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: Noctu idae) larvae on the quantity and distribution of extrafloral nectar product ion by leaves of castor ((Ricinus communis) and cotton (Gossypium herbaceum ) were investigated. Following larval feeding, the total volume of nectar s ecreted by foliar nectaries increased 2.5- and 12-fold, respectively. As HP LC-analysis showed no difference in sugar composition between extrafloral n ectar from insect-damaged and control plants, it can be concluded that the plants increased the secretion of carbohydrates in response to herbivory. I n damaged castor leaves, the amount of sugar excreted through extrafloral n ectaries represented approx. 1 parts per thousand of the leaf's daily assim ilate production. Induction of nectar production was mainly restricted to t he 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 recruit ment of predators and parasitoids on the site, and at the time, of attack. (C) 2001 Annals of Botany Company.