Increased population of the aphid Aphis pomi at a motorway. Part 2—The effect of drought and deicing salt

Abstract

Potted hawthorn plants Crataegus spp. were treated in winter with an NaCl spray to simulate the influence of deicing salt spray at motorways. This treatment significantly increased their susceptibility to the green apple aphid Aphis pomi. Analysis of the phloem exudate revealed that asparagine and glutamine were increased by over 400%, aspartic acid by over 100% and many other amino acids to a lesser extent. The sugar content in the phloem exudate was also raised. It is thought that these biochemical differences contributed considerably to the better development of the aphids, although a direct sodium effect or other factors cannot be excluded. A moderate drought stress also increased the aphid population. It is suggested that deicing salt and, to a lesser extent, drought, play an important rôle in the increased aphid population at the motorway.