Number Of Light Hours Research Articles

Modelling the interaction between a pest (Aculops lycopersici), two predators (Pronematus ubiquitus and Macrolophus pygmaeus) and climate variables: a 3-year greenhouse study in a tomato crop.

The tomato russet mite, Aculops lycopersici, is a major pest in tomato crops, causing damage through leaf and stem browning, defoliation and russeting of fruit. Biological control of this mite on tomato plants is difficult. While several phytoseiid mites feed on the pest, they cannot survive, move, or reproduce on tomato plants due to the presence of glandular trichomes. Pronematus ubiquitus has recently been identified as a biocontrol agent of A. lycopersici in tomato crops, but the predator-prey interaction between these two species is not well studied. In this paper, we present a validated logistic regression predator-prey model based on a 3-year study supplemented with additional datasets. Besides the predator and the prey, this model takes into account an extra generalist predator, Macrolophus pygmaeus, and various climate parameters. The population trend of A. lycopersici is best explained by the presence of the predator P. ubiquitus, the relative humidity and the fact that the crop was lit or unlit using artificial light. P. ubiquitus has proved to be an efficient biocontrol agent of A. lycopersici. For P. ubiquitus the presence of M. pygmaeus, the vapour pressure deficit, the number of light hours and radiation explained the population trend best. For both the predator and the prey density-dependent interactions were identified. Model outcomes are discussed in detail. Our study provides insights into the potential use of P. ubiquitus as a biocontrol agent for A. lycopersici in tomato crops in combination with M. pygmaeus. However, we highlight the importance of considering the presence of other predators and environmental conditions when developing integrated pest management strategies. © 2023 Society of Chemical Industry.

Patrones de actividad de la chachalaca pálida (Ortalis poliocephala)

Los patrones de actividad de las poblaciones animales fluctúan a lo largo del año, como respuesta a la disponibilidad de recursos, cambios en el clima y actividad de depredadores. Estudiar los patrones de actividad de las especies es necesario no sólo para aumentar el conocimiento de su historia natural sino también para la planeación de muestreos acordes a los periodos de mayor actividad. Con la finalidad de reconocer los patrones de actividad de la chachalaca pálida (Ortalis poliocephala) en una selva seca del suroeste de México en dos temporadas, usamos la información recabada con cámaras-trampa durante los inviernos de 2011-2012 y 2012-2013 y las primaveras de 2012 y 2013. La actividad diaria de la chachalaca pálida fue bimodal con mayor actividad de 10:00 a 11:00 h y de las 18:00 a 20:00 h. Los patrones de actividad temporal presentaron similitud en dos de los cuatro periodos de muestreo (P > 0.05), lo que indica que los patrones de actividad se mantienen independientemente de la cantidad de horas luz. En contraste, la actividad de las chachalacas fue diferente en el invierno de 2012-2013 (P < 0.05), posiblemente como respuesta a la presencia de elementos exógenos no climáticos, como depredadores. Durante los diseños de muestreo para estudios poblaciones se deben considerar los patrones de actividad de las especies de crácidos para entender su biología y contribuir a las estrategias de manejo y conservación.

Qualidade dos pêssegos da região da Beira Interior no ciclo 2015

In Portugal, peach production is mainly located in Beira Interior, representing 45% of the national area, corresponding to 1630 ha. The commercialization of peaches occurs between June to September and this offer is based on a wide range of cultivars. For each cultivar besides the harvest date, the fruits have different characteristics which are influenced by cultural techniques and by the soil and climate conditions. The Beira Interior region has predominantly light-textured soils and high number of light hours these conditions are favourable for stone fruit production, especially cherry and peach, which are recognized in Portugal for their quality. This study aims to characterize the fruits of the different peach cultivars produced in Beira Interior region during the 2015 season. Fruits samples from de all the cultivars produced in four local peach growers were analized. In total were analysed 1208 fruit, 47 samples corresponding to 33 different cultivars. Fruit weight firmness and total solids soluble content (SSC) was evaluated in each fruits. The titrable acidity (RTA) was evaluated for groups of 10 peaches. Based on the characteristics evaluated it has been possible to group the cultivars into three groups according the season of maturation, namely, early cultivars (9 cultivars), season cultivars (17 cultivars), and late cultivars (7 cultivars). The season cultivars have a firmness of 5.1±1.4 kg/0.5 cm2, an SSC 13.2±1.7°Brix and 5.7±2.8 g. of malic acid L‑1 and the late cultivars group has higher values of firmness, IR index and acidity, respectively 6.4±1.4 kg/0.5 cm2, 14.5±1.8°Brix and 8.6±1.5 g. of malic acid L‑1.

Embryonic mortality in buffalo cows

In buffalo species embryonic mortality is considered one of the major causes of fertility loss, especially in the animals that are not mated during their reproductive period. Embryonic loss in animals mated by artificial insemination (AI) is 20–40% during seasons characterized by high number of light hours. Also in buffalo naturally mated the incidence of embryonic mortality is about 20% and a higher incidence is observed between 28–60 days of gestation in buffaloes that conceive during increasing daylight length. A reduced capacity to secrete progesterone seems to explain in part this embryonic mortality but other as yet unidentified factors contribute between 40–50% to the embryonic losses. Treatments with hCG, GnRH agonist or progesterone on Days 5 after AI not always reduce embryonic mortality in buffalo species. Embryonic mortality in buffaloes appears to occur later (Day 25–40) than in cattle and P4 treatments should perhaps be applied later in buffaloes.

Photoperiod affects growth, behaviour and stress variables in Clarias gariepinus

Short periods of light or no light (18D : 06L and 24D : 00L) resulted in an increased growth compared to extended periods of light (06D : 18L and 12D : 12L) in African catfish Clarias gariepinus. Fish under longer periods of light (12D : 12L and 18D : 06L) showed higher swimming activity, more aggression (injuries on the body) and higher lactate, free fatty acids and cortisol levels compared to those who were reared at shorter periods of light (24D : 00L and 18D : 06L). Feeding activity during light and dark periods in this experiment showed that C. gariepinus had both night and day feeding activities, with a preference to diurnal feeding in the 12D : 12L photoperiod. The results showed that light plays an important role in the African catfish behaviour and its well‐being. As the hours of light increased during the 24 h cycle, data suggests that the fish were more stressed and aggressive, compared to those under a reduced number of light hours.

Net CO 2 exchange rate of in vitro plum cultures during growth evolution at different photosynthetic photon flux density

CO 2 concentration was monitored during three 15-day subculturing cycles in vessels containing actively proliferating plum cultures of Prunus cerasifera, clone Mr.S. 2/5. The effects of two photosynthetic photon flux density regimes: 50 ± 5 μmol m −2 s −1 and 210 ± 5 μmol m −2 s −1 were compared. Three distinct phases in the CO 2 trend were distinguished during each culturing cycle of both light treatments. In the first, occurring at the beginning of the culture cycle, the amount of CO 2 emitted by the cultures during dark periods was greater than that assimilated during the light periods. In the second phase, the opposite trend was detected, while in the third, the range of CO 2 day–night fluctuations increased or remained stable according to the number of explants per vessel. The treatment with 210 ± 5 μmol m −2 s −1 did not modify the CO 2 phase trend but induced more pronounced fluctuations in day–night CO 2 concentration. Under this light treatment, cultures reached CO 2 compensation point for a period as long as 48% of the total number of light hours, while under 50 ± 5 μmol m −2 s −1, it was only 8%. The different range in CO 2 day–night fluctuations monitored throughout a subculturing cycle, appeared to be mainly induced by changes in culture growth dynamics.

Seasonal variability in fertilization and embryo quality rates in women undergoing IVF

Objective: IVF-ET provides unique controlled conditions for the study of seasonal influences on the human reproductive process. This study was designed to evaluate the effects of seasonality on fertilization rate, embryo quality, and conception rates. Design: A retrospective observational cohort study. A chart review of all individuals undergoing IVF-ET from 1988 to 1991 at our institution was performed. Setting: An assisted reproduction unit at a university-based tertiary medical center. Patient(s): 657 women, for a total of 1074 IVF-ET treatment cycles, were evaluated. From this population, we chose 305 women undergoing their first IVF-ET cycle for reasons of pure mechanical infertility. Intervention(s): IVF-ET cycles. Main Outcome Measure(s): Seasonal variability in fertilization rates and quality-A embryo rates, and the correlation with the absolute number of light hours, as well as the influence of temperature, humidity, and other environmental parameters. Result(s): A significant seasonal variability in the fertilization rate and the quality-A embryo rate was demonstrated. The highest fertilization and quality-A embryo rates were observed during the spring and the lowest in the autumn. These changes correlated with the absolute number of light hours and its increment over time, but not with the temperature, humidity, or other environmental parameters. Conclusion(s): Seasonality seems to have a significant influence on the fertilization process and on the quality of the human embryos that are obtained in vitro, possibly because of the light/dark variations over time. If this finding is confirmed, these seasonal changes should be taken into account when evaluating infertility data and in everyday clinical practice.

Development of collared lemmings, Dicrostonyx groenlandicus, is influenced by pre‐ and postweaning photoperiods

We examined the role of pre- and postweaning photoperiod on postweaning development of collared lemmings. Lemmings were gestated and reared to weaning (19 days of age) in one of three photoperiods: 22L:2D (22 hr of light:2 hr of dark), 16L:8D, and 8L:16D. At weaning, lemmings were either maintained in their natal photoperiod or transferred to one of the other two photoperiods. At the termination of the experiment (10 weeks postweaning) data were collected on somatic characters (body weight, bifid claw width, pelage stage, and guard hair length), serum prolactin (PRL), and reproductive parameters (testes, seminal vesicle, and uterine weights). Somatic characters were predominantly influenced by postweaning photoperiod, when that photoperiod was either long (22L:2D) or short (8L:16D). When lemmings were exposed to an intermediate postweaning photoperiod (16L:8D), development of somatic characters was significantly influenced by the preweaning photoperiod; animals reared in 8L:16D regarded 16L:8D as a long day, whereas those reared in 22L:2D regarded 16L:8D as a short day. Serum PRL responded to photoperiod changes, often reflecting either the increase or decrease in day length, rather than simply the absolute number of light hours per day. Whereas reproductive indices in both sexes were stimulated by transfer from short to long photoperiod, chronic exposure to long photoperiod inhibited male development. No other photoperiod manipulations significantly influenced reproductive parameters. These observations suggest that, in the collared lemming, the neural and/or humoral factors regulating somatic and reproductive characters differ in their response to photoperiod. These results also suggest that the postweaning responses to photoperiod are programmed by earlier (gestational and/or neonatal) photoperiod exposure of the mother and/or the neonates.

Effect of light and temperature on wool growth

SummaryWool samples were collected from 39 rams representing five breed groups of sheep: Merino (M), Ossimi (0), and the crosses between them, viz. ¾ Ossimi–¾ Merino (¾ O), ½ Ossimi–½ Merino (½ O) and ½ Ossimi–¾ Merino (¼ O) maintained at Sakha Experiment Station, Kafrelsheikh, Egypt, with the objectives of detecting the effect of the seasonal changes in normal light rhythm and temperature on wool fibre length and diameter. Animals were divided into two light treatments groups, the first consisting of four animals from each breed kept under continuous dim light conditions throughout the year and the second of three animals from Ossimi and four from each breed group kept inside an open pen free to sunlight and shade zones under daylight rhythm throughout the year. It was found that fibre length as well as fibre diameter in normal light exceeded that in dim light except in winter time. Breed groups showed different responses to the absence of light especially the Ossimi and the ¾ O whose fibre lengths were most affected. The breed groups had larger fibre diameters in normal light than in dim light except Merino and ¼ O. Seasonal changes in temperature had a highly significant effect on fibre length but not on fibre diameter. Higher temperature coincided with lower increases in fibre length. Season to season variation in wool growth seemed to suggest that the number of light hours per day and atmospheric temperature counteracted each other resulting in a non-significant seasonal pattern.

Effect of a skeleton photoperiod on the daylength-dependent response to oestrogen in canaries (Serinus canarius).

Previous studies have shown that ovariectomized canaries, injected with 50 mug oestradiol benzoate thrice weekly, show more oestrogen-induced nest-building on a long day than on a short day. In this study the same effect was obtained with castrated canaries. The influence of time available for building was assessed first by comparing castrated males on skeleton long days with birds on short days, the total number of light hours being equal. More birds in the skeleton long-day group placed material in the nest, and did so with a shorter latency, than birds in the short-day group. Thus the differences between short- and long-day birds are unlikely to be due entirely to differences in the time available. However, some of the long-day birds were no more active than the short-day ones suggesting that the skeleton long-day schedule does impose some constraint. In a third experiment photorefractory females (whose ovaries do not secret oestrogen in response to long days) kept on a long skeleton-day scored similarly on all measures of building as birds kept on a full 14 h day and significantly more than birds on a short day. The results also indicate that the birds are measuring daylength by means of a diurnal rhythm of photosensitivity, an effect comparable to that of longer photoperiods on gonadal growth.

Suppression of Inventions

Question.-You are a monopolist of light bulbs, which now have a service life of 1,000 hours. Your engineers discover a way of doubling the service life, without any change in the cost of producing bulbs. If you, as a monopolist, fail to suppress the invention, what will be the price-quantity solution (assuming that consumers are fully informed about the improved quality) at the new equilibrium, ignoring transient states? Will it pay to suppress the invention? Answer.-The demand curve for bulbs shifts in rather a tricky way. One's first impression might be that the demand price for a bulb generating twice the number of light-hours would be everywhere twice as high as for an unimproved bulb. But this ignores the declining marginal value in use of light-hours associated with the doubling of their quantity. The demand curve for improved bulbs is twice as high, but at halved quantities (in the steady-state solution); the curve shifts upward, but also twists so as to become more vertical. The solution is simpler to obtain if the analysis runs in terms of quantities of light-hours rather than of bulbs, and if total rather than average magnitudes are employed. Since the demand function for light-hours remains unchanged, so will the total-revenue function R(L). The totalcost function of bulbs C(B) is unchanged, which means that the total-cost function of light-hours C(L) is stretched (doubled) in the horizontal direction. (At a given cost, the same number of bulbs and hence twice the number of light-hours can be produced.) We can assume that marginal cost is positive, C 0, and that marginal revenue is declining, R(L) < 0. If marginal cost is rising or constant, the horizontal stretching of C(L) clearly lowers C'(L) evaluated at the original output of lighthours (now representing half the original quantity of bulbs). Since R'(L) is unchanged, this dictates an increased output of light-hours, that is, the optimum output of new bulbs must be at least half the previous profit-maximizing output of unimproved bulbs. The profit-maximizing output of new bulbs may even exceed the previous output of unimproved bulbs if R'(L) is falling very slowly; in that case, the output of light-hours will more than double. (The corresponding implications for the price of light-hours and the price of bulbs are quite clear, and need not be