(excerpt)
Scotch pine (Pinus sylvestris L.), a forest tree introduced from Eurasia, is commonly planted for Christmas tree and timber use in northeastern United States. In this country it has numerous insect enemies. Among the most important are European pine shoot moth, Rhyacionia buoliana (Schiffermiieller); pine root collar weevil, Hylobius radicis Buchanan;,European pine sawfly, Neodiprion sertifer (Geoffroy); and eastern white-pine shoot borer, Eucosma gloriola Heinrich. Previous studies (Wright et al., 1967; Wright and Wilson, 1972; Steiner, 1974) have revealed large genetic differences in resistance to some of these pests.
Another destructive pest is the Zimmerman pine moth, Dioryctria zimmermani (Grote). In 1968 this insect, native to the United States, was found attacking trees in a Scotch pine provenance test in southwestern Michigan. The attack rate was heavy and by 1973 it was obvious that some rams or varieties were attacked more heavily than others. This is a report on those differences

Bright, John N

Wilson, Louis F

Wright, Jonathan W

English

Valparaiso University

The Great Lakes Entomologist Volume 8 Number 4 - Winter 1975 Number 4 - Winter 1975 Article 8 December 1975 Genetic Variation in Resistance of Scotch Pine to Zimmerman Pine Moth Jonathan W. Wright Louis F. Wilson USDA Forest Service John N. Bright Michigan State University Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Wright, Jonathan W.; Wilson, Louis F.; and Bright, John N. 1975. "Genetic Variation in Resistance of Scotch Pine to Zimmerman Pine Moth," The Great Lakes Entomologist, vol 8 (4) Available at: https://scholar.valpo.edu/tgle/vol8/iss4/8 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. THE GREAT LAKES ENTOMOLOGIST GENETIC VARIATION I N  RESISTANCE OF SCOTCH PlNE TO ZIMMERMAN PlNE MOTH1 Jonathan W. Wright, Louis F. Wilson and John N. ~ r i ~ h t ~  Scotch pine (Pinus sylvestris L.), a forest tree introduced from Eurasia, is commonly planted for Christmas tree and timber use in northeastern United States. In this country it has numerous insect enemies. Among the most important are European pine shoot moth, Rhyacionia buoliana (Schiffermiieller); pine root collar weevil, Hylobius radicis Buchanan;,European pine sawfly, Neodiprion sertifer (Geoffroy); and eastern white-pine shoot borer, Eucosma gloriola Heinrich. Previous studies (Wright et  al., 1967; Wright and Wilson, 1972; Steiner, 1974) have revealed large genetic differences in resistance to some of these pests. Another destructive pest is the Zimmerman pine moth, Dioryctria zimmermani (Grote). In 1968 this insect, native to the United States, was found attacking trees in a Scotch pine provenance test in southwestern Michigan. The attack rate was heavy and by 1973 it was obvious that some rams or varieties were attacked more heavily than others. This is a report on those differences. THE INSECT DAMAGE Zimmerman pine moth larvae injure several native and exotic species of pine, but prefer open-grown, sapling-size Scotch pine. The larvae may attack lateral shoot tips, the base of the terminal shoot, or the main stem. After the adult females lay their eggs on the bark in late summer, the larvae hatch in a few days but do not start feeding until the following spring. In May or June of the next year they tunnel through the bark into the cambial region where they feed on wood and adjacent cambium. The injured tree exudes pitch or oleoresin which becomes coagulated and mixed with frass. This material accumulates outside the entrance holes. These pitch accumulations may be 1-3 inches in diameter and are the most visible signs of attack. An injured lateral or terminal shoot usually dies rapidly and ultimately falls off. Many attacks are along the main stem, a t  the bases of branches (Fig. 1). An injured branch may die, or it may become weakened and break off during an ensuing storm. Lightly damaged trees may recover completely with little external evidence of injury. If several larvae feed at the same level on the main stem, the tree may be completely girdled. If this happens, the tree may die within 2-3 years. Or, only the portion above the girdle may die, in which case a lateral branch assumes the place of the leader and the tree becomes misshaped. Heavily damaged trees are of no value commercially and may be esthetically undesirable. TREE MATERIALS AND METHODS The host materials in this study are part of a Scotch pine geographic origin study started in 1959 as part of the NC-99 (formerly NC-51) regional project, "Improvement of Forest Trees Through Selection and Breeding". They include trees grown from seed collected in 108 natural stands located in all parts of the species' natural range in Europe and Asia (Fig. 2). Test plantations were established in various parts of Michigan and other 11he work reported here was supported in part by regional research funds from the U.S. Dept. of Agriculture allotted to Project NC-99, "Improvement of Forest Trees through Selection and Breeding". Approved for publication as Journal Article No 7196 of the Michigan Agticultural Experiment Station. 2Professor of Forestry, Associate Professor of Forestry, and Resident Forester of Dunbar Forest Experiment Station of Michigan State University, respectively. Dr. Wilson is also Principal Insect Ecologist and Project Leader, U.S.D.A. Forest Service, North Central Forest Experiment Station, headquartered at East Lansing, Michigan 48824. 1Wright et al.: Genetic Variation in Resistance of Scotch Pine to Zimmerman PinePublished by ValpoScholar, 1975THE GREAT LAKES ENTOMOLOGIST Vol. 8, No. 4 Fig. 1 .  Top of a young Scotch pine tree showing a branch (upper left) broken as the result of feeding by Zimmerman pine moth larvae and the pitch mass exudations (lower center) typical of larval feeding along the main stem. Such feeding along the main stem can result in branch breakage, death of the leader and subsequent stem deformity, or complete girdling and death of the entire tree. north central states. Information on growth rate, foliage color, minter hardiness, etc. in those plantations is contained in a paper by Wright e t  al. (1966). The Zimmerman pine moth outbreak occurred in plantation MSFGP 7-61 located on the Fred Russ Forest near Volinia, Cass County, southwestern .Mi-. The plantation occupies a level site with a sandy loam soil favorable for the growth of Scotch pine. The 108 seedlots were planted as 2-year-old seedlings in 1961. A randomized complete block design with 1 0  replicates was used Each replicate contains one 4-tree plot per seedlot. Original spacing was 8 X 8 ft. As of 1967, when the Zimmerman pine moth damage was first noticed, mortality in the plantation averaged 19%. Mean height in 1971 was 14.9 ft, about 10% lower than in the best of 12 similar plantations established in the state. The Russ Forest plantation was pruned during the summer of 1966, to one-third of total height. Other observers have noted that adult Zimmerman pine moth females are attracted to  fresh pitch. That appeared to  be true a t  the Russ Forest. During 1966 and 1967 a heavy infestation started to develop. By 1968, up to 50% of the trees of some seedlots had fresh pitch masses. By the next year, the attack rate had risen to 8 6 5  in some seedlots, and 2% of all trees had died as a result of girdling by the larvae. Xiany new attacks were visible again in 1970 although by then the infestation had begun to decline. By 1973, 49% of all trees had been attacked and 2m were dead as the result of girdling or were girdled so badly that they seemed destined to die. However, by 1973 the new attack rate had decreased to a low level and some trees which had been injured i-R 1968 or 1969 were completely recovered. Thus it appears that the infestation has run its course and that additional damage will be slight. Two other Scotch pine experimental plantations were established at the Russ Forest in 1961 and 1963. Thcy wcre left unpmned until the winter of 1974-75. They were 2The Great Lakes Entomologist, Vol. 8, No. 4 [1975], Art. 8https://scholar.valpo.edu/tgle/vol8/iss4/81975 THE GREAT LAKES ENTOMOLOGIST 233 Fig. 2. Natural range (shaded), points of seed collection for the Russ Forest plantatioq (black dots) and varieties of Scotch pine. The varieties mentioned in this paper are AQUitana, ARMena, CARpatica, HAGuenensis, HERcynica, IBErica, ILLyrica, LAPponica, PANnonica, POLonica, RIGensis, PHOdopaea, SCOtica, SUBillyrica and URAlensis. The Siberian range of var. MONgolica is not shown. Varieties PYRenaica (probably resistant), ROManica, ROSsica and VINdelica (all probably susceptible) were not represented in the plantation. situated one-fourth to one-half mile distant from plantation 7-61 and have contained some Zimmerman pine moth damage since 1967. However, the infestations have never reached epidemic proportions and less than 1% of the trees have died or been seriously deformed as the result of attack. Light infestations have also occurred in similar experimental plantations in other parts of the state. Plantation 7-61, last measured in 1971, has been measured several times previously for height, foliage color, cone production, and other characters. Zimmerman moth damage was assessed in 1968, 1969 and 1973. Each time number of trees attacked, number of trees dead, and number of trees with larvae<aused bole crooks larger than 2 inches were counted. Each set of measurement data was subjected to analysis of variance. VARIETAL DIFFERENCES IN SUSCEPTIBILITY Scotch pine is a genetically variable species. It has been subdivided by taxonomists into a number of geographic varieties (Ruby and Wright, in press), whose ranges are shown in Fig. 2. In Michigan plantations as a whole, differences among these varieties account for 75-9076 of the total genetic variation in traits such as growth rate, foliage color, and oleoresin composition. The same is true with regard to the data presented here. Differences among seedlots belonging to the same variety were not statistically significant although there were large and important differences among varieties. Thus, for conven- ience, the data are summarized in terms of the geographic varieties (Table 1). Fast growing timber-type varieties from England and central Europe suffered most. That is true no matter what the criterion-per cent attack, per cent mortality or per cent 3Wright et al.: Genetic Variation in Resistance of Scotch Pine to Zimmerman PinePublished by ValpoScholar, 1975234 THE GREAT LAKES ENTOMOLOGIST Vol. 8, No. 4 Table 1. Differences among Scotch pine varieties in growth rate, susceptibility to Zirnmer- man moth attack and larval-caused bole crooks. - Trees attacked by Zimmerman pine moth Variety lapponica septentrionulis rigensis mongolica uralensis polonica hercynica carpatica haguenensis pannonica 'E. ,4ngliaY scotica iberica aquitana subillyrica illvrica rhodopaea armena Trees dead Average Total trees or with height attacked Trees crooked Country of in 1971 dead boles origin* atage 11 1969 1973 1973 1973 feet per cent of trees liv-0 in 1966 Varieties from northern Eurasia FIN SWE SIB 7.5 11 15 7 8 SWE NOR 12.1 30 38 18 32 SWE LAT 14.3 46 4 7 22 4 0 SIB 12.9 50 55 39 46 SIB 14.4 58 6 1 31 49 Varieties from England and Central Europe POL 17.4 55 6 2 25 5 5 GER CZE 17.1 56 5 7 22  4 8 CZE 18.0 66 6 5 26 49 BELFRAGER 18.0 71 74 35 70 HUN 16.5 55 62 19 5 7 ENG 16.4 63 75 3 7 69 Varieties from Scotland, S. Europe and Asia Zfinor SCO 14.8 41 - ,  i7 26 49 SPA 14.3 43 33 3 18 FR A 16.1 33 29 I 2 2 - ITA 15.1 46 48 7 38 YUG 15.4 48 43 9 20 GRE 16.1 42 41 6 3 1 TUR GEO 14.7 37 29 3 18 *BELgium, CZEchoslovakia, ENGland, FINland, FR-ince, GEOrghn S.S.R., GERmany (East and West), GREece, HUNgary, lTAly, LATvian S.S.R., SORa-al--, F'OLand, Scotland, SlBeria, SPAin, SWEden, TURkey, YUGoslavia. crooked trees. In most of these varieties the attack rates were above 605 and more than 50% of the trees died or became severely misshaped. Next most heavily attacked were the slower growing varieties from Scotland or northern Eurasia. They are also regarded as timber variedes because in man!- h a t i o n s  they grow straight and have relatively f i e  branches. Houever, a l l  except var. lappunica suffered almost as much mortality as did those from central Europe and had a high proportion of misshaped trees. One northern variety, lapponica, was exceptional 11s narive r a n e  is close to the Arctic Circle and trees of this variety g o w  very slo\vl>-. AI the hekht of the epidemic they were only 2-4 ft tall, so small as to present littIe attraction to a flying insect. Probably because of its small size, this variety also has been relatively free from darnage by other types of insects at other tests plantations. The least damaged varieties were from southern Europe and Asia Minor. The) are characterized by moderate gowth rates and foliage which remains nearIy as e e n  dur iq  the winter as during the summer. Accordingly they are most in demand by Christmas tree growers. Among the southern seedlots, 3040% of the trees were attacked, but there 4The Great Lakes Entomologist, Vol. 8, No. 4 [1975], Art. 8https://scholar.valpo.edu/tgle/vol8/iss4/81975 THE GREAT LAKES ENTOMOLOGIST 235 were usually only one or two pitch masses per tree. Several trees with visible signs of attack in 1968 or 1969 had completely recovered by 1973. The mortality rate was low, averaging only 3-9%. For the southern varieties as a whole, only 23% experienced severe stem crooks or mortality, as compared with 32-70% for trees of more northern origin. If the plantation had been composed entirely of southern trees, the Zimmerman moth infestation would probably have amounted to no more than a light thinning. POSSIBLE NATURE OF THE RESISTANCE This is the fourth insect for which resistance data have been obtained from plantings similar to plantation 7-61. One of our first concerns was to learn whether the resistance is general for all insects or specific for particular insects. This can be done by comparing attack patterns, as follows: Varieties which are Insect Most resistant Most susceptible European pine sawfly uralensis iberica Pine root collar weevil scotica & southern central & northern Eastern white-pine shoot borer northern southern Zimmerman pine moth southern central & northern There was a general similarity between the attack patterns for the pine root collar weevil and the Zimmerman pine moth. However, even in that case there were important differences. Variety scotica was resistant t o  the pine root collar weevil but not to the Zimmerman pine moth whereas trees from one place in Greece succumbed to the pine root collar weevil but not t o  Zimmerman pine moth. The attack pattern is totally different for the other insects, indicating that the resistance mechanism of the trees to each insect is probably different. The six southern varieties resistant to Zimmerman pine moth larvae have two morphological features in common. They have shorter needles (45-57 mm) than more northern trees (60-75 mm), and have greener winter foliage (less green in var. subillyrica than in var. scotica) than more northern trees. It is doubtful whether either of these foliage characteristics explains the relative freedom from damage from an insect which feeds on the cambium Certain features of the oleoresin content of the cortex (inner bark) seem to offer a more probable explanation. The cortical oleoresin composition was studied by Tobolski et a1 (1971). According to their data there are striking differences in concentration of two monoterpenes, as follows: Concentration in cortical oleoresin of Monoterpene 6 resistant southern varieties Other, non-resistant varieties 3-carene 1-6%* 26-58% terpinolene 0.3-0.9%* 2.44.6% -- *The single seedlot representing resistant var. illyrica had 20% and 1.8% concentrations of 3-carene and terpinolene, respectively, higher than in other southern trees but still be- low that found in non-resistant trees. These monoterpenes are volatile substances present in the fresh pitch. They have characteristic odors recognizable to humans and some insects. One or both mgy be attractants to female moths seeking oviposition sites, or may contribute to the nutrition of the larvae. The possible importance of 3carene was indicated by the study of Renwick 5Wright et al.: Genetic Variation in Resistance of Scotch Pine to Zimmerman PinePublished by ValpoScholar, 1975236 THE GREAT LAKES ENTOMOLOGIST Vol. 8, No. 4 and Vitd (1970). Working with western pines, they observed that 3carene combined with beetle pheromones was a potent attactant during the initial attack phase of the western pine beetle (Dendroctonus brevicornis LeConte). PRACTICAL APPLICATION Zimmerman pine moth is one of the most important pests of Scotch pine, especially in the western part of the lower Peninsula of Michigan where ,Christmas tree plantations are abundant. It may be that Christmas tree plantations are more prone to  attack than others because of the practice of annual shearing which creates many small wounds and fresh oleoresin which can act as an attractant to  female Zimmerman pine moths. Two decades ago, much of the Christmas tree planting stock was of central European origin. Because they are among the most susceptible, their use helps to explain why the moth has been such a pest in some of the early plantations. Now, most growers plant the winter-green varieties, most of which are resistant to Zimmerman pine moth and the pine root collar weevil. However, two Susceptible varieties, scotica and 'East Anglia' are still planted on a large scale. Their further use should probably be restricted in areas where either of these pests has been important. For timber production it is necessary to use a fast growing, susceptible variety, otherwise growth rate is too slow. That being the case, any pruning or mechanical thinning should be done during the winter if Zimmerman moth damage is to  be avoided. SUMMARY A heavy infestation of Zimmerman pine moth started in 1966 in an experimental plantation established in 1961 at  the Fred Russ Forest, Cass County, Michigan. The plantation consists of 108 seedlots of Scotch pine, representing the species' entire natural range. The plantation consists of 10 replicates, each containing one 4-tree plot per seedlot. The infestation abated in 1972. As of 1973, six southern varieties suffered an attack rate of 2948% and a mortality rate of 3-9%; northern and central varieties suffered an attack rate of 38-75% and a mortality rate of 18-37%. Resistance may be owing to  low levels of 3carene and terpinolene in the cortical oleoresin of the varieties from southern Europe and Asia Minor. LITERATURE CITED Renwick, J. A. A. and J. P. Vitd. 1970. Systems of chemical communication in Dendrocronus. Contrib. Boyce Thompson Inst. 24: 283-292. Ruby, J. L. and J. W. Wright. 1975. A revised classification of geographic varieties in Scotch pine. Silvae Genet. (in press) Steiner, K. 1974. Genetic variation in resistance of Scotch pine to eastern pineshoot borer. The Great Lakes Entomol. 7:103-107. Tobolski, J. J., J. W. Hanover and J. W. Wright. 1971. Genetic variation in the monoterpenes of Scotch pine. Forest Sci. 17:293-299. Wright, J. W., S. S. Pauley, R. B. Polk, J. J. Jokela and R. A. Read. 1966. Performance of Scotch pine varieties in the north central region. Silvae Genet. 15:lOl-110. Wright, J. W. and L. F. Wilson, 1972. Genetic differences in Scotch pine resistance to pine root collar weevil. Mich. Agric. Exp. Sta. Res. Rept. 159. Wright, J. W., L. F. Wilson and W. K. Randall. 1967. Differences among Scotch pine varieties in susceptibility to  European pine sawfly. Forest Sci. 13:175-181. 6The Great Lakes Entomologist, Vol. 8, No. 4 [1975], Art. 8https://scholar.valpo.edu/tgle/vol8/iss4/8

Genetic Variation in Resistance of Scotch Pine to Zimmerman Pine Moth

ValpoScholar

The Great Lakes Entomologist 
Volume 8 
Number 4 - Winter 1975 Number 4 - Winter 
1975 
Article 8 
December 1975 
Genetic Variation in Resistance of Scotch Pine to Zimmerman 
Pine Moth 
Jonathan W. Wright 
Louis F. Wilson 
USDA Forest Service 
John N. Bright 
Michigan State University 
Follow this and additional works at: https://scholar.valpo.edu/tgle 
 Part of the Entomology Commons 
Recommended Citation 
Wright, Jonathan W.; Wilson, Louis F.; and Bright, John N. 1975. "Genetic Variation in Resistance of Scotch 
Pine to Zimmerman Pine Moth," The Great Lakes Entomologist, vol 8 (4) 
Available at: https://scholar.valpo.edu/tgle/vol8/iss4/8 
This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. 
It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. 
For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 
THE GREAT LAKES ENTOMOLOGIST 
GENETIC VARIATION I N  RESISTANCE OF SCOTCH 
PlNE TO ZIMMERMAN PlNE MOTH1 
Jonathan W. Wright, Louis F. Wilson and John N. ~ r i ~ h t ~  
Scotch pine (Pinus sylvestris L.), a forest tree introduced from Eurasia, is commonly 
planted for Christmas tree and timber use in northeastern United States. In this country 
it has numerous insect enemies. Among the most important are European pine shoot 
moth, Rhyacionia buoliana (Schiffermiieller); pine root collar weevil, Hylobius radicis 
Buchanan;,European pine sawfly, Neodiprion sertifer (Geoffroy); and eastern white-pine 
shoot borer, Eucosma gloriola Heinrich. Previous studies (Wright et  al., 1967; Wright and 
Wilson, 1972; Steiner, 1974) have revealed large genetic differences in resistance to some 
of these pests. 
Another destructive pest is the Zimmerman pine moth, Dioryctria zimmermani 
(Grote). In 1968 this insect, native to the United States, was found attacking trees in a 
Scotch pine provenance test in southwestern Michigan. The attack rate was heavy and by 
1973 it was obvious that some rams or varieties were attacked more heavily than others. 
This is a report on those differences. 
THE INSECT DAMAGE 
Zimmerman pine moth larvae injure several native and exotic species of pine, but 
prefer open-grown, sapling-size Scotch pine. The larvae may attack lateral shoot tips, the 
base of the terminal shoot, or the main stem. After the adult females lay their eggs on 
the bark in late summer, the larvae hatch in a few days but do not start feeding until the 
following spring. In May or June of the next year they tunnel through the bark into the 
cambial region where they feed on wood and adjacent cambium. The injured tree exudes 
pitch or oleoresin which becomes coagulated and mixed with frass. This material 
accumulates outside the entrance holes. These pitch accumulations may be 1-3 inches in 
diameter and are the most visible signs of attack. 
An injured lateral or terminal shoot usually dies rapidly and ultimately falls off. Many 
attacks are along the main stem, a t  the bases of branches (Fig. 1). An injured branch may 
die, or it may become weakened and break off during an ensuing storm. Lightly damaged 
trees may recover completely with little external evidence of injury. 
If several larvae feed at the same level on the main stem, the tree may be completely 
girdled. If this happens, the tree may die within 2-3 years. Or, only the portion above the 
girdle may die, in which case a lateral branch assumes the place of the leader and the tree 
becomes misshaped. Heavily damaged trees are of no value commercially and may be 
esthetically undesirable. 
TREE MATERIALS AND METHODS 
The host materials in this study are part of a Scotch pine geographic origin study 
started in 1959 as part of the NC-99 (formerly NC-51) regional project, "Improvement of 
Forest Trees Through Selection and Breeding". They include trees grown from seed 
collected in 108 natural stands located in all parts of the species' natural range in Europe 
and Asia (Fig. 2). Test plantations were established in various parts of Michigan and other 
11he work reported here was supported in part by regional research funds from the 
U.S. Dept. of Agriculture allotted to Project NC-99, "Improvement of Forest Trees 
through Selection and Breeding". Approved for publication as Journal Article No 7196 of 
the Michigan Agticultural Experiment Station. 
2Professor of Forestry, Associate Professor of Forestry, and Resident Forester of 
Dunbar Forest Experiment Station of Michigan State University, respectively. Dr. Wilson 
is also Principal Insect Ecologist and Project Leader, U.S.D.A. Forest Service, North 
Central Forest Experiment Station, headquartered at East Lansing, Michigan 48824. 
1
Wright et al.: Genetic Variation in Resistance of Scotch Pine to Zimmerman Pine
Published by ValpoScholar, 1975
THE GREAT LAKES ENTOMOLOGIST Vol. 8, No. 4 
Fig. 1 .  Top of a young Scotch pine tree showing a branch (upper left) broken as the 
result of feeding by Zimmerman pine moth larvae and the pitch mass exudations 
(lower center) typical of larval feeding along the main stem. Such feeding along 
the main stem can result in branch breakage, death of the leader and subsequent 
stem deformity, or complete girdling and death of the entire tree. 
north central states. Information on growth rate, foliage color, minter hardiness, etc. in 
those plantations is contained in a paper by Wright e t  al. (1966). 
The Zimmerman pine moth outbreak occurred in plantation MSFGP 7-61 located on 
the Fred Russ Forest near Volinia, Cass County, southwestern .Mi-. The plantation 
occupies a level site with a sandy loam soil favorable for the growth of Scotch pine. The 
108 seedlots were planted as 2-year-old seedlings in 1961. A randomized complete block 
design with 1 0  replicates was used Each replicate contains one 4-tree plot per seedlot. 
Original spacing was 8 X 8 ft. As of 1967, when the Zimmerman pine moth damage was 
first noticed, mortality in the plantation averaged 19%. Mean height in 1971 was 14.9 ft, 
about 10% lower than in the best of 12 similar plantations established in the state. 
The Russ Forest plantation was pruned during the summer of 1966, to one-third of 
total height. Other observers have noted that adult Zimmerman pine moth females are 
attracted to  fresh pitch. That appeared to  be true a t  the Russ Forest. During 1966 and 
1967 a heavy infestation started to develop. By 1968, up to 50% of the trees of some 
seedlots had fresh pitch masses. By the next year, the attack rate had risen to 8 6 5  in 
some seedlots, and 2% of all trees had died as a result of girdling by the larvae. Xiany 
new attacks were visible again in 1970 although by then the infestation had begun to 
decline. By 1973, 49% of all trees had been attacked and 2m were dead as the result of 
girdling or were girdled so badly that they seemed destined to die. However, by 1973 the 
new attack rate had decreased to a low level and some trees which had been injured i-R 
1968 or 1969 were completely recovered. Thus it appears that the infestation has run its 
course and that additional damage will be slight. 
Two other Scotch pine experimental plantations were established at the Russ Forest 
in 1961 and 1963. Thcy wcre left unpmned until the winter of 1974-75. They were 
2
The Great Lakes Entomologist, Vol. 8, No. 4 [1975], Art. 8
https://scholar.valpo.edu/tgle/vol8/iss4/8
1975 THE GREAT LAKES ENTOMOLOGIST 233 
Fig. 2. Natural range (shaded), points of seed collection for the Russ Forest plantatioq 
(black dots) and varieties of Scotch pine. The varieties mentioned in this paper 
are AQUitana, ARMena, CARpatica, HAGuenensis, HERcynica, IBErica, ILLyrica, 
LAPponica, PANnonica, POLonica, RIGensis, PHOdopaea, SCOtica, SUBillyrica 
and URAlensis. The Siberian range of var. MONgolica is not shown. Varieties 
PYRenaica (probably resistant), ROManica, ROSsica and VINdelica (all probably 
susceptible) were not represented in the plantation. 
situated one-fourth to one-half mile distant from plantation 7-61 and have contained 
some Zimmerman pine moth damage since 1967. However, the infestations have never 
reached epidemic proportions and less than 1% of the trees have died or been seriously 
deformed as the result of attack. Light infestations have also occurred in similar 
experimental plantations in other parts of the state. 
Plantation 7-61, last measured in 1971, has been measured several times previously for 
height, foliage color, cone production, and other characters. Zimmerman moth damage 
was assessed in 1968, 1969 and 1973. Each time number of trees attacked, number of 
trees dead, and number of trees with larvae<aused bole crooks larger than 2 inches were 
counted. Each set of measurement data was subjected to analysis of variance. 
VARIETAL DIFFERENCES IN SUSCEPTIBILITY 
Scotch pine is a genetically variable species. It has been subdivided by taxonomists 
into a number of geographic varieties (Ruby and Wright, in press), whose ranges are 
shown in Fig. 2. In Michigan plantations as a whole, differences among these varieties 
account for 75-9076 of the total genetic variation in traits such as growth rate, foliage 
color, and oleoresin composition. The same is true with regard to the data presented here. 
Differences among seedlots belonging to the same variety were not statistically significant 
although there were large and important differences among varieties. Thus, for conven- 
ience, the data are summarized in terms of the geographic varieties (Table 1). 
Fast growing timber-type varieties from England and central Europe suffered most. 
That is true no matter what the criterion-per cent attack, per cent mortality or per cent 
3
Wright et al.: Genetic Variation in Resistance of Scotch Pine to Zimmerman Pine
Published by ValpoScholar, 1975
234 THE GREAT LAKES ENTOMOLOGIST Vol. 8, No. 4 
Table 1. Differences among Scotch pine varieties in growth rate, susceptibility to Zirnmer- 
man moth attack and larval-caused bole crooks. 
- 
Trees attacked by Zimmerman pine moth 
Variety 
lapponica 
septentrionulis 
rigensis 
mongolica 
uralensis 
polonica 
hercynica 
carpatica 
haguenensis 
pannonica 
'E. ,4ngliaY 
scotica 
iberica 
aquitana 
subillyrica 
illvrica 
rhodopaea 
armena 
Trees 
dead 
Average Total trees or with 
height attacked Trees crooked 
Country of in 1971 dead boles 
origin* atage 11 1969 1973 1973 1973 
feet per cent of trees liv-0 in 1966 
Varieties from northern Eurasia 
FIN SWE SIB 7.5 11 15 7 8 
SWE NOR 12.1 30 38 18 32 
SWE LAT 14.3 46 4 7 22 4 0 
SIB 12.9 50 55 39 46 
SIB 14.4 58 6 1 31 49 
Varieties from England and Central Europe 
POL 17.4 55 6 2 25 5 5 
GER CZE 17.1 56 5 7 22  4 8 
CZE 18.0 66 6 5 26 49 
BELFRAGER 18.0 71 74 35 70 
HUN 16.5 55 62 19 5 7 
ENG 16.4 63 75 3 7 69 
Varieties from Scotland, S. Europe and Asia Zfinor 
SCO 14.8 41 - ,  i7 26 49 
SPA 14.3 43 33 3 18 
FR A 16.1 33 29 I 2 2 - 
ITA 15.1 46 48 7 38 
YUG 15.4 48 43 9 20 
GRE 16.1 42 41 6 3 1 
TUR GEO 14.7 37 29 3 18 
*BELgium, CZEchoslovakia, ENGland, FINland, FR-ince, GEOrghn S.S.R., GERmany 
(East and West), GREece, HUNgary, lTAly, LATvian S.S.R., SORa-al--, F'OLand, Scotland, 
SlBeria, SPAin, SWEden, TURkey, YUGoslavia. 
crooked trees. In most of these varieties the attack rates were above 605 and more than 
50% of the trees died or became severely misshaped. 
Next most heavily attacked were the slower growing varieties from Scotland or 
northern Eurasia. They are also regarded as timber variedes because in man!- h a t i o n s  
they grow straight and have relatively f i e  branches. Houever, a l l  except var. lappunica 
suffered almost as much mortality as did those from central Europe and had a high 
proportion of misshaped trees. 
One northern variety, lapponica, was exceptional 11s narive r a n e  is close to the 
Arctic Circle and trees of this variety g o w  very slo\vl>-. AI the hekht of the epidemic 
they were only 2-4 ft tall, so small as to present littIe attraction to a flying insect. 
Probably because of its small size, this variety also has been relatively free from darnage 
by other types of insects at other tests plantations. 
The least damaged varieties were from southern Europe and Asia Minor. The) are 
characterized by moderate gowth rates and foliage which remains nearIy as e e n  dur iq  
the winter as during the summer. Accordingly they are most in demand by Christmas 
tree growers. Among the southern seedlots, 3040% of the trees were attacked, but there 
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The Great Lakes Entomologist, Vol. 8, No. 4 [1975], Art. 8
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1975 THE GREAT LAKES ENTOMOLOGIST 235 
were usually only one or two pitch masses per tree. Several trees with visible signs of 
attack in 1968 or 1969 had completely recovered by 1973. The mortality rate was low, 
averaging only 3-9%. For the southern varieties as a whole, only 23% experienced severe 
stem crooks or mortality, as compared with 32-70% for trees of more northern origin. If 
the plantation had been composed entirely of southern trees, the Zimmerman moth 
infestation would probably have amounted to no more than a light thinning. 
POSSIBLE NATURE OF THE RESISTANCE 
This is the fourth insect for which resistance data have been obtained from plantings 
similar to plantation 7-61. One of our first concerns was to learn whether the resistance 
is general for all insects or specific for particular insects. This can be done by comparing 
attack patterns, as follows: 
Varieties which are 
Insect Most resistant Most susceptible 
European pine sawfly uralensis iberica 
Pine root collar weevil scotica & southern central & northern 
Eastern white-pine shoot borer northern southern 
Zimmerman pine moth southern central & northern 
There was a general similarity between the attack patterns for the pine root collar 
weevil and the Zimmerman pine moth. However, even in that case there were important 
differences. Variety scotica was resistant t o  the pine root collar weevil but not to the 
Zimmerman pine moth whereas trees from one place in Greece succumbed to the pine 
root collar weevil but not t o  Zimmerman pine moth. The attack pattern is totally 
different for the other insects, indicating that the resistance mechanism of the trees to 
each insect is probably different. 
The six southern varieties resistant to Zimmerman pine moth larvae have two 
morphological features in common. They have shorter needles (45-57 mm) than more 
northern trees (60-75 mm), and have greener winter foliage (less green in var. subillyrica 
than in var. scotica) than more northern trees. It is doubtful whether either of these 
foliage characteristics explains the relative freedom from damage from an insect which 
feeds on the cambium Certain features of the oleoresin content of the cortex (inner 
bark) seem to offer a more probable explanation. The cortical oleoresin composition was 
studied by Tobolski et a1 (1971). According to their data there are striking differences in 
concentration of two monoterpenes, as follows: 
Concentration in cortical oleoresin of 
Monoterpene 6 resistant southern varieties Other, non-resistant varieties 
3-carene 1-6%* 26-58% 
terpinolene 0.3-0.9%* 2.44.6% 
-- 
*The single seedlot representing resistant var. illyrica had 20% and 1.8% concentrations 
of 3-carene and terpinolene, respectively, higher than in other southern trees but still be- 
low that found in non-resistant trees. 
These monoterpenes are volatile substances present in the fresh pitch. They have 
characteristic odors recognizable to humans and some insects. One or both mgy be 
attractants to female moths seeking oviposition sites, or may contribute to the nutrition 
of the larvae. The possible importance of 3carene was indicated by the study of Renwick 
5
Wright et al.: Genetic Variation in Resistance of Scotch Pine to Zimmerman Pine
Published by ValpoScholar, 1975
236 THE GREAT LAKES ENTOMOLOGIST Vol. 8, No. 4 
and Vitd (1970). Working with western pines, they observed that 3carene combined with 
beetle pheromones was a potent attactant during the initial attack phase of the western 
pine beetle (Dendroctonus brevicornis LeConte). 
PRACTICAL APPLICATION 
Zimmerman pine moth is one of the most important pests of Scotch pine, especially 
in the western part of the lower Peninsula of Michigan where ,Christmas tree plantations 
are abundant. It may be that Christmas tree plantations are more prone to  attack than 
others because of the practice of annual shearing which creates many small wounds and 
fresh oleoresin which can act as an attractant to  female Zimmerman pine moths. Two 
decades ago, much of the Christmas tree planting stock was of central European origin. 
Because they are among the most susceptible, their use helps to explain why the moth 
has been such a pest in some of the early plantations. Now, most growers plant the 
winter-green varieties, most of which are resistant to Zimmerman pine moth and the pine 
root collar weevil. However, two Susceptible varieties, scotica and 'East Anglia' are still 
planted on a large scale. Their further use should probably be restricted in areas where 
either of these pests has been important. 
For timber production it is necessary to use a fast growing, susceptible variety, 
otherwise growth rate is too slow. That being the case, any pruning or mechanical 
thinning should be done during the winter if Zimmerman moth damage is to  be avoided. 
SUMMARY 
A heavy infestation of Zimmerman pine moth started in 1966 in an experimental 
plantation established in 1961 at  the Fred Russ Forest, Cass County, Michigan. The 
plantation consists of 108 seedlots of Scotch pine, representing the species' entire natural 
range. The plantation consists of 10 replicates, each containing one 4-tree plot per 
seedlot. The infestation abated in 1972. As of 1973, six southern varieties suffered an 
attack rate of 2948% and a mortality rate of 3-9%; northern and central varieties 
suffered an attack rate of 38-75% and a mortality rate of 18-37%. Resistance may be 
owing to  low levels of 3carene and terpinolene in the cortical oleoresin of the varieties 
from southern Europe and Asia Minor. 
LITERATURE CITED 
Renwick, J. A. A. and J. P. Vitd. 1970. Systems of chemical communication in 
Dendrocronus. Contrib. Boyce Thompson Inst. 24: 283-292. 
Ruby, J. L. and J. W. Wright. 1975. A revised classification of geographic varieties in 
Scotch pine. Silvae Genet. (in press) 
Steiner, K. 1974. Genetic variation in resistance of Scotch pine to eastern pineshoot 
borer. The Great Lakes Entomol. 7:103-107. 
Tobolski, J. J., J. W. Hanover and J. W. Wright. 1971. Genetic variation in the 
monoterpenes of Scotch pine. Forest Sci. 17:293-299. 
Wright, J. W., S. S. Pauley, R. B. Polk, J. J. Jokela and R. A. Read. 1966. Performance 
of Scotch pine varieties in the north central region. Silvae Genet. 15:lOl-110. 
Wright, J. W. and L. F. Wilson, 1972. Genetic differences in Scotch pine resistance to 
pine root collar weevil. Mich. Agric. Exp. Sta. Res. Rept. 159. 
Wright, J. W., L. F. Wilson and W. K. Randall. 1967. Differences among Scotch pine 
varieties in susceptibility to  European pine sawfly. Forest Sci. 13:175-181. 
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The Great Lakes Entomologist, Vol. 8, No. 4 [1975], Art. 8
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Genetic Variation in Resistance of Scotch Pine to Zimmerman Pine Moth

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