bluuebunny/crossref_metadata_2025 huggingface dataset:
THE CORRELATION OF APHID NUMBERS WITH THE SPREAD OF LEAF ROLL AND RUGOSE MOSAIC IN POTATO CROPS
Authors: BROADBENT L.
Published: February 2008

An analysis of the results of experiments in different parts of England and Wales from 1941 to 1947 on the spread of potato leaf roll and rugose mosaic showed that leaf roll spread was correlated with the number of alate Myzus persicae (Sulzer) caught on sticky traps throughout the potato‐growing season; there was some correlation with the maximum count of M. persicae per 100 leaves, but this possibly results from the correlation between trapped aphids and the number per 100 leaves. Spread of rugose mosaic (potato virus Y) was correlated to a lesser degree with number of M, persicae, perhaps because other aphid species are often vectors. With both diseases higher correlations were obtained when the infected plants were dispersed among the healthy crop than when they were placed together in a row. It is concluded that it is possible to predict the average health of potato stocks in the following year from average trap data; further work may enable the health of individual stocks to be predicted.
STUDIES ON LUCILIA SPECIES (DIPTERA) UNDER DANISH CONDITIONS
Authors: CRAGG J. B.
Published: February 2008

Whilst sheep myiasis caused by Lucilia sericata is a severe economic problem in Great Britain, it rarely reaches such proportions in countries bordering Western Europe. Possible reasons for this relative absence of myiasis were investigated in Denmark.

During the period 19 July‐15 August 1948, trapping studies showed that blowflies normally associated with myiasis in Great Britain, and particularly L. sericata, occurred fairly abundantly in the Mols area of Jutland.

The reactions of Danish L. sericata to attractive materials placed on sheep were similar to those shown by the species under British conditions. The number of egg batches laid on sheep in response to chemical stimuli were fewer than would have been expected in Great Britain.

Studies on the fleece microclimate showed that relative humidities of 50 % or more frequently occurred on the skin surface. Humidities 3 cm. above the skin were markedly lower. Except during or immediately after rain, humidities high enough to ensure the hatching of blowfly eggs were never recorded.

It is concluded that the absence of myiasis in Denmark and its relatively low incidence in other countries is not due to the existence on the Continent of a strain of L. sericata differing in oviposition habits from the British species.
A SUCTION TRAP FOR SMALL AIRBORNE INSECTS WHICH AUTOMATICALLY SEGREGATES THE CATCH INTO SUCCESSIVE HOURLY SAMPLES
Authors: JOHNSON C. G.
Published: February 2008

This paper describes the design and operation of a suction trap which takes in air at a constant rate in winds up to 12 m.p.h. The catch is deposited in a collecting tube into which closely fitting disks fall, one every hour, thus segregating the catch into successive hourly samples. The trap is electrically driven; it operates in all weathers and heavy rain does not disorganize the catch.
STUDIES ON TWO APHID‐TRANSMITTED VIRUSES OF LEGUMINOUS CROPS
Authors: CHAUDHURI R. P.
Published: February 2008

Pea mosaic virus was transmitted by Myzus persicae Sulz., Macrosiphum pisi Kalt., M. solanifolii Ash. and Aphis fabae Scop., but not by Hyperomyzus staphyleae Koch. It is a ‘non‐persistent’ virus (Watson & Roberts, 1939), and is most readily transmitted when vectors are fasted and then given a short infection feeding. Vector efficiency was not increased by increases in preliminary fasting beyond 15 min. or with increasing infection feeding beyond 1 hr. Most aphids became non‐infective within 15 min. when feeding, but fasting aphids remained infective for 3 hr. Species that fed readily on the infected plants were less efficient vectors than those which did not. Seed set by infected plants produced healthy seedlings.

Pea enation mosaic virus persisted in Myzus persicae and Macrosiphum pisi for more than 140 hr.; its transmission was unaffected by preliminary treatments of aphids. No transmission was obtained until at least 4 hr. after aphids had left infected plants; usually the ‘latent’ period exceeded 1 day and its duration was apparently unaffected by the length of the infection feeding.
VIRUS DISEASES OF CACAO IN WEST AFRICA
Authors: POSNETTE A. F. , ROBERTSON N. F.
Published: February 2008

Increasing the number of Pseudococcus njalensis per test plant increased the infection rate with cacao virus 1A and 1M to 95 % with twenty‐five insects. Young leaves with the red vein‐banding symptoms were better sources of virus than mature leaves, and there was evidence of virus localization in the plant. It was estimated that Ps. njalensis nymphs took about 16 min. to penetrate plant tissues with their stylets.

Infection rates increased with time of test feeding up to 50 min. The virus was non‐persistent in the feeding insect, but persisted up to 36 hr. in insects starved after the infection feed. Starvation before the infection feed increased the infection rate with infection feeds up to 10 hrs., after which the infection rate with pre‐starved insects declined to the level attained by unstarved insects.
VIRUS DISEASES OF CACAO IN WEST AFRICA
Authors: POSNETTE A. F.
Published: February 2008

Thirteen species in the Coccoidea were tested as vectors of seventeen cacao viruses or virus strains; in addition to the vectors previously recorded, the following species transmitted some of the viruses: Paraputo ritchiei Laing, Phenacocctis sp. H 6418 (? sp.nov.) Pseudococcusbukobensis Laing, Ps. brevipes (Ckll.), Pseudococcus sp. near celt is Strickland, Pseudococcus sp. near gahani Green, Ps. longispinus T.‐T. and Pseudo‐coccus sp. near masakensis James. The viruses transmitted by Ps. longispinus were not usually transmitted by Ferrisia virgata (Ckll.), but there was no other virus‐vector specificity.
BIOASSAY SYSTEMS FOR THE PYRETHRINS
Authors: BLACKITH R. E.
Published: February 2008

The special properties of pyrethrum assays with crawling insects by the film technique lend themselves to the twin cross‐over design, hitherto restricted to assays with graded responses. The conditions under which this design is appropriate, and the treatment of control responses, are discussed. The design is particularly efficient with laboratory cultures of insects with fairly stable tolerance levels, and is also useful with heterogeneous populations collected in the field. Examples of the increased precision afforded are considered. The reversibility of the primary responses of grain weevils to the pyrethrins is also demonstrated.
FIELD METHOD FOR THE DETERMINATION OF THE PARTICLE SIZE OF OIL MISTS
Authors: JONG J. R. de
Published: February 2008

For the control of plant pests, e.g. insects, spraying machines have of late been developed, especially in the U.S.A., with which low dosages of fairly concentrated solutions of toxicants in mineral oils are sprayed. The efficiency of such products is no doubt influenced by the fineness of the spray. An accurate method of determining this fineness was desirable both for the control of the spraying operation and for evaluation of the merits of spraying apparatus.

Knowledge of the average drop size is inadequate in this respect; it is necessary to know the distribution of the oil in droplets of different sizes. A reliable impression of this percentage can be obtained only if a large number of particles are measured. These measurements can be used to plot frequency curves based on number or volume distribution.

A simple microphotographic method is described whereby these measurements can be made both in the laboratory and in the field. The procedure makes it possible to obtain, shortly after spraying, a good idea of the size of the oil drops in the deposit.

An apparatus was designed and constructed to determine the diameter frequency curve and the volume distribution curve of oil droplets deposited in field spraying on coated glass plates.

The method gave characteristic results for field sprayings with the Strawsonizer and a helicopter fitted with a spraying boom and also in the laboratory when using a spraying apparatus with different arrangements of the nozzle.
STATISTICAL ASPECTS OF THE INDEPENDENT JOINT ACTION OF POISONS, PARTICULARLY INSECTICIDES
Authors: HEWLETT P. S. , PLACKETT R. L.
Published: February 2008

Methods are described for discovering whether a mixture of two poisons is as toxic as predicted on the hypothesis of independent joint action. These include X2tests and a procedure for finding the maximum likelihood estimate of the coefficient of correlation in resistance to the poisons. The methods are illustrated using data from insecticidal tests.

In the insecticidal tests, flour beetles, Tribolium castaneum Herbst, were sprayed with, or exposed to films of, different insecticides in solution in Shell oil P 31. The insecticides were pyrethrins, D.D.T., and B.H.C., singly and in pairs. The statistical analysis of the results showed that pyrethrins and D.D.T. could have acted independently both as films and as direct sprays; D.D.T. and B.H.C. could have acted independently as films but not as direct sprays; and B.H.C. and pyrethrins could not have acted independently either as films or as direct sprays.

These findings are discussed, and it is concluded that independent action should be regarded as a special case of a more general type of joint action for which the term dissimilar is proposed. A general method of approach is suggested for the conception and development of hypotheses of the joint action of poisons.
ON THE BACTERIA RESPONSIBLE FOR SOFT ROT IN STORED POTATOES, AND THE REACTION OF THE TUBER TO INVASION BY BACTERIUM CAROTOVORUM (JONES) LEHMANN & NEUMANN
Authors: JONES D. RUDD , DOWSON W. J.
Published: February 2008

Bacterium carotovorum (Jones) Lehmann & Neumann and Pseudomonas syringae van Hall were the only two species of Gram‐negative bacteria isolated from rotting potatoes collected from clamps in England in 1945‐7. Both were found capable of producing a rot under known conditions, and both were isolated on plates of a pectate‐gel medium which is liquefied by these bacteria. Ps. syringae has not been recorded before as causing a rot of stored potatoes. In a slightly different type of rot which was ropy or gassy and often pink in colour, Gram‐positive spore‐forming bacilli were found, generally associated with Bacterium carotovorum. These bacilli proved to be anaerobes–species of Clostridium–one of which, when inoculated together with Bacterium carotovorum, produced a gassy rot pink in colour.

On infection by Bad. carotovorum the tuber reacts to form a barrier of suberized cells, the extent and efficiency of which depend on temperature and relative humidity. Low temperatures and a low humidity favour the formation of the barrier and eventually of periderm; high temperatures favour the multiplication of the bacteria the advance of which is limited by humidities not reaching saturation. Fluctuations of temperature or humidity may promote a succession of barriers.
THE USE OF PROBITS IN COMBINING PERCENTAGE KILLS
Authors: JOLLY G. M.
Published: February 2008

The problem is discussed of how to combine percentage kills obtained in an experiment repeated under different sets of conditions. Treatment effects and their interaction with replicates are defined in terms of probits, and, assuming the absence of such interaction, a method is evolved of finding maximum likelihood estimates of the mean treatment differences. An example is used to illustrate details of the method. The merits of the logit and angular transformations applied to the same type of data are also discussed.
THE EFFECT OF ASSOCIATED SOIL MICROFLORA ON FUSARIUM UDUM BUTL., THE FUNGUS CAUSING WILT OF PIGEON‐PEA (CAJANUS CAJAN (L.) MILLSP.)
Authors: VASUDEVA R. S. , ROY T. C.
Published: February 2008

Inoculation with Fusarium udum Butl. produced more wilt of pigeon‐pea in sterilized than in unsterilized soils at the same pH. From unsterilized soils with low disease incidence, nine fungi, Bacillus subtilis and an Actinomyces were isolated. The number of isolations of a particular organism varied from month to month during the cropping season of pigeon‐pea in Delhi. Interaction of Fusarium udum and other organisms isolated was studied. Aspergillus niger and A. terreus secreted inhibitory substances in potato‐dextrose broth: Bacillus subtilis inhibited growth on solid medium and also produced a toxic substance in potato‐dextrose broth. The nature of the medium employed and period of growth were important factors in the production of the inhibitory principle, which is thermostable. The low incidence of pigeon‐pea wilt in unsterilized soils may result from the inhibitory activity of the associated microflora in the soil.
THE SUBEPIDERMAL FUNGI OF CEREAL GRAINS
Authors: HYDE M. B.
Published: February 2008

Examination of samples received in 1947 and 1948 showed that a subepidermal mycelium occurred in normal wheat grains from almost all the wheat‐growing areas of the world. The amount of mycelium varied widely: there are indications that the degree of infection is dependent on the atmospheric humidity during the ripening of the grain. No subepidermal mycelium was found in wheat grains from some crops grown under irrigation.
THE IDENTITY OF THE SWEDE MIDGE, WITH NOTES ON ITS BIOLOGY
Authors: BARNES H. F.
Published: February 2008

A brief historical summary is given of the literature concerning Contarinia nasturtii Kieffer, C. torquens de Meijere and C. geisenheyneri Riibsaamen, three gall midges (Cecidomyidae) which have been associated respectively with leaf damage on Brassica spp. in England, identical malformation on the Continent and swollen and closed flowers of Brassica spp. in Europe.

Following the discovery in England of the true Contarinia nasturtii causing swollen and closed flowers oiRorippa amphibia, preliminary experiments have shown that midges from this source will also cause similar damage to swede flowers and that they are the same species as those attacking R. amphibia blossom in the Netherlands.

Further preliminary experiments have shown that swede midge derived from rape leaf axils will also cause identical damage to radish flowers in addition to breeding successfully on the leaves of turnip, swede, cabbage and radish.

Male midges derived from Rorippa blossom have been mated with females from rape leaf axils, and their offspring have been reared on Rorippa flowers and on turnip leaves.

This biological evidence confirms the previous supposition based on morphological grounds that the swede midge is Contarinia nasturtii Kieffer and will cause either flower or leaf damage. Consequently, C. torquens de Meijere and C. geisenheyneri Riibsaamen must remain synonyms.

The shortest time for a generation (from parent to first offspring midge) to develop was 24–39 days in an unheated open glasshouse during June‐July in 1949 at Harpenden. Under the same conditions, the shortest time for the next generation from late July to August was 29–32 days. C. nasturtii is the first Contarinia species in which unisexual families have been discovered.
OBSERVATIONS ON THE BIOLOGY OF CORYMBITES CUPREUS F. (COLEOPTERA, ELATERIDAE)
Authors: EDWARDS E. E. , EVANS J. R.
Published: February 2008

The life history of Corymbites cupreus F. is described, and its economic importance is assessed from field observations and laboratory experiments. The females are on the wing in May and June, egg‐laying takes place in June and the incubation period is about 34 days. The larval stage probably occupies 5 years under field conditions and pupation occurs towards the end of July or beginning of August. The imagines emerge in about 21 days, but they do not always remain in their earthen pupal cells until the following spring as do several other Elaterid species. The larvae feed principally on the roots and underground stems of plants, but they can exist on decayed organic matter in the soil. Individually they are far more injurious to potatoes, wheat, oats, barley and other cultivated crops than those of either Agriotes spp. or Athous niger, but because they are restricted to comparatively high altitudes, they are seldom pests of major importance. Birds and cara‐bid larvae readily feed on them and they are also subject to attack by a hymeno‐pteran parasite and the fungi, Metarrhizium anisopliae (Metsch) Sor. and Synglio‐cladium cleoni (Wize) Petch. All attempts to obtain control of the larvae by the use of these fungi failed.
THE STRUCTURE AND FORMATION OF THE EGG OF THE FRUIT TREE RED SPIDER MITE, METATETRANYCHUS ULMI KOCH
Authors: BEAMENT J. W. L.
Published: February 2008

The summer egg, and the overwintering diapausing egg of the fruit tree red spider mite, Metatetranychus ulmi Koch are described in detail; there is no reliable factor by which these two may be distinguished on inspection.

Both types of egg have a common basic shell structure, consisting of an outer thick wax layer of very high melting point and a cement layer of oil and protein which attaches the wax to the underlying ‘shell’ layer enclosing the living material. The shell layer is extremely resistant to penetration and to attack by chemicals or solvents; it appears to be composed of a material similar to keratin. This layer is formed in the ovary, towards the end of yolk accumulation. The egg is apparently fertilized precociously, and there are no associated nurse or follicle cells; only one egg is matured at a time.

The female reproductive system is described in some detail; the egg receives its shell layer in the simple sac‐like ovary, and then passes into a glandular ovipositing pouch which is evaginated through the genital aperture at oviposition. The shell layer makes contact with the substrate, and the pouch secretes the cement over the rest of the shell layer so that the egg adheres to the substrate by a ring of cement around the base. The outer wax is then secreted over the cement, and it also leaves large hole at the base of the egg, bordered by the cement.

The female leaves the egg by rotating into an almost vertical position. In this process the ovipositing pouch is drawn off the egg, and withdrawn into the female; consequently, the wax, which is plastic when first secreted, is drawn up into the characteristic spike which surmounts the egg. The spike is of no further physiological significance to the egg.

Owing to the hole in the egg‐coverings at the base, the shell structure is not waterproof. The developing organism waterproofs the summer egg by secreting wax layer into the inside of the shell about 6 hr. before laying, previous to which the egg will only survive in humidities greater than 85 yo R.H. After waterproofing, the egg readily develops in humidities of 30 yo R.H.

The waterproofing wax has a transition point of 68°C. The shell of the winter egg is similarly composed and waterproofed, but winter eggs are held up in the female until a later stage of embryonic development, so that they are waterproofed when they are deposited on the bark.

Some discussion is made of the importance of leaf and bark humidities in relation to the different times at which summer and winter eggs are waterproofed.
INVESTIGATIONS ON THE SYSTEMIC INSECTICIDAL ACTION OF SODIUM FLUOROACETATE AND OF THREE PHOSPHORUS COMPOUNDS ON APHIS FABAE SCOP.
Authors: DAVID W. A. L. , GARDINER B. O. C.
Published: February 2008

The general insecticidal properties of bis (bis‐dimethylamino phosphonous) anhydride (anhydride), bis (dimethylamino) fluorophosphine oxide (oxide), diethyl paranitro‐phenyl phosphate (E600), and sodium fluoroacetate (acetate) are described. All are toxic to aphids when infested plants are dipped in solutions. Although this is thought to be a contact action the possibility that the materials are first absorbed by the leaves and that the aphids are killed by imbibing toxic sap is not excluded. The order of decreasing toxicity by dipping is E 600 > acetate > anhydride = oxide. At the lowest concentration giving a complete kill of aphids, the anhydride is the most persistently effective of the four compounds. E600 is the most phytotoxic compound.

When applied to the roots the order of decreasing toxicity is acetate > oxide > anhydride > E600 in sand and soil, and acetate > oxide > anhydride = E600 in culture solution. The anhydride and acetate are more persistent in the plants than the oxide and E600. The margin of safety between insecticidal dosage and phytocidal dosage is appreciably larger with the acetate than with the other three compounds.

When equal dosages are administered to plants by the cut tap root technique the order of decreasing toxicity to aphids is seen to be acetate > oxide > E600 > anhydride. All compounds, except possibly E600, appear to be absorbed by the intact roots of the plants.

Systemic insecticidal action following application made to the leaves of the broad bean is easy to demonstrate with the acetate, demonstrable with difficulty with the anhydride and not at all with E600 and the oxide.

Only the oxide is sufficiently volatile to kill insects by a fumigant effect either as the pure substance or after absorption into the plant. Plants treated with it give off a toxic vapour which may be collected by condensation and shown to be systemically active. The material concerned is presumed to be the unchanged oxide.

Sodium fluoroacetate is an extremely effective systemic insecticide whether applied to the leaves or the roots of the broad bean. It is apparently not phytotoxic at several times the concentration necessary for insecticidal action but may prove to be too generally toxic or persistent for practical use.
MICROBIOLOGICAL CONTROL OF BOTRYTIS CINEREA PERS. II. ANTAGONISM BY FUNGI AND ACTINOMYCETES
Authors: NEWHOOK F. J.
Published: February 2008

Botrytis cinerea has been inhibited by pure cultures of many fungi and actinomycetes on lettuce extract agar and by these and by the mixed flora of soil suspensions on wounded detached lettuce leaves and on wounded leaves of living plants under conditions of high moisture and humidity. Control was exhibited in many cases at 4° C. though this was less marked than that at 15–25° C. Most fungal activity raised the pH to 7.8–8‐4 but the use of buffered media showed that most species were antagonistic because of the production of antibiotic substances independently of the high pH. Prior inoculation with soil suspensions was necessary to obtain control of B. cinerea on wounded leaves of living plants although such suspensions and several fungi had given control on simultaneous inoculation with B. cinerea on wounded detached leaves.

Saprophytic antagonism is responsible for some of the natural control of B. cinerea in the field. The amount of available moisture, which in turn is affected by the relative position of the dead tissue on the plant as well as by climatic factors, greatly influences the establishment and growth of B. cinerea and the amount of microbiological antagonism likely to be exerted.

Three‐weekly applications of suspensions of Cephalosporium sp., Fusarium flocciferum and Phoma eupyrena failed to give a significant increase in the final survival of lettuce in the field. On the other hand, 3‐weekly applications of a dust containing tetrachloronitrobenzene gave a highly significant increase in survival, efficiency being greatly increased by the use of cloches.

Earthing up induces early rotting of the petioles of ageing leaves and so probably prevents entry of Botrytis cinerea into the stem. Increased survival in hollows as compared with ridges is apparently due largely to this earthing up effect and possibly also to increased microbiological activity on dead tissue under the wetter conditions.

B. cinerea can enter the soil by invasion down the root systems of attacked plants and can attack other root systems in contact with these. Furthermore it has been recovered from the soil over 6 weeks after the disappearance of infected plants from above ground, despite the antagonism shown to be exerted by soil organisms.

Control of B. cinerea on Epilobium sp., Ranunculus repens, R. flammula and Lamium amplexicaule was obtained by prior inoculation of killed tissue with soil suspensions.
THE CONFIRMATION OF THE VARIETY FABAE KEAY OF SCLEROTINIA TRIFOLIORUM ERIKSSON
Authors: LOVELESS A. R.
Published: February 2008

There is confusion as to whether the Sclerotinia on Vicia faba is a normal strain of Sclerotinia trifoliorum as found on clover and related legumes or a distinct variety (var. fabae). Pathologically the two fungi appear to be the same, and field observations indicate that beans in the rotation may aggravate the incidence of clover rot. A re‐investigation of the morphology of the two fungi is made to assess the status of var. fabae.

The two fungi could not be distinguished by apothecial characters or cultural behaviour. Ascospore measurements confirm the existence of S. trifoliorum var. fabae, although 5. trifoliorum proper also occurs on beans. Var. fabae has not been found on any legume besides beans. Isolates from trefoil and sainfoin agree in spore size with S. trifoliorum on clover.

When isolates of S. trifoliorum are co‐inoculated on the same Petri plate, they either do not react, or react to form a ‘demarcation line’. Although a demarcation line is assumed to imply a genetic difference, non‐reaction does not necessarily imply genetic identity. Non‐reaction and the formation of a demarcation line also occur when var. fabae strains are co‐inoculated together. When an isolate of S. trifoliorum is co‐inoculated with an isolate of S. trifoliorum var. fabae an ‘incompatibility line’ is formed. Use can be made of this fact in identification.

On the basis of co‐inoculations 5. trifoliorum and S. trifoliorum var. fabae are both shown to constitute a diverse range of biotypes. Segregation of biotypes in the ascus as a result of heterokaryosis in the ascus‐initial is demonstrated. The view is expressed that heterokaryosis is the mechanism underlying the production of new biotypes.
A COMPARISON OF THE GROWTHS OF WILD AND OF CULTIVATED OATS IN MANGANESE‐DEFICIENT SOILS
Authors: THURSTON JOAN M.
Published: February 2008

Two species of wild oats, Avena fatua and A. ludoviciana, and two varieties of cultivated oats for comparison, were grown to maturity in pots of manganese‐deficient soil with and without added manganese.

A. ludoviciana showed different leaf symptoms of manganese deficiency from A. fatua and the cultivated varieties. In other respects wild and cultivated oats were similar in their responses to the level of manganese supply, though differences were observed in the severity of the effects. These are summarized in Table 6. The relative susceptibility to manganese deficiency of the wild and cultivated oats differed according to the effect considered. The total dry weight at harvest is an integration of all the preceding effects on growth and is therefore presumably the best single criterion for determining susceptibility to manganese deficiency. On the basis of per cent loss of total dry weight at harvest due to lack of manganese, A. fatua is judged less susceptible and A. ludoviciana more susceptible than the two cultivated varieties and no distinction can be made between the latter.

The most interesting differences between wild and cultivated oats in response to the level of manganese supply occurred in seed production. Manganese‐deficient wild oats showed a smaller reduction in the number of seeds formed but a greater reduction in the size and manganese content of individual seeds than the cultivated varieties.

Manganese deficiency lowered the percentage of viable seeds and the percentage of dormant seeds produced by both A. fatua and A. ludoviciana.
THE ACTION OF MERCURY AS A SOIL FUNGICIDE
Authors: BOOER J. R.
Published: February 2008

Metallic mercury and mercury compounds in the soil retard the growth of plants. The development of mosses and lichens is inhibited, and experimental evidence shows that the growth of toadstools on turf and the activity of ascomycetes is retarded by mercury. In vitro, mercury has no fungicidal action but the rate of growth of hyphae is reduced by mercury vapour.

The lack of fungicidal properties of mercury and its good performance in controlling certain soil‐borne diseases are reconciled by assuming that a differential retardation disturbs the relationships necessary for infection. This assumption is supported by diagrams which treat the rates of growth of the parasite and the host as population characteristics normally distributed.
THE INFLUENCE OF DENSITY OF PLANT POPULATION ON THE INCIDENCE OF YELLOWS IN SUGAR‐BEET CROPS
Authors: BLENCOWE J. W. , TINSLEY T. W.
Published: February 2008

The incidence of yellows virus in sugar‐beet crops was reduced by increasing the density of plant population. The variations in plant population were obtained by differences in row width and singling distance. The differences in susceptibility between large‐ and small‐topped varieties, and between early and late sown crops, could not be attributed solely to differences in plant size. It is suggested that close planting would increase the yields of sugar beet and reduce the losses caused by yellows virus. Roguing infected plants during the early part of the growing season did not reduce the incidence of disease.
SEROLOGICALLY RELATED STRAINS OF POTATO VIRUS Y THAT ARE NOT MUTUALLY ANTAGONISTIC IN PLANTS
Authors: BAWDEN F. C. , KASSANIS B.
Published: February 2008

Tobacco veinal necrosis virus is serologically related to potato viruses Y and C. It does not protect tobacco, Nicotiana glutinosa, or potato plants from infection by them, and tobacco and N. glutinosa plants infected with either virus Y or C are still susceptible to it. There is some evidence that it does not multiply normally in potato plants infected with virus Y and that it is sometimes suppressed in such plants.

The possession of antigenic groups in common with viruses Y and C is considered to justify identifying tobacco veinal necrosis virus as a strain of virus Y, and to be of greater taxonomic significance than failure to protect plants against other strains. A further difference from other strains is that it is more virulent towards tobacco than towards potato.
WING COLORATION AS A MEANS OF DETERMINING THE AGE OF THE COLORADO BEETLE (LEPTINOTARSA DECEMLINEATA SAY)
Authors: DUNN E.
Published: February 2008

The age of Colorado beetles can be determined, for at least 20–23 days after emergence, by means of the colour of the membranous hind‐wings. The colour changes are described and a series of colour reproductions illustrate the appearance of a selection of wings during the first 25 days after emergence from the soil.
STUDIES ON THE MECHANISM OF INSECTICIDAL ACTION OF ORGANO‐PHOSPHORUS COMPOUNDS WITH PARTICULAR REFERENCE TO THEIR ANTIESTERASE ACTIVITY
Authors: LORD K. A. , POTTER C.
Published: February 2008

The preparation of an extract of the mealworm larvae, Tenebrio molitor L. which hydrolyses ethyl butyrate and o‐nitrophenyl acetate, but not acetylcholine, is described. The inhibition of this esterase by TEPP‐containing materials and parathion was determined.

An enzyme that hydrolysed o‐nitrophenyl acetate and was inhibited by a TEPP‐containing material was demonstrated in the five other insect species used.

The relative toxicities as contact insecticides to adult Tribolium castaneum Hbst. of ten samples of TEPP‐containing materials were compared with their relative activities as esterase inhibitors. There was not an exact quantitative correlation between TEPP content estimated chemically, insecticidal activity and anti‐esterase activity; but the correlation was sufficient to suggest interdependence of these factors.

Eggs of Diataraxia oleracea L. and Ephestia kühniella Zell, were shown to contain an enzyme that hydrolysed o‐nitrophenyl acetate and was inhibited by the TEPP‐containing materials. This enzyme was present in eggs less than 24 hr. old, i.e. before there was any visible signs of development. The TEPP was shown to be toxic to these eggs and in high concentrations kills at an early stage of development before differentiation of the nervous system. This, in conjunction with the other evidence, suggests that esterases other than the choline‐esterase of the nervous system are important when considering the toxic action of these compounds.

Comparison of the anti‐esterase activity and toxicity of parathion and TEPP‐containing materials as insecticides showed that although the TEPP materials were the more potent enzyme inhibitors, parathion was the more potent contact insecticide to five species of insects. This appears to be due to the relative instability of TEPP. The study of the rates of action of the two poisons applied at different concentrations supports this view.
THE PENETRATION OF THE INSECT CUTICLE BY ISOMERS OF BENZENE HEXACHLORIDE
Authors: ARMSTRONG G. , BRADBURY F. R. , STANDEN H.
Published: February 2008

The penetration of the α‐, β‐, γ‐ and δ‐isomers of benzene hexachloride through the insect cuticle has been studied by a micro‐colorimetric technique.

Grain weevils were exposed for varying periods to deposits of pure isomers of benzene hexachloride on filter‐paper. The amounts of each isomer picked up by the insects were determined as two fractions, one ‘outside’ representing that which could be removed by cold methanol washing, and the other ‘inside’ recovered after decomposing the insects with nitric acid.

The results show that the amounts of each isomer taken up by the insects are in the approximate ratio of their solubilities in hydrocarbon solvents, and that the y‐isomer penetrates through the outer layers of the insect integument much more rapidly than the other three isomers tested.

On the basis of these results it is concluded: (i) that the first stage of pick‐up of insecticide by the insects is simple solution of the insecticide in the outer waxy covering of the epicuticle; and (ii) that structural effects play an important part in the penetration through the insect cuticle as well as in toxic effects at the site of action.
PARTICLE SIZE OF INSECTICIDAL SUSPENSIONS AND THEIR CONTACT TOXICITY III. TEMPERATURE COEFFICIENTS AND TESTS BY INJECTION
Authors: McIntosh A. H.
Published: February 2008

Aqueous DDT suspensions containing particles of different sizes gave different temperature coefficients of mortality in dipping tests against adult Oryzaephilus surinamensis and Tribolium castaneum. In the range 12–30°C., colloidal DDT showed a large negative coefficient, but the coefficient for a suspension of DDT crystals of 400μ was smaller (T. castaneum) or negligible (O. surinamensis). Thus, although a suspension of crystalline DDT was more toxic than colloidal DDT to warm insects, it was less toxic than the colloid to cool insects.

A test was made of rotenone suspensions against adult milkweed bugs (Oncopeltus fasciatus Dall.) by application of measured droplets under the wings. Colloidal rotenone was more toxic than a crystalline suspension. Milkweed bugs could not be killed in this way by DDT suspensions.

Tests were also made by injecting suspensions of rotenone, DDT and its fluorine analogue (DFDT) into milkweed bugs. A suspension of rotenone crystals was equitoxic with colloidal rotenone against insects kept for 3 days at 27°C. after treatment. The same was true of crystalline and colloidal DDT suspensions. If the bugs were kept at 10°C., colloidal rotenone was much more toxic than crystalline rotenone 2 days after treatment. But if the insects were kept for about 3 weeks and inspected at intervals, the first apparent difference in toxicity grew smaller, and in the end it nearly disappeared. With DDT the time for this to occur was about 10 days; and suspensions of colloidal and crystalline DFDT were equitoxic after only 2 days, even at 10°C.

In the application test, the difference between colloidal and crystalline rotenone was a real difference in toxicity. It did not disappear with the lapse of time; but in the injection tests the two forms of each poison differed only in speed of action, and not in ultimate toxicity.
AN IMPROVED SUCTION TRAP FOR INSECTS
Authors: TAYLOR L. R.
Published: February 2008

A suction trap for airborne insects, which automatically segregates the catch at pre‐set intervals and standardizes the samples for volume of air, has been previously described by Johnson. Experience with this trap has shown that certain structural improvements were advisable. These have now been incorporated. Constructional details are given and the design of larger traps discussed. It is shown that aphids and lacewings taken are in good condition.
A STUDY OF THE BIOLOGY AND CONTROL OF ANISOPUS FENESTRALIS (SCOPOLI, 1763), A FLY ASSOCIATED WITH SEWAGE FILTERS
Authors: HAWKES H. A.
Published: February 2008

In work on the control of the sewage fly Anisopus fenestralis (Scopoli, 1763), it was shown that the larval phase was considerably lengthened by limiting the food supplied. The effects of food supply and temperature are considered in relation to the incidence of the adult fly in the filters. The assessment of the fly population of sewage filters by tray traps, as previously used by other workers, was investigated. Both light and temperature were found to affect the number of A. fenestralis entering the trays: it is concluded that although the trays do not accurately assess the A. fenestralis population of a bed, nor measure the rate of emergence from the bed, they are of value in assessing the relative effect of different control measures. In the filters the period of maximum abundance was during the spring, followed by a period of reduced numbers throughout the summer, with a recovery in the autumn giving relatively high numbers throughout the winter. Emergence of A. fenestralis from the filters is influenced by climatic factors, especially temperature and light; a diurnal variation in the rate of emergence was also observed. Because of this effect of temperature on emergence, the flies were only present above the filters in the warmer periods of the year; and because of the reduced numbers in the filters in the summer, the flies were only abundant above the beds during the spring and early summer and in the autumn. BHC applied as a water‐dispersible powder was more effective than in the form of an emulsion. It was also most effective when used against the larval phase.
SOME INTERRELATIONSHIPS BETWEEN MANGANESE, MOLYBDENUM AND VANADIUM IN THE NUTRITION OF SOYBEAN, FLAX AND OATS
Authors: WARINGTON KATHERINE
Published: February 2008

Soybean and flax were grown in nutrient solutions containing high and low levels of molybdenum and vanadium, in combination with toxic (10–25 p.p.m.) and non‐toxic (1 p.p.m.) manganese. Molybdenum (20 and to a less extent 10 p.p.m.) intensified the chlorosis induced by manganese excess, though these concentrations were harmless in the presence of 1 p.p.m. Mn. Vanadium (= 1.0, 5 and 10 p.p.m. Mo) counteracted some of the symptoms of manganese toxicity, but the two higher rates were harmful to growth irrespective of the manganese supply. Toxic concentrations of vanadium at first deepened the green colour of the shoot, though apical iron‐deficiency chlorosis was generally induced later. Low molybdenum (0.1 p.p.m.) or equivalent vanadium had no influence on growth or iron nutrition at either level of manganese. Visual differences were corroborated by changes in the nitrogen, phosphorus and iron contents of the plants. There was no evidence of replaceability of molybdenum by vanadium.

Oats were grown in nutrient solutions containing various combinations of manganese (nil–400 p.p.m.) and molybdenum (nil–20 p.p.m.). The appearance of manganese‐deficiency symptoms was not affected by the quantity of molybdenum provided, and the manganese and molybdenum contents of the leaves were mutually independent of the quantity of each element supplied.
OBSERVATIONS ON THE BIOLOGY OF CLOVER ROT
Authors: LOVELESS A. R.
Published: February 2008

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.
THE SPREAD OF LETTUCE MOSAIC IN THE FIELD
Authors: BROADBENT L. , TINSLEY T. W. , BUDDIN W. , ROBERTS E. T.
Published: February 2008

The epidemiology of lettuce mosaic was studied on two farms in Buckinghamshire during 1947–50. Two patterns of spread were obvious on Farm A during 1947–8: (1) spread within a crop from sources initiated by seed‐borne virus; and (2) spread into a crop from nearby infected old plants. The first type caused serious losses only when aphids were unusually numerous and the incidence of seed‐borne infection was high; serious losses more often resulted from the second type. Winter crops usually suffered severely, and they initiated a cycle of infection in the spring which continued from crop to crop throughout the year when aphids were sufficiently numerous. Spread from crop to crop was much reduced during 1949–50 by planting or drilling lettuce in large blocks, well separated from each other, and by omitting a winter crop. Killing the infesting aphids with an insecticide did not prevent the introduction of virus from nearby diseased crops. The insecticidal treatment of old diseased and aphid‐infested crops (but before alatae are produced) is recommended.

More diseased plants often occurred near hedges, woods, trees or buildings than in the open field, presumably because such barriers halted flying aphids.

Three species of aphids were common on lettuce: Nasonovia ribis‐nigri (Mosley), which infests the heart leaves; and Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer), which infest the outer leaves. M. euphorbiae and M. persicae are vectors of lettuce mosaic, but the former is less effective than M. persicae which, although rarely as numerous as the other two species, is the most important vector. All three species overwintered on lettuce, and migrated from the winter crops during April–May.

One obvious need to control lettuce mosaic is the production of virus‐free seed. Without this, however, the disease can be ameliorated by adopting these measures whenever practicable: lettuce crops should be planted or drilled in large blocks, well separated from each other; diseased crops and crop‐remains should be destroyed as soon as possible; winter crops should be treated with an insecticide in late November, and insecticides should be used to prevent the production of large aphid populations, especially on old crops.
THE SPREAD OF BEET YELLOWS AND BEET MOSAIC VIRUSES IN THE SUGAR‐BEET ROOT CROP I. FIELD OBSERVATIONS ON THE VIRUS DISEASES OF SUGAR BEET AND THEIR VECTORS MYZUS PERSICAE SULZ. AND APHIS FABAE KOCH
Authors: WATSON MARION A. , HULL R. , BLENCOWE J. W. , HAMLYN BRENDA M. G.
Published: February 2008

A survey of aphids and virus diseases of sugar‐beet root crops in eastern England was made between 1940 and 1948. Prior to 1943 the observations were made on fertilizer experiments; from 1943 onwards they were made on commercial fields selected for position in relation to beet and mangold seed crops. The incidence of beet yellows increased with increasing numbers of Myzus persicae, but not of Aphis fabae. The relation with M. persicae was sufficiently close to suggest that it is the most important, possibly the only important, vector of beet yellows virus. Beet mosaic virus also increased with increasing numbers of M. persicae, but the relation was not close enough to exclude the possibility of other vectors.

Numbers of A. fabae on sugar beet were slightly, but consistently, depressed by the use of salt as a fertilizer. Other fertilizers had variable effects. Neither aphids nor virus are likely to be greatly affected by fertilizers.

Beet yellows is most prevalent in areas where seed crops are grown, but within these areas nearness to individual seed crops did not appear to increase its incidence. M. persicae were more numerous on sugar beet in seed‐crop areas than elsewhere, and this alone might account for the prevalence of yellows. Beet mosaic virus is more closely associated with seed crops than is beet yellows. It is most prevalent near to seed crops within the seed‐crop areas.
SOME EXPERIMENTS AND FIELD OBSERVATIONS ON THE GERMINATION OF WILD OAT (AVENA FATUA AND A. LUDOVICIANA) SEEDS IN SOIL AND THE EMERGENCE OF SEEDLINGS
Authors: THURSTON JOAN M.
Published: February 2008

The distinguishing characters of Avena fatua and A. ludoviciana are described.

Pot experiments and field observations showed that most seeds of A. fatua germinated in spring and a few in autumn; hardly any germinated in summer or winter. Seeds of A. ludoviciana germinated in winter only. The greatest depth of sowing from which seedlings of either species reached the surface was 9 in., but seedlings from this depth were weak and yellow when they first appeared. A. ludoviciana gave more and sturdier seedlings than A. fatua from 6 and 9 in. There was no evidence of induced dormancy in seeds of A. fatua buried at depths down to 20 in. Germination of this species was hastened by monthly cultivation of the soil. The maximum survival of A. fatua was 3 years in pots and slightly longer in the field; seeds of A. ludoviciana in pots survived only 2 years. The two or three seeds of each spikelet of A. ludoviciana germinated in turn, starting with the largest, but the interval between germination of successive seeds varied.

Seedlings from freshly sown seeds of both species were more vigorous than seedlings from seeds which had been buried for a year or more. Germination and subsequent growth of both species took place in soil of pH 4.5 to 7.0 approx.
OBSERVATIONS ON BROWN ROT (SCLEROTINIA FRUCTIGENA) OF APPLES IN RELATION TO INJURY CAUSED BY EARWIGS (FORFICULA AURICULARIA)
Authors: CROXALL H. E. , COLLINGWOOD C. A. , JENKINS J. E. E.
Published: February 2008

Observations in West Midlands orchards in 1947–50 on the apple varieties Cox's Orange Pippin and Laxton's Superb showed that brown rot was often associated with shallow holes in the fruit. Laboratory experiments with undamaged apples proved that earwigs (Forficula auricularia) could cause this type of injury.

Bands of sacking soaked in BHC placed around trunks of Laxton's Superb trees in 1949 and 1950 trapped many earwigs; less brown rot occurred in the banded than on control trees. A survey of picked fruit in 1950 showed close correlation between degree of earwig damage and amount of brown rot.

Earwig damage was appreciable in fruit from ten out of thirteen grass orchards, but was negligible in fruit from nine arable plantations.
THE INFLUENCE OF NOSEMA APIS ON THE LARVAL HONEYBEE
Authors: HASSANEIN M. H.
Published: February 2008

In experiments on the infection of bee larvae with Nosema apis, the parasitic spores did not germinate and infected adults did not result. In hives of bees infected with N. apis about 10–20% of the eggs laid did not complete their development probably because of inadequate care and feeding.