Abstract
Critical population density was evaluated for three foliage browsing insects: winter moth (Operophtera brumata L.: Lepidoptera, Geometridae), brown oak tortrix (Archips crataegana Hb.: Lepidoptera, Tortricidae) and fall webworm (Hyphantria cunea Drury: Lepidoptera, Arctiidae) in pedunculate oak (Quercus robur) and European ash (Fraxinus excelsior) of different sanitary condition. At the same foliage dry mass contents, the critical population density of H. cunea is 7.7 and 8.8 less than those of O. brumata and A. crataegana respectively. At real foliage dry mass contents (43 and 35 % for oak and ash respectively), the critical population density of all analyzed insects is 1.8 higher for oak, than for ash. Critical population density of foliage browsing insect for healthy tree is 1.25; 2.5 and 6.25 higher than for the trees of the IInd, IIIrd and IVth category of sanitary condition. Algorrhythm of practically use of given approach to predict the threat to the stands (expected defoliation, %) is described.
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