Johan Andersen

Transpiratory water loss and metabolism of beetles from arid areas in East Africa

Abstract 1. 1. Carabid beetles have rates of transpiratory water loss and metabolic rates which are higher than those of tenebrionid beetles. Within each family, dry habitat beetles have lower rates of water loss than beetles from mesic or hygric habitats, but no habitat-related difference was observed with regard to metabolic rates. 2. 2. When rates of transpiratory water loss of beetles of the two families are plotted as a function of metabolic rates, it appears that for dry habitat beetles, the metabolic rate is the single determinant of transpiratory water loss. 3. 3. This is interpreted as indicating that respiratory water loss is the dominating component of water loss in both carabids and tenebrionids in dry habitats, and that the difference between the families with respect to rates of water loss reflects the difference in metabolic rates. 4. 4. Carabid beetles have considerably higher extracellular concentrations of sodium than the tenebrionids. Seen in the light of the high energetic cost claimed to be involved in sodium transport, this observation is interpreted as indicating that the high rates of water loss and metabolism of the carabids are due to active extrusion of sodium from the cells of the beetles. 5. 5. The ecophysiological significance of these differences is discussed.

Primary attraction and host tree selection in deciduous and conifer living Coleoptera : Scolytidae, Curculionidae, Cerambycidae and Lymexylidae

Abstract: Primary attraction and host tree selection among bark and wood living Coleoptera were investigated in this research. The experiments were carried out in Dividalen, Troms County, and lasted from May to August, in 1993 and 1994. Beetles living in deciduous trees were the main objects of the present study. Trap type used excluded pheromones in the host tree selection. The traps were placed in areas dominated by Scots pine (Pinus sylvestis) and birch (Betula pubescens), and areas that contained both tree species. The traps were baited with billets of Betula pubescens, Alnus incana and Pinus sylvestris. Empty traps were used as controls. Beetle species found to have both primary attraction and host tree selection prior to landing were the conifer living Tomicus piniperda, Hylastes brunneus, Pityogenes quadridens, Pissodes pini, Hylobius abietis, Magdalis phlegmatica, and the deciduous living Magdalis carbonaria, Hylecoetes dermestoides and Rhagium mordax. Also, Scolytus ratzeburgi and Trypodendron signatum were able to distinguish between suitable and unsuitable host tress prior to landing. Ips acuminatus was found to have neither primary attraction nor host tree selection prior to landing, probably because pheromones were excluded in the attraction. According to the literature, the mechanism used in the host selection is mainly olfactory sensing and vision.

Primary attraction in host recognition of coniferous bark beetles and bark weevils (Col., Scolytidae and Curculionidae)

The hypothesis of primary attraction in Scolytidae and Curculionidae was tested in the field from late May throughout June 1979 and 1980 with 20 and 14 flight traps, respectively. The traps, designed especially to exclude the possibility of secondary attraction, were baited with billets of Scots pine (Pinus sylvestris) or Norway spruce (Picea abies), and empty controls. Tomicus piniperda, Hylastes brunneus, Hylastes cunicularius, Pityogenes bidentatus, Pityogenes chalcographus, Hylobius abietis and Pissodes pini were significantly more frequently caught in traps baited with pine or spruce than to empty controls, and the random flight hypothesis was rejected. The same species, except P. chalcographus, were also able to discriminate significantly between pine and spruce before landing. H. cunicularius was exclusively attracted to traps baited with Norway spruce, whereas the rest of the species preferred the traps baited with Scots pine. The mechanism used by the beetles in their host selection is olfactory sensing of chemical compounds. Host acceptance and nonhost rejecting starts before landing, implying the ability the perceive plant characteristics at a distance (primary attraction).

Riparian Beetles, a Unique, but Vulnerable Element in the Fauna of Fennoscandia

A survey of the distribution and ecology of riparian beetles in Fennoscandia and adjacent countries is presented and the conservation value of, and threats to, the element are discussed. Contrary to most other taxa or ecological groups, the number of riparian species increases from south to north in Scandinavia. The inner parts of the counties of Sør-Trøndelag (STI) in Central Norway and Troms (TRI) in North Norway have the largest total number of riparian species, the largest number of vulnerable (red-listed) riparian species, and the largest importance index, rarity factor and algorithmic ranking in Fennoscandia. These provinces may be regarded as hot spots for riparian species in northwestern Europe and therefore have high conservation value. In addition to river regulation, river banks are exposed to a number of impacts such as removal of sediment and fluvial woodlands, wear and tear, construction of flood-prevention walls, canalization and various other developments (road building, industrial activity, etc.). These impacts seem to be more severe in Norway than in Northern Sweden and Finland. Due to human impacts, riparian carabid beetles have become extinct in parts of their former range in Scandinavia. The possibility of re-invasion of species after restoration is discussed.

Low thigmo-kinesis, a key mechanism in habitat selection by riparian Bembidion (Carabidae) species

In laboratory choice experiments species of Bembidion showed preferences towards natural cover types which coincided with those found in their natural habitats. Some species preferred to hide under stones (lithophilous species), whereas others (vegetation species) preferred grass and withered foliage. Responses of beetles to artificial cover similar in size, shape and weight to natural cover were often not significantly different from the responses shown to natural cover. The mechanism governing these reactions may be a low thigmo-kinetic response, and the response to mechanical stimulation appears to be a key factor in habitat selection by the riparian species of Bembidion.

Humidity responses and water balance of riparian species of Bembidiini (Col., Carabidae)

Abstract. 1. The humidity responses of Asaphidion pallipes (Duftschmid) and Bembidion spp. were studied at various temperatures in choice chambers.

Photoresponse of carabid beetles depends on experimental design

Light orientation of riparian species of the carabid beetle genus Bembidion was studied in three different types of experiments: 1) In chambers with a light and a dark zone and a light source placed vertically above the chamber; 2) With directed light situated aside of the arena and a dark screen placed at the opposite side of the direction of the light source; 3) with the same design as in 2) but with a white, instead of a dark, screen. The results of the experiments do not support the traditional separation in darkand light-prefering (photonegative and photopositive) species. Several species (e.g., B. prasinum, B. petrosum) select the dark zone in design 1 (photonegative reaction), but orients towards light in designs 2 and 3 (photopositive reaction). B. schuppelii reacts indifferently to directed light, but orients towards dark silhouettes and prefers darkness (design 1). The orientation of species to light in this study is related to their natural habitat selection. Light or silhouette orientation is thus a key factor (besides substrate and cover) in the habitat selection by riparian species.

Mechanisms in the Shift of a Riparian Ground Beetle (Carabidae) Between Reproduction and Hibernation Habitat

Factors affecting the light response of the riparian species Bembidion petrosum (Coleoptera: Carabidae) were studied with various experimental designs in laboratory and in field. B. petrosum, which lives in open gravely/stony sites, oriented towards directed light at higher temperatures (above 15.0°C). This positive phototaxis was replaced by an orientation towards a dark silhouette (screen) at low temperatures. The orientation towards silhouettes is mainly a simple type of form vision, although a fraction of the individuals seems to exhibit a negative phototaxis. In experiments with a dark zone and a zone with directed light, individuals of B. petrosum mainly selected the dark zone. However, if two stones were placed in the light part of the arena, individuals tended to hide under them. This applied independent of light intensity and whether a tuft of grass was present or absent in the dark part of the arena. The experiments indicate that the shift of the species between the reproduction (spring/summer) and hibernation (autumn/winter) habitat involves a change from an orientation towards silhouettes at low temperatures in autumn to an orientation towards directed light at higher temperatures in spring. This is combined with a specialized low thigmokinesis (preference of heavy and rough objects) and lower moisture requirements of the species in autumn/winter than in spring/summer.

Species Composition, Abundance, Habitat Requirements and Regional Distribution of Terrestrial Gastropods in Arctic Norway

SummaryThe species composition, abundance and habitat distributions of the terrestrial gastropods at lat. 70° N in Finnmark county, northern Norway were studied. Within an area with bedrocks of sandstone there were few snail species and abundance was low. Calciumrich bogs and birch woods with a luxuriant undergrowth had a richer gastropod fauna both in number of species and abundance. The snail fauna consisted of a mixture of stenoecious, calciphile species (Columella columella, Vertigo genesii, V. modesta) and very euryoecious species, e.g., Discus ruderatus, Vitrina pellucida. Cochlicopa lubrica and Nesovitrea hammonis were found only in moist, rather eutropic habitats and seemed to be more stenoecious than further south in their geographical range. There were few snails within the study area (16 species) compared with >30 species found in the coastal areas of northern Norway (Troms county) at the same latitude. This difference in the faunal composition coincides with regional divisions based on the vegetation, and may indicate a general difference in the biota of oceanic and continental areas of northern Norway. The changes in snail fauna along a coast-inland transect at about lat. 70° N are similar to those occurring along a vertical gradient in the inner fjord districts of Western Norway. It is suggested that low temperatures during the coldest part of the year are responsible for this common change in the species composition.

Adaptations of carabid beetles to dry habitats in East Africa

The rates of water loss and humidity preference of carabids from dry tropical habitats have been studied and compared with corresponding data from temperate carabids and tropical tenebrionids. Within each group of beetles the rate of relative water loss decreases with increasing body size. Carabids from dry tropical areas have rates of water loss which are lower than those of temperate species, but considerably higher than the values for tenebrionids from dry tropical habitats. Small temperate carabids can stay in dry air for only a few hours, whereas large tropical tenebrionids may survive for weeks without becoming critically dehydrated. Given the choice between a dry and a humid atmosphere, well hydrated beetles of all groups will initially choose the dry atmosphere. Most temperate carabids will switch to humid atmosphere after a few hours and tropical carabids after 1–3 days, whereas tropical tenebrionids may remain in dry air for almost 3 weeks. The temperate carabids are very sensitive to dehydration and will shift to a humid atmosphere when dehydrated by only 2–5%. Tropical carabids and tenebrionids will shift first when they are dehydrated by 7–20% of their body weight in a hydrated state, implying that these beetles are considerably less sensitive to water loss than temperate carabids.