Host Tree Foliage Research Articles

Saprotrophic and ectomycorrhizal fungal sporocarp stoichiometry (C : N : P) across temperate rainforests as evidence of shared nutrient constraints among symbionts.

Quantifying nutritional dynamics of free-living saprotrophs and symbiotic ectomycorrhizal fungi in the field is challenging, but the stoichiometry of fruiting bodies (sporocarps) may be an effective methodology for this purpose. Carbon (C), nitrogen (N) and phosphorus (P) concentrations of soils, foliage and 146 sporocarp collections were analyzed from 14 Pseudotsuga menziesii var. menziesii stands across a podzolization gradient on Vancouver Island (Canada). N and P concentrations were considerably higher in saprotrophic fungi. Fungal N% increased with soil N content at a greater rate for saprotrophs than ectomycorrhizal fungi, while fungal P% of saprotrophs was more constrained. Fungal N : P was more responsive to soil N : P for ectomycorrhizal fungi (homeostatic regulation coefficient 'H' = 2.9) than saprotrophs (H = 5.9), while N : P of ectomycorrhizal fungi and host tree foliage scaled almost identically. Results underscore the role of ectomycorrhizal fungi as nutrient conduits, supporting host trees, whereas saprotrophs maintain a greater degree of nutritional homeostasis. Site nutrient constraints were shared in equal measure between ectomycorrhizal fungi and host trees, particularly for P, suggesting neither partner benefits from enhanced nutrition at the expense of the other. Sporocarp stoichiometry provides new insights into mycorrhizal relationships and illustrates pervasive P deficiencies across temperate rainforests of the Pacific Northwest.

A mimetic nesting association between a timid social wasp and an aggressive arboreal ant

In French Guiana, the arboreal nests of the swarm-founding social wasp Protopolybia emortualis (Polistinae) are generally found near those of the arboreal dolichoderine ant Dolichoderus bidens. These wasp nests are typically protected by an envelope, which in turn is covered by an additional carton ‘shelter’ with structure resembling the D. bidens nests. A few wasps constantly guard their nest to keep D. bidens workers from approaching. When alarmed by a strong disturbance, the ants invade the host tree foliage whereas the wasps retreat into their nest. Notably, there is no chemical convergence in the cuticular profiles of the wasps and ants sharing a tree. The aggressiveness of D. bidens likely protects the wasps from army ant raids, but the ants do not benefit from the presence of the wasps; therefore, this relationship corresponds to a kind of commensalism.

Importance of Arboreal Cyanolichen Abundance to Nitrogen Cycling in Sub-Boreal Spruce and Fir Forests of Central British Columbia, Canada

The importance of N2-fixing arboreal cyanolichens to the nitrogen (N)-balance of sub-boreal interior hybrid spruce (Picea glauca × engelmannii) and subalpine fir (Abies lasiocarpa) forests was examined at field sites in central BC, Canada. Host trees were accessed by a single-rope climbing technique and foliage as well as arboreal macrolichen functional groups were sampled by branch height in eight random sample trees from each of two high (High Cyano) and two low (Low Cyano) cyanolichen abundance sites for a total of 32 sample trees. Natural abundances of stable isotopes of N (15N, 14N) and carbon (13C, 12C) were determined for aggregate host tree and epiphytic lichen samples, as well as representative samples of upper organic and soil horizons (Ae and Bf) from beneath host trees. As expected, N2-fixing cyanolichens had 2–6-fold greater N-contents than chlorolichens and a δ15N close to atmospheric N2, while foliage and chlorolichens were more depleted in 15N. By contrast, soils at all trees and sites were 15N-enriched (positive δ15N), with declining (not significant) δ15N with increased tree-level cyanolichen abundance. Lichen functional groups and tree foliage fell into three distinct groups with respect to δ13C; the tripartite cyanolichen Lobaria pulmonaria (lightest), host-tree needles (intermediate), and bipartite cyanolichens, hair (Alectoria and Bryoria spp.) and chlorolichens (heaviest). Branch height of host trees was an effective predictor of needle δ13C. Our results showed a modest positive correlation between host tree foliage N and cyanolichen abundance, supporting our initial hypothesis that higher cyanolichen abundances would elevate host tree foliar N. Further study is required to determine if high cyanolichen abundance enhances host tree and/or stand-level productivity in sub-boreal forests of central BC, Canada.

Bacillus thuringiensis efficacy in reducing spruce budworm damage as affected by host tree species

Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki (Btk) against spruce budworm Choristoneura fumiferana in black spruce (Picea mariana (Mill.) BSP), white spruce (P. glauca (Moench) Voss) and balsam fir (Abies balsamea (L.) Mill.) was investigated in Quebec’s Cote-Nord region. As expected, larval mortality was higher in Btk-treated plots (80.26 ± 2.34 %) than in control plots (66.32 ± 2.80 %). There were no differences in larval mortality among the three host tree species tested. Btk was most efficient in reducing spruce budworm defoliation when applied to black spruce and white spruce trees. Black spruce and white spruce exhibited lower final defoliation in Btk-treated plots than balsam fir. Btk applications produced a reduction in defoliation of 36 % in balsam fir, 44 % in white spruce and 41 % in black spruce. Control plots exhibited about 35 % higher amount of current-year foliage destroyed (AFD) and 56 % lower amount of current-year foliage remaining (ARF) than Btk-treated plots, whereas no differences in the amount of current-year foliage produced (AFP) were observed among host tree species. Black spruce trees showed the lowest AFD. Although not statistically significant, black spruce also showed the highest ARF. Our results suggest that Btk application is more efficient in protecting against spruce budworm damage when it is applied to spruce species than it is to balsam fir. It appears that the observed inter-specific differences in host tree foliage protection might be related to interactions between Btk, host tree foliage, and larval feeding behaviour.

Spruce budworm biological and nutritional performance responses to varying levels of monoterpenes

Dose effect of six monoterpenes (α-pinene, bornyl acetate, camphene, δ-3-carene, terpinolene, tricyclene) found in the foliage of host trees was tested on sixth-instar spruce budworm (Choristoneura fumiferana (Clem.)) using artificial diet. The larval mortality, growth and food utilization have been observed. Two monoterpenes, α-pinene and δ-3-carene caused 22 and 12% mortality respectively at concentrations found in balsam fir foliage. Bornyl acetate and camphene reduced larval survival when their concentration was higher than the foliage. Terpinolene and tricyclene have no effect on mortality. All six tested monoterpenes reduced larval growth rate. Spruce budworm tried to minimize this negative growth impact by increasing his digestibility in presence of camphene and δ-3-carene, and by increasing his efficiency of conversion of ingested-digested food with α-pinene and bornyl acetate. These results support the traditional theory that monoterpenes are a defense agent against spruce budworm and that each monoterpene has a different mode of action and effects which are not necessarily proportional to its concentration.

Biology of Creiis lituratus Froggatt: (Hemiptera: Psyllidae), pest on Eucalyptus dunnii Maiden in plantations: morphology, life cycle and parasitism

Summary The psyllid Creiis lituratus Froggatt is the most significant defoliating pest of young Eucalyptus dunnii Maiden plantations growing in north-eastern New South Wales. This paper describes aspects of the life history of C. lituratus, information required to monitor psyllid populations and develop management strategies. The psyllid has five nymphal instars. Feeding by these nymphs causes considerable damage to the foliage of host trees. The different nymphal instars are distinguishable on the basis of body and lerp dimensions, colouration and wing bud morphology. Mean fecundity in captive populations was 95 eggs per female (observed range 130–148). Egg and juvenile development had threshold temperatures of 3°C and 10°C respectively, and the relationship between development rate and temperature was determined for both stages. Adult longevity was reduced at high temperatures, which affected fecundity and may account for the low psyllid population densities observed in plantations over summer. Parasitism of the nymphal instars by two species of Psyllaephagus wasps was observed. While parasitism may exceed 90% in field surveys it is uncertain what role it plays in regulating populations. No specialised parasitism or predation of eggs or adults was observed.

How do primary nutrients affect the performance and preference of forest tent caterpillars on trembling aspen?

AbstractVariation in leaf quality includes differences in both primary nutrients and secondary metabolites. Both of these factors can influence the feeding preference and resulting performance of herbivores in ways that are difficult to disentangle when comparing foliage from different sources. Our study was designed to assess the effects of the ratio of the primary nutrients in host-tree foliage, protein and sugar, on the performance and feeding behaviour of the forest tent caterpillar (Malacosoma disstria Hübner (Lepidoptera: Lasiocampidae)). Fourth-stadium larvae were fed trembling aspen leaves (Populus tremuloides Michx (Salicaceae)) supplemented with casein, sucrose, or buffer only (control). No differences in taste responses to the three leaf types were detected. In a cafeteria situation, feeding behaviour over the short term was largely determined by the use of pheromone trails and hence depended on which leaf was contacted first. Over the longer term, caterpillars fed most on the control leaf and the sugar-supplemented leaf and discriminated against the protein-supplemented leaf. Sugar supplementation increased survivorship relative to the control treatment but slowed development and did not affect growth; protein supplementation decreased growth. These findings are consistent with past research comparing forest tent caterpillar performance and feeding preference on different host plants.

Rainforest air-conditioning: the moderating influence of epiphytes on the microclimate in tropical tree crowns.

Epiphytes are often assumed to influence the microclimatic conditions of the tree crowns that they inhabit. In order to quantify this notion, we measured the parameters "temperature" (of the substrate surface and the boundary layer of air above it), "evaporative drying rate" and "evapotranspiration" at various locations within tree crowns with differing epiphyte assemblages. The host tree species was Annona glabra, which was either populated by one of three epiphyte species (Dimerandra emarginata, Tillandsia fasciculata, or Vriesea sanguinolenta) or was epiphyte-free. We found that during the hottest and driest time of day, microsites in the immediate proximity of epiphytes had significantly lower temperatures than epiphyte-bare locations within the same tree crown, even though the latter were also shaded by host tree foliage or branches. Moreover, water loss through evaporative drying at microsites adjacent to epiphytes was almost 20% lower than at exposed microsites. We also found that, over the course of several weeks, the evapotranspiration in tree crowns bearing epiphytes was significantly lower than in trees without epiphytes. Although the influence of epiphytes on temperature extremes and evaporation rates is relatively subtle, their mitigating effect could be of importance for small animals like arthropods inhabiting an environment as harsh and extreme as the tropical forest canopy.

Induced resistance of host tree foliage during and after a natural insect outbreak

1. Plant resistance against insect herbivores often increases after experimental damage to foliage, but few studies have obtained field estimates of the effect of induced resistance on insect populations during and after a natural insect outbreak. 2. This study measured the effect of quality of the host tree, mountain birch (Betula pubescens ssp. czerepanovii), on the periodically fluctuating folivore Epirrita autumnata (Lepidoptera, Geometridae) during peak and postpeak years of an outbreak in Finnish Lapland. Comparisons were made both within and between study sites to assess host plant quality, and thereby the effect of delayed induced resistance (DIR). 3. In within‐site comparisons, a set of experimental trees was defoliated by wild larvae in the peak year of the outbreak, whereas control trees were protected from defoliation by spraying with an insecticide. The effect of host plant quality was quantified in the following year by measuring the pupal mass of E. autumnata larvae reared in enclosures on these trees. 4. In between‐site comparisons, the sizes of pheromone‐trapped males were measured at both outbreak and low density sites during the progress of the outbreak. The size of trapped males was subsequently used to estimate the corresponding fecundity of females at the same sites. 5. Pupal mass of E. autumnata reared on trees defoliated in the previous year was 0–10% lower than on those trees protected from defoliation by the insecticide. Field‐collected adults indicated a similar pattern: they were smaller at outbreak sites than at low‐density sites, and the size reached its minimum in the post‐peak year. However, the estimated loss of reproductive capacity of females resulting from DIR was too small to be the sole explanation for the termination of the outbreak. 6. Whether the weak DIR response in this system was a characteristic of the 1990s outbreak alone remains unclear, because different terminating agents may be important for different individual outbreak peaks. During this outbreak, larval parasitism and developmental asynchrony between larvae and birch were probably more important reasons for population collapse than DIR.

One and two years impact of commercial thinning on spruce budworm feeding ecology and host tree foliage production and chemistry

Field rearing experiments of spruce budworm, Choristoneura fumiferana (Clem.), were conducted in conjunction with foliar chemical analyses, one and two years after a commercial thinning (removal of 25% stand basal area) in a 50-year-old balsam fir, Abies balsamea (L.) Mill., stand. The first year after thinning, spruce budworm larvae reared on the residual trees developed five days faster and removed 43% more foliage than those reared on control trees, but in the second year they developed two days faster and removed 37% more foliage. The increase in larval development rate was related to an increase in foliar soluble sugars while a reduction in foliar monoterpenes caused by the thinning apparently accounted for the greater amount of foliage ingested by the larvae. The first year after thinning, trees were more vulnerable to spruce budworm because there was no increase in foliage production and the trees were more heavily defoliated. However, in the second year trees were less vulnerable to the insect because there was an increase in foliage production that exceeded the increase in defoliation, hence a net gain in foliage. Results from this study showed that commercial thinning could reduce the vulnerability of balsam fir trees to spruce budworm if thinning is conducted two years prior to budworm outbreak, but the same silvicultural procedure could increase the vulnerability to the insect if it is conducted during an outbreak. Key words: spruce budworm, balsam fir, chemistry, thinning, defoliation

Accumulation of Cu and Ni in successive stages of Lymantria dispar L. (lymantriidae, lepidoptera) near ore smelters at Sudbury, Ontario, Canada

The accumulation of Cu and Ni in successive life stages of the gypsy moth ( Lymantria dispar), feces, and foliage near an ore smelter at Sudbury, Ontario and a control site was investigated. Higher concentrations of Cu and Ni were found in all larval stages collected at Sudbury than in those from the control site indicating that elevated levels of these metals in the Sudbury environment is an important factor influencing body burdens. These differences were associated with higher metal concentrations in the foliage of host trees from this site. However, differences between sites became less significant for pupae and adult stages. At the Sudbury site, concentrations of Cu (μg g −1 dry wt) decreased in successive instars and then increased in tissues of pupae and adults. In contrast, Cu content (μg/individual) increased during larval development and then decreased in pupae and adults. The pattern of Ni concentration and content in larvae from the Sudbury site was similar to that of Cu. Patterns of Cu and Ni concentration and content throughout the life stages are explained by changes in weight resulting in a dilution effect in early stages, and a concentrating effect in later stages. Differences in Cu and Ni concentration and content between Sudbury and control populations became less significant following the pupal stage suggesting metal elimination with the exuviae and meconium. This study also illustrates the importance of sampling all stages in an insect's development when measuring accumulation of metals. Fecal and foliar concentrations of Cu and Ni from Sudbury were not significantly different suggesting that metal assimilation is low. Even though gypsy moths from Sudbury contain elevated levels of Cu and Ni, metal burdens in their tissues do not represent a significant route through the food chain. However, the conversion of foliage with high metal content to feces implies that other ecosystem consequences should be investigated.

Why do guava fruit flies,Anastrepha striata(Tephritidae), avoid the upper canopy of host trees?

Abstract The within‐tree distribution of the guava fruit fly, Anastrepha striata in sour guava, Psidium friedrichsthalianum and common guava, P. guajava in the seasonal highlands and non‐seasonal lowlands of Costa Rica, was examined in relation to host fruit distribution, temperature, and ambient light levels. Larvae and adult flies were significantly more abundant in the middle and lower parts of trees than in the upper canopy layer where temperatures inside sun‐exposed, potential host fruits reached lethal levels for eggs and larvae of A. striata. The number of adult flies was also significantly greater in relatively compact foliage than in fairly open foliage of host trees. The results suggest that the foliage structure of host trees, through its influences on the temperature inside host fruits, is determining the within‐tree distribution of Anastrepha fruit flies.

Diapause termination and changes in thermal responses during postdiapause development in larvae of the spruce budworm, Choristoneura fumiferana

Diapause termination was examined in field-overwintering populations of the spruce budworm, Choristoneura fumiferana (Clem.). The time required for emergence of overwintering larvae decreased rapidly until the end of December following which photoperiod had no effect on diapause termination. There was no detectable yearly or geographical variation in the duration of postdiapause development, or in its relationship with temperature, when measured in early March. Thus, it is concluded that diapause in this spcies ends before the end of February. Cycling temperatures led to slower development than expected from temperature responses of the overwintering larvae, suggesting developmental inertia to temperature fluctuations. There was a brief but pronounced increase in developmental rate in the first few days after transfer from the field to experimental conditions. Sensitivity of overwintered larvae to warm temperature increased gradually during postdiapause. This is hypothesized as a mechanism by which adequate synchrony is achieved between the emergence of larvae from diapause, the appearance of suitable food, and optimal weather conditions for the establishment of young larvae on host-tree foliage. A method was developed to incorporate age-dependence in mathematical descriptions of relationships between temperature and development rates for the purposes of simulation.

Experimental aerial application of Matacil flowable insecticide to control spruce budworm (Lepidoptera: Tortricidae)

Matacil® (aminocarb)_180F flowable insecticide mixed in both water and insectide diluent ID585 and Matacil 1 · 8D oil-soluble concentrate (OSC) mixed in ID585 were sprayed aerially at 70 g a.i./1 · 51 of spray mix/ha in two applications to control spruce budworm, Choristoneura fumiferana (Clem.). The spray droplet density on Kromekote cards, the spray volume recovered on glass slides, larval population reductions and host tree defoliation were compared. The data indicate that Matacil 180F was as effective in controlling budworm populations and protecting the foliage of host trees as Matacil 1 · 8D and that the aqueous mix was as efficacious as the ID585 mix.