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Three species of orchard mites and their predators on apple trees in the southern Okanagan valley of… Chant, Donald Alfred 1952

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THREE SPECIES OF ORCHARD MITES AND THEIR PREDATORS ON APPLE TREES IN THE SOUTHERN OKANAGAN VALLEY OF BRITISH COLUMBIA, AND THE EFFECTS OF THREE INSECTICIDES ON THIS COMPLEX. by DONALD ALFRED CHANT A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n the Department of Zoology We~accept t h i s thesis as conforming to the standard required from candidates for the degree of MASTER OF ARTS. Members of the Department of Zoology THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1952. I . ABSTRACT The behaviour of the orchard mites Bryobia pretiosa (Koch) and Metatetranychus ulmi (Koch) and four species of predators was investigated both on unsprayed and on sprayed apple trees. On unsprayed trees the host mites were found to be most abundant on the east sides; no consistent d i r e c t i o n a l preference was found for the predacious species. Small apple leaves supported the same number of M. ulmi per u n i t area as large leaves, but more mites of the genus Tetranychus. On unsprayed trees a negative c o r r e l a t i o n between the t o t a l number of predators and the number of host mites was recorded• In abandoned orchards the predators were capable of c o n t r o l l i n g the host mites and maintaining them at a l e v e l below that of economic signific a n c e . Each of the in s e c t i c i d e s DDT, Parathion, and lead arsenate, was found % to be very toxic to a l l species of predators recorded, and thus hindered or e n t i r e l y prevented natural control of the host mites.. In every instance lead arsenate and DDT produced an increase i n the population of B* pretiosa T > t h i s effect being p a r t i a l l y chemical and p a r t i a l l y due to a lack of predators on the sprayed trees. Lead arsenate caused an increase i n the population of M. ulmi whereas DDT reduced i t to a s l i g h t extent. Under a r i d conditions Parathion caused an increase i n the population of B.pretiosa;' under les s a r i d conditions the mite was eliminated., Parathion^ I I . had no effect on M. ulmi i n a commercial orchard while,, i n the same orchard, i t caused a great increase i n Tetranychus spp. The l a t t e r species were reduced by DDT i n the commercial orchard., TABLE OF CONTENTS Page ABSTRACT I, ACKNOWLEDGEMENTS i INTRODUCTION i i Economic importance of Orchard Mites i i General Characteristics and L i f e H i s t o r i e s of Phytophagous Mites 1 Synonomy of Tetranychid Mites ........ 7 L i f e H i s t o r i e s and Characteristics of Four Predators Found i n Apple Orchards of the Southern Gkanagan Valley 9 Acarina 9 Coleoptera .... • 12 Thysanoptera ............ ih METHODS AND PROCEDURE 18 Descriptions of Study Orchards 18 Mc In tyre Creek 18 Meyer's F l a t 19 G a r t r e l l ' s .............. 21 Leaf Sampling 26 C o l l e c t i o n Technique .... 27 Sample Size 27 Brushing Machine . . . . . . . 3 3 Mite Counting 39 Page MEYER'S FLAT ORCHARD hO, Clover mite (Bryobia pretiosa) .hi. Unsprayed population ...,.> hi. Sprayed populations *+3-Typhlodromus rhenanus h$, Unsprayed population ........... h$. Sprayed populations • •.••••••..»• h?, Mediolata sp.. • .... ....... h?. Unsprayed population ........... **7. Sprayed populations ............ 50. Thrips ...»....... — 52. Unsprayed population • 52. Sprayed populations 52. Host-predator relationships 55» Unsprayed trees 55. Sprayed trees ....... ..... 60. MCINTYRE CREEK ORCHARD 66. Clover mite (Bryobia pretiosa) • 66. Unsprayed population 66. Sprayed populations .......... 67. Typhlodromus rhenanus .................. • 69. Unsprayed population 69. Sprayed populations •••••••••••• 71. Medi olata sp. 71. Unsprayed population ........... 71. Sprayed populations ............ ?h. Page Thrips • . . . . . . . . . . . . . . . . . 7 1 * . Unsprayed population 7*+. Sprayed population ................. 77. Host-predator relationships 77. Unsprayed trees .. 77. Sprayed trees 85. GARTBBLL' S ORCHARD . . ••••» 91. . European red mite (Metatetranyehus ulmi) . 91. Unsprayed population ••••• -... 91. Sprayed populations 93. Tetranychus sp. ........ • 95. Unsprayed population ....... 96. Sprayed population ................. 96. Stethorus picipes 99. Unsprayed population ...100. Sprayed population 100., Typhlodromus rhenanus 102. Unsprayed population ....... 102. Sprayed populations ,10h. Host-predator relationships ................10^ -. Unsprayed trees • •....10 -^Sprayed trees • .... ....110.. DISCUSSION OF OBSERVATIONS MADE IN STUDY ORCHARDS 117. Host mites ............ • •.. • •.•»••••...... • .117. Unsprayed populations ..117. Sprayed populations •••••••••• ••.••••117» Page Pr edator s 130. Unsprayed populations ............ 130.. Sprayed populations .............. 133« Host-predator relationships ........... 138. Unsprayed trees 138. Sprayed trees ......... ..... lh2. CONCLUSIONS ... lMf. SUMMARY .................... ........ Ik6. BIBLIOGRAPHY . ... ... ......... .... 1?1. APPENDIX ... ................ . 159. ACKNOWLEDGEMENTS I should l i k e to express my appreciation to the following persons for the assistance I received from them while carrying out this project: To Dr. W. A. Clemens, Head, Department of Zoology, University of British Columbia, for his kind permission to use the material presented i n this paper as a thesis to be presented i n partial fulfilment of the requirements for a Master of Arts degree, and for his assistance in deciding upon the form i n which these data should be presented. To Professor G. J . Spencer, Department of Zoology, University of British Columbia, for his interest i n , and constructive criticism of this paper. To; Mr. J. H. McLeod, Officer-in-Gharge, Biological Control Investigations Laboratory, Vancouver, B.C., to Dr. J . M. Marshall, Officer-in-charge, Fruit Insect Investigations Laboratory, Summerland, B.C. and to Mr. C. V. G. Morgan, Associate Entomologist, Fruit Insect Investigations Laboratory, Summerland, for their many helpful suggestions made during the course of this project and for their comments on this paper, and to Mr. D. B. Vaddell, Assistant Entomologist, Fruit Investigation Laboratory, Summerland, who provided the photographs appearing in this paper. - i (a) -and to my mother who typed the "body of t h i s paper, to Miss Vera B e l l who typed the tables appearing i n the appendix, and to my wife who helped with the graphs appearing throughout t h i s paper. - i i -INTRODUCTION Economic Importance of Orchard Mites Mites have been known i n the Okanagan Valley of Br i t i s h Columbia for a long time, since before World War I, but only within the last fifteen years have they become troublesome and of great economic importance. In the days of their more casual occurrence between 191M- and 1930, they were easily controlled by spraying trees with water alone; this knocked the mites from the trees and injured them sufficiently that they could not regain the foliage. This treatment lost i t s efficacy i n time and was replaced chiefly by dormant o i l or wettable sulphur sprays. Eventually, these also lost their control value and were i n turn replaced by summer o i l s , rotenone-summer o i l , dinitrocyclohexyphenol and other substancesuntil at the present time very violent poisons are used, such as Paratlhion and Aramite.. During these years there has been a similar .evolution of spray equipment. The f i r s t applications of insecticides in the Okanagan Valley were made by a hand-operated barrel pump; this was replaced by a small, one-cylindered gas engine sprayer which was i n turn replaced by a high-pressure, two-gun sprayer. Finally, i n the mid-forties, an automatic sprayer was developed. With this machine, men did not have to direct the spray by hand; the spray machine was simply towed through an orchard by a tractor and automatically sprayed the trees on both sides of the route. Recently,: th i s type of machine has been widely replaced by the concentrate - i i i -spray machine which i s similar to the automatic sprayer of 19*+5 but delivers a very much smaller amount of more concentrated spray, discharged by a powerful turbine. Despite the Immense amount of research that has been done to develop new poisons and new methods of application, the entire orchard mite problem i s Increasing in serious-ness. Until 1935 the Codling moth, Carnocapsa pomonella (L) was considered the major pest of apple crops i n the Okanagan Valley, and indeed, in nearly a l l the major apple-growing areas i n the world., However, the European red mite and various other members of the family Tetranychldae began to increase In importance during the mid-thirties and since the early forties have replacedthe Codling moth as the most Important pest of commercial orchards In this area (Marshall 19H6). Massee (1951) considers the European red^mite may/ be justly regarded as one of the principal pests of apple, plum, damson, and other tree f r u i t s i n most parts of the world (see Legislation, 1935). The reasons for the increasing importance of the orchard mites, despite a l l human efforts, are not f u l l y understood. Many worker* have postulated very plausible theories concerning this increase; these theories are discussed below. Boyce (19*+8) and Pickett (191+8) state that the reason our insect control problems are increasing, although our insecticides and equipment have become more efficient, i s that our spray chemicals have interfered with the agencies that promote natural balance. When an Insecticide i s - i v -applied there may at f i r s t he a drastic reduction in the pest population, but once the applications are routine a new balance between the insect and i t s environment (which now includes the insecticide) i s reached, and the insecticide replaces in part other control factors, such as parasites and predators, i n the environmental resistance and i s not added to i t * Also, a chemical which controls one insect may increase the survival potential of another.. These conclusions apply particularly well to orchard mites. Until the application of Dichloro-diphenyl-trichloro' ethane (DDT) as a codling moth spray in 19*+5, orchard mites were not considered as primary pests in commercial orchards, although they had certainly increased enormously In Importance in the years Immediately preceding this time. Since the widespread use of this chemical, however, the increase i n abundance and importance has been phenomenal. The reason for this, as has been clearly shown by many authors, i s that DDT has no lethal effect on the host mites commonly found i n orchards, but has an extremely lethal effect on a l l known predators, both mites and insects. Thus, wherever i t has been used, DDT has eliminated most i f not a l l . of the natural controllf actors, without contrib-uting to the control of the orchard mites. How, DDT i s not the only chemical that has been found to have an adverse effect on natural control! agents in* orchards:; most of the chemicals used prior to 19 5^ for the control of orchard mites were much more toxic to predacious insects and mites than to the host mites* - V -Thus, nearly a l l . the chemicals that have been used against these pests, while effecting a certain degree of immediate control, have, over a period of time, been detrimental to orchard economy by destroying the agents of natural control, and have been responsible for the great increase of orchard mites that has occurred i n the last few years. However, there are two other factors that have undoubtedly contributed to this increase. The f i r s t of these was mentioned by Marshall (19^8) who stated that the chemicals used i n an effort to control these pests have accelerated the evolutionary process by chemical selection, so that strains of mites have appeared which are, to some extent, immune to the toxic effects of the chemical employed. In support of this, i t has been noted by several workers especially Garman (1950), that some species of mites,, particularly the European red mite, exhibit a tolerance to many of the most widely used acaricides. The second factor which has contributed to the increase of orchard mites i s that of orchard culture. Several workers (Keunen, 19*fl; Garman and Kennedy, 19W have reported that unsprayed, unfertilized trees usually have fewer mites on them than do cultivated trees. It i s also known that mites are less abundant on leaves with a high Ph value, and are more abundant on trees that have been subjected to nutritional sprays, which are thought to lower the H-ion concentration. Since the early days of orchard culture there has been a great improvement of cultural methods* irrigation i s now widely practiced; - v i -most growers f e r t i l i z e the trees i n their orchards; nutritional sprays have been introduced; trees are more widely spaced today than they were i n the past; and there has been an improvement i n pruning techniques. All- of these have resulted i n extremely healthy and productive trees. Unfortunately, healthy trees are able to support much larger mite populations than are unhealthy trees, and thus the improvements i n cultural practices have resulted i n an Increase i n orchard mites. There are, therefore, three factors which are thought to have caused the problem of orchard mite control to be of great moment — the up-setting of natural balance in orchards due to chemical applications, the acceleration of the evolutionary process by the introduction of chemical selection, and the increased a b i l i t y of the trees to support mite populations caused by the increased efficiency of cultural methods. The f i r s t of these i s undoubtedly the most important, and of a l l the chemical materials used in orchards DDT has causedthe greatest harmful, effects* Since DDT was f i r s t synthesized in 19^ 5 i t has been used univers-a l l y as a control for the codling moth.. It i s the best control for this pest ever devised, but i t has been responsible for more mite damage to trees than has any other single factor. There are two reasons for this, the f i r s t being that DDT i s extremely toxic to a l l known predators of orchard mites. When i t i s applied to a tree a l l natural control agents are eliminated, and the mite population i s able to increase greatly since i t i s not - v i i -harmed by this chemical. Most workers feel that the second reason that DDT has been responsible for much of the mite damage occurring in orchards i s that DDT has a stimulatory effect on the mite population, although the reasons for this are not known. It may be a purely physical effect causing the mites to reproduce more rapidly, or i t may be that DDT alters the nutritional value of the host tree i n such a way that a larger population of mites can be supported,. In any event,, i t i s known that after DDT has been applied to an orchard one may expect the host mites, i n the absence of any natural control agents, and with their reproductive capacity stimulated, to cause severe damage. Today, after l i t e r a l l y hundreds of chemicals have been tested as acaricides, there i s as yet no completely satis-factory method of controlling orchard mites. The growers are having to contend with an organism which can produce more than ten generations per season under favorable conditions; one whose reproductive potential i s such that even i f 98$ of the winter eggs are destroyed, i t i s necessary to apply some means of controil several times during the following summer CCutright, 1939)• It Is true that parathion 0 O,0-diethyl-0-p_-nitrophenyl thiophosphate) and several other organic insecticides can usually be depended upon to give control at a commercial level, but these chemicals are expensive, must be applied several times throughout the season, are extremely toxic to humans (so much so that parathion has been removed from the 1952 spray calendar for the Gkanagan Valley), and under certain. - v i i i -climatic conditions do not give adequate control. Chemists are endeavoring to develop insecticides which are innocuous to mammals, which are relatively inexpensive, and which w i l l be successful in controlling the orchard mites. However, no matter how inexpensive these chemicals w i l l f i n a l l y be, i t w i l l s t i l l cost the growers money to apply them, money to purchase the materials, money to purchase spray equipment, and money to hire the equipment operators. As the prime purpose of any control measure i s to save the growers from expense, i t would seem then that expensive chemical methods will, never be entirely satisfactory: biological means of controlling these mite pests offer the only alternative, Chemieal control! applied year after year and many times each season involves an expense which the margin of profit on many crops does not justify. With biological control the i n i t i a l cost incurred while studying the problem and introducing parasites and predators, or encouraging those already present, i s often the total cost i f the damage done by the host i s reduced to below the economically important le v e l . Biological control- may not be completely successful by i t s e l f , but i t s contribution may be such that chemical means of control need be used on a reduced scale only. This has been demonstrated by the work of Ullyet ( 19Yf). When an outbreak of an econom-i c a l l y important species occurs, i n other words when an emergency occurs, i t must be met by chemical methods, but successful exploitation of the biological method should not be hampered by these. - i x - . , Boyee (19^8) sums up the need for biological control in Canadian orchards i n the following statement:: "Man has created problems by his cultivation and altering of environments (e.g. application of chemicals). He attempts to solve these problems i n a mechanistic manner. Sooner or later the time w i l l arrive when he w i l l have to turn back to nature for a solution to his d i f f i c u l t i e s . B i o l -ogical control offers the way." In Canadian orchards neither biological nor chemical methods w i l l be successful alone because of the great diversity of phytophagous enemies. It i s necessary, there-fore, to obtain combinations of the two methods which do not render them mutually ineffective. In order to place the control practices on a sound scientific basis, i t w i l l be necessary to obtain a complete knowledge of the existing ecologieal conditions and of the nature of the interactions of the populations of organisms within the orchard environ-ment. This paper i s a report of the f i r s t steps in such a study. An investigation, whose f i n a l objective i s to increase the effectiveness of the natural enemies of the important orchard mites by careful timing and regulation of the chemical control program, was initiated during the summer of 1951 at Summerland, B.C., i n the Okanagan Valley. The work was undertaken as a joint project of the Fruit Insect Investigations Unit and the Biological Control: Investigations Unit, both of the Canada Department of Agriculture. The work - X -was performed at the Fruit Insect Investigations Laboratory at Summerland, under the direction of Dr. J . H» Marshall, Officer-in-charge of this laboratory, and Mr. J . H. McLeod, Officer-in-charge of the Biological Control Investigations Laboratory in Vancouver. Mr. C. V. G. Morgan represented the Fruit Insect Investigations Unit and the author of this paper the Biological Control!. Investigations Unit. The work performed during the summer of 1951 was i n th e nature of a preliminary survey designed to determine what host mites and predators are present in the Okanagan Valley and also to determine i f the existing predacious species have the potential a b i l i t y to control the host mites under suitable conditions. In addition, an investigation of the effects of the application of three common chemical compounds was Initiated and the results from this also are reported in this paper. Both of these investigations w i l l be continued for a number of years on varieties of apple only as these are the most important f r u i t s grown in the Okanagan Valley and the ones most favored by phytophagous mites. Despite the fact that this problem has been under study for one season only, i t was f e l t that the results of the f i r s t season's work were of sufficient interest and importance to warrant their being used as the basis for this paper. Work of this nature has not been performed before i n North America and i t i s hoped that this paper w i l l provide future investigators with important basic information. - 1 -General Characteristics and Life Histories of  Phytophagous Mites The following species of phytophagous mites have been found to be of economic importance in the Okanagan Valley of British Columbia: the European red mite, Metatetranychus ulmi (Koch); the Clover or Brown mite, Bryobia pretiosa Koch: the Two-spotted spider mite, Tetranychus telarlus (L.), the Pacific mite, Tetranychus  pacificus McGregor; the Willamette mite, Tetranychus  willamettei McGregor; and the yellow mite, Tetranychus  flavus Ewing. These six species are a l l members of the family Tetranychidae, and as such have similar l i f e histories and habits. The internal morphology and exact l i f e history has been described for only one of the above, the European red mite:: The internal morphology was described by W. E. Blauvelt (19^5), and the l i f e history by Catherine A. Blair and Joan Groves (195D. A l l of these Tetranychid mites cause similar damage and are capable of i n f l i c t i n g severe injury to an orchard. Unlike the codling moth, an extremely important pest of f r u i t , phytophagous mites damage both f r u i t and foliage. They feed by thrusting their lance-like mouth-parts into a leaf and extracting the plant juices and chlorophyll. Thus water i s lost to the tree, and, as the chloroplasts are damaged, the tree cannot produce carbohydrates (Kotte, 19^1). The leaves become speckled and bronzed and f a l l from the tree prematurely (Caesar and Ross, 1921). The - 2 -growth of the tree i s checked i n this manner, the f r u i t i s dwarfed, and ripening i s retarded. The f r u i t may even remain unripe and sour causing the f r u i t buds for the following year to be diminished in number. Defoliated trees may set f r u i t again i n the autumn, and are then susceptible to winter damage since there i s l i t t l e stored food in the buds (Melander, 1923). The feeding of mites has no toxic effect transmissable from one part of the leaf to another, as has often been reported (Henderson & Holloway, 19^2). Most damage i s done to the apple varieties having the thinnest cuticle, and most i s done when the mites feed on the upper surfaces of the leaves. Triploid and tetra-ploid varieties seem to be less badly attacked than are the diploid ones, perhaps due to their thinner epidermis (Lewis, 19^5). In addition to the damage described above, these mites have been known to transmit virus diseases of plants. There i s an instance recorded in which ten per cent of a f i e l d crop, in Russia, was infected with a virus disease trans-mitted by mites (Moskovetz, 19kO). Tetranychid mites possess incomplete metamorphosis: the progressive stages from the newly hatched larva to the adult do not include a true pupal phase, and the develop-mental changes chiefly involve an enlargement of size. During ontogeny, a fourth pair of legs i s added following the f i r s t larval moult. The l i f e histories of the mite species considered - 3 -i n this paper conform closely to one pattern, differing only i n the number of generations produced each season, varying with climate, and i n the method of over-wintering. In general, the eggs are deposited on the leaves of the food plant and hatch i n a very few days during' the active season, giving rise to minute six-legged larvae. These commence feeding immediately. The female larvae, upon moulting, are succeeded by eight-legged protonymphs which again moult to become the deutonymphs. The third moult i n the females gives rise to the adult form. The nymphal stages d i f f e r from each other very l i t t l e except in size. The development of the males dif f e r s from that of the females in that there i s but one nymphal stage. In a l l cases, females may deposit unfertilized eggs which invariably produce only male individuals*. The European red mite and the Clover mite overwinter as eggs on the trunk and branches of the host plant. The other species overwinter i n a special female overwintering form, usually in the s o i l at the base of the host plant. Since the f i r s t two species are present on the trees a l l winter and thus do not waste time in migration in the spring, they are able to commence feeding very early i n the season, often when the host leaves are in the "mouse ear" stage of development. Many tetranychld mites spin webbing on the host plant which i s used for protection and for anchoring eggs to the surface of the leaves, and a single strand of s i l k i s often / - If -used as a parasite enabling both immature and adult mites to be carried long distances by wind. The glands producing t h i s s i l k are located over coxae I and I I , and t h e i r ducts extend along the front of the body where they unite into a common duct which runs antero-ventrad to a point under the t i p of the rostrum. Mites of the family Tetranychidae have the following general characteristics:, they are soft-bodied, oval to e l l i p t i c a l i n outline i n the females and long-oval i n the males (Figure 1 (a) - Appendix);; the c o l l e c t i v e complex of the mouthparts i s not moveable forward and backward, and forms a short cone which i s p a r t l y sheltered by an overlying f o l d of the dorsal body t i s s u e ; the c h i t i n i z e d portion of the mouthparts consists of a pa i r of b r i s t l e - l i k e elements, recurved sharply behind, the dorsal arm imbedded i n the mandibular plate, the longer ventral arm protruding anter-i o r l y from under the spina; the terminal thumb-like segment of the palpus a r t i c u l a t e s with the preceding segment so as often to appear to be deflexed from i t ; a dorso-terminal claw i s borne on the penultimate segment of the palpus, overlying the terminal segment;; the eyes are usually very noticeable as red spots; the g e n i t a l and anal openings are situated near the caudal end of the venter, the anus being sub-terminal. (McGregor,, 1950). The body of a tetranychid mite i s d i v i s i b l e i n t o a cephalothorax, or proterosoma, and an abdomen, or hyster-osoma. The former bears the two anterior pairs of legs and the rostrum; the latter hears the two hind pairs of legs and the genital apparatus. The dorsum of the body bears a varying number of setae, ranging from 22 to 56 i n number, arranged in transverse and longitudinal rows. One or two eye corneae occur on each side of the cephalothorax, usually between the subfrontal and humeral setae. The mouthparts of tetranyehid mites ( F i g . l . — appendix)1 consist of mandibles, palpi, and the spina, Basally, the mandibles are coalesced to form the mandibular plate; d l s t a l l y , they project anteriorly as the needle-like stylets and t i p of the rostrum, or spina. These stylets are solid, and are used for piercing plant tissue. The rostrum i s a conical extension from the ventral portion of the cephalothorax, lying between the palpi; i t i s s l i g h t l y truncate in front, and bears several minute setae near i t s t i p . The oral o r i f i c e opens near the tip of the rostrum.. The palpi arise between coxae I, under the mandibular plate^" straddling the rostrum, and are five-segmented, the last segment forming a "thumb" to the preceding joint which bears a strong claw. This "thumb" bears from 5 to 8 segments.-, A pair of tracheae border the mandibular plate and lead inward as variously shaped tubes. The shape of these has taxonomic significance.. The legs are six-segmented, consisting of coxa, vir-'• ' . . -4 - 6 -trochanter, femur, patella, t i b i a , and tarsus. Their relative lengths are of taxonomie value. There i s great variation i n the structure of the terminal tarsal appendages and these characters are very useful in distinguishing between certain genera, and the species within these genera. The strongly chitinlzed copulatory organ of the male individuals corresponds to the aedeagus of insects. It varies greatly i n shape between species and i s of the utmost importance in their identification. As indicated by i t s name, the European red mite i s indigenous to European countries. The f i r s t record of i t s occurrence in this country was made some time around the turn of the century. Since i t s description by Koch in 1835 i t has been recorded from the following countries* Belgium, Czechoslovakia, Denmark, England, Finland, Germany, Holland, Ireland, Italy, Norway, Sweden, Switzerland, Wales, Russia, Canada, United States of America, Bermuda, Japan, Australia,, and New Zealand. It has been recorded as occurring on the following plant genera:; Acer (Maple), Amygdalus (Peach), Buxus.(Boxwood). Crataegus (Hawthorn))T Ficus (Buttercup), Juelans (Walnut), Magnolia. Malus (Apple), Medicago (Alfalfa), Phlox « Pinus (Pine), Pittosporum;Prunus (Cherry and Plum)) Pyrus (Pear)^ Quercus (Gak), Ribes (Currant), Rosa  Rubus (Bramble), Salix (Willow), Sorbus (Mountain Ash), Thea^Tllia (Basswood), Ulmus (Elm), V i t i s (Grape), and Zinnia (Mabry & Walton, 1939) - 7 -The Clover mite, the Pacific mite, the Willamette mite, and the Two-spotted spider mite and Yellow mite are thought to be indigenous to this continent, and i n addition to being found on most commercial varieties of f r u i t trees, are also found on mueh of our native flora* Synonomy of the Tetranvchld Mites. Because of poor and inadequate descriptions, the European red mite has been described as a new species no less than four times in the last 12G years. A similar situation exists with some of the other economically important species in the family Tetranychldae. For this reason synonyms and popular names that exist for each of the mite species considered i n this paper are appended. List of Synonyms and Popular Names 1. Metatetranycfaus ulmi (Koch) Tetranychus ulmi Koch 18*^ 5. Tetranychus pilosus Canestrini & Fanzago 1876. x Paratetranychus pilosus ( C.& F») Zacher 1913. Oligonvchus ulmi (Koch)T Hirst 1920. Ollgonychus alni Oudemns 1929. Metatetranyehus alnla (Oudemans) Oudemans 1931. Tetranychus (Penthalodes) mytilaspidls (Riley 1885)auct. Fruit tree red spider mite Fruit tree red spider Red spider European red mite Red mite Obstbaumspinnmilbe Fruitspint It'araignee rouge de pommier Hedelmapuupunkista 2. Tetranychus pacificus McGregor 1919. Pacific mite 3» Tetranvchs yip »m^e,i-±^ McGregor 19lk. Willamette mite - 8 -V h. Tetranvchus telarius (1.) 1758. Tetranychus urticae Koch I836. Tetranvchus bimaculatus Harvey 1892. Epitetrarivchus althaeae Van Hanstein 1901. Common red spider mite Common red spider Greenhouse red spider Hop red spider Red spider-Two- spotted spider mite 5. Bryobia pretiosa Koch 1836. Bryobia mite Bryobia pratensls Garman 1885. Brown mite Bryobia nobilis Berlese Clover mite Bryobia speclosa Koch I838. Gooseberry Bryobia , mite 0. Tetranychus flavus Ewing 1913. Yellow mite 4. k - 9 -Life Histories and Characteristics of Four Predators Found in Apple Orchards of the Southern Okanagan Valley. The most important natural control, factors of orchard mites are predators. No internal parasites have ever been recorded. The known predators include the order Acarina of the Arachnida, and the Hexapod orders Hemiptera, Goleoptera, Diptera, and Thysanoptera. Other insects and mites occurring in the Okanagan Valley may be predacious on orchard mites but only seven species were recorded during the season of 1951• These were two species of mites, a thrips, a coccinelid beetle, the larvae of a species of Syrphid f l y , an anthocorid and a neuropteran. ACABINA: Typhlodromus rhenanus: This species of Gamasid mite i s probably the most important predator of orchard mites occurring in the Okanagan Valley; i t i s present in greater numbers than any other species of predator and i s active throughout the entire season of the host's activity. The following discussion i s based on G i l l i a t (1935)*= The adults and more mature stages of this mite attack a l l stages of the European red mite and other members of the Family Tetranychidae but prefer the eggs of these mites. Typhlodromus rhenanus adults hibersjhte on twigs of the host plants, concealed under roughnesses in the bark. The mites are active at low temperatures and consume the winter eggs of both the European red mite and the Clover mite on the warmest days u n t i l late i n the autumn. Feeding i s resumed in the spring a considerable time before the - 10 -host eggs hatch. G i l l i a t (ibid) found on his check plots that there was a f i n a l reduction of 80.2$ i n the winter eggs of the European red mite produced mainly by T. rhenanus although other predators, fungus diseases, heavy winds, frosts, sleet, desiccation, low temperatures, and small birds a l l contributed. There are several generations of this mite each season. The eggs are pearly white, ovate, 0.062 mm. long and 0.052 mm. broad. They are deposited on the undersides of the leaves near the mid-rib and larger veins and are held in place by the leaf hairs, being otherwise unattached. Usually the adults are pale without characteristic markings, although individuals showing pale brownish markings of the dorsum, or ones on which the entire dorsum i s pale reddish or wine colour, may be found. The latter coloration i s apparently due to the mites having gorged themselves on the eggs of the European red mite and the Glover mite, whose colour shows through the integument. They are usually found on the under sides of the leaves, mostly near the mid-rib. They can move very rapidly. The immature stages of this mite are similar to the adult except that they are smaller. This species\ of predacious mite can be successfully reared on apple foliage In the absence of any host mites, V the leaf juices being i t s only food. It has been found that this mite i s extremely susceptible to the toxic effects of a l l sulphur sprays - 11 -(lime-sulphur i n particular), a l l sprays containing o i l s 3 and to DDT. Nicotine however, has no detrimental effect on i t . ' / Mediolata Sp.; This mite belongs to the Family Stigmaeidae Oudemans 1931. The species occurring i n the Okanagan Valley has not yet been identified and i s probably undes-cribed. Nesbitt (19**6) has described a species of this genus which he found in apple orchards of Nova Scotia and named i t Mediolata novae-scotiae. It i s very similar to the one found in British Columbia and the following description i s based on that of Nesbitt. Nesbitt observed that members of this genus are commonly found on the under side of apple leaves near the mid-rib and occasionally on associated orchard f l o r a such as cover crops and weeds. L i t t l e i s known of their l i f e -histories although i t has been found that they over-winter as adults beneath oystershell scales and bits of loosened bark. They are known to feed on the eggs of the Clover mite and the European red mite and in addition have been observed feeding on the eggs of mites of the genus Typhiodromus and on bl i s t e r and rust mites. These mites are normally slow-moving but when dis-turbed they are capable of moving very rapidly. The adults are yellow-orange or red with chalky-white or creamy-yellow stripes down the dorsum. There are no morphological differences between individuals of different colors. These - 12 -differences are apparently caused by different foods or as a result of genetic or physiological differences. The male individuals are approximately 0.23 mm. in length, ovoid with the point directed posteriorly, and are covered with nine sclerotlzed plates dorsally. The females are approximately 0.32 mm. in length. The body is more oval than that of the male since the posterior end i s much broadened. The female body i s covered with 15 sclerotized plates. C0LE0PTEBA; Stethorus niclnes Casey:-This insect i s a small beetle belonging to the family Coccinellidae. It i s commonly found in orchards infested with orchard mites i n Washington State and in British Columbia. The following description i s based on a paper by Newcomer and Yothers (1929). The adults are active f l i e r s over short distances and hibernate during the winter in orchard debris. They do not emerge from hibernation u n t i l late July or early August, but from then u n t i l late October produce several generations. The average l i f e cycle requires 30 days. (Newcomer et a l , 1929). During the larval and adult stages these insects feed on a l l stages of Tetranychid mites, and probably on a l l . stages of any. predacious mites which may be present* Each Insect i s capable of consuming several hundred mites - 13 -during i t s lifetime. Newcomer and Yothers observed that one adult beetle consumed k65 winter eggs of the European red mite in 10 days i n September. Radzievskaya (1931) reported that i n Tashkent, Russia, one larvae consumed 6UO eggs and 160 adults of Tetranvchus telarius before entering the pupal stage. Stethorus picipes has d i f f i c u l t y i n finding hosts when they are scarce. Larvae suck the contents of the host and adult beetles suck and devour both eggs and adult mites, f i r s t sucking them nearly dry and then eating the remaining shell or skin. The eggs of this insect are small, cream-yellow or white, oval, and measure 0.30 mm. i n length. The larvae are dark ash grey in colour and are 1.5 to 2.0 mm. i n length. Each segment of the thorax has a pair of irregular black spots on the dorsal surface. The head, thorax, and abdomen are covered with long hairs. Each of the 9 segments of the abdomen, except the terminal one, has 6 whorls of b r i s t l e s . The pupae are reddish at f i r s t but later turn brown and f i n a l l y black in contact with the air.. They are flattened and covered with fine hairs which are knobbed at their tips. They are attached to the leaf at their posterior extremities. i The adult beetles are 1.5 mm. in length, black, and are clothed with fine hairs. Radzievskaya (ibid) found that the adults of this beetle hibernate on the trees in batches of from 10 to 50 Individuals. In the spring they are f i r s t to be found - Ih -on weeds harboring mites and later migrate from these to the trees. It i s the opinion of the author that this i s true i n orchards infested solely with the Two-spotted spider mite or other members of the genus Tetranychus which hibernate on the ground and begin feeding i n the spring on the cover crop of the orchard. However, when the European red mite or Clover mite i s present, the adult beetles need not commence feeding on the ground since these mites hibernate i n the trees, and are thus available throughout the entire year. Steiner et a l (19^7) observed that S. plcipes was absent from trees sprayed with DDT but was numerous on trees sprayed with lead arsenate. Approximately one month later the beetles migrated into the DDT plot and produced noticeable control of the European red mite.. THYSANBPTERA t. Many species of thrips have been recorded as feeding on various species of orchard mites.. The thrips collected at Summerland during the 1951 season have not been Identified as yet but they are probably Scolothrips sexmaculatus Pergande. which i s common i n Washington in the orchards of Yakima and Wenatchee. The following discussion of S. sexmaculatus Is condensed from Newcomer and Yothers (1929). These insects apparently prefer the eggs of the host mites but w i l l also feed on the larvae, nymphs and adults. They are capable of consuming 7 eggs of the European red mite i n 30 minutes when they are i n the last larval stage* Other larvae have been recorded as consuming 5 eggs i n 17 minutes and one consumed 55 eggs, 3** larvae, 7 nymphs, and 6 adults in 3 days. These thrips feed by puncturing the prey with their mouthparts and removing their body juices. When a thrips has sucked most of the f l u i d contents of the host, i t r o l l s the mite over with i t s front legs and again inserts i t s mouthparts, sucking out the remaining f l u i d . Newcomer and Yothers (ibid) state that these thrips probably overwinter among fallen leaves and other s o i l debris as adults.. They are commonly found during the summer slowly moving over the leaves and twigs of apple trees, or resting between leaves, in the axils, or in other more or less concealed places. They w i l l run swiftly when, disturbed or hungry but are much less active than are the more familiar plant-feeding thrips. Their wings are well developed but the adults seldom take f l i g h t even when disturbed. The eggs of the f i r s t generation i n the spring are l a i d early on leaves and twigs. There may be several generations per year which results in a l l stages being present at the same time. In general the adult insects are shiny black and approximately 2.3 mm. in length. The larvae are pale yellow or green and develop from 0.6 to 1.25 mm. i n length. As mentioned above, only seven species of predators have been observed feeding on orchard mites i n the Okanagan Valley, four of which are described above. Nothing i s known of the other three species, a Syrphid f l y , an Anthocorid, and - 16 -a Neuropteran. Undoubtedly, more predacious species will, be observed as this project progresses since in most other areas where orchard mites occur the predacious species are very numerous. For example, Miss Collyer (19^9) found the following predacious species i n the orchards of Essex County, England, from 19hb to 19^8:; Hemiptera-Heteroptera Anthocoridae Nabidae Miridae Thysanoptera Neuroptera Hemerobiidae Ghrysopidae Coniopterygidae Anthocorls nemorum (L.) " nemoralis (Fab./ M confusus Reut. Orius minutus (L.J Orius malusculus (• Reut.) Himacerus apterus (Fab.) Phvtocoris t l l i a e (Fab.) Phvtocoris reuterl Saund. Phytocoris ulmi (L.) Camptobrochis lutescens ( (Schill.) Daraocorls ruber (L•) Campvloneura vireula (H.S.) Pilophorus pernlexus D . S . Blepharidopterous angulatus (Fall.) Orthctvlus marginalis Reut. Cansus merlopterous (SCOP.) Malacocorischlorizans (Pz.) Psallus varlans - ( H. S.)' Psallus amblgnus (Fall.) Atractotomus mall (M.D.) Plaglognathus arbustorum (Fab.) Thrips tabaci Lind. Aeolothrips melaleucus Hal. Several spp. Da carnea Steph, zia psociformis (Curt.) - 17 -Coleoptera Staphylinldae Diptera Cecidomyida© Syrphidae Acarlna Trombidioidae Parasltidae Arachnida Oligota flavicornis Bolsd> Ada!la blpunctata (L.) Cocclnella sentempunctata L, Stethorus punetlllum (Wei.) Gecidomyid larva (Unidentified) Several spp. of larvae Anvstls a g i l i s Banks. Chevlefcus SP. Typhlodromus poml (?) and other spp.. Therldion pallens. B l . Of these, the mirlds are thought to be the most effective i n controlling the European red mite, particularly the Black-kneed mirid, Blenharidopterous angulatus (Fall.) There i s no reason why insects such as these should not be found in British Columbia also, since they are known to occur in Washington. (Newcomer and Yothers, 1929.) H • - 18 -METHODS AND PROCEDURE Description of Study Orchards It vas decided that the i n i t i a l studies connected with this project should be performed under as nearly "natural" conditions as possible, so that the information obtained would be uncomplicated by any chemical or cultural considerations. If the work had been performed in commercial orchards one would not have been able to determine the effect of the chemical programs to which the orchards had been subjected for a number of years on the host and predator populations. For this reason, two abandoned orchards were selected to be used i n these studies;; both of these were abandoned more than 15 years ago and since that time have had no chemical or cultural treatments of any kind. Mclntyre Creek Orchard This i s located approximately 30 miles south of Penticton, B.C., at Mclntyre Creek on the highway to Oliver. It occupies about an acre of ground beside the Okanagan River, not far from i t s junction with Mclntyre Creek. Early i n the year this orchard i s very damp with standing surface water which seeps i n from the creek* Later i n the year this creek dries up, although not sufficiently to prevent adequate subirrigation provided - 19 -by seepage through an underlying layer of coarse gravel* The prevailing winds are north and south along the length of the orchard.. The orehard at Mclntyre Creek i s comprised of, 29 trees, 28 of which were used in this study. The varieties are Mcintosh and Delicious, with one Heslop crabapple tree. A map of the orchard i s shown as figure 2* • Meyer's Flat Orchard The second abandoned orchard used i s located at Meyer's Flat approximately 30 miles by road south-west of Penticton. It was planted shortly after World War I but was abandoned several years later because of the d i f f i c u l t y i n obtaining water for irr i g a t i o n . The trees were cut down at this time but new growth arose from the remaining trunks and root stocks. The resulting trees are f a i r l y large in size, averaging approximately 20 feet i n height. There i s amixture of varieties i n this orchard due f i r s t to the fact that i t was originally a mixed planting,, and secondly, the original root stocks were of different varieties from the crowns of the trees.. When the original trees were destroyed some of the new trees were produced by growth from the original trunks and some from the root stocks. The varieties found at present are Northern Spy, Rome, Sweet seedling, Newton, Winesap and Jonathan. - 2 0 -S C R U B W I L L O W A-VaTt 2. 21 There are 65 trees in this orchard, of which 29 were used i n this study. Many of the other trees were being used i n other experiments, and the remainder were not suitable. There i s a small- amount of subirrigation in the orchard during the early part of the year from a nearby creek, but by midsummer the conditions are extremely arid. For this reason the trees are not as healthy as those in the McIntyre Creek orchard and their leaves are thick and tough. A map of this orchard i s shown as figure 3 and a photograph as figure 3a (Appendix). Gartrell's Orchard In addition to the abandoned orchards described above, 30 trees were leased in a commercial orchard (figure h)9 a l l of the Yellow Transparent variety. They were of limited use only this season since the trees had been subjected to chemical treatments for a considerable number of years, and were sprayed early in 1951 with Elgetol, a blossom thinning chemical. Elgetol i s an aqueous solution containing kO% of the sodium salt of dinitro-o-cresylate, and undoubtedly had some effect on the mite population. However, i n future years these trees w i l l provide an opportunity to study the host mites under controlled commercial conditions, and w i l l i provide a testing ground for new methods of control indicated by this project. The most useful function of this orchard this season was to provide information concerning the extent to which the host mites are controlled by natural agents in - 2 2 -I • 2 • 3# 5 • CHECK PBAS IDDT ) PARATHION O o 3ft 2ft 2» !• 4« 3« 6ft o o 4 • 6 • y 6.« s t 4ft o o 0 4ft O 0 o 3ft 2ft o o o o o o 0 10* 11 • o o MEYERS FLAT ORCHARD Sft 6ft o o o o o o o o N ROAD Fi a *> r fc ~b. 2 3 -P E A C H E S O O o o o A P R I C O T S A P R I C O T S G A R T R E L L S O R C H A R D A P R I C O T S • C H E C K • P B A S O D D T • P A R A T H I O N N "O F L U M E Figure >+. - 2*f « i i commercial orchards at present. The Gartrell orchard i s situated 3 A mi. from the Fruit Insect Investigations Laboratory at Summerland, i n a westerly direction., From the Mclntyre Creek and Gartrell orchards ten trees, and from the Meyer's Flat orchard eleven trees, were selected. These were not selected at random but were chosen as being the trees least l i k e l y to be contaminated by spray d r i f t . These were to f i l l a dual purpose. From data obtained from leaf collections i t was hoped that the effectiveness of biological agents i n controlling the host mites under "natural" conditions — In an environment free from f e r t i l i z e r s and insecticides — could be assessed. i These trees were also to serve as controls or checks for the plots treated with various poisons. The remaining trees used i n each orchard were divided into 3 blocks of 6 trees each. Each of these three bloeks was treated with a different insecticide three times during the season — from May 1st to September 15th. The insect-icides used were lead arsenate (PbAs) applied at the rate of h lbs. per 100 gallons of water, DDT (97$ wettable powder) at 3 ^ Iks. per 100 gallons of water, and Parathion (15#) at 1 l b . per 100 gallons of water. Approximately 100 gallons of each spray were used for the 6 trees in a plot each time that plot was treated. Lead arsenate was used in this study because i t was the universal insecticide when mites f i r s t became of economic •^25-importanee and i t was hoped to determine whether i t was in any way responsible for the general increase in orchard mite populations. In other words, i t was hoped to determine whether Pbas has any stimulatory effect on a population of host mites, or causes any repression of a predator population.. DDT was used because i t i s generally conceded to have been of major importance i n the later stages of this general increase in orchard mites. It has been used since 19^5, and i s s t i l l being used very generally as a Codling moth control* Therefore i t i s necessary to know precisely what i t s effects on a host mite population are as well as on a > predator population. Parathion was used because i t i s the acaricide most commonly used in British Columbia, indeed in a l l regions where orchard mites have created a problem of economic importance. It was desired to determine the effects of this virulent poison on host and predator populations. Figure 5 (Appendix) shows the machine used when applying the sprays described above. It consisted of the chassis of a Ford truck to which had been attached a 300 gallon tank, a pump, and two 10© foot hoses. A pressure of *K)0 lbs. was used.. The three figures i l l u s t r a t i n g the plans of the three orchards under study (Figures 2, 3, and h) show that the check plots i n each orchard were l a i d parallel to the direction of the prevailing winds and to the spray plots. This was done so that there would be no possibility either - 26 -of host mites or predators feeing carried by wind from the unsprayed trees of the check plots to the sprayed trees of the test plots. It also eliminated the danger of spray d r i f t i n g from the test plots to the check plots during spraying operations. DDT and Parathion were placed at each end of the three test plots in each orchard so that when the wind was favorable they could be sprayed with no poss i b i l i t y of spray d r i f t contaminating any other test plot. This was unnecessary with PbAs since i t i s not a contact insecticide and would have to be present i n large quantities to affect the mite population.; Leaf Sampling Bach tree in the check plots was divided into quadrants — north, south, east and west. When making collections from these points, 20 leaves were picked from the branch most nearly bisecting the quadrant at shoulder level, ; and 20 were picked at random from the entire tree at the same lev e l . An attempt was made to pick the leaves at random, with the exception that no very immature leaves were taken. The trees were divided into quadrants in order to determine which exposure, i f any, was preferred by the host mites and predators. On the same day that collections were taken from the check trees, 20 leaves were collected from a marked branch on the south side of each of the trees in the three test plots. The data from these collections, when compared to those obtained from the south sides of the check trees, - 27 -provided an indication of the effect of the various insecticides on the host and predator populations. Collection technique:. During collection and , subsequent manipulation the leaves were handled only by their petioles. As the leaves were removed from the trees, they were placed in small waxed-cardboard containers of the type obtainable from frozen food lockers. Prior to use, these containers had had a l l seams and irregularities f i l l e d i n with paraffin wax. After collection, the containers and leaves were brought to the laboratory where, i f the leaves were not to be examined the same day, they were placed in a cool place so that the mites and predators would become quiescent. When the leaves were to be examined they were removed from cold storage and the mites on them were removed by means of a brushing maehime.; Sample Size' ». For the purpose of this study i t was decided that a maiiimum experimental error of 1$% would be acceptable, since the work was performed under f i e l d conditions and a smaller error could hardly be hoped for. Once this level had been established, i t was necessary to determine the number of leaves each sample must be composed of to maintain the error below this figure.= This could not be done u n t i l the host mite population was at i t s highest level since the maximum variation in animal populations - 28 - i occurs under conditions of maximum density (Dr. G. B*. Oakland, 1951.). In order to determine the number of leaves necessary in each sample, ten leaves were collected from each of four trees, and were kept separately. Each leaf had the mites on i t brushed on to an individual plate. The data obtained when these mites were counted are shown as Table I. The European red mite was the only species present i n sufficient numbers to be used for this test* However, as this mite occurs i n the greatest density throughout the season, i t possesses the greatest population variation.. Table I. Data Obtained from a Test Designed to Determine the Inter-leaf Variation in a Population of European Red Mite. Tree Number Leaf Number European Red Mite Egg Immature Adults 1.. 60 h? 23 2. 59 28 11 ?- lh? 56 10 h. 130 76 10 5- 3£ 17 if 6. 35 6 >: 7. 79 61 17 8. 33 53 h 9. 63 5* 11 10J. 138 83 Ik TfT ~ 112 2. 269 280 29 3*. 2*f2 157 27 h. 63 101 13 5. f 53 * 6.. 61 9t 11 7. 65 57 £ 8. 92 66 17 9. ^5 51 3 10. 120 10^ - 16 - 29 ~ Table I. (Continued) Tree Number Leaf Number European Red Mite : ~" Egg Immature Adults j- > 21 9 2. 77 21 8 3. HO 59 7 1. 77 96 9 5. 69 h7 9 6. • l £ 89 2| 7. 136 26 6 8. 28 16 8 9. 112 13^ 15 10. p -5-— — IT 175 8 0 ^ W 2. 1^ 3 90 13 3. 120 30 21 h. 55 17 9 5. l l i 61 28 6. 128 70 13 7. **5 31 12 8. 363 168 32 9. 57 70 9 10. 25 25 ;  1. The procedure of analysis is as follows: Sum of squares s Tree #1.. * 622,978 Tree #H. = 235,0*f8 Tree #3. = 250,727 Tree #5. = 715,017 Total sum of squares = 1, 823, 770.. Standard deviation - 225*6 Standard error = 225.6 • 35.8 Coefficient of variation » 35.8 j£100 = 19# where x = the mean of a l l kO leaf samples (180.1). If the error is to be no more than 1$%, the number of leaves required for each collection (n) is as follows: 225.6 X 100 JBlZ =15, 180.1 n * 68.9 for four trees - 30 -Therefore, i t i s necessary to collect 68.9 = 17 leaves per tree for,an accuracy of this magnitude. As this exper-iment could not he performed u n t i l the period of peak host mite abundance, this figure could not be appliedthls season. It was decided at the beginning of this season that the samples would consist of 20 leaves, yielding an experimental error of not more than 13.8$. Next season the data obtained from this experiment w i l l be u t i l i z e d . A second study of sampling methods was that of deter-mining whether large apple leaves support a greater mite population per unit area than do small leaves. Prior to making this study an attempt was made to pick representative leaves when making a collection. However, i f , as a result of this study, i t had been found that a particular species of mite preferred one size of leaf to another, then any sample taken for the purpose of investigating this species must be composed of leaves representative o f t h e favored size, not merely representative of a l l leaves on the branch from which the collection i s being made. For the purpose of this study 20 large leaves and 20 small leaves were collected from one branch on the south side of each of five apple trees. These leaves were taken from the centres of the branches since i t i s known that certain mite species prefer the proximal parts of the branches and certain others favor thedistal portion. The leaf circum-ferences were taken as a measure of leaf size, since a l l the leaves were regularly oval i n outline.. The circumference - 31 -was measured by means of a planimeter. Each collection, consisting of 20 leaves, was then brushed. The results are shown as Table II. (page 32). The number of mites per unit circumference of large and small leaves i s sown as Table III. A Table III. Number of Mites per large and Small Leaves. Tree Number Size European Red Mite Tetranychus-sp. 1. Large 10.6 1.2 2. Large 3.9 .9 3. Large 7.1 1.1 *f. Large 5.1* .7 5. Large 11.2 1.5 Average liarge 7.6 1.0 1. Small 8.3 2.h 2. Small 3.^ 2.5 3. Small 7.1 2.7 h. Small 6.6 3.7 5. Small 11.6 3.0 Average Small 7.h 2.8 From these results i t i s evident that large apple leaves support the same number of European red mites per unit circumference as do the small, leaves. It i s , there-fore, a matter of available space rather than an attraction exhibited by the large leaves, or a repulsion by the small leaves, which accounts for the larger numbers of these mites being found inhabiting large apple leaves. It appears that small apple leaves have some attraction for mites of the genus Tetranychus (Willamette mite, Two-spotted spider mite, Y/ellow mite and Pacific mite), or the large leaves repel them in some way. The former i s probably the case since small leaves are more tender than large ones, TABLE II Number of Mites per collection of Large and Small Apple Leaves. Total Tree Mo. Leaf Size European Red Mite Tetranychus sp. Circumference Egg Immature Adult Egg Immature Adult in inches 1 Large 580 1176 72 20 140 56 1 7 2 . 0 2 Large 268 46O 32 . 2 4 140 8 189.5 3 Large 344 948 56 8 148 56 188.0 4 Large 34O 603 68 - 112 24 186.0 5 Large 46O 1492 56 4 196 76 179.0 1 Small 372 424 68 - 232 24 103.0 2 Small 172 144 32 24 224 16 102.0 3 Small 252 396 32 12 232 20 95.0 4 Small 292 296 76 32 316 29 100.0 5 Small 480 596 84 4 248 52 99.0 - 33 -and conceivably are more favored as food. This information was not of use this season since the primary purpose was to study the entire mite complex, hot any particular species. However, in future seasons i t i s proposed to study each mite species, in which case inform-ation such as this must be obtained. Brushing Machine The brushing machine used to remove the mites and predators from the foliage was developed and f i r s t used by Henderson and McBurnie (19^3) and i s illustrated in figures 6, 7 and 8. (Appendix). Brushing technique:: The leaves were held by their petioles between the revolving brushes of this machine so that a l l mites and insects on the leaves were knocked from them on to a revolving glass plate. This circular plate was coated with some sticky substance prior to brushing. Most workers coat the plates with clear varnish diluted 5Q% with benzene, but this was found to be unsatisfactory sinee i t was very d i f f i c u l t to remove the varnish when cleaning the plates after counting. This season i t was discovered that a mixture of amyl alcohol, ethyl alcohol, and benzene was f a i r l y satisfactory for removing the varnish but i t was expensive and was damaging to human respiratory tissues. Several other coating substances such as glycerin, heavy o i l , a linseed o i l and rosin mixture called "Tanglefoot", and honey, were tested; the honey was most satisfactory - 3h -since a l l others required the use of stove o i l for their removal. Honey i s hydroscopic, however, and in a short time becomes toor liquid for use. It was f i n a l l y decided to use an alkanolamine condensate manufactured by the Emulsol Corporation, Chicago, called Bncol 5100. This i s a soapless detergent which can be removed from the plates in one washing operation with water, and also acts as a cleaning agent for the plates themselves. When Emeol 5100 Is diluted to 12% with water, a s t i f f , tacky li q u i d results.. It was found to trap the mites and insects brushed from the leaves, very well., ' •• <, The 20 leaves from each tree were a l l brushed on to the same glass disc.. When the leaves of a l l collections had been brushed, the mites adhering to the plates were counted with the aid of a stereoscopic microscope. As the mite brushing machines are made by hand their accuracy was suspect. It was therefore necessary to test the machine's efficiency, this being done by brushing 5 samples of ten leaves each on which any particular species was known to be present. The efficiency of the machine was tested for each of the following mite speciesr, European red mite, Clover mite, Tetranychus flavus. and the predators Typhlodromus rhenanus and Mediolata SP. In each casethe number of mites on each leaf in each sample was counted with the aid of a wide f i e l d stereoscopic microscope.. The leaves were then brushed, and microscopically examined for individuals that had not been removed by the brushing operation. For this experiment - 35 -collections of Delicious variety apple leaves were used sincethese possess larger and deeper veins and mid-ribs than do the leaves of any other variety. It was reasoned that i f the machine performed satisfactorily with these leaves, i t would be satisfactory for the leaves of any other variety since the eggs and immature stages of the mites are to be found under and around these veins. The results of this experiment are shown as tables IV and V. These results show that the machine method i s superior to personal observation. With reasonable speed ah operator cannot detect mites on foliage with as great accuracy as on a glass plate after brushing. Theoretically, the operator should be 100% accurate i f given sufficient time to examine the leaf. In practice, however, there were several cases in which more mites in the active stages were counted by hand than by the machine method;: yet the latter removed a l l mites from the leaves. Mites crawling from an examined portion of the leaf to an unexamined portion may have caused these errors by being counted twice. Cooling the leaves before counting might have eliminated this source of error by causing the mites to become quiescent. It is very d i f f i c u l t to separate the different mites in different stages of development when counting them on foliage,, but this can be done by using the machine method since the mites are stationary when counted. The small numbers of mites used in the second tests (Table V.) make the results even more conclusive since one would expect that with small numbers the method of personal TABLE IV Efficiency of the Mite Brushing Machine in Removing European Red Mite and Glover Mite from Delicious Apple Leaves*  Treatment Sample Number ; 1 2 3 4 5 Eggs Other Eggs, Other Eggs Other Eggs Other Eggs Other Counted on Leaves 94 169 153 140 219 167 405 107 35O 144 Counted on Disc 139 I S 4 170 145 311 163 432 97 38O 130 Left on Leaves 6 - - - 2 - 3 - - -TABLE V Ef f i c i e n c y of Mite Brushing Machine i n Removing Mediolata sp., Typhlodromus rhenanus, and Clover Mite from Delicious Apple Leaves. Sample No. Treatment Mediolata sp. T. rhenanus Clover Remaining; Eggs Other E^gs Other Eggs Other 1 Counted on Leaves _ — 5 11 8 4 -Counted after Brushing - - 18 16 7 5 -2 . Counted on Leaves 2 2 2 2 7 5 Counted af t e r Brushing 5 1 5 7 9 5 mm 3 Counted on Leaves 1 _ 6 9 4 2 Counted afte r Brushing 2 - 9 7 4 - 2 Clover 4 Counted on Leaves 1 mm • 5 11 _ 4 eggs Counted af t e r Brushing 8 1 16 8 - 5 -5 Counted on Leaves _ mm 6 17 1 3 Counted a f t e r Brushing 6 - 8 22 4 5 mm - 37 -observation would have less chance of error. There i s l i t t l e doubt that the machine method i s equal or superior to the method of counting the mites directly on the foliage and there is absolutely no doubt concerning the egg stages* p The machine was not compared with simle microscopic observation i n the case of Tetranychus flavus. On one occasion 100 leaves moderately infested with this species were brushed and then examined under magnification. No specimens were found remaining on the leaves, despite the fact that this mite has a habit of covering the leaves with a fine silken webbing. Cursory observations have been made for rust mites, Immature thrips, immature anthocorids, and the eggs, larvae,, pupae, and adults of Stethorus picjpes r a coleopteran predator oforchard mites* In every case the machine did a satis-factory 30b. One species of rust mite, Phvllocoptes  schlechtendali. i s extremely small and i s very d i f f i c u l t to count on the leaves* They are, however, easily counted on the glass plates after brushing. For the information of workers in this f i e l d who have not had an opportunity to observe and use these brushing machines, a l i s t of the advantages and disadvantages of t h i s method i s given below*. Disadvantages:; Succulent young leaves at the beginning of the season have a tendency to tear In the brushes and - 38 -f a l l onto the plates. This d i f f i c u l t y can largely he overcome by practice. Broken leaves (injured by weather*, sprays, etc.) are not handled satisfactorily by this method and should be avoided whenever possible when making collections.. Advantages: 1. Increased accuracy. The brushing technique i s more accurate than the microscopic examination of leaves. The larger the number of mites and the smaller their size, the more accurate i s the machine method. 2. Increased speed. Two operators can brush 50 samples of 10 leaves each in less than 90 minutes. With the help of a recorder they can count the individuals on the plates in from 2 to h hours, depending upon the degree of infestation. Microscopic examination of the same number of leaves requires from 2 to 3 days. After counting the mites on the plates i t i s necessary to wash the adhesive substance from the plates. When Emcol 5100 has been used, two workers can clean 100 plates i n approximately 25 minutes. By means of this technique, 50#, 25% T or even less of the plate can be counted i f the infestation i s heavy. This increases the speed of the counting operation and reduces the amount of time involved. It cannot be done when examining the leaves under a microscope. 3. Saves time for research personnel.. Much of the procedure can be performed by untrained assistants, thus releasing research workers for other duties. k. More f l e x i b i l i t y . If necessary, the plates can be stored for several days before countings - 39 -At the requestof Mr. W. A. Ross, Chief, Fruit Insect Investigations Unit, Division of Entomology, Canada Depart-ment of Agriculture, the machine was also tested for peach leaves. No d i f f i c u l t y was encountered In handling these leaves, although they are much longer and larger than apple leaves. The results were similar to those obtained with apple leaves. Mite Counting The mites adhering to the glass plates after brushing were eounted by means of a stereoscopic microscope.: To f a c i l i t a t e this operation, paper counting discs (figre 9) were glued to the bottoms of the glass discs with rubber, cement. When the count had been completed, the paper discs were removed and used again. With these discs, a st a t i s t -i c a l l y accurate count could be made of the mites and insects on 100$, 50% or 25% of the surface of the glass disc. This was very time-conserving when large numbers of mites were present. The usual percentage count was 50%, but when the mites on one plate were In excess of 2,000, a 25% count was used*. MEYER'S FLAT ORCHARD In the following sections of this paper the data obtained during the summer of 1951 w i l l be examined in three ways:, (1) for information concerning the bionomics of each host and predacious species, and the manner in which each i s affected by the application of PbAs, DDT and Parathion; (2) for the relationships between the host and predacious species and the manner in which these are affected by the three chemicals; (3)) the three sets of data from each orchard w i l l be integrated to determine which reactions and relationships are consistent and which have been caused by the particular conditions obtaining in each orchard. As described above, each of the f i r s t five check trees in each orchard were divided into four quadrants, north, south, east and west. Each time a collection was made 20 leaves were taken from each branch most nearly bisecting each quadrant of a tree, and 20 leaves were taken from the entire tree at random to determine whether a collection made i n this way would provide information representative of the entire tree. The data obtained from the latter collections are not illustrated below since i t was found that they were not truly representative. - hi -The data obtained from the collections taken from each quadrant were averaged for each collection data, the averaged values being presented i n the figures below,. The averaged data from which these figures were drawn are shown in tabular form i n the appendix* For the effects of the three chemicals, the host: and predator populations observed on the branches most nearly bisecting the southern quadrants of each of the check trees were compared as an average with the average populations observed on the southern quadrants of each of the test plots*. The trees i n this orchard were sprayed three times during the season, on the afternoon of June 6, on the morning of July 5, and on the morning of August ih. Each species of host and predator i s considered i individually below, and then all - species are considered as a group* Clover Mite (Brvobia pretiosa) Unsprayed population: Figure 10 shows that the Glover mite was found i n greatest numbers from May to October on the east sides of the check trees i n the Meyer's Flat orchard. A directional relationship; such as this has not been noted before i n the literature available. This relationship may have been due to the presence of more favorable micro-climatic conditions on the east sides of the trees, or i t may have been that the east sides aa*e less favorable to the predators vie. re. of the Clover mite than ase the other parts, thus favouring the host mites. Figure 1© also shows that at both the beginning and end of the active season the Clover mite population was higher on the east sides of the trees than on any-other side. This might indicate that the higher population on the east was not the result of some unusual influence which was peesent only this season,, but i s an annual and permanent condition.. Snraved populations t Figure 11. shows the effects: of the three insecticides. Parathion, which i s generally/ held to be the most effective acaricide available at presaot, was extremely favourable to the development of the Clover mite population under the arid conditions obtaining i n this orchard. DDT, which i s generally held to promote greater increases in orchard mite populations than any other commonly used insecticide, did not provide conditions as favourable as those provided by Parathion. Since no significant numbers of predators were found on either the DDT-sprayed trees or the Parathion-sprayed trees, i t would appear that Parathion stimulated the host mite population, under the precise climate and environmental conditions of the Meyer's Flat orchard. Such a stimulation has been suspected of DDT for some years but this i s thee f i r s t recorded indication that Parathion may have a similar effect. Lead arsenate apparently prevented to a slight extent,, z o I-o U J _l _J o o <\J or u a. O z I d o < or u > < MAY 3 0 JUNE 20 JULY 2 4 SEPT. 4 OCT 2 3 C L O V E R MITE PO PUL AT ION — ALL P L O T S J Figure 11 - k$ -the increaseoof the host population early i n the season* Later i n the season, however, a larger host population was observed on the trees sprayed with PbAs than on the unsprayed trees. It has been recorded that there i s an Increase i n mites on trees which have been dusted with chemicals and also on trees growing adjacent to unpaved, dusty, roads, (Koberti, 19^;: Wood 19^7; and DeBach 19^7)* This may be due to inert chemical residues, to some physical properties of the deposits on the leaves, or to a lack of predators on such trees. On the trees sprayed with PbAs i n this orchard, a very heavy chemical residue was evident after the second spray had been applied.. Figure 11 also shows that the peaks in the host mite population occurred a month earlier on the unsprayed check trees and on those sprayed with PbAs than on the trees sprayed with DDT and Parathion. The reasons for this are given below. Tvphlodromus rhenanus  Unsprayed population: Figure 12 shows that T.rhenanus. a predacious mite, was found in greatest numbers on the west sides of the cheek trees. This phenomenon was probably caused either by the presence of micro-climatic and other environmental factors which are most favourable to this predator on the west sides of the trees or by the predators having been attracted to a Clover mite population which i s potentially greater on this side of the trees than on any other. The presence of the greater proportion of predators -hS-Figure 12. - if 7 ~ would have held this population at a level lower than that on other parts of the tree despite i t s greater potential. Sprayed populations; Figure 13 i l l u s t r a t e s the drastic effects of DDT and Parathion on a population of T, rhenanus: the populations on the various plots of trees were approximately the same prior to the f i r s t application of sprays (June 6). Parathion immediately exterminated this predator and i t s effects prevented a small population of T. rhenanus from developing even after the f i n a l spray was applied i n August, DDT also had a very detrimental effect on the predator population, although not as great as that of Parathion. A month after the f i r s t spray was applied a l l the individuals of this species had been exter-minated, but, early in the autumn, after the f i n a l DDT spray had been applied, a small population of T. rhenanus was found. via, s Lead arsenate -is- also detrimental to the development of these predacious mites, although not tb the extent of DDT and Parathion. This tendency for sprays which leave heavy chemical deposits on the leaves, to inhibit the development of predacious mites has been previously reported by P.. DeBach (19H7), although specific reference to T, rhenanus has not been made, Mediolata sp. Unsprayed population? Figure Ik shows that this predacious mite exhibited no preference for any quadrant of a tree u n t i l the time of i t s greatest population density, Figure 13. Figure l*f. occurring in late August and early September, At this time the mites occurred mostly on the south sides of the unsprayed trees,, possibly due to the presence of favourable micro-climatic conditions on these sides or unfavourable conditions on the other parts of the trees.. At this time of year the southern aspect of the trees was undoubtedly/ warmer during the day than other parts, and the temperature here may have most closely approached the optimum for this species. This theory i s borne out by the fact that the north and coolest sides of the trees supported the smallest mite population at this time of the year. It i s true that the south sides of the trees are the warmest throughout the entire year but the absence of any indication that this species of mite preferred the south sides earlier i n the year may be explained by the supposition that during early summer and mid-summer the south sides of the trees were too hot for the development of this mite i n semi-arid areas such as the Southern Okanagan Valley.. Sprayed populations: Figure 15 shows the effects of the insecticides used i n this project on the populations of Mediolata sp.. in a l l plots. On the plots sprayed with DDT and Parathion this species was recorded only once, — on July 2h. On the trees sprayed with PbAs there was an abnormally uniform, but very small, population evident throughout the season u n t i l September h. Thus, the residue remaining after the trees had been sprayed with PbAs was almost as prohibitive to the development of these predators as were the effects of such extremely toxie substances as -51-Figure 15. - 52 -DDT and Parathion. On none of the sprayed trees were there any individuals of this species remaining at the end of the season.*, Thrips Unsprayed population: Figure 16 shows that during the period of their greatest density,, thrips preferred the east sides of the check trees, as Figure 10 shows the same to be < true for the Clover mite. It i s possible that the same environmental factors were influential in both cases. These insects were present i n relative abundance early in the season and had their population peak several months before that of the host mites. For this reason i t Is doubtful whether thrips are of much importance i n the biological control of orchard mites i n the Okanagan Valley, although they may be of some value i n preventing great increases in host population. There i s no explanation for the peak in thrips population occurring one month later on the west sides of the trees than on the other sides. Sprayed populations: Figure 17 shows that DDT and Parathion were almost immediately effective i n reducing and eliminating this insect. PbAs reduced the population, or prevented i t s increase,but not to the same extent. It had a greater effect i n i t i a l l y than i t did later in the season, as i s shown by the fact that the thrips population became less after the f i r s t application of this insecticide, during the period of peak population of the check trees, but later began to increase. This increase took place at the time Figure 1.6* Figure 17 - 55 -when the population on the check trees had passed Its peak and was beginning to decline. Host-predator relationships Unsprayed trees: Figures 18, 19, 20 and 21 show the average population of a l l species observed per 20-leaf collection from each of the four quadrants on the check trees numbered 1 - 5. It i s shown that the host mite population was under continual attack from some one of the three predacious species throughout the entire season. Early in the season the thripspopulation was the most important agent of biological control. In mid-summer Typhlodromus  rhenanus became of primary importance, and i n late summer and early f a l l Mediolata sp. assumed this status. This was important since i t meant that the host mite population was never free from predatory enemies and thus was never afforded opportunity to develop a population density sufficient to i n f l i c t severe damage on the trees.. These figures also show that the predator populations were more stable numerically than were the host mites. This indicates that the host mites were more influenced by environ-mental conditions than were the predators. It also Indicates that the predators observed in this orchard were not ideal since they did not exploit the host mites to the f u l l e s t extent. Thus, some factor other than host mite density must have limited the density of the predator populations., If the density of the predator populations was entirely dependent on host density, one would expect the density of -56-o I-u UJ -I _J o u u. < UJ _ J o <\J or u CL 6 z U J O < or u > < 56 4 8 4 0 32 24 16 CLOVER MITE MEDIOLATA SP .TYPHLODROMUS RHENANUS THRIPS 8 MAY 30 JUNE 20 JULY 24 SEPT 4 OCT 2 3 POPULATION ON NORTH SIDE OF CHECK TREES Figure 18 -57-CLOVER MITE MEDIOLATA SP A R . _ . _ TYPHLODROMUS RHENANUS THRIPS Z Q 4 0 • I-u u _J _J O MAY JUNE JULY SEPT OCT 3 0 20 24 4 2 3 POPULATION ON SOUTH SIDE OF CHECK TREES Figure 19• - 5 6 -Figure 20. - 5 9 -56 d o u < u _l o <\J cc U J b z I d O 4 8 4 0 32 24 16 8 CLOVER MITE MEDIOLATA SP TYPHLODROMUS RHENANUS THRIPS ^ MAY 3 0 JUNE 2 0 JULY 2 4 SEPT 4 OCT 2 3 POPULATION ON WEST SIDE OF CHECK TREES Figure 21. - 60 -the predators to vary directly with that of the host* From figures 18 - 21 i t can he seen that this was not the case* Figure 22 shows the average population, per 20 leaf collection, of a l l the species recorded on the south sides of all- ten check trees*, The peak i n the host population occurred on June 20, one month earlier than the host peaks for the DDT and Parathion sprayed trees, as shown by figure 11* Figures 13, 15 and 17 show that the three predacious species were rapidly exterminated on the trees sprayed with DDT and Parathion- It would seem, therefore, that the natural peak i n host mite population should have occurred i n July, but that the predacious species present on the check trees prevented the expression of this, the result being an a r t i f i c i a l population peak in June* Figure 22 shows that on July 2h there were more than twice as many predators observed as host mites, a fact which renders the above Interpretation entirely plausible. Figure 22 shows more plainly than any other the three successive waves of predators to which the host mites are subjected throughout the season.. Snraved trees? Figure 23 shows the average population of a l l species per 20 leaf collection on the south sides of the six trees sprayed with lead arsenate. The same situation existed on these trees as on the ten check trees;; the peak in host mite population occurred i n June, a month earlier than on the trees sprayed with DDT and Parathion. However, on these trees the predators were only par t i a l l y responsible -61-CLOVER MITE 4 2 MEDIOLATA SP / 3 6 TYPHLODROMUS RHENANUS , THRIPS ' Z g i -u u -I d o ( \ J or u 6 z I d O < or i d > < 3 0 24 8 MAY 30 JUNE 20 JULY 2 4 SEPT 4 OCT 23 POPULATION OF ALL SPECIES - CHECK PLOT Figure 22. -62-Figure 23. for the repression of the natural population peak.v The population reduction was toco drastic to have been caused by the predacious species alone which were themselves less dense than on the check trees, and part of the effect must be credited to the PbAs, This interpretation i s at variance with the accepted views concerning the action of this insecticide on a population of orchard mites. Among others, P. DeBach (19^7) has reported that PbAs i s capable of causing an increase i n a host mite population, while M.D* Austin (19*+6) claims that PbAs has no effect on such a population. Figure 23 r shows that, i n i t i a l l y , the insecticide stimulated the host population, since the population peak in June i s greater than that observed on the check trees. However, the thrips population, which was at i t s greatest density on the check trees at this time was prevented from developing by the f i r s t PbAs spray. Possibly the release of the host population from these enemies resulted in the greater population density. The effect of lead arsenate became greater towards the latter half of the season as the spray deposit became heavier with successive applications. This was true of i t s effect on both the host and predacious species, particularly on Mediolata sp. whose normal population peak in September was entirely inhibited. Figure 2h shows the effect of DDT on both the host and predacious populations.. This chemical destroyed virtually/ alH agents of natural control i n this orchard, thus completely freeing the host mite population from their influences and ^ I t -Figure 2*t. causing the population peak to occur in July, instead of June. Figure 25 shows that Parathion also destroyed a l l natural control,, with the same results.. It should he noted, however, that the population on the trees sprayed with Parathion achieved a greater density than that on the trees sprayed with DDT. This indicates that under certain conditions Parathion i s capable of increasing the potential of the Clover mite. As mentioned above, this has often been suspected of DDT but never before of Parathion. It i s possible that DDT also had a stimulatory effect, but not of the same extent as that of Parathion i n the Meyer's Flat orchard. -65 (a)-Figure 25. 66 MCINTYRE CREEK ORCHARD The trees in this orchard were sprayed three times during the season; a l l plots were sprayed on the morning of June 12; the Parathion plot was sprayed on the morning of July 3 and the DDT and lead arsenate plots on the morning of July 9j a l l plots were sprayed on the morning of August 13. The data obtained from this orchard were treated in the same manner as that described above for the Meyer's Flat orchard. Clover mite (Bryobia pretiosa) Unsprayed population: Figure 26 shows that there were two peaks in Clover mite population i n this orchard* The population was greatest on the south sides of the check trees during the f i r s t peak, which occurred in June, and on the east sides of the trees during the second peak,, which occurred in August. On the north, west, and east sides of the trees, the i n i t i a l population peak occurred late in May and there Is no explanation for the fact that this did not occur u n t i l a month later on the south sides of the trees. t The change in preference from the south to the ease sides may have been caused by the south sides of the trees becoming too hot during late July and August for the develop-ment of this mite. During June the south sides, being warmer than the others, may have provided the mites with optimum, or more nearly optimum, conditions for development. Figure 26 shows that the populations on a l l sides of the trees were of equal densities at the beginning of the -66 (a) Figure 26. - 67 ~ season. At the end of the season this was not the case* It w i l l be noted in May of 1952 i f di f f e r e n t i a l winter mortality has reduced the populations to a point where they are again of equal densities, or whether the west sides, which ended the 1951 season with the greatest density commence the season in a similar relative position. Snraved populationst Figure 27 shows the effects of the three insecticides used on the Clover mite. Parathion prevented the development of this mite completely in this orchard. The f i r s t application was applied on June 12 and was immediately effective i n reducing the population. The second application, made on July 3» eliminated the mite completely, no mites being recorded on the trees in this plot for the remainder of the season, even two months after the f i n a l application. Lead arsenate inhibited the development of this mite u n t i l after i t s f i n a l application. At this time, there was a stimulation of the mite population with the result that greater numbers were found on the treated trees than on the untreated check trees. This population peak coincided with a similar peak recorded on the DDT-treated trees and with the second, and smaller, peak observed on the check trees. The Clover mite population on the trees sprayed with DDT became approxiiately fifteen times more dense than that on the unsprayed check trees. This great increase may have been due to either a lack of predators or a stimulation of the mite population caused by this chemical, or to both. -68-Figure 27. On only one plot, the check plot, were two peaks in population density recorded. Since this phenomenon was not observed on the trees sprayed with DDT possibly i t was caused by the various predacious species, and thus was a r t i f i c i a l . Tvphlodromus rhenanus XJnspraved population? Figure 28 shows that on the north, east and west sides of the check trees there were two peaks i n the T. rhenanus population. Since there were also two peaks in the host mite population (figure 26) possibly climatic conditions were instrumental in direct** ing the development of both host and predator. However, i t may have been that climate influenced only the host population, and the predacious population, being dependent on the host, varied accordingly. Conversely, climate may have directed the predator population, which i n turn directed the host population. The south sides of the unsprayed trees supported the smallest predator population. These sides supported the greatest host mite population during the f i r s t part of the season* Possibly some factor unfavourable to the.predator population was active on these parts of the trees, resulting in an increase in host population. There was more disparity between population densities on the various parts of the trees at the beginning of the active season than at the end. Possibly some climatic or other environmental factor acted during the winter with TYPHLODROMUS RHENANUS POP. - CHECK PLOT Figure 28. - 7 H -greater Influence on certain aspects of the trees than others. Sprayed populations? Figure 29 shows the extremely lethal effects of DDT, Parathion, and lead arsenate sprays on Typhlodromus rhenanus, Gf the three, DDT was the most toxic under the conditions prevailing in this orchard. The predacious mites were completely exterminated by the i n i t i a l application of this chemical; with the other two insecticides, a second spray was necessary for complete eradication to be accomplished. Figure 29 shows that individuals of this predacious species had not reappeared two months after the f i n a l applications of the sprays. This may have been due to a lack of migrating tendencies in this species or to the con-tinued effects of the three insecticides,. Mediolata sp> Unsprayed populations; Figure 30 shows that there were two peaks in the population of this predator on all-sides of the check trees but north,. The dates on which these peaks occurred correspond with the dates on which the peaks in Typhlodromus rhenanus population occurred, but each i s one month earlier than the two peaks i n host mite population. Possibly the same environmental factor, directed the develop-ment of both predacious species, and may even have had an effect on the host population.. Figure 30 also shows i n general, the west sides of the unsprayed trees supported the largest population of Mediolata sp. while the north and east sides supported Figure 30 - 7k -the smallest populations* Sprayed populations: Figure 31 shows the effects of the three insecticides. A l l three had a very similar effect in that they caused a reduction i n these predators iiut did not eradicate them entirely; individuals were present on both the DDT-sprayed and Parathion-sprayed trees throughout the entire season, although in small numbers. On the PbAs-sprayed trees i t was not u n t i l the f i n a l spray had been applied that this predator was eliminated completely. However, PbAs, considered to be the most innocuous of the three chemicals, was the only spray to accomplish complete elimination. Possibly, the effects of the apparently indestructible deposit of lead arsenate on the leaves was more inhibitive to predators migrating i n from unsprayed trees than were the more rapidly dissipated, purely chemical, effects of DDT and Parathion.. Thrips Unsprayed population? Figure 32 shows that the peak i n thrips population occurred late in May on the south and east sides of the unsprayed check trees, and late i n June on the north and west sides of these trees. It also shows that no thrips were recorded on the north and east sides after the end of August, but that they persisted on the south and west sides for several weeks after this time. This figure shows that the south sides of the check trees supported the densest thrips population after the end Figure 32. - 77 of May. Prior to this, the most dense population was to he found on the north sides of the trees. Sprayed populations. Figure 33 shows that both DDT and Parathion were very detrimental to these insects. One application of DDT and two of Parathion were sufficient to eliminate completely the thrips population. Lead arsenate was i n i t i a l l y detrimental to the thrips, but i n July they were able to increase to a density only sl i g h t l y less than that recorded on the unsprayed check trees. However, no thrips were observed on the PbAs-sjorayed trees after the end of August, whereas they persisted for several more weeks on the check trees. Host-predator relationships \ Unsprayed trees? Figures 3S 35> 3^ and 37 show the average population of a l l species observed per 20 leaf collection from check trees numbers 1 - 5> from each of the four quadrants. In this orchard, as i n the Meyer's Flat orchard, the host mites were under continual attack from some one of the three predators throughout the entire season. Typhodromus rhenanus was the most abundant predator early, and in the middle, of the season; Mediolata sp. did not become abundant u n t i l the end of July, at which time on several sides of the trees i t was more abundant than the host mites. The thrips population on the south and east sides of the check trees was most dense on June 25, while on the north and west sides of the trees the greatest density occurred on July 19. Figure 33. - 7 9 -Figure 3h. -80-CLOVER MITE MAY MAY JUNE JULY AUG. OCTl 7 22 25 19 22 10 POPULATION ON SOUTH SIDE OF CHECK TREES Figurev35« -81-CLOVER MITE U UJ O O rsj ox 6 z U l 42 36 30 l 24 18 12 6 MEDIOLATA SP. TYPHLODROMUS RHENANUS THRIPS \ MAY 7 MAY 22 JUNE 25 JULY 10 AUG. 22 odTj 10 POPULATION ON EAST SIDE OF CHECK TREES Figure 36 - 8 2 -CLOVER MITE 42 O o OJ or UJ a b z < or UJ 5 36 30 24 16 12 6 MEDIOLATA SR TYPHLOOROMUS RHENANUS THRIPS MAY 7 MAY 22 JUNE 25 JULY 19 AUG. OC71 22 10 POPULATION ON WEST SIDE OF CHECK TREES Figure 37. - 83 ~ The above figures also show that there was a correlation between the total numbers of predators present on the leaves and the numbers of host mites. In general, the more host mites present, the more predators. There are two^  possible explanations for this, the f i r s t being that the same factors which rendered a certain side of a tree most favourable to the host mites, also rendered that side most favourable to the predators.. The second, and more probable explanation i s that certain environmental factors rendered a certain side of the tree most favourable to the host mites, and the abundance of these rendered that side most favourable to the predacious species, which depend upon the host species for food. Figure 38 shows the average population per 2G leaves of a l l the species recorded on the south sides of the ten check trees. The f i r s t peak i n host mite density occurred on June 25, and the second on August 22.= There was but a single peak in the abundance of Typhlodromus rhenanus. which occurred on May 22, there being , however, a relatively dense population of this predator present u n t i l the end of July. There were two peaks i n the abundance of Mediolata sp., the f i r s t occurring at the same time as the peak in T. rhenanus population, and the second on July 19. The thrips population was most dense during June and July, and was uniform in density with no distinctive peaks in population being apparent. This figure shows very well that the host mite population was at a l l times subjected to attack from some one of the three predacious species present in this orchard. Until the end of August more predators -git-Figure 38, - 85 -were observed per 20 leaves than were host mites; such numbers of predators must have contributed greatly to the control of the hostpopulation. Sprayed trees? Figure 39 shows the average population of a l l species observed per 20 leaf collection taken from the south sides of the six trees sprayed with lead arsenate. It shows that this chemical prohibited the development of a l l predators, thus entirely freeing the host population from biological control, and enabling i t to achieve a density approximately nine times that of the host population on the unsprayed check trees. However, the increase i n host population probably was not due entirely to the absence of natural control agents; many workers feel that the chemical residue l e f t on leaves sprayed with PbAs i s capable of stimulating a mite population. (P. DeBach.l9ty7)y although this contention has never been satisfactorily proven* Undoubtedly, the absence of predators on these trees was • i par t i a l l y responsible for the increase i n host population. Figure 39 also shows that the thrips and T. rhenanus populations were greatly affected by the application of PbAs, being entirely eradicated by the f i r s t application. Mediolata sp., however, was not eliminated u n t i l after the second application. In the absence of predacious enemies, there was but a single peak In host density on the trees sprayed with PbAs. This suggests that, on the unsprayed check trees, the three predacious species were the factors responsible for causing the occurrence of two peaks i n host mite density.. - 8 6 -Figure 39. - 87 -Figure shows the effect of DDT both on the host and predacious populations. This chemical destroyed a l l agents of natural control, T> rhenanus being the only predator present in sufficient quantity for graphing. The f i r s t application of DDT completely eliminated this small population.. In the absence of any natural control agents, on the DDT-sprayed trees the host population increased to a density approximately kO times as great as that of the population on the unsprayed check trees. However, this increase was not caused entirely by the absence of predacious enemies, since on the trees sprayed with PbAs, which also eliminated the predacious species, the host population became only approximately nine times as dense as the population on the unsprayed check trees. Assuming that PbAs had no stimulatory/ effect on the host population, which i s probably untrue, then slightly more than 75% of the increase observed on the DDT-sprayed trees can be attributed to some effect of this chemical on the host population, and not to the absence of predacious enemies. The population on the DDT-sprayed trees and that on the PbAs-sprayed trees were approximately of the same density early i n the season before any sprays had been applied. Figures 39 and ^ tO also show that the effects of these two chemicals were relatively lasting, since no predators had reappeared nearly two months after the f i n a l applications« Figure IfO. - 8 9 -CLOVER MITE Q o UJ _j _j o o < UJ o CM cr UJ D. 6 z or u i > < MEDIOLATA SP TYPHLOOROMUS RHENANUS -THRIPS POPULATION OF ALL SPECIES - f*RATHION PLOT Figure hi. Figure **1 shows the effect of Parathion on hoth the host and predacious populations. This chemical eliminated the thrips, T. rhenanus. and host mite populations after the second application. Neither of the predacious species reappeared on these trees for the remainder of the season, although a small population of host mites appeared late in the f a l l after the f i n a l application of Parathion had been a p p l i e d M e d i o l a t a sp.,, on the other hand, was able to survive u n t i l the third and f i n a l application of this insecticide, but did not reappear late in the season. This indicates that the reason for the continued presence of this predator u n t i l after the f i n a l spray application, was due to a resistance to the chemical's toxic effects rather than to superior powers of dispersal.. If the latter had been the case individuals of this species would have reappeared after the last spray application.. It should be noted that under the conditions prevailing i n this orchard Parathion was completely effective in controll-ing the host population, whereas, under the conditions prevail-ing in the Meyer's Flat orchard this insecticide stimulated rather than depressed the host population (fig.25)»> - 91 -GARTRELL;s ORCHARD The trees in this orchard were sprayed three times during the season; the DDT and PbAs plots were sprayed on the morning of June 13, and the Parathion plot the follow-ing day; a l l plots were sprayed the morning of July 9 5 a l l plots were sprayed the morning of August 16. The data obtained from this orchard were treated i n the same manner: as that described for the above orchards except that collections from the west sides of the trees, instead of the south, were used when comparing the populations on the various plots. Each species of host and predator i s cons-idered individually below,, and then they are considered as a group. European red mite (Metatetranvchus ulmi) This host mite was rare both in the Mclntyre Creek orchard and the Meyer's Flat orchard. In this orchard, however, i t was the most plentiful and important mite species observed.. Unsprayed population?: Figure h2 shows that the greatest abundance of this species was recorded during late July. The population was most dense on the east sides of the trees, the population on the west sides being next in order of magnitude:: the south sides supported the least dense population. This directional preference may be explained by the fact that six of the ten check trees were irrigated chiefly on their north sides, the remaining four mostly on -92-NORTH z o o UJ _ i o o u. < o rvj or a 6 z U J < tr U J > < 980 840 700f 560} 42d-2cX> 140-SOUTH EAST WEST JUNE JUNE JULY 5 28 30 SEPT. OCT II 15 EUROPEAN RED MITE POP. - CHECK PLOT Figure h2» - 93 -I their south sides. The irrigating ptfpes were always placed in an east-west direction, and i t i s possible that the majority of the north and south sides received too much moisture on their leaves, with the result that many of the mites were washed off and injured. Thus, the populations on the east and west sides would have been greatest, as was the case. Figure h2 shows that, with the exception of the population on the east sides of the trees, a l l populations were approximately equal i n density at the beginning of the active season. The population on the east sides was cons-iderably greater. At the end of the season, however, the populations on a l l sides were approximately equal. It w i l l be noted in May, 1952, i f diffe r e n t i a l winter mortality has again given the population on the east sides an advantage. The mites in this orchard achieved a density of approx-imately **0 per leaf. It has been recommended that control measures be employed i f the host population i s i n excess of 2-8 mites per leaf (Hammer, 19^3)• In neither of the other two orchards studied was the host density of economic importance on the unsprayed trees* Sprayed populationst Figure **3 shows the effects of the three insecticides used i n this study on populations of the European red mite. The effect of Parathion i n this orchard was somewhat intermediate between that in the Meyer's Flat orchard, where the host increased beyond the population on the check trees, and that in the McIntyre Creek orchard, where the host was completely eliminated. In this orchard the host population on the Parathion-sprayed tree was almost Figure *+3 equal in density with that on the unsprayed check trees. On the trees sprayed with lead arsenate the host population was not as dense as that on the check trees, but the peak in density was delayed approximately one month. Thus, the presence of lead arsenate on the leaves delayed the decline i n host population which normally occurs in late summer.. On the trees sprayed with lead arsenate the leaves became sickly and yellow, and f e l l from the trees earlier in the autumn than did the leaves on the other trees In the orchard. This effect was not observed in the other study orchards. Both i n the Meyer's Flat orchard and the Mclntyre Creek orchard, DDT stimulated the host population. In this orchard, however, the host was prevented from developing u n t i l after the f i n a l application of DDT had been applied, at which time the population increased to approximately one half the maximum density recorded on the unsprayed check trees. The peak in population density occurred approximately one month later than on the check trees, as was also the case on the PbAs-sprayed trees* Tetranychus species In the other study orchards mites of this genus were not commonly observed, although they were recorded in very small numbers. In this orchard, however, they were observed in moderate numbers on the unsprayed check trees, and on the sprayed trees achieved the greatest density recorded during thl$ study. The species of this gerr&s which were present - 96 -were probably the Willamette mite, Tetranychus willamettei T the Two-spotted spider mite, Tetranychus telarius, and the Pacific mite, Tetranychus pacificus. As i t i s impossible to distinguish between these species u n t i l each specimen has been mounted on a slide and observed under high magnification, they are considered here merely as a group. Unsprayed populations? Figure ¥f shows that the population of this species achieved i t s greatest density on the north sides of the check trees, the south sides supporting the next greatest population.. There was l i t t l e difference between the densities of the populations on the east and west sides. Since the water from the sprinkler irrigation system struck either the north or south sides of the trees (see above), the sides supporting the largest populations of these mites, there was a correlation between the amount of water present on the surface of the leaves and the density of the population of Tetranychus sp. The populations on a l l sides of the check trees were of approximately equal densities at the beginning of the active season. The populations on the north, south,, and east sides were approximately equal at the end of the season, while that on the west sides was significantly greater. Sprayed populationss Figure k5 shows the effects of the three insecticides used on these host mites* On the lead arsenate-sprayed trees they were more than twice as dense as on the check trees. Unlike the population on the check trees, whose greatest density occurred late in July, the population on the PbAs-sprayed trees was s t i l l increasing -97-49 z o U U J _ J _J O O 42 35 28 o CVJ QC U J a UJ O < a: UJ > < 21 14 NORTH SOUTH EAST WEST JUNE JUNE JULY SEPT. OCT. 5 28 30 II 15 TETRANYCHUS SP. POPULATION - CHECK PLOT Figure hh* -98-2700* 240Q z o o UJ - i 2100 - J O O ui 1000 O (VJ tr U J a 1600 < or UJ > < 200 100 _ C H E C K _ P B A S . DDT _ PARATHION f I / l / \ 7 / / / » r l JUNE JUNE JULY SEPT OCT 5 28 30 II 15 TETRANYCHUS SP. POPULATION - ALL PLOTS Figure - 99 «-in density on October 15. After the i n i t i a l application of DDT the host population increased to a density more than twice that of the population on the check trees. After the second and third applications, however, these mites were completely eliminated u n t i l late in September- when they again Increased to a density more than 32 times as great as the greatest density recorded on the unsprayed check trees. Parathion had a great stimulatory effect on these host mites. After i t s i n i t i a l application there was areduction In the host population, but after the second and third applications the population increased u n t i l i t was more than 51*- times as dense as that recorded on the check trees during the period of greatest density.. At the time of greatest abundance on the Parathion-sprayed trees there were more than 130 mites per leaf — a condition which may have been extremely damaging to the health of the trees. Figure 4-5 also shows that the peak i n abundance on the Parathion-sprayed trees occurred early in September, more than a month later than the peak on the check trees. The f i r s t peak in abundance on the DDT-sprayed trees occurred simultaneously with that on the check trees, but at the end of the season these mites were s t i l l Increasing in number, as was also the case on the PbAs-sprayed trees. Stethoms picipes This small, black, coeclnellid beetle i s known to destroy great numbers of mites wherever i t occurs (Newcomer - 100 -.1-and Yothers 1929; Radzievskaya, 1931)• Unsprayed populations: These insects were not present in sufficient numbers to determine i f they exhibit a preference for any one side of the unsprayed trees. Figure k6 shows that on the south sides of the cheek trees there was but an average of 2.5 beetles per twenty leaves during the period of their greatest abundance.. Sprayed populations s Figure **6 shows the effects of the three insecticides on this insect. S. piclpes i s predacious and i s therefore s t r i c t l y dependent on the host population for food (unlike T_. rhenanus. and possibly Medio- lata sp.| which are able to feed on the host plants in the absence of animal food) thus understanding their d i s t r i b -ution in this orchard i s very d i f f i c u l t . A l l peaks i n abundance occurred after the applications of insecticides were completed., However, as the same i s true of the population on the check trees, this must be regarded as a natural phenomenon. Under favourable conditions, however,, there was a small population present in the f i e l d throughout the entire season. When DDT and Parathion were applied at frequent intervals, so that there was no opportunity for their lethal effects to become dissipated, these insects were unable to survive. They were, however, able to exist in the presence of PbAs, although their numbers were fewer than on the unsprayed cheek trees •> After the f i n a l applications of the chemicals these insects spread and increased on both the DDT- and Parathion— sprayed trees, although the toxic effects of DDT were more -101-z o o U J o o < or U J > < CHECK PBAS 7 f U J 4 O C M or U J a DDT PARATHION /» / * / \ / ^ \ / \ JUNE JUNE JULY SEPT. OCT 5 28 30 II 15 STETHORUS PICIPES POPULATION - ALL PLOTS Figure k6 - 102 -i lasting since the insects appeared later and did not achieve as great a density on the trees sprayed with this substance. The greatest density of beetles was observed on the Parathlon-sprayed trees — the trees supporting the greatest host populations at that time. Trees sprayed with PbAs also supported a larger population of both host mites and beetles than did the unsprayed check trees. It would seem, then, that these predators were attracted to the most dense host populations and thus tended to congregate where they were of greatest use to the orchard grower, Typhlodromus rhenanus Unsprayed populations Figure ^7 shows that this predator did not appear in this orchard u n t i l late i n June, one month later than in the other orchards studied. Possibly this was because this orchard has been sprayed for a number of years with DDT and other insecticides which would eliminate this predator. In a season in which no insecticides were applied, such as the one under discussion, i t would take some time for a population to migrate into the orchard. The period of greatest abundance occurred late in the season on a l l sides of the trees. Whether this was a natural phenomenon under the environmental conditions of this orchard, or whether this was due to a delay caused by the necessity of reestablishing a population by migration i s not definitely known.. The population was most dense on the north sides of the trees, with a slightly less dense population recorded on the east sides. The west sides supported a significantly -103-Flgure k-7 smaller population than d i d any of the others. On October 15, T. rhenanus was s t i l l moderately abundant. Sprayed populations* Figure kS shows that t h i s predacious mite became abundant only on the unsprayed check trees. The presence of each of the three i n s e c t i c i d e s used prevented the estblishment of a population, although a f t e r the f i n a l a pplication of EDT, a very few i n d i v i d u a l s were observed on trees which had been treated with t h i s chemical. None of these predators were observed at any time on trees sprayed with either PbAs or Parathion.. Host-predator relationships:: Figures **9, 50, 51 and 52 show the average populations of a l l species, recorded per 20-leaf c o l l e c t i o n from the check trees numbered 1 -5,; from each of the four quadrants. In t h i s orchard, i n contrast to the other orchards studied, b i o l o g i c a l control of the host mites was i n e f f e c t i v e . On no side of the trees was there a s i g n i f i c a n t number of predators recorded p r i o r t o the end of June, and none were present i n e f f e c t i v e numbers u n t i l the end of July, at which time the host mites were most abundant. Several workers have reported that Stethorus picipes normally does not appear i n quantity i n the f i e l d u n t i l l a t e summer and early autumn.. (Newcomer and Yothers, 1929). Typhlodromus rhenanus normally appears i n early spring,, but, as discussed above, the f a c t that t h i s orchard has been subjected to applications of many to x i c substances f o r a number of years accounts f o r only small AVERAGE NO. PER 20 LEAF COLLECTION H -< T> I f- 73 m O C CO c_ roc 7} ODZ m m z > z c CO or < TJ O !U I CO > — m — "0 r-H "0 r~ O H _ x 10 cn O cn Co o CO cn i O o o H o I m O -106-EUROPEAN RED MITE 800 TYPHLODROMUS RHENANUS T E T R A N Y C H U S SP. z 700 o h-u 1.1 COLL! 600 A u_ < UJ 500 A _J O fM or 150 Ul a / \ b z / \ :RAGE 100 • / A > < * 50 / - \ V J U N E JUNE JULY S E P T O C T 5 28 30 II 15 POPULATION ON NORTH SIDES OF C H E C K TREES Figure **9. -107-EUROPEAN RED MITE 8 0 0 r _ TYPHLODROMUS RHENANUS O LkJ o u < U J o OJ cc U J a. < cc U J 5 TETRANYCHUS SP. 700 600h POPULATION ON SOUTH SIDES OF CHECK TREES Figure 50. -108-»-O o u o tr U J a 6 z < or U J > < 800 700 600 500 150 100 50 EUROPEAN RED MITE __-TYPHLODROMUS RHENANUS TETRANYCHUS SP POPULATION ON EAST SIDES OF CHECK TREES Figure 51• -109-Figure 52. - 110 numbers being observed u n t i l late in the season., These figures show that, i n every instance, the great-est density of both species of host mites occurred at the same time.. The Tetranychus spp*, however, did not become as abundant as the European red mite* On every side of the trees the total host population was in excess of 30 mites per leaf, and in one instance there were more than 50 per leaf. This was very damaging to the trees and by the end of the season most leaves showed the characteristic "peppery" appearance caused by the feeding of these mites* The greatest abundance of the predators occurred at a time when the host mite populations were declining. It Is, however, impossible to say whether the host mite decline was a natural phenomenon occurring at the end of the active season, or whether i t was caused by the predators. Probably the most important factor in this decline was the approach of autumn. Figure 53 shows the average population of a l l the species recorded on the west sides of the ten check trees. There were nearly 60 host mites per leaf during the period of their greatest abundance. It i s very evident from this figure that the predators appeared too late i n the season to prevent the host population's greatest develop--ment and to protect the host trees from damage. Sprayed trees: Figure 51* shows the average population of a l l species recorded per 20-leaf collection taken from the west sides of the six trees sprayed with lead arsenate*. -111. EUROPEAN TYPHLODROMUS RED MITE RHENANUS JUNE JUNE JULY SEPT. OCT. 5 28 30 II 15 POPULATION OF ALL SPECIES - CHECK PLOT Figure 53• -112-Figure - 113 -Typhlodromus rhenanus was effectively prevented from establishing a population on these trees. The European red mite population was somewhat less dense than on the check trees, hut the population of Tetranychus spp. was more than three times as large. This supports the belief of many workers that PbAs deposits on leaves stimulate certain species of mites, and thus increase their density. Figure 55 shows the effects of DDT on the host and predator populations. Typhlodromus rhenanus appeared In very small numbers only, not u n t i l more than one month* after the f i n a l application of this insecticide. Stethorus  picipes also did not appear on these trees u n t i l some time after the cessation of spraying a c t i v i t i e s . The effect of DDT on the Tetranychus spp.. was not readily understood.. Apparently this insecticide was i n i t i a l l y detrimental to the development of these mites, but later, after the f i n a l application was applied, the population was stimulated.- In October, an average of more than 80 mites was recorded per leaf. At i t s greatest density the European red mite was present in approximately the same density as on the unsprayed check trees. Thus, DDT did not stimulate the population of this mite in this orchard. Figure % shows the effect of Parathion on the host and predator populations. Typhlodromus rhenanus was prevented from developing on these trees entirely: Stethorus picipes. became relatively abundant after the f i n a l application of this insecticide.had been applied. The European red mite population was approximately -ll*f-1600 1500 z o u U J O U u. < U J o CVI tr U J a O z U J O < or U J > < 1400 1300 1200 1100 EUROPEAN RED MITE TETRANYCHUS SP. i TYPHLODROMUS RHENANUS/; STETHORUS PICIPES / 52 6 9 _ 5 6 / JUNE 5 POPULATION OF ALL SPECIES - DDT PLOT -115-EUROPE AN RED MITE z o h-u U J O u < U J o C M or U J o. 6 z U J O < or U J > < 280Q Z700i 500 400 300 200 100 TETRANYCHUS SP STETHORUS PICIPES JUNE 5 JUNE 28 POPULATION Of ALL SPECIES - PARATHION PLOT Figure 56.. - 12i6 -one half as dense as that on the check trees, 'although the infestation was of economic importance* At the period of i t s greatest abundance there were more than 20 European red mites recorded per leaf, four times the maximum population which can safely be tolerated. The Tetranychus sj>p> was greatly stimulated by Parathion, there being more than 130 mites per leaf recorded at the period of their greatest density. The periods of greatest density of the European red mite and Tetranychus spp* populations on the DDT-sprayed and Parathion-sprayed trees occurred more than one month after the population peaks on the PbAs-sprayed trees and the check trees,. Thus, the presence of DDT or Parathion either delayed the development of these populations, or rendered them less sensitive to the stimulations i n i t i a t i n g the formation of winter eggs, in the case of the European red mite, and of the overwintering female forms in the case of the Tetranychus spp* - 117 -f Discussion of observations made In study orchards Host Mites In the two abandoned orchards studied the only-species of host mite recorded i n significant numbers was the Clover mite, Bryobia pretiosa., In the commercial orchard, Gartrell's, both the European red mite, Meta- tetranychus ulmi. and members of the genus Tetranychus were important. The preference shown by the European red mite for cultivated trees has been noted by Kuenen (19^-1). The species of host mite found i n the Gartrell orchard were observed only in very small, numbers in the abandoned orchards, and towards the latter part of the season. The Clover mite, the most abundant host mite species i n the abandoned orchards, was present i n small numbers i n the commercial orchard throughout the season. Unsprayed populations:: The most consistent feature of the host mite populations observed on the unsprayed check trees was their preference for the east sides of the trees. When the two abandoned orchards alone are considered i t might be thought that some other aspect of the trees was in reality more favourable for the develop--ment of these mites, but that the presence of a greater number of predators on these sides reduced the potentially greater populations and made the east sides appear more favourable. When, however, the population i n the commercial orchard i s also considered this i s proved false. - 118 There were no significant numbers of predators present in this orchard u n t i l after the period of greatest host abundance, and yet the greatest host density was recorded on the east sides of the trees. The discovery of this directional preference i s possibly of no great commercial significance, although the growers should take particular pains to achieve adequate coverage of the east sides of their trees when spraying to control orchard mites. Possibly a concentration that would control them on the north, south, and west sides of the trees would leave on the east sides a small number of unharmed mites which would act as a source for reihfestation of the entire tree. It i s shown below that the predacious species also exhibited a directional preference which was frequently different from that exhibited by the host mites. Under these conditions i t may be possible to plan a spray program which would have least effect on those sides of the tree supporting the densest predator populations. Figure 57 shows the host mite densities recorded in each of the three study orchards. Each density was plotted as a percentage increase or decrease from the i n i t i a l density recorded at the beginning of the active season. It i s explained above that the populations i n the Mclntyre Creek orchard and the Meyer's Flat orchard were composed of Clover mites, whereas the population i n the Gartrell orchard was composed of the European red mite. These -119-Figure 57. two species are thought to be very closely related, and possibly they react in similar manners to insecticides and environmental.conditions. The host population of Tetranychus spm.. present in the Gartrell orchard was not included in this figure since these mites are known to d i f f e r greatly from the other two species, and were not present in any of the other orchards in significant numbers. Figure 57 shows that the environment in each of the three orchards differed in i t s favourability for the increase and development of the host populations. Figures 27, 11 and **3 show the differences i n the densities of the i n i t i a l populations.. The i n i t i a l population was greatest in the Gartrell. orchard, next in the Mclntyre Creek orchard (about one third that of the f a r t r e l l orchard) and least in the Meyer's Flat orchard (about one seventh that-of the Gartrell orchard).. Figure 57 shows, however, that the populations in certain orchards possessed a greater percentage increase than in others, thus indicating that the conditions in these orchards were more favourable to the development of the host mites. The population i n the Gartrell. orchard, the most dense throughout the season, increased the greatest per-centage. The population in the Meyer's Flat orchard, the least dense throughout the season, increased more than the population in the Mclntyre Creek orchard, which was second in order of density.. Thus, the orchard which was cultivated, f e r t i l i z e d , and irrigated most regularly - 121 - f. supported the most dense population and that which increased most during the season. This i s understandable since the trees i n this orchard were undoubtedly more healthy and vigorous than those in the other two orchards,, and thus were able to provide more food material for the development of the host population.. The Meyer's Flat orchard, however, contained the least healthy and vigorous trees, and yet i t s population was second i n order of per-centage Increase, although least dense. The trees in the Mclntyre Creek orchard appeared to be well irrigated by sub-surface water, and to be reasonably healthy, and yet they supported the population with the least percentage increase, although the second in density. In addition to an actual difference i n vigour between the trees i n the two abandoned orchards, there appeared to be a decided difference i n the environmental conditions prevailing i n each.. The Meyer's Flat orchard Is situated in a very hot, arid valley in the fo o t h i l l s of the Okanagan Valley. There i s l i t t l e irrigation of any kind occurring after the f i r s t week In June, and the season i n this orchard i s shorter than that i n the Mclntyre Creek orchard since the valley in which i t i s situated i s somewhat higher in elevation than i s the Okanagan Valley, in which the Mclntyre Creek • orchard i s situated. In addition to the differences observed i n the population density and percentage increase i n the three orchards, there was a difference i n the time at which the greatest density occurred. In the Gartrell orchard th© - 122 -period of greatest host mite density occurred during the latter part of July and early part of August. In the Meyer's Flat orchard the period of greatest density occurred late in June, as did the f i r s t , and largest, population peak in the Mclntyre Creek orchard. A second peak i n population was observed in the Mclntyre Creek orchard late i n August. It i s suggested above that the population peaks in the two orchards i n which a significant number of predators were recorded, may have been a r t i f i c i a l * Possibly, the true peaks should have occurred ane month later, but due to the presence of large numbers of predators these peaks were suppressed. This theory Is discussed more f u l l y below.. As stated above, the Clover and European red mites overwinter as special overwintering eggs l a i d on the branches of the host tree. These eggs are l a i d after the middle of August, and when a female has l a i d i t s eggs i t dies-Because these eggs are l a i d on the branches they were not observed during the course of this study, only the mite stages on the leaves being considered* Thus, there were apparently fewer mites of a l l stages present on the leaves in the autumn than there were in early spring, giving the false impression that there was a reduction i n total population this season.. Sprayed populations:: Figure 58 shows the effects of lead arsenate on the three host populations. It shows that the effect varied under the environmental conditions pre-vailing in each orchard. In the Meyer's Flat orchard,. -123-Figure 58. - 12h -where the PbAs deposit on the leaves was greatest since there was no irrigation or rain to remove i t , there was an i n i t i a l stimulation followed by a repression of the population. Figure 11 shows that the host mite population was approximately one third larger on the PbAs-sprayed trees during this period of stimulation than on the un-sprayed check trees. The possibility of this havirig< been due to the repression of the predator population i s ,dls-cussed below,, Following the f i n a l application of PbAs the population in the Meyer's Flat orchard did not recover, probably be-cause the supposed effect of this insecticide on orchard mites i s physical rather than chemical, and thus requires more time to become dissipated. In the Mclntyre 6reek orchard the effect of PbAs was the reverse of that i n the Meyer's Flat orchard. There was an i n i t i a l reduction in the number of host mites followed by a moderate increase.. Figure 27 shows thatthe population was i n i t i a l l y redueed to approximately one tenth and then stimulated to approximately three times the population on the check trees. The latter effect i s generally conceded to be the true one for lead arsenate, and as the deposit on the leaves i s increased, the host population i s more fcreatly stimulated- This does not, however, explain why there was an i n i t i a l reduction in population. From figure 58, the effect of this insecticide in the Bartreljl orchard appears to have been purely stimulatory-- 125 -Figure *t3, shows, however, that this was not the case* The population was slightly less than on the check trees u n t i l the period of greatest abundance on the check trees was passed. The population on the PbAs-sprayed trees continued to increase at this time, never, however,, achieving as great a density as that recorded on the check trees during the population peak. Apparently, then, this chemical merely delayed the development of the hostr population, and only slightly repressed i t . In the Meyer's Flat orchard the period of peak abundance on the Pbas-sprayed trees was also delayed by this chemical., -^n the Mclntyre Creek orchard, however, the population peaks on the BbAs-sprayed trees and on the unsprayed check trees coincided* Figure 59 shows the effects of the application of DDT on the populations in the three orchards. In two of the orchards the effects were very similar. In one instance the host population was reduced by this insecticide.. In the Meyer's Flat orchard the DDT-sprayed population increased approximately 1900 percent over i t s i n i t i a l density. Figure 11 shows that this greatly exceeded the increase of the population on the check trees.. In the Mclntyre Creek orchard the DDT-sprayed popul-ation increased approximately 2100 percent over i t s i n i t i a l density, the greatest increase recorded for DDT-sprayed populations during this study* Figure 27 shows that the population on the check trees increased only about 100 percent during this time.-- 1 2 6 -Figure 59. - 127 -In the Gartrell- orchard the DDT-sprayed population increased approximately 2G00 percent over i t s i n i t i a l density, hut Figure **3 shows that the unsprayed check population increased 2700 percent during this time. Therefore, i t must be inferred that DDT had no stimulatory effect on the European red mite population i n the Gartrell orchard but rather repressed i t . The reason for this may have been that the European red mite reacts i n a manner different from the Clover mite when treated with DDT* The results observed in the Meyer's Flat and Mclntyre Creek orchards support the generally held theory that DDT. effects a stimulation of orchard mites, and for this reason i t s use should be avoided in commercial orchards* Figure 6GC shows the effects of the application of Parathion on the host populations i n the three study orchards. This insecticide did not act consistently, but apparently was affected by the climatic and other environ-mental conditions prevailing at the site of i t s use. In the Melntyre Creek orchard satisfactory control at a commercial level was obtained. After the second application of Parathion the host population was reduced 100$. After the f i n a l application Glfcuer mites again appeared on these trees but achieved a density of only about 10% of the i n i t i a l population. Figure 27 shows that the i n i t i a l host population prior to the application of this chemical was approximately two mites per leaf, a density of about one half the minimum density considered economically important* -128-2800 r 2600 z o < 2400 _j D % 80 0 CL = 600 2 O or 400 z o < > U J o 200 -100 M'INTYRE GARTRELL ' S MEYER'S \ /1 / i / • i / 1 ; \ i \ 1 / \ \ \ 1 / \ \ 1 \ / / \ v 1 1 1 / / \ 1 1 / \ \ 1 / \ \ 1 / V 1 / / \ I \ 1 / 1 / . \ 1 / 1 JUNE JULY AUG. SEPT. OCT. •HOST MITE - PARATHION PLOTS IN ALL ORCHARDS Figure 60. - 129 -In the Meyer's Flat orchard this Insecticide had an effect opposite to that observed i n the Mclntyre Creek orchard. Immediately following the application of Para-thion the host population was stimulated u n t i l there were more than 1800 times as many mites per leaf on the xx sprayed trees as on the check trees (fig.11)* Therefore, under the environmental conditions prevailing in the Meyer's Flat orchard, Parathion stimulated rather than reduced the host population. The applications made this season were the f i r s t ever applied i n this orchard.. Thus there had been no opportunity for a Parathion-resistant population to develop by chemical selection., i Figure 11 shows that the period of greatest density occurred on the trees sprayed with Parathion in the Meyer's Flat orchard approximately one month later than on the unsprayed check trees. As explained above, i t i s believed that the true population peak on the unsprayed check trees should also have occurred at this time, but that i t was prevented by a relatively dense predator population* In the Gartrell orchard the host mite population increased 2700 over i t s i n i t i a l density. Figure **3, however, shows that the host population on the check trees increased the same percentage over i t s i n i t i a l density. Therefore, under the conditions prevailing in this orchard,, Parathion had no effect on the host population.. Figure ^3 shows that the periods of greatest host - 130 -density on the Parathion-sprayed trees and on the check trees occurred simultaneously i n the Gartrell orchard, where no significant numbers of predators were recorded u n t i l late in the season., Predators Only one species of predator, Typhlodromus rhenanus. was recorded in a l l orchards studied. Predacious mites of the genus Mediolata and predacious thrips were recorded in both abandoned orchards but not in the commercial one, whereas the predacious beetle, Stethorus picipes, was recorded only in the commercial orchard. Unsprayed populations: Figures 12, 28 and k7 show that T. rhenanus was not consistent i n i t s preference for any one side of the trees. In the Meyer's. Flat orchard the west sides were preferred, whereas in the Mclntyre Creek they preferred the east sides early i n the season but later transferred their preference to the west sides. In the Gartrell orchard they preferred the north sides of the trees.. Also, these predators were not consistent in the sides least preferred since i n the Meyer's Flat Orchard the least dense population was recorded on the north sides, i n the Mclntyre Creek orchard on the south sides, and in the Gartrell orchard on the west sides* Mediolata sp.. were similarly inconsistent. In the Meyer's Flat orchard they preferred the south sides of the trees, and i n the Mclntyre Greek orchard the west sides. - 131 -In these orchards the north and east sides respectively were least preferred ( f i g s . l 1 * and 30). In the Meyer's Flat orchard the thrips population showed a preference for the east sides of the trees (fig . l 6 ) and i n the Mclntyre Greek orchard for the south sides (fig . 3 2 ) . Figure 61 shows the percentage increase or decrease over the i n i t i a l population densities recorded for T. rhenanus during the season i n each orchard. In the Meyer's Flat orchard the conditions were extremely favourable for the development of these predacious mites; they increased more than ^500 percent over their i n i t i a l density. The greatest density recorded here was not so great as that in either of the other orchards, but the population increase was the greatest.. In the Mclntyre Creek orchard T. rhenanus was recorded in greatest density.at the end of May (fig.29) and from that time steadily decreased in numbers. During late summer and early autumn they had decreased almost 100 percent of the density observed late in May. Under the conditions prevailing in this orchard this predator was probably not effective i n controlling the host population, since the host did not become abundant u n t i l well after the period of greatest predator abundance. Figure 6l shows that in the Gartrell orchard this predator increased inearly 3200 percent over i t s i n i t i a l density and this increase was recorded much later in the season than those in the other two orchards. An explanation for this i s given under the above section dealing with -132-Figure 6 l . - 133 -this orchard. Figure 62 (b) shows the percentage increase or decrease recorded for the populations of Mediolata sp. in the aban-doned orchards, the only orchards in which this species was present- In the Mclntyre Greek orchard the i n i t i a l popul-ation was the greatest, a gradual decline i n numbers being observed for the remainder of the season-In the Meyer's Flat orchard Mediolata sp. steadily increased i n numbers u n t i l in early September i t reached a density ^300 percent greater than the i n i t i a l density. This i s merely a percentage increase, and actually there were fewer of these mites observed i n this orchard than i n the Mclntyre Creek orchard. The figures expressed as percentages merely indicate that the conditions prevailing in the Meyer's Flat orchard were more favourable for the development of the Mediolata sp. than those in the Mclntyre Creek orchard* Sprayed Populations; Figure 63 shows the population trends of T.. rhenanus on trees sprayed with lead arsenate. Apparently PbAs favoured an increase of population i n the Meyer's Flat orchard and caused a decrease In the Mclntyre Creek orchard. Figure 29 shows, however, that thev tendency of the T. rhenanus population was to decline at this time of year in the Mclntyre Greek orchard, although the application of PbAs seemingly hastened this process. Figure 13 shows that the tendency i n the Meyer's Flat orchard was to increase at this time of year, but that PbAs repressed this tendency to a considerable extent. In the -135-Figure 63 - 136 -Gartrell orchard this species was prevented from becoming established by the application of PbAs (fig.M-5.). Thus, PbAs consistently was effective in reducing the population of T« rhenanus. and therefore i s detrimental to one of the most abundant predators of orchard mites. Figures 6^ - (a) and (b) show the effect of DDT and Parathion on T. rhenanus i n the abondoned orchards. Figure shows that i n the commercial orchard this species was prevented entirely from becoming established on trees sprayed with these materials. The effects of these chemicals were very similar i n each of the abandoned orchards. Both were effective i n drastically reducing the predator population. However, after the f i n a l application of DDT i n the Meyer's Flat orchard these mites were again recorded on the foliage. This was not the case in the Mclntyre Creek orchard* Figure 62 (a) shows the effects of PbAs on Mediolata sp. i n both abandoned orchards. Figures 15 and 31 show that this chemical tended to reduce the population in each orchard.. They also show that DDT and Parathion had a similar effect on this predacious mite. Apparently this mite was susceptible to the toxic effects of each of the chemicals used, and their application tended to reduce i t s effectiveness i n controlling orchard mites. Figures 17 and 33 show the effects of the three insecticides on the thrips in each abandoned orchard* In each the application of any one of the chemicals was very -137-Figure 6h (a) & (b). - 138 -damaging too the thrips population, and thus to the natural control; of orchard mites. Figure k6 shows that the predacious beetle Stethorus  picipes was less affected by the insecticides than any other predator observed during this study. It was recorded in small numbers during the period of spray applications and after the f i n a l sprays i t became relatively abundant. This species of predator, the one which exhibited th<e greatest tolerance to DD^ ,, Parathion, and PbAs, the most commonly used orchard insecticides, was the only species found to occur in commercial orchards throughout the i season. Possibly i t has developed some degree of tolerance to insecticides by means of chemical selection.. Host-Predator Relationships  Unsprayed trees; Figures 65 (a) and (b) show that there was a negative correlation between the total predator population and the host mite population i n the two abandoned orchards. It i s mentioned above that the normal population peak of the host mites i n these two orchards would probably have occurred in July, but that the presence of large numbers of predators at this time suppressed i t s natural tendencies. Figure 65 (a) shows that i n the Mclntyre Creek orchard the predator population declined at the time of the f i r s t population peak, considered here as "artificial". 1', and again at the second population peak, again considered " a r t i f i c i a l " . The reduction in population producing these -139-Figure 65 (a) & (b). two peaks, i . e . the reduction occurring in July, occurred when the greatest number of predators were active on the trees. Therefore, i n the absence of predators of any kind, this period of low host density would probably have been the period of greatest host density, and thus the host population would have developed In a uni-modal rather than a bi-modal manner. In the Meyer1s Flat orchard the same relationship was observed. At the time of greatest host density the predator population was just beginning to develop. When the predators became sufficiently numerous the host population was immediately reduced. Had no predators been present, the host population probably would have continued to increase u n t i l a peak was reached during July or early August. Thus, Figures 65 (a) and (b) show that, given the opportunity, the predators recorded in these orchards probably were f u l l y capable of controlling the host mites and maintaining them at a level below that considered economically important. Figure 66 shows the relationship between the host population in the Gartrell orchard, a commercial orchard, and the total predator population (composed of T. rhenanus and Stethorus picfoesY It shows that, whereas the predator population may have hastened slightly the normal decline in host population caused by the approach of autumn and winter, the predators were not present in -1*4-1-Figure 66.. - lk-2 -the orchard sufficiently early to effect any appreciable control of the host population. It i s explained above that this orchard has been subjected to applications of various insecticides for a considerable number of years, and that the predators have been nearly or entirely eliminated $y this treatment. It i s encouraging to the proponents of biological control that a considerable population of T. rhenanus succeeded in establishing i t s e l f towards the end of the season, the f i r s t season in which chemicals have not been applied to the check trees. This indicates that a chemical program favourable to this species of predacious mite i s a l l that i s necessary to effect' partial biological control i n the orchards of the Okanagan Valley. It w i l l not be necessary to reintroduce this species of predator but merely to provide conditions more favourable to i t s development than those prevailing at present. Snraved trees. The effectiveness of the predators on the sprayed trees i s very d i f f i c u l t to estimate since each of the chemicals used have powers of stimulation under certain conditions, and, of course, are effective i n reducing the host population under other circumstances. As the fluctuations in the host population are the only indications of the control, value of the predators, the situation i s considerably complicated by the presence of DDT, Parathion or PbAs. The author feels that the only positive statement that can be made at this time i s that each of the three - 1**3 -insecticides applied during the course of this study • ' ' ' i reduced the predator population and thus hindered or prevented natural control of the orchard mites,. The insecticides reducing the predator population to the greatest extent were, of course, the most detrimental to this control since the predators remaining afte r the application of an insecticide probably were s t i l l effective i n reducing the host population to some extent. - ihh -CONCLUSIONS The long-r'ange objective of the project initiated at Summerland, B.C., in May, 195l» i s to increase the effective-ness of the existing species of predators in controlling orchard mites by means of careful regulation and timing of the spray program. The Immediate aims of the work performed during the summer of 1951, the results of which are reported in this paper, were threefold? 1. To determine what host mites and predators are present in the Okanagan Valley of Br i t i s h Columbia. 2.. To determine i f the existing predacious species are capable of controlling the host mites under favourable conditions. 3.. To investigate the effects of lead arsenate, DDT, and Parathion both on populations of host mites and of predators. The various species of host mites and predators found to occur in the study orchards are reported above in the sections concerned with each orchard. From an analysis of the data obtained during the summer of 1951, "the following conclusions have been made concerning the poss-i b i l i t y of the host mites being controlled by the exist-ing predators under favourable conditions and the effects of the 3 insecticides.. 1. In the abandoned orchards, which have been free from a l l cultural practices, particularly the application of insecticides, for a number of years, three species of - ]>5 -predators, Typhlodromus rhenanus. Mediolata sp. , and an unidentified species of predacious thrips, were able to .control, successfully populations of the host mite Bryobia  pretiosa (Clover mite) and maintain them at levels sufficiently low that no damage of economic significance occurred. It i s further concluded that these predators could also control!host mite populations in commercial orchards, provided they were free from the effects of toxic chemicals such as DDT and Parathion.. 2. DDT, Parathion, and lead arsenate were a l l very toxic to the predators recorded in the study orchards, and under certain conditions were capable of stimulating the host mite population.. It i s therefore concluded that the use of any one of these ehemicals may aggravate rather than relieve the problems of orchard mite control. - Ik6 -SUMMARY The project reported i n this paper was initiated in May, 1951, at Summerland, B.C. Its -ultimate purpose i s to increase the effectiveness of the existing species of / predators in controlling the phytophagous mites occurring in apple orchards i n the Okanagan Valley., The immediate aim of the work herein reported was to determine: ( 1 ) Ihe species of host mites and predators present in the Okanagan Valley at this time. (2) The potential effectiveness of the existing predacious species. (3); The effect of DBT, Parathion and lead arsenate both on the host mites and their predators. The importance of such a project i s stated, with a history of the problem of orchard mite control, and of the control measures which have been used. General l i f e histories of the host mites encountered during the summer of 1951 are given, as are the l i f e histories of the most important predators. The two abandoned orchards and the commercial orchard used for this study are described and an account i s given of the manner i n which they were divided into plots. Each tree on the check plots was divided into north, south, east, and west quadrants from which 20 leaves were taken each time a collection was made. It i s shown that 20 leaves - 1^7 -afforded an error of not more than 13.8 percent, and that small", leaves supported the same number of European red mite per unit area as the large leaves. There were more Tetranychus spp.. mites per unit area on small leaves than on large. A description of the machine used to brush the mites and predators from the collected leaves i s given and i t i s shown that the machine method was more accurate than personal observation toy means of a stereoscopic microscope.-The following items summarize the data recorded in the 3 study orchards during this study: 1.. The European red mite and the Clover mite were found in greatest abundance on the east sides of the check trees from May to October. Presumably environmental conditions on these sides were most favourable to the development of these species. 2. The application of DDT resulted i n an increase of the Clover mite population i n the abandoned orchards. This increase in density was probably caused both by a lack of predators and by an actual stimulation of the host mites. 3., DDT reduced the density of the European red mite in the commercial orchard. This effect was entirely chemical since no predators were recorded on the DDT-sprayed trees at that time. h. DDT stimulated a population of Tetranychus spp* in the commercial orchard.. 5. Lead arsenate had variable effects. Under certain environmental conditions the Clover mite was stimulated i n i t i a l l y and later reduced in numbers. Under other conditions the reverse was true,. Applied to a population of European red mites this chemical reduced the population and delayed i t s development* A population of Tetranychus spp. in the same orchard as the European red mite population (the commercial orchard) was i n i t i a l l y reduced and later stimulated. 6. Tfee effect of Parathion varied according to the conditions prevailing at the site of application. In the most arid abandoned orchard this chemical stimulated the Blover mite population to a point where foliage damage occurred. In the less arid abandoned orchard the Clover mite was eliminated. The European red mite population in the commercial orchard was unaffected by Parathion, whereas the Tetranychus spp..= population was stimulated to an extreme degree,., . 7. The danger of relying solely on a chemical control program is clearly shown. Parathion, the most widely used acaricide today, i s extremely effective under certain circumstances, but has no effect on, or actually stimulates, the host mite population under other conditions... 8. The arid conditions of the abandoned orchards were unsuitable for the development of the European red mite - lH-9 -and Tetranychus spp., while the Clover mite was most abundant under these conditions. 9. Typhlodromus rhenanus.. Mediolata sp. and pred-acious thrips were effective in controlling the Clover mite in the abandoned orchards on the unsprayed trees. 1G. In the commercial orchard T. rhenanus and Stethorus  picipes developed too late in the season to contribute greatly to the control of the European red mite and Tetranychus spp* 11. In the commercial orchard, which has been > subjected to applications of toxic materials for a number of years, a population of T. rhenanus was able to deyelop the f i r s t season no insecticides were applied. This fact i s of great importance when attempting to devise means of increasing the effectiveness of natural control agents in commercial orchards. It w i l l not be necessary to introduce predacious mites of this species to orchards once a spray program has been devised that i s not harmful to them. 12. The presence of various predators prevented the natural population peak of the Clover mite on the unsprayed trees in the abandoned orchards. 13. All'predacious species observed were drastically reduced i n numbers by the application of lead arsenate, DDT, or Parathion, the latter two having the greatest toxic effect, a l l natural control being prevented by their application* - 150-lh„ The number of host mites present on a tree varies inversely as the total numberof predators. It i s concluded that the existing predacious species are capable of controlling the host mites in the absence of insecticides, and maintaining them at a level where economically important damage i s impossible. It i s also concluded that the use of any one of the insecticides .tested during this study may be of greater harm than benefit to an orchard since, in almost every case, the host mite population increased after their use* - 151 -BIBLIOGRAPHY It was the original intention of the author to include in this bibliography a l l references to the major papers written on the subject of orchard mites and their control.. However, during the summer of 1951 Miss J. R. Groves published asynopsis of the world literature on the Fruit Tree red spider which includes a l l such references* This bibliography, then, includes only references to papers actually referred to in the text and to papers containing specific references to the predators of orchard mites. The t i t l e s of the papers actually referred to in the text are marked with a plus{-0 sign. + 1. Andersen, V.S.19^7. Investigations on the biology and control of the Fruit Tree red spider, P.pilosus Can. & Fan-z., Dissertation Universitat Bonn. 2. Andre, M. 19*t2. Hibernation among; Tetranychids. ande i t s relationship to the struggle against the phytophagous Acarina. Bull. Mus. nat. Paris (2) l*f, n o . l r pp.57-62. 3. Annand, P.. N. 19^2. Report of the Chief of the Bureau of Entomology and Plant Quarantine, 19*fl-'*+2.. Washington,D.C. + h» Austin, M.D. 19k6. Entomological Investigations. Rep.Coun.Sci.. Industries.Aust .20 (1914.5.11+6), p p a 8 - 2 i f . 5. Austin, M.D.& A*M.Massee. 19^7* Investigations on the control of the Fruit Tree red spider mite (Metatetranychus ulmi Koch..) during the dormant season. J. Pomol. 23*3*ks 227-253. 6. Baten, W»D« & R. Hutson.. 19^3* Precautions necessary when estimating populations of smaUl. animals * J.Ec. Ent.365^: 501-50V. + 6. Blair, Catherine A.., Joan R.. Groves 1951- Biology of the Fruit Tree red spider mite, Metatetranychus ulmi (Koch), in South-east England. JJbur. Hort*Sci. 27 a a 1 * - 1 ^ . 7. Blauvelt, W.E.19 -^5. The internal morphology of the Common red spider mite (Tetranychus telarius L.) Mem.Cornell Agric.. Exp.sta. #270* - 152 -8.. Borden, A.D., & L. R. Jepson. 19^5. Field tests with DDT to control codling moth on Bartlett pears- In Investigations with DDT in California, 1 9 ^ . Berkeley, Calif.. C a l i f . Agric. Exp., Sta., 9 . Bourne, A.L.& others. 19^0. Apple pests and their control. Leaf 1.. Mass. St.. C o l l . Ext. Ser., #189. +10.. Boyce, H.R- 19^8- The role of biological control. in Canadian orchard entomology. 79th Ann- Rep- Ent. Soc. Ont. 2 8 - 3 3 -11 . Brittain, W.H. 1929- Insects of the season In 1928 i n Nova Scotia. Rep., Ent. Soc. Ont-59 ( 1 9 2 8 ) : 8 - 1 0 . +12- Caesar, L. & W.A.Ross, 1921. Insects of the Season i n Ontario.. Rep- Ent. Soc. Ont. 51(1920): 3 5 - ^ 2 -1 3 - Caldwell, N..E.H-, 19*t6. DDT and codling moth control. Qd. Agric. Journ. 6 3 : 8 6 . ih. Chandler, 3.0.19^-6. Codling moth control. A study of growers practices. Bu l l . 111. Agric. Exp- Sta. #519, PP - 2 9 ^ 3 3 2 -+15. Chapman, P.J., 19^7. Dormant and semi-dormant sprays with special reference to the control! of mites. Proc. Pa. Hort. Ass. 8 8 : 7 3 - 8 2 -16. Clancy, D.W- & H.N.Polloard. Effect of DDT on several apple pests and their natural enemies. J. Ec. Ent. ^+1:3:507-508. +17. Collyer, El s i e , 19^9. The predator aspects of the Fruit Tree red spider problem. Ann. Rep.E.Malling Res.Sta.. 19*w.pp. 108-110. 18., Connecticut, 1939.. Annual report for the year ending October 31 ,1939. B u l l - Gonn-Agric- Exp.Sta.#^21, f ; .26. 1 9 - Cottier, W.,193^.. The natural enemies of the European red mite in New Zealand. N.Z. J.Sci.Tech.16:2:68-80. +Cutright, C.R.,1939. A significant feature of biotic potential as related to insect control.-Ann. Ent. Soc- Amer.. 23:l:l*+5-ihQ.. +21. DeBach, P., 19^7. Predators, DDT, and Citrus red mite populations. J.Ec.Ent. l+0:if:598-599* - 153 -22- Bean, R.W.,. 19^2. Early summer vs summer control measures for European red mite. Proc.N.Y.,St. Hort-Soc- 87$202-206. 23. Evans, J.A-, 19hl. Fruit insect problems In 19U©'. Proc.N.Y.St.Hort. Soc.,, 86:211-213. 2*f. Garlick, "W.G., 1929. Notes on red spider on bush f r u i t s . Rep-Ent.Soc.Ont. 59 (1928), pp> 86-93. 25. Garman, P- 1921. The European red mite, a new orchard pest in Connecticut. B u l l . Conn- Agric. Exp- Sta., #226, pp. 18U-I89.. +26.. Garman, P.. 1923. The European red mite in Conn-ecticut orchards. Bull. Conn. Agric* Exp. Sta.#252, pp. 103-125* 27- Garman,, P- & J.F.Townsend- 1938. The European red mite and i t s control. B u l l - Conn. Agric. Exp- Sta. #fl8. 28. Garman, P* & B- H. Kennedy, 19^. Effect of s o i l f e r t i l i z a t i o n on the rate of reproduction of the Two-spotted spider mite. J - Ec. Ent- M-2rl:l57-158.. +29. Garman, P- 1950.. Parathion resistant red spiders. J - Ec. Ent. *f3 :;53- 56. , +30- G i l l i a t t , F.C. 1935. Some predators of the European red mite, Paratetranychus pilosus C.& F.. in Nova Scotia.. Can.J. Res-D13-19-38. 31. G i l l i a t t , F.C. 1935. The European red mite in Nova Scotia- Can. J. Res. B13* 1:1-17. 32. Groves, Joan R. 1951. A synopsis of the world literature on the Fruit Tree red spidery Metatetranychus ulmi (Koch) and i t s predators- Commonwealth Inst. Ent., Lond., *fl Queen's Gate, London, S.W.7. +33. Hammer, 0. H. 19^3. Some facts and observations regarding summer control of red mite. Proc. N.Y.St.Hort.Soc. 88: 171<-180-- i9+ -+3*f. Henderson, C.F. & H.V.McBurnie.. 19^3. Sampling technique for determining populations of the Citrus red mite and Its predators. Circ.U.S.D.A. #671. +35. Henderson, C.F. & J.K.Hollaway. 19^2. Influence of leaf age and feeding injury on the Citrus red mite. J.Ec.Ent. 35* 5*683-686.. 36. Heschner, C.A.1950. Studies on the searching capacity of the larvae of three predators of the Citrus red mite. Hilgardia 20:13:233-265. October. +37. Hollaway, J. E., C.F.Henderson & H.V.McBurnie.19^2. Population increase of Citrus red mite associated with the use of sprays containing inert granular residues. J.Ec.Ent.35s;3'+8-350* 38. Houser, J.S. & C.R•Outright.19HI. The European red mite. Proc. Ohio.Hort.Soc 7lf?26-lf3* 39. Howard, L*0.. 1927. The parasite element of natural control of injurious insects and i t s control by man.. Smith. Rept.. 1926:kLl-lf20. HO. Jary, S.G.1935.. Some observations upon the "Red Spider". Tetranychus telarius T on hops and Its control, with notes on some predatory insects. Ann.Appl. B i o l . 22 (3)* 538-5^8. hi. Jones, L..S.& D*T.Prendergast. 1937. Method of obtaining an index to density of f i e l d populations of the Citrus red mite. J.Ec.Ent.30:;6:93H-9i4-0* lf2. Kelsall, A* 1939. Thirty year's experience with orchard sprays in Nova Scotia. Sci.Agric. 19^7:^05-^10. +U-3. Koch, C.L. 1835. Deutsehlands Crustaceen Myria-poden und Arachnid en.. Fa.l.T.10* +hh» Kotte, 19^1«- Krankheiten und schadlinge im obstbau und ihre bekampfung. (Diseases and pests in f r u i t growing and their control). Berlin, (revised 19*f8). - 155 -+V5. Kuenen, D.J.. 19H-1. Onderzoek over de biologie en bestrijding van het f r u i t -snint Metetranychus ulmi .Koch. . (Investigations on the biology and control of the Fruit Tree red spider, Metetranychus ulmi Koch). In Dutch.Versl* Zeelands Proeftuin Goes 19^1. H6. Kuenen, D.J. 19^3. Spint op vruehtboomen (Mites on f r u i t trees);. In Dutch. Tijdschr. Plziekt. ^9:^-. 130-131. Kuenen, D.J. 19h6. Het fruitspint en zi j n bestrl-jding. (The Fruit Tree red spider and i t s control) In Dutch with English summary. Meded. Tuinbow-evoorlichtingsdienst.- norMf,. k6. Kuenen, D.J. 19*4-7. On the ecological significance of two predators of Metatetrany- chus ulmi C.L.Koch (Acarl. Tetranychidae). Tijdschr. Ent. 88:303-312. *f9. Kuenen, D.J.. 19^9. The Fruit Tree red spider (Metatetranychus ulmi Koch. Tetranychidae, Aeari) and i t s relations to i t s host plant. T i j d s c r i f t voor Entomologie vitgegeven door De Nederlandshe Entomologische Vereeniging. 19*4-8 • pp. 83-102* 50. Lamiman, J.F. 1935. The Pacific mite. J.Ec.Ent. 28:6:900-903. +51. Legislation, 1935. Fruit tree pests (Berkshire) order of 1935- S.R.0.1935 no.183. +52. Lewis, D. 19^ -5. How shall we defeat the Red Spider on f r u i t trees? Bul l . John Innes Hort. Inst. #1. PP.. 5^-57. +53. Mabry, J.E. & M. M. Walton. 1939. Distribution and food plant records of Para-tetranychus c l t r l McG. P . i l i c i s McG., P.. pilosus C.&F.j" Tetry- anychus telarius L., and T. nacificus McG. Insect Pest Survey B u l l . 589-602. - 156 -51*. MacPhee, A.W. 19^7. The hionomics and morphology of the predacious thrips Hanlo- thrins faurei. Hood (unpublished)i Thesis. McGill University. +55* Marshall, J. M. 19*+8. 79th Ann. Rep. Ent. S o c Ont. 26-28. 56. Massee, A. M. 1930. The control of the Fruit tree red spider of Plum during the growing season. J. Pomol. 8:2* 18M-19M-. 57. Massee, A. M. 1932. Some beneficial and injurious mites of top and soft f r u i t s . J * Pomol. and Hort. Sci. 10:2. 58. Massee, A., M. 19^8. Notes on the insect fauna of sprayed and unsprayed apple orchards, Rep. E. Mailing Res. Sta. 19*+7. pp. 132-131*. +59. Massee, A. M„ 1951. Introduction to a synopsis of the world literature on the Fruit Tree red spider, by J.R.Groves, 60. McGregor, E. A. 19*$. Classification, distribution, and food plants of the spider mites. J. Ec. Ent. *fl:5:68U-687* +61. McGregor, E. A. 1950. Mites of the family Tetrany-chidae. Amer. Midland Nat. ¥f:;2: 257-^20* +62.. Mel and er, A. L. 1923. Red spiders. Proc. Wash. St.. Hort. Ass. 18(1922):77-79. +63.. Moskovetz, S. N. l$kO. (Virus disease of cotton and i t s control. Jn Plant virus diseases and their control. In Russian).. Trans. Conf. Plant Virus. Dis., Moscow, k-7/H/19kQ. pp.173-190. +6*4-. Nesbitt, H. H.. J. 19^6. Three new mites from Nova Scotian Apple trees. Can. Ent. 78: 1:15-22. 65. Nesbitt, H.H.J. 19**7. Studies on three predacious mites and the role they play in orchard economy. Ann. Rep. Fruit Insect Unit, 19V7. - 157 -+66. Newcomer, E. J . & M. A. Yothers. 1929. Biology of the European red mite i n the P a c i f i c Northwest. U.S.D.A.Tech.Bull. #89. 67. Newcomer, E. J . &.F.P.Dean* 19h6, E f f e c t of Xanthone, DDT, and other i n s e c t i c i d e s on the P a c i f i c mite. J . Ec. Ent. 39:6: 783-786. 68. Nicholson, A. J . 1933. The balance of animal populations. J . Anim. Ecol. 2:1:132-178.. 69. Nicholson, A. J . 1939. Indirect effects of spray practices on pest populations. Verhantl* 7 Int. Kongr. Ent. B e r l i n k:2927-3079. +70. Oakland, G. B. 1951. Personal Communication.. 71. Parks, T. H. 1939* European red mite and Aphis. Proc. Ohio. Hort. Soc. 72:53-71. 72. Parrot, P.J.., H. E. Hotchkiss, & W.J.Schoene. 1906. The apple and pear mites. N.Y.Agric. Exp. Sta. B u l l . #283. December 1906. +73. P i c k e t t , A. D. 19*4-8. The philosophy of orchard insect control 79th Ann. Rep. Ent. Soc. Ont. 37-^1. 7k. Putman, W. L. 191+2. Notes on the predacious t h r i p s * Can. Ent. 7l»-s3s37-lf3. .. +75. Radzievskaya, S. 1931. A Destroyer of the red spider. (In Russian). Za Khlopkov Nezavisim 6-7:75-81. 76. Ripper, W. E. 19kk. B i o l o g i c a l control, as a supplement to chemical control of insect pests. Nature, Lond., 153ikk&-k52., +77. Roberti, D. 19**6. A serious attack of red spide r (Tetranychus t e l a r i u s ) on Ci t r u s along the Sorrento Coasts. I n t . B u l l . PI. Prot. 20*3-lf:;26M-28M. +78., Robertson, W. H. 1939. Report of the H o r t i c u l t u r a l Branch Rep. B.C.Dep. A g r i c * 1938. 33s 27-1+2., +79. Steiner, L. F. , C.H.Arnold, S.A.. Summer land. 19*4-7. Laboratory and f i e l d tests of DDT f o r control of the codling moth. J.EC.Ent* 37(1):156-157. - 158 -80. Steiner, L- F. 19k&. Parathion for f r u i t insect and mite predators.. Proc. 3rd Ann-Meeting North Cent. Sts- Br. Amm* Ass. Ent. pp.105-106. +81. Ullyet, G. C. 19**8. Insecticide programs and biological control in South Africa. Jour.. Ec. Ent. *fl:337-9. 82. Woglum, R. S.-. , J.R-LaFollette, W. E. Landon & II.C- Lewis- 19^7. The effect of field-applied insecticides on beneficial insects of Citrus in California- J - Ec- Ent. kO:6t 818-820-+83- Wood, M- N- 19^7. Almond culture i n California. Circ. C a l i f . Agric. Ext. Ser.#103. * &+. Zacher, F. 1923. Biology, economic significance, and control of mites. (Biologie, wirtschaftlische bedentung. und bekampfung der spinnmllhen)- Verh. Deutsch Ges. angew. Ent. 3 Mitglied-erversammlung zu Eisenach, 28 bis 30 Sept. 1921. - 159 -A P P E N D I X - i -TABLE VI • • - • v Clover Mite Population - A l l Plots, Meyer Ts F l a t Orchard. Average numbers per 20 leaves May 14 May 30 June 20 July 24 Sept. 4 Oct. 23 Unsprayed Check Plot EGG - 4 . 0 2 . 0 1 3 . 0 9 . 0 1.2 IMMATURE - .2 2 4 . 0 5.0 7 . 0 . 1 ADULT . 8 . 0 9 . 2 2 . 0 2 . 0 2 .3 TOTAL . 8 4.29 26.2 2 0 . 0 18 .0 3 . 6 DDT-sprayed Plot EGG 8 . 0 1.0 2 3 . 0 24.0 4 . 0 IMMATURE — 28 .0 125.0 107.0 1 .0 ADULT . 3 . 3 8 . 0 3 . 0 1.3 TOTAL 6.3 2 9 . 3 156.0 71.0 6 . 3 PbAs-sprayed Plot EGG 3 . 0 1 .0 3 . 0 1.0 .3 IMMATURE . 2 3 3 . 0 1 .0 mm 1.0 ADULT .3 _ _ . 6 TOTAL 3.5 3 4 . 0 4 . 0 1.0 1 .9 Parathion-sprayed Plot EGG 7 .0 2 . 0 6 2 . 0 28 .0 7.3 IMMATURE - 4 8 . 0 80 .0 17 .0 ' 2 .3 ADULT . 2 1.0 3 8 . 0 1 4 . 0 4 . 0 TOTAL 7.2 51 .0* 180 .0 59.0 13 .6 - i i -TABLE VII Clover Mite Population - A l l Sides of Check Trees. Average numbers per 20 leaves May 14 May 30 June 20 July 24 Sept. 4 Oct. 23 NORTH SOUTH EAST WEST 1.0 5.4 4.8 6.6 2.6 16.4 20.8 22.8 19.2 22.0 20.0 23.6 19.2 19.2 20.8 53.2 14.8 3.2 4.8 12.0 3.2 - i i i -TABLE VIII Typhlodromus rhenanus Population - A l l Plo t s , Meyer's F l a t Orchard Average numbers per 20 leaves • - • May 14 May 30 June 20 July 24 Sept. 4 Oct. 23 Unsprayed Check Plot EGG — • 2 2.0 3.0 1.0 -IMMATURE _ .09 4.0 25.0 9.0 -ADULT .1 • .7 4.0 18.0 27.0 6.3 TOTAL .1 .99 10.0 46.0 37.0 6.3 DDT-sprayed Plot 1.0 EGG - mm - - -IMMATURE — .3 - . - -ADULT 1.0 .7 - - .6 TOTAL 2.0 1.0 - - .6 PbAs-sprayed Plot EGG .2 1.0 .3 - -IMMATURE 1.0 3.0 10.0 - -ADULT , .2 4.0 4.0 1.0 .3 TOTAL 1.4 8.0 14.3 1.0 .3 Parathi on-sprayed Plot EGG IMMATURE ADULT TOTAL I V -TABLE IX Typhlodromus rhenanus Population - A l l Sides of Check Trees. Average numbers per 20 leaves May 14 May 30 June 20 July 24 Sept. 4 Oct. 23 NORTH 2.3 12.4 28 .4 24.4 6.4 SOUTH . 4 .8 9.2 29.6 29.2 6.3 EAST. 1.2 7.6 32.8 29.6 10.4 WEST . 2 1.6 13.6 4 0 . 4 40.8 6.6 TABLE X Mediolata sp. Population - A l l Plo t s , Meyer's F l a t s Orchard Average numbers per 20 leaves  May 14 May 30 June 20 July 24 Sept. 4 Oct. 23 Unsprayed Check Plot EGG .09 - 1 .0 IMMATURE - 1 .0 6 . 0 ADULT - - .3 .7 6 . 0 4 . 0 TOTAL - .09 . 3 1.7 13..0 4 . 0 DDT-sprayed Plot EGG - - -IMMATURE - - - .3 -ADULT - 1.0 - -TOTAL - - - 1.3 PbAs-sprayed Plot EGG - - - - -IMMATURE .2 - . 7 .3 ADULT .2 .7 - - -TOTAL . 4 .7 .7 .3 Parathion-sprayed Plot EGG - -IMMATURE -ADULT - - . 7 TOTAL - - . 7 TABLE XI Mediolata sp. Population - A l l Sides of Check Trees. Average numbers per 20 leaves ' May 14 May 30 June 20 July 24 Sept. 4 Oct. 23 NORTH - - - - 4.4 1.2 SOUTH;: . 8 .4 16..0 5.2 EAST. - - 1.2 .4 7.6 .4 .WEST - - . 4 2.0 10.0 4 . 0 - v i i -TABLE XII Thrips Population - A l l Sides of Check Trees and on A l l Plots, Meyer's F l a t Orchard. Average numbers per 20 leaves  Check Trees NORTH SOUTH EAST WEST Check Plot DDT-sprayed Plot PbAs-sprayed Plot Parathion-sprayed Pint. : May 14 May 30 June 20 July 24 Sept. 4 Oct. 23 2.8 10.8 5.6 .8 -.8 2 . 6 10.0 4.8 2.4 -mm 3.2 15 .6 4*4 3.2 -mm 1.8 6.8 . 3.8 2.4 -1.0 3 .1 13 .6 3.5 3 .1 -2.4 . 4 - - — 5.6 4 . 0 5.6 .4 -4 . 0 .4 - - -- v i i i -TABLE X I I I Clover Mite Population - A l l Plots, Mclntyre Creek Orchard. Average numbers per 20 leaves May 7 May 22 June 25 July 19 August 22 Oct. 10 Unsprayed Check . . . . ..•„ Plot EGG - - 11.5 22.6 10.9 2 0 . 4 ' 2.8 IMMATURE mm .6 6 .4 11.1 7 .7 3 . 7 ADULT . 2 1.2 2.8 1.1 2.2 3 .5 TOTAL .2 13.4 31.3 22.8 28 .4 10.2 DDT-sprayed Plot EGG 21.3 52.0 149.0 198 .0 96.6 IMMATURE - 14.3 187 .0 236.0 16 .0 ADULT 1.3 7.6 24.3 56.1 28 .0 TOTAL 22.6 74.0 360.3 490.1 140.6 PbAs-sprayed Plot EGG 22.3 6 .6 9 . 0 4 6 . 6 13 .0 IMMATURE — 10 .0 10.3 52.0 12.3 ADULT . 6 .6 .3 10.6 12.6 TOTAL 22.9 17.2 19.3 109.2 37.9 Parathion-sprayed Plot EGG IMMATURE ADULT TOTAL 18.8 .3 1.0 20.1 1.3 3 .3 4 . 6 .3 .3 1 .0 ~6 1.6 - i x -TABLE XIV Clover Mite Population - A l l Sides of Check Trees, Mclntyre Creek Orchard. Average numbers per 20 leaves May 7 May 22 June 25 July 19 August 22 October 10 NORTH 17.5 5.5 9 . 0 10.5 11.5 SOUTH . . 5 18 .5 4 2 . 0 22.5 19.5 8 .5 EAST .5 13 .0 15 .0 12.5 3 3 . 0 8 .5 WEST . 7 22.5 2 0 . 0 14 .0 21.5 14.0 - X -TABLE XV Typhlodromus rhenanus Population - A l l Plots, Mclntyre Creek Orchard. Average numbers per 20 leaves  Unsprayed Check Plot May 7 May 22 June 25 July 19 August 22 October 10 EGG . 4 7.3 2.8 1.5 _ ... IMMATURE — 10.3 9.5 11.1 . .6 ADULT ' 2.2 8 .5 8 .2 2.6 . 2 1.6 TOTAL 2.6 26.1 20.5 15.2 .8 1.6 DDT-sprayed Plot EGG 2.0 . — _ IMMATURE 6 . 0 .3 mm ADULT 5.0 .3 _ mm TOTAL 13.0 .6 - - -PbAs-sprayed Plot ' . . . EGG 19 .0 . 7 _ _ mm IMMATURE 2 0 . 0 2.0 1.0 _ ADULT 11.0 .3 mm TOTAL 50.0 3 . 0 1.0 - — Parathion-sprayed Plot EGG IMMATURE ADULT TOTAL 8 .0 . 7 14.0 2 .0 4 . 0 2 6 . 0 2 .7 - x i -TABLE ..XVI Typhlodromus rhenanus Population - A l l Sides of Check Trees Mclntyre Creek Orchard. Average numbers per 20 leaves  May 7 May 22 June 25 July 19 August 22 October 10 NORTH 2.7 21.0 15.5 14.5 1.0 mm SOUTH 3 . 2 16 .0 15.5 11.0 1.0 1.0 EAST 3.7 31.5 22.5 20.5 1.5 1.0 WEST 1.2 24.5 12 .0 ; 21.5 2.0 -- x i i -TABLE XVII Mediolata sp. Population - A l l Plots, Mclntyre Creek Orchard. Average numbers per 20 leaves May 7 May 22 June 25 July 19 August 22 October 10 Unsprayed Check Plot EGG - 10 .7 3.3 5.7 1 .3 -IMMATURE —• _ 3.3 7.7 2 .6 .'2 ADULT 3.6 3.1 2 .6 6.6 4.2 2.2 TOTAL 3.6 13.8 9.2 20.0 8.1 2.4 DDT-sprayed Plot EGG 4.0 - • — — .6 IMMATURE .3 .5 .3 — — ADULT 1.0 _ _ . 6 TOTAL 5.3 .5 .3 mm 1.2 PbAs-sprayed Plot EGG 10.0 .3 — — _ IMMATURE - 3.0 2.0 — _ ADULT .7 1.0 1.0 1.0 1.0 TOTAL 10 .7 4 .3 3.0 1.0 1.0 Parathion-sprayed Plot EGG 5.0 m. _ IMMATURE .3 2.0 1.0 ADULT 2.0 .7 1.0 TOTAL 7.3 2.7 2.0 - x i i i -TABLE XVIII Mediolata sp. Population - A l l Sides of Check Trees, Mclntyre Creek Orchard. Average numbers per 20 leaves May 7 May 22 June 25 July 19 August 22 October 10 NORTH . 2 .7 2 .5 6.5 15 .0 5.5 1.5 SOUTH 4 . 0 12.5 10.0 23.0 5.5 1.5 EAST 2 .5 12.2 5.5 14.5 2.5 3 . 0 WEST - 4 . 7 2 6 . 0 7 .0 25.0 6 . 0 2 .0 - x i v -TABLE XIX. Thrips Population - A l l Plots, Mclntyre Greek Orchard. . Average numbers per 20 leaves Unsprayed Check Plot DDT-sprayed Plot PbAs-sprayed Plot Parathi on-sprayed Plot Check Plot NORTH SOUTH EAST WEST May 7 May 22 June 25 July 19 August 22 October 10 - • 1.2 3.8 3.0 .8 -— .4 —, — , — — - .6 «4 2.6 — _ — ' 1.6 .2 — - -c . s 1.2 2.0 3.0 .2 1.0 5.0 3.5 1.0 _ .2 1.0 2.5 1.5 — _ .5 1.0 2.0 3.5 .5 — - XV -TABLE XX European Red Mite Population - A l l Plots, G a r t r e l l 1 s Orchard. Average numbers per 20 leaves Unsprayed Check June 5. June 28 July 30 September 11 October 15 Plot EGG 54.1 100.0 651.6 56.0 5.6 IMMATURE 2.5 . 7 .2 414.9 47 .2 8 .2 ADULT — 6.2 54.0 9 . 0 4 . 2 TOTAL 56.6 113.4 1120.5 112.2 18 .0 DDT-sprayed Plot 35.6 897.3 . - , . EGG 4 3 . 4 11.3 20.3 IMMATURE 17 .0 2 . 8 170.0 , 2 .0 .6 ADULT - 2.2 52.6 2.6 36.6 TOTAL 5 2 . 6 , 4 8 . 4 1119.9 15.9 57.5 PbAs-sprayed Plot EGG IMMATURE ADULT TOTAL 3.6 32 .7 683.3 445.2 3 . 0 5 .0 77.6 228 .7 - 3 . 4 35.0 230.6 6.6 41 .1 750.9 904.5 38.3 22 .0 53.0 113.3 Parathi on-sprayed Plot EGG IMMATURE ADULT TOTAL 11.6 5.6 10.0 281.0 4.6 1.0 1.0 91.6 - ' - 1.0 86.0 16.2 6.6 12.0 458.6 2.6 4 . 0 2 .0 8.6 - x v i -TABLE XII European Red Mite Population - A l l Sides of Check Trees, Gartrell»s Orchard. Average numbers per 20 leaves  June 5 June 23 July 30 September 11 October 15 NORTH SOUTH EAST WEST 34.8 3 0 . 0 97.2 29.6 53.2 3 2 . 0 134.8 7 4 . 0 594.0 527.8 918.0 709.2 32 .4 9 3 . 0 135.2 104.0 13.2 15.6 19.2 17.2 - x v i i -TABLE XXII Tetranychus spp. Population - A l l Plo t s , G a r t r e l l * s Orchard, June 5 June 28 July 30 September 11 October 15 Unsprayed Check Plot EGG _ .8 .8 2.0 .8 IMMATURE 1.8 2.6 24.6 15.8 5.2 ADULT — — 2.2 2.2 3 .4 TOTAL 1.8 3.4 27.6 2 0 . 0 9 .4 DDT-sprayed Plot EGG IMMATURE ADULT TOTAL .3 6 .6 6 .9 .3 5.3 5.6 61.3 29.3 21.3 111.9 • 3 .3 21 .3 1043.3 569.3' 1633.9 PbAs-sprayed Plot EGG IMMATURE 4 . 0 ADULT TOTAL 4 . 0 .3 5.3 7.6 5.0 4 . 6 15.6 81 .0 73.3 1.6 2 .0 17.0 41.6 6.5 23.1 105.6 119.9 Parathion-sprayed Plot EGG IMMATURE 9 .6 ADULT TOTAL 9 .6 .6 . 6 1143.3 1336.3 272.0 2751.6 1.0 1.3 2.3 - x v i i i -TABLE XXIII Tetranychus spp. Population - A l l Sides of Check Trees, Gartrell»s Orchard. Average numbers per 20 leaves  June 5 June 28 July 30 September 11 October 15 NORTH .8 2.4 50.4, 2 2 . 4 SOUTH 1.6 7.2 37.6 2 4 . 0 EAST 1.2 2.0 29.2 2 6 . 4 WEST 1.6 3 . 6 27.6 19.6^ 1.6 3 . 0 3 .6 10.0 - x i x -TABLE XXIV Stethorus picipes Populations A l l Plots, G a r t r e l l ' s Orchard. ' Average numbers per 20 leaves Unsprayed Check Plot EGG IMMATURE ADULT TOTAL June 5 June 28 July 30 September 11 October 15 DDT-sprayed Plot EGG IMMATURE ADULT TOTAL .1 .1 ,5 • 2 ,.1 ..8 .1 .1 .8 1.4 2 .6 y6 .6 PbAs-sprayed Plot EGG IMMATURE ADULT TOTAL .1 .1 2,3 1.0 3.3 Parathion-sprayed Plot EGG - -IMMATURE - - _ 2 3 ADULT - - 4 . 0 TOTAL - . 6 .3 - XX -Unsprayed Check Plot EGG , IMMATURE ADULT TOTAL TABLE XXV Typhlodromus rhenanus Population - A l l P l o t s , G a r t r e l l ' s Orchard, Average numbers per 20 leaves  June 5 June 28 July 30 September 11 October 15 .4 .4 .8 1.0 8.8 12.8 22.6 .6 32.4 33.0 DDT-sprayed Plot EGG . IMMATURE ADULT TOTAL PbAs-sprayed Plot EGG IMMATURE ADULT TOTAL -Parathion-sprayed Plot EGG IMMATURE ADULT TOTAL .6 .6 TABLE XXVI Typhlodromus rhenanus Population - A l l Sides of Check Trees, G a r t r e l l T s Orchard. Average numbers per 20 leaves  June 5 June 23 July 30 September 11 October 15  .6 .3 49*6 23.6. 1 .2 37.2 13 .4 . 4 4 6 . 0 24.4' -1.2 21.2 19.6 NORTH SOUTH EAST WEST 1 Figure 1 (a). - x x i i l -Figure l / - x x i v -F i g u r e 5. Truck and Equipment u s e d when S p r a y i n g O r c h a r d s . F i g u r e 6. Leaf--brushing machine. F i g u r e 7, Leaf--brushing machine w i t h one s i d e removed to show b r u s h e s . F i g u r e 8. Leaf--brushing machine showing the g l a s s p l a t e i n p o s i t i o n . F i g u r e 9. C o u n t i n g d i s c and m i c roscope u s e d when c o u n t i n g m i t e s . 

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