ÜBER DIE URSACHEN DER UNTERSCHIEDLICHEN RESISTENZ VON VICIA FABA L. GEGENÜBER DER BOHNENBLATTLAUS, APHIS (DORALIS) FABAE SCOP. VIII: Das Verhalten geflügelter Bohnenläuse nach der Landung auf Wirten und Nichtwirten*

Abstract

Landungen alienkoler Aphis fabae Scop, und Myzus persicae Sulz, erfolgten im Freien auf Jungpflanzen von Futterrübe, Ackerbohne, Mohn, Kartoffel und Senf mit statistisch gleicher Häufigkeit. Die überwiegende Mehrzahl der gelandeten Bohnenläuse verließ aber die angeflogene Pflanze nach wenigen Minuten wieder, Nichtwirte lediglich etwas rascher als die potentiellen Wirte, auf denen im Mittel auch mehr (2–4) Probestiche je Besuch ausgeführt wurden als auf jenen (ca 1). Nur 1–2% der Gelandeten setzten sich für längere Zeit, bevorzugt auf Wirtspflanzen, fest. Das Wirtswahlvermögen dieser Aphiden scheint sich erst allmählich gegen die motorischen Antriebe der vorausgehenden Migrationsphase durchsetzen zu müssen, ein Prozeß, dessen Reifung von den Eigenschaften der Wirtspflanzen nur allmählich gefördert, von denen der Nichtwirte aber nicht sofort gehemmt wird.SummaryON THE BEHAVIOUR OF ALATE BEAN APHIDS (APHIS FABAE SCOP.) AFTER LANDING ON HOST PLANTS AND NON HOSTS.In a further study of host selection behaviour of the black bean aphid (Aphis fabae Scop.) and of Myzus persicae (Sulz.) alate alicnicolae were caught immediately after landing on young plants of equal size and growth of beet (Beta vulgaris var. rapa Dum.), field beans (Vicin 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.