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ŠUMARSKI LIST 5-6/1999 str. 14     <-- 14 -->        PDF

B. Hrašmi-c i M. Harapin: DIJAGNOZNO - l´ROCiNO/.NI- METODE I GRADAC. ZNAČAJNIJIH Sili . KUKACA.,.
SUMMARY: In 1980 the Croatian Ministry of Agriculture and Forestry established
a Diagnose and Prognose Service located in Forest Research
Institute Jastrebarsko. 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 šume". 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. Egg
masses of Lvmantria 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. 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.
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.). Modern 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 nubi/alis, Zeu-zera pyrina).
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, M. 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 J 993). 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.


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, 70-80 cms 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


Šumarski list br. 5 6, C XXIII (1999), 1X3-193