Distribution pattern of entry holes of the tree-killing bark beetle Polygraphus proximus.

Bark beetles attack their hosts at uniform intervals to avoid intraspecific competition in the phloem. Bark texture and phloem thickness also affect bark beetle attacks, and the bark characteristics are not spatially homogeneous; therefore, the distribution patterns of entry holes can demonstrate an aggregated distribution. Polygraphus proximus Blandford (Coleoptera: Scolytinae) is a non-aggressive phloephagous bark beetle that feeds on Far Eastern firs. They have caused mass mortality in Russia and Japan. However, the distribution pattern of entry holes of P. proximus and spatial relationships with bark characteristics have not been studied. Thus, we investigated the distribution pattern of entry holes of P. proximus. The distribution of entry holes was significantly uniform in most cases. As the attack density increased, an aggregated distribution pattern within a short distance (< 4.0 cm) was observed. The rough bark had a significantly higher number of entry holes than the remaining bark. The distribution pattern of entry holes demonstrated a significantly aggregated spatial association with rough bark. Finally, rough bark around knots had significantly thicker phloem than the remaining barks. These suggest that P. proximus may preferentially attack rough bark to reproduce in the thicker phloem under a rough bark surface.

Phytophthora abietivora, A New Species Isolated from Diseased Christmas Trees in Connecticut, U.S.A.

A number of fir species (Abies) are produced as Christmas trees around the world. In particular, Fraser fir (Abies fraseri (Pursh) Poir.) is popular as it yields high-quality Christmas trees in temperate North America and Europe. A Phytophthora sp. causing root rot on Fraser fir was isolated from a Christmas tree farm in Connecticut, U.S.A., and found to be new to science according to morphological and molecular phylogenetic analysis using multilocus DNA sequences from ITS, Cox1, ß-Tub, Nadh1, and Hsp90 loci. Thus, it was described and illustrated as Phytophthora abietivora. An informative Koch's postulates test revealed that P. abietivora was the pathogen causing root rot of Fraser fir.

Interactions Between Root Rotting Phytophthora, Abies Christmas Trees, and Environment.

Defining host-pathogen interactions between species of root-rotting Phytophthora and Abies in Christmas tree production areas is important for tailoring management activities on a regional scale and for developing molecular tools for identifying resistant host species. Classifying Abies species as resistant or susceptible is complicated by regional variation in abundance and aggressiveness of Phytophthora species and the influence of environment on symptom expression and host vigor. Because previous studies performed to assess host response to Phytophthora root rot (PRR) have focused on one or a few species of either the host or pathogen, a multifactorial experiment was conducted to assess the responses of seven species of Abies challenged with three isolates each of four Phytophthora species under contrasting temperature conditions. Evaluation of mortality, root rot severity, and remaining root biomass after 16 weeks of exposure to the pathogen confirmed prior inferences regarding inherent variation in the resistance responses of various species of Abies and demonstrated evidence of variation in aggressiveness among species of Phytophthora as well as different isolates of the same Phytophthora species. The ambient temperatures at which studies were conducted had a conspicuous effect on host mortality, root rot severity, and radial growth of Phytophthora. Understanding how host responses differ under variable pathogen attack and ambient environment will improve efforts to control PRR using host species substitutions on infested ground.

Phenological shifts in conifer species stressed by spruce budworm defoliation.

Synchrony between host budburst and insect emergence greatly influences the time window for insect development and survival. A few alterations of bud phenology have been reported under defoliation without clear consensus regarding the direction of effects, i.e., advance or delay. Here, we compared budburst phenology between conifers in defoliation and control treatments, and measured carbon allocation as a potential mechanistic explanation of changes in phenology. In a 2-year greenhouse experiment, saplings of balsam fir, black spruce and white spruce of two different provenances (north and south) were subjected to either control (no larvae) or natural defoliation treatment (larvae added) by spruce budworm. Bud and instar phenology, primary and secondary growth, defoliation and non-structural carbohydrates were studied during the growing season. No differences were observed in bud phenology during the first year of defoliation. After 1 year of defoliation, bud phenology advanced by 6-7 days in black spruce and balsam fir and by 3.5 days in white spruce compared with the control. Because of this earlier bud break, apical and shoot growth exceeded 50% of its final length before mature instar defoliation occurred, which decreased the overall level of damage. A sugar-mediated response, via earlier starch breakdown, and higher sugar availability to buds explains the advanced budburst in defoliated saplings. The advanced phenological response to defoliation was consistent across the conifer species and provenances except for one species × provenance combination. Allocation of carbon to buds and shoots growth at the expense of wood growth in the stem and reserve accumulation represents a shift in the physiological resources priorities to ensure tree survival. This advancement in bud phenology could be considered as a physiological response to defoliation based on carbohydrate needs for primary growth, rather than a resistance trait to spruce budworm.

Site factors and management influence short-term host resistance to spruce budworm, Choristoneura fumiferana (Clem.), in a species-specific manner.

BACKGROUND: This study examined the interactions between thinning and soil drainage classes on the resistance of balsam fir, Abies balsamea (L.) Mill, white spruce, Picea glauca (Moench) Voss, and black spruce, P. mariana (Mill.) BSP, to spruce budworm, Choristoneura fumiferana (Clem.), defoliation 1 year after treatment. To estimate host tree resistance, foliage production and larval foliage consumption were determined to generate an index of resistance quantifying the amount of residual foliage available for photosynthesis after insect defoliation. RESULTS: Significant interactions on tree resistance and foliage chemistry were detected between thinning and soil drainage in balsam fir. Drainage class affected spruce budworm performance, foliar chemistry and balsam fir resistance to spruce budworm, whereas no effect was found in white spruce. Thinning had a significant effect on the foliar chemistry of balsam fir and white spruce, but no effect on black spruce. CONCLUSION: Thinning reduced balsam fir resistance to spruce budworm defoliation. This response is due to increased defoliation linked to reduction in concentrations of certain monoterpenes, and a decrease in foliage production, except on hydric drainage, demonstrating the importance of drainage class to tree resistance. The results suggest that the use of Bacillus thuringiensis might be required when conducting stand thinning during spruce budworm outbreaks.

Carry-over effect of host nutritional quality on performance of spruce budworm progeny.

The effect of host nutritional quality on spruce budworm (Choristoneura fumiferana (Clemens)) parental and offspring performance was studied using field and laboratory rearing experiments, and foliar chemical analyses. Foliage of balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss) and black spruce (P. mariana (Mill.) BSP) was used to rear the parental generation in the field, whereas an artificial diet was used to rear the progeny under laboratory conditions. Important differences in the food quality were provided by the three hosts. Black spruce foliage had higher concentrations of certain monoterpene deterrents and total phenolics, together with stronger seasonal declines in nutrients such as N, P and Mg, compared with the other hosts. We hypothesise that this trend may be related to poor performance and survival of the progeny. Laboratory rearing showed that progeny of parents that fed on black spruce exhibited longer developmental times and greater mortality, and had lower pupal mass than progeny of parents fed on the other hosts. Further, artificial food-fed progeny of insects reared on black spruce reached sixth-instar later, with lower mass, and exhibited higher relative growth rate (RGR) than progeny of parents fed on the other hosts. These results suggest nutritionally-based parental effects. These results also confirmed that the quality of food consumed by the parents can influence the fitness of the next generation.

Two novel techniques to screen Abies seedlings for resistance to the balsam woolly adelgid, Adelges piceae.

Since its introduction into the Southern Appalachians in the 1950s, the balsam woolly adelgid, Adelges piceae Ratzeburg (Hemiptera: Adelgidae), has devastated native populations of Fraser fir, Abies fraseri (Pursh) Poir. (Pinales: Pinaceae), and has become a major pest in Christmas tree plantations requiring expensive chemical treatments. Adelges piceae-resistant Fraser fir trees would lessen costs for the Christmas tree industry and assist in the restoration of native stands. Resistance screening is an important step in this process. Here, four studies directed toward the development of time- and cost-efficient techniques for screening are reported. In the first study, three methods to artificially infest seedlings of different ages were evaluated in a shade-covered greenhouse. Two-year-old seedlings had much lower infestation levels than 7 year-old seedlings. Placing infested bark at the base of the seedling was less effective than tying infested bark to the seedling or suspending infested bolts above the seedling. Although the two latter techniques resulted in similar densities on the seedlings, they each have positive and negative considerations. Attaching bark to uninfested trees is effective, but very time consuming. The suspended bolt method mimics natural infestation and is more economical than attaching bark, but care must be taken to ensure an even distribution of crawlers falling onto the seedlings. The second study focused on the density and distribution of crawlers falling from suspended bolts onto paper gridded into 7.6 × 7.6 cm cells. Crawler density in a 30 cm band under and to each side of the suspended bolt ranged from 400 to over 3000 crawlers per cell (1 to 55 crawlers per cm²). In the third study, excised branches from 4 year-old A. fraseri and A. vetchii seedlings were artificially infested with A. piceae to determine whether this technique may be useful for early resistance screening. The excised A. fraseri branches supported complete adelgid development (crawler to egg-laying adult), and very little adelgid development occurred on A. vetchii branches. The fourth study compared infestation levels and gouting response on excised versus intact branches of 4 year-old A. fraseri seedlings from three different seed sources, and excised branches from 4 year-old and 25 year-old trees. There were no differences in infestation levels between excised versus intact branches nor in very young versus mature trees; gouting response was observed only on intact branches.

Evaluation of chemical controls and entomopathogenic nematodes for control of Phyllophaga white grubs in a Fraser fir production field.

The results of 2 yr of field trials evaluating various chemical and biological controls of Phyllophaga anxia (LeConte) white grubs in a Fraser fir [Abies fraseri (Pursh) Poir] Christmas tree production field are reported here. Chemical insecticides evaluated included bifenthrin, chlorantraniliprole, thiamethoxam, and time-released imidacloprid tablets (Coretect, Bayer CropScience, Research Triangle Park, NC). Entomopathogenic nematodes evaluated included Heterorhabditis bacteriophora (Poinar) and Steinernema carpocapsae (Weiser). Overall, the chemical controls provided the best root protection and grub control. Targeted treatments of an insecticide in the root zone may provide adequate tree protection and can be a way to reduce overall insecticide input compared with banded sprays. The nematode H. bacteriophora provided limited root protection and grub control, whereas S. carpocapsae did not provide effective control. Differences in efficacy and persistence of the two entomopathogenic nematode species can be attributed to the biology and environmental preferences of these organisms.

Fluctuations in density of an outbreak species drive diversity cascades in food webs.

Patterns in food-web structure have frequently been examined in static food webs, but few studies have attempted to delineate patterns that materialize in food webs under nonequilibrium conditions. Here, using one of nature's classical nonequilibrium systems as the food-web database, we test the major assumptions of recent advances in food-web theory. We show that a complex web of interactions between insect herbivores and their natural enemies displays significant architectural flexibility over a large fluctuation in the natural abundance of the major herbivore, the spruce budworm (Choristoneura fumiferana). Importantly, this flexibility operates precisely in the manner predicted by recent foraging-based food-web theories: higher-order mobile generalists respond rapidly in time and space by converging on areas of increasing prey abundance. This "birdfeeder effect" operates such that increasing budworm densities correspond to a cascade of increasing diversity and food-web complexity. Thus, by integrating foraging theory with food-web ecology and analyzing a long-term, natural data set coupled with manipulative field experiments, we are able to show that food-web structure varies in a predictable manner. Furthermore, both recent food-web theory and longstanding foraging theory suggest that this very same food-web flexibility ought to be a potent stabilizing mechanism. Interestingly, we find that this food-web flexibility tends to be greater in heterogeneous than in homogeneous forest plots. Because our results provide a plausible mechanism for boreal forest effects on populations of forest insect pests, they have implications for forest and pest management practices.

Developmental polymorphism in a Newfoundland population of the hemlock looper, Lambdina fiscellaria (Lepidoptera: Geometridae).

The hemlock looper [Lambdina fiscellaria (Guenée)], a widespread and highly polyphagous Geometridae, is considered one of the most economically important defoliators of North American coniferous forests. Variations in the number of larval instars between geographic populations of this species have been previously reported in the literature. However, whether such developmental polymorphism occurs within a given population is unknown. In this study, we report the presence of both four and five larval instar individuals within a population of hemlock looper in Newfoundland when reared on balsam fir. For both sexes, the majority of individuals reared on balsam fir shoots went through four larval instars, but more than one third of the females (35.3%) went through five larval instars. Females with four larval instars developed faster and had smaller pupal weight than females with five larval instars. However, a growth-related index (weight gain per unit of time) was similar for the two ecotypes (four or five larval instars). No significant difference was observed between the two ecotypes in terms of reproductive capacity (fecundity and egg size). We also found significant differences in life history traits between males and females. Results indicate that developmental polymorphism, in this case, the variation in the number of larval instars, might provide some adaptive attributes that allowed exploitation of a broader ecological niche.

In vivo replication kinetics and transcription patterns of the nucleopolyhedrovirus (NeabNPV) of the balsam fir sawfly, Neodiprion abietis.

DNA replication and transcription of NeabNPV, the nucleopolyhedrovirus (NPV) of the balsam fir sawfly, Neodiprion abietis (Hymenoptera: Diprionidae), in host larvae were investigated. NPV DNA replication kinetics and gene-expression patterns have been resolved only in lepidopteran cell-culture systems and in limited in vivo experiments with lepidopteran larvae. Furthermore, there are significant differences in pathologies caused by lepidopteran NPVs, which replicate in many tissues, and hymenopteran NPVs, known to replicate in midgut epithelium only. Despite the differences in host specificity and pathology, NeabNPV DNA replication kinetics were similar to those reported for lepidopteran NPVs. Maximal NeabNPV DNA synthesis was observed between 4 and 24 h post-inoculation (p.i.) but, in contrast to lepidopteran NPVs, synthesis continued at a lower rate up to 72 h p.i. Selected NeabNPV genes exhibited a cascade pattern of transcription similar to that of lepidopteran NPVs. RT-PCR products of the NeabNPV lef-1, lef-2 and dnapol transcripts were observed as early as 2 h p.i., whilst lef-8 and lef-9, encoding putative viral RNA polymerase subunits, were detected at 1 and 6 h p.i., respectively. Two structural late transcripts (gp41 and p74) were observed from 6 h p.i. The very late factor 1 (vlf-1) transcript, a transactivator of very late genes, was observed from 12 h p.i., but the very late transcript polh, encoding the major occlusion protein, polyhedrin, was observed from 24 h p.i. This study provides the first insight into DNA replication and gene expression of a non-lepidopteran baculovirus.

Comparative use of Mindarus abietinus (Homoptera: Aphididae) by two coccinellids (Coleoptera: Coccinellidae), the native Anatis mali and the exotic Harmonia axyridis, in a Christmas tree plantation.

The exotic coccinellid Harmonia axyridis (Pallas) recently expanded its range into eastern Canada and elsewhere in North America. We hypothesized that this coccinellid should be less well adapted to the prey Mindarus abietinus Koch. on balsam fir trees than the native coccinellid Anatis mali (Say), which evolved in close association with aphids on conifers in North America. We compared, under field conditions, prey use by both species by collecting data on their synchrony with M. abietinus, their prey searching and predation behaviors, life stage distribution in fir canopy, and their overall reproductive success in this system. The seasonal life cycle of A. mali was better synchronized with that of M. abietinus compared with that of H. axyridis. In spring, A. mali adults appeared nearly 2 wk earlier on trees than H. axyridis and were active predators of the aphid fundatrices. A. mali oviposition thus began before the aphid population started to grow, and its larvae were most active during peak aphid colonies. Behavioral observations showed that both adults and larvae of the native A. mali searched for prey more actively than those of H. axyridis. Distribution of life stages also showed that eggs and pupae had different distributions on trees and that the adult-to-adult net reproductive rate of A. mali was three times higher than that of H. axyridis. Thus, the native A. mali was better adapted than H. axyridis to prey on M. abietinus, possibly because it evolved for a much longer period of time with this prey in conifer habitats.

Influx of double labelled glutamine into mistletoes (Viscum album) from the xylem sap of its host (Abies alba).

The flux of glutamine into the mistletoe Viscum album from the xylem sap of a coniferous host was analyzed. For this purpose, a perfusion system was used in which the xylem sap of the host was replaced by an artificial perfusion solution. With this system, flux rates into the mistletoe were determined in feeding experiments with the organic nitrogen source U(13)C/(15)N-Gln. At the end of the experiments the delta values of C and N were significantly depleted in the outflow compared to the percolation solution. Since this depletion was higher for C than for N, a combination of Gln uptake and simultaneous uploading of organic compounds in the host xylem can be assumed. Gln was strongly metabolized during its allocation in the mistletoe. As a consequence, the C skeleton of Gln was equally distributed between leaf and stem tissue, whereas N of Gln preferentially accumulated in the stem. Apparently, the C atoms of the Gln taken up are transported faster in the mistletoe to the sink tissues than the N atoms. It is concluded that C liberated from Gln is transported rapidly to different sink tissues, whereas N in the oversupplied mistletoes is transported slowly to sinks in the leaves.

Forest dynamics after successive spruce budworm outbreaks in mixedwood forests.

In order to assess the long-term spatiotemporal influence of the spruce budworm in sub-boreal mixedwood forests, we studied the effect of three successive outbreaks in a region of western Quebec, Canada. We used dendrochronology to detect past outbreaks in three areas (111-185 ha), based on the recruitment age of balsam fir (Abies balsamea) and on growth patterns of white spruce (Picea glauca), the two main host species of this defoliating insect. We also used a series of aerial photographs taken between 1935 and 2003 to evaluate overstory mortality and post-outbreak succession patterns in these same areas. Individual outbreaks had a spatially homogenous impact on host species throughout the region, but successive outbreaks differed in intensity: the two outbreaks around 1910 and 1980 caused widespread mortality in the overstory, but an outbreak around 1945 had little impact, probably because the forest mosaic had not yet recuperated from the 1910 outbreak. No clear outbreak was detected in the later part of the 19th century. In portions of the study areas where the 1910 outbreak had a major impact, between 36% and 50% of the stands were reoccupied by balsam fir stands in the period up to the 1980 outbreak (cyclic succession), the rest being at least partly replaced by nonhost species such as Betula spp. Changes in forest composition after the 1910 outbreak were mostly associated with upper-slope positions in all study areas. The 1980 outbreak also had a higher impact than earlier outbreaks in lower-slope positions dominated by black spruce (Picea mariana)-balsam fir mixtures. These results suggest that, at the regional scale, the abundance of mature or over-mature balsam fir stands does not determine the outbreak cycle. When an outbreak occurs, however, its impact will be strongly constrained by forest characteristics such as stand composition and structure, which are themselves influenced by previous disturbances and slope position.

Geographic biotype and host-associated local adaptation in a polyphagous species, Lambdina fiscellaria (Lepidoptera: Geometridae) feeding on balsam fir on Anticosti Island, Canada.

The debate about mechanisms underlying the evolution of host specialization by herbivorous insects remains open. Natural selection may act locally and lead to different patterns of geographic variation in life history traits of polyphagous herbivores. The hypothesis of genetically-based trade-offs in offspring performance on different hosts has been proposed but this has rarely been demonstrated. Under laboratory conditions, the biological performance of two populations of the hemlock looper Lambdina fiscellaria (Guenée), a highly polyphagous lepidopteran, was compared when reared on three different tree host species: balsam fir, eastern hemlock and sugar maple. One population originated from Anticosti Island, Québec, Canada, where the insect has evolved without having access to two of the three tree species tested, the other being from the mainland where all tree species are present. When reared on balsam fir foliage, which was naturally available to each population, larvae from Anticosti Island underwent four instars compared with five for the mainland population, indicating the existence of geographic biotypes in L. fiscellaria. When reared on the foliage of non-naturally available host trees, larvae from Anticosti Island had a higher incidence of supernumerary instars. This is a unique example where local adaptation to environmental conditions of an insect herbivore is expressed through a differential number of larval instars. Moreover, the Anticosti Island population showed a higher growth related index on the host available to both populations indicating that a fitness trade-off was the evolutionary process underlying the local adaptation of this population on balsam fir.

Bacillus thuringiensis subsp. kurstaki aerial spray prescriptions for balsam fir stand protection against spruce budworm (Lepidoptera: Tortricidae).

Although commercial formulations of Bacillus thuringiensis subsp. kurstaki (Btk) are being widely used in forest protection against lepidopteran defoliators, optimal application prescriptions have often yet to be worked out in detail. We conducted field experiments over a 6-yr period (1996-2001) in southwestern Québec to determine application prescriptions for optimal protection of balsam fir, Abies balsamea (L.), healthy stands against the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). At moderate larval densities (<30 larvae per 45-cm branch tip), similar foliage protection was achieved with one or two Btk applications of 30 billion international units per hectare (BIU/ha). When larval densities exceeded 30 larvae per branch tip, two successive applications of 30 BIU/ha significantly increased foliage protection. Whether the second application took place 5 or 10 d after the first spray did not affect treatment efficacy. Increasing the application dosage from 30 to 50 BIU/ha did not lead to better foliage protection against high larval densities, but the current standard dosage of 30 BIU/ha saved more foliage than 15 BIU/ha against moderate populations. The recommended dosage of 30 BIU can be applied in lower application volumes (1.5 liters/ha) by using a high-potency product (20 BIU/liter), because we did not observe a reduction in efficacy compared with the application of a lower potency product (12.7 BIU/liter) in 2.37 liters/ha. We also demonstrated that Btk can be applied much earlier in the season without compromising spray efficacy: there was no difference in treatment efficacy of double applications at 30 BIU/ha when the first spray was timed for early third, peak third, or early fourth instars.

Spatial and seasonal variation in amino compounds in the xylem sap of a mistletoe (Viscum album) and its hosts (Populus spp. and Abies alba).

In a field study, the composition and concentrations of amino compounds in the xylem sap of the mistletoe, Viscum album L., and in the xylem sap of two host species, an evergreen conifer (Abies alba Mill.) and a deciduous broad-leaved tree (Populus x euramericana), were analyzed. The xylem sap of both hosts and mistletoe contained large, but similar amounts of total organic nitrogen in low molecular weight amino compounds (TONLW). Nevertheless, individual amino compounds accumulated in the xylem sap of mistletoe relative to the host xylem sap, indicating selective uptake. In the xylem sap of Populus, major amino compounds (asparagine (Asn) and glutamine (Gln)) and the bulk parameters, TONLW and proteinogenic amino acids, showed significant seasonal variation. In Abies and in mistletoe on either host, variation of amino compounds in xylem sap was largely explained by inter-annual differences, not by seasonal variation. In both hosts, TONLW in the xylem sap was dominated by Gln. There was a steady decrease in relative abundance of Gln from the host xylem sap to the mistletoe xylem sap and to the stems and leaves of mistletoe. Simultaneously, the abundance of arginine (Arg) increased. Arginine was the predominant amino compound in the stems and leaves of mistletoe, occurring at concentrations previously observed only in leaves of trees exposed to excess nitrogen. We conclude that Gln (2 mol N mol(-1)) delivered by the host xylem sap is converted, in mistletoe, to Arg (4 mol N mol(-1)) and that the organic carbon liberated from Gln contributes significantly to the parasite's heterotrophic carbon gain. Statistical analyses of the data support this conclusion. Accumulation of Arg in mistletoe is an indication of excess N supply as a result of the uptake of amino compounds from the host xylem sap and a lack of phloem uploading.