The effect of herbivory on temporal and spatial dynamics of foliar nectar production in cotton and castor

The effects of feeding Spodoptera a littoralis (Boisd.) (Lepidoptera: Noctuidae) larvae on the quantity and distribution of extrafloral nectar production by leaves of castor ((Ricinus communis) and cotton (Gossypium herbaceum) were investigated. Following larval feeding, the total volume of nectar secreted by foliar nectaries increased 2.5- and 12-fold, respectively. As HPLC-analysis showed no difference in sugar composition between extrafloral nectar from insect-damaged and control plants, it can be concluded that the plants increased the secretion of carbohydrates in response to herbivory. In damaged castor leaves, the amount of sugar excreted through extrafloral nectaries represented approx. 1 parts per thousand of the leaf's daily assimilate production. Induction of nectar production was mainly restricted to the damaged leaf, although a weaker systemic response was found in adjacent younger leaves. Spatial and temporal patterns of induced nectar production could help plants to optimize indirect defence by concentrating the recruitment of predators and parasitoids on the site, and at the time, of attack. (C) 2001 Annals of Botany Company.