ALBERT

Description / Table of Contents: Zusammenfassung Als primäre Ursache des unterschiedlichen Befalls der beiden Ackerbohnensorten Rastatter und Schlanstedter durch die Schwarze Bohnenlaus, Aphis (Doralis) fabae Scop., wird Präferenzresistenz nachgewiesen. In mehrjährigen Beobachtungsreihen ergab sich bei 24-stündigen Kontrollen ein Unterschied in der Anzahl der Initialkolonien von 1 : 3 bis 1 : 5 auf Rastatter und Schlanstedter. Direktes Abfangen bzw. eingehende Beobachtung der auf den Pflanzen gelandeten Geflügelten zeigte, daß diese Initialbefallsdifferenz erst sekundär entsteht. Die Pflanzen beider Sorten werden statistisch in gleicher Häufigkeit beflogen, jedoch siedeln sich auf Rastatter nur 1%, auf Schlanstedter 10% der Gelandeten für längere Zeit (bis zum Absetzen wenigstens einer Junglarve) an. Die Bedeutung der sogenannten Probesaugstiche sowie der Größe und Verteilung der Interzellularräume in den Pflanzengeweben für das Auffinden des Phloems und somit für die Wirtswahl wird diskutiert.

Description / Table of Contents: Summary In the course of comparative investigations of the significance of the infestation flight of Aphis fabae Scop. on the distribution of virus diseases, the virus infection which is frequently different on the edges and in the centre of virus diseased potato fields, has been analysed in the potato degeneration area (i.e. where seed potatoes cannot be grown year after year due to the high incidence of virus) of Middle Germany (Quedlinburg) and in the seed growing area of Northern Germany (Groß-Lüsewitz, Mecklenburg). In 1956 a nearly square plot of 500 healthy Ackersegen plants was kept free from apterae (aphids) by a weekly treatment with insecticides (Wofatox spray) and in 1957 the following generation (from 5 by 5 tubers taken separatedly from each bush) was tested for virus infection. The infection was found to be by 12 times more frequent in the degeneration area than in the seed production district. This can only have been due to the visits of alate vectors, especially Myzus persicae Sulz., the infestation flight of which was 29 times greater in Middle than in Northern Germany. In both places the virus infestation in the test plots was observed to decrease quickly from edge to centre. At Quedlinburg the third row showed barely one half of the infestation of the edge and the 5th row only one third of the infestation of the outer rows. At Groß-Lüsewitz it dropped to a tenth in the second row. This phenomenon is due to the nature of the infestation flight of the vectors, which glide extremely near to the ground. The flight is stopped at the bordering rows because of the density of the crop, effecting a far higher infestation rate here than in the centre, where it penetrates only very sparsely. This was evident from an experiment on planting times, described by v. Bernuth 1948: The later the potatoes grow up, the smaller is the virus infestation quotient edge to centre, for when the plants are all small the whole crop is equally exposed to the infestation flight of the vectors, which begins by the end of June. From this experience the demand of agricultural practice for the earliest possible planting and quickest possible covering of the ground by crop is be easily unterstood.

Description / Table of Contents: Summary In a further study of host selection behaviour of the black bean aphid (Aphis fabae Scop.) and of Myzus persicae (Sulz.) alate alienicolae were caught immediately after landing on young plants of equal size and growth of beet (Beta vulgaris var. rapa Dum.), field beans (Vicia faba L.), poppies (Papaver somniforum L.), potatoes (Solanum tuberosum L.) and white mustard (Sinapsis alba L.). A total of 1495 A. fabae and 1054 M. persicae were collected during 59 observation periods totalling 107 hours, with two or more persons operating. The aphid numbers showed no statistically significant differences between the five plants, so it is concluded that host selection cannot take place during the initial approach, but only after alighting. The subsequent behaviour of the aphids after landing on the five plant species was studied by continuous observations by several observers. 1556 bean aphids landed over a total period of 44 hours. The behaviour included slow or fast walking, frequent or less frequent changes in walking and in probing, and, in almost all cases, the aphids took off again in a few minutes. On an average the insects took off sooner from the non-hosts, mustard and potato, than they did from the potential hosts, poppy, beans and beet. Thus 75 per cent left the mustard and potatoes within one and a half minutes, but the same proportion remained for nearly four minutes on poppy and field beans and more than five and a half minutes on beet. The number of probes on the non-hosts was about 1, but was greater (2–4) on the hosts, the number increasing from poppy to bean to beet. The walking and probing behaviour on each plant was characteristic. On beet most aphids showed short probing times and rapid continuous walking, on potatoes walking and probing times were short, and long sequences of intermediate behaviour took place on beans. Only 1.7 per cent of the aphids which alighted settled down, but lack of observations during darkness makes it impossible to state whether this is the whole measure of the selection process. However a study of these potential “settlers” showed that the numbers of probes increased from non-host to host plants, in parallel with previous results. These results from systematic field studies confirm those of Bruce Johnson and of Ibbotson & Kennedy based on laboratory experiments regarding the change-over from the motor phase of the migrating aphids to the vegetative phase of the parasitic period, and support also the unpublished results of Hennig regarding the gradual development of host selection and of plant puncturing reactions. The processes are promoted by specific qualities of the host plants, particularly those of the leaf surface. Thus on host plants only do the motor impulses die away. These quantitative measurements of field reactions show how aphid behaviour may be important in transmitting nonpersistant viruses.

Description / Table of Contents: Summary The developmental cycle of the aleyrodid Aleurochiton complanatus was studied at fortnightly intervals during 1961 in a wild population on Norway leaves (Acer platanoides) from a park in Quedlinburg. The seasonal dimorphism of the puparia, previously described by Haupt in 1934, from a few observations, was confirmed. The species is almost completely bivoltine and forms two different puparial types: teneral, almost colourless summer puparia which develop immediately, and more sclerotised, dark-coloured winter puparia with white wax patterns and strongly marked dormancy. Summer puparia are found during July, predominating in the first generation produced by the spring adults hatching from the over-wintering puparia. A small proportion of summer puparia are also found in the next generation. The winter puparia develop mainly during late summer and are produced in the second generation. However, up to 10% of the first generation pupae are of the over-wintering type. The winter puparia were examined for development and hatching at 20° C after exposure to 0°, 5°, 8°, 15°, and 20° for different periods. The results demonstrated the typical features of a diapause; i.e. almost complete check of development at 20° C, strong retardation and reduced hatching rate at 15° C, rapid and complete hatching after chilling for at least one to two months at the lower temperatures. Chilling to 0° C for this period was most effective. Only when the chilling period lasted more than five months was there a significantly increased mortality. Seasonal dimorphism is thus connected with a facultative diapause. Nevertheless some individuals in each generation behave abnormally and there is some tendency to a monovoltine and a trivoltine cycle in addition to the normal bivoltinism. Breeding Aleurochiton acerina Hpt. in nylon bags on Field Maple (Acer campestre) showed similar results. However, under the same conditions Nealeurochiton pseudoplatani (Visnya) formed only one generation on its host, sycamore (Acer pseudoplatanus), due to the slow speed of development in the climate of Central Germany. It is probable that offspring of the few summer puparia, formed in the first (summer) generation, are seldom able to finish their development before the leaves wither in autumn. The normal latent seasonal dimorphism may be developed fully where favourable conditions are provided, including long day illumination and a healthy host plant, with an adequate environmental temperature.

Description / Table of Contents: Summary The biggest and smallest seeds of Schlanstedt (S or s) and Rastatt (R or r) field beans were selected in order to produce under otherwise identical conditions young plants of differing growth. When the third primary leaf pair unfolded the plants were decapitated so as to leave only one leaflet of the first pair. On such seedlings were determined the numbers and lengths of young Aphis fabae specimens borne by each young virginoparous aptera during the time from birth to maturity of her first-born daughter. The young plants formed the series S〉s≧R〉r according to the size of the first leaf, and another series S〉R〉s〉r according to the cross sectional area of the stem. Quite similarly, the mean numbers and lengths of the first-born daughters were found to decrease as the leaf area of their host plants diminished, though the difference between R and s was not so great as between other members of the series. The mean length of the adult daughters was shown to be proportional to the mean leaf area available to each larva during postembryonic development. When R- and s-plants of identical growth activity were used, the antibiotic effects of their differing resistance against the bean aphids were no longer demonstrable between Schlanstedt and Rastatt field beans. Therefore one wonders whether the differing antibiotic resistance of these varieties should not be interpreted in terms of their differing growth intensities rather than as the result of some other quantitative or qualitative difference between them.

Description / Table of Contents: Summary Different coloured summer lettuces of the Quedlinburg Assortment (Saatzuchtleiter Fabig) allowed tests of the landing reaction of aphids, especially Aphis fabae Scop. and Myzus persicae Sulz., on plants of different colours to be compared with Moericke's findings using artificial coloured carriers. Direct captures of landing aphids, as described by H. J. Müllér (1962), showed twice as many aphids, and from three to five times as many Myzus persicae, on green varieties Ramses and Rhenania and on yellow-green Rudolfs Liebling than on the almost completely dark reddish brown Indianerperle. However the brown-red but yellow-green striped variety Pirat was landed upon by almost as many aphids as the green varieties. When the yellowish and yellow-green varieties Rudolfs Liebling and Ramses were planted within a plot of whitish-green young winter wheat, many more aphids alighted than would have been expected if chance only had operated. Fewer alighted on the whitish-green Rhenania in the same situation. The dark brown Indianerperle received few aphids when grown among wheat. The landing impulse on yellow and green lettuces is thus increased when their colour contrasts with that of the surroundings, but this does not apply to the brown varieties. Colourless glass dishes, filled with water, were used as traps and set in the middle of plots of different coloured lettuces (using many replicates during the whole growing period) caught only twice as many aphids among yellow as among green or brown varieties; this was due to an edge effect. The stronger the impulse to land on a lettuce variety, the more aphids are caused to land at the edge of the plot. Thus only a few reach the trap in the middle. When yellow dishes replace the colourless traps, a much higher number of aphids is caught among reddish-brown lettuces. Brown lettuce varieties are known to show a lower incidence of lettuce mosaic than yellow or green varieties. This is presumably due to the smaller number of aphids alighting, thus diminishing the chance of infection.