摘要:

The summer egg, and the overwintering diapausing egg of the fruit tree red spider mite,Metatetranychus ulmiKoch 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 In this process the ovipositing pouch is drawn off the egg, and withdrawn into the female; consequently, the wax, which is plastic when first secreted, is drawn up into the characteristic spike which surmounts the egg.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 wate

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07787.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

The feeding preferences and comparative fecundity of laboratory‐bred, alienicolae alatae ofAphis fabaewere investigated in small leaf cages on spindle and sugar beet leaves, representing a winter and a summer host respectively, both in pots in the greenhouse and while growing naturally outdoors.The aphids' readiness to stay and feed, and their average reproduction rate, both varied between leaves of different ages and kinds, and there was evidence of true fecundity differences among aphids feeding on different leaves. As a general rule, readiness to settle and reproduction rate varied together in the same sense, but they did so significantly less often in comparisons between leaves of different kinds, spindle and beet, than in comparisons between leaves of one kind only. Among the leaves on the same kind of plant, the aphids preferred to feed and reproduced faster, on the whole, on young and early senescent leaves than on mature ones. To a limited extent, this rule seemed to govern also the aphids' comparative readiness to settle and reproduce, as between leaves of the two different kinds of plant. Allowing for age‐differences among the leaves, the aphids settled and reproduced better on spindle than on beet leaves. Since the aphids used were alienicolae, this tends to confirm the usual designation of the winter host as primary and the summer hosts as secondary, for a given aphid species.These findings form the basis of a dual discrimination theory of host selection, which assumes that aphids respond behaviourally to at least two main classes of leaf property: one associated with the age of the leaf and the other with the kind of plant. It is suggested that in nature these two sensory requirements of the aphids may be essentially contradictory, and that the shifting patterns of aphid distribution among leaves and plants may depend on the shifting distribution of leaves offering a satisfactory compromise between them. The phenomenon of host alternation is considered in the light of the dual discrimination theory, as a particular instance of a shifting distribution‐pattern probably connected with the alternation of the seasons of active growth and senescence in the winter and summer host p

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07788.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

A study of free infestations ofAphis fabaeScop. on the leaves of its host plants, spindle and sugar beet, showed that the clustered distribution of the aphids within the boundaries of each leaf was not a matter of chance but involved active aggregation. Experiments in small leaf cages showed that aggregation could take place independently of any differences between portions of a leaf, being brought about by truly gregarious reactions between the aphids. Experiments in which walking aphids were made to encounter other live or dummy aphids fixed to leaves, showed that the gregarious reactions were of at least two kinds. The aphids both probed more often, and remained inserted for longer, near other aphids than apart from them.It appears that the unequal distribution of aphids among the leaves of a plant is due primarily to intrinsic differences between leaves, but is aided by gregariousness, while the aggregations observed on leaves are due primarily to gregariousness, and only secondarily to differences between portions of a leaf. It is suggested that the primary function of gregariousness is to concentrate the aphids on to the best feeding sites, both among the parts of a plant, and among whole plants; that is, it acts as an aid in host selection, even with aphids which do not aggregate so compactly asA. fabae.The functions of compact aggregation and other specialized forms of gregarious behaviour remain to be discovered.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07789.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

For about twenty‐five years a fairly widespread disease of bulbous iris has been known, the cause of which has always been attributed to a biologic race of the stem eelwormDitylenchus dipsaci(Kühn, 1857), Filipjev, 1936.Thorne (1945) showed that the nematode causing rot in potato tubers is different fromD. dipsaciand named itD. destructor.This nematode has since been reported fromMentha arvensisL. by Hurst (1948) and fromSonchus arvensisL. by Goodey&Goodey (1949).Examination of nematodes from diseased iris bulbs showed them to possess rounded tail tips and six incisures on each lateral field; characters by whichDitylenchus destructoris distinguished fromD. dipsaci.Cross‐inoculation experiments showed that the eelworm causing disease in potato tubers would invade and set up characteristic symptoms in iris bulbs and, in the opposite direction, the eelworm responsible for disease in iris bulbs would give rise to characteristic symptoms in potato tubers. Transfer was also effected from potato and iris toMentha arvensisand from iris toSonchus arvensis.The history of the disease in bulbous iris is briefly reviewed and the biology ofDitylenchus destructordiscussed and compared with that ofD. dipsaci.The conclusion thatD. destructoris the nematode causing eelworm disease of bulbous iris has been reported earlier (Goodey, J. B. 1

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07790.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

The general insecticidal properties ofbis(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

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07791.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Heat treatment of parathion at 140° C. and above resulted in isomerization and then thermal decomposition; the loss of toxicity toCalandra granariabeing correlated with a reduction of the thiono‐sulphur content. Similar results were obtained with O:O‐dimethyl‐(4‐nitrophenyl)‐thiophosphate. Paraoxon, O:S‐diethyl‐(4‐nitrophenyl)‐thiophosphate, and O:O‐diethyl‐S‐(4‐nitrophenyl)‐thiophosphate, although all possessing considerable contact activity, were less insecticidal than parathion; O:O‐dimethyl‐(4‐nitrophenyl)‐thiophosphate, on the other hand, was considerably more effective than parathion. O:O‐bis(2‐chloroethyl)‐O‐(4‐nitrophenyl)‐thiophosphate was considerably less toxic than parathion and appeared to have a different mode of action. Compounds, S‐ethyl‐bis‐(4‐nitrophenyl)‐thiophosphate, O‐ethyl‐bis‐(4‐nitrophenyl)‐thiophosphate, and triethyl thiophosphate were ineffective as contact insecticides.In the series of compounds examined, replacement of the group P = S by P = O or alteration in size of the groups attached to the

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07792.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Gamma benzene hexachloride has been used successfully as a seed dressing in field trials for wireworm control. For application to cereals at 2 oz./bushel, the optimum concentration of γ‐isomer was 20–30 % in a dressing which advantageously included an organomercurial seed disinfectant.Risks to germination and plant growth were thoroughly explored in the field. The 20 and 30 % dressings were safe; over‐strength dressings containing 50 or 70 %γ‐B.H.C. did not reduce grain yields significantly.Seed dressed with 20 or 30 %γ‐B.H.C. germinated normally after storage for 12 months. When seed was dressed at 4 oz./bushel with 35 %γ‐B.H.C. and 1 % mercury as organomercurial, germination was delayed but total emergence w

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07793.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Out of thirty‐four newer fungicides tested in greenhouse and field trials, red cuprous oxide (Cuprocide), tetrachloroparabenzoquinone (Spergon), methyl mercury dicyandiamide (Panogen), tetramethylthiuram disulphide (T.M.T.D.), ferric dimethyldithiocarbamate (F.D.D.), zinc trichlorophenate (Dow 7B) and 1‐p‐sulphamylphenyl‐3:5‐dimethyl‐4‐nitrosopyrazole (36L) were selected for detailed investigation on lettuce, pea, French bean, turnip, red beet, tomato and celery. Derivatives of dithiocarbamic acid, and 36L and Spergon among non‐metallic compounds compared favourably with cuprous oxide and organomercurial compounds. Addition of hormones, insecticides or nemacides did not improve emergence. Soil tests were more satisfactory than laboratory selection. Rates of application recommended by manufacturers often injured small seeds, and the optimum dosages were determined by extensive tests.Results obtained depended on conditions of test. Under glass, emergence was lower at 5–12° C. than at 16–20° C. Emergence was optimum at 45 % water‐holding capacity, and additional tests are required at higher and lower moisture to assess phytocidal and protectant action.In field trials seed treatments were generally most beneficial in cool and moist soil, and improved emergence in all but driest soil. T.M.T.D., Spergon and 36L were the most effective seed protectants. Mixing of these materials did not improve emergence. Emergence in relatively dry soil (25 %w.h.c.) was improved by watering after sowing, but emergence was decreased in moist soil by watering within 2 days of sowing.A seed‐borne form ofRhizoctonia solaniwas isolated from most seeds.Pythium, RhizoctoniaandFusariumwere commonly isolated from seedlings.Pythiumwas commoner at low andFusariumat higher temperatures. Surface disinfection of seed by Spergon and Panogen compared favourably with acidulated mercuric chloride.Ascochytaon pea seed was not controlled, but all treatments except Cuprocide improved emergence of spotted pea seed. T.M.T.D., 36L and Spergon were the most efficient in controlling pre‐emergence damping off. Seed treatment was more beneficial for pea than other vegetables, but emergence was usually improved by protectants except for turnip and celery seed.Treated seed stored dry for 10 months gave better emergence than untreated seed, and showed no evidenc

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07794.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Strains ofBacillus, PseudomonasandChromobacteriumisolated from dead leaves of lettuce seedlings overwintering in the open have been proved to be antagonistic in various degrees toBotrytis cinereaon nutrient agar, on wounded detached lettuce leaves and on wounded leaves of lettuce seedlings at temperatures ranging from 4 to 25° C. under conditions of high moisture and humidity. A strain ofMicrococcuswas completely non‐inhibitive. Antagonism by the strains ofBacillusand byBacterium coliwas evident only at temperatures above 15–20° C. while the other strains were effective also at temperatures as low as 4° C. Bacterial growth on agar and on dead lettuce tissue usually raised the pH from 6.1 to 7.8–8.4 at which level growth ofBotrytis cinereais almost negligible and the activity of any pectinase it produces is very much reduced. The antagonism of the bacteria investigated, however, was largely due to antibiotic substances quite independently of the effect of the high pH. Some bacteria which did not give rise to wide inhibition zones were nevertheless strongly antagonistic in the immediate neighbourhood of the colony.B. cinereaon nutrient agar and on lettuce leaves produced a strongly acid reaction. This was capable of neutralizing the alkaline reaction due to most bacterial activity only if the latter was not already well established. The mixed bacterial flora of all dead lettuce leaves tested was potentially inhibitory toB. cinereato a level as high as or higher than that shown by the majority of the test strains in pure culture. Many strains of bacteria cause lysis of young activeBotrytismycelium and germ tubes. In association with many bacteria,B. cinereahas exhibited features such as stimulation or depression of sporulation, continuation of aerial growth with inhibition of lateral spread of mycelium, vesicular distortion of hyphae and germination of spores while still attached to the conidiophores. Some spores of the test strain ofB. cinereaused gave rise to new strains more resistant to antagonism than the

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07795.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Botrytis cinereahas 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 ofB. cinereaon wounded leaves of living plants although such suspensions and several fungi had given control on simultaneous inoculation withB. cinereaon wounded detached leaves.Saprophytic antagonism is responsible for some of the natural control ofB. cinereain 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 ofB. cinereaand the amount of microbiological antagonism likely to be exerted.Three‐weekly applications of suspensions ofCephalosporiumsp.,Fusarium flocciferumandPhoma eupyrenafailed 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 ofBotrytis cinereainto 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. cinereacan 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 ofB. cinereaonEpilobiumsp.,Ranunculus repens, R. flammulaandLamium amplexicaulewas obtained by prior inoculation of killed tissue with soil

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07796.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY