Heterogeneity of plant phenotypes caused by herbivore-specific induced responses influences the spatial distribution of herbivores

Abstract.  1. Herbivory can induce resistance in a plant and the induced phenotype may be disfavoured by subsequent herbivores. Yet, as the distance between plants in a population increases, limited mobility may make a herbivore more likely to feed and oviposit on host plants in its immediate surroundings.
2. The present study tested whether a herbivore's preference and distribution across plants with different induced phenotypes was influenced by the spatial distribution of plants. A fragmented population of Solanum dulcamara plants was created. This consisted of discrete, spatially separated patches with different histories of damage, either herbivory from adult flea beetles ( Psylliodes affinis ), tortoise beetles ( Plagiometriona clavata ), or mechanical damage. Each patch was separated by 7 m and consisted of 12 plants that were spaced 30 cm apart. Then a fixed number of adult tortoise beetles were introduced to each patch, and movement and oviposition within and between spatially separate homogeneous patches (receiving one type of damage) were compared with movement and oviposition within heterogeneous patches (containing all three types of damage) over the growing season.
3. Flea beetle and tortoise beetle herbivory consistently induced different phytochemical responses in S. dulcamara (polyphenol oxidase and peroxidase), and adult tortoise beetles avoided oviposition on the flea beetle induced plants within heterogeneous patches. However, between homogeneous patches, plant phenotype did not influence oviposition. Colonisation by naturally occurring flea beetle adults followed a similar pattern.
4. These results suggest that the heterogeneity of plant phenotypes can influence herbivore choice and distribution at small but not large spatial scales.     

Genetic variation in resistance and tolerance to insect herbivory in Salix cordata

1. This study investigated whether sand-dune willow Salix cordata , exhibits genetic variation in resistance and tolerance to herbivory.
2. A field experiment using cuttings from nine willow clones demonstrated genetic variation in resistance to the specialist herbivore Altica subplicata , as measured by beetle densities. Willow clones differed significantly in both total biomass and leaf trichome densities, and herbivore densities were marginally correlated with both of these parameters.
3. Tolerance to herbivory was measured in a greenhouse experiment by comparing growth response of plants experiencing 50% artificial defoliation and plants experiencing no defoliation. Clones showed significant differences in tolerance to herbivory for some growth measures (changes in height and number of leaves), but not for other growth measures (stem diameter growth and final biomass).
4. Despite the significant genetic variation in both resistance and tolerance, no trade-off was found between resistance and tolerance to herbivory.     

Effects of herbivory and genotype on growth and survivorship of sand-dune willow (Salix cordata)

Abstract.

• 1 The response of different clones of sand-dune willow, Salix cordata, to herbivory by a specialist herbivore, Altica subplicata, was studied in three glasshouse experiments. Plants were caged and exposed to three herbivory treatments: no beetles, low number of beetles, and high number of beetles.
• 2 Plants consistently had significantly higher growth rates in the absence of herbivory than under conditions of low or high herbivory (1.5–6 times higher).
• 3 Herbivore treatment influenced mortality from drought stress; more plants from the low and high herbivory treatments (40% and 80%) died from drought stress than did control plants (0%).
• 4 Clone genotype significantly influenced growth rates and the susceptibility of plants to drought stress. However, clones showed similar growth responses to herbivory, suggesting a lack of genetic variation in tolerance or resistance to herbivory.

     

Variation in arbuscular mycorrhizal fungi colonization modifies the expression of tolerance to above-ground defoliation

1.  Plant association with arbuscular mycorrhizal fungi (AMF) has been considered a factor increasing plant tolerance to herbivory. However, this positive effect could decrease with colonization density if the benefit : cost ratio of the AMF–plant association changes. We measured plant performance and tolerance to defoliation across a gradient of commercial AMF ( Glomus sp.) inoculum concentration.
2.  Six genetic families of Datura stramonium were grown under greenhouse conditions and subjected to five increasing levels of AMF inoculum concentration and to defoliation treatments, i.e. the presence/absence of 50% artificial damage, following a full-factorial design.
3.  AMF colonization increased linearly with inoculum concentration while foliar area, root mass, flowering phenology and seed production expressed nonlinear functions. Plant genetic variation in the benefit function of AMF colonization was also detected. We show a negative interaction between AMF concentration and plant tolerance to defoliation.
4.   Synthesis . The negative correlation between plant tolerance and AMF concentration suggests that defoliation can reduce AMF benefits and that natural variations in AMF can limit the evolution of optimum levels of tolerance. Moreover, genetic variation in the shape of the reaction norms to AMF in the presence/absence of defoliation suggests that plants may evolve in response to variation in densities of AMF and herbivores.     

Interactive effects of herbivory and sand burial on growth of a tropical dune plant, Ipomoea pes-caprae

1. This study examined the effects of insect herbivory, sand burial, and the interactive effects of these factors, on the growth of beach morning glory, Ipomoea pes-caprae, a common tropical dune plant. Levels of herbivory and sand burial were manipulated on individual shoots, and effects on stem growth, leaf production, and production of adventitious roots and axillary branches by nodes were examined.
2. Sand burial had a significant positive effect on the production of roots, but did not affect growth in stem length or leaf production.
3. Effects of herbivory were consistently negative, and persisted for 6 weeks after the herbivore damage was incurred. Stem growth rates and leaf production decreased and the production of bare nodes (with no roots or branches) and mortality of apical meristems increased.
4. Interactive effects of herbivory and sand burial influenced both leaf production and root production. In the case of root production, the effects of herbivory in decreasing the proportion of nodes that produced roots occurred only in the presence of burial. In contrast, burial masked the negative effects of herbivory on leaf production.     

Resistance and tolerance to herbivory changes with inbreeding and ontogeny in a wild gourd (Cucurbitaceae)

Herbivory is a ubiquitous component of terrestrial communities that reduces plant growth and reproduction. Consequently, a goal of evolutionary ecology is to identify the causes and consequences of variation in herbivory within plant populations. This three-year study examined the effects of inbreeding on the resistance of wild gourd plants (Cucurbita pepo subsp. texana) to herbivory by cucumber beetles and the impact of the timing of herbivory on reproduction. We grew families of inbred and outbred gourds and recorded beetle damage at three developmental stages, incidence of beetle-vectored wilt disease, survival, and reproduction. While total beetle damage significantly depressed flower and fruit production, damage until mid-July did not depress any measure of reproduction, indicating that these gourds are tolerant of moderate levels of herbivory for most of the growing season. However, beetle damage accumulating after mid-July significantly depressed reproduction, indicating that plants have reduced tolerance during peak reproduction. Early damage, however, did increase the probability of contracting a deadly wilt disease that is vectored by the beetles, suggesting that tolerance and resistance are not alternative defense strategies. Inbreeding significantly reduced resistance to herbivory and, independently of beetle damage, reproductive output. Finally, we found additive genetic variation for both resistance and tolerance that varies with ontogeny.     

Host specificity of ambrosia and bark beetles (Col., Curculionidae: Scolytinae and Platypodinae) in a New Guinea rainforest

Abstract.  1. Bark and ambrosia beetles are crucial for woody biomass decomposition in tropical forests worldwide. Despite that, quantitative data on their host specificity are scarce.
2. Bark and ambrosia beetles (Scolytinae and Platypodinae) were reared from 13 species of tropical trees representing 11 families from all major lineages of dicotyledonous plants. Standardised samples of beetle-infested twigs, branches, trunks, and roots were taken from three individuals of each tree species growing in a lowland tropical rainforest in Papua New Guinea.
3. A total of 81 742 beetles from 74 species were reared, 67 of them identified. Local species richness of bark and ambrosia beetles was estimated at 80–92 species.
4. Ambrosia beetles were broad generalists as 95% of species did not show any preference for a particular host species or clade. Similarity of ambrosia beetle communities from different tree species was not correlated with phylogenetic distances between tree species. Similarity of ambrosia beetle communities from individual conspecific trees was not higher than that from heterospecific trees and different parts of the trees hosted similar ambrosia beetle communities, as only a few species preferred particular tree parts.
5. In contrast, phloeophagous bark beetles showed strict specificity to host plant genus or family. However, this guild was poor in species (12 species) and restricted to only three plant families (Moraceae, Myristicaceae, Sapindaceae).
6. Local diversity of both bark and ambrosia beetles is not driven by the local diversity of trees in tropical forests, since ambrosia beetles display no host specificity and bark beetles are species poor and restricted to a few plant families.     

Prior flea beetle herbivory affects oviposition preference and larval performance of a potato beetle on their shared host plant

Abstract 1. The herbaceous plant Solanum carolinense (L.) (Solanaceae) is host to a number of specialist insects, including the leaf-feeding beetles Epitrix fuscula (Crotch) and Leptinotarsa juncta (Germar) (Coleoptera: Chrysomelidae). Potted individuals of S. carolinense were subjected to one of two treatments: exposure to herbivory by E. fuscula or exclusion of all herbivores. The effects of E. fuscula herbivory on larval performance and oviposition preference of L. juncta were investigated.
2. Although the masses of the L. juncta pupae did not differ between the two treatments, larvae feeding on damaged plants developed more slowly than those feeding on undamaged plants.
3. In both paired leaf choice trials and whole plant choice trials, larvae of L. juncta showed no preference for undamaged versus damaged hosts.
4. In a field transplant experiment, adult L. juncta females showed slight feeding preferences and strong oviposition preferences for undamaged plants versus plants that had been fed on by E. fuscula .
5. The results are discussed with reference to their implications for plant-mediated competition among herbivores and constraints on the evolution of plant resistance.     

The timing of induced resistance and induced susceptibility in the soybean-Mexican bean beetle system

Induced plant responses to herbivory have been demonstrated in many systems. It has been suggested that the timing of these responses may influence the impact of induced resistance on herbivore populations, and may affect the evolution of induced defenses. This study used a bioassay to characterize the time course of systemic induced responses to Mexican bean beetle herbivory in four genotypes of soybeans. The results suggest that the time course of induced responses in this system is more complex than most previous studies have indicated. Herbivory provoked both rapid induced resistance and subsequent induced susceptibility to beetle feeding. All four genotypes of soybean induced significant resistance to beetle damage (beetles preferred undamaged to damaged plants) by 3 days after damage. By 15 days after damage, this resistance had decayed (beetles showed no preference for undamaged over damaged plants), and by 20 days after damage, all four genotypes exhibited significant induced susceptibility (beetles preferred previously damaged plants over undamaged plants). The magnitude of induced resistance in each genotype correlated strongly with the magnitude of induced susceptibility in that genotype. Received: 28 September 1997 / Accepted: 1 December 1997     

Restoration Ecology of an Endangered Plant Species: Establishment of New Populations of Cirsium pitcheri

We determined the effects of shade, burial by sand, simulated herbivory, and fertilizers on the survival and growth of artificially planted population of Cirsium pitcheri—an endangered plant species of the sand dunes along Lake Huron. Sand burial experiments showed that greenhouse grown plants should optimally be transplanted into areas receiving 5 cm of sand deposition: burial at this depth maximized emergence, survivorship, and below‐ground biomass. Under field conditions, simulated herbivory of up to 50% of the plant height produced a slight increase in biomass after one year of growth. Field observations showed that when white‐tailed deer removed more than 50% of the transplant's leaf tissue, the plant died. The application of a 20:20:20 (N:P:K) water‐soluble fertilizer produced a significant increase in the dry leaf biomass, total leaf area, and total dry biomass relative to control plants. We also tested for the presence or absence of a persistent seed bank. Few seeds were recovered from soil samples collected from Pinery Provincial Park and Providence Bay. However, C. pitcheri has the ability to form a persistent seed bank under field conditions but only at soil depths of 15 cm. Cirsium pitcheri seeds are able to germinate and seedlings can emerge from a burial depth of up to 6 cm. Thus, seeds planted in open, sunny areas will probably maximize emergence, growth, and survivorship of seedlings. Populations of C. pitcheri can be restored by planting seeds at shallow depths, transplanting greenhouse‐grown plants, applying water soluble fertilizers, and protecting plants from herbivores.     

Effects of environmental context on the susceptibility of Atriplex patula to attack by herbivorous beetles

The susceptibility of plants to attack by insect herbivores often depends on local environmental conditions. This study documents variation in herbivore damage by the chrysomelid beetle Erynephala maritima to the annual forb Atriplex patula in two microhabitats within New England salt marshes: bare patches and dense matrix vegetation. Environmental conditions within bare patches differ from those within matrix vegetation in a number of ways. Bare patches are characterized by the absence of perennial grasses and rushes (matrix vegetation) and greater levels of physical stress, and are rapidly colonized by the fugitive annual, Salicornia europaea, a second host plant of these beetles. Surveys of herbivore damage across three marshes revealed that A. patula in bare patches had a greater proportion of leaves damaged by beetles than those within matrix vegetation. Presence or absence of matrix vegetation and presence or absence of S. europaea were experimentally manipulated to determine the proximate cause of this pattern. The presence of S. europaea significantly increased the susceptibility of A. patula to herbivory in experimental plots. Both the extent of herbivore damage to plants and the proportion of plants damaged through time were greater in treatments with S. europaea than in controls, regardless of the presence or absence of matrix vegetation. Plants in S. europaea addition treatments were also less likely to survive to reproduction. Decreased survival appears to result from increased herbivory, suggesting that the negative effect of S. europaea on A. patula is mediated indirectly through shared insect herbivores. These results support the hypothesis that indirect interactions between alternative host plants, mediated by insect herbivores, can be important in natural communities. Received: 9 January 1999 / Accepted: 29 April 1999     

Petal herbivory by chrysomelid beetles (Phyllotreta sp.) is detrimental to pollination and seed production in Lepidium papilliferum (Brassicaceae)

Abstract.  1. Insect herbivory directed at flowers can decrease fruit and seed production by decreasing the attractiveness of a damaged flower to potential pollinators, by disrupting the transfer of pollen between pollinators and stigmas, or both.
2. Effects of petal herbivory by a chrysomelid beetle ( Phyllotreta sp.) on pollination and seed production in Lepidium papilliferum (Brassicaceae) were examined.
3. Under natural conditions, flowers with a hole chewed in a petal produced fruit and seed at a significantly lower rate than undamaged flowers (44% vs. 80% respectively). However, when damaged and undamaged flowers were hand pollinated, there was no significant difference in fruit or seed set (84% vs. 80% respectively).
4. Petal herbivory in L. papilliferum disrupts the effectiveness of insect-mediated pollination, but it does not physically inhibit pollination or seed production.     

The evolution of plant response to herbivory: simultaneously considering resistance and tolerance in Brassica rapa

Although the evolution of plant response to herbivory can involve either resistance (a decrease in susceptibility to herbivore damage) or tolerance (a decrease in the per unit effect of herbivory on plant fitness), until recently few studies have explicitly incorporated both of these characters. Moreover, theory suggests these characters do not evolve independently, and also that the pattern of natural selection acting on resistance and tolerance depends on their costs and benefits. In a genotypic selection analysis on an experimental population of Brassica rapa (Brassicaceae) I found a complex set of correlational selection gradients acting on resistance and tolerance of damage by flea beetles (Phyllotreta cruciferae: Chrysomelidae) and weevils (Ceutorhynchus assimilis: Curculionidae), as well as directional and stabilizing selection on resistance to attack by weevils. Evolution of response to flea beetle attack is constrained by a strong allocation cost of tolerance, and this allocation cost may be caused by a complex correlation among weevil resistance, weevil tolerance, flea beetle resistance, and flea beetle tolerance. Thus, one important conclusion of this study is that ecological costs may involve complex correlations among multiple characters, and for this reason these costs may not be detectable by simple pairwise correlations between characters. The evolution of response to weevil attack is probably constrained by a series of correlations between weevil resistance, weevil tolerance, and fitness in the absence of weevil damage, and possibly by a cost of tolerance of weevil damage. However, the nature of these constraints is complicated by apparent overcompensation for weevil damage. Because damage by both flea beetles and weevils had non-linear effects on plant fitness, standard measures of tolerance were not appropriate. Thus, a second important contribution of this study is the use of the area under the curve defined by the regression of fitness on damage and damage-squared as a measure of tolerance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evidence for rapid evolutionary change in an invasive plant in response to biological control

We present evidence that populations of an invasive plant species that have become re‐associated with a specialist herbivore in the exotic range through biological control have rapidly evolved increased antiherbivore defences compared to populations not exposed to biocontrol. We grew half‐sib families of the invasive plant Lythrum salicaria sourced from 17 populations near Ottawa, Canada, that differed in their history of exposure to a biocontrol agent, the specialist beetle Neogalerucella calmariensis. In a glasshouse experiment, we manipulated larval and adult herbivory to examine whether a population's history of biocontrol influenced plant defence and growth. Plants sourced from populations with a history of biocontrol suffered lower defoliation than naïve, previously unexposed populations, strongly suggesting they had evolved higher resistance. Plants from biocontrol‐exposed populations were also larger and produced more branches in response to herbivory, regrew faster even in the absence of herbivory and were better at compensating for the impacts of herbivory on growth (i.e. they exhibited increased tolerance). Furthermore, resistance and tolerance were positively correlated among genotypes with a history of biocontrol but not among naïve genotypes. Our findings suggest that biocontrol can rapidly select for increased defences in an invasive plant and may favour a mixed defence strategy of resistance and tolerance without an obvious cost to plant vigour. Although rarely studied, such evolutionary responses in the target species have important implications for the long‐term efficacy of biocontrol programmes.     

A fungal endosymbiont affects host plant recruitment through seed- and litter-mediated mechanisms

1.  Many grass species are associated with maternally transmitted fungal endophytes. Increasing evidence shows that endophytes enhance host plant success under varied conditions, yet studies have rarely considered alternative mechanisms whereby these mutualistic symbionts may affect regeneration from seed.
2.  We performed a microcosm experiment to evaluate whether infection with Neotyphodium occultans affects recruitment in the annual grass Lolium multiflorum either directly, by infecting the seeds, or indirectly, by altering the suitability of recruitment microsites through the litter shed by host plants. Endophyte effects on establishment were tested for different litter depths and watering regimes under natural herbivory by leaf-cutting ants.
3.  Seed infection increased seedling emergence through the litter as well as final recruitment, irrespective of microsite conditions. However, litter produced by infected plants delayed emergence and decreased density of both infected and non-infected grass populations.
4.  Individual plant biomass did not change with seed infection but was increased under deep litter from endophyte-infected plants. Although seed infection did not protect establishing plants from leaf-cutting ants, herbivory was reduced in the presence of deep litter shed by infected plants.
5.  We conclude that fungal endophytes may affect host plant recruitment across subsequent generations not only by infecting the seeds but also through the host's dead remains. While the former effect entailed an advantage to infected plants, litter-mediated effects did not discriminate by infection status, and generally promoted the establishment of fewer and larger plants. Thus hidden foliar symbionts may play an underappreciated role in maintaining host species dominance through the litter produced by prior patch occupants.     

COSTS OF INDUCED RESPONSES AND TOLERANCE TO HERBIVORY IN MALE AND FEMALE FITNESS COMPONENTS OF WILD RADISH

Theory predicts that plant defensive traits are costly due to trade-offs between allocation to defense and growth and reproduction. Most previous studies of costs of plant defense focused on female fitness costs of constitutively expressed defenses. Consideration of alternative plant strategies, such as induced defenses and tolerance to herbivory, and multiple types of costs, including allocation to male reproductive function, may increase our ability to detect costs of plant defense against herbivores. In this study we measured male and female reproductive costs associated with induced responses and tolerance to herbivory in annual wild radish plants (Raphanus raphanistrum). We induced resistance in the plants by subjecting them to herbivory by Pieris rapae caterpillars. We also induced resistance in plants without leaf tissue removal using a natural chemical elicitor, jasmonic acid; in addition, we removed leaf tissue without inducing plant responses using manual clipping. Induced responses included increased concentrations of indole glucosinolates, which are putative defense compounds. Induced responses, in the absence of leaf tissue removal, reduced plant fitness when five fitness components were considered together; costs of induction were individually detected for time to first flower and number of pollen grains produced per flower. In this system, induced responses appear to impose a cost, although this cost may not have been detected had we only quantified the traditionally measured fitness components, growth and seed production. In the absence of induced responses, 50% leaf tissue removal, reduced plant fitness in three out of the five fitness components measured. Induced responses to herbivory and leaf tissue removal had additive effects on plant fitness. Although plant sibships varied greatly (49–136%) in their level of tolerance to herbivory, costs of tolerance were not detected, as we did not find a negative association between the ability to compensate for damage and plant fitness in the absence of damage. We suggest that consideration of alternative plant defense strategies and multiple costs will result in a broader understanding of the evolutionary ecology of plant defense.     

Increased Reproductive Allocation of Rumex japonicus Caused by Leaf Clipping

Abstract To elucidate the effects of herbivory by chrysomelid beetles on Rumex japonicus, rosette leaves were clipped and the subsequent fruit production and root growth were observed. The increase of leaf biomass of some clipped plants was greater than that of control plants, although this varied among individual plants. The root growth of clipped plants was less than that of control plants. Fruit production increased with plant size, and there was no difference in fruit production between clipped and control plants. Reproductive allocation (fruit biomass, relative to fruit biomass plus root growth) increased with plant size; it was greater in clipped plants than in control ones. Based on these results, reproductive allocation strategy against herbivory was discussed.     

TWO HERBIVORES AND CONSTRAINTS ON SELECTION FOR RESISTANCE IN BRASSICA RAPA

Although most plants experience herbivory by several insect species, there has been little empirical work directed toward understanding plant responses to these simultaneous selection pressures. In an experiment in which herbivory by flea beetles (Phyllotreta cruciferae) and diamondback moths (Plutella xylostella) was manipulated in a factorial design, I found that selection for resistance to these herbivores is not independent in Brassica rapa. Specifically, the effect of flea beetle damage on B. rapa fitness depends on the amount of diamondback moth damage a plant experiences: damage by these herbivores has a nonadditive effect on plant fitness. When diamondbacks are abundant, plants that sustain high levels of damage by flea beetles are favored by natural selection, but when diamondbacks are rare, a low level of damage by flea beetles is favored. However, resistance to the later-feeding diamondback moth is not affected by the presence or absence of damage by early-feeding flea beetles. Thus, there are no plant-mediated ecological interactions between these herbivores that affect the outcome of selection for resistance. Because these herbivores do not independently affect plant fitness, neither is likely to develop a pairwise coevolutionary relationship with its host. Instead, coevolution is diffuse.     

Resource regulation by a twig-girdling beetle has implications for desertification

Abstract.  1. Resource regulation by insects is the phenomenon by which herbivory enhances resources for the progeny of the herbivore. This report provides an example of resource regulation with implications for desertification in the Chihuahuan Desert of North America.
2. Female Oncideres rhodosticta beetles chew girdles around mesquite ( Prosopis glandulosa ) stems before ovipositing in those stems. The mesquite plants respond by producing compensatory stems below the girdle. Mesquite volume was significantly correlated with the total number of beetle girdles across a suite of low shrub density grassland and high shrub density dune sites, and plants in dune sites had more old and new girdles than mesquite in grasslands.
3. Smaller, younger shrubs in grassland responded more vigorously to girdling than did larger, older shrubs in dune landscapes. Stems on shrubs within grassland produced significantly more and longer compensatory stems per girdle than stems on shrubs in dunes. Soil capture by individual plants positively correlated with stem density, and stem density is increasing in the younger plants as a response to beetle damage.
4. This study suggests that the interaction between O. rhodosticta and mesquite is an example of resource regulation that increases the stem density and soil capture ability of mesquite. Because the conversion of productive grasslands to mesquite dune landscapes is one of the most important drivers of desertification in the Chihuahuan Desert, feedbacks between organisms that promote an increase in the size and soil capture ability of mesquite may exacerbate desertification.     

Variation in trichome density and resistance against a specialist insect herbivore in natural populations of Arabidopsis thaliana

Abstract.  1. The annual herb Arabidopsis thaliana is a prime model organism of plant molecular genetics, and is currently used to explore the molecular basis of resistance to herbivores. However, both the magnitude and the causes of variation in resistance among natural populations of A. thaliana are poorly known. The hypotheses (a) that resistance to a specialist herbivore, the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is positively related to the density of leaf trichomes, and (b) that oviposition preference by female moths is positively correlated to larval performance on different populations and maternal lines of the host plant were examined.
2. Variation in leaf trichome density and resistance to P. xylostella within and among six natural populations of A. thaliana in Sweden was quantified . Resistance was quantified by examining the number of eggs laid on plants exposed to ovipositing female moths and by monitoring larval development on plants of different origin.
3. Trichome density varied significantly among populations; for 4-week-old plants (exposed to ovipositing moths), it also varied significantly among maternal families within populations. The rate of oviposition varied significantly both among populations and among families within populations. This variation could partly be explained by a negative relationship between trichome density and egg number, and a positive relationship between plant size and egg number. Time to pupation, pupal mass, and time to adult eclosion did not vary among populations or maternal lines of the host plant, and offspring performance was not related to P. xylostella oviposition preference . The results indicate that A. thaliana populations may respond to selection for increased resistance to P. xylostella , and suggest that trichome production contributes to resistance against this specialist herbivore.