Decrease In Daylength Research Articles

Biological and ecological studies of the parasitoidChelonus inanitus [Hym.: Braconidae] in Israel

The oviposition rate of fertilized and unfertilized females ofChelonus inanitus (L.) was studied at different temperatures. The average number of eggs laid by fertilized females at 20°C was 612 and at 28°C, 1219. Unfertilized females laid an average of 689 eggs at 20°C and 1323 eggs at 28°C.C. inanitus can develop in various hosts such as:Anagasta kuehniella (Zeller),Cadra cautella (Walker) andSitotroga cerealella Olivier, but the females prefer to lay their eggs in those of their natural hosts,Spodoptera littoralis (Boisduval) andSpodoptera exigua (Hubner). The sex ratio ofC. inanitus was affected by environmental conditions. Increase in the size of the egg host and decrease of daylength or temperature, increased significantly the number of females in the population. The ratio females/males at light-dark regimes of 14∶10 was 0.66 and at L:D 12∶12, 1.11. An increase of the temperature from 20°C to 25°C and 28°C decreased this ratio from 1.22 to 1.05 and 0.72 respectively.

Induction of diapause in female mosquitoes, Culiseta inornata by a decrease in daylength

Female Culiseta inornata that had been transferred from 16 hours daylength at 20°C (16 hr, 20°C) to 12 hr, 10°C shortly after ecdysis to the fourth larval instar, or shortly after larval-pupal ecdysis, developed their ovarian follicles to a size and stage characteristic of diapause. Females reared and maintained at constant 16 hr, 20°C or at 12 hr, 10°C, or transferred shortly after pupal-adult ecdysis, developed significantly larger follicles characteristic of gonoactivity. In a second experiment, females were reared at 16 hr, 20°C until larval-pupal ecdysis, then transferred to a 16 hr or 12 hr daylength at 10, 15, or 20°C. At 14 to 15 days after adult emergence, follicles of the females at 12 hr daylength were as small as those of diapausing females, and signiticantly smaller ( P < 0.01) than those of females at 16 hr daylength. The proportion of females 7 to 8 days after emergence that fed on a man, and the proportion of blood-fed females that matured eggs, increased both with daylength and with temperature, the lowest rates being seen in females at 12 hr, 10°C (20% fed and none matured eggs) and the highest in females at 16 hr, 15°C (72% fed and 96% matured eggs). The proportions of blood-feds at 12 hr, 15°C and at 12 hr, 20°C that matured eggs were higher than predicted from their follicle development. Four of 191 females over 12 days after emergence in the two experiments (2.1%) were autogenous.

Reproductive Strategies of the Alate Morphs of the Bird Cherry-Oat Aphid Rhopalosiphum padi L.

Host alternating aphids like the bird cherry-oat aphid exist in several distinct morphs (Dixon 1973). The alate morphs are difficult to separate morphologically (Rogerson 1948) but are easily separated behaviourally. The emigrants leave the primary host, bird cherry, Prunus padus L., before the end of June and colonize various grasses. The alate exules, which are then produced on the secondary hosts, spread to other grass plants. Triggered by fall in temperature and decrease in day-length in autumn, exules no longer produce more exules, but gynoparae and males instead, which finally return to the primary host on which the aphid overwinters as an egg (Dixon & Glen 1971). Each morph in the sequence that is produced in the annual cycle of a host alternating aphid has a different function to perform. Associated with their different functional roles it is acceptable that these morphs also exhibit different reproductive strategies. It is the aim of this paper to describe these differences in the reproductive behaviour of all the alate female morphs of Rhopalosiphum padi L. and to relate the differences to the aphid's way of life.

Effect of photoperiod on a winter and on a summer diapause in two species of cranefly (Tipulidae)

Two craneflies, Tipula subnodicornis and Tipula pagana, both undergo diapause in the final larval instar. The species showed differences in the intensity of diapause and in the timing of the photoperiodic reaction during diapause, that could be related to season. Tipula subnodicornis undergoes a winter diapause that is induced and maintained in its early stages by short photoperiod (L:D:6:18). In the laboratory individuals in the early stages of diapause terminated diapause and pupated earlier when they were exposed to daylengths of, or greater than, 12 hr. However, it is suggested that in the field diapause is broken before the natural daylength is long enough to have any accelerating effect on development. Tipula pagana has a summer diapause which is of greater intensity than that of Tipula subnodicornis and some larvae were maintained for 197 days in the laboratory, without pupating, on an 18 hr daylength. Diapause was broken by a L:D;16:8 photoperiod and development was accelerated by a further decrease in daylength. The acceleration in development rate was attended by a decrease in the variance about the mean date of emergence and resulted in a highly synchronised emergence period. It is suggested that this quantitative response to daylength is particularly important to a species that emerges in the autumn when the temperature in the field is falling.

The influence of seasonal variation on survival and yield of lettuce irradiated with constant rate, fallout decay or buildup and fallout decay simulation treatments

Bottino P. J. and Sparrow A. H. The influence of seasonal variation on survival and yield of lettuce irradiated with constant rate, fallout decay or buildup and fallout decay similation treatments. Radiation Botany 13, 27–36, 1973.—Experiments were conducted to determine the effect of seasonal variation on lettuce seedling responses to 137Cs gamma radiation given a series of exposures at a constant rate (CR) for 8 or 16 hr, or as a buildup and fallout decay simulation (Bu + FDS) or fallout decay simulation (FDS) treatment for 36 hr. After irradiation the seedlings were transplanted to the field. The experiment was performed three different times during the growing season (June–September) to encompass the natural variation in climatic conditions. Comparisons among the three experiments and the four types of exposures were made for survival and yield. The Bu + FDS and FDS treatment showed no difference in survival for the three experiments but there was a slight increase in survival at later times in the season for the 16-hr CR treatment. The yield for similar total exposures continually decreased through the season regardless of the type of exposure. This decreasing yield paralleled a steady decrease in day length as the growing season progressed. The overall ratios of effectiveness at the LD 50 for the 16-hr CR/FDS and Bu + FDS/FDS were 1·42 and 1·01 respectively, showing the greater effectiveness of the FDS treatment over the 16-hr CR treatment and the lack of difference between the FDS and the Bu + FDS treatments. However, no difference in the mean survival time occurred among the experiments or treatments. The 8-hr CR treatment was found to be almost equal to the 36-hr FDS treatment for reducing survival and yield. A statistically significant amount of growth stimulation occurred at low exposures for all treatments in the first experiment. This diminished to a minimal amount of stimulation in the third experiment. The results show the variability which can occur in radiobiological field experiments due to variation in environmental conditions.

Photoperiodism in the ewe 5. An attempt to induce sheep of three breeds to lamb every eight months by artificial daylength changes in a non-light-proofed building

SUMMARYAn attempt to induce ewes to lamb at intervals of 8 months using high levels of artificial daylength applied in a non-light-proofed building was carried out over a period of 2½ years.Thirty each of Dorset Horn, Clun Forest and Kerry Hill ewes were used. There were two different light regimes, both involving abrupt changes in daylength, all of which occurred at daylengths in excess of natural daylength. In both treatments the artificial daylength was abruptly increased to 22 hr at conception. In one treatment there was an abrupt decrease in daylength at parturition whilst the other treatment was an abrupt decrease in daylength approximately 50 days before parturition. The size of the daylength decrease possible was determined by the natural daylength at the time the decrease was applied and at the estimated time of onset of next oestrus.The majority of ewes lambed four times in the 2½ year period, parturition occurring in March-April 1969, December 1969-January 1970, September-October 1970 and May 1971. The Clun Forest ewes produced 38, 29, 20 and 22 lambs at the four lambings, whilst the Dorset Horn ewes produced 41, 35, 26 and 25 lambs at the four lambings. Only 11 of the Kerry Hill ewes lambed throughout the whole experiment producing 3, 5,0 and 7 lambs at the four lambings. It is suggested that the changes in daylength at these high levels controlled the breeding activity of the ewes.

Growth and Development of Alfalfa Plant under Controlled Environment : I. The effects of daylength and temperature on the growth and chemical composition

Propagated plants of a clone of Du Puits alfalfa were grown for six weeks under combined environments of three photoperiods (8 hr, 12 hr and 16 hr) and four temperature regimes (30°C day 25°C night, 25-20, 20-15, ahd 15-10°C). 1) Long day and warmer temperatures promoted elongation of shoot with longer mean internode and with upright growth habit. Leaf expansion rate increased with increased temperature, but branching ability (b)/c)) decreased as temperature increased, except under long day where it was little affected by temperature (table 1). 2) Under 16hr photoperiod flowering was decreased as temperature decreased, although no flower opened at both 20-15°C and 15-10°C. Under 12 hr photoperiod only one of 5 plants flowered at 30-25°C, none at other temperatures. Under short day no plant formed flower bud at any temperature (table 2). 3) Dry weights of tops, roots and total plant were a little affected by photoperiod. Production of tops increased a little as temperature raised except at 30-25°C where it decreased. Roots weight, on the contrary, increased with decrease of temperature except at 15-10°C where it was small. The weight of whole plant was greatest at 25-20°C, followed by 20-15°C, 30-25°C, then by 15-10°C (fig. 4, 5). 4) Leaf/stem ratio and root/total ratio increased under shorter photoperiods and lower temperatures, while dry matter production of whole plant was little affected by daylength (tab1e 3). Nodule weight per unit top weight increased with decrease of daylength and temmperature, and that per unit root weight also increased with decrease of temperature (fig. 1). 5) Crude protein concentration (CP) of tops increased with decrease of temperature, being little effected by photoperiod. CP of roots and TAC concentration (TAC) of all plant parts were variable under longer photoperiods probably due to difference of plant in matulity stage caused by differential temperatures. Under shortday condition, however, TAC of all parts increased with decrease of temperature (fig. 2). Alcohol-soluble non-protein N % and its ratio to total N% were lower under 16 hr photoperiod as compared with those of shorter daylengths, being increased with decrease of temperature (table 4). 6) It may be a significant fact in view of the regrowth after cutting that plants receiving short days and cooler temperatures accumulated relatively greater amount of TAC and CP in the roots than did plants under longer daylength and higher temperatures (fig. 3, 4).

Daylength Effects on Growth, Tracheid Development, and Photosynthesis in Seedlings ofPicea sitchensisandPinus sylvestris

Effects of change in day length on tracheid expansion and tracheid wall thickening are con sidered in relation to shoot and root growth, assimilation rate, and starch content, in seedlings of Picea sitchensii and Pinus sylvestris grown in controlled environments. Rates of wall thickening decreased in the first tracheids to begin wall thickening after decrease in daylength. A sharp decrease in starch-grain size at the same time supports previous suggestions that wall thickness is related to available substrate ; however, rates of assimilation were found to be far greater in short days than in long, suggesting that a surplus of carbohydrate may be produced in long days. It is pointed out that if available substrate does limit wall thickening it is likely bj determine to al accumulation of wall material ; wall material per tracheid would follow logistioally from this , depending on the number of tracheids around the xylem, and wall thickness would depend also on the radial tracheid diameter. Unexpectedly, rate of shoot growth accelerated after transfer to short days before its final cessation with terminal-bud formation. Root growth declined in short days, but later increased again after terminal bud formation. Rate of root growth did not appear to be associated with tracheid development in the shoot.

Photoperiodism in the ewe: 4. A note on the effect on onset of oestrus in Clun Forest ewes of applying the same decrease in daylength at two different times of the year

SUMMARYExperiments were carried out with Clun Forest ewes to determine the effect on the onset of oestrus of applying the same abrupt decrease in daylength at two different times of the year. An abrupt decrease in daylength of 3·75 hr was applied to the ewes on 1 July 1968 and on 24 April 1969. The mean number of days from the commencement of the light treatment to the onset of oestrous activity was 59·5 and 87·0 days, respectively. It is concluded that the time of year at which the light treatments were applied, or the previous light treatment of the Clun Forest ewes, or both, significantly (P&lt;0·001) affected the date of onset of oestrus.

Photoperiodism in the ewe: 2. The effects of various patterns of decreasing daylength on the onset of oestrus in clun forest ewes

SUMMARYIn six light-proofed buildings experiments were conducted with Clun Forest ewes to determine whether the date of first oestrus was affected by the absolute size of reduction in the case of an abrupt decrease in daylength and by the rate of reduction in the case of a given total decrease in daylength.The mean number of days from the onset of the light treatments to first oestrus (the reaction interval) for ewes receiving gradual decreases in daylength of 3·5, 7·2 or 10·9 min/day from 1 July were 66·4, 53·7 or 33·6 days, respectively. The reaction interval for ewes receiving abrupt decreases in daylength of 3·75, 7·75 or 11·75 hr on 1 July were 59·5, 44·8 or 33·6 days, respectively. A control group of ewes at pasture on natural daylength had a mean reaction interval of 66·2 days.It is concluded that the various light treatments applied significantly affected the date of onset of oestrus in Clun Forest ewes.

Photoperiodic Induction and Termination of Diapause in an Insect: Response to Changing Day Lengths

Chrysopa carnea diapaused after experiencing a decrease in day length above the critical photoperiod. Animals experiencing increasing day lengths less than the critical photoperiod did not diapause, and those in diapause began to reproduce. These experiments are the first to demonstrate that insects respond to the direction of change in photoperiods (both increasing and decreasing) which do not encroach on the critical photoperiod.

Effect of light on spring breeding of mutton merino ewes

SUMMARYMutton Merino ewes, all of which had lambed in the preceding in-season, were divided into two groups some 30 days after lambing.The ‘light’ group was subjected, over 84 days, to a simulated decrease in daylength, achieved by first adding artificial light to the daylight and then stepping down the light at weekly intervals, from approximately 17 h, on 22 January, to natural daylength (13 ¾ h), on 20 April 1967. The control group was exposed to the normally increasing daylength.Starting on 1 March, the ewes in both groups were ‘teased’ and hand-service commenced on 20 April.The breeding activity (oestrus, ewes lambing, lambs born and twin births) as well as the length of gestation and birth weight appeared to be unaffected by the light.It would appear that the ‘short-day’ photoperiodic theory is not applicable to all breeds of sheep, and it is suggested that in sheep with a long sexual season genetic heterozygosity may be responsible for regulating the breeding season by allowing other environmental stimuli, besides light, to trigger-off sexual activity.

Effect of Light on Economic and Physiological Characters of Laying Hens ,

THE influence of light on reproduction in birds has been reported recently, and reviewed by King (1961), Lanson and Sturkie (1961), Morris and Fox (1960), Fox (1961), Shutze et al. (1961), Bowman and Jones (1961), Lowe and Heywang (1961), and Farner (1961). McClary (1960a, b) reported that he was able to increase egg production and egg size by increasing the day length at hatching time approximately 51/2 hours beyond that which would be available under natural conditions at 22 weeks of age, then gradually decrease the day length 51/2 hours during the rearing period, followed by an abrupt or gradual increase in day length in the laying house.The experiment being reported was designed to determine if a reduction in day length from 22 hours at hatching to 16 hours at 20 weeks of age was comparable in enhancing production to a decrease in day length from 16 to 9 …

Short day-length and egg production in the fowl

1. The effect of a short, unchanging day-length of 6 hr. on age at sexual maturity and egg production has been observed.2. The birds matured at the same age as the controls but at a lower body weight.3. Egg production over 58 weeks was considerably reduced.4. An increase in day-length between December and August always increased production.5. A decrease in day-length between February and August always decreased production; this decrease was greater the later in the year that the change occurred.6. It is concluded that age at sexual maturity is not affected by the absolute length of the day, and that egg production is affected both by the absolute length and by the change in length.

Cumulative concentrations of tobacco mosaic virus in tobacco at different photoperiods and light intensities

Photoperiods of 12 and 16 hours increased concentration of TMV in inoculated and in systemically infected leaves of tobacco 4 days after inoculation over concentrations of 8- and 4-hour periods. Order of concentrations in intratime comparisons among the treatments in composite-leaf samples underwent a transition around 18 days after inoculation and finally increased, with a decrease in day length 4 weeks after inoculation, this being the reverse of the initial gradient. Concentrations in the tip leaves increased with a decrease in day length 4 and 18 days after inoculation, whereas the reverse situation was found 7 and 32 days after inoculation. High light intensity generally favored virus multiplication in the inoculated leaves and initially in the tip leaves. At 4 days after inoculation, concentration in composite samples of leaves increased with increased light intensity in the summer but not in the winter, when the reverse order occurred. At 28 days after inoculation the concentration increased with a decrease in light intensity, this being the reverse of the initial summer order. Concentrations in the tip leaves increased with an increase in light intensity at 4 and 32 days after inoculation, whereas the reverse order was found at 18 days. Experiments combining both light intensity and photoperiod gave results reconcilable with those given above. A relationship existed between rate of host growth and virus concentration such that after maximum virus concentrations were reached virus concentration decreased as host growth increased. Experiments with inoculated tobacco-leaf disks cultured on water agar under various light intensities and day lengths at approximately 29° indicated that 16 hours per day of intense light represses virus multiplication to or below the level in disks receiving no light. Disks receiving nearly equal amounts of light energy per day in different ways had markedly different virus concentrations. Long days of diffuse light were more favorable for virus multiplication than short days of intense light. Under the conditions of the experiment, the optimum light for multiplication of TMV in tobacco-leaf disks at 29° was 1100 foot-candles for 16 hours per day.

The seasons in a tropical rain-forest (New Hebrides).-Part 3. Fruit-bats (Pteropidae).

SUMMARY. 1 In the remarkably unvarying climate of Hog Harbour, Espiritu Santo, New Hebrides (15o 15'S. in the Pacific), the fruit-bat Pteropus geddiei usually copulates about February to March and gives birth to young about August to September. One young is produced at each birth. 2 A review of the literature reveals that fruit-bats in both northern and southern hemispheres tend to copulate in ‘autumn’, and the constancy of the climate of the northern New Hebrides does not prevent them from keeping to this rule. 3 The size of the testes increases gradually till January, after which it falls away to a little less than half the January weight in July. 4 The males keep their epididymides full of sperms throughout the year. 5 The social habits of both sexes vary seasonally. 6 The food varies at different times of the year, as the various fruits and flowers become available; but certain fruits are available and eaten at all times. 7 It appears that temperature does not control the onset of the copulating season. Possibly decrease in length of day and amount of ultra-violet light are important. 8 Pterojms eotinus, which was studied less intensively than Pt. geddiei, has about the same breeding season.