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Integrated pest management of the nun moth, Lymantria monachaa (Lepidoptera: Lymantriidae) in Denmark
Forest Ecology and Management, 39 ( 1991 ) 29-34
29
Elsevier Science Publishers B.V., Amsterdam
Integrated pest management of the nun moth, Lymantria monacha a ( Lepidoptera: Lymantriidae) in Denmark Thomas Secher Jensen Zoological Laboratorv, Universityof Aarhus. DK-8000 Aarhus C Denmark
ABSTRACT Jensen, T.S., 1991. Integrated pest management of the nun moth Lymantria monacha (Lepidoptera: Lymantriida) in Denmark. For Ecol. Manage: 39:29-34 In Denmark, the nun moth, Lymantria monacha L., has been intensively studied since 1970 when a series of outbreaks started. Several aspects of the basic ecology and the nutritional ecology have been studied, and chemical, microbial and behavioural control measures have been tested. Also monitoring systems using pheromone-baited traps, sampling the numbers of females on tree trunks, and collecting larval frass on sticky boards, have been evaluated. Based on this knowledge, a tentative control plan was developed for new outbreaks.
INTRODUCTION
The nun moth, Lymantria monacha L., is one of the most important insect pest species of European conifers. Outbreaks have been the most frequent in central Europe but have also occurred in forests at more northern and southern latitudes (Wellenstein and Schwenke, 1978). Recently, the largest outbreak in history occurred in Poland and adjacent countries, covering more than 2 million ha of forests (Sliwa and Sierpinski, 1986) and primarily defoliating species of spruce and pine. At the northern limit of the distribution of the nun moth, in Denmark, several outbreaks have taken place in the last two decades, following a period of low populations for more than 70 years (Jensen and Bejer, 1985 ). Because of the large size of these outbreaks, many different control methods have been tried to develop an effective management program for this species. ~Known in Great Britain as the 'black arches' moth (Chinery, 1976).
0378-1127/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
30
T.S. JENSEN
C H A R A C T E R I S T I C S O F O U T B R E A K SITES A N D C L I M A T E
The nun-moth outbreak localities in Denmark are all situated on very sandy soils, most on diluvial sands and a few on marine deposits. Although conifer plantations are mainly restricted to poorer soils, large areas of coniferous forests occur on the richer clayey soils, where as yet outbreaks have not occurred. These observations are in general agreement with results from other nun-moth outbreak areas. For example, large outbreaks in Poland have occurred in forests on sandy soil (Sliwa and Sierpinski, 1986) and generally the nun moth repeatedly attacks the same areas of poor forests at intervals of several decades (Wellenstein and Schwenke, 1978 ). The distribution of outbreak localities in Denmark does not conform to any general local climatic pattern. The localities are situated in dry warm coastal areas, cool moist coastal areas and cool moist inland areas. However, analysis of climatic variables in the years preceding outbreaks has shown that several warm dry summers in a row, especially in June, seem to be a prerequisite for nun-moth outbreaks (Bejer, 1985; Jensen, 1985 ). HOST-PLANT RELATIONS
The nun moth is a highly polyphagous herbivore, and many different host plants have been attacked during outbreaks in Denmark. Most often, Norway spruce ( Picea abies ), Sitka spruce ( Picea sitchensis ), Scots pine ( Pinus silvestris), and lodgepole pine (Pinus contorta) have been defoliated. However, several other species, mainly other conifers but also deciduous trees and shrubs, have also been severely defoliated by the nun moth. First-instar nun-moth larvae are unable to utilise old spruce and pine needles nutritionally (Jensen, 1983). Moreover, the young larvae do not consume new pine needles, probably because these needles contain deterrent secondary compounds. Instead, first-instar larvae on pine depend entirely on male flowers. Flowering in pine is quite frequent; however, male flowers are often very scattered and unevenly distributed within the stand. Therefore, defoliation of pines often leads to total destruction of next year's flowering buds, even when some new needles are left. Accordingly, the next generation of larvae starve to death or disperse from the pines. For this reason, pine stands often tolerate defoliation better then spruce stands. First-instar larvae feeding on spruce primarily consume newly flushed needles. But, if larvae hatch before budbreak, they may feed on male flowers. Flowering in spruce is infrequent and probably induced by warm, dry summers; thus, there might be an indirect relation between flowering, climate and outbreaks of nun moths in spruce forests. Severe defoliation of more than 80% will cause mortality of spruce trees within a year.
I.P.M. OF THE NUN MOTH, LYMANTRIA, IN DENMARK
31
MONITORING SYSTEMS
Distribution patterns of sites, forest composition, and climatic characteristics can be used to predict whether nun-moth outbreaks may occur in certain years and in certain localities in Denmark. However, the use of these criteria in a monitoring system will of course be only applicable on a very large scale. More detailed knowledge about the population dynamics of the species are obtained by use of pheromone-baited traps. In Denmark, the sex-attractant disparlure (Bierl et al., 1970), identical to that of the gypsy moth, Lymantria dispar L., has been used to lure male nun moths into sticky traps since 1980 (Jensen, 1983; Jensen and Nielsen, 1984). Pheromone traps are presently used country-wide, in a widely-spaced grid survey system operated by the Danish Forest Service. In such a network, the trap catch of male moths can probably only be expected to monitor rather large-scale population changes. The detection of near-outbreak population levels can only be made by using a much more closely spaced network of pheromone traps. For such monitoring, traps should be placed at intervals of less than 1 km from each other (Jensen, 1983). Such an intensive trapping effort can only be warranted if there is an immediate danger of an outbreak. Earlier work on the nun m o t h (Wellenstein, 1942 ) used the number of females on tree trunks, to predict nun-moth population levels. The use of pheromone traps seems superior to that m e t h o d at low moth densities, and pheromone traps are also more convenient to use in less-accessible areas. In preoutbreak and outbreak situations, pheromone traps are less suitable, and estimates of the number of females per tree trunk are necessary. Females are counted on representative trees twice weekly, and the cumulative number is used to estimate the number of egg-laying females per tree. These estimates can be related to expected defoliation, as the critical number of females per tree causing 100% defoliation is known for the nun moth (Wellenstein, 1942 ) for several tree species, tree ages and vigour. If necessary, the larval density can be estimated by means of frass collections on sticky boards the following year. Sampling of egg masses has been attempted (H. Hiibertz and K. Raae, Agricultural University, Copenhagen, unpublished data, 1979) but nun moths deposit eggs in small batches hidden beneath bark flakes on the trunk or even between needles. Thus, reliable population estimates require sampling efforts too large to be practical. CHEMICALCONTROL
Since 1972, nun moths have been controlled by different means. In the outbreaks of 1972-1974, contact pesticides such as lindane, endosulphane, fenitrothion, and trichlorfone were used with moderate to high success, depend-
32
T.S. JENSEN
ing on larval size (Bejer-Petersen, 1972). Because of unacceptable environmental effects, i.e. nestling and adult bird mortality, the main emphasis in the most recent outbreak of 1978-1983 was placed on the use of diflubenzuron, an insect growth-regulator hormone analogue. Diflubenzuron caused 95-100% larval mortality, but the number of larvae per tree in certain areas was so high, at 20 000-30 000, that extensive damage occurred before the larvae were killed during their next moult (Jensen and Bejer, 1985 ). MICROBIOLOGICAL CONTROL
In 1973, attempts were made to control a part of an outbreak with a nuclear polyhedrosis virus (NPV) that naturally occurs in the nun moth (Zethner, 1976 ). The immediate effect of the virus on the larvae was low, but a high proportion of the pupae died. The larval kill was too late and many trees died from severe defoliation. In the following year the population crashed, mainly from NPV infection, but this happened in the untreated areas as well. In the most recent outbreaks, the NPV was sprayed in only a small area due to a general shortage of NPV, and no signs of the disease appeared in the population. Bacillus thuringiensis (B.t.) formulations (Dipel) were only tried during the 1972 outbreak. The preparations failed completely (0% larval mortality) in one year and had only moderate effect the other (Bejer, 1986). It has been suggested that the total failure was caused by a cold spell after the B.t. application, inhibiting larval feeding in the period when the B.t. was active. MATING DISRUPTION
In 1980 and 1982, small-scale (1-ha) experiments tested the use of pheromones in mating disruption. The sex pheromone, disparlure, in micro-encapsulated form, was sprayed on tree trunks (Jensen, 1983 ). In both years, pheromone traps within the disparlure-treated area captured few or no males, whereas traps in the control area adjacent to the treated area captured a considerable number. Interestingly, this effect persisted the following year. The number of egg masses and number of newly hatched larvae per egg-laying female the following spring were 2.5-3.0 times greater in the control area than in the disparlure-treated area. INTEGRATED CONTROL
Based on ecological investigations and experience from past chemical-control measures, and in the hope that further pheromone investigations would mean progress in respect to warning thresholds and control measures, a tentative control program (Fig. 1 ) has been worked out (Jensen and Bejer, 1985 ).
I.I:'.M. OF THE NUN MOTH, LYMANTRIA, IN DENMARK . OBSERVATION
.
33
. . . . . / TREATMENT
1 Time
of year
....... Outoreak d!scoveredq defol ation
i
Ear'? summer
-
I Areal deliniation - ffass boards
I
Mating di~o,io~ i~ I
ow
! Outbreak ~isco~r~d ]
density ~om 1 ~
II
-- moths tlying
~te summer
i
Areal deliniation - pheromone traps, ~ l g coqnts ] Winter
Areal subdivision
, II
!
"0 control
L ~--
! ]
F
~.
|
[_ .
.
-. . . .
1
'~i1~e°n uron | z ] . . I__: ~_ ~
f~ont-ioq-~--
.:
Soring
|Oifiubenzuron increasing pop. [+ Pyrethroid , "-~"=="~" ~[~ " ~:aecreasmgtaop, ......... .
New 9-counts or pheromone trap registration
Late summer
h Fig. 1. G e n e r a l
integrated-management scheme for Lymantria monacha
in D e n m a r k .
In this program, the use of biological pesticides has not been included, since NPV at present is not available in larger quantities and the newer, more potent formulations of B.t. have not been fully tested. Currently, the presence of an outbreak of the nun moth will not be known until trees are defoliated or when a large numbers of moths are seen in the forest or are trapped. If defoliation is discovered in late summer, chemical control is normally useless, as the late-instar larvae are rather resistant to pesticides. However, at that time it would be advisable to survey for the distribution and intensity of the outbreak, either by visual observations or with the use of frass sticky boards. If the outbreak is small or at an early stage, mating disruption could be attempted if commercial products are available. Whether or not mating disruption is attempted, the density of adult moths (especially females) should be surveyed within the outbreak, and in fairly
34
T.S. JENSEN
large areas around the outbreak. Nun-moth outbreaks normally start at separate 'nuclei', later to coalesce, Quite often, these nuclei of infestations are situated in the darker and denser parts of the stands. If the outbreak is discovered at the time of the flight period, the number of females on the tree trunks should be sampled immediately. If a part of the flight period passed, the number of dead females around the base of the tree should be included in the count. The number of females counted can be compared to a threshold of critical number of moths for a particular stand. The ratio of cumulative number of females in the sample to the critical number of females is then used to reach a control decision.
REFERENCES Bejer, B., 1985. Nun moth (Lymantria monacha L.) outbreaks in Denmark and their association with site factors and climate. In: D. Bevan and J.T. Stoakley (Editors), Site Characteristics and Population Dynamics of Lepidopteran and Hymenopteran Forest Pests. I U F R O / Forestry Commission 1980 Meeting, Dornock, Great Britain, 1-7 September. For. Comm. Res. Devel. Pap., 135. Bejer, B., 1986. Outbreaks of the nun moth (Lymantria monacha) in Denmark with remarks on their control. Anz. Schaedlingskd. Pflanz. Umweltschutz, 59: 86-89. Bejer-Petersen, B., 1972. The nun moth, Lymantria monacha L., in Denmark. Entomol. Medd., 40: 129-139. Bierl, B.A., Beroza, M. and Collier, C.W., 1970. Potent sex attractant of the gypsy moth: its isolation, identification and synthesis. Science, 170: 87-89. Chinery, M., 1976. A Field Guide to the Insects of Great Britain and Northern Europe (2nd edition). Collins, London, 352 pp. Jensen, T.S., 1983. Registration and control of the nun moth, Lymantria monacha L. by means of pheromone. Mitt. Dtsch. Ges. Alg. Angew. Entomol., 4: 146-149. Jensen, T.S., 1985. Outbreak and latency populations of the nun moth, Lymantria rnonacha L. Mitt. Dtsch. Ges. Alg. Angew. Entomol., 5:133-136. Jensen, T.S. and Bejer, B., 1985. Registration and control of the nun moth, Lyrnantria monacha L. in Denmark 1978-84. - Dan. Skovforen. Tidsskr., 70:182-205. Jensen, T.S. and Nielsen, B.O., 1984. Evaluation of pheromone catches of the nun moth, Lymantria rnonacha L. Influence of habitat heterogeneity and weather conditions. Z. Angew. Entomol., 98:399-413. Sliwa, E. and Sierpinski, Z., 1986. Gradation der Nonne (Lymantria monacha L. ) in Polen von 1978 bis 1984. Anz. Schaedlingskd., Pflantz. Umweltschutz, 59:81-86. Wellenstein, G., 1942. Die Nonne in Ostpreussen. Monogr. Z. Angew. Entomol., 15:682 pp. Wellenstein, G. and Schwenke, W., 1978. Lymantria monacha. In: W. Schwenke (Editor), Die Forstschadlinge Europas. Schmetterlinge, Hamburg, 472 pp. Zethner O., 1976. Control experiments on the nun moth (Lymantria monacha L.) by nuclearpolyhedrosis virus in Danish coniferous forests. Z. Angew. Entomol. 82:192-207.
29
Elsevier Science Publishers B.V., Amsterdam
Integrated pest management of the nun moth, Lymantria monacha a ( Lepidoptera: Lymantriidae) in Denmark Thomas Secher Jensen Zoological Laboratorv, Universityof Aarhus. DK-8000 Aarhus C Denmark
ABSTRACT Jensen, T.S., 1991. Integrated pest management of the nun moth Lymantria monacha (Lepidoptera: Lymantriida) in Denmark. For Ecol. Manage: 39:29-34 In Denmark, the nun moth, Lymantria monacha L., has been intensively studied since 1970 when a series of outbreaks started. Several aspects of the basic ecology and the nutritional ecology have been studied, and chemical, microbial and behavioural control measures have been tested. Also monitoring systems using pheromone-baited traps, sampling the numbers of females on tree trunks, and collecting larval frass on sticky boards, have been evaluated. Based on this knowledge, a tentative control plan was developed for new outbreaks.
INTRODUCTION
The nun moth, Lymantria monacha L., is one of the most important insect pest species of European conifers. Outbreaks have been the most frequent in central Europe but have also occurred in forests at more northern and southern latitudes (Wellenstein and Schwenke, 1978). Recently, the largest outbreak in history occurred in Poland and adjacent countries, covering more than 2 million ha of forests (Sliwa and Sierpinski, 1986) and primarily defoliating species of spruce and pine. At the northern limit of the distribution of the nun moth, in Denmark, several outbreaks have taken place in the last two decades, following a period of low populations for more than 70 years (Jensen and Bejer, 1985 ). Because of the large size of these outbreaks, many different control methods have been tried to develop an effective management program for this species. ~Known in Great Britain as the 'black arches' moth (Chinery, 1976).
0378-1127/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
30
T.S. JENSEN
C H A R A C T E R I S T I C S O F O U T B R E A K SITES A N D C L I M A T E
The nun-moth outbreak localities in Denmark are all situated on very sandy soils, most on diluvial sands and a few on marine deposits. Although conifer plantations are mainly restricted to poorer soils, large areas of coniferous forests occur on the richer clayey soils, where as yet outbreaks have not occurred. These observations are in general agreement with results from other nun-moth outbreak areas. For example, large outbreaks in Poland have occurred in forests on sandy soil (Sliwa and Sierpinski, 1986) and generally the nun moth repeatedly attacks the same areas of poor forests at intervals of several decades (Wellenstein and Schwenke, 1978 ). The distribution of outbreak localities in Denmark does not conform to any general local climatic pattern. The localities are situated in dry warm coastal areas, cool moist coastal areas and cool moist inland areas. However, analysis of climatic variables in the years preceding outbreaks has shown that several warm dry summers in a row, especially in June, seem to be a prerequisite for nun-moth outbreaks (Bejer, 1985; Jensen, 1985 ). HOST-PLANT RELATIONS
The nun moth is a highly polyphagous herbivore, and many different host plants have been attacked during outbreaks in Denmark. Most often, Norway spruce ( Picea abies ), Sitka spruce ( Picea sitchensis ), Scots pine ( Pinus silvestris), and lodgepole pine (Pinus contorta) have been defoliated. However, several other species, mainly other conifers but also deciduous trees and shrubs, have also been severely defoliated by the nun moth. First-instar nun-moth larvae are unable to utilise old spruce and pine needles nutritionally (Jensen, 1983). Moreover, the young larvae do not consume new pine needles, probably because these needles contain deterrent secondary compounds. Instead, first-instar larvae on pine depend entirely on male flowers. Flowering in pine is quite frequent; however, male flowers are often very scattered and unevenly distributed within the stand. Therefore, defoliation of pines often leads to total destruction of next year's flowering buds, even when some new needles are left. Accordingly, the next generation of larvae starve to death or disperse from the pines. For this reason, pine stands often tolerate defoliation better then spruce stands. First-instar larvae feeding on spruce primarily consume newly flushed needles. But, if larvae hatch before budbreak, they may feed on male flowers. Flowering in spruce is infrequent and probably induced by warm, dry summers; thus, there might be an indirect relation between flowering, climate and outbreaks of nun moths in spruce forests. Severe defoliation of more than 80% will cause mortality of spruce trees within a year.
I.P.M. OF THE NUN MOTH, LYMANTRIA, IN DENMARK
31
MONITORING SYSTEMS
Distribution patterns of sites, forest composition, and climatic characteristics can be used to predict whether nun-moth outbreaks may occur in certain years and in certain localities in Denmark. However, the use of these criteria in a monitoring system will of course be only applicable on a very large scale. More detailed knowledge about the population dynamics of the species are obtained by use of pheromone-baited traps. In Denmark, the sex-attractant disparlure (Bierl et al., 1970), identical to that of the gypsy moth, Lymantria dispar L., has been used to lure male nun moths into sticky traps since 1980 (Jensen, 1983; Jensen and Nielsen, 1984). Pheromone traps are presently used country-wide, in a widely-spaced grid survey system operated by the Danish Forest Service. In such a network, the trap catch of male moths can probably only be expected to monitor rather large-scale population changes. The detection of near-outbreak population levels can only be made by using a much more closely spaced network of pheromone traps. For such monitoring, traps should be placed at intervals of less than 1 km from each other (Jensen, 1983). Such an intensive trapping effort can only be warranted if there is an immediate danger of an outbreak. Earlier work on the nun m o t h (Wellenstein, 1942 ) used the number of females on tree trunks, to predict nun-moth population levels. The use of pheromone traps seems superior to that m e t h o d at low moth densities, and pheromone traps are also more convenient to use in less-accessible areas. In preoutbreak and outbreak situations, pheromone traps are less suitable, and estimates of the number of females per tree trunk are necessary. Females are counted on representative trees twice weekly, and the cumulative number is used to estimate the number of egg-laying females per tree. These estimates can be related to expected defoliation, as the critical number of females per tree causing 100% defoliation is known for the nun moth (Wellenstein, 1942 ) for several tree species, tree ages and vigour. If necessary, the larval density can be estimated by means of frass collections on sticky boards the following year. Sampling of egg masses has been attempted (H. Hiibertz and K. Raae, Agricultural University, Copenhagen, unpublished data, 1979) but nun moths deposit eggs in small batches hidden beneath bark flakes on the trunk or even between needles. Thus, reliable population estimates require sampling efforts too large to be practical. CHEMICALCONTROL
Since 1972, nun moths have been controlled by different means. In the outbreaks of 1972-1974, contact pesticides such as lindane, endosulphane, fenitrothion, and trichlorfone were used with moderate to high success, depend-
32
T.S. JENSEN
ing on larval size (Bejer-Petersen, 1972). Because of unacceptable environmental effects, i.e. nestling and adult bird mortality, the main emphasis in the most recent outbreak of 1978-1983 was placed on the use of diflubenzuron, an insect growth-regulator hormone analogue. Diflubenzuron caused 95-100% larval mortality, but the number of larvae per tree in certain areas was so high, at 20 000-30 000, that extensive damage occurred before the larvae were killed during their next moult (Jensen and Bejer, 1985 ). MICROBIOLOGICAL CONTROL
In 1973, attempts were made to control a part of an outbreak with a nuclear polyhedrosis virus (NPV) that naturally occurs in the nun moth (Zethner, 1976 ). The immediate effect of the virus on the larvae was low, but a high proportion of the pupae died. The larval kill was too late and many trees died from severe defoliation. In the following year the population crashed, mainly from NPV infection, but this happened in the untreated areas as well. In the most recent outbreaks, the NPV was sprayed in only a small area due to a general shortage of NPV, and no signs of the disease appeared in the population. Bacillus thuringiensis (B.t.) formulations (Dipel) were only tried during the 1972 outbreak. The preparations failed completely (0% larval mortality) in one year and had only moderate effect the other (Bejer, 1986). It has been suggested that the total failure was caused by a cold spell after the B.t. application, inhibiting larval feeding in the period when the B.t. was active. MATING DISRUPTION
In 1980 and 1982, small-scale (1-ha) experiments tested the use of pheromones in mating disruption. The sex pheromone, disparlure, in micro-encapsulated form, was sprayed on tree trunks (Jensen, 1983 ). In both years, pheromone traps within the disparlure-treated area captured few or no males, whereas traps in the control area adjacent to the treated area captured a considerable number. Interestingly, this effect persisted the following year. The number of egg masses and number of newly hatched larvae per egg-laying female the following spring were 2.5-3.0 times greater in the control area than in the disparlure-treated area. INTEGRATED CONTROL
Based on ecological investigations and experience from past chemical-control measures, and in the hope that further pheromone investigations would mean progress in respect to warning thresholds and control measures, a tentative control program (Fig. 1 ) has been worked out (Jensen and Bejer, 1985 ).
I.I:'.M. OF THE NUN MOTH, LYMANTRIA, IN DENMARK . OBSERVATION
.
33
. . . . . / TREATMENT
1 Time
of year
....... Outoreak d!scoveredq defol ation
i
Ear'? summer
-
I Areal deliniation - ffass boards
I
Mating di~o,io~ i~ I
ow
! Outbreak ~isco~r~d ]
density ~om 1 ~
II
-- moths tlying
~te summer
i
Areal deliniation - pheromone traps, ~ l g coqnts ] Winter
Areal subdivision
, II
!
"0 control
L ~--
! ]
F
~.
|
[_ .
.
-. . . .
1
'~i1~e°n uron | z ] . . I__: ~_ ~
f~ont-ioq-~--
.:
Soring
|Oifiubenzuron increasing pop. [+ Pyrethroid , "-~"=="~" ~[~ " ~:aecreasmgtaop, ......... .
New 9-counts or pheromone trap registration
Late summer
h Fig. 1. G e n e r a l
integrated-management scheme for Lymantria monacha
in D e n m a r k .
In this program, the use of biological pesticides has not been included, since NPV at present is not available in larger quantities and the newer, more potent formulations of B.t. have not been fully tested. Currently, the presence of an outbreak of the nun moth will not be known until trees are defoliated or when a large numbers of moths are seen in the forest or are trapped. If defoliation is discovered in late summer, chemical control is normally useless, as the late-instar larvae are rather resistant to pesticides. However, at that time it would be advisable to survey for the distribution and intensity of the outbreak, either by visual observations or with the use of frass sticky boards. If the outbreak is small or at an early stage, mating disruption could be attempted if commercial products are available. Whether or not mating disruption is attempted, the density of adult moths (especially females) should be surveyed within the outbreak, and in fairly
34
T.S. JENSEN
large areas around the outbreak. Nun-moth outbreaks normally start at separate 'nuclei', later to coalesce, Quite often, these nuclei of infestations are situated in the darker and denser parts of the stands. If the outbreak is discovered at the time of the flight period, the number of females on the tree trunks should be sampled immediately. If a part of the flight period passed, the number of dead females around the base of the tree should be included in the count. The number of females counted can be compared to a threshold of critical number of moths for a particular stand. The ratio of cumulative number of females in the sample to the critical number of females is then used to reach a control decision.
REFERENCES Bejer, B., 1985. Nun moth (Lymantria monacha L.) outbreaks in Denmark and their association with site factors and climate. In: D. Bevan and J.T. Stoakley (Editors), Site Characteristics and Population Dynamics of Lepidopteran and Hymenopteran Forest Pests. I U F R O / Forestry Commission 1980 Meeting, Dornock, Great Britain, 1-7 September. For. Comm. Res. Devel. Pap., 135. Bejer, B., 1986. Outbreaks of the nun moth (Lymantria monacha) in Denmark with remarks on their control. Anz. Schaedlingskd. Pflanz. Umweltschutz, 59: 86-89. Bejer-Petersen, B., 1972. The nun moth, Lymantria monacha L., in Denmark. Entomol. Medd., 40: 129-139. Bierl, B.A., Beroza, M. and Collier, C.W., 1970. Potent sex attractant of the gypsy moth: its isolation, identification and synthesis. Science, 170: 87-89. Chinery, M., 1976. A Field Guide to the Insects of Great Britain and Northern Europe (2nd edition). Collins, London, 352 pp. Jensen, T.S., 1983. Registration and control of the nun moth, Lymantria monacha L. by means of pheromone. Mitt. Dtsch. Ges. Alg. Angew. Entomol., 4: 146-149. Jensen, T.S., 1985. Outbreak and latency populations of the nun moth, Lymantria rnonacha L. Mitt. Dtsch. Ges. Alg. Angew. Entomol., 5:133-136. Jensen, T.S. and Bejer, B., 1985. Registration and control of the nun moth, Lyrnantria monacha L. in Denmark 1978-84. - Dan. Skovforen. Tidsskr., 70:182-205. Jensen, T.S. and Nielsen, B.O., 1984. Evaluation of pheromone catches of the nun moth, Lymantria rnonacha L. Influence of habitat heterogeneity and weather conditions. Z. Angew. Entomol., 98:399-413. Sliwa, E. and Sierpinski, Z., 1986. Gradation der Nonne (Lymantria monacha L. ) in Polen von 1978 bis 1984. Anz. Schaedlingskd., Pflantz. Umweltschutz, 59:81-86. Wellenstein, G., 1942. Die Nonne in Ostpreussen. Monogr. Z. Angew. Entomol., 15:682 pp. Wellenstein, G. and Schwenke, W., 1978. Lymantria monacha. In: W. Schwenke (Editor), Die Forstschadlinge Europas. Schmetterlinge, Hamburg, 472 pp. Zethner O., 1976. Control experiments on the nun moth (Lymantria monacha L.) by nuclearpolyhedrosis virus in Danish coniferous forests. Z. Angew. Entomol. 82:192-207.