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Zur Massenentwicklung der Nonne (Lymantria monacha L.) in Kiefernbeständen des nordöstlichen Niedersachsens
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The larch casebearer and its host tree II. Changes in needle physiology of the infested trees
No full textThe population dynamics of the larch casebearer (Coleophora laricella Hbn.) in the field and the physiology of larch needles serving as their feeding basis were analysed from 1991 to 1995 using a differential analysis: one insect species feeding at the same time on two needle types (spurshoot and longshoot needles) of two host species (European and Japanese Larch) under different environmental conditions (Solling hills, lowlands). Resistance mechanisms were found which allow a coexistence of the tree and of the insect population at an economically 'bearable' cost for the host trees. With increasing casebearer densities, physiological changes within the intraannual course of the tree's needle physiology were induced. However, they did not prevent the further growth of the casebearer population. High mortality rates of the sensitive needle mining L1-larvae resulted from specific local defence mechanisms of the single needle followed by a premature leaf abscission. A decrease of casebearer densities was initiated when L4-densities in the spring exceeded a tolerance level which seemed to be adjusted to the environmental conditions. The induced physiological changes led to a sudden deterioration of the digestibility of the needles, caused by an increase of procyanidine and tannin contents and a decrease of protein-amino acid contents. The strong disadvantageous effect of these mechanisms on the casebearer population was coinciding with the highest consumption rates of the casebearer larvae. (C) 2000 Elsevier Science B.V. All rights reserved
Untersuchungen zur Nadelphysiologie von Lärchen (Larix ssp.) bei Befall durch die Lärchenminiermotte Coleophora laricella Hbn. (Lepitoptera, Coleophoridae)
No full textPhysiologische Reaktionen in Lärchennadeln (Larix ssp. ) nach Befall durch die Lärchenminiermotte Coleophora laricella Hbn. (Lepidoptera, Coleophoridae)
No full textZur Massenentwicklung der Nonne (Lymantria monacha L.) in Kiefernbeständen des nordöstlichen Niedersachsens
No full textUntersuchungen zur Nadelphysiologie von Lärchen (Larix ssp.) bei Befall durch die Lärchenminiermotte Coleophora laricella Hbn. (Lepitoptera, Coleophoridae)
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Physiologische Reaktionen in Lärchennadeln (Larix ssp. ) nach Befall durch die Lärchenminiermotte Coleophora laricella Hbn. (Lepidoptera, Coleophoridae)
No full textThe larch casebearer and its host tree:
No full textThe population changes of two larch casebearer (Coleophora laricella Hbn.) populations were analysed under field conditions from 1991 to 1995 using a differential analysis: one insect species feeding at the same time on two needle types (spurshoot and longshoot needles) of two host species (European and Japanese Larch) under two different environments (Solling hills: resource-rich stand, lowlands: resource-poor stand). Casebearer density in the lowlands was always significantly lower than in the Selling hills. The main factors regulating casebearer density were obviously the same for both populations, although feeding intensity and environmental conditions differed. The most important factors influencing density changes were the mortality of the mining young larvae and, to a lesser degree, the hibernation and spring mortality of the L3/L4 larvae. The rates of pupal parasitism were low in the Selling hills (max. 8.7%) although density was much higher than in the lowlands where pupal parasitism was higher (max. 18.5%). There was no evidence for regulative effects of parasites or predators in both populations. It is supposed that larval mortality mainly depends on needle physiology, which in turn is supposed to be influenced by environmental conditions. Different environmental conditions seemed to determine the feeding tolerance levels of the infested host trees. Therefore, Larch trees growing under optimal conditions may be able to tolerate periodical defoliation by the casebearer but Larch trees growing under suboptimal conditions may have to reduce the risk of defoliation to a sustainable degree. (C) 2000 Elsevier Science B.V. All rights reserved
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