Population dynamics of Bythotrephes cederstroemii in south-east Lake Michigan 1995–1998

1. Population characteristics (density, size, reproductive patterns) of the predatory cladoceran Bythotrephes cederstroemii in south-east Lake Michigan were monitored at an offshore station (110 m) in 1995–98 and at a nearshore station (45 m) in 1997–98.
2. The mean density of B. cederstroemii at the offshore station was generally highest in July–September (145–914 m⁻²) and at the nearshore station in October–November (168–1625 m⁻²). In 1995 and 1998, density was also high at the offshore station in November (211–284 m⁻²). Fish predation may limit B. cederstroemii in nearshore regions in the summer. The maximum annual densities of B. cederstroemii for 1995–98 were generally similar to those reported from the late 1980s, when the species arrived in Lake Michigan.
3. Body size increased rapidly each year to a maximum in August. Thereafter, body size declined and converged for stage-2 and 3 individuals, suggesting food scarcity or size-selective fish predation was affecting large individuals.
4. Most reproduction occurred asexually (90%), and by stage 2 or 3 females (99%). Asexual brood size was highest when B. cederstroemii first appeared each year, and decreased in August, when larger neonates were produced. There appeared to be differences in reproductive mode for stage 2 and 3 females, with a higher percentage of stage 2 females reproducing sexually.     

The epidemiology of potato blight in the East Midlands 1923–74

Examination of the East Midlands records of potato blight epidemics and the meteorological data on critical 90 % relative humidity infection periods for the years 1923–74 indicates the importance of the amount of inoculum carried over from one season to the next in influencing the rapidity of progress of the disease and the date of destruction of the haulm. The success of forecasting outbreaks based on 90% r.h. periods is reviewed. The importance of taking into account both amount of inoculum and weather conditions in devising a disease control programme is discussed. It is concluded that the succession of seasons since 1968 without a major potato blight epidemic was due mainly to a combination of low carry-over of infection and sub-optimal weather conditions for the development of the disease and that the current control measures have not yet been subjected to a severe test.     

The development and yield of autumn- and spring-sown barley in south east Scotland

As part of a study of the relationship between plant development and grain yield, winter and spring barleys were sown in the autumn and spring. Apical development and leaf area development were monitored and the final yield was partitioned into grain weight and grain number. The photosynthetically active radiation (PAR) absorbed was calculated.
The main differences found were between sowings rather than between genotypes within sowings. The autumn sowing outyielded the spring sowing because the grains were heavier, although the autumn sowing tended to have fewer grains m^-2. In the autumn sowing the rate of initiation of spikelet primordia was slower, due to the lower temperatures encountered, but the initiation phase lasted longer and a larger proportion of primordia survived. However, the increased proportions of tillers to mainstem reduced the mean number of grains/ear.
The numbers of grains m^-2 and the yield were related to the PAR absorbed. In this analysis the earlier anthesis of the autumn-sown plants could be seen to be reducing the PAR absorbed and consequently the grains m^-2.     

A case-control study of cervical cancer screening in north east Scotland.

To estimate the relative risk of invasive cervical cancer in each succeeding year after a negative screening result the screening records of all women tested in the north east of Scotland were examined as the basis for a case-control study. The cases consisted of 115 women in whom invasive cervical cancer had been diagnosed in 1968-82 and who had appeared in the screening records at least once before diagnosis. For each patient five controls were selected from women of the same age who appeared in the screening records before the date of diagnosis in the patient. If the patient''s cancer had been detected by screening the controls were chosen from women of the same age screened the same year. A comparison was made between cases and controls of the number of negative smears taken before the diagnosis. The results showed a high relative protection (inverse of the relative risk) in the first two years after a negative test, falling steadily as time since the last negative test elapsed. Even after 10 years, however, a considerable residual effect was observed.     

Teenagers' knowledge of emergency contraception: questionnaire survey in south east Scotland.

OBJECTIVE--To determine the level of knowledge of emergency contraception among 14 and 15 year olds. DESIGN--Confidential questionnaire survey. SETTING--10 secondary schools in Lothian, south east Scotland. SUBJECTS--1206 pupils predominantly (98.7%) aged 14 and 15 in the fourth year of secondary school. MAIN OUTCOME MEASURES--Knowledge of the existence of emergency contraception; of its safety, efficacy, and time limits; and of where to obtain it. RESULTS--1121 (93.0%) fourth year pupils aged 14-16 had heard of emergency contraception. 194 girls (32.7%) and 168 boys (27.5%) had experienced sexual intercourse. Of girls who had experienced sexual intercourse, 61 (31.4%) had used emergency contraception. Knowledge of correct time limits was poor, sexually active girls being the most knowledgeable. Pupils attending schools ranked lower than the national average for academic attainment were less likely to have heard of emergency contraception and more likely to have been sexually active. 861 (76.8%) pupils knew they could obtain emergency contraception from their doctor. 925 (82.5%) pupils believed emergency contraception to be effective but 398 (35.5%) thought it more dangerous than the oral contraceptive pill. CONCLUSIONS--One third of sexually active girls aged under 16 in Lothian have used emergency contraception. This may help explain the fairly constant teenage pregnancy rates despite increasing sexual activity. Scottish teenagers are well informed about the existence of emergency contraception. However, many do not know when and how to access it properly. Health education initiatives should target teenagers from less academic schools as they are more likely to be sexually active at a young age and are less well informed about emergency contraception.     

Pectolytic Clostridium spp. in soils and rhizospheres of carrot and other arable crops in east Scotland

Carrot root tissue discs rotted rapidly in anaerobic conditions after inoculation with soil from 40 different carrot fields and from ten fields of a mixed arable farm. Significant differences occurred in rotting potential between the soils and pectolytic Clostridium spp. were isolated from the rotted discs. Direct counts of pectolytic clostridia on selective pectate plates detected populations of 44–23.5 × 10³ viable propagules/g dry soil in field soils. Significant increases in viable propagules were found in the rhizosphere soils of most carrot crops and in a range of other arable crops examined. The ratios of populations in the rhizospheres and surrounding soils varied between 1.8 and 8.2. Irrigating to excess and inter-row cultivation of carrot crops did not consistently affect populations in soil or on roots.     

Field trials of copper fungicides for the control of potato blight; spray retention

Spray-retention estimations were made during four seasons at Dartington in south Devon, on maincrop potatoes, twice-sprayed, as in farm practice, with about 120 gal./acre for the first application and 160 gal. for the second.
Evidence is given concerning the limits of reliability of the disk method of leaf sampling; and an alternative method, batten.' washing, is described.
With from 2,1/2 to 3,1/2 in. of rain over test periods of 3-4 weeks, 1% Bordeaux mixture showed about 40 % spray retention. Cuprous oxide and copper oxychloride sprays at the same copper dosage but compounded with sulphite lye or other water-soluble dispersing agent showed less than 20% retention. Compounding of these materials with an insoluble sticker (bentonite) improved the adhesion.
The percentage retention of 1/2% Bordeaux mixture was found to be less than that of the usual 1 % mixture, but adequate spray deposits could be maintained with this and other low-copper fungicides by more frequent applications.
A rapid method for determining total expanse of foliage in the field is described, and the importance of such determinations in connexion with spray-retention trials, and practical spray timing, is stressed.
Experiments were made to determine whether any copper is absorbed by potato leaves from the spray deposits. Absorption, or acid-resistant adsorption, of the order of 0.02 mg. Cu/120 sq.cm. of leaf area was indicated.