Factors affecting oral regurgitation by larval spruce budworm

This study evaluated factors that influence the regurgitation behaviour of sixth instar spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), reared on balsam fir, Abies balsamea (L.) Mill. (Pinaceae), under various experimental conditions in the laboratory. Upon physical disturbance, larvae discharged a median volume of regurgitant of 0.4 μl when fed and 1.6 μl when food‐deprived. Larvae deprived of food for 24 or 48 h disgorged more regurgitant than larvae feeding on balsam fir foliage, and the effect was consistent for laboratory‐reared and field‐collected larvae. The water content of the foliage fed upon by larvae had no immediate impact on the volume of regurgitant; following a 24‐h period of food deprivation, however, larvae that previously fed on fresh foliage discharged >2.5 times more regurgitant than larvae that previously fed on dry foliage. Self‐regulated regurgitation by larvae, measured using the number of regurgitant stains on filter paper, was >10 times higher when larvae had access to balsam fir foliage than when they were starved. The number of larvae confined inside the Petri dish (one or four individuals) had a relatively small effect on regurgitation. Larvae were deterred from feeding when balsam fir needles were entirely covered with regurgitant, but not when only a portion of the foliage was treated. These results suggest that the regurgitant does not serve as resource marking or spacing pheromone. The high level of regurgitation by larvae after contact with ants suggests that the regurgitant has evolved in part as a defence mechanism against natural enemies.     

Factors affecting low temperature preservation of the marine rotifer Brachionus rotundiformis Tschugunoff

Experiments were performed to determine suitable conditions for low temperature preservation of small S (Fukuoka) and ultra-small SS (Thai) strains of B. rotundiformis. For this, single rotifers (an adult bearing one egg or a 4-h neonate) were incubated for 10 days in 1 ml seawater (22 ppt salinity). The highest survival was achieved at 10 and 12 °C for S-strain and 12 °C for SS-strain. The effect of salinity, change of culture medium and feeding regime were further tested on rotifers (300 ind. ml^–1) cultured in vials containing 10 ml seawater and microalgae at 12 °C. Survival of S-strain was highest (55.5±0.8%) at 35 ppt, while SS-strain survived best (43.1±2.6%) at 17 ppt. Survival was suppressed by changing the culture medium every 4 days. Feeding rotifers every 2 days yielded better survival (66.2±6.6%: S-strains, cultured at 35 ppt and 81.8±5.2%, SS-strains cultured at 17 ppt) than feeding them only at the beginning of the experiment or at 4-day intervals. An acclimation at 20 °C for 24 h before transferring them from their usual culture temperature (28 °C) to 12 °C resulted in higher survival of SS-strain. For S-strain, however, no significant improvement resulted from acclimation. SS-strain was more susceptible to lower temperature and higher salinity than S-strain.     

Influence of the green spruce aphid on defoliation and radial stem growth of Sitka spruce

Premature abscission of older Sitka spruce foliage on trees within forests in Northern Ireland was compared with green spruce aphid population levels 2 to 3 months earlier. Each aphid has a lower relative impact on needle loss at higher aphid population density; nevertheless, more aphids on a tree results in greater rates of needle loss. Evidence from horizontal stem increment sequences suggested that aphid feeding inhibited incremental growth, and that this inhibition might be delayed for up to two field seasons. However, the effect of aphids on stem growth in most years and on most trees seems relatively small compared with the potential of other tree-or year-specific processes.     

Interactions between green spruce aphid (Elatobium abietinum (Walker)) and Norway and Sitka spruce under high and low nutrient conditions

1 Green spruce aphid (Elatobium abietinum) is a serious pest of spruce (Picea spp.) in north‐west Europe, causing defoliation of one‐year‐old and older needles. 2 Relationships between population development of E. abietinum, needle loss and tree growth were compared for five pure genotypes of Sitka spruce and mixed‐genotype material of Sitka and Norway spruce, grown under high and low nutrient conditions. 3 Despite wide differences in flushing date between spruce genotypes, E. abietinum populations peaked on the same date on each genotype and on the mixed‐genotype material, irrespective of nutrient supply. 4 Larger aphid populations developed on trees grown under high nutrient conditions than under low nutrients. However, more needles were lost per aphid in the low nutrient treatment and overall defoliation rates in the two nutrient treatments were similar. 5 Total aphid numbers differed significantly between Sitka spruce genotypes within nutrient treatments, but not in relation to bud‐burst or needle terpene content. Reductions in height growth caused by infestation were greater (15–44%), and related to mean aphid densities and defoliation, in the low nutrient treatment, but were smaller (11–27%) and not related to aphid density and defoliation in the high nutrient treatment. 6 Development of E. abietinum populations was similar on Norway and Sitka spruce, but Norway spruce lost fewer needles. However, the effects of infestation on tree growth were more closely related to aphid density and were similar for Norway and Sitka spruce. 7 Infestation caused a decrease in total root dry weight of Norway and Sitka spruce in proportion to the reductions observed in above‐ground growth.     

Factors affecting survival of bacteriophage on tomato leaf surfaces

The ability of bacteriophage to persist in the phyllosphere for extended periods is limited by many factors, including sunlight irradiation, especially in the UV zone, temperature, desiccation, and exposure to copper bactericides. The effects of these factors on persistence of phage and formulated phage (phage mixed with skim milk) were evaluated. In field studies, copper caused significant phage reduction if applied on the day of phage application but not if applied 4 or 7 days in advance. Sunlight UV was evaluated for detrimental effects on phage survival on tomato foliage in the field. Phage was applied in the early morning, midmorning, early afternoon, and late evening, while UVA plus UVB irradiation and phage populations were monitored. The intensity of UV irradiation positively correlated with phage population decline. The protective formulation reduced the UV effect. In order to demonstrate direct effects of UV, phage suspensions were exposed to UV irradiation and assayed for effectiveness against bacterial spot of tomato. UV significantly reduced phage ability to control bacterial spot. Ambient temperature had a pronounced effect on nonformulated phage but not on formulated phages. The effects of desiccation and fluorescent light illumination on phage were investigated. Desiccation caused a significant but only slight reduction in phage populations after 60 days, whereas fluorescent light eliminated phages within 2 weeks. The protective formulation eliminated the reduction caused by both of these factors. Phage persistence was dramatically affected by UV, while the other factors had less pronounced effects. Formulated phage reduced deleterious effects of the studied environmental factors.     

Season and drought stress mediate growth and weight of the green spruce aphid on Sitka spruce

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Factors affecting the survival of Neisseria sicca

Cultures of Neisseria sicca incubated at 37 degrees C died rapidly (within 36 h) after growth ceased. Re-suspending cells in a brain heart infusion broth and storing at 4 degrees C greatly reduced the rate of decline in viability (decimal reduction time 6 days). An important factor in maintaining viability was apparently the presence of external energy source(s). Survival comparable to that in broth was obtained by incubation in Ringer's solution with pyruvate plus glucose (but not with pyruvate or glucose alone). Medium pH had little effect on survival in the range pH 7.0 to 8.5. Energy sources also promoted survival of cells in Ringer's solution or a buffered salts solution at 37 degrees C. Highest levels of survival (up to 30% at 24 h) were obtained with pyruvate, lactate, proline and glutamate. A number of other amino acids and the tricarboxylic acid cycle intermediates, isocitrate, oxoglutarate, succinate, fumarate, malate and oxaloacetate, enhanced survival to a lesser extent.     

Performance of the green spruce aphid, Elatobium abietinum (Walker) on previously defoliated Sitka spruce

Abstract 1 The green spruce aphid, Elatobium abietinum, is an important defoliator of Sitka spruce in the U.K. However, it is usual for years in which high E. abietinum populations occur to be followed by a year with low aphid densities. The possibility that the performance of E. abietinum is reduced on previously infested Sitka spruce, and that this is the cause of year‐to‐year fluctuations in population density, was investigated by comparing population development and the growth rate of individual aphids on experimentally defoliated trees. 2 Separate experiments were performed to determine whether aphid performance was reduced either in the autumn immediately after defoliation in the spring, or was reduced in the spring of the next year. Different rates of initial defoliation on trees used to test aphid performance were created by artificially infesting the trees with aphids in the spring before the experiments, and varying the time of infestation. 3 Population development and the mean relative growth rate (MRGR) of individual aphids on previously defoliated and undefoliated Sitka spruce did not differ significantly in the spring of the next year. No differences were observed in the nutrient content of the 1‐year‐old needles of previously defoliated or undefoliated trees at this time. 4 In the autumn and winter immediately after spring defoliation, aphid MRGR was significantly higher on trees that had been heavily defoliated earlier in the season compared with trees that had been lightly defoliated. However, the difference in MRGR decreased over the winter period. Nitrogen, phosphorous and potassium concentrations were 9.4–12.2% higher, at the beginning of the autumn, in the current year needles of heavily defoliated trees than in the current year needles of lightly defoliated trees. 5 The experiments indicate that high populations of E. abietinum in the spring do not induce any defensive mechanisms in Sitka spruce that adversely affect subsequent generations of the aphid. By contrast, the results suggest that high spring densities of the aphid improve the nutritional quality of the current year's foliage for autumn generations.     

The effect of some aspects of low temperature and radiation on the survival of Latheticus oryzae eggs

In an attempt to delay hatching without affecting their viability, the eggs ofLatheticus oryzae W. were subjected to cold treatment at 5° for varying periods and at different stages of their development. A small dose of 0.5 krad of gamma radiation was also given at each of those temperature treatments. Most of the eggs hatched at 30° following low-temperature exposures of 1 and 2 days. There was a significant decrease in hatch as the exposure period increased further (P<0.05). An egg exposure to 5° also led to an increase in egg period and the increase was nearly equal to the period of cold exposure. Radiation did not alter the situation.     

Within-crown distribution of male and female cones on clonal Sitka spruce trees

The within-crown distribution of cones (strobili) was mapped on 48 mature grafts of Sitka spruce [Picea schensis (Bong.) Carr.]. The total number of cones per tree was increased by a mainstem injection of 20 mg GA_4/7 and 8 mm wide bark ring. The cones and buds were classified as either lateral or terminal on each individual branch. The distribution of lateral female, terminal female, lateral male and terminal male cones, showed a general progression from the upper distal to lower proximal regions of the tree crown in all 12 clones. Evidence for preferential allocation of cones to particular branch types is presented. The region of the tree with the greates number of cones varied with treatment and reflected differences in the sex ratio of the individual trees. There is evidence for a relationship between branch length, position within the crown and the type of cone produced.     

Promotion of cone and seed production on Sitka spruce by gibberellin application

Gibberellin mixtures were applied to large, mature scions of Sitka spruce, growing in the open at Wauchope Tree Bank in 1975, 1976 and 1977. Large increases in coning and seed production, and in the numbers of clones producing seed, occurred in the year after treatment. Cone and seed yields varied with the timing and concentration of hormone treatment, and were greatest when applications were made in the top two branch whorls on the tree. Clonal differences in seed production were observed among gibberellin-treated branches. Seed quality, judged by seed weight and percentage germination, appeared normal. Promotion of male strobili was greater in lower branch whorls than in the top branch whorl on the tree. Ways in which these findings can be applied in breeding and seed production are discussed.     

Effects of starch additions on N turnover in Sitka spruce forest floor

Starch and carboxymethyl starch were added to forest floor samples collected from a sitka spruce stand near Aberdeen, Scotland. Samples were incubated for one month and were periodically analyzed for respiration, biomass-C, net and gross N-mineralization/immobilization. Gross mineralization/immobilization was measured by using a ¹⁵N-isotope pool dilution technique. Starch additions did not significantly affect respiration rates or biomass-C but caused net immobilization. The mechanism of this appeared to be inhibition of the decomposition of N-containing soil organic matter by the available starch-C, which resulted in decreased gross mineralization. Carboxymethyl starch acted as a biocide, probably as a result of an osmotic effect.     

Insects associated with the Sitka spruce weevil,Pissodes Strobi [Col.: Curculionidae] on Sitka spruce,Picea sitchensis in British Columbia,Canada

BioControl - Insects associated with the Sitka spruce weevil,Pissodes strobi (Peck), on Sitka spruce,Picea sitchensis (Bong.) Carr. were sampled at 9 locations in British Columbia. Fourteen species...     

Factors affecting the survival of frozen-thawed mouse spermatozoa

Mouse epididymal spermatozoa were frozen in solutions containing various compounds with different molecular weights, and the factors affecting the postthawing survival were examined. Monosaccharides (glucose, galactose) had almost no protective effect regardless of the concentration and the temperature of exposure. On the other hand, disaccharides (sucrose, trehalose) and trisaccharides (raffinose, melezitose) resulted in higher survival rates, especially at a concentration of around 0.35 mol/kg H(2)O (0.381-0.412 Osm/kg). Macromolecules, such as PVP10, Ficoll 70, bovine serum albumin, and skim milk had almost no effect, but compounds with a molecular weight of about 800, such as metrizamide and Nycodenz, had some protective effect. When a raffinose solution was supplemented with 10% metrizamide, resulting in an osmolality of approximately 0.400 Osm/kg, a high survival rate was obtained. Solutions at about 0.400 Osm/kg containing trehalose alone, trehalose + metrizamide, raffinose alone, and raffinose + metrizamide, were all effective for sperm freezing; frozen-thawed sperm could fertilize oocytes, and the resultant embryos could develop to live young after transfer. For freezing mouse spermatozoa, aqueous solutions at approximately 0.400 Osm/kg containing a disaccharide or a trisaccharide seem to be effective.     

Enhanced enzymatic hydrolysis of spruce by alkaline pretreatment at low temperature

Alkaline pretreatment of spruce at low temperature in both presence and absence of urea was studied. It was found that the enzymatic hydrolysis rate and efficiency can be significantly improved by the pretreatment. At low temperature, the pretreatment chemicals, either NaOH alone or NaOH-urea mixture solution, can slightly remove lignin, hemicelluloses, and cellulose in the lignocellulosic materials, disrupt the connections between hemicelluloses, cellulose, and lignin, and alter the structure of treated biomass to make cellulose more accessible to hydrolysis enzymes. Moreover, the wood fiber bundles could be broken down to small and loose lignocellulosic particles by the chemical treatment. Therefore, the enzymatic hydrolysis efficiency of untreated mechanical fibers can also be remarkably enhanced by NaOH or NaOH/urea solution treatment. The results indicated that, for spruce, up to 70% glucose yield could be obtained for the cold temperature pretreatment (-15 degrees C) using 7% NaOH/12% urea solution, but only 20% and 24% glucose yields were obtained at temperatures of 23 degrees C and 60 degrees C, respectively, when other conditions remained the same. The best condition for the chemical pretreatment regarding this study was 3% NaOH/12% urea, and -15 degrees C. Over 60% glucose conversion was achieved upon this condition.     

Factors affecting the survival ofRhizoctonia bataticola in black soil

Summary Survival ofRhizoctonia bataticola was adversely affected at high soil moisturei.e. 60 and 80% MHC (moisture holding capacity); activity was good below 40% MHC. Half-life period was considerably reduced at 80% MHC. Variations in soil pH and addition of saltsviz Na₂SO₄, MgSO₄, CaCl₂ and NaCl did not affect the saprophytic activity of the fungus.     

Factors affecting post-dispersal seed survival in a tropical forest

Summary Using the subcanopy tree Faramea occidentalis in Panama, I studied post-dispersal seed survival as a function of five characteristics describing seed locations. By simultaneously considering distance from a conspecific adult, size of the nearest conspecific adult, leaf litter quantity, proximity to logs or tree trunks, and whether or not the seed was in a gap, I was able to analyze the influences of individual factors, as well as the interactions among factors. Seed survival was significantly less in treefall gaps than in the forest understory. Seed survival was also influenced by the size of the nearest adult but in a complex interaction with distance to an adult. For seeds beneath adults, survival decreased with increasing tree size, while for seeds away from adults, survival was independent of the size of the nearest conspecific adult. Distance did not directly affect seed survival, nor did the quantity of leaf litter or the proximity to a tree trunk or a log. In a separate analysis, the relationship between distance and seed survival was consistent over four years, suggesting that single cohort studies may provide accurate insights into the consequences of dispersal. In contrast, the spatial locations of surviving seeds were not consistent over the four-year period. Transects with high survival one year did not tend to have high survival in other years, and the locations of surviving seeds in any particular year could not be predicted from the knowledge of where seeds survived in other years. While survival is patchy within a year, the locations of patches shift from year to year.