FIELD STUDIES ON THE INFLUENCE OF WEATHER ON EGG-LAYING BY THE CABBAGE ROOT FLY, ERIOISCHIA BRASSICAE BCHÉ. II

Observations on the intensity and duration of egg-laying by Erioischia brassicae Bché were continued in 1953 on the same site as in 1952. Eggs were first observed on 31 April and the spring peak period of egg-laying lasted from 3 to 30 May with a daily average of 40 eggs/plant. The mean total in spring 1953 was 1287 eggs/plant. Summer peaks occurred on 1–20 July (average 17 eggs/day/plant) and 5–11 August (average 21 eggs/day/plant).
In the field the threshold of reproduction was approximately 60° F. The rate of egg-laying was highest at 65–70° F. and it declined during prolonged periods of higher temperatures.
The annual cycle of generations, as shown by egg counts and confirmed by the examination of puparia, consisted of two generations and a partial third. The spring generation developed without a prolonged diapause, and there was complete emergence during the summer. The overwintering puparia came from the second and third generations of larvae.     

FACTORS AFFECTING THE BEHAVIOUR AND ACTIVITY OF THE CABBAGE ROOT FLY (ERIOISCHIA BRASSICAE BCHÉ)

The behaviour of cabbage root flies is governed by their need for food and shelter. Captive flies fed on sugar solution lived for periods up to 62 days, and a bred female laid 122 eggs.
Weather conditions determine the activity and the length of life of the flies. Feeding and egg-laying occur in warm sunny weather, and long periods of sunshine with temperatures of at least 60° F. in the latter half of April are associated with the onset of attack on the host plants. In cold or wet weather the flies shelter in soil or in thick herbage, and if they are immobilized for some time they die of starvation. In this way, the onset of cold weather checks the development of cabbage root fly attack. Details are given to show how the weather affected the activity of the flies in the springs of 1948–50 inclusive.
Eggs are laid in batches of varying size at irregular intervals during approximately 4 weeks. The position of the eggs about the host plants is affected by weather conditions. They are usually laid in the soil, but when the pressure of sunshine and drought is removed they are laid freely on aerial parts of the plants.
Knowledge of the influence of the weather on the activity of the flies enables attack to be anticipated with some degree of accuracy and control measures to be carefully timed.     

THE EFFECT OF CERTAIN PREDATORS ON THE NUMBERS OF CABBAGE ROOT FLY (ERIOISCHIA BRASSICAE (BOUCHÉ)) AND ON THE SUBSEQUENT DAMAGE CAUSED BY THE PEST

To determine the importance of beetle predators on the natural control of cabbage root fly, experiments were carried out in 1958 and 1959 using various types of barriers to obtain different levels of beetle populations on cauliflower plots. A barrier of DDT-treated straw, placed in the soil around some plots, decreased the numbers of beetles within them and allowed a greater number of eggs and larvae of cabbage root fly to survive than on the untreated plots, resulting in a greater crop damage. Another type of barrier allowed the beetles to enter plots but made it difficult for them to leave. On these, fewer cabbage root-fly eggs and larvae survived and the crop damage was much less than on the plots surrounded by straw barriers. Where plants were treated with insecticide the root-fly population was reduced to a minimum and crop yields were considerably increased. The insecticide, however, caused a reduction in the numbers of predatory beetles.     

OBSERVATIONS ON THE BIOLOGY OF CLOVER ROT

The field behaviour of clover rot in eastern England indicates that infection takes place by ascospores, and not by soil-borne mycelium developing directly from the sclerotia. To support this view, experimental evidence is presented to show that cutting of red clover at the time when the ascospores are being shed, reduces the percentage infection in the following spring.
Ascospore infection of clover causes a 'non-aggressive' spotting which may develop into an 'aggressive' infection. Sclerotinia trifoliorum has been shown to remain viable in non-aggressive spots for at least 16 weeks. Similar symptoms occur when beans are infected with S. trifoliorum var. fabae. Non-aggressive and aggressive infections are two phases of a sequence in time, and not two alternative types of infection dependent on the initial spore load. The occurrence of non-aggressive and aggressive phases in nature explains (1) the observed delay between ascospore discharge and the appearance of obvious disease symptoms, and (2) the seasonal nature of the disease.
Aggressive infection develops only in a saturated atmosphere and within a temperature range of 5–20° C., and its establishment is favoured by a heavy dosage of inoculum. In most seasons humidity is the main 'limiting' factor; over the 18-year period, 1930–47, there is a significant regression between the severity of clover rot and the previous December plus January rainfall.
Crop rotation and autumn grazing check the disease, but the latter must be practised with discretion because, under certain conditions, its effects are more drastic than those of the disease. The only hopeful method of effective control is the breeding of resistant strains of legumes.     

OBSERVATIONS ON THE BREEDING BIOLOGY OF THE FISCAL SHRIKE

Ward, D. 1989. Behaviour associated with breeding of Crowned, Blackwinged and Lesser Blackwinged Plovers. Ostrich 60: 141–150.

The behaviour of Crowned Plovers Vanellus coronatus, Blackwinged Plovers V. melanopterus and Lesser Blackwinged Plovers V. lugubris in mate and territory acquisition and defence was documented and related to the habitats these birds occupy. The open habitat occupied by vanelline plovers makes them particularly vulnerable to predation and as a result, they have a highly-developed ability to detect potential predators and have developed a number of behavioural strategies to avoid predation. This has resulted in these birds having a higher reproductive success than that documented for other precocial birds.     

FURTHER OBSERVATIONS ON THE MECHANISM OF PHAGE ACTION

1. The reaction between an antistaphlycoccal phage and the homologous bacterium has been studied, applying the following experimental technics not used in earlier work reported from this laboratory: (a) Both the activity assay and the plaque count were utilized for determining [phage]. (b) Sampling was done at short intervals; i.e., every 0.1 hour. (c) Extracellular phage was separated from the cell-bound fraction by a filtration procedure permitting passage of < 95 per cent of free phage. 2. Using these technics, the reaction was followed: (a) with pH maintained at 6.10 and temperature at 28°C. to slow the process; (b) with pH maintained at 7.2 and temperature at 36°C. 3. In addition separate experiments were performed on the sorption of phage by bacteria at 30°, 23°, and 0°C. 4. At pH 6.10 and 28°C. the phage-bacterium reaction proceeds in the following sequence: (a) There is an initial phase of rapid logarithmic sorption of phage to susceptible cells, during which the total phage activity and the plaque numbers in the mixtures remain constant. (b) When 90 per cent of the phage has been bound, there is a sudden very rapid increase in phage activity not paralleled by an increase in plaques; i.e., phage is formed intracellularly, but is retained within cellular confines. (c) After a further drop in the extracellular phage fraction there occurs a pronounced increase in the total phage plaque count not accompanied by any increase in total activity. This indicates a redistribution of phage formed intracellularly. At the same time there is a rise in the extracellular phage curves (both activity and plaque). (d) With the concentrations of phage and bacteria used in the experiment carried out at pH 6.1 and 28°C. there are two further increments in [phage]_act. before massive lysis begins. (e) During terminal lysis there are sharp rises in the curves for [total phage]_plaq., [extracellular phage]_act., and [extracellular phage]_plaq.. (f) Immediately after the completion of lysis there is a considerable disparity between measurements of total phage and extracellular phage, probably occasioned by the association of phage molecules with cellular debris, the latter being of sufficient size to be removed by the super-cel filters. 5. At pH 7.2 and 36°C. the steps in the phage production curve as determined by activity assay and plaque count are much less prominent than those observed at pH 6.1 and 28°C. However, the plateaus described by Ellis and Delbrück (10) for B. coli and coli phage can be detected also in the present case if frequent samples are taken. 6. The sorption experiments show a significant rise in the rate of phage uptake with increase in temperature, again supporting the view that the reaction involves more than a purely physical adsorption. 7. Delbrück''s objections to: (a) the use of the activity assay for determining [total phage] in mixtures of phage and susceptible cells, and (b), to the demonstration of phage precursor in "activated" bacteria have been analyzed. 8. The activity assay has been demonstrated to be an accurate procedure for determining either phage free in solution or phage bound to living susceptible cells, under the conditions of the experiments reported here and in earlier work. 9. The titration values obtained in the experiments designed to exhibit intracellular phage precursor are not the result of artifacts as Delbrück has inferred. The data can be interpreted in terms of the precursor theory, although other explanations are not ruled out.     

FURTHER OBSERVATIONS ON THE STRUCTURE OF SELAGINELLITES CRASSICINCTUS

Leisman , Gilbert A. (Kansas State Teachers Coll., Emporia.) Further observations on the structure of Selaginellites crassicinctus. Amer. Jour. Bot. 48(3): 224–229. Illus. 1961.—Specimens of Selaginellites crassicinctus Hoskins and Abbott in coal balls from southeastern Kansas have yielded new information concerning the anatomy of this strobilus. The axis contains an exarch protostele apparently suspended in an air-cavity by endodermal trabeculae. Sporophylls are attached in alternating whorls of 4 each. The strobilus is compared with modern Selaginella and a related compression fossil species.