ALBERT

Description / Table of Contents: Summary Using the adult size (length, weight, frontal projection of surface) of young virginoparous bean aphids as a parameter for antibiotic effects of the host plant, detailed knowledge is wanted of postembryonic growth reactions of the aphids to different environmental factors. On the same food material daughters of small mothers grow bigger, those of big ones smaller than their mothers, but they still differ significantly from each other. Direction and scope of the size modification between two generations depend on the nutritional difference of the substratum on which mothers and daughters develop. On a substratum of high value and with 20°, big mothers produce nearly two-thirds of their total offspring during the first week and another third in the second week, while the small ones begin only with a quarter. But then they recover with 40% in the second and a quarter in the third week and so they finally reach 84% of the total production of big mothers, though with a retardation of one week. Also the quantitative proportions of embryogenesis during pro- and postmetamorphic development and therefore the sequence of births are results of the nutritional situation during the larval and imaginal stages, respectively, of the virginoparae. Whereas with rising temperature the developmental speed increases in the usual manner —with the minimum at 5° and the maximum not much above 30° —, growth is already optimal at 14–15° and decreases promptly with temperatures above the optimum. Obviously with temperatures too high or too low the surplus of high energy material (amino acids) necessary for growth processes is consumed by the maintenance metabolism or blocked under these conditions. Aphis fabae-virginoparae grown on leaf discs floating upside down on tap water develop into smaller adults as diameters (22–16–10.5 mm) decrease or population density (2, 6 or 20 larvae on 200 mm2 leaf disc each) increases (differences significant at the 0,1% level). While on leaves in situ such differences do not prove significant, young virginoparae grow the bigger, the more the leaf area increased relatively during their larval development. Therefore the differences in the antibiotic aphid resistance of young Rastatt and Schlanstedt field bean plants of the same age may be reduced to a difference in phase of the growth of their leaves. On leaf discs of different age the biggest adults develop on discs from mature assimilating foliage, which after isolation may evidently mobilize more protein reserves than younger or older ones, probably as the young leaf itself yet depends on an influx of amino acids, and the old leaf already is more or less exhausted of them. Bean aphids developing on normal intact, detached, or detached and re-rooted primary leaves of the susceptible field bean “Schlanstedter” show nearly no significant differences in adult size, but on corresponding leaves of the resistant “Rastatter” they react with increased and decreased growth respectively (in comparison with their normal diminished size). The Schlanstedt field beans provide an uniform and equivalent feeding basis for the growth of black bean aphids during nearly all stages of their physiological development. They represent a main host (host of class I in the sense of Mosbacher These are plants, which are suitable hosts for an aphids in any of their physiological stages, whereas host plants of class II being so only in a distinct phase (growth or senescence) of development. ). The Rastatt field beans on the other hand are secondary hosts (hosts of class II), which guarantee a sufficient promotion of aphid growth (in the sense of Kennedy et al.) only in stages of an increased mobility of soluble protein elements in growing or senescent organs.

Description / Table of Contents: Summary Aphis fabae, Aphis craccivora, Acyrthosiphon pisum, and Megoura vicae (abbreviated Af, Ac, Ap and Mv, respectively) were allowed to develop under similar uncaged conditions on Rastatter (R) and Schlanstedter (S) field beans. Large, sometimes contradictory, differences in the fecundities and weights attained by adult apterous virginoparae on these plants were recoreded and ascribed to “postinfestation” resistance effects. Ap, which feed only on leaves, and Mv, which feed exclusively on internodes, weigh significantly more (17–18%) on R than on S. In contrast, Af, which feed on various plant parts, are 61% heavier on the leaves and 33% heavier on the stems of S than on the corresponding parts of R.However, Ac, which have a distribution on the plants similar to that of Af, are somewhat heavier (12%) on R-leaves and on S-stems than on the corresponding plant parts of the other variety. Such differences are greatly diminished if the aphids are reared on excised leaves and stems immersed in water. In this case growth of the aphids on excised parts of the “resistant” varieties (on which they previously grew poorly) closely approaches that on the intact “satisfactory” varieties (on which they grew well). Only small (Af, Ac) or no (Ap, Mv) improvement in growth results when the aphids are reared on excised parts of the “satisfactory” variety. Thus, the weights of apterous adults of Ap on excised S-leaves were only 17% greater than on intact S-leaves, whereas they were similar on excised and intact R-leaves. For Af, adult weights were 81% greater on excised R-leaves, 51% greater on excised S-leaves, and only 19% or no greater on excised R- and S-stems, respectively, than those on the corresponding intact plant parts. The possibility is discussed that these contradictory effects result from a mobilization and increase of proteinaceous constituents in the excised plant parts. Whereas the nutrition and growth of aphids on the “resistant” variety may thus become optimal, such an increase above an already optimal nutrient level on the “satisfactory” variety would not increase growth beyond the limit already achieved by a species. It is further deduced that “postinfestational” resistance to aphids of field beans depends on the nutrient value of the sap available to the aphids. However, since the nutritional demands of different aphid species may also differ, it is unlikely that a single plant species will be resistant to aphids in general.

Description / Table of Contents: Summary The rate of reproduction and the velocity of development of Black Aphids, Aphis (Doralis) fabae Scop., are proofed on first-formed leaves (see Abb. 1 above) of Rastatter (R) and Schlanstedter (S) fieldbeans 1) by numbering the daughters, which are born by one young virginogen mother in the time between birth and maturity of her first born daughter and 2) by measuring this time (of a such a “firstborn generation”) in days for many generations, which are continued by placing the young ripe first born daughter as mother of the next generation on a new leaf each time. The breedings are made during half a year in two parallel series of five lines each on R and S a) on cut and watered first-formed leaves and b) on equivalent leaves of rooted plants. On the cut leaves in water the velocity of development, the total number of progeny, and the rate of reproduction (calculated by dividing the number of daughters in the first-born generation by the period from birth to maturity of the first-born daughter) were on the average much greater than on rooted seedlings of the same varieties. The duration of each generation and the mortality of the mothers was significantly lower on the cut leaves. The differences between the two varieties were only slight on cut leaves in water, but they were more conspicuous on the rooted leaves. With reference to Kennedy's idea of the nutritional value of differently aged leaves, it is suggested that the different concentrations of soluble protein components in the phloem may be the cause of these antibiotic effects. As this concentration is probably the same in cut leaves as in ageing ones, the aphids find more food there and therefore produce more progeny more rapidly than on the mature leaves of rooted plants. As the optimum conditions for reproduction are found on cut leaves of R, and as these seem similar to those found on S, the increase in food available apparently compensates for the differences in antibiotic resistance between the two varieties. Some possible mechanisms for this antibiotic resistance are discussed, especially as it has formerly been stated that R beans appear to be resistant to alate aphids when these choose their host plants.

Description / Table of Contents: Summary Reciprocal grafts of aphid-resistant (Rastatter) and susceptible (Schlanstedter) field beans (Vicia faba) should demonstrate whether the resistance of the scions is influenced by the stock or not. To ensure a solid and inflexible connection between the partners to be grafted a glass capillary was fitted in the stem hollows of both the scion and the stock. In “pertelar” cages (Müller 1954) one young aptera of Aphis fabae could choose to infest a leaf of a grafted scion or a leaf of a normal plant. The percentage of initial colonies established by 740 such tested virginoparae decreased from 90,6 (S/R+S) to 78,5 (S/R+R), 76,7 (R/S+S) and 48,8% (R/S+R). In all cases, where a decision was possible at all, S-leafs were preferred to R-leafs, independently of whether they grew on a scion or on a normal plant (Table I): With reproduction rate experiments the percent of apterous virginoparae settling on grafts and controls dropped in a similar manner from 51,0 on S and 43,9 on S/R to 21,8 on R and 17,7 on R/S respectively (Table II). Also the reproductive rate (number of larvae born by an apterous virginopara in the time between the birth and maturity of its first born daughter decreased from S (33,6+-9,0) and S/R (31,8+-8,3) to R (27,2+-8,2) and R/S (26,7+-7,9)). There is no statistically significant difference between S and S/R on the one side and R and R/S on the other (Fig. 4). The diminution of numbers from S to S/R and from R to R/S respectively in all experiments is suggested to be an effect of grafting in itself rather than a mutual influence of the partners. The present results prove that both the preference-nonpreference-und the antibiosismechanism of the relative aphid resistance of R-and S-field beans are not altered by the stock after reciprocal grafting. In view of this and the findings of Harvey & Hackerott (1958) on alfalfa resistance against Therioapbis maculata substances produced by the roots cannot be the cause of aphid resistance.