Virulence and Molecular Diversity of Venturia inaequalis in Commercial Apple Growing Regions in Kashmir

Seventy‐one isolates of Venturia inaequalis collected from commercial apple growing areas of Kashmir were characterized on international differential apple hosts and analyzed by Random Amplified Polymorphic Microsatellites (RAMS), PCR–RFLP and sequencing of rDNA for elucidation of variability. Virulence analysis on a differential set categorized them into four pathogenic races, viz. (0), (1), (2) and (1,2) in the first time comprehensive molecular analysis of this in India and especially from Jammu and Kashmir, a north‐western Himalayan state of India. Race groups (0), (1), (2) and (1,2) contained isolates from diverse areas without specificity to any geographical zone or region. Cluster analysis of the RAMS and PCR–RFLP revealed a high genotypic diversity within V. inaequalis isolates. Three major clusters were obtained and the isolates could not be categorized on the basis of either their geographical distribution or the cultivar from which they were isolated. amova analysis of pathogen populations at regional or race level revealed high diversity within the populations. Pairwise F_ST comparisons between the populations revealed less genetic differentiation, thereby indicating existence of frequent gene flow in Kashmir. The 24 rDNA sequences of V. inaequalis showed high haplotype diversity of 0.938 and 0.40 nucleotide diversity. Again clustering at regional or race level detected greater part of variability within groups than among groups, thereby indicating high diversity in V. inaequalis populations in Kashmir valley.     

Woodland canopy structure and the light response of juvenile Quercus lobata (Fagaceae)

I investigated competition for light between canopy plants and juvenile valley oaks (Quercus lobata Nee) in a mixed-broadleaf woodland of California's northern Coast Ranges. Canopy effects on understory light supply were separated among the overlying adult valley oak, the adult's woody understory, and neighboring trees and shrubs through a series of light sampling surveys and measurements of the number, size, and spatial distribution of neighboring plants. Light supply in the understory was primarily influenced by neighboring plants, with no detectable effect of the overlying adult valley oak. Light supply in the understory averaged 25% full sun due to a high frequency of canopy gaps and a typically open understory. Seedling response to understory light supply was investigated in an experimental sunfleck gradient (10%, 19%, and 100% full sun). Between 10% and 100% full sun, seedling growth increased by 90% and the shoot:∗∗∗root ratio changed from 1.561 to 0.607. Shade seedlings were also taller and produced fewer, larger, and thinner leaves than seedlings grown in full sun. A field survey of the spatial distribution and crown morphology of saplings and young adults found 1) the distance between young valley oaks and neighboring overstory trees to increase with neighbor size, and 2) crowns of the young oaks to be skewed away from neighbors. Although shading by the canopy was only moderate, canopy effects on understory light supply may restrict juvenile recruitment of valley oak in this woodland.     

Regional patterns of recruitment success and failure in two endemic California oaks

Oak woodlands and savannas are key defining landscapes in the California Floristic Province, making up almost a quarter of the region's forests and woodlands. Two endemic Californian oak species, valley oak (Quercus lobata Neé) and blue oak (Quercus douglasii Hook. & Arn.), are widely considered at risk of decline from persistent recruitment failures in the last century. However, decades of research have produced no definitive conclusion about the existence, extent, or causes of this ‘regeneration problem’. Underlying causes of perceived recruitment failure are unclear and could include drivers at distribution‐wide to local scales including climate and atmospheric changes, habitat fragmentation, altered herbivore populations, changing fire regimes, exotic plant and animal invasions, livestock grazing, and soil conditions altered by past land uses. We performed meta‐analyses of existing stand‐scale data from the published and grey literatures on seedling and sapling recruitment in blue and valley oaks throughout each of their distributions. We sought to evaluate whether distribution‐wide regeneration ‘problems’ exist for either species and to assess what factors correlate with distribution‐wide recruitment patterns. Nearly 80% of sites surveyed for blue oaks but fewer than 50% of sites surveyed for valley oaks contained some evidence of seedling or sapling recruitment. A majority of sites surveyed for both species appear to have insufficient recruitment to replace adult populations, though further demographic work would be required to quantify minimum replacement recruitment rates. Reserve sites were seven times more likely than non‐reserve sites to contain valley oak populations with evidence of recruitment. Blue oak recruitment patterns were weakly related to climate and geographical factors and strongly variable at subregional scales. We suggest several lines of additional research that could fill gaps in the existing literature and clarify the patterns emerging from this analysis.     

Leaf phenology mediates provenance differences in herbivore populations on valley oaks in a common garden

1. Plants from different populations often display a variation in herbivore resistance. However, it is rarely understood what plant traits mediate such differences. 2. It was tested how leaf phenology affects herbivore populations in a 15‐year‐old common garden of valley oaks (Quercus lobata Née) with different populations and maternal parents from throughout the Q. lobata range. 3. The abundance of leaf miners (Stigmella sp. Shrank) and leaf phenology of oaks in the common garden was measured. 4. Leaf miner abundance varied among provenance locations (population), but not among maternal parents within populations. Leaf phenology varied by provenance location and maternal parent, and trees that leafed out earlier accrued higher leaf‐miner abundance. Path analysis indicated that leaf phenology was the likely driver of provenance and parental differences in resistance to leaf miners. 5. Understanding population differences is particularly important when considering transport of genotypes for ornamental or restoration purposes. The present study suggests that similarity in leaf phenology may be one factor that could be used to find genotypes with a similar herbivore resistance to local genotypes.     

Function of defensive volatiles in pedunculate oak (Quercus robur) is tricked by the moth Tortrix viridana

The indirect defences of plants are comprised of herbivore‐induced plant volatiles (HIPVs) that among other things attract the natural enemies of insects. However, the actual extent of the benefits of HIPV emissions in complex co‐evolved plant‐herbivore systems is only poorly understood. The observation that a few Quercus robur L. trees constantly tolerated (T‐oaks) infestation by a major pest of oaks (Tortrix viridana L.), compared with heavily defoliated trees (susceptible: S‐oaks), lead us to a combined biochemical and behavioural study. We used these evidently different phenotypes to analyse whether the resistance of T‐oaks to the herbivore was dependent on the amount and scent of HIPVs and/or differences in non‐volatile polyphenolic leaf constituents (as quercetin‐, kaempferol‐ and flavonol glycosides). In addition to non‐volatile metabolic differences, typically defensive HIPV emissions differed between S‐oaks and T‐oaks. Female moths were attracted by the blend of HIPVs from S‐oaks, showing significantly higher amounts of (E)‐4,8‐dimethyl‐1,3,7‐nonatriene (DMNT) and (E)‐β‐ocimene and avoid T‐oaks with relative high fraction of the sesquiterpenes α‐farnesene and germacrene D. Hence, the strategy of T‐oaks exhibiting directly herbivore‐repellent HIPV emissions instead of high emissions of predator‐attracting HIPVs of the S‐oaks appears to be the better mechanism for avoiding defoliation.     

Evaluation of Endophytic Bacteria as Potential Biological-Control Agents for Oak Wilt

Endophytic bacteria were isolated from surviving live oaks (Quercus fusiformis) in Texas, where oak wilt is epidemic, and evaluated as potential biological control agents for the disease. Of the 889 bacterial isolates tested, 183 showed in vitro inhibition of the pathogen, Ceratocystis fagacearum. Six isolates were further evaluated for colonization of containerized Spanish oaks (Quercus texana) and live oaks. In general, when injected into the stems, Bacillus species colonized Spanish oaks more extensively than Pseudomonas species; whereas, the opposite was true for live oaks. In containerized live oaks inoculated with the oak wilt pathogen, preinoculation with Pseudomonas denitrificans 1-15 reduced the number of diseased trees by 50% and in the same trial decreased the percentage of crown loss by 17%. In a second trial, no reduction in numbers of diseased trees was observed; however, preinoculation with either strain 1-15 or Pseudomonas putida 5-48 significantly reduced crown loss. These studies indicate that a potential exists for the utilization of selected bacteria to control oak wilt.     

Growth of Valley Oak (<Emphasis Type="Italic">Quercus Lobata Nee</Emphasis>) in Four Floodplain Environments in the Central Valley of California

Although there have been numerous studies of California upland oak regeneration and growth there has been no research investigating oak sapling growth in riparian environments. This study looks at the growth response of young valley oak (Quercus lobata Nee), a dominant late successional riparian species in California, across environmental variation on a floodplain. Growth was measured over the course of three years at four different sites. The sites were chosen to represent the range of successional stages and surface age. Growth was significantly higher on younger, unforested sites. There was no difference in growth rate in the two forested sites (early successional cottonwood willow forest and late successional mature oak forest). Herbivory was highest in the cottonwood willow forest, where density of young oaks was also highest. The impact of flooding was measured on the youngest floodplain surface, an open floodplain restoration site where acorns were planted the year our study began. There was a significant negative impact of flooding on sapling growth in all but the first year of growth. Taken together these results suggest that existing forest trees and flooding both inhibit the growth of valley oaks on the floodplain, and that restoration in open sites may be more successful than restoration under an existing canopy.     

Ten years after: Release cutting around old oaks still affects oak vitality and saproxylic beetles in a Norway spruce stand

1. It is often suggested to release oaks (Quercus robur) from competition, to ensure their survival and boost their conservational value. However, few studies have explored how long-lasting this effect is and how it affects saproxylic beetles.
2. Ten years after cutting, we investigated effects of different release cutting levels (high, medium, and no release) around 140-year-old retained oaks in a commercial forest with Norway spruce (Picea abies).
3. We evaluated oak vitality using crown and dead wood measurements. Saproxylic beetles were caught in window traps, identified to species level, and grouped according to their association with oak and/or Norway spruce.
4. Released oaks had more light, higher temperatures, greater crown growth, and less dead wood in the crown compared to the no-release control.
5. After 10 years we still found a higher abundance of oak-associated beetles and higher overall species richness of saproxylic beetles in the released oaks. Beetle species composition significantly differed between released oaks and control.
6. We suggest avoiding planting trees beneath retained oaks when regenerating conifer forests and to proceed with conservation management during subsequent thinning by removing regeneration under the oak crowns. We emphasize the benefits of monitoring the retained oaks to maintain tree vitality, habitat quality, and insolation.

     

A glimpse at future forests: predicting the effects of <Emphasis Type="Italic">Phytophthora ramorum</Emphasis> on oak forests of southern Appalachia

The highly pathogenic Phytophthora ramorum, causal organism of sudden oak death (SOD), is established in forests of the Pacific Northwest (USA) and is threatening invasion of other regions. Given the breadth of its host range, with dozens of asymptomatic ornamental hosts and with oaks, Quercus spp., in the red oak (Erythrobalanus) subgenus particularly susceptible, we investigated the consequences of its invasion and establishment in oak-dominated deciduous forests of the eastern USA. We evaluated the nature and extent of pathogen invasion using vegetation assessments coupled with growth simulations. The woody plant community was assessed in three strata (upper, mid- and lower) and was used to characterize forest composition and structure. Using the Forest Vegetation Simulator (FVS), we then projected woody vegetation growth 50 years into the future with and without the effects of SOD. In forest simulations lacking pathogen invasion, little change in composition or structure is forecasted. Both red oaks and white oaks (subgenus Leucobalanus) increase slightly but significantly over the length of the simulation. In contrast, in SOD-affected forests our projections predict a significant loss of red oaks within 10 years of pathogen invasion. Basal area of white oaks and non-oaks is expected to increase more so in the absence of red oaks. The loss of red oaks to pathogen infection will result in greater increases in red maple, Acer rubrum, and yellow poplar, Liriodendron tulipifera, than in forests free of SOD. Loss of red oak represents a significant loss of hard mast, with potentially devastating consequences for wildlife. Red oak loss will also affect decomposition rates, nutrient cycling, forest structure, and timber values, with consequences for forest health and sustainability.     

Suitability of native and ornamental oak species in California for Agrilus auroguttatus

Goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is a new invasive species in southern California, USA. The extent of the host range of this insect is not known, but this knowledge will have a major impact on assessment of the risks that this pest poses to oaks [Quercus spp. (Fagaceae)]. We conducted laboratory tests to determine the potential suitability of native and ornamental oak species for larvae and adults of A. auroguttatus. We infested 179 cut logs (from 163 different trees) with eggs or larvae, measured neonate survival and, after 5 months, counted feeding galleries, and noted the proportion of galleries with late instars. Initial larval survival was generally high when larvae penetrated the phloem (range: 62–98% among oak species), and low by the time larvae began to feed at the phloem/xylem interface (range: 0–25% among oak species). The majority of larvae that established a visible feeding gallery survived to the fourth instar (total of 73% for all oak species). Larval galleries were established with greater frequency in red oaks (Section Lobatae) compared with other oaks (19 vs. 7 or 4%). All red oaks tested (Q. agrifolia Née, Q. kelloggii Newberry, and Q. wislizeni A. DC.) were likely suitable hosts for larvae. Larvae were apparently able to feed on some of the other oaks (Q. chrysolepis Leibmann, Q. suber L., Q. lobata Née, and Q. douglasii Hook & Arn), although it remains unclear whether these species would be preferred hosts under natural conditions. Adult longevity and fecundity varied little by species of oak foliage fed to adults. The host range of A. auroguttatus is likely limited by suitability of oak species for the larval rather than the adult life stage. Results support published field observations that red oaks are more suitable hosts than white oaks.     

Trunk injection of fosetyl‐aluminium controls the root disease caused by Phytophthora cinnamomi on Quercus ilex woodlands

In Spain, Quercus open woodlands are animal ranching systems of organic production seriously threatened by the exotic pathogen Phytophthora cinnamomi. The root disease it causes kills thousands of oaks annually. Effective disease management needs to integrate different techniques, and the use of a resistance inducer such as fosetyl‐Al can play a key role, because the use of potassium phosphite is prohibited in Spain. In a woodland where the pathogen recently arrived, 60 holm oaks in three different defoliation classes (asymptomatic, slight and moderate defoliation) were selected for trunk injection with pressurised capsules containing 4% of commercial fosetyl‐Al or water (controls). Holm oaks were checked periodically for defoliation and presence of the pathogen in roots and rhizosphere soil. Three years after treatments, defoliation was significantly lower in oaks treated with fosetyl‐Al, which even increased canopy cover, in comparison with control oaks, independent of the initial defoliation class considered. Chlamydospore density in rhizosphere soil, as well as the presence of the pathogen into the roots, was not significantly influenced by fosetyl‐Al treatments, although a trend to a lower presence of P. cinnamomi in roots was observed in treated oaks at every soil inoculum density detected. This study has shown that fosetyl‐Al, a phosphonate registered as a fungicide in the European Union, provides protection to holm oaks against P. cinnamomi, even exhibiting a therapeutic effect on pre‐existing infections. Consequently, this effective measure should be considered as part of the integrated approach to control this highly destructive pathogen in holm oak woodlands.     

Spread and potential host range of the invasive oak lace bug [Corythucha arcuata (Say, 1832) – Heteroptera: Tingidae] in Eurasia

1. The North American oak lace bug feeds on leaves of ‘white oaks” in its native range. In Europe, it was first discovered in northern Italy in 2000. In recent years, it has subsequently spread rapidly and population outbreaks have been observed in several European countries. In the present study, we summarize the steps of its expansion.
2. To predict its potential host range, we checked 48 oak species in 20 sentinel gardens in seven countries between 2013 and 2018.
3. In total, 27 oak species were recorded as suitable hosts; 13 of them are globally new ones, 23 out of the 29 in section Quercus (～ white oaks, an intrageneric taxonomic unit within genus Quercus), including Asian oaks, native to Japan, Korea and China, and four out of five in section Cerris (another intrageneric unit of the same genus), were accepted as hosts. None of the species in section Lobatae (red oaks) or in the Ilex group was accepted.
4. Host records were also collected in forest stands of 10 countries. We found 11 oak species that were infested. Outbreak populations were most commonly found on Quercus robur, Quercus frainetto, Quercus petraea and Quercus cerris, comprising widespread and outstandingly important oaks species in Europe.
5. Based on our findings, we conclude that suitable hosts for oak lace bug are present in most of Europe and Asia. This means that a lack of hosts will likely not restrict further range expansion.

     

Molecular data reveal that the tetraploid Tragopogon kashmirianus (Asteraceae: Lactuceae) is distinct from the North American T. mirus

Tragopogon kashmirianus (Asteraceae: Lactuceae) (2n = 24) was described based on collections from Kashmir. The tetraploid is morphologically similar to allotetraploid T. mirus from North America that has formed in western North America from the introduced T. dubius (2n = 12) and T. porrifolius (salsify; 2n = 12). Singh and Kachroo (1976 ) suggested that T. kashmirianus might have formed from the same diploid parental combination as T. mirus. To determine this, we investigated internal and external transcribed spacers (ITS, ETS) and five plastid regions of T. kashmirianus and species reported from Kashmir, northern India and neighbouring countries (T. badachschanicus, T. longirostris, T. porrifolius, T. pratensis, T. orientalis, T. subalpinus, T. trachycarpus, T. gracilis and T. dubius). Molecular data indicate that the parents of T. kashmirianus are not the European T. porrifolius and T. dubius. The exact parentage of T. kashmirianus is still unclear, but if it is an allotetraploid, at least one parent is a species native to Kashmir/India. Alternatively, it may represent an autopolyploid, again with the diploid parent native to Kashmir/India. We also found that ‘T. dubius’ from Kashmir is phylogenetically and morphologically distinct from collections of T. dubius from Europe and probably represents a previously unrecognized species. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 391–398.     

Hydraulic properties and freezing-induced cavitation in sympatric evergreen and deciduous oaks with contrasting habitats

We investigated the hydraulic properties in relation to soil moisture, leaf habit, and phylogenetic lineage of 17 species of oaks (Quercus) that occur sympatrically in northern central Florida (USA). Leaf area per shoot increased and Huber values (ratio of sapwood area to leaf area) decreased with increasing soil moisture of species’ habitats. As a result, maximum hydraulic conductance and maximum transpiration were positively correlated with mean soil moisture when calculated on a sapwood area basis, but not when calculated on a leaf area basis. This reveals the important role that changes in allometry among closely related species can play in co‐ordinating water transport capacity with soil water availability. There were significant differences in specific conductivity between species, but these differences were not explained by leaf habit or by evolutionary lineage. However, white oaks had significantly smaller average vessel diameters than red oaks or live oaks. Due to their lower Huber values, maximum leaf specific conductivity (K_L) was higher in evergreen species than in deciduous species and higher in live oaks than in red oaks or white oaks. There were large differences between species and between evolutionary lineages in freeze–thaw‐induced embolism. Deciduous species, on average, showed greater vulnerability to freezing than evergreen species. This result is strongly influenced by evolutionary lineage. Specifically, white oaks, which are all deciduous, had significantly higher vulnerability to freezing than live oaks (all evergreen) and red oaks, which include both evergreen and deciduous species. These results highlight the importance of taking evolutionary lineage into account in comparative physiological studies.     

Leaf morphological analyses in four European oak species (Quercus) and their hybrids: A comparison of traditional and geometric morphometric methods

Abstract

In this study, leaf morphology was assessed in a mixed oak stand (western France) using two geometric morphometric (landmark and outline) datasets and one dataset of 19 leaf measures. Adult oaks (817 oaks), comprising four white oak species (Quercus petraea, Q. robur, Q. pubescens and Q. pyrenaica), were sampled for DNA extraction and genetic analysis (nuclear microsatellites). Leaf morphology was assessed on 336 oaks, comprising pure species and hybrids as determined by genetic assignment. This comparative study of oak leaf morphology, based on the use of two free size geometric morphometric methods and a set of leaf measurements, combined with the genetic assignment of individuals to pure species or hybrids, provided information about the differences among species and the intermediate leaf morphology of their hybrids.     

Restoration of Florida scrub vegetation in an old field through 23 years after planting

Florida scrub, a fire‐maintained, xeromorphic shrubland, hosts many rare and declining species, but most scrub habitat has been lost to development and agriculture. Formerly cultivated sites offer an opportunity to restore Florida scrub. In this 23‐year study, we test whether scrub species could be restored to an old field and whether scrub vegetation composition and structure could be reestablished over time. Scrub oaks were planted in a section of an old field in 1992 after the site was cleared and treated with herbicide. Additional oaks and other scrub species were planted in 1993. We determined survival and growth annually of a marked sample of scrub species. We sampled vegetation cover in two height strata annually on 10 permanent line‐intercept transects in the old grove and on 20 transects in adjacent, intact scrub. Initial survival of Quercus geminata exceeded that of Q. chapmanii or Q. myrtifolia. Cover of scrub oaks greater than 0.5 m increased from 1.3% in 1992 to 65.2% in 2010. However, the vegetation structure of large Q. geminata did not resemble that of native scrub. Adaptive management led to cutting large oaks in the fall of 2010, and burning the site in early 2011. Cutting and burning appeared to stimulate sprouting and clonal spread of scrub oaks. Ordination analysis indicated directional change related to increasing scrub oak cover and time since planting but the old field still differed from intact scrub. Vegetation has developed toward scrub composition and structure but exotic grasses persist.     

Influence of canopy openness,ungulate exclosure,and low‐intensity fire for improved oak regeneration in temperate Europe

Failed oak regeneration is widely reported in temperate forests and has been linked in part to changed disturbance regimes and land‐use. We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks (Quercus robur, Quercus petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and low‐intensity surface fire (burn/no burn). Survival, relative height growth (RGR_H), browsing damage on naturally regenerated oaks (≤300 cm tall), and changes in competing woody vegetation were monitored over three years. Greater light availability in canopy gaps increased oak RGR_H (p = .034) and tended to increase survival (p = .092). There was also a trend that protection from browsing positively affected RGR_H (p = .058) and survival (p = .059). Burning reduced survival (p < .001), nonetheless, survival rates were relatively high across treatment combinations at the end of the experiment (54%–92%). Most oaks receiving fire were top‐killed and survived by producing new sprouts; therefore, RGR_H in burned plots became strongly negative the first year. Thereafter, RGR_H was greater in burned plots (p = .002). Burning altered the patterns of ungulate browsing frequency on oaks. Overall, browsing frequency was greater during winter; however, in recently burned plots summer browsing was prominent. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals (p < .001) and their heights (p < .001). Our results suggest that young, temperate European oaks may respond similarly to fire as their North American congeners. However, disturbance from a single low‐intensity fire may not be sufficient to ensure a persistent competitive advantage—multiple fires and canopy thinning to increase light availability may be needed. Further research investigating long‐term fire effects on oaks of various ages, species‐specific response of competitors and implications for biodiversity conservation is needed.     

A hypothesis on the evolution of isoprenoid emission by oaks based on the correlation between emission type and Quercus taxonomy

We show that Mediterranean oaks that emit isoprene, monoterpenes or no isoprenoids belong to different subgenera as indicated by morpho-taxonomy and molecular genetics. On the other hand, oaks from North America and Asia that are taxonomically similar to the Mediterranean monoterpene emitter Q. ilex emit isoprene only. We surmise that isoprene emission is a genetic character which evolved ancestrally in the oak genus since this is the prevalent emission type in oaks widespread around the world and adapted to different environments. This ancestral character may have been either lost or modified in more recent clades such as those originating the Mediterranean oaks. If our hypothesis is correct then the taxonomy of European oaks is validated by this independent trait. Isoprenoid emission could serve as a chemo-taxonomical marker and could be used to reconstruct the phylogeny of oaks in association with molecular markers. Received: 30 November 1997  / Accepted: 28 February 1998     

Occurrence of Larca lata H.J. Hansen (Pseudoscorpionida: Garypidae) and Allochernes wideri C.L. Koch (Pseudoscorpionida: Chernetidae) in tree hollows in relation to habitat quality and density

Many beetles associated with old trees are on national red lists, but pseudoscorpions living in similar habitats have received little attention. This study reports the habitat and occurrence patterns of two species of pseudoscorpions living in hollow trees. Their occurrence has been assessed by sieving wood mould from 274 oaks in southeastern Sweden and from museum specimens collected in Sweden. Larca lata is confined to hollow oaks with a large girth and a plentiful supply of wood mould. Allochernes wideri is much less particular about wood mould volume, trunk diameter and tree species. Larca lata inhabits hollow trunks with characteristics that are typical of very old trees, whereas A. wideri predominantly occurs in trunks in an earlier stage of hollow formation. Larca lata was almost exclusively found in larger assemblages of hollow oaks, which suggests long-term survival may be difficult when the network of suitable hollow trees is too sparse. Larca lata is a rare species in Europe and probably vulnerable to extinction, since it is dependent on a habitat which has declined severely in the last few centuries.     

Colonization, survival, and causes of mortality of Camerariu hamadryadella (Lepidoptera: Gracillariidae) on four species of host plants

Abstract.

• 1 The abundance, survival, and causes of mortality of Cameraria hamadryadella (Clemens) (Lepidoptera: Gracillariidae) were examined on four host plant species in Virginia, U.S.A. Quercus alba L. and Q.rubra L. are native within the geographic range of C.hamadryadella, and Q.robur L. and Q.benderi Baenitz are exotic. Q.robur is native to Europe, North Africa, and Asia and was probably introduced prior to 1850, and Q.benderi is of hybrid origin and introduced to cultivation before 1900. Q.alba and Q.robur are in the subgenus Lepidobalanus (white oaks), and Q.rubra and Q.benderi are in the subgenus Erythrobalanus (red oaks).
• 2 Larval mines of C. hamadryadella were abundant on both white oak species, including the exotic Q.robur, but were rare on host plants in the red oak subgenus. Un-hatched eggs of C.hamadryadella were not observed on red oaks. Other observations on host distribution indicate that C.hamadryadella is rarely found on red oaks. These observations are interpreted as circumstantial evidence that C. hamadryadella generally avoids ovipositing on red oaks.
• 3 Survival of C.hamadryadella to the adult stage was similar among all host species, but larvae tended to survive longer on hosts in the red oak subgenus. The observation of higher survival rates of early instar larvae on red oaks suggests that no nutritional or secondary chemical barrier reinforces the observed pattern of oviposition.
• 4 Significant differences in the distribution of the causes of mortality were detected between native and exotic host plant species. Larvae and pupae on native hosts were more likely to die because of predation, while those on exotic host plants were more likely to die because of parasitism and host feeding by adult female parasitoids. This pattern could arise because parasitoids prefer to forage on exotic host plants or because predators avoid foraging on exotic plants.
• 5 This study shows for C. hamadryadella that the only barriers to colonization and use of exotic hosts, in the white and red oak subgenera, are the presence of cues sufficient to stimulate oviposition and/or the absence of cues to deter oviposition. It also suggests that the presence of closely related native host plants in the region of introduction will increase the probability that exotic plants will be colonized by phytophagous insects.