Plant Herbivore Research Articles

Discreet but diverse and specific: Determining plant‐herbivore interactions across a species‐rich plant family in a tropical rain forest

AbstractStudying plant–herbivore interactions within tropical rain forests is fundamental to understanding their ecology and evolution. An important aspect of plant–herbivore dynamics is the role of temporal and taxonomic variables in determining associations between herbivores and their host. Using the diverse and chemically rich plant family Annonaceae (Magnoliales), we conducted a year‐long study in Ecuador's Yasuní National Park in lowland Amazonia. We focused on nine understory tree species across a broad phylogenetic range within Annonaceae. For these species, we investigated patterns of herbivory, identified herbivores through DNA barcoding, and documented unique ant–butterfly associations. In general, leaf damage ranged from 0.09% to 25%, with significant temporal fluctuations for three species. Notably, Anaxagorea brevipes and Unonopsis veneficiorum faced higher herbivore pressure when compared to the other studied species. We document a discreet but diverse herbivore community, with 40 larvae from 12 Lepidoptera families collected throughout the year. Our findings identify, for the first time across a phylogenetically diverse sampling of Annonaceae, the specialization of herbivores on our focal species. Overall, our data provide valuable information on herbivory patterns at the local scale for this important rain forest plant family. Furthermore, these findings contribute to our understanding of the ecological processes that influence plant species diversity in tropical rain forests.Abstract in Spanish is available with online material.

Shifting interactions between ectomycorrhizae, plants and insect herbivores in a CO2‐enriched world

Abstract Increasing atmospheric CO2 concentrations are changing how plants interact with their biotic mutualists and antagonists, but few syntheses consider how the three‐way interactions between mycorrhizae, plants and herbivores will shift under rising CO2. We summarise the mechanisms by which ectomycorrhizal (EcM)‐associated plants, their mycorrhizae and insect herbivores interact with each other under current conditions and evaluate a set of expectations for how these interactions might shift under higher CO2. We then outline priorities for future work on EcM–plant–herbivore interactions as atmospheric CO2 continues to rise. EcM colonisation has variable but often positive effects on herbivory, while herbivory has consistently negative impacts on EcM colonisation. Mechanistic evidence suggests that the positive EcM effect on herbivory will strengthen and the negative impact of herbivory on EcM will be ameliorated under higher CO2. Synthesis: While more empirical evidence on fungal–plant–herbivore interactions is needed in EcM systems, our synthesis suggests that EcM associations may play an under‐recognised role in dictating future terrestrial carbon capture by mediating herbivory and the ability of plants to compensate for herbivory as atmospheric CO2 continues to rise.

New observations on prey scarab beetles and host plants of the green lynx spider, Peucetia viridans (Hentz, 1832) (Araneae: Oxyopidae) in Oaxaca, Mexico

ABSTRACT Peucetia viridans (Hentz), commonly called the lynx spider, is an important predator with a diet that encompasses a wide variety of insects and arachnids, including cannibalism. Although several studies that address aspects related to its ecology and behaviour have been carried out, there is a notable lack of studies focused on the recording of its prey and hosts. This information gap is particularly evident regarding the interaction of the spider with beetles belonging to the family Scarabaeidae. To contribute to the knowledge of the feeding habits and host preferences of P. viridans, observations were made in two localities of the Valles Centrales region of Oaxaca, Mexico. Lynx spiders were observed on Croton ciliatoglandulifer Ortega, Lantana camara Linnaeus, Solanum mitlense Dunal, and Wigandia urens (Ruiz and Pav.) Kunth. Spiders utilise these plants as shelter and to ambush their prey, thereby reducing herbivore populations and protecting the plants. In return, the plants provide the spiders with prey and floral and extrafloral nectaries as food sources. Therefore, spiders and plants have a facultative mutualistic relationship, whereas the relationship between spiders and herbivores is antagonistic. For the first time Diplotaxis trapezifera Bates, Macrodactylus fulvescens Bates, Paranomala discoidalis (Bates), Strigoderma costulipennis Bates, Strigoderma sulcipennis Burmeister, and Euphoria pulchella (Gory and Percheron) as prey, and Wigandia urens, Lantana camara and Solanum mitlense as host plants are recorded. A checklist of host plants for P. viridans is given. Overall, these new observations highlight the importance that tritrophic interactions (plant–herbivore–natural enemy) have in wild systems, which are essential for maintaining ecological balance.

Geographic variation in leaf traits and palatability of a native plant invader during domestic expansion.

Like alien plant invasion, range expansion of native plants may threaten biodiversity and economies, rendering them native invaders. Variation in abiotic and biotic conditions across a large geographic scale greatly affects variation in traits and interactions with herbivores of native plant invaders, which is an interesting yet mostly unexplored issue. We used a common garden experiment to compare defensive/nutritional traits and palatability to generalist herbivores of 20 native (23.64° N-30.18° N) and introduced range (31.58° N-36.87° N) populations of Reynoutria japonica, which is a native invader following range expansion in China. We analyzed the relationships among herbivore pressure, climate, plant chloroplast haplotypes, leaf traits, and herbivore performance. Of the 16 variables tested, we observed range differences in 11 variables and latitudinal clines in nine variables. In general, herbivores performed better on the introduced plants than on the native plants, and better on the high-latitude plants than on the low-latitude plants within the introduced populations. Three key traits (leaf thickness, specific leaf area, and carbon-to-nitrogen [C:N] ratio) determined palatability to herbivores and were significantly associated with temperature and/or precipitation of plant provenance as well as with plant haplotypes but not with herbivore pressure. Our results revealed a causal sequence from plant-range-based environmental forces and genetic context to plant quality and palatability to herbivores in R. japonica. These findings suggest a post-introduction evolution of R. japonica, which may partly explain the colonization success of this important native, but invasive plant.

Landscape forest cover and local vegetation structure mediate multitrophic relationships but not the leaf damage in cacao trees

Cacao is the most important agricultural product in the southern region of Bahia state, Brazil, with 70 % of its production occurring under the traditional agroforestry where cacao is mostly shaded by native trees. This traditional system allows to reconcile the production with the maintenance of the portion of original biodiversity. However, increased deforestation and intensified agroforestry management aimed at boosting productivity may impact the diversity of native species and the services they provide. In this context, our aim was to disentangle the role of landscape forest cover and the local vegetation complexity on predation of caterpillars and herbivory of cacao plants located in agroforestry systems. The study was conducted across 18 cacao agroforest sites in southern Bahia located in landscapes with different amounts of forest cover. We assessed predation rate using dummy caterpillars, sampling understory birds and arthropods and collected leaves of cacao trees to analyze damage by herbivory. We also measured shading levels and the abundance of cacao trees in each agroforestry. Predation pressure on dummy caterpillars was positively influenced by the abundance of total predators and the level of landscape forest cover and negatively by the number of cacao trees. Even so, we found no evidence that landscape, local features or the actual invertebrate assemblages (predators or herbivores) influenced the cacao leaf damage. The findings highlight the multifaceted interactions between ecological factors, predation pressure, and leaf damage within cacao agroforestry systems.

Intercropping Alters Phytochemical Defenses Against Insect Herbivory.

Given the multiple possible mechanisms for interspecific chemical interaction between adjacent heterospecific plants, phytochemical defenses of pest-susceptible crop species could potentially be enhanced or altered by intercropping with phytochemically diverse neighbors. We assessed the influence of intercropping between phytochemically diverse plants on aerial volatile organic compound (VOC) emission profiles by intercropping Melilotus alba and Triticum aestivum with Silphium integrifolium in AMF-inoculated soil. We also assessed the impact of intercropping on induced plant defenses by conducting an in-situ, no-choice bioassay with Spodoptera frugiperda. Of eight compound classes we identified across the three plant species, prenol lipids (terpenoids) were upregulated in silflower plants when monocropped with wheat and when herbivory was induced. Carboxylic acids and organooxygen compounds were reduced in sweetclover when intercropped with silflower, but increased under herbivory. Uninfested wheat plants emitted more organooxygen compounds and fatty acyls than infested plants when intercropped with silflower, but not when monocropped. This study showed that VOC emissions of plants from three diverse taxa are altered by both intercropping and herbivory in ways that may impact their resistance to insect herbivory. Further research into the role of intercropping on pest resistance in agroecological systems could help farmers to design intercropping systems that optimize natural plant herbivory defenses, thus improving agricultural sustainability.

Ant sharing by plant species bearing extrafloral nectaries has a low impact on plant herbivory in a tropical system

Abstract Plant species bearing extrafloral nectaries (EFNs) may indirectly influence other plant species by sharing protective ants, potentially altering herbivory levels. However, the propagation of indirect effects in this type of mutualism has seldom been investigated. We investigated indirect effects via ant sharing among 21 EFN‐bearing plant species of the tribe Bignonieae distributed on 28 plots in the central Brazilian Amazon. We used an ecological network index to quantify potential indirect effects among plant species through shared dominant and subordinate ant species. Plant species that were more attractive to ants (promoter species) had the highest potential to indirectly influence ant visitation to less attractive plant species (receptor species) in the community, primarily through changes in the attraction of dominant ant species. However, these potential indirect effects did not result in significant differences in herbivory patterns among the studied plants. Ant attendance and herbivory levels were similar among promoter species, neighbouring plants, and non‐neighbouring plants. Unlike other mutualisms involving plants (e.g., pollination), the indirect effects among plant species that share protective ants had limited consequences. The low levels of herbivory and the small foraging areas of shared ant defenders could be responsible for the observed limited impact of indirect interactions among plant species in this system. Synthesis: This study demonstrates that plant species with EFNs can indirectly influence other plant species through ant sharing. The attractiveness of certain plants to ants enables them to affect the ant visitation patterns of less attractive plants in the community. However, these indirect effects did not significantly alter herbivory levels among plants. Overall, this study advances ecological understanding by showing that the sharing of protective ants among plant species can in some cases confer limited costs and benefits, leading indirect interactions to have minimal impact on herbivory patterns.

Multi-habitat landscapes are more diverse and stable with improved function

Conservation, restoration and land management are increasingly implemented at landscape scales1,2. However, because species interaction data are typically habitat- and/or guild-specific, exactly how those interactions connect habitats and affect the stability and function of communities at landscape scales remains poorly understood. We combine multi-guild species interaction data (plant–pollinator and three plant–herbivore–parasitoid communities, collected from landscapes with one, two or three habitats), a field experiment and a modelling approach to show that multi-habitat landscapes support higher species and interaction evenness, more complementary species interactions and more consistent robustness to species loss. These emergent network properties drive improved pollination success in landscapes with more habitats and are not explained by simply summing component habitat webs. Linking landscape composition, through community structure, to ecosystem function, highlights mechanisms by which several contiguous habitats can support landscape-scale ecosystem services.

Green Lacewing Chrysoperla externa Is Attracted to Volatile Organic Compounds and Essential Oils Extracted from Eucalyptus urograndis Leaves.

Plant herbivore interactions have long been recognized as a complex interplay influenced by various factors, including plant volatile emissions. Understanding the role of these volatiles in mediating plant predator interactions is crucial for developing sustainable pest management strategies. This study investigated the olfactory preferences of Chrysoperla externa larvae for volatiles emitted by Eucalyptus urograndis leaves, focusing on both seedlings and essential oils (EOs). We used Y-tube olfactometry to compare larval preferences between the clean air and various plant treatments, including undamaged and herbivore-damaged leaves. Chemical analysis of EOs revealed higher concentrations of oxygenated monoterpenes and sesquiterpenes in young and damaged leaves, particularly linalool, which has been implicated in insect attraction. Our results showed a significant preference for volatiles emitted by young damaged leaves over clean air for both seedlings (χ2 = 11.03, p = 0.001) and EOs (χ2 = 9.76, p = 0.002). Chrysoperla externa larvae are significantly attracted to specific volatiles from damaged E. urograndis leaves, suggesting these compounds could serve as cues for natural enemy foraging. Our findings enhance the understanding of plant-predator dynamics and suggest potential applications of eucalyptus plantations to sustain C. externa populations for biocontrol purposes.

Network structure and taxonomic composition of tritrophic communities of Fagaceae, cynipid gallwasps and parasitoids in Sichuan, China

Abstract A key question in insect community ecology is whether parasitoid assemblages are structured by the food plants of their herbivore hosts. Tritrophic communities centred on oak‐feeding cynipid gallwasps are one of the best‐studied tritrophic insect communities. Previous work suggests that host plant identity is a much stronger predictor of oak–cynipid interactions than of cynipid–parasitoid interactions. However, these relationships have not been formally quantified. We reason that the potential for ‘bottom‐up’ effects should increase with host plant phylogenetic diversity. We, therefore, generated quantified interaction network data for previously unstudied tritrophic cynipid communities in Sichuan, China, where, in addition to Quercus, cynipid host plants include Castanea, Castanopsis and Lithocarpus. We characterise these communities taxonomically and compare the extent to which host plant taxonomy predicts plant–herbivore and plant–parasitoid associations. We sampled 42,620 cynipid galls of 176 morphotypes from 23 host plant species, yielding over 4500 specimens of 64 parasitoid morphospecies. Many parasitoids were identifiable to chalcidoid taxa present in other Holarctic oak cynipid communities, with the addition of Cynipencyrtus (Cynipencyrtidae). As elsewhere, Sichuan parasitoid assemblages were dominated by generalists. Gallwasp–plant interaction networks were significantly more modular than parasitoid–plant association networks. Gallwasps were significantly more specialised to host plants (i.e. had higher mean d' values) than parasitoids. Parasitoid assemblages nevertheless showed significant plant‐associated beta diversity, with a dominant turnover component. We summarise parallels between our study and other Fagaceae‐associated cynipid communities and discuss our findings in light of the processes thought to structure tritrophic interactions centred on endophytic insect herbivores.

Distribution patterns of glandular trichomes in the flora of the Hengduan Mountains, southwestern China

Abstract Glandular trichomes are traditionally regarded as a defence against insect herbivores in plants. A comprehensive examination of their occurrence across an entire flora is essential for understanding how plant-herbivore interactions influence species abundance, traits, and diversity. In this study, we gathered data on the presence of glandular trichomes in a diverse flora comprising 7751 angiosperm species from the Hengduan Mountains region in southwestern China, testing the effects of plant organ, life form, leaf habit, phylogenetic position, and geographical element on the occurrence of glandular trichomes. Our results showed that 1021 species (13.2%) in the studied flora possessed glandular trichomes. Reproductive organs (88.0%) displayed a significantly higher occurrence of glandular trichomes compared to vegetative organs (59.1%). Within flowers, the calyx (81.1%) was the most defended, followed by the corolla (17.4%), and the gynoecium (12.5%). The androecium (1.8%) was the flower component least associated with glandular trichomes. Herbaceous species (14.0%) were more likely to have glandular trichomes than woody species (11.6%). For woody plants, leaf habit (deciduous/evergreen) had no significant effect on the presence of glandular trichomes on leaf blades, but had a significant effect on the occurrence of glandular trichomes on reproductive organs, with deciduous woody species (11.0%) displaying a higher prevalence compared to evergreen woody species (8.3%). Interestingly, the proportion of species with glandular trichomes was notably lower in the tropical elements (6.8%) compared to both temperate and cosmopolitan elements (15.3% and 15.6%, respectively). Our findings suggest that in the Hengduan Mountains region, the evolution of glandular trichomes exhibits distinct patterns among various life forms, plant organs, leaf habits, and geographical elements, while showing limited influence from phylogenetic relatedness, highlighting the remarkable evolutionary adaptability of this defensive plant trait.

Convergent evolution of fern nectaries facilitated independent recruitment of ant-bodyguards from flowering plants

Plant–herbivore interactions reciprocally influence species’ evolutionary trajectories. These interactions have led to many physical and chemical defenses across the plant kingdom. Some plants have even evolved indirect defense strategies to outsource their protection to ant bodyguards by bribing them with a sugary reward (nectar). Identifying the evolutionary processes underpinning these indirect defenses provide insight into the evolution of plant-animal interactions. Using a cross-kingdom, phylogenetic approach, we examined the convergent evolution of ant-guarding nectaries across ferns and flowering plants. Here, we discover that nectaries originated in ferns and flowering plants concurrently during the Cretaceous, coinciding with the rise of plant associations in ants. While nectaries in flowering plants evolved steadily through time, ferns showed a pronounced lag of nearly 100 My between their origin and subsequent diversification in the Cenozoic. Importantly, we find that as ferns transitioned from the forest floor into the canopy, they secondarily recruited ant bodyguards from existing ant-angiosperm relationships.

Chronic anthropogenic disturbance mediates the bottom-up influence of plant diversity on arthropods in tropical forests.

Understanding how primary productivity and diversity affect secondary productivity is an important debate in ecology with implications for biodiversity conservation. Particularly, how plant diversity influences arthropod diversity contributes to our understanding of trophic cascades and species coexistence. Previous studies show a positive correlation between plant and arthropod diversity. The theory of associational resistance suggests that plant herbivory rate will decrease with increasing plant diversity indicating feedbacks between primary diversity, productivity, and secondary productivity rates. However, our understanding of how these relations are mediated by anthropogenic disturbance is still limited. We surveyed 10 forest sites, half of which are disturbed by fire, logging, and tree pruning, distributed in two climatic zones in Benin, West Africa. We established 100 transects to record plant species and sampled arthropods using pitfall traps, ceramic plates with bait, and sweeping nets. We developed a structural equation model to test the mediating effect of chronic anthropogenic disturbance on plant diversity and how it influences arthropod diversity and abundance. Arthropod diversity increased but arthropod abundance decreased with increasing intensity of disturbance. We found no significant bottom-up influence of the plant diversity on arthropod diversity but a significant plant diversity-arthropod abundance relationship. Some arthropod guilds were significantly affected by plant diversity. Finally, herbivory rates were positively associated with arthropod diversity. Synthesis. Our results highlight how chronic anthropogenic disturbance can mediate the functional links between trophic levels in terms of diversity and productivity. Our study demonstrated a decoupled response of arthropod diversity and abundance to disturbance. The direct positive influence of plant diversity on herbivory rates we found in our study provides counter-support for the theory of associational resistance.

Plant Cyanogenic-Derived Metabolites and Herbivore Counter-Defences.

The release of cyanide from cyanogenic precursors is the central core of the plant defences based on the cyanogenesis process. Although cyanide is formed as a coproduct of some metabolic routes, its production is mostly due to the degradation of cyanohydrins originating from cyanogenic glycosides in cyanogenic plants and the 4-OH-ICN route in Brassicaceae. Cyanohydrins are then hydrolysed in a reversible reaction generating cyanide, being both, cyanohydrins and cyanide, toxic compounds with potential defensive properties against pests and pathogens. Based on the production of cyanogenic-derived molecules in response to the damage caused by herbivore infestation, in this review, we compile the actual knowledge of plant cyanogenic events in the plant-pest context. Besides the defensive potential, the mode of action, and the targets of the cyanogenic compounds to combat phytophagous insects and acari, special attention has been paid to arthropod responses and the strategies to overcome the impact of cyanogenesis. Physiological and behavioural adaptations, as well as cyanide detoxification by β-cyanoalanine synthases, rhodaneses, and cyanases are common ways of phytophagous arthropods defences against the cyanide produced by plants. Much experimental work is needed to further understand the complexities and specificities of the defence-counter-defence system to be applied in breeding programs.

Spatial and temporal variability in the structure of the multiple-herbivore community of horsenettle, and evidence for evolutionary responses in host-plant resistance

The geographic mosaic model of plant–herbivore coevolution asserts that interactions between a plant species and an herbivore species vary in intensity among populations across the plant’s geographic range. Despite this model’s intuitive appeal, data to investigate its implications for the type of complex, multiple-herbivore communities that occur in nature are scant. This paper reports on the results of 2 years of field surveys of damage by five leaf herbivores and one stem herbivore in four Solanum carolinense (horsenettle) populations, combined with results of a common-garden study quantifying the mean resistance levels of the plants from each field against each of the six herbivores. The relative amounts of damage caused by each species (representing the “herbivore-community structure”) differed significantly among the four fields. The plants were much more heavily damaged in the 2nd year than in the first, but the herbivore-community structure remained stable within each field between years. Overall, the amount of damage by species of herbivores in a field tended to be positively correlated with the plants’ levels of resistance that were measured in the common garden (r = 0.40, P = 0.05). Specifically, for five of the six herbivores, greater damage in the field was associated with greater plant resistance. This result suggests that horsenettle’s evolution of resistance against specific herbivores can occur rather quickly within fields, creating a local-scale mosaic of populations specifically adapted to the particular structure of the herbivore community that they are facing, but that herbivore-community structure is not strongly determined by plant resistance.

Layer‐specific imprints of traits within a plant–herbivore–predator network – complementary insights from complementary methods

Who interacts with whom is a key question in community and network ecology. The concept that these interactions may be driven by a match between the traits of consumer and resource species is known as trait‐matching. If trait‐matching would allow for general predictions of interaction structure based on sufficiently few and easily‐measurable traits, then this approach could replace the laborious description of each individual pairwise interaction. To resolve imprints of trait‐matching in a species‐rich tri‐trophic Salix–galler–parasitoid network, and to identify the most relevant traits, we applied five different methods, each approaching the same phenomenon from a different perspective. As traits, we used, body sizes, gall type (position on plant, structure of gall) and phenology, among others, as well as phylogenetic proxies. When jointly applied, the methods demonstrate distinctly different imprints of traits within the two bipartite network elements (Salix–galler versus galler–parasitoid interactions). Of the galler–parasitoid sub‐network's interactions, approximately half were explainable by the species traits used; of the Salix–galler sub‐network's interactions, traits explained at most two‐fifths. Gall type appeared to be the most important structuring trait in both networks. Phylogeny explained as much, or more than did our tested traits, suggesting that traits may be conserved and phylogeny therefore an effective proxy. Overall, the more specialized structure of the Salix–galler network versus the more nested structure of the galler–parasitoid network meant that different methods were more effective at capturing interactions and interaction structure in the different sub‐networks. Thus, our analysis reveals how structuring impacts may vary even between levels within the same multitrophic network, and calls for comparative analyses of trait matching across a wide set of systems and methods.

Modelling effects and control of soil contaminants on the dynamics of plant–herbivore species system

In this paper, we have proposed and analysed a mathematical model to study the effects of impulsive input of contaminants in soil on the dynamics of interacting species system consisting of contaminants, soil-nutrients, plant biomass and herbivore population in order to investigate the criteria for the survival or extinction of plant biomass and herbivore population. The uptake function for herbivore population considered in the model of the paper shows saturation effect and this type of uptake function behave linearly with respect to plant biomass for low density. Also, the saturation for large plant biomass is a reflection of the limited herbivore capability or perseverance when the plant biomass is abundant. Therefore, the uptake function considered in this paper is more natural to lotka volterra and holling type functional responses. We have shown that the plant–herbivore extinction periodic solution exists and also the plant–herbivore extinction periodic solution is locally and globally stable if the impulsive depletion rate of nutrients due to contaminants is more than some critical value. Further, it is concluded that if the impulsive input period for contaminants is increased and impulsive depletion rate of nutrients due to contaminants is decreased then both the plant and herbivore population will survive otherwise they will tend to extinction.

Food-limited plant–herbivore model: Bifurcations, persistence, and stability

This research paper delves into the two-dimensional discrete plant–herbivore model. In this model, herbivores are food-limited and affect the plants’ density in their environment. Our analysis reveals that this system has equilibrium points of extinction, exclusion, and coexistence. We analyze the behavior of solutions near these points and prove that the extinction and exclusion equilibrium points are globally asymptotically stable in certain parameter regions. At the boundary equilibrium, we prove the existence of transcritical and period-doubling bifurcations with stable two-cycle. Transcritical bifurcation occurs when the plant’s maximum growth rate or food-limited parameter reaches a specific boundary. This boundary serves as an invasion boundary for populations of plants or herbivores. At the interior equilibrium, we prove the occurrence of transcritical, Neimark–Sacker, and period-doubling bifurcations with an unstable two-cycle. Our research also establishes that the system is persistent in certain regions of the first quadrant. We demonstrate that the local asymptotic stability of the interior equilibrium does not guarantee the system’s persistence. Bistability exists between boundary attractors (logistic dynamics) and interior equilibrium for specific parameters’ regions. We conclude that changes to the food-limitation parameter can significantly alter the system’s dynamic behavior. To validate our theoretical findings, we conduct numerical simulations.

Plant–herbivore–natural enemy trophic webs in date palm agro-ecosystems

Understanding the composition and dynamics of ecological communities is challenging because of the large number of organisms present and their numerous interactions. Among agricultural systems, intercropping considerably increases the complexity of communities compared to monocultures and alternative host plants can influence insect pest damage. Using literature records, we construct and analyse connectance trophic webs of date palm (Phoenix dactylifera) agro-ecosystems, including and excluding intercrops. Estimates of connectance (community complexity) are relatively low and little affected by consideration of intercrops. Plant–herbivore overlap is relatively high, suggesting that herbivores are typically not specialists. Herbivore–natural enemy overlap is greater when intercrops are considered, suggesting that diffuse apparent competition regulates pest populations. We pay particular attention to how trophic web structure might affect Batrachedra amydraula (Lesser date moth), an important economic pest. Records indicate it having 15 species of natural enemies and sharing 9 of these with other herbivores; these may maintain populations of natural enemies when the moth is seasonally rare, contributing to pest suppression. The estimated potential for apparent competition between the lesser date moth and other herbivores is higher when intercrops are considered. The consequent expectation of less severe infestations in plantations that are intercropped compared to monocultures matches empirically derived reports. Further, comparing results obtained from the literature on one country (Oman) and from 15 Middle Eastern countries, we find that community metric estimates are relatively little affected by the geographical scale considered. Overall, our results suggest that literature-based trophic web construction can provide an efficient and robust alternative, or in addition, to direct empirical methodologies and that the presence of intercrops will contribute to major pest suppression via indirect apparent competition.

Promoting student interest in plant biology through an inquiry-based module exploring plant circadian rhythm, gene expression, and defense against insects.

We present a weeklong curricular module for high school biology students that promotes knowledge of phytohormones, the circadian clock, and the Central Dogma. The module, which relies on easily accessible items and requires minimal space, integrates a hands-on experiment that guides students through replicating research examining circadian entrainment in postharvest cabbage from groceries. This work found that plants have cyclical, circadian expression of genes that produce phytohormones, and that such cyclical expression influences herbivory by caterpillars. Such cyclical patterns were found in plants both in situ and in postharvest cabbage. This work thus provides an ideal platform to shape student conceptions of circadian rhythms, gene expression, and plant herbivory by having students use light timers to entrain postharvest cabbage to alternating light and dark cycles and then measuring herbivory in these plants. The results should replicate previous work and demonstrate less herbivory when both plant and caterpillar are entrained to the same light and dark cycles since the expression of phytohormones involved in plant defense will be greatest when caterpillars are active. The module then concludes with a discussion of gene regulation and how this influences phytohormones. This module was field tested at four public schools, reaching over 600 students, and we present data demonstrating that the module led to learning gains and likely increases in interest in plant biology and self-efficacy.