Treesearch

Entomological monitoring is part of a total ecological monitoring system. Its purpose is the identification, prognosis, and estimation of forest ecosystem impacts induced by insects. The entomological monitoring of a forest is based on a clear understanding of the role played by insects in forest ecosystems. The patterns of insect population dynamics in space and time have to be discovered. Mathematical models can be used to make a prognosis and determine the components and parameters of a given system.

The resistance of woody plants to phytophage damage consists of a universal system of mechanisms: 1) repellent chemicals, 2) defensive reactions both mechanical and chemical, 3) retention of viability under disturbed metabolism and low biomass accumulation, and 4) recuperative capacity. Siberian coniferous tree species, with the exception of Larix, are less resistant to phytophage damage than deciduous ones. Evergreen conifers evolved toward constitutive antibiosis by improving their chemical mechanisms of defense, i.e. terpenoid repellents and toxins. In deciduous species, there was...

Several scolytid species are known to use host volatiles such as monoterpenes and the degradation product, ethanol, when searching for suitable host material. The release rates of terpenes and ethanol and the proportions in which they are released can be expected to differ depending on the breeding substrate preferences of the various scolytid species. The aim of this study was to compare the attraction of various scolytid species and associated beetles to combinations of α-pinene and ethanol in proportions of approximately 1:1 and 1:10 when released at three different rates. α-Pinene was...

In an earlier field experiment, natural enemies of the bark beetle, Ips typographus (L) were estimated to have reduced bark beetle productivity by more than 80 percent. To test this hypothesis, spruce logs (Picea abies) were placed in the forest in the spring, prior to commencement of flight by I. typographus. The logs were screened at different times following onset of bark beetle attack. The screens prevented further colonization by bark beetles and associated insects. The insects were subsequently collected as they emerged from the logs the following autumn or the following spring.

During the years 1971 to 1982, major epidemics of the spruce bark beetle, Ips typographus L., occurred in southeastern Norway and adjoining parts of Sweden. The outbreaks were triggered by large-scale wind-felling and long-lasting drought (Worrell 1983). This "epidemic of the century," hitting our important timber tree, Norway spruce, Picea abies (L), stimulated research in Norway and other countries of the region on the relationship between the beetle, its fungal symbionts, and the host tree.

It is widely known that xylophagous insects do not usually attack healthy, resistant trees. In order to overcome these defenses, inner-bark feeding insects have developed symbiotic interrelationships with various organisms, fungi in particular. In this paper, using our own data together with that available in the literature, we analyze the forms of relationships between insects and fungi and the role of these interactions at various stages of wood decomposition. In doing so, we distinguish between the following fungal-insect relationships: 1) ambrosia mycetophagous insects, symbiotically...

Patchy and ephemeral resources, such as the cones of conifers, can be very useful in the study of plant-insect relationships. Studies of such relationships in forest entomology are typically complicated by the spatial and temporal characteristics of the host plants, which occur over vast areas and have lifespans of decades or even centuries. The reproductive structures of conifers, on the other hand, are much more easily studied because they mature within 1 to a few years and occur as discrete, easily sampled units. They also play a unique role in forest ecosystems.

Semudobia betulae Winnertz, described in 1853, is the most common species of gall insect occurring on the genus Betula in the Palearctic and Nearctic regions of the world. S. betulae has been observed on four species of Betula according to Barnes (1951) and on 14 additional species according to Roskam (1977). At the Arboretum of Mlynany affiliated with the Institute of Dendrobiology of the Slovak Academy of Sciences, eight species of Betula from the Palearctic and Nearctic regions have been planted. Three of them are mentioned in the papers of Barnes and Roskam: B. pendula, B. manii, and...

Insects attacking seeds and cones of trees are significant for their economic consequences as well as for the ecological role in vegetation dynamics. Currently much is known about seed and cone insects feeding on upright trees (see Roques, this volume), but almost nothing is known about cone inhabitants of prostrate pines Pinus pumila (Pall.) Rgl., P. albicaulis Engelm., P. mugo Tur. These three vicariant species from young mountain systems of the northern hemisphere have evolved in unfavorable environments which have favored peculiar patterns of seed production and insect-host relations....

Trees do not actively respond to herbivore grazing, they react to the deterioration in the balance of their roots and crowns functions, which comes when transpiration powers fall off. Such inherent reactions of plants originated as abilities to restore photosynthesis.