摘要:

SUMMARYIn several sets of counts ofAphis fabaecolonies on bean stems, obtained with different sampling methods, variance was always proportional to the same power of the mean;s2=ambwhereb= 1.72 andadiffered by different sampling methods. The resulting standard transformation forA. fabaeon beans,z=x0 2, is marginally more effective thanz= log (x+1).

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04577.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYA technique for rearing aphids in dense populations is described. Apterae were reared in high (‘C’) and low (‘U’) population densities and the proportions of alatae among their progenies were compared. Proportions of alatae were larger among progenies of ‘C’ apterae, and the proportions also increased as the density of the population in which the progenies were reared increased. Progenies of alatae never be

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04578.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYApterae reared at different population densities produced alatae among their progeny, but not all these alatae behaved in the same way. Some flew before depositing nymphs (here called migrants), others flew after parturition (flyers) and some never flew (non‐flyers). The proportions of alatae, among the progeny from both uncrowded (‘U’) and crowded (‘C’) parents, that flew before depositing nymphs increased as the population density in which they were reared increased. Both crowded and uncrowded apterous parents produced similar numbers of larvae but, on average, ‘C’ apterae produced 17% more migrants. The proportions of migrants among alate progenies were closely correlated with the proportions of alatae am

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04579.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYA wide range of morphological differences, from apterae to alatae, and of differences in the behaviour of alatae were produced by isolating alatiform nymphs ofAphis fabaeon successive days after their birth. Alatiform. nymphs isolated soon after birth developed into the extreme apterous form, whereas when kept in a crowd until shortly before their final ecdysis a large proportion became alatae that flew before depositing young (migrants). Alatiform nymphs isolated on successive days after birth developed either into alatae that flew after depositing nymphs (flyers) or did not fly (non‐flyers). Aphids thus show a continuous polymorphism, comparable to that of locusts, and possibly related to concentrations of juvenile hormone present in the aphid during larval developmen

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04580.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYThe distribution of shelter to leeward of a windbreak of tall trees was compared with the pattern of distribution of insects above and within a wheat crop.The pattern for flying insects blown from elsewhere resembled the shelter profile, in contrast to insects originating in the windbreak, which accumulated immediately behind the trees, and those originating a few metres to windward, which accumulated in a zone between 1/2 and 1 H (10–20 m) to leeward. These patterns were more distinct in direct than in oblique incident winds.The pattern of infestation of a breeding population of cereal thrips in the wheat resembled the distribution of airborne primary migrants 1–2 months earlier; the pattern of scatophagid flies on the crop also resembled that of airborne populations of other dung feeders originating slightly to windward of the tr

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04581.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYIn laboratory studies mites ofAceria sheldoniwere reared on citrus fruit peels, beneath coloured cellophane hoods, to cater for their thigmotaxis and sensitivity to light of particular wave lengths. Hatching was most successful at 25°C and 98% r.h. but was reduced by low humidities (35–40% r.h.), when abnormal dwarf larvae emerged. The eggs hatched in 3–14 days; the length of a generation (egg to egg) was 12–33 days.The threshold of embryonic development was 9 °C and that for completion of the life cycle, egg to egg, was 12.5 °C. The average number of eggs laid per female was six (4–8). It increased to twelve (5–19) if the mite, during its larval stages, had been fed on buds. The vitality of both the eggs and the mature mites was tested by exposure to extreme low and high temperatures (below 0 °C, 39 °C): 50% of mites died after 30 min at 30 °C; 50% died after 30 min at

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04582.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYIn examinations between September 1966 and December 1968 of 741 specimens of rose species and cultivars, cleistocarps ofSphaerotheca pannosawere found on thirty‐two cultivars, mostly ramblers and old shrub roses, and on nine of these they were found in two or three successive seasons.On stem pieces placed on soil in each of the winters 1966‐7, 1967‐8 and 1968‐9 the number of cleistocarps with asci and ascospores decreased during November and December and rose slightly in January, but none showed dehiscence.Cleistocarps on rose bushes examined during the winters of 1967‐8 and 1968‐9 showed a progressive degeneration of ascospores, and by December none was found.Perennation ofS. pannosain buds was demonstrated by field observations, by inducing bursting of dormant buds on surface‐sterilized shoots and by dissection of dormant apical buds.In field studies in 1968 of the development of mildew, infected buds were noted on 22 March but secondary infections did not appear until 17 April, though viable conidia and susceptible leaf tissue were present during this period. Low temperatures appeared to be partly responsible for this lag. On detached leaves in the laboratory the fungus developed from germination to sporulation in 4 days at 20°, 7 days at 15°, 11 days at 10° and 28 days at 3°. Keeping inoculated detached leaves at 0° for 10 days apparently did not affect the viability of the conidia.In both 1967 and 1968 there were two host growth periods, each culminating in flowering, between May and September; mildew did not develop on the shoots until the second growth phase, then the disease increased logarithmically on shoots and blooms during August and September.The disease on the shoots was effectively controlled in the field during 1968 by applications of ‘Benlate’ (benomyl) or dinocap, but not by methy‐rimol; these fungicides were less effective in controlling mildew on pedicels.Laboratory tests showed that ‘Benlate’ inhibited sporulation ofS. pannosaby

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04583.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYIn studies on the control ofSeptoriaon celery seed, ¼ and 1 lb (113 and 454 g) samples of infected seed treated by the thiram‐soak method produced disease‐free seedlings under glass and disease‐free plants at maturity in the field. Hot‐water treatment of infected seeds, however, failed to give complete disease control in either situation. Thiram soaking was not harmful to seed germination and produced field crops of equal quality to those obtained from hot‐water‐treated seeds.In N.A.A.S. extension trials a total of 18½ lb (8.3 kg) of celery seed was treated by the thiram‐soak method and effective disease control was obtained in crops raised from this seed through

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04584.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYRace T1ofPhytophthora infestanswas first isolated in Central Europe. Tomato varieties carrying the dominant gene Ph were easily infected by T1but showed a different degree of field resistance. In September 1967 more than 80% of all isolations from the experimental plots at Greifswald were determined as the aggressive race T1. This race was also isolated in a large screening test over several provinces of the GDR from potato and tomato fields where no plants carrying dominant resistance genes were present in the neighbourhood.The fungus was able to pass from potato leaves or tubers to detached tomato leaves or intact tomato plants (cv. Fanal) without any reduction in sporulation.The field‐resistant tomato variety Ružový Ker and the highly field‐resistant variety Atom were crossed. In F2and subsequent generations, young plants were selected following inoculation of 14 mm leaf‐discs. Weak sporulations on the leaf‐discs were almost invariably correlated with a reduced level of infection of fruit in the field. Data from crosses of Atom with more or less susceptible varieties suggested the presence of incompletely dominant genes. It is concluded that at least two genes in the variety Atom control field resistance and the gene‐symbols Phf and Phf‐2 are prop

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04585.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYThe sexual stage ofE. graminisf.sp.hordeiwas found to be functional in Israel, and adapted to the climate of the region. Cleistothecia serve as the principal, and perhaps the only means for persistence of the pathogen in the host‐less, hot and rainless summer, and induce initial infection on wild and cultivated barleys in late autumn. The cool and rainy weather, which induces germination of seeds of the host in the field, also permits ascospore differentiation and ejection. Details are given of the conditions favouring or delaying cleistothccial maturation during and after the growing seaso

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04586.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY