1. The addition of nectar-rich flower patches in human-modified ecosystems is a common practice to mitigate pollinator declines and boost pollination. However, the benefits of these additions for pollinator communities and pollination services are rarely tested, especially in urban environments. 2. In a city-scale experiment we added floral resources to urban allotments and monitored the effects on bees, hoverflies and moths, and tested for improved seed set in a model crop (tomato, Solanum lycopersicum). 3. The addition of wildflowers did not benefit all insect communities. Only social bee abundance (Bombus and Apis) benefitted from increasing floral resource area whereas other insect taxa showed no changes in abundance potentially due to the divergence in foraging patterns of moths, hoverflies, social bees and solitary bees. The addition of wildflower patches enhanced pollination by supporting a 25.3% increase in tomato seed set, providing evidence that wildflower interventions can improve urban pollination. Seed set was higher in more urban sites, suggesting an 'oasis effect' where pollinating insects are concentrated into limited greenspaces. This highlights the precarity of pollination services in highly urban areas. 4. Our results suggest that the practice of planting wildflower patches can positively affect pollination services in urban areas. The continued promotion of flower patch addition is likely to benefit some key insect taxa, however, the common wildflower species in seed mixes may not benefit hoverflies and moths compared to bees. The taxon-specific foraging patterns we observed should inform the design and development of pollinator-friendly wildflower seed mixes. ### Competing Interest Statement The authors have declared no competing interest.

Insect pollinators are essential for terrestrial ecosystems, delivering key ecosystem functions in the face of anthropogenic disturbance. Urbanization may be a key threat to pollinator communities. However, the scale of the threat remains unknown due to an overwhelming research emphasis on bees and a lack of comparative studies on hyper-diverse pollinating taxa such as nocturnal moths. As a result, it remains unclear which pollinator groups are most vulnerable to urbanization, and which habitat features are most critical for supporting them. We conducted a large-scale assessment of the effects of increasing urbanization on the diversity of bees, hoverflies and nocturnal moths in urban horticultural sites (allotments) across three cities. We report up to a 43% reduction in species richness along urbanization gradients, suggesting that a wide range of pollinators are under threat in urban landscapes. We show that these declines are driven by taxon-specific landscape drivers such as the reduction of tree canopy and semi-natural habitat, suggesting that urban insect conservation depends on the preservation or expansion of habitat features specific to different threatened taxa. We found that relative to bees, moths and hoverflies are particularly sensitive to urbanization, and we highlight the importance of including these frequently overlooked pollinator groups when assessing the biodiversity impacts of environmental change.

Societal Impact Statement The urban forest provides important environmental and health and well‐being benefits to people living in cities. However, sustainable management of urban trees is challenging as they face interrelated pressures from the urban environment, pests and diseases and climate change. Here, we use knowledge exchange with stakeholders to identify four key research priorities (1. tree species resilience to climate change; 2. tree species selection for biodiversity; 3. tree equity; and 4. community engagement) and detail an ongoing programme of research co‐designed with stakeholders to support effective decision making that ensures the sustainability and resilience of the urban forest.

Innovations in plant and soil sciences are revolutionising our approach to sustainability, offering solutions with broad societal impacts. Discoveries in these fields hold great potential for combatting, mitigating and adapting to climate change; enhancing food security; and revitalising urban environments. By harnessing the power of plants and the soils they grow in, it is possible to cultivate resilience in the face of environmental challenges, informing policy and practice, and thereby guiding us towards a more sustainable future.

1. Cavity-nesting bees and wasps provide essential ecosystem services such as pollination and pest control. Within urban environments, it is likely that cavity-nesting insects are using greenspaces to forage for food and nesting resources, and thus may benefit from urban greenspace management interventions, such as the addition of flower patches and "bee hotels" (trap nests). 2. In contrast to the relatively large body of work demonstrating the effects of wildflower provisioning on bees in an agricultural context, there have been few studies testing the benefits of floral provisioning, or the relative importance of nest site and food constraints on urban cavity-nesting bees and wasps. Consequently, we lack an empirical evidence base for optimising and informing conservation interventions for these taxa. 3. To understand how the addition of floral resources influences cavity-nesting insect communities, we conducted a 2-year study in urban greenspaces used for horticulture (allotments). We manipulated floral and nesting resources by adding nectar-rich flower patches and artificial trap nests, and compared nest colonisation by cavity-nesting bees and wasps in sites with floral additions and where no additions were made. Our sites were configured along an urbanisation gradient, allowing us to examine how surrounding urbanisation influenced these patterns. 4. Contrary to our predictions, we found no significant difference in trap nest uptake in sites where floral resources were added, compared to control sites. However, cavity-nesting insect abundance showed a 6-fold decrease over our urbanisation gradient. The addition of floral resources did not mitigate the negative effects of urbanisation on cavity-nesting insects. ### Competing Interest Statement The authors have declared no competing interest.

Pollinating insects are declining due to habitat loss and climate change, and cities with limited habitat and floral resources may be particularly vulnerable. The effects of urban landscapes on pollination networks remain poorly understood, and comparative studies of taxa with divergent niches are lacking. Here, for the first time, we simultaneously compare nocturnal moth and diurnal bee pollen-transport networks using DNA metabarcoding and ask how pollination networks are affected by increasing urbanisation. Bees and moths exhibited substantial divergence in the communities of plants they interact with. Increasing urbanisation had comparable negative effects on pollen-transport networks of both taxa, with significant declines in pollen species richness. We show that moths are an important, but overlooked, component of urban pollen-transport networks for wild flowering plants, horticultural crops, and trees. Our findings highlight the need to include both bee and non-bee taxa when assessing the status of critical plant-insect interactions in urbanised landscapes.

Forest bathing is based upon a Japanese practice known as Shinrin–Yoku and is a nature-based therapy involving mindful walks through ancient woodland to reduce stress and anxiety. One proposed mechanism behind the effectiveness of Forest bathing is based on the potential mental and physical health benefits of the natural volatile organic compounds (NVOCs) that fill the forest understory. Surprisingly little is known about the concentrations and diversity of plant NVOCs in ambient air particularly in the UK and this study aims to increase that knowledge. Air samples were collected in July 2022 in a UK forest and compared with samples from a walled garden environment. The samples were collected over a 2 h time period and analysed using GC-MS and showed clear differences in the chemical composition of the air. This study revealed NVOCs including limonene, carvone, terpenes, terpenoids and sesquiterpenoids were present within a UK forest but were either not present or present at little to low levels in the control setting of a walled garden. This study also found that the typical 2 h duration of a Forest bathing session was a long enough sampling period to detect these NVOCs, indicating that Forest bathers could benefit from exposure to NVOCs.

Reactive nitrogen from human sources (e.g., nitrogen dioxide, NO 2 ) is taken up by plant roots following deposition to soils, but can also be assimilated by leaves directly from the atmosphere. Leaf uptake should alter plant metabolism and overall nitrogen balance and indirectly influence plant consumers; however, these consequences remain poorly understood. Here we show that direct foliar assimilation of NO 2 increases levels of nitrogen-based defensive metabolites in leaves and reduces herbivore consumption and growth. These results suggest that atmospheric reactive nitrogen could have cascading negative effects on communities of herbivorous insects. We further show that herbivory induces a decrease in foliar uptake, indicating that consumers could limit the ability of vegetation to act as a sink for nitrogen pollutants (e.g., smog from mobile emissions). Our study suggests that the interactions of foliar uptake, plant defence and herbivory could have significant implications for understanding the environmental consequences of reactive nitrogen.

Intercropping can reduce agricultural pest incidence, and represents an important sustainable alternative to conventional pest control methods. Understanding the ecological mechanisms for intercropping could help optimize its use, particularly in tropical systems which present a large number of intercropping possibilities. Citrus is threatened worldwide by greening disease (huanglongbing, HLB) vectored by the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae). Control of HLB and citrus psyllid can be partially achieved through intercropping with guava, Psidium guajava L., but the mechanisms remain unclear. We tested the hypothesis that guava olfactory cues affect psyllid behavior by altering the attractiveness of citrus through plant-plant interactions. In choice and no-choice cage experiments, psyllid settlement was reduced on citrus shoots that had been exposed to guava shoot odors for at least 2 h. In Y-tube olfactometer experiments, psyllids oriented to odors of unexposed, compared with guava-exposed, citrus shoots. These behavioral results indicate that a mechanism for the success of guava intercropping for sustainable, ecological disease management may be the indirect effect of guava on citrus attractiveness.

The diversity of flowering plants is evident in two seemingly unrelated aspects of life history: sexual reproduction, exemplified by the stunning variation in flower form and function, and defence, often in the form of an impressive arsenal of secondary chemistry. Researchers are beginning to appreciate that plant defence and reproduction do not evolve independently, but, instead, may have reciprocal and interactive (coevolutionary) effects on each other. Understanding the mechanisms for mating-defence interactions promises to broaden our understanding of how ecological processes can generate these two rich sources of angiosperm diversity. Here, I review current research on the role of herbivory as a driver of mating system evolution, and the role of mating systems in the evolution of defence strategies. I outline different ecological mechanisms and processes that could generate these coevolutionary patterns, and summarize theoretical and empirical support for each. I provide a conceptual framework for linking plant defence with mating system theory to better integrate these two research fields.

Gregarious feeding is a common feature of herbivorous insects and can range from beneficial (e.g. dilution of predation risk) to costly (e.g. competition). Group age structure should influence these costs and benefits, particularly when old and young larvae differ in their feeding mode or apparency to predators. We investigated the relative value of gregarious feeding by aposematic larvae of Uresiphita reversalis that we observed feeding in groups of mixed ages and variable densities on wild Lupinus diffusus. In a manipulative field experiment, the survivorship and growth of young larvae were enhanced in the presence of older conspecifics, but not in large groups of similarly aged larvae. Estimates of insect damage and induced plant responses suggest that mixed-age groups enhance plant quality for young larvae while avoiding competition. We conclude that benefits of gregariousness in this species are contingent on group age structure, a finding of significance for the ecology and evolution of gregariousness and other social behaviours.

Coevolution is among the most important evolutionary processes that generate biological diversity. Plant–pollinator interactions play a prominent role in the evolution of reproductive traits in flowering plants. Likewise, plant–herbivore interactions select for myriad defenses that protect plants from damage. These mutualistic and antagonistic interactions, respectively, have traditionally been considered in isolation from one another. Here, we consider whether reproductive traits and antiherbivore defenses are interdependent as a result of pollinator- and herbivore-mediated selection. The evolution of floral traits, self-fertilization, and separate sexes frequently affects the expression and evolution of plant defenses. In turn, the evolution of defense can affect allocation to reproductive traits, and herbivores often impose strong selection directly on floral traits. Theory and empirical evidence suggest that herbivores can influence the evolution of selfing from outcrossing and potentially the evolution of separate sexes from combined sexes. We identify several areas in which future research is needed to increase our understanding of the evolutionary interplay between reproduction and defense in plants.

SummaryThe diversity of flowering plants is evident in two seemingly unrelated aspects of life history: sexual reproduction, exemplified by the stunning variation in flower form and function, and defence, often in the form of an impressive arsenal of secondary chemistry. Researchers are beginning to appreciate that plant defence and reproduction do not evolve independently, but, instead, may have reciprocal and interactive (coevolutionary) effects on each other. Understanding the mechanisms for mating–defence interactions promises to broaden our understanding of how ecological processes can generate these two rich sources of angiosperm diversity. Here, I review current research on the role of herbivory as a driver of mating system evolution, and the role of mating systems in the evolution of defence strategies. I outline different ecological mechanisms and processes that could generate these coevolutionary patterns, and summarize theoretical and empirical support for each. I provide a conceptual framework for linking plant defence with mating system theory to better integrate these two research fields.

The fitness consequences of mating system variation (e.g. inbreeding) have been studied for at least 200 years, yet the ecological consequences of this variation remain poorly understood. Most plants are capable of inbreeding, and also exhibit a remarkable suite of adaptive phenotypic responses to ecological stresses such as herbivory. We tested the consequences of experimental inbreeding on phenotypic plasticity in resistance and growth (tolerance) traits in Solanum carolinense (Solanaceae). Inbreeding reduced the ability of plants to up-regulate resistance traits following damage. Moreover, inbreeding disrupted growth trait responses to damage, indicating the presence of deleterious mutations at loci regulating growth under stress. Production of the phytohormones abscisic and indole acetic acid, and wounding-induced up-regulation of the defence signalling phytohormone jasmonic acid were all significantly reduced under inbreeding, indicating a phytohormonal basis for inbreeding effects on growth and defence trait regulation. We conclude that the plasticity of induced responses is negatively affected by inbreeding, with implications for fragmented populations facing mate limitation and stress as a consequence of environmental change.

Understanding the factors that shape macroevolutionary patterns in functional traits is a central goal of evolutionary biology. Alternative strategies of sexual reproduction (inbreeding vs. outcrossing) have divergent effects on population genetic structure and could thereby broadly influence trait evolution. However, the broader evolutionary consequences of mating system transitions remain poorly understood, with the exception of traits related to reproduction itself (e.g., pollination). Across a phylogeny of 56 wild species of Solanaceae (nightshades), we show here that the repeated, unidirectional transition from ancestral self-incompatibility (obligate outcrossing) to self-compatibility (increased inbreeding) leads to the evolution of an inducible (vs. constitutive) strategy of plant resistance to herbivores. We demonstrate that inducible and constitutive defense strategies represent evolutionary alternatives and that the magnitude of the resulting macroevolutionary tradeoff is dependent on the mating system. Loss of self-incompatibility is also associated with the evolution of increased specificity in induced plant resistance. We conclude that the evolution of sexual reproductive variation may have profound effects on plant-herbivore interactions, suggesting a new hypothesis for the evolution of two primary strategies of plant defense.

Invasive species represent the second greatest threat to biodiversity after habitat loss, and significantly affect agriculture worldwide. The Common Starling (Sturnus vulgaris) is one of the world's worst invasive species and has established pest populations across the globe, with low-density, highly persecuted populations in Western Australia (WA) since the 1970s. This study examines the ongoing control of low-density populations of Common Starlings in WA. From May 2006 to June 2009 we monitored use by Common Starlings of 180 artificial nest-cavities of three designs, across three habitat types; the artificial cavities were standard wooden nest-boxes, and terracotta pipes orientated vertically or horizontally. During the trial, Common Starlings nested exclusively in wooden nest-boxes in swamps containing predominantly dead trees; they did not nest in the terracotta pipes. Wooden nest-boxes may have helped concentrate breeding Common Starlings in a defined area, thereby assisting control efforts.

Flowering phenology is an important determinant of a plant's reproductive success. Both assortative mating and niche construction can result in the evolution of correlations between phenology and other reproductive, functional, and life history traits. Correlations between phenology and herbivore defence traits are particularly likely because the timing of flowering can allow a plant to escape herbivory. To test whether herbivore escape and defence are correlated, we estimated phenotypic and genetic correlations between flowering phenology and latex production in greenhouse-grown Lobelia siphilitica L. (Lobeliaceae). Lobelia siphilitica plants that flower later escape herbivory by a specialist pre-dispersal seed predator, and thus should invest fewer resources in defence. Consistent with this prediction, we found that later flowering was phenotypically and genetically correlated with reduced latex production. To test whether herbivore escape and latex production were costly, we also measured four fitness correlates. Flowering phenology was negatively genetically correlated with three out of four fitness estimates, suggesting that herbivore escape can be costly. In contrast, we did not find evidence for costs of latex production. Generally, our results suggest that herbivore escape and defence traits will not evolve independently in L. siphilitica.

Worldwide, many crops rely on insect pollination. Insufficient pollination can reduce fruit and seed set by directly reducing pollen deposition, and can also affect offspring quality, such as growth rate and resistance to herbivores, by limiting outcrossing opportunities. Both effects are important in fruit agroecosystems where fruit size and the quality of seeds for re-planting are dependent on sufficient pollination. We experimentally manipulated pollination of the cape gooseberry, Physalis peruviana L. (Solanaceae), to test the effects of honey and bumble bee pollination compared to manual outcrossing and autonomous self-pollination on fruit and offspring characteristics. Compared to manual and self-pollination, bee pollination increased fruit size, seed set and germination rates, supporting the hypothesis that sufficient pollination increases plant fitness. Interestingly, plant growth rate and herbivore resistance were significantly and marginally greater in manually outcrossed plants compared to self-pollinated offspring, suggesting that inbreeding reduces offspring quality. Herbivore resistance and plant growth did not differ between one honeybee visit and self-pollination suggesting that multiple pollinator visits are needed to prevent inbreeding events. Our data suggest that the quantity and quality of pollen deposited by bee visitation can significantly alter ecologically and economically relevant traits in this agroecosystem.

The cost of inbreeding (inbreeding depression, ID) is an important variable in the maintenance of reproductive variation. Ecological interactions such as herbivory could modulate this cost, provided that defence traits harbour deleterious mutations and herbivores are responsible for differences in fitness. In the field, we manipulated the presence of herbivores on experimentally inbred and outcrossed plants of Solanum carolinense (horsenettle) for three-years. Damage was greater on inbred plants, and ID for growth and fitness was significantly greater under herbivory. Inbreeding reduced phenolic expression both qualitatively (phytochemical diversity) and quantitatively, indicating deleterious load at loci related to the biosynthesis of defence compounds. Our results indicate that inbreeding effects on plantherbivore interactions are mediated by changes to functional plant metabolites, suggesting that variation in inbreeding could be a predictor of defence trait variation. The magnitude of herbivore-mediated, ecological ID indicates that herbivores could maintain outcrossing mating systems in nature.