Foliar Herbivory Research Articles

Local and landscape predictors of herbivory on subsistence croplands in Brazilian dry forests

ABSTRACT Understanding the impact of herbivores on croplands is critical to developing sustainable agricultural landscapes. Here, we test the hypothesis that field size and landscape structure modulate the levels of herbivory in cowpea and maize subsistence croplands in Brazilian drylands. We conducted the study in nine small-scale farms with varying levels of landscape structure and field sizes (0.10–1.67 ha). In each farm, we haphazardly sampled 20 plants of maize and cowpea. The frequency of foliar herbivory was high for both crops (0.45–0.72), but the average magnitude of damage was low (<3% of leaf surface in both crops), indicating that herbivory is not an ecosystem disservice. Nonetheless, the field size and level of human impact on the landscape matrix were positively related to the frequency and magnitude of damage on maize foliage and cowpea foliage and pods. Landscape composition (proportion of woodland/forest surrounding the field) and configuration (number of surrounding woodland/forest patches) had weaker effects on herbivory levels, mixing positive and negative effects on both crops. Our findings indicate that herbivory attack is not concerning in the agricultural fields studied, but suggest that maize and cowpea should be preferably grown in small fields surrounded by an environmental-friendly matrix and patches of conserved ecosystems.

Prolonged drought legacies influence the performance of foliar herbivores on legumes through shifts in plant–soil biotic interactions

Prolonged drought legacies influence the performance of foliar herbivores on legumes through shifts in plant–soil biotic interactions

Foliar herbivory‐enhanced mycorrhization is associated with increased levels of lipids in root and root exudates

Abstract Insect herbivory can affect interactions between plants and arbuscular mycorrhizal (AM) fungi through herbivore‐modified root carbon pools, while the specific metabolic changes underlying fungal responses to herbivory are poorly understood. Here we explored the impacts of foliar herbivory and mechanical wounding on AM colonisation and AM community composition of common ragweed (Ambrosia artemisiifolia) and the role of root metabolites in mediating these effects. Foliar insect herbivory enhanced AM colonisation, whereas mechanical wounding only enhanced AM colonisation in combination with application of caterpillar oral secretions. Meanwhile, the relative abundance of Glomus species was increased in root endosphere, rhizoplane and rhizosphere soils after foliar herbivory. Foliar herbivory also increased the concentrations of fatty acids in roots but decreased phenolics, and their concentrations were significantly correlated with AM colonisation. Addition of exudates from plants exposed to herbivory resulted in increases in AM colonisation of plants without herbivory. Moreover, widely targeted metabolomic analyses revealed that foliar herbivory enhanced the relative abundance of lipids and decreased phenols in root exudates. Synthesis. We show that plants can enhance their associations with arbuscular mycorrhizal (AM) fungi when subject to above‐ground herbivory, possibly mediated by herbivore‐induced increases in the levels of root lipids. Our findings highlight the role of root lipids in above‐below‐ground biological interactions, providing novel insights into plant‐AM fungi integrative responses to biotic stresses.

Plant-insect interactions across the Triassic–Jurassic boundary in the Sichuan Basin, South China

Plants and insects are the most diverse and ecologically important organisms in the terrestrial biosphere. Their interactions are also among the richest biotic relationships, and offer significant insights into the evolution of terrestrial ecosystem complexity through the geological record. This investigation of the late Rhaetian Xujiahe and the earliest Jurassic Zhenzhuchong floral assemblages provides the first data on foliar herbivory generated by terrestrial arthropods across the Triassic–Jurassic transition in the eastern Tethys (East Asia) region. The damage types from two fossil assemblages are collectively attributed to seven functional feeding and egg-laying categories (i.e., hole feeding, margin feeding, surface feeding, skeletonization, piercing and sucking, oviposition, and galling). Most feeding strategies are spread across the major plant groups and persist through the Triassic–Jurassic boundary, with the exception of skeletonization (a category of external foliage feeding), which was restricted to the latest Triassic within dipteridacean ferns. The survey reveals that the respective frequency and diversity of interactions between plants and insects prior to and following the end-Triassic mass extinction event are almost the same, despite a substantial turnover of floral components. This suggest that insect herbivores were largely able to transfer to alternative (but commonly related) plant groups during the dramatic floristic turnover and environmental changes at the end of the Triassic. Sporadic occurrences of foliar modifications, such as marginal cusps on pinnules of Pterophyllum and prominent ridges on the rachises of some ferns and bennettites are interpreted as adaptations for defense against insect herbivores. A few differences in taxonomic composition and herbivory representation between the latest Triassic Xujiahe flora and the earliest Jurassic Zhenzhuchong flora are more likely to be related to collection and preservational biases rather than reflecting palaeoecological changes. We encourage further investigations exploring the distribution of insect damage in fossil floras from other palaeolatitudinal zones and spanning other major extinction events to develop a better understanding of terrestrial ecosystem responses to major crises in Earth’s history.

Abiotic factors similarly shape the distribution of fruit, seed and leaf traits in tropical fleshy-fruited tree communities

The distribution of plant traits is related to abiotic and biotic factors, but it is unknown whether different types of plant traits respond similarly to these factors. We simultaneously studied seed, fruit and leaf traits and their associations with abiotic and biotic factors for tree communities in the tropical mountains of southern Ecuador. We measured seed, fruit, and leaf traits on 18–33 fleshy-fruited plant species and recorded the abundance for these species on nine 1-ha forest plots located at 1000, 2000, and 3000 m a.s.l. On the same plots, we recorded abiotic (soil C/N ratio, mean temperature, and annual rainfall) and biotic factors (avian fruit removal and foliar herbivory) potentially relevant for the measured traits. We conducted principal component and RLQ analyses to test for trait-environment covariation, controlling for phylogenetic relatedness and spatial autocorrelation. We identified a trade-off between (i) seed number and seed size and between (ii) the production of few costly (nitrogen-rich) vs. many cheap (carbon-rich) fruits. Likewise, leaf trait variation was primarily associated with (i) the leaf economics spectrum and (ii) leaf size. Controlling for phylogenetic and spatial covariation, seed, fruit and leaf traits were associated with abiotic and, to a lesser extent, with biotic factors. Fruit and leaf traits linked to production costs were mainly related to soil C/N ratios, whereas traits associated with the size of seeds, fruits, and leaves were related to rainfall. Our study suggests that associations between seed, fruit and leaf traits and the abiotic environment follow similar principles in tropical tree communities.

Combined effects of aboveground herbivores and belowground microorganisms on dynamics of soil nematode communities in grassland mesocosms

Nematodes are the most abundant animals in soil. They are active in all trophic levels and functionally important for plant growth and plant diversity. Nematode community structure not only can be directly influenced by other belowground organisms such as soil microbes via trophic interactions, but also indirectly by aboveground organisms like herbivores through plant-mediated aboveground-belowground linkages. In the current study, by introducing foliar-feeding aphids (Rhopalosiphum padi) and soil microbial suspensions to mesocosms planted with 12 grassland plant species and where an identical nematode community was introduced in all mesocosms, we aimed to investigate the individual and combined effects of soil microbes and foliar herbivores on the dynamics of plant and the soil nematode community. Introduction of aphids reduced shoot and root biomass of the plant community, and in particular decreased the proportional biomass of the dominant plant species Anthoxanthum odoratum, resulting in a higher diversity of the plant community but without affecting the nematode communities. In contrast, the inoculation of soil microbes did not significantly alter plant composition structure, but it reduced the total nematode abundance and enhanced nematode diversity by increasing the abundance of carnivorous nematodes and decreasing the abundance of plant-feeding nematodes. There were no significant aboveground-belowground interactions in the current study via effects of aphids on the soil nematode communities or via soil microbes and nematodes on the plant communities. Collectively, our study indicates that soil nematode communities in grasslands can be strongly steered by soil microbial inoculations but weakly influenced by aboveground herbivory despite its resulting changes in plant communities, notwithstanding that these effects appeared to be largely independent.

Nutrient stress can have opposite effects on the ability of plants to tolerate foliar herbivory and floral herbivory.

Discovering how organisms respond to the combinations of stressors they face in their environment is an enduring challenge for ecologists. A particular focus has been how natural enemies and abiotic stressors faced by plants may interact in their effect on the ecology and evolution of plant defense strategies. Here, we report on the results of an experiment measuring how reproduction in the clonal herbaceous plant horsenettle (Solanum carolinense) is affected by damage by leaf-feeding and by flower-feeding herbivores-as well as how horsenettle's tolerance of these different types of herbivory may be altered by nutrient stress. Leaf herbivory by lace bugs reduced horsenettle's seed production and root growth, and the relative impacts were greater in fertilized than in nutrient-stressed plants. In contrast, simulated-floral herbivory reduced seed production to a similar degree in fertilized and nutrient-stressed plants. However, compensation for floral herbivory through increased root growth occurred to a much greater extent in the fertilized than in the nutrient-stressed plants. These results can be explained in terms of the limiting resource model of plant tolerance, with leaf damage interpreted as exacerbating carbon limitation in the fertilized plants and floral damage ameliorating carbon limitation in the fertilized plants. These results can be extended to predicting patterns in the field: Although plants in a nutrient-poor environment may have overall low fitness, they are likely to be more tolerant of leaf herbivores-though this benefit may be countered by lower tolerance of any floral herbivores that share the environment.

Two-way plant-mediated interactions between a plant parasitic nematode and a foliar herbivore arthropod

Interactions between belowground and aboveground heterotrophic communities with no direct physical contact can be connected by the plant as a mediator. Plants respond to the attack of herbivores by producing a suite of defensive compounds that can affect the choice and performance of other herbivores. The aim of this study was to determine the impact of one herbivore's activity on the acceptability of that plant to another species of herbivore. Two herbivores were tested; root-knot nematode, Meloidogyne incognita (RKN), a belowground plant-parasitic nematode, and the two-spotted spider mite, Tetranychus urticae (TSSM), an aboveground folivore. We conducted herbivore preference and performance tests on Lima bean (LB) (Phaseolus lunatus cv. Henderson) as an optimal host for TSSM, and tomato (Solanum lycopersicum cv. Rutgers) which is a sub-optimal host for TSSM but optimal host for RKN. We used two-choice glass olfactometers to measure the response of RKN to plants that were exposed to TSSM versus a clean LB plant. RKN infected the clean plants at a significantly greater rate than the TSSM exposed plants. TSSM preference was measured, using leaf discs and two-choice olfactometers containing a RKN infected plant versus a clean plant at different days post-inoculation (DPI) of the RKN. TSSM preferred the clean plants to those with 25-day old RKN infections on LB, but preferred RKN infected tomato plants at 1 DPI. We also tested the effect of the inoculation (1 DPI) of the entomopathogenic nematode (EPN) Steinernema carpocapsae on tomato plants and TSSM preferred the EPN inoculated plants. We carried out a non-choice performance test for TSSM on both LB and tomato on plants inoculated with RKN versus clean plants and observed no effect of RKN exposure on TSSM performance. This research shows that plants can mediate interactions between below and aboveground herbivores that share the same plant.

Root exudates from maize plants with high levels of foliar herbivory alters beneficial plant fungus growth

Plant roots have developed complex interactions with microbes to resist stressful growth conditions. Therefore, root exudation is important for determining rhizosphere microbial community structure. However, the shoot/root dynamics of metabolites at different degrees of herbivory and their effects on the growth of rhizosphere microorganisms remain poorly explored. Here, we identified some of the chemical components that coordinate the interactions between maize (Zea mays) plants, the chewing insect Spodoptera frugiperda, and the rhizosphere fungus Trichoderma atroviride. The results showed that during herbivory the leaf area and biomass parameters decreased proportionally with the number of pests feeding on the shoots, and phenotypic alterations in maize were correlated with changes in the root exudation of compounds. Bioassays with root exudates from leaves with mechanical damage and oral secretions of S. frugiperda suggested that Trichoderma specifically responds to the presence of larvae in maize plants. Furthermore, the degree of herbivory modulated the content of non-structural carbohydrates (NSCs), the anti-herbivore compound 6-methoxy-2-benzoxazolin-2-one (MBOA), and the reactive oxygen species H2O2 in the root exudates, which affected the growth of T. atroviride in a dose-dependent manner. These results revealed that foliar herbivory and the degree of damage can modulate, at least in part, three fundamental aspects of multitrophic interactions: (i) both the leaf area and biomass of the plant host, (ii) root exudates, and (iii) T. atroviride growth.

Non-host plant odors influence the tritrophic interaction between tomato, its foliar herbivore Tuta absoluta and mirid predator Nesidiocoris tenuis.

The tomato leafminer, Tuta absoluta is a destructive invasive pest of cultivated tomato and other Solanaceae plants, with yield losses of 80-100%. Mirid predators are key natural enemies of T. absoluta, but they also feed on host plants in the absence of their prey. Management of T. absoluta is a challenge due to its high biotic potential, resistance to many insecticides and the absence of sufficiently adapted auxiliary fauna in its new dispersion zones. Olfaction plays an important role in the tritrophic interaction between tomato, its herbivore pest T. absoluta and its mirid predators, which can be influenced by non-host plant odors. However, how non-host odours shape this interaction is poorly understood. Previously, we had demonstrated belowground crop protection properties of certain Asteraceae plants against the root-knot nematode Meloidogyne incognita, pest of tomato and other Solanaceae plants. Additionally, Asteraceae plants impact negatively on feeding behavior of above-ground pests of Solanaceae plants, including the greenhouse whitefly (Trialeurodes vaporariorum) and green peach aphid (Myzus persicae). Here, we tested the hypothesis that foliar volatiles from some of these non-host Asteraceae plants can influence the tomato-T. absoluta-mirid predator tritrophic interaction. In olfactometer assays, T. absoluta females were attracted to volatiles of the Solanaceae host plants tomato and giant nightshade but avoided volatiles of the Asteraceae plants, blackjack and marigold, and the positive control, wild tomato, when tested alone or in combination with the host plants. Coupled gas chromatography-mass spectrometry analysis showed that host and non-host plants varied in their emission of volatiles, mainly monoterpenes and sesquiterpenes. Random forest analysis combined with behavioral assays identified monoterpenes as the host plant attractive blend to T. absoluta and its mirid predator, with sesquiterpenes identified as the non-host plant repellent blend against T. absoluta. Contrastingly, the mirid predator was indifferent to the non-host plant repellent sesquiterpenes. Our findings indicate that terpenes influence the tomato-T. absoluta-mirid predator tritrophic interaction. Further, our results emphasize the importance of studying crop protection from a holistic approach to identify companion crops that serve multi-functional roles.

Effects of arbuscular mycorrhizal fungi on plant growth and herbivore infestation depend on availability of soil water and nutrients.

Fitness of plants is affected by their symbiotic interactions with arbuscular mycorrhizal fungi (AMF), and such effects are highly dependent on the environmental context. In the current study, we inoculated the nursery shrub species Artemisia ordosica with AMF species Funneliformis mosseae under contrasting levels of soil water and nutrients (diammonium phosphate fertilization), to assess their effects on plant growth, physiology and natural infestation by herbivores. Overall, plant biomass was synergistically enhanced by increasing soil water and soil nutrient levels. However, plant height was surprisingly repressed by AMF inoculation, but only under low water conditions. Similarly, plant biomass was also reduced by AMF but only under low water and nutrient conditions. Furthermore, AMF significantly reduced leaf phosphorus levels, that were strongly enhanced under high nutrient conditions, but had only minor effects on leaf chlorophyll and proline levels. Under low water and nutrient conditions, specific root length was enhanced, but average root diameter was decreased by AMF inoculation. The negative effects of AMF on plant growth at low water and nutrient levels may indicate that under these conditions AMF inoculation does not strongly contribute to nutrient and water acquisition. On the contrary, the AMF might have suppressed the direct pathway of water and nutrient absorption by the plant roots themselves despite low levels of mycorrhizal colonization. AMF inoculation reduced the abundance of the foliar herbivore Chrysolina aeruginosa on plants that had been grown on the low nutrient soil, but not on high nutrient soil. Fertilization enhanced the abundance of this herbivore but only in plants that had received the high water treatment. The lower abundance of the herbivore on AMF plants could be related to their decreased leaf P content. In conclusion, our results indicate that AMF negatively affect the growth of Artemisia ordosica but makes them less attractive to a dominant herbivore. Our study highlights that plant responses to AMF depend not only on the environmental context, but that the direction of the responses can differ for different components of plant performance (growth vs. defense).

Foliar herbivory affects the rhizosphere microbial assembly processes and association networks

Insect herbivores are prevalent in terrestrial ecosystems, and plants inevitably and continuously suffer damage by insect herbivores. Numerous studies have reported the effect of insect herbivory on plants; however, its effect on the belowground soil microbial community remains understudied. In the present study, using high-throughput sequencing, we investigated the effect of foliar insect herbivory on rhizosphere soil bacterial community. Our results showed that both herbivory intensity and duration after herbivory had no significant effect on the rhizosphere microbial community structure, but microbial assembly processes and association networks were strongly affected by the above two factors. Under moderate and high herbivory and at 6 weeks after herbivory, variable selection explained 55.56% and 51.52% of the community variation indicating that deterministic processes played a dominant role. Network complexity decreased from no herbivory (1.07) to high herbivory (0.97), and network complexity at 2 weeks after herbivory (0.92) was higher than that at 4 and 6 weeks after herbivory (0.79 and 0.84, respectively). The proportion of negative correlations decreased with increasing herbivory intensity and duration after herbivory. The number of keystone species decreased with increasing duration after herbivory but showed no change with increasing herbivory intensity. To our knowledge, this is among the first studies to illustrate the response mechanisms of rhizosphere microbial assembly processes and association networks to foliar herbivory. Our findings suggest that the assembly process and association network patterns of microbes are closely associated with herbivory intensity and duration after herbivory and enhance the understanding of insect-plant-soil microbe interactions.

Plants with extrafloral nectaries share indirect defenses and shape the local arboreal ant community.

Associational resistance (AR) is a positive interaction in which a plant suffers less herbivoredamage due to its association with a protective plant. Here, we evaluated whether plants with extra-floral nectaries (EFNs) can share indirect defenses with neighboring plants. We sampled 45 individuals of an EFN-bearing liana (Smilax polyantha) and recorded whether their support species had EFNs. In S. polyantha, we measured foliar herbivory and flower and fruit production. We examined the ant species composition and visitation of S. polyantha and whether they changed according to the supporting plant type (with or without EFNs). We experimentally determined whether S. polyantha supplemented with artificial nectaries could share indirect defenses with defenseless neighboring plants. Support plants with EFNs indirectly benefited S. polyantha by sharing mutualistic ant species. Smilax polyantha supported by plants with EFNs had a more specific ant species composition, a higher number of visiting ants and ant species richness, and exhibitednearly 3 times less foliar herbivory. However, we did not observe differences in fruit production between the two groups of S. polyantha. Finally, we observed that S. polyantha with artificial nectaries increased ant visitation on neighboring plants 2.5 times. We provide evidence that interspecific neighbors with EFNs can experience reciprocal benefits by sharing indirect defenses. Such local effects might escalate and affect the structure of plant communities.

Testing enemy release of non‐native plants across time and space using herbarium specimens in Norway

Abstract The enemy release hypothesis predicts that invasive plant success is in part due to the absence of natural enemies in the invaded range. However, few studies have assessed how enemy release may vary over time or space. Norway has seen a large increase in non‐native plant species over the past few decades. We used historical herbarium records to test whether 10 non‐native plant species in Norway have suffered less from natural enemies (foliar herbivores) at different latitudes and over the past 195 years, compared to closely related (congeneric) native species. We analysed over 2200 specimens over 26 species. Chewing herbivory was lower at higher latitudes for both non‐native and native species. However, there was no evidence of change over time in overall chewing herbivory for either native or non‐native species on average. Chewing herbivory of native and non‐native species differed within the genera Centaurea, Epilobium and Salix across latitudes, and in the genera Acer, Barbarea, Campanula and Epilobium across time. Synthesis: Our results suggest that enemy release is unlikely to facilitate these non‐native plants in Norway since herbivory levels are similar between both non‐native and native plant species. Herbivory of these non‐native plants did not change over time, suggesting that they were quickly recognized as food sources by native herbivores. Lower levels of herbivory at higher latitudes suggest that herbivory is unlikely to limit non‐native plants further north and that herbivory is likely to increase at higher latitudes as the climate warms.

Beneficial and Pest Arthropod Responses to Tillage and Cover Crop Residues in Organic Cucurbits.

Reduced tillage methods such as strip tillage are often combined with cover crop mixtures to provide agronomic benefits which can support crop and soil health. However, reduced tillage and cover crop species/arrangements effects on arthropods is less understood and results of previous studies have varied. In this study, we examined how agriculturally relevant pest and beneficial arthropod species were impacted by tillage and cover crop methods in USDA-certified organic Cucurbita (L.) (Cucurbitales: Cucurbitaceae). Aphididae were the most observed foliar pests and abundance was highest in full tillage treatment plots while foliar herbivores overall, excluding Aphididae, were more abundant in strip tillage treatment plots regardless of cover crop arrangement. Formicidae was also observed more on foliage, flowers, and in pitfall traps in full tillage, similarly to Aphididae. Parasitica were the most observed foliar natural enemies with increased abundance in strip tillage treatments. Activity densities of several epigeal natural enemies were also higher in strip tillage compared to full tillage. No significant effects of tillage and cover crop treatments were observed on flower visitation rates of Eucera pruinosa (Say) (Hymenoptera: Apidae), an important pollinator of Cucurbita, while the highest visitation rates of Apis mellifera (L.) (Hymenoptera: Apidae) and Bombus spp. (Latreille) (Hymenoptera: Apidae) were in strip tillage treatments. These results suggest that reduced tillage methods can support greater abundances of natural enemies and possibly pollinators. This may lead to enhanced biological control and pollination, but impacts may vary for different arthropod species and crops.

Ant nest distribution and richness have opposite effects on a Neotropical plant with extrafloral nectaries

Abstract Studies assessing the effects of the spatial distribution of ant nests on ant‐plant mutualisms are rare, even though they could be decisive to the outcomes of such interactions. Here, we investigated how ant nest abundance and richness affected a Neotropical plant with extrafloral nectaries (EFN), Smilax polyantha (Smilacaceae). We used baits to sample all nests of mutualistic ants within a 12 m radius of each plant. All neighbouring plants with EFN within 10 m of each tagged plant were also sampled. We measured foliar herbivory and fruit production of each S. polyantha. We hypothesized that (i) high numbers of ant nests near S. polyantha individuals would reduce foliar herbivory and increase fruit production, and that (ii) high ant nest richness would increase foliar herbivory and reduce fruit production. Results showed that plants surrounded by more ant nests had lower foliar herbivory and higher fruit production. However, ant nest richness was associated with higher foliar herbivory. Furthermore, plants producing more leaves and those surrounded by more neighbouring plants with EFN had reduced herbivory. Despite this, S. polyantha had low numbers of ant nests and reduced fruit production when surrounded by high numbers of neighbours with EFN. We suggest that the spatial distribution of ant nests and resources (plants with EFN) play an important role in ant‐mediated mutualisms, where both ants and plants are likely competing for each other's services. Thus, incorporating these two variables in ecological models should provide insights into how protective mutualisms are structured.

Foliar Herbivory Reduces Rhizosphere Fungal Diversity and Destabilizes the Co-occurrence Network.

Insect herbivores can adversely impact terrestrial plants throughout ontogeny and across various ecosystems. Simultaneously, the effects of foliar herbivory may extend belowground, to the soil microbial community. However, the responses in terms of the diversity, assembly, and stability of rhizosphere fungi to aboveground herbivory remain understudied. Here, using high-throughput sequencing, the effects of foliar insect herbivory on rhizosphere fungal microbes were investigated in a common garden experiment that manipulated herbivory intensity and time from herbivore removal. The number of observed fungal species was reduced by a greater herbivory intensity, with some species evidently sensitive to herbivory intensity and time since herbivore removal. Rhizofungal assembly processes were altered by both herbivory intensity and time since herbivore removal. Further, we found evidence that both factors strongly influenced fungal community stability: a high intensity of herbivory coupled with a shorter time since herbivore removal resulted in low stability. These results suggest that foliar herbivory can adversely alter fungal diversity and stability, which would in turn be harmful for plant health. Fortunately, the effect seems to gradually diminish with time elapsed after herbivore removal. Our findings provide a fresh, in-depth view into the roles of rhizofungi in enhancing the adaption ability of plants under environmental stress.

Do experimental drought stress and species' drought sensitivity influence herbivory in tropical tree seedlings?

AbstractIn tropical forests, drought and herbivory represent two potent stresses on seedlings. Climate change is expected to increase the frequency of severe droughts in many tropical forests, which may influence seedling vulnerability to herbivores if drought stress affects seedling palatability. Furthermore, contrasting selective pressures in wetter vs drier forests could mean that species well‐adapted to herbivores are less drought resistant and vice versa. In this study, we measured seedling performance and herbivory in a common garden experiment where seedlings of 15 tree species were subjected to irrigation or rainfall exclusion treatments across two dry seasons in Panama. Water manipulation had no effects on foliar herbivory during the experiment for all species combined and for 14 of the 15 focal species when analyzed separately. There was large variation among species in herbivore damage, but no relationship between the sensitivity of species to drought and the amount of herbivory they experienced. Altogether, our findings suggest that increasing drought stress is unlikely to directly alter tropical tree seedling susceptibility to herbivore attack in this forest. Additional studies are needed to determine whether drought alters tropical plant‐herbivore interactions via other mechanisms, such as through changes in herbivorous insect communities and/or increases in fitness costs of herbivory.Abstract in Spanish is available with online material.

Foliar herbivory on plants creates soil legacy effects that impact future insect herbivore growth via changes in plant community biomass allocation

ABSTRACT Plants leave legacy effects in the soil they grow in, which can drive important vegetation processes, including productivity, community dynamics and species turnover. Plants at the same time also face continuous pressure posed by insect herbivores. Given the intimate interactions between plants and herbivores in ecosystems, plant identity and herbivory are likely to interactively shape soil legacies. However, the mechanisms that drive such legacy effects on future generations of plants and associated herbivores are little known. In a greenhouse study, we exposed 10 common grasses and non‐leguminous forbs individually to insect herbivory by two closely related noctuid caterpillars, Mamestra brassicae and Trichoplusia ni (Lepidoptera: Noctuidae) or kept them free of herbivores. We then used the soil legacies created by these plant individuals to grow a plant community composed of all 10 plant species in each soil and exposed these plant communities to M. brassicae. We measured conditioning plant biomass, soil respiration and chemistry of the conditioned soils, as well as individual plant, plant community and herbivore biomass responses. At the end of the conditioning phase, soils with herbivore legacies had higher soil respiration, but only significantly so for M. brassicae. Herbivore legacies had minimal impacts on community productivity. However, path models reveal that herbivore‐induced soil legacies affected responding herbivores through changes in plant community shoot: root ratios. Soil legacy effect patterns differed between functional groups. We found strong plant species and functional group‐specific effects on soil respiration parameters, which in turn led to plant community shifts in grass: forb biomass ratios. Soil legacies were negative for the growth of plants of the same functional group. Synthesis. We show that insect herbivory, plant species and their functional groups, all incur soil microbial responses that lead to subtle (herbivory) or strong (plants and their functional group) effects in response plant communities and associated polyphagous herbivores. Hence, even though typically ignored, our study emphasizes that legacies of previous insect herbivory in the soil can influence current soil–plant–insect community interactions. A free Plain Language Summary can be found within the Supporting Information of this article.

Earthworm services: an agroecological perspective

Objective: To review and discuss the invisible and silent role of the activity of earthworms, which are considered “agroecosystem engineers”. Design/methodology/approach: A database search of scientific articles published in Mexico and worldwide was performed. Results: The literature reviewed shows that earthworms constitute the most abundant biomass in the vast majority of tropical agroecosystems. In addition, earthworms have long been shown to improve a) soil structure; b) interaction with symbiotic microorganisms; c) nutrient mineralization and availability; d) pollutant removal; e) regulation of foliar herbivory; and f) crop yields. Limitations on study/implications: Most studies have been conducted in laboratories and greenhouses. Findings/conclusions: Earthworms increase soil quality and agricultural productivity. Their protection, promotion, and management are suggested in order to manage, preserve, and restore soil health, as well as to ensure a sustainable crop production.