The attraction of bark and ambrosia beetles as well as associated beetles to α-pinene and ethanol was studied in field experiments with flight barrier traps. α-Pinene and ethanol were released individually and as combinations in approximately 1∶1 or 1∶10 ratios and at four different release rates. Ethanol attractedTomicus piniperda (L.),Hylurgops palliatus (Gyll.),Trypodendron lineatum (Oliv.),Hylastes cunicularius Er.,H. brunneus Er.,H. opacus Er., andAnisandrus dispar (F.) (Scolytidae);Glischrochilus quadripunctatus (L.) andEpuraea spp. (Nitidulidae);Thanasimus formicarius (L.) (Cleridae); andRhizophagus depressus (F.) (Rhizophagidae). α-Pinene attracted all these species with the exception ofT. lineatum, H. cunicularius, andA. dispar. Combinations of a-pinene and ethanol resulted in synergistically increased attraction of all species with the exception ofH. opacus andA. dispar. A. dispar, the only hardwood-associated species in the study, was repelled by α-pinene. Both the release rates and the ratio at which the two substances were released influenced the response of the beetles. The differences in response between the beetle species seem to reflect dissimilarities in the release of the two substances among the various types of breeding material to which the species are adapted.

1 To maintain biodiversity in forests more wind-felled trees must be left where they fall. However, there is concern among forest owners that this may result in higher tree mortality caused by the spruce bark beetle, Ips typographus (L.) (Col.: Scolytidae). 2 In the 5 years following a major storm disturbance the number of standing spruces killed by I. typographus was determined in a total of 53 stands. In five of the stands all wind-thrown trees were left (unmanaged stands) and in 48 of the stands, which were situated at distances of 1.4±10.0 km from each focal unmanaged stand, the wind-felled trees were removed directly after the storm (managed stands). In the winter preceding the fifth summer new stormfellings occurred in the study area. 3 In the 4-year period between the first and second storm-fellings, 50±322 standing trees were killed by I. typographus per unmanaged stand. There was a direct linear relationship between the number of storm-felled spruces colonized by I. typographus and the number of trees subsequently killed in the unmanaged stands. 4 Tree mortality caused by I. typographus in the unmanaged stands was almost nil in the first year, peaked in the second or third year, and decreased markedly to a low level in the fourth and fifth years. 5 In the 4-year period between the first and second storm-fellings twice as many trees were killed per ha in the unmanaged stands than in the managed stands: the average difference being 6.2 killed trees per ha, equivalent to 19% of the number of spruce trees felled by the first storm in the unmanaged stands. 6 Much higher numbers of trees were killed per ha in the stand edges than in the interiors of both the unmanaged and the managed stands.

No abstract

The Eurasian spruce bark beetle, Ips typographus, is one of the major forest insect pests in Europe, capable of mass-attacking and killing mature Norway spruce trees. The initiation and development of a new generation are strongly controlled by temperature and a warmer climate may affect the number of generations that is produced per year and hence the outbreak dynamics. Experimental knowledge regarding reproductive diapause adaptations is, however, too sparse for largescale assessments of future trends. We developed a model description of diapause induction, and used gridded observational temperature data to evaluate multiple combinations of day length and temperature thresholds to find the model parameterisation most coherent with I. typographus monitoring data from Scandinavia. The selected model parameterisation is supported by European literature data, though further experimental studies are required to analyse population specific adaptations and capacity for adjustments to changing climate conditions. Implementing the 696 Climatic Change (2011) 109:695-718 model description of reproductive diapause in a temperature driven model of bark beetle phenology (swarming activity and development from egg to mature bark beetle), enabled us to assess the length of the late summer swarming period that is a critical determinant of the risk of forest damage. By using regional climate model data we show that higher temperatures can result in increased frequency and length of late summer swarming events, producing a second generation in southern Scandinavia and a third generation in lowland parts of central Europe. Reproductive diapause will not prevent the occurrence of an additional generation per year, but the day length cues may restrict the length of the late summer swarming period.

No abstract

Large‐scale natural disturbances pose challenges for the management of protected areas and may have undesirable consequences for commercial plantations nearby. A storm, which felled nearly 10 000 m3 of spruce forest in the Osaby nature reserve in southern Sweden, allowed us to study the subsequent population development of the spruce bark beetle (Ips typographus L.). Two summers after the storm, an exceptionally high proportion (74%) of wind‐felled trees had been successfully colonized by the bark beetle, and all living spruce trees had been killed. On standing trees, colonization density was three times higher, and reproductive success one‐fourth, that on wind‐felled trees. The negative relationship between colonization density and reproductive success indicates that intra‐specific competition is one of the main mechanisms reducing I. typographus population growth when the beetles switch from wind‐felled to standing trees after storm disturbances. Indeed, there was no significant difference in beetle production between wind‐felled and standing trees. Furthermore, there were no differences in colonization density, reproductive success or production at different heights in standing trees; however, a higher proportion of the new adults emerged at the tree‐tops rather than lower down before overwintering. Our results also demonstrate that a large proportion (ca. 50%) of the I. typographus population that developed in the storm‐fell area apparently overwintered under the bark of standing trees.

The attraction of some bark-and ambrosia beetles as well as associated beetles to the host volatiles ot-pinene and ethanol was studied in fieldtests with flight barrier traps. Tomicuspiniperda (L.) (Scolytidae), Thanasimus formicarius (L.) (Cleridae), and Rhizophagusferrugineus (Payk.) (Rhizophagidae) were attracted by o~-pinene, while Hylurgops palliatus (Gyll.) and Trypodendron lineatum (Oliv.) (Scolytidae) were attracted by ethanol and Epuraea spp. (Nitidulidae) by both o~-pinene and ethanol. Combinations of ot-pinene and ethanol attracted high numbers ofH. palliatus, T. lineatum, R. ferrugineus, Epuraea spp., and Glischrochilus spp. (Nitidulidae) and the catches increased with increasing release rates of ethanol. By contrast, lower numbers of T. piniperda were caught in traps baited with combinations of ~-pinene and ethanol than in traps baited with ~-pinene alone, and the catches of this species decreased with increasing release rates of ethanol. Traps baited with a combination of o~-pinene and ethanol or with et-pinene alone caught similar numbers of T. formicarius. The results are discussed on the basis of species differences in preference for breeding substrate.

Bark beetle population dynamics is thought to be primarily driven by bottom-up forces aff ecting insect performance and host tree resistance. Although there are theoretical predictions and empirical evidences that predation and parasitism may play an important role in driving bark beetle population fl uctuations, long-term studies testing the role of both biotic and abiotic controls on population dynamics are still rare. Th e aim of the study was to quantify the relative importance of predation, negative density feedback and abiotic factors in driving Ips typographus population dynamics. We analyzed a unique time series of population density of I. typographus and its main predator Th anasimus formicarius over almost two decades in four regions across Sweden. We used a discrete population model and a multi-model inference approach to evaluate the importance of both bottom-up and top-down factors. We found that availability of breeding substrates in the form of storm-felled trees was the main outbreak trigger, while strong intra-specifi c competition for host trees was the main endogenous regulating factor. Although temperature-related metrics are known to have strong individual eff ect on I. typographus development and number of generations, they did not emerge as important drivers of population dynamics. A positive eff ect of low summer rainfall was evident only in the region located in the southernmost and warmest part of the spruce distribution range in Sweden. Predator density did not emerge as an important prey regulating factor. As the reported damage from storms seems to have increased across whole Europe, spruce forests are expected to be increasingly susceptible to large outbreaks of I. typographus with important economic and ecological consequences for boreal ecosystems. However, the observed negative density feedback seems to be a natural regulating mechanism that impedes a strong long-term propagation of the outbreaks.