bluuebunny/crossref_metadata_2025 huggingface dataset:
ANNONA SPECIES AS INSECTICIDES
Authors: HARPER S. H. , POTTER C. , GILLHAM (Mrs) E. M.
Published: February 2008

By extraction and precipitation from several solvents the toxic principle present in Annona reticulata and A. squamosa seeds and roots has been concentrated up to one hundred‐fold. A preliminary chemical examination of this concentrate is described, leading to the conclusion that the toxicity is due to a glyceride or glycerides of a hydroxylated unsaturated acid or acids of high molecular weight.

These extracts have been examined for contact and stomach poison and ovicidal properties in a variety of media. When used as a contact insecticide against Aphis fabae, Macrosiphoniella sanborni and Macronphum solanifolii, the concentrate exhibited a toxicity of the same order as that of rotenone, but against Oryzaephilus surinamensis the toxicity was considerably less. As a stomach poison the ether extract was both toxic and repellent to Plutella maculipennis larvae, but was neither toxic nor repellent to Diataraxia oleracea larvae. Ovicidal tests against the eggs of Plutella maculipennis and of Ephestia kühniella were inconclusive. The potency of this concentrate is therefore of a limited nature and although of roughly the same order as that of rotenone to certain aphides, it has neither the intensity of effect nor the range of insecticidal action of that compound.
THE BEHAVIOUR OF ADULT CLICK BEETLES OF THE GENUS AGRIOTES (A. OBSCURUS L., A. LINEATUS L., AND A. SPUTATOR L.)
Authors: ROEBUCK A. , BROADBENT L. , REDMAN R. F. W.
Published: February 2008

Various methods of trapping click beetles were tried, the aim being to devise a method which could be used for population and movement studies in grass fields. It is shown that a trap consisting of a 3 in. thickness of hay over closely clipped grass is suitable for this purpose. Annual and daily activity are discussed. Maximum activity occurred in late May and early June, and during the afternoon and evening. The beetles showed a preference for the most humid sites during dry weather. Numbers fell as the hedge was approached and very few occurred under the hedge. Marked beetles were released, and the maximum distance at which they were recovered was 26 yards (23.8 m.). The majority moved in a very restricted area.
SOME OBSERVATIONS ON DAMAGE TO POTATOES BY SLUGS
Authors: THOMAS D. C.
Published: February 2008

The garden slug, Arion hortensis Fér., and the keeled slugs, Milax spp., are the slugs mainly responsible for primary damage to potato tubers in the south‐west of England. A variety trial clearly demonstrated the existence of significant differences in susceptibility to slug attack between the three varieties tested. Arran Banner was the most damaged variety, Arran Peak the least, while Majestic occupied an intermediate position. Varietal differences in the amount and time of damage to tubers were associated with differences in the dates of maturity, and little damage occurred prior to the maturing of the tuber. The results confirm the need for prompt lifting of the potato crop on maturity, in order to avoid damage by slugs.
THE COMPETITION BETWEEN BARLEY AND CERTAIN WEEDS UNDER CONTROLLED CONDITIONS: II. COMPETITION WITH HOLCUS MOLLIS
Authors: MANN HAROLD H. , BARNES T. W.
Published: February 2008

The nature of the competition between barley and the twitch grass, Holcus mollis, has been studied. H. mollis has overrun much of the light, semi‐acid arable land near Woburn on Lower Greensand soils; about 2 1/2 tons of dry rhizomes and roots per acre were dug up on land where it had grown for 10 months. All this rhizome growth occurred within the top 8 in. of the soil. H. mollis commonly increases until the roots occupy from 0.11 to 0.141. root space per 1 g. dried roots and rhizomes. It is slightly superior to barley in ability to utilize available nitrogen.

When barley and this Holcus are grown together with abundance of food and water for both plants, the effect of the weed on the yield of barley depends on whether the barley or the weed first becomes established and on the rate of sowing of the barley. If barley growth begins before that of Holcus, it may smother the weed completely and sustain no loss of yield provided the barley is planted thickly enough. If the two competing plants start at the same time, thickness of planting is still able to limit the extent to which the weed can reduce the yield of barley, though even with the thickest planting the Holcus can reduce barley yield by one‐third. Where Holcus is already established in the ground from the previous year and the crop is thinly planted, the weed is able to eliminate the barley completely, but where barley is sown thickly it is still able to give a 50% yield.

With a sparse crop of barley, an increase in the number of weed units makes no difference to the growth of the barley provided the crop becomes well established. Where the crop and the weed start together and so compete on equal terms, any increase of Holcus growth is obtained at the cost of an almost equal falling off in the yield of barley, showing that the respective plant growths are almost complementary. Once the weed has fully occupied the soil, it is able to suppress the growth of the barley almost entirely. The barley and the Holcus reduce the growth of each other even when the root space and supply of plant food are ample for both.
EXPERIMENTS ON THE EFFECT OF CHLORINATED NITROBENZENES ON THE SPROUTING OF POTATO TUBERS
Authors: BROWN W.
Published: February 2008

The addition of a small quantity of a dust containing pentachloronitrobenzene to clamps of certain early and second‐early potato varieties has a marked effect in reducing the amount of sprouting which takes place over winter and in protecting the sprouts from damage by the fungus Rhizoctonia Solani.

A series of yield trials carried out over six seasons has shown that tubers which have been stored in clamps in presence of the dust give yields equal to those of chitted tubers.

A dust containing a tetrachloronitrobenzene applied to potatoes kept in a closed space represses sprouting to a very pronounced degree. The possible use of this dust for conserving ware potatoes is suggested.
INVESTIGATIONS ON THE GOUT FLY (CHLOROPS PUMILIONIS BJERK.) IN DEVON AND CORNWALL
Authors: LILLY A. H. R.
Published: February 2008

Field observations from 1943 to 1946 on attacks by gout fly on wheat in south‐west England show that there are two generations of the fly during the year, the first emerging in May from October‐laid eggs and the second emerging in late July and early August. The first generation severely damages spring wheat and may also attack very late sown and backward autumn wheat; wheat not above ground before 20 October escapes attack by the second generation. In south‐west England, the optimum period for drilling wheat to escape gout‐fly damage is mid‐October. In this area, both generations of gout fly show a marked preference for wheat; attacks on barley are negligible.
Observations on the Development of the Cotton Boll, With Particular Reference to Changes in Susceptibility to Pests and Diseases
Authors: Rainey R. C.
Published: February 2008

Continuous and well‐marked changes in composition are demonstrated during the development of the cotton boll, and discussed in relation to changes in susceptibility to pests and diseases occurring over this period.

Cotton buds and flowers, the main food of the earlier instars of Heliothis and Diparopsis, and, at the beginning of the season, of Platyedra, represent the richest recorded source of nitrogen available to the larvae.

The first 2 weeks of boll development, when most physiological shedding occurs, are characterized by extremely rapid growth, the dry weight of the ovules being approximately doubled every 2 days throughout this period.

The developing ovules are richest in reducing sugars during the second and third weeks, when moisture‐content is also highest. Bolls of this age are attacked by the later instars of Heliothis and Diparopsis, which are the stages at which the accumulation of larval fat is likely to be most active. Male Dysdercus, which can survive for prolonged periods on simple sugar solutions, show a marked preference for bolls of this age, which are punctured to a varying extent by other stages of Dysdercus, probably primarily as a source of water. This is also the stage at which attack by Nematospora is most damaging; reducing sugars provide a highly suitable source of carbon for this fungus.

The cellulose of the mature lint and the oil and protein of the ripe seed are mainly laid down after the boll reaches full size (at 4–5 weeks under local conditions), about half‐way through its maturation period, and are largely derived from materials entering the boll in the course of its subsequent development. Premature senescence, such as that associated with Alternaria attack, can thus affect yield even when defoliation does not occur until after most of the bolls have attained full size.

The ripening seed, becoming steadily richer in oil and protein during the latter part of boll development, forms the main food of Platyedra towards the end of the season, a change of diet reported to induce the larval diapause. Ripe seed provides food which is essential for satisfactory nymphal development and probably also for oviposition in Dysdercus; specific protein requirements are possibly involved.

Examples of direct effects of environmental factors on the development and composition of the boll are described. Over the range of conditions experienced by the experimental material these effects were relatively small.
The Phytotoxicity of D.D.T. and of Benzene Hexachloride
Authors: Stoker Rosemary I.
Published: February 2008

Spraying with two preparations of D.D.T. had a negligible effect on the maturation of outdoor tomatoes and of summer cabbage. Spraying with a commercial D.D.T. suspension damaged cucurbits and treatment with the suspension base distorted glasshouse cucumbers during one season only.

Benzene hexachloride (B.H.C.) sprays did not affect the yield or flavour of tomatoes, but, at concentrations higher than those normally used, they severely scorched radish, turnip, swede, kale, spinach and beetroot seedlings. The application of B.H.C. dusts stunted seedlings of radish.

On one occasion young potato foliage was damaged by relatively high concentrations of two compounded B.H.C. sprays and by B.H.C. dust but late‐season older foliage was unaffected. A spray compounded from B.H.C. dispersible powder caused tainting of potatoes, peas, carrots, beetroot, marrows, cauliflowers and lettuce. Apples and plums treated with B.H.C. spray preparations developed a taint after cooking.
Problems in the Cultivation of Winter Lettuce
Authors: Brown By W. , Montgomery N.
Published: February 2008

In a four‐year study of winter lettuce cultivation, attention has been given to the effects of variety, dates of sowing and transplanting, method of preparing seed‐beds, nature of field soil, and fungicidal treatments upon percentage survival and date of maturity of the crop

The inferiority of the variety Trocadero Improved to such a winter variety as Imperial is due mainly to its susceptibility to Pythium root rot. This disease often causes severe thinning of the stand of Trocadero seedlings and dwarfing of many of the survivors

Late autumn plantings of Imperial and other winter varieties survived better overwinter on a medium‐heavy loam than on a light sandy soil. The disparity varied in different seasons and was not associated with severity of winter

The dates of maturity of the crop in relation to dates of sowing and transplanting have been determined over the four‐year period. On the basis of these, and on the records of survival and of market prices, an estimate can be obtained of the financial aspects of different cultural methods

Fungicidal treatment in the seed‐bed of plants set out in the field in November gave little improvement in survival; but pronounced benefit was obtained by February or March dusting of seedlings which had overwintered in the seed‐bed

The onset of disease in overwintering seed‐beds was found to be influenced by the nature of the soil and by the manner of preparation of the seed‐bed

The interrelations of overwintering and soil type are briefly discussed, with special reference to the effects of soil type (i) on the root system, and (ii) on microbiological interference with invasion of die stem by Botrytis
The Use of Metaldehyde Against Slugs
Authors: Thomas D. C.
Published: February 2008

One part of metaldehyde in thirty parts of bran by volume is the minimum effective concentration for obtaining an economic kill of slugs under average weather conditions. For use against Milax gracilis Leydig. heaps of bait should not be normally more than 2 yd. apart and against Arion hortensis Fer. not more than 3 ft. apart. The mortality of slugs attracted to metaldehyde‐bran baits is dependent on the drying property of the soil and atmosphere around the baits. D.D.T. flea‐beetle dust and powdered pyrethrum flowers are sufficiently distasteful to slugs to prevent their consuming a lethal dose of the poison mixed with bran. The addition of 10%, by volume, of dried blood to metaldehyde‐bran bait increases the catch of some slugs under certain conditions but does not increase the mortality. The addition of 10%, by volume, of dextrose increases the mortality produced by metaldehyde but does not increase the numbers attracted to the bait. A metaldehyde‐bran bait compacted into ‘biscuit’ form with anhydrous calcium sulphate catches more slugs than an ordinary metaldehyde‐bran bait, but almost completely counteracts the effect of the metaldehyde. A metal‐dehyde‐bran‐casein glue bait in ‘biscuit’ form increases the catch and kill of Milax gracilis and Agriolimax reticulatus Müll., but not of Arion hortensis. Metaldehyde‐bran‐casein glue bait broadcast in ‘broken biscuit’ form is effective over a longer period, thus producing a greater kill of slugs, than a broadcast metaldehyde‐bran bait.
Verticillium Wilt of the Hop (Humulus Lupulus)
Authors: Isaac I. , Keyworth W. G.
Published: February 2008

An account is given of the methods used to determine the relative pathogenicity of isolates of Verticillium albo‐atrum from fluctuating and from progressive outbreaks of the wilt disease of hops. Isolates from fluctuating outbreaks were less pathogenic to young hop plants than those from progressive outbreaks, and it is suggested that this is the main cause of the differences in symptom incidence and intensity between the two types of outbreak in the field.
Studies on the Importance and Control of Potato Virus X
Authors: Bawden F. C. , Kassanis B. , Roberts F. M.
Published: February 2008

The success of seed certification schemes in controlling the aphis‐transmitted viruses that cause leaf roll and rugose mosaic has greatly increased the relative importance of potato virus X, in spite of the value of such schemes in reducing the prevalence of the most virulent strains. Virus X occurs throughout commercial stocks of most varieties and is responsible for many of the uncertainties and difficulties encountered in field inspections, for the production of leaf symptoms by many strains depends on the weather. Also, the predominating virus strain in a stock may change from season to season.

Methods of testing for the presence of avirulent strains in potatoes are described. These include transmission to suitable indicator plants, plant‐protection tests, and serological methods. The virus content of different parts of the plant varies widely, but is everywhere high enough for transmission to indicator plants at all times of the year. The virus content of immature tubers is too low to give a precipitin reaction, but extracts from developing sprouts contain nearly as much virus as those from foliage, and can be used reliably.

Infection of virus‐free stocks of the varieties Majestic and Arran Banner with four different strains of virus X reduced their yields by amounts varying from 5 to 24%. Scotch Stock Seed Majestic, however, cropped better than the virus‐free seed, and the need for considering additional factors to freedom from viruses when selecting clonal lines for propagation is stressed.

Virus X was not transmitted by cutting healthy tubers with a knife previously used to cut infected ones, and cut tubers whose storage parenchyma was rubbed with infective sap gave rise to virus‐free plants. Infection occurred when sprouts were rubbed with infective sap, and the virus also spread from infected to healthy sprouted tubers stored in the same sack.

Spread of the virus under natural conditions is slow, and it is concluded that the maintenance of virus‐free stocks under commercial conditions is feasible, provided that precautions are taken to prevent contact with infected plants. The relative importance of volunteer plants and other sources of infection is discussed, and methods of testing the virus‐free stocks are suggested.
Some Notes on Holcus Mollis L.
Authors: Fenton E. Wyllie
Published: February 2008

The natural woodland habitat of Holcus mollis is discussed and its ability to survive after removal of the trees. Its presence under other environmental conditions is recorded, Examples of its occurrence as a weed are quoted from Scotland, including an instance of competition with an oat crop. The effect of grazing and cultivation on H. mollis is described.
Studies on the Relationships Between Earthworms and Soil Fertility
Authors: Evans A. C. , Guild W. J. McL.
Published: February 2008

The rate of cocoon production in British Lumbricidae differs considerably from species to species and is greatly affected by soil temperature, moisture and the food supply of the adult worms. Only two out of fourteen species studied frequently produced more than one worm per cocoon, and twins were only recorded once in many hundreds of observations on four species of the genus Lumbricus.

The incubation period of the cocoons and the growth period to sexual maturity varies from species to species and also depends on the time of year at which the cocoons are deposited and the young worms emerge.
Studies on the Relationships Between Earthworms and Soil Fertility
Authors: Evans A. C. , Guild W. J. McL.
Published: February 2008

The ploughing of a permanent pasture in spring was not followed by a reduction of the earthworm population during the first 6 months but further arable cultivation did greatly reduce the population. Leys, 4–7 years old, carry a total population similar to that of permanent pastures, but with differing proportions of certain species. Some trends in population changes during a period of nearly 1 year are described for five common species. The population of a permanent pasture did not show appreciable change for a period of nearly 3 years but that of a ley, in its first year following arable, showed a significant increase.
The Contact Toxicity of a Number of D.D.T. Analogues and of Four Isomers of Benzene Hexachloride to Macrosiphoniella San Born I and Oryzaephilus Surinamensis*
Authors: Lord K. A.
Published: February 2008

Twenty‐three analogues of D.D.T. and four isomers of benzene hexachloride have been compared with D.D.T. for toxicity as contact insecticides using a direct spraying technique. Each substance has been tested against two insect species: Macrosiphoniella sanborni and Oryzaephilus surinamensis. The substances tested included a number of halogen and alkyloxy analogues of D.D.T. and a number of compounds of varying degrees of chlorination between diphenylethane and D.D.T.

The biological data have been examined, as far as possible, by the method of probits.

The probit lines for the D.D.T. analogues varied both in position and in slope: those for the isomers of benzene hexachloride in position but not in slope. In general, neither the relative positions nor the relative slopes of the probit lines for the various substances were the same against the two insect species.

The toxicity of substances analogous to D.D.T. appears to be related to molecular weight, with maximum toxicity occurring in the molecular weight range 300–450.

Among D.D.T. analogues the slope of the probit line is apparently correlated with molecular volume. The variation of the slope of the probit lines has been discussed, and it has been concluded that it arises from differences in the interaction of the poisons with the test‐subjects.

The various theories relating to the toxicity of D.D.T. and B.H.C have been discussed in relation to the experimental data described here. To account for all the experimental results by means of one theory it is necessary to postulate a physico‐chemical mechanism of toxic action. Such a mechanism implies that the intensity of biological action will be dependent upon the physico‐chemical properties of the poisons, whether or not a specific molecular configuration is involved, and toxicity is therefore dependent on the molecule as a whole.
The Toxicity of Vapours to the Grain Weevil
Authors: Ferguson J. , Pirie H.
Published: February 2008

The values for concentrations in air of the vapours of approximately one hundred different chemical substances required to produce 50% mortality in samples of the grain weevil Calandra granaria, have been determined. Relationships between chemical constitution of these substances and their toxicity to the grain weevil are discussed, using as a measure of toxicity the relative saturation of the vapour concentration producing 50 % kill. The relative saturation is equal to the thermodynamic activity of the vapour at the concentration in question.

It is found that the substances used can be divided into two broad classes: (a) one class in which the toxic thermodynamic activities lie between o‐1 and 1 ‐o and (b) another in which the activities are much lower—down to 0–0004.

The first class exhibits certain linear relationships between the logarithms of toxic concentration and saturated vapour pressure, which are not shown by the second class. The toxicity of the first class is ascribed to a physical mechanism, and is believed to be such that phase equilibrium relations play a predominant part in determining the value of the toxic concentration measured externally to the insect (Ferguson, 1939).

The toxicities of members of the first class, as measured by their toxic thermodynamic activities, show the following relations with chemical constitution:

Toxicity in homologous series decreases steadily from the first member as the chain length increases, finally disappearing.

Halogen substitution in hydrocarbon skeletons has only a small effect on the ‘physical’ toxicity, increasing it slightly. There is practically no difference in the effect of different halogens.

Hydroxyl substitution markedly decreases ‘physical’ toxicity.

The substitution of—CO or —CHO groups markedly increases ‘physical’ toxicity. The aliphatic amines and the alkyl formates examined do not appear to act by a physical mechanism, nor do many of the alkyl bromides and iodides.
Methods of Recording Aphid Populations for Use in Research on Potato Virus Diseases
Authors: Broadbent L.
Published: February 2008

Methods of counting aphids infesting potato crops are reviewed and discussed. The results of an aphid survey in different parts of England during 1946 and of counts at Rothamsted during 1947 are given and used to illustrate methods of expressing the counts; the extent of virus spread in 1946 showed no close correlation with aphid numbers. It is concluded that an estimate of the number of aphids per plant is better for virus disease research than the number per 100 leaves. A method of estimating the number of aphids per plant with tolerable accuracy is described, but it is concluded that for most surveys a method which does not necessitate the counting of the aphids is adequate. Such a method, based on the percentage of leaves infested, is described.
On Estimating the Population of Aphids in A Potato Field
Authors: Anscombe F. J.
Published: February 2008

This appendix to the preceding paper by L. Broadbent deals with the statistical problem of estimating the population of aphids per plant in a field of growing potatoes. An unbiased method is described, in which a definite proportion of a number of plants is sampled, and also a more rapid, method of stratified sampling. (An account of the statistical principles involved has been given by Yates (1946).) Sampling for purposes of inspection is then considered, using practices current in industrial statistics and described, for example, by Peach (1947). Finally, some counts on Myzus persicae are examined, to obtain information on the. type of variation in aphid numbers to be expected.
Studies on Bacterium Fascians*
Authors: Lacey Margaret S.
Published: February 2008

Seedlings were treated with cell‐free filtrates of cultures of Bad. fascians, Bad. tumefaciens and other bacterial species, and the effects on the growth noted and compared with malformations resulting from the inoculation of living bacteria. The power to produce or destroy growth‐promoting substances in various culture fluids by Bad. fascians was examined and compared with that of other bacterial species. It is suggested that seedlings infected by Bad. fascians produce ‘leafy‐galls’ or ‘dwarfing’ owing to a disturbance of the normal auxin content or distribution in the plant.
Observations on a Virus Disease of Certain Crucifers in Trinidad
Authors: Dale W. T.
Published: February 2008

A virus disease ofBrassica juncea Coss., B. Mnensis L. and Raphanus sativus L. var.hortensis Backer occurs in Trinidad, but is not serious. Rape (Brassica napus L.), turnip(B. rapa L.) and Lepidium virginicum L. are susceptible, but cabbage, cauliflower, kohlrabi and the European radish seem to be immune. Zinnia elegans Jacq. and tobacco (Nicotiana tabacum L.) are also susceptible, but no infections were obtained on six other Nicotiana species, beetroot, Swiss chard and cowpea. Tobacco gives only necrotic local lesions, whereas the other hosts give no local lesions, but a systemic mottling, usually accompanied in crucifers by leaf deformation and stunting of the plant.

The virus is transmitted by Rhopalosiphum pseudobrassicae (Davis), which is probably responsible for spread in the field. Its thermal inactivaticm‐point is 58d̀ C, dilution end‐point 1:1000, and longevity in vitro 4 days at 16–18d̀ C. and 3 days at 24–30d̀ C. The properties and host range of this virus are compared with those of others affecting the Cruciferae. It has affinities with some of them, but is considered to be distinct.
Growth Cycle Metabolism of Plants in Relation to Flowering
Authors: Grainger John
Published: February 2008

An examination of the percentages of total carbohydrate, nitrogen (Kjeldahl) and ash has been made at various times in the growth cycle in six plants of varying growth habit. The time of formation of the flower initial in four species (fumitory, leek, radish and yellow water‐lily) corresponds to a maximum in the curve showing percentage of total carbohydrate plus percentage of ash in the whole plant. The other two species (pea and bean) make their flower initials very early in the growth cycle, at a time when the amounts of carbohydrate plus ash are high because of the attachment of the plant to the large seed. These two species therefore also make their flower initials at a virtual maximum of carbohydrate plus ash. All six species of plants studied have mobile carbohydrate. The distribution of nutrients after flowering is discussed.
A TECHNIQUE FOR DETERMINING THE STOMACH POISON EFFECT OF INSECTICIDES USED AGAINST LEAF‐EATING INSECTS
Authors: WAY M. J.
Published: February 2008

Methods devised for feeding individual insects with leaf areas bearing known deposits of insecticides are described, and the problems associated with incomplete consumption of the treated leaf portions are discussed. An account is given of the difficulties of applying the technique to small insects and to those with erratic feeding habits.

Experimental data are given to illustrate the effects on insect resistance of the following: (i) rearing conditions, (ii) larval age and body weight, (iii) acute and chronic poisoning, (iv) the diluting effect of the leaf tissue consumed with the poison dose.

The dosage mortality curve for stomach poisons was found to be typically sigmoid: analysis of results by the method of probits (Bliss, 1934) therefore proved satisfactory. Using lead arsenate against fifth‐instar larvae of Phlogophera meticulosa the ratio of weight increase to increase in median lethal dose was found to be constant.
THE TRANSFORMATION OF LOCAL LESION COUNTS FOR STATISTICAL ANALYSIS
Authors: KLECZKOWSKI A.
Published: February 2008

An analysis of the frequency distribution of local lesions, produced by viruses on half‐leaves of a number of plants, shows that their standard error increases with increasing mean. Hence analysis of variance and statistical tests of significance should not be applied to lesion numbers unless they are suitably transformed. The transformation into logarithms over‐corrects so that the standard error decreases with increasing mean. A satisfactory transformation is y= log10 (x+c), where x is the number of lesions and c is a constant. A method is given of assessing c for different experiments. Great accuracy is not needed; in an experiment discussed in detail a satisfactory transformation is obtained with any value for c between 15 and 80.

On individual plants the numbers of lesions formed on half‐leaves are distributed more or less normally, whereas their distribution about the common mean for many plants is skew and ‘leptokurtic’. The distribution of the transformed numbers is almost normal, both for individual plants and about the common mean for a number of plants.
STUDIES OF WIREWORM POPULATION III. SOME EFFECTS OF CULTIVATION
Authors: SALT GEORGE , HOLLICK F. S. J.
Published: February 2008

The number of wireworms in successive collections from five Cambridgeshire fields declined during the first year of cultivation to 25 % of the number present before the fields were ploughed from old grass. The decline in numbers was accompanied by a change in the composition of the wireworm population; the marked inverse correlation between number and size of larvae, which held for the wireworm populations under grass, progressively altered towards uniform numbers of the different size‐groups. The incidence of natural control on the different sizes of larvae was obscured by their growth, and more medium‐sized and large larvae were lost than would appear from the population‐size histograms.

Three groups of factors are considered as contributing to the decline in numbers after ploughing. Direct observation showed that many wireworms were destroyed in the actual process of cultivation. Evidence was insufficient to prove that the physical condition of cultivated soil adversely affects the number of wireworms. Comparison of the smaller size‐groups in pasture and in the cultivated fields showed that the wireworm population failed to replenish itself under arable conditions.
THE INSECTICIDAL ACTION OF SOME D.D.T. ANALOGUES AND CHLORINATED (4‐CHLOROPHENYL)‐ETHANES
Authors: STRINGER A.
Published: February 2008

The insecticidal effectiveness of D.D.T. is dependent upon the combination of the two chlorophenyl groups with the trichloroethane group. Modification of the latter group results in a loss of toxicity. The toxicity of the compounds possessing =CH.CC13, =CH.CHC12 and =CH.CH2C1 groups decreases as the degree of chlorination decreases.

None of the chlorinated (4‐Chlorophenyl)‐ethane compounds are of the same order of toxicity as D.D.T. The relative potency increases with increasing chlorine content of the side‐chain, although complete chlorination results in a compound possessing negligible toxicity. A relationship between toxicity and chlorine content is also seen in the ethylenic compounds, which were formed as intermediates in the synthesis of the ethane derivatives. The comparatively non‐toxic ethylenic derivatives of D.D.T. when contrasted with (4‐CIC6H4) CC1=CC12, suggests that the spatial configuration of the molecule may be of importance.
A SIMPLE METHOD FOR ASSAYING CONTACT TOXICITIES OF INSECTICIDES, WITH RESULTS OF TESTS OF SOME ORGANIC COMPOUNDS AGAINST CALANDRA GRAN ARIA L
Authors: STRINGER A.
Published: February 2008

A simple method of testing the contact action of insecticides either as residual dry deposits or as oil films is described. Tests with crystalline deposits of D.D.T. indicated that this method of assay was not sufficiently sensitive for practical use, but tests with oil films could be used. Some of the factors governing the toxicity of D.D.T. in the two systems are discussed, and the results of tests with several organic compounds are given.
BIOASSAY SYSTEMS FOR THE PYRETHRINS I. WATER‐BASE SPRAYS AGAINST AXDËS AEGYPTI L. AND OTHER FLYING INSECTS
Authors: PAGE A. B. P. , STRINGER A. , BLACKITH R. E.
Published: February 2008

A bioassay system for the pyrethrins is discussed in which the quantity of toxicant that flying insects accumulate is measured, as well as the responses of the insects. The determination of spray pick‐up from water‐base sprays is described, and the use of primary responses, such as activation and paralysis, in biological assays is advocated. The test system is discussed in detail for Aëdes aegypti L. and the special characteristics of some other species of flying insects noted. It is considered that the location of the site of action of the pyrethrins under these conditions is at the peripheral nervous system of the test insects.
INVESTIGATION INTO THE PRODUCTION OF BACTERIOSTATIC SUBSTANCES BY FUNGI A REVISION OF THE TESTING METHOD
Authors: WILKINS W. H.
Published: February 2008

Discrepancies in the comparative results of workers on antibacterial substances produced by fungi can usually be attributed to the use of different testing methods. The method described here for testing fungus metabolism solutions is designed to facilitate comparison in that its characteristic features are simplicity and rapidity. A nutrient broth of the standard ingredients of peptone, salt and water only, plus agar, ensures that a test involving IOO plates, i.e. 400 tests, can be set up by one assistant in 3 hr. The sensitivity of the test is almost equal to that of a dilution series and the results are consistent over a wide range of individual and circumstantial variation.
THE COMPETITION BETWEEN BARLEY AND CERTAIN WEEDS UNDER CONTROLLED CONDITIONS III. COMPETITION WITH AGROSTIS GIGANTEA
Authors: MANN HAROLD H. , BARNES T. W.
Published: February 2008

The twitch grass Agrostis gigantea var. dispar occurs commonly as a serious weed on the light semi‐acid soils found on the lower greensand near Woburn, Beds. It spreads rapidly by means of rhizomes, rarely forming stolons. All the rhizome growth takes place within 6 in. of the surface: I g. dry weight of roots and rhizomes may occupy up to 260 C.C. of soil. A. gigantea is slightly more easily eradicated than Holcus mollis.

When barley and this Agrostis are planted together, with abundance of water and nutrients for both, it is found that increasing the density of planting of the barley reduces the crop loss due to Agrostis competition, but the weed can, nevertheless, diminish the yield of close‐planted barley by about a quarter. In a sparse crop of barley, any increase in Agrostis growth is reflected in an almost equal reduction in yield of barley. In proportion to its relative density the barley secures a larger share of the soil nitrogen than does the Agrostis.

Evidence is given suggesting that there is a marked effect of the one grass on the other even when there is no competition for root space and an ample supply of water and nutrients.
THE MOVEMENT OF TOBACCO MOSAIC VIRUSES AND POTATO VIRUS X THROUGH TOMATO PLANTS
Authors: Capook S. P.
Published: February 2008

Tomato aucuba mosaic virus, tobacco mosaic virus and potato virus X took 3'5‐4, 5 and 3 days respectively to move from inoculated tomato leaflets into the petioles and stems

On reaching the stem each virus usually first moved downward, but in some plants both upward and downward movement occurred simultaneously and in a few

upward movement occurred first.

All three viruses travelled through the stem at approximately the same rate. Each was capable of travelling more than 80 cm. during the first 12 hr. after entering the stem, giving a minimal average rate of about 8 cm. per hr.

Uninfected pieces of stem invariably occurred between infected pieces. Maximum lengths of stem through which virus particles had apparently passed without causing infection, were 44.5, 49 and 39 cm. for the three viruses.
ASPERMY—A NEW VIRUS DISEASE OF THE TOMATO
Authors: Blencowe J. W‐. , Caldwel John
Published: February 2008

‘Aspermy’ is suggested for the name of a virus disease of tomato apparently distinct from any previously described. The virus was transmitted by Myzus persicae from infected to healthy tobacco plants, but not from or to other hosts. Some properties of the virus are described together with the symptoms it causes in various hosts.
FIELD TRIALS WITH D‐D MIXTURE* AGAINST POTATO‐ROOT EELWORM
Authors: Peters B. G. , Fenwick D. W.
Published: February 2008

A D‐D mixture has been tested against Heterodera rostochiensis at seven 2‐acre sites on sands, silts and blackland soils. Apart from a pilot trial where soil was injected in spring, injections were carried out in the autumn, and potatoes were grown the following year. Factors investigated were rate of application (0, 200, 400 and 800 lb. D‐D/acre), depth of injection (4 or 8 in.) and the effect of rolling after injection. At the most responsive of the sites (Wainfleet), increases in yield, kill, and the post‐crop eelworm population were all roughly proportional to the rate of application. Under favourable circumstances a 50% increase in yield and something like a 50% reduction in eelworm population 4 weeks after injection can be expected from 800 lb./acre, but the reduction is more than made good during the growth of the subsequent crop; accelerated multiplication of eelworm on the treated plots leads to their having a larger population than the untreated controls at lifting time. Of the sites tested, the blackland soils gave a lower eelworm kill and a much lower yield increase from D‐D than silts or sands. After autumn injection the nematocidal, and probably the phytocidal, effects of D‐D persist in the soil for many weeks. The hypochlorite method of ‘hatching’ eelworm larvae for counting has proved unreliable.
VIRUS DISEASES OF CACAO IN WEST AFRICA: IV. EFFECT OF VIRUS INFECTION ON GROWTH AND WATER CONTENT OF CACAO SEEDLINGS
Authors: GOODALL D. W.
Published: February 2008

Apparently healthy cacao seedlings were compared with those infected before planting with ‘swollen shoot’ viruses. The leaf area and the fresh and dry weights of each organ were measured. Infected plants were lower in dry weight, leaf area, relative growth rate and net assimilation rate; a smaller proportion of the dry matter was in the leaves and lateral roots, a larger proportion in stems and tap roots. Infection caused extensive necrosis of the lateral roots, and reduced the rate of depletion of reserves in the cotyledons and the water content of the plant. Many of these effects were apparent within a month of infection and planting.
OBSERVATIONS ON APPLE CANKER III. THE ANATOMY OF THE STEM CANKER
Authors: CROWDY S. H.
Published: February 2008

The development of cankers caused by Nectria galligena on apple is described; the pathogen exploits all the tissues outside the xylem and will also penetrate the xylem to an appreciable depth, invading the xylem parenchyma, vessels and fibres.

Spread in the peripheral tissues is checked to some extent by successive barriers laid down by wound phellogens, but the barriers are eventually passed by the mycelium. There appear to be two distinct ways in which these barriers are passed: there may be direct penetration which appears to be associated with an aggregation of the mycelium into blocks, and symptoms suggestive of mechanical rupture; or there is an alternative route in which the pathogen grows in the lumen of the fibres and emerges behind the barrier.

In the xylem the spread of the pathogen is checked by tyloses and gumming in the vessels, and by gumming in the parenchymatous tissues, but in the fibres there appears to be no defence mechanism, and the spread beyond the gum barriers was usually recorded in the xylem fibres. It is suggested that the presence of the pathogen in the xylem fibres might provide the explanation of the formation of cankers on partially healed pruning cuts, and this type of canker is described in some detail.

The development of the canker depends on the balance between the development of the pathogen and the resistance of the host, and there is some discussion on the relation of this balance to the control of the disease.
THE RELATION BETWEEN MOISTURE CONTENT AND MOULDING IN CURED HAY
Authors: WAITE R.
Published: February 2008

Samples of cured hay have been stored in closed containers at relative humidities of 0–95% at temperatures varying from 5 to 25° C. A curve relating equilibrium moisture content to relative humidity of the store has been constructed and the incidence of first mould growth noted. An explanation has been suggested to account for the apparent discrepancy between earlier published work concerning the onset of moulding and conditions normally prevailing on the farm. In laboratory storage experiments temperature conditions are relatively constant, whereas with hay stacked in the open air the high atmospheric humidity in winter is offset by a lowered temperature, and the higher summer temperature is accompanied by a lower moisture content in the hay.
OVERWINTERING OF APHIDS, ESPECIALLY MYZUS PERSICAE (SULZER), IN ROOT CLAMPS
Authors: BROADBENT L. , CORNFORD C. E. , HULL R. , TINSLEY T. W.
Published: February 2008

Mangold clamps in many districts of the British Isles were found to provide overwintering sites for Myzus persicae (Sulz.), Hyperomyzns staphyleae (Koch) and Aulacorthum solani (Kalt.). After a severe winter, when other means of overwintering are few, clamps may be the most important source of Myzus persicae. Only Myzus ascalonicus Doncaster was found in swede clamps.

Factors affecting the infestation of clamped mangolds by M. persicae were the number of aphids on the crop when lifted, the methods of topping and clamping the roots, and the temperature in the clamp. M. persicae was introduced on the leaves, and close topping was often an efficient means of control. Close topping did not control Hyperomyzus staphyleae; normally, this aphid does not seem to be a root‐feeding species, but with artificially colonized mangolds it fed on both exposed roots and foliage. It is not known how this species enters the clamps. The temperature in clamps was influenced by that of the outside air and the type of cover, but changes were long‐term and did not reflect diurnal variations in external air temperature. Straw, covered with soil, was the best form of cover.

In addition to harbouring Myzus persicae, mangold clamps are also important sources of sugar‐beet yellows virus.
EXPERIMENTS ON THE CONTROL OF CHRYSANTHEMUM EELWORM(APHELENCHOIDES RITZEMA‐BOSI, SCHWARTZ) HOT WATER TREATMENT
Authors: STANILAND L. N.
Published: February 2008

The minimum times required for killing the chrysanthemum eelworm (Aphelenchoides ritzema‐bosi, Schwartz) in water, over a range of temperatures have been determined and the technique employed is described. A temperature of 115° F. for 5 min. is preferable to the usual standard treatment of 110° F. for 20–30 min. and enables stools to be treated with less retardation of cuttings or death of stools, with a consequent great increase in the number of cuttings obtained. The results are of special value in connexion with varieties susceptible to damage by the hot water treatment.
STUDIES OF THE CLOVE TREE
Authors: SHEFFIELD F. M. L.
Published: February 2008

A detailed study was made of the histology of apparently healthy clove trees and of trees expected to die from sudden death disease, in an attempt to find either a diagnostic character of the disease or some indication of a possible pathogen.

The apparently healthy clove tree differs from a typical dicotyledon in a number of ways. This is especially true of the vascular system where, not only are the bundles bicollateral, but, in the stem, secondary thickening occurs in the internal phloem, necrosis of the first formed cells keeping pace with the production of new cells. A definite cambium is found only to the exterior of the xylem and this is exceptionally narrow and the cells have very delicate walls. Phloem necrosis may occur in any part of the tree. The development and lignification of the xylem is very uneven, but this seems to bear no relation to the season. Tyloses are formed in the vessels of the root and, to a less extent, in those of the stem. Starch reserves are usually small, but large quantities of tannins, oils and calcium oxalate are secreted in all tissues. The oil may be contained in special schizogenous glands which are abundant in the aerial parts of the tree. Much mechanical tissue, consisting of fibres and stone cells, is formed in the pith and cortex of the stem and in the phloem in all parts of the tree, but lignification of this tissue is very uneven. Occasional dead cells are found in all tissues, even in the primary meristem. In the leaf, the plastids develop very unevenly; this is followed by retarded development of the pigment in some parts, resulting in a flecked appearance. Stomata are exceptionally numerous; in the leaf, they are confined to the lower surface and always communicate with very small cavities. Air spaces in the mesophyll are very small and are almost non‐existent in other tissues. Bodies, morphologically similar to the amorphous intracellular inclusions due to some viruses but differing chemically from them, are abundant in the leaves.

Some of these characters are usually associated with a diseased condition, but they occur in both healthy and diseased cloves in the Zanzibar Protectorate. In the sudden death suspect, some may occur earlier or be more accentuated than in the healthy tree. This evidence alone might suggest that sudden death is merely the culmination of a long period of adverse conditions, but other evidence suggests very strongly that the disease is due to a pathogen. Of the groups of organisms which may cause disease, only fungi were found. These occurred in the absorbing roots but are unlikely to be the pathogens causing sudden death, for, until the tree has actually wilted, very few hyphae are present, and no more than are found in healthy trees. Nothing incompatible with the suggestion that sudden death is caused by a virus was found.
SOME EFFECTS OF HOST NUTRITION ON THE SUSCEPTIBILITY OF PLANTS TO INFECTION BY CERTAIN VIRUSES
Authors: BAWDEN F. C. , KASSANIS B.
Published: February 2008

Fertilizer treatments that greatly influenced the growth of tobacco and potato plants in pots had little effect on the number that became infected with potato virus Y when the plants were colonized by equal numbers of infective aphids, though the number was slightly decreased by nitrogen and increased by phosphorus.

The number of local lesions produced on leaves of tobacco and Nicotiana glutinosa by tomato aucuba mosaic and tobacco mosaic viruses was increased by additions of both nitrogen and phosphorus, provided that these also increased growth. The predominant effect of both nutrients in increasing susceptibility was indirect by increasing plant size, but over certain critical ranges both elements also increased the numbers of lesions produced per unit leaf area. Conditions of maximum susceptibility approximated closely to those producing optimal growth, and susceptibility, whether measured by lesions per half‐leaf or per unit area, was decreased by a deficiency or excess of either element. Sometimes the addition of nitrogen reduced susceptibility when still increasing plant growth.