Nitrogen, water stress and the feeding efficiency of lepidopteran herbivores.
Abstract
A study was carried out to test, under carefully controlled conditions, White's hypothesis that when plants are subjected to stress, the tissues become more palatable to insect herbivores. Experiments were conducted over 3 years in glasshouses using saplings of Betula pendula and Salix cinerea, subjected to varying levels of water and nitrogen availability both individually and in combination. The feeding/survival responses of the sphingids Smerinthus ocellata and Mimas tiliae and the notodontid Phalera bucephala were measured. The digestive efficiency and growth rate of the larvae generally reflected the soluble nitrogen content in the ingested food plant tissues, but the response was not linear. The results supported White's hypothesis but also suggest that effects will be greatest for insects feeding on plants growing in soils of low nitrogen status which are subjected to drought stress.