Rauno Väisänen

Sub-cortical Coleoptera in dead pines and spruces: is primeval species composition maintained in managed forests?

The sub-cortical beetle fauna of dead Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) trunks was compared in primeval forests and managed forests in central Finland. The numbers of both individuals and species were higher in the managed forest in spite of the smaller trunk surface area examined. The proportion of rare species was higher in the primeval forest. Although most species occurred both in primeval and managed forests, there were striking differences in the abundance relations: there was only one species (Pytho depressus) in common among the ten most abundant species. The proportion of bark beetles (Scolytidae) was more than 50% in the managed forests, and less than 5% in the primeval forests. The number of species per site was associated with observation date, occurrence of snails and trunk position (standing or lying) in the primeval forest, and with trunk diameter in the managed forests. The occurrence of rare beetle species in dead conifer trunks was related to mans effects on the forest. Although many sub-cortical species can live in managed forests, the fauna differs drastically from that of primeval forests.

Heavy metal levels in two biennial pine insects with sap-sucking and gall-forming life-styles.

The concentrations of cadmium, copper, nickel and lead were studied in two biennial pine insects in relation to the deposition of heavy metals in the environment around the industrialised town of Harjavalta in southwestern Finland. Sap-sucking pine bark bugs, Aradus cinnamomeus (Heteroptera, Aradidae), and gall-forming pine resin gall moths, Petrova resinella (Lepidoptera, Tortricidae) were collected on sample plots located at logarithmic distances along 9 km-long transects from the distinctive emission source. The responses of these insects representing different life-style were compared. Heavy metal concentrations in A. cinnamomeus were highest (Cd 17 microg g(-1), Cu 1900 microg g(-1), Ni 220 microg g(-1), Pb 32 microg g(-1)) in the vicinity of the factor complex, and lowest in the outermost zones. This trend followed a linear regression model. The pattern was less clear in P. resinella, the concentrations being only one-tenth of those recorded in A. cinnamomeus. Correlations between metal levels in A. cinnamomeus and previously examined Sphagnum moss bags proved to be highly significant in every case. The differences in the heavy metal concentrations of these two insect species, which occupy the same trophic position, would appear to be due to the differences in their feeding characteristics. Heavy metals accumulate in the posterior bulb of the midgut in the discontinuous alimentary system of A. cinnamomeus, while P. resinella is likely to secrete most of the metals into the walls of the galls. The almost total absence of these two insect species near the factory complex seems to be associated with the high concentrations of metals.

Change of pupal size of Panolis flammea (Lepidoptera; Noctuidae) and Bupalus piniarius (Geometridae) in response to concentration of industrial pollutants in their food plant

SummaryLarvae of Panolis flammea and Bupalus piniarius were reared in the laboratory on needles of Scots pine affected by industrial air pollutants in Finland. Needles were collected at different distances from a distinctive source of emission along two 9-km-long transects, and from independent control plots. The elemental composition of the needles used as larval food was analysed. Pupal weight, length and width were negatively correlated wiht the distance from the source of emission. The elemental composition of the pine needles explained 24–53% of the variation in pupal weight. Most of the explained variation was assoicated with the concentration of heavy meals in the pine needles.

Industrial air pollution and the pine bark bug, Aradus cinnamomeus Panz. (Het., Aradidae)

The population density of the pine bark bug Aradus cinnamomeus Panz. (Het., Aradidae) was studied along an air pollutant gradient in the industrialized town of Harjavalta, western Finland. In the 71 sample plots, the bug density in the bark of 1380 Scots pines (Pinus sylvestris L.) varied from 0.1 to 12.2 bugs per 100 cm2. Zones are presented on the basis of the bug densities. The lowest density is usually observed in the immediate vicinity of the factory complex, and at several kilometres from it. The highest bug density, also evident from the poor growth of the pines (Aradus injury), usually occurs 1–2 km from the factories, the numbers decreasing rather steeply towards the pollutant source. When the bug density was compared with the deposits of heavy metals (Cd, Cu, Ni, Pb, Zn), which indicate the general level of air pollution, it showed positive and mostly statistically significant correlations. It is concluded that the pine bark bug, like many other sucking insects, has benefited from the increasing atmospheric pollution, which cause physiological alterations in the host trees.

Air Pollution Levels and Abundance of Forest Insects

This chapter investigates and reviews the effects of industrial air pollution on forest damage through insect pests. A spatial pollution gradient (SO2, heavy metals) was utilized in southwestern Finland around a factory complex producing copper, nickel, sulphuric acid and fertilizers. Several insects associated with the Scots pine, including bark bugs, aphids, diprionids and tortricids, abounded in the moderately polluted pine stands, but were scarce (excluding aphids) in the immediate vicinity of the industrial plants probably due to the toxic effects of heavy metals. Preliminary results showed no clear patterns for parasitization of pests in relation to the pollution level. Chemical analyses of the needles showed that the concentrations of heavy metals decreased exponentially with increasing distance from the emission source. Also the concentrations of potassium, sodium as well as ash weight and air-dry weight decreased, while those of magnesium, manganese and calcium increased with increasing distance. The peaked abundance patterns in the gradient found in many species could not be completely explained by findings in the laboratory. The pupal/cocoon weight of defoliator species reared was the smaller, the nearer to the emission source their larval food originated from. A considerable amount of variation in the weight could be explained by the heavy metal concentrations in the needles. In the European pine sawfly, the number of eggs laid was positively correlated with the cocoon weight. However, smaller females produced more viable eggs, which masked the effect of female size on the number of offspring produced. Contaminated food increased the pupal mortality and decreased the developmental rate of the large pine sawfly. Although air pollution affected several essential population parameters of insect pests, the available results cannot be generalized uncritically, since causal relationships are still insufficiently known. All signs suggest that the adverse effects of forest pests increase with pollutant load, which may lead to unexpected problems in forest management.

Bugs in bags: intraspecific competition affects the biogeography of the alternate-year populations of Aradus cinnamomeus (Heteroptera)

Aradus cinnamomeus, a pest of pines, shows a two-year life cycle with two widely distributed parapatric alternate-year populations and a narrow overlap zone in southern Finland. To explain the dynamics of this unique biogeographical pattern the intraspecific competition hypothesis was tested by field experiments involving crowding, transplantation and mixing the two reproductively isolated populations. The study was carried out simultaneously in both the evenand odd-year populations areas (defined according to the reproduction year of the locally dominant population) and in the narrow overlap zone. In addition to the mortality of both age-classes, the growth rate of larvae and the adult size were studied in the tests. The results suggest that younger larvae are better exploitation competitors than older larvae or adults. They can penetrate deeper into smaller crevices in the bark than the larger bugs, and thus exploit a wider range of resources. However, exploitation (within test bags) competition plays only a minor role in the regulation of the biogeographic pattern of the pine bark bug. The presence of the natural background population in the test trees (mostly outside the test bags) increased the mortality of the transplantated bugs of the other age-class to about the same extent as on a highly unfavourable site. Interference competition between the two age-classes, reinforced by the impact of exploitation competition and parasitism, can reasonably well explain the parapatry of the alternate-year populations, although direct evidence for interference is still lacking.

The biogeographical mystery of the alternate-year populations of Aradus cinnamomeus (Heteroptera, Aradidae)

Etude realisee en mai 1982 et 83 en Finlande. La competition intraspecifique controlerait la repartition des populations ayant un cycle de deux ans. Le role des parasites est aussi a prendre en consideration

Between-species differences in heavy metal levels in four pine diprionids (hymenoptera) along an air pollutant gradient.

The concentrations of copper, iron, nickel and cadmium were studied in cocoons of four pine sawfly species, viz. Gilpinia virens, G. frutetorum, Microdiprion pallipes and Neodiprion sertifer. Larvae were reared in the laboratory on needles of Scots pine collected along a pollution gradient around a copper smelter in SW Finland. Heavy metal concentrations in all the species and needles decreased with increasing distance from the pollution source in accordance with linear regression models. Metal levels were highest in M. pallipes and lowest in G. virens, being only about one half to one quarter of those in M. pallipes. Concentrations of copper, iron and nickel in the insects were lower than in their food. Cadmium bioaccumulated in N. sertifer, G. frutetorum and, especially, in M. pallipes. The differences in these closely related pine defoliators are comparable to those between different trophic levels or species with entirely different feeding characteristics.

Morphological variation in Aradus cinnamomeus (Heteroptera): geographic patterns and character displacement

Morphological variation in the pine bark bug Aradus cinnamomeus Panzer was studied in 43 metric measurements of the head, thorax and abdomen of adult males and 40 of females. The extent of geographic variation in males and females was studied among Finnish two-year bug populations, 14 of which belonged to the eastern even-year reproducing cohort and 11 to the western odd-year cohort. These allochronic cohorts have a parapatric distribution. The first three dimensions obtained in canonical discriminant analysis together accounted for 57% of the variation present in the males and 60% in the females, respectively. The first three canonical variables were statistically significantly correlated in both sexes with the latitude and longitude of the locality. The alternate-year cohorts formed two separate groups of populations. The closer the allochronic bugs originated to each other, the greater the morphological difference between them. The possibility of intraspecific character displacement is discussed in this context, and a new definition is presented for the concept of character displacement including within-species cases.

Gall density of Retinia resinella (Lepidoptera, tortricidae) in relation to pine stand development

Patterns of host plant utilization of the pine resin gall moth Retinia resinella in a young Scots pine stand were studied along a belt transect in southeastern Finland. The gall distribution in 1984–1989 was retrospectively analysed. The moth preferred leaders to lateral shoots. In 1984, 60% of the galls occurred on the leaders, while the respective proportion was 40% in 1986 and 38% in 1988. The mean height of pines attacked by the moth changed from 74 to 127 cm. In 1984, moth galls on leaders occurred on higher and better‐growing trees than the average, while the opposite was true in 1988. There was an indication of clumping of R. resinella, with clumps spaced about 20 m apart which may be‐due to microhabitat distribution, the behaviour of ovipositing females or spatial dynamics of predators. The galls occurred more frequently on trees with a previous years gall, but this tendency was not observed in the leader galls. The results support the view that the pattern of host plant utilization by a herbivor...