Effect of leaf surface extraction on palatability of romaine lettuce to Diabrotica balteata

Abstract The leaf surface of a plant, especially its chemical components, constitutes the first line of resistance to herbivores and other pests. Our previous research indicated that ‘Valmaine’ (Val) romaine lettuce, Lactuca sativa L., was highly resistant to feeding by adult banded cucumber beetle, Diabrotica balteata LeConte, while ‘Tall Guzmaine’ (TG) was highly susceptible. We investigated the leaf surface chemistry of these two cultivars for its possible role in their resistance to D. balteata. Three solvents with different polarity (hexane, methylene chloride, and methanol) were tested to remove leaf surface chemicals, but only methylene chloride and methanol extracts were used in feeding bioassays. Adult D. balteata consumed much more of the leaf tissue of Val and TG when their surface chemicals were removed with methylene chloride, but not methanol, compared to nonextracted leaf tissue, leading us to hypothesize that methylene‐chloride extractable leaf surface chemicals may have a role in the expression of lettuce resistance. However, leaf surface chemicals extracted from Val with methylene chloride were not a deterrent to adult D. balteata when applied to palatable lima bean leaf surfaces at various concentrations in dual‐choice tests. Furthermore, the application of surface extracts from TG did not stimulate beetle feeding in similar choice tests. In a no‐choice feeding test, there was no significant difference in leaf area consumption on lima bean leaves sprayed with extracts of Val or TG. These results suggest that leaf surface chemicals in romaine lettuce do not explain the resistance of Val to adult D. balteata, and that factors inside the leaf may play a role in resistance. We discuss the possibility that the solvent may have increased the palatability of lettuce leaves to D. balteata by causing enzymatic browning and cellular damage, which is likely to have degraded internal feeding deterrents and impaired the plant's ability to emit latex.     

Geometric relationships between whitefly feeding behavior and vascular bundle arrangements

This study revealed strong evidence that nymphs of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, are obligate feeders on vascular bundles and that there are large differences between different host plants as to the availability of vascular bundles to silverleaf whitefly nymphs. The relationship between nymphs and leaf vascular bundles was studied using 1) leaf sectioning and 2) techniques of leaf clearing of intact leaves. A geometric model is presented of the feeding relationship of vascular bundle-using homopterans. The relative abundance of vascular bundles was examined in six species of host plants that varied from highly preferred to tolerably acceptable. Included in order of acceptance were cantaloupe, cotton, hibiscus, broccoli, lantana and lettuce. The length of vascular bundle per 1.0 mm² of leaf surface ranged from about 10 mm in cantaloupe to 2.8 mm in lettuce. Salivary sheaths were found to connect with vascular bundles in 100% of the intact nymphs examined by the staining and clearing technique. However only 64% of those examined by the sectioning technique appeared to be connected to vascular bundles. This indicates that the sectioning technique leads to a high rate of error, causing an underestimation of the importance of direct contact with vascular bundles. About 50% of epidermal stylet penetrations were through epidermal cells; the remaining 50% went through intercellular junctions. On cotton leaves, the distance between the point of labial contact with the leaf surface and the nearest point of the vascular bundle rarely exceeded 60 m. Our studies show that while 50% of lettuce leaf-surface was beyond 60 m of a vascular bundle, only 10% of cantaloupe leaf surface area was outside of the 60 m range. In cotton, mean distance from labium to the nearest point of the vascular bundle was 40.9 m (SEM=2.66, N=50, range 0–80 m). Over 98% of all salivary sheaths went to minor veins (78% to single-filament vascular bundles, nearly 20% to double filament bundles). Fewer than 2% went to bundles with 3 or more filaments.     

The Spatial Distribution of Alkaloids in Psychotria prunifolia (Kunth) Steyerm and Palicourea coriacea (Cham.) K. Schum Leaves Analysed by Desorption Electrospray Ionisation Mass Spectrometry Imaging

Introduction

Species of the genera Psychotria and Palicourea are sources of indole alkaloids, however, the distribution of alkaloids within the plants is not known. Analysing the spatial distribution using desorption electrospray ionisation mass spectrometry imaging (DESI‐MSI) has become attractive due to its simplicity and high selectivity compared to traditional histochemical techniques.

Objectives

To apply DESI‐MSI to visualise the alkaloid distribution on the leaf surface of Psychotria prunifolia and Palicourea coriacea and to compare the distributions with HPLC–MS and histochemical analyses.

Methodology

Based upon previous structure elucidation studies, four alkaloids targeted in this study were identified using high resolution mass spectrometry by direct infusion of plant extracts, and their distributions were imaged by DESI‐MSI via tissue imprints on a porous Teflon surface. Relative quantitation of the four alkaloids was obtained by HPLC–MS/MS analysis performed using multiple‐reaction monitoring (MRM) mode on a triple quadrupole mass spectrometer.

Results

Alkaloids showed distinct distributions on the leaf surfaces. Prunifoleine was mainly present in the midrib, while 10‐hydroxyisodeppeaninol was concentrated close to the petiole; a uniform distribution of 10‐hydroxyantirhine was observed in the whole leaf of Psychotria prunifolia. The imprinted image from the Palicourea coriacea leaf also showed a homogeneous distribution of calycanthine throughout the leaf surface.

Conclusion

Different distributions were found for three alkaloids in Psychotria prunifolia, and the distributions found by MSI were in complete accordance with HPLC–MS analysis and histochemical results. The DESI‐MSI technique was therefore demonstrated to provide reliable information about the spatial distribution of metabolites in plants. Copyright © 2017 John Wiley & Sons, Ltd.     

Ultra morphology of sensilla on the head and mouth parts of the earwig Anisolabis martima (Bonelli) (Dermaptera: Carcinophoridae)

The earwig Anisolabis maritima is a cosmopolitan insect with a worldwide distribution, omnivorous in feeding, eating the eggs of different insects. Recently recorded in Saudi Arabia as a beneficial predator on eggs and newly hatched larvae of the red palm weevil Rhyncophrous ferrugineus, scanning electron microscopy (SEM) observations revealed the presence of different kinds of receptor sensillae occurring on the head and mouth parts of A. maritime. The sensillae are the same, but differ in numbers on both sexes. The head surface bears three subtypes of trichoid sensillae, one type of ceoloconica. Labrum, labium, labial palps and maxillary palps, possess different kinds of sensillae. Three subtypes of trichoid have been identified on the labrum. The labium contained one type of tricoid and basiconic sensillae. There are great numbers and numerous sensillae cheatica differing in length distributed on the maxillary and the labial palps on all segments between other stutter spines. The last terminal segment of maxillary or labial palps bears the greatest number of the sensillae cheatica. Adult A. maritima may be introduced in the future as a beneficial predator of eggs of R. ferrugineus as a tool for integrated pest management.     

Unique features of pedicellate attachment of the upper jaw teeth in the adult gobiid fish Sicyopterus japonicus (Teleostei,Gobiidiae): Morphological and structural characteristics and development

Sicyopterus japonicus (Teleostei, Gobiidae), a hill‐stream herbivorous gobiid fish, possesses an unusual oral dentition among teleost fishes on account of its feeding habitat. By using scanning electron microscopy, light microscopy, and transmission electron microscopy, including vital staining with tetracycline, we examined the development of the attachment tissues of the upper jaw teeth in this fish. The functional teeth of S. japonicus had an asymmetrical dentine shaft. The dentine shaft attached to the underlying uniquely shaped pedicel by means of two different attachment mechanisms. At the lingual base, collagen fiber bundles connected the dentine shaft with the pedicel (hinged attachment), whereas the labial base articulated with an oval‐shaped projection of the pedicel (articulate attachment). The pedicel bases were firmly ankylosed to the crest of the thin flange of porous spongy bone on the premaxillary bone, which afforded a flange‐groove system on the labial surface of the premaxillary bone. Developmentally, the pedicel and thin flange of spongy bone were completely different mineralized attachment tissues. The pedicel had a dual origin, i.e., the dental papilla cells, which differentiated into odontoblasts that constructed the internal surface of the pedicel, and the mesenchymal cells, which differentiated into osteoblasts that formed the outer face of the pedicel. A thin flange of spongy bone was deposited on the superficial resorbed labial side of the premaxillary bone proper, and later rapid bone remodeling proceeded toward the pedicel base. These unique features of pedicellate tooth attachment for the upper jaw teeth in the adult S. japonicus are highly modified teeth for enhancing the ability of individual functional teeth to move closely over irregularities in the rock surfaces during the scraping of algae. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Leaf surface wax layers of Brassicaceae lack feeding stimulants for Phaedon cochleariae

Numerous reports have indicated that glucosinolates are important stimulants for specialist herbivores feeding on Brassicaceae, and that these metabolites might be present on the plant surface and thereby detectable by an alighting insect. We investigated the outermost layer of leaves of two species of Brassicaceae, Brassica napus L. var. ‘Martina’ and Nasturtium officinale R. Br., using two highly selective extraction methods. When the epicuticular wax layer was mechanically removed with gum arabic, no glucosinolates were detectable in the lower and upper leaf surfaces. Extracting the leaf surfaces with a threefold short rinse with chloroform/methanol/water (2 : 1 : 1 vol/vol/vol) led to varying results, depending on the light conditions under which plants had been kept in the period prior to extraction. In plants kept under light, glucosinolates were detectable in a first extraction in minor concentrations, with increasing amounts in a second and third extraction. In plants kept in darkness, glucosinolates were almost absent in the first extraction. We postulate that the polar glucosinolates are washed from the inner leaf tissue through open stomata to the outside during solvent extraction, but are not naturally present in the outermost wax layer. The response of the crucifer specialist Phaedon cochleariae (F.) (Coleoptera: Chrysomelidae) to leaf surfaces of the host plants B. napus and N. officinale and to a glucosinolate was tested. Adults preferred both the adaxial and abaxial leaf surfaces of host plants that had been treated with gum arabic in order to remove the epicuticular waxes over intact surfaces. Waxes may therefore prevent direct contact with the stimulants. Sinigrin (allyl glucosinolate) and/or surface extracts of N. officinale leaves applied on Pisum sativum leaf discs did not evoke feeding, but feeding did occur when total leaf extracts of B. napus or N. officinale were applied on this non‐host. We conclude that glucosinolates might only act as feeding stimulants for P. cochleariae in concert with compounds other than surface waxes.     

New reconstruction of <Emphasis Type="Italic">Kimberella</Emphasis>, problematic Vendian metazoan

Six groups of fossil remains of Kimberella quadrata are described. They represent the imprints of the body in different types of preservation (including the group of specimens that are elongated more than twice in comparison with the common ones) and also the feeding traces and mucus secretions. The imprint is considered to be created only by the upper side of the body. The fossil material shows that Kimberella had hard sclerites, probably of aragonite, and several teeth in its mouth. Kimberella is suggested to have “the mantle” with sclerites, wider foot, which was spread over the outer surface of the mantle, and the strong transverse and longitudinal musculature.     

Microscopic observations of a compatible host/pathogen interaction between a potential biocontrol agent (Uromyces pencanus) and its target weed (Nassella neesiana)

Uromyces pencanus is a prospective biocontrol agent for Nassella neesiana in Australia and New Zealand. The infection process of U. pencanus urediniospores in leaves of its susceptible host N. neesiana was found to be similar to that of most other rust species. A pattern against which to compare nonhost reactions in host range experiments was achieved using a modification of Bruzzese and Hasan’s whole leaf clearing and staining technique. The staining of microtome leaf sections provided supplemental information about this pathosystem.     

Importance of fungi in the diet of Gammarus pulex and Asellus aquaticus I: feeding strategies

The importance of fungi in the trophic biology of the freshwater detritivores Gammarus pulex and Asellus aquaticus was investigated. Inspection of leaves used in feeding trials indicated that whereas A. aquaticus scrapes at the leaf surface, G. pulex bites through the leaf material. Both species discriminated between fungal mycelia, fungally colonized and uncolonized leaf material but, although A. aquaticus selectively consumed fungal mycelia, G. pulex fed preferentially on leaf material. Fungi appear to be an important food source for A. aquaticus and selection of food material was positively correlated with fungal biomass. In contrast, for G. pulex, fungi appear to be more important as modifiers of leaf material. However, no significant correlations were found between food preference and any of the leaf modifications measured.     

Sensillary morphology on the rostral apex and their possible role in prey location behaviour of the carnivorous stinkbug,Eocanthecona furcellata (Wolff) (Heteroptera: Pentatomidae)

Eocanthecona furcellata (Wolff), the carnivorous heteropteran, demonstrates interesting feeding mechanisms that suggest the involvement of the antennal and labial tip sensilla. This study was conducted to identify the morphology of various sensilla present on the labial tip of this insect using scanning electron microscopy. Four morphologically different types of trichoid sensilla comprise the largest and most numerous sensilla and occur throughout the surface of the labial tip. Three new and unique types of sensilla were discovered. Long hairs with profusely branched shafts are present at the entrance of the rostral groove. An oval‐shaped peg surrounded by sensory hairs with branched shafts and a short, stout peg encircled by a group of long hair‐like sensilla was found among the sensilla population of two lobes. The morphology of the new sensilla is given and possible functions of individual receptors are suggested on morphological grounds.     

Mechanism of resistance to the spotted stalk borer,Chilo sacchariphagus,in the sugarcane cultivar R570

Resistance in sugarcane [Saccharum spec. (Poaceae)] to the spotted stalk borer, Chilo sacchariphagus (Bojer) (Lepidoptera: Pyralidae), was studied by comparing feeding behaviour on resistant cv. R570 and susceptible cv. R579. In a field survey, the feeding behaviour of C. sacchariphagus larvae was described to identify their feeding sites on the plant. In a greenhouse artificial infestation study, we compared the establishment of larvae on potted plants. In laboratory choice and no‐choice experiments, we studied the establishment of larvae on plant organs (stalk, sheath, leaf spindle). Study of the feeding behaviour showed that: (1) first to fourth instars are able to feed on stalk, sheath, and leaf spindle, (2) boring into the stalk occurs mostly in the four uppermost internodes, and (3) most young larvae bore through the abaxial surface of leaf sheaths to reach the stalk. In greenhouse experiments, we observed an early two‐fold reduction of the number of larvae on R570 plants within the first 48 h after infestation. In laboratory experiments, larval antixenosis was demonstrated at the abaxial surface of R570 leaf sheath, but was observed neither in the leaf spindle nor in the stalk. First, second, and third instars were susceptible to this antixenosis. We hypothesize that the main resistance mechanism in R570 is an early reduction of larval establishment on plants, due to antixenosis located at the abaxial surface of leaf sheaths.     

The oral apparatus of tadpoles of Rana dalmatina, Bombina variegata, Bufo bufo, and Bufo viridis (Anura)

The morphology and development of the larval oral apparatus of Rana dalmatina, Bombina variegata, Bufo bufo, and Bufo viridis are described and compared using scanning electron microscopy. The species show different arrangements of the mouthparts. The small oral apparatus of R. dalmatina larvae has three labial tooth rows on the upper labium, while there are four tooth rows on the lower labium with a medial gap in row proximal to the mouth. The margins of the oral apparatus are defined by papillae that encircle the lower labium. B. variegata tadpoles have two upper labial tooth rows and three lower labial tooth rows that are uninterrupted, unlike the ones of R. dalmatina. The mouth is encircled by papillae that are larger than those of R. dalmatina. The oral discs of tadpoles of both B. bufo and B. viridis are similar. They are defined by two upper labial tooth rows (the second of which is interrupted by a medial gap) and by three lower tooth rows that differ in lengths in the two Bufo species. Both species develop papillae on the mouth angles and in two rows on the upper labium. Some morphological differences among the oral discs of R. dalmatina, B. variegata, B. bufo, and B. viridis tadpoles can be attributed to phylogenetic differences, but most can be related to their varying feeding habits and/or to their dietary specializations.     

Role of bone marrow imprints in haematological diagnosis: a detailed study of 3781 cases

X. Gong, X. Lu, X. Wu, R. Xu, Q. Tang, G. Xu, L. Wang, X. Zhang and X. Zhao Role of bone marrow imprints in haematological diagnosis: a detailed study of 3781 cases Objectives: To explore the role of imprints in routine bone marrow (BM) diagnosis. Methods: The cellularity and diagnostic accuracy of BM imprints, aspirate smears and trephine biopsy sections from 3781 patients were assessed using routine cytochemical staining. Seventy‐nine cases of lymphoma and 114 cases of plasma cell myeloma (PCM) were selected for correlation analysis of tumour cell infiltration patterns. Another 21 cases of lymphoma were selected to detect t(14;18)(q32;q21) and t(11;14)(q13;q32) by fluorescent in situ hybridization (FISH) on BM imprints, and the G‐banding technique was performed for comparison. Results: BM imprints were better than smears for evaluating cellularity. In the BM imprint group, diagnostic accuracy for metastatic carcinoma, myeloproliferative neoplasm, myelodysplastic/myeloproliferative neoplasm and PCM was better than in the smear group, while accuracy for megaloblastic anaemia, acute myeloid leukaemia, refractory cytopenia with unilineage or multilineage dysplasia, refractory anaemia with excess blasts and lymphoplasmacytic lymphoma was higher than in the section group, but not statistically different from the smear group. Good correlation of infiltration patterns of lymphoma and myeloma cells was found between BM imprints and sections (r = 0.90 and 0.78, respectively). Detection of t(11;14)(q13;q32) by FISH on imprints was higher than G‐banding analysis. Conclusions: BM imprints show features of both smears and trephine sections. Imprints are superior to smears for evaluation of cellularity, and are also better than sections for analysis of cytological changes. In addition, FISH on BM imprints markedly improves the identification of chromosomal abnormalities.     

Quantification of plant surface metabolites by matrix‐assisted laser desorption–ionization mass spectrometry imaging: glucosinolates on Arabidopsis thaliana leaves

The localization of metabolites on plant surfaces has been problematic because of the limitations of current methodologies. Attempts to localize glucosinolates, the sulfur‐rich defense compounds of the order Brassicales, on leaf surfaces have given many contradictory results depending on the method employed. Here we developed a matrix‐assisted laser desorption–ionization (MALDI) mass spectrometry protocol to detect surface glucosinolates on Arabidopsis thaliana leaves by applying the MALDI matrix through sublimation. Quantification was accomplished by spotting glucosinolate standards directly on the leaf surface. The A. thaliana leaf surface was found to contain approximately 15 nmol of total glucosinolate per leaf with about 50 pmol mm^?2 on abaxial (bottom) surfaces and 15–30 times less on adaxial (top) surfaces. Of the major compounds detected, 4‐methylsulfinylbutylglucosinolate, indol‐3‐ylmethylglucosinolate, and 8‐methylsulfinyloctylglucosinolate were also major components of the leaf interior, but the second most abundant glucosinolate on the surface, 4‐methylthiobutylglucosinolate, was only a trace component of the interior. Distribution on the surface was relatively uniform in contrast to the interior, where glucosinolates were distributed more abundantly in the midrib and periphery than the rest of the leaf. These results were confirmed by two other mass spectrometry‐based techniques, laser ablation electrospray ionization and liquid extraction surface analysis. The concentrations of glucosinolates on A. thaliana leaf surfaces were found to be sufficient to attract the specialist feeding lepidopterans Plutella xylostella and Pieris rapae for oviposition. The methods employed here should be easily applied to other plant species and metabolites.     

Anatomy of the feeding apparatus of the nurse shark,Ginglymostoma cirratum

The anatomy of the feeding apparatus of the nurse shark, Ginglymostoma cirratum, was investigated by gross dissection and computer axial tomography. The labial cartilages, jaws, jaw suspension, muscles, and ligaments of the head are described. Palatoquadrate cartilages articulate with the chondrocranium caudally by short, laterally projecting hyomandibulae and rostrally by ethmoorbital articulations. Short orbital processes of the palatoquadrates are joined to the ethmoid region of the chondrocranium by short, thin ethmopalatine ligaments. In addition, various ligaments, muscles, and the integument contribute to the suspension of the jaws. When the mouth is closed and the palatoquadrate retracted, the palatine process of the palatoquadrate is braced against the ventral surface of the nasal capsule and the ascending process of the palatoquadrate is in contact with the rostrodorsal end of the suborbital shelf. When the mandible is depressed and the palatoquadrate protrudes slightly rostroventrally, the palatoquadrate moves away from the chondrocranium. A dual articulation of the quadratomandibular joint restricts lateral movement between the mandible and the palatoquadrate. The vertically oriented preorbitalis muscle spans the gape and is hypothesized to contribute to the generation of powerful crushing forces for its hard prey. The attachment of the preorbitalis to the prominent labial cartilages is also hypothesized to assist in the retraction of the labial cartilages during jaw closure. Separate levator palatoquadrati and spiracularis muscles, which are longitudinally oriented and attach the chondrocranium to the palatoquadrate, are hypothesized to assist in the retraction of the palatoquadrate during the recovery phase of feeding kinematics. Morphological specializations for suction feeding that contribute to large subambient suction pressures include hypertrophied coracohyoideus and coracobranchiales muscles to depress the hyoid and branchial arches, a small oral aperture with well‐developed labial cartilages that occlude the gape laterally, and small teeth. J. Morphol. 241:33–60, 1999. © 1999 Wiley‐Liss, Inc.     

Distribution of the black pecan aphid,Melanocallis caryaefoliae,on the upper and lower surface of pecan foliage

Three aphid species regularly feed on pecan [Carya illinoinensis (Wangenh.) K. Koch (Juglandaceae)] foliage: the black pecan aphid, Melanocallis caryaefoliae (Davis), the yellow pecan aphid, Monelliopsis pecanis Bissell, and the blackmargined aphid, Monellia caryella (Fitch) (all Hemiptera: Aphididae). Adults of M. caryaefoliae and both the nymphs and adults of M. pecanis and M. caryella mainly feed on the lower surface of leaves. Nymphs of M. caryaefoliae appear unique by frequently feeding on the upper surface of pecan leaves. This is risky behavior given the environmental hazards (e.g., rain, solar radiation, and dislodgement) associated with the upper surface. Thus, we determined the leaf surface distribution of M. caryaefoliae on trees in an orchard and on pecan seedlings in the laboratory. A pecan orchard survey found all three aphid species and stages predominantly on the lower leaf surface, except for the nymphs of M. caryaefoliae, which were evenly distributed between upper and lower leaf surfaces. This survey also found aphidophagous lacewing (Neuroptera) larvae predominantly on the lower leaf surface, whereas ladybird beetle (Coleoptera: Coccinellidae) larvae were more evenly distributed between upper and lower surfaces. Laboratory experiments using single or multiple pecan aphid species revealed M. caryaefoliae distribution on pecan seedlings similar to orchard data. Nymphal M. caryaefoliae require nearly 2 days to elicit chlorotic feeding lesions on leaves; without these lesions, nymphal development is hindered. The similar distribution of nymphs of M. caryaefoliae on both leaf surfaces likely reflects a strategy of predator avoidance allowing a proportion of the population to survive.     

Ultrastructure of sensory receptors on the labium of the cassava mealybug,Phenacoccus manihoti Matile Ferrero

The ultrastructure of the sensory receptors located on the labium of the cassava mealybugPhenacoccus manihoti Matile-Ferrero (Homoptera, Pseudococcidae) was studied with scanning and transmission electron microscopes. Trichoid hairs of probable mechanoreceptive function are distributed over the labium. Uniporous chemosensilla which possess a mechanoreceptive dendrite, multiporous chemosensilla and mechanoreceptive pegs are present on the tip of the labium. The presence of contact and olfactory chemoreceptors on the labial tip ofP. manihoti suggests that tapping it on the cassava leaf provides the pest with information about the chemical nature of the leaf surface. ORSTOM     

The shredding activity of gammarids facilitates the processing of organic matter by the subterranean amphipod Niphargus rhenorhodanensis

1. The functional feeding group approach has been widely used to describe the community structure of benthic invertebrates in relation to organic matter resources. Based on this functional framework, positive interactions between feeding groups (especially shredders and collector‐gatherers) were postulated in the River Continuum Concept. However, relationships with organic matter have been poorly documented for invertebrates living in the hyporheic zone. 2. We hypothesised that the common subterranean amphipod Niphargus rhenorhodanensis would feed on fine particulate organic matter (FPOM), which is more abundant than coarse particulate organic matter (CPOM) in hyporheic habitats, and should be favoured by the occurrence of shredders that produce FPOM from CPOM. 3. We used laboratory experiments to quantify leaf litter processing by N. rhenorhodanensis and a common shredder, the surface amphipod Gammarus roeselii. We estimated rates of feeding and assimilation (using nitrogen stable isotopes) of the two species separately and together to reveal any potential shredder–collector facilitation between them. 4. Measured leaf litter mass loss showed that N. rhenorhodanensis did not act as a shredder, unlike G. roeselii. Organic matter dynamics and ¹⁵N/¹⁴N ratios in tissues of niphargids indicated that N. rhenorhodanensis was a collector‐gatherer feeding preferentially on FPOM. We also found a positive influence of the gammarid shredders on the assimilation rate of N. rhenorhodanensis, which fed on FPOM produced by the shredders, supporting the hypothesis of a positive interaction between surface shredders and hyporheic collector‐gatherers.     

Feeding damage by larvae of the mustard leaf beetle deters conspecific females from oviposition and feeding

Herbivorous insects may be informed about the presence of competitors on the same host plant by a variety of cues. These cues can derive from either the competitor itself or the damaged plant. In the mustard leaf beetle Phaedon cochleariae (Coleoptera, Chrysomelidae), adults are known to be deterred from feeding and oviposition by the exocrine glandular secretion of conspecific co-occurring larvae. We hypothesised that the exocrine larval secretion released by feeding larvae may adsorb to the surface of Chinese cabbage leaves, and thus, convey the information about their former or actual presence. Further experiments tested the influence of leaves damaged by conspecific larvae, mechanically damaged leaves, larval frass and regurgitant on the oviposition and feeding behaviour of P. cochleariae. Finally, the effect of previous conspecific herbivory on larval development and larval host selection was assessed. Our results show that (epi)chrysomelidial, the major component of the exocrine secretion from P. cochleariae larvae, was detectable by GC-MS in surface extracts from leaves upon which larvae had fed. However, leaves exposed to volatiles of the larval secretion were not avoided by female P. cochleariae for feeding or oviposition. Thus, we conclude that secretion volatiles did not adsorb in sufficient amounts on the leaf surface to display deterrent activity towards adults. By contrast, gravid females avoided to feed and lay their eggs on leaves damaged by second-instar larvae for three days when compared to undamaged leaves. Mechanical damage of leaves and treatment of artificially damaged leaves with larval frass or regurgitant did not affect oviposition and feeding of P. cochleariae. Since no adverse effects of previous herbivory on larval development were detected, we suggest that female P. cochleariae avoid Chinese cabbage leaves damaged by feeding larvae for other reasons than escape from competition or avoidance of direct negative effects that result from consuming induced plant material.