Saproxylic Insects Research Articles

Dispersal ecology of deadwood organisms and connectivity conservation.

Limited knowledge of dispersal for most organisms hampers effective connectivity conservation in fragmented landscapes. In forest ecosystems, deadwood-dependent organisms (i.e., saproxylics) are negatively affected by forest management and degradation globally. We reviewed empirically established dispersal ecology of saproxylic insects and fungi. We focused on direct studies (e.g., mark-recapture, radiotelemetry), field experiments, and population genetic analyses. We found 2 somewhat opposite results. Based on direct methods and experiments, dispersal is limited to within a few kilometers, whereas genetic studies showed little genetic structure over tens of kilometers, which indicates long-distance dispersal. The extent of direct dispersal studies and field experiments was small and thus these studies could not have detected long-distance dispersal. Particularly for fungi, more studies at management-relevant scales (1-10 km) are needed. Genetic researchers used outdated markers, investigated few loci, and faced the inherent difficulties of inferring dispersal from genetic population structure. Although there were systematic and species-specific differences in dispersal ability (fungi are better dispersers than insects), it seems that for both groups colonization and establishment, not dispersal per se, are limiting their occurrence at management-relevant scales. Because most studies were on forest landscapes in Europe, particularly the boreal region, more data are needed from nonforested landscapes in which fragmentation effects are likely to be more pronounced. Given the potential for long-distance dispersal and the logical necessity of habitat area being a more fundamental landscape attribute than the spatial arrangement of habitat patches (i.e., connectivity sensu strict), retaining high-quality deadwood habitat is more important for saproxylic insects and fungi than explicit connectivity conservation in many cases.

Unraveling Saproxylic Insect Interactions in Tree Hollows from Iberian Mediterranean Forest.

Tree hollows are complex microhabitats in which a variety of abiotic and biotic factors shape the community assembly of saproxylic insects. Detecting non-random species co-occurrence patterns is a fundamental goal in ecology in order to understand the assembly mechanisms of communities. We study association patterns of species of Coleoptera and Diptera (Syrphidae), belonging to different trophic guilds, on 72 tree hollows at a local and regional scale in three protected areas in Mediterranean forests using a fixed-fixed null model. Our matrix-level analysis shows a tendency for segregation in species association (species exclusion) at the regional and site levels. However, the high complexity of tree-hollow habitats, offering different resources for a more or less specialized fauna, makes it difficult to prove competition interactions. Indeed, pairwise analysis shows a dominance of non-random aggregation patterns (species coexistence) at the local and regional levels. Both aggregation and segregation of non-random patterns were more common among species from different trophic guilds than within the same guilds, with predators being a common denominator for a high percentage of the inter-guild pairs. Our results suggest that predation and facilitation interactions, together with habitat segregation, are the main factors shaping tree-hollow assemblages, while competition seems to be less important. We conclude that species interactions take an important part of the process of assemblage structuration and special attention should be paid to 'ecosystem engineers' and threatened species in the conservation of tree hollow assemblages.

Dispersal limitation of saproxylic insects in a managed forest? A population genetics approach

Dispersal is a key trait of species enabling gene flow among populations. For species persistence dispersal may therefore be crucial especially in a patchy or changing environment. Tree hollows are a patchy habitat as their number is locally limited and in addition to that, habitat quality of tree hollows differs. Both factors are important for colonization by saproxylic insects as species may be specialized on a particular age or quality of a tree hollow and may be dispersal-limited. Intensive forest management may further decrease the number of tree hollows and increase distances between them, if trees with hollows are removed. However, not much is known about the dispersal abilities of most saproxylic species, even though such knowledge could improve conservation efforts. To investigate the genetic population structure of saproxylic species, we collected saproxylic organisms with emergence traps from 40 hollows in beech trees in a managed forest in Germany (approximately 14×14km). We focused on three threatened species, one coleopteran and two dipteran (Anaspis ruficollis, Scraptiidae; Criorhina floccosa, Syrphidae; Xylomya maculata, Xylomyidae) emerging from our tree hollows. Microsatellite analysis was used to assess gene flow among tree hollows and population genetic structure. In contrast to other studies reporting limited dispersal in saproxylic insects, we found no indication for restricted gene flow in all three species investigated. However, we studied relatively abundant species and our study site may not have been large enough to detect genetic substructure. This study indicates that the amount and quality of a suitable habitat may at least in some cases be more limiting than the physical ability to disperse.

Use of a genetically informed population viability analysis to evaluate management options for Polish populations of endangered beetle Cerambyx cerdo L. (1758) (Coleoptera, Cerambycidae)

A paucity of genetic information and the drastic decline in population size of the beetle Cerambyx cerdo has made this species a high priority for research and conservation management. The state-listed beetle, a saproxylic insect associated with oaks, has a discontinuous range, with larger and more connected populations in southern Europe and small and isolated populations in the continent’s central and northern parts. Here, we used seven microsatellite loci and one DNA fragment of the mitochondrial gene COI to examine the population structure, genetic diversity, and contemporary gene flow between two Polish populations of the beetle. A population viability analysis summarizing collected genetic data as well as field records and species-specific information was performed to investigate the probability of the populations’ persistence over 20 years under different simulation scenarios. Genetic drift due to spatial isolation and bottleneck(s) is probably a major evolutionary force responsible for a low number of haplotypes and lower gene diversity in these populations as compared to the neighboring Czech populations. Despite a large geographic distance between the Polish populations, genetic differentiation between them was low, which could reflect shared ancestral polymorphism and stochasticity of retained alleles rather than the homogenizing effect of gene flow. Differences among probabilities of extinction over 20 years were detected between populations, and, in the worst-case scenarios, one population will disappear within four generations. Conservation efforts must focus on supplementation, habitat restoration, and post-release monitoring. The results of our study provided information that can be incorporated into future management actions to aid in the conservation of the beetle.

Response of saproxylic insect communities to logging history, tree species, stage of decay, and wood posture in the central Nearctic boreal forest

Saproxylic insect assemblages are essential functional components of forest ecosystems that can be affected by forest management. We used a split-plot ANOVA design to analyze differences in selected saproxylic insects (all arthropod orders and dipteran and parasitic hymenopteran families) emerging from dead wood of sites with different logging histories (horse-logged, mechanically-logged and unlogged), tree species (Populus and Picea), stage of decay (early- and late-decay stages) and posture (standing and downed logs) in the boreal forest of central Canada. No clear effects of logging history were seen for the studied taxa; however, interaction between logging history and other dead wood features was apparent. Cecidomyiidae consistently emerged more from Populus than from Picea dead wood. Most of the studied saproxylic families were more abundant in late-decay than in early-decay wood. Dipterans of the Cecidomyiidae, Ceratopogonidae, Empididae, Mycetophilidae and Sciaridae families, and hymenopterans of the Diapriidae and Ichneumonidae families were significantly more abundant in downed than in standing dead wood. In contrast, Mymaridae was most abundant in standing dead wood. Our study provides evidence that some insects at high taxonomic levels respond differently to dead wood quality, and this could inform future management strategies in the boreal forest for the conservation of saproxylic fauna and their ecological functions.

Head shape variation in cerambycid saproxylic beetles as a function of host plant selection

Saproxylic insects depend on deadwood for larval development, and a certain degree of specialization may be involved in their choice of host plants and/or wood in a particular stage of degradation. The plant species chosen for oviposition in turn act as an environmental pressure on the head morphology of larvae and it is expected that head shape plasticity varies directly with the number of woody plant species used for larval development in each insect species. We analyzed head shape variation in saproxylic beetles with respect to host plant species, maximum time of larval emergence and season of the year when insects colonized branches. Generalist species in the use of host plants showed significant variation in head shape and size. Time of emergence and season did not appear to affect head shape, although season was a determinant factor of abundance and possibly head size variation.

“Primeval forest relict beetles” of Central Europe: a set of 168 umbrella species for the protection of primeval forest remnants

Identification of forest stands with priority for the conservation of biodiversity is of particular importance in landscapes with a long cultural and agricultural history, such as Central Europe. A group of species with a high indicator value for the naturalness of forest ecosystems are saproxylic insects. Some of these species, especially within the order Coleoptera, have been described as primeval forests relicts. Here, we compiled a list of 168 “primeval forest relict species” of saproxylic beetles based on expert knowledge. These species can serve as focal and umbrella species for forest conservation in Central Europe. They were selected because of their dependence on the continuous presence of primeval forest habitat features, such as over-mature trees, high amounts of dead wood, and dead wood diversity, as well as their absence in managed Central European forests. These primeval forest relict species showed a moderately strong clumping pattern within the phylogeny of beetles, as indicated by phylogenetic signal testing using the D-statistic. When we controlled for phylogenetic relatedness, an ordinal linear model revealed that large body size and preference for dead wood and trees of large diameter are the main characteristics of these species. This list of species can be used to identify forest stands of conservation value throughout Central Europe, to prioritize conservation and to raise public awareness for conservation issues related to primeval forests.

Use of space and dispersal ability of a flagship saproxylic insect: a telemetric study of the stag beetle (Lucanus cervus) in a relict lowland forest

Abstract The stag beetle, Lucanus cervus (Linnaeus, 1758) (Coleoptera: Lucanidae), is a flagship species for the conservation of European old‐growth forests. Despite its popularity and many studies conducted, the lack of knowledge of its habits and ecological requirements leads to difficulties in locating the species in the field and to provide information for suitable planning conservation actions suitable for the species. In order to gather information on dispersal ability and space use, a radio‐telemetry study was conducted in a relict floodplain forest surrounded by intensively cultivated land. During 2014 and 2015, from May to July, 55 beetles (34 males, 21 females) were radio‐tagged, and 9 of these (7 males, 2 females) were telemetered immediately after the emergence from their development sites, by means of emergence traps. The use of radio‐telemetry allowed to detect the oviposition sites and to study the first part of the adult life, when they resulted to be more active. Males were more prone to disperse than females but the home range size did not differ between the sexes. Dividing the season in three intervals, the most active individuals were recorded during the first and the second ones (first and second half of June).

Larval assemblages of large saproxylic cerambycids in Iberian oak forests: wood quality and host preference shape resource partitioning

AbstractOak open woodlands are widespread in southwestern Iberia and present outstanding ecological, biodiversity and socio‐economic values. Evergreen species (holm and cork oaks) are prevalent but deciduous oaks may be also locally important. Three large xylophagous cerambycids are associated to these oaks, Cerambyx welensii (Cw), C. cerdo (Cc) and Prinobius myardi (Pm). Like other saproxylic insects, these cerambycids are essential to the nutrient cycle, wood degradation and tree hollow formation, significantly contributing to biodiversity in oak forests. These cerambycids may also potentially colonise healthy living trees and become harmful or pest species. Factors driving their larval ecology are almost unknown, especially in oak forests harbouring mixed populations living in sympatry. Wood samples (n = 500 bolts) from 348 colonised trees were examined during 2011–2016 across the Extremadura region (41,634 km2). Bolts were measured, scored into five wood quality classes, dissected, and all target cerambycids were collected, measured, reared and taxonomically identified. We then determined species‐specific prevalence, niche breadth, niche overlap, age structure and population density depending on wood quality, host preference, tree part, wood size, altitude and sun exposure. Wood quality and host preference were major factors segregating interspecific resource partitioning. Cw was prevalent on cork oak decayed wood, and Pm on holm oak degraded wood. Host tree part was involved in Cerambyx larval niche segregation, with Cw prevalent in the fork/branches and Cc in the trunk/base. Pm was never found inhabiting deciduous oaks. Our results may be useful to improve sustainable forest management practices in Iberian oak open woodlands.

The LIFE Project “Monitoring of insects with public participation” (MIPP): aims, methods and conclusions

The Life Project “Monitoring of insects with public participation” (LIFE11 NAT/IT/000252) had as the main objective to develop and test methods for the monitoring of five beetle species listed in the Annexes of the Habitats Directive (92/43/EEC): Osmodermaeremita (hermit beetle, Scarabaeidae), Lucanuscervus (European stag beetle, Lucanidae), Cerambyxcerdo (great capricorn beetle, Cerambycidae), Rosaliaalpina (rosalia longicorn, Cerambycidae) and Morimusasper/funereus (morimus longicorn, Cerambycidae). The data gathered represent an important contribution to the monitoring of these target species in Italy. The methods developed for monitoring of the target species are intended for use by the local management authorities and staff of protected areas. These developed methods are the result of extensive fieldwork and ensure scientific validity, ease of execution and limited labour costs. The detailed description of methods and the results for each species are published in separate articles of this special issue of Nature Conservation. A second objective of the project was to gather faunistic data with a Citizen Science approach, using the web and a mobile application software (app) specifically built for mobile devices. The validation of the records collected by the citizens was carried out by experts, based on photographs, which were obligatory for all records. Dissemination activities represented the principal way to contact and engage citizens for the data collection and also offered the possibility of providing information on topics such as Natura 2000, the Habitats Directive, the role of monitoring in nature conservation, the importance of forest ecosystems and the ecological role of the saproxylic insects. An innovative method tested during the project was the training of a dog for searching and monitoring the elusive hermit beetle; the trained dog also added a “curiosity” factor to attract public attention towards this rare insect and the issues mentioned above.

Training of a dog for the monitoring of Osmoderma eremita

One aim of the MIPP Project (http://www.lifemipp.eu) was to develop non-invasive monitoring methods for selected saproxylic beetles. In this paper, a method is proposed for monitoring the larvae of Osmoderma eremita in their natural habitat (i.e. hollow trees), using a conservation detection dog (CDD). Wood mould sampling (WMS), the standard method to detect hermit beetles and other saproxylic insects inside tree hollows, is time-consuming and exposes the target species and the whole saproxylic communities to some risks. In contrast, CDDs pose no risk to the species living inside trees while, at the same time, offer a powerful tool for surveying the insects. In this paper, the methods applied to train the dog are presented, together with the results for accuracy (the overall proportion of correct indications), sensitivity (the proportion of correct positive indications) and specificity (the proportion of correct negative indications) obtained once the CDD had been fully trained. Results are presented for nitrocellulose filters with the odour of the target species, for larvae living inside hollow trees, for frass and for the remains of adults. A comparison of the efficiency between CDD and WMS showed that employing the dog was much less time-consuming than WMS. The literature on training CDDs for nature conservation tasks, with particular reference to cases involving Coleoptera, was also reviewed.

Novel, male-produced aggregation pheromone of the cerambycid beetle Rosalia alpina, a priority species of European conservation concern.

Several recent studies have demonstrated the great potential for exploiting semiochemicals in ecology and conservation studies. The cerambycid beetle Rosalia alpina represents one of the flagship species of saproxylic insect biodiversity in Europe. In recent years its populations appear to have declined substantially, and its range has shrunk considerably as a result of forest management and urbanization. Here, we collected volatile chemicals released by males and females of R. alpina. Analyses of the resulting extracts revealed the presence of a single male-specific compound, identified as a novel alkylated pyrone structure. In field bioassays in Slovenia, traps baited with the synthesized pyrone captured both sexes of R. alpina, indicating that the pyrone functions as an aggregation pheromone. Our results represent the first example of a new structural class of pheromones within the Cerambycidae, and demonstrate that pheromone-baited traps can provide a useful tool for sampling R. alpina. This tool could be particularly useful in the ongoing development of conservation strategies for the iconic but endangered Alpine longicorn.

What shapes cerambycid beetle communities in a tropical forest mosaic? Assessing the effects of host tree identity, forest structure, and vertical stratification

Due to anthropogenic activities, tropical rain forests face many challenges in sustaining biodiversity and maintaining global climates. This study explores how forest successional stage, tree composition, and stratum affect communities of saproxylic cerambycid beetles—concealed feeders that play important roles in forest nutrient cycling. Forty trees in five families (Fabaceae, Lecythidaceae, Malvaceae, Moraceae, and Sapotaceae) were sampled in a mosaic of old-growth and secondary forest on the Osa Peninsula, Costa Rica. Bait branches yielded 3549 cerambycid individuals in 49 species. Species richness was almost identical in old-growth and secondary forest, and both yielded specialists, but abundance was higher in old-growth forest. Overall community structure was most strongly influenced by host plant species; within most plant families it was also impacted by forest successional status. Moraceae was the exception, presumably because the focal tree species was abundant in both old-growth and secondary forest. Several host and old-growth specialist species reached high densities within patches of old-growth forest, but seldom colonized apparently suitable trees within secondary forest. This suggests that even small areas of old-growth forest can act as refuges, but that secondary forest may act as a barrier to dispersal. The vulnerability of specialized saproxylic insects to land use change will be linked to the ability of their preferred hosts to disperse to and persist in successional habitats; rearing studies may provide the most accurate method to monitor community changes over time.

An experimental test of the habitat-amount hypothesis for saproxylic beetles in a forested region.

The habitat-amount hypothesis challenges traditional concepts that explain species richness within habitats, such as the habitat-patch hypothesis, where species number is a function of patch size and patch isolation. It posits that effects of patch size and patch isolation are driven by effects of sample area, and thus that the number of species at a site is basically a function of the total habitat amount surrounding this site. We tested the habitat-amount hypothesis for saproxylic beetles and their habitat of dead wood by using an experiment comprising 190 plots with manipulated patch sizes situated in a forested region with a high variation in habitat amount (i.e., density of dead trees in the surrounding landscape). Although dead wood is a spatio-temporally dynamic habitat, saproxylic insects have life cycles shorter than the time needed for habitat turnover and they closely track their resource. Patch size was manipulated by adding various amounts of downed dead wood to the plots (~800m³ in total); dead trees in the surrounding landscape (~240km2 ) were identified using airborne laser scanning (light detection and ranging). Over 3 yr, 477 saproxylic species (101,416 individuals) were recorded. Considering 20-1,000m radii around the patches, local landscapes were identified as having a radius of 40-120m. Both patch size and habitat amount in the local landscapes independently affected species numbers without a significant interaction effect, hence refuting the island effect. Species accumulation curves relative to cumulative patch size were not consistent with either the habitat-patch hypothesis or the habitat-amount hypothesis: several small dead-wood patches held more species than a single large patch with an amount of dead wood equal to the sum of that of the small patches. Our results indicate that conservation of saproxylic beetles in forested regions should primarily focus on increasing the overall amount of dead wood without considering its spatial arrangement. This means dead wood should be added wherever possible including in local landscapes with low or high dead-wood amounts. For species that have disappeared from most forests owing to anthropogenic habitat degradation, this should, however, be complemented by specific conservation measures pursued within their extant distributional ranges.

Veteran trees and saproxylic insects in the floodplains of Lower Morava and Dyje rivers, Czech Republic

ABSTRACTVeteran and solitary trees are key structures supporting biodiversity in many wooded ecosystems. Their global decline threatens numerous organisms associated with them, including several insect species protected by law that serve as umbrella species. The floodplain along the lower Morava and Dyje rivers is considered a hotspot for saproxylic organisms associated with veteran trees. The area is a UNESCO Biosphere Reserve and part of NATURA 2000. Between 2006 and 2015, we mapped 11,596 veteran and habitat trees in the area. The mapping also included the distribution of several insects associated with veteran trees including three beetle species (Cerambyx cerdo, Osmoderma barnabita, and Eurythyrea quercus) and two ant species (Liometopum microcephalum and Lasius fuliginosus). The data on the position, abundance, diameter, forest structure and health of the veteran trees and trees inhabited by the above species are presented in a map created in ArcGIS Online. These data serve as an important source of information for the management of nature conservation of the area.

Use of novel attraction compounds increases monitoring success of a rare beetle, Elater ferrugineus

Abstract The use of pheromones to determine distributions of rare saproxylic insects is an increasingly popular technique. Pheromones may, however, also be used to elucidate the biology of these cryptic species, a vital requirement if they are to be accurately monitored and conserved. We used non‐invasive aerial trapping to compare the effectiveness of chemicals produced by Elater ferrugineus L (Coleoptera: Elateridae), namely 7‐methyloctyl (Z)‐4‐decenoate (the female‐produced sex pheromone), and male compounds (geranyl and neryl acetone and 6‐methyl‐5‐heptene‐2‐one). The male compounds were identified using headspace analysis by solid phase micro‐extraction gas chromatography‐mass spectrometry. We discovered that males only produce these two compounds after having been attracted to a female, and that this serves to attract further males to a female. Such compounds do not appear to attract females but for a species that has a short activity period and is non‐feeding in the adult stage, may ensure breeding success when populations are low. By marking all beetles caught, we were able to demonstrate that recapture rate using this method is low (approximately 11% of total captures annually). Therefore, the method does not limit dispersal or breeding opportunities, making it a valuable tool for monitoring endangered saproxylic beetle species.

Combinando datos LiDAR e inventario forestal para identificar estados avanzadosde desarrollo en bosques caducifolios

Palop-Navarro, E., Banuelos, M. J., Quevedo, M. 2016. Using LiDAR and forest inventory data to identify late development stages in broad-leaved forest. Ecosistemas 25(3): 35-42. Doi.: 10.7818/ECOS.2016.25-3.04 Old-growth forests are generally scarce because of historic human exploitation of forest ecosystems. Their structure – characterized by trees of varying sizes and ages, presence of forest gaps and abundant deadwood – is particularly hard to recover after homogenization derived from forest exploitation. Moreover, the conservation of forest specialists, like saproxylic insects or woodpeckers, depends on this type of structure. Characterizing and identifying this structure is therefore important for conserving and restoring this type of forests and their communities. Forest structure and composition has been historically recorded in forest inventories. These inventories provide valuable information, albeit of discrete nature, and may be less efficient in areas of difficult access. From this regard, LiDAR (Light Detection and Ranging) technology provides tridimensional and continuous information of forest structure, making it a useful tool for complementing field work of forest inventories. In this study we evaluated the possibility of quantifying late successional stages in broad-leaved forests in the NW corner of the Iberian Peninsula from public LiDAR data (density 0.5 points m-2). First, we compared LiDAR-derived variables with field-derived variables from the 4th National Forest Inventory (IFN4), which showed the existence of correlations, especially at maximum and averaged heights, though the adjustment varies considerably with the diameter of the inventory considered. Later we built simple predictive models for the identification of old-growth forests in IFN4 plots (binary variable Bosque Viejo). The final model was built by variables namely Altura desvest and Altura media2 (indicators of heterogeneous structures and size varying trees in late successional stages of development), together with dominance of different tree species in plots derived from the IFN4. Results show that publically available Spanish LiDAR data can be used to identify forest structures compatible with old-growth broadleaved forests.

Bacteria and Hoverflies (Diptera: Syrphidae) in Tree Hollows From the Iberian Mediterranean Forest

Saproxylic insect communities inhabiting tree hollows in Mediterranean forests depend on a combination of physical characteristics and interactions occurring between community member species. Despite the need to preserve these organisms, little is known about their interrelationships, in particular those relationships between saproxylic insects and microbiota occurring in these microhabitats. In tree hollows of Quercus rotundifolia Lamark that hold water and contain dead leaves, abundant microbial populations can be found. Developing on them are the larvae of Mallota dusmeti Andréu, 1926 (Diptera: Syrphidae), a vulnerable species (IUCN category: Marcos-García and Quinto 2011). This study provides the first data on the microbiota living inside the gut of the larvae of M. dusmeti, as well as the microbiota in the hollow where these larvae develop. Bacteria were identified by amplification and partial sequencing of the V1-V3 regions and the complete nucleotide sequence of 16S rRNA genes. We found eight species of bacteria living in tree hollows and three species in the gut of M. dusmeti larvae: Bacillus cereus, Bacillus toyonensis, and Lysinibacillus sphaericus. The filter-feeding mechanism characteristic of M. dusmeti larvae is selective in enabling ingestion of bacteria only above 2.1 µm in diameter.

Vertical distribution of saproxylic beetles within snag trunks retained in plantation forests

Retention of snags (standing dead trees) is considered to have important effects on saproxylic species conservation in plantation forests because snags would provide vertically stratified deadwood habitats. However, the vertical distribution of saproxylic insects within snag trunks is still unclear. We felled 33 naturally occurring snags of Todo fir Abies sachalinensis in plantation forests and extracted insects from 99 logs sampled from three vertical positions of the snag trunks (basal stem: 5 m). The mean number of species that emerged from a single log was only 2.69, but we identified 51 morphospecies of saproxylic beetles in total. The total number of species that emerged from the basal stem (34 spp.) was greater than those that emerged from the lower trunk (25 spp.) or the upper trunk (30 spp.). However, rarefaction-extrapolation analysis did not demonstrate a significant difference in species richness among the log positions. Beetle assemblages were separated into two groups by constrained correspondence analysis; one group emerged only from lower and upper trunk logs, while another emerged mainly from basal stem logs. Additionally, vertical position had a significant effect on the distribution of the five main species. Our results show that beetle assemblages within snags in the plantation forests were highly variable, and retaining a sufficient number of high stumps may be important for saproxylic beetle conservation in plantation forests. We propose ‘retention thinning’ as an appropriate method to combine efficient timber production with biodiversity conservation in plantation forests.

Long-term monitoring of saproxylic beetles from Mediterranean oak forests: an approach to the larval biology of the most representative species

Branches of Quercus species killed by Coraebus florentinus (Coleoptera, Buprestidae) are a chief resource for many saproxylic insects, mainly of the orders Coleoptera and Diptera, in the oak forests of the southern Iberian Peninsula. To investigate the biology of these species, a total of 127 dry oak branches that had been previously colonised by C. florentinus were collected and kept in the laboratory, in conditions comparable to the outdoor climate. For 4 years, the emergence of saproxylic insects from the branches was monitored. We obtained 651 individuals, belonging to 19 species of 6 families. Three buprestids (Anthaxia hungarica, A. millefolii and Agrilus angustulus) and one cerambycid (Chlorophorus ruficornis) made up 68% of the total abundance. Results on host tree preferences indicated that A. hungarica and C. ruficornis show more affinity to holm oaks (Q. ilex). Conversely, A. angustulus and A. hastulifer prefer cork oaks (Q. suber). Preimaginal stages have long durations, but vary in relation to the body size of species: smaller species such as A. angustulus and A. millefolii exhibit shorter larval time, reaching the maximum of emergences after 12 months monitoring, whereas larger species such as A. hungarica and C. ruficornis display a longer pre-adult period (3 and 4 years, respectively). The insects were found to be active in spring and summer and to have a balanced sex ratio in all of the species studied. Finally, our results also indicate the importance of long-term maintenance of these branches in the natural environment for the conservation of saproxylic biodiversity in the Iberian “dehesa”.