Mônica F. Kersch-Becker

Leaf bacterial communities shape plant defense and interactions with herbivores, yet how host filtering and stochastic processes assemble them remains unclear. We predicted that host identity, chemistry, and arthropods structure them, and that stochastic and deterministic contributions shift seasonally. Across one growing season we sampled leaf bacteria monthly and arthropods weekly on four Asclepias species (Apocynaceae: A. curassavica , A. incarnata , A. syriaca , A. tuberosa ) spanning a cardenolide gradient. We sequenced 16S rRNA genes and quantified selection and dispersal contributions to turnover using null models. Host identity shaped bacterial richness and composition, with A. tuberosa hosting the richest communities, and both richness and phylogenetic diversity rose through the season. Early on, homogenizing dispersal made communities more similar among plants; by mid-season no single process dominated turnover, and by late season dispersal limitation prevailed. Homogeneous selection was episodic, not sustained, and arthropod associations were host-specific, negatively so on A. syriaca. Phyllosphere assembly thus shifts from convergence to divergence in one season: young leaves recruit from a shared pool delivered by wind, rain, and arthropods, whereas exchange among ageing plants declines and communities drift apart. Herbivores arriving late meet plant-specific microbial environments, so microbial mediation of herbivory should be host-specific and seasonally contingent.

Methyl salicylate (MeSA) is an herbivore‐induced plant volatile (HIPV) known to attract natural enemies of herbivores; however, its effectiveness as a semiochemical across diverse cropping systems and broad geographic regions remains unclear. In this 2‐year field study, we sampled natural enemies using MeSA‐baited and unbaited (control) yellow sticky traps across multiple cropping systems in the Mid‐Atlantic and Northeastern United States (New York, Pennsylvania, Virginia and New Jersey), including three annual crops (corn, potatoes, and soybean) and four perennial crops (apples, blueberries, cranberries and grapes). Sticky traps were deployed for 4 weeks during the preharvest period, with deployment timing adjusted to the phenology of each crop. For each trap, we recorded both the number of natural enemies and their community composition, including abundance and diversity (Shannon index). We found that hoverflies (Diptera: Syrphidae) were specifically attracted to MeSA in perennial cropping systems. Although natural enemy communities were overall more diverse in annual crops, MeSA tended to increase Shannon diversity in perennial systems. Collectively, these results suggest that HIPVs such as MeSA may be useful for enhancing hoverfly attraction in less‐disturbed perennial cropping systems.

Plants deploy multiple defense pathways to deter herbivores, with consequences that can drive predator–prey interactions. While the effects of interspecific variation in plant defenses on herbivores and natural enemy are well understood, far less is know about the consequences of intraspecific differences in defense phenotypes. This limits our ability to predict how plant trait diversity influences pest control. Herein, we tested how intraspecific defense diversity in tomato (Solanum lycopersicum Linnaeus) affects potato aphid populations (Macrosiphum euphorbiae Thomas) and interactions with the convergent ladybeetle (Hippodamia convergens Guérin-Méneville). We independently primed the jasmonic acid (JA) pathway and the salicylic acid (SA) pathway and established four treatments: monocultures of untreated controls, JA-treated plants, SA-treated plants, and mixtures of all three defense phenotypes. Half of the cages received one ladybeetle per 100 aphids. We hypothesized that defense mixtures would reduce aphid populations, increase their dispersal relative to monocultures, and strengthen predator effects. Instead, our findings suggest that while combining multiple defense phenotypes can directly limit herbivores, it may also disrupt predator-prey interactions. In the presence of predators, SA-treated monocultures resulted in the highest reduction in aphid density and population growth, while JA-treated monocultures led to increased aphid dispersal. Predator effects were reduced in defense mixtures which emitted a distinct volatile blend that partially overlapped with SA- and JA-treated monocultures but differed from controls. Integrating knowledge of defense pathways with natural enemy effectiveness is crucial for developing integrated pest management strategies that suppress pests both directly and through biological control.

Drought is a major abiotic stressor that can restructure trophic interactions by limiting herbivore success and disrupting chemical signaling between plants and natural enemies. In tritrophic systems, plant volatiles guide natural enemy foraging and reproductive investment, often scaling with herbivore density; however, it is unclear whether drought alters this relationship and weakens top-down control. Using a tomato-aphid-ladybeetle system, we tested how drought and herbivore density jointly affect plant VOC emissions, predator behavior, and aphid dynamics. We manipulated water availability (well-watered vs. drought) and aphid density (low vs. high), and measured plant physiology, volatile profiles, predator visitation and oviposition, and aphid responses. Drought reduced stomatal conductance, plant biomass, and both total and compositional output of VOCs. Emission of key predator-attracting compounds (e.g., methyl salicylate, β-myrcene) peaked in well-watered, high-density plants but was suppressed under drought. Ladybeetle visitation increased with aphid density but declined under drought, reflecting conserved shifts in volatile cues. Oviposition was concentrated on well-watered, high-density plants and associated with specific compounds (e.g., methyl salicylate, carvacrol), while others (e.g., cymene-7-ol, para, 1-octanol) were negatively associated. Aphid suppression by predators occurred only under well-watered, high-density conditions. Under drought, aphid growth was already constrained, and predators had little additional effect on their abundance. However, both drought and predator presence influenced aphid demography, increasing production of dispersive alates. These findings underscore the sensitivity of chemically mediated trophic interactions to environmental stress. Increased drought disrupts plant signaling, reducing natural enemy effectiveness, weakening biocontrol, and shifting herbivore population structure. Understanding how stress alters cue reliability is key to predicting community dynamics and managing ecosystem functions under stress.

Induced plant defences regulated by jasmonic acid (JA) and salicylic acid (SA) initiate a cascade of effects, from defence expression to changes in arthropod community structure and species interactions that can ultimately influence plant fitness. Yet the long‐term consequences of these processes remain poorly understood, particularly in perennial tropical systems. We investigated how activation of JA and SA signalling pathways shapes arthropod community composition and plant reproductive success in Trichogoniopsis adenantha (Asteraceae), a glandular trichome‐bearing shrub native to the Brazilian Atlantic rainforest. Using chemical elicitors, we induced JA and SA defences for up to 16 months and monitored herbivore and predator assemblages, herbivory patterns, trichome expression, pyrrolizidine alkaloid concentrations and plant short‐term fecundity. JA‐elicited plants exhibited higher pyrrolizidine alkaloid levels in flowers, reduced leaf herbivory and lower seed damage by pre‐dispersal seed predators. However, these plants experienced increased colonization by sap‐feeding insects. In contrast, SA‐elicited plants were more vulnerable to chewing herbivores but more resistant to sap‐feeders. Despite similar reductions in seed predation across both treatments, JA and SA induction significantly reduced ovary fertilization, likely due to changes in floral traits and decreased pollinator visitation, ultimately imposing substantial fitness costs. Additionally, seasonal turnover in arthropod communities was accompanied by temporal variation in how defences structured species composition and abundance. Our findings demonstrate that phytohormone‐mediated defences can simultaneously induce resistance and susceptibility across herbivore guilds, with divergent impacts on predator associations. Although defence induction reduced herbivore damage, it compromised short‐term fecundity, revealing trade‐offs between defence and reproduction. By linking induced defences to multitrophic interactions over time, this study highlights the ecological complexity of plant defence strategies in biodiverse tropical ecosystems.

Neonicotinoid insecticides were initially hailed as safer alternatives to organochlorine and organophosphate pesticides due to their perceived lower toxicity to non-target organisms. However, it has been recently discovered that sublethal exposure to neonicotinoids negatively affects beneficial arthropods that are essential for a functional ecosystem. These beneficial arthropods include pollinators, biological control agents, and decomposers. This review synthesizes current research on the physiological, behavioral, and reproductive consequences of neonicotinoids on non-target arthropods and their broader ecological impact. The chemical and physical properties of neonicotinoids raise concerns about long-term ecological consequences of neonicotinoid use because these chemicals are persistent in plants and soil, which contributes to prolonged exposure risks for organisms. Sublethal doses of neonicotinoids can disrupt the ecological services provided by these organisms by impairing essential biological processes including motor function, odor detection, development, and reproduction in insects, while also altering behavior such as foraging, mating, and nesting. Furthermore, neonicotinoid exposure can alter community structure, disrupting trophic interactions and food web stability. Recognizing the sublethal impacts of neonicotinoids is critical for the development of more sustainable pest management strategies. It is imperative that future research investigates the underlying mechanisms of sublethal toxicity and identifies safer, more effective approaches to neonicotinoid-based pest control to mitigate adverse ecological effects. Incorporating this knowledge into future environmental risk assessments will be essential for protecting biodiversity and maintaining ecosystem functionality.

Ecological communities are linked not only by energy flows, but also by sensory and behavioral pathways that allow organisms to locate, recognize, and interact with one another. Environmental stressors such as drought may disrupt these pathways by altering both resource availability and interactions that regulate both population and community dynamics. While species-level responses to drought are well documented, far less is understood about how drought-driven changes in plant resources initiate bottom-up effects that cascade through multiple trophic levels. Here, we tested how drought affects a plant-herbivore-carnivore system by quantifying plant physiological changes and their cascading effects on herbivore performance, nutritional quality, and carnivore behavior. Drought reduced plant growth and stomatal conductance, which lowered herbivore feeding efficiency, survival, and reproduction. Herbivores feeding on drought-stressed plants also displayed lower protein content and biomass. Drought also suppressed the emission of herbivore-induced plant volatiles (HIPVs), limiting the chemical cues carnivores use to locate prey. Despite higher prey consumption rates in no-choice assays, carnivores suppressed herbivore populations less effectively under drought. At the community level, these disruptions caused disproportionate declines in arthropod abundance and diversity, particularly among carnivores, leading to trophic simplification. These findings show that drought not just reduce resource availability, it disrupts chemical cues and trophic feedbacks that maintain food web structure. By linking changes in resource limitations to community-level responses, this study demonstrates how environmental stressors can weaken top-down control and destabilize multitrophic dynamics. Predicting ecological resilience depends not only on responses but on how stress disrupts the information signals that maintain ecosystem services and function.

Plant‐induced defences can shape multitrophic interactions by affecting herbivore performance and altering their suitability as prey. While the direct effects of these defences on herbivores are well documented, their indirect consequences—particularly for predator behaviour and biological control effectiveness—remain less understood. In our study, we examined how activating salicylic acid (SA)‐mediated defences in tomato plants affects the performance and nutritional quality of the aphid, Macrosiphum euphorbiae , and how this intraspecific variation in aphid quality as prey impacts the predation by the lady beetle predator, Hippodamia convergens . Aphids on SA‐treated plants exhibited reduced body mass, protein and lipid content, indicating lower nutritional value as prey. Correspondingly, we recorded a stronger decline in aphid population on SA‐treated plants in the presence of predators. To investigate the effects of reduced aphid quality on predation, we conducted a controlled no‐choice assay, which showed that individual lady beetle predators consume more aphids from the SA‐treated plants. This increased consumption is consistent with compensatory feeding in response to nutrient‐poor prey, although alternative explanations, such as increased prey vulnerability, should also be considered. Our findings demonstrate that SA‐mediated defences can shape predator–prey interactions through bottom‐up effects on prey quality and underscore the need to consider these cascading effects when evaluating the ecological impact of plant resistance traits in biological control strategies.

Premise: Plants produce an array of floral olfactory and visual cues to attract pollinators, including volatile organic compounds (VOC), which mediate plant–pollinator interactions and may be influenced by herbivory and neighboring plants. Consequently, these factors may affect plant fitness by disrupting pollination. However, most evidence comes from controlled experiments, limiting our understanding of how VOCs function in natural populations. This study investigated how herbivory and conspecific ramet density influence floral VOC profile, pollination, and seed production in a naturally occurring population of Solidago altissima.Methods: We recorded leaf herbivory and ramet density surrounding one focal ramet in 1‐m² plots. We collected VOCs from the floral headspace and measured ovary fertilization as a proxy for pollination success and the number of seeds produced by the focal ramet.Results: Our findings revealed interactive effects between ramet density and herbivory on floral VOC emission, richness, and diversity. Specifically, at lower ramet densities, herbivory did not affect floral volatile emissions. However, in highly dense stands, herbivory suppressed floral volatile emissions. Despite these changes, floral volatiles did not affect pollination and the number of seeds in S. altissima.Conclusions: Our field‐based findings underscore the importance of understanding the complex responses of floral VOCs to environmental stressors and their contributions to plant reproduction within natural communities. Our results suggest that while herbivory and ramet density influence floral scent, these changes do not affect reproduction in our study. Ultimately, generalist‐pollinated plants like S. altissima might not rely heavily on chemical signaling during pollination.

Plants adapt to balance growth–defense tradeoffs in response to both biotic and abiotic stresses. Green leaf volatiles (GLVs) are released after biotic and abiotic stresses and function as damage-associated signals in plants. Although, GLVs enter plants primarily through stomata, the role of stomatal regulation on the kinetics of GLV uptake remains largely unknown. Here, we illustrate the effect of stomatal closure on the timing and magnitude of GLV uptake. We closed stomata by either exposing maize (Zea mays) plants to darkness or applying abscisic acid, a phytohormone that closes the stomata in light. Then, we exposed maize seedlings to (Z)-3-hexen-1-ol and compared its dynamic uptake under different stomatal conditions. Additionally, we used (E)-3-hexen-1-ol, an isomer of (Z)-3-hexen-1-ol not made by maize, to exclude the role of internal GLVs in our assays. We demonstrate that closed stomata effectively prevent GLV entry into exposed plants, even at high concentrations. Furthermore, our findings indicate that reduced GLV uptake impairs GLV-driven induction of biosynthesis of sesquiterpenes, a group of GLV-inducible secondary metabolites, with or without herbivory. These results elucidate how stomata regulate the perception of GLV signals, thereby dramatically changing the plant responses to herbivory, particularly under water stress or dark conditions.