A Technique to Ar y Infest 

Fbrest Service Beech Bark with the Beech Scale, 

Mort heastern Forest 

Experiment Station 

C~~~~OCOCCUS fagisuga Lindinger) 

Research 

Paper N E-507 

1982 

David R. Houston 
The Author 

David R. Houston obtained a 

B.S. degree in forestry from the University of Massachusetts, a M.F. degree in forest pathology from Yale 

University, and a Ph.D, in plant pathology from the University of Wisconsin. Dr. Houston has been employed 

by the USDA Forest Service since 

1961. He is now principal plant pathologist at the Northeastern Forest 

Experiment Stations's Forest Insect 

and Disease Laboratory in Hamden, 

Connecticut, and is project leader of 

a team conducting research on dieback and decline diseases in the 

Northeast. From May 1975 to May 

1976, Dr. Houston studied beech 

bark disease in the United Kingdom 

as an exchange scientist with the 

British Forestry Commission in 

Farnham, Surrey, English. 

Manuscript received for 

publication 15 May 1981 

Abstract 

Beech bark disease is initiated 

when bark of beech trees (Fagus 

spp.) is attacked by the beech scale, 

Cryptococcus fagisuga Lindinger. 

The effects of the insect predispose 

tissues to bark cankering fungi of 

the genus Nectria. Critical studies 

of insect-fungus-host interactions 

had been stymied by the inability to 

artificially infest beech with the initiating agent. This paper describes a 

technique using covers of polyurethane foam to initiate or enhance 

the development of local infestations of the beech scale on both 

seedlings and large trees. 
Beech bark disease is a cornplex disease of American (Fagus 

grandifolia) and European (Fagus 

sylvatica) beech trees and is initiated by the beech scale, Cryptococcus fagisuga (Lindinger) (Ehrlich 

1 934). 

The beech scale is a tiny, wingless sucking insect that infests the 

bark of beech trees. Reproduction is 

parthenogenetic, and eggs are laid 

in June or July. The 0.5-mm-long 

eggs hatch from mid-August 

through September, the emerging 

crawlers locate feeding niches, 

usually within a few centimeters of 

where they hatched, insert their 

feeding stylets, molt, and overwinter 

as second-stage nymphs (Ehrlich 

1934). Feeding resumes in spring, 

and in June the scales molt once 

more to become adults. In this 

stage, they secrete most of the conspicuous white, wool-like wax that 

covers their bodies. Feeding by the 

scale renders the bark susceptible 

to several bark canker fungi of the 

genus Nectria (Ehrlich 1934, Parker 

1974, Lohman and Watson 1943). Because the full expression of the disease requires the effects of both 

agents, studies of host-disease interactions require manipulating 

each of them. The fungi are relatively easy to work with and can be introduced to bark tissues using 

standard inoculation techniques 

(Ehrlich 1934, Parker 1974a, Perrin 

1979). Manipulation of the scale has 

proven more difficult. 

European beech trees were infested generally with beech scale by 

affixing heavily infested bark segments to tree trunks with wire 

(Houston et al. 1979). However, several years were required for significant population levels to develop. 

This paper describes a technique to initiate or enhance the rapid development of local infestations 

of the beech scale on both seedlings and large trees. 
Background 

In June 1976, enclosures designed to trap scale parasites were 

placed over colonies of 6, fagisuga 

on beech trees in Maine, Vermont, 

and Pennsylvania.' The frames of 

the 30- by 60-cm rectangular enclosures were 5- by 5-cm polyurethane 

foam strips glued at the corners. 

Covers of nylon mesh screening, 44 

strands per inch (17.3fcm), glued to 

the foam framework completed the 

enclosures. The traps were oriented 

in a vertical position with 4-cm-wide 

wooden laths positioned over the 

side frames. The traps were held 

snugly to the trees with ropes (Fig. 

1). The foam frame conformed to 

bark irregularities and prevented the 

migration of insects into or out of 

the trap enclosure. 

No parasites were detected in 

subsequent examinations, But, 1 

year after installation colonies of C. 

fagisuga had developed in abundance beneath the foam side and 

top frames (Fig. 2). This unexpected 

and fortunate observation triggered 

the following series of studies on 

the use of foam covers to artificially 

infest beech trees with the beech 

scale. 

The Studies 

Study 1.-Infestation of Seedlings 

with C. fagisuga 

Experimenl" 7. In September 

1977, strips cut from a trap frame 

that bore large numbers of scale 

eggs and crawlers were used to inoculate 15-month-old beech seedlings in the greenhouse, The 1.3- by 

1.3- by 5-cm foam strips were secured in place, eggs toward the 

stem, with a copper wire wrapped 

Figure 1.-A nylon screen-covered enciosure with foam framework placed over 

colonies of C. fagc'suga. 

Figure 2.-Colonies of 6. fagisuga (arrow) developed under the Foam framework of the enclosure. 

' A cooperative exploratory study with 

W. E. Wallner, principal entomologist, 

Hamden, CT. 
Figure 3.-Strips of the foam frames 

bearing eggs of C, fagisuga held in place 

on a young beech seedling. 

Figure 4.-Colonies of 6, fagisuga (ar- row) developed on the seedling beneath 

the foam strip. Note the distortion of the 

stem caused by scale feeding. 

spirally around the stem (Fig. 3). 

Some strips were also wrapped with 

Parafilmm2 After 42 months, the coverings were removed and the stems 

examined. 

Results. Successful infestation 

occurred in all but a few of the 30 

seedlings inoculated. "The eggs 

hatched, nymphs established themselves, overwintered, laid eggs, and 

The use of trade, firm, or corporaliot-: 

names in this oublication is for the information and cohvenience of the reader. 

Such use does not constitute an officiar 

endorsement or approval by the U.S, Department of Agriculture or the Forest 

Service of any product or service to the 

exclusion of others that may be suitabie, 

the new crawlers successfully colonized the bark tissues. In some instances, infestations were very 

heavy, and the young stems exhibited growth distortions (Fig. 4) similar 

to the ""dimpling" symptom common on some young European 

beech trees after heavy localized infestation (Parker 1974b). Wrapping 

with Parafilm did not enhance infestation. The success of this initial experiment using large and undetermined numbers of eggs prompted 

ano"ier experiment using small, discrete numbers of eggs. 

Experiment 2. In September 

1979, 40 beech seedlings grown for 

4 seasons in the greenhouse were 

inoculated with either 1, 2, 4, 5, 10, 

or 50 eggs at each of four places 

chosen to include bark tissues 2, 3, 

and 4 seasons old. Usually, two inoculations per seedling were made 

on the oldest tissue. Eleven seedlings planted in 1979 and representing 1-year-old tissue also were inoculated once with either 1, 4, or 50 

ews. 

For this and other artificial infestation experiments, eggs were 

collected and prepared for use as 

follows: in late June to mid-July 

heavily infested bark segments were 

removed from naturally infested 

trees or from beneath the frames of 
Figure 5.- Heavy infestation of beech 

scale beneath foam frames after 3 years. The white is wax secreted by the insect. 

traps installed 3 years earlier (Fig. 

5). The segments of colonized bark 

were placed in covered plastic cups, 

kept cool in ice chests, and brought 

to the laboratory. Eggs were separated from wax and bark debris by 

gently teasing and tapping masses 

of egg-laden "wool" and bark fragments over a nylon mesh screen. 

The eggs were sieved onto the inverted covers of small plastic cups 

in lots of 50 to 200 and stored in a 

dessicator over KOH (20 g 

KOH1100 g H20) at 83.8 percent RH 

at 40°C until used.3 

The eggs were carefully lifted 

from the covers with a moistened 

dissecting needle and pfaced on the 

Storage conditions recommended by 

Mr. D. Wainhouse, Forestry Commission, 

Farnham, England. 

Figure 6.-Greenhouse seedling inoculated at varioug points with specific numbers of C. fagisuga eggs. 

centers of fresh 1.3- by 1.3- by 5-cm 

polyurethane foam strips each 

dampened with a drop of sterile water. The strips were affixed to the 

seedlings with wire as in Experiment 1, and half also were wrapped 

with Parafilm (Fig. 6). The wrappings 

were removed and the seedlings 

were examined in June 1980. 

Results. Twenty-two of the 40 

seedlings were infested in June 

1980. Percentage of infestation increased as more eggs were used: 

No, seedlings 

No. of eggs inoculated 

1 6 

2 8 

4 7 

5 7 

10 7 

50 5 

All seedlings inoculated with 10 or 

50 eggs per point were infested, 

whereas only one of the seedlings 

inoculated with one egg per point 

was infested. However, among infested seedlings all inoculations 

were not successful. The relative 

frequency of the successful infestation among infested seedlings 

ranged from about 2 percent for 

1-egg inoculations to 39 percent for 

50-egg inoculations. 

No. seedlings 

infested 

I 

2 

3 

4 

7 

5 

Percentage of 

infestation 

16.7 

25 

43 

57 

1 00 

100 
Figure 7,-Foam cover in piace over natural populations of beech scale. Infestation success was not inFigure 8.-Population of beech scale increased markedly on bark under 

foam cover (dark area) 1 year after being installed. 

fluenced by age of bark; tissues 2-, 

3-, and 4-seasons-old were equally 

susceptible-25.6, 26.8 and 29.3 percent, respectively. And, 4 of the 11 

l-season-old seedlings inoculated 

became infested: three inoculated 

with 50 eggs and one inoculated 

with four eggs. Wrapping with Parafilm was detrimental; fewer seedlings were infested and fewer insects developed with this treatment. 

Study 2.-Enhancement of Natural 

Populations on Larger Forest Trees 

Experiment 3. The development 

of scale beneath the foam trap 

frames prompted a study to see if 

foam covers could be used to increase naturally existing populations on large forest trees. In August 1978, 10- by 10- by 5-cm polyurethane foam squares were placed 

on large, lightly infested beech 

trees growing in central Vermont. 

The foam blocks held in place with 

10- by 10- by 0.6-cm covers of tempered Ma~onite,~ were secured to 

the tree with rope (Fig. 7). At least 

four foam squares, usually on four 

different sides of the tree, were held 

by each rope. In September 1979, 

the blocks were removed, and the 

populations of beech scale beneath 

them were examined. 

Results. In most instances, 

more insects had developed beneath the foam covers than on the 

bark adjacent to them (Fig. 8). Insects were absent beneath some 

covers located on the lower sides .of 

leaning trees, often in the runnels 

where water ran down the trunks. 

These covers were often wet and 

darkly discolored. 

The results of Experiment 3 and 

Study 1 set the stage for trials to introduce insects to specific locations on previously uninfested forest trees. 

Study 3.-Artificial Infestation of 

Large Forest Trees with C. fagisuga 

Experiment 4. Foam-Masonite 

covers identical to those used in Experiment 3 were placed on 28 trees 

growing in southcentral Connecticut 
Figure 9.-Frequency distribution in May 1980 of C. fagisuga colonies established under foam covers inoculated with approximately 200 to 300 

eggs in July to August 1979. 

Number of Colonies of C, fagisuga 

in July and August of 1979. The four with a stiff-bristled brush. In May Although results suggest that more 

covers per tree were arranged so 1980, the covers were removed and scales developed at the lower levels 

that two were located on the north the individual colonies present were and on the north sides of the trees, 

and south sides of the tree-one at counted. the variable number of eggs used 

1 m and another at 2 m above initially precluded statistical analvground. For two of the trees, an additional cover was placed at each 

height and randomly assigned to 

the north or south side. Notches in 

the Masonite covers facilitated securing the two covers at each 

height with one rope. Eggs coliected from trees in Vermont and New 

York were prepared as described in 

Experiment 2. Approximately 280 to 

300 eggs were brushed onto the 

centers of moistened foam blocks 

Results. The frequency distribution of colonies beneath covers is 

given in Figure 9. Seven covers 

were devoid of insects. As in Experiment 3, these were located in runnels on the tree where stem flow 

kept them too wet for insects to develop. The average number of colonies that developed beneath infested covers at different heights and 

aspects was: 

*. 

sis. 

Experiment 5. Ten trees growing in southcentral Connecticut 

were inoculated in July 1979 by using a foam cover of different design. 

Cages 25 cm square were constructed similar to the parasite trap enclosures described earlier. A 5- by 5- by 

5-cm block of foam was cemented 

to the center of the nylon screen 

cover. Approximately 200 to 400 

and then placed against the trunks. A eggs were brushed onto the moisfew trees bearing very sparse nat- Height tened inner surface of the small, 

ural populations of beech scale above North central block and the cages were 

were used, but insects were re- ground side side held securely against the tree. Presmoved before inoculation by scrub- 1 m 75 59 sure exerted by the screening held 

bing the bark surfaces vigorously 2 m 69 51 the block against the trunk. The 
Figure 40.-Average number of colonies of C. fagisuga developing in enclosures on 20 trees arranged by groups of 65susceptibility". 

Trees 

cages were gtaced at three heights 

an each tree: miderswn, below the 

crown, and at breast height. Laths 

were placed over the sides of the 

foam frame, and each cage was secured snugly against the tree with 

ropes at the top and bottom. In May 

4980, the cages were carefully removed, the insects counted, and the 

cages f hen replaced. 

Results. In general, infestations 

aeveloped readily in the enclosures, 

and no differences in population 

levels were detected that were related to height on the stem, aspect of 

the enclosures, or source of eggs. 

Two cages, one at the highest level 

and one at "ie lowest, were devoid 

of insects. Both of these were in 

runnels and were wet and darkly 

stained. In many instances, the 

populations were not confined to 

bark beneath the smail, central 

inoculation blocks. Many insects 

were located beneath the very inner 

margins of the foam frames. The insects apparently hatched and migrated from the relatively loosely 

held block to the nearby frames. 

Results suggest that different 

trees varied in their susceptibility or 

suitability for colonization (Fig. 10). 

The 10 trees can be separated into 

three groups based on the average 

number of colonies per enclosure: 

for the four trees in the lowest 

group-25.2, for the next group of 

three trees-67.4, and for the three 

trees in the highest group-198. 

Discussion 

Critical study of the host-insect-fungus interaction of the beech 

bark disease complex had been stymied by the inability to develop 

populations of the scale "on demand". This difficulty has been 

overcome by the successful use of 

foam covers to enhance naturally 

existing populations on large trees 

and to establish new populations on 

both large and small trees. The 

foam technique ensures the availability of a continuous and reliable 

supply of insect-affected tissues. 

The relatively high rate at which 

seedlings were artificially infested, 
even when relatively few eggs were 

used, is encouraging. This indicates 

that very young tissues can be used 

for critical studies of insect-host interactions, and also suggests that 

screening For resistance to scale attack can perhaps can be accomplished at an early age. 

Now large forest trees can be 

challenged with the insect to confirm their apparent resistance. In addition, studies can be conducted to 

determine the influence of host predisposition on susceptibility to 

scale attack and to determine the 

effects of specific infestation densities and durations on host-bark 

changes and susceptibility to 

Nectria. Also, studies of biological 

control of both the scale and Nectria can proceed now that specific 

levels of infestation can be 

achieved. 

The success of this technique 

can be ascribed to the physical protection afforded the scale from its 

predators and from such adverse environmental factors as rain, wind, 

and alternate freezing and thawing. 

In addition, the snug-fitting foam 

covers serve to prevent dispersion 

of the crawlers. 

Foam covers also exclude light 

from the photosynthetically active 

bark tissues. In nature, populations 

of scale often develop first beneath 

'%overs" of lichens and mosses, beneath large branches, or in other 

shaded refuges such as bark fissures or callus margins of wounds. 

And in many sites, populations are 

highest on-sometimes restricted 

to-the north sides of trees. Whether the scale succeeds beneath covers because it is protected or because the bark is rendered susceptible by the physiological effects of 

shade, or both, is not yet known. 

Studies are underway to clarify 

these relationships because they 

have a bearing on approaches to 

control. 

Literature Cited 

Ehrlich, J. The beech bark disease-a 

Nectria disease of Fagus following 

Cryptococcras fagi (Baer.). Can. J. 

Res. 10:593-692; 1934. 

Houston, D. R., Parker, E. J.; Perrin, 

R.; Lang, K. L. Beech bark disease: 

A comparison of the disease in 

North America, Great Britain, 

France and Germany. Eur. J. For. 

Pathol. 9:199-211; 1979. 

Lohman, M. L.; Watson, A. J. Identity and host relations of Nectria 

species associated with diseases 

of hardwoods in the eastern 

States. Lloydia 6:77-108; 1943. 

Parker, E. J. Beech bark disease. 

Guilford, Surrey, U. K.: Univ. of Surrey; 1974a. 161 p. Ph.D. Thesis. 

Parker, E. J. Beech bark disease. 

1974b; 15 p. For. Comm. For. Rec. 

No. 96. 

Perrin, R. Contribution a la 

connaissance de I'etiologie de la 

maladie de I'ecorce du hgtre. I. Etat 

sanitaire des h6traies frangaisss 

R6le de Nectria coccinea (Pers ex 

Fries) Fries. Eur. J. For. Pathol. 

9: 148- 166; 1979. 
Houston, David R. A technique to artificially infest beech bark 

with the beech scale, Cryptococcus fagisuga (Lindinger). 

Braomal19 PA: Northeast. For. Exp. Stn.; 1982; USDA For. 

Serv. Res. Pap. NE-507. 8 p. 

Beech bark disease is initiated when bark of beech trees 

(Fagus spp.) is attacked by the beech scale, Cryptococcus 

fagisuga Lindinger. The effects of the insect predispose tissues lo bark cankering fungi of the genus Nectria. Critical 

studies of insect-fungus-host interactions had been stymied 

by the inability to artificially infest beech with the initiating 

agent This paper describes a technique using covers of polyurethane foam to initiate or enhance the development of local 

infestations of the beech scale on both seedlings and large 

QDC "i82.4, 416.4, 443, 453 

Keywords: Beech bark disease; Fagus grandifolia 
Headquaden of the Northeastern Forest Experiment Station are in 

Broomall, Pa, Field labratories are maintained at: 

@ Amhemt, Massachusetts, in emperation with the University of 

Muaehu~tts. 

@ Bema, Kentucky, in cmpration with krea College. 

Burlington, Vermont, in cooperation with the University of 

Vermont , 

Delaware, OGo. 

Durham, New Hampshire, in cooperation with the University of 

New Hanrpshire. 

0 Hmden, Connecticut, in coowration with Yale University. 

@ Morgantown, West Virginia, in cooperation with West Virginia 

University, Morgmtown. 

Orono, Maine, in enopesation with the University of Maine, 

Orono. 

@ Pamns, West Virginia. 

@ hineeton, West Virginia, 

@ Syracuse, New York, in cooperation with the State University of 

New York College of Environmental Sciences and firestry at 

Syracuse University, Syracuse. 

0 University Park, Pennsylvania, in emperation with the 

Pennsylvania State University. 

@ Warren, Pennsylvania,