Host Plant Organs Research Articles

Evolution of secondary metabolites, morphological structures and associated gene expression patterns in galls induced by four closely related aphid species on a host plant species.

Gall-forming insects induce various types of galls on their host plants by altering gene expression in host plant organs, and recent studies have been conducted for gene expression in galls. However, the evolutionary trajectories of gene expression patterns and the resulting phenotypes have not yet been studied using multiple related species. We investigated the speciation and the diversification process of galls induced by four closely related aphid species (Hormaphidini) on a host plant species (Hamamelis japonica) by examining the phylogenetic congruence between the geographical divergences of aphids and the host plant, and by comparing their gene expression patterns and resulting phenotypes. Phylogenetic analysis of aphids and the host plant showed that geographical isolation among host plant populations has interrupted gene flow in aphids and accelerated the speciation process. The concentration of phenolics and the complexity of the internal structure of galls were correlated with the expression levels of genes for the biosynthesis of phenolics and morphogenesis respectively. These results suggest that the expression levels of genes for the biosynthesis of phenolics and morphogenesis have evolutionarily increased in galls accelerated by the speciation process of aphids due to the distribution change of the host plant, leading to the related phenotypic evolution. Our study showed the evolutionary process of phenotypic traits in galls in the wild from both gene expression and actual phenotype levels.

Tandemly expanded OR17b in Himalaya ghost moth facilitates larval food allocation via olfactory reception of plant-derived tricosane

Herbivorous insects utilize intricate olfactory mechanisms to locate food plants. The chemical communication of insect-plant in primitive lineage offers insights into evolutionary milestones of divergent olfactory modalities. Here, we focus on a system endemic to the Qinghai-Tibetan Plateau to unravel the chemical and molecular basis of food preference in ancestral Lepidoptera. We conducted volatile profiling, neural electrophysiology, and chemotaxis assays with a panel of host plant organs to identify attractants for Himalaya ghost moth Thitarodes xiaojinensis larvae, the primitive host of medicinal Ophiocordyceps sinensis fungus. Using a DREAM approach based on odorant induced transcriptomes and subsequent deorphanization tests, we elucidated the odorant receptors responsible for coding bioactive volatiles. Contrary to allocation signals in most plant-feeding insects, T. xiaojinensis larvae utilize tricosane from the bulbil as the main attractant for locating native host plant. We deorphanized a TxiaOR17b, an indispensable odorant receptor resulting from tandem duplication of OR17, for transducing olfactory signals in response to tricosane. The discovery of this ligand-receptor pair suggests a survival strategy based on food location via olfaction in ancestral Lepidoptera, which synchronizes both plant asexual reproduction and peak hatch periods of insect larvae.

Genotype and organ effect on the occupancy of phyllosphere prokaryotes in different rice landraces.

Bacteria community provides essential ecological services to rice plants. The bacterial diversity of rice varies across host plant genotype and organs. This study employed 16S rDNA amplicon sequencing to characterise the bacterial community associated with three rice landraces using leaf blade and stem samples. The prokaryotic community found in these rice landraces comprised of two kingdoms, 12 phyla, 25 classes, 40 orders, 80 families, and 118 genera. Proteobacteria (53.9%) was the most abundant phylum. The most abundant genus was an undefined genus under Cyanobacteria (33.0%). Homogeneity of prokaryotic community was observed across the three rice landraces, which may suggest a high similarity in biological and genetical properties of the rice landraces. The difference in prokaryotic composition between leaf blade and stem was depicted based on principal coordinate analysis. This study observed that the prokaryotic inhabitants in rice plants is predominantly determined by rice plant organs.

Complex meristematic activity induced by Eucecidoses minutanus on Schinus engleri turns shoots into galls.

Gall-inducing organisms change the development of their host plant organs, resulting in ontogenetic patterns not observed in the non-galled plants. Distinct taxa induce galls on Schinus spp., manipulating meristematic patterns in the host plant in distinct ways. Here we report ontogenetic novelties induced in the lateral buds of S. engleri by Eucecidoses minutanus, a Cecidosidae, whose galls have been poorly understood. The anatomy, histochemistry, and histometry of galls in distinct phases of development, non-galled buds, and stems of Schinus engleri were analyzed in parallel with the instars of E. minutanus to detail the morphogenetic changes in the host with each larval stage. Ontogenetic phases of the galls were intricately associated with larval development. First and second-instar larvae induced pericycle and pith cells to dedifferentiate into the gall inner meristem, where hyperplasia and cell hypertrophy characterized the growth and development phase of the gall. The innermost layers were lipid-rich nutritive cells that lined the larval chamber. Additional vascular bundle rows were produced in young galls. Third and fourth instar-larvae were associated with the gall maturation phase: centripetal lignification of the outer parenchyma cell layers, epidermal stratification, and activation of a cambium-like meristem (CLM). The CLM activity resulted in new layers of nutritive cells that differentiated inward as the first layers of nutritive cells were consumed by E. minutanus larvae, and, also, in more parenchyma cell layers that formed outward. All tissues between the innermost layer of nutritive tissue that surround the gall chamber and the outermost layer of the dermal system that externally covers the gall form the gall wall, and increased in thickness until the end of gall maturation. E. minutanus induces a structurally complex globoid stem gall, modifying all host plant tissues and stimulating a novel meristematic pattern in S. engleri. The gall developmental stages are each related to specific gall-inducing instars, as gall development progresses according to the development of E. minutanus.

Allelopathic potential of the extracts of non-galled stems and globoid stem galls of Eremanthus erythropappus (DC) McLeish (Asteraceae)

Eremanthus erythropappus (DC) McLeisch (Asteraceae), commonly known as “candeia”, is a native species of Minas Gerais state, Brazil, frequently used in medicine as an anti-inflammatory and antimicrobial agent. Eremanthus erythropappus hosts six different gall morphotypes, whose associated inducers manipulate plant cells and tissues and stimulate the neo-synthesis, maintenance, or inhibition of both primary and secondary metabolites on their host plant organs. Based on the premise that galls can potentialize the chemical composition of their associated host plants, our study investigated the allelopathic potential of methanolic extracts of E. erythropappus non-galled stems and globoid stem galls on Lactuca sativa seeds. We also studied the anatomical alterations induced on lettuce plantlets submitted to the methanolic extracts to describe diagnostic features related to the allelopathic effect. Five pentacyclic triterpenes constituted the major class of the identified compounds, followed by volatile oils, alkane hydrocarbons, alkanes, and ketones. The germination rates were statistically different between the treatments, and among the treatments, and the controls (water and methanol). The pentacyclic triterpenes of the extracts of the non-galled stems and the stem galls have a powerful allelopathic effect on the germination of L. sativa; a higher effect than that of the sesquiterpenes of the essential oils previously described for the leaf chemical compounds. The galling Neolasioptera sp. activity on E. erythropappus stems elicited the synthesis and accumulation of new chemical compounds, two triterpenes (ɤ-taraxasterol, and β-amyrone) and one alkane (tricosane), and inhibited the synthesis of compounds previously related to extracts of E. erythropappus stems, i.e., two triterpenes (A-neooleana-3(5),12-diene, and lupenone) and one ketone (2(1H)naphthalenone). These extracts altered the differentiation of root parenchyma cells of L. sativa germinated plantlets, but our premise was not corroborated as the galling activity did not potentialize the allelopathic effects.

Inherent tolerance of Colletotrichum gloeosporioides to fludioxonil

Colletotrichum spp. cause devastating diseases in agricultural crops, including fruit crops. They can differ in host plant and plant organ specificity and even in fungicide sensitivity. In strawberry, members of the C. gloeosporioides species complex (referred to as C. gloeosporioides) primarily cause crown rot and those of the C. acutatum species complex (referred to as C. acutatum) primarily cause fruit rot. Fludioxonil is registered for use (in combination with cyprodinil; Switch 62.5WG in the US) in strawberry against anthracnose disease caused by Colletotrichum spp. In this study we examined the sensitivity of C. gloeosporioides (C. fructicola and C. siamense) and C. acutatum (C. nymphaeae and C. fioriniae) isolates from different hosts and different geographical locations in the US to fludioxonil and examined possible mechanisms of inherent fungicide tolerance. The dose response to fludioxonil of C. gloeosporioides isolates (including 4 isolates of C. theobromicola) revealed about 70% inhibition of mycelial growth at 1 mg/L that was maintained at 10 mg/L and 100 mg/L and lead to minimum inhibitory concentration (MIC) values >100 mg/L. In contrast, mycelial growth of C. acutatum isolates was completely inhibited at 1 mg/L. C. gloeosporioides isolates were also significantly less sensitive to iprodione. An investigation into possible mechanisms of C. gloeosporioides isolates tolerance to fludioxonil and iprodione revealed no evidence of OS-1 gene involvement. Isolates of both species complexes were equally sensitive to salt stress based on mycelial growth inhibition on potato dextrose agar amended with 2%, 4%, and 6% NaCl. In addition, orthologous amino acid alterations in OS-1 previously linked to fludioxonil resistance in Botrytis cinerea were not found in C. gloeosporioides or C. acutatum isolates. This study also showed limited in vitro inhibitory activity of cyprodinil against isolates of both species complexes (MIC values >100 mg/L) and unveils a potential weakness of the fludioxonil+cyprodinil premixture marketed as Switch 62.5WG against C. gloeosporioides species complexes.

The influence of gall position over xylem features in leaflets of Inga ingoides (Rich.) Willd. (Fabaceae: Caesalpinioideae)

The origin of xylem cells, intracellular variation, and gall position relative to the host plant organ are related to mechanisms that positively compensate hydraulic conductivity in galls. Gall position in its host organ may be determinant for the new patterns of xylem differentiation. Leaf galls may be attached to the host leaf by a peduncle, as the extralaminar galls, or may develop in a morphological continuum with their host organ, as the intralaminar galls. Due to these two distinct positions and the related patterns of cell differentiation, gall vascular cells and tissues may vary in area and size, which were investigated in the structural features of the vessel elements in galls and in their connections with their host leaflets in three gall morphotypes associated to Inga ingoides. Also, as phytohormones orchestrate the differentiation of vascular cells, the sites of accumulation of auxins and cytokinins were detected by histochemical techniques. Besides aspects of cell differentiation, cytometric and histometric xylem features, as well as the relative water content were evaluated looking for compensatory mechanisms related to hydraulic status of the galls and the gall constriction hypothesis. The detection of auxins was related with the differentiation of new vascular cells. The origin of xylem cells, intracellular variation, and gall position relative to the host plant organ are related to mechanisms that positively compensate the hydraulic conductivity in galls. Extralaminar galls develop as appendages of adventitious origin, which theoretically imply in rupture with the host leaf ontogenetical pattern. Based on the fact that gall position influences xylem cell features, the gall-constriction hypothesis was revisited with leaflet galls as models of study, but was corroborated just for the intralaminar galls.

Hemicelluloses and associated compounds determine gall functional traits.

The intriguing questions concerning gall development refer to the processes of the remodelling of the host plant organ. Such processes involve the restructuring of cell walls and can be influenced by phenolics, indole-3-acetic acid (IAA) and reactive oxygen species (ROS). Alterations in cell walls demand the interference in the coupling of cellulose fibrils and hemicelluloses (xyloglucans) at specific stages of gall development. In addition to cell wall remodelling, hemicelluloses, such as the, xyloglucans and heteromannans can act as reserve carbohydrates, while xylans provide rigidity to the secondary cell walls. Developmental traits of the lenticular, fusiform and globoid galls on Inga ingoides (Fabaceae) were analysed using anatomical, cytometric, histochemical and immunocytochemical tools. Phenolics, IAA and ROS accumulated in similar gall tissue compartments, and may have influenced the restructuring of hemicelluloses and pectins. Contrary to expectations, cell wall flexibility regarding the dynamics of xyloglucans and cellulose fibrils does not relate to a temporal scale. The detection of xyloglucans in nutritive cell walls relate to carbohydrate nutritional resources to the galling insect, while xylans were associated to the lignified cell walls. Heteromanans were not detected, either in non-galled or galled tissues. The patterns of cell expansion during gall development relied on the relationship among phenolics, ROS and IAA with the hemicelluloses (xyloglucans and xylans) and cellulose fibrils. Although cell wall dynamics is specific to each gall morphotype in I. ingoides, the xyloglucans function as carbohydrate reserve to the gall inducers, which constitutes a functional trait common to the three morphotypes.

Characterization and comprehensive analysis of the ecological interaction networks of bacterial communities in Paullinia cupana var. sorbilis by 16S rRNA gene metabarcoding.

Endophytes improve the host performance in areas of high plant endemicity. Paullinia cupana is an Amazonia plant species of economic and social importance due to the high caffeine concentration in its seeds. An interesting strategy to identify endophytic microorganisms with potential biotechnological application is to understand the factors that influence the endophytic community to rationalize the host management programs. We used the next-generation sequencing for bacterial 16S rRNA gene to examine how the P. cupana organ, genotype, and geographic location influenced its endophytic bacterial community. We obtained 1520 operational taxonomic units (OTUs) distributed in 19 phyla, 32 classes, 79 orders, 114 families and 174 genera. The P. cupana roots and leaves were specifically colonized by the bacterial genera Acidothermus and Porphyromonas, respectively, with high relative frequency. The plant organ type influenced the endophytic community's richness, diversity, OTUs composition, relative abundance of phyla and genera, and genera interaction network. However, the host plant genotype and geographic location influenced the composition and interaction among genera in the network analysis. Prevotella is a super-generalist genus in the interaction network of endophytic bacteria of P. cupana. This study revealed endophytic bacterial groups of importance to P. cupana and stressed that the host plant organ modulates the structure and interactions within this community. Our results indicated that the microbial community adapted to colonize P. cupana by adjusting to its composition and interaction network. The isolation of abundant and super-generalist bacterial genera shall help to examine their functionality to the composition and fitness of the endophytic community of P. cupana.

Feeding and Other Gall Facets: Patterns and Determinants in Gall Structure

Galls are neoformed structures induced by specific animals, fungi, bacteria, virus or some parasitic plants on their host plant organs. Developmental processes are well known in Agrobacterium tumefasciens galls, but the animal-induced galls have a striking anatomical diversity, concerning several patterns, which were reunited herein. Anatomical traits observed in animal-induced galls involve manipulation of plant morphogenesis in convergent ways. Nematode, mite and insect galls usually contain homogeneous storage parenchyma and develop due to hyperplasia and cell hypertrophy. The development of typical nutritive tissues, giant cells, or hypertrophied vascular bundles may occur. Some other anatomical features may be usually restricted to galls induced by specific taxa, but they may eventually be related to the developmental potentialities of the host plants. The combination of distinct morphogenetic peculiarities in each gall system culminates in extant gall structural diversity. Convergent anatomical traits are observed according to the feeding mode of the gall inducers, representing potentiation or inhibition of similar events of host plant morphogenesis and cell redifferentiation, independent of gall-inducing taxa.

Volatiles from Maruca vitrata (Lepidoptera, Crambidae) host plants influence olfactory responses of the parasitoid Therophilus javanus (Hymenoptera, Braconidae, Agathidinae)

Plants damaged by herbivores are known to release odors attracting parasitoids. However, there is currently no information how leguminous plants damaged by the pod borer Maruca vitrata attract the exotic larval parasitoid Therophilus javanus, which was imported into Benin from the putative area of origin of the pod borer in tropical Asia for assessing its potential as a biological control agent. In this study, we used Y-tube olfactometer bioassays to investigate T. javanus response towards odors emitted by four M. vitrata-damaged host plants: cowpea Vigna unguiculata, the most important cultivated host, and the naturally occurring legumes Lonchocarpus sericeus, Sesbania rostrata and Tephrosia platycarpa. Olfactory attraction of T. javanus was influenced by the species of plant damaged by the pod borer. Moreover, odors released from M. vitrata-infested host plant organs (flowers and pods) were discriminated over non-infested organs in cowpea and T. platycarpa, respectively. These results are discussed in the context of the possible impact of M. vitrata host plants on T. javanus foraging activity and subsequent establishment in natural environments following experimental releases.

Factors influencing the morphogenesis of galls induced byCalophya mammifex(Calophyidae) onSchinus polygama(Anacardiaceae) leaves

Environment, plant, and gall-inducing insect genotypes are key factors in determining the morphogenesis of galls. However, the exact roles of these factors have not been clarified. We used anatomical and histochemical methods to evaluate the determining factors in the final structure of galls induced by Calophya mammifex on leaves of Schinus polygama (Cav.) Cabrera under the Mediterranean climate conditions of southern Chile. Also, we compared mature galls with those induced by the congeneric Calophya rubra on the same host plant. Calophya mammifex develops a univoltine life cycle and a diapause period in the Mediterranean climate conditions of southern Chile. Morphogenetic and histochemical leaf patterns were altered by C. mammifex feeding activity. For the first time, two specialized tissue compartments, a nutritive-like tissue and a common storage tissue, are reported for Calophyidae-induced galls in the Mediterranean region of southern Chile. Galls induced by C. mammifex and C. rubra have sufficient anatomical and histochemical alterations to be diagnosed as complex structures, whose distinction in vascular system differentiation implies structural constraints imposed by host plant organs.

Structural, histochemical and photosynthetic profiles of galls induced by Eugeniamyia dispar (Diptera, Cecidomyiidae) on the leaves of Eugenia uniflora (Myrtaceae)

Gall-inducing insects manipulate the structural, histochemical and physiological profiles of host-plant tissues to develop galls. We evaluated galls induced by Eugeniamyia dispar on the leaves of Eugenia uniflora in an attempt to answer the following questions: (i) How does this gall-inducing insect change the structural and histochemical profiles of the host-plant organ? (ii) Despite structural changes, can gall tissues maintain photosynthetic activity? Starch, proteins, reducing sugars and reactive oxygen species were detected mainly in the nutritive tissue surrounding the larval chamber. Despite structural changes, the galls induced by E. dispar on E. uniflora retain chlorophyllous tissue, although its amount and photosynthetic activity are less than that of non-galled leaves. This reduced photosynthetic activity, in association with the presence of large intercellular spaces, could improve gas diffusion and, consequently, avoid hypoxia and hypercarbia in gall tissue.

Biology and development of galls induced by Lopesia sp. (Diptera: Cecidomyiidae) on leaves of Mimosa gemmulata (Leguminosae: Caesalpinioideae)

Analyses of gall biology and development allow determination of morphogenesis events in host-plant organs that are altered by galling insects. Currently, we assume that there is a correlation between Lopesia sp. instars and the alterations in gall tissues on Mimosa gemmulata that generate the gall shape. The development of Lopesia sp. (three larval instars, pupae and adult) correlates positively with gall growth, especially on the anticlinal axis. First-instar larvae are found in galls at the stage of induction, Instar 2 in galls at early growth and development, Instar 3 in galls at late growth and development, pupae in galls at maturation, and the adult emerges from senescent galls. At induction, the larva stimulates cell differentiation in pinnula and pinna-rachis tissues on M. gemmulata. At early growth and development stages, cell division and expansion are increased, and non-glandular trichomes assist gall closing. Homogenous parenchyma and neoformed vascular bundles characterise late growth and development. At maturation, tissues are compartmentalised and cells achieve major expansion through elongation. At senescence, galls open by the falling of trichomes, and mechanical and nutritive cells have thickened walls. The neoformed nutritive tissue nurtures the developing Lopesia sp., whose feeding behaviour influences the direction of cell elongation, predominantly periclinal, determinant for gall bivalve shape.

Description of the Asian chili pod gall midge, Asphondylia capsicicola sp. n., with comparative notes on Asphondylia gennadii (Diptera: Cecidomyiidae) that induces the same sort of pod gall on the same host plant species in the Mediterranean region

A new species of the genus Asphondylia (Diptera: Cecidomyiidae) that infests pods of chili, Capsicum annuum L. and Capsicum frutescens L. (Solanaceae), is described as Asphondylia capsicicola sp. n. based on specimens collected from Indonesia and Vietnam. The new species is similar to Asphondylia gennadii (Marchal) (=Asphondylia capsici) that induces chili pod galls in the Mediterranean region, but is distinguishable from it by the morphological features of pupa such as the nonlinear arrangement of the lower frontal horns, and the narrower longitudinal band of transverse wrinkles on the tergite of the mesothorax. Differences between the two species in the DNA sequencing data were 69 bp (16%) to 77 bp (19%) among 413 bp of the partial cytochrome oxidase subunit I region examined, supporting the morphological identification. This is one of the examples in which two congeners induce the same sort of gall on the same host plant organ and species, which means that the two species are not distinguishable based solely on gall shape and host plant information, unlike many other gall midges.

Horizontal Gene Transfer Contributes to the Evolution of Arthropod Herbivory.

Within animals, evolutionary transition toward herbivory is severely limited by the hostile characteristics of plants. Arthropods have nonetheless counteracted many nutritional and defensive barriers imposed by plants and are currently considered as the most successful animal herbivores in terrestrial ecosystems. We gather a body of evidence showing that genomes of various plant feeding insects and mites possess genes whose presence can only be explained by horizontal gene transfer (HGT). HGT is the asexual transmission of genetic information between reproductively isolated species. Although HGT is known to have great adaptive significance in prokaryotes, its impact on eukaryotic evolution remains obscure. Here, we show that laterally transferred genes into arthropods underpin many adaptations to phytophagy, including efficient assimilation and detoxification of plant produced metabolites. Horizontally acquired genes and the traits they encode often functionally diversify within arthropod recipients, enabling the colonization of more host plant species and organs. We demonstrate that HGT can drive metazoan evolution by uncovering its prominent role in the adaptations of arthropods to exploit plants.

Characterization of Egyptian <i>Botrytis cinerea</i> Isolates from Different Host Plants

Gray mold causes considerable economic losses of fruit and vegetable production. The current study on Egyptian population structure of Botrytis cinerea demonstrates that this species is composed of four TE genotypes: transposa, vacuma, boty and flipper types using transposable elements and sensitivity to the hydroxyanilide fungicide, fenhexamid. The results show that transposa is the predominant isolate type (63.6%) in the sampled populations of B. cinerea. However, the four isolate types are fenhexamid-sensitive regardless of location, host plant and plant organ. Additionally, B. cinerea isolates collected from different host plants do not exhibit any host preference using artificial infection test on lettuce. Furthermore, no relation is found between isolate type and aggressiveness and no divergence event has occurred among the isolates collected from different locations and host plants. The results suggest that host specialization of B. cinerea has not been occurred in the current sampled crops.

Cytological cycles and fates in Psidium myrtoides are altered towards new cell metabolism and functionalities by the galling activity of Nothotrioza myrtoidis.

The morphogenesis of galls occurs by the redifferentiation of cells that assume new functions in the modified host plant organs. The redifferentiated cells in the galls of Nothotrioza myrtoidis on Psidium myrtoides have low complexity metabolism and are photosynthesis-deficient. These galls were studied in search for evidences of the establishment of new cell cycles and fates and cytological gradients that corroborate their metabolic profile. Young and mature leaves of P. myrtoides and leaf galls induced by N. myrtoidis at different developmental stages were collected along 24 months and analyzed under light and transmission electron microscopy. The leaves of P. myrtoides are long-lasting and did not senesce within the analyzed period, while the galls have a shorter cycle, and senesce within 1 year. A homogenous parenchyma is established by a "standby-redifferentiation" of the chlorophyllous tissues, and sclerenchyma cells redifferentiate from parenchyma cells in the outer cortex of the mature galls. The lack of organelles, the underdeveloped lamellation of chloroplasts, and the occurrence of few plastoglobules are related to the photosynthetic deficiency of the galls. No cytological gradients were observed, but the organelle-rich cells of the vascular and perivascular parenchymas are similar to those of the nutritive tissues of galls induced by other insect taxa. These cells nearest to the feeding sites of N. myrtoidis present higher metabolism and well-developed apparatus for the prevention of oxidative stress. The features herein described corroborate the low metabolic profile of the galls as the cell cycles and fates of P. myrtoides are manipulated for completely new functionalities.

Species and organ specificity of fungal endophytes in herbaceous grassland plants

Summary1. aFoliar endophytic fungi in herbaceous plants are known to be diverse, yet studies characterizing the fungal communities in roots and shoots of plants across time are absent. These fungi are supposedly ubiquitous in nature, infecting plants through airborne spores. As many foliar endophytes can also exist in soil, we hypothesized that there would be a strong similarity between root and shoot endophytes in any given plant species and that differences between plant species would be greater than those between organs within a species.2. Leaf and root fungal endophyte communities were assessed in field‐collected plants of three co‐occurring grassland forbs (Cirsium arvense, Plantago lanceolata and Rumex acetosa) in two contrasting seasons (winter and summer). The former two species are mycorrhizal, whilst the latter species is not so.3. The highest fungal species richness was recorded from P. lanceolata with R. acetosa hosting the least endophyte diversity. Endophyte communities were more diverse in root than leaf tissues and in summer than in winter. Similarity of endophyte communities between different host plant species and organs within an individual host was very low. Negative correlations were found between mycorrhizal colonization and endophyte presence in the roots of C. arvense and P. lanceolata, suggesting some degree of antagonism or competition between the fungi. Consistent positive associations were found between the number of endophyte species in roots and shoots of plants.4. Synthesis. In contrast to previous studies, the results show that many endophytes do not occur ubiquitously, but instead exhibit both plant and tissue specificity. There is a strong seasonal change in endophyte communities, but the differences between roots and shoots at any one time can be just as large. This dissimilarity suggests a lack of systemic growth by the fungi from one tissue to another. Mycorrhizas may interact negatively with other root endophytes, indicating that the latter should not be ignored in future mycorrhizal studies. We should begin to think of individual plants as ecosystems of interacting microbes, whose community is structured by plant genetics and environmental conditions, coupled with interactions between the microbes themselves.

Gall induction by hemipteroid insects1

The Thysanoptera and sternorrhynchous Hemiptera induce galls through feeding action, a behavior similar to that in the Cecidomyiidae. Salivary glands of gall-founding female thrips include greater quantities of hydrolyzing enzymes and soluble proteins than those in either males or pupae, which possibly alter the host-tissue metabolism, enabling galls to develop. Piercing-and-sucking mouthparts of the Hemiptera are adapted for an exclusively liquid diet – either the plant sap from vascular elements or the fluids from living nonvascular cells. Hemipteran-salivary chemistry alters the hormonal balance in the host, triggering gall development. Soluble proteins in the saliva of nymphs are critical. Gall-inducing Hemiptera vigorously take oxygen from the ‘gall’ tissue, which triggers auxin activity. Gall-inducing behaviors in the Thysanoptera and Sternorrhyncha are similar in that gall induction occurs by the feeding action of a single female, and gall-founding females disperse over short distances seeking young host-plant organs. Besides providing a comparative overview of gall induction by hemipteroids, this paper highlights the subtle but noteworthy differences in behaviors among these insects, thus offering pointers to their evolution within the specialist guild of herbivory. 1To Warren Gene Abrahamson III (Bucknell University, Lewisburg, PA, USA), who blazed new trails in interpreting the evolutionary ecology of galls and inducing insects. Memories of my stay in his laboratory in 1990–1991 are pleasant.