Glandular trichomes on perennial alfalfa affect host-selection behavior of Empoasca fabae

Selected behavior of Empoasca fabae (Harris) (Homoptera: Cicadellidae) was examined to elucidate resistance of commercially-available glandular-haired alfalfa to this key forage pest. The overall objective was to assess the effects of the glandular trichomes on the behavior of nymphs and adults. Studies of host-plant acceptance by E. fabae nymphs found first and third instars to show a higher degree of change in settling location on the glandular-haired FGplh13 alfalfa than on the nonglandular P5373 alfalfa. Nymphs also cleaned their tarsi more frequently when in contact with the glandular trichomes on FGplh13 alfalfa, and in addition a larger number of nymphs jumped/fell off the surface of FGplh13 alfalfa. The glandular trichomes on FGplh13 also impeded nymphal mobility more effectively than the nonglandular trichomes on P5373. No choice, time-course analysis of adult host-plant acceptance behavior found that adults settled less frequently on FGplh13 alfalfa with the glandular trichomes intact, than on either FGplh13 with the glandular trichomes removed, or P5373 alfalfa with the nonglandular trichomes intact or removed. Free choice, time-course analysis of adult host-preference behavior determined that at each observation, stems of the nonglandular P5373 alfalfa were preferred over FGplh13 alfalfa. Similarly, at each observation, stems of FGplh13 alfalfa with the glandular trichomes removed were preferred over FGplh13 with the glandular trichomes intact. These data provide additional evidence for the localization of a resistance factor in the glandular trichomes of FGplh13 alfalfa. An antixenotic resistance mechanism also appears to be present, which may function, in part, through a tactile avenue.     

Role of the glandular trichomes in resistance of perennial alfalfa to the potato leafhopper (Homoptera: Cicadellidae)

Experiments were performed to elucidate resistance of glandular-haired alfalfa, Medicago sativa L., to the potato leafhopper, Empoasca fabae (Harris). The primary objective was to examine the potential role of the glandular trichomes and stem lignification for imparting resistance to this pest. During free-choice foliar discoloration experiments, the resistant alfalfa clone FGplh13 expressed lower levels of injury than the susceptible P5373 after 13 d. No-choice tests performed using nymphal potato leafhoppers showed higher levels of mortality associated with the resistant glandular-haired clone FGplh13, and no nymphs survived after 48 h. Additional no-choice experiments using FGplh13 and P5373 alfalfa with the glandular and nonglandular trichomes intact or removed show that mortality of nymphs and adults decreased after removal of the glandular trichomes from FGplh13. Nymphal and adult mortality and nymphal development time did not differ on FGplh13 with the trichomes removed and P5373 with the trichomes intact or removed. Firstinstar, and possibly second-instar, potato leafhoppers were entrapped by an exudate produced by the glandular trichomes on the FGplh13 alfalfa. Stem lignification and the number of vascular bundles did not differ between FGplh13 and P5373 alfalfas. The glandular trichomes on FGplh13 alfalfa appeared to provide the major host resistance factor, with resistance to adults being chemically based and resistance to nymphs being chemically and mechanically based. To maintain levels of potato leafhopper resistance, breeders would appear to benefit by continuing to select for the expression of the glandular trichome phenotype.     

Glandular Trichomes on Alfalfa Impede Searching Behavior of the Potato Leafhopper Parasitoid

New cultivars of alfalfa, Medicago sativa L., have been released with glandular trichomes for resistance to potato leafhopper, Empoasca fabae (Harris). Yet, the impact of the glandular trichomes on the primary natural enemy of the leafhopper, Anagrus nigriventris Girault, is unknown. We compared the host searching behavior of the egg parasitoid on four alfalfa clones varying in trichome characters. Female wasps were videotaped on Ranger, a susceptible clone with relatively sparse trichomes, B14, a resistant clone with dense but nonglandular trichomes, and FG12 and FG18, two resistant clones with glandular trichomes. Although the number of leafhopper eggs per stem exposed to wasps did not significantly differ among the four clones, the frequency of foraging and total foraging time were less on the two clones with glandular trichomes than on the two clones with nonglandular trichomes. In addition, an analysis of covariance demonstrated that, although the number of ovipositional probes increased with egg density on a stem, the number of probes on stems with glandular trichomes was significantly less than that on stems without glandular trichomes. The allocation of time by wasps among drumming, probing, and grooming behaviors was similar among the clones. Wasps tended to fly off of clones with glandular trichomes more often than off of clones with nonglandular trichomes. This study suggests that cultivars with glandular trichomes may interfere with host searching by A. nigriventris.     

Developmental plasticity in birch leaves: defoliation causes a shift from glandular to nonglandular trichomes

The structures on leaf surfaces, e.g. trichomes, can act as effective antiherbivory mechanisms as chemical repellents. Structural defences usually represent constitutive resistance, but there are also a few cases of inducible morphological defences. We tested whether defoliation may induce changes in trichome production in white birch (Betula pubescens). The studied birches were either 0, 50 or 100% defoliated during the previous or current summer, and we measured the alterations in the production of glandular vs. nonglandular leaf trichomes, developmental instability (fluctuating asymmetry, FA) and leaf and shoot growth. We detected a clear shift from glandular to nonglandular leaf trichomes following previous‐year defoliation but not after current‐year defoliation. Furthermore, the density of nonglandular trichomes around the mid‐vein of leaves increased following previous‐year defoliation but decreased after current‐year defoliation. While leaf and shoot growth showed a distinct decrease in response to defoliation, FA turned out to be less sensitive. Consequently, previous‐year defoliation can induce the production of nonglandular trichomes in birch leaves. Because this response was accompanied by a reduction in glandular trichomes, the present results may suggest a trade‐off between the different trichome types of birch leaves.     

Identification of phloem sieve elements as the site of resistance to silverleaf whitefly in resistant alfalfa genotypes

Experiments were conducted to locate the plant tissue where resistance is expressed against silverleaf whitefly, Bemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae), in alfalfa, Medicago sativa L. (Fabaceae), genotypes previously shown to have high levels of resistance against this pest. Previous work demonstrated that resistance in the resistant alfalfa genotypes was expressed primarily as high first‐instar mortality; consequently this study focused on first‐instar nymphs. Examination of stylets in cleared leaf tissue indicated that first‐instar nymphs located vascular bundles with equal success on resistant and susceptible alfalfa genotypes. Furthermore, direct current electrical penetration graphs (DC‐EPG) indicated that sieve elements were penetrated and phloem ingestion behavior was initiated with equal success on resistant and susceptible genotypes. Thus, the mechanism of resistance does not reside in tissues encountered by the stylets prior to penetrating a phloem sieve element. Honeydew production (as a proxy for ingestion) was greatly reduced on two resistant genotypes compared to the two susceptible genotypes. The frequency distribution of honeydew production was bimodal, indicating that most individuals on the resistant genotypes produced little or no honeydew while some produced as much honeydew as whiteflies on the susceptible genotypes. This indicates that expression of resistance is an all‐or‐nothing phenomenon; an individual nymph either encounters resistance and cannot sustain ingestion or it does not encounter resistance and ingests just as well as on a susceptible plant. Intermediates are rare. DC‐EPGs indicate that phloem ingestion behavior is significantly reduced on two of the resistant genotypes compared to the susceptible genotypes. The primary reason for this appears to be more frequent termination of phloem ingestion behavior on at least one of the resistant genotypes. On one of the resistant genotypes, the productivity of EPG‐measured phloem ingestion behavior (honeydew produced per min of phloem ingestion behavior) was reduced compared to a susceptible control.     

Comparative morphology of the leaf epidermis in the genera Codonanthe (Martius) Hanstein and Nematanthus Schrader (Gesneriaceae)*

The leaf epidermis of 14 species ofCodonanthe and 10 species of Nematanthus has been examined. Species of Codonanthe section Codonanthe are geographically restricted to south-eastern Brazil, and are diploid. They possess multicellular-uniseriate nonglandular trichomes, glandular trichomes with a four-celled head and a short body, anisocytic stomata and lack extrafloral nectaries. Species of Codonanthe section Spathuliformae and Codonanthe subgenus Codonanthella are distributed from southern Mexico through Central America to north-western South America and are tetraploid. They possess unicellular non-glandular trichomes (except C. caribaea), glandular trichomes with a two-celled head (except C. caribaea) and a short body, anisocytic stomata and extrafloral nectaries (except C. caribaea). All Nematanthus species are distributed in south-eastern Brazil and are diploid (N=8). Six species of Nematanthus consistently have multicellular-uniseriate nonglandular trichomes, glandular trichomes with a four-celled head and a short (unicellular) or long (multicellular) body, anisocytic stomata and lack extrafloral nectaries. Four species of Nematanthus have multicellular-uniseriate non-glandular trichomes, glandular trichomes with a head of more than four cells and a short body, anisocytic and helicocytic stomata and lack extrafloral nectaries.     

Characteristic Trichomes and Indumentum Specialization in African and European Parasitic Scrophulariaceae

Trichomes and their distribution patterns have been observed in the aerial parts of plants of the genera Striga, Buchnera, Rhamphicarpa, Euphrasia, Melampyrum and Rhinanthus, using both light (LM) and scanning electron microscopy (SEM). All trichomes belong to the multicellular, uniseriate category and can be classified as glandular and nonglandular types. On nearly all organs, the two types can be observed side by side. Apart from a large group of ubiquitous trichomes, some characteristic trichome types are reported; they are restricted either to chlorophyllous organs (foliage leaves, bracts, calyx and stem) or to the corolla. In some nonglandular trichomes mineral deposits have been found. Other morphological and anatomical trichome features are discussed with regard to their possible function.     

Comparative anatomy of leaves and stems in some species of the South American genus Chrysolaena (Vernonieae,Asteraceae) and taxonomic implications

Vegetative anatomical features are poorly known in the South American genus Chrysolaena. In this study, leaves and stems of six Chrysolaena species were described and compared morphologically and anatomically using diaphanization, microtome serial sectioning and scanning electron microscopy. The species differed in leaf epidermis, type of stomata, shape of anticlinal walls of epidermal cells, trichome density, and presence or absence in stems of small air spaces in the cortical parenchyma and of druse‐shaped oxalate crystals. Furthermore, glandular trichomes and three types of non‐glandular trichomes with different number of basal cells were identified on leaves and stems. Collectively, these features proved instrumental to discriminate among the six studied species, suggesting that leaves and stems of Chrysolaena can represent a source for taxonomically useful characters. We also discuss anatomical features in relation to the environmental conditions in the species’ habitats.     

Location of resistance factors in the leaves of potato and wild tuber-bearing Solanum species to the aphid Myzus persicae

Analysis of electrically recorded feeding behaviour of aphids was combined with colony‐development tests to search for sources of resistance to Myzus persicae (Sulzer) (Homoptera: Aphididae) in tuber‐bearing Solanum species (Solanaceae), aiming at a reduction of potato leaf roll virus (PLRV) transmission. Twenty genotypes, originating from 14 gene bank accessions, representing 13 wild tuber‐bearing Solanum spp., three Solanum tuberosum L. (potato) cultivars, and one S. tuberosum breeding line, were selected. Colony‐development tests were carried out in no‐choice experiments by placing adult aphids on plants of each genotype and counting numbers of nymphs and adults on young plants after 8 and 15 days, and on flowering plants after 14 and 30 days. Large differences were observed among genotypes: some developed small colonies and others developed large ones. Also, in a few genotypes, resistance in mature plants was different for leaves of different ages; young leaves were resistant to aphids whereas old senescent leaves were susceptible. The electrical penetration graph (DC‐EPG system) technique was used to study aphid feeding behaviour on each Solanum genotype for 6 h. Electrical penetration graph (EPG) results also showed large differences among the genotypes, indicating resistance at the leaf surface and at three different levels of plant tissue (epidermis, mesophyll, and phloem). Therefore, it was concluded that different mechanisms of resistance to M. persicae exist among the genotypes analysed. EPGs recorded from aphids on Solanum berthaultii Hawkes and Solanum tarijense Hawkes with and without glandular trichomes showed that strong surface resistance can bias EPG parameters associated with resistance located in deeper tissues. Experimental evidence is presented that the resistance to aphids in the genotypes with glandular trichomes strongly depends on these morphological structures.     

Petunia hybrida PDR2 is involved in herbivore defense by controlling steroidal contents in trichomes

As a first line of defense against insect herbivores many plants store high concentrations of toxic and deterrent secondary metabolites in glandular trichomes. Plant Pleiotropic Drug Resistance (PDR)‐type ABC transporters are known secondary metabolite transporters, and several have been implicated in pathogen or herbivore defense. Here, we report on Petunia hybrida PhPDR2 as a major contributor to trichome‐related chemical defense. PhPDR2 was found to localize to the plasma membrane and be predominantly expressed in multicellular glandular trichomes of leaves and stems. Down‐regulation of PhPDR2 via RNA interference (pdr2) resulted in a markedly higher susceptibility of the transgenic plants to the generalist foliage feeder Spodoptera littoralis. Untargeted screening of pdr2 trichome metabolite contents showed a significant decrease in petuniasterone and petuniolide content, compounds, which had previously been shown to act as potent toxins against various insects. Our findings suggest that PhPDR2 plays a leading role in controlling petuniasterone levels in leaves and trichomes of petunia, thus contributing to herbivory resistance.     

Aspects of potato leafhopper (Homoptera: Cicadellidae) biology on Solanum berthaultii and other potato genotypes

Survival of nymphs and adult males and females of potato leafhopper, Empoasca fabae (Harris), on six potato (Solanum spp.) genotypes with varied levels of resistance was evaluated and related to type, density, and droplet/head size of foliar glandular trichomes. Survival was greater on Solanum tuberosum cultivars ('Allegany' and 'Elba') compared with accessions of the wild S. berthaultii (PI 473331 and PI 473334). The barrier provided by glandular trichomes may affect survival of E.fabae by restricting nymph and adult feeding. PI 473331 was the most pubescent host, bearing type A and type B trichomes and the most unsuitable host for E. fabae. Allegany possesses leaflets with low trichome densities and small gland diameter and was the most suitable host for adult E. fabae survival. Females generally had higher survival rates than males. Nymphal and adult leafhoppers differed greatly in their survival rates, particularly on S. tuberosum x S. berthaultii hybrids (Q174-2 and NY123). Interestingly, nymphs had longer (190 d) mean lethal time (LT50) than adults (31 d) when held on Q174-2, and a lower LT50 (19 d) when held on NY123 compared with adults (104 d). Starvation, dehydration, or both were likely associated with mortality of nymphs confined on PI 473331 and PI 473334. Nymphs on these accessions died at a comparable rate to those confined on a starvation treatment and more rapidly than those supplied with water only, sucrose solution or other potato genotypes. Darkened trichome exudates were observed on insects held on PI 473331 and PI 473334, consistent with previous reports that glandular trichomes of S. berthaultii contain phenolic oxidation chemistry. This study aids in the identification of the probable mechanisms of resistance to E. fabae used by S. berthaulti and its hybrids with S. tuberosum.     

Glandular trichomes and sesquiterpene lactones of Artemisia nova (Asteraceae)

The leaves of Artemisia nova Nelson are covered with a dense layer of nonglandular trichomes that obstruct the observation of glandular trichomes on the leaf surfaces. An acid-staining technique was developed that eliminates interference from the nonglandular trichomes and stains the glandular ones red, allowing them to be seen under a light microscope. Using this method it was found that these glands develop on both leaf surfaces, except over veins, and cover 21–35% of the leaf surface area at densities of 50–70 per mm². Mature glands are sac-like structure with a thin sheath or cuticle surrounding a clear transparent fluid. This fluid contains all of the sesquiterpene lactones present in the leaves, and some of the monoterpenes. These terpenoids were responsible for the red color of the glands after acid treatment.     

Micromorphological and anatomical characteristics of Salvia amplexicaulis Lam., S. jurisicii Košanin and S. ringens Sibth. & Sm. (Lamiaceae)

Abstract

In this study, we examined Salvia amplexicaulis Lam., S. jurisicii Ko?anin and S. ringens Sibth. & Sm. collected in the Republic of North Macedonia, which are for the first time subjected to detailed micromorphological and structural analysis using light and scanning electron microscopy. The nutlets and mucilage were additionally subjected to spectroscopic analysis using Raman and Attenuated Total Reflectance Fourier Transform Infrared spectroscopy. The anatomical structure of stems and leaves is described and compared. The stems, leaves and calyces bear numerous one- and multi-cellular nonglandular trichomes, and various peltate, capitate and digitiform glandular trichomes. The nutlets differ in size and shape, as well as in myxocarpy. The nutlets predominantly contained α-linolenic and linoleic acid, whereas the mucilages are primarily formed of polysaccharides. The results obtained in this study confirmed the importance of micromorphological and anatomical analysis of Salvia L. spp. plant parts, particularly trichomes and nutlets, and hence contributing to the knowledge about the variety of micromorphological characteristics within the genus Salvia L.     

Trichomes of Lycopersicon species and their hybrids: effects on pests and natural enemies

1 The cultivated tomato, Lycopersicon esculentum, is an economically important worldwide crop. Current pest management techniques rely heavily on pesticides but trichome‐based host‐plant resistance may reduce pesticide use. 2 A review of the literature is provided on trichomes of wild Lycopersicon species and the effects of trichome‐based host‐plant resistance on arthropods. Solvents have been used to remove glandular trichome exudates and the resulting dimminution of their effects quantified. Correlational approaches to assess the relationship between the different trichome types and effects on pests have also been used. 3 Most studies have focused on Lepidoptera and Hemiptera, although some work has included Coleoptera, Diptera and Acarina, and both antibiotic and antixenotic effects have been demonstrated. 4 Natural enemies are a cornerstone of international pest management and this review discusses how the compatibility of this approach with trichome‐based host‐plant resistance is uncertain because of the reported negative effects of trichomes on one dipteran, one hemipteran and several Hymenoptera. 5 For trichome‐based host‐plant resistance to be utilized as a pest management tool, trichomes of wild species need to be introgressed into the cultivated tomato. Hybrids between the cultivated tomato and the wild species Lycopersicon hirsutum f. glabratum, Lycopersicon pennellii and Lycopersicon cheesmanii f. minor have been produced and useful levels of resistance to Acarina, Diptera and Hemiptera pests have been exhibited, although these effects may be tempered by effects on natural enemies. 6 This review proposes that studies on genetic links between fruit quality and resistance, field studies to determine the compatibility of natural enemies and trichome‐based host‐plant resistance, and a strong focus on L. cheesmanii f. minor, are all priorities for further research that will help realize the potential of this natural defence mechanism in pest management.     

Trichomes of Lycopersicon species and their hybrids: effects on pests and natural enemies

1 The cultivated tomato, Lycopersicon esculentum, is an economically important worldwide crop. Current pest management techniques rely heavily on pesticides but trichome‐based host‐plant resistance may reduce pesticide use. 2 A review of the literature is provided on trichomes of wild Lycopersicon species and the effects of trichome‐based host‐plant resistance on arthropods. Solvents have been used to remove glandular trichome exudates and the resulting dimminution of their effects quantified. Correlational approaches to assess the relationship between the different trichome types and effects on pests have also been used. 3 Most studies have focused on Lepidoptera and Hemiptera, although some work has included Coleoptera, Diptera and Acarina, and both antibiotic and antixenotic effects have been demonstrated. 4 Natural enemies are a cornerstone of international pest management and this review discusses how the compatibility of this approach with trichome‐based host‐plant resistance is uncertain because of the reported negative effects of trichomes on one dipteran, one hemipteran and several Hymenoptera. 5 For trichome‐based host‐plant resistance to be utilized as a pest management tool, trichomes of wild species need to be introgressed into the cultivated tomato. Hybrids between the cultivated tomato and the wild species Lycopersicon hirsutum f. glabratum, Lycopersicon pennellii and Lycopersicon cheesmanii f. minor have been produced and useful levels of resistance to Acarina, Diptera and Hemiptera pests have been exhibited, although these effects may be tempered by effects on natural enemies. 6 This review proposes that studies on genetic links between fruit quality and resistance, field studies to determine the compatibility of natural enemies and trichome‐based host‐plant resistance, and a strong focus on L. cheesmanii f. minor, are all priorities for further research that will help realize the potential of this natural defence mechanism in pest management.     

Glandular trichomes of Solanum berthaultii and its hybrids with Solanum tuberosum affect nymphal emergence, development, and survival of Empoasca fabae (Homoptera: Cicadellidae)

The influence of foliar glandular trichomes on developmental biology of the potato leafhopper, Empoasca fabae (Harris) (Homoptera: Cicadellidae), was examined by selective removal of trichomes on resistant and susceptible potato germplasm comprising two glandular trichome-bearing genotypes (PI 473331 and PI 473334) of wild potato, Solanum berthaultii (Hawkes), two interspecific hybrids of S. berthaultii with Solanum tuberosum L. (Q174-2 and NY123), and two commercial S. tuberosum cultivars ('Elba' and 'Allegany'). Adult mortality was affected, whereas nymphal emergence was unaffected by removal of glandular trichome exudates. No nymphs were observed emerging from leaves of PI 473331 or PI 473334. Regardless of the trichome removal treatment, no nymphs completed development on PI 473331, and only a small percentage of nymphs survived to adulthood on NY123 and PI 473334. PI 473331 had the greatest frequency of adults and nymphs with trichome exudate deposition on their bodies, followed by PI 473334. Nymphs, but not adults, had exudate accumulation when caged on foliage of Q174-2. Removal of type A trichome heads and type B droplets eliminated exudate deposition. The results of these studies provide evidence that phenolic oxidation chemistry and the physical barrier imposed by trichomes of S. berthaultii are responsible for much of the observed resistance but that other factors possibly linked to the presence of trichomes aid in the expression on resistance.     

COST OF GLANDULAR TRICHOMES,A “RESISTANCE” CHARACTER IN DATURA WRIGHTII REGEL (SOLANACEAE)

Models regarding the evolution of plant resistance to herbivory often assume that the primary mechanism maintaining resistance polymorphisms is the balance between benefits of increased resistance to herbivores and costs associated with the production of a resistance character. However, rarely has it been demonstrated that genetically based resistance traits are costly. Here, we document costs associated with the production of glandular trichomes, a resistance character in Datura wrightii that is predominantly under the control of a single gene of large effect. In the absence of herbivores, plants with glandular trichomes (sticky) produced 45% fewer viable seeds than plants with nonglandular trichomes (velvety). Although both plant types flowered with similar frequency, sticky plants matured fewer capsules and fewer of their seeds germinated. The fitness difference between the types in herbivore-free conditions was not mitigated by the addition of water, a potentially limiting resource for sticky plants. Under herbivore pressure, there was no significant fitness difference between the types, although the fitness of velvety plants was still higher than that of sticky plants. This occurred even though velvety plants sustained more herbivore damage than sticky plants and were more likely to be attacked by most herbivore species present. The fitness difference between the plant types was especially reduced when herbivore-attacked plants were watered, which indicates that sticky plants may have higher tolerance for damage than velvety plants when supplied with a potentially limiting resource. Yet, the maintenance of a fitness deficit (albeit small and nonsignificant) for sticky plants when attacked by herbivores indicates no net benefit associated with the production of glandular trichomes in this first year of our study. These results add to our current understanding that herbivore resistance characters can be costly and raise the question of how this genetic polymorphism is maintained in wild populations.     

Effect of tomato genotypes with varying levels of susceptibility to Tetranychus evansi on performance and predation capacity of Phytoseiulus longipes

Tetranychus evansi Baker & Pritchard (Acari: Tetranychidae) is an invasive tomato pest in several African, American, Asian and European countries, with potential to reduce yield by up to 90%. Populations of the predaceous phytoseiid mite Phytoseiulus longipes Evans (Acari: Phytoseiidae) has been reported to have high potential for controlling T. evansi. However, tomato genotypes can potentially affect the performance of T. evansi and the predation ability of P. longipes. We evaluated the performance and predation capacity of P. longipes feeding on T. evansi nymphs on the two cultivated genotypes widely grown in Western Africa and a breeding genotype. The two commercial evaluated genotypes were Tounvi (susceptible, with few trichomes), TLCV15 (susceptible, with many trichomes), and the breeding genotype was SPJ-05–2018 (partially resistant with many glandular trichomes) selected from interspecific crossing TLCV15 and PI 13447 (highly resistant wild tomato genotype). We hypothesized that the susceptible genotype (with fewer trichomes) would be more favorable for P. longipes when compared to the susceptible or partially resistant genotypes (with a higher numbers of non-glandular or glandular trichomes). Intrinsic rate of increase (r) and predation potential (ω) of P. longipes were significantly reduced on SPJ-05–2018, possibly due to a negative effect of its glandular trichomes. Although the intrinsic rate of increase was higher on both susceptible genotypes (TLCV15 and Tounvi), predation potential was higher on TLCV15. Our results refuted the hypothesis that T. evansi-susceptible genotype with fewer trichomes would be more favorable to P. longipes.

     

Plant glandular trichomes mediate protective mutualism in a spider–plant system

1. Although several species of Peucetia (Oxyopidae) live strictly in association with plants bearing glandular trichomes worldwide, to date little is known about whether these associations are mutualistic. 2. In this study we manipulated the presence of Peucetia flava on the glandular plant Rhynchanthera dichotoma in the rainy and post‐rain season, to test the strength of its effects on leaf, bud, and flower damage and plant reproductive output. In addition, we ran independent field experiments to examine whether these sticky structures improve spider fidelity to plants. 3. Peucetia suppressed some species of foliar phytophages, but not others. Although spiders have reduced levels of leaf herbivory, this phenomenon was temporally conditional, i.e. occurred only in the post‐rain but not in the rainy season. Floral herbivory was also reduced in the presence of spiders, but these predators did not affect plant fitness components. 4. Plants that had their glandular trichomes removed retained fewer insects than those bearing such structures. Spiders remained longer on plants with glandular trichomes than on plants in which these structures had been removed. Isotopic analyses showed that spiders that fed on live and dead labelled flies adhered to the glandular hairs in similar proportions. 5. Spiders incurred no costs to the plants, but can potentially increase individual plant fitness by reducing damage to reproductive tissues. Temporal conditionality probably occurred because plant productivity exceeded herbivore consumption, thus dampening top‐down effects. Specialisation to live on glandular plants may have favoured scavenging behaviour in Peucetia, possibly an adaptation to periods of food scarcity.