Effect of nitrogen and light on nutrient concentrations and associated physiological responses in birch and fir seedlings

We grew seedlings of two co-occurring high elevation tree species in controlled light and nitrogen (N) environments to examine the effect on foliar N and P concentrations and the resulting correlation with photosynthesis and growth. Foliar N concentrations in both heart-leaf paper birch (Betula cordifolia) and balsam fir (Abies balsamea) seedlings were greater in low light treatments than in high light treatments. P concentrations, however, were lower in birch and fir foliage grown in low light than in high light. N-availability had no effect on foliar N in birch but tended to increase N concentration in fir needles at all but 100% ambient light. N-availability had no effect on P concentration in fir seedlings, but high N decreased foliar P in birch. There was a positive relationship between foliar N-concentration (mg g^–1) and mass-based maximum photosynthetic rate (Asat) in birch seedlings and a corresponding growth response to increased N-availability (suggesting N-limitation). Fir photosynthesis exhibited a positive correlation up to 22 mg g^–1 – N and a negative correlation above that point, suggesting that high N concentrations may be detrimental to photosynthesis in the fir seedlings. There was no significant effect of N-treatment on growth.     

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.     

The effects of enriched CO2 atmospheres on plant-insect herbivore interactions: growth responses of larvae of the specialist butterfly,Junonia coenia (Lepidoptera: Nymphalidae)

Summary Little is known about the effects of enriched CO₂ environments, which are anticipated to exist in the next century, on natural plant-insect herbivore interactions. To begin to understand such effects on insect growth and survival, I reared both early and penultimate instar larvae of the buckeye, Junonia coenia (Lepidoptera: Nymphalidae), on leaves from one of their major hostplants, plantain, Plantago lanceolata (Plantaginaceae), grown in either ambient (350 PPM) or high (700 PPM) CO₂ atmospheres. Despite consuming more foliage, early instar larvae experienced reduced growth on high CO₂-grown compared to ambient CO₂-grown leaves. However, survivorship of early instar larvae was unaffected by the CO₂ treatment. Larval weight gain was positively correlated with the nitrogen concentration of the plant material and consumption was negatively correlated with foliar nitrogen concentration, whereas neither larval weight gain nor consumption were significantly correlated with foliar water or allelochemical concentrations. In contrast, penultimate instar larvae had similar growth rates on ambient and high CO₂-grown leaves. Significantly higher consumption rates on high CO₂-grown plants enabled penultimate instar larvae to obtain similar amounts of nitrogen in both treatments. These larvae grew at similar rates on foliage from the two CO₂ treatments, despite a reduced efficiency of conversion of ingested food (ECI) on the low nitrogen, high CO₂-grown plants. However, nitrogen utilization efficiencies (NUE) were unaffected by CO₂ treatment. Again, for late instar larvae, consumption rates were negatively correlated with foliar nitrogen concentrations, and ECI was also very highly correlated with leaf nitrogen; foliar water or allelochemical concentrations did not affect either of these parameters. Differences in growth responses of early and late instar larvae to lower nitrogen, high-CO₂ grown foliage may be due to the inability of early instar larvae to efficiently process the increased flow of food through the gut caused by additional consumption of high CO₂ foliage.     

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.     

Japanese oak silkmoth feeding preference for and performance on upper-crown and lower-crown leaves

We quantified differences in leaf traits between upper and lower crowns of a deciduous oak, Quercus acutissima, and examined feeding preference, consumption and performance of the Japanese oak silkmoth, Antheraea yamamai, for those leaves. Upper‐crown leaves had significantly smaller area, larger dry mass per area, greater thickness, lower water content, higher nitrogen content and a higher N/C ratio than lower‐crown leaves. When simultaneously offered upper‐crown and lower‐crown leaves, moth larvae consumed a significantly larger amount of the former. However, when fed with either upper‐crown or lower‐crown leaves (no choice), they consumed a significantly larger amount of the latter. Female larvae reared on upper‐crown leaves had a significantly smaller fresh weight, but attained a significantly larger pupal fresh and dry weight, with a significantly higher relative growth rate than those on lower‐crown leaves. Although, like female larvae, male larvae had a significantly smaller fresh weight when reared on upper‐crown leaves, they had a significantly larger value only for pupal dry weight. These results suggest that: (i) larvae ingest a greater amount of lower‐crown leaves to compensate for the lower nitrogen content of the foliage, resulting in having an excess of water because of the higher water content of the foliage; (ii) feeding preference for upper‐crown leaves accords with better performance (with respect to dry pupal weight and relative growth rate) on the foliage; (iii) better performance is explained by a higher nitrogen content and N/C ratio of the upper‐crown foliage; and (iv) the effects of leaf quality on performance differ between sexes.     

Diet-switching by gypsy moth: effects of diet nitrogen history vs. switching on growth, consumption, and food utilization

Gypsy moth (Lymantria dispar (L.) (Lepidoptera: Lymantriidae)) larvae were reared from hatch on 1.25% N or 3.5% N artificial diet (previous diet) and switched reciprocally to the other diet (current diet) after molting into the second, third, fourth, or fifth instar. The nitrogen concentration of food consumed during previous instars had a strong residual effect on the growth rate in subsequent instars when a diet switch was made during instars two through four, but did not affect growth rate of fifth-instar larvae despite effects on food consumption and utilization. In early instars, larvae reared on 1.25% N artificial diet and then switched to 3.75% N diet had lower mass-adjusted growth rates than larvae continuously reared on 3.75% N diet. Conversely, larvae reared on 3.75% N diet and switched to 1.25% N had higher mass-adjusted growth rates than larvae reared continuously on 1.25% N diet. Relative to larvae previously reared on 1.25% N diet, fifth-instar male larvae previously reared on 3.75% N diet had slightly lower consumption rates, higher net growth efficiency (ECD), and higher gross growth efficiency (ECI). Larvae previously reared on 3.75% N diet tended to have lower food assimilation efficiency (AD) and lower nitrogen assimilation efficiency (AD(N)). Although both previous and current diet nitrogen concentration strongly affected larval growth and food utilization, the interaction term between these was not significant for any response variables except ECD and ECI. Because the interaction term reflects the effect of switching per se, the results indicate that there was a metabolic cost associated with switching, but no inherent net cost or benefit of diet-switching to growth.     

Changes in western wheatgrass foliage quality following defoliation: consequences for a graminivorous grasshopper

We determined the effects of defoliation by a graminivorous grasshopper on the foliage quality of the C3 plant, western wheatgrass (Pascopyrum smithii [Rydb] A. Love). Additionally, we determined the effects of this defoliation upon the subsequent feeding of the graminivorous grasshopper Phoetaliotes nebrascensis Thomas (Orthoptera: Acrididae). In field and greenhouse studies, graminivorous grasshopper herbivory altered the quality of remaining western wheatgrass foliage. In the greenhouse, severe (50% foliage removal) grasshopper grazing (638 grasshoppers/m² for 72h) resulted in decreased foliar nitrogen (–12%), carbohydrate (–11%) and water (–2.5%) concentrations, and increased phenolic concentrations (+43%). These changes were associated with decreased adult female grasshopper mass gain, consumption rate, approximate digestibility, and food conversion efficiencies. In the field, moderate (14% foliage removal) grasshopper grazing (20 grasshoppers/m² for 20 days) led to a 10% reduction in foliar nitrogen concentrations. Foliage quality changes in the field were not associated with any reductions in grasshopper mass gain, consumption rates, food digestibility, or conversion efficiencies. The results presented here are consistent with the hypothesis that defoliation leads to a reallocation of carbon and nitrogen compounds within the plant such that foliage quality for P. nebrascensis is reduced.     

Effects of inoculation method on efficacy of wettable powder and oil dispersion formulations of Beauveria bassiana against Colorado potato beetle larvae under low-humidity conditions

The effects of inoculation method on efficacy of two formulations of Beauveria bassiana strain GHA against Colorado potato beetle larvae were investigated. Under dry greenhouse conditions, ca. 58% mortality was observed among second-instar larvae exposed directly to sprays of B. bassiana conidia, whereas mortality among larvae exposed to similarly treated foliage (either leaf dorsal or ventral surfaces) was <10%. Mortality was ca. 64% among larvae exposed to both direct sprays and foliar spray deposits. Equivalent rates of mortality were observed among larvae treated with a clay-based wettable powder versus an emulsifiable oil-based formulation of B. bassiana conidia; however, this was observed despite application of an approximately 40% greater dose of WP-formulated conidia, indicating greater efficacy of the emulsifiable oil formulation. These results suggest that, under dry conditions, potato beetle larvae do not readily acquire an effective dose of conidia from treated foliage and that development of improved application technologies to more effectively target the larvae may ultimately prove more beneficial than development of formulations with greater foliar persistence.     

Phenology and nutrition of miombo woodland trees in Zambia

Seasonality in nitrogen (N) and phosphorus (P) concentration in soil and shoots of five Brachystegia-Julbernardia (miombo) woodland trees was studied from September 1991 to March 1993 at two regrowth miombo sites in central Zambia. Shoot growth started in the dry season (September–November) and lasted until April during the 1991/92 season but had virtually ceased by January 1993 during the 1992/93 season. The shoot growing season was associated with low foliar N/P ratios. These ratios were much lower (<5) during the 1991/92 season than in the 1992/93 season (12–15). The increase in foliar N/P ratios after the shoot growing season was caused by a sharp drop in foliar P concentration, apparently due to reabsorption before leaf fall. There were no annual variations in biomass N concentration in contrast to P. During the 1992/93 growing season P concentrations in foliage and wood were a quarter and a third, respectively, of the 1991/ 92 levels. Since the short shoot growing season observed during the 1992/93 season is typical of savanna woodland trees in southern Africa, the high biomass P concentration and longer growing season in 1991/92 season were exceptional and may have been related to reduced competition by shallow rooting herbaceous plants caused by the severe drought of that season.     

Effect of dietary nitrogen on gypsy moth larval nutritional indices, development and lipid content

Nutritional indices, development rates, percent dry weights and total lipids were determined in gypsy moth larvae (Lymantria dispar L.) reared on a high wheat germ (HWG) diet or diets prepared from lyophilized, ball-milled oak or pine foliage as the only source of dietary nitrogen (N). With regard to both total and proteinaceous N content, HWG diet>oak diet>pine diet. All nutritional indices measured were significantly lower in second instars fed pine diet vs. oak diet. Protein supplementation of pine diet with either casein or ovalbumin to bring total N up to the level present in oak diet resulted in small increased in approximate digestibility (AD) and effciency of conversion of ingested food (ECI), but relative growth rate (RGR) remained unaffected. The low RGR of larvae fed pine diet (unsupplemented or protein supplemented), as compared to those fed HWG or oak diet, was accompanied by significantly lower larval percent dry weight and percent total lipid. In contrast, RGR, larval percent dry weight and total lipid values were comparable in second instars fed HWG or oak diet. Insects reared from the first through the final instar on oak diet exhibited lower pupal weights compared to those reared on HWG. Casein addition to oak diet generally resulted in even more extended larval development times and further reduced pupal weights, but wheat germ addition to oak diet did not alter development rates and caused an increase in pupal weights.     

叶面肥对柑橘全爪螨生长发育和繁殖及柑橘苗生长的影响(英文)

【目的】柑橘全爪螨Panonychus citri在中国是一种重要的柑橘害虫,叶面肥在橘园的应用很普遍。本研究是为了明确柑橘施用尿素和复合氨基酸2种叶面肥对这种害螨生长发育和繁殖及柑橘苗生长的影响。【方法】在室内分别用尿素(0.50%)和复合氨基酸(0.17%)2种叶面肥喷施盆栽沙糖橘Citrus reticulata Blanco cv. Shatangju苗,以喷施清水为对照,探究叶面施肥对柑橘全爪螨生命表参数［净 增殖率(R₀)、平均代时(T)、内禀增长率(r_m)、周限增长率(λ)和种群趋势指数(I)］及柑橘苗生长参数(叶长、宽和面积, 茎长, 株高, 新梢的长度和数量)和叶片养分(N, P和K)含量的影响。【结果】柑橘全爪螨未成熟螨态的发育历期没有受到叶面肥的影响,但施用0.50%尿素的柑橘苗上第2若螨的存活率(95.40%)显著高于施用清水的对照(78.26%)和喷施0.17%复合氨基酸的处理(75.61%),其雌螨的繁殖力(42.1/♀)也显著高于对照(33.1/♀)。复合氨基酸处理柑橘苗上的雌螨寿命(19.5 d)显著长于尿素处柑橘苗上的雌螨寿命(14.8 d)和对照(14.5 d),复合氨基酸处理柑橘苗上的雄螨寿命(17.6 d)也显著长于对照(13.1 d)。总体上,在尿素处理的柑橘苗上柑橘全爪螨的净增殖率(R₀)(17.88)和种群趋势指数(I)(18.08)值最高,2个参数都显著高于对照(分别为10.08和11.17)。施用2种叶面肥显著促进了柑橘苗叶片生长(叶长、叶宽、叶面积),其N, P和K含量以及氮钾比(N/K)也显著增加。【结论】柑橘苗叶面喷施尿素和复合氨基酸都可促进柑橘苗生长,喷施尿素会导致柑橘全爪螨种群的显著增长,而喷施复合氨基酸没有导致柑橘全爪螨种群显著增长。因此,推荐使用复合氨基酸代替尿素作为柑橘的叶面肥施用。但是,喷施复合氨基酸可显著延长柑橘全爪螨成螨的寿命,所以在使用时还应该加强对其种群的监测。     

Red foliage color reliably indicates low host quality and increased metabolic load for development of an herbivorous insect

Plant chemical defense and coevolved detoxification mechanisms in specialized herbivorous insects are fundamental in determining many insect–plant interactions. For example, Brassicale plants protect themselves from herbivory by producing glucosinolates, but these secondary metabolites are effectively detoxified by larvae of Pierid butterflies. Nevertheless, not all Brassicales are equally preferred by these specialist herbivores. Female Pieris butterflies avoid laying eggs on anthocyanin-rich red foliage, suggesting red color is a visual cue affecting oviposition behavior. In this study, we reared P. brassicae larvae on green and red cabbage leaves, to determine whether foliage color reliably indicates host plant quality. We did not find a difference in survival rates or maximal larval body mass in the two food treatments. However, larvae feeding on red cabbage leaves exhibited significantly lower growth rates and longer durations of larval development. Interestingly, this longer development was coupled with a higher consumption rate of dry food matter. The lower ratio of body mass gain to food consumption in larvae feeding on red cabbage leaves was coupled with significantly higher (ca. 10 %) larval metabolic rates. This suggests that development on red foliage may incur an increased metabolic load associated with detoxification of secondary plant metabolites. Energy and oxygen allocation to detoxification could come at the expense of growth and thus compromise larval fitness as a result of extended development. From an evolutionary perspective, red foliage color may serve as an honest defensive cue, as it reliably indicates the plant’s low quality as a substrate for larval development.     

Seasonal patterns of herbivory,leaf traits and productivity consumption in dry and wet Patagonian forests

1. Endemic herbivory can influence forest ecosystem function, but how annual productivity consumption relates to seasonal resource utilisation by folivore guilds remains poorly understood. 2. Monthly changes in leaf damage and foliage traits were monitored in ‘dry’ and ‘wet’Nothofagus pumilio (Fagales: Nothofagaceae) deciduous forests in northern Patagonia, Argentina. Herbivore‐induced leaf abscission was assessed and foliar productivity consumption was measured in the canopy and in litterfall harvests. 3. Seasonal damage ranged from 8% to 32% in dry forest, but remained below 5% in wet forest although foliar quality was higher in the latter. In dry forest, dominant guilds were temporally separated; leaf miners consumed younger foliage in spring to early summer, whereas leaf tiers prevailed in late summer to autumn. In wet forest, damage created by external chewers was concentrated in early summer. 4. Insect damage induced premature leaf abscission, especially in dry forest. Although foliar production in wet forest doubled that in dry forest, the percentage of productivity lost to folivores was higher in dry (14–20%) than in wet (1.2–1.8%) forest. 5. The overall greater impact of herbivory in dry forest canopies countered the expectation that consumption would increase with plant productivity and nutritional quality. Lower temperatures and a shorter growing season are likely to constrain folivory in wet forest stands.     

Responses of alfalfa and Barley to foliar application of N and P on a coal mine spoil

Summary To ensure adequate growth of plants on the highly impoverished and erodable surface mined lands, the application of N and P fertilizers by suitable methods is essential. In the present study, five growth chamber experiments were conducted to evaluate the relative efficacy of foliar and spoil application of N and P using alfalfa (Medicago sativa L. var. Erand) and barley (Hordeum vulgare L. var. Manker) as test crops on a freshly exposed coal mine spoil collected from western North Dakota. In general, barley responded to both N and P, but alfalfa mainly to P. Growth responses of barley to foliar or spoil-applied N+P were substantial and similar in magnitude. However, the yields were much higher when the plants received 3–4 sprays of 1.5–2.2% urea, with P supplied through the spoil. Increasing the number of 2.2% urea sprays from 1 to 3 increased the growth response from 40 to 243%. In another study, increasing the concentration of foliar-applied urea from 0 through 1% resulted in further increases in the dry weights of barley at all the levels of spoil-applied (0, 25, 75, 225 g/g) N.Foliar sprays of 0.5–1.0% NaH₂PO₄ increased the dry weights of alfalfa and barley by an average of 366% and 86%, respectively. However, the yield response of alfalfa to spoil-applied P (100 g/g) was as high as 782% compared to only 117% for barley. Alfalfa responded significantly to increasing concentrations of H₃PO₄ (0–0.3%) in foliar sprays only in the absence of spoil-applied P. With increasing rates of spoil-applied P, alfalfa yields increased steadily, but additional supply of P sprays caused leaf burning which intensified as the P concentration in sprays increased.The results of chemical analyses indicated that foliar applications were more effective than soil applications in increasing the concentration of N or P in the plants. Moreover, urea sprays increased the uptake of K, Zn, and Fe in barley, whereas spraying alfalfa with P compounds caused increases in its K and Fe content and decreases in those of Zn and Na. The results of these experiments indicated that the nutritional requirements of plants grown on coal mine spoils can be met through foliar fertilization as effectively as, or better than, through conventional soil fertilization methods.Presented at the Annual Meeting, American Society of Agronomy, Chicago, Illinois, Dec. 3–8, 1978.     

Leaf age and larval performance of the leaf beetle Paropsis atomaria

ABSTRACT.

• 1 Larval performance of the leaf beetle Paropsis atomaria Oliver was determined for larvae raised on both new and mature leaves of Eucalyptus blakelyi Maiden. Larvae were transferred to mature leaves at different ages; control larvae stayed on new leaves through all instars.
• 2 Only larvae reared on new leaves through the third instar survived to pupate on mature leaves; developmental time was prolonged by 20% and pupal weight was reduced by 50% in these larvae compared with larvae reared entirely on new leaves. Almost all larvae died when transferred to mature leaves as first, second or third instars.
• 3 Low survival and slow development on mature leaves was mainly due to failure by larvae to feed. Larvae palpated leaves and could discriminate among leaf ages immediately, without biting into the leaf tissue.
• 4 New leaves had higher concentrations of oil and tannins than old leaves, while there were no significant differences in nitrogen concentrations in the two types of leaves. Mature leaves were more than 3 times tougher than new leaves, in terms of g mm^?2 of penetrometer force.
• 5 In drought years E. blakelyi may not produce sufficient new leaves to supply specialist herbivores with their preferred food resource. We infer that drought years reduce P. atomaria larval performance significantly, and influence the population dynamics of the insect.

     

Effects of phytochemical variation in quaking aspen Populus tremuloides clones on gypsy moth Lymantria dispar performance in the field and laboratory

1. This study investigated how phytochemical variation among clones of quaking aspen Populus tremuloides, growing in a common habitat, affects the growth and fecundity of a model herbivore. 2. Gypsy moth Lymantria dispar larvae were reared from egg hatch to pupation on 10 aspen clones in the field or on excised foliage in the laboratory. Foliage was collected from each clone, and concentrations of phenolic glycosides, condensed tannins, nitrogen, and water were determined. 3. Herbivore fitness parameters and aspen phytochemical concentrations varied significantly among clones. In both the field and laboratory, larvae reared on clones containing high concentrations of phenolic glycosides exhibited prolonged developmental times and reduced pupal weights and fecundity. Herbivore performance parameters were also related positively to foliar nitrogen concentrations in the laboratory. Food consumption, but neither growth nor reproductive parameters, were related positively to condensed tannin concentrations. 4. In this study, foliar concentrations of phenolic glycosides were implicated as a significant determinant of food quality for gypsy moths, consistent with results of previous laboratory experiments. Additionally, this study documents a case in which host plant variation at a local level influences the performance and possibly the distribution and abundance of an important herbivore.     

Establishment of Beauveria bassiana as a fungal endophyte in potato plants and its virulence against potato tuber moth,Phthorimaea operculella (Lepidoptera: Gelechiidae)

The potato tuber moth, Phthorimaea operculella, is the most damaging potato pest in the world and is difficult to control as the larvae are internal feeders in the foliage and tubers. Entomopathogenic fungi that colonize plants as endophytes have lethal and sublethal pathological effects on insect pests. We show that Beauveria bassiana colonizes the aerial parts of potato plants endophytically after inoculation through soil drenching. Endophytic B. bassiana persisted in potato foliage for more than 50 days postinoculation. Bioassays indicated that foliage of B. bassiana-inoculated potato plants were pathogenic against larvae of P. operculella. Sublethal experiments indicated that B. bassiana negatively affected the growth, development, and reproduction of P. operculella. Development experiments showed that the weight of P. operculella pupae reared on B. bassiana-colonized potato plants (4.25 mg) was significantly less than that of those reared on uninoculated control plants (8.89 mg). Compared with newly eclosed larvae fed on control plants, those fed on B. bassiana-inoculated plants had significantly lower survivorship, with only 17.8% developing to the adult stage. Oviposition of P. operculella females reared on B. bassiana endophytically colonized plants was significantly lower (35 eggs/female) than of those reared on uninoculated plants (115 eggs/female). This study demonstrates that endophytic B. bassiana can be a potential biological control agent for the control and management of P. operculella. Comparing pupal weights of P. operculella reared on potato plants inoculated with the B. bassiana strain GZGY-1-3 and on untreated control plants, pupae from the control plants were significantly heavier than those from treated plants.     

Seasonal respiration of foliage, fine roots, and woody tissues in relation to growth, tissue N, and photosynthesis

Autotrophic respiration may regulate how ecosystem productivity responds to changes in temperature, atmospheric [CO₂] and N deposition. Estimates of autotrophic respiration are difficult for forest ecosystems, because of the large amount of biomass, different metabolic rates among tissues, and seasonal variation in respiration rates. We examined spatial and seasonal patterns in autotrophic respiration in a Pinus strobus ecosystem, and hypothesized that seasonal patterns in respiration rates at a common temperature would vary with [N] for fully expanded foliage and fine roots, with photosynthesis for foliage, and with growth for woody tissues (stems, branches, and coarse roots). We also hypothesized that differences in [N] would largely explain differences in maintenance or dormant‐season respiration among tissues. For April–November, mean respiration at 15 °C varied from 1.5 to 2.8 μmol kg^?1 s^?1 for fully expanded foliage, 1.7–3.0 for growing foliage, 0.8–1.6 for fine roots, 0.6–1.1 (sapwood) for stems, 0.5–1.8 (sapwood) for branches, and 0.2–1.5 (sapwood) for coarse roots. Growing season variation in respiration for foliage produced the prior year was strongly related to [N] (r² = 0.94), but fine root respiration was not related to [N]. For current‐year needles, respiration did not covary with [N]. Night‐time foliar respiration did not vary in concert with previous‐day photosynthesis for either growing or fully expanded needles. Stem growth explained about one‐third of the seasonal variation in stem respiration (r² = 0.38), and also variation among trees (r² = 0.43). We did not determine the cause of seasonal variation in branch and coarse root respiration, but it is unlikely to be directly related to growth, as the pattern of respiration in coarse roots and branches was not synchronized with stem growth. Seasonal variations in temperature‐corrected respiration rates were not synchronized among tissues, except foliage and branches. Spatial variability in dormant‐season respiration rates was significantly related to tissue N content in foliage (r² = 0.67), stems (r² = 0.45), coarse roots (r² = 0.36), and all tissues combined (r² = 0.83), but not for fine roots and branches. Per unit N, rates for P. strobus varied from 0.22 to 3.4 μmol molN^?1 s^?1 at 15 °C, comparable to those found for other conifers. Accurate estimates of annual autotrophic respiration should reflect seasonal and spatial variation in respiration rates of individual tissues.     

Uniconazole effect on growth and chlorophyll content of pyracantha,photinia, and dwarf Burford holly

Pyracantha, photinia, and dwarf Burford holly were treated with a uniconazole medium drench at 0, 0.5, 1.0, or 3.0 mg · container^–1 a.i. or a foliar application at the following rates: pyracantha at 0, 50, 100, or 150 mg · L^–1 a.i.; photinia at 0, 25, 50, or 100 mg · L^–1 a.i.; and holly at 1, 10, 25, or 50 mg · L^–1 a.i. Height, width, leaf area per plant, and dry weights of all species decreased as uniconazole drench rate increased. Foliar applications were less effective than drenches in pyracantha and photinia, and holly did not respond to the foliar treatment. Chlorophyll content of pyracantha increased with rate in both application methods. Leaf N, P, and Zn increased in pyracantha and photinia with increasing medium drench rate, but only P was increased in holly. Zn also increased in pyracantha and photinia with foliar applications, but only N in photinia and P in pyracantha increased with increasing uniconazole foliar application rates.     

Experimental estimation of the food intake of larval vendace (Coregonus albula L.) under field conditions

We estimated the food intake of larval vendace (Coregonus albula L.) directly in an experimental chamber under field conditions. The larvae were stocked into net enclosures and reared without additional feeding for 6 weeks immediately after the ice melted in Lake Ylä-Enonvesi, Eastern Finland. The food intake was estimated on the basis of the decrease in zooplankters due to larval predation in the transparent plastic chambers anchored in the littoral zone. The experiments were carried out twice in 1988 and three times in 1989 (May–June). The numbers of zooplankters inside the chambers were counted from the subsamples using an inverted microscope. The relative daily ingestion rate (mg dry mass of prey animals mg dry mass of fish ^–1 24 h^–1) of the larvae of different sizes was: 1.09 and 0.84 for 9–11 mm larvae, 1.27 for 11–13 mm larvae and 0.34 for 17–20 mm larvae. The measured ingestion rate is presumed to be near the maximum consumption of the larvae. This method could provide accurate estimates of food consumption in the field or in the laboratory.