Natural disturbances are spatially diverse but temporally synchronized across temperate forest landscapes in Europe

Natural disturbance regimes are changing substantially in forests around the globe. However, large‐scale disturbance change is modulated by a considerable spatiotemporal variation within biomes. This variation remains incompletely understood particularly in the temperate forests of Europe, for which consistent large‐scale disturbance information is lacking. Here, our aim was to quantify the spatiotemporal patterns of forest disturbances across temperate forest landscapes in Europe using remote sensing data and determine their underlying drivers. Specifically, we tested two hypotheses: (1) Topography determines the spatial patterns of disturbance, and (2) climatic extremes synchronize natural disturbances across the biome. We used novel Landsat‐based maps of forest disturbances 1986–2016 in combination with landscape analysis to compare spatial disturbance patterns across five unmanaged forest landscapes with varying topographic complexity. Furthermore, we analyzed annual estimates of disturbances for synchronies and tested the influence of climatic extremes on temporal disturbance patterns. Spatial variation in disturbance patterns was substantial across temperate forest landscapes. With increasing topographic complexity, natural disturbance patches were smaller, more complex in shape, more dispersed, and affected a smaller portion of the landscape. Temporal disturbance patterns, however, were strongly synchronized across all landscapes, with three distinct waves of high disturbance activity between 1986 and 2016. All three waves followed years of pronounced drought and high peak wind speeds. Natural disturbances in temperate forest landscapes of Europe are thus spatially diverse but temporally synchronized. We conclude that the ecological effect of natural disturbances (i.e., whether they are homogenizing a landscape or increasing its heterogeneity) is strongly determined by the topographic template. Furthermore, as the strong biome‐wide synchronization of disturbances was closely linked to climatic extremes, large‐scale disturbance episodes are likely in Europe's temperate forests under climate changes.     

Effect of different semiochemicals blends on spruce bark beetle,Ips typographus (Coleoptera: Scolytidae)

The spruce bark beetle, Ips typographus, is a recent new introduction to the Qilian Mountains of China. An outbreak of these beetles has infested over 0.03 million hectares of spruce forests in this area. Although primary attraction to volatiles has been clearly demonstrated for I. typographus, the existence and role of attraction to insect‐produced pheromones have been widely debated. Currently, commercial lures for I. typographus include only the volatiles ipsdienol, cis‐verbenol, trans‐verbenol, 2‐methyl‐3‐buten‐2‐ol and 2‐phenylethanol in Europe. Several potential pheromone candidates have been identified for I. typographus. Our GC–MS and GC–FID analyses volatiles from hindgut extracts of I. typographus in different attack phases demonstrated that the 2‐methyl‐3‐buten‐2‐ol, ipsdienol, cis‐verbenol and trans‐verbenol as major hindgut components, and ipsenol, 2‐phenylethanol, trans‐ myrtenol and verbenone as minor components. We tested various combinations of semiochemical candidates, to determine an optimal blend. Our results suggest that addition of 2‐methyl‐3‐buten‐2‐ol to either ipsenol alone, or to blends of ipsenol and other semiochemical candidates, significantly enhanced attraction of I. typographus. Therefore, a simple lure consisting of ipsenol and 2‐methyl‐3‐buten‐2‐ol would be an optimal blend of I. typographus in the Qilian Mountains, China. We conclude that this optimal semiochemical blend may provide an effective biological pest control method for use in forest ecosystem against I. typographus.     

Modified pheromone traps help reduce bycatch of bark‐beetle natural enemies

• 1 Thanasimus formicarius and Temnochila caerulea, two of the main predators of Ips sexdentatus, a well‐known forest pest in Southern Europe, are captured in high numbers when trapping I. sexdentatus as a result of the kairomonal effect of the lures used.
• 2 A preliminary field trial showed that predators could survive for at least 1 week within trapping containers, although predator mutilation and high predator death rates were observed.
• 3 Different modifications of conventional multiple funnel and slot traps with the objective of reducing natural enemy entrance into trap containers were bioassayed in field experiments conducted over four seasons. Based on the larger sizes of predators, different designs using welded wire‐mesh screens improved performance to different extents. Providing escape windows just above the screen on multiple funnel traps gave the most promising results, including when effect sizes among all tested designs were compared.
• 4 Thus, a simple modification of the lowest funnel of the multiple funnel traps would reduce the bycatch of T. formicarius and T. caerulea, hence improving the efficiency of trapping programmes by lowering the likely impact on natural populations of these predators.

     

Characterization of microsatellite loci in the spruce bark beetle Ips typographus (Coleoptera: Scolytinae)

Ips typographus is an economically important pest of Norway spruce stands. We developed five polymorphic microsatellite markers using a biotin enrichment protocol. The number of alleles ranged from three to 11 per locus and no strong evidence for null alleles was found. Heterozygosity ranged from 0.3 to 0.97. These markers could be useful tools to study the population structure and genetic consequences of I. typographus population outbreaks.     

Survival of within-treeIps calligraphus [Col.: Scolytidae]: Effect of insect associates

Mechanical exclusion methods were used on the preferred portion of the hosttree bole to evaluateIps calligraphus brood mortality caused by the insect associate complex with and without the contribution ofMonochamus sawyer foraging. The studies compared brood adultIps calligraphus emergence from beetle infested bolts from which all insect associates were excluded, from which onlyMonochamus sawyers were excluded, and those bolts which were exposed to all insect associates. The least mortality occurred in bolts from which all insect associates were excluded, significantly more mortality occurred in bolts from which only sawyers were excluded, and the greatest mortality occurred in bolts exposed to all insect associates. Average monthly mortality due to insect associates was 89%, with 51% due to sawyer foraging. Insect associates were found to be more effective from May through July, while sawyer foraging produced the greatest within-bolt mortality from August through October.     

Electronic fraction collector used for insect sampling in the photoperiod-induced diel emergence of bark beetles

ABSTRACT. An electronic timer and fraction collector consisting of CMOS integrated circuits is described. It converts 50- or 60-Hz AC to real-time pulses in programmable whole-number increments (1, 10 or 60s) from 3 to 16659, producing timing periods from 3 s to more than 11 days. The fraction collector contains a leaf-switch feedback circuit that automatically adjusts to various gear motor speeds and sample tube spacings so that proper positioning results. Hourly collections by the device of the bark beetles Ips typographus L. and Pityogenes chalcographus L. (Scolytidae) emerging from logs of Norway spruce, Picea abies , indicated that both species emerged with a diel periodicity. A unimodal emergence peak for both sexes of both species occurred at midday in LD 20:4 at a constant 25°C and 80% r.h.     

Northward shift in temperature sum isoclines may favour Ips typographus outbreaks in European Russia

1. As the development of the eight‐toothed spruce bark beetle Ips typographus is temperature‐dependent, climate change may encourage development of its additional generations per year and facilitate mass outbreaks further north than previously known.
2. The aim of the study was to analyse historical changes in effective temperature sums (ETSs) and early season swarming weather for I. typographus in different forest zones of European Russia between 1960 and 2016. The difference in ETSs was analysed with linear regression using daily temperature data from the 30 meteorological stations. Historical data regarding the location of I. typographus outbreaks were examined and changes in their distribution during the entire study period were analysed.
3. There was a substantial increase in ETSs, especially in the latter half of the study period. Increased ETSs coincided with more favourable conditions for swarming of I. typographus. Areas with favourable ETSs for the complete development of bivoltine populations of I. typographus (>1500 DD) shifted northwards on average 450 km during the entire study period.
4. The northward shift of ETSs may enhance the transition from univoltine to bivoltine life cycles of I. typographus in the south and middle taiga and from bivoltine to trivoltine life cycles in conifer‐broadleaf forests.

     

Drought and stand susceptibility to attacks by the European spruce bark beetle: A remote sensing approach

1. Several time-series analyses have demonstrated that after extreme summer drought bark beetle damage increased. However, studies predicting stand susceptibility over large spatial extents are limited by technical constraints in obtaining detailed, spatially-explicit data on infestation spot occurrence.
2. Using a unique dataset of georeferenced bark beetle infestation data, we tested whether the spatial variation of local growing conditions of forest stands, topography, and landscape variables modified the local occurrence of Ips typographus infestations after a severe hot drought in Central Europe.
3. Bark beetle infestation occurrence depended on soil-related aridity intensity, elevation, slope, and soil conditions. We showed that elevation interacted with growing conditions and topography. At low elevations, spruce forests growing on flat areas and wetter soils were more sensitive to the infestations. On the contrary, forests on steep slopes and soils with low water availability were rarely attacked. At the landscape scale, bark beetle damage increased with host tree cover but decreased with compositional diversity.
4. Our findings are generally consistent with the growth-differentiation balance hypothesis that predicts that trees growing under chronic dry conditions tend to be more resistant against biotic disturbances.
5. Spruce stands at low elevations located in homogeneous landscapes dominated by spruce were those more exposed to bark beetles in the initial phase of a drought-induced outbreak.

     

Functional investigation of monoterpenes for improved understanding of the relationship between hosts and bark beetles

Spruce bark beetle (Ips typographus L.) is the most destructive insect pest of spruce forests in Eurasia. However, contact toxicity, in vivo metabolism, and ecological functions of host monoterpenes are poorly understood at the spruce tree–bark beetle–predator tritrophic level. Spruce monoterpenes including S-(–)-α-pinene, R-(+)-α-pinene, and myrcene showed contact toxicity to I. typographus, with LD₅₀ values ranging from 22–32 μg/mg. When topically treated with S-(–)-α-pinene or R-(+)-α-pinene, the amounts of volatile metabolites, including 4S-(–)-cis-verbenol, 4S-(+)-/4R-(–)-trans-verbenol, R-(+)-/S-(–)-verbenone and 1R-(–)-/1S-(+)-myrtenol, in the hindgut extracts of I. typographus varied significantly between sexes, and their quality (enantiomeric composition) varied significantly with the chirality of α-pinene. More importantly, S-(–)-α-pinene induced male adults to produce large amounts of 4S-(–)-cis-verbenol and S-(–)-verbenone. When topically treated with myrcene, the expected semiochemicals such as E-myrcenol, ipsenol and ipsdienol were not detected in the beetle hindguts, indicating that the pheromone biosynthetic system of I. typographus does not participate in the metabolism of host myrcene. In trap tests, S-(–)-α-pinene and R-(+)-α-pinene increased the catches of I. typographus and its predator Thanasimus substriatus in pheromone-baited traps, whereas myrcene exhibited a strong repellent (or inhibitory) effect on I. typographus but not on its predator. I. typographus seems to adopt different ecological strategies (e.g. avoidance to myrcene and preference for α-pinene) to adapt to and tolerate different host monoterpenes. Extensive investigation of these monoterpenes will help us understand their roles in manipulating the arms race between host trees and bark beetles, and potentially improve the efficacy of controlling I. typographus via the push-pull strategy using host kairomones.