Variation in preference and performance of Frankliniella occidentalis (Thysanoptera: Thripidae) on three strawberry cultivars

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major pest of strawberry, causing substantial yield loss through direct feeding on the flowers and fruit. Insecticides are the main method used for its control; however, F. occidentalis has developed resistance to insecticides from all major chemical classes. Chemical control is not a long-term strategy and integrated pest management is required. This study determined whether F. occidentalis damage could be reduced by host plant resistance or tolerance in three commercial strawberry cultivars (Fragaria X ananassa [Rosaceae]: 'Albion', 'Camarosa', and 'Camino Real'). Determination of resistance or tolerance to F. occidentalis was based on olfactory response, feeding damage, ovipositional preference, and host suitability for reproduction on leaves. F. occidentalis adults preferred to feed on Camarosa; however, if leaves had been fed on previously by conspecifics, there was no difference in feeding preference. Camarosa was the most preferred cultivar for oviposition, and more eggs were laid by F. occidentalis on Camarosa than either Albion or Camino Real. More larvae hatched and adults were reared from Camarosa than either Albion or Camino Real. The percentage of unhatched eggs, larvae, and pupae that died was highest on Camino Real. Survival rate was highest on Camarosa. Egg incubation, prepupation, pupation, and total developmental periods were shortest on Camarosa, but the larval period was longest on Camarosa. Camarosa was the most favorable cultivar for F. occidentalis population growth on leaves.     

Optimum plant densities for three semi-leafless combining pea (Pisum sativum) cultivars under contrasting field conditions

Yield and yield components of three semi-leafless pea (Pisum sativum) cultivars, of contrasting seed type/growth habit, were assessed at target planting densities of 40–140 plants/m² on nine sites over three years. Flat-topped parabolic/asymptotic yield/density relationships were obtained. The plant density required to maximise (p max) and optimise (p opt) yield differed between cultivars: Helka, small blue, p max 126 plants/m², p opt 101 plants/m²; Solara, large blue, p max 124 plants/m², p opt 94 plants/m²; and Countess, white-seeded, p max 104 plants/m², p opt 71 plants/m². Near-maximum yields were maintained between 70 and 140 plants/m² due to the ability of the pea crop to make compensatory increases in the number of pods per plant as density declined. Yield/density responses were influenced by site (e.g. soil type) more than by seasonal factors. The risk of yield reductions occurring at densities below 70 plants/m² was greater on a mineral soil than on a fertile organic soil. On the basis of agronomic and economic considerations, there was no evidence that target plant densities required to optimise yield should necessarily be higher for semi-leafless cultivars studied than for conventional leafed peas.     

Candida spp. morphotype differentiation on Sabouraud-Triphenyltetrazolium-Agar (STTZ-Agar) under three different experimental conditions

One hundred and thirty-two strains of Candida spp. were cultured on STTZ-Agar at 37 degrees C for 6 days and at 25 degrees C for 6 and 21 days to determine the culture conditions that would ensure maximum reproducibility in the discrimination of the strains of the same species. Standardization is of utmost importance, as varying experimental conditions can alter the results of the tests. Further studies are needed also implementing molecular tests to establish possible relationships between morphotype, genotype and virulence.     

Variation in abundance and feeding impact of tarnished plant bug (Hemiptera: Miridae) for different cultivars of strawberry: role of flowering phenology and yield attributes

The current study evaluated whether flowering phenology and yield attributes of different strawberry cultivars affect the abundance and feeding impact of tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), as well as behavioral decisions made by feeding nymphs and ovipositing adults. The distribution of emerged nymphs in cage experiments involving nine different cultivars of June-bearing strawberry cultivars suggests that females lay more eggs on plants with numerous flower receptacles, while cultivar per se did not influence their oviposition behavior. A large number of nymphs emerged from receptacles of strawberry plants, while the distribution of emerged nymphs among receptacles, petioles, leaves, and stems varied for different cultivars. These results suggest that the relative intensity of damage caused by ovipositing females may vary for different cultivars. Foraging nymphs did not exhibit a preference for any strawberry cultivar per se, although the abundance of nymphs increased with the weight of receptacles, especially for late instars. Evaluating the density and feeding impact of L. lineolaris for different cultivars under field conditions revealed that some host plant attributes affect the abundance of plant bugs, such as early flowering season and high productivity. Decreasing number of emerged nymphs per flower per plant with increasing density of receptacles per plant suggests that females lay relatively more eggs per receptacle on plants with few receptacles; this pattern of oviposition may explain, in part, why patches with low density of plants typically have high incidence of damage. Planting a high yielding early season cultivar such as 'Cavendish' may contribute to reduce the incidence of damage by L. lineolaris.     

Experimental and simulated light responses of photosynthesis in leaves of three tree species under different soil water conditions

Water deficit is one of the major limiting factors in vegetation recovery and restoration in loess, hilly-gully regions of China. The light responses of photosynthesis in leaves of two-year old Prunus sibirica L., Hippophae rhamnoides L., and Pinus tabulaeformis Carr. under various soil water contents were studied using the CIRAS-2 portable photosynthesis system. Light-response curves and photosynthetic parameters were analyzed and fitted using the rectangular hyperbola model, the exponential model, the nonrectangular hyperbola model, and the modified rectangular hyperbola model. Under high light, photosynthetic rate (P _N) and stomatal conductance (g _s) were steady and photoinhibition was not significant, when the relative soil water content (RWC) varied from 56.3–80.9%, 47.9–82.9%, and 33.4–92.6% for P. sibirica, H. rhamnoides, and P. tabulaeformis, respectively. The light-response curves of P _N, the light compensation point (LCP), and the dark respiration rate (R _D) were well fitted using the above four models. The nonrectangular hyperbola was the best model in fitting the data; the modified rectangular hyperbola model was the second, and the rectangular hyperbola model was the poorest one. When RWC was higher or lower than the optimal range, the obvious photoinhibition and significant decrease in P _N with increasing photosynthetic photon flux density (PPFD) were observed in all three species under high light. The light saturation point (LSP) and apparent quantum yield also decreased significantly, when the upper limit of PPFD was 200 μmol m^?2 s^?1. Under these circumstances, only the modified rectangular hyperbola model was able to fit well the curves of the light response, LCP, LSP, R _D, and light-saturated P _N.     

Berry productivity and molluscicidal saponin yield ofPhytolacca Dodecandra (Phytolaccaceae) under different sunlight,watering and nutrient conditions

The cultivation ofPhytolacca dodecandra has been studied in Zimbabwe in order to initiate local production of the berries from which molluscicidal saponins can be extracted and used in schistosomiasis control programs. The effect of shading, water and nutrient type on growth and berry yield of an imported Ethiopian and a Zimbabwean cultivar were monitored. The molluscicidal potency and saponin concentration of the aqueous extracts of berries, harvested at the full grown, unripe development stage, were determined. There was a marked seasonal variation in berry production with both cultivars being highly productive in the dry season. The best growth and the highest berry yield was obtained with plants grown in full sunlight, under irrigation and with application of cattle manure. The Ethiopian cultivar showed in general better growth and higher berry yield than the Zimbabwean cultivar. Cultivation in shade gave a substantially lower berry yield and saponin concentration in both cultivars, compared to full sunlight. Irrigation was beneficial to the berry yield in both cultivars but lowered the saponin concentration in berries of the Ethiopian cultivar. However, it did not counteract the advantage of irrigation on the total yield. Addition of manure did significantly increase the growth and the berry yield of both cultivars compared to fertilizer application and to the control. The saponin concentration was in general lower with addition of manure, with exception of irrigated Ethiopian plants. The combination of cattle manure and irrigation resulted in the highest saponin yield. Although the two cultivars had different saponin patterns, these patterns and the relative proportions of the saponins were constant, irrespective of the treatments.     

Comparative analysis of oyster (Crassostrea gigas) immune responses under challenge by different Vibrio strains and conditions

Screening a virulent Vibrio strain to study the interactions between bacterial infection and host immune defence is important to resolve large-scale summer oyster mortalities. Using adductor muscle injection we tested the oyster responses to phosphate-buffered saline (PBS), lipopolysaccharide (LPS), or Vibrio strains. Mortalities and stress gene expressions were used to characterize oyster immune responses. At 5 days post injection, the cumulative mortality rates in PBS, LPS, Vibrio tubiashii, Vibrio anguillarum, Vibrio alginolyticus and Vibrio aestuarianus groups were 8%, 16%, 36%, 40%, 40% and 76%, respectively, indicating that V. aestuarianus induced the highest death rate. Two-factor analyses of variance revealed that expression of SOD, CAT, GPX and HSP70 was influenced by bacterial injections in a time-dependent manner. The expression of all genes increased and reached their peak 3 or 12 h after bacterial injection and then decreased. These genes could be applied as immune responsive biomarkers to monitor early changes in oysters in response to bacterial infection. The greatest changes were observed in the V. aestuarianus-injected group, which may indicate that V. aestuarianus could be used as one of the more virulent strains for experimental infections.     

Demographic fitness of Belminus ferroae (Hemiptera: Triatominae) on three different hosts under laboratory conditions

Triatominae are widely recognised for their role as vectors of Trypanosoma cruzi. One of the main biological characteristics of this subfamily is their obligate haematophagous condition. However, previous studies on Belminus herreri and Belminus ferroae suggested that cockroaches are their principal hosts in domiciles. Due to this peculiar behaviour, the aim of this study was to analyse several demographic and reproductive parameters of B. ferroae fed on three different hosts (mice, cockroaches and Rhodnius prolixus) and relate B. ferroae fitness to these alternative hosts. The cohorts were reared under constant conditions. The egg hatching rate was similar for cohorts fed on cockroaches (69.4%) and R. prolixus (63.8%), but was much lower for the cohort fed on mice (16%). The development time from the nymph to adult stage and the average age of first reproduction (α) presented lower values in the cohort fed on cockroaches, which is consistent with the higher population growth rate associated with this host. Demographic parameters [intrinsic rate of natural increase, finite rate of population growth, net reproductive rate and damping ratio] showed statistically significant differences between the cohorts. Analysis of the life history of B. ferroae revealed a higher fitness related to the cockroach. The implications of these results for the origin of the subfamily are discussed.     

Respiratory responses of Oreochromis niloticus (Pisces, Cichlidae) to environmental hypoxia under different thermal conditions

The oxygen uptake ( V O₂), breathing frequency ( f _R), breath volume ( V _S.R), gill ventilation ( V G) and oxygen extraction (%) from the ventilatory current of four groups of Oreochromis niloticus during graded hypoxia were measured under the following acclimation temperatures: 20. 25. 30 and 35°C. The critical oxygen tensions ( P O₂), determined from V O₂ v. P O₂ of inspired water at each experimental temperature were, respectively. 19±1±3±1. 18±0±4±9, 29±7± 4±1 and 30±2± 0.6 mmHg. The f _R remained nearly constant during the reductions of O₂ at all the temperatures studied. V G increased discretely from normoxic levels until the P O₂ was reached, below which it assumed extremely high values (17-fold higher or more). The increases observed in V G resulted, at all the acclimation temperatures, in an elevation in V _S.R rather than in f _R. The extraction of O₂ decreased gradually from normoxia until the P O₂ was reached, below which an abrupt reduction of extraction was recorded, except at 35°C when fish showed a gradual reduction in extraction just below the tension of 80 mmHg.     

Photosynthetic responses of cassava cultivars (Manihot esculenta Crantz) from different habitats to temperature

Maximum photosynthetic CO₂ exchange rates (P_n) of single attached leaves were determined for several cassava cultivars selected from different habitats and grown in pots outdoors at CIAT, Colombia, S.A. P_n rates were in a narrow range of 22 to 26 mol CO₂ m^–2s^–1 for all cultivars tested when measured at high photon flux density, normal air, optimum temperature and with low leaf-air vapor pressure differences. For all tested cultivars (9 cvs.), there was a broad optimum temperature for P_n between 25 to 35°C. At temperatures below and above this range P_n declined in all cultivars with P_n rates reaching 80% of maximum at 20 and 40°C. P_n temperature coefficient (Q₁₀) from 15–25°C was 1.6±0.2 across cultivars. No consistent relation existed between P_n, optimum temperature, and the original habitat.     

Stem canker (Rhizoctoniu solani) on three early and three maincrop potato cultivars: effects of seed tuber size on growth and yield

Large seed tubers (mean 134 g) and small seed tubers (50 g) of three early and three maincrop potato cultivars, spaced respectively 48 and 30 cm apart within rows, were inoculated with Rhizoctonia solani at planting in 1985 and 1986. All seed of early cultivars was sprouted and maincrop seed was either sprouted or not sprouted. In all cultivars, plant emergence was slower from small than large seed and with both was delayed by inoculation. From 11 wk after planting numbers of stems and tubers and weights of foliage and tubers/m² were usually similar from small and large seed when not inoculated, but inoculating delayed plant growth and decreased tuber numbers and yield more from small than large seed. Inoculating decreased mean yields from large and small seed of early cultivars at 11 wk by respectively 24% and 31% (Arran Comet), 12% and 18% (Estima) and by 10% and 28% (Wilja) and losses were greatest with saleable sized tubers (3–4 cm). When grown to maturity inoculating decreased yields by 7% (Arran Comet), 5% (Estima) and 14% (Wilja). With maincrop cultivars, yields in October from large and small seed were decreased by respectively 4% and 10% (DCsirke), 9% and 12% (Maris Piper) and by 14% and 22% (Pentland Squire). In all cultivars yields of tubers < 44 mm and 44–70 mm were decreased and, with Pentland Squire, tubers > 82 mm were increased. The incidence of stem canker and of black scurf on progeny tubers was not affected by seed size but in all cultivars the percentage of greened tubers was slightly increased by inoculation.     

Intraspecific responses of six cultivars of wheat (Triticum aestivum L.) to supplemental ultraviolet-B radiation under field conditions

The solar ultraviolet-B (UV-B) background level is often high and posing an environmental challenge in most of the tropical region of the world, including India. This prompted the present study to investigate the effects of supplemental UV-B (sUV-B) radiation (ambient + 7.2 kJ m⁻² day⁻¹) on various growth, physiological and biochemical characteristics of six locally grown cultivars of wheat (Triticum aestivum L.). Plants being sessile protect themselves from the harmful UV-B radiation by synthesizing flavonoids to screen UV-B and also by inducing antioxidant defence system. sUV-B radiation negatively affected the growth of wheat seedlings but the response varied amongst the cultivars. Leaf injury was maximum in cv. PBW154 and minimum in HD2824. Values of sensitivity index also revealed that HD2824 was least sensitive to sUV-B, while PBW154 was most sensitive. All the assessed biochemical parameters corresponded well with the sensitivity index of different cultivars of wheat.     

Leaf gas exchange,phosphorus uptake,growth and yield responses of cotton cultivars to different phosphorus rates

Photosynthetica - Growth and physiological responses of cotton (Gossypium hirsutum L.) cultivars with different phosphorus (P) efficiencies under variable P environment are poorly known. Therefore,...     

苗期干旱及复水条件下不同花生品种的光合特性

为探索不同花生(Arachis hypogaea)品种的旱后恢复能力, 研究花生品种耐旱性与光合特性的关系, 通过盆栽土壤水分控制实验, 测定了12个花生品种苗期对干旱胁迫与复水过程的光合响应特征, 并讨论了所测各性状参数与抗旱性强弱的关系, 包括对水分胁迫伤害的修复能力。结果表明, 根据苗期生物量抗旱系数, ‘山花11号’、‘如皋西洋生’、‘A596’、‘山花9号’、‘农大818’的抗旱性较强, 且复水后植株产生超补偿生长效应, 补偿生长能力与抗旱性呈极显著正相关。叶片净光合速率(P_n)、气孔导度(G_s)、胞间CO₂浓度(C_i)、最大光化学效率(F_v/F_m)、实际光化学效率(Φ_PSII)、光化学猝灭系数(q_P)随干旱进程逐渐降低, 复水后逐渐增加, 抗旱性强的花生品种变幅较小。干旱7天, 大多数花生品种的光合参数值未有显著性差异。干旱14天, 抗旱性越强的花生品种光合参数值越高, 不同抗旱性花生品种的光合参数值有显著差异。‘山花11号’、‘如皋西洋生’、‘A596’、‘山花9号’的P_n、G_s、Φ_PSII、F_v/F_m、q_P在复水5天时恢复至对照水平, 复水10天时超过对照, ‘79266’、‘ICG6848’、 ‘白沙1016’、‘花17’在复水10天时仍未达到对照水平, 复水过程中抗旱性强的品种的光合参数显著高于抗旱性弱的品种。相关分析表明, 干旱胁迫14天和复水5天后, 花生的P_n、Φ_PSII、F_v/F_m、q_P与品种抗旱性呈极显著正相关。因此, 可在苗期用40%土壤相对含水量胁迫14天及复水5天时花生的P_n、Φ_PSII、F_v/F_m、q_P鉴定品种的干旱伤害程度及修复能力, ‘山花11号’可作为强干旱适应性鉴定的标准品种。     

耐冬山茶对不同光照和水分的生理生态学响应

耐冬山茶作为第三纪孑遗植物,是山茶自然分布最北缘的种群,具有丰富的形态特征与独特的遗传特性.以野生耐冬山茶幼苗为对象,设置2个光照梯度(全光照的65%、15%)、3个干旱梯度(田间持水量的75%、50%、25%),研究耐冬山茶在不同光照、水分条件下生理生态学响应机制,验证现存的4个理论假设是否能够解释耐冬山茶幼苗对遮荫与干旱的响应.结果表明:15%全光照限制了耐冬山茶幼苗的生长.与65%全光照相比,15%全光照使叶片的净光合速率、蒸腾速率和叶绿素含量下降,最大降幅分别为63.3%、82.9%和17.5%,显著提高了叶片的比叶面积、叶片含水量和PSⅡ最大光化学效率,最大分别提高了60.3%、8.3%和6.4%.干旱抑制耐冬山茶的生长,使株高、基径下降.随着干旱胁迫的加重,植株叶片的净光合速率、蒸腾速率和气孔导度显著降低,最小值分别为0.83μmol·m^-2·s^-1、0.30μmol·m^-2·s^-1和11.56 mmol·m-2·s-1.随干旱胁迫的加重,过氧化物酶和过氧化氢酶含量总体呈下降趋势,而丙二醛和脯氨酸含量显著上升.15%全光照缓解了干旱对耐冬山茶幼苗的消极影响,遮荫与干旱对耐冬山茶幼苗的交互作用符合"促进理论".耐冬山茶幼苗能够通过多种调节机制适应环境变化,且能适应较大的光照和水分范围.此外,通过改善耐冬山茶生长的光照和水分条件,为其提供理想的生长环境,可以扩大其园林应用.     

Photosynthetic characteristics in different peanut cultivars under conditions of drought and re-watering at seedling stage

Aims In China, peanut (Arachis hypogaea) is mainly cultivated in the semi-arid and rain-fed areas, and drought is the most prominent environmental stress to its growth. However, studies on the physiological responses of different peanut cultivars to drought and re-watering are lacking. Our objectives were to investigate the relationship between photosynthetic characteristics and drought tolerance, and to explore the ability to recover from drought damage in different peanut cultivars.
Methods A pot experiment was conducted with artificial water stress treatment, and the photosynthetic characteristics were determined in twelve peanut cultivars under the conditions of drought stress and re-watering at the seedling stage. The drought tolerance was assessed by drought resistance coefficient of biomass in seedling. The recovery capacity was assessed by compensatory growth of plant.
Important findings Five cultivars, including ‘Shanhua 11’, ‘Rugaoxiyangsheng’, ‘A596’, ‘Shanhua 9’, and ‘Nongda 818’, showed over-compensatory growth after re-watering, and their capacity of compensatory growth had significant positive correlation with drought tolerance (p < 0.01). The net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), maximum photochemical efficiency (F_v/F_m), PSII actual quantum yield (ΦPSII), and photochemical quenching coefficient (q_P) all decreased over the course of drought stress, and then increased following re-watering, with the amplitude of changes being smaller in the more drought tolerant cultivars. Seven days of drought did not result in significant differences in the photosynthetic characteristics among majority of the peanut cultivars tested (p > 0.05). After 14 days of drought, the values of photosynthetic variables differed significantly among the peanut cultivars with different drought tolerance (p < 0.05). The values of P_n, G_s, Φ_PSII, F_v/F_m, and q_P in the cultivars ‘Shanhua 11’, ‘Rugaoxiyangsheng’, ‘A596’, and ‘Shanhua 9’fully recovered five days after re-watering, while those in the cultivars ‘79266’, ‘ICG6848’, ‘Baisha 1016’, and ‘Hua 17’ did not fully recover even after 10 days of re-watering; the values of those photosynthetic variables were significantly greater (p < 0.05) in the more drought tolerant cultivars following re-watering. Correlation analysis showed that the drought tolerance was significantly and positively correlated with P_n, Φ_PSII, F_v/F_m, and q_P after 14 days of drought stress and after five days of re-watering, respectively (p < 0.01). Therefore, under drought stress at 40% of relative water content (RWC) for 14 days and after five days of re-watering at the seedling stage, the P_n, Φ_PSII, F_v/F_m, and q_P could be used for identifying the level of damage and recovery capacity of peanut cultivars. The cultivar ‘Shanhua 11’ can be used as a reference for drought adaptability identification in peanut.     

Effect of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum on the essential oil yield related characters and nutrient acquisition in the crops of different cultivars of menthol mint (Mentha arvensis) under field conditions.

The effects of inoculation with vesicular-arbuscular mycorrhizal (VAM) fungus Glomusfasciculatum on the root colonization, growth, essential oil yield and nutrient acquisition of three cultivars of menthol mint (Mentha arvensis); Kalka, Shivalik and Gomti, were studied under field conditions. The VAM inoculation significantly increased the root colonization, plant height, fresh herbage and dry matter yield. oil content and oil yield as compared to non-inoculated cultivars. The effect of VAM inoculation on the root colonization, growth and yield of mint was more pronounced with the cv Shivalik than the cvs Kalka and Gomati, indicating Shivalik as a highly mycorrhizal dependent genotype. VAM inoculation significantly increased the uptake of N, P and K by shoot tissues of mint, but most markedly increased the uptake of P. The VAM-inoculated mint plants depleted the available N, P and K in the rhizosphere soil as compared to non-inoculated control plants, however the extent of nutrient depletion was greater for P than N and K. We conclude that the VAM inoculation could significantly increase the root colonization, growth, essential oil yield and nutrient acquisition of mint for obtaining economic production under field conditions.     

Resistance of wheat cultivars and lines to Schizaphis graminum (Hemiptera: Aphididae) under laboratory conditions

Greenbug, Schizaphis graminum (Rondani), is a worldwide pest of cereals including rice, sorghum, wheat, barley, etc. The relative impact of resistance modalities, including antibiosis and antixenosis, and tolerance of seven wheat cultivars and lines (three wheat cultivars, namely Kouhdasht, Bezostaya and Hirmand, and four wheat lines, namely ERWYT 87-7, ERWYT 87-8, ERWYT 87-15 and ERWYT 87-16) with different levels of resistance against S. graminum was studied under laboratory conditions in Ardabil, Iran. In the antibiosis test, S. graminum produced the most and fewest progeny on Kouhdasht and ERWYT 87-16 in the reproduction period, respectively. In the tolerance test, ERWYT 87-16 and ERWYT 87-7 had the highest tolerance against S. graminum. However, in the antixenosis test, we did not detect any significant differences among tested cultivars and lines in terms of the number of adult aphids attracted to them. Overall, the plant resistance index (PRI) values were greatest for ERWYT 87-16 (4.95) and ERWYT 87-7 (4.11) and least for Hirmand (1.11) and Kouhdasht (1.20).     

Channeling of bacterioplanktonic production toward phagotrophic flagellates and ciliates under different seasonal conditions in a river

The objective of this study was to analyze the flux of biomass through the communities of bacteria and phagotrophic protists in the cold and warm conditions occurring seasonally in Butrón River. Bacterial and heterotrophic protistan (flagellate and ciliate) abundance was determined by epifluorescence direct counts; protistan grazing on planktonic bacteria was measured from fluorescently labeled bacteria uptake rates; and the estimate of bacterial secondary production was obtained from [³H]thymidine incorporation rates. The abundance of bacterial, flagellate, and ciliate communities was similar during cold and warm situations. However, we observed that estimates of dynamic parameters, i.e., secondary bacterial production and protistan grazing, in both situations were noticeably different. In the warm situation, grazing rates of flagellates and ciliates (bacteria per protist per hour) were, respectively, 7 times and 18 times higher than those determined in the cold situation, and the grazing rates of the protistan communities (bacteria per protists present in 1 ml of water per hour) increased up to 5 times in the case of flagellates and 42 times in the case of ciliates. Estimates of bacterial secondary production were also higher during the warm situation, showing a ninefold increase. The percentage of bacterial production preyed upon by flagellates or ciliates was not significantly different between the two conditions. These results showed that in the different conditions of a system, the flux of biomass between the trophic levels may be quite different although this process may not be reflected in the abundance of each community of bacteria, flagellates, and ciliates. Offprint requests to: J. Iriberri.     

Stability of snakehead (Ophiocephalus striatus) rhabdovirus under different environmental conditions

Snakehead rhabdovirus stored in cell culture medium was found to be relatively temperature resistant with ≥ 99.9% reduction in infectivity only occurring after 6 months at 15°C, 6 weeks at 25°C and 10 days at 35°C. At 25°C, virus stability was greatest in the range pH 5–7. Infectivity was less well retained at pH9 and rapidly lost at pH3 and pH11. Stability was poor in serum-free media with a 99.9% reduction in infectivity occurring in less than 48 hours at 25°C in de-ionized water, tap water, balanced salt solutions and artificial seawater.