摘要:

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 genusLumbricus.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.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07391.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

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 increas

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07392.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Acid and alkaline soils, both alone and mixed with 2 % of D.D.T. or 2 % of benzene hexa‐chloride (mixed isomers, containing 10% of the γ‐isomer) have been exposed outdoors or subjected to controlled leaching in the laboratory. Residual insecticide has been estimated at intervals by a method involving dehydrohalogenation, and determinations have also been made of chloride content of soil, chloride leached and pH.Results showed that both D.D.T. and benzene hexachloride were very stable in the soils, about 95 % of the former and 80 % of the latter being recoverable after 18 months. Very little chloride was leached during this period. The residual insecticide exhibited marked toxicity towards woodlice.Eighteen months after treatment the benzene hexachloride soils prevented root growth of germinating seeds, while germination and early growth were normal in the D.D.T. soils. This harmful effect of the residual benzene hexachloride was still apparent when 1 part of the treated soil was mixed with 99 parts of the control soil (representing a concentration of less than 0–002 % of the γ

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07393.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

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 sanborniandOryzaephilus 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 a

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07394.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07395.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

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 weevilCalandra 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:1Toxicity in homologous series decreases steadily from the first member as the chain length increases, finally disappearing.2Halogen 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.3Hydroxyl substitution markedly decreases ‘physical’ toxicity.4The 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 alk

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07396.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

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.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07397.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

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 onMyzus persicaeare examined, to obtain information on the. type of variation in aphid numbers to be expected.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07398.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Seedlings were treated with cell‐free filtrates of cultures ofBad. fascians, Bad. tumefaciensand 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 byBad. fascianswas examined and compared with that of other bacterial species. It is suggested that seedlings infected byBad. fasciansproduce ‘leafy‐galls’ or ‘dwarfing’ owing to a disturbance of the normal auxin content or distribution

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07399.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY

摘要:

Field experiments, using contaminated seed, have been carried out from 1941 to 1947 to study the reaction of a wide range of both fibre and oil varieties ofLinum usitatissimumto attack byPolyspora LiniLaff.,Colletotrichum linicolaPethybr.&Laff.,Phomasp. andMelampsora Lini(Ehrenb.) LéV. The tests made with Colletotrichum linicola were supplemented by direct inoculation experiments with young seedlings grown under greenhouse or laboratory conditions.None of the varieties tested proved to be immune to attack byPolyspora Lini, Colletotrichum linicola or Phomasp. Herkules, Concurrent, Hindi, La Plata, Saginaw x Ottawa 770 B and Winona x Ottawa 770 B were resistant to the stem‐break and browning phases of attack byPolyspora Lini; Bison, Hindi and La Plata were resistant to attacks byColletotrichum linicola, while Hindi and La Plata showed some resistance toPhomasp. Immunity or a ‘high’ measure of resistance to attack byMelampsora Liniwas exhibited by Formosa, Stakhanovets, Textilshchik, U.S.S.R. No. 2 (ex Dugejheshchya), Wada, Argentine Selection (C.I. 112), Baladi, Bolley Golden (C.I. 644), Bombay (C.I. 42), Hindi, Italia Roma (C.I. 1005–2), J.W.S. (C.I. 708–1), Koto (C.I. 872), Kenya (C.I. 709–1), La Plata, Newland (C.I. 188), Ottawa 770B (C.I. 355), Pale Blue Crimped (C.I. 647), Tammes Pale Blue (C.I. 333–1), Williston Golden (C.I. 25–1) and C.I. 836.All varieties did not show the same reactions to stem‐break as to the browning phase of attack byPolyspora Liniand similar differences were noted in the case of the uredospore and teleutospore stages ofMelampsora Lini.In certain varieties the stems showed a greater resistance to attack byPolyspora Lini or Melampsora Linithan the leaves.Seeds of all varieties tested in the field experiments became heavily attacked withPolyspora Lini(except in La Plata),Colletotrichum li

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1948.tb07400.x

出版商:Blackwell Publishing Ltd    

年代:1948

数据来源: WILEY