Forster, B.; Knizek, M.; Grodzki, W. (eds.) 1999: Methodology of Forest Insect and Disease Survey in Central Europe.
Proceedings of the Second Workshop of the IUFRO WP 7.03.10, Apri120-23, 1999, Sion-Chateauneuf, Switzerland.
Birmensdorf, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) 158-163.
THE POPULATION DYNAMICS OF GREGARIOUS SPRUCE SA WFL Y (PRISTIPHORA ABIETINA) IN THE EASTERN PART OF THE CZECH REPUBLIC
Jaroslav Holusa
Forestry and Game Management Research Institute vULHM Jiloviste-Strnady Office Fcydek-Mistek
Pionyru 1758, CZ-73802 Fcydek-Mistek Introduction
In the surroundings of Ostrava city ( the north-eastern part of the Czech Republic), large damage caused by Norway spruce saw-flies pseudocaterpillars has occurred during last 50 years. However, no precise study of species diversity and bionomy of these insect species have been made there. Ktistek (1980) has studied the Norway spruce saw-flies and their pseudocaterpillars in the whole territory of Moravia (23 sites - except the surroundings of Ostrava) and only part of the results has been published (Ktistek 1973). Abundance of the saw-flies was characterised as a latency in majority of sites.
Kolubajiv (1958) has studied the cocoons of saw-flies in this area. During the period 1949 - 1952, about 70% of cocoons belonged to the gregarious spruce saw-fly (Pristiphora abietina (Christ, 1791)), but in the nearby Beskydy Mts. the proportion of this species was 10- 18% only. The age of the forest stands where the samples were taken was not mentioned.
Kanecka (1995) carried out an basic (till now, unpublished) investigation by using the photoeclectores and the method of knocking down of pseudocaterpillars.
I present the main results of my research made in 1998 in this paper.
Methods
The studied area ·includes a lowland (about 300 m above sea level) surrounded on the west by the Nizk)' Jesenik Mts. and on the south by the Beskydy Mts. The average annual temperature is about 9°C and the average annual precipitation varies from 680 to 1000 mm.
To make sampling, eight studied plots were chosen transversely in the Norway spruce thickets or samplings in this area. Six of the plots were situated in lower altitudes and two of them in the mountains (500 m a.s.l. and 700 m a.s.l.).
A Malaise trap and 5 white and 5 yellow sticky boards (15x21 cm) were exposed in each plot. They were visited every 3 days from April 18-th to June 6-th 1998. I also used the method of sweeping in each plot (100 sweeps per transect- the sunny woodland borders) as well. I situated 30 photoeclectores (50x50x25 cm) in forest stands of various stages (5 in thicket, 5 in samplings, 10 in pool timber and 10 in high forest stemwood) in one of the plots.
The cocoons were counted in January and February 1998 in these sites.
Knocking down method was used in thickets after the hatching of pseudocaterpillars on the five Norway spruce trees in each experimental plot. First checking in a third day- then the checking was done in one week period.
To make objective evaluation of an insects feeding and the possibility of a comparison between the damage in each plot the scale of the damage on spruce has been made. In each plot 100 trees were investigated to assess the percentage of defoliation of each whorl beginning from the top of the tree using 4 degrees.
Rare - very light defoliation of annual shots - below 10 % 1- light defoliation of annual shots 10-50%
2 - heavy defoliation of annual shots 50 - 90 % 3 -total defoliation of annual shots over 90 %
The average defoliation was counted out per tree and then the results of each whorl was accumulated.
Results and Discussion
Totally, 4200 adults were captured belonging to 12 species of Norway spruce saw-flies.
The data showed that the species of Pristiphora abietina has been the most abundant in samples taken by using the methods of yellow sticky boards and sweeping (Fig. 1). The important information is that Pristiphora abietina is the most abundant in mountains as well.
Dominance (%)
Species
photoeclectors sticky boards
Fig.1 The dominance of Norway spruce saw-flies captured by different methods
By using the photoeclectores was found, that the most abundant species were Pristiphora abietina and Pikonema scutellata. The relatively higher abundance of Pikonema scutellata is possible to explain by following information: More adults of this species were captured in high stem wood (while the methods were used only in young forest stands) and the dominance was therefore shifted to Pikonema scutellata. Pikonema scutellata proved to be more attracted to older stands. The number of adults increased with the age of the stands, on the other hand the number of Pristiphora abietina decreased (Fig. 2) The important fact is, that Pristiphora abietina is a serious forest pest in mature forest stands. This was found even by studying the cocoons (Svestka and Holusa 1998). The fact, that saw-flies were observed even in thicket proved that pseudocaterpillars pupate not only in leaf litter but also in turfs being dominant in the undergrowth of thicket In such a place it is impossible to obtain the cocoons by digging and sieving.
90 80 70
';!. 60 50 40 30 20 10
0 f - - ' - - - high forest stemwood
pool timber samplings thicket
DP.abietina
Fig. 2 The proportion of Pristiphora abietina and Pikonema scutellata in forest stands of various stages (locality Paskovsky les wood)
Pikonema scutellata became more abundant in the Malaise traps and sweeping samples (47 resp. 13%) due to high vagility of males (males were much more abundant in samples
than females). The relatively high abundance can be explained by the fact that the trap was placed near the high forest stem wood in one site. 85% of all specimens of Pikonema scutellata were obtained here (the sex ratio was here 12:1). Males migrated to younger forest stands which is the reason for the high dominance of this species.
The number of adults captured by photoeclectores make 10 to 70% of total number of cocoons counted during January and February 1998. These results are not exact due to the low number of photoeclectores and soil probes used.
The swarming of Pristiphora abietina started at the end of April (the first adults were collected on April 30-th) in the majority of plots. However, it started later (May 6-th) in the plots at higher altitudes. The peak was recorded in former plots from May 9-th to 12-th. The swarming of males started approximately three days earlier (Fig. 3, 4). The majority of specimens were captured till May 15-th. After that, only singular adults were collected (to the end of May). The large number of eggs was found at this time, in relationship with this fact.
No parasites have been found in 194 eggs taken to the laboratory.
Number
350 300 250 200
Date of collection
sticky boards Malaise trap photoeclectors sweeping
Fig. 3 Male swarming of Pristiphora abietina based on data obtained by using various methods (locality Paskovsey les wood)
60 50 40 Number 30
Date of collection
l.C) 0 C')
Malaise trap sticky boards photoeclectors sweeping
Fig. 4 Female swarming of Pristiphora abietina based on data obtained by using various methods (locality Paskovsky les wood)
Various methods showed the similar results concerning the swarming (Fig. 2, 3) and particularly the diversity of species (Fig. 1). A significant relationship were found among all used methods for female samples (Fig. 8-1 0). In spite of this, between Malaise traps and yellow sticky boards methods showed high correlation for male samples only (Fig. 5-7).
300 250 :U200
,Q
E150
50 0
Fig. 5 Correlation between the number of specimens (Malaise traps vs. sticky boards • males)
•
y = 0,5824x + 1 ,3771
• R2 = 0,7002
0 100 200 300 400 500
Number
Fig. 6 Correlation between the number of specimens (sticky boards vs. sweeping- males)
25
:u
20,Q
E 15 :::1
z 10 5
•
y = 0,0525x + 1,774 R2 = 0,4976
•
0
30 25 ... 20
G) ,Q 15
E :::1 Z10
5 0
0
100 200 300 400 500
Number
Fig. 7 Correlation between the number of specimens (Malaise traps vs. sweeping- males)
•
50
•
y = 0,0353x + 5,1349 R2=0,1129
•
100 150 200 250 300 Number
...
G) ,QE :::1
z
Fig 8 Correlation between the number of specimens (Malaise traps vs. sticky boards -females)
250 200 150 100 50 0
0 50 100
Number
Fig 9 Correlation between! he number of specimens (sticky boards vs. sweeping- females)
•
150
70 60 ... 50 .840.
E3o :::1
•
Z 20 y = 0,439x- 1,661
10 • • R2 = 0,7671
80 70 60
:u
50,Q 40
E :::130
z 20 10 0
0 50 100
Number
Fig 10 Correlation between the number of specimens (Malaise traps vs. sweeping- females)
150
y = 0,3123x + 0,5173 R2 = 0,8899
0 50 100 150 200 250
Number
The sweeping method is very time consuming and depending on the moment's sun- light. The installation of photoeclectores is money and time consuming. Both these methods are limited on the number of captured insects. However, sweeping is considered most ineffective due to high vagility of adults. On the other hand, Malaise traps are very effective for experimental purposes, however for practice are useless. Another disadvantage of the Malaise trap is as follows: All species of flying insects are attracted. To sort out the insect is
very time consuming. The sticky yellow boards seemed to be very efficient with easy installation. Yellow boards attract only saw-flies and especially Pristiphora abietina adults only (Fig. 1) (they are placed in the top of trees). This give us the possibility to use yellow boards not only for the swarming monitoring, but for finding the critical number as well.
There is high significant relationship between the number of captured adults in sticky boards and the percentage of defoliation (Fig. 11 ).
7
8,6 e
s"'
"C4
-
0 3 G)e
C) 2
0 0
•
y = 1,1995Ln(x)- 1,7977 R2 = 0,9519
100 200 300 400 500 600 700 BOO 900
Number
Fig. 11 Relationship between defoliation of forest stands and the number of captured specimens (by using sticky boards)
The first pseudocaterpillars were observed on May 15-th and its abundance increased rapidly till May 18-th. This corresponds with the fact, that the majority of adults were captured till May 15-th (embryonic development takes from 3 to 5 days at the room temperature (Schwenke 1982). Therefore ,on May 18-th, the majority of the first instar pseudocaterpillars were found (Fig. 12). As the weather was cool and rainy during the following days, the embryonic development was longer and the development of the population irregular and variable. This was probably the reason for the first instar proportion increasing on May 21-st. The development was regular later and finished at about June 10-th. (only several pseudocaterpillars of the oldest instar ware found - males have four instars, females five ) (Fig. 12). The larval development of the whole population took about 25 days. The insect feeding culminated at the end of May, because in this period the highest numbers of pseudocaterpillars were found.
A very low presence of parasites eggs on pseudocaterpillars was observed - 4-th instar parasitation was 0.4% and 5-th instar parasitatlon was 2.4% only.
100
90 • 5th i.
80
70 FEd 4th i.
60
0 50 D 3rd i.
40
30 mt 2nd i.
20
10 1st i.
0
18.5. 21.5. 26.5. 29.5. 2.6. 10.6.
Date
Fig. 12 The proportion of instars Pristiphora abietina during spring (locality Paskovsk)r les wood)
Conclusion
1. The results showed: Pristiphora abietina is the most abundant species of Norway spruce saw-flies in younger forest stands. It damages forest stands of different ages in the lowland as well as at higher altitudes (about 800 m a.s.l.). The abundance of this species in mature forest stands is a bit lower than population density of Pikonema scutellata.
2. Flight period of Pristiphora abietina in different sites starts almost at the same time in the eastern part of the Czech Republic, only adults in the highest altitudes emerge later.
Generally, swarming starts at the end of April. The majority of adults could be observed at the middle of May. The feeding of pseudocaterpillars takes about 25 days till the beginning of June. These results confirmed the published data (Kolubajiv 1952, Schwenke 1982).
3. The sticky yellow boards seems to be very efficient, not only for adults swarming monitoring, but for finding the critical number as well. High significant relationship was found between the numbers of adults captured in sticky boards and the defoliation percentage.
Sticky boards are almost absolutely selective for Pristiphora abietina, their weight is low and installation is easy to do.
4. The scale of 4 degrees used for evaluation of forest stands defoliation seems to be very efficient, when comparison of different stands is made especially.
Literature
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Kolubajiv S. 1952: nase nejskodlivejsi pilatky a boj proti nim. Brazda, Praha, 48 pp.
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Kfistek J. 1980: Diprionidae, Nematinae a Pamphilidae zijici na smrku- poznatky z rozsireni na Morave a z populacni dynamiky. Pfiloha c.l6, 82 s. In: Kfistek J.: Populacni dynamika hmyzich lesnich skiidcii jako zaklad integrovane ochrany lesii proti nim.
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