The response of aphids to plant water stress - the case of Myzus persicae and Brassica oleracea var. capitata

The possible repercussions of decreasing water availability in plantinsect interactions largely remain unclear. To study this, we designed two factorial studies applying two levels of water stress to Brassica oleraceae var. capitata L. (Brassicaceae) plants inoculated with the aphid Myzus persicae Sulzer (Hemiptera: Aphididae: Macrosiphini). One study investigated the effect of aphids and water stress on leaf water potential components, aphid population size, aphid intrinsic rate of increase (rm), and fecundity. The other investigated the effect of aphids and water stress on gas exchange, leaf fluorescence yield, estimation of leaf chlorophyll, and above-ground dry weight. Drought treatment reduced the size of the M. persicae population. Aphid numbers were strongly and positively correlated with soil moisture and negatively correlated with leaf temperature. Aphids on droughted plants had lower rm and lower fecundity per aphid. Under aphid stress, plants showed reduced maximum photosynthetic rate (Amax), lower leaf chlorophyll as estimated by soil plant analysis development (SPAD) values, higher osmotic potential, and reduced final above-ground dry weight compared with control plants. Aphid infestation also led to significantly higher leaf water potentials and reduced light-adapted fluorescence yield. Compared with control plants, water-stressed plants showed reduced Amax, lower SPAD values, reduced leaf water potential, lower turgor, and reduced final above-ground dry weight. Osmotic potential was lower in droughted plants when aphids were not present. Plants under combined aphid and water stress showed significantly reduced SPAD and final above-ground dry weight, with comparatively higher leaf water potentials. These results show that aphid infestation limits solute accumulation in the vacuole of drought stressed cabbage. Aphid infestation reduced the hosts ability to photosynthesise optimally and led to reduced growth. Plant stress hypotheses propose that a senescence feeder such as M. persicae would show higher rates of growth in response to the increasing quality of the phloem sap under water shortage. In the case of M. persicae, our results do not support the hypothesis that drought leads to improved aphid population growth and survival.