Insect communities are facing contrasting responses due to global change. However, knowledge on impacts of communities’ reorganizations is scarce. Network approaches could help to envision community changes in different environmental scenarios. Saproxylic beetles were selected to examine long-term variations in insect interaction/diversity patterns and their vulnerability to global change. We evaluated interannual differences in network patterns in the tree hollow–saproxylic beetle interaction using absolute samplings over an 11-year interval in three Mediterranean woodland types. We explored saproxylic communities’ vulnerability to microhabitat loss via simulated extinctions and by recreating threat scenarios based on decreasing microhabitat suitability. Although temporal diversity patterns varied between woodland types, network descriptors showed an interaction decline. The temporal beta-diversity of interactions depended more on interaction than on species turnover. Interaction and diversity temporal shifts promoted less specialized and more vulnerable networks, which is particularly worrisome in the riparian woodland. Network procedures evidenced that saproxylic communities are more vulnerable today than 11 years ago irrespective of whether species richness increased or decreased, and the situation could worsen in the future depending on tree hollow suitability. Network approaches were useful for predicting saproxylic communities’ vulnerability across temporal scenarios and, thus, for providing valuable information for management and conservation programs.

Light Detection and Ranging (LiDAR) is a remote sensing technique with multiple uses throughout scientific fields. It can also be used to transfer point data measured in the field to broader spatial scales, which might enable the evaluation of habitats over large areas and define biodiversity hotspots. Our study took place in Cabañeros National Park, which is situated in the Mediterranean, namely, central Spain, and its vegetation is dominated by forest and impenetrable scrubland. LiDAR was used to detect veteran trees as key elements for a highly diverse saproxylic community. The saproxylic beetle community inhabiting tree hollows was studied among different forest types and habitats to determine its preferences. We identified potential hotspots for the saproxylic beetle community of tree hollows both inside and outside of the park, as well as the connectivity of suitable habitat patches. This was based on the species response to the spatial partitioning of the landscape. We found that not all potentially suitable forest types hosted the same saproxylic diversity or similar species compositions. In addition, forest distribution and connectivity inside and outside of the park also varied highly among forest types and habitats, where the most diverse deciduous oak forest was also the least connected together with the riparian forest. The evergreen oak forest could act as a habitat linkage for most of the threatened and less mobile species in the park. However, the low connectivity of the most diverse forest types in the park surroundings can compromise the persistence of saproxylic diversity in the near future. We concluded that LiDAR data were an effective tool for estimating saproxylic beetle diversity distribution over large-scale areas in the context of landscapes with low accessibility. Additionally, this tool allowed us to identify the most threatened forest types and critical patches for connectivity persistence where management practices capable of accelerating tree veteranisation could help to increase adequate forest connectivity in the region.

With over 80 species, Milesia Latreille, 1804 is a hoverfly genus (Diptera: Syrphidae) is found in all continents except for Australia and the Antarctica. However, little is known about its life cycle and biology. The three Milesia species for which early stages are known have saproxylic larvae, suggesting that the larvae of all other Milesia species are also saproxylic. The early stages of the three Milesia species occurring in Europe are undescribed. Milesia crabroniformis (Fabricius, 1775), a mimic of the hornet Vespa crabro Linnaeus, 1758, is the largest hoverfly in Europe and is listed as Least Concern in the IUCN European Red List of Hoverflies. We here report the first early stages of Milesia ever found in Europe, describing them and their breeding sites. Larvae of M. crabroniformis were collected in water-filled tree holes of live chestnut trees (Castanea sativa Mill.) in Málaga, Southern Spain in 2020-2021. Various studies based on stereomicroscope and scanning electron microscopy (SEM) techniques have proven useful in diagnosing hoverfly early stages by the observation of their fine morphology. Thus, these techniques were also used here to characterize the second (L2) and third (L3) stage larvae of M. crabroniformis, as well as the puparium. A Leica M205 C binocular stereomicroscope and a Jeol JSM-ITH500HR SEM were used. The head skeleton and chaetotaxy of the L3 larva were described and illustrated. Adjustments to the diagnosis of the larvae of Milesia are proposed based on the number of hooks from the primary row of the main group of hooks. The new early stages are compared with those of other Milesia hoverflies, as well as with those of the sister group Spilomyia Meigen, 1803. The knowledge of the larval biology and breeding sites of saproxylic insects is useful for implementing forest management measures and species’ conservation programs.

Mediterranean Quercus woodlands are socio-ecological systems where biodiversity associated with tree-related microhabitats remains poorly known despite its potential importance for ecosystem functioning and conservation. Tree cavities, in particular, provide buffered microclimates and key nesting and shelter resources for numerous taxa, yet the diversity of organisms associated with these microhabitats remains incompletely documented across multiple trophic groups in Mediterranean woodlands. Here we compile an integrative inventory of cavity-dwelling biota and their ecological roles by combining high-throughput sequencing of fungal communities in holm oak (Quercus ilex) cavities with long-term data on saproxylic beetles and vertebrates across Mediterranean Quercus forests in Spain. Fungal communities are taxonomically diverse (> 2,000 OTUs) and functionally heterogeneous, dominated by saprotrophic Ascomycota but including plant pathogens, endophytes, and ligninolytic Basidiomycota, indicating multi-stage decay processes. Cavities also hosted a diverse saproxylic beetle communities (> 200 species, > 40 families), rich in wood-dependent, mycophagous, and predatory taxa, including numerous EU- and regionally threatened hollow specialists. Vertebrate inventories documented 67 cavity-using species (birds, mammals, reptiles, amphibians), largely secondary cavity users spanning broad dietary and foraging guilds, with woodpeckers representing a small excavator guild and several threatened mammals and reptiles depending on cavity-bearing trees. Taken together, these inventories document substantial taxonomic and functional diversity associated with tree cavities across fungi, saproxylic beetles, and vertebrates, highlighting their relevance as microhabitats for a wide range of organisms. Conserving cavity-bearing trees and the processes that generate them can therefore contribute to maintaining habitat heterogeneity and biodiversity associated with mature trees under ongoing global change in the Mediterranean region.

Despite growing research on insect decline, long-term temporal analyses integrating functional approaches remain scarce. Understanding how functional traits relate to temporal changes in community composition is particularly important for saproxylic communities, which are highly sensitive to forest environmental changes. In this study, we analysed interannual and spatial changes in the taxonomic and functional dimensions of saproxylic beetle and spider communities inhabiting tree hollows across three Mediterranean forest types (riparian ash forest, deciduous oak forest and sclerophyllous oak woodland). Specimens were sampled monthly using emergence traps during two complete years separated by an 11-year period. We assessed variation in species richness, functional diversity (functional richness and divergence), and functional structure. We also explored whether species-level temporal changes in relative abundance were associated with species’ positions in functional trait space. Beetle and spider species richness differed among forest types and between sampling periods, whereas functional richness varied mainly spatially. Trait-associated shifts in species relative contribution were not consistent across taxa or forests. The clearest trait-associated changes in relative abundance were detected in wood-dependent beetles (saprophagous, saproxylophagous and xylophagous) from Quercus pyrenaica forests, where larger and less dispersive species showed lower relative abundance in the second sampling period. In contrast, there was little evidence of consistent trait-mediated changes in spider assemblages over time. Overall, our results indicate that temporal functional responses of saproxylic arthropod communities are context dependent, varying across forest types and trophic guilds and suggest maintaining structurally complex forests and continuous networks of suitable tree hollows to buffer these communities under ongoing environmental change, specially in Q. pyrenaica forests.

Background: Flight performance and dispersal behaviour can differ between sexes, resulting in sex-biased dispersal. The primary sex ratio of populations may also explain dispersal bias between sexes, as this bias may evolve with the primary sex ratio to reduce intrasexual competition. Although dispersal bias between sexes is relevant to population dynamics, there are few studies on sex-biased dispersal in insects. We studied the flight performance and dispersal behaviour of seven saproxylic beetle species associated with tree hollows from a sex perspective. We also analysed the possible coevolution of flight performance with the primary sex ratio. Methods: Wing loading and wing aspect ratio were used as measures of the flight performance of species and sexes. Dispersal behaviour was explored by analysing the frequency of each sex in interception traps versus the primary sex ratio obtained by tree hollow emergence traps using contingency tables and posthoc standardized residuals. A more active flight behaviour was expected for the sex with higher capture frequency in the interception traps. To explore the causes of flight performance bias between sexes, we searched for possible correlations between wing loading or wing aspect ratio and primary sex ratio using Pearson’s correlation coefficient. Results: Wing loading and wing aspect ratio differed between species and sexes, with flight performance being higher in males than in females for four of the seven species analysed. Dispersal behaviour and flight performance matched in the case of Elater ferrugineus; males showed higher flight performance and were the most collected sex in the interception traps (more active flyers). In contrast, the higher flight activity of Cetonia carthami aurataeformis females was not correlated with a higher flight performance than that of males. Moreover, we found that a bias in the primary sex ratio towards females is often correlated with a decrease in female flight performance. Conclusions: We stress that flight performance and dispersal behaviour of sexes do not always go hand in hand. Moreover, the relationship between the sex ratio and flight performance bias between sexes is not driven by competition within the most abundant sex. The inclusion of a sex perspective in insect dispersal studies would be useful to detect dispersal bias between sexes and its causes and would allow for further analysis of its effects on population dynamics.

Shifts in insect phenology represent a critical and understudied concern, even as we gather more evidence about the effects of climate change on insect communities. This is particularly true for saproxylic beetles, where a lack of long-term data hinders research. Here, we explored interannual changes in a saproxylic beetle community in Mediterranean woodlands by comparing two one-year sampling events conducted 11 years apart. We analysed trends in air temperature and relative humidity over the past 22 years and explored if differences in phenological patterns were detectable between the two sampling periods, also considering functional traits (i.e., trophic guild and body size). Our key findings reveal significant shifts in the community’s activity patterns, with different climatic variables influencing them each year. This suggests a potential adaptive phenological response to the warming trend in the area. Our analysis also showed differential responses among trophic guilds and body size classes, reinforcing the importance of functional approaches in climate change studies. Overall, our research highlights that species activity periods may become increasingly unpredictable, underscoring the critical need for continued long-term research.

Forests of the Mediterranean Basin provide a wide range of provisioning and regulating services that are currently jeopardised by land-use change. Although many ecosystem services are mediated by insects, most of the studies that have focused on how to enhance diversity in traditionally managed forests are about plants and vertebrates. Quercus pyrenaica woodlands of the Western Iberian Peninsula constitute a scenario in which traditional human practices (i.e., extensive livestock grazing, pollarding, firewood, forest thinning, etc.), and their progressive abandonment, have generated differences in landscape that affect habitat and microhabitat structures. We used saproxylic beetles (deadwood-dependent species) as biological indicators because they are the most diverse taxa and provide important ecosystem services related to deadwood decomposition, forest pest control and pollination. We modelled the response of two taxonomic (species richness and abundance), one ecological (species diversity of order 1) and two functional (functional richness and redundancy) diversity metrics to the environmental variables that result from traditional management or its abandonment at habitat and microhabitat levels. We included 16 explanatory variables related to forest structure, tree microhabitats and abiotic factors, which were grouped into eight principal components. Linear regression was the best fitting model for data. The resulting models were used to perform diversity predictions in different scenarios. We found that abandonment of some traditional forest management activities in the Mediterranean Region reduced taxonomic saproxylic beetle diversity, which may be further aggravated by climate change. We suggest minimal management actions to improve taxonomic and ecological saproxylic beetle diversity related to habitat and tree management (i.e., maintenance of >20% scrub coverage, >20 m3/ha of deadwood on soil and >20 hollow trees/ha). However, actions that boost saproxylic biodiversity do not ensure the community’s higher functional resilience. We should also promote tree microhabitat diversity to reduce the vulnerability of saproxylic beetle functions to environmental changes.