On the inability of ants to protect their plant partners and the effect of herbivores on different stages of plant reproduction

Ants co‐occur with herbivorous thrips in several tropical plants, but their interactions are largely unexplored. Should thrips be deterred by ants, a positive effect of ants on plant fitness might be expected. Here, by using an experimental study design with ant‐present and ant‐excluded treatments, we investigated the influence of Camponotus blandus on Pseudophilothrips obscuricornis abundance and herbivory in three extrafloral nectaried species: Banisteriopsis malifolia, B. laevifolia and B. stellaris. In addition, we examined the effect of thrips herbivory on flower set and fruit development and dispersion. Thrips abundance and herbivory were higher on ant‐present stems of B. malifolia and B. laevifolia, where thrips managed to escape from ants by hiding in between clusters of flower buds (thygmotaxis behaviour). In B. stellaris the results were the opposite, as flower bud clusters did not offer hiding places, so thrips were unable to hide from ants; thus both thrips abundance and herbivory were lower on ant‐present stems. Thrips herbivory had no significant effect on flower and fruit set, but samaras (V‐shaped winged fruits of Malpighiaceae) attacked by thrips presented severe distortions and asymmetries. This caused damaged fruits to be dispersed closer to the mother plant, whereas uninjured fruits were dispersed further away. This study is evidence that ant–plant–herbivore systems have variable outcomes depending on the species involved, their behaviour and the plant structure under consideration. Unlike other herbivores, thrips negatively influence the very last stage of plant reproduction. The minute and furtive herbivorous thrips have long been ignored in natural systems, but because of their wide host range, they may be important herbivores even in extrafloral nectaried plants, which are usually fiercely protected by ants.     

Augmentation of soil detritus affects the spider community and herbivory in a soybean agroecosystem

If soil detritivores provide a significant prey source for predators in the vegetation, then augmentation of the soil community could affect the grazing food web. Specifically, increases in predator density could enhance any top‐down effects and reduce herbivory. We tested this hypothesis by providing detrital subsidies in the form of composted vegetable matter to 36 m² plots in soybean, Glycine max (L.) Merr. (Fabales: Fabaceae), fields that were managed using either conventional or conservation tillage practices. The foliage‐dwelling spiders, insect predators, and leaf‐chewing insects were censused and the body size of one large spider species, Argiope trifasciata (Forskål) (Araneae: Araneidae), was measured. In addition, the density and size of the plants were assessed and leaf damage was quantified. Any effects of treatments on the palatability of soybean plants to herbivores were determined in two laboratory experiments. Compost increased the density of foliage dwelling spiders and the abdomen size of A. trifasciata. We uncovered no treatment effects on insect predators, herbivorous insects, or plant characteristics except that compost addition reduced leaf damage. In addition, there was a negative correlation across plots between spider abundance and soybean leaf damage and abdomen width of A. trifasciata and weed herbivory levels across plots. These results suggest a connection between the soil community and the foliage food web, but the spiders appear to have exerted a top‐down effect without a shift in herbivore abundance. Further study of the specific seasonality of the herbivores and their behavior in the presence of spiders are needed to uncover the underlying mechanism. Nevertheless, these results provide evidence for complex linkage between the soil and grazing food webs that may be important to biological control.     

Insect herbivory and plant adaptation in an early successional community*

To address the role of insect herbivores in adaptation of plant populations and the persistence of selection through succession, we manipulated herbivory in a long‐term field experiment. We suppressed insects in half of 16 plots over nine years and examined the genotypic structure and chemical defense of common dandelion (Taraxacum officinale), a naturally colonizing perennial apomictic plant. Insect suppression doubled dandelion abundance in the first few years, but had negligible effects thereafter. Using microsatellite DNA markers, we genotyped >2500 plants and demonstrate that insect suppression altered the genotypic composition of plots in both sampling years. Phenotypic and genotypic estimates of defensive terpenes and phenolics from the field plots allowed us to infer phenotypic plasticity and the response of dandelion populations to insect‐mediated natural selection. The effects of insect suppression on plant chemistry were, indeed, driven both by plasticity and plant genotypic identity. In particular, di‐phenolic inositol esters were more abundant in plots exposed to herbivory (due to the genotypic composition of the plots) and were also induced in response to herbivory. This field experiment thus demonstrates evolutionary sorting of plant genotypes in response to insect herbivores that was in same direction as the plastic defensive response within genotypes.     

The effects of host plant species on adult oviposition and larval performance of the aphid predator Aphidoletes aphidimyza

1. Although preference–performance relationships in insects are typically studied in a bi-trophic context, it is well known that host plants can affect both the preference and performance of natural enemies of herbivorous insects. 2. This study presents evidence from field and laboratory studies that two species of milkweeds, the putatively less defended Asclepias incarnata and the putatively more defended Asclepias syriaca, differentially affect adult oviposition and larval performance in Aphidoletes aphidimyza, an aphid-feeding predatory midge, independent of aphid density. 3. Host plant species affected predatory fly larvae abundance by a factor of 50 in the field and a factor of 8 in the laboratory. Larval and adult emergence rates in our laboratory studies provided strong evidence for reduced performance on A. syriaca. Oviposition in choice and no-choice settings provided some evidence for preference for A. incarnata, and a potentially suppressive effect of A. syriaca. 4. The results provide limited support for the hypothesis that natural selection can lead to positive correlations between adult oviposition preferences and larval performance upon various food sources, even when predatory insects oviposit onto host plants of their herbivorous prey. 5. Preference and performance are not perfectly aligned in this system, however, because ovipositing females do not reject A. syriaca entirely. Potential explanations for mismatches between preference and performance in this system include the neural constraints associated with being a generalist, adaptive time-limited foraging strategies, and unique evolutionary histories of laboratory colonies compared with wild insects.     

Parasitoids follow herbivorous insects to a novel host plant,generalist predators less so

The ‘enemy‐free space’ hypothesis predicts that herbivorous insects can escape their natural enemies by switching to a novel host plant, with consequences for the evolution of host plant specialisation. However, if natural enemies follow herbivores to their novel host plants, enemy‐free space may only be temporary. We tested this by studying the colonisation of the introduced tree Eucalyptus grandis (Hill) Maiden (Myrtaceae) by insects in Brazil, where various species of herbivores have added eucalyptus to their host plant range, which consists of native myrtaceous species such as guava. Some herbivores, for example, Thyrinteina leucoceraea Ringe (Lepidoptera: Geometridae), cause outbreaks in eucalyptus plantations but not on guava, possibly because eucalyptus offers enemy‐free space. We sampled herbivores (mainly Lepidoptera species) and natural enemies on eucalyptus and guava and assessed parasitism of Lepidoptera larvae on both host plant species during ca. 2 years. Overall, predators were encountered more frequently on guava than on eucalyptus. In contrast, parasitoids were encountered equally and parasitism rates of Lepidoptera larvae were similar on both host plants. This indicates that herbivores may escape some enemies by moving to a novel host plant. However, this escape may be temporary and may vary with time. We argue that studying temporal and spatial patterns of enemy‐free space and the response of natural enemies to host use changes of their herbivorous prey is essential for understanding the role of natural enemies in the evolution of host plant use by herbivorous arthropods.     

Can imitation companion planting interfere with host selection by Brassica pest insects?

• 1 Companion planting with nonhosts may offer a non‐insecticidal means of controlling pests, although the results of studies can be variable and species‐dependent.
• 2 The effect of companion planting on two pests of Brassica crops, Plutella xylostella (L.) and Brevicoryne brassicae (L.), was examined using Brussels sprout as the host plant and imitation cereal plants made from green plastic as the nonhost. For P. xylostella, the effect of nonhost density was also investigated.
• 3 Oviposition (P. xylostella) and abundance (B. brassicae) were lower on Brussels sprout plants presented on a background of high‐density imitation cereal plants (reductions of 59% and 85%, respectively).
• 4 The results are discussed in the context of host location by pest insects and the selection of nonhost companion plants for pest management.
• 5 It is concluded that nonhost plants interfere with pest host selection through disruption to visual host location processes.

     

Phytophagous insect fauna tracks host plant responses to exotic grass invasion

The high dependence of herbivorous insects on their host plants implies that plant invaders can affect these insects directly, by not providing a suitable habitat, or indirectly, by altering host plant availability. In this study, we sampled Asteraceae flower heads in cerrado remnants with varying levels of exotic grass invasion to evaluate whether invasive grasses have a direct effect on herbivore richness independent of the current disturbance level and host plant richness. By classifying herbivores according to the degree of host plant specialization, we also investigated whether invasive grasses reduce the uniqueness of the herbivorous assemblages. Herbivorous insect richness showed a unimodal relationship with invasive grass cover that was significantly explained only by way of the variation in host plant richness. The same result was found for polyphagous and oligophagous insects, but monophages showed a significant negative response to the intensity of the grass invasion that was independent of host plant richness. Our findings lend support to the hypothesis that the aggregate effect of invasive plants on herbivores tends to mirror the effects of invasive plants on host plants. In addition, exotic plants affect specialist insects differently from generalist insects; thus exotic plants affect not only the size but also the structural profile of herbivorous insect assemblages.     

Effects of plant quality and ant defence on herbivory rates in a neotropical ant‐plant

1. Understanding the degree to which populations and communities are limited by both bottom‐up and top‐down effects is still a major challenge for ecologists, and manipulation of plant quality, for example, can alter herbivory rates in plants. In addition, biotic defence by ants can directly influence the populations of herbivores, as demonstrated by increased rates of herbivory or increased herbivore density after ant exclusion. The aim of this study was to evaluate bottom‐up and top‐down effects on herbivory rates in a mutualistic ant‐plant. 2. In this study, the role of Azteca alfari ants as biotic defence in individuals of Cecropia pachystachya was investigated experimentally with a simultaneous manipulation of both bottom‐up (fertilisation) and top‐down (ant exclusion) factors. Four treatments were used in a fully factorial design, with 15 replicates for each treatment: (i) control plants, without manipulation; (ii) fertilised plants, ants not manipulated; (iii) unfertilised plants and excluded ants and (iv) fertilised plants and ants excluded. 3. Fertilisation increased the availability of foliar nitrogen in C. pachystachya, and herbivory rates by chewing insects were significantly higher in fertilised plants with ants excluded. 4. Herbivory, however, was more influenced by bottom‐up effects – such as the quality of the host plant – than by top‐down effects caused by ants as biotic defences, reinforcing the crucial role of leaf nutritional quality for herbivory levels experienced by plants. Conditionality in ant defence under increased nutritional quality of leaves through fertilisation might explain increased levels of herbivory in plants with higher leaf nitrogen.     

Insect herbivory in climber–host shrubs associations: Benefit or detriment?

Spatial proximity between different plant species could modify the sign (positive or negative) of plant–herbivore interaction. The chance of a plant being detected and colonized by herbivorous insects depends not only on the plant's own traits but also on the identity of the neighbouring plants that grow with it. The closest proximity between plants occurs in climbers and their host. We conducted a field experiment to assess the effect of spatial association between a climber plant, Vicia nigricans (Fabaceae), and two host shrubs, Berberis buxifolia (Berberidaceae) and Schinus patagonica (Anacardiaceae), on insect herbivory levels, reproductive output and growth. The presence and identity of the host shrubs affected the herbivory levels of the climber V. nigricans, but not the reproductive output. For the climber, the probability of being attacked by insects could depend on the characteristics of the host shrub. Taking the opposite perspective, climber association affected different traits of the host shrubs. The association with the climber decreased leaf damage (positive), tended to decrease leaf production (negative) and did not affect reproductive output (neutral). Our findings suggest that spatial association between plant species could change the sign of the interactions between plants and insects affecting different traits. By taking into account the perspective of both plants involved in the association, this study shows and emphasizes that plant–animal interactions strongly depend on the community context.     

Contemporary evolution of host plant range expansion in an introduced herbivorous beetle Ophraella communa

Host range expansion of herbivorous insects is a key event in ecological speciation and insect pest management. However, the mechanistic processes are relatively unknown because it is difficult to observe the ongoing host range expansion in natural population. In this study, we focused on the ongoing host range expansion in introduced populations of the ragweed leaf beetle, Ophraella communa, to estimate the evolutionary process of host plant range expansion of a herbivorous insect. In the native range of North America, O. communa does not utilize Ambrosia trifida, as a host plant, but this plant is extensively utilized in the beetle's introduced range. Larval performance and adult preference experiments demonstrated that native O. communa beetles show better survival on host plant individuals from introduced plant populations than those from native plant populations and they also oviposit on the introduced plant, but not on the native plant. Introduced O. communa beetles showed significantly higher performance on and preference for both introduced and native A. trifida plants, when compared with native O. communa. These results indicate the contemporary evolution of host plant range expansion of introduced O. communa and suggest that the evolutionary change of both the host plant and the herbivorous insect involved in the host range expansion.     

Birds exploit herbivore‐induced plant volatiles to locate herbivorous prey

Arthropod herbivory induces plant volatiles that can be used by natural enemies of the herbivores to find their prey. This has been studied mainly for arthropods that prey upon or parasitise herbivorous arthropods but rarely for insectivorous birds, one of the main groups of predators of herbivorous insects such as lepidopteran larvae. Here, we show that great tits (Parus major) discriminate between caterpillar‐infested and uninfested trees. Birds were attracted to infested trees, even when they could not see the larvae or their feeding damage. We furthermore show that infested and uninfested trees differ in volatile emissions and visual characteristics. Finally, we show, for the first time, that birds smell which tree is infested with their prey based on differences in volatile profiles emitted by infested and uninfested trees. Volatiles emitted by plants in response to herbivory by lepidopteran larvae thus not only attract predatory insects but also vertebrate predators.     

Con‐specific neighbours may enhance compensation capacity in an invasive plant

Facilitation, both by inter‐ and intra‐specific neighbours, is known to be an important process in structuring plant communities. However, only a small number of experiments have been reported on facilitation in plant invasions, especially between invasive con‐specific individuals. Here, we focus on how con‐specific neighbours of the invasive alien plant alligator weed affect the tolerance of alligator weed to herbivory by the introduced biological control agent, Agasicles hygrophila. We conducted greenhouse and garden experiments in which invasive plant density and herbivory intensity (artificial clipping and real herbivory) were manipulated. In the greenhouse experiment, artificial clipping significantly reduced plant biomass when plants were grown individually, but when con‐specific neighbours were present in the same pot, biomass was not significantly different from control plants. Similarly, when compared to control plants, plants that were subjected to herbivory by A. hygrophila produced more biomass when grown with two con‐specific neighbours than when grown alone. Real herbivory also resulted in an increased number of vegetative buds, and again when two con‐specific neighbours were present this effect was increased (a 55.3% increase in buds when there was no neighbour, but a 111.6% increase in buds when two con‐specific neighbours were present). In the garden experiment, in which plants were grown at high density (6 plants per pot), alligator weed fully recovered from defoliation caused by insects at levels from 20–30% to 100%. Our results indicate that the con‐specific association may increase the compensatory ability to cope with intense damage in this invasive plant.     

Entrapped carrion increases indirect plant resistance and intra‐guild predation on a sticky tarweed

Many plants employ indirect defenses against herbivores; often plants provide a shelter or nutritional resource to predators, increasing predator abundance, and lessening herbivory to the plant. Often, predators on the same plant represent different life stages and different species. In these situations intraguild predation (IGP) may occur and may decrease the efficacy of that defense. Recently, several sticky plants have been found to increase indirect defense by provisioning predatory insects with entrapped insects (hereafter: carrion). We conducted observational studies and feeding trials with herbivores and predators on two sticky, insect‐entrapping asters, Hemizonia congesta and Madia elegans, to construct food webs for these species and determine the prevalence of IGP in these carrion‐provisioning systems. In both systems, intraguild predation was the most common interaction observed. To determine whether IGP was driven by resource abundance, whether it reduced efficacy of this indirect defense and whether stickiness or predator attraction was induced by damage, we performed field manipulations on H. congesta. Carrion supplementation led to an increase in predator abundance and IGP. IGP was asymmetric within the predator guild: assassin bugs and spiders preyed on small stilt bugs but not vice versa. Despite increased IGP, carrion provisions decreased the abundance of the two most common herbivores (a weevil and a mealybug). Overall seed set was driven by plant size, but number of seeds produced per fruit significantly increased with increasing carrion, likely because of the reduction in the density of a seed‐feeding weevil. Observationally and experimentally, we found that carrion‐mediated indirect defense of tarweeds led to much intraguild predation, though predators effectively reduced herbivore abundance despite the increase in IGP.     

Host‐plant genotype mediates supply and demand of animal food in an omnivorous insect

1. Omnivorous predators can protect plants from herbivores, but may also consume plant material themselves. Omnivores and their purely herbivorous prey have previously been thought to respond similarly to host‐plant quality. However, different responses of omnivores and herbivores to their shared host plants may influence the fitness, trophic identity, and population dynamics of the omnivores. 2. The aim of the present study was to show that an omnivorous heteropteran (Anthocoris nemorum L.) and two strictly herbivorous prey species respond differently to different genotypes of their shared host plant, Salix. Some plant genotypes were sub‐optimal for the omnivore, although suitable for the herbivores, and vice versa. 3. The contrasting patterns of plant suitability for the omnivore and the herbivores highlight an interaction between plant genotype and omnivores' access to animal food. Plant genotypes that were sub‐optimal for the omnivore when herbivores were experimentally excluded became the best host plants when herbivores were present, as in the latter situation additional prey became available. By contrast, the quality of plant genotypes that were intrinsically suitable for omnivores, did not improve when herbivores were present as these plant genotypes were intrinsically sub‐optimal for herbivores, thus providing omnivores with almost no additional animal food. 4. The differential responses of omnivores and their prey to the same host‐plant genotypes should allow omnivores to colonise sub‐optimal host plants in their capacity as predators, and to colonise more suitable host plants in their capacity as herbivores. It may thus be difficult for Salix to escape herbivory entirely, as it will rarely be unsuitable for both omnivores and pure herbivores at the same time.     

Solar ultraviolet-B radiation alters the attractiveness of Arabidopsis plants to diamondback moths (Plutella xylostella L.): impacts on oviposition and involvement of the jasmonic acid pathway

Solar ultraviolet-B radiation (UV-B) can have large impacts on the interactions between plants and herbivorous insects. Several studies have documented effects of UV-B-induced changes in plant tissue quality on the feeding performance of insect larvae. In contrast, the effects of UV-B-induced plant responses on the behavior of adult insects have received little attention. We carried out a series of field and glasshouse experiments using the model plant Arabidopsis thaliana L. and the crucifer-specialist insect Plutella xylostella L. (diamondback moth) to investigate the effects of UV-B on natural herbivory and plant–insect interactions. Natural herbivory under field conditions was less severe on plants exposed to ambient UV-B than on plants grown under filters that attenuated the UV-B component of solar radiation. This reduced herbivory could not be accounted for by effects of UV-B on larval feeding preference and performance, as P. xylostella caterpillars did not respond to changes in plant quality induced by UV-B. In contrast, at the adult stage, the insects presented clear behavioral responses: P. xylostella moths deposited significantly more eggs on plants grown under attenuated UV-B levels than on plants exposed to ambient UV-B. The deterring effect of UV-B exposure on insect oviposition was absent in jar1-1, a mutant with impaired jasmonic acid (JA) sensitivity, but it was conserved in mutants with altered ethylene signaling. The jar1-1 mutant also presented reduced levels of UV-absorbing phenolic compounds than the other genotypes that we tested. Our results suggest that variations in UV-B exposure under natural conditions can have significant effects on insect herbivory by altering plant traits that female adults use as sources of information during the process of host selection for oviposition. These effects of natural UV-B on plant quality appear to be mediated by activation of signaling circuits in which the defense-related hormone JA plays a functional role.     

Community‐wide impacts of herbivore‐induced plant regrowth on arthropods in a multi‐willow species system

It has been widely accepted that herbivory induces morphological, phenological, and chemical changes in a wide variety of terrestrial plants. There is an increasing appreciation that herbivore‐induced plant responses affect the performance and abundance of other arthropods. However, we still have a poor understanding of the effects of induced plant responses on community structures of arthropods. We examined the community‐level effects of willow regrowth in response to damage by larvae of swift moth Endoclita excrescence (Lepidoptera: Hepialidae) on herbivorous and predaceous arthropods on three willow species, Salix gilgiana, S. eriocarpa and S. serissaefolia. The leaves of sprouting lateral shoots induced by moth‐boring had a low C:N ratio. The overall abundance and species richness of herbivorous insects on the lateral shoots were increased on all three willow species. Densities of specialist chewers and sap‐feeders, and leaf miners increased on the newly emerged lateral shoots. In contrast, the densities of generalist chewers and sap‐feeders, and gall makers did not increase. Furthermore, ant and spider densities, and the overall abundance and species richness of predaceous arthropods increased on the lateral shoots on S. gilgiana and S. eriocarpa, but not S. serissaefolia. In addition to finding that effects of moth‐boring on arthropod abundance and species richness varied among willow species, we also found that moth‐boring, willow species, and their interaction differentially affected community composition. Our findings suggest that moth‐boring has community‐wide impacts on arthropod assemblages across three trophic levels via induced shoot regrowth and increase arthropod species diversity in this three willow species system.     

Is top‐down control by predators driving insect abundance and herbivory rates in fragmented forests?

The effects of forest fragmentation on ecological interactions and particularly on food webs have scarcely been analysed. There is usually less herbivory in forest fragments than in continuous forests. Here we hypothesize that forest fragmentation enhances top‐down control of herbivory through an increase in insectivorous birds and a decrease in herbivorous insects, with a consequent decrease in plant reproductive success in small forest fragments. In the Maulino forest in central Chile, we experimentally excluded birds from Aristotelia chilensis (Elaeocarpaceae) trees in both forest fragments and continuous forest, and analysed herbivore insect abundance, herbivory and plant reproductive success during two consecutive growing seasons. We expected that insect abundance and herbivory would increase, and reproductive success would decrease in A. chilensis from which birds have been excluded, particularly in forest fragments where bird abundance and predation pressure on insects is higher. The abundance of herbivorous insects was lower in the forest fragments than in the continuous forest only in the first season, and herbivory was lower in forest fragments than in the continuous forest throughout the study. Moreover, during the second growing season herbivory was greater in the excluded trees than in the control trees, and as expected, there was a greater difference in the fragments than in the continuous forest, but this was not statistically significant. Exclusion of birds did not affect the reproductive success of A. chilensis. Our results, after 2 years of study, demonstrate that birds affect the levels of herbivory on A. chilensis in the Maulino forest, but do not support our hypothesis of enhanced top‐down control in fragmented forests, as the strength of the effect of excluding birds did not vary with fragmentation.     

History of exposure to herbivores increases the compensatory ability of an invasive plant

Release from natural enemies is frequently cited as an important factor contributing to plant invasions. But such effects are likely to be temporary—native herbivores can form new plant-herbivore associations and co-evolved insects might reach the new range. While the potential effects of the initial enemy release have been well studied, the consequences of any resumption of herbivory are poorly understood. Alternanthera philoxeroides is one of the most widespread invasive plants in China and is attacked both by a specialist herbivore introduced from the native range, Agasicles hygrophila, and a native beetle Cassida piperata Hope which has formed a new association. However, these insects are not found throughout the invaded range. To test the effect of the history of population exposure to herbivory on compensatory ability, plants were cultured from 14 populations around China that differed in whether A. hygrophila or C. piperata were present. Treatment plants were exposed to herbivory by A. hygrophila for a week until 50% of the leaf area was defoliated, then grown for 80 days. Plants from populations with prior exposure to herbivory (of any kind) accumulated more root mass than populations without prior exposure, indicating that prior exposure to insects can stimulate plant compensation to herbivory. We would recommend that potential changes in plant tolerance in response to prior exposure to herbivory are considered in invasive plant management plans that employ bio-control agents.     

Ecological and Evolutionary Interactions between Wild Crucifers and Their Herbivorous Insects

Abstract Insects feeding on ten species of wild crucifer were investigated. Differences in host plant range and insect community structure were examined with regard to anti-herbivore defense mechanisms. Most of the crucifer species deterred insect herbivory by disappearing in the summer or by lowering their intrinsic quality as food for insects. Species with these defense mechanisms were exploited by only a few specialized herbivorous insects that seemed to have counter defenses. The plants without these defense mechanisms were used by many herbivorous insect species. Rorippa indica lacked direct defenses, but supported a low total density of herbivore individuals. This crucifer has an indirect defense mechanism: ants attracted to floral nectar defended the plant from deleterious herbivores. Crucifers that disappeared seasonally lacked other anti-herbivore defense mechanisms. This suggests that the phonological response is an alternative other responses to herbivore attack.     

Environmental and genetic control of insect abundance and herbivory along a forest elevational gradient

Environmental conditions and plant genotype may influence insect herbivory along elevational gradients. Plant damage would decrease with elevation as temperature declines to suboptimal levels for insects. However, host plants at higher elevations may exhibit traits that either reduce or enhance leaf quality to insects, with uncertain net effects on herbivory. We examined folivory, insect abundance and leaf traits along six replicated elevational ranges in Nothofagus pumilio forests of the northern Patagonian Andes, Argentina. We also conducted a reciprocal transplant experiment between low- and high-elevation sites to test the extent of environmental and plant genetic control on insect abundance and folivory. We found that insect abundance, leaf size and specific leaf area decreased, whereas foliar phosphorous content increased, from low-, through mid- to high-elevation sites. Path analysis indicated that changes in both insect abundance and leaf traits were important in reducing folivory with increasing elevation and decreasing mean temperature. At both planting sites, plants from a low-elevation origin experienced higher damage and supported greater insect loads than plants from a high-elevation origin. The differences in leaf damage between sites were twofold larger than those between plant origins, suggesting that local environment was more important than host genotype in explaining folivory patterns. Different folivore guilds exhibited qualitatively similar responses to elevation. Our results suggest an increase in insect folivory on high-elevation N. pumilio forests under future climate warming scenarios. However, in the short-term, folivory increases might be smaller than expected from insect abundance only because at high elevations herbivores would encounter more resistant tree genotypes.