« L [B R A F; Y Mfiflligan 312.323 E University { , "fl, mu; [U fllfllllll Lu; ii i Jim mug "(MIL n This is to certify that the thesis entitled Interactions of the bronze birch borer (Agrilus anxius Gory) and European white birch (Betula pendula Roth) in Urban Environments presented by John J. Ball has been accepted towards fulfillment of the requirements for M. S . degree in Foresmv I . ’Major professor Date ’4/7’1/77 0-7639 OVERDUE FINES ARE 25¢ PER DAY PER ITEM Return to book drop to remove this checkout from your record. INTERACTIONS OF BRONZE BIRCH BORER (AGRILUS ANXIUS GORY) AND EUROPEAN WHITE BIRCH (BETULA PENDULA ROTH) POPULATIONS IN URBAN ENVIRONMENTS By John Ball A THESIS Submitted to Hichigan State University in partial fuifiliment of the requirements for the degree of MASTER OF SCIENCE Department of Forestry 1979 ABSTRACT INTERACTIONS OF BRONZE BIRCH BORER (AGRILUS ANXIUS GORY) AND EUROPEAN WHITE BIRCH (BETULA PENDULA ROTH) POPULATIONS IN URBAN ENVIRONMENTS By ‘ John Ball Surveys were conducted in three Okemos, Michigan neighborhoods to classify the vigor of the birch population. Of the three species sur- veyed, European white birch was the most affected by dieback. Grey birch (§;_populifolia) was occasionally afflicted, while paper birches (§;_papyrifera) showing symptoms of decline were rare. In addition to the survey, European white birches in various stages of decline were cut down and examined for presences of Agrilus 3351 s larvae and galleries. Trees that were healthy or displayed a slight degree of flagging contained few or no larvae and galleries. Trees exhibiting various stages of branch dieback were infested throughout the bole and crown. Adult borer emergence was limited to the upper bole and crown except in trees near death. In these trees emergence also occurred along the lower bole. The implications of these findings in light of current control measures is discussed. ACKNOWLEDGMENTS Several people deserve thanks for their contribution to my thesis. My advisor, Dr. Gary Simmons provided encouragement, guidance and most of all the freedom to make my own mistakes. My committee, Drs. J. Kielbaso and K. Kennedy furnished valuable suggestions for the final preparation of this thesis. Special thanks are due to Mr. J. Mahar and Ms. J. Jaworski for their assistance in the field work. One additional person to thank is my wife, Phyllis. Without her friendship and sacrifice none of this would have been possible. ii TABLE OF CONTENTS Page LIST OF TABLES .......................... iv LIST OF FIGURES ......................... v INTRODUCTION ........................... l Objectives ......................... l Literature review ..................... 2 Bronze birch borer ................... 4 Natural control .................... 6 European white birch .................. 8 Host-pest interaction ................. 9 A brief history of bronze birch borer research ..... lO METHODS ............................. 13 Tree vigor classification and species survey ........ l3 Larval sampling ...................... l4 Adult sampling ....................... l6 Chemical control study ................... l6 RESULTS AND DISCUSSION ...................... l7 Tree vigor ......................... l7 Class differences in larval density and gallery length . . . 23 Branch influence on larval density and gallery length . . . 33 Adult emergence ...................... 35 Control considerations ................... 38 Progression of borer attack ................ 4O LITERATURE CITED ......... ' ................ 43 APPENDICES ............................ 47 l. Map of survey area within Okemos, Michigan ....... 47 2. European white birch crown vigor classification . . . . 48 3. Branch vigor classification .............. 49 TABLE LIST OF TABLES Page Parasites and predators of Agrilus anxius .......... 7 Class change of European white birch from 1977 to l978. Data taken from two neighborhoods in Okemos, Michigan ...... 21 Class changes of grey birch from l977 to l978. Data taken from two neighborhoods in Okemos, Michigan ......... 22 Class change of paper birch from l977 to l978. Data taken from two neighborhoods in Okemos, Michigan ......... 22 Comparison of average number of Agrilus anxius larvae per lOD cm? (i5E) of inner bark between European white birch bole and branches for each vigor class ................ 27 Comparison of average Agrilus anxius gallery length per l00 cm2 (:SE) of inner bark between European white birch bole and branches for each vigor class ................ 27 Number of sample points in each Agrilus anxius gallery length class at 50 cm intervals along European white birch branches 36 2 Average number of Agrilus anxius emergence holes per lOO cm (:std. dev.). Data taken between 0.5 and 1.5 m on European white birch boles ...................... 37 iv LIST OF FIGURES FIGURE Page l. Percentage of birch stems in each vigor class. Data taken in 1977 from two neighborhoods in Okemos, Michigan ..... l8 2. Percentage of birch stems in each vigor class. Data taken in l978 from three neighborhoods in Okemos, MIchigan . . . . l9 3. Mean number of Agrilus anxius larvae per 100 cm2 (:55) of bole inner bark for each European white birch vigor class . 24 4. Mean Agrilus anxius gallery length per lOO cm2 (+SE) of bole inner bark for each European white birch vigor cTass . . . . 24 5. Percentage of B;_pendula bole sample points containing Agrilus anxius larvae. Percentage broken down by height and vigor class ........................ 25 6. Percentage of B;_pendula bole sample points containing Agrilus anxius galleries. Percentage broken down by height and vigor class ...................... 26 7. Mean number of Agrilus anxius larvae per branch sample (:SE) for each EurOpean white birch vigor class ......... 29 8. Mean Agrilus anxius gallery length per branch sample (:SE) for each European white birch vigor class ......... 3O 9. Mean number of Agrilus anxius larvae per sample in European white birch branches of each vigor grade .......... 34 l0. Mean number of Agrilus anxius larvae per sample at 50 cm intervals along European white birch branches ....... 34 INTRODUCTION Objective Birch dieback is of major concern to homeowners. While many are aware that an insect is at least partially to blame for the decline of their birch trees, there are many differences in bronze birch borer control. These differences are based on disagreement on larvae and gallery density and adult borer emergence within trees in various stages of dieback. Since this information is not well known, control methods have not had a great deal of success and urban birches have continued to decline. Birch dieback is a serious problem in the urban centers of Indiana, Illinois and the southern lower peninsula of Michi— gan. European white birch has always been a quite popular ornamental in this region due to the slightly weeping form and attractive white bark. Unfortunately with the continual decline of these trees, home- owners become discouraged and seek a substitute. The uniqueness of this tree is apparent when one realizes that the search for a substitute has continued for the past eighty years. This study was initiated to gather base-line data on the effect of bronze birch borer on birch growing under urban conditions. While the borer in the farest situations is well documented, little information is known about bronze birch borer in urban areas and no work has been widely published on the borer-European white birch interaction. The objectives of this study are as follows: 1. To describe changes in birch tree vigor and distribution by species over time. 2. To determine larval distribution within European white birch bole and branches stratified by vigor class. 3. To determine larval gallery distribution within European white birch bole and branches stratified by vigor class. 4. To establish average density of adult borer from European white birch boles stratified by vigor class. Literature Review The bronze birch borer, Agrilus anxuis Gory, a native North Ameri- can species, is a serious pest of Eur0pean white birch (Betula pendula Roth) (Syn §;_verrucosa Ehil). European white birch is highly prized as an ornamental and is frequently planted throughout urban areas of the Northeastern and Northcentral United States. Bronze birch borer is credited with a condition known as birch dieback; the gradual decline of birch commencing at the tip of the crown and progressing with the death of all limbs and ending in the death of the tree. Bronze birch borer was first recognized as an urban problem in the late l890's at which time it was found infesting many Eur0pean white birch trees in Buffalo, New York (Chittenden,1898; Chamberlain, l900). This insect did not receive a great deal of attention until the l930's when dieback of native birches was noted in forests across Maine and Southeastern Canada. This disease continued into the l940's with large acreages of paper birch (B;_papyrifera Marshall) and yellow birch (§;_allegheniesis Britton) exhibiting gradual decline and death. Many studies concluded that bronze birch borer was not initially respon- sible for the dieback; instead it was unfavorable weather conditions which prevailed during the twenty year span (Hansbrough, 1952; Redmond, 1954). It was noted that precipitation was less than normal white average temperatures were higher during those decades (Hawboldt and Stolke, 1948). As both paper and yellow birch are shallow rooted spe- cies, they were greatly affected by the more hostile environment (Hansbrough, 1952; Redmond, 1933, 1954). Bronze birch borer may hasten death of these native species but it is not the primary cause of morta- lity (Anderson, 1944; Barter, 1957). ASide from the aforementioned Species, bronze birch borer larvae have been known to feed on grey birch (B;_populifolia Marshall) and sweet birch (B;_lgntg_Linnaeus) (Carlson and Knight, 1968). Western paper birch (B;_papyrifera occidentalis (Hooker) Sargent) and B; fonti- nalis (Sargent) have also been listed as hosts (Barter and Brown). Several asiatic species are considered resistant to successful bronze birch borer attack, though the type of resistance is unknown. These include Japanese white birch (B; mandshumca Miquel) and Monarch birch (§;_maximowicziana Regel) (Kozel and Toth, 1975; Kozel and Smith, 1976). However, this resistance remains to be demonstrated. True Monarch birches are so rare that less than ten have been found in this country (Santamour and Meyer, 1977). Japanese white birch plantings are also rare. This small pool of species to study raises questions as to their resistance. I have observed a dying Japanese white birch with a large number of larvae and old emergence holes. Since first noticed many control measures have been tried, few with any success. One of the greatest drawbacks to control of bronze birch borer is the nature of the insect. Being a phloem feeder during the larval stage its movements and location are hidden from view. Many nurserymen have advocated pruning the top branches off dying trees to reduce larvae infestation. It has also been suggested to thoroughly soak the crown with an insecticide spray to destroy the majority of egg laying adults. Advice such as this suggests that bronze birch borer activity is similar to a related borer, the two-lined chestnut borer (Agrilus bilinaetus Weber), in that the attack begins at the top and proceeds downward (Craighead, 1950). L The majority of studies performed on host-pest interactions were made during the 1930's on native birch stands in Northeastern North America. Little work has been performed on European white birch under urban conditions. This has resulted in most of our information being taken from a different host tree growing under environmental conditions different than those commonly found in urban areas. Bronze Birch Borer The adult stage begins in early summer. Adults emerge from D- shaped holes cut through the bark. Emergence in lower Michigan usually begins in early June and continues for several weeks. Adults live for an average of 23 days (Balch and Prebble, 1940) and can be observed from early June till mid-July in lower Michigan (Wellso, Manley and Jackman, 1976). As the name implies, the adult is bronze in color. The body shape is slender sub-cyclindrical. Female length ranges from 7.7 to 11.3 mm with the male being slightly small (Barter, 1957). The adults feed sparingly on the foliage of many trees. Nash et a1. (1951) rated bronze birch borer preference for foliage and obtained the following ranking from most to least desirable, Populus grandidentala Michaux, £;_tremuloides Michaux, Salix spp., B; alleghaniensis, B;_papyrifera, E;_balsamifera Linnaeus and Alnus spp. Oviposition usually does not occur until about six days following emergence (Barter, 1957). Eggs are laid singularly in bark crevices or under loose bark flakes. Since adults are known to be sun loving (Anderson, 1944), more oviposition will occur on the southern side of the bole (Barter, 1957). Hutchings (1923) described the eggs as oval, 1.3 to 1.5 mm long, 0.8 to 1.0 mm wide and creamy white in color when first laid. The eggs take on a yellowish tinge after a few days. The female coats the eggs with a semi-transparent substance which acts as both a protective shield and a cement. Eggs generally hatch in 14 days. After ecolosion the first instar begins to burrow into the bark and proceeds to the phloem region. Not all larvae move directly to the phloem. Some may meander 25 cm before reaching this zone (Anderson, 1944). The physiology of the host tree plays an important role in the feeding behavior and development of the larvae. An element of larval behavior which may be tied to the physiological condition of the host is the phenomenon of xylem departures. Larsen (1902) first noted this aspect of larval behavior where larvae would leave the phloem region and dip into the xylem tissue for a short distance. Hall (1933) attributed this behavior to molting. Anderson (1944) reached a similar conclu- sion. He found cast skins at the base of each departure in vigorous host materials. Carlson and Knight (1968), however, believe that these departures result from larval avoidance of suffocation by sap flow in the damaged phloem. Barter (1957) noted that more departures were made in vigorous trees as opposed to those in decline. The larva passes through five instars. Several instars might be found overwintering due to the long time period in which adult females are ovipositing (Mac Aloney, 1968). A shorter, thicker larva forms the 'prepupal' stage (Barter, 1957). Pupation occurs in the spring with adults emerging in June. In Northern regions bronze birch borer may have a two year cycle (Balch and Prebble, 1940). It may also have a two year cycle in vigorous hosts (Nash et al., 1951). Natural Control Bronze birch borer has relatively few natural regulating factors aside from host tree conditions (Table 1). A few parasites have been reported. Slingerland (1906) reared a hymenopterous parasite Phasgono- phora sulcata Westw. from the borer. He felt this was a major controll- ing factor. Britton (1923) reared this same species from a borer. Balch and Prebble (1940) and Nash et a1. (1951) reared several other parasites from larvae but concluded that the percentage of larval parasitism was relatively small. During a study performed by Barter (1957) egg parasitism proved to be the major mortality factor. Parasitism averaged about 55 percent over the five year study; Nash et a1. (1951) recorded similar percen- tages. Woodpeckers and other birds do play a role in regulating borer population. The importance of their control is not clear. Hutchings (1923) felt they provide important control. Barter (1957) found up to 51 percent of mature larvae and prepupae removed by woodpeckers. The most common larval mortality factor is host tree resistance (Barter, 1957; Carlson and Knight, 1968). Larval feeding causes dis- ruption of phloem cells which in vigorous trees, due to high phloem Akmmpv tmptam Ammmpv coupwtm x mtmxumauooz mcopmumta AmmmFV pzmwcx ccm compcmu x vmw52m< msewppwewm mzwspmmw Amom_v psmwcx new compcau x zmm counmwfi mmuwcoopm: Amom_v uzmwcx new :OmFLmu x tmzocm>0ta mwmwcum mmpuxuoo AmomFV pcmwcx ucm compcmu x commmtu mamcopcomTLOmmmE mauweosowwpoo Amoopv ucmwcx new comptmu x xwwm magmco mspooxcmp< mmuwcoomtm nonwoco23mccoH AummFV cmpcmm x .mm m:pt%ucmuwooou Aumm_v cmpcmm x .Qm mzcmmxgk Aoom_v uca_tmm=w_m x abmupzm atoeaacomWMSa wantoumu_a;o mcmuaocmEAI mmuwmmcma “Faun woman mm>cmp mam mawxcm mz—wcm< co mtoumumca ucm mmuwmmtma .P m_nMH pressure, may cause suffocation of the larvae. Also, trees which die too quickly cause larval mortality as larvae require living phloem tissue to complete development. European White Birch As the name implies, European white birch is not a native species, but extends throughout Europe into Asia Minor. While the United States possesses several native birches, the European white birch is by far the most widely planted. A survey of a mid-western town revealed one out of every three homeowner yards contained a European white birch (Dirr, 1975). The reason for its widespread popularity across the Northeast and Northcentral United States is due to the slightly exfoliating white bark and the graceful, pendulous branching habit. European white birch may reach a height of 30 m, though 15 m is more common. It usually lives anywhere from 40 to 100 years. However, under urban conditions of compacted soil and polluted air the useful life is shortened. The majority of European white birch are propagated by seed (Santamour, 1977). This means a larger genetic variability is main- tained than if a vegetative form of propagation was employed. European white birch does exhibit genetic variability across its range with Finland provenances developing a whiter, more ornamental bark than other provenances (Gaggini, 1977). It is not known if provenances vary in susceptibility to bronze birch borer. European white birch, as many other birch species, is affected by a variety of pest problems. Trees may have their appearance altered by birch skeletonizer (Bucculatrix canadensisella Chambers), birch leaf miner (Fenusa pysilla Lepeletren) and bronze birch borer. Of these three, the birch leaf miner and bronze birch borer are the most serious pests in lower Michigan. European white birch has several varieties. The most popular variety is the cutleaf or Swedish birch (B;_pendula dalecarlica Schneider). Originating from Sweden (Whitehead, 1979) this variety has Very long, pendulous branchlets covered with deeply cut leafs. Host-Pest Interactions Bronze birch borer larvae feed on the cambium and phloem tissue within the bole and branches (Balch and Prebble, 1940). By disrupting the conducting sieve tubes bronze birch borer has, in effect, girdled the length of a segment of the bole within which it has fed. This damage is expressed as flagged and dead twigs at the extremity of the tree if sufficient damage has resulted. Continued feeding for several years will result in tree death. Carbohydrates accumulate above the girdled area due to the release of tugor in the sieve tubes. High sugar concentrations also develop in the same area (Baldwin, 1934). In relation to these two events, dis- turbances begin occurring in the major metabolic systems of the plant (Noel, 1970). Auxin imbalance precedes the production of fewer and smaller leaves. This is expressed as a reduction in photosynthesis. As photosynthesis decreases and respiration increases, carbohydrate depletion begins. Initially, girdling does not affect the upward movement of water (Kurtzman, 1966). Water stress begins as the available carbohydrates below the girdle are exhausted thereby reducing root area. Water stress often results in premature autumn coloration and defoliation 10 (Baldwin, 1934). This further reduces photosynthesis. Finally, carbo- hydrate reserves are exhausted and the cambium and phloem dies. Girdled trees may survive for many years depending upon the species and environmental conditions. Usually the final deterioration is rapid, often occurring within a season. Premature defoliation begins, upper branches die, with death of the lower limbs quickly following (Noel, 1970). A Brief History of Bronze Birch Borer Research A brief summary of previous studies is given to provide insight into how investigators have arrived at the current understanding of the problem. The first cited evidence of widespread mortality of birch related to the bronze birch borer is in a letter to the editors of Garden and Forest, July 15, 1896. A Mr. J. Jack of the Arnold Arboretum noticed some foreign birches being attacked by a boring Agrilus beetle. Chittenden (1898) was informed of the dieback of many birches around the Buffalo, New York area. He captured adult beetles flying around the trees and identified them as Agrilus anxius. Since a common name was not yet provided Chittenden named the beetle the bronze birch borer in reference to the color of the adults and the host that they fed on. He was the first to mention that the insect attacks the top of the tree first, though how he arrived at this conclusion is not stated. Larsen (1902) was the first to publish information on bronze birch borer in Michigan. He noted that European white birch in the Detroit and Ann Arbor areas were usually first attacked at the top where limbs were only 3/4 to 1-1/2 inches in diameter. Only on badly infected trees were galleries found at the base of the bole. Slinger- land (1906) also agreed that infestations began at the top but added 11 that pruning out dead limbs may not be advisable as the entire tree may be infested by that time. The first report of the bronze birch borer as a forest pest was by Swaine (1918); he noted dying birch in the Ottawa River watershed. Pierson (1927) also mentioned borer being a problem in a forested area. He stated that the top of the tree was first attacked, with infection proceeding downward in later years. Trees usually died in three to four years after attack. Felt and Bromley (1930, 1931) were the first to advocate fertilizing and watering as a means of stimulating tree vigor to combat the attack of the borer. They documented one case where such treatment proved successful in stimulating growth in a badly infested tree. Spaulding and Mac Aloney (1931) were the first to state that ini- tial attack began on the lower stem and crown. Prior to this it was assumed that the top was infested first. They also observed that trees at the beginning stages of decline (bare twigs and some flagging at the tip of crown) were free of borers. Another forest study performed by Balch and Prebble (1940) on yellow birch disagreed with Spaulding and Mac Aloney and suggested that bronze birch borer begins in the branches, usually the smaller ones. However, they also noted that trees with a few dead twigs were free of borer. This observation was confirmed by Hawboldt and Stolkes (1948) in their study on white and yellow birch in undisturbed stands in Maine. They found trees that were healthy and those with only a few dead twigs to be free of larval galleries. Trees which had several dead limbs in the crown had between 0 and 41 galler- ies with some being listed only as numerous. Trees with up to half of 12 the crown dead had a gallery count range from 0 to 83 with several trees being listed as numerous. METHODS Tree Vigor Classification and Species Survey Surveys were made through three neighborhoods of Okemos, Michigan during August of 1977 and 1978 (Appendix I). The neighborhoods sur- veyed were middle class, consisting of single family dwellings sur- rounded by lawn supporting several shade trees. These neighborhoods contained many birch trees which were planted 15 to 20 years ago. 1 Therefore, older trees were available for study. The purpose of the survey was to delineate differences in health between the three major birch Species, European white, paper and grey. The survey consisted of assigning each stem a crown vigor classification (Appendix II). This classification was applied to individual stems, rather than clumps as birch dieback is noted for destroying one stem at a time until the entire clump is dead. A crown vigor classification system was considered a necessary step in separating differences in larval number and gallery density of trees in various stages of die- back. The development of the crown vigor classification system was taken, in part, from a classification system developed from an earlier work. Greenridge (1953) used a crown classification system to describe differences in birch trees based on the amount of dieback. His system consisted of six classes, with each class further subdivided into two subclasses. Class 1 was a completely healthy tree while class six described a tree which had been dead for several seasons. Greenridge's 13 14 crown classification was simplified for this study. Only five classes were used and non was subdivided. The reason for this reduction in the number of classes was that several of Greenridge's classes and sub- classes were not pertinent to an urban study. For example, no birch in the study area suffered from mechanical injuries and therefore the 18 subclass was excluded. Classes 4, 5 and 6 were not considered necessary as trees in these classes are dead or near death. Trees were generally removed by homeowners before they reached this stage. In addition to crown vigor, other characteristics recorded for each stem were location, percent of chlorotic foliage, percent of leaves damaged by leaf miners and diameter of stem at 1.37 m above the ground. The surveys conducted in 1977 and 1978 permitted observing class change. To aid in locating the same tree from one year to the next the address of the home at which the tree was located was recorded. Also the diameter at 1.37 m was recorded so that individual stems in a clump could be separated. Since this method permitted accurately pinpointing the location of each stem a graphic analysis of locality was feasible. This permitted determining if low vigor trees were concentrated at any particular location. Larval Sampling_ In late August of 1978, 28 trees were cut down to examine the bole and branches for larvae and galleries. At least four trees were selected from each vigor class. Trees were cut during the time period of active feeding so new galleries were discernible from old ones. Ten cm strips of bark were removed completely around the bole every 50 cm. The first strip was made at ground level and then every 50 cm contin- uing to the top of the tree. Branches were sampled in a similar 15 fashion. This allowed approximately 20 percent of the inner bark area to be examined on the bole and branches. Branches selected for sampling were chosen in the following manner. At every meter the closest four branches over 1.2 cm in basal diameter were selected for sampling. The height from the ground and the branch angle was recorded. The crown of the tree was divided into quadrants and the quadrant in which the branch was positioned was recorded. In addition to an overall crown vigor classification, a branch vigor classification was developed (Appendix III). This per- mitted examining the relationship of branch vigor to larval density and gallery length. The branch classification system was divided into four grades. Grade 1 described a healthy branch while grade 4 described a branch near death. Dead branches were excluded from grading as larvae do not live in dead phloem. The branch grading system was only used on trees which were stripped of their bark. Secondary branches on each selected branch were also sampled with the position on the primary branch recorded. A vigor grade was not assigned to secondary branches. The total gallery length in each section was recorded. No attempt was made to measure individual galleries. The large number of galleries in many sections formed a network which made it impossible to follow individual galleries. The stripped areas were also examined for the presence of larvae. Several larvae were collected from each tree and examined to determine their developmental stage. These larvae were randomly chosen and collected without regard to location on the bole or branches. 16 Adult Sampling In the spring of 1979, 20 stems were selected for a study con— cerning adult bronze birch borer emergence. This study was to test differences between vigor classes in the number of adult borers emerging from an area of .5 to 1.5 m from the base of the bole. The importance of this study was to determine if borers emerged from the base of the bole, and if so, in what vigor classes. Chemical Control Study Two stems, a class 3 and 4 were selected for cutting in August 1978 which had been sprayed with Lindane the spring of that year. Three applications of Lindane were applied two weeks apart beginning the first week of June. The sprays were applied by a homeowner with no special instructions. The purpose of this study was to test the effectiveness of homeowner chemical control against the borer. RESULTS AND DISCUSSION Tree Vigor During late August of 1977, a survey was made of birch in the Indian Hills and Tacoma Hills subdivisions of Okemos, Michigan (Figure l). A total of 249 stems were studied. Eighty-eight of the stems were paper birch, 94 were EurOpean white birch, while the remaining 64 were grey birch. There were major differences between these three species based on tree vigor. While 68 percent of the paper birch were class 1, only 42 percent of the grey and 29 percent of the European could be consi- dered class 1. None of the paper birch was below class 2 while 14 percent of the grey were. European white birch was the only species surveyed in 1977 which had trees in classes 4 and 5. In total, 34 per- cent of the European white birches were of class 3 or poorer. In 1978 this survey was expanded to include the Forest Hills subdivision in Okemos (Figure 2). In total 671 stems were included in the 1978 survey. 247 stems were European white birch, paper birch accounted for 228 of the stems and 196 were grey birch. In this survey all three species had at least one stem in each of the classes. Eighty seven percent of the paper birches were still in class 1, however. Only two percent could be considered class 3 or poorer. Grey birch had the next highest percentage of healthy trees, 65 percent were class 1. Eighteen percent were class 3 or poorer. 17 18 1rch 1rch irch 5 European white b grey b n=64 paper b n=88 .:.:.:.:.:.:.:.:.:.:.:. 0....... .::::.:..:..0.......:.:...:. .:.:..::.:::. N . . . .0.- .. .0 . .o.:.::. ooooooooo ..o.:.. ooooooo P -——- ~ 0.4 -~o-—o-T own—w -c-‘w-- . .._- .. -i‘... .._.._......_.. ' C) C) O O 0 Q3 KO Q‘ N 100-? percentage of stems in each vigor class lass Vigor c 1977 from two 1n Data taken igan. lCh Okemos, M 111 hborhoods ' Percentage of birch stems in each vigor class (appendix II). neig ' Figure l. 19 .C U L '1'- .0 LO (I) .p ‘r— ..C .C 3 .1: u U S. C S— '1'- M 'I— .Q Q) .0 QR to Lw O'U' >305 moo LN 0"- ON 311 $- II (U 11 LAJ C 03: CL: II --l:l g we 3 4 Vigor c O “I .09.... .H“............. .0.I.OUOICIIOIOII.0.0.0.0900... . . .CMOOOI...:..HOCCCOOOIOIICOOIIOIIOIIIOOOOCOOIO 0......0000. 0...... 0......- .00....0. n ' I..-" ”I.” . ”I W: o o o o o 00 \D <1" (\l 100-1 percentage of stems in each vigor class lass 1978 from three 1" Data taken igan. in Okemos, Mich hborhoods Percentage of birch stems in each vigor class (appendix II). neig ‘ Figure 2. European white birch had the lowest percentage of class 1 trees; only 43 percent could be placed in that class. Over 40 percent of the Euro- pean white birch were in classes 3 through 5. While paper and grey birch had very low numbers of 4's and 5's in comparison to 3'5, European white birch had almost equal numbers of trees in classes 3, 4 and 5. The majority of low vigor trees in both surveys were European white birch. A random survey of homeowners found that few attempted bronze birch borer chemical control or were even aware of the organism that was partially responsible for the dieback problem. There appears to be no appreciable difference between Species as far as bronze birch borer control is concerned. Therefore, it appears that European white birch is more sensitive to environmental stresses than the other two Species and hence is more vulnerable to attack by the borer. Since the survey of 1978 was an expanded survey of 1977, it was an excellent opportunity to observe class changes in the species from one year to the next. In one year, 33 percent of the trees changed class. European had the greatest change (Table 2). Fifty two percent of the European white birch changed class. Almost half of this change was from class 2 to 1. Eight percent of the class 1 trees dropped to class 2. Over half of the class 2 trees improved to class 1 while 23 percent remained in class 2. Eleven percent dropped to class 3 with seven percent becoming class 4 in one year's time. One class 2 tree was cut down by the homeowner. Class 3 stems did not Show any improvement. Forty-four percent of the class 3 European white birch stems remained class 3 one year later, 31 percent dropped to class 4 and the remainder became 5's. The group having the largest number of trees drop to lower classes was 21 Table 2. Class change of European white birch from 1977 to 1978. Data taken from two neighborhoods in Okemos, Michigan vigor class (1978) vigor class (1977) (n) 1 2 3 4 5 dead removed 1 (27) 25 2 2 (44) 25 10 5 3 1 3 (16) 7 5 4 4 (9) 1 4 3 1 5 (4) 2 1 l class 4 trees; only one tree remained stable, the rest became 5's or died. Class 5 trees had two trees remain stable, one died and the other was removed. Grey birch stems were more stable than European, 73 percent remained in the same class (Table 3). Ninety-four percent of the change in an upward direction from class 2 to 1. Only one stem changed in a downward direction and that was from class 3 to 4. Paper birch had 18 percent change class (Table 4). All this change was class 2 trees improving to class 1. The most apparent fact which came out of the class change study was that trees can improve from class 2 to class 1. The only visible differences between these two classes is cattered patches of flagging. This may have been due to minor water deficiency, an elastic strain which can be corrected with proper watering. It should also be noted that once a tree has reached class 3, further decline is inevitable and no improvement can be expected unless the tree is intensively cared for by timely bronze birch borer chemical control and pruning. The 22 Table 3. Class changes of grey birch from 1977 to 1978. Data taken from two neighborhoods in Okemos, Michigan vigor class (1978) vigor class (1977) (n) l 2 3 4 5 dead removed 1 (27) 27 2 (28) 16 12 3 (9) 8 l 4 (0) 5 (0) Table 4. Class change of paper birch from 1977 to 1978. Data taken from two neighborhoods in Okemos, Michigan vigor class (1978) vigor class (1977) (n) 1 2 3 4 5 dead removed 1 (60) 6O 2 (22) 15 7 3 (O) 4 (O) 5 (O) greatest change in a downward direction was exemplified by European white birch stems. Again, this indicates European white birch inabi- lity to withstand environmental stresses and the borer. This continual decline may take several years. While this study has not been in existence long enough to observe the progress of many trees through the sequence, several trees dropped from class 2 to class 23 4 within a one year period. Barter (153) Showed that it took from one to nine years for a paper birch to regress from a healthy to a dead state. He also noted that dieback progressed slower in the beginning than after the stage when several large limbs were dead. This analysis compares favorably with the data from the urban European white birch and also what would be expected from girdling (Noel, 1970). Relatively few of the class 2 trees dropped in class during a one year period, while this percentage increased for class 3 and 4 trees. Class Differences in Larval Density and Gallery Length Class 1 and 2 trees are discussed together due to their similar- ity. Class 1 and 2 trees were equal in bole larval density (Figure 3) and were quite similar in gallery length (Figure 4). The densities were extremely low in both cases, with the few larvae and galleries present randomly scattered throughout the bole. Several trees in each class were completely free of infestation. Class 1 boles had 94.0 percent of the sampling points free of larvae (Figure 5). Class 2 boles were similar to class 1. Ninety-three percent of the sample points were free of larvae. Larvae were not found higher than 4.5 m above the base of the tree. The total bole height of class 1 and 2 trees varied from 5 to 11 m. Class 1 and 2 boles had 86.6 and 78.0 percent bole area free of galleries (Figure 6). The sample points which contained galleries were randomly distributed throughout the boles. Branches for class 1 nad 2 trees were identical in'level of infes- tation as neither class contained larvae or galleries (Tables 5 and 6). The fact that branches were free of galleries and larvae, while the bole contained low densities of each indicates that initial bronze average number of larvae/100 cm2 Figure 3. average gallery length/100 cm2 Figure 4. 24 1' 1.25- ‘1 1.00- w h 0.75- A J? 0.50- 0.25- i I 0.00- I 1 2 3 4 5 vigor class Average number of Agrilus anxius larvae per 100 cm2 (:SE) of bole inner bark for each European white birch vigor class. 16.0- L 14.0- 12.0- " 10.0- I 8.0- A 6.0- 4.0- I 2.0- I 0.0- vigor class Average Agrilus anxius gallery length per 100 cm2 (:SE) of bole inner baFk for each European white birch vigor class. 25 1004 class 1 754 254 H Oil—TL [—1 r1 r1 r1 r1 [—1 TO- .571. -3 3- .5 4T5-6 6-7.5 7.5-9 9-10.5 10.5-12 n=16 n=12 n=12 n=10 n=7 n=5 n=3 n=2 1004 class 2 cu 75-1 g 504 L. ,2 254 5’ 0* .F—I [—1 I—T J—TL r—i r11 '5 O-l.5 1. -3.0 3.0-4.5 4.5-6.0 6.0-7.5 7.5-9.0 '; n=16 n=12 n=12 n=1O n=8 n=3 4.) C 8 1004 r-5 T" class 3 :3 75i r— °8 501 D. m 254 3' 0‘ j . r-1 3 O-l.5 1.5-3.0 3.0-4.5 4.5—6.0 6.0-7 57T7l5-9.O a. n=16 n=12 n=12 n=1l n=ll n=8 0 8, 1004 class 4 f6 2 754 E" Q) 8 504 (1) °- 254 o- O-1.5 l. -3.0 3.0-4.5 n=l4 n=12 n=9 1004 class 5 754 F— 504 254 04 g [‘1 041.5 1. -3.0 3.0-4.5 n=16 n=5 n=2 height (m) Figure 5. Percentage of §;_pendula bole sample points containing Agrilus anxius larvae. Vigor class. Percentage broken down by height and 26 class class 100- 75- 50- 25- 0- 100- .. 75- (U 'E 50- (I) : 25- ‘3. 0- Cl C :E 5 c 100- O 3 75- E 50- 8. 25- CD 'a 0' E 8 q. ° 100- a) g“ 75- 5 50- 8 cu 25- D. 0- 100- 75- 50- 25- 0.. Figure 6. _ class F_- '1 "T “1 O-l.5 1.5-3.0 '3.0-4.5 4.5-6.0 6.0-7.5 n=16 n=12 n=12 n=ll class class I” ”'1 rf1 O-l.5 1.5-3.0 3.0-4.5 n=16 n=5 n=2 height (m) Percentage of B; endula bole sample points containing Agrilus anxius gaileries. and vigor class. Percentage broken down by height 27 Table 5. Comparison of average number of Agrilus anxius larvae per 100 cm2 (1 SE) of inner bark between European white birch and branches for each vigor class. bole average number of larvae vigor class bole n branches n l 0.05:0.02 67 0.00:0.00 179 2 0.05:0.02 61 0.00:0.00 184 3 0.74:0.09 69 0.45:0.08 165 4 0.90:0.19 35 0.30:0.09 85 5 1.05:0.33 22 0.17:0.08 4O Table 6. Comparison of average agrilus anxius gallery length per 100 cm2 (:SE) of inner bark between European white birch bole and branches for each vigor class. average gallery length (cm) vigor class bole n branches n l 1.38:0.65 67 0.00:0.00 179 2 1.89:0.57 61 0.00:0.00 184 3 4.56:0.48 69 4.81:0.54 165 4 8.99:1.41 35 9.91:4.90 85 5 12.5414.39 22 4.25:1.09 4O birch borer attack is not concentrated in the crown as had been assumed by earlier investigators. AS mentioned before, the majority of trees in classes 1 and 2 had sample points completely free of infestation. The few attacks noted may simply be random. It is also interesting to note that class 1 and 2 trees Showed little between-class variation in the level of 28 infestation. Therefore, it appears that neither class is more appealing to bronze birch borer, nor could symptoms exhibited by class 2 trees be attributed to bronze birch borer. While class 1 and 2 trees were almost identical in the level of infestation, class 3 trees Showed a definite increase in larval density and gallery length in comparison with the first two classes. Bole larval density showed a much greater percent increase than gallery length. However, the increase in both were greater between class 1 and 2 versus 3 than between any other classes. Class 3 boles differed greatly from those in class 1 and 2. Only 31.9 and 15.9 percent of the sample points were free or larvae and galleries, respectively. Sample points with the highest larval density were between bole heights of O and 4.5 m. Total bole heights for this class ranged from 6.5 to 9 m. Another distinction between class 3 and the first two classes is that primary branches in class 3 contained larvae and galleries (Figures 7 and 8). Class 3 crowns contained 0.37 larvae per sample point. The area sampled at each point varied from 150 to 40 cm2. This was the highest crown value obtained. Crown gallery length averaged 10.01 cm per sample point. Class 3 trees had a lower larval density in the branches than the bole. Gallery length was about equal for both bole and branches. The dramatic increase in larvae density and gallery length between class 3 trees and the first two classes indicates that class 3 trees are definitely susceptible to bronze birch borer. Larval density is still lower in the branches as compared to the bole, however. There- fore, it cannot be concluded that attack begins in the crown and 29 3 0.44 7 Q. 5 1 m (I '5 c 0.34 + 2 .1 .D \ O) m 1 i 02.. 1 2 u q. ° 1 b 0.14 ‘ .Q E 3 C 8: J ' o g 0.0 I I I I I g 1 2 3 4 5 vigor class Figure 7. Average number of Agrilus anxius larvae per branch sample point (15E) for each European white birch vigor class. proceeds downward, especially since the greatest larval density and gallery length is in the lower half of the tree. The reason for the great differences between class 2 and 3 trees in level of borer infestation remains unclear. Kozlowski (1969) stated that trees usually must undergo a physiological change before becoming attractive to insects. Many investigators of birch dieback concluded the primary cause of this disorder was the unseasonably warm summer temperatures which occurred from 1930 to 1950. Paper birch is a cold climate species. The extent of its southern range across north- eastern United States parallels the 70°F mean July isotherm. The warm temperatures and low precipitation of the 1930's and 1940's may have resulted in physiologically altering inner bark tissue to the advantage of the borer. Figure 8. 30 26.0- 24.0- 22.0- 20.0- 18.0- 16.0- 14.0- 12.0- N -I> 03 O I O C) I o o I 1 I I m vigor class Average Agrilus anxius gallery length per branch sample point (:_SE) for each European white birch vigor class. 31 The reason for the initial dieback of European white birch is not certain. Rushforth (1975) mentions that birches in Britain suffer die- back after about forty years. No organism has been linked with this condition. Perhaps European white birch is unable to withstand urban condition such as air pollution (Warren and Delavault, 1962; Townsend, 1974; Jensen and Masters, 1975) and infertile soil (Rushforth, 1975). Such sites must be considered poor ones, and Since trees physiologically age much quicker on poor sites (Brown, 1971), perhaps European white birch becomes physiologically over-mature at 15 or 20 years on these poor Sites. Since bronze birch borer normally is associated with mature trees (Balch and Prebble, 1940), the heavy attack on physiologi- cally mature urban birches would be considered normal. Class 4 trees clearly exhibit symptoms of dieback. Usually sever- al branches in the upper crown are completely dead. Internally, small necrotic sections appear in the cambium throughout the bole. Much of the cambium is in a moribund state. Class 4 trees have a greater larval density and gallery length than class 3 trees. Class 4 trees exhibited a still lower percentage of sample points without larvae. Only 25.7 percent of sample points were free of larvae. Points with the highest larval density were located below 1.5 m on the bole. While total tree height was similar to trees in the previous classes, living cambium and phloem tissue in the bole ceased to exist beyond 2.5 to 4.5 m, depending on the tree. Class 4 trees had 14.3 percent of the bole sample points free of galleries. All sample points between 0 and 1.5 m in height contained galleries. Class 4 trees do not appear more susceptible to bronze birch borer than class 3. In fact, branches actually contain fewer larvae 32 than branches in class 3. Class 4 trees show signs common to any other advanced dieback. This continual dieback is due to inner bark girdling by the bronze birch borer. The initial stress which caused the begin- ning stages of decline has now been replaced by the borer as a stress- ing agent. In the absences of the borer it is unlikely that decline would continue beyond symptoms observed on trees just becoming class 3. This same type of stress-host change-organism attack relationship has been documented for several other hardwood species (Houston, 1973). Class 5 trees contained less than half living crown. Internally large sections of the cambium-phloem zone were dead. Class 5 exhibited the highest larval density and gallery length. Class 5 boles differed greatly from those in class 3 and 4; 87.5 percent of the area sampled was free of larvae. Larvae were found only between 0 and 3 m. Above 3.5 m living cambium and phloem tissue did not exist. Class 5 boles differed from those in class 3 and 4 in that 30.4 percent of the sample points were free of galleries. Galleries were not concentrated at any particular height. As with class 4, the crowns of class 5 trees also showed a decrease in the average number of larva per sample point over the pre- vious class. The reduction was of less magnitude, however. Average gallery length per crown sample point was the lowest for class 5 trees. Class 5 is the last stage before death. The majority of branches are dead, the remainder in a state of low vigor. The larvae are now concentrated in the few sections of inner bark that remain alive. The girdling of these live areas is soon completed and the tree dies. 33 Branch Influences on Larval Density and Gallery Length Branches were sampled using several approaches. All branches from class 3, 4 and 5 were grouped for analysis of larvae and gallery density with respect to vigor of branch, direction of branch and distance out on branch from the main bole. Branches from class 1 and 2 were excluded since they did not contain larvae or galleries. The majority of points sampled of classes 3, 4 and 5 were vigor grade 1 branches. Sample points on vigor grade 2 branches were second- most numerous followed by vigor grade 3 and 4 respectively. Larvae were found in greatest numbers in vigor grade 2 branches (Figure 9). Forty- five percent of the 86 larvae were located in vigor grade 2 branches. Three points were sampled in grade 2 branches that contained four larvae each. Vigor grade 1 branches had the next highest total with 21 larvae. Vigor grade 3 and 4 branches were quite close at 15 and 11 larvae respectively. No sample points in vigor grades 1, 3 or 4 contained over two larvae. There was a Significant relationship (P>0.10) between larval numbers and location on the branch with respect to the distance from the bole (Figure 10). Larvae occurred in greatest numbers at the point of attachment to the bole. Forty-one larvae were located at this point. As the distance from the bole increased, larval numbers decreased. At 50 cm from the bole only 22 larvae were found. These numbers continued to decrease until at 250 cm from the bole zero larvae were found. The location of branches with respect to direction was tabulated to deter- mine if larvae were more prevalent in any direction. This was not feund to be so. In each of the four quadrants, 80 to 89 percent of the sample points remained clear of larvae. average number of larvae/branch sample Figure 9. average number of larvae/branch sample Figure 10. 34 0.5- 0 4_ n=29O 0 3- 1" 0.2- ”—1 0.1- 0.0- f _ f 1 2 3 4 vigor grade Average number of Agrilus anxius larvae per sample point in Eur0pean white birch branches of each vigor grade. "T n=290 O O O O O O m 1 .0- [—1 ['1 0 50 100 150 200 250 distance from bole (cm) Average number of Agrilus anxius larvae per sample point at 50 cm intervals along European white birch branches. 35 Gallery density was also examined following the same approach. Branch vigor was found not to be a major influence on gallery length. Roughly one-half of the points sampled in every vigor grade was free of any galleries. Gallery length and distance from the bole were quite closely related (P>0.02) (Table 7). The greatest gallery length was located at the crotch of the branch. The length decreased with the distance from the bole. Larvae and galleries were not concentrated at any particular height within the crowns of trees in any class. The majority of crown sampling points were free of both larvae and galleries in all trees. The percentage changed with respect to class, however. Class 3 had the lowest percentage of sample points clear of larvae and galleries while class 5 had the highest, though the difference was not statistically significant. Adult Emergence Trees selected for the emergence hold study were examined in mid- May 1979. At this time a tally was made of old emergence holds on the lower bole. Only two trees had emergence holes from previous seasons. The numbers were quite small in both cases, two for one tree and one for the other. Both trees were class 5's the previous season and produced foliage on a few branches in the spring. The trees expired by mid-July 1979. The first emergence was noted on June 6 on a class 5 tree. Emer- gence peaked on June 10 with a total of 69 adults emerging within a two day time period. Thirty-six of these were produced from a single tree. Emergence declined until June 25 when the last new emergence hold was 36 Table 7. Number of sample points in each Agrilus anxius gallery length class at 50 cm intervals along European white birch branches. distance from bole (cm) gallery length (cm) 0 50 100 150 200 250 0.0 33 50 38 21 15 4 0.0-25.0 31 27 18 10 3 1 25.1-50.8 18 6 2 2 0 0 50.9-76.2 5 0 2 1 0 0 76.2 1 l l 0 0 0 noted. Trees were checked until July 30, however, no new emergence holes were found. A difference in the number of emergence holes in the one meter strip 50 cm from the base of the bole was noted between class 5 trees and trees of the remaining four classes (Table 8). One hundred and Sixty-five new emergence holes were counted on the bark area of class 5 trees surveyed; only two were noted on the class 4 trees. No emergence holes were found for class 1, 2 and 3. No emergence holes would be expected as a class 1 or 2 tree since few larvae are ever present in the bole. However, for class 3 and 4 trees large numbers of larvae are located throughout the lower bole. It was assumed that adults Should be emerging from this general area, but this is not the case. Four of the trees which were in class 5 at mid-May were dead by mid-July; the remaining two declined further, the living crown consist- ing of foliage on a few branches. The trees which produced the most 37 Table 8. Average number of Agrilus anxius emergence holes per 100 cm2 (istd. dev.). Data taken between 0.5 and 1.5 m on European white birch boles. Vigor class emergence holes/cm2 n bark area examined (cmz) l 0.00:0.00 6 24,239 2 0.00:0.00 6 29.463 3 0.00:0.00 6 27,154 4 0.00:0.00 6 31,450 5 0.60:0.35 6 30,160 larvae were class 5 trees the previous August, and leafed out normally in 1979. They were dead by mid-summer. All trees which were class 4 in the spring of 1979 were still class 4 at the end of July. All but two were 4's the previous August. Trees which were class 3 during spring of 1979 were still class 3 at the end of the summer with the exception of one tree which had dropped to a class 4. Trees in classes 1 and 2 exhibited several switches between the two classes. Only the boles of class 5 trees near death exhibit large numbers of emerging adult bronze birch borers. Balch (1946) stated that larvae need living cambium and phloem tissue to feed on, but adults can only emerge from dead wood. Such conditions would, of course, best occur in class 5 trees. While many necrotic areas are found in the inner bark of class 5 trees, living tissue remains. If the tree then dies before the following Spring, large numbers of adults can emerge from the dead bark. 38 While small numbers of adults can emerge from the crown of class 3, 4 and 5 trees, only class 5 trees exhibit Significant emergence from the lower portion bole. A few adults may emerge from the necrotic spots along the bole of class 4 trees, however. Since class 5 trees have the highest larval density and also allow adult emergence from any portion of the tree, they are the greatest source of adult beetles in the spring. Perhaps removing claSS 5 trees from neighborhoods, might over time, reduce the adult borer population. Whether adults could move in from adjacent areas is unknown Since studies on the flying distance have not been published (Carlson and Knight, 1968). For a sanitation measure like this to be effective as large an area as possible Should be included in the cut. Though these techniques have been known for over half a century (Kotinsky, 1921), it is diffi- cult to put into practice because the majority of homeowners refuse to remove a birch until it is completely dead. Control Considerations Control of the bronze birch borer has centered around the belief that attack begins at the periphery of the crown. Control, therefore, has consisted of removal of the dying upper limbs in the hopes of reducing the borer infestation. This form of control has some merit. Though a dying tree has larvae throughout the bole, many of these larvae are not capable of reaching the adult stage due to the vigor of the tree. Adult emergence will only occur from cambium-phloem tissue which has died during that season (Balch, 1946). This condition first arises near the tip of the crown. Therefore, removal of the dying branches furthest from the ground may be effective in reducing the 39 number of adults emerging Since adults do not yet emerge from the basal portion of the bole. The fact that adult emergence only occurs from recently dead inner bark may be responsible for the confusion over the location of borer attack. Birch trees moderately girdled by the larvae begin dying at the extremities. This means that while the larvae are Spread throughout the bole and crown, adults will only be able to emerge from the dead inner bark at the t0p of the tree. Anyone observing a class 3 or 4 birch would only find emergence holes near the top of the crown, hence may incorrectly conclude that the infestation in concentrated in that area. While pruning may not be effective in reducing the larval popula- tion of a tree, pruning can be useful since it can reduce the number of emerging adults. Pruning would involve the removal of low vigor limbs to reduce the number of Sites for adult emergence. Normal pruning is performed in the early Spring to permit quicker healing of the wound. For species such as birch and maple which bleed easily in the spring, many nurserymen recommend pruning in late Spring or early summer. This practice may have an adverse effect on control since adult borers are attracted to fresh wounds for the purpose of ovipositing (Barter, 1957). If this management approach is used it would be advisable to include as many trees as possible. If pruning is used on a single tree, the usefulness is much reduced as the adult beetles can fly from nearby infested trees. A community-wide approach would prove more beneficial. While pruning is sometimes used for control, chemicals still pro- vide the major defense against the bronze birch borer (Smith and Barter, 40 1951; Williams and Neiswander, 1959; Appleby et al., 1973). However, time and placement of application is critical for successful control. On the two stems selected for borer chemical control the Spray appeared to reduce the number of larvae and gallery density in the lower 4 m of the bole. Above this point larvae numbers and gallery density increased to that expected for class 3 and 4 trees. Larval numbers and gallery density were reduced throughout the lower crown to a height of 5 m above the ground. Therefore, spraying may be viewed as a means of reducing the number of larvae in the lower sections of the bole and crown. Most homeowners do not have Sprayers with sufficient pressure to reach the upper portions of a mature birch. Consequently, larvae will be able to develop in the upper portions of the bole and crown. Since the majority of the larvae in an unsprayed tree are located in the lower bole, control with chemicals is still warranted as the lower bole can be covered adequately by Spraying. Perhaps chemical control should be applied only on the lower 4 m of the main stem rather than having the homeowner attempt to spray the total crown. This approach may reduce the homeowner's exposure to potentially harmful chemicals while still providing adequate control of the bronze birch borer. Progression of Borer Attack A major point of disagreement between investigators is the loca- tion of the first successful bronze birch borer attack on the birch. The majority have concluded that the attack begins in the upper crown. I disagree with this conclusion based on information obtained in this study. Birch trees follow a progression from class 1 to 5 and even- tually death. Therefore, assuming each class represents a stage in the 41 life of a European white birth, the following progression can be con- structed. Trees begin in class 1 or 2, moving between the two classes as environmental stresses permit. The tree may be lightly attacked, with the first successful larval penetration beginning on the main bole rather than the crown. Larvae are unable to develop into adults due to the vigor of the tree, however. At some point, physiological changes occur within the birch tree. These changes may be induced by environ- mental stresses or possibly repeated unsuccessful attack from the borer. At this time dieback begins in the upper crown and the tree enters class 3. A class 3 tree contains larvae throughout the bole and crown. The larvae are not significantly concentrated at any particular height within the bole. Larvae in branches are equally distributed with respect to neight. The following Spring adult borers emerge from inner bark which has died over the winter. Since the tree is dying back from the extremities the majority of freshly killed phloem is in the upper crown, hence this is the Site of adult borer emergence. Within several years the succession of girdles due to galleries results in additional dieback of the crown. The tree now enters class 4. AS living cambium and phloem in the crown decreases the number of larvae in the branches also decreases. Within the bole the number of larvae increase further stressing the tree by additional girdling. Internally, the inner bark of the upper third of the bole is dead. The remainder of the bole contains small areas of dead inner bark. This increase in recently dead phloem increases the potential adult borer spring emergence. Though adult emergence is still concentrated in the 42 crown, an occasional emergence will occur from the necrotic tissue in the bole. Finally, the tree has less than half the crown alive. The upper half of the bole is dead with the basal portion containing many areas of dead cambium. These areas range from large spots several centimeters in diameter to bands ten or more centimeters wide. The larval popula- tion continues to decrease in the crown while increasing in the lower bole. Due to the large amount of cambium which dies during the winter, adult beetle emergence peaks. Within a year or two the tree is com- pletely dead. LITERATURE CITED LITERATURE CITED Anderson, R. F. 1944. The relation between host condition and attacks by the bronzed birch borer. J. Econ. Ent. 37:588-96. Appleby, J. E., R. Randell and S. Rachesky. 1973. Chemical control of the bronze birch borer. J. Econ. Ent. 66:258-9. Balch, R. E. and J. S. Prebble. 1940. The bronze birch borer and its relation to the dying birch in New Brunswick forests. Forestry Chron. 16:179-201. Balch, R. E. 1946. The problem of the dying birch in eastern Canada. Pulp and Paper Magazine 47:104-7. Baldwin, H. I. 1934. Some physiological effects of girdling northern hardwoods. Bull. Torrey Bot Club 61:249-57. Barter, G. W. and W. J. Brown. 1949. On the identity of A rilus anxius Gory and some allied Species (Coleoptera Buprestidae). Can. Entomol. 81:240-5. Barter, G. W. 1953. The variation within injury classes from year to year in sample trees. Symposium on birch dieback, Part 11. Forest Biology Division, Can. Dept of Agr. pp. 150-155. Barter, G. W. 1957. Studies of the bronze birch borer, Agrilus anxius Gory, in New Brunswick. Can. Entomol. 97:12-36. Britton, W. E. 1923. 22nd Report of the state entomologist for 1922. Conn. Agr. Sta. Bull. No. 247 pp. 269-381. Brown, C. L. 1971. Growth and Form, pgs. 125-65. M. H. Zimmermann nad C. L. Brown. Trees Structure and Function. New York: Springer VerLag, New York Inc. 336 pp. Carlson, R. W. and F. B. Knight. 1968. Biology. taxonomy and evolution for four sympatric Agrilus beetles (Coleoptera: buprestidae). Contrib. Amer. Entomol. Instit. 4(3):l-105. Chamberlain, J. 1900. A new insect pest. Scientific American. 82:42. Chittenden, F. H. 1898. 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APPENDICES 47 campgupz .mosoxc eager: mmc< Am>c=m we an: .P xmucmcqa< Ifil”.lHIn“l£1-ln\v| ’. 52m 553 .mm 1%,, _/ yfiimhhfififldflfl/ 0 <0 1 I o he< I .non-none???“o”one“cocoon.no.ooooooccooooococococooo- ecu-nonononononunuonooaa v. 01708 SOWSXO me are meme... mm”mmmmmmmmmmmmmH mmmmm. wwwmmws . . . . .. .. ..........owm ammop agatu use we open . .mmpzu .mmappom um :wmucou ___um “was -mco cusp uses no: +mcm>wm mo sounwwo cwwcm .oNPm pesto: :zotu use .mmmW_oc co .cm>wzo; .zumcmp cw .czocu we» we now we» we acmam_m=ou ecu u_o>mu czotu on» we E F :_ masocnta m .xomnwwv uaogmzotgu mcwmmuFm Ffisu crato och .owcu cpuc-wco ems» ego: umump no we xomnmmn zucmtn ~_msm ucm mes» mo uwzuuua notmuumom m30tomw> .»;u_mw; < m mm exocu cotwm muwgz :moaocam .N x_u:onn< 49 Appendix 3. Branch Vigor Classification 1. Healthy green foliage 2. Several brown, wilting throughout the branch. leaves at tip of branch. 3. Several twigs bare of 4. Majority of twigs bare, foliage, many brown only a few green leaves leaves. remain. NST 111111 HICHIG T WW” 1 312931 EU NIV. LIBRARIES WWWWMWWNH 00632300 1