LIBRARY STATE PLANT BOARD May 1943 E-595 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine PABLATGRIA CHIEENSIS XABL&XS l/ By Howard Baker and Nathan Stahler, Divisioii of Fruit Insect Investigations, and A. C. Johnson, Division of Control Inves- tigations, Bureau of Entomology and Plant Quarantine, Agri- cultural Research Administration, and Lloyd Adams and P. C, Froesckner, Missouri State Department of Agriculture Specimens of a scale insect found in St. Louis, Mo., in April 1940 "by an entomologist of the Missouri State Department of Agriculture were subse- quently determined "by the Bureau of Entomology and Plant Quarantine of the United States Department of Agriculture as Parlatoria chinensis Marlatt, a scale insect not heretofore reported as occurring in the United States. A preliminary survey conducted by the Missouri State Department of Agriculture during the spring and summer of 1940 revealed that this insect was well estab- lished on such plants as althea, privet, lilac, buckthorn, red chokeberry, o.nd purpleleaf plum in the Missouri Botanical Garden and lower G-rove Park, and on other properties radicating therefrom for a distance of several blocks. This scale insect has ^een reported in Japan, China, Egypt, and India and has been intercepted by inspectors of the United States Department of Agriculture on plants from Japan, China, and India. Despite all efforts that have been made to trace the origin of the infestation of Parlatoria chinensis in St, Louis, the time and method of its introduction are unknown. 1/ This circular supersedes E-535, Parlatoria chinensis Marlatt, A Scale Insect Recently Discovered in the United States, which was issued in April 1941. Information given in circular 3—535 has been utilized freely in this revision. /JUN1 -^943 - 2 ~ Little information is available? in the literature with regard to the seasonal history, habits, or status of Pa rlatoria chin en sis as a pest. Other species of Pa.rlatoria are se'rious pests in this and other countries, however, and the host list of this Species, as recorded in available records and litera- ture, is such as to indicate that it could become ar. important pest of many of our deciduous fruit trees, shade trees, and shrubs, She following plants hays been mentioned as hosts of this insect in foreign countries and from plant importations: Albizzia 3auhinia (mountain— ebony, orchid tree) Cassia f i stula (pudding-pipe tree, golden-shower) Pi ens (fig, etc.) Hibiscus (rosemallow) Juglans (walnut) Justicia alba Malug (crab apple only) ITerium (oleander) Plea (olive) Prunus (plum only) Pyrus (flowering varieties of pear only) Hobinia (black locust only) Salix (Babylon weeping willow only) Syringa (lilac) Hecoma capons is Thuja orientalis (Chinese arborvitae) Thymelaea Xanthoxylum (prickly-ash) Zizyphus (Juj ube ) Since, so far as known, Parlatoria chinensl s is not widely distri- buted in the United States and is a member of a destructive grcxip of plant pests, it is essential that the area in which it is established be known so that its increase and spread can be restricted or prevented, as far as possible, until the status of the insect as a post, the need for a control program, and the basis for control can be established. Accordingly, surveys have been conducted ~oy the Bureau of Entomology and Plant Quarantine in cooperation with the Missouri State Department of Agriculture, the Missouri Agricultural Experiment Station, the city of St. Louis, and the Missouri Botanical Garden to delimit the infestation and to determine the host plants on which it occurs. Studies have been made by the" same agencies to de- termine the seasonal history, habits, host-plant relations, and natural enemies, and to develop possible control measures. Control and regulatory activities to restrict and prevent the spread of the scale have been con- ducted by the Missouri State Department of Agriculture, and a survey in East St. Louis, 111., was conducted in 1941 in cooperation with the Illinois State Department of Agriculture, Information obtained prior to ITo-v.caber 194-2 is summarized and brought up to date in this circular. - 3 ~ 0CCTJRR31TCE IN THE U1TITED STATES Parlatoria chinonsis is not yet known to occur in the United States outside tho city and county of St. Louis, Mo. Surveys conducted during December 1940 and January 1941 and from November 3, 1941, to March 31, 1942, have resulted in its being found on plants in the Missouri Botanical Garden, Tower Grove, and Forest Parks, on 1,274 other properties in 173 blocks in the city of St. Louis, and on 2 properties in a small area (partly in Brentwood and po.rtly in Maplewood) in St. Louis County. It is estimated that the area in which infected plants have been found, together with a narrow border area in which infestations have not been found, covers about 8 square miles in the city of St. Louis. Surveys are being continued to obtain farther information on the status of the infestation in the known infested area and to delimit more exactly the area of infestation. The plants in the following list have been found as hosts of Parlatoria chinensis in St. Louis. Those most commonly infested or which appear to be satisfactory hosts of Parlatoria chinensis are marked with an asterisk. Aesculus hippocastanum (common horsechestnut) Aesculus carnea (red horsechestnut) Albizzia julibrissin Aln us sp. (alder) Aral i a spinosa (angelica tree) * Aronia arbuti folia (red chokeberry) A similar 1 , triloba (papaw) Be tula nigra (river birch) Betiila populi folia (gray birch) Betula spp. (birch) Broussonetia papyri f era (paper mulberry) Caragana arborescens (Siberian pea-tree) Catalpa bignonioides (common catalpa) Catalpa bungei (umbrella catalpa) Catalpa ovata (Japanese catalpa) Catalpa specie sa (western, catalpa) C elt is occidentalis (hackberry) Chaenomeles lagenaria (flowering quince) * Chaenomeles spp« (quince) - 4 ~ Chip nan thus yirginica (white fringetree) Oladrastis lutea (yellow-wood) C o rnu s asperifolia Cornus flava Cornus florida (flowering dogwood) Cornus mas Cornus sanguinea Cornus spp. (dogwood) Corylus avellana (filbert) Cotinus coggygria (purple smoke tree) Cotoneaster acutifolia (Peking cotoneaster) Cotoneaster horizontal! s Cotoneaster lucida Cotoneaster praecox Crataegus mollis (red hawthorn) Crataegus oxyacantha (English hawthorn) Crataegus phaenopyrum (Washington hawthorn) Crataegus spp. (hawthorn) Diospyros virginiana (persimmon) Elaeagnus angustifolia (Russian-olive) E uonymus alatus (winged euonymus) Euonymus "bungeana (winterherry) Suonvmus euroioaeus (swindle tree) Euonymus yedoensis (wahoo) Exo chorda gi-andi flora (pearlbush) Forsythia fragrant i s si ma Eorsythia spp. (golden hell) «* 5 ** Fraxinus americana (white ash) Fraxinus lanceolata (green ash) .Sled.it sia aquatica (waterlocust) G-leditsia triacanthos (common honeylocust) Halssia Carolina ( silverbell) Hanamelis virginiana (witch-hazel) * Hibiscus syriacus * Hibiscus spp. (althea, rose-of-Sharon) Hydrangea sp. Ilex docidua (deciduous holly) Ilex opaca (American holly) Ilex verticillata (holly, common winterberry) Juglans nigra (black walnut) Juglans rupestris * Koelreuteria paniculata (varnish-tree) * Ligustnm ibolium * Li gust run ibo ta * Li gastrin obtu si folium ■ * Li gust rum ovali folium (California privet) * Li gust run quihoui * Ligu strum regelianum (regel privet) * Ligustr^;^ spp. (privet) Lindera benzoin (spice bush) • . Lonicera bella Lonicera chrysantha Lonicera fragrant i s sima Lonicera xylosteun _ 6 - Lonlcera spp. (honeysuckle) Maclura pomifera (0 sage-orange) * M alus baccata (Siberian crab) * Malus floribunda. (flowering crab) * Malus pumila (apple) * M alus spp. (apple, crab apple, flowering crab) Phellodendro n amurense (Amur cork tree) Photinia vill osa Pistacia chinense * ^ ninus amygdalus ( common peach) * Prunus ermeniaca (apricot) * Prunus cerasifera pissardii (purpleleaf plum) * Prunus Padus commutatis * Prunus salicina (Japanese plum) * Prunus serotina (black cherry) * Prunus serrulata (Oriental cherry) * Prufli* 3 tomentosa (Nanking cherry) * Prunus triloba (flowering plum) * Prunus spp. (apricot, cherry, flowering almond, peach, plum) Ptelea trifoliata (waferash, hoptree) Pyracantha sp. (firethorn) * Pyru- 3 communis (pear) .* Rhamnus cathartica (common buckthorn) Rhamnus frangula angusti folia Rhamnus saxatilis Rhajnnus utilis Rho do typos kerrioides (jetbead) Rhus canadensis (fragrant sumac) _ 7 - Rhus glabra Rhus typhina (staghorn sumac) R ib as auroum (yellow flowering currant) Ribcs spp. (currant) Robinia hispida (rose~acacia) Robinia kolseyi Robinia psoud o acac ia Rosa hibernica Rosa rubiginosa (sw.^etbriar) * Rosa r ugoq a. Rosa spp. (rose) Salix babylonica (Babylon weeping willow) Sambucus sp. (alder) Sassafras albidum (sassafras) Securincga surf rut icosa Sopliova japonica (pagoda tree) Sorbus aqcuparia (white mountain-ash) Spiraea douglasii Spiraea vanhouttei Spiraea spp. Sraphoricarpo s albus (snowberry) * Syringa amurense * Syringa josikaea (Hungarian lilac) * Syringa nanceiana var. floreal * Syringa oblata * Syringa reflexa * Syringa tomentella - 8 - * Syringa vulgar! s (common lilac) * Syringa spp. (lilac) Tamarix gallica Tamarix spp. Tilia americana (American linden) Tilia europaea (large-leaved basswood) Tilia heterophylla Ulmus americana (American elm) Ulmus pumila (Chinese elm) Viburnum americana (American cranberrybush) Viburnum cas'slnoides (withe-rod) Viburnum Ian tana (wayfaring-tree) Viburnum lentago (sheepberry) Viburnum pruni folium (blackhaw) Viburnum spp. Xant hoc eras sorbi folia (Chinese buckeye) Zelkova serrata Infested plants reported as Porestiera sp. and G-inkgo biloba on page 2 of mimeographed circular 5-535, dated April 1941, are now believed to have been misidentified, and these should not be considered as proved hosts of this scale in the United States. Althea, privet, and lilac have been most commonly found infested, but, since they occur more frequently and in greater numbers than other plants that appear to be satisfactory hosts, they cannot be considered necessarily as the greatly preferred hosts. Species of plants other than those so indi- cated may be satisfactory hosts of Parlatoria chinensis , but they occur too infrequently in the infested area to provide sufficient information to per- mit their classification as such at the present time. Plants present in the infested area in moderate to large numbers that do not appear to be hosts of this scale include barberry, maple, mockorange, poplar, and most, if not -all, evergreens. - 9 - DESCRIPTION OF PARIATORIA CHi rDKSIS KARLATT 2/ Within or around the present known area of infestation, Parlatoria chinensis can probably be differentiated superficially from other encountered species of armored scales "by the following characteristics: Adult female scale flat or only very slightly convex, short elliptical to oval, length up to 1.25 mm., exuviae marginal at the anterior end of the scale and Covered with a thin, easily detachable film of secretion, no trace of a cone or a ring and dot arrangement of the scale surface; adult male scale, which usually occurs along with the female, distinctly elongated and narrow, with the larval exuvia at the end, length up to 1 mm., the secretionary material not loose, scale not c^rinated, the texture approximating that of the female scale; body of mature female when exposed not peg-top shaped or turbinate, as with the aspidiotines which are most apt to be found in the area of infestation — in- stead, the head end appearing somewhat narrowed and protuberant because of the presence of slight notches, one on each side of the body, about one- fourth of the way back from the head. Color of the live adult female light purple, becoming darker as it be- comes older; of the dried adult female, strong reddish brown. Scale covering tending toward coloration of host bark, more so on some hosts than on others. The two most valuable indicators of the presence of this scale on plants in the present known .infested area are (l) the purple color of the adult female and (2) the ventral molt skins of the males, which remain as tiny white specks on infested plants long after the male covers slough off. Those specks have been aptly termed "footprints, M and are not so characteristic of any other scale insect encountered in the St. Louis area as they are of Parlatoria chinensis . Microscopically the insect has a strongly triangular pj/gidium super- ficially suggesting that of the San Jose scale ( Aspidiotus perniciosus Comst.), but it is in no way related to this insect. Por discussion of species of Parlatoria hitherto known to occur in this country, see Perris, Atlas of the Scale Insects of Uorth America, 1937, pages SI-84, SI-90; and 1942, pages SIV- 400-405; and Morrison, Taxonomy of Some Scale Insects of the Genus Parlatoria Encountered in Plant Quarantine Inspection Work (U.S. Dept. Agr. Misc. Pub. 344, 1939, 34 pp., illus.). Prcm the species discussed in these references, chinensis is readily differentiated by the following combination of characteristics? Duct tubercles present on head and opposite anterior spiracles; a tubular duct between median lobes, this relatively small and slender; all dorsal ducts much reduced in size and number, small and inconspicuous, only a fo\v (perhaps a half-dozen) on each half of the p3^gid.ium strongly produced, triangular; median lobes large, close together, triangular, outer margins crenulate, no intermediate plates, second lobes much smaller, also asymmetrical, notched or faintly crenulate externally, other lobes wanting; plates greatly reduced in number and size, slender, tapering to an approximate point, 1, obscure, between first and second lobes, 2 beyond the spine outside each second lobe, 6 to 8, short and obscure, scattered along the rest of the pygidial margin on each side, this in contrast to the relatively numerous large and conspicuous plates present in most of the other species that have been reported from the United States; no derm pocket oivbside posterior spiracle. Among the species discussed in parsers listed, probably nearest to P. cinerea Hadden. 2/ Most. of the material in this section has been quoted verbatim from circular E-535. - It) - 831SQE&£ HISTORY »«* _• J e i° pment of ?arlatori a chinensis under natural conditions has been aetermined by the examination of specimens on samples of infested plants taken irom three^ or more locations at regular weekly intervals during that part of tne year wnen the scale i s undergoing development, and less frequently during jne dormant season. All specimens on each unit randomly selected plant area nave been included in each examination. A sufficient number of unit areas were selected for examination to furnish apf.roxima.tGly 300 specimens per sample when all, or most, of the stages through which the insect passes in its develop- ment were represented. Pewsr specimens per sample were examined when a more limited number of stages were re^esonted. Ills seasonal development of this scale insect under natural conditions at St.. Louis during 1942, as determined from periodical examinations, is summarized in table 1. Adult males that had emerged were not included in the record be- cause of the impossibility of accurately separating the new male covere from the old. Consequently, since specimens of this scale do not remain in any one immature stage very long, the data in table 1 do not indicate the proportion of the sexes. However, it has been found that males predominate over females in about the proportion of 2 to 1. Differences in the time and rate of develop- ment of specimens on different plants of the same species or on plants of different species have been small and were apparently due largely to differences m exposure. Specimens on plants in sunny locations, begin development a little sooner and develop a little faster than those on plants in shaded locations. There wore two complete generations and a partial third of Parlatoria chinensis in St. Louis in 1941 and two complete generations and a trace of a third in 1942. Apparently only fertilized, adult, second-brood females over- winter, although it is possible that a few third-brood females might reach the adult stage and overwinter in some seasons. Immature specimens appear to be un- able to survive the winter. About 40 eggs are formed over a period of approximately 2 months within the body of each producing adult female. They, are extruded a few at a time •and^ hatch after about 5 to 10 or 12 days according to prevailing weather con- ditions. During 1942, extruded eggs were first found April' 24 and were present almost continuously to October 30. As will be noted from table 1, there is a distinct overlapping of the periods during which adult females of the overwintering and first broods and t^ose of the first and second broods occur. A similar overlapping occurs in the ^ periods during which eggs, crawlers, and other developmental stages of individuals of the first and second broods are present. As a result of this overlapping there is a considerable period during the summer months when indi- viduals in each stage of development are present. In 1941, first-brood crawlers were present from May 14 to early July, second-brood crawlers from near July 15 to mid-October, and third-brood crawlers from the last of September to near the middle of November. In 1942, data in table 1, coupled with those obtained as a result of regular weekly examinations of cleared areas on infested plants in the field, indicate that first-brood crawlers were present from May 1 to about July 24, second-brood crawlers from JuJ.y 10 to near the and *£ Copta^ar^ $mA ». few o-f the third brood during the - 11 - Crawlers were normally present on the plants in greater numbers during the morning and early afternoon than during other parts of the day. They settle in a comparatively short time, and do not ordinarily travel far. In special tests, three-fourths of all crawlers that settled did so during the first hour after their transfer to the test plant s> and all that settled did so by the end of the fourth hour. Crawlers may wander over plants for much longer periods, but if they do they usually die, and few are able to settle after the fourth hour. In throe tests no crawler settled farther than 7 inches from the point at which it was placed, 67.4 percent settled within 1 inch of the point of transfer, and 86.8 percent settled within 2 inches of it. In two other tests no transferred crawler settled more than 5 inches from the point at which it was placed, and 86.8 percent settled within 1 inch of it. It is possible to transfer crawlers from one host plant to another with- out detriment to their ability to settle, develop, or reproduce. They usually settle about some obstruction, as another scale, a crotch, bud, lenticel, bark scale, scar, or' other place of similar nature, although some also settle on smooth surfaces. They do not settle readily or very successfully on the more succulent growth of the current season or on plant surfaces that are hairy or have thick, rough bark. The scales have never been found settled on fruit and only rarely on foliage in the field, and rone ever settled on fruit or foliage as a result of transfers made in the laboratory. INCB3A.S3 AKD SPRSAD Observations in 1941 indicated that P arlatoria chin en sis could increase during the second-brood period from a low population level — so low that they could scarcely be seen with the unaided' eye — to a moderate or high population level at which they were easily visible. In 1942 the change in size of scale populations from brood to brood and for the season as a whole wag determined' by comparisons made on 73 comparable sample areas en 13 plants in 4 locations. The comparisons were on number of live, mature or nearly mature, adult females that survived the winter, the number present near the end of the period of first-brood development in July, and the number present near the end of the period of second-brood develop- ment in October. The scale population on the sample areas decreased from an average of 4.87 to 3.48 specimens per square centimeter, or 28,5 percent, during the de- velopmental period of the first brood; increased from 3.48 to 7.02 specimens per square centimeter, or 101.7 percent, during the developmental period of the second brood; and increased from 4.87 to 7.02' specimens per square centimeter, or 44.1 percent, during the season as a whole. Probably because of lower mean temperatures and greater rainfall during 1942, the scale population did not in- crease so much as it did during 1941. Weather conditions during Kay 1942 were especially unfavorable for the hatching of first-brood eggs and emergence, settling, and development of crawlers, with the result that mortality of the insects in these stages was high. During the last half of the second-brood period in August and September the mean temperature was approximately 5 degrees below that for the corresponding period in 1941, a condition which appeared to eurtail second— brood activitv. STATE f^BOABO - 12 - Parlatoria chinensia is known to ba spread "by the removal of infested plants from one placa to another, by the natural movement of crawlers from infested plants to other nearby plants, and by air movement. It is also prob- able that it can be spread by other insects and by birds. During the 1942 sea-son crawlers were captured on sticky traps located as far as 28 feet from the nearest known infested plant, and adult males were captured as far as 42 feet from the nearest knovm infested' plants, indicating that this scale can be and is disseminated by air movement. Young apple, peach, pear, plum, .and cherry trees that were uninfested when set in an experimental nursery planting in the spring of 1942 were found infested when examined in the fall of 1942. Since some of these young trees wore 6 to 8 feet from the nearest infer, tec 1 , plants, and some of the infestations were 1 well up in their branches, it s sen's probable that they became infested by wind-blown crawlers. NATURE OE INJURY Sufficient observations have not yet been made for an opinion to be formed as to the potentialities of Parlatoria chinensis as a pest. Experiments are under way which, it is expected, will eventually furnish such information. "he writers have observed a few plants which they believe to have been killed by this scale, and have also observed young apple trees in which local injury was caused "oj only a few specimens of the scale. On these trees tho bark tissue first became red o.nd then died at and about tho points of infestation. Observations of infested plants indicate that injury ordinarily develops slowly and gradually over an extended period and is first evident in the form of weak, sparse foliage. Later, snail limbs may be killed. NATURAL ENEMIES Natural enemies have not been found present in sufficient numbers to indicate that they can be expected or depended upon to hold infestations of this insect in check. The most important appear to be a predacious mite, Eemisar copter, malus Shiner (determined by H. S. Ewing) , and a parasite, Aphytis sp. (determined by A. B. G-ahan) . METHODS 01 CONTROL Experiments have been conducted, and others are underway or planned, to develop a suitable method or methods for the control of Parlatoria chinensis . Spray tests have n oeen limited, for the most part, to oil sprays with and with- out added toxicants applied during the dormant and delayed-dormant periods and during the summer* Commercial, but not complete, control has been obtained in all periods with concentrations of oil that have not caused noticeable plant injury, but further work is essential to determine the most satisfactory materials and concentrations. In addition, experiments with tent fumigation, and modifications of it, are being conducted in the field with methyl bromide and calcium cyanide. Information concerning this method of field treatment is incomplete, and more data are needed before its practicability can be determined. - 13 - Dormant and Delayed-Dormant Applications On the "basis of present information, a 4-percent concentration of a properly emulsified dormant-type oil is recommended for use to control heavy to encrusted infestations daring the dormant and delayed-dormant periods, and a 3-percent concentration is recommended for use to control medium or lighter infestations. *"'ith regard, to the timing of dormant applications, it is Re- lieved that the .commonly recommended practice of spraying only when the tempera- ture is above 40° F. should be followed. Other factors being equal, it has been found that any given oil will effect about the same degree of control of this scale on one plant species as on another. Oils whose specifications fall within the range of those of oils commonly recommended for dormant use have proved equally effective when tested for the control of this insect. On the other hand, the type of emulsifier used has been found to be an important factor influencing the insecticidal efficiency of the oils, and the quick-breaking types of oil emulsions have been more effective than more stable types. Sufficient tests have not 3 r et boon made, however, to' justify the recommendation of any particular emulsifier or type of emulsifier. The addition of such materials as rotenone (in the form of cube resins) and dinitro-o-cyclohexylphenol to low concentrations of oil has increased their efficiency markedly, but the exact quantities of these materials needed has not yet been determined. Summer Applications In all tests of oils suitable for use in summer applications, a 5-percent concentration of oil has been highly effective, a 2-percent concentration has been moderately effective in some instances and highly so in others, and a 1-percent concentration has been ineffective. Oils within a viscosity range of 80 to 100 seconds Saybolt at 100° 2P. and with unsulfonated residue contents of 90 to 95 percent by volume have been more effective than lighter ones with a viscosity range of 55 to 62 seconds Saybolt at 100° F. and unsulfonated residue contents of 80 to 35 percent by volume, and they have boon as effective as the one heavier oil tested. Applications made shortly after the peak period of emergence and settling of firat-brood crawlers and at the corresponding period of emergence and settling of second-brood crawlers were about equally effective and more so than those made in the interval between the period of first-brood and second-brood activity, when a majority of firr,t-brood specimens were present as adult fe- males. Two applications of 2-percent light-medium summer oil made about 1 month apart reduced an infestation more than did one application at either time. In all tests made to date, rotenone in the form of cube resins has markedly improved the efficiency of low concentrations of light-medium summer oils when used to effect control of this scale. One-percent light-medium summer oil containing from 6.01 to 0.02 percent of cube resins (cube resins contained 16.4 percent of rotenone) has been nearly equal in efficiency to 3 percent of the same oil without added toxicant. Also, a 1-percent concentration of a light- medium summer oil which contained 0.05 percent of rotenone in the stock emulsion - 14 - has given a high degree of control. Rotenone, however, is not available at the present time for the spraying of fruit trees, and it is also considered de- sirable that further tests "be conducted before definite recommendations are made for its use. On the basis of present information, if it is considered necessary or desirable to supplement dormant or delayed— dormant applications with summer sprays for the control of Parlatoria chinensis , it is recommended that a concentration of 2 percent of an oil having a viscosity of from 80 to 100 seconds Saybolt at 100° E. and an un sulfonated residue content of from 90 to 95 percent \>i t volume be applied at or near the peak period of first- or second- brood crawler emergence and settling, or at both periods if the degree of infes- tation warrants. ERADICATION AH) CONTROL During the spring and summer of 1942, a control program designed to eliminate all known infested plants outside the primary infested area was carried out by officials of the Missouri State Department of Agriculture. Per- mission to remove infested plants was solicited from home owners and others on whose properties such plants had been found in the area involved, and the re- sponse was so favorable that, as far as was known at the time, all infested plants were removed from all parts of the infested area in the city of St. Louis outside that bounded on the north ~by Vande venter and Polsom Avenues, on the east l>" Spring Avenue, on the south "o^ Arsenal Street, and on the west by Kingshighway. In addition, all infested plants were removed from the two infested properties on which such plants had been found in St. Louis County. The total number of known infested plants was reduced by approximately 4 percent and the number of known infested properties by about 15.5 percent. The removal program was supplemented with a spray program designed to reduce the size of, or eliminate, if possible, scale infestations that might have been overlooked in the survey. A 3- or 4-percent dormant oil emulsion was applied in the spring of 1942 to all possible host plants on many properties from which all known infested plants had been removed, and a 2-percent summer oil emulsion was similarly applied during the period of emergence and settling of first-brood crawlers. In some instances possible host plants on properties adjoining infested ones were sprayed also. The movement of woody plants and plant part's from within the infested area to any point outside of said area has been regulated and restricted by a quarantine invoked ~by the Missouri State Department of Agriculture, which was made effective April 18, 1941, and revised April 18, 1942. Experimental fumigation work is being conducted by the Division of Con- trol Investigations, Bureau of Entomology and Plant Quarantine, for the purpose of developing a treatment of plants or plant parts infested with Parlatoria chinensis that can be depended upon to destroy all stages of this insect with- out injury to the plant' so that such material can be subsequently released from quarantine restrictions. - 15 - Although the fumigation of plants with methyl bromide has not as yet "been authorized for this purpose, the following schedules appear to be satis- factory for treatment in fumigation chambers: 2l/2 pounds of methyl bromide - 3 pounds of methyl bromide pi 4 pounds of methyl bromide pe: 4 pounds of methyl bromide pe: 4 pounds of methyl bromide per 1,000 cu. ft. for 4 1/2 hrs. at 40 ( There is a seasonal period, beginning apparently with the approach of cold weather, when Pa rlat oria chinensis becomes increasing! y more resistant to fumigation, ever, though the temperature has not changed. Shis period extends into March, at which time the insects seem to lose this resistance to some degree. This variation cf resistance has been observed for about 15 months, and there is evidence that it may vary in intensity from year to year. Fumi- gation experiments are being continued for the purpose of obtaining additional data on this seasonal cycle. If these annual cycles of resistance variation shall be found to have a reasonable conformation, fumigation schedules may be determined for the period of lover resistance in order to reduce the time of exposure or the dosage and in turn widen the margin between complete inrect mortality .and plant injury. 16 3 • <0 t 1 £ « o u 9 s. B t ! £ 9 ■o 4* « • c t> iH • •3 s O u • CO z I e *> 9 • c •e »d « 1 8 u 9 II rt a "o © J CO JO s 4» x> SI 4» TJ &« -O *» .O a 9 a. ■*> % 9 (X 1 t 9 P-. J8 CVOOOOOOOCV O «r\»r\ cm cm U>r-IH»CN|>t > »-CMr-IOC>-CMr-iir\C»NCM-40«»\OH CM -4»r\rH iH H <0 «V H rH iH -4 «H <*\ CM C\ r-l «-l to «^ -4- CO to CO «r\0«H tf\^ -*vOCO«^CVt~0>00 9iooo«oooo»o»oo«o»«»o O>t0>OCC*-4a>OHW*O4WNC'f0W<«ftHO -4 ,, o o oooooocooooo»o«oo««oo»eo «0-*CMCAC^C>CM>Oc«>«QQ»«>C»-O-*C0t*-r-«ir\>Or-«rM ^v©«0C0^<^f«"vCMCM-4«rvNOt>-«^>C< r \cH Hr(0H(r>4«\H^40 «0 C\<*> 0©rH-4eM • o«oooooo»eo»o >fivO«>6M)NHn4>000 ooo«»o«»ooo» >Oc»Mr>o«*N»f\c*ACMc>>oe^o rHCM«r>fl0C0t00*O«00^OO C\«0 00©OC\«Ol>->0-4-4»r\Or-<0-4 SS^M^^ OtOOOOHMr\r\ir>0404N • •••ooooo«oo«*«ooeo OQCMCMOl>-CM-4flO«rNC^CMC^kH C* O e»-tp>OCMr-ICMrHC>-'>C CM «H 4 4 0>>r\rjt^a*P\O\0ift«\4if\6c0>oF->0^OO^ONCNH X »QCMCMf^«0QC r \-4«r\rM>Ot^C*-CM 9«fl(hC0>OQQ}tfN>O'4)pHSQ4 44H^OrtO«OOOC i N'Of : '« CM t-{ r-i r-( r-» iH r-« r-i r-t €»>«*% C\>© -4 irvNO CM O^vO iHCMCMCMHCMrHtOi-«CMCM»r\rHr-»CM • • «•<♦?■♦»•«» «ftft« «< ««3S§§3 3B3?3 ?f 3 3 i> « « • o o O OO OO a< >»si , ? > » > 5 > ?<<<(«<