RESPONSES OF APHIS FABAE SCOP. TO WATER SHORTAGE IN HOST PLANTS IN POTS

Abstract

Water strain in the host plant reduced aphid feeding and larviposition and sometimes increased the proportion of winged offspring. These negative effects on the aphids occurred despite the enrichment of the phloem sap that could be inferred from the senescence and changing composition of the leaves under water strain, tended to obliterate the normal effects of leaf age, and were readily reversible. They are attributed to stimuli associated with a reduction in the quantity of sap obtainable by the aphids owing to reduced turgor pressure or increased sap viscosity. The opposite, positive effects recorded previously with various aphids may be associated with less severe or intermittent water strain in the plant when the reduced quantity of sap obtainable is more than compensated by its improved quality. Zusammenfassung 1. Die Wirkungen beträchtlichen Wassermangels getopfter Wirtspflanzen auf Ansiedlung und Vermehrung von Aphis fabae Scop. wurde in Gewächshausversuchen mit im Labor herangezogenen geflügelten Virginoparen an Evonymus europaeus L. und mit Ungeflügelten an Vicia faba L. sowie in einem Feldversuch bei der natürlichen Besiedlung von E. europaeus untersucht. 2. Der Wassermangel verminderte Ansiedlung und Larvenproduktion und vergrößerte den Anteil geflügelter Nachkommen. Diese negativen Wirkungen können, die normalen Wirkungen des Blattalters auslöschen, waren aber durch Wiederversorgung der Topferde mit Wasser leicht reversibel. Sie traten trotz der Bereicherung des Phloemsaftes ein, die aus dem Altern und der veränderten Zusammensetzung der Blätter bei Wasserverknappung zu schließen war. Sie werden auf Reize zurückgeführt, die auf einer Reduktion der für die Blattläuse zur Verfügung stehenden Saftmenge beruhen, welche als Folge reduzierten Turgordruckes oder steigender Saftviskosität entsteht. 3. Die gegenteiligen günstigen Auswirkungen des Wassermangels, über die früher bei verschiedenen Blattläusen berichtet wurde, können auf weniger starkem oder vorübergehendem Wassermangel in der Pflanze beruhen, wenn die Verringerung der erreichbaren Saftmenge von ihrer erhöhten Qualität mehr als ausgeglichen wird.

Relation between plant water status and Macrosiphum euphorbiae (Hemiptera: Aphididae) population dynamics on three cultivars of tomato

“…The results presented in most of the literature on the performance of aphids on continuously stressed plants support the "pulsed stess" hypothesis (Kennedy et al, 1958;Sumner et al, 1986;McVean & Dixon, 2001), but the situation seems to be much more complex in the case of intermittent stress. Variation in aphid reproductive fitness on intermittently stressed plants is strongly dependent on the species of aphid, even when infesting the same species of host plant (Wearing, 1967;Wearing & Van Emden, 1967).…”

“…In addition, we recorded the numbers of dead aphids stuck on leaf trichomes. In the case of Aphis fabae on broad bean and Brevicoryne brassicae on rape, aphids become restless on water stressed plants (Kennedy et al, 1958;Miles et al, 1982). It is reasonable to believe that this "restless" behaviour on stressed tomato plants would result in an increase in the numbers of aphids trapped by glandular trichomes and therefore an increase in mortality.…”

“…The plant vigour hypothesis, in contrast, predicts that phytophagous arthropods will prefer and perform better on rapidly growing plants and, consequently, less well when the plants are subject to stress. The plant vigour hypothesis (Price, 1991) is mainly based on experimental studies showing that imposed water stress conditions often negatively affect herbivore performance, either in terms of reduced population growth (Pons & Tatchell, 1995;McVean & Dixon, 2001), reduced fecundity and reproduction (Kennedy et al, 1958;Wearing & van Emden, 1967;Wearing, 1972;Sumner et al, 1983;Inbar et al, 2001) or survival (Sumner et al, 1983;Watt, 1986). Most of these references relate to work with aphids, and in particular with different species of aphid, feeding on different host plants, and experiencing a variety of water stress treatments.…”

“…In some cases the level of stress is kept constant by means of polyethylene glycol used as a medium for growing plants (Sumner et al, 1983), in other cases the maximum level of stress is kept constant by varying the water supply (Fereres et al, 1988). Sometimes the level of stress experienced by plants is not measured (Kennedy et al, 1958;Wearing, 1967;Wearing & van Emden, 1967) or an indirect measure is provided (McVean & Dixon, 2001). The main negative effect of water stress on the aphids is recorded in terms of the reduction in their reproductive capacity (Fereres et al, 1988;Pons & Tatchell, 1995) and sometimes in terms of their "restless" behaviour (Kennedy et al, 1958;Miles et al, 1982).…”

“…Sometimes the level of stress experienced by plants is not measured (Kennedy et al, 1958;Wearing, 1967;Wearing & van Emden, 1967) or an indirect measure is provided (McVean & Dixon, 2001). The main negative effect of water stress on the aphids is recorded in terms of the reduction in their reproductive capacity (Fereres et al, 1988;Pons & Tatchell, 1995) and sometimes in terms of their "restless" behaviour (Kennedy et al, 1958;Miles et al, 1982). Nevertheless, the response to stress is not the same for all species of aphid and is affected by feeding site (Wearing, 1967;Wearing & Van Emden, 1967).…”