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.     

The impact of two gall-forming arthropods on the photosynthetic rates of their hosts

The impact of herbivores on host plant photosynthetic rates can range from negative to positive. While defoliation by chewing herbivores can result in increases in photosynthesis followed by compensatory growth, other herbivore guilds, such as mesophyll feeders which damage photosynthetic leaf tissues, almost always reduce photosynthetic rates. The impact of galling herbivores on host photosynthesis has rarely been examined, even though the limited tissue disruption and the strong metabolic sinks induced by gall-forming herbivores could potentially stimulate photosynthetic rates. I examined the hypothesis that gall-inducing herbivores could stimulate photosynthesis in neighboring leaves in response to increased sink-demand by the gall. To address this hypothesis, I measured photosynthetic rates of galled leaves or leaflets, neighboring ungalled leaves or leaflets, and ungalled leaves or leaflets on ungalled shoots on naturally growing Prunus serotina (wild cherry) and Rhus glabra (smooth sumac). The leaves of wild cherry were galled by an eriophyid mite, Phytoptus cerasicrumena; the leaves of smooth sumac by an aphid, Melaphis rhois. I found that both species reduced the photosynthetic rates of the leaves or leaflets they galled from 24 to 52% compared to ungalled leaves in ungalled areas of the plants. Contrary to my hypothesis, mite galls on wild cherry reduced photosynthesis of neighboring ungalled leaves within the same shoot by 24% compared to ungalled leaves on gall-free shoots. Aphid galls on sumac leaflets did not significantly alter the photosynthetic rates of neighboring leaflets relative to ungalled leaves on ungalled shoots. Although gall-formers would appear to have the potential to stimulate photosynthesis in the same manner as defoliating herbivores, i.e., by increasing sink demand relative to source supply, I found only negative impacts on photosynthesis. I suggest that sink competition for nutrients between developing leaves and growing gall tissue may account for the negative impacts of sink-inducing gallers on photosynthesis. Received: 17 October 1997 / Accepted: 2 February 1998     

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.     

Aphid galls accumulate high concentrations of amino acids: a support for the nutrition hypothesis for gall formation

The nutrition hypothesis for the adaptive significance of insect gall formation postulates that galls accumulate higher concentrations of nutritive compounds than uninfested plant tissue, resulting in a high performance of the gall former. This hypothesis has been supported by some taxa of gall insects, but not by taxa such as cynipid wasps. Aphid galls are expected to require higher levels of nitrogen than other insects’ galls with a single inhabitant, because aphid galls are required to sustain a number of aphids reproducing parthenogenetically over two generations. The present study tested this hypothesis by evaluating aphid performance and amino acid concentration in phloem sap, using the aphid Rhopalosiphum insertum (Walker) (Homoptera: Aphididae), which establishes colonies on leaves of Sorbus commixta Hedlund or in galls of the aphid Sorbaphis chaetosiphon Shaposhnikov (Homoptera: Aphididae). We prepared the gall and non‐gall treatments on trees of S. commixta, in which R. insertum fundatrices were reared and allowed to reproduce. In S. chaetosiphon galls, R. insertum colonies propagated more rapidly, and the second generation grew larger and more fecund than on ungalled leaves. The amount of amino acids exuding from cut galled leaves was fivefold that in ungalled leaves; however, there was no significant difference in the amino acid composition between galled and ungalled leaves. In the intact leaves, total amino acid concentration in the phloem sap declined rapidly from late April to late May; however, the galls retained this high amino acid concentration in developing leaves for 1 month. These results indicate that the improved performance in R. insertum is ascribed to the increased concentration of amino acids in galled leaves. We suggest that S. chaetosiphon galls function to promote the breakdown of leaf protein, leading to an increased performance of gall‐inhabiting aphids.     

Manipulation of host plant cells and tissues by gall-inducing insects and adaptive strategies used by different feeding guilds

Biologists who study insect-induced plant galls are faced with the overwhelming diversity of plant forms and insect species. A challenge is to find common themes amidst this diversity. We discuss common themes that have emerged from our cytological and histochemical studies of diverse neotropical insect-induced galls. Gall initiation begins with recognition of reactive plant tissues by gall inducers, with subsequent feeding and/or oviposition triggering a cascade of events. Besides, to induce the gall structure insects have to synchronize their life cycle with plant host phenology. We predict that reactive oxygen species (ROS) play a role in gall induction, development and histochemical gradient formation. Controlled levels of ROS mediate the accumulation of (poly)phenols, and phytohormones (such as auxin) at gall sites, which contributes to the new cell developmental pathways and biochemical alterations that lead to gall formation. The classical idea of an insect-induced gall is a chamber lined with a nutritive tissue that is occupied by an insect that directly harvests nutrients from nutritive cells via its mouthparts, which function mechanically and/or as a delivery system for salivary secretions. By studying diverse gall-inducing insects we have discovered that insects with needle-like sucking mouthparts may also induce a nutritive tissue, whose nutrients are indirectly harvested as the gall-inducing insects feeds on adjacent vascular tissues. Activity of carbohydrate-related enzymes across diverse galls corroborates this hypothesis. Our research points to the importance of cytological and histochemical studies for elucidating mechanisms of induced susceptibility and induced resistance.     

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.     

Patterns of gall-forming in Ossaea confertiflora (Melastomataceae) by Lopesia brasiliensis (Diptera: Cecidomyiidae) in an area of Atlantic Rainforest in southeastern Brazil

Patterns of galling by the gall midge Lopesia brasiliensis (Diptera: Cecidomyiidae) were studied in Ossaea confertiflora (Melastomataceae) in an Atlantic forest site at Ilha Grande, RJ. Out of the 81 plants surveyed, 55 (67.9%) bore galls. The number of galls per galled individual ranged from 1 to 261 and 94.4% of the galls were in leaves. The number of galls per galled leaf varied from 1 to 25. Total gall number was positively correlated with plant height. Larger and more ramified plants tended to have a smaller percentage of their leaves with galls and a lower density of galls per leaf than smaller plants. Plants that were close to other individuals of the same species tended to have more galls per leaf than relatively isolated plants. The observed patterns may be linked to strategies of optimization in the use of resources (i.e. oviposition sites) and predation avoidance by the gall midges.     

The chemical composition of plant galls: are levels of nutrients and secondary compounds controlled by the gall-former?

The chemical composition of galled and ungalled plant tissue was compared in a series of experiments. Gall and adjacent plant tissue was analysed for 20 species of gall-former on 11 different plant species. There were clear differences between galled and ungalled tissue in levels of nutrients and secondary compounds. Gall tissue generally contained lower levels of nitrogen and higher levels of phenolic compounds than ungalled plant tissue. The gall tissue produced by the same plant in response to different species of gall-former differed in chemical composition, as did the gall-tissue from young and mature galls of the same species. The chemical differences between gall and plant tissues were studied in more detail in two field manipulations. Firstly, the seasonal changes in phenolic biosynthesis in Pontania proxima and P. pedunculi (Hymenoptera: Tenthredinidae) gall tissue were compared to those of their host plants, Salix alba and S. caprea. In both types of gall tissue, phenolic levels declined as the season progressed, but levels in the surrounding plant tissue increased. When the gall insects were killed with insecticide, phenolic levels in the galled tissue dropped to the same level as those in adjacent plant tissue. Secondly, the density of Cynips divisa (Hymenoptera: Cynipidae) galls on Quercus robur leaves was reduced by removing half the galls present, either those from the central region of the leaf or those from the edge. Decreasing gall density increased the size of the remaining galls and the weight of the insects, but these effects were most marked when the galls remaining were growing centrally on the leaf, i.e. when the galls from the edge had been removed. Decreasing gall density increased the nitrogen content of the remaining galls, again to a greater extent in galls growing centrally on the leaf. The results of these studies suggest that the levels of nutrients and secondary compounds in gall tissue are usually markedly different to those of surrounding plant tissue, and that gall-formers may produce species-specific and temporally variable changes in the chemical composition of gall tissue. Received: 7 July 1997 / Accepted: 29 September 1997     

Plant organ abscission and the green island effect caused by gallmidges (Cecidomyiidae) on tropical trees

Plants exhibit a wide array of inert and induced responses in defense against herbivore attack. Among these the abscission of organs has been argued to be a highly effective mechanism, depending, however, on the herbivore’s feeding mode. While consisting of plant tissues, insect induced galls are seen as the extended phenotype of the gall inducer which might circumvent many or most of the plant defenses. There is very little information whether and how far beyond the gall tissue gall inducers might affect plant tissues. A localized impact is likely to leave the abscission of galled organs as a viable defense although at a cost. Here, we report on an instance where the host plant, Neea madeirana (Nyctaginaceae) abscises leaves galled by two species of Bruggmannia (Diptera: Cecidomyiidae), more frequently than ungalled leaves in a rain forest in Amazonia, Brazil. Once on the forest floor the leaves decay quickly, while both gall types show signs of localized maintenance of healthy tissues for a while (the green island effect). However, on the forest floor galls are exposed to a new set of potential natural enemies. Both gall types show a minimum of a five-fold increase in mortality due to pathogens (fungi and bacteria) compared to galls that were retained on the host tree. We discuss the adaptive nature of plant organ abscission as a plant defense against gallers and as a gall inducer adaptive trait. Handling editor: Graham Stone.     

Feeding by a gall-inducing caterpillar species alters levels of indole-3-acetic and abscisic acid in Solidago altissima (Asteraceae) stems

Various plant antagonists appear to alter phytohormone levels for their own benefit. Among insects, gall-inducing species appear to influence phytohormones and it is widely believed that they alter levels of indole-3-acetic acid (IAA) to help produce their galls, but evidence exists for only a limited number of species. To further explore the role of phytohormones in gall formation, we measured levels of IAA and abscisic acid (ABA), a hormone involved in plant defenses and that can influence IAA, in tissues of control stems of Solidago altissima (Asteraceae) and those galled by Gnorimoschema gallaesolidaginis (Gelechiidae). This gall-inducing caterpillar species significantly altered the distribution of IAA in galls and the larvae themselves contained high concentrations of IAA. In contrast, the generalist caterpillar Heliothis virescens (Noctuidae) neither altered IAA nor accumulated significant concentrations of IAA, suggesting that G. gallaesolidaginis may have a distinctive influence over IAA. The gall-inducing caterpillars, particularly younger larvae, also contained high levels of ABA but did not increase levels of ABA, which is induced by herbivory of H. virescens. Because G. gallaesolidaginis also does not increase levels of other defense-related hormones, avoiding generalized plant defenses may facilitate gall induction and formation.     

Leaf Production and Morphology in the Artichoke Gall of Yew (Taxus baccata L.)

Comparative leaf production rates and leaf morphology studiesfor galled and normal shoots of yew trees have been obtainedthroughout the life cycle of the causative agent, the gall midge,Taxomyia taxi. Normal and galled shoot leaf numbers have beenrelated to those of their parent shoots. It was found that whereasthe annual leaf production of normal shoots was positively relatedto that of the parent shoots, galled shoot leaf production remainedconstant regardless of parent shoot vigour showing leaf stimulationby the midge to be a special case. The midge larva appears tobe determining the rate of leaf production in galled shoots.In galls leaf production continues throughout the winter monthswith no dormant period. From morphological evidence, alternationof leaves and cataphylls is continued in galled buds.     

The impact of kleptoparasitic invasions on the evolution of gall-size in social and solitary Australian Acacia thrips

Many species of gall-inducing Acacia thrips are attacked by kleptoparasitic thrips who enter the gall, destroy the occupants, and then use the gall for producing their own offspring. The hypothesis tested here is that pressure exerted by ldeptoparasites （genus Koptothrips） not only provoked the evolution of soldiers in the gall-inducing clade, but have also influenced the evolution of gall size and morphology. Various size dimensions of invaded galls were compared to those of uninvaded galls using data from six gall-inducing species and their kleptoparasites. For the non-social gall-inducing species （K. ellobus and K. nicholsoni） invaded galls showed no significant size differences from galls that had not been invaded. For the four social gall-inducingspecies （K. habrus, K. intermedius, K. waterhousei and K. morrisi） invaded galls were significantly narrower and/or shorter than uninvaded galls. Galls of social species that had not been invaded and contained adult soldiers were significantly larger than galls where soldiers were still at a larval stage, suggesting that gall size is related to gall age in these species. An hypothesis is proposed that links the timing of invasion by kleptoparasites to size of the host gall： induction of a smaller gall by host founders will reduce the period of vulnerability to invasion （before soldiers become adults） for social thrips by allowing foundresses in these smaller galls to begin laying soldierdestined eggs relatively sooner.     

Qualitative and Quantitative Evaluation of Gall Induced by <Emphasis Type="Italic">Pseudophacopteron alstonium</Emphasis> Yang et Li 1983 (Hemiptera: Psyllidae: Phacopteronidae) as Plant Parasite,in <Emphasis Type="Italic">Alstonia scholaris</Emphasis> Leaves

Alstonia scholaris (Dr C. Alston, 1685–1760) (Family Apocynaceae) (Chattim tree), commonly known as devil tree, is an evergreen tropical tree. The tree is native to India and also found in Sri Lanka, Southern China, throughout Malaysia to northern Australia. This plant is seriously damaged by formation of tumor like galls across the Kolkata city,West Bengal which affects its ornamental and medicinal value. Gall is formed by ovipositing adults of Pseudophacopteron alstonium Yang et Li 1983 (Hemiptera: Psyllidae: Phacopteronidae) and results in destruction of host plant. The nymphal stage undergoes moulting through first instar to third instar to reach the adult within galls. It is observed that highly infested leaves can bear 60–80 galls. The gallmaker Pseudophacopteron sp. stresses the host organ, and the host counters it with physiological activities supplemented by newly differentiated tissues. In infested leaves, chlorophyll and carbohydrate contents decreased sequentially with the age of the gall. There were no significant changes in protein and total amino acid content in gall tissue. But total lipid content was highest in mature galled leaves. Increased phenolic content after psylloid herbivory, which exerted oxidative stress on the host plants, was observed in gall infested leaves as compared to fresh ungalled leaves of Alstonia scholaris. Moisture content was highest in ungalled healthy leaves than the young galled, mature galled and perforated galled leaves.     

Optimal clutch size of the chestnut gall-wasp,Dryocosmus kuriphilus yasumatsu (Hymenoptera: Cynipidae)

Optimal clutch size of the chestnut gall-wasp, Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), was examined in galls on wild and resistant chestnut trees in 1988 and 1989. The rate of escape success of newly-emerged adults from galls was an average of 60%, irrespective of cell numbers per gall. Dry mass per cell of a gall (as an index of nutritive condition) decreased with increasing cell number per gall, but was proportional to the mean number of mature eggs of new adults per gall. The number of cells per gall that occurred most frequently did not agree with that attained by the maximum survival rate from young larva to adult emergence of the gall-wasp. This discrepancy was examined from the viewpoint of three factors: 1) quality of offspring, 2) defensive response of the host plant causing mortality of the gall-wasp before cell formation, and 3) fitness per gall vs. fitness per egg. It is concluded that the third factor is most likely to be the one best in explaining the discrepancy.     

Impact of whole-canopy and systemic insecticidal treatments on Callirhytis cornigera (Hymenoptera: Cynipidae) and associated parasitoids on pin oak

The gall wasp Callirhytis cornigera (Osten Sacken) is a cynipid with alternating generations that produce large, woody stem galls and tiny blister-like leaf galls on pin oak, Quercus palustris Muenchhausen, in the United States. We tested 3 approaches to control the leaf-galling generation, and determined their impact on associated parasitoids and effectiveness in reducing numbers of new stem galls. First, trees were sprayed with bifenthrin or chlorpyrifos in late March to kill females emerging from stem galls before they oviposited into buds. Second, concentrated solutions of abamectin, imidacloprid, or bidrin were injected from pressurized containers into tree sapwood to control larvae developing in young leaf galls. Finally, systemic insecticides (acephate, abamectin, dimethoate, or imidacloprid) were sprayed at early leaf expansion (2 May) or to young, expanded leaves (17 May) to target larvae in leaf galls. Parasitoids, mostly eulophids, accounted for approximately 70% mortality of leaf-galling C. cornigera larvae on untreated trees. Whole-canopy sprays during C. cornigera emergence from stem galls reduced overall numbers of galled leaves and leaf galls. Trunk injections of bidrin or abamectin resulted in significant mortality of gall inhabitants, including parasitoids. However, neither of the aforementioned approaches significantly reduced numbers of new stem galls. Sprays of abamectin, dimethoate, or imidacloprid applied on 2 May caused high mortality of all gall inhabitants. There was no net benefit, however, because parasitism caused a similar reduction in C. cornigera survival on unsprayed shoots. Sprays applied later in leaf expansion had little impact on gall inhabitants. Of the treatments tested, bifenthrin sprays at bud break provided the greatest reduction in new leaf galls, whereas bidrin injections provided the greatest reduction in gall wasps emerging from galled leaves. This study suggests that gall wasp outbreaks are unlikely to be controlled by a single treatment, regardless of application method.     

Oxycephalomyia, gen. nov., and life history strategy of O. styraci comb. nov. (Diptera: Cecidomyiidae) on Styrax japonicus (Styracaceae)

A new genus Oxycephalomyia is described to contain the gall midge that was previously known as Asteralobia styraci (Shinji). Oxycephalomyia styraci, comb. nov., produces leaf vein galls on Styrax japonicus (Styracaceae). The adult of O. styraci is redescribed, and its full‐grown larva and pupa are described for the first time. The annual life cycle of the gall midge in northern Kyushu was clarified; the first instars overwinter in the galls on the host plant. However, the galls of O. styraci mature much later in the season than those of other gall midges with a similar life history pattern, and the durations of second and third larval instars are remarkably short. Such a life history pattern is considered to have an adaptive significance in avoiding larval parasitism, particularly by early attackers. The number of host axillary buds as oviposition sites decreased in bearing years and increased in off years, but there was no sign of oviposition site shortage even in bearing years, probably due to the low population density of the gall midge. An unidentified lepidopteran that feeds on galled and ungalled host buds and a Torymus sp. that attacks pupae of O. styraci were recognized as mortality factors of the gall midge.     

The gall-inducing habit has evolved multiple times among the eriococcid scale insects (Sternorrhyncha: Coccoidea: Eriococcidae)

The habit of inducing plant galls has evolved multiple times among insects but most species diversity occurs in only a few groups, such as gall midges and gall wasps. This phylogenetic clustering may reflect adaptive radiations in insect groups in which the trait has evolved. Alternatively, multiple independent origins of galling may suggest a selective advantage to the habit. We use DNA sequence data to examine the origins of galling among the most speciose group of gall-inducing scale insects, the eriococcids. We determine that the galling habit has evolved multiple times, including four times in Australian taxa, suggesting that there has been a selective advantage to galling in Australia. Additionally, although most gall-inducing eriococcid species occur on Myrtaceae, we found that lineages feeding on Myrtaceae are no more likely to have evolved the galling habit than those feeding on other plant groups. However, most gall-inducing species-richness is clustered in only two clades ( Apiomorpha and Lachnodius  +  Opisthoscelis ), all of which occur exclusively on Eucalyptus s.s . The Eriococcidae and the large genus Eriococcus were determined to be non-monophyletic and each will require revision.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 441–452.     

A gall-inducing arthropod drives declines in canopy tree photosynthesis

Mature forest canopies sustain an enormous diversity of herbivorous arthropods; however, with the exception of species that exhibit large-scale outbreaks, canopy arthropods are thought to have relatively little influence on overall forest productivity. Diminutive gall-inducing mites (Acari; Eriophyoidae) are ubiquitous in forest canopies and are almost always highly host specific, but despite their pervasive occurrence, the impacts of these obligate parasites on canopy physiology have not been examined. We have documented large declines in photosynthetic capacity (approx. 60%) and stomatal conductance (approx. 50%) in canopy leaves of mature sugar maple (Acer saccharum) trees frequently galled by the maple spindle gall mite Vasates aceriscrumena. Remarkably, such large impacts occurred at very low levels of galling, with the presence of only a few galls (occupying approx. 1% of leaf area) compromising gas-exchange across the entire leaf. In contrast to these extreme impacts on the leaves of adult trees, galls had no detectible effect on the gas-exchange of maple saplings, implying large ontogenetic differences in host tolerance to mite galling. We also found a significant negative correlation between canopy tree radial increment growth and levels of mite galling. Increased galling levels and higher physiological susceptibility in older canopy trees thus suggest that gall-inducing mites may be major drivers of “age-dependent” reductions in the physiological performance and growth of older trees.     

Molecular ecology of some Cecidophyopsis mites (Acari: Eriophyidae) on Ribes species and evidence for their natural cross colonisation of blackcurrant (R. nigrum)

Ribosomal DNA from Cecidophyopsis mites from different Ribes species was amplified using the polymerase chain reaction and the products digested using restriction enzymes. After separating the DNA fragments on gels, it was possible to identify specimens of mites obtained from field samples by comparing the profiles of their DNA banding patterns with those of known Cecidophyopsis species. Using this analysis, a non-gall forming mite found infesting blackcurrant buds in New Zealand was identified as the gooseberry mite (C. grossulariae). On wild red currant (Ribes spicatum) from Finland showing two sizes of galled buds, the red currant gall mite (C. selachodon) was identified in the larger galls located at the tips of branches and a distinct mite in the smaller galls located on the lower parts of the branches. A mite with a DNA banding profile indistinguishable from this latter mite from R. spicatum was also identified in galled buds of blackcurrant genotypes growing in Finland, including those containing the blackcurrant gall mite (C. n'ftw)-resistance genes P or Ce. The DNA banding profile of this mite resembled most closely that of C. ribis , but was distinct from it. The occurrence of C. grossulariae and this distinct Cecidophyopsis mite on blackcurrant has implications for the genetic control of Cecidophyopsis mites and possibly for the spread of the reversion disease agent in this crop.