Forster, B.; Knizek, M.; Grodzki, W. (eds.) 1999: Methodology of Forest Insect and Disease Survey in Central Europe.
Proceedings ofthe Second Workshop ofthe IUFRO WP 7.03.10, April20-23, 1999, Sion-Chateauneuf, Switzerland.
Birmensdorf, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) 17-23.
RECENT PEST OUTBREAKS AND SURVEY METHODOLOGY PRACTICED IN CROATIAN FORESTRY
INTRODUCTION
Boris Hra.Sovec
Forest Protection Department Faculty of Forestry, University of Zagreb Svetosimunska 25, HR-10000 Zagreb, Croatia
e-mail: boris.hrasovec@zg. tel.hr Miroslav Harapin
Forestry Institute Jastrebarsko Pokomog10, HR-10000 Zagreb, Croatia
Close to one half of Republic of Croatia is covered by forests and their various degradation stages (2,49 million hectares- 44% of total state area). State forests comprise 81,4% of these while only 18,6% are privately owned. Among state forests, the majority (80,1%) are
managed by public enterprise "Hrvatske sume" (i.e. "Croatian Forests"), and the rest (1,3%) reside under various protection categories like national parks, natural parks, forest reserves etc. About 1 million hectares managed by state enterprise are very valuable high forests and about '14 million hectares are various continental and Mediterranean coppices. Growing stock amounts to 324 million m3, with an annual volume increment of 9,6 million m3 and annual felling of approximately 5,3 million m3. Most numerous tree species are: beech (37% by growing stock), pedunculate, sessile and other species of oak growing in lowland riparian forests and hilly belt (24%) while conifers represent only 14% by growing stock and most important one is common frr growing in mountainous natural mixed beech-fir forests.
It is clear that such natural wealth, managed mainly by state company, calls for an adequate pest survey organization and related forest protection measures. This is why in 1980 the Croatian Ministry of Agriculture and Forestry established a Diagnose and Prognose Service located in Forest Research Institute Jastrebarsko.
SURVEY METHODOLOGY
Since ownership structure of Croatian forest land is largely dominated by state forests, ac- tivity of the Diagnose and Prognose Service (DPS) is closely connected with closely related department in state enterprise "Hrvatske sume". Field data is collected by trained personnel working in 16 Regional Forestry Administrations which cover the majority of the Croatian forested land through network of 171 Forest Stations. These specialists collect data, prepare them for periodical yearly report, coordinate peld activities regarding detection, survey, evaluation and suppressive measures, should they be needed. Collected data prepared in predefined forms are sent to DPS where further analysis takes place. Here, all the regional data are summarized, biological samples are reared and tested on parasitism and health condition and finally, decisions are being made where and when to undertake suppressive measures. According to need, professionals from DPS often check the situation in the field and help regional foresters through permanent education and expertise with less often occurring pests and diseases.
Various methods are applied in order to asses the population densities of most important forest pests and these being adapted to specific biological cycles and practical aspects of
survey techniques. Fundamental principles governing the use of certain method are as
follows: it (method) should be simple enough for the field personnel to be able to conduct it, it should be accurate enough, i.e. give the satisfying density estimations and fmally, it should be finished well ahead possible damages occur so there is sufficient time left for planning the suppression measures. We can classify these survey methods in several groups. Some of the oldest ones and still very much used are those involving counting of various insect develop- ment stages on sample plots or transect paths (Harapin et al. 1996).
Egg masses of Lymantria dispar are counted regularly on a yearly basis and this is done both on continental (transect method) and coastal area (sample plots). Intensity of attack is ex- pressed by percentage of trees with egg masses for current year and these are classified into five classes, lowest having less than 1% "attacked" trees and highest having more than 50%
"attacked" trees. Regarding the qualitative analysis and determining the health state of defoli- ating insects, egg masses are often checked against parasitism for the following pests: Lyman- tria dispar, Euproctis chrysorrhoea, Malacosoma neustria, Thaumetopoea processionea, T.
pityocampa and Neodiprion sertifer.
Larvae of some insect pests are counted in some special circumstances and this applies more to forest nurseries where grubs and larvae of Scarabaeidae, Noctuidae and Elateridae are counted and if critical numbers are achieved suppressive measures have to be undertaken. On a qualitative basis, larvae are often laboratory reared and checked against parasitism or other biological agents expected to contribute the crack-down of heavy infestation period. Besides formerly mentioned defoliators larvae of Tortrix viridana, Apethymus abdominalis, various Geometridae and some more important Scolytidae are also being laboratory checked. In the continental region caterpillar nests of overwintering E. chrysorrhoea are counted on a transects in lowland riparian forests. The same is done throughout coastal and island pine forests with T. pityocampa.
Pupae or cocoons are sometimes being counted and used for assessment of population buildup for several pests among which more often T. pityocampa, N sertifer, Stereonychus fraxini and Dendrolimus pini. Laboratory analysis of qualitative population elements is
periodically carried out on pupae of the above mentioned pests.
Adults are also targeted for population density assessment and this is done in several ways.
Most often, adults are collected by some means of trapping technique. Well established method for assessment of population densities and critical population levels is used for two of the most important loopers: Erannis defoliaria and Operophthera brumata. Their wingless females are caught and counted on sticky trap-belts during the emergence period October- January. Another method for trapping the soil emerging pests is by using the wire-mesh covered cages (some Geometridae, A. abdominalis and acorn pests such as Curculio spp. and Cydia spp. ).
Modem methods for adult trapping in monitoring purposes involving sexual pheromones are used only fragmentary and more as an experimental addition to permanent evolvement of survey techniques (Paranthrene tabaniformis, Gypsonoma aceriana, Ostrinia nubilalis, Zeu- zera pyrina). Aggregation pheromones of lps typographus, Pityogenes chalcographus and Trypodendron lineatum are being consistently used as a monitoring tool in continental region.
Though spruce forest in Croatia are not nearly endangered as those in Central Europe, this method has caught foothold especially in those limited areas where spruce has been introdu- ced during mid century and where it grows out of its natural habitat.
There is however one special method of branch sampling developed for specific needs of population density and defoliation risk assessment in our broadlived oak forests. Its
originator, Dr. Miroslav Harapin introduced it by the late eighties with intention to better
assess unclear situation regarding flowering and acorn production and causes for early crop loss (Harapin 1993). Another important issue were problems with population density
assessment of some early defoliators which overwinter on oak twigs in egg stage. Today, this has become a widely accepted method providing fairly accurate predictions of what is going to happen in sampled forests in the following spring.
Table 1. Sample results of a four-year branch analysis regarding flowering capacity, defoliation prediction and insect pests involved (regional forestry administration samples given in the table represent larger part of Quercus robur forests in Croatia, "?"
symbol means no data available)
Number
Number Dead Flowers Defolia-
Year of Sprouted tion Pest
samples of twigs shoot tips Male Female (%)
BJELOV AR REGIONAL FORESTRY ADMINISTRATION
1989/90 12 88 57 30 15 8 25 leafroll., loopers, casebearer, sawfly 1990/91 36 252 130 74 585 119 35 leafroll., loopers, casebearer, sawfly 1991192 62 400 233 166 1810 425 20 leafroll., loopers, casebearer, sawfly 1992/93 53 283 228 168 732 239 75 leafroll., loopers, casebearer, sawfly
:E(%) 163 1023 648 (63) 438 (42) 3142 791 (20) 39
KARLOVAC REGIONAL FORESTRY ADMINISTRATION
1989/90 2 68 63
-
628 7 15 leafrollers, loopers1990/91 11 88 56 41 1217 132 60 oak sawfly
1991192 3 17 6 16 67 47
- -
1992/93 17 73 55 67 295 198 30 leafrollers, loopers
L (0/o) 33 246 180 (73) 124 (50) 2207 384 (15) 35
ZAGREB REGIONAL FORESTRY ADMINISTRATION
1989/90 10 67 36
-
471 8 30 leafrollers, loopers, casebearer 1990/91 27 187 125 32 633 209 45 oak sawfly, loopers1991192 12 88 35 47 164 8 15 oak sawtly, loopers
1992/93 65 367 256 157 936 274 65 oak sawfly, loopers, casebearer :E(%) 114 709 452 (64) 236 (33) 2204 499 (18) 36
VINKOVCI REGIONAL FORESTRY ADMINISTRATION
1989/90 40 219 170 29 1357 95 50 leafroll., loopers, casebearer, sawfly 1990/91 41 229 210 41 868 170 20 oak sawtly, 1oopers, casebearer
1991192 ? ? ? ? ? ? ? ?
1992/93 25 164 86 73 104 42 25 leafroll., loopers, casebearer, sawfly :E(%) 106 612 466 (76) 143 (23) 2329 307 (12) 32
:E<%>1 422 2590 1746 (67) 941 (36) 9882 1981 (17) 36
During late fall and winter, samples are taken from randomly chosen oak trees from upper strata. Usually, trees are felled down (which is mainly during the normal felling period in these forests), then 4-7 branches, 7(}-80 ems in length, are taken from upper parts of crown, preferably from all four aspects. Branches are transported to a centralized laboratory managed by DPS service where they are given water supply, room temperature and daily supply of sunlight. Underneath, white sheets of paper are secured on which early signs of defoliation can be recorded (excrements). Also, the defoliating fauna, their composition and densities can be easily assessed and related to available food supply, i.e. buds and sprouting leaves.
Another important outcome of this method is prediction of flowering capacity for sampled trees (ratio between female and male buds) which is becoming more and more important from the silvicultural standpoint since eighties and nineties were the years of growing problems with acorn production and reforestation, especially in our pedunculate oak stands.
Furthermore, another assessment can be made on the basis of ratio between nonsprouting branches. This data (assuming the samples were correctly picked and promptly transported to laboratory) will predict the intensity of oak dieback ("Waldsterben") so often addressed during seventies and onwards.
Table 2. More important insect pests recorded during the 1979-1998 period, area attacked and most recent short-term trends
Area attacked during the
Insect Order Host period 1979-1998 (ha) Trend
average maximum
Lymantria dispar Lepidoptera Broadlives 77943 136000 --+
Geometridae Lepidoptera Broadlives 19096 64013 --+
Tortrix viridana Lepidoptera Oaks 13983 64013 t
Euproctis chrysorrhoea Lepidoptera Quercus robur, Q. 2712 11091 ttt tpetraea
I,Apethymus abdomina/is Hymenoptera Quercus robur 1005 3640 t
Malacosoma neustria Lepidoptera Quercus robur 737 8022 ttt
Stereonychus fraxini Coleoptera Fraxinus angustifolia 6996 31529 t
Thaumetopoea pityocampa Lepidoptera Pinus spp. 4702 18193 -!.
!Argyresthia fundella Lepidoptera Abies alba 2766 39582 --+
Coleophora laricel/a Lepidoptera Larix europaea 14 287 t
iRhyacionia buo/iana Lepidoptera Pinus spp. 42 189 t
Dioryctria sp/endidella Lepidoptera Pinaceae 12 135 -!.
Pristiphora abietina Hymenoptera Picea abies 17 209 --+
Neodiprion sertifer Hymenoptera Pinus spp. 16 92 -!.
Sacchiphantes viridis, S. abietis Homoptera Picea abies 160 1203 --+
Dreyfusia nuesslini Homoptera Abies alba 49 820 -!.
Scolytidae Coleoptera Pinaceae 1594 4410 --+t
Melasoma populi Coleoptera Poplar cultivars 683 2927 -!.
Phyllodecta vitellinae Coleoptera Poplar cultivars 537 2967 -!.
Saperda populnea Coleoptera Poplar cultivars 141 1020 -!.
Cryptorrhynchus lapathi Coleoptera Poplar and willow 124 954 --+
cultivars
Paranthrene tabaniformis Lepidoptera Poplar cultivars 95 986 -!.
Thaumetopoea processionea Lepidoptera IQuercus spp. 298 2000 tt
PEST OUTBREAKS AND RECENT TRENDS
As in many neighboring countries, situation in Croatia, regarding more important insect pests is in many ways similar. There are, off course, some differences due to a specific forest phy- tocoenoses and climatic predisposing factors. We will discuss only the main pest species and some important groups regarding their relative importance to Croatian forestry.
There is more than twenty species of defoliators, sap suckers and xylophages screened regu- larly or on a periodical basis with various survey methods used in Croatian forests and forest nurseries. Table 2 lists those which caused some serious damage in the past twenty years and some that show rising short-term trends during the last two years.
The most serious pests in the lowland riparian forests and partly in the hilly belt of continental Croatia are L. dispar, T. viridana and several geometrid species among which E. defoliaria
and 0. brumata lead in severity of attack.
During the past two decades three major peaks in L. dispar population density occurred (Fig.
1 ). The highest one was by the beginning of eighties with more than 130000 hectares atta- cked. Second peak followed by the late eighties and the third one peaked in 1994 (Androic &
Harapin 1996). Each of the following was smaller by attacked area. It is worth mentioning that L. dispar became more serious pest in coastal area in last decade and less important in inland Croatia. Its last gradation starting on the Istria peninsula swiftly plagued the whole coast reaching the southern parts near Metkovic in merely three years. The problems concer- ning suppression in coastal region arise from fact that no economic damage can be calculated in these brush type degraded forests composed mainly from pubescent oak where no measures are taken and gradation is left to end by itself. In valued lowland Q. robur forests, potential
(ha)
Fig. 1. Population density trends of the most important pests
Lymantria dispar Tortrix viridana
economic loss is calculated by the fact that about 30% of the increment is lost if total defo- liation occurs (Klepac & Spaic 1965). Parasitism levels and occurrence of other biotic re- gulators are checked during the gradation period and they play important role in creating prognostic charts and yearly suppression plans.
Geometrids are the second most important group of forest defoliators whose importance grew especially in lowland forest ecosystems during eighties and nineties. It seems that similar trends have been experienced in some regionally close countries (Cs6ka 1998, Mihalache et al. 1998). Two of the aforementioned species are by far most widely dispersed causing major damages but some other species contribute regionally by incrementing the defoliating effect (Colotois pennaria, Agriopis aurantiaria).
Tortrix viridana and its close relatives (Archips xylosteanus, A. crataeganus, A. podanus) also play an important role both in continental
Q.
robur andQ.
petraea forests as in coastalQ.
ilex forests and maquis. Infested areas very often coincide with those attacked by geometrids therefore prognostic charts are compiled taking this additive effect into account. Both geome- trid and tortricid group of defoliators are being monitored predominantly by winter branch samples.Among other defoliating insects some deserve special attention due to their periodical and regional defoliating impact. Euproctis chrysorrhoea and Malacosoma neustria are good examples. Both are constantly present throughout the whole lowland region but not causing damages in larger areas. E. chrysorrhoea occurs in coastal region but there its caterpillars prefer feeding on Arbutus unedo, sparing the oak trees. However, in areas where they occur periodically, and this is just the case in two last years in central riparian area of Sava river (SE of Zagreb ), damages are very serious and intensive measures are being undertaken. In such gradation years egg masses (M neustria) and caterpillar nests (E. chrysorrhoea) are being collected for the survey purposes.
Ape thymus abdomina/is and A. braccatus are the two tenthredinids which were recorded in lowland oak forests by late fifties and have periodically entered gradation stages since then.
Latest gradation was in mid-eighties.
Stereonychus fraxini is causing severe damages on Fraxinus angustifolia and there are several factors that hamper our efforts to efficiently survey and suppress this serious defoliator. For the population density assessment overwintering adults are collected by scrubbing the moss from tree trunks covering the 1m high imaginary cylinder area. This is where at least one half of the population overwinters. It is still not quite certain whether this holds true in various stand situations. Next crucial problem occurs when suppression measures are definitively needed. Since first damages occur practically during sprouting there is always a problem with inadequate area for any kind of pesticide deposition. And thirdly, narrow-leafed ash grows predominantly in mixed oak-ash forests where dispersed ash trees cause additional treatment difficulties.
Among other defoliating insects we would like to point out some rising populations of ten- thredinid species among which Caliroa annulipes seems to have the leading role in the last three years. It started damaging young plants in some forest nurseries but in 1998 it heavily attacked some young oak stands.
Conifer species are most numerous in coastal and mountainous region. Pine processionary moth is widespread and sometimes very important pest in whole coastal region. It is regularly monitored since it is always present in some parts in relatively large numbers. Egg masses, cocoons and caterpillar nests are collected and quantitatively and qualitatively analyzed. If suppression measures are needed they are conducted either by mechanical collecting and bur- ning of winter nests or by chemical treatments with BT or IGR based compounds.
Abies alba, as our most important conifer species, has specific guild of defoliators. However, one lepidopterous species emerged as far most important and destructive. During mid-fifties Argyresthia fundella started its devastating gradation in the hearth of mountainous region. It remained important pest with this first eruption being the strongest. In the past twenty years its average attack area amounts 2766 hectares with 1980 being the year of largest occurrence (almost 40000 ha). Population density assessment is done by counting the cocoons on sample branches and calculating this number per thousand fir needles. Regarding this ratio, attacked area is charted into five infestation classes. During the last two decades there have not been any major gradation occurrences.
Problems regarding xylophages can be categorized in three main groups: technical damages occurring on logged and dying trees both in lowland oak forests as in fir and spruce forests of mountainous region (Trypodendron spp., Xyleborus spp. and Platypus cylindrus), physio- logical damages with resulting tree dyout (Agrilus spp., Pityokteines spinidens, 1 typogra- phus, Pytiogenes chalcographus) and combined technical and physiological damages in pop-
lar and willow cultures caused by various Coleoptera and Lepidoptera (Table 2). We should underline that scolityd damages on spruce are by far smaller in scale compared to other
central European countries since common spruce grows mainly in mixed beech-fir forests of central Croatia and is not endangered like in other countries. Off course, same trends like in other countries are evident but in much smaller scale (Cs6ka 1998, Grodzki 1998, Knffek et al. 1998, Zolubas & Ziogas 1998).
CONCLUSION
Diagnostic and survey procedures practiced in Croatian forestry play important role in imple- menting the sustainable forestry principles. All the serious and most damaging insect pests are regularly monitored and their damage impact properly and aptly prognosed. Suppressive mea- sures, coordinated from DPS service, are shifting toward ecologically more appropriate biote- chnical and biological compounds. Less and less synthetic pesticides are used and when nece- ssary, only those with lesser toxicity and shorter persistency are used.
Improvements should be made in future through the following: intensifying the sampling procedures for some insects occurring on irregular basis and especially in areas with high degree of tree dyout, implementing the pheromone monitoring programs for more species with special regard to some lepidopteran pests in poplar cultures and lowland oak forests, intensifying the branch sampling method and widening its use on other types of forests.
Clearly, all of this can be obtained only with substantial support from the relevant state institutions and major forestry company but if benefits from DPS activities are confronted to its cost, only positive conclusion can be achieved.
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