Induced responses in Nicotiana attenuata affect behavior and growth of the specialist herbivore Manduca sexta

Many plants employ induced responses against generalist herbivores. Specialist herbivores, however, may employ several mechanisms to overcome the negative effects of induced plant defenses. Here we test how the behavior and development of specialist Manduca sexta larvae are affected by induced responses in their natural host plant Nicotiana attenuata. On a spatial scale relevant to both the plant and the herbivore, we first determined how methyl jasmonate (MeJA)-induced responses, such as increased nicotine production, affect the tendency of larvae to leave induced plants. When larvae were allowed to move between two plants planted in one pot, they left an MeJA-treated plant faster than a control plant. When both plants in the pot were MeJA-treated, the larvae developed more slowly than when both plants were uninduced, or when the larvae had the opportunity to move to an uninduced neighbor. The sooner larvae moved from an MeJA-treated plant to an untreated neighbor, the larger the body mass they attained. This demonstrates that M. sexta larvae can compensate behaviorally for the deleterious effects of induced plant responses. These effects were observed in plants grown under both low and high N supply rates, though the effects were more pronounced under high N. To examine the consequences of the timing and the direction of the host plant switching behavior for larval development, neonate larvae were fed leaves excised from induced and uninduced plants. Larvae confined to MeJA-treated leaves had higher mortality rates and grew slower than larvae fed only control leaves. This demonstrates that MeJA-induced responses decrease growth and development of specialist herbivores that do not have the behavioral option of moving to an uninduced plant. The sooner the larvae were switched to MeJA-treated leaves, the slower their development compared to larvae fed only uninduced leaves. In contrast, the sooner larvae fed MeJA-treated leaves were switched to control leaves, the faster they developed. Again the effects of MeJA treatment were stronger in plants grown under high N supply. We propose that induced plants growing in close competition with an uninduced conspecific may offset the fitness costs of these induced responses and perhaps obtain a fitness benefit by motivating herbivores to move to their neighboring competitors. Received: 25 March 1999 / Accepted: 8 October 1999     

Herbivore-induced plant volatiles mediate host selection by a root herbivore

In response to herbivore attack, plants mobilize chemical defenses and release distinct bouquets of volatiles. Aboveground herbivores are known to use changes in leaf volatile patterns to make foraging decisions, but it remains unclear whether belowground herbivores also use volatiles to select suitable host plants. We therefore investigated how above- and belowground infestation affects the performance of the root feeder Diabrotica virgifera virgifera, and whether the larvae of this specialized beetle are able to use volatile cues to assess from a distance whether a potential host plant is already under herbivore attack. Diabrotica virgifera larvae showed stronger growth on roots previously attacked by conspecific larvae, but performed more poorly on roots of plants whose leaves had been attacked by larvae of the moth Spodoptera littoralis. Fittingly, D. virgifera larvae were attracted to plants that were infested with conspecifics, whereas they avoided plants that were attacked by S. littoralis. We identified (E)-β-caryophyllene, which is induced by D. virgifera, and ethylene, which is suppressed by S. littoralis, as two signals used by D. virgifera larvae to locate plants that are most suitable for their development. Our study demonstrates that soil-dwelling insects can use herbivore-induced changes in root volatile emissions to identify suitable host plants.     

Herbivores do not discriminate between leaves of female and hermaphrodite individuals of gynodioecious Daphne laureola (Thymelaeaceae)

The outcome of plant-animal interactions in dioecious plant species frequently depends on the gender of the plant individuals. It has even been proposed that these interactions could mediate the evolution of plant reproductive systems from hermaphroditism to dioecy. Gynodioecy is the most frequent intermediate stage in this evolutionary process, however, little is known about the relevance of gender dimorphism in plant-animal relationships others than pollination for gynodioecious species. In this study herbivores (Noctuid larvae) were used as subjective referees to detect differences between leaves of female and hermaphrodite Daphne laureola individuals. Larvae collected in the field were allowed to choose between leaves of female and hermaphrodite individuals at both flowering and fruiting period. There was no preference for either of the genders suggesting that the absence of male reproductive function in D. laureola shrubs does not cause dissimilarities in leaf characteristics that can affect herbivores.     

Leaf traits and herbivore selection in the field and in cafeteria experiments

Abstract Despite the vast diversity and complexity of herbivores, plants and their interactions, most authors agree that a small number of components of leaf quality affect preference by generalist herbivores in a predictable way. However, herbivore preference is determined not only by intrinsic plant attributes and herbivore biology but also by the environmental context. Within this framework, we aimed to analyse general interspecific trends in the association between herbivory and leaf traits over a wide range of angiosperms from central Argentina. We (i) tested for consistent associations between leaf traits, consumption in the field, and preference of generalist invertebrate herbivores in cafeteria experiments; (ii) assessed how well herbivore preferences in cafeterias matched leaf consumption in the field; and (iii) developed a simple conceptual model linking leaf traits, herbivore preference in cafeterias and consumption in the field. In general, we found that tender leaves with higher nutritional quality were preferred by herbivores, both in the field and in cafeteria experiments. According to our model, this relationship between field and cafeteria consumption and leaf quality is observed when generalist herbivores and plants of high accessibility are considered. However, differences between leaf consumption in the field and in cafeteria experiments can also be found. At least two reasons can account for this: (i) specialized plant–herbivore relationships often occur in the field, whereas cafeteria experiments tend to consider only one or a few generalist herbivores; (ii) different plant species growing in the field often differ in their degree of accessibility to herbivores, whereas in cafeteria experiments all species are equally accessible. Our results add new evidence to a growing consensus that, although herbivory in the field is determined by many factors, consistent patterns of differential susceptibility to foliar feeders can be found in leaves differing in nutritional quality and thus in resource‐use strategy.     

Temporal dynamics of herbivore‐induced responses in Brassica juncea and their effect on generalist and specialist herbivores

Herbivore feeding may induce an array of responses in plants, and each response may have its own temporal dynamics. Precise timing of these plant responses is vital for them to have optimal effect on the herbivores feeding on the plant. This study measured the temporal dynamics of various systemically induced responses occurring in Brassica juncea (L.) Czern. (Brassicaceae) leaves after insect herbivory in India and The Netherlands. Morphological (trichomes, leaf size) and chemical (glucosinolates, amino acids, sugars) responses were analysed. The effects of systemic responses were assessed using a specialist [Plutella xylostella L. (Lepidoptera: Plutellidae)] and a generalist [Spodoptera litura Fabricius (Lepidoptera: Noctuidae)] herbivore. We tested the hypotheses that morphological responses were slower than chemical responses and that generalist herbivores would be more affected by induced responses than specialists. Glucosinolates and trichomes were found to increase systemically as quickly as 4 and 7 days after herbivore damage, respectively. Amino acids, sugars, and leaf size remained unaffected during this period. The generalist S. litura showed a significant feeding preference for undamaged leaves, whereas the specialist herbivore P. xylostella preferred leaves that were damaged 9 days before. Performance bioassays on generalist S. litura revealed that larvae gained half the weight on leaves from damaged plants as compared to larvae feeding on leaves from undamaged plants. These studies show that although morphological responses are somewhat slower than chemical responses, they also contribute to induced plant resistance in a relatively short time span. We argue that before considering induced responses as resistance factors, their effect should be assessed at various points in time with both generalist and specialist herbivores.     

Tritrophic interactions among coumarin, the herbivore Spodoptera litura and a gregarious ectoparasitoid Bracon hebetor

The secondary metabolites that play a defensive role in plants not only affect the growth and development of herbivores, but they can also influence their natural enemies. In the present study, the effect of coumarin was evaluated on a braconid parasitoid, Bracon hebetor (Say) (Hymenoptera: Braconidae) using polyphagous pest, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae). Reproductive potential of the parasitoid declined significantly due to parasitization of host larvae feeding on coumarin supplemented diet. Total development period of B. hebetor extended significantly (2.17–2.38 days) when the host larvae were reared on diet amended with higher concentrations (625–3,125 parts per million) of coumarin as compared to unamended diet. Ingestion of coumarin supplemented diet by S. litura adversely affected the emergence and parasitization potential of B. hebetor. As compared to the control a significant decline in hatching of eggs was recorded when parasitoid wasps developed on host larvae fed on diet containing higher concentrations of coumarin (625–3,125 ppm). Negative effects of coumarin were also recorded from the next generation of the parasitoid.     

Behavioral and morphological responses of an insect herbivore to low nutrient quality are inhibited by plant chemical defenses

Animals have several strategies to contend with nutritionally poor diets, including compensatory consumption and enhanced food utilization efficiencies. Plants produce a diversity of defense compounds that affect the ability of herbivores to utilize these strategies in response to variation in food nutritional quality. Little is known, however, about effects of allelochemicals on herbivores utilizing integrated behavioral and morphological responses to reduced food quality. Our objectives were to (1) examine how variation in diet nutritional quality influences compensatory responses of a generalist insect herbivore, and (2) determine how plant defenses affect these processes. Gypsy moth (Lymantria dispar) larvae were administered one of nine combinations of diet having low, moderate, or high nutritional quality and 0, 2, or 4 % purified aspen (Populus tremuloides) salicinoids. We quantified larval growth, consumption, frass production, and biomass allocation to midgut tissue over a 4-day bioassay. In the absence of salicinoids, larvae compensated for reduced nutritional quality and maintained similar growth across all diets through increased consumption, altered midgut biomass allocation, and improved processing efficiencies. Dietary salicinoids reduced larval consumption, midgut biomass allocation, digestive efficiencies, and growth at all nutritional levels, but the effect size was more pronounced when larvae were fed nutritionally suboptimal diets. Our findings demonstrate that integrated behavioral and morphological compensatory responses to reduced food quality are affected by plant defenses, ultimately limiting compensatory responses and reducing larval performance.     

Poleward increase in feeding efficiency of leafminer Stigmella lapponica (Lepidoptera: Nepticulidae) in a latitudinal gradient crossing a boreal forest zone

Damage to plant communities imposed by insect herbivores generally decreases from low to high latitudes. This decrease is routinely attributed to declines in herbivore abundance and/or diversity, whereas latitudinal changes in per capita food consumption remain virtually unknown. Here, we tested the hypothesis that the lifetime food consumption by a herbivore individual decreases from low to high latitudes due to a temperature-driven decrease in metabolic expenses. From 2016 to 2019, we explored latitudinal changes in multiple characteristics of linear (gallery) mines made by larvae of the pygmy moth, Stigmella lapponica, in leaves of downy birch, Betula pubescens. The mined leaves were larger than intact leaves at the southern end of our latitudinal gradient (at 60°N) but smaller than intact leaves at its northern end (at 69°N), suggesting that female oviposition preference changes with latitude. No latitudinal changes were observed in larval size, mine length or area, and in per capita food consumption, but the larval feeding efficiency (quantified as the ratio between larval size and mine size) increased with latitude. Consequently, S. lapponica larvae consumed less foliar biomass at higher latitudes than at lower latitudes to reach the same size. Based on space-for-time substitution, we suggest that climate warming will increase metabolic expenses of insect herbivores with uncertain consequences for plant–herbivore interactions.     

Feeding patterns of monophagous,oligophagous, and polyphagous insect herbivores: The effect of resource abundance and plant chemistry

Summary Leaf tissue preferences of monophagous, oligophagous, and polyphagous insect herbivores were determined using young and mature leaf tissue abundances and herbivore feeding observations. Larvae of monophagous and oligophagous herbivores preferred young leaf tissues while, overall, larvae of polyphagous species preferred mature leaves of their various host plants. Even though a species is often polyphagous over its geographical range, larvae from local populations may be very specialized in their diet. When this occurs these specialized larvae prefer the more nutritious and perhaps more toxic young leaves of some of their host plants. Resource abundance and plant chemistry are discussed as major factors influencing herbivore feeding patterns.     

Uptake of Bt-toxin by herbivores feeding on transgenic maize and consequences for the predator Chrysoperla carnea

Abstract  1. Chrysoperla carnea is an important predatory insect in maize. To assess the ecological effects of Bt-maize, expressing the Cry1Ab protein, on larvae of this predator, the following factors were examined: (1) the performance of three prey herbivores ( Rhopalosiphum padi , Tetranychus urticae , and Spodoptera littoralis ) on transgenic Bt and non‐transgenic maize plants; (2) the intake of the Cry1Ab toxin by the three herbivores; and (3) the effects on C. carnea when fed each of the prey species.
2. The intrinsic rate of natural increase (r_m) was used as a measure of performance for R. padi and T. urticae . No difference in this parameter was observed between herbivores reared on Bt or non‐transgenic plants. In contrast, a higher mortality rate and a delay in development were observed in S. littoralis larvae when fed Bt-maize compared with those fed the control maize plants.
3. The ingestion of Cry1Ab toxin by the different herbivores was measured using an immunological assay (ELISA). Highest amounts of Cry1Ab toxin were detected in T. urticae , followed by S. littoralis , and only trace amounts detected in R. padi .
4. Feeding C. carnea with T. urticae , which were shown to contain the Cry1Ab toxin, or with R. padi , which do not ingest the toxin, did not affect survival, development, or weight of C. carnea . In contrast, a significant increase in mortality and a delay in development were observed when predators were fed S. littoralis larvae reared on Bt-maize.
5. A combined interaction of poor prey quality and Cry1Ab toxin may account for the negative effects observed on C. carnea when fed S. littoralis . The relevance of these findings to the ecological risks of Bt-maize on C. carnea is discussed.     

Effects on oviposition behaviour and larval development of Spodoptera littoralis by herbivore-induced changes in cotton plants

Herbivore feeding induces chemical defence responses in plants. In this study we investigate how herbivore-induced changes in cotton plants, Gossypium hirsutum L., influence the oviposition behaviour and larval development of Spodoptera littoralis Boisd. (Lepidoptera: Noctuidae). In two-choice experiments female moths preferred to oviposit on small plants (3–4 leaves) that had been fed on by 3rd to 4th instar larvae (72%) over non-damaged control plants. However, when using larger plants (8 to 10 true leaves) the preference was reversed, with only 31% of the eggs deposited on the induced plants. The same trend was found with plants that had been given a similar level of damage by 6th instar larvae. However, the difference between the treatments was in both cases smaller with only 60% of the eggs deposited on the preferred plant treatment. If cotton plants subjected to artificial damage were compared with undamaged plants, none of the treatments were preferred for oviposition. No significant difference was found in larval weight, pupal weight, survival, or development time, between larvae reared their entire development on leaves from induced or from non-induced plants.     

Do exotic generalist predators alter host plant preference of a native willow beetle?

1 Selection can favour herbivores that choose host plants benefitting their offspring either by enhancing growth rates or by increasing larval defences against native predators. For exotic predator species that feed on herbivores, their success with invading new habitats may depend upon overcoming defences used by native prey. Whether exotic predators can alter herbivore host choice has remained unexamined. Therefore, we compared the efficacy of larval defence by Chrysomela knabi (a native beetle species) that had fed on two native willow hosts: Salix sericea (a phenolic glycoside (PG)-rich species) and Salix eriocephala (a PG-poor species), when attacked by exotic generalist predators. In addition, the preference and performance of C. knabi on S. sericea and S. eriocephala was examined.
2  Chrysomela knabi preferred and performed better on S. sericea. In a common garden, adult C. knabi were nine-fold more common and oviposited five-fold more frequently on S. sericea than on S. eriocephala . In the laboratory, adult feeding preference on leaf discs and survival rates of larvae were both greater on S. sericea , and time to pupation was shorter.
3  Chrysomela knabi larvae produced significantly more salicylaldehyde when fed S. sericea leaves than when fed S. eriocephala leaves. Additionally, those larvae with greater salicylaldehyde had reduced predation by two exotic generalist predators, Harmonia axyridis larvae and juvenile Tenodera aridifolia sinensis .
4 The results obtained in the present study suggest that selection favoured the preference of C. knabi for PG-rich willow plants because larvae grew and survived better and that selection by common exotic generalist predators would reinforce this preference.     

Interactions between above- and belowground insect herbivores as mediated by the plant defense system

Plants are frequently attacked by both above- and belowground arthropod herbivores. Nevertheless, studies rarely consider root and shoot herbivory in conjunction. Here we provide evidence that the root-feeding insect Agriotes lineatus reduces the performance of the foliage feeding insect Spodoptera exigua on cotton plants. In a bioassay, S. exigua larvae were allowed to feed on either undamaged plants, or on plants that had previously been exposed to root herbivory, foliar herbivory, or a combination of both. Previous root herbivory reduced the relative growth rates as well as the food consumption of S. exigua by more than 50% in comparison to larvae feeding on the undamaged controls. We found no effects in the opposite direction, as aboveground herbivory by S. exigua did not affect the relative growth rates of root-feeding A. lineatus . Remarkably, neither did the treatment with foliar herbivory affect the food consumption and relative growth rate of S. exigua in the bioassay. However, this treatment did result in a significant change in the distribution of S. exigua feeding. Plants that had been pre-exposed to foliar herbivory suffered significantly less damage on their young terminal leaves. While plant growth and foliar nitrogen levels were not affected by any of the treatments, we did find significant differences between treatments with respect to the level and distribution of plant defensive chemicals (terpenoids). Exposure to root herbivores resulted in an increase in terpenoid levels in both roots as well as in mature and immature foliage. Foliar damage, on the other hand, resulted in high terpenoid levels in young, terminal leaves only. Our results show that root-feeding herbivores may change the level and distribution of plant defenses aboveground. Our data suggest that the reported interactions between below- and aboveground insect herbivores are mediated by induced changes in plant secondary chemistry.     

Root herbivore identity matters in plant-mediated interactions between root and shoot herbivores

Plants are simultaneously attacked by a multitude of herbivores that affect plant responses and plant-mediated interactions in a variety of ways. So far, studies on indirect interactions between below- and aboveground herbivores have almost exclusively focused on interactions between only one root and one shoot herbivore species at the same time. Since these studies show a variety of outcomes, we test the hypothesis that root herbivore identity matters in below-/aboveground interactions. We studied the combined effects root-feeding nematodes (Pratylenchus penetrans) and wireworms (Agriotes lineatus larvae) on Plantago lanceolata and on the performance of aboveground phloem-feeding aphids (Myzus persicae) and chewing caterpillars (Chrysodeixis chalcites larvae). Since root herbivores may also affect resource availability and the microbial community in the rhizosphere, we examined resource utilization by soil microorganisms using BIOLOG EcoPlates™.

Wireworms decreased root biomass by 13%, but led to compensatory shoot growth. Nematodes and the aboveground herbivores did not affect the biomass of Plantago lanceolata. Feeding by C. chalcites larvae enhanced the concentration of aucubin in leaves, which might explain the high mortality of the caterpillars. Aphids and the belowground herbivores did not change iridoid glycoside levels in the leaves. However, the number of aphid offspring was reduced by 44% when nematodes had been added to the soil, whereas wireworms had no effect. We observed higher utilization of BIOLOG carbon sources by the soil microorganisms only in the presence of Pratylenchus penetrans. Our results suggest that the outcome of below–aboveground interactions highly depends on herbivore identity.     

Ratite and ungulate preferences for woody New Zealand plants: influence of chemical and physical traits

Ratites (ostriches Struthio camelus) and ungulates (red deer Cervus elaphus scoticus and goats Capra hircus) were presented with 14 indigenous shrubs in cafeteria-style trials. The shrubs represented the spectrum of woody plant architecture, ranging from broadleaved monopodial species through to small-leaved highly branched divaricates. Trials were stopped when almost all shoots of the plant expected to be most preferred had been consumed. There were considerable differences between the herbivores in their selection of certain plant species. Aristotelia fruticosa was avoided by deer, neutrally selected by goats, and preferred by ostriches. All herbivores strongly avoided two species, Pseudopanax crassifolius and Coprosma rugosa. Analysis of relative offtake (proportion of biomass consumed from each species, relative to total biomass consumed) showed that all three herbivores ate less of species with small leaves. Consumption by all herbivores was reduced by structural plant traits (i.e. divarication and related attributes) more than by chemical plant traits. The immediate impact of browsing on the plants, measured as the rank of proportion of shoots eaten, was broadly similar across the herbivores. The broadleaved species (e.g. Myrsine australis, Aristotelia serrata) experienced the greatest browsing, while divaricate (e.g. Coprosma rugosa) and conifer species (e.g. Podocarpus hallii) were generally least browsed. Although cafeteria-style experiments have limitations, our results for deer broadly correspond to those of field-based diet preference studies.     

Compensatory responses of Samea multiplicalis larvae when fed leaves of different fertilization levels of the aquatic weed Pistia stratiotes

Compensatory responses of caterpillars fed low quality food include increased consumption and utilization of essential nutrients. Information about an insect's responses to nutritional challenges from their host plants could benefit weed biological control efforts in the selection and establishment of new agents. The target weed, Pistia stratiotes L. (Araceae) is a floating aquatic plant that has relatively low nitrogen levels which are further diluted with high water content. Efforts to establish the insect Spodoptera pectinicornis (Hampson) (Lepidoptera: Noctuidae) for biological control of P. stratiotes could benefit by examining the nutritional responses of a similar widely established lepidopteran species, Samea multiplicalis (Guenèe) (Lepidoptera: Pyralidae). Larvae of this species were fed leaves of P. stratiotes plants that had been fertilized (NPK) at high and low rates. The leaves of the fertilized plants had a 4.3-fold increase in nitrogen (dry weight) and a 1.6-fold increase in water content. The results suggest that no compensatory increases occurred in larvae fed leaves from the low fertilized plants as no changes were found in fresh mass consumption or nitrogen utilization efficiency. Consequently, development time from second-third instars to pupation was delayed about 3 days compared with larvae fed the high nitrogen leaves. Furthermore, consumption of nitrogen was only 30% and its accumulation into larval tissues was only 60% compared with the larvae fed the high fertilized leaves. The resulting larvae had both a final biomass and a growth rate that were reduced by 40%. Regardless of plant fertilizer level, the larvae fed at a rate 5–10 times greater than that of similar lepidopteran species consuming either low or high quality diets, suggesting that the S. multiplicalis larvae may be functioning at their biological limit for ingesting food.     

A High Concentration of Glucogallin, the Common Precursor of Hydrolyzable Tannins, Does Not Deter Herbivores

The diversity of structures of plant phenolic compounds suggests that their interactions with insect herbivores may be compound specific. In this study, we modified the natural covariances observed in mature leaves of mountain birch, Betula pubescens ssp. czerepanovii (Orlova) Hämet-Ahti, by supplying gallic acid, the common precursor of gallotannins, through the stems of cut branches. Only one gallotannin, glucogallin, was consequently increased, and responses to this change on larvae of Epirrita autumnata Bkh. were evaluated by choice and nonchoice experiments. Glucogallin-increased leaves were consumed equally to control leaves in a nonchoice situation and they were preferred by E. autumnata larvae when they had to choose. No other short-term postingestive effects in E. autumnata larvae were observed and therefore our studies did not suggest a defensive role for glucogallin.     

Contrasting consequences of plant domestication for the chemical defenses of leaves and seeds in lima bean plants

Plant domestication is assumed to result in reduced levels of defensive compounds in crops, because this makes the plants more suitable for consumption by humans and livestock. We argue that this should mainly be reflected in the concentrations of defense compounds in the plant parts that are used for consumption and not necessarily for other parts of crop plants. We tested this hypothesis for domesticated lima bean (Phaseolus lunatus), by comparing its chemical defenses against a leaf herbivore, the beet armyworm (Spodoptera exigua), and a seed predator, the beetle Zabrotes subfasciatus. For seeds and leaves we determined the concentrations of cyanogenic glycosides (CNGs) in cultivated varieties and wild populations and evaluated the preference and performance of the herbivores when exposed to leaves and seeds from wild and cultivated plants. Concentrations of CNGs were significantly different between wild and cultivated plants. In the leaves the concentration of CNGs in the cultivated varieties were more than double that of the wild leaves. In contrast, seeds from cultivated plants had up to 20 times lower CNG concentration compared to seeds from the wild populations. Insect preference and performance do not parallel the chemical data. Larvae of S. exigua preferred wild leaves but had higher survival on cultivated leaves. The beetles, however, strongly preferred seeds from cultivated plants and females developed more quickly on these seeds. We conclude that domestication of P. lunatus has altered the concentration of CNGs in both the seeds and the leaves in opposite directions. This results in differential effects on the herbivores that attack these two plant structures. The contrasting effect of domestication on different plant tissues can be explained by the fact that bean plants have been specifically selected for human consumption of the seeds. Tissue-specific effects of plant domestication on plant defenses can be expected for other crops as well.     

Consumption rates and food preferences of slugs in a calcareous grassland under current and future CO<Subscript>2</Subscript> conditions

This study explored consumption of a generalist herbivore feeding on leaf tissue of various plant species of a calcareous grassland, and tested whether consumption levels and preferences changed when plants were exposed to 5 years of in situ CO₂ enrichment. The first part of this experiment tested whether the consumption patterns of slugs (Deroceras reticulatum) observed in single-species feeding tests were altered when slugs were given a choice of food sources. Overall consumption increased 270% when slugs were given a choice, and they preferred having a choice of food sources more than they preferred having any one food source. Surprisingly, slugs consumed fewer legumes and grasses and more non-leguminous forbs when given a choice. In the second part of this experiment, feeding behaviors of slugs in response to elevated CO₂ were investigated by feeding them leaves of two legumes, one grass, and a non-leguminous forb (Trifolium medium, Lotus corniculatus, Bromus erectus, and Sanguisorba minor, respectively) in two or four species combinations. In the leguminous species mix, the non-leguminous species mix, and the combined mix (legumes and non-legumes), neither overall consumption by herbivores nor species preference was significantly altered by long-term CO₂ enrichment. In the combined species mix, slugs preferred legumes to non-legumes (P=0.012) and exhibited a weak functional group preference shift from non-legumes to legumes (P=0.089) in response to CO₂ enrichment. This is the first time such a shift has been observed, and provides evidence that there may be multiple herbivore responses to rising atmospheric CO₂ concentrations. Numerous single-species feeding tests using insects have shown that consumption by herbivores may increase when herbivores are fed plants grown in enriched CO₂ atmospheres. This study clearly demonstrates the limited applicability of non-choice feeding trials to generalist herbivores in species-rich communities. Received: 19 August 1999 / Accepted: 20 April 2000