Floral-like destiny induced by a galling Cecidomyiidae on the axillary buds of Marcetia taxifolia (Melastomataceae)

The galls induced by Cecidomyiidae, Diptera, are very diverse, with conspicuous evidence of tissue manipulation by the galling herbivores. Bud galls, as those induced by an unidentified Cecidomyiidae species on Marcetia taxifolia, Melastomataceae, can be considered as one of the most complex type of prosoplasma galls. The gall-inducer manipulate the axillary meristem of the plant in a way that gall morphogenesis may present both vegetative and reproductive features of the host plant. Herein, we analyzed traces of determinate and indeterminate growth in the bud gall of M. taxifolia, looking for parallels between the features of the leaves and flowers, natural fates of the meristematic cells. The bud galls are induced by the cecidomyiid fly, and are formed by the connation of eight leaf primordia, a common process in ovary morphogenesis. The bud gall corresponds to a pistil-shaped gall morphotype, with anatomical features similar to those of an hypanthium and sepals. The gall mimics an ovary, which has protective barriers at the apex, and a nutritive tissue (with storage of lipids and proteins) or a placenta, respectively, at the basal portion. The redifferentiation of the promeristem into a nutritive tissue at the base of the gall confers a determinate destiny to the axillary bud. Comparatively, the gradients of cell expansion and of accumulation of primary metabolites also indicate that the gall and the ovary are convergent structures. Some constraints of the host plant cells, such as the absence of lignification, and the accumulation of polyphenols, lipids and terpenoids, are not altered and may confer chemical protection for plant tissues and the larva against oxidative stress.     

The role of olfactory cues in the sequential radiation of a gall‐boring beetle,Mordellistena convicta

1. Herbivorous insects often have close associations with specific host plants, and their preferences for mating and ovipositing on a specific host‐plant species can reproductively isolate populations, facilitating ecological speciation. Volatile emissions from host plants can play a major role in assisting herbivores to locate their natal host plants and thus facilitate assortative mating and host‐specific oviposition. 2. The present study investigated the role of host‐plant volatiles in host fidelity and oviposition preference of the gall‐boring, inquiline beetle, Mordellistena convicta LeConte (Coleoptera: Mordellidae), using Y‐tube olfactometers. Previous studies suggest that the gall‐boring beetle is undergoing sequential host‐associated divergence by utilising the resources that are created by the diverging populations of the gall fly, Eurosta solidaginis Fitch (Diptera: Tephritidae), which induces galls on the stems of goldenrods including Solidago altissima L. (Asteraceae) and Solidago gigantea Ait. 3. Our results show that M. convicta adults are attracted to galls on their natal host plant, avoid the alternate host galls, and do not respond to volatile emissions from their host‐plant stems. 4. These findings suggest that the gall‐boring beetles can orient to the volatile chemicals from host galls, and that beetles can use them to identify suitable sites for mating and/or oviposition. Host‐associated mating and oviposition likely play a role in the sequential radiation of the gall‐boring beetle.     

Life history of <Emphasis Type="Italic">Stenopsylla nigricornis</Emphasis> (Hemiptera: Psylloidea: Triozidae) and phytohormones involved in its gall induction

Many phytophagous insects have an ability to manipulate plant tissue and induce galls, but the mechanism is not yet fully understood. Some insects have multivoltine life cycles, and each generation induces galls on different plant species or different organs in the same host. Such host-use patterns are interesting study subjects to clarify the gall-inducing mechanisms of insects. We focused on a multivoltine and gall-inducing psyllid Stenopsylla nigricornis Kuwayama (Hemiptera: Psylloidea: Triozidae), which is associated with Symplocos lucida Sieb. (Symplocaceae). Based on periodic field surveys in Kyushu, Japan, S. nigricornis is revealed to have a bivoltine life history. Then, we revealed that the spring generation induces galls on leaves, while the autumn generation does so on flower buds and overwintering leaf buds. We also analyzed phytohormones in normal plant tissue, S. nigricornis nymphs, and their galls. As a result, nymphs were discovered to contain much higher concentrations of isopentenyladenosine and its possible precursor, isopentenyladenosine riboside than plant tissues, strongly suggesting that the phytohormone is involved in gall induction by S. nigricornis. Because flower bud galls contained significantly lower concentrations of abscisic acid (ABA) than normal flower bud, the autumn generation nymphs are considered to regulate the ABA level and to promote the earlier opening of host flower buds.     

Benefits of photosynthesis for insects in galls

Insect-induced plant galls are predominantly reputed to act as strong carbon sinks, although many types of galls contain chlorophyll and have the potential to photosynthesize. We investigated whether the photosynthetic capacity of bud galls induced by a Pteromalid wasp, Trichilogaster acaciaelongifoliae, in Acacia longifolia subsidises carbon budgets or provides O₂ to the larvae while concurrently consuming CO₂ in the dense gall tissue, thereby maintaining (O₂) and (CO₂) within the range of larval tolerance. Low (O₂) (<5?%?v/v) were found within the internal tissues of galls, and these concentrations responded only marginally to light, suggesting that the photosynthetic activity within the gall is inconsequential in the provision of O₂ to the larvae. The metabolic response of larvae to reduced (O₂) and elevated (CO₂) indicated that larvae were tolerant of hypoxia/hypercarbia and also capable of reducing their respiratory rates to cope with hypercarbia. The low mortality of larvae in galls shaded with Al-foil for 20?days showed that photosynthesis was not vital for the survival of the larvae, although growth of shaded galls was substantially reduced. Gas exchange measurements confirmed that, while photosynthesis never fully compensated for the respiratory costs of galls, it contributed substantially to the maintenance and growth, especially of young galls, reducing their impact as carbon sinks on the host. We conclude that, although photosynthesis may contribute to O₂ provision, its main role is to reduce the dependence of the insect-induced gall on the host plant for photosynthates, thereby reducing intra-plant, inter-gall competition and enhancing the probability that each gall will reach maturity.     

Histological Comparisons of Fergusobia/Fergusonina-Induced Galls on Different Myrtaceous Hosts

The putative mutualism between different host-specific Fergusobia nematodes and Fergusonina flies is manifested in a variety of gall types involving shoot or inflorescence buds, individual flower buds, stems, or young leaves in the plant family Myrtaceae. Different types of galls in the early-to-middle stages of development, with host-specific species of Fergusobia/Fergusonina, were collected from Australian members of the subfamily Leptospermoideae (six species of Eucalyptus, two species of Corymbia, and seven species of broad-leaved Melaleuca). Galls were sectioned and histologically examined to assess morphological changes induced by nematode/fly mutualism. The different gall forms were characterized into four broad categories: (i) individual flower bud, (ii) terminal and axial bud, (iii) ''basal rosette'' stem, and (iv) flat leaf. Gall morphology in all four types appeared to result from species-specific selection of the oviposition site and timing and number of eggs deposited in a particular plant host. In all cases, early parasitism by Fergusobia/Fergusonina involved several layers of uninucleate, hypertrophied cells lining the lumen of each locule (gall chamber where each fly larva and accompanying nematodes develop). Hypertrophied cells in galls were larger than normal epidermal cells, and each had an enlarged nucleus, nucleolus, and granular cytoplasm that resembled shoot bud gall cells induced by nematodes in the Anguinidae.     

Characterisation of the effects of leaf galls of Clusiamyia nitida (Cecidomyiidae) on Clusia lanceolata Cambess. (Clusiaceae): Anatomical aspects and chemical analysis of essential oil

Galls develop in different plant organs and are induced by the activity of various organisms. Some studies have investigated the ecological interactions between species of Clusia and gall-inducing insects. The goal of our study is to characterise changes in leaf anatomy caused by the activity of gall insects in Clusia lanceolata. Additionally, we also investigated the chemical composition of volatile compounds of normal leaves and those with galls to detect possible effects on the host plants. For anatomical studies, we used botanical material fixed in FAA₅₀. Transversal sections of the leaf blade were obtained from samples of leaves located on the third and fourth nodes from both male and female individuals. Material was studied from both sexes both with unaffected leaves and leaves containing galls. Fresh leaves of C. lanceolata were used for the extraction of volatile compounds, which were submitted to stem distillation using a modified Clevenger apparatus determining the oil yields subsequently (w/w). The unaffected leaves of female and male individuals of C. lanceolata exhibit similar anatomical structures. However, galls on leaves of both sexes show anatomical differences. The activity of the gall insect Clusiamyia nitida induces several changes in the foliar anatomy and the distribution of metabolic compounds in new tissues during gall development. However, the larvae are not able to induce significant changes in the volatile compounds of inflected leaves from male and female individuals.     

Plant host relationships of three lineages of the gall-inducing fly <Emphasis Type="Italic">Fergusonina</Emphasis> Malloch (Diptera: Fergusoninidae) on <Emphasis Type="Italic">Eucalyptus</Emphasis> L’Hérit.

The gall-inducing fly family Fergusoninidae, in association with a mutualist nematode, induces galls on Myrtaceae. Each fly species typically targets a particular site on its host plant, giving rise to a range of gall types, and one plant species may host at least four fly species. While incongruent fly–host evolutionary time scales preclude early cospeciation, it is possible that Fergusoninidae have been diverging with their host plants more recently at correspondingly finer taxonomic levels, such as within host subgenera. To test this possibility, we reduced the scale of our analysis and focussed on a clade of ten Eucalyptus species, sampling intensively and using a phylogenetic approach to compare the relationships between these plant hosts and their associated flies. We also took advantage of the fact that three different gall types, each with its own clade of Fergusonina flies, could be sampled on this focal host clade, in effect giving us three different host/fly association tests on the one set of hosts. The phylogenies of flies from the three different gall types were estimated using Bayesian analysis of mtCOI sequences and compared with an existing phylogeny of the eucalypt host clade. While each gall type showed a different pattern of host relationships, heuristic and quantitative analyses showed that there was little correspondence between plant and fly phylogenies and we conclude that host switching is prevalent in this system. There was more host fidelity in the flower bud gallers on this group of eucalypts, and there was least in the leaf blade gallers, with the shoot bud gallers demonstrating an intermediate level of host fidelity. We discuss the possible factors which may have led to their patterns of host association. This is the first study of Fergusonina to focus on one clade of Eucalyptus L’Hérit. (Myrtaceae) with intensive sampling and shows that each host plant species is commonly used by multiple fergusoninid species. This has provided us with the opportunity to study in detail the host relationships of three separate clades of Fergusonina from different plant tissue types, and has revealed many previously unrecorded host plant/gall site associations.     

Arthropod-induced neoplastic formations on trees change photosynthetic pigment levels and oxidative enzyme activities

Abstract

In order to test the hypothesis that arthropod-induced neoplastic formations on trees affect biochemical characteristics of both the newly formed galls and host plant tissues, biochemical characteristics with a possible adaptive role were determined in nine gall-former–host tree combinations. Photosynthetic pigments, extractable protein content, and oxidative enzyme activities were determined in gall tissues, leaf tissues of galled leaves, and leaves on ungalled tree branches. Neoplastic tissues were characterized by a low content of photosynthetic pigments, decreased chlorophyll a/b ratio, lower extractable protein content, and decreased activities of peroxidase and polyphenol oxidase as compared with ungalled host leaf tissues. In galled leaves or in leaves adjacent to galls, increased level of peroxidase activity was found. In several gall-inducer–host plant combinations, galled host plant tissues contained increased activity of polyphenol oxidase as well. The presented data reflect long-term systemic effects of neoplastic formation on host tree physiology suggesting that gall inducers affect potential adaptive responses of host plants.     

High mean relatedness among communally galling Tamalia aphids revealed by AFLP analysis

Cooperative or eusocial behavior occurs in gall-inducing insects, but the ecological and evolutionary contexts for these behaviors vary in their details. Foundresses of the manzanita leaf-gall aphid, Tamalia coweni, regularly share galls. Because aphids undergo parthenogenesis, communal foundresses are potential clone mates. Under the kin selection hypothesis, a high level of relatedness is predicted to lower genetically based conflict among females in a group and thereby favor communal gall occupation. We recorded the frequency of communal behavior in a population of T. coweni on its host plant, Arctostaphylos patula, and measured reproductive output in single- and multiple-occupant galls. Eleven percent of the 375 galls examined were communally occupied, with double-foundress galls the commonest class, up to a maximum of five foundresses within galls. Total productivity of communal galls (measured by numbers of offspring per gall) was higher than for single-foundress galls on a per-gall basis, but lower per capita. We genotyped foundresses with amplified fragment length polymorphism (AFLP)-PCR markers, to estimate relatedness among gall co-occupants and foundresses from randomly selected galls in the population. Analysis of genetic distance between communal foundresses revealed that relatedness among gall cohabitants was significantly higher, on average, than for foundresses drawn from the population at random (P < 0.001). Phylogenetic analysis using parsimony (PAUP) of the AFLP profiles indicated that half the foundresses sharing galls were most closely related to their gall mates. Our results are consistent with kin selection theory, and suggest that communal gall occupation in this species may be interpreted as cooperative behavior.     

Linking Avicennia germinans (Acanthaceae) architecture to gall richness and abundance in Brazilian Amazon mangroves

The diversity and abundance of gall‐inducing organisms are directly proportional to the structural complexity of the host plant. This hypothesis is controversial for forest environments, such as mangroves. Avicennia germinans (L.), a principal mangrove tree species found in the Neotropical region, is considered to be a superhost for gall‐inducing insects. Using a generalized linear mixed model (GLMM) based on the analysis of 1000 apical branches from 50 A. germinans trees, we examined the diversity and abundance of gall morphotypes (GM), together with the structural attributes of replanted 5‐ to 9‐year‐old mangroves, in the Amazon coast of Brazil. A total of 7602 galls were registered, averaging 1.3 ± 0.4 galls per leaf. Sixteen of the 22 morphotypes identified were found at all study sites. Two gall morphotypes (GM7 and GM4) were the most abundant, representing approximately 40 percent of the total. The structural complexity of the plant (mainly based on the number of leaves) directly affected the abundance and diversity of these organisms. While A. germinans is a superhost, this type of parasitism did not affect plant development or survival. The ample distribution of A. germinans, the formation of monospecific forests, and the high palatability of this plant make it an essential resource for the survival of the gall‐inducing guild in the mangroves of the Neotropics.     

Hormaphis hamamelidis and gall size: a test of the plant vigor hypothesis

We tested the Plant Vigor Hypothesis by determining the distribution of galls formed on leaves of witch hazel, Hamamelis virginiana , by the aphid Hormaphis hamamelidis , and by determining various factors that affect the fecundity of the gall-forming fundatrices. We also studied the role of the fundatrix in host plant manipulation. While the mean number of galls per leaf was low, galls had an aggregated distribution among leaves. Among trees, the average number of galls per leaf was not related to the mean leaf size, contrary to the preference prediction of the Plant Vigor Hypothesis. While fundatrices preferred the distal leaves of buds, which grew more than the proximal leaves, being on distal leaves conferred no increase in fecundity for fundatrices, contrary to predictions of the Plant Vigor Hypothesis. Gall size was the factor that explained the largest proportion of variation in fundatrix fecundity; fundatrix size explained somewhat less of the variation. Also, gall position on the leaf, number of aphid galls on the leaf, and on which leaf of the bud the gall was located all played small, statistically significant roles in explaining fundatrix fecundity, but their effects were variable between experiments. Removal of fundatrices shortly after galls had enclosed them limited the growth of galls, indicating the role of the fundatrices in gall growth. We compare and contrast this system versus other gall-forming insects, as well as discuss the adaptive significance of the aphid manipulation of the host plant. Much of the data contradict predictions of the Plant Vigor Hypothesis, and we discuss how gall size, as a measure of plant growth caused by insect manipulation, explains the observed patterns.     

Anti-insect effects of the gall wall of Baizongia pistaciae [L.], a gall-inducing aphid on Pistacia palaestina Boiss

The Enemy hypothesis is a theoretical framework for understanding the adaptive nature of galls induced in host plants by insects. Contrary to other gall inducing insects, like Cynipids or sawflies, this hypothesis has not been studied for the gall aphids on pistachio trees in the Middle East. Galls on plants are supposed to protect their inducers from other organisms, including herbivores feeding on the host plant and possibly feeding on the gall tissue. Assuming that among aphid enemies there are numerous insects which have to perforate the gall wall to access the aphids inside, determining whether the gall wall has anti-insect properties should be one of the first steps in dealing with this hypothesis. In the present research using Baizongia pistaciae [L.], an aphid that creates perfectly closed galls in Pistacia palaestina Boiss, laboratory experiments were first conducted on a herbivore, the stored grain pest, Tribolium castaneum Herbst, to assess chemical anti-insect activities of the gall tissue, and an effort was made to understand why these properties do not harm the aphids inside the gall. Addition of fresh gall tissue to food reduced the population growth of flour beetles. Non-polar organic extracts had contact toxicity for larvae of these insects, and an impact on the feeding preferences of the adults. These results indicate chemical anti-insect activities of the gall tissue. The research also reveals that the permeability of the gall wall to non-polar volatile compounds is important to the survival of the aphids inside the gall cavity. These findings do not allow us to reject the Enemy hypothesis in the gall-inducing aphids/Pistacia trees interactions.     

Phenotypic plasticity and similarity among gall morphotypes on a superhost,Baccharis reticularia (Asteraceae)

Understanding factors that modulate plant development is still a challenging task in plant biology. Although research has highlighted the role of abiotic and biotic factors in determining final plant structure, we know little of how these factors combine to produce specific developmental patterns. Here, we studied patterns of cell and tissue organisation in galled and non‐galled organs of Baccharis reticularia, a Neotropical shrub that hosts over ten species of galling insects. We employed qualitative and quantitative approaches to understand patterns of growth and differentiation in its four most abundant gall morphotypes. We compared two leaf galls induced by sap‐sucking Hemiptera and stem galls induced by a Lepidopteran and a Dipteran, Cecidomyiidae. The hypotheses tested were: (i) the more complex the galls, the more distinct they are from their non‐galled host; (ii) galls induced on less plastic host organs, e.g. stems, develop under more morphogenetic constraints and, therefore, should be more similar among themselves than galls induced on more plastic organs. We also evaluated the plant sex preference of gall‐inducing insects for oviposition. Simple galls were qualitative and quantitatively more similar to non‐galled organs than complex galls, thereby supporting the first hypothesis. Unexpectedly, stem galls had more similarities between them than to their host organ, hence only partially supporting the second hypothesis. Similarity among stem galls may be caused by the restrictive pattern of host stems. The opposite trend was observed for host leaves, which generate either similar or distinct gall morphotypes due to their higher phenotypic plasticity. The Relative Distance of Plasticity Index for non‐galled stems and stem galls ranged from 0.02 to 0.42. Our results strongly suggest that both tissue plasticity and gall inducer identity interact to determine plant developmental patterns, and therefore, final gall structure.     

Modification of tree architecture by a gall-forming aphid

Herbivory may substantially alter the architectural structure of plants. Among insects, gall-formers that substantially manipulate host traits may have a profound effect on the plants even at low densities. The aphid, Baizongia pistaciae induces banana-like large galls on the terminal buds of Pistacia palaestina. We hypothesized that these large galls are associated with the shape of the plant which may grow as a tree or a bush. In the natural Mediterranean forest, we monitored the effects of the galls on infested branches. In the year of gall formation, usually (~95%) there is neither elongation nor branching beyond the position of the gall. However, in the following years, galled branches produced more lateral branches (branching) than ungalled branches. This effect persists for at least 2 years. Consequently, galled branches carried more leaves and tended to gain more biomass than ungalled branches. Galling did not affect fruit yield. We suggest that repeated galling by B. pistaciae may promote bush-like architecture in P. palaestina.     

An Endoparasitoid Avoids Hyperparasitism by Manipulating Immobile Host Herbivore to Modify Host Plant Morphology

Many parasitic organisms have an ability to manipulate their hosts to increase their own fitness. In parasitoids, behavioral changes of mobile hosts to avoid or protect against predation and hyperparasitism have been intensively studied, but host manipulation by parasitoids associated with endophytic or immobile hosts has seldom been investigated. We examined the interactions between a gall inducer Masakimyia pustulae (Diptera: Cecidomyiidae) and its parasitoids. This gall midge induces dimorphic leaf galls, thick and thin types, on Euonymus japonicus (Celastraceae). Platygaster sp. was the most common primary parasitoid of M. pustulae. In galls attacked by Platygaster sp., whole gall thickness as well as thicknesses of upper and lower gall wall was significantly larger than unparasitized galls, regardless of the gall types, in many localities. In addition, localities and tree individuals significantly affected the thickness of gall. Galls attacked by Platygaster sp. were seldom hyperparasitized in the two gall types. These results strongly suggest that Platygaster sp. manipulates the host plant''s development to avoid hyperparasitism by thickening galls.     

Abundance of Gall Midges on Poulsenia armata (Moraceae): Importance of Host Plant Size and Light Environment in Tropical Rain Forests1

We studied the effects of contrasting light environments on the relationship between the host plant size of Poulsenia armata and the abundance of two gall midges in a tropical rain forest in Veracruz, Mexico. The number and density of two gall morphs (i.e., laminar and vein‐petiole galls) were positively correlated with plant size only in trees found in the forest but not in gaps. The availability of foliar area of P. armata trees was greater in forest gaps than in the forest. The foliar area was positively correlated with the abundance of laminar galls in trees in forest sites, but not with vein‐petiole galls. We concluded that the abundance of two morphs of gall midges on P. armata was associated with host plant size only in the forest trees. Larger plants had more galls than small plants, although this relationship was affected by local light environments.     

Discovery of cryptic diversity in phytophagous gall midges (Diptera: Cecidomyiidae) associated with different ecotypes of the perennial herb Cimicifuga simplex

Studying the diversification patterns of species-rich phytophagous insect taxa can help us understand the factors that cause species diversification. We conducted a molecular phylogenetic analysis of the mitochondrial COI gene of larvae of gall midges (Diptera: Cecidomyiidae) using three genetically differentiated morphs of Cimicifuga simplex plants and found that the gall midges could be divided into five major clades. Gall midges collected from morph I of C. simplex belonged to four Schizomyia clades. Gall midges collected from morph II of C. simplex belonged to one of the four Schizomyia clades collected from morph I. Gall midges collected from morph III belonged one Contarinia clade. On morphs I and II of C. simplex, the Schizomyia species induced galls on the flower bud, whereas on morph III of C. simplex, the Contarinia species was collected from normal fruits (not gall inducer); thus, morph III plants were used differently by gall midges than plants of morphs I and II. These results indicate that the cryptic diversity of these phytophagous insects correspond to that of plant ecotypes, and suggests that the diversification of the host plant contributed to parallel diversification of the phytophagous gall midges.     

Influence of galls of Phanacis taraxaci on carbon partitioning within common dandelion, Taraxacum officinale

We examined how leaf galls, induced by the cynipid wasp Phanacis taraxaci, influence the partitioning of photoassimilates within the host, the common dandelion, Taraxacum officinale. Galled and ungalled plants were exposed to ¹⁴CO₂ and the labelled photoassimilates accumulating within galls and other parts of the host were measured. During the growth phase of the gall they were physiological sinks for photoassimilates, accumulating 9% to 70% of total carbon produced by the host, depending upon the number of galls per plant. High levels of ¹⁴C assimilation in the leaves of galled plants compared to controls, suggest that galls actively redirect carbon resources from unattacked leaves of their host plant. This represents a significant drain on the carbon resources of the host, which increases with the number and size of galls per plant. Active assimilation of ¹⁴C by the gall is greatest in the growth phase and is several orders of magnitude lower in the maturation phase. This finding is consistent with physiological and anatomical changes that occur during the two phases of gall development and represents a key developmental strategy by cynipids to ensure adequate food resources before larval growth begins.     

Volatiles associated with different flower stages and leaves of Acacia cyclops and their potential role as host attractants for Dasineura dielsi (Diptera: Cecidomyiidae)

Acacia cyclops (Fabaceae) is an Australian species which was introduced into South Africa in the nineteenth century. Because of its invasive status in South Africa, a gall midge, Dasineura dielsi (Diptera: Cecidomyiidae), was released in 2001 in order to impact its reproduction by inducing galls on the flowers and thereby preventing seed set. Nothing is known about the cues used by D. dielsi for locating its host flowers. As part of an initial investigation into whether or not chemical cues might play a role in host finding, we analysed headspace samples of Acacia cyclops volatiles from leaves and reproductive parts at different stages (early bud, late bud, early flowering, and senescing flowering stages) using gas chromatography–mass spectrometry (GC–MS). In total, 72 different compounds were detected of which 62 were identified. The analyses showed that open flowers, the stage used by D. dielsi for oviposition, and yellow buds had similar odour compositions with (Z)-3-hexen-1-ol acetate, 4-oxoisophorone, (Z)-β-ocimene, an unknown aliphatic compound, heptadecane, and nonadecane dominating in open flowers. Leaf volatiles were distinct from those in the reproductive plant parts by their high relative amount of (Z)-β-ocimene. (Z)-3-Hexen-1-ol acetate had its maximum relative amount in the green bud samples and was much lower in the later floral stages. In contrast, 4-oxoisophorone peaked in yellow buds and open flowers with little or none of it found in younger or older stages. The volatile compounds of the different flower stages and leaves are discussed in relation to their potential role as attractants used by the biocontrol agent D. dielsi to locate its host plant.     

Histocytological aspects of four types of ambrosia galls on Machilus zuihoensis Hayata (Lauraceae)

Four types of prosoplasmatic galls induced by Daphnephila midges are found on leaves of Machilus zuihoensis, a species endemic to Taiwan: urn- and small urn-shaped, obovate, and hairy oblong galls. In addition to containing nutritive tissues, these galls are lined with fungal hyphae. The objective of this study was to describe and compare the structural organization of the various gall morphologies and to examine the ultrastructure of the nutritive and fungal cells lining the gall chambers. The morphology and ultrastructure of mature-stage galls were examined by light, scanning electron, and transmission electron microscopy. Diverse epidermal cell shapes and wax textures were observed in the leaves and galls of M. zuihoensis. In small urn-shaped, obovate, and hairy oblong galls vascular bundles extend from the gall base to near the centre of the gall top. In contrast, vascular bundles in urn-shaped galls are distributed in the gall wall and extend to close to the outer gall top. Trichomes were present only abaxially on leaves and on hairy oblong gall surfaces. Starch granules, tannins, and mucilage were distributed differently among the four gall types. Further, fungal mycelia spread in the interior gall wall and partially passed through the intercellular spaces of nutritive cells and reached the sclerenchyma. Histological analyses revealed that the surface structure of galls differs from that of the leaf and that the epidermal organization differs among the four gall types. Different types of leaf galls on the same plant have different patterns of tissue stratification and contain different ergastic substances. The results of this study will contribute to the understanding of tritrophic relationships and the complex interactions among parasitic gall-inducing insects, mutualistic fungi, and host plants.