Enriched atmospheric CO2 and defoliation: effects on tree chemistry and insect performance

We examined the effects of CO₂ and defoliation on tree chemistry and performance of the forest tent caterpillar, Malacosoma disstria. Quaking aspen (Populus tremuloides) and sugar maple (Acer saccharum) trees were grown in open-top chambers under ambient or elevated concentrations of CO₂. During the second year of growth, half of the trees were exposed to free-feeding forest tent caterpillars, while the remaining trees served as nondefoliated controls. Foliage was collected weekly for phytochemical analysis. Insect performance was evaluated on foliage from each of the treatments. At the sampling date coincident with insect bioassays, levels of foliar nitrogen and starch were lower and higher, respectively, in high CO₂ foliage, and this trend persisted throughout the study. CO₂-mediated increases in secondary compounds were observed for condensed tannins in aspen and gallotannins in maple. Defoliation reduced levels of water and nitrogen in aspen but had no effect on primary metabolites in maple. Similarly, defoliation induced accumulations of secondary compounds in aspen but not in maple. Larvae fed foliage from the enriched CO₂ or defoliated treatments exhibited reduced growth and food processing efficiencies, relative to larvae on ambient CO₂ or nondefoliated diets, but the patterns were host species-specific. Overall, CO₂ and defoliation appeared to exert independent effects on foliar chemistry and forest tent caterpillar performance.     

Erythroneura lawsoni abundance and feeding injury levels are influenced by foliar nutrient status in intensively managed American sycamore

• 1 Abundance and feeding injury of the leafhopper Erythroneura lawsoni Robinson was measured in an intensively‐managed American sycamore Platanus occidentalis L. plantation. Trees were planted in spring 2000 in a randomized complete block design, and received one of three annual treatments: (i) fertilization (120 kg N/ha/year); (ii) irrigation (3.0 cm/week); (iii) fertilization + irrigation; or (iv) control (no treatment).
• 2 Foliar nutrient concentrations were significantly influenced by the treatments because only sulphur and manganese levels were not statistically greater in trees receiving fertilization.
• 3 Over 116 000 E. lawsoni were captured on sticky traps during the study. Leafhopper abundance was highest on nonfertilized trees for the majority of the season, and was positively correlated with foliar nutrient concentrations. Significant temporal variation in E. lawsoni abundance occurred, suggesting five discrete generations in South Carolina.
• 4 Significant temporal variation occurred in E. lawsoni foliar injury levels, with the highest injury ratings occurring in late June and August. Foliar injury was negatively correlated with foliar nutrient content, and higher levels of injury occurred more frequently on nonfertilized trees.
• 5 The results obtained in the present study indicated that increased E. lawsoni abundance occurred on trees that did not receive fertilization. Nonfertilized trees experienced greater foliar injury, suggesting that lower foliar nutrient status may have led to increased levels of compensatory feeding.

     

The potential role of ectomycorrhizal fungi in determining Douglas-fir resistance to defoliation by the western spruce budworm (Lepidoptera: Tortricidae)

There is phenotypic variation among individual trees of interior Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) in their resistance to defoliation by the western spruce budworm (Choristoneura occidentalis Freeman). We evaluated the potential role of ectomycorrhizal fungi in determining this resistance using half-sib seedlings derived from parent trees that are resistant versus susceptible to budworm defoliation in the field. The seedlings were inoculated with Laccaria bicolor ectomycorrhizal fungi, fertilized, or untreated. Approximately 48 d after treatment, late-instar larvae from a nondiapausing laboratory colony of C. occidentalis were allowed to feed on pairs of resistant versus susceptible seedlings for 1 wk. Chemical analyses of current-year shoots for nitrogen (N), phosphorus (P), magnesium (Mg), and zinc (Zn) indicated that the fungus increased foliar concentrations of P and Mg in resistant seedlings, but it did not increase their growth rate. However, L. bicolor had no effect on foliar concentrations of P or Mg in susceptible seedlings, even though seedling growth rates increased slightly in response to the inoculation. L. bicolor had no effect on foliar levels of N or Zn in any of the seedlings. As expected, fertilization increased levels of N and P in the foliage of both resistant and susceptible seedlings, but it did not affect levels of Mg and Zn. Surprisingly, the fertilizer treatment had no effect on seedling growth rates. Despite these differences, late-instar budworms showed no feeding preference among untreated, mycorrhizal, or fertilized seedlings. The fact that seedlings from resistant versus susceptible Douglas-firs responded differently to the L. bicolor treatment lends preliminary support to the hypothesis that ecotmycorrhizae might play a role in Douglas-fir resistance to damage from the western spruce budworm. Finally, differences in foliar concentrations of N and P among untreated seedlings from different maternal trees suggested that foliar nutritional chemistry is influenced by the tree's genotype.     

Effects of tree age and stand thinning related variations in balsam fir secondary compounds on spruce budworm Choristoneura fumiferana development,growth and food utilization

• 1 The effect of tannins and monoterpenes on the development, mortality and food utilization of spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) was investigated under laboratory conditions using an artificial diet. Tannins were extracted from balsam fir foliage of thinned and unthinned stands to reproduce stand thinning related variations in tannins. A mixture of synthetic monoterpenes was utilized to simulate the concentration found in young and old balsam fir trees.
• 2 Longer development time and lower pupal weight were observed for insects fed on diets with a lower nitrogen concentration and a higher tannin concentration (unthinned treatment). Tannins induced higher insect mortality at a low nitrogen concentration compared with the diet with a higher nitrogen concentration.
• 3 Approximate digestibility was higher for larvae fed on diets with high concentrations of nitrogen at both low and high concentrations of tannins. Efficiency of conversion of digested food (ECD) decreased with an increase in tannin concentration. Tannins reduced both the relative consumption and growth rate (RCR and RGR).
• 4 Monoterpenes increased spruce budworm mortality and this mortality reached almost 50% under concentrations of monoterpene typical of the young trees compared with 20% under monoterpene concentrations found in old trees.
• 5 A higher digestibility was observed for larvae fed on diet with a higher concentration of monoterpenes, whereas efficiency of conversion of ingested food (ECI), ECD, RCR, and RGR decreased with an increase in monoterpenes in the diet.
• 6 The results obtained in the present study are consistent with the defensive role of secondary compounds such as tannins and monoterpenes in the spruce budworm–balsam fir system.

     

Effects of bud phenology and foliage chemistry of balsam fir and white spruce trees on the efficacy of Bacillus thuringiensis against the spruce budworm, Choristoneura fumiferana

Abstract 1 Efficacy of commercial formulations of Bacillus thuringiensis ssp. kurstaki (Btk) against spruce budworm Choristoneura fumiferana was investigated in mixed balsam fir‐white spruce stands. Btk treatments were scheduled to coincide with early flaring of balsam fir shoots, and later with flaring of white spruce shoots. Btk efficacy on the two host trees was compared and examined according to the foliar content of nutrients and allelochemicals and the insect developmental stage at the time of spray. 2 Larvae fed white spruce foliage were less vulnerable to Btk ingestion than larvae fed balsam fir foliage. Higher larval survival on white spruce, observed 10 days after spray, was related to higher foliage content in tannins and a lower N/tannins ratio, which might have induced inactivation of Btk toxins. 3 Larval mortality due to Btk did not depend on spruce budworm larval age. 4 Foliage protection of both host trees was similar in plots treated with Btk: larval mortality due to Btk treatment reduced insect grazing pressure on balsam fir trees; meanwhile, suitability of white spruce foliage seemed to decrease very rapidly, which induced high larval mortality among spruce budworm fed on white spruce trees. Nevertheless, following Btk sprays, 50% more foliage remained on white spruce than on balsam fir trees, because of the higher white spruce foliage production. 5 Both spray timings achieved similar protection of white spruce trees, but Btk treatments had to be applied as early as possible (i.e. during the flaring of balsam fir shoots to optimally protect balsam fir trees in mixed balsam fir‐white spruce stands).     

A dendroecological reconstruction of western spruce budworm outbreaks (Choristoneura occidentalis) in the Front Range,Colorado, from 1720 to 1986

Radial increment cores from Douglas-fir (Pseudotsuga menziesii) and blue spruce (Picea pungens), defoliated by western spruce budworm (Choristoneura occidentalis), were analyzed by means of dendrochronological methods and compared with cores from undefoliated ponderosa pine (Pinus ponderosa) and lodgepole pine (Pinus contorta) growing on the same sites in the Front Range, Colorado. Extensive deforestation during the gold and silver booms in the second part of the nineteenth century led to dense and almost pure stands of shadetolerant budworm host species. By using the skeleton plot method, the number of trees with clear growth reductions is obtained, thus representing an exact record of forest insect attacks. The analysis of abrupt growth reductions revealed at least nine outbreaks of western spruce budworm between 1720 and 1986, the majority occurring in the nineteenth century. The outbreaks were graphically compared with periods of attack in New Mexico and Colorado which were detected by other scientists employing tree-ring measurement techniques. No increase in the frequency of severe outbreaks during the twentieth century was observed, yet there is some evidence that the most recent outbreak might be the most severe ever recorded. Open Douglas-fir stands on higher sites were more susceptible to heavy budworm attack than dense stands on lower sites. Blue spruce was less frequently and less severely attacked than Douglas-fir. The spatial pattern of historical outbreaks generally was very patchy.     

Spruce budworm growth,development and food utilization on young and old balsam fir trees

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing, gravimetric analyses, a transfer experiment, and foliage chemical analyses at six dates during the period of budworm feeding activity indicated that the age of balsam fir, Abies balsamea, trees (70-year-old mature trees or 30-year-old juvenile trees) affected tree suitability for the spruce budworm via the chemical profile of the foliage. Insects reared on old trees had greater survival and pupal weight, shorter development times, and caused more defoliation than those reared on young trees. Young trees were more suitable for the development of young larvae (instars 2–5), while old trees were more suitable for the development of older, sixth-instar larvae. These results were confirmed by the laboratory transfer experiment. Young larvae fed foliage from young trees had higher relative growth rates (RGR), digestibility (AD), and efficiency of conversion of ingested foliage (ECI) than those fed foliage from old trees. These differences appeared to be related to the high N:tannins ratio, and the high contents of P present in young trees during the development of the young larvae. Old larvae fed foliage from old trees had higher relative growth rates, relative consumption rates (RCR), and digestibility of the foliage than those fed foliage from young trees. The high digestibility of the foliage of old trees was compensated for by a lower efficiency of conversion of digested food (ECD), which in turn resulted in no significant effect of tree age on the efficiency of conversion of ingested foliage by old larvae. The low relative consumption rate of old larvae fed foliage from young trees appeared to be related to the low N:tannins ratio, and the high contents of bornyl acetate, terpinolene, and °-3-carene present in young trees during the budworm sixth instar. Variations in these compounds in relation to tree age may serve as mechanisms of balsam fir resistance to spruce budworm by reducing the feeding rate of sixth instar larvae.     

Taste receptor activity and feeding behaviour reveal mechanisms of white spruce natural resistance to Eastern spruce budworm Choristoneura fumiferana

The pattern of feeding of Eastern spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera, Tortricidae) is compared on foliage from white spruce Picea glauca (Moench) Voss. (Pinaceae) trees previously determined to be susceptible and resistant to defoliation by budworm. No differences are observed in electrophysiological responses from taste sensilla to aqueous extracts of the two foliage types, nor is there a preference for either extract type in a choice test. Acetone extracts from the two foliage types are both preferred to a control sucrose solution, although neither elicits a preference relative to the other. These results suggest that there is no difference in phagostimulatory power of internal leaf contents of the two foliage types. Longer‐term observation of feeding behaviour in a no‐choice situation shows no difference in meal duration, confirming the lack of difference in phagostimulatory power. However, on average, intermeal intervals are twice as long on the resistant foliage, leading to an overall lower food consumption during the assay. This result suggests an anti‐digestive or toxic effect of the resistant foliage that slows behaviour and limits food intake. Previous research has shown that waxes of the resistant foliage deter initiation of feeding by the spruce budworm and that this foliage contains higher levels of tannins and monoterpenes. The data suggest that the resistant foliage contains a post‐ingestive second line of defence against the spruce budworm.     

Impact of balsam fir flowering on pollen and foliage biochemistry in relation to spruce budworm growth, development and food utilization

The impact of balsam fir (Abies balsamea (L.) Miller) flowering on nutritional and allelochemical quality of pollen, current-year and one-year-old foliage is studied in relation to spruce budworm (Choristoneura fumiferana Clem.) (Lepidoptera: Tortricidae) growth, development and utilization of food and nitrogen. In the laboratory, using fresh food from the field, we simulated conditions of low larval population density, in which there is no current-year foliage depletion during the spruce budworm feeding period. Similarly, we simulated conditions of high larval population density when current-year foliage depletion occurs.Because of the high nutritive value of pollen (high amounts of amino acids and minerals, especially nitrogen; low monoterpene content), insects from flowering trees reached the fifth instar five days earlier than those from non-flowering trees, and had heavier dry- and nitrogen-weights at the beginning of the fifth instar. At budbreak, switching from pollen to current-year foliage negatively affected conversion efficiencies and digestibilities of food and nitrogen (AD; ADN; ECDN; ECI; ECIN). The switch from pollen to new foliage had a detrimental impact on fifth-instar survival and on newly-moulted sixth-instar dry- and nitrogen-weights. Moreover, during the fifth instar, balsam fir flowering reduced the nutritive value of current-year foliage, which in turn, might have contributed to the reduced larval growth. Nevertheless, during the sixth instar, balsam fir flowering affected the biochemistry of current-year foliage in ways that enabled larvae to compensate for their low fifth-instar biological performance; larvae also managed to reach pupal dry weight similar to larvae reared on non-flowering trees. Current-year foliage from flowering trees contained less nitrogen, total soluble sugars and total monoterpenes. Those foliar characteristics enabled larvae to increase food and nitrogen consumption rates (RCR; RNCR), because of lower repellency and/or post-ingestional feedback from monoterpenes.As for current-year foliage, balsam fir flowering reduced nitrogen, total soluble sugar and total monoterpene contents in one-year-old foliage during the sixth-instar feeding period. These characteristics enabled sixth-instar larvae, fed on old foliage from flowering trees, to have high relative food and nitrogen consumption rates (RCR; RNCR). Larvae were also able to reach higher relative growth rates (RGR) and relative nitrogen accumulation rates (RNAR) compared to larvae reared on one-year-old foliage from non-flowering trees. Finally, larvae on flowering trees had pupal dry weight similar to those from non-flowering trees, but reached the adult stage nine days earlier.Regardless the foliage type consumed by spruce budworm larvae during the sixth instar, pollen consumption during early larval stages reduced total development time, and thus exposure time to natural enemies. This phenomenon might increase larval survival. Balsam fir flowering changed the biochemistry of one-year-old and current-year foliages, but did not affect pupal dry weights of larvae reared on flowering trees compared to those reared on non-flowering trees. Thus, at low population density, spruce budworm populations in balsam fir flowering stands might be favoured over those in balsam fir non-flowering stands. In addition, when larvae consumed one-year-old foliage during the entire sixth instar, those on flowering trees are probably favoured over those on non-flowering trees. However, because flowering trees produce less new foliage than non-flowering trees, current-year foliage depletion may occur earlier on flowering trees than on non-flowering trees. Thus, at similar larval population density, larvae on flowering trees might have to feed on one-year-old foliage earlier than those on non-flowering trees. In that case, spruce budworm populations on non-flowering stands would be favoured over those on flowering stands.     

Calcium addition at the Hubbard Brook Experimental Forest increases the capacity for stress tolerance and carbon capture in red spruce (Picea rubens) trees during the cold season

Red spruce (Picea rubens Sarg.) trees are uniquely vulnerable to foliar freezing injury during the cold season (fall and winter), but are also capable of photosynthetic activity if temperatures moderate. To evaluate the influence of calcium (Ca) addition on the physiology of red spruce during the cold season, we measured concentrations of foliar polyamines and free amino acids (putative stress-protection compounds), chlorophyll (a key photosystem component), and sapwood area (a proxy for foliar biomass), for trees in Ca-addition (CaSiO₃ added) and Ca-depleted (reference) watersheds at the Hubbard Brook Experimental Forest (NH, USA). Ca-addition increased concentrations of the amino acids alanine and γ-aminobutyric acid (GABA) and the polyamines putrescine (Put) and spermidine (Spd) in November, and Put in February relative to foliage from the reference watershed. Consistent with increased stress protection, foliage from the Ca-addition watershed had higher total chlorophyll and chlorophyll a concentrations in February than foliage from the reference watershed. In contrast, foliage from the reference watershed had significantly lower glutamic acid (Glu) and higher alanine (Ala) concentrations in February than foliage from the Ca-addition watershed. Imbalances in Ala:Glu have been attributed to cold sensitivity or damage in other species. In addition to concentration-based differences in foliar compounds, trees from the Ca-addition watershed had higher estimated levels of foliar biomass than trees from the reference watershed. Our findings suggest that Ca-addition increased the stress tolerance and productive capacity of red spruce foliage during the cold season, and resulted in greater crown mass compared to trees growing on untreated soils.     

Effect of Different Sugars on Photosynthesis and Chlorophyll Fluorescence in Photoautotrophic Tomato Suspension Cell Cultures

The effects of metabolisable sugars sucrose and glucose along with non-metabolisable isomers of sucrose palatinose and turanose were tested. Rate of oxygen evolution (P), electron transport rate (ETR), and photochemical quenching (q_p) showed substantial decrease after 24 and 48 h by glucose and sucrose treatments, whereas there was no effect on all these parameters by the treatment with palatinose and turanose. Also the F_v/F_m ratio remained constant through the time of studies revealing that the maximal photochemical capacity of the cells was unchanged. Non-photochemical quenching (q_N) showed a decrease compared to the control values by all the treatments. Hence P and Chl fluorescence parameter were affected only by those sugars which are used in the metabolic pathways and not by sugar analogues.     

Effects of food quality,particularly nitrogen concentrations,of Eucalyptus blakelyi foliage on the growth of Paropsis atomaria larvae (Coleoptera: Chrysomelidae)

Five groups of E. blakelyi seedlings were differentially fertilized to obtain a range of N concentrations from 0.8–3.0% dry wt in the foliage. Groups of P. atomaria larvae were reared from eclosion to the prepupal stage on these seedlings. The effects on larval growth and development caused by foliar concentrations of N, moisture content, and tannins and leaf toughness were measured. Pupal dry weight and development time of P. atomaria did not differ between those reared on foliage with N levels of 1.7–3.0% but there was a significant decrease in pupal weight and increase in development time for individuals fed foliage with N below this level. Larvae fed foliage with an average of 0.8% N died before reaching instar III. Total dry matter consumption increased with a decrease in N concentration. Larval nitrogen utilization efficiency increased as foliar N level decreased until N reached a level somewhere between 1.7%–1.2% below which it decreased. There appeared to be an N concentration threshold above which P. atomaria larvae received adequate N by regulating consumption and nitrogen utilization efficiency but below which they could no longer accumulate enough N by compensation to maintain an optimum growth rate and development time. Effects of food quality variables on relative growth and consumption rates are presented and discussed.     

Lifespan and patterns of accumulation and mobilization of nutrients in the sugar-fed phorid fly, Pseudacteon tricuspis

Abstract. The effect of sugar feeding on the survival of adult phorid fly Pseudacteon tricuspis is investigated. Flies fed 25% sucrose in aqueous solution continuously throughout their lifespan have greater longevity (mean ± SE longevity: female = 7.9 ± 0.8 days, male = 8.9 ± 0.9 days) than completely starved (provided no water and no sugar solution) flies, sugar-starved (provided water only) flies, or flies fed sugar solution only on their first day of adult life. Completely starved flies rarely lived beyond one day. Provision of water increases longevity by 2 days, and one full day of sugar feeding further increases longevity by an additional 1–2 days. Flies fed 50% sucrose have similar survivorship as those fed 25% sucrose. The temporal patterns of nutrient accumulation and utilization are also compared in P. tricuspis fed different diets: sugar-starved, sucrose-fed on the first day of adult life only, and sucrose-fed continuously. Adult P. tricuspis emerge with no gut sugars, and only minimal amounts of body sugars and glycogen. Although the levels of body sugars and glycogen decline gradually in sugar-starved flies, a single day of sugar feeding results in the accumulation of maximum amounts of gut sugars, body sugars and glycogen. High levels of these nutrients are maintained in female and male phorid flies fed on sucrose continuously over the observation period, whereas nutrient levels decline in flies fed only on the first day of life, beginning 1 day postfeeding. Female and male P. tricuspis emerge with an estimated 12.3 ± 2.3 and 7.2 ± 1 g of lipid reserves per fly, respectively. These teneral amounts represent the highest lipid levels detected in adult flies, irrespective of their diet, and are maintained over the life times of sucrose-fed female and male flies, but declined steadily in sugar-starved females. These data suggest that adult P. tricuspis are capable of converting dietary sucrose to body sugars and glycogen, but not lipids.     

Effects of artificial and western spruce budworm (Lepidoptera: Tortricidae) defoliation on growth and biomass allocation of Douglas-fir seedlings

Artificial defoliation has been used commonly to simulate defoliation by insect herbivores in experiments, in spite of the fact that obvious differences exist between clipping foliage and natural defoliation due to insect feeding. We used a greenhouse experiment to compare the effects of artificial and western spruce budworm (Choristoneura occidentalis Freeman) defoliation on the growth and biomass allocation of 3-yr old half-sib seedlings from mature Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco variety glauca] trees that showed phenotypic resistance versus susceptibility to budworm defoliation in the forest. Artificial clipping of buds mimicked the effects of budworm feeding on total seedling biomass when 50% of the terminal buds were damaged. However, artificial defoliation decreased seedling height, relative growth rate of height, and shoot: root ratio more than budworm defoliation, whereas budworm defoliation decreased stem diameter relative growth rate more than artificial defoliation. Half-sib seedling progeny from resistant maternal tree phenotypes had greater height, diameter, biomass, and shoot: root ratio than seedlings from susceptible phenotypes. We concluded that careful artificial defoliation could generally simulate effects of budworm defoliation on total biomass of Douglas-fir seedlings, but that the two defoliation types did not have equal effects on biomass allocation between shoot and root. Further, an inherently higher growth rate and a greater allocation of biomass to shoot versus root are associated with resistance of Douglas-fir trees to western spruce budworm defoliation.     

Effects of base cation fertilization on the nutrient status,free amino acids and some carbon fractions of the leaves of sugar maple (Acer saccharum Marsh.)

A study was conducted in the Lower Laurentians of southern Quebec to test the hypothesis that base cation fertilization would improve the nutrient status of declining sugar maples (Acer saccharum Marsh.) and alter the partitioning of leaf C and N. Six 40×40 m plots were delineated in an 80 year old stand of sugar maple. Three plots received a mixture of fertilizer and liming materials (500 kg ha^–1 of K₂SO₄, 250 kg ha^–1 of CaCO₃ and 250 kg ha^–1 of CaMg(CO₂)₂) in the spring of 1989. Leaves from mid crown of dominant or co-dominant maples were sampled monthly during the 1990 growing season. Trees were cored in 1992 to measure their response in diameter growth. Fertilization increased diameter growth and foliar K concentration of trees but reduced foliar Ca concentration. Fertilization resulted in lower starch concentrations and higher ratios of soluble sugars to starch in June and September, and in higher free amino acid concentrations but lower ratio of total non-structural carbohydrates to free amino acids in September. Leaf proline concentration was correlated with leaf starch concentration (r=0.39). The results suggest that amelioration of K deficiencies in sugar maple through fertilization with a mixture of base cations can increase tree growth and affect the seasonal dynamics of foliar C and N pools.Abbreviations FAA free amino acids - TNC total non-structural carbohydrates     

Photosynthetic responses of Eucalyptus nitens (Deane and Maiden) Maiden to green pruning

 Three-year-old Eucalyptus nitens (Deane and Maiden) Maiden trees and 1-year-old ramets of a single clone of E. nitens were pruned to remove 0, 50% or 70% of the green crown length. This was equivalent to removal of 0, 55% or 88% of foliage area of trees, and 0, 77% or 94% of foliage area of ramets. CO₂ assimilation (A) and stomatal conductance (g_s) were measured at constant illumination in five height zones and three foliage-age classes of trees over a 16-month period following pruning. Foliar nitrogen (N) and phosphorus (P) concentrations were determined for each measurement time during the first 12 months of the experiment. In ramets A and g_s were measured in four height zones and two foliage-age classes over a six-week period, and N and P concentrations were measured only once, at the end of the experiment. Rates of A increased by up to 175% following pruning. This response occurred throughout the canopy irrespective of position in the crown or foliage age. The magnitude of the response was generally greater in ramets than in trees, and increased with increasing severity of pruning. The initiation of the response was later, and the duration of the response was longer, in trees than ramets. In the lower crown of trees there was evidence of delayed senescence following pruning. Photosynthetic enhancement was not related to changes in foliar N concentrations. The ratio of A/N increased in many zones following pruning, especially after more severe defoliation. There was no evidence that changes in P concentrations were responsible for the result. The increases in A may have been related to changes in g_s, as maximum values of g_s were greater, and the ratio of A/g_s was generally lower, in pruned than unpruned plants. Received: 31 December 1996 / Accepted: 19 August 1997     

Nectar sugar and amino acid preferences of Battus philenor (Lepidoptera, Papilionidae)

Abstract.

• 1 Butterflies of Battus philenor were tested for their preferences for nectar sugars and amino acids in an outdoor cage experiment.
• 2 The butterflies clearly preferred both sucrose and fructose over glucose. They also preferred sucrose over fructose.
• 3 No other preferences were found to be statistically significant, although male butterflies tended to prefer a plain sugar solution over a sugar solution containing a mixture of amino acids: females consumed both of these solutions in almost equal proportions.
• 4 The results are discussed with respect to nectar composition of butterfly pollinated flowers, flower preferences, physiological and reproductive aspects of butterflies.

     

Do trees in urban or ornamental plantings receive more damage by insects than trees in natural forests?

Abstract.

• 1 To determine if trees in urban or ornamental plantings are more susceptible to attack and receive more damage to foliage by herbivores than trees in natural forests, we compared the amount of leaf damage caused by several guilds of insects feeding on seven species of native, broadleaf trees in two geographic locations.
• 2 Total leaf damage did not differ significantly between urban or ornamental and natural forests, although trees in natural forests tended to have slightly higher levels of leaf damage.
• 3 Damage caused by chewing insects was consistently higher on trees in natural forests than in urban or ornamental plantings. All other feeding guilds showed no consistent pattern in levels of damage between the two habitats.
• 4 Total damage levels were highest on canopy trees and lowest on understorey trees.
• 5 These results are inconsistent with the view that trees in urban or ornamental settings are more susceptible to insect attack than trees in natural forests.
• 6 The lower level of foliar damage caused by chewing insects on trees in urban or ornamental plantings may arise because of low rates of dispersal by insects into urban environments, higher levels of plant resistance to insect attack in urban or ornamental plantings, or lower survival rates of herbivorous insects in urban environments.

     

Variation in foliar nutrients in Eucalyptus trees in eastern and Western Australia

Abstract Levels of nitrogen, phosphorus and potassium were measured for the foliage of two co-dominant eucalypts at each of two sites, one in eastern Australia and the other in Western Australia. In eastern Australia, foliage was sampled in the canopy and subcanopy for narrow-leaved ironbark Eucalyptus crebra and grey box E. mollucana and in Western Australia, for jarrah E. marginata and marri E. calophylla. The Western Australian trees were also sampled for ‘young’ and ‘old’ leaves. Both eucalypts in eastern Australia had greater nitrogen and phosphorus levels, but lower potassium, than E. marginata or E. calophylla. Eucalyptus calophylla foliage had greater levels of all three nutrients than E. marginata foliage as did E. crebra relative to E. mollucana. At both sites, foliar nutrient levels were greater in the canopy than subcanopy foliage, and, at least in Western Australia, the younger leaves had greater nutrient levels than the older leaves. The observed differences in foliar nutrient levels are consistent with observed trends in the abundance and diversity of foliage arthropods and the use of the trees as foraging substrates by birds.