Temporal and spatial variation in palatability of soybean and cotton leaves following wounding.

Leaves of soybean (Glycine max (L.) Merr.) and cotton (Gossypium hirsutum L.) were mechanically damaged with a single hole and offered to Spodoptera littoralis Boisd (Lep., Noctuidae) larvae in laboratory bioassays at intervals of between 0 and 7 days from damage. The subsequent within-leaf grazing patterns of damaged and undamaged areas were compared using an image-analysing computer, and estimations were made by eye of percentage, areas grazed at three spatial scales. Reduction in palatability of damaged areas of both plant species was detected, at time intervals ranging from 0 to 7 days after damage. This effect was strongest for the longer time intervals and the effect became weaker with increasing distance from the site of damage. These results are discussed in relation to possible defensive roles of wound-induced changes.