Bark Discs Research Articles

Oviposition sites constructed in Pinus densiflora phloem by Monochamus alternatus and Monochamus saltuarius (Coleoptera, Cerambycidae)

ABSTRACT Monochamus alternatus Hope and M. saltuarius (Gebler) (Coleoptera: Cerambycidae) transmit Bursaphelenchus xylophilus causing pine wilt disease. They excavate a pit in the bark of pine trees, insert the ovipositor into the phloem through the pit, and oviposit. The size of oviposition sites in the phloem and positioning (array) of eggs in them were investigated to determine the size of bark samples to inspect B. xylophilus transmitted through the oviposition wounds. Both species constructed an oval, flat hollow as an oviposition site, in which there were 0−2 eggs for M. alternatus and 0−5 eggs for M. saltuarius. The mean length and width were 9.31 mm and 5.82 mm, respectively, for M. alternatus and 7.28 mm and 3.32 mm for M. saltuarius. The greatest length was 15.00 mm for M. alternatus and 10.10 mm for M. saltuarius. The distance from the ovipositor-inserted opening in the oviposition wound to the posterior end of egg increased with female body mass in both species. Each oviposition wound had one or two oviposition sites. Thus, the number of eggs per oviposition wound did not always represent the number of eggs deposited per oviposition behavior. Bark disks of >30 mm and >21 mm in diameter were suitable for inspecting the nematodes transmitted by M. alternatus and M. saltuarius, respectively.

Transmission of Bursaphelenchus mucronatus Mamiya et Enda (Nematoda, Aphelenchoididae) from Monochamus saltuarius (Gebler) (Coleoptera, Cerambycidae) to pine branches via vector’s oviposition wounds in comparison to B. xylophilus (Steiner et Buhrer) Nickle carried by M. alternatus Hope

ABSTRACT Non-pathogenic Bursaphelenchus mucronatus and pathogenic B. xylophilus are transmitted to pine trees by cerambycid beetles of the genus Monochamus. This study investigated the transmission of the two nematode species via vector’s oviposition wounds and their initial dispersal with relation to vector’s oviposition behavior and age for the B. mucronatus−Monochamus saltuarius and B. xylophilus−M. alternatus systems. M. saltuarius females were provided individually with a Pinus densiflora branch section. Immediately after the oviposition, branch sections were held at 25°C. The transmission of B. mucronatus was examined using the 15-mm-diam. bark disks containing an oviposition wound and their surrounding bark and xylem samples taken from branch sections 0 − 24 h after the oviposition. B. mucronatus was recovered only from the 15-mm-diam. bark disks. The proportion of oviposition wounds harboring B. mucronatus was 0.27 and the number of B. mucronatus transmitted into an oviposition wound averaged 2.1. When M. alternatus females were provided individually with a P. densiflora stem bolt, their oviposition behavior did not differ from M. saltuarius one. The inspection indicated that B. xylophilus was recovered from the 25-mm-diam. bark disks containing an oviposition wound and the surrounding bark and xylem samples taken from the bolts 0 − 24 h after the oviposition. The proportion of oviposition wounds harboring B. xylophilus was 0.31 and the number of B. xylophilus transmitted into an oviposition wound averaged 1.0. This study suggested that B. mucronatus left the vector’s oviposition wounds more slowly than B. xylophilus.

Wound occlusion and annual stem growth rates of five woodland tree species in South Africa

Sustainable management strategies for trees are informed by research on growth rates and regeneration. In a 1998 study of bark thickness and tree size, six species (all used for traditional medicine) were sampled by removing 5 cm-diameter bark disks at four height intervals on 210 stems at 15 sites in South Africa. An impromptu revisit to one site in 2003 revealed that wounds for one species exhibited very little wound occlusion. These observations prompted a 2004 study on wound occlusion and stem growth for five of the species at six sites (Albizia adianthifolia, Balanites maughamii, Elaeodendron transvaalense, Searsia chirindensis, Warburgia salutaris), where 84 stems were re-measured. There were species-specific stem growth and wound occlusion rates. In general, annual lateral stem growth at 1.3 m was inversely related to stem size (corroborated by lateral widening responses of the original wound edges). There was also a tendency for smaller and/or faster growing stems to exhibit more wound occlusion and faster rates of bark regrowth – except in W. salutaris, where smaller individuals exhibited comparatively lower rates of occlusion compared to bigger individuals. All wound occlusion was by bark edge growth (typically <3 mm y−1); only A. adianthifolia showed complete wound closure, whereas B. maughamii showed the least (17%±19%). An inverse relationship existed between density (timber and bark) and stem growth, wound occlusion and lateral widening of the old scar edges – except for S. chirindensis. Hence trees with softer wood and bark generally grew quicker and exhibited more wound occlusion than trees with harder wood and bark.

Nutrient accumulation in Eucalyptus bark at different population densities

ABSTRACT The objective of this study was to quantify the accumulation of nutrients in the bark of four eucalyptus clones at 12 years-of-age, planted at different population densities, and the values were extrapolated to kg of nutrients per hectare. The experiment used randomized blocks in a 4 × 3 factorial design and three replications, with four Eucalyptus clones (2486, I182, I144, and GG100) planted at three population densities (416, 833, and 1111 trees ha-1). The rigorous cubage of three trees per plot was performed by collecting discs of bark at the following heights: diameter at breast height (1.30 m), 0, 25, 50, 75, and 100% of the commercial height of the stem. The bark discs of each tree were grouped and used to determine N, P, K, Ca, Mg, and S content, in addition to the basic density. The volume and dry mass of bark per tree was estimated and the accumulation of nutrients per tree ha-1 was estimated sequentially, for each population density. Analysis of variance and Tukey’s post-hoc tests verified that Ca showed the greatest accumulation in the bark, followed by N, K, S, Mg, and P. The increase in population density contributed to higher bark production and greater nutrient accumulation per hectare. However, this increase was not evident when comparing densities of 833 and 1111 trees ha-1.

First Report of Canker and Root Rot of Almond Caused by Phytophthora plurivora in Turkey

HomePlant DiseaseVol. 100, No. 7First Report of Canker and Root Rot of Almond Caused by Phytophthora plurivora in Turkey PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Canker and Root Rot of Almond Caused by Phytophthora plurivora in TurkeyO. Çiftçi, Ş. Türkölmez, S. Derviş, and Ç. U. SerçeO. ÇiftçiSearch for more papers by this author, Ş. TürkölmezSearch for more papers by this author, S. DervişSearch for more papers by this author, and Ç. U. SerçeSearch for more papers by this authorAffiliationsAuthors and Affiliations O. Çiftçi Ş. Türkölmez , Diyarbakır Plant Protection Research Station, 21110 Yenişehir, Diyarbakır, Turkey S. Derviş , Department of Plant Protection, Agriculture Faculty, Mustafa Kemal University, 31034 Antakya, Hatay, Turkey Ç. U. Serçe , Department of Plant Production and Technologies, Faculty of Agricultural Sciences and Technologies, Niğde University, 51240 Niğde, Turkey. Published Online:5 May 2016https://doi.org/10.1094/PDIS-12-15-1533-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Almond [Prunus dulcis (Miller) D.A. Webb.] is one of the most frequently consumed nut species grown in Turkey. In early March 2015, ∼20% of 13,000 one-year-old almond (P. dulcis cv. Ferragnes) seedlings in a nursery in Gaziantep showed sunken and blackened cankers on aboveground parts and root rot. Tissue samples taken from the margins of stem cankers and root lesions were placed on grated apple corn meal agar (Türkölmez et al. 2015) amended with P5ARPH per liter. Plates were incubated for 4 days at 20°C in the dark and a Phytophthora species was consistently isolated from the tissues. Isolates were homothallic with paragynous antheridia, smooth-walled spherical oogonia (24.7 to 29.6-μm diam), and both plerotic (1.3 to 1.4-μm wall diam) and aplerotic golden brown oospores (23.3 to 27.8 μm diam) on V8 juice agar (V8A) and produced semipapillate, noncaducous sporangia (35.5 to 53.2 × 26.3 to 38.4 μm; L:B ratio from 1.3 to 1.4 μm), which were usually obpyriform, ovoid, ellipsoid or irregular, and rarely possessed more than one apex, formed on simple or sympodial sporangiophores in nonsterile soil extracts. On V8 agar, colonies had a slight chrysanthemum growth pattern with limited aerial mycelium at the center of the colonies, whereas on PDA the colonies had a clear chrysanthemum growth pattern and aerial mycelia at the center of the colony. The minimum, optimum, and maximum temperatures for mycelium growth on V8A were 5, 25, and 32°C, respectively. On the basis of the morpho-physiological features, isolates were identified as P. plurivora T. Jung & T.I. Burgess from the ‘P. citricola complex’ (Jung and Burgess 2009). Genomic DNA was extracted from two representative isolates. The internal transcribed spacer (ITS) region of rDNA was amplified using the ITS6/ITS4 primer pair and sequenced (GenBank Accession Nos. KU221328 and KU310937). BLAST searches showed a 100% identity with a type isolate of P. plurivora (FJ665225). The sequence also contained the polymorphic nucleotides that are distinctive of this species (Jung and Burgess 2009). Pathogenicity was tested on shoot segments from ten 1- to 2-year-old P. dulcis cv. Ferragnes (5 to 7 mm diam, 20 cm length) by replacing the 5-mm bark disks of shoots in the middle of each shoot segment with the same-sized mycelial disks of P. plurivora grown on V8 agar. Ten control segments were similarly inoculated with sterile V8 agar disks. The wounds were wrapped with Parafilm, and the shoots were incubated in moist chambers in 100% RH at 23°C. Phytophthora plurivora caused cankers on almond shoots within 5 days after inoculation, and the noninoculated control shoots remained symptomless. To test the pathogenicity on roots, primary roots of 10 P. dulcis cv. Ferragnes seedlings (1-year-old) were wounded with a scalpel, and mycelial disks (3 per plant) of P. plurivora grown on V8 agar were placed under the cortical tissue after removing 10 to 15 cm of soil around the root base. The inoculated and exposed roots were then covered with soil. Ten control seedlings were similarly inoculated with sterile disks. The soil was kept wet by watering plants daily as required. All seedlings were grown in a greenhouse at air temperatures from 24 to 30°C. No disease developed in the controls, but P. plurivora caused wilt and root rot after 2 months. Koch’s postulates were satisfied after reisolating P. plurivora from all inoculated shoots and roots. To our knowledge, this is the first report of P. plurivora causing canker and root rot on almond plants. In late April 2015, all naturally infected almond seedlings in the nursery were collapsed and destroyed by this oomycete, indicating that it might be a significant threat to almond plantations and orchards in the postnursery phase.

Evaluation of Insecticides for Control of Overwintering Hylurgopinus rufipes (Coleoptera: Curculionidae)

A bark disk bioassay was used to assess the effectiveness of different insecticides for control of overwintering adult native elm bark beetles, Hylurgopinus rufipes (Eichoff) (Coleoptera: Curculionidae). Insecticides were applied to the base of the trunks of living American elm trees, Ulmus americana L., and bark disk samples were removed at intervals with a hole saw. Adult H. rufipes were exposed in bioassay chambers for which the bark disks formed the floor of the chamber. In September 2005, chlorpyrifos, permethrin, and a water control were applied to trees in five replicated blocks, and bark disk samples were taken at intervals over the following 725 d. In September 2006, chlorpyrifos, permethrin, carbaryl, bifenthrin, and a water control were applied to trees in six replicated blocks, and disk samples were removed at intervals up to 1,163 d after application. In both experiments, beetle mortality was 100% on chlorpyrifos-treated disks removed up to 725 d after treatment and, in the 2006 trial, declined thereafter. The pattern of mortality in the bifenthrin treatment did not differ significantly from that in the chlorpyrifos treatment in the 2006 experiment. Average corrected mortality on disks treated with permethrin or carbaryl declined below 100% by 11 d after application. On disks removed in the May following treatment, 248 d after application, average corrected mortality was 42-44% on permethrin-treated disks and 26% on carbaryl-treated disks.

Biological control of chestnut canker, caused by Cryphonectria parasitica, by antagonistic organisms and hypovirulent isolates

Biological control of chestnut blight was investigated by using 3 hypovirulent isolates of Cryphonectria parasitica, 5 Trichoderma sp., 4 Penicillium sp., and 4 Bacillus sp. isolates. Hypovirulent isolates and antagonistic organisms were obtained from samples collected from the Black Sea region of Turkey, in 2008 and 2009. Effectiveness of the hypovirulent isolates and antagonistic microorganisms was tested on 3-year-old chestnut saplings. In the tests, bark disks of 6 mm were removed from the stem bases and culture disks of the virulent isolate of C. parasitica were first placed into the hole and then the hypovirulent isolate or the antagonistic fungi. Bacillus strains were applied as bacterial suspensions of 10^{10} cell mL^{-1} to the holes; then the virulent isolate of C. parasitica was placed. Evaluations were made by measuring the canker lengths in 3 periods and effectiveness was given as percent inhibition (PI) of the treatments. Antagonistic microorganisms yielded varying PI values in 3 time periods and the highest rate of inhibition (68%) was obtained from the Trichoderma sp. isolate T - 2. A Penicillium sp. isolate (P - 3) and 2 Bacillus spp. isolates (B - z and B - b) also provided 30%, 40%, and 31% disease inhibition, respectively, 58 days after the inoculation. Effectiveness of the hypovirulent isolates varied depending on the virulent isolates and the hypovirulent isolate Z - 1 provided 59% inhibition against the most virulent isolate K - 19, while it gave 32% inhibition against the less aggressive isolate K - 44. The other hypovirulent isolate Ba - 6 also inhibited the canker development of the virulent isolate by 42%.

Spatial distribution of Neonectria species associated with beech bark disease in northern Maine

Beech bark disease (BBD) requires prior infestation of bark by an exotic scale insect, Cryptococcus fagisuga, to permit infection by one or more fungi, primarily Neonectria ditissima and Neonectria faginata. Previous studies in North America report a progression in which N. faginata replaces N. ditissima as the dominant pathogen in the BBD complex. To examine the status of the Neonectria populations in forests that have developed for decades with and without BBD a survey was conducted 2005–2006 in northern Maine. Ascospore measurements from 201 beech bark disks containing mature perithecia support reports that, once established, N. faginata dominates the BBD complex. However stands did contain more N. ditissima when other highly susceptible hardwood tree species were present (R2 = 0.775), regardless of disease severity. Abundance of N. ditissima in areas long affected by BBD suggests that N. ditissima, by continually supplying inocula from nonbeech hosts, continues to affect BBD.

Winter mortality in sub‐corticolous populations of Ips typographus (Coleoptera, Scolytidae) and its parasitoids in the south‐eastern Alps

Abstract A study concerning the winter mortality of a sub‐corticolous population of Ips typographus and its parasitoids has been carried out in the south‐eastern Alps (Italy) during the winter 1997/98. Three attacked spruce trees were sampled three times (November, February and April) by collecting infested bark disks (1 dm2 each). All insects that emerged from the bark or died in the samples before emergence were counted. The mean number of living Ips typographus occurring under the bark decreases by 49 % from November to April. Winter mortality mainly affects larval stages and young adults. The same trend was observed for the parasitoids Coeloides bostrychorum (48.5 %) and Roptrocerus xylophagorum (47.5 %).

Egg allocation by Bracon hylobii Ratz., the principal parasitoid of the large pine weevil (Hylobius abietis L.), and implications for host suppression

Summary 1 The braconid parasitoid Bracon hylobii Ratz. is one of the few specialist natural enemies of the large pine weevil, Hylobius abietis L., a destructive pest of conifer transplants. An assessment of its role as an agent of biological control requires a detailed knowledge of the allocation of its reproductive effort. 2 Parasitoid females were continuously observed in laboratory culture with individually reared host larvae in bark discs. The outcome of sequential parasitoid–host encounters was recorded by subsequent examination of hosts and by rearing all parasitoids. 3 Parasitoids avoided ovipositing on host larvae < 100 mg fresh weight, even though such larvae represented sufficient biomass for complete parasitoid development. All larger larvae were vulnerable to attack, which leaves a window of vulnerability for parasitoids of about 90% of weevil larval life. 4 Parasitoids presented with a range of host sizes showed no preference above 100 mg for the size of host first attacked, but allocated more eggs and a greater total handling time to larger hosts. 5 Most eggs were deposited on the first host attacked, with progressively fewer allocated to subsequent hosts. However, oviposition experience did not affect the time spent on the next host. 6 From these results it is anticipated that when weevil larval size is reduced by less favourable feeding substrates, fewer parasitoid eggs will be allocated to each but more host larvae will ultimately be attacked. 7 Generation time, host finding, oviposition rate, clutch size, life expectancy and diapause induction are strongly affected by temperature. Life expectancy is substantially shorter for parasitoids deprived of non-host food supplement. At 15 and 20 °C the number of hosts attacked and the number of eggs deposited decreased with female age. 8 Bracon hylobii is inevitably poorly synchronized with a variable life-cycle host; it is egg-limited and can enter diapause at a relatively high field temperature. None of these characteristics suggest that it could stabilize the abundance of its host below an economically acceptable threshold density. However, the reproductive potential of the parasitoid suggests that it could make a significant contribution to larval mortality and suppress adult recruitment, thus complementing other control strategies.

Adverse Effects of Epiphytic Crustose Lichens upon Stem Photosynthesis and Chlorophyll of Populus tremula L.

AbstractDry cork layer (phellem) in stems of Populus tremula transmitted 35–55 percent of incident irradiation, depending upon moisture content. A cover of crustose Lecanora lichens reduced transmission through phellem to 10 percent or less of incident irradiation. The bark contains photosynthetically active cells. Apparent quantum yield for photosynthetic O2‐evolution was 0.017 in bark covered with dry Lecanora compared with 0.070 in naked bark. The capacity for gross photosynthesis in high light (1090 μmol photons m−2 s−1) was reduced by 50 percent in Lecanora‐covered bark. Lecanora did not reduce the ratio between variable and maximal chlorophyll a fluorescence (Fv/Fm). Chlorophyll content per unit area was similar in leaves and naked bark of Populus tremula. The chlorophyll content in the bark decreased with increasing chlorophyll content in Lecanora. Chlorophyll a/b ratio was 2.5 in the bark compared with 4.0 in leaves and in Lecanora, and the ratio decreased down the stems. The a/b ratio was 2.3 in Lecanora covered bark compared with 2.6 in naked bark. The changes in bark photosynthesis below a Lecanora crust were probably due to acclimation of bark photosynthesis to shade, since the lichen acids in the measured lichens neither suppressed photosynthetic O2‐evolution nor changed the Fv/Fm in bark disks.

Diffusion of 14C-Flurprimidol in Various Carriers Through Excised Silver Maple Bark

Bark banding is one alternative to trunk injection of tree growth regulators (TGRs). The objective of this study was to compare the penetrability of various oils as carriers for a TGR applied to the bark. Five p.l of 14C-flurprimidol (225,000 dpm) and unlabeled flurprimidol dissolved in isopropyl alcohol and selected oils (Androc Basal Oil, ArborChem Basal, Arborchem Clean Cut, CWC Hy-Grade I, Exxon Aromatic 200, Exxon Orchex 796, Leffingwell Carrier #9, and N.G. Gilbert Riteway Oil) were applied to bark excised from silver maple (Acer saccharinum ). Bark discs, 1.35 cm diameter, were sealed in a diffusion chamber and the rates and amounts of 14C-flurprimidol that moved through the bark were measured by liquid scintillation spectrometry. Rate of diffusion, measured as dpm/day for nine days, was similar for each oil. The pattern of penetration was an initial flux the first 24 hours followed by a diminished rate of penetration by the end of day two and a gradual increase during the next seven days.

Stilbene glucoside levels and the resistance of Sitka spruce (Picea sitchensis) tissues to colonization by root‐ and butt‐rotting fungi

The relationship between constitutive stilbene glucoside (astringin and isorhapontin) levels in Sitka spruce (Picea sitchensis) bark and resistance of these tissues to colonization by the root‐ and butt‐rot fungi Heterobasidion annosum and Phaeolus schweinitzii was determined in vitro in excised bark tissues. Two experimental systems were developed. In one, 15‐mm‐diameter bark discs taken from mature forest trees were challenged with mycelial cultures of the fungi; in the other, 70‐ or 100‐mm lengths of stem, up to c. 30 mm diameter, were similarly challenged at the lower cut end. The extent of fungal colonization or necrosis in the challenged tissues was determined. The results indicated that both systems were capable of detecting differences in bark susceptibility to colonization between individual trees. No consistent correlation between stilbene levels and resistance to colonization by either fungus was found.

Patterns of Hyperparasitism of Cotesia melanoscela (Hymenoptera: Braconidae) in Southern Ontario

Patterns of hyperparasitism of cocoons of Cotesia melanoscela in southern Ontario were studied by periodic sampling of naturally occurring cocoons found under burlap bands and by deploying laboratory-produced sentinel cocoons on bark disks. At least six species of hyperparasitoids were recovered. The most common species of hyperparasitoids showed definite associations with sampling method and with red or white oak trees. Hyperparasitism of C. melanoscela began in early June and persisted throughout the summer. Peak activity of hyperparasitoids was in late June and early July and was coincident with the maximum number of available natural C. melanoscela cocoons in diapause. The probability of C. melanoscela survival during any single sampling interval declined steadily over the sampling period (14 June–3 August 1989). During this sampling period, 95.9% of the available C. melanoscela cocoons were killed by hyperparasitoids. This estimate of hyperparasitism is a minimum rate for Ontario; cocoons not attacked by the end of our sampling period were in diapause and thus were vulnerable to hyperparasitism for up to 10 mo after sampling ended.

Microfungi from Carpinus caroliniana

The microfungal flora and community structure of the bark of Carpinus caroliniana is described as perceived by a direct isolation method. Twenty-four bark discs were removed from 10 trees at five different sites in New Jersey and West Virginia and applied to three different isolation media. From 1200 bark discs from 50 trees, 155 species of fungi were isolated. The overall recovery rate was 11.5 species/tree. A medium with cycloheximide gave the highest species recovery rates and isolated the highest percentage of all the species recovered. A medium of malt–yeast extract gave the most isolates but lowest species recovery rate. Eleven of the 12 dominant species were preferentially isolated on one of the three isolation media. The community structure of the fungi recovered from Carpinus bark exhibited the typical dominance–diversity curve that has been reported for other saprobic fungal communities. Generally, the floristic composition was similar to the bark of other tree species previously studied in temperate deciduous forests. The total number of isolates was dominated by a few species of ubiquitous epiphytic taxa, but a large percentage of the species recovered appeared either at a single site or on a single tree. Sterile isolates accounted for 39% of the species and Coelomycetes for 13% of the species. The sites from West Virginia had a significantly higher recovery rate of species per tree than the New Jersey sites. In a search for fungi for potential biotechnological applications, bark is an easily utilized and rich resource. Simple isolation methods yield several ecological groups of fungi, including terrestrial epiphytes, soil decomposers, endophytes, entomopathogenic fungi, Ingoldian Hyphomycetes, and decomposer Basidomycetes. Key words: bark, ironwood, isolation methods, microbial diversity.

The role of stilbenes in resistance of Sitka spruce ( Picea sitchensis (Bong.) Carr.) to entry of fungal pathogens

The major constitutive antifungal compounds present in the bark of Sitka spruce ( Picea sitchensis) were the stilbene glucosides astringin (5,3′,4′,-trihydroxystilbene-3-β- d-glucoside) and rhaponticin (5,3′-dihydroxy-4′-methoxystilbene-3-β- d-glucoside). In healthy bark, levels of astringin and rhapontirin of around 10–15 mg g −1 tissue (fresh weight) were found. At concentrations above 1 mg ml −1 these compounds inhibited the growth in vitro of two weakly pathogenic decay-causing fungi Phaeolus schweinitzii and Sparassis crispa. Other, more pathogenic fungi responded in a different way. Heterobasidion annosum and Rhizina undulata were less severely inhibited, whereas Armillaria ostoyae and Stereum sanguinolentum were stimulated. In excised bark discs, maintained in vitro, levels of the glucosides fell markedly following fungal challenge. Concomitant with this loss, their aglycones, astringenin (5,3,3′,4′-tetrahydroxystilbene) and isorhapontigenin (5,3,3′-trihydroxy-4′-methoxystilbene) accumulated. Based on estimates of ED 50 values, the antifungal activity in vitro of isorhapontigenin against P. schweinitzii was six times greater than that of rhaponticin. Loss of stilbene glucosides from challenged discs appeared to be associated with the production of β-glucosidase enzymes by the invading fungi. Sensitivity to rhaponticin of the six test fungi appeared to be correlated broadly with their ability to metabolize this compound in vitro. After incubation with rhaponticin, culture filtrates of the two weak pathogens contained substantial quantities of both the glucoside and the aglycone isorhapontigenin, whereas only small amounts of these compounds remained in the medium after incubation with the other more pathogenic species tested. Colonization of bark discs by P. schweinitzii, measured by a chitin assay, was considered in relation to levels of stilbene aglycones produced following challenge. During the period from 3 to 10 days after challenge when stilbene aglycone levels were increasing, chitin levels remained static. Quantities of chitin increased 12 days after challenge concomitantly with a fall in the level of stilbene aglycones. Penetration of excised bark discs by the six fungi showed only a doubtful relationship with pathogenicity, with H. annosum showing the most mycelial growth and S. sanguinolentum the greatest depth of penetration. The necrotic response of the host tissues was similar with all rapidly growing species. Stilbene agiycones also accumulated around wounds made into root bark of standing trees, although because of fluctuating environmental conditions, results were much more variable than with the excised bark disc system. The excised bark disc system proved to be of considerable value in the study of the chemical responses of Sitka spruce roots to fungal challenge, overcoming the physical and environmental problems associated with such experiments conducted on trees in the field. The significance of these chemical mechanisms in the defence of Sitka spruce root bark against the ingress of potential pathogens and decay-causing fungi is discussed.

Comparative laboratory studies on three fungal pathogens of the elm bark beetle Scolytus scolytus: Pathogenicity of Beauveria bassiana, metarhizium anisopliae, and Paecilomyces farinosus to larvae and adults of S. scolytus

The entomogenous fungi Beauveria bassiana (nine isolates), Metarhizium anisopliae (seven isolates), and Paecilomyces farinosus (four isolates) were tested as pathogens of larvae of the elm bark beetle, Scolytus scolytus. Single isolates of B. bassiana and M. anisopliae were also tested against adult beetles. Of the 21 isolates tested as conidial suspensions against larvae, all proved pathogenic. The three most and least virulent isolates were, respectively, isolates of B. bassiana and M. anisopliae. The other isolates fell between these two extremes, with the four P. farinosus isolates all moderately virulent. Spore retention on larvae following inoculation was estimated by washing conidia off the larvae. From the results it was possible to relate larval mortality to the approximate spore dose causing infection at different spore concentrations. Thus, application of spores of the three pathogens at a concentration of 10 3 spores/ml resulted in limited mortality. At this concentration, an average of only a single spore was recovered from the inoculated larva. Adult bark beetles also proved susceptible to infection by isolates of B. bassiana and M. anisopliae. They were exposed to discs of elm bark dipped in a conidial suspension. It was estimated that a dose of less than 100 spores could cause infection of beetles following feeding on the elm bark discs.

FEEDING AND BORING BEHAVIOR OF THE BARK BEETLEIPS PARACONFUSUS(COLEOPTERA: SCOLYTIDAE) ON THE BARK OF A HOST AND NON-HOST TREE SPECIES

AbstractMaleIps paraconfususselected a host, ponderosa pine (Pinus ponderosa), over a non-host, white fir (Abies concolor), only after the beetles had bored through the outer bark and into the phloem. Males, when given a choice between bark discs of these tree species in petri dishes, bored readily through the outer bark of either species. However, the beetles penetrated no more than 1 mm into the phloem of white fir, but they bored extensively in the phloem of ponderosa pine. The beetle’s preference for the pine over fir phloem was apparent with intact samples of phloem with the outer bark removed and with ground phloem. No preferences were apparent for the ground or intact pine or fir outer bark, with the phloem removed. The beetles bored preferentially in fissured as opposed to smooth outer bark of either tree. Beetles did not feed in the outer bark but did feed in the phloem of either species. In field experiments beetles attracted to logs of pine and fir bored through the outer bark of each species in nearly equal numbers. In white fir they re-emerged and departed soon after penetration of the phloem, whereas in ponderosa pine they continued excavation of tunnels in the phloem. In contrast, few beetles penetrated even the outer back of incense cedar (Calocedrus decurrens), another non-host species.

THREE METHODS OF SAMPLING MITES PHORETIC ON BARK BEETLES: A COMPARISON

AbstractWhen a few large trees are to be sampled, emergence traps provide more reliable counts of mites that are phoretic on southern pine beetles than either removal of bolts or removal of 100 cm2 bark discs. When a large sample from smaller trees is required, removal of bolts is preferable to removal of disc samples. Emergence traps or bolt samples are preferable to disc samples because: (1) fewer mites are lost during transportation and rearing; (2) mites are not left on the xylem; (3) fewer die from desiccation during rearing; and (4) fewer non-phoretic stages accumulate in the collecting medium.

Effects of Sulphur Dioxide on Lichen and Moss Transplants

Injury symptoms in lichen and moss transplants have been correlated with the SO_2 concentrations prevailing at their exposure sites in the Sudbury area during 1970. For this purpose bark—discs bearing lichens and mosses were cut out from an unpolluted region nearly 40 km E of Sudbury. The discs were individually photographed and the epiphytes on them were inventoried. These were then arranged in groups of six in cut—out holes on wooden boards. Two such boards were fixed at a height of 8—10 m on a tall, exposed tree at each of the 19 sites selected in the five SO_2—pollution zones delineated for the area. After one year of exposure, the boards were carefully removed and the discs were rephotographed. The changes in epiphytes, especially in Parmelia sulcata, taking place in the different pollution zones were compared with respect to external and internal morphology, biomass, acidity, total sulfur, and chlorophyll. The results indicate that different concentrations of SO_2 produce different sets of harmful effects which appear to be more or less directly related to the levels of pollution. So far the trend has been to relate the floristic and/or phytosociological characteristics of lichens and mosses to the ambient concentrations of SO_2, but in the present study a quantitative correlation has been sought between the levels of injuries produced in these organisms and the levels of SO_2 to which they are exposed in the field.