Consuelo M. De Moraes

Nectar is a primary floral reward, which can also deter non-specialist pollinators; yet, the role of complex nectar composition in plant-pollinator interactions and its relationship to other floral traits remain understudied, particularly in natural communities. We profiled the nectar metabolome of 43 co-occurring species in an alpine grassland to evaluate relationships among nectar chemistry, phylogeny, floral display traits and pollinator visitation. Field observations revealed a dominant bee vs fly visitation gradient. Several aggregated nectar traits tracked this gradient independently of plant phylogeny, indicating functional convergence: specifically, bee visitation was associated with higher nectar sucrose proportion, greater compound richness, and more divergent profiles of uncommon sugars. Nectar traits exhibited variable relationships to floral display traits, suggesting partial inter-trait phenotypic integration. Together, these findings indicate that detailed features of nectar composition, including phytochemical diversity, play a functional role in floral phenotypes, with previously unappreciated implications for plant-pollinator community ecology.

Insect‐vectored plant viruses frequently alter plant–insect interactions in ways favourable to their own transmission (often referred to as manipulation). Variation in virus‐induced effects is often attributed to genetic variability and local adaptation in virus and host‐plant populations, but emerging evidence suggests that vector‐associated microbial symbionts may also play important roles. Vector insects harbour both obligate and facultative endosymbionts that can strongly influence vector traits and their interactions with host plants. Yet relatively few studies to date have examined how endosymbionts influence virus effects on plant–insect interactions and transmission. We argue that endosymbionts are often a key component of the selective environment experienced by vectors and viruses and hypothesize that they may play important roles in modulating the direction and magnitude of virus‐induced effects on plant–insect interactions. We outline key questions and priorities for research that will integrate virus–endosymbiont interactions into disease ecology. Such integration is crucial for understanding the evolution and ecology of viral and endosymbiont effects on vector biology, as well as the implications for disease transmission in agricultural and natural systems.

Human‐driven landscape change, particularly urbanization, is reshaping pollinator communities, yet the functional traits that mediate species persistence remain poorly understood. Dietary specialization is commonly used to predict species vulnerability. However, conventional measures based on taxonomic plant host breadth may not reflect pollinators' actual nutritional needs, especially in cities where exotic and native plants coexist. Because insects cannot synthesize sterols de novo, they must obtain these essential lipids from their diet, making sterol requirements a critical and overlooked axis for understanding pollinator persistence. Here, we analysed 22 sterols in 274 pollen provision samples and 1267 bee individuals from four common wild bee species, ranging from specialists to generalists, sampled following urban intensity gradients across five European cities. We reveal that regardless of host–plant specialization levels, all species relied on a shared set of four abundant sterols, commonly found in plant pollen, suggesting that sterol generalization may contribute to their urban persistence. Nonetheless, the full sterol profiles, both composition and concentration, varied between the bees' bodies and their pollen provisions, as well as across species and cities. This suggests that wild bees do not simply mirror their diet, but rather assimilate sterols in a species‐specific manner. The most specialized bee, Chelostoma florisomne , showed more uniform sterol use and was often absent in highly urbanized areas, possibly due to frequent mowing of its main host, Ranunculus flowers. These findings underscore the limitations of using solely on plant host composition in pollen for predicting pollinator responses to urban intensity and highlight the importance of nutritional needs, such as sterols, in shaping ecological niches and guiding conservation strategies. Read the free Plain Language Summary for this article on the Journal blog.

Vector-borne pathogens frequently modify host-vector interactions, and their influence can be modulated by other microbial symbionts. We recently documented endosymbiont effects on aphid traits involved in plant virus transmission, showing that facultative endobacteria—particularly Hamiltonella defensa—enhanced transmission of pea enation mosaic virus (PEMV). Here we examine transmission steps and associated molecular signatures in winged and wingless aphid morphs. Consistent with our previous findings, we observed enhanced PEMV transmission, as well as elevated viral titer in wingless aphids harboring H. defensa. However, winged aphids with this endosymbiont displayed similar effects on virus titer but not transmission. Furthermore, whereas wingless aphids exhibited higher transmission than winged aphids when H. defensa was present, this pattern was reversed for aphids harboring only the obligate endosymbiont Buchnera aphidicola; in parallel, we observed no differences between morphs of lines harboring other facultative endosymbionts. Subsequent experiments comparing lines harboring H. defensa vs the obligate symbiont alone revealed divergent effects on winged and wingless morphs on (i) virus inoculation efficiency (i.e., delivery of acquired virus; H. defensa), (ii) key salivary proteins (carbonic anhydrases, CAs; both lines), and (iii) plant defense-related marker transcripts (PR-1, salicylic acid pathway; LOX, jasmonic acid pathway; both lines). The correspondence of these patterns to the observed transmission effects suggests that endosymbiont-mediated effects on transmission may reflect changes in salivary secretions and related feeding traits. Our findings highlight the role of vector endosymbionts in disease transmission and provide insights into candidate processes by which they may influence virus-vector-host interactions.

Summary: Beneficial rhizobacteria and viral pathogens can both alter host plant phenotypes, yet little is known about how their simultaneous presence influences plant metabolism and species interactions. We investigated how two rhizobacteria, Bradyrhizobium japonicum and Delftia acidovorans , together with bean pod mottle virus (BPMV), shape soybean metabolism and interactions with the BPMV vector Epilachna varivestis . Using a multifactorial experimental design, we combined metabolomics, transcriptomics, and pathway analyses with behavioral assays to assess the impacts of rhizobacteria inoculation and BPMV infection on soybean physiology and E. varivestis feeding preferences. Beetle adults preferred feeding on rhizobia‐inoculated and virus‐infected plants, and larvae gained more weight on these hosts. Rhizobacteria inoculation and BPMV infection both increased primary metabolites (e.g. beta‐alanine, myo‐inositol, amino acids, and organic acids) while reducing secondary metabolites (e.g. kaempferol, rutin, and other flavonoids). Transcriptome analyses revealed shifts in defense‐ and metabolism‐related pathways, particularly under combined treatments. Our findings demonstrate that mutualistic and pathogenic symbionts reshape soybean metabolism in unique ways when they cocolonize the same host. These changes can alter symbiont fitness, as well as vector feeding behavior and performance in ways that enhance pathogen transmission.

Summary: Glyphosate-tolerant Roundup Ready (RR) soybean, engineered with the CP4 EPSPS gene, is one of the world’s most widely cultivated GM crops, yet its ecological consequences under realistic multi-species biotic conditions remain poorly understood. We investigated how RR soybean and its near-isogenic non-GM counterpart respond to concurrent colonization by two rhizobacteria, Bradyrhizobium japonicum and Delftia acidovorans , infection by Bean pod mottle virus (BPMV), and feeding by the virus vector Epilachna varivestis . Using a fully factorial multi-species design, we combined LC-MS/GC-MS metabolomics, weighted co-expression network analysis (WGCNA), and herbivore performance bioassays to assess genotype-dependent shifts in soybean metabolism and their consequences for herbivore performance. Under baseline conditions, RR and non-GM plants were metabolically indistinguishable. Under concurrent microbial and viral stress, RR plants diverged markedly, prioritizing selective isoflavonoid accumulation and lipid remodeling over broad-spectrum defenses, and showing attenuated rhizobacteria-mediated benefits for herbivore survival. These genotype-specific effects were entirely absent in single-species treatments. Transgene effects on soybean metabolism and tritrophic interactions are cryptic under simplified experimental conditions but emerge clearly under ecologically realistic multi-species stress, with direct implications for how GM crops are evaluated in agricultural and regulatory contexts.

Fire is a major global disturbance affecting the evolution of organisms and shaping plant and animal diversity, especially in fire‐prone regions like the Mediterranean. Yet its impacts on insect‐pollinator communities remain poorly understood. We conducted a 3‐year study on a Greek island, examining spatial and temporal impacts of fire on bee communities and species' functional traits. We compared bee diversity and population sizes in burnt and unburnt sites, by including in our analysis fire severity metrics using dNBR (differenced Normalized Burn Ratio) derived from satellite imaging. We show that fire initially led to increased bee abundance despite having a strong negative impact on floral resources. Burnt and unburnt communities differed significantly in species composition revealing that specific bee taxa drove post‐fire recovery. In post‐fire year 1, the population spike in burnt sites was driven by an increased abundance of below‐ground nesters, excavators and trophic generalists (polylectic); in contrast, the populations of trophic specialists (oligolectic) were negatively affected. By year 3, most differences between burnt and unburnt sites had been alleviated. Multivariate models incorporating fire severity, plant diversity and floral resources revealed that the heterogeneity of fire severity, even within small spatial scales, drove most of the variation in bee populations, followed by flower numbers. Our findings highlight the role of fire as an environmental filter, selecting species with specific traits and shaping distinct post‐fire communities. Notably, within 3 years, burnt bee communities started converging with the unburnt sites, suggesting a relatively rapid recovery of functional composition.

Summary: Aromatic plants occur in many plant lineages and have widespread ethnobiological significance. Yet, the ecological significance and evolutionary origins of aromatic volatile emissions remain uncertain. Aromatic emissions have been implicated in defensive interactions but may also have other important functions. In this Viewpoint article, we propose an ecologically relevant definition for the aromatic phenotype and evaluate available evidence relating to the ecological role of aromatic emissions, focusing specifically on their role in pollinator attraction. We synthesize available literature addressing the use of extrafloral volatiles by pollinators, including evidence that aromatic plant emissions are primary foraging cues for some species, and present new behavioral findings documenting bee attraction to the aromatic lemon thyme in the absence of flowers. We highlight recent ecological research showing that aromatic species are highly influential in Mediterranean plant–pollinator communities and their emissions predict key interactions, particularly with bees. Based on the available evidence, we hypothesize that aromatic plants represent a form of chemical aposematism, wherein high levels of constitutive defense enable signaling phenotypes that convey information to both potential antagonists and mutualists. Finally, we outline future research priorities to clarify the role of aromatic emissions in information ecology and explore their application in agricultural systems.

Around 6% of flowering plants, including most solanaceous species, have flowers specialized for buzz-pollination (sonication). The poricidal anthers of these flowers release pollen in response to frequency-specific vibrations, which buzz-pollinating bees, including bumble bees and many solitary bees, generate via rapid oscillation of flight muscles. Honeybees are incapable of sonication and typically avoid visiting buzz-pollinated plants, although they have previously been observed to scavenge residual pollen from petals of buzz-pollinated flowers in natural settings. Here, we report a novel interaction in which honeybees consistently visit and extract pollen from flowers of Solanum elaeagnifolium (silverleaf nightshade) within a large invasive plant population in Northern Greece. We postulate that honeybee foraging effort on S. elaeagnifolium reflects the shortage of alternative floral resources at the peak of the Mediterranean summer, consistent with observations for pollen-starved bees in captivity. This newly established behavioral shift of honeybees may convey important implications for plant invasions, particularly under climate change, and requires further investigation for untangling its ultimate drivers.

Urbanization is transforming ecosystems and food webs, yet the role of nutritional needs in species persistence in cities remains poorly understood. For bees, sterols are essential lipids they cannot synthesize de novo and must obtain from pollen. Pollen sterol composition varies widely across plant species, potentially constraining bee--plant interactions. However, sterol composition in wild bees and their pollen sources is understudied. To fill the gap, we analyzed 22 sterols in 274 nest pollen samples and 1,267 individuals from four wild bee species, ranging from specialists to generalists, in five European cities. The most abundant sterols in bee bodies were shared across species and overlapped with those in their nest pollen, yet overall sterol profiles varied by species and city. The specialist bee showed more conserved sterol patterns and was less common in highly urbanized areas. Our findings highlight species-specific nutritional strategies and the importance of integrating nutritional traits into urban bee conservation.