Environmental factors affecting the life-tables ofTetranychus urticae (Acari: Tetranychidae) III. Host-plant nutrition

First, the literature of the last two decades on nutritional effects of host plants on spider mites is briefly reviewed. Second, experiments are described that subjected micro-propagated apple trees to four different levels of each macronutrient N, P and K. Spider mites (Tetranychus urticae Koch) feeding on leaf disks of these plants were checked for their developmental time, egg production and longevity. Plant analysis revealed that the concentration of N, P and K corresponded to the respective treatments. The content of phenolic compounds in the leaves increased with N and P deficiency. In the N experiment, spider-mite preimaginal developmental rate and oviposition rate were both positively correlated with leaf N. Often, fecundity was positively correlated with N and carbohydrate content of the leaves, and negatively with the phenolic content. Longevity of the two-spotted spider mite was not significantly affected by any treatment. The K experiments yielded only minor differences in plant contents as well as in spider-mite biology.From these mite data, file-tables were constructed and statistically analyzed by the Jackknife technique. The life-table analysis showed a gradual decline in the intrinsic rate of natural increase (r _m) with N and P deficiency. With all experiments pooled,r _m was clearly correlated to leaf N and particularly to the content of phenolic compounds in the leaves. Nitrogen shortage had the most distinct influence on mite population growth: in a range of 1.5–3.0% leaf N,r _m increased by a factor of 4, the number of multiplications per generation (R ₀) by 11, and the doubling time of the population was prolonged 4-fold on severely N deficient leaves.     

Effect of host plant nitrogen fertilization on the biology of the two-spotted spider mite, Tetranychus urticae

Females of Tetranychus urticae Koch were reared on leaf discs of apple trees and bush beans grown at different N concentrations (0.6–75 mM NO _inf3 ^sup- ). N-deficiency increased pre-imaginal development time, preoviposition period, and decreased female weight, fecundity and oviposition rate of the mites. N, water, amino acid, and sugar content of the apple leaves were positively correlated with weight and egg production and negatively correlated with development time and pre-oviposition period. The reverse correlations were found with total phenol content of the leaves and above mite parameters. A reduction of leaf N by 50% was related with a tenfold decline in fecundity on apple leaves. The stress mainly affected the oviposition rate and to a lesser extent the oviposition period. On apple leaves the net reproductive rate (av. no. offspring per , R_o), mean length of a generation (T), and innate capacity for increase (r_m) were R_o=40.3, T=17.1, and r_m=0.22 for the standard N concentration, and 4.7, 25.0, and 0.06 for strong N-deficiency, respectively.

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Zusammenfassung Die polyphage Gemeine Spinnmilbe ist ein wirtschaftlich bedeutender Schädling. Die Rolle einzelner Nährstoffe bei der Milbenvermehrung wurde schon von einigen Autoren mit unterschiedlichen Ergebnissen untersucht. Der Stickstoff scheint aber einer der Hauptfaktoren zu sein.Ueber Gewebekulturen klonierte Apfelbäume sowie aus Samen gezogene Buschbohnen wurden in Nährlösungen mit verschiedenen N-Angeboten kultiviert. Aus solchen Pflanzen wurden Blattscheiben ausgestanzt und mit Weibchen von T. urticae besetzt. Gemessen wurden die tägliche Eiablage bis zum natürlichen Tod, die Entwicklungsdauer und das Weibchengewicht. Mit dem bei N-Mangel abnehmenden N, Aminosäuren- und Zuckergehalt (v.a. Sorbit) im Blatt korrelierend nahmen auch Gewicht, Ablagerate und Fekundität ab, bzw. die Entwicklungsdauer und Praeovipositionsperiode zu. Die umgekehrte Wirkung auf diese Milbenparameter hatte der Gesamtphenolgehalt. Eine Reduktion des N-Gehalts der Blätter auf die Hälfte (1.5% N) bewirkte auf Apfelblättern eine Abnahme von Fekundität und Ovipositionsrate um das zehnfache, bzw. eine Zunahme der Präovipositionsperiode um mehr als das dreifache. Der Stress beeinflusste v.a. die Maxima der Ablageverläufe und weniger die Lebensdauer. Der Wassergehalt war ebenfalls mit der Fekundität positiv korreliert.Auf Bohnenblättern legten die Tiere mehr Eier und erreichten ein höheres Gewicht als auf Apfel, dies bei gleichem N-Gehalt beider Pflanzen. Es wirken somit noch andere Faktoren auf die Reproduktion der Spinnmilben.Die Populationsparameter wurden ebenfalls sehr stark beeinflusst. Auf Apfelblättern ergab sich bei der Kontrolle eine Nettoreproduktionsrate R_o von 40.3 und bei starker N-Defizienz 4.7. Die mittlere Generationsdauer T sowie die spezifische natürliche Wachstumsrate r_m betrugen für die Kontrolle 17.1 Tage, bzw. 0.22 und für starken N-Mangel 25.0 Tage, bzw. 0.06.Die Ergebnisse zeigen, dass sich bereits kleinere Unterschiede im Stickstoffgehalt und damit zusammenhängend im Zucker- und Phenolgehalt stark auf die Populationsdynamik der Gemeinen Spinnmilbe auswirken können.

     

Effects of boron on growth of tomato cell suspensions

The effects of various B levels in the culture medium on the biomass production and B concentrations of cells were studied using tomato ( Lycopersicon esculentum Mill. cv. Rodeo) cell suspensions in three separate experiments. In the initial study, no increase in cell biomass was observed after day 4 in the absence of B in the medium. These cells had lost their viability by day 6. Cells grown at a B level of 0.09 or 0.55 m M in the medium had the highest biomasses (doubled by day 6). Cells grown at 0.92 or 1.85 m M B had lower biomasses (doubled by day 8). In the other two studies, both under low (0.005–0.07 m M ) and high (2.30–4.15 m M ) concentrations of B in the media, there was only a slight increase in biomass and the cultures failed to double their biomasses even by day 10. Cells grown with 3.70 or 4.15 m M in the medium showed a black discolouration by day 6 and were no longer viable. Except in the high B study, the B concentrations in the cells did not vary after day 2. With increasing B levels in the medium, the B concentrations of cells were in near equilibrium with the media B. Due to increasing toxicity which may have altered the membrane properties of the cell, this relationship did not continue with B levels of 1.85 m M or higher. These results indicate that B enters the tomato cells through passive transport and that a passive equilibrium exists between B concentrations in the cells and in the media.     

Découverte de microfaunes de l'Albienmoyen et supérieur dans la vallée de Joux (Jura Vaudois,Suisse)

The discovery of Foraminifera and Ostracodesin the dark green, sandy-glauconitic marl clay in the Joux Valley (in the Vaudois Jura) suggests to date these sediments Middle and Upper Albian. The Ostracode associations are similar to those found in the Paris Basin, but different from those which characterize the subalpine region.     

Root-zone temperature and salinity: Interacting effects on tillering,growth and element concentration in barley

The effects of root-zone salinity (0, 30, and 60 mmol L^–1 of NaCl) and root-zone temperature (10, 15, 20, and 25°C) and their interactions on the number of tillers, total dry matter production, and the concentration of nutrients in the roots and tops of barley (Hordeum vulgare L.) were studied. Experiments were conducted in growth chambers (day/night photoperiod of 16/8 h and constant air temperature of 20°C) and under water-culture conditions. Salinity and root temperature affected all the parameters tested. Interactions between salinity and temperature were significant (p<0.05) for the number of tillers, growth of tops and roots, and the concentration of Na, K, P in the tops and the concentration of P in the roots. Maximum number of tillers and the highest dry matter were produced when the root temperature was at the intermediate levels of 15 to 20°C. Effect of salinity on most parameters tested strongly depended on the prevailing root temperature. For example, at root temperature of 10°C addition of 30 mmol L^–1 NaCl to the nutrient solution stimulated the growth of barley roots; at root temperature of 25°C, however, the same NaCl concentration inhibited the root growth. At 60 mmol L^–1, root and shoot growth were maximum when root temperature was kept at the intermediate level of 15°C; most inhibition of salinity occurred at both low (10°C) and high (25°C) root temperatures. As the root temperature was raised from 10 to 25°C, the concentration of Na generally decreased in the tops and increased in the roots. At a given Na concentration in the tops or in the roots, respective growth of tops or roots was much less inhibited if the roots were grown at 15–20°C. It is concluded that the tolerance of barley plant to NaCl salinity of the rooting media appears to be altered by the root temperature and is highest if the root temperature is kept at 15 to 20°C.     

Germination of Pistacia vera L. pollen in liquid medium

Summary The osmotic effect of Polyethylene glycol (PEG) has been shown to be sufficient to induce the germination of Pistacia vera L. pollen in liquid medium. The prehydration of the pollen in a saturated atmosphere for approximately 10 h was necessary to obtain maximum in vitro germination. Imbibition of the pollen in water resulted in the rapid leakage of solutes into the medium. These solutes consisted of approximately 50% carbohydrates, of which sucrose (0.65 mol/mg), glucose (0.77 mol/mg) and fructose (0.78 mol/mg) were the major sugars; the remaining 50% comprised proteins with the following major molecular weights 63 kDa, 60 kDa, 59 kDa, 40 kDa, 36 kDa, 35.5 kDa, 31 kDa, other organic matter and minerals.     

How can we conserve cold stenotherm communities in warming Alpine ponds?

Freshwater biodiversity has shown to be highly vulnerable to climate warming, alpine cold stenotherm populations being especially at risk of getting extinct. This paper aims at identifying the environmental factors favouring cold stenotherm species in alpine ponds. This information is required to provide management recommendations for habitats restoration or creation, needed for the mitigation of the effects of climate warming on alpine freshwater biodiversity. Cold stenotherm species richness as well as total (i.e. stenotherm and eurytherm) richness were analyzed for aquatic plants, Coleoptera and Odonata in 26 subalpine and alpine ponds from Switzerland and were related to environmental factors ecologically relevant for pond biodiversity. Our results confirmed that the set of environmental variables governing pond biodiversity in alpine or subalpine ponds is specific to altitude. Altitude and macrophyte presence were important drivers of cold stenotherm and total species richness, whereas connectivity did not show any significant relation. Therefore, the management of pond biodiversity has to be ‘altitude-specific’. Nevertheless, cold stenotherm species from the investigated alpine ponds do not show some specific requirements if compared to the other species inhabiting these ponds. Therefore, both total and cold stenotherm species richness could be favoured by the same management measures.     

Biodiversity in eutrophicated shallow lakes: determination of tipping points and tools for monitoring

Nutrient-rich freshwater ecosystems are generally considered as having low ecological quality and low associated biodiversity. In such systems we analysed the effects of water quality on biodiversity of several species groups, to determine tipping points and tools for monitoring. We investigated the water quality of 99 eutrophic and hypertrophic shallow lakes with extensive fish culture during a 3-year study, through the measures of physico-chemical parameters, phytoplankton biomass and structure. In a second step, we related the water quality with richness of aquatic plants, macroinvertebrates and dragonflies. With concentrations of chlorophyll-a above 30 or 70 μg l^?1, shallow lakes are normally classified, respectively, in a poor or bad ecological state. However, our results show that chlorophyll-a concentrations up to 78 μg l^?1 could be found together with relatively high species or family richness of aquatic plants, invertebrates and dragonflies. We identified most tipping points with 50–60 μg l^?1 of chlorophyll-a, values above which a significant decrease of species diversity was found. For monitoring of these shallow lakes we propose to use chlorophyll-a concentrations in combination with water transparency during spring. These parameters are easily applicable and cheap and they yield a good forecast of the biodiversity for the species groups studied.