Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices 7 U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF ENTOMOLOGY— BULLETIN No. 117. L. O. HOWARD, Entomologist and Chief of Bureau. THE RED SPIDER ON HOPS IN THE SACRAMENTO VALLEY OF CALIFORNIA. BY WILLIAM B. PARKER, M. S., Entomological Assistant. Issued May 3, 1913. \ WASHINGTON: GOVERNMENT PRINTING OFFICE. iyi3. U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF ENTOMOLOGY— BULLETIN No. 117. L. O. HOWARD, Entomologist and Chief of Bureau. THE RED SPIDER ON HOPS IN THE SACRAMENTO VALLEY OF CALIFORNIA. BY WILLIAM B. PARKER, M. S., Entomological Assistant. Issued May 3, 1913. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1913. BUREAU OF ENTOMOLOGY. L. 0. Howard, Entomologist and Chief of Bureau. C. L. Marlatt, Entomologist and Acting Chief in Absence of Chief. R. S. Clifton, Executive Assistant. W. F. Tastet. Chief Clerk. F. H. Chittenden, in charge of truck crop and stored product insect investigations. A. D. Hopkins, in charge of forest insect investigations. W. D. Hunter, in charge of southern field crop insect investigations. F. M. Webster, in charge of cereal and forage insect investigations. A. I,. Quaintance, in charge of deciduous fruit insect investigations. E. F. Phillips, in charge of bee culture. D. M. Rogers, in charge of preventing spread of moths, field work. Rolla P. Currie, in charge of editorial work. Mabel Colcord, in charge of library. Truck Crop and Stored Product Insect Investigations. F. H. Chittenden, in charge. C. H. Popenoe, Wm. B. Parker, H. O. Marsh, M. M. High, John E. Graf, Fred A. Johnston, C. F. Stahl, D. E. Fink, A. B. Duckett, entomological assistants. I. J. Condlt, R. S. Vaile, collaborators in California. W.N. Ord, collaborator in Oregon. Thos. H. Jones, collaborator in Porto Rieo. Marion T. Van Horn, Pauline M. Johnson, Anita M. Ballinger. Cecilia Sisc© preparators. o LETTER OF TRANSMITTAL. U. S. Department of Agriculture, Bureau of Entomology, Washington, D. C, November 15, 1912. Sir: I have the honor to transmit herewith, and to recommend for publication as Bulletin No. 117 of the Bureau of Entomology, a manuscript entitled "The Red Spider on Hops in the Sacramento Valley of California," by William B. Parker, an entomological assistant in this bureau. This manuscript deals with a pest the study of which has been hitherto largely neglected and which of recent years has attracted much attention from an economic standpoint, on account of immense losses to growers of hops and other crops in the Pacific coast region and elsewhere. Mr. Parker's studies, as outlined in this paper, have added con- siderably to the knowledge of the habits of this pest and have shown methods by which it may be economically controlled. Respectfully, L. O. Howard, Entomologist and Chief of Bureau. Hon. James Wilson, Secretary of Agriculture. a CONTENTS. Page. Introduction 9 Economic importance fc ... 9 Life history 10 The egg 10 Description 10 Where laid ,..'. 10 Incubation 10 The larva and nymph 11 Descriptive 11 Length of stages 11 The adult 12 Description 12 Copulation 12 Parthenogenesis 12 Habits 13 Habitation 13 Protection 13 Hibernation 13 Locomotion 14 Emergence from hibernation 15 First appearance of mites on hops 15 Migratory activities 15 Food plants 16 Nature of damage 17 General effect of mites upon foliage 17 Relative effect of mites upon male and female hopvines 17 Effect upon the quality of the hops 17 Effect upon man 18 Distribution in the field. 18 Predaceous enemies 19 Experiments for the control of the red spider 20 Methods of experimentation 20 Tag counts 20 Field counts 20 Sulphur 20 Reason for inefficiency ,. 22 Lime-sulphur solutions. 22 Flour paste 24 Lye-sulphur 25 Nicotine solutions and other materials 25 Pure water 26 Value of second application 26 Formulas for sprays 27 Banding with tanglefoot 28 Application 28 Methods of applying sprays 29 Cost of spraying 30 5 O THE BED SPIDER OX HOPS IN CALIFORNIA. Experiments for the control of the red spider — Continued. Page. Cultural methods 30 Stripping the vines 30 Irrigation 32 Fertilization 33 Clean culture. 34 General summary with recommendations 34 Control of the red spider on plants other than hops and cotton 34 Sweet peas 35 Roses 35 Carnations 35 Use of sulphur 35 Bibliography 35 Index - 37 ILLUSTRATIONS. Page. Plate I. Fig. 1. — Fallen hopvine, showing characteristic silvery web and clusters of red spiders {Tetranychus bimaculatus). Fig. 2. — Fallen hopvines, showing silvery web, on which red spiders are clustered . . 16 II. Fig. 1. — Male hopvine injured by the red spider. Fig. 2. — Male hop- vine uninjured by the red spider 16 III. Fig. 1. — Spraying hopvines with power outfit for the red spider. Fig. 2. — Applying precipitated sulphur in dust form as a remedy against the red spider 20 IV. Fig. 1. — Sweet peas infested by the red spider, but protected by dusting, at intervals of one week, with precipitated sulphur. Fig. 2. — Sweet peas, growth aborted, blossoms indifferent, and vines nearly killed by the red spider 20 V. Fig. 1. — Comparison of healthy hops with those infested by the red spider. Fig. 2. — Leaf of hop, the left half of which was sprayed with lime-sulphur and flour paste and the right half with lime- sulphur alone 24 VI. Fig. 1. — Cooking flour paste out of doors. Fig. 2. — Large power spraying outfit, showing lines of hose running into hopyard 28 TEXT FIGURES. Fig. 1. The red spider ( Tetranychus bimaculatus) : Egg 10 2. The red spider: Larva 11 3. The red spider: Adult female 12 4. The red spider: Adult male 12 5. Track of a red spider on blotter 14 6. Hopvines banded with tanglefoot in an attempt to prevent the mites from ascending 28 7. Hopvine tied high and not stripped; lower leaves difficult to spray.'. . . 31 8. Hopvine tied high and stripped; lower leaves matted and difficult to spray 32 9. Hopvine tied low and stripped; leaves readily sprayed 33 74955°— Bull. 117—13 2 7 THE RED SPIDER ON HOPS IN THE SACRAMENTO VALLEY OF CALIFORNIA. INTRODUCTION. The common "red spider" (Tetranychus himaculatus Harvey) has long been known as a pest in flower gardens and greenhouses, where it is often very injurious on ornamental plants. This damage, how- ever, becomes quite insignificant when the injury to hop vines is con- sidered. During the past few years this mite has become recognized as one of the most injurious of hop pests on the Pacific coast and especially so in the Sacramento Valley of California. The investigation upon which this bulletin is based was begun January 1, 1911, at the request of the horticultural commission of Sacramento County and in cooperation with the E. Clemens Horst Hop Co., of San Francisco, and extended over a period of 18 months. Observations were made throughout this period in the 'hop fields in all parts of the Sacramento Valley, and spraying experiments were conducted on both a large and a small scale. The recorded efficiency of the various insecticides tested during this investigation is based upon actual counts of mites present before and after spraying, as well as upon general observations under ordinary field conditions. ECONOMIC IMPORTANCE. The red spider was reported in injurious numbers in the hop fields at Wheatland, Yuba County, Cal., in 1902. Since then it has done some injury to hops in the Sacramento Valley every year and in 1910 the hop crop was seriously injured in many localities. One company, the E. Clemens Horst Co., estimated their financial loss due to this mite in a few of their hopyards near Sacramento, Cal. (allowing 14 cents per pound for hops), to be from $10 to $68 per acre. Other growers were not able to pick their hops so rapidly as did this com- pany, and their loss was necessarily much greater. In some yards near Sacramento the hops were so badly injured that they could not be picked at all and w.ere allowed to remain in the field. Note.— Obligations are due to the manager of the E. Clemens Horst Co. and to the superintendent of the ranches at Perkins and at Wheatland, who placed at my disposal every means possible to cany on the work; to Prof. W. B. Herms, for many valuable suggestions; to Mr. E. K. Carnes, superintendent of the State insectary, Sacramento, Cal., who generously provided me with desk room; and to Dr. F. H. Chittenden, under whose directions the investigation was carried on. — W. B. P. 9 10 THE EED SPIDEE OX HOPS IN CALIFORNIA. An extract from a letter from a former hop grower in Washington State describes conditions there as follows: "The 'red spider' was here in 1901, but did little damage. It gradually increased until 1905, when we let 25 of 85 acres blow away and what we did bale was trash. Then we gave up the fight." The red spider is reported to have been very destructive to hops at Agassiz, British Columbia, but for the past few years has not ap- peared in injurious numbers. The past seasons were very late, and the mites were not present in noticeable numbers in the hop fields near Sacramento until the middle of June. Even so, they had done much damage by August, 1911, and if the crop had not been promptly and rapidly picked many of the hops would have " blown away/' resulting in the total loss of a great portion of the crop. LIFE HISTORY. THE EGG. Description . — T he eggs of Tetranychus bimaculatus (fig. 1) are small, spherical, pearl-like objects, about one-sLxth of a millimeter in diameter, though somewhat variable in size. From 10 to 450 are usually present on a leaf, and with the aid of a hand lens they are readily found upon infested foliage. Where laid. — The eggs are deposited singly and are promiscuously distributed among the webs and upon the underside of the leaves. They are not attached to the host plant by protecting webs, as are the eggs of the citrus "red spider" {Tetranychus mytilaspidis Riley), but are held by strong filaments with which they chance to come in contact. Many eggs have been observed on the loose web which is ordinarily spun over infested leaves. Incubation. — The incubation period varies according to temperature and general climatic conditions. In the experiments conducted at Berkeley, Cal., during February, 1912, the incubation period was found to be from 8 to 10 days. This period during May was from 5 to 10 days, with an average of 7.2 days, while in July, 1911, and during some very warm weather in 1912 it was only 44 days. The relatively higher temperatures of the summer are responsible for this shortening. Fig. 1.— The red spider ( Tetranychus bimaculatus): Egg (position indicated by white circle) among webs on surface of leaves. Greatly enlarged. (Original.) LIFE HISTORY. 11 THE LARVA AND NYMPH. Descriptive. — The larva (fig. 2) is a minute, almost globular object, and differs from the adult in the possession of only three pairs of legs. This six-legged condition lasts only during the first stage, i. e., until the first molt, from which the mites emerge as nymphs, with four pairs of legs, and, except for size and the maturity of the sexual organs, similar to the adults. According to C. H. Perkins,1 the sex- ual organs appear with the second molt, but copulation does not take place until after the third. Length of stages. — The length of the larval and nymphal periods varies, being from 8 to 16 days, according to the prevailing temperature. As shown in Table I, this period under the temperature conditions given in the plat was 15 to 16 days. During May, however, this period was found to be 11 to 12 days and in July, 1911, which was an exceptionally warm month, two mites were observed to be mature 8 days after emerging from the egg. Under field conditions in 1911 it was impos- sible to carry out any very extensive life-history experiments. During the winter, however, a series was carried out in the insectary of the University of California, at Berkeley, Cal. This series is recorded in Table I. Fig. 2.— Larva of the red spi- der. The legs in this stage are transparent. Greatly en- larged. (Original.) Table I. — Transformations and length of stages of the red spider in California , 1912. No. Eggs laid. Hatched. Length of stage. First molt. Length Date. Time. Date. Time. Date. Time. of stage. 1 2 3 4 5 6 7 Feb. 6 6 6 6 8 9 a. m 9 a. m 1 p. m 3.30 p. m.. 8 a. m 3 p. m 9 a. m Feb. 16 15 18 16 16 16 16 8 a. m 12m 3p. m 11 a. m 3 p. m 3p. m 3 p. m Days. 10 9 10 10 9 8 9 Feb. 20 20 20 20 20 20 21 5 p. m. . 9 a. m. . . 4p.m.. 4p. m... 9 a. m. .. 9 a. m. . . 4 p. m... Days. 5 4 4* 31 13| 5 No. Second molt. Length of stage. Third molt. Length of stage. First egg laid. Total time, egg to adult. Date. Time. Date. Time. Date. Time. 1 2 3 4 5 6 7 Feb. 25 25 25 25 25 4 p. m... 4 p. m... 4 p. m... 4 p. m... 4p. m... Days. 5 P 5 5§ 5 4 Feb. 29 29 29 29 9 a. m 9 a. m 9 a. m 9 a. m Days. 3§ 3§ Mar. 2 2 11 a. m.. 11 a. m.. Days. 25 25 2 2 2 3 11 a. m.. 11 a. m.. 11 a. m.. 11 a. m.. 25 24 2 2 5 5 9 a. m. 4 p. m. 29 Mar. 1 9 a. m 11 a. m 4 it- 23 25 Report of the Vermont Agricultural Experiment Station, 1896-97. 12 THE EED SPIDER OX HOPS IN CALIFORNIA. THE ADULT. Description. — The adults of Tetranyclius bimaculatus (figs. 3, 4) are small, greenish yellow or, in some eases, reddish mites ranging in size from 0.27 mm. in the male to 0.50 mm. in the female. The abdomen joins the cephalothorax, formed by the fusion of the head and thorax, at its full width and extends over the portion to which the posterior pair of legs is attached. The abdomen, the cephalothorax, and particularly the appendages are well provided with hairs. The two sexes are very distinct. The female is much the larger and has a broad, rounded abdomen, while in the male the abdomen is narrow and tapering. These dif- ferences are so well marked that the sexes may be distinguished under an ordinary hand lens. Fig. 3.— The red spider: Adult female, dorsal view. Greatly enlarged . (Original.) Copulation. — Copulation begins as soon as the mites become adult, the female often receiving several males. Contrary to the usual method, how- ever, the male operates from beneath the female. The male mite forces its way under the abdomen of the female, braces its legs against the leaf, and directs the genitalia over its back. Parthenogenesis. — The idea that par- thenogenesis occurs with the red spider is an old one, and during this investigation a few experiments were carried on along this line. A morn- ing-glory (Ipomcea sp.) was cleaned of all mites and eggs, the petioles of the leaves were banded with tree tanglefoot, and adult mites were placed upon 10 of the leaves. After eggs were observed the female and all but one of the eggs were Fig. 4.— The red spider: Adult male, dorsal view. Greatly enlarged. (Original.) HABITS. 13 carefully removed from each leaf. When mature the two females that survived upon the isolated leaves were carefully watched to be sure that no male mite reached them. Thirty-three eggs were deposited by these virgin mites and all of the 26 that hatched were males. % HABITS. HABITATION. Small numbers of mites were observed during the early summer on the underside of hop leaves. A few strands of web were usually pres- ent to begin with, and as the number of mites increased the web became more extensive and was observed frequently to cover, in an irregular manner, the entire underside of the infested foliage. The lower leaves were first attacked, but as infestation increased these leaves, which were severely injured, began to dry and thus forced an upward migration of the mites. By August the entire vines were infested and in severe cases mites were observed upon the surface as well as the underside of the leaves. PROTECTION. Inhabiting as they do the underside of the leaves, the mites are well protected from wind and other climatic conditions. Further than this, the web which is spun indiscriminately across the under- side of the infested foliage affords the mites much protection. Where the finer mist sprays were used the webs were frequently not pene- trated and the mites beneath remained uninjured. This combina- tion of web and leaf affords the mites great freedom from injury. The web of the red spider is spun by either sex, and is at all times carried about by the mite as a guard against falling. It thus becomes scat- tered over the underside of infested leaves and other objects over which the mites may crawl. HIBERNATION. A careful examination, during February and March, 1911, of soil and hop roots taken from fields which were badly injured by the red spider in 1910 failed to reveal any hibernating mites or overwintering eggs. During 1911 the mites were found only upon violets and mal- low ( Malva parviflora) which grew in a flower garden half a mile from the hopyards, but they were observed in considerable numbers the following fall, winter, and spring upon wild morning-glory and mallow in all parts of the hopyards. It is evident, therefore, that the mites pass the winter upon wild plants in and around the hopyards, as has been found true of the red spider attacking cotton in the Southern States, by Mr. E. A. McGregor of this bureau. 14 THE RED SPIDER ON HOPS IN CALIFORNIA. LOCOMOTION. In order to determine the probable distance that an adult female mite is capable of crawling in one day, experiments were conducted in the laboratory. A sheet of paper 3 by 4 feet was placed in front of a window in a warm room, a female mite placed in the center of the paper, and its progress followed with a pencil for one hour. (See 40. 7 J Fig. 5. — Track of a red spider on blotter, covering a distance of 40 feet 9 i nches and representing movements during one hour. Sacramento, Cal., 1912. (Original.) fig. 5.) In two cases loose soil was placed on the paper. Table II sums up the results. Table II. — Distance traveled by adult female red spiders in one hour on smooth paper and on loose soil. Ex- peri- ment No. Surface used. Distance traveled. Distance gained. 1 Ft. in. 22 4 23 8 3 7J Ft. in. 2 do 3 .... do 2 0 4 o m 5 20 5 15 9 40 9 6 2 6 do 7 do .. 8 21 1 o m 6 2 The surface of the paper corresponds very well with that of the hopvine, and at this rate an average female mite is capable of cover- ing 211 feet of vine surface during a period of 10 hours. HABITS. 15 In the case of soil, the lumps and sand interfered greatly with prog- ress and were responsible for many changes in direction. The dis- tance gained by these mites in 10 hours varied greatly, approximat- ing 1 0 to 60 feet from the starting point. The actual distance traveled over soil may in some cases exceed the above where the soil is very smooth and hard, but on rough ground is probably much less. From the foregoing experiments it seems probable that the mites can travel some distance over the bare soil, thus infesting plants more or less widely removed from those on which they passed the winter. EMERGENCE FROM HIBERNATION. First appearance of mites on hops. — The hopvines in yards that were known to be infested during 1910 were frequently inspected for mites during the following spring. The first mite observed upon a hopvine was found April 21 in the center of a yard near Sacramento. This lone mite was surrounded by eight eggs and protected by a small amount of dusty web. No more mites were observed until May 9, when a single mite was discovered on a hopvine situated 100 feet from a fence dividing two large hopyards near Perkins, Cal. Mites were later found upon some early hops which were growing along a fence and were also present in about the same numbers upon hopvines some distance from the borders of the hopyards. The mites gradually increased in numbers, and by June 1 occasional hopvines were found on which the lower leaves harbored from 5 to 33 mites each. As is shown by the foregoing data, the mites appeared simultane- ously in various parts of the hop fields and did not, as was formerly supposed, invade the yards from along the edges and work toward the center of the fields. MIGRATORY ACTIVITIES. Before the infestation became severe the mites were observed upon the underside of the lower leaves, over which they had spun a small amount of web. No distinct migration was noted at this time, but as the mites increased in numbers the infested leaves were seriously injured and partially dried. In this condition they furnished very little food and forced the mites to migrate to fresh foliage, leaving behind them from 100 to 450 eggs and at least one-tenth as many larvae. Gradual upward migrations continued until the last of July, at which time the plants were entirely infested. During the month of August a new condition was observed. The morning-glory in the hopyards had become seriously injured by mites. A migration caused by the sudden decrease in the food supply was begun and soon became very extensive. Myriads of mites were seen crawling from the dying morning-glory, over the clods, up the vines and trellis poles, and covering everything with a fine web. A similar condition was noticed on a few hopvines that had fallen from the wire. The leaves that were farthest from the ground were -74955°— Bull. 117—13 3 16 THE EED SPIDER ON HOPS IN CALIFORNIA. covered and often connected by a web which appeared reddish-brown or silvery, according to the number of mites present. The mites were frequently found clustered like swarms of bees (PL I, figs. 1, 2), and the lower ones in dropping off were blown several inches by the wind. That migration did not take place during the early part of the sea- son was evidenced by the fact that 26 vines which were planted that season were noted to be free from mites July 25, 1911, while the sur- rounding older vines were thoroughly infested. Soon after the migra- tions commenced, however, mites were seen upon these vines. FOOD PLANTS. Tetranychus bimaculatus has a remarkably large number of host plants, and as will be seen from the following list, these plants belong to a wide range of families, including glabrous and hirsute plants. For convenience the following list has been divided into three parts. The first part contains a list of greenhouse and ornamental plants attacked by the mites; the second, a list of plants attacked hi the field; and the third, a list of plants which were observed to be infested hi and around the hopyards hi the Sacramento Valley, Cal. List of food plants of Tetranychus bimaculatus. Greenhouse and ornamental plants, etc. — Rose, violet, carnation, mignonette, clematis, pelargonium, abutilon, fuchsia, passiflora. manettia, bouvardia, feverfew, verbena, heliotrope, honeysuckle, hydrangea, salvia, morning-glory, moonflower. cypress vine, phlox, aster, chrysanthemum, dahlia, sunflower, goldenglow (Rudbeckia sp.), calla, Easter lily, Boston smilax, mimulus. slipper flower (Calceolaria sp.). canary bird vine (Tropxolum peregrinum), thunbergia. wedding bells (Burgmansia arborea), castor-oil bean. Asparagus plumosus. cuphea, godetia. caladium. tomato, cucumber, onion, and sweet pea. Field plants, shrubs, and trees.- — Bean, lima bean, cowpea, pea. cucumber, chayote (Sechium edule). cantaloupe, watermelon, squash, celery, eggplant, pepper, tomato, pepino (Solanum muricatum), cotton, okra, corn, raspberry, blackberry, table and sugar beets, hops, hemp, alfalfa, clover, peanut, groundnut (Apios apios), English ivy, ferns, privet, hollyhock, Kentucky coffee tree (Gymnocladus canadensis), wistaria, hop tree (Ptelea trifoliata), pecan, ornamental sassafras, cedar, arborvitse, Colorado blue spruce, maple, horse-chestnut, Carolina poplar, and birch. Host plants in and near hopyards. — Mat-grass (Lippia nodifiora), Amaranthus blitoides, hedge mustard (Sisymbrium officinale), wild sunflower (Helianthus lenticularis), alkali mallow (Disella hederacea), Persicaria lapathiflora (perennial of Persicaria), rough pig- weed (Amaranthus retroflexus) , prickly lettuce (Lactuca scariola), blessed thistle (Cnicus benedictus), alfalfa (Medicago sativa), burdock (Arctium lappa), bun- clover (Medicago hispida), wild morning-glory (Convolvulus sp.), and cheese weed (Malva parviflora). It has also been observed on Jamestown or Jimson weed (Datura stra- monium), ironweed, Jerusalem-oak weed, wild geranium (Geranium memlatum), and Ligustrum amurense. From the foregoing list it is evident that this mite is nearly omniv- orous x so far as plant life is concerned, and without doubt there are many other food plants not included in this list. i It is more than likely, since its feeding habits are of a suctorial nature, that this mite will thrive upon nearly any form of vegetation in which the pubescence of the underside of the leaf is not so heavy or luxuriant as to prevent its direct attack upon the leaf tissue proper. Bui. 1 17, Bureau of Entomology, U. S. Dept. of Agriculture. Plate I. Fiq. 1.— Fallen Hopvine, Showing Characteristic Silvery Web and Clus- ters of Red Spiders (Tetranychus bimaculatus), Indicated by Arrows. (Original.) Fig. 2.— Fallen Hopvines, Showing Silvery Web, on which Red Spiders are Clustered. (Original.) WORK OF THE RED SPIDER ON HOPS. Bui. 117, Bureau of Entomology, U. S. Dept. of Agriculture. Plate THE RED SPIDER ON HOPS IN CALIFORNIA. 17 NATURE OF DAMAGE. GENERAL EFFECT OF MITES UPON FOLIAGE. These mites feed upon the juices and cell contents which they suck from the tissues of the host plant. This extraction of cell contents usually results in the formation of a light spot at the point where the mite has fed. The presence of mites upon a vine during the early summer is readily detected by these yellow spots in the surface of the leaves. As the mites increase in numbers the leaves become more "speckled," turn yellowish, and when severely injured dry up and fall to the ground. Severely infested vines, at the time that the hop cones are forming, were observed to be very yellow and to lose many leaves. The decrease in the vitality of the vine, which is the direct result of the attack by mites, produces a premature ripening of the hops. The hop cones in infested yards were much further advanced than those in uninfested hopyards under similar soil and climatic con- ditions. This premature ripening results in a decrease in yield and a weakening of the roots, tending to decrease the crop of the following year. RELATIVE EFFECT OF MITES UPON MALE AND FEMALE HOPVINES. The male vines throughout the season showed more immediate and serious injury than the surrounding female vines. In many cases they were almost entirely defoliated (PL II, figs. 1, 2), while the neighboring female vines were but slightly injured. Some leaves which expanded late in the season on the lower parts of the pistillate vines were thin and papery, appearing identical in texture with the leaves of the male vine, and showed an injury similar to that of the male foliage. This severe injury to the male vines appears to be due largely to the nature of the foliage and not to the presence of a larger number of mites than are found upon the female vines. EFFECT UPON THE QUALITY OF THE HOPS. Although the foliage upon the arms of the vines was infested at the time the hops were coming out of the burr, the mites were not observed actually to feed upon them until they were nearly full-sized. No direct injury was noted when the mites were first found upon the cones, but soon reddish-brown spots appeared upon the scales and gradually the natural green and yellow turned to reddish brown, the scales became scraggly, and in severe cases the hop cones became so brittle that they could not be picked. (See PL V, fig. 1.) 18 THE RED SPIDEE OX HOPS IN CALIFORNIA. Even when they can be picked the quality is often severely injured. Dr. W. W. Stockberger, of the Bureau of Plant Industry, reports upon some samples of "spider hops" as follows: Of these No. 1 is, I should say, practically unsalable. Not only is the color very poor, but it is not uniform and shows very evidently the red discoloration produced by the activities of the "spider."' The aroma is also far from pleasing. The second sample, which showed some damage by the spider, is far from being a first-class hop; it of course is still marketable. Thus, even though a large crop is harvested its value may be greatly reduced by the injury due to the attack of the red spider. EFFECT UPON MAX. Some of the workmen of the hop ranches stated that during hop picking they had been troubled by the mites getting upon their bodies and causing an irritation. This point was investigated; several hundred mites were liberated upon the hands and arms of the writer and allowed to crawl around for 20 minutes. A barely detectable itching was the only sensation observed. The irritation mentioned by the men was probably due to scratches of the hop- vines and not to any irritation caused by mites. DISTRIBUTION IN THE FIELD. It was the opinion of some hop growers that the red spider appeared first along the roads and fences and gradually worked into the fields, but observations in several localities did not bear out this point. The mites first appeared within the hopyards and not especially along the borders, and although the increase was rapid, the infestation was evenly distributed. The dust from the roads collecting on the foliage made the web show very distinctly and the growers, judging the extent of an infestation by the amount of web that can be seen, would naturally think that the infestation started where the web was most noticeable. This accounts for the erroneous opinion mentioned above. Mr. W. H. Volck, who made some observations upon the red spider at Wheatland, Cal., in 1902, suggested that since the infestation was so sudden the mites might possibly have traveled through the air on webs, like the ''balloon" spiders. To test this point four dozen sheets of tanglefoot fly paper were tacked to the trellis poles in various parts of the infested yards at Perkins. Cal. They were put out in June. 1911, and when collected in September many insects were found embedded in the hardened tanglefoot, but no mites were observed. During the migrations in August mites dropping from PREDACEOUS ENEMIES. 19 the clusters were blown from 6 to 8 inches from where they would naturally drop, but it is very unlikely that they are carried any distance by any but a very strong wind. The only probable means of distribution other than the natural migrations are by horses used in cultivating, or by the hands and clothing of the men, and possibly on the bodies of the larger insects found on the hopvines. PREDACEOUS ENEMIES. Several predaceous insects were observed destroying red spiders on the hopvines near Sacramento, Cal., but their numbers were insuffi- cient to have any effect upon the infestation. The most numerous predaceous insect was a small anthocorid bug ( Triphleps tristicolor White) . This insect, both in the nymphal and adult stages, was very common in some sections of the yards and was frequently seen feeding on the mites. Certain small ladybirds have been noticed preying upon this species in infested yards, but were not found in large numbers. Among these are the following : Scymnus nanus Lee, observed at Sacramento, Cal., July, 1911. Scymnus marginicollis Mann., observed at the same time and place. Pentilia sp., found in some infested yards but present only in small numbers. During July Chrysopa calif ornica Coq., in the larval stage, was very abundant and probably did more good than all the rest of the pre- daceous insects together. Dr. F. H. Chittenden 1 reports (Scymnus) Stethorus punctum Lee, Cecidomyia coccidarum Ckll., Aplianogmus varipes Ashm., Chrysopa rufilabris Burm., and (Tlirips) Scoloihrips sexmaculatus Perg. as feed- ing upon the red spider at Washington, D. C, and elsewhere., Mr. E. A. McGregor,2 an agent of this bureau, has recorded the fol- lowing natural enemies of the red spider on cotton at Batesburg, S. C, in 1912: Triphleps insidiosus Say. Chrysopid larvae. Euthrips fuscus Hinds. Euthrips occidentalis Perg. Scolothrips sexmaculatus Perg., recorded by both Pergande and Duffy. Coccinella 9-notata Hbst. (larvae). Hippodamia convergens Guer. (larvae). While predaceous insects destroy many of the mites in the hop fields, their work has no appreciable effect upon the infestation. 1 The common red spicier, Cir. 104, Bur. Ent., U. S. Dept. Agr., 1909. 2 The red spider on cotton, Cir. 150, Bur. Ent., U. S. Dept. Agr., 1912. 20 THE RED SPIDER ON HOPS IN" CALIFORNIA. EXPERIMENTS FOR THE CONTROL OF THE RED SPIDER. METHODS OF EXPERIMENTATION. The sudden and widely distributed appearance of the red spiders in the hopyards, the rapidity of their increase, and the fact that the old remedy (sulphur) had not controlled the mites in the hopyards during the preceding season made the control problem appear a difficult one. As soon as the mites became numerous enough on the hop vines to warrant experimental work, the first of a long list of experiments which was planned during the spring of 1911 was applied. The lime- sulphur solutions, because of their efficiency and relatively low cost, soon became the most promising of the contact insecticides. They were therefore applied more extensively and were given more atten- tion than the other materials which were listed during the investiga- tion. The materials were applied, except in the small-scale work, with a power outfit (PL III, fig. 1) which maintained from 120 to 150 pounds pressure. Seven-foot rods tipped with a nozzle throwing a fine but washing spray were used for the work. In making the tests with the various insecticides it was found desirable to express their efficiency with as near an approach to numerical exactness as possible. Tag counts and field counts were employed in obtaining the percentage of mites killed and were found to be very accurate. In most cases only one of these methods was used on a plat, but occasionally both were employed. These counts were made both before and after spraying. Tag counts. — Twenty tags were attached to the petioles of as many leaves, and the numbers of mites found upon the several leaves, both before and after spraying, were recorded upon the attached tags. The percentage of mites killed by the spray was thus very accurately obtained. Field counts. — Field counts were made by picking 20 leaves from various parts of as many vines chosen throughout the plat. The numbers of mites found upon the leaves, which were taken b'oth before and after spraying, were compared and the precentage of mortality obtained. This method gave a good idea of field conditions but did not prove as effective as the tag count. SULPHUR. Sulphur in a dry and finely divided form has in past years been used very extensively against red spiders with supposedly good results. One experimenter states that although the sulphur does not affect the adult mites, it kills the larvae when they emerge from the eggs and thus checks the infestation. Several hop growers stated that the red Bui. 11 7, Buieiu of Entomology, U. S. Dept. of Agriculture. Plate III. Fig. 1.— Spraying Hopvines with Power Outfit. (Original.) Fig. 2.— Applying Precipitated Sulphur in Dust Form as a Remedy Against the Red Spider. (Original.) SPRAYING AND DUSTING FOR THE RED SPIDER ON HOPS. Bui. 117, Bureau of Entomology, U. S. Dept. of Agriculture. Plate IV. Fig. 1.— Sweet Peas Infested by the Red Spider, but Protected by Dusting, at Intervals of One Week, with Precipitated Sulphur. Los Angeles, Cal., 1910. i Original.) Fig. 2.— Sweet Peas, Growth Aborted, Blossoms Indifferent, and Vines nearly Killed by the Red Spider. Los Angeles, Cal., 1910. (Original.) THE RED SPIDER ON SWEET PEAS. EXPERIMENTS FOE CONTROL. 21 spider could be easily controlled; that sulphur dusted or blown onto the vines would soon check their progress. General observations made in the infested fields that were thoroughly dusted with finely powdered sulphur, however, lead the writer to believe that dry sulphur is of no value whatever in checking the ravages of this mite upon hops. This point was most conclusively proved, as will be seen from the following data. In testing the efficiency of this material upon the mites, all the available forms of dry sulphur were purchased and a precipitated form was prepared by treating a lime-sulphur solution with hydrochloric acid. These sulphurs were applied in the form of dust (PI. Ill, fig. 2) and also with water as a "wet spray." Table No. Ill gives results which were obtained from tag counts taken at various times during the season of 1911 and 1912. Table III. — Negative results produced by sulphur in various forms used against the red spider on hops. Date. 1911. June 30 July 15 18 18 25 1912. July 10 Material. Precipitated sulphur, 10 pounds; flour paste, 4 pounds; water, 100 gallons Flowers of sulphur, 20 pounds; water, 100 gallons Precipitated sulphur, 10 pounds; water, 100 gallons do Precipitated sulphur dust, applied dry Precipitated sulphur dust. Num- ber of mites present before. 271 201 264 305 560 638 Num- ber of mites killed by ap- plica- tion. 146 163 Per cent of mites killed by ap- plica- tion. 55.3 53.4 Days be- tween appli- cation and third count. 0) Num- ber of mites, third count. In- crease of mites, 282 1,458 1,533 C1) 670 1,198 11 1,257 1,269 C1) 560 Per cent of in- crease. 4.06 625.00 480. 68 19.64 87.77 1 Tags lost after second count. Mites of all ages (larvae, nymphs, and adults) were observed from time to time on the tagged leaves. This table definitely illustrates the inefficiency of sulphur in con- trolling the red spider on hops. It will be noted that a certain percentage of mites was killed or washed off by the spray, but the increase which followed proves definitely that sulphur in the dry form has little or no effect upon the mites. Observations in fields where sulphur had been applied by hand and by a traction dust machine also bore out this statement. In some cases there were few mites upon the sulphured vines, and growers claimed that the sulphur had destroyed the mites. Near-by unsulphured foliage, however, was invariably found to be as free from mites as the " sul- phured" vines, and this assumption did not hold. Sulphur as a control of the red spider on hops has been tested and found wanting and is superseded by the contact insecticides. . 22 THE RED SPIDER ON HOPS IN CALIFORNIA. Reason for inefficiency. — Some experiments with sulphur upon Tetranychus bimaculatus attacking prune, pumpkin, and sweet peas proved very satisfactory. Similar results were obtained when sulphur was applied to infested sweet peas in Los Angeles, Cal., by Mr. H. M. Russell, as is shown in Plate IV, figures 1 and 2. The efficiency of sulphur against the red spider on these plants and its inefficiency when applied on hops and cotton led to some careful observations as to conditions. It was noted that the pumpkin and sweet peas expose nearly all of both surfaces of their leaves to the direct rays of the sun at some time during the day and that the mites on the prune were attacking the upper and therefore the exposed surfaces. The hopvines and cotton plants, however, expose princi- pally the upper surfaces of the leaves to the sun and the mites living upon the undersides are thus protected. From these observations it is evident that sulphur is effective upon the red spiders only when the infested surfaces of the plant are exposed to direct sunshine at some time during the day or to intense reflected heat. LIME-SULPHUR SOLUTIONS. The results obtained in a small preliminary field experiment in which lime-sulphur in combination with nicotine sulphate, 40 per cent, was applied gave such good results that these materials were at once placed at the head of the list of sprays to be fully tested out during the course of the investigation. The lime-sulphur solutions are much cheaper than the nicotine solutions when used at the sum- mer dosage; therefore it seemed desirable to try the lime-sulphur solution alone hi order to reduce the cost of spraying, provided the omission of the more expensive nicotine solution did not alter the results. During the early work with these sprays it was evident that the straight lime-sulphur solutions, instead of spreading out in a film, formed beadlike drops on the foliage. Mites found in actual contact with these drops of spray were seen to draw away from them and escape uninjured. The results obtained with straight lime-sulphur solutions were most unsatisfactory. Soap formed a precipitate with the polysulphid, and as it was very evident that some " spreader" must be used if the lime- sulphur solutions were to prove effective, this subject was thoroughly investigated. Upon the suggestion of Prof. A. L. Quaintance, of this bureau, "black-strap" molasses, a cheap grade, was used with the lime-sul- phur spray at the rate of 2 gallons to 100 gallons of spray. This EXPERIMENTS FOR CONTROL. 23 mixture spread more rapidly than the straight solutions, but did not prove entirely satisfactory. While applying a spray composed of lye-sulphur, flowers of sul- phur, and flour paste, it was observed that the material spread over the leaves very rapidly. This flour paste seemed to meet the demand for a " spreader" and was accordingly mixed with the lime-sulphur solutions. The result was a smooth mixture, without precipitate, which spread over the leaves in a most effective manner (PI. V, fig. 2) and gave unusually effective results as an insecticide. The proper proportions were found, on experimentation, to be 4 gallons of flour paste (4 pounds of flour) to 100 gallons of spray. Lime-sulphur and flour paste proved a very effective and rela- tively cheap spray for use against the red spider and was extensively used in the control work carried on in the Sacramento Valley in 1911. Table IV. — Spraying experiments with lime-sulphur solutions against the red spider No. Date. Material. Applica- tion. CO i_, co a CO 1 a CO Is o u o a CD m s 1 2 3 4 5 6 7 8 9 10 June 23 27 July 1 5 6 6 9 19 19 19 Lime-sulphur, 36° Baume, 1-75 i. Lime-sulphur, 36° Baume, 1-75; flour paste, 4-100. Lime-sulphur, 36° Baume, 1-50; flour paste, 4-100. Lime-sulphur, 36° Baume, 1-60; flour paste, 4-100. Lime-sulphur, 36° Baume, 1-86; flour paste, 4-100. Lime-sulphur, 36° Baume, 1-86; flour paste, 4-100. Lime-sulphur, 36° Baume, 1-100; flour paste. 4-100. Lime-sulphur, 33° Baume, 1-70; flour paste, 4-100. Lime-sulphur, 33° Baume, 1-70; flour paste, 4-100. Lime-sulphur, 33° Baume, 1-70; flour paste, 4-100. Thorough. ...do ...do ...do ...do ...do ...do ...do ...do Careless . . . 360 698 697 964 593 593 906 143 509 509 135 692 691 945 534 586 892 142 440 55 37.5 99.0 99.0 98.1 90.0 98.8 98.4 99.7 86.4 10.8 97.1 99.7 92.9 .10. 26 .35 .49 .51 .32 .32 .29 .38 .38 .38 Tag. ...do. ...do. ...do. ...do. Field Tag. ...do. Field ...do. None. Do. Slight in- jury. Do. None. Do. Do. Do. Do. Do. 1 The terms "lime-sulphur, 1-75," " flour paste, 4-100," etc., denote 1 gallon of lime-sulphur to 75 gallons of water, 4 gallons of flour paste to 100 gallons of water, etc. Note.— The amount of material necessary per acre varies from 300 gallons in light foliaged hops to 500 gallons in heavy foliaged hops. Table IV gives an accurate conception of the efficiency of the lime- sulphur-and-flour-paste spray. The percentages obtained in Nos. 1 and 2 of this table represent graphically the relative efficiency of lime- sulphur solutions with and without the flour paste. A great differ- ence in the percentage is again noted in Nos. 9 and 10. In No. 9 the material was thoroughly applied and in No. 10 applied very care- lessly. The lower percentages obtained late in the season as compared with the higher percentages secured earlier in the season are due to 24 THE RED SPIDEE ON HOPS IN CALIFORNIA. the condition and extent of the foliage on the vines. During the early part of the work the foliage was light and could be easily sprayed, while later on it became dense, and thorough work was quite difficult. The results, however, prove the efficiency of the lime-sulphur-and- flour-paste spray in killing the red spider on the hop vine. FLOUR PASTE. The efficiency of flour paste as an arachnicide was indicated in the experiment which is recorded under No. 14 of Table VII, but it was not until the summer of 1912 that its value was fully realized. During spraying experiments with nicotine sulphate and flour paste upon the hop aphis it was observed that many of the smaller aphides had become pasted to the leaves. From this data it was assumed that a solution containing a larger proportion of flour paste should be effective against the more delicate aphides and mites, and the follow- ing experiments were accordingly conducted upon the red spider on hops: Table V. — Experiments with flour paste against the red spider on hops. Date. Formula. Number of mites present. Per cent of mites killed. Cost per 100 gal- lons. June 18 Flour paste. S-100 435 781 452 882 477 908 100.0 99.8 99.8 100.0 100.0 99.8 SO. 176 J une 27 do .176 July 12. ...do .. .176 Aug. 6 do .176 Do do .176 Aug. 9 . do .176 Total 3,759 i 99.9 Flour paste, 10-100 July 16 805 908 99.9 99.9 .22 Aug. 6 ....do: .22 Total 1,712 199.9 1 Average. These experiments prove that the flour paste, 8-100 and 10-100, is effective against Tetranychus bimaculatus. The spray pastes the mites onto the leaves, but has no effect upon the eggs, and in control- ling the mites a second application is necessary. The neutrality of this spray was proved by the fact that when applied upon the foliage and blossoms of the hop, in proportions as high as 12 gallons of paste to 100 gallons of spray, no injurious effects resulted. When sprayed onto the burrs and delicate hop cones, it did not prevent pollination or injure the appearance of the scales. When mixed in the spray tank, flour paste has a tendency to settle, and in order to do satisfactory work agitation is necessary. It is, Bui. 1 17, Bureau of Entomology, U. S. Dept. of Agriculture. Plate V. Fig. 1. —Upper Row: Large, Full-Sized, Healthy Hops. Lower Row: Small, Rough Hops, Showing Loss in Weight Due to the Red Spider. (Original.) Fig. 2.— Leaf of Hop, the Left Half of which was Sprayed with Lime- Sulphur and Flour Paste, and the Right Half with Lime-Sulphur Alone. (Original.) Note that the spray is uniformly distributed on the left half of the leaf; on the right half, however, it is collected in separate drops or patches, owing to the pubescence of the leaf. EXPERIMENTS FOR CONTROL. 25 however, an effective, convenient, and nonoffensive spray, and the cheapest one that has been successfully used against the red spider. LYE-SULPHUR. The lye-sulphur solution (Formula No. 1), used with success against the red spider on the almond by Mr. W. H. Volck, was applied with flour paste and with cresol soap in various proportions. The results of these experiments (Table VI) were obtained from tag counts and are very promising. The lye-sulphur solution, used with either the cresol soap or the flour paste, was very effective, and when used in the proper propor- tions did not injure the foliage in the least. It would have been used more extensively in field experiments had not the lye been disagreeable to handle in making up the stock solution. The lime- sulphur on the market at a relatively low figure proved just as effective as the lye-sulphur and, being much more convenient, was preferred. Table VI. — Spraying experiments with lye-sulphur in various combinations against the red spicier on hops. No. Date. Material. Applica- tion. Num- ber of mites present. Num- ber of mites killed. Per cent of mites killed. Cost per 100 gallons. Effect on vine. 1 2 3 4 June 23 June 26 July 2 July 15 ...do Lye-sulphur, 4-100; cresol soap, 1-300. Lye-sulphur, 2-100; sul- phur, 15 pounds to 100 gallons; flour paste, 4-100. Lye-sulphur, 1-100; sul- phur, 15 pounds to 100 gallons; flour paste, 4-100. Lye-sulphur, 1-100 Lye-sulphur, 2-100 Thorough. ...do ...do ...do ...do... 377 374 371 518 437 367 366 361 458 384 97.4 97.8 97.4 88.5 87.8 $1.05 .708 .55 .15 .31 Slight injury. No injury. Do. Do. Do. Although the lime-sulphur, or lye-sulphur, and flour-paste solution did not injure the foliage or the blossoms of the hop vines, it did injure the more tender hop cones. The late spraying with lime- sulphur, if practiced, should be completed before the hop cones come out from the burr. NICOTINE SOLUTIONS AND OTHER MATERIALS. The nicotine solutions, used with the Lima-sulphur, or with soap, or alone, were quite expensive, as may be seen in Table VII. The lime-sulphur and flour paste was so much cheaper and so effective that the nicotine experiments which had been outlined were conducted on a small scale only. The results of these experiments, together with the results of some miscellaneous experiments, are given in Table VII. 26 THE RED SPIDER ON HOPS IK CALIFORNIA. Table VII. — Spraying experiments with various combinations against the red spider on hops. No. Date. 1 July 15 2 3 4 5 6 ...do ...do ...do July 16 ...do 7 ...do 8 ...do 9 ...do 10 July 17 11 ...do 12 ...do 13 ...do 14 ...do Material. Application. Num- ber of mites present. Num- ber of mites killed. Per cent of mites killed. 450 263 58.4 414 762 414 237 312 376 677 263 185 273 90.8 98.9 63.6 78.1 87.5 361 280 78.6 330 225 68.3 164 111 67.7 269 174 64.7 201 115 57.2 273 191 70 163 157 96.3 657 444 67.5 Cost per 100 gallons. Nicotine sulphate, 40 per cent, 1-750. . Nicotine sulphate, 40 per cent, 1-1,000. Nicotine sulphate, 40 per cent, 1-2,000. Nicotine sulphate, 40 per cent, 1-3,000. Nicotine sulphate, 40 per cent, 1-60 Nicotine sulphate, 40 per cent, 1- 2,000; lime-sulphur, 1-86. Nicotine sulphate, 40 per cent, 1- 3,000; lime-sulphur, 1-86. Nicotine sulphate, 40 per cent, 1-750; cresol soap, 1-300. Nicotine sulphate, 40 per cent, 1- 1,000; cresol soap, 1-300. Nicotine sulphate, 40 per cent, 1- 2,000; cresol soap, 1-300. Nicotine sulphate, 40 per cent, 1- 3,000; cresol soap, 1-300. Lime-sulphur and nicotine sulphate, 1-50. Lime-sulphur and 40 per cent nicotine sulphate, 1-50; flour paste, 4-100. Flour paste, 4-100 Thorough, but beaded. ....do ....do ....do ....do ....do ....do Thorough, not beaded. do Thorough, but beaded. Thorough, not beaded. do SI. 66 1.25 .62 .416 1.08 .85 .64 2.08 1.67 1.04 .83 . 09 PURE WATER. Spraying with water is one of the most successful and most com- monly used methods of controlling the red spider in greenhouses. With a strong but fine stream of water the mites are washed from the foliage of infested plants and the infestation is reduced to a minimum. It was thought possible to wash the mites from the hop leaves by spraying water through a coarse nozzle at 200 pounds pressure with about as successful results. This experiment was accordingly carried out, and although some of the mites were washed off, many were left and were later seen to have been uninjured by the force of the spray. The hme-sulphur-and-flour paste and the flour paste, 8-100, are so cheap that even though between 50 and 70 per cent of the mites could be killed by pure water, one of the former materials, which destroys about 98 per cent, is preferred. VALUE OF A SECOND APPLICATION. After a few spraying experiments had been conducted it was seen that the sulphur, the lime-sulphur, and the lye-sulphur had no effect upon the mites except by actual contact ; therefore the idea of placing a material on the vines which would kill the larvae on emergence was abandoned. Although nearly 100 per cent of the mites living upon the leaves could be destroyed by the spray, the eggs were uninjured and the newly hatched larvae reiufested the leaves as badly as before. It was therefore decided to spray a second time after all the eggs had hatched and yet early enough to prevent any larvae from becoming mature. EXPERIMENTS FOR CONTROL. 27 During July the mites passed from larva to adult in 8 days and during April the incubation period was 7 to 10 days.1 Basing the time of a second application on this data, 7 days was decided upon as the interim between the first and second sprayings, and by follow- ing out this plan some very encouraging results were obtained, as shown in Table VIII. Table VIII. — Experiments showing value of a second application in spraying for the red spider on hops. No. Date. Material. Applica- tion. Num- ber of mites pres- ent. Num- ber of mites killed. Per- cent of mites killed. Second appli- cation, per cent killed. 1 2 3 July 6 July 19 ...do Lime-sulphur, 36° Baume, 1-86; flour paste, 4-100. Lime-sulphur, 33° Baume, 1-70; flour paste, 4-400. Lime-sulphur, 33° Baume, 1-70; flour paste, 4-100. Thorough . do do 593 143 509 543 142 440 90 99.7 86; 4 97.1 99.7 92.9 It will be noted that only from 0.3 to 7.1 per cent of the original number of mites present on the vines were present after the second application. The mites which hatched from the few eggs that remained were not sumcisnt to form the basis for a reinfestation and the work was accordingly considered satisfactory. Unfortunately some of the plats treated were covered with infested morning-glory vines, which were severely injured by the mites, and which later resulted in a migration that soon reinfested the hop- vines. Morning-glory was not present in one plat, however, and although the applications were made so late that the vines were severely injured, the results to be expected from such a plan were clearly proved. These vines were comparatively free from mites at the end of the season and had a much more healthy color than the vines in the adjoining plats which were used as checks. FORMULAS FOR SPRAYS. To prepare the flour paste, mix a cheap grade of wheat flour with cold water, making a thin batter without lumps; or wash the flour through a wire screen with a stream of cold water. Dilute until there is 1 pound of flour in each gallon of mixture. Cook until a paste is formed, stirring constantly to prevent caking or burning. Add suffi- cient water to make up for evaporation. (See PL VI, fig. 1.) For spraying with flour paste alone, use 8 gallons of paste as pre- pared above to each 100 gallons of water. For the flour-paste and lime-sulphur spray, use 4 gallons of paste to each 100 gallons of spray containing the lime-sulphur. 1 In moderate weather allow 10 and in hot weather 7 days between applications. THE EED SPIDER OX HOPS IX CALIFORNIA. BAXDIXG WITH TANGLEFOOT. Banding with tanglefoot has become the chief method of control- ling the hop flea-beetle (PsyUiodes punctulata Melsh.) hi British Columbia, and as the mites also work up the vine mainly by crawling it was deemed advisable to attempt to check their progress by means of the tanglefoot bands. In order to test this method, 10 infested hop vines were selected. A few leaves were removed to prevent brids:in£, and in some cases the vines were stripped; tree tanglefoot was then applied to the vines in 3- inch bands. (See fig. 6.) About 20 badly infested leaves were next at- tached to the vines below the bands and the lower parts thus thoroughly infested . During the f oUo wing week these vines were continuously ob- served. Hundreds of mites were found around the lower edges of the bands, and in cases where the lower leaves had been stripped off some web was found at the base of the tanglefoot, but there was no evidence that the mites had crossed over. Although mites were seen above the bands, these probably were car- ried there on the observer's hands during previous observations. Similar experiments were con- ducted in 1912, except that some foliage was left below the bands on which the mites could multiply and from which they could migrate. Three weeks' observation failed to reveal mites above properly banded vines, but after this time the tanglefoot became filled with sand and was not effective. One large-scale experiment with tanglefoot was attempted, but the work was done so late hi the season that a few mites were already above the point of banding and no definite results could be obtained. Banding with tanglefoot in itself will probably not act as a control for the red spider, but hi yards where late clean culture is not practi- cable it will probably protect the sprayed vines from the late summer migrations. Application. — It is necessary to get the tanglefoot well into the spaces between the two vines, the simplest way to accomplish this Fig. 6.— Hopvines banded with tanglefoot, in an attempt to prevent the mites from ascending. (Original.) Bui. 1 1 7, Bureau of Entomology, U. S. Dept. of Agriculture. Plate VI. Fig. 1.— Cooking Flour Paste Out of Doors; Kiln-House for Drying Hops, Pre- paratory to Baling, in Distance. (Original.) Fig. 2.— Large Power Spraying Outfit, Showing Lines of Hose Running into Hopyard. (Original.) SPRAYING FOR THE RED SPIDER ON HOPS. EXPERIMENTS FOR CONTROL. 29 being with the hands. A section about 3 inches long should be coated with the tanglefoot, care being taken that no parts are missed and that no leaves are left to form a bridge across it. Although the tanglefoot is apparently very disagreeable material to apply, it is easily washed off the hands with a little kerosene or even with soap and hot water. METHODS OF APPLYING SPRAYS. No spraying for the red spider should be attempted unless the proper appliances and machinery are at hand. Hand pumps which will maintain 150 pounds pressure can be used, but power outfits are preferable. Traction and compressed-air sprayers which will maintain the proper pressure are light, convenient, and readily hauled through the hopyards, but unless the required pressure is maintained they will not give satisfactory results in spraying. The outfits used in the experimental work at Sacramento were composed of a gaso- line engine, a spray pump, and a 50-gallon barrel mounted upon a light three-wheeled truck. These outfits did effective work, but carried so little spray material that they required refilling entirely too often. A large orchard power outfit (PL VI, fig. 2) equipped with two 150-foot lines of hose was operated around the edges of some of the yards with good results. The driver assisted the rodmen in get- ting the hose in and out of the rows and a wide strip around the yards was treated. In cases where the infestation appears on one side of a field such machines can be readily employed. The mites are almost entirely found on the underside of the leaves, and in order to wash them thoroughly the spray must be directed from below. When angle nozzles are not available the spray rod may be bent so that the spray may be readily directed to the underside of the leaves. If one or the other of these methods is not employed the material will not be satisfactorily applied. In order to penetrate all of the webs and reach all of the mites it is necessary to use a nozzle that will throw a washing rather than a mist spray. The Bordeaux or " stopcock" type is usually too coarse and wastes material, so that a nozzle should be chosen somewhere between that and the Vermorel type. Some of the recent makes can be regulated by the alteration of the size of the opening in the disk so that any degree of spray can be obtained. Such nozzles are very well adapted to the red-spider work. In controlling the red spider in the hop fields it is necessary that a large territory be covered in a short time and that the material be applied very thoroughly. To do this several outfits are necessary and these must be in good working condition. Disabled machinery not only increases the expense of spraying but reduces the chance of controlling the mites. 30 THE RED SPIDER OX HOPS IN CALIFORNIA. COST OF SPRAYING. The following estimate of the cost of spraying for the red spider is made from data taken from actual field work on high-trellis yards. The amount of material needed for hops on short poles will be some- what less. It has been found that one machine will spray from 2 to 3 acres per day and that in order to do thorough work it is necessary to apply from 300 to 500 gallons per acre, according to the amount of foliage on the vines. The following data are based on a machine winch will spray 2 acres per day. Table IX. — Cost of spraying hopyards for the red spider. Cost of application per acre. Flour paste, 8-100; cost and cooking, 19 cents per 100 gallons. Lime sulphur, 1-100, and flour paste, 4-100: cost per 100 gallons, 26 cents. 300 gallons. 500 gallons. 300 gallons. 500 gallons. Labor: 3 men at $2 per dav for one-half day SO. 57 3.00 .25 $0.95 3.00 .25 SO. 78 3.00 .25 SI. 30 3.00 .25 Total cost 3.82 4.20 4.03 4.55 Cost of two applications 7.64 8.40 8.06 9.10 The cost of stripping the vines preliminary to spraying will be from $1.80 to $2 per acre. Comparing the cost of spraying for the red spider with the loss that may result from its ravages, it is evident that money spent in controlling this mite will be well invested. CULTURAL METHODS. Stripping the vines. — The practice of stripping the vines is a common one in regions where the hop aphis (Phorodon humuli Schrank) is troublesome. A large amount of aphis-breeding foliage is cleared from the vines and only the more readily sprayed leaves are left. In experimenting along this line several vines were stripped and tied together at various points to determine which method would most readily facilitate spraying. The lower foliage on vines which were not stripped but were tied together 4 feet from the ground (fig. 7) was found to be matted and very difficult to spray thoroughly. When the lower 3 feet of the vines were stripped and the two vines tied at the 4-foot mark (fig. 8), 1 foot of the vine was still in a condi- tion difficult to spray. But when stripped and tied a few inches below the lower leaves (fig. 9), the vines spread out nicely and the EXPERIMENTS FOR CONTROL. 31 leaves were readily sprayed. It is always difficult to spray thor- oughly, and any cultural method which will facilitate effective work is worth while. During the early part of the seasons of 1911 and 1912 the mites were observed upon the lower leaves only and from there migrated upward. It is estimated that the stripped area contains about 40 or 50 leaves; taking the average number of mites as 42 Fig. 7.— Hop vine tied high and not stripped; lower leaves difficult to spray. (Original.) per leaf for an average infestation, the theoretical number of mites that would be removed would be about 1,680 or 2,100 per vine. One hopyard which was stripped before the mites were above the point to which the vines were to be stripped was observed August 9. It was found that the infestation had been materially checked. It is believed that timely stripping of the vines and removal and burning of the infested leaves will severely check the infestation and in some cases where the yards are not filled with food plants will 32 THE RED SPIDER ON HOPS IN CALIFORNIA. successfully control the mites. Too much faith should not be placed in this operation, however, as spraying may have to be resorted to as a final measure. The cost of stripping is about $2 per acre and is more than offset by the results obtained. Irrigation. — Vines which have not a large supply of moisture dry and change color more rapidly than those growing in moister soil, so that the work of the red spider is most noticeable on light soil in Fig. 8— Hopvine tied high and stripped; lower leaves matted and difficult to spray. (Original.) the drier parts of the hopyards. Several growers, believing that irrigation of the infested vines would counteract the effect of the mites, pumped water onto their yards and gave the soil a thorough wetting. The vines responded and put out a few fresh leaves, but the mites infested these in the same manner as before and reduced the quality of the hops in the same proportion as on unirrigated and equally infested parts of the adjoining hopyards. Irrigation will not control the mites, but when the soil lacks sufficient moisture it will EXPERIMENTS FOR CONTROL. 33 stimulate the vines, causing them to put out some fresh foliage so that the loss in weight of the hops will not be so great as it would be otherwise. Fertilization. — In parts of the hopyards where the vines were very vigorous, as a result of fertilization, the presence of mites was not so noticeable as in parts where the foliage was not so dense. The increase of mites was just as rapid, however, and at the end of the season the densely foliaged vines were just as badly injured, and the Fig. 9.— Hopvine tied low and stripped; leaves readily sprayed. (Original.) hops in many cases were discolored. The denser foliage gives a larger surface to be injured, and with equal infestation plats with light foliage will necessarily be more seriously injured than the denser ones. Fertilization will increase the vigor and the productiveness of the hopvines and, while it will not in any way control the mites, it should be practiced on general principles. 34 THE BED SPIDER ON HOPS IN CALIFORNIA. Although the red-spider injury is relatively not so great on vines invigorated by fertilization, it is present and will be extensive accord- ing to the severity of the infestation. Clean culture. — In September, 1911, a block in an infested hopyard was carefully cleared of all vegetation in an attempt to destroy all of the mites present. When examined October 16, however, a few mites were observed on some morning-glory which had come up since the plat was cleared. The practice of clean culture is very important and has a great influence upon an infestation, but it can not be relied upon as a complete control. GENERAL SUMMARY WITH RECOMMENDATIONS. The investigation of the control of the red spider on hops has brought out the following points: Great financial loss may be caused by the red spider. The mites on hops are not affected by any form of dry sulphur, but are readily killed by several contact insecticides, the cheapest and most convenient of which are flour paste (8-100) or a combination of lime-sulphur, 36° Baume (1-100), and flour paste (4-100). To get the best results it is essential that the vines should be thoroughly sprayed. Stripping the vines and burning the leaves is an excellent measure, but should not be entirely relied upon as a complete control. When the inf estation s severe early in the season and the mites are above the point of stripping, spraying operations should be commenced as soon as the vines are stripped. The infested area must be thoroughly and rapidly covered and must be sprayed a second time, 7 or 10 days later. Banding with tree tanglefoot will check migrations and is recom- mended where the hopyards are infested by food plants of the red spider. Two later spray applications may be necessary if the mites again appear in injurious numbers. The red spider on the hopvine may be economically controlled if the foregoing measures are carefully carried out. CONTROL OF THE RED SPIDER UPON PLANTS OTHER THAN HOPS AND COTTON. The flour paste, 8-100, as described on pages 24 and 27 of this bulletin, is a successful remedy for the control of the red spider in its attacks on all plants except sweet pea, carnation, green- house roses, and plants having a heavy pubescence on the leaves. Experiments have been conducted with this material against the mites upon the following plants without the slightest injury to open- ing buds, foliage, or fruit; BIBLIOGRAPHY. 35 Outdoor plants: Pumpkin, squash, cucumber, roses, violets, box- elder, and bean. Greenhouse plants: Cucumber, violets, and chrysanthemums. Judging from the data gathered in the foregoing experiments this spray, when properly used, should control the red spider on all plants except those mentioned in the following paragraphs : Sweet -peas. — The foliage of the sweet pea is very hairy, and that of the carnation and greenhouse rose is so smooth that the flour paste will not stick to it and therefore does not work satisfactorily. The control of mites upon these plants is taken up separately in succeeding paragraphs. The finer forms of sulphur are effective upon the red spider attacking sweet pea (see p. 22) provided that the plants are growing in a warm, sunny place. The sulphur should be thoroughly dusted onto the infested plants, the application being repeated every week or so. Roses. — Most roses can be sprayed with flour paste, 8-100, but the leaves of roses grown in greenhouses are so smooth and glossy that the paste will not stick to them. The old method of washing them with the garden hose remains as the best remedy in this case. Carnations. — A weak salt or soap solution is used by some growers as a control for the red spider, but continual spraying with water is the universal method of control. Use of sulphur.— As stated on page 22, dry -sulphur will control the mites upon those plants which expose most of both surfaces of their leaves to the sun during the day, but the Hour-paste spray is so cheap, available, and effective that where large areas are involved it is recommended in preference to the sulphur treatment. Sulphur, however, has proved more or less effective upon the squash, pumpkin, sweet pea, and bean. BIBLIOGRAPHY. There have been few publications issued upon Tetranychus bimacu- latus under that name, but it has been recently decided by Mr. Nathan Banks, of the Bureau of Entomology, that the cotton red spider {Tetranychus gloveri Banks) is synonymous with Tetranychus bimacu- latus Harvey, and references to this name are included in the following list. It is also more than probable that many of the mites referred to by American writers under the name of Tetranychus telarius are really T. bimaculatus , so that the more important references to that species are included below. 1. Saunders, Wm — Can. Ent., vol. 12, pp. 237-238, fig. 22, 1880. Mention as Tetranychus telarius; popular account of red spider on violet. 2. Atkinson, G. F.— Kept. S. C. Agr. Exp. Sta. for 1888, pp. 28-29, 1888. Mention as Tetranychus telarius; brief notes on injury to cotton. 3. Washburn, F. L.— Bui. 18, Oreg. Agr. Exp. Sta., p. 10, 1892. T. telarius; brief note on red spider. 36 THE RED SPIDEE ON HOPS IN CALIFORNIA. 4. Harvey, F. L.— Ann. Rept. Maine Agr. Exp. Sta. for 1892, pp. 133-134, 1893. Tetranychus bimaculatus n. sp.; describes a new species distinct from the red spider of Europe. 5. Davis, G. C.— Bul. 102, Mich. Agr. Exp. Sta., p. 51, 1893. Notes on injury to celery. 6. Perkins, C. H.— 10th Ann. Rept. Vt. Agr. Exp. Sta., pp. 75-86, figs. 1-4, 1897. An account of the life history and habits of the red spider. 7. Morgan, H. A.— Bui. 48, La. Agr. Exp. Sta., pp. 130-135, 1897. Notes on the life history and habits of the cotton red spider, with means of control. 8. Hillman, F — Bul. 36, Nevada Agr. Exp. Sta., p. 39, 1897. 9. Goff, E. S.— Bul. 63, Wis. Agr. Exp. Sta., p. 16, 1897. Brief notes on the red spider. 10. Galloway, B. T.— Commercial Violet Culture, pp. 190-198, 1899. 11. Banks, Nathan.— Tech. Ser. 8, Bur. Ent., U. S. Dept. Agr., pp. 73-74, figs. 10-11, 1900. List of hosts and distribution of Tetranychus bimaculatus. 12. Banks, Nathan.— Tech. Ser. 8, Bur. Ent., U. S. Dept. Agr., pp. 76-77, fig. 15, 1900. Tetranychus gloveri n. sp.; described as cotton red spider. 13. Chittenden, F. H. — Bul. 27, n. s., Bur. Ent., U. S. Dept. Agr., pp. 35-42. figs. 9-11, 1901. Account of injury by Tetranychus bimaculatus to roses in greenhouses, etc. 14. Titus, E. S. G.— Cir. 65, Bur. Ent,, U. S. Dept. Agr., 1905. The cotton red spider ( Tetranychus gloveri Banks). 15. Gahan, A. B.— Bul. 119, Md. Agr. Exp. Sta., pp. 20-21, 1907. Tetranychus bimaculatus. A biologic account. 16. Russell, H. M— Journ. Econ. Ent,, vol. 1, pp. 377-380, December, 1908. An account of experiments in the control of Tetranychus bimaculatus on snap beans in Florida. 17. Swaine, J. M. — 1st Ann. Rept. Quebec Soc. for Protection of Plants from Insects and Diseases, pp. 18-19, 1909. An account of experiments with insecticides for Tetranychus bimaculatus. 18. Weldon, G. P.— Bul. 152, Colo. Agr. Exp. Sta., pp. 9-12, 1909. Tetranychus bimaculatus. Description and treatment. 19. Chittenden, F. H— Cir. 104, Bur. Ent., U. S. Dept. Agr., 1909. The common red spider. A full account of the work of this mite in greenhouses, with measures for its control. 20. Weldon, George P.— Bul. 152, Colo. Agr. Exp. Sta., pp. 9-12, pi. 1, fig. 2, Octo- ber, 1909. Tetranychus bimaculatus here treated as pest to fruit trees, with an account of its habits and the experiments made to control it. 21. Davis, J. J.— Journ. Econ. Ent., vol. 3, p. 186, April, 1910. Account of injury to elm by Tetranychus bimaculatus. 22. Slingerland, M. V., Herrick, G. W., and Crosby, C. P. — Bul. 283, N. Y. (Cor- nell) Agr. Exp. Sta., p. 473, 1910. Tetranychus bimaculatus. Brief account of remedies for greenhouses. 23. Parrott, P. J., and Schoene, W. J.— Bul. 330, N. Y. (Geneva) Agr. Exp. Sta., p. 474, 1910. 24. Weldon, George P.— Bul. 169, Colo. Agr. Exp. Sta., pp. 12-13, November, 1910. Tetranychus bimaculatus; a brief account of injury to peach trees and measures of control. 25. Worsham, E. L.— Bul. 92, Ga. Agr. Exp. Sta., pp. 135-141, pis. 1-5, 1911. The cotton red spider, Tetranychus telarius. Extended account with 5 colored plates. 26. Ewing, H. E— Ent. News, vol. 23, pp. 145-148, pi. 10, April, 1912. Tetranychus telarius; notes on the molting process of our common red spider. 27. McGregor, E. A— Cir. 150, Bur. Ent., TJ. S. Dept, Agr., Apr. 25, 1912. The common red spider ( Tetranychus bimaculatus). An extended account, with remedies, deal- ing with this insect as infesting cotton in South Carolina. INDEX. Page. Abutilon, food plant of Tetranychus bimaculatus 16 Alfalfa, food plant of Tetranychus bimaculatus. 16 Amaranthus blitoides, food plant of Tetranychus bimaculatus 16 retroflexus, food plant of Tetranychus bimaculatus 16 Aphanogmus varipes, enemy of red spider 19 Apios apios, food plant of Tetranychus bimaculatus 16 Arborvitse, food plant of Tetranychus bimaculatus 16 Arctium lappa, food plant of Tetranychus bimaculatus 16 Asparagus plumosus, food plant of Tetranychus bimaculatus 16 Aster, food plant of Tetranychus bimaculatus 16 Banding with tanglefoot against hop flea-beetle and red spider 28-29 Bean, food plant of Tetranychus bimaculatus 16 lima, food plant of Tetranychus bimaculatus 16 protection from red-spider injury 35 Beets, table and sugar, food plants of Tetranychus bimaculatus 16 Birch, food plant of Tetranychus bimaculatus 16 Blackberry, food plant of Tetranychus bimaculatus 16 Bouvardia, food plant of Tetranychus bimaculatus 16 Box-elder, protection from red-spider injury 35 Burdock. (See Arctium lappa.) Burgmansia arbor ea, food plant of Tetranychus bimaculatus 16 Burr clover. (See Medicago hispida.) Caladium, food plant of Tetranychus bimaculatus 16 Calceolaria sp. , food plant of Tetranychus bimaculatus 16 Calla, food plant of Tetranychus bimaculatus 16 Canary bird vine. (See Tropseolum peregrinum.) Cantaloupe, food plant of Tetranychus bimaculatus 16 Carnation, food plant of Tetranychus bimaculatus 16 Carnations, protection from red-spider injury 35 Castor-oil bean, food plant of Tetranychus bimaculatus 16 Cecidomyia coccidarum, enemy of red spider 19 Cedar, food plant of Tetranychus bimaculatus 16 Celery, food plant of Tetranychus bimaculatus 16 Chayote. (See Sechium edule.) Cheese weed. (See Malva parviflora.) Chrysanthemum, food plant of Tetranychus bimaculatus 16 Chrysanthemums, protection from red-spider injury 35 Chrysopa californica, enemy of red spider 19 rufilabris, enemy of red spider 19 Clean culture against red spider on hops 34 Clematis, food plant of Tetranychus bimaculatus 16 Clover, burr. (See Medicago hispida.) food plant of Tetranychus bimaculatus 16 37 38 THE EED SPIDEE ON HOPS IN CALIFORNIA. Page. Cnicus benedictus, food plant of Tetranychus bimaculatus 16 Coccinella 9-notata, enemy of red. spider 19 Coffee tree, Kentucky. (See Gymnocladus canadensis.) Convolvulus sp. (See Morning-glory, wild.) Copulation of Jed spider 12 Corn, food plant of Tetranychus bimaculatus 16 Cost of spraying hopyards for red spider 30 Cotton, food plant of Tetranychus bimaculatus 16 Cowpea, food plant of Tetranychus bimamlatus 16 Cucumber, food plant of Tetranychus bimaculatus 16 protection from red-spider injury 35 Cultural methods against red spider on hops 30-34 Cuphea, food plant of Tetranychus bimaculatus 16 Cypress vine, food plant of Tetranychus bimaculatus 16 Dahlia, food plant of Tetranychus bimaculatus 16 Datura stramonium, food plant of Tetranychus bimaculatus 16 Disella hederacea, food plant of Tetranychus bimaculatus 16 Eggplant, food plant of Tetranychus bimaculatus 16 Euthripsfuscus, enemy of red spider 19 occidentalism enemy of red spider 19 Ferns, food plants of Tetranychus bimaculatus 16 Fertilization against red spider on hops 33-34 Feverfew, food plant of Tetranychus bimaculatus 16 Flea-beetle, hop. (See Psylliodes punctulata.) Flour paste against red spider on hops 24-25. 26 plants other than hops and cotton 34-35 and lime-sulphur against red spider on hops 23-24 value of a second ap- plication 26-27 preparation 27 lye-sulphur against red spider on hops 25 lime-sulphur, and nicotine sulphate against red spider on hops ... 26 spray, preparation 27 Fuchsia, food plant of Tetranychus bimaculatus 16 Geranium memlatum, food plant of Tetranychus bimaculatus : 16 Geranium, wild. (See Geranium memlatum.) Godetia, food plant of Tetranychus bimaculatus 16 Goldenglow. (See Rudbeckia sp.) Groundnut. (See Apios apios.) Gymnocladus canadensis, food plant of Tetranychus bimaculatus 16 Hedge mustard. (See Sisymbrium officinale.) Helianthus lenticularis, food plant of Tetranychus bimaculatus 16 Heliotrope, food plant of Tetranychus bimaculatus 16 Hemp, food plant of Tetranychus bimaculatus 16 Hippodamia convergent, enemy of red spider 19 Hollyhock, food plant of Tetranychus bimaculatus 16 Honeysuckle, food plant of Tetranychus bimaculatus 16 Hop flea-beetle. (See Psylliodes punctulata.) Hop tree. (See Ptelea trifoliata.) vines, male and female, relative effect of red spider thereon 17 stripping them for control of hop aphis 30 red spider 30-32 INDEX. 39 Page. Hops, foliage, as affected by red spider 17 food plant of Tetranychus bimaculatus 1 G quality, as affected by red spider 17-18 Horse-chestnut, food plant of Tetranychus bimaculatus 16 Hydrangea, food plant of Tetranychus bimaculatus 16 Iron weed, food plant of Tetranychus bimaculatus 16 Irrigation against red spider on hops 32-33 Ivy, English, food plant of Tetranychus bimaculatus '. 16 Jamestown weed. (See Datura stramonium.) Jerusalem-oak weed, food plant of Tetranychus bimaculatus 16 Jimson weed. (See Datura stramonium.) Lactuca scariola, food plant of Tetranychus bimaculatus 16 Lettuce, prickly. (See Lactuca scariola.) Ligustrum amurense, food plant of Tetranychus bimaculatus 16 Lily, Easter, food plant of Tetranychus bimaculatus 16 Lime-sulphur against red spider on hops 22-24 and flour paste against red spider on hops 23-24 value of second applica- tion 26-27 preparation 27 nicotine sulphate against red spider on hops 26 nicotine sulphate, and flour paste against red spider on hops 26 Lippia nodiflora, food plant of Tetranychus bimaculatus 16 Lye-sulphur against red spider on hops 25 and cresol soap against red spider on hops , 25 flour paste against red spider on hops 25 Mallow. (See Malva parviflora.) alkali. (See Disella hederacea.) Malva parvijlora, food plant of Tetranychus bimaculatus 16 hibernating place of red spider 13 Man as affected by red spider .. 18 Manettia, food plant of Tetranychus bimaculatus 16 Maple, food plant of Tetranychus bimaculatus. 16 Mat-grass. (See Lippia nodiflora.) Medicago hispida, food plant of Tetranychus bimaculatus 16 sativa. (See Alfalfa.) Mignonette, food plant of Tetranychus bimaculatus 16 Mimulus, food plant of Tetranychus bimaculatus 16 Moonflower, food plant of Tetranychus bimaculatus 16 Morning-glory, food plant of Tetranychus bimaculatus : 16 wild, food plant of Tetranychus bimaculatus 16 hibernating place of red spider 13 Mustard, hedge. (See Sisymbrium officinale.) Nicotine solutions against red spider on hops 25-26 sulphate against red spider on hops 26 and cresol soap against red spider on hops 26 lime-sulphur against red spider on hops 26 lime-sulphur, and flour paste against red spider 26 Okra, food plant of Tetranychus bimaculatus 16 Onion, food plant of Tetranychus bimaculatus 16 Parthenogenesis in red spider 12-13 Passiflora, food plant of Tetranychus bimaculatus 16 40 THE RED SPIDER ON HOPS IN CALIFORNIA. Page. Pea, food plant of Tetranychus bimaculatus , 16 sweet, food plant of Tetranychus bimaculatus 16 Peanut, food plant of Tetranychus bimaculatus 16 Pecan, food plant of Tetranychus bimaculatus 16 Pelargonium, food plant of Tetranychus bimaculatus 16 Pentilia sp. , enemy of red spider 19 Pepino. (See Solanum muricatum.) Pepper, food plant of Tetranychus bimaculatus 16 Persicaria lapathifolia, food plant of Tetranychus bimaculatus 16 Phlox, food plant of Tetranychus bimaculatus 16 Pigweed, rough. (See Amaranthus retro fiexus .) Poplar, Carolina, food plant of Tetranychus bimaculatus 16 Privet, food plant of Tetranychus bimaculatus 16 Psylliodes punctulata, banding of hopvines with tanglefoot in control 28 Ptelea trifoliata, food plant of Tetranychus bimaculatus 16 Pumpkin, protection from red-spider injury 35 Raspberry, food plant of Tetranychus bimaculatus ' 16 Red spider, adult, description, copulation, parthenogenesis 12-13 bibliography 35-36 citrus. (See Tetranychus mytilaspidis.) control experiments on hops 20-34 methods of experimentation 20 recommendations on hops 34 upon plants other than hops and cotton 34-35 cost of spraying hopyards 30 cultural methods on hops 30-34 damage to hops, nature 17-18 distribution in the field 18-19 economic importance on hops 9-10 effect upon man 18 egg, description, location, incubation 10 emergence from hibernation 15 enemies, predaceous 19 first appearance en hops in season 15 food plants 16 habitation on hops 13 habits 13-16 hibernation 13 emergence therefrom 15 larva, descriptive, length of stages 11 life history on hops 10-12 locomotion 14-15 methods of applying sprays on hops 29 migrating activities 15-16 nymph, descriptive, length of stages .■ 11 protection on hops 13 summary, with recommendations for control 34 Rose, food plant of Tetranychus bimaculatus 16 Roses, greenhouse, protection from red-spider injury 35 protection from red-spider injury 35 Rudbeckia sp., food plant of Tetranychus bimaculatus 16 Salvia, food plant of Tetranychus bimaculatus 16 Sassafras, ornamental, food plant of Tetranychus bimaculatus 16 fNDEX. 41 Page. colothrips sexmaculatus, enemy of red spider ,...„„ 19 Scymnus marginicollis, enemy of red spider 19 nanus, enemy of red spider ' 19 punctum. (See Stethorus punctum.) Sechium edule, food plant of Tetranychus bimaculatus 16 Sisymbrium officinale, food plant of Tetranychus bimaculatus 16 Slipper flower. (See Calceolaria sp.) Smilax, Boston, food plant of Tetranychus bimaculatus 16 Soap, cresol, and lye-sulphur against red spider on hops 25 nicotine sulphate against red spider on hops 26 Solanum muricatum, food plant of Tetranychus bimaculatus 16 Spider, red. (See Red spider.) Spraying apparatus and methods against red spider on hops 29 cost, against red spider on hops . 30 Spruce, Colorado blue, food plant of Tetranychus bimaculatus 16 Squash, food plant of Tetranychus bimaculatus 16 protection from red-spider injury 35 Stethorus punctum, enemy of red spider 19 Sunflower, food plant of Tetranychus bimaculatus 16 wild. (See Helianthus lenticularis .) Sulphur against red -spider on bean 35 hops 20-22 reason for inefficiency 22 plants other than hops 22 pumpkin 35 squash 35 powdered, against red spider on sweet peas 35 Sweet peas, protection from red-spider injury 35 Tanglefoot bands against hop flea-beetle 28 red spider on hops , 28-29 Tetranychus bimaculatus. (See Red spider.) gloveri= Tetranychus bimaculatus 35 mytilaspidis, eggs, location 10 telarius, name wrongly used for Tetranychus bimaculatus 35 Thistle, blessed. (See Cnicus benedictus.) Thrips sexmaculata. (See Scolothrips sexmaculatus.) Thunbergia, food plant of Tetranychus bimaculatus 16 Tomato, food plant of Tetranychus bimaculatus 16 Triphleps insidiosus, enemy of red spider 19 tristicolor, enemy of red spider 19 Tropxolum peregrinum, food plant of Tetranychus bimaculatus 16 Verbena, food plant of Tetranychus bimaculatus 16 Violet, food plant of Tetranychus bimaculatus 16 Violets, hibernating place of red spider 13 protection from red-spider injury 35 Watermelon, food plant of Tetranychus bimaculatus 16 Water spray against red spider on hops 26 Wedding bells. (See Burgmansia arborea. ) Wistaria, food plant of Tetranychus bimaculatus f 16 o