Global forest ecosystems are experiencing increasingly frequent and severe insect outbreaks, driven by complex interactions among climate change, land-use alterations, and shifting species distributions. Species that are morphologically indistinguishable — often referred to as cryptic species — can differ significantly in distribution, host use, and susceptibility to natural enemies and might thereby differ in outbreak dynamics. Yet, the contribution of cryptic species to temporal changes in the frequency and severity of insect outbreak dynamics remains poorly understood. Motivated by recent defoliation events in northern European oak forests, we investigated an emerging leaf-miner outbreak in Sweden. Through targeted surveys, rearing from 22 sites and Malaise trapping at 34 sites (56 sites total), we identified a pronounced spatial clustering of outbreaks at higher latitudes. The newly recognised cryptic species Acrocercops andreneli was strongly associated with these outbreaks, whereas sites with only Acrocercops brongniardella never showed outbreaks. Host-parasitoid networks related to the two cryptic moth species were strikingly similar. Our findings demonstrate the importance of cryptic species for outbreak dynamics and their consequences for host plant health in ways that are easily overlooked by traditional taxonomy. Moreover, such outbreak dynamics cannot always be linked to a lack of top-down control by natural enemies.

Cultivation of crops close to their wild relatives may jeopardise the integrity of wild genetic resources. Detecting cultivars among wild plants is necessary to characterise crop-wild gene flow, but can be challenging if cultivars and wild plants are phenotypically highly similar. Genomics tools can be used instead, but the selection of diagnostic loci for cultivar identification can be difficult if the wild and cultivated genepools are closely related. In Ethiopia, Arabica coffee cultivars resistant to coffee berry disease (CBD) occur near wild Coffea arabica plants and local landraces. However, the abundance and distribution of these cultivars across coffee sites remains unclear. Here, we present a new module of the SMAP package called SMAP relatedness pairwise to characterise pairwise genetic relationships between individuals based on haplotype calls and to identify diagnostic loci that distinguish (sets of) individuals from each other. Next, we estimate the relative abundance of CBD-resistant cultivars across 60 Ethiopian Arabica coffee sites using a genome-wide fingerprinting approach. We confirm the presence of these cultivars in around 75% of the coffee sites with a high agreement between a field survey and our DNA fingerprinting approach. At least 20 out of 60 sites with supposedly wild C. arabica individuals contain signatures of the cultivated genepool. Overall, we conclude that CBD-resistant cultivars are widespread in Ethiopian coffee sites. The development of SMAP relatedness pairwise opens opportunities to assess the distribution of coffee cultivars in other regions in Ethiopia and to apply similar screenings near wild relatives from other crops.

Introducing non-native tree species into forest ecosystems is a growing trend, in part as climate change may cause a decline of native species and shifts in species distributions. In European forestry, Quercus rubra (northern red oak) has increasingly been considered a candidate substitute species for native oaks. However, it remains largely unknown how this substitution affects associated biodiversity. This study compares the biodiversity supported by the native oak species Q. petraea (sessile oak) and Q. robur (pedunculate oak) and the invasive Q. rubra in southern Sweden, focusing on both oak-associated organisms and general forest biodiversity. Arthropods were sampled using Malaise traps at the site level. At the same time, vascular plants, leaf herbivory and endophytic insects (leaf miners and gallers) were recorded at the tree level in three sites per oak species. Our results reveal guild-specific effects of oak species on biodiversity. The introduced Q. rubra supported significantly fewer endophytic insects than native oak species. Vascular plant species richness was marginally lower in Q. petraea and Q. rubra sites compared to Q. robur. In contrast, the species richness, abundance, biomass and community composition of arthropods and leaf herbivory did not differ significantly between the three oak species. These findings indicate that the ecological consequences for biodiversity of introduced tree species, such as Q. rubra, are most pronounced for specialised herbivores, including leaf miners and gallers, and suggest that broader forest biodiversity measures may be less responsive to changes in tree species than to local environmental conditions.

Agroforestry systems have the potential to provide benefits for conservation, natural pest control and farmer livelihoods. Yet, we need a clearer understanding of how environmental drivers shape different components of biodiversity, how these biodiversity components contribute to suppressing pest levels, and how biodiversity trades off with yield. We focused on the diversity and role of birds and bats across different types of coffee farms in Arabica coffee’s native range in southwestern Ethiopia. While elevation, canopy cover, shade tree community composition and surrounding forest cover did not explain bird and bat species richness, the composition of the bird and bat community was significantly influenced by the composition of the shade tree community. Herbivory was unrelated to the species richness and community composition of insectivorous birds and bats. We found no trade-off between bird and bat species richness and coffee yield, but the composition of the bird, but not bat, community changed with increasing yield, where forest specialist birds rapidly declined in abundance from low to mid-yielding sites. Overall, we suggest that the similar levels of bird and bat species richness and an absence of a relationship with herbivory across different types of agroforests are due to the diverse mosaic agricultural landscape and lack of agroforests with very high management intensities (which are common in other parts of the world). From a conservation point of view, intensification of coffee management in the lowest-yielding sites would threaten biodiversity in terms of forest specialist birds. However, is it also important to learn more on the potential positive roles of biodiversity in those parts of the landscape where coffee is managed for high yields. From both a conservation and sustainable management point of view we urgently need more insights into the taxonomy, life-history, habitat preferences and foraging ranges of East African bats.

We present the data from the Insect Biome Atlas project (IBA), characterizing the terrestrial arthropod faunas of Sweden and Madagascar. Over 12 months, Malaise trap samples were collected weekly (biweekly or monthly in the winter, when feasible) at 203 locations within 100 sites in Sweden and weekly at 50 locations within 33 sites in Madagascar; this was complemented by soil and litter samples from each site. The field samples comprise 4,749 Malaise trap, 192 soil and 192 litter samples from Sweden and 2,566 Malaise trap and 190 litter samples from Madagascar. Samples were processed using mild lysis or homogenization, followed by DNA metabarcoding of CO1 (418 bp). The data comprise 698,378 non-chimeric sequence variants from Sweden and 687,866 from Madagascar, representing 33,989 (33,046 Arthropoda) and 77,599 (77,380 Arthropoda) operational taxonomic units, respectively. These are the most comprehensive data presented on these faunas so far, allowing unique analyses of the size, composition, spatial turnover and seasonal dynamics of the sampled communities. They also provide an invaluable baseline against which to gauge future changes.

An increase in biotic interactions towards lower latitudes is one of the most consistent patterns in ecology. Higher temperatures and more stable climatic conditions at low latitudes are thought to enhance biotic interactions, accelerating biological evolution and leading to stronger anti-herbivore defences in plants. However, some studies report contradictory findings, highlighting the need for further investigation into the underlying mechanisms. We used a combination of field observations and feeding trials in controlled environments to investigate the effect of climate on chemical defences and insect herbivory in pedunculate oak (Quercus robur L.) throughout most of its geographic range in Europe, while controlling for physical defences. The concentration of lignin, flavonoids, and total phenolics increased significantly with temperature, whereas both field herbivory and weight of spongy moth (Lymantria dispar L.) larvae were negatively influenced by temperature. Lignin concentration positively influenced the weight of spongy moth larvae whereas it had no effect on field herbivory. We found no evidence of strong positive relationships between insect herbivory and larvae growth with leaf defences. Our study underscores the complexity of plant–herbivore interactions along climatic gradients and highlights the need for further research to disentangle these intricate relationships.

Fermentative yeasts play important roles in both ecological and industrial processes, but their distribution and abundance in natural environments are not well understood. We investigated the diversity of yeasts at the northern range limit of their oak tree hosts (Quercus spp.) in Sweden, and identified climatic and ecological conditions governing their distribution. Yeasts were isolated from bark samples from 28 forests and identified to the species level using DNA metabarcoding. Most communities were dominated by species in the Saccharomycetaceae family, especially by species of Saccharomyces, Kluyveromyces and Pichia. Each genus showed a distinct latitudinal and longitudinal distribution, and both temperature and precipitation metrics predicted significant variation in their abundance. Consistent with this, laboratory assays revealed significant effects of temperature on the growth of strains collected from different longitudes and latitudes. We found that older trees harbour more diverse and more balanced fermentative yeast communities with more evenly distributed species abundances. Communities across trees were more similar when sharing a common dominant species. This work provides a baseline for future studies on the impact of climate change on the fermentative yeast biodiversity of temperate forests in northern latitudes and contributes to a growing collection of wild isolates for potential biotechnological applications.

DNA metabarcoding of species-rich taxa is becoming a popular high-throughput method for biodiversity inventories. Unfortunately, its accuracy and efficiency remain unclear, as results mostly pertain to poorly known taxa in underexplored regions. This study evaluates what an extensive sampling effort combined with metabarcoding can tell us about the lepidopteran fauna of Sweden - one of the best-understood insect taxa in one of the most-surveyed countries of the world. We deployed 197 Malaise traps across Sweden for a year, generating 4749 bulk samples for metabarcoding, and compared the results to existing data sources. We detected more than half (1535) of the 2990 known Swedish lepidopteran species and 323 species not reported during the sampling period by other data providers. Full-length barcoding confirmed three new species for the country, substantial range extensions for two species and eight genetically distinct barcode variants potentially representing new species, one of which has since been described. Most new records represented small, inconspicuous species from poorly surveyed regions, highlighting components of the fauna overlooked by traditional surveying. These findings demonstrate that DNA metabarcoding is a highly efficient and accurate biodiversity sampling method, capable of yielding significant new discoveries even for the most well known of insect faunas.

Global change threatens a vast number of species with severe population declines or even extinction. The threat status of an organism is often designated based on geographic range, population size, or declines in either. However, invertebrates, which comprise the bulk of animal diversity, are conspicuously absent from global frameworks that assess extinction risk. Many invertebrates are hard to study, and it has been questioned whether current risk assessments are appropriate for the majority of these organisms. As the majority of invertebrates are rare, we contend that the lack of data for these organisms makes current criteria hard to apply. Using empirical evidence from one of the largest terrestrial arthropod surveys to date, consisting of over 33 000 species collected from over a million hours of survey effort, we demonstrate that estimates of trends based on low sample sizes are associated with major uncertainty and a risk of misclassification under criteria defined by the IUCN. We argue that even the most ambitious monitoring efforts are unlikely to produce enough observations to reliably estimate population sizes and ranges for more than a fraction of species, and there is likely to be substantial uncertainty in assessing risk for the majority of global biodiversity using species-level trends. In response, we discuss the need to focus on metrics we can currently measure when conducting risk assessments for these organisms. We highlight modern statistical methods that allow quantification of metrics that could incorporate observations of rare invertebrates into global conservation frameworks, and suggest how current criteria might be adapted to meet the needs of the majority of global biodiversity.

Aim: Ecological theory predicts lower herbivory on islands. However, most island-mainland comparisons have focused on vegetative tissues, while reproductive structures remain understudied despite their direct influence on plant fitness and recruitment. This study investigates how insularity affects insect herbivory in oak (Quercus) acorns across multiple island-mainland regions and explores the role of acorn traits (chemical defences and nutrients) and climate as potential drivers. Location: Three island-mainland regions in Europe: Lesbos Island—mainland Greece, the Balearic Islands—mainland Spain, and Bornholm Island—mainland Sweden. Time Period: Acorns were collected in autumn 2023. Climatic data are long-term averages for each population. Major Taxa Studied: Seven oak (Quercus) species across regions. Methods: We aimed to sample up to three island and three mainland populations per species, with four trees per population, but logistical constraints reduced these numbers, resulting in a total of 150 sampled trees. We assessed acorn damage by insect herbivores and analysed chemical defences (phenolics) and nutrients (nitrogen and phosphorus) to test their influence on island–mainland differences in herbivory. Climatic data from the WorldClim database were used to assess climate-mediated insularity effects on acorn traits and herbivory. Results: Acorn damage did not differ overall between mainland and island populations. However, in the Balearic Islands, damage was higher than in mainland Spain, while no significant differences were found in the other regions. There were no general insularity effects on acorn traits, but a region-by-insularity interaction influenced phosphorus levels, with higher values in mainland Sweden than Bornholm Island, while the reverse was observed in Greece. Climate influenced acorn traits, but trait differences did not explain herbivory patterns. Main Conclusions: Our findings challenge the expectation that insularity reduces herbivory, highlighting region-specific processes. While climate influenced acorn traits, these traits did not mediate insularity effects on herbivory, suggesting local ecological factors drive variation across regions.