others the trees were snail and could be sprayed from the ground with an ordinary bucket pump. This was the apparatus used, except in the first four experiments, where water was applied. All but one of the experiments were performed at San Jose, Calif., upon the elms growing on the normal school grounds. WASHING EXPERIMENTS. Washing the scale from the elm trees with a solid stream of water was experimented with, since fairly good results had been obtained in this manner by Prof. S. B. Doten, of Nevada (3, 4). In fact, his results seemed more satisfactory than spraying onale a lime-sulphur solution or kerosene emulsion. In preliminary experiments, it was found ‘that the best nozzle that could be obtained for the usual pressure of 50 pounds to the square inch on the garden hose was one with a 3/16-inch outlet and a long taper, 14 BULLETIN 1223, U. S. DEPARTMENT OF AGRICULTURE. On small trees this equipment was used to good advantage to wash the mature scale insects from their resting places. (Fig. 4.) All limbs were within easy reach and the trees so small that a thorough washing was possible. The results obtained were highly satisfac- tory and the trees remained clean until reinfested in the fall. On medium-sized trees the same apparatus was used, with the ad- dition of a 12-foot platform and a 7 or 8 foot extension rod. This proved to be too te- cious and was only moderately success- ful even when done- carefully. On large trees it yas necessary tog have a greater pres- © sure and volume of water in order to obtain satisfactory results. This was obtained by using a fire engine, supple- mented with 1,000 feet of 23-inch hose, a short tapering noz- zle with a circular g-inch opening, and— a stand to facilitate holding the nozzle. (Fig. 5.) It was possible to use a pressure of 160 pounds without doing any damage to the foliage al- ready out. It proved beneficial, in fact, by removing all dead twigs and branches and incidentally giv- Fre. 4.—Washing young elm tree with garden hose and ing the trees and nozzle to remove the European elm scale. lawns a good ITTrl- gating. The crew consisted of one foreman, one engineer, and three hose- men, this number being necessary in order to move the heavy hose without delay. te With this apparatus and crew 191 large trees were satisfactorily washed in six days at an approximate cost of $1.20 per tree. Dur- ing al] the following summer the trees remained very clean, one or two showing evidence of the presence of a few scale insects by a shght drip. The writer estimated that about 85 per cent of the scales had been removed. One year later, however, the trees were again infested rather badly, owing partly to the remaining 15 per cent and to a reinfestation from the surrounding well-infested trees. P ’ ; , = THE EUROPEAN ELM SCALE IN THE WEST. 15 The results of these washing experiments have been previously re-— ported in considerable detail (7). SPRAYING EXPERIMENTS. Sprays consisting of distillate emulsion, kerosene emulsion, or erude-oil emulsion at strengths varying eae. 3 to 5 parts water to 1 part emulsion proved entirely unsatisfactory for the control of the European elm scale, only 20 to 60 per cent of them being killed. A solution of 1 pound of fish-oi] soap and 7 gallons of w ater was used upon some molting females but was completely unsuccessful. . = = ss eo oe HENRY C. WALLACE. Assistant. Secrevary No Sa. Se Howarp M. Gore, TPC CLOT-OF SCICTLANG WOnl 222 Wee BD. Bar, Director of Regulatory Work _~__- 2 -~ W ALTER G. CAMPBELL. Director of Hzxtension Work______- Ps Pe SO C. W. WARBURTON. pre CET 00 = one ap Os 2 ie a ee R. W. WILLIAMS. NEDTA CLAS EXD 211 |) Se a ep APM ee EE CHARLES F. MArvIN, Chief. Bureau of Agricultural Heonomics___________- HENRY C. TAYtor, Chief. Bureau of Animal Industry___ 2s JOHN R. MouHTLER, Chief. iGareawo; Plant nausi yg ee ae eee WILLIAM A. TAYLOR, Chief. PIGMENT ES EIUICE.. 2-3 a5: + an Cee e 18 7 EE ee ee! W. B. GREELEY, Chief. Bareau of Chemistry 2 ae ree ee te C. A. BRowNng, Chief. WSUTEDUAO/. SOUS Soe Se ont AWS Sal er MILTON WHITNEY, Chief. Perea Of Entomol gus2 = a se es L. O. Howarp, Chief. Bureau of Biological Survey____. 2 EK. W. NELSON, Chief. BUTetu OF PUbUG ROGdS. =k. 2 3.) a ee = THOMAS H. MACDONALD, Chief. Bureau of Home Hconomics.__-—___-—_-__-____- LOUISE STANLEY, Chief. Office of Experiment Stations_________ ______ EK. W. ALLEN, Chief. Fixed Nitrogen Research Laboratory________ F. G. CoTTretyt, Director. CATT CHIROILS © =< om eee tS 78 Sg ee oe L. J. HAYNES, in Charge. JOLT, x | ea NE ee ee, eee eA CLARIBEL R. BARNETT, Librarian. Meceral Horlicitihirel Board _. ao C. L. MARLATT, Chairman. Insecticide and Fungicide Board_____________ J. K. HAYwoop, Chairman. Packers and Stockyards Administration______. CHESTER MorrRIL, Assistant to the Grain Futures Administration________-____. Secretary. This bulletin is a contribution from Bureaworpatomowgy. > ee L. O. Howarp, Chief. Forest Insect Investigations________.____. F. C. CRAIGHEAD, Entomologist in Charge. 20 ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT 10 CENTS PER COPY V