Studies on the Relations of Insect and Host Plant: I. Effects of Water Stress in Host Plants on Infestation by Aphis fabae Scop., Myzus persicae (Sulz.) and Brevicoryne brassicae (L.)

Abstract

IT is generally agreed that the reproduction of aphids is influenced by water stress in the host plant. The nature of this influence is, however, not so clear and both increases¹ and decreases² in the reproduction of aphids have been reported in connexion with such water stress. One effect of the shortage of water in plants is the hydrolysis of protein in the leaves^3,4. Such enrichment of the phloem sap with soluble nitrogen would be favourable to aphids⁵. Another effect of water shortage in the plant is loss of cell turgor. This loss of turgor may be disadvantageous to aphids by reducing the assistance in food uptake provided by sap pressure^6,7. Thus the effects on aphids of water shortage in the plant can be regarded in terms of two main interacting and largely conflicting factors: (1) the concentration of nitrogen, and (2) the pressure in the phloem (compare ref. 2).