Air sampling of its pheromone to monitor the occurrence of Osmoderma eremita, a threatened beetle inhabiting hollow trees

Osmoderma eremita is a threatened scarab beetle living in the hollows of old deciduous trees and is regarded as an umbrella species of the beetle fauna associated with this habitat. Several methods like pitfall trapping and wood mould sampling have been used to monitor the occurrence of O. eremita, but these methods cannot be applied for trees with certain characteristics. Recently, (R)-(+)--decalactone was identified as a male-produced sex pheromone of the species. Here, we show that -decalactone can be detected in hollow trees by air sampling and that the presence of the compound is strongly correlated with the occurrence of living male beetles in the same trees. Air was sampled from tree cavities and extracts analysed using gas chromatography–and mass spectrometry. There was a 89% match between the detection of -decalactone in extracts and the occurrence of male O. eremita±2 days from the sampling event. In the absence of males, samples never contained -decalactone, and the presence of this compound in a tree cavity appears to be a good predictor of O. eremita occupancy. Air sampling can be a useful complement to other methods when trying to detect as many trees housing this beetle as possible, which is crucial when estimating populations sizes and developing conservation strategies for this species.     

Restricted dispersal in a flying beetle assessed by telemetry

Many insects living in ancient trees are assumed to be threatened as a result of habitat loss and fragmentation. It is generally expected that species in habitats with low temporal variability in carrying capacity have lower degree of dispersal in comparison to those in more ephemeral habitats. As hollow trees are long-lived, species in that habitat are expected to be sensitive to habitat fragmentation, due to a low capacity to establish new populations far from present ones. Using radio telemetry, we studied the dispersal for a beetle, Osmoderma eremita, living in hollow trees. O. eremita exhibited philopatry and only dispersed over short ranges. About 82–88% of the adults remained in the tree where they were caught. All observed dispersal movements ended up in nearby hollow trees and 62% in the neighbouring hollow tree. These results corroborate the suggestion that habitat fragmentation may be detrimental to insects living in temporally stable but spatially variable habitats. In order to preserve such species, we propose that conservation efforts should be focused on maintaining or increasing the number of suitable trees in and near presently occupied stands.     

Occurrence of Larca lata H.J. Hansen (Pseudoscorpionida: Garypidae) and Allochernes wideri C.L. Koch (Pseudoscorpionida: Chernetidae) in tree hollows in relation to habitat quality and density

Many beetles associated with old trees are on national red lists, but pseudoscorpions living in similar habitats have received little attention. This study reports the habitat and occurrence patterns of two species of pseudoscorpions living in hollow trees. Their occurrence has been assessed by sieving wood mould from 274 oaks in southeastern Sweden and from museum specimens collected in Sweden. Larca lata is confined to hollow oaks with a large girth and a plentiful supply of wood mould. Allochernes wideri is much less particular about wood mould volume, trunk diameter and tree species. Larca lata inhabits hollow trunks with characteristics that are typical of very old trees, whereas A. wideri predominantly occurs in trunks in an earlier stage of hollow formation. Larca lata was almost exclusively found in larger assemblages of hollow oaks, which suggests long-term survival may be difficult when the network of suitable hollow trees is too sparse. Larca lata is a rare species in Europe and probably vulnerable to extinction, since it is dependent on a habitat which has declined severely in the last few centuries.     

Vacuum cleaning for conservationists: a new method for inventory of Osmoderma eremita (Scop., 1763) (Coleoptera: Scarabaeidae) and other inhabitants of hollow trees in Natura 2000 areas

Recording the insect species of hollow trees, particularly in larger cavities, presents a major methodological challenge. A whole range of endangered saproxylic beetles and other wood-inhabiting species live together in this habitat. In order to conduct preliminary surveys and monitor populations of the hermit beetle (Osmoderma eremita) in Natura 2000 areas designated for nature conservation according to the EU Habitats Directive, a vacuum cleaner has been used for the first time. Sampling of 127 trees with cavities revealed 39 trees in which O. eremita was present and for which submission of a report is mandatory. A total of 35 species was found, including 17 species in the German red data book as well as six species which are classified as relict species of ancient woodland. The method has therefore proved itself to be very appropriate and is now routinely used in southern Germany.     

Monitoring spatiotemporal variation in abundance and dispersal by a pheromone-kairomone system in the threatened saproxylic beetles <Emphasis Type="Italic">Osmoderma eremita</Emphasis> and <Emphasis Type="Italic">Elater ferrugineus</Emphasis>

Pheromone monitoring could provide unique spatial and temporal information about rare and threatened insect species for conservation purposes. Pheromone traps may be especially valuable in detecting fluctuations and declines in vulnerable species, if trap catch can be related to population density. We exploited the pheromone-kairomone system of the hermit beetle Osmoderma eremita and its predator, the red click beetle Elater ferrugineus, to monitor variation in their flight activity during 7 years (2001–2002, 2005–2009). Spatial and temporal flight activity of O. eremita and E. ferrugineus were highly correlated over individual trap replicates and trap days. Yearly flight activities of both species were correlated within two core sites included during all years of the study, and positively affected by temperature both within and between years. Flight activity could not be directly translated to variation in abundance in either species, however. Dispersal rate was likely the main factor explaining flight activity in O. eremita. Normalizing the flight activity of E. ferrugineus against that of O. eremita did not eliminate most of the variability, however, suggesting that flight activity of E. ferrugineus was governed both by dispersal rate and by population density. Higher fluctuations in population density of E. ferrugineus likely render it more vulnerable to local extinction, which may explain the greater rarity of this species. We suggest that preserving large assemblies of suitable hollow trees would be absolutely essential for buffering against stochastic population fluctuations and securing the long-term persistence of E. ferrugineus.     

Surveying an endangered saproxylic beetle, Osmoderma eremita, in Mediterranean woodlands: a comparison between different capture methods

Measuring population size is riddled with difficulties for wildlife biologists and managers, and in the case of rare species, it is sometimes practically impossible to estimate abundance, whereas estimation of occupancy is possible. Furthermore, obtaining reliable population size estimates is not straightforward, as different sampling techniques can give misleading results. A mark-recapture study of the endangered saproxylic beetle Osmoderma eremita was performed in central Italy by applying four independent capture methods within a study area where 116 hollow trees were randomly selected to set traps. Detection probability and population size estimates were drawn from each of these four capture methods. There were strong differences in detection probability among methods. Despite using pheromone and beetle manipulation, capture histories were not affected by trap-happiness or trap-shyness. Population size estimates varied considerably in both abundance and precision by capture method. A number of 0.5 and 0.2 adult beetles per tree was estimated using the whole data set by closed and open population models, respectively. Pitfall trap appeared the optimal method to detect the occurrence of this species. Since in the southern part of its distribution range, a single population of O. eremita is widespread in the landscape, and includes beetles from more than one hollow tree, conservation efforts should focus not only on preserving few and isolated monumental hollow trees, but should be extended to large stands.     

The dispersal rate of a beetle, Osmoderma eremita, living in tree hollows

The dispersal of an endangered beetle, Osmoderma eremita, that lives in tree hollows, was studied by mark-release-recapture with pitfall traps. As only a small proportion of all dispersals is observed by this method, a simulation model was constructed to estimate the dispersal rate per individual. The model results suggest that 15% of the adults leave the original tree for another hollow tree, and consequently most individuals remain in the same tree throughout their entire life. This suggests that each hollow tree sustains a local population with limited connection with the populations in surrounding trees. It supports the view that O. eremita has a metapopulation structure, with each tree possibly sustaining a local population, and with the population in an assemblage of trees forming a metapopulation. Low dispersal rate and range make the species vulnerable to habitat fragmentation, probably at a scale of only a few hundred meters.     

Early responses of bark and wood boring beetles to an outbreak of the hemlock looper Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) in a boreal balsam fir forest of North America

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Constancy and asynchrony of Osmoderma eremita populations in tree hollows

A species rich beetle fauna is associated with old, hollow trees. Many of these species are regarded as endangered, but there is little understanding of the population structure and extinction risks of these species. In this study I show that one of the most endangered beetles, Osmoderma eremita, has a population structure which conforms to that of a metapopulation, with each tree possibly sustaining a local population. This was revealed by performing a mark-release-recapture experiment in 26 trees over a 5-year period. The spatial variability between trees was much greater than temporal variability between years. The population size was on average 11 adults tree^-1 year^-1, but differed widely between trees (0-85 adults tree^-1 year^-1). The population size in each tree varied moderately between years [mean coefficient of variation (C.V.)=0.51], but more widely than from sampling errors alone (P=0.008, Monte Carlo simulation). The population size variability in all trees combined, however, was not larger than expected from sampling errors alone in a constant population (C.V.=0.15, P=0.335, Monte Carlo simulation). Thus, the fluctuations of local populations cancel each other out when they are added together. This pattern can arise only when the fluctuations occur asynchronously between trees. The asynchrony of the fluctuations justifies the assumption usually made in metapopulation modelling, that local populations within a metapopulation fluctuate independently of one another. The asynchrony might greatly increase persistence time at the metapopulation level (per stand), compared to the local population level (per tree). The total population size of O. eremita in the study area was estimated to be 3,900 individuals. Other localities sustaining O. eremita are smaller in area, and most of these must be enlarged to allow long-term metapopulation persistence and to satisfy genetic considerations of the O. eremita populations.     

Occurrence of the marbled rose-chafer (Protaetia lugubris Herbst, Coleoptera, Cetoniidae) in rural avenues in northern poland

The occurrence of Protaetia lugubris, an endangered species developing in hollow trees, was studied in a network of rural avenues in northern Poland. We detected 1002 trees from nine species with hollows suitable for beetle development (25% of all trees inspected). Among them, 74 trees (7.4%) from seven species were occupied by P. lugubris. The distribution of P. lugubris was random with respect to tree species identity. The beetle preferred trees above 200 cm in circumference with a tendency towards higher occupancies of the bigger trees having circumferences above 300 cm. P. lugubris did not show any significant preferences according to hollow entrance area, exposition and road surface type. Our results indicate that P. lugubris is a generalist species colonizing all suitable hollows. Its occurrence indicates suitable conditions for many other species associated with tree cavities and decaying wood.     

Extinction risks in metapopulations of a beetle inhabiting hollow trees predicted from time series

Ancient and dead trees are declining habitats harbouring many threatened species. These habitats are naturally patchy, and inhabiting species might exhibit metapopulation dynamics at a small spatial scale. In this study, the demography and metapopulation dynamics was analysed for Osmoderma eremita , which is an endangered beetle species associated with tree hollows in Europe. Extinction risks of O. eremita populations were predicted using Monte Carlo simulations based on time series of population assessments. Predicted occurrence patterns were consistent with field observations from an area with many small stands in which the populations are believed to have been more or less isolated from each other during the last 150–200 yr. Population growth was found to be density dependent. Carrying capacity was proportional to the volume of wood mould (i.e. loose material of dead wood in the tree hollows), which varied widely between hollow trees. This generates large differences in local extinction risks between hollow trees. The predicted metapopulation extinction risk was much higher if the habitat dynamics (formation, gradual increase and deterioration of tree hollows) were taken into consideration than in predictions yielded by models in which the amount of wood mould was assumed to be constant over time. Thus, this system has features from both mainland-island metapopulations and habitat-tracking metapopulations, and is rather far from a classic metapopulation. For the long-term persistence of the species in hollow trees, the habitat dynamics seem to be more important than demographic processes. Since the formation and deterioration of suitable tree are partly stochastic processes, there is a considerable extinction risk for many O. eremita populations, because they mainly rely on only one or a few trees with large amounts of wood mould.     

Osmoderma eremita as an indicator of species richness of beetles in tree hollows

The beetle Osmoderma eremita has received much attention in the last few years, as it is among those species with the highest priority in the European Union's Habitat Directive. In this paper the species is evaluated as a potential indicator and umbrella species for the endangered beetle fauna in tree hollows. To be useful as an indicator of a species-rich fauna it should be easy to inventory and be strongly correlated with the presence of other species. An umbrella species is a species which is so demanding that the protection of this species will automatically save many others. The species richness of saproxylic beetles and occupancy of O. eremita were surveyed in tree hollows in an area in southeastern Sweden by assessing the presence/absence of living and dead adults (including fragments) and larvae. The species richness was higher when O. eremita was present, both at tree and stand level. Several threatened species were associated with the presence of O. eremita, whereas others did not correlate with the occurrence of O. eremita. As O. eremita is easy to find and identify, it is useful as an indicator of stands with a rich beetle fauna in tree hollows. Osmoderma eremita can be used as an umbrella species, because if measures are taken to conserve O. eremita, many other species in the same habitat are also conserved. However, there are some beetles in tree hollows which seem to be more sensitive to habitat fragmentation than O. eremita, and may go extinct if only O. eremita is taken into consideration.     

Phenological observations and trapping tactics for the granulate ambrosia beetle Xylosandrus crassiusculus (Coleoptera: Curculionidae,Scolytinae) in New Zealand

1. The granulate ambrosia beetle (GAB) Xylosandrus crassiusculus, was first formally detected in New Zealand in 2019. Since then, GAB has subsequently been found infesting numerous tree species in the Auckland region.
2. Flight intercept traps baited with ethanol lures were deployed from October 2019 to May 2021 at three sites in the Auckland region to ascertain the phenology of GAB in New Zealand. Two distinct peak flight periods were identified in early and late summer, while a smaller and inconsistent third peak was detected in early autumn. Logistical analysis of GAB captures in the ethanol-lured traps and degree-day (DD) accumulation indicated that 90% of flight activity is completed by 800 DD.
3. To assess monitoring tactics, flight intercept traps were baited with three different ethanol lures with varying release rates or ethanol-soaked or non-soaked wood bolts from three species of trees. A lure releasing 2 g ethanol per day was most effective at capturing GAB. Ethanol-soaked bolts were less effective than the lures.
4. Xylosandrus crassiusculus represents a significant risk for shrubs and trees native to New Zealand, as well as commercial horticultural and forestry trees. We recommend using ethanol-lured panel traps for monitoring purposes.

     

Micro-habitat drivers of saproxylic beetle assemblages in old woodlands of Mediterranean cork oak (Quercus suber)

1. Cork oak landscapes are fascinating ecosystems, historically managed for cork extraction. The persistence in this habitat of many hollow veteran trees provides suitable micro-habitats for saproxylic beetles.
2. We investigated the saproxylic beetle community of two isolated cork oak woodlands of central Italy with different degree of recovery after human transformation: (1) an open woodland and (2) a dense mixed woodland, both dominated by cork oak trees.
3. We found endemic, rare and threatened saproxylic beetles in both the areas, confirming the important conservation value of cork oak landscapes. In the open woodland we observed a higher number of species in all trophic categories, except for mycophagous specialists. Several microhabitat variables reflected the different stage of recovery of the two woodlands.
4. Our findings suggest the crucial role of diversified environments in protected areas: even a small difference in the degree of recovery (i.e., tree closeness) can affect the number of beetle species. Specifically, we found (1) more xerophilous species in the open woodland and (2) more mesophilous species in the dense mixed woodland.

     

Boxes mimicking tree hollows can help conservation of saproxylic beetles

Old hollow trees have declined in Europe and many saproxylic (i.e. wood-dwelling) invertebrates living on them are threatened. The aim of this study was to investigate to what extent artificial habitats can be exploited by saproxylic beetles. To mimic the conditions in tree hollows, we constructed wooden boxes filled with different combinations of substrates like oak saw dust, oak leaves, a dead hen (Gallus domesticus), chicken dung, lucerne flour or potatoes and placed them on tree trunks. To investigate the importance of distance from dispersal sources, we placed boxes at different distances (0–1,800 m) from three species-rich sites with high densities of hollow oaks. Over 3 years, 3,423 specimens of 105 saproxylic beetle species were caught in 47 boxes. Among beetles found in hollow oaks that were either tree-hollow species, bird nest species, or wood rot species, 70% were also found in the boxes. A dead hen added to the artificial wood mould gave a higher number of beetle specimens. The number of species associated with tree hollows in oak decreased with distance from sites with hollow oaks. In conclusion, the prospects for using artificial environments for boosting substrate availability, or to fill spatial and temporal gaps therein, for saproxylic beetles are good.     

Robinia pseudoacacia as a surrogate for native tree species for saproxylic beetles inhabiting the riparian mixed forests of northern Italy

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Enantiomeric conservation of the male‐produced sex pheromone facilitates monitoring of threatened European hermit beetles (Osmoderma spp.)

Hermit beetles of the genus Osmoderma (Coleoptera: Scarabaeidae: Cetoniinae) are known for their fruity odour, which is released in large amounts by males. Two species of the genus occur in Europe, the eastern Osmoderma barnabita (Motschulsky) and the western Osmoderma eremita (Scopoli). Previous studies on Swedish populations of O. eremita showed that the compound responsible for the characteristic scent, γ‐decalactone, functions as a sex pheromone for the attraction of conspecific females. Male O. eremita only release the (R)‐enantiomer of the lactone, and both sexes are anosmic to the opposite enantiomer. As the distribution areas of the two hermit beetle species partly overlap, it may be expected that they use different enantiomeric compositions of γ‐decalactone as pheromones to promote species discrimination. This paper reports on the identification of the sex pheromone of O. barnabita. Surprisingly, males from a Polish population produce only the (R)‐enantiomer of γ‐decalactone, and conspecific females show equal attraction to the (R)‐enantiomer and a racemic mixture of the compound, indicating that O. barnabita is anosmic to the (S)‐enantiomer, similarly to what was observed for O. eremita. A mtDNA sequence analysis of the cytochrome oxidase subunit I gene of Polish and Swedish beetles confirmed their taxonomical status as O. barnabita and O. eremita, respectively, with an average sequence divergence of 10.5% between beetles from the two studied areas. Although genetic data suggest that these species diverged several million years ago, they still rely on the same enantiomer of γ‐decalactone for mate finding. Thus, the male‐produced pheromone in Osmoderma spp. may be regarded as a territorial signal being exploited by females, rather than a cue for determining species identity. Our data show that the same compound can be used to facilitate monitoring of both beetle species, which are considered indicator species of the species‐rich fauna of saproxylic insects in Europe.     

Temperature and the pollinating activity of social bees

Abstract.

• 1 Thermal constraints on flight acivity limit the pollinating effectiveness of bees. Each species of social bee has a microclimatic ‘window’ within which foraging flight can be sustained.
• 2 To predict whether a given species of social bee is worth testing as a pollinator in a given climate, it is useful to know at least the lower limits of that microclimatic ‘window’. We consider how information from a series of bee counts through a day can be used to characterize a bee species in terms of activity/microclimate relations as a basis for predicting the diel pattern of foraging activity of a bee introduced into a new climate as a pollinator.
• 3 We discuss the relative merits of bee counts at a foraging patch and counts based on hive traffic as indices of the proportion of bees active.
• 4 We suggest that the activity/microclimate relations of a species be expressed in terms of the lower threshold black globe temperature for flight activity. Black globe temperature, T_g, is easily measured with inexpensive equipment, and can substitute for measurements of ambient temperature and radiation as a predictor of diel patterns of bee activity.
• 5 We use examples of field data to explore the relationship between microclimate and activity for the honeybee Apis mellifera and several species of bumblebee, Bombus. Regression analysis is used to relate activity to T_g and to identify the lower temperature threshold for activity from field bee counts.
• 6 In field studies analysed here, the bumblebees Bombus terrestrisllucorum, B.pascuorum and B.hortorum began foraging at lower temperatures than honey-bees or B.lapidarius.

     

Wood ants prefer conifers to broadleaved trees in mixed temperate forests

1. Wood ants, species of the subgenus Formica s. str., are one of the most important groups of insects in forest ecosystems due to their high abundance and activity.
2. We assessed the foraging pressure of Formica polyctena and Formica rufa, two dominant wood ant species in the Białowieża Forest. In addition, we compared coniferous and mixed stands in these respects.
3. In mixed stands F. polyctena visited more trees per plot than F. rufa. F. polyctena might forage a larger area due to higher population sizes, which further confirms higher foraging pressure of F. polyctena in comparison with F. rufa.
4. In our study area, host trees of the ant–aphid mutualism were larger in diameter than nonhost trees. The ants also preferred trees situated closer to their nests. In both mixed and coniferous stands, the most visited tree species was Norway spruce. Thus, we can conclude that Norway spruce seems to be preferred by the ant. The decline of living spruce in the Białowieża Forest may endanger their food source and impact the vitality of ant colonies.

     

Bark beetle and woodborer responses to stand thinning and prescribed fire in northeastern US coastal and inland pitch pine barrens

1. Southern pine beetle, Dendroctonus frontalis, has expanded its range further into the northeastern United States. This expansion threatens rare and ecologically valuable interior and coastal pitch pine barrens.
2. Pitch pine barrens restoration and southern pine beetle infestation suppression often involve leaving downed dead wood that saproxylic insects can exploit.
3. Semiochemical-baited traps were used to investigate the response of bark beetles and woodborers to restoration treatments at Rocky Point State Forest and the Albany Pine Bush Preserve, examples of coastal and interior pitch pine forests, respectively.
4. A total of 29,598 saproxylic insects from 116 species of bark beetles and woodborers were captured at Rocky Point State Forest, while 23,117 individuals from 67 species were captured at Albany Pine Bush Preserve.
5. Ips spp. were abundant at both sites with 28%–47% and 42%–74% of total collections at Rocky Point State Forest and Albany Pine Bush Preserve, respectively.
6. Ips grandicollis did not respond to treatments at either site. However, Ips pini was found in higher numbers in thinned blocks in Rocky Point State Forest.